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A selective acetate anion binding receptor: participation via cationic CH3 donors
Accepted Manuscript A selective acetate anion binding receptor: participation via cationic CH3 donors Thiravidamani Senthil Pandian, V. Srinivasadesikan, M.C. Lin, Jongmin Kang PII:
S0040-4020(15)01207-7
DOI:
10.1016/j.tet.2015.08.015
Reference:
TET 27037
To appear in:
Tetrahedron
Received Date: 17 June 2015 Revised Date:
3 August 2015
Accepted Date: 5 August 2015
Please cite this article as: Pandian TS, Srinivasadesikan V, Lin MC, Kang J, A selective acetate anion binding receptor: participation via cationic CH3 donors, Tetrahedron (2015), doi: 10.1016/ j.tet.2015.08.015. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Graphical Abstract
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A selective acetate anion binding receptor: participation via cationic CH3 donors
a.
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Thiravidamani Senthil Pandiana, V. Srinivasadesikanb, M. C. Linb, Jongmin Kang*a
Department of Chemistry, Sejong University, Seoul, 143-747, South Korea [email protected]
Center for Interdisciplinary Molecular Science, Department of Applied
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b.
Chemistry, National Chiao Tung University, Hsinchu 300, Taiwan
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Email: [email protected] Abstract
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A novel receptor 1 which has only C-H hydrogen bonds as recognition element has been designed and synthesized. The receptor 1 utilizes cationic CH3 in 2-methyl benzimidazole and naphthalene benzylic C-H as hydrogen bonding donor. The binding cavity formed in receptor 1
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prefers to accommodate small negatively charged atom such as oxygen. Therefore, acetate and nitrite show strong affinity for receptor 1 in acetonitrile due to negatively charged oxygen in
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them. In addition, the order of binding affinity for halides are Br- > Cl- > I-. These results reflect the size and basicities of halides. Further, 1H NMR titration of halide clearly indicates the anionπ interaction. The experimental data from UV-vis, fluorescence and 1H NMR titration are consistent with DFT results. Key words: anion receptor, C-H hydrogen bonds, acetate, nitrite, anion-π interaction
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Introduction
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Carboxylate anion sensor has been thriving area of research getting much attraction from all over the supramolecular groups because of enormous applications in pharmaceutical, biological areas.1 In addition, carboxylates are the most fundamental importance in nature and in chemical
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technology.2 Recent physiological studies evidenced that the anions of weak aliphatic acids such as acetate transiently inhibits myocardial contraction by increasing mitochondrial calcium
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uptake.3. For these logical reasons selective detection of acetate is an impressive facet of anion receptor chemistry. Generally, as the recognition unit for anions, N-H hydrogen such as urea, thiourea, and amide has been utilized.4 However, various polarized C-H groups are proven to be effective hydrogen bond donors. For example, imidazolium5, triazolium6, perimidium7 groups are successfully utilized for anion recognition elements. In addition, aliphatic hydrogen bond
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donor units such as benzylic8 and pure aliphatic9 have been shown to be effective hydrogen bonding element in anion recognition. Further, there have been many detailed studies of C-H
anions.
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level as well as solution level for the diverse
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hydrogen bonding in gas phase10 and solid state
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In addition, Sensors for nitrite anion based on gas phase reactions, electrochemical, colorimetric determination of paper micro fluidic devices and gelators have been developed. However, nitrite sensors generally have developed by using Griess reaction because of its high selectivity. Still, a simple probe for detection of NO2- anion is challenging among the field of supramolecular analytical chemistry. Besides, the primary source of nitrite in our diets is processed (cured) meat or fish, and nitrites are considered a potential reactant precursor for nitrosamines. The serious
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health risks caused by high nitrite exposure are blue baby syndrome, spontaneous abortion, and birth defects in the central nervous system. Because of these reasons determination of nitrite anion has received great interest.12
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Anion - π interactions are usually restricted to aryl derivatives bearing electron-withdrawing substituents. The aryl rings are electron-deficient π center. This phenomenon is ascribed to Coulombic attraction between a negatively charged anion and electron-deficient aromatic ring.
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Even though the numerous solid-state examples, theoretical experiments, few solution-phase examples recognize the anion–π interaction.13
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As an effort to develop a new anion receptor which utilizes only C-H hydrogen bonding, we designed and synthesized a new anion receptor 1 which has naphthalene spacer and 2-methyl benzimidazole as anionic recognition element. Here we’d like to report the synthesis and binding properties of receptor 1. The binding phenomena of receptor 1 could be monitored by UV-vis,
Results and Discussion
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Synthesis
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fluorescence and 1H NMR spectra and the results are consistent with DFT analysis.
1) CH3CN,NaOH
N H
2) CH3I, CH3CN
N
3) aq. NH4PF6
PF6-
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Br
N
Br
N
N N PF61
Receptor 1 was synthesized by the reaction between 2 equivalents of 2-methybenzimidazole and 1,8-bis(bromomethyl)naphthalene. Then, anion exchange with ammonium hexafluorophosphate
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gave receptor 1 bearing two 2-methybenzimidazole arms on naphthalene in 49% overall yield. Receptor 1 was characterized by 1H NMR, 13C NMR, and high-resolution mass spectrometry
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Interactions with acetate The ability of receptor 1 to recognize acetate was studied in acetonitrile using UV–vis titration spectra. The receptor 1 displayed strong absorption band at 226 nm in acetonitrile. Figure 1a
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shows the family of UV-vis spectra obtained over the course of the titration of solution 1 with tetrabutylammonium acetate in acetonitrile. As acetate ions were added to the 20 µM acetonitrile
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solution of 1, the absorbance peak at 279 nm was gradually decreased with small bathochromic shift. In addition, there were well-defined isosbestic points at 223nm, 231nm, 238nm, which indicated that new species were formed by the interaction of 1 and acetate. In addition, the receptor 1 displayed strong fluorescence emission in acetonitrile as shown in Figure 1b. The excitation and emission wavelength were 271 and 347nm, respectively. The intensity of emission
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spectrum from 20 µM solution of the receptor 1 gradually decreased as the concentration of tetrabutylammonium acetate was increased (1–26 equiv), which also indicates the association
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between the receptor 1 and acetate.
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(b)
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Figure 1. Family of UV–vis spectra (a) and fluorescence spectra (b) recorded over the course of titration of 20 µM acetonitrile solutions of the receptor 1 with the standard solution tetrabutylammonium acetate
The complexation abilities of receptor 1 to acetate was also measured by standard 1H NMR titration experiments in CD3CN using a constant host concentration (2 mM) and increasing
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concentrations of acetate anions. The addition of tetrabutylammonium acetate salts to the solution of receptor 1 in CD3CN resulted in large downfield shifts of benzimdazole C2-CH3 and benzylic C-H. (Figure 2) For example, addition of tetrabutylammonium acetate moved
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benzimdazole C2-CH3 from 2.84 to 2.89 ppm and benzylic C-H from 6.41 to 6.70 ppm. The downfield shifts of these protons indicate the presence of a hydrogen bond interaction between
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these C-H hydrogens and acetate ion.
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Figure 2. 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium acetate (0 –2.5 equiv.) in CD3CN
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The stoichiometry between receptor 1 and acetate was determined to be 1:1 using a UV Job plot in acetonitrile (Figure 3).
Figure 3. Job plots of receptor 1 with tetrabutylammonium acetate, nitrate and bromide obtained by UV-vis in acetonitrile.
A Benesi–Hildebrand plot 14 by use of change at 279 nm in UV–vis spectrum and 347 nm in fluorescence spectrum gave the association constants. The association constants calculated were
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1.0 X 104 M-1 from UV–vis titration and 1.0 X 104 M-1 from fluorescence titration, respectively. In addition, analysis of chemical shift utilizing EQNMR15 gave the association constant of
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1.1 X 104 M-1 which is similar to the values obtained from UV–vis and fluorescence titrations.
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Interactions with nitrite
The abilities of receptor 1 to recognize with nitrite were also studied in acetonitrile using UV–vis
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titration spectra. The receptor 1 in acetonitrile exhibits absorption band at 226nm, 271nm and 279nm. When the amount of nitrite was increased, small bathochromic shift of λmax observed with an isosbestic point at 254 nm (Figure 4a). The existence of isosbestic point for UV-vis titrations of receptor 1 with nitrite suggests a 1:1 complexation, and this binding stoichiometry
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was confirmed by UV –vis Job’s plot analysis (Figure 3)
(a)
(b)
Figure 4. Family of UV–vis spectra (a) and fluorescence spectra (b) recorded over the course of titration of 20 µM acetonitrile solutions of the receptor 1 with the standard solution tetrabutylammonium nitrite
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In addition, the intensity of emission spectrum from the receptor 1 gradually decreased as the concentration of tetrabutylammonium nitrite salts was increased (1 –30 equiv), which also indicates the association between the receptor 1 and nitrite (Figure 4b). From these experiments,
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association constants for nitrite were calculated as 8.8 X 103 M-1and 8.7 X 103 M-1 from the UV– vis and fluorescence titrations, respectively.
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Hydrogen bond formation was confirmed by 1H NMR titration. When nitrite was added, benzimdazole C2-CH3 and benzylic C-H moved to downfield (Figure 5). For example,
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benzimdazole C2-CH3 moved from 2.84 to 2.87ppm and benzylic C-H from 6.41ppm to 6.66ppm respectively. The association constants calculated for nitrite were calculated as 9.2 X 103 for 1H NMR titration. Surprisingly, the resulting association constant for nitrite anion is much
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comparable with acetate anion complex with receptor 1.
Figure 5. 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium nitrite (0 –5.1 equiv.) in CD3CN
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Interactions with halides
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The receptor 1 showed similar titration behaviors for halides. For example, when the amount of bromide was increased, small bathochromic shift of λmax along with sharp isosbestic points at 223 and 236 nm were observed (Figure 6a). The stoichiometry between receptor 1 and bromide was confirmed by Job’s plot analysis (Figure 3). In addition, the intensity of emission spectrum
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from the receptor 1 gradually decreased as the concentration of tetrabutylammonium bromide
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salts was increased (10–190 equiv), which also indicates the association between the receptor 1 and bromide (Figure 6b). From these experiments, association constants for bromide were calculated as 1.4 X 103 M-1and 1.5 X 103 M-1 from the UV–vis and fluorescence titrations,
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respectively.
(a)
(b)
Figure 6. Family of UV–vis spectra (a) and fluorescence spectra (b) recorded over the course of titration of 20 µM acetonitrile solutions of the receptor 1 with the standard solution tetrabutylammonium bromide
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Hydrogen bond formation was also confirmed by 1H NMR titration. For example, addition of tetrabutylammonium bromide moved benzimdazole C2-CH3 from 2.84 to 3.04 ppm and benzylic C-H from 6.42 to 7.09 ppm (Figure 7). The downfield shifts of these protons indicate the
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presence of a hydrogen bond interaction between these C-H hydrogens and bromide ion, whereas the upfield shift of benzimidazole’s aromatic CH proton from xx ppm to xx ppm could be ascribed to charge transfer interaction of bromide with electron deficient aromatic ring, namely
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anion-π interaction16 (Figure 7). These anion-π interactions are pronounced with halide anions. Therefore, Chloride and bromide showed similar 1H NMR spectral changes with receptor 1. (see
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Figure S18 and S19). Calculated binding constants for other anions are summarized in Table 1.
Figure 7. 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium bromide (0 – 66 equiv.) in CD3CN
We also tried dihydrogen phosphate and hydrogen sulfate However, dihydrogen phosphate only gave precipitation with receptor 1 and hydrogen sulfate did not bind to receptor 1 at all. 11
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From the experiment we concluded that the selectivity of halide anions were in the order of Br>Cl->I1
UV
H NMRa
Fluorescence
1.0 X104
1.1X104
1.0X104
NO2-
8.8 X 103
9.2X 103
8.7 X 103
Br-
1.4 X103
1.5 X103
1.5 X103
Cl-
1.2 X 103
1.2 X 103
1.3 X 103
I-
7.8X 102
7.9X 102
7.4X 102
Errors are less than 15 %
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a.
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CH3COO-
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TBA-Anions
Table 1 Association constants (M-1) of receptors 1 with various anions in Acetonitrile
Deprotonation of C2-CH3 was observed with highly basic fluoride 17 and it was confirmed through titration with hydroxide ion. Changes in the absorbance spectra in the presence of
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other anions. (Figure 8)
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hydroxide and fluoride were almost identical and were clearly different from those observed for
12
(b)
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(a)
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Figure 8. Family of UV-vis spectra recorded over the course of titrating a 20 µM Acetronitrile solution of receptor 1 with increasing amounts of tetrabutylammonium fluoride (a) and tetrabutylammonium hydroxide (b).
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Binding Energy Studies
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Figure 9. Most stable structure for Host2+.CH3COO- complex in solvent phase (Acetonitrile as a solvent) optimized using B3LYP/6-31g(d) in Gaussian 09. Dashed lines denote the hydrogen bonds (strong and weak). See Table 3 for geometrical parameters and Mulliken charges. Atom numbering included. Atom colors: Grey- Carbon; Red- Oxygen; Blue- Nitrogen; White- Hydrogen.
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To corroborate the experimental results of anion binding with naphthalene receptor the state-of-the-art density functional theory (DFT) calculations have been performed at B3LYP18 level of theory in gas and solvent (acetonitrile) phase. In this study naphthalene containing
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receptor binding with CH3COO-, NO2-, Br-, Cl- and I- anions have been investigated. The proton NMR results show the downfield shifting of naphthalene benzylic CH2 and cationic CH3 peaks for the formation of H-bonding with host2+. anion (CH3COO-, NO2-, Br-, Cl-, I-) complexes. Therefore, we have investigated the binding poses more accurately using the computational methods. All the calculations are carried out using the Gaussian 09 suit of program.19 Figure 9 shows the structure of host2+ and their CH3COO- complex optimized at the B3LYP level using the 6- 31g (d) basis set. The binding energies estimated by experiment and theory are presented in Table 2. 14
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Table 2.Experimental and Computational Binding Energies (BEs) for Host2+ with X-complexes in acetonitrile solvent.a Binding Energies calc
Host2+.CH3COO-
-5.47
-19.98
Host2+.NO2-
-5.38
-17.96
Host2+.Br-
-4.29
-14.86
Host2+.Cl-
-4.15
-9.09
Host2+.I-*
-3.94
-5.94b
a
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Exp
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Complex
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Units are in kcal/mol. Experimental binding energies are derived from UV binding constants. DFT calculations are performed at B3LYP/6-31G(d) level using a polarizable continuum model in solvent phase (acetonitrile) (Zero point corrections are included). bBinding energy of Iodine complex is calculated at the B3LYP/ LANL2DZ level of theory.
The present receptor seems to be formed four C-H…O type H-bonding with acetate anion. On
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the other hand, six C-H…O type hydrogen bonds has been observed in nitrite complex as shown in Figure S20 (see supporting information). The nitrite anion is located between the two arms of N-methylated 2-methylbenzimidazole groups of naphthalene receptor and the nitrite anion
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complex’s hydrogen bonding length is comparable to acetate complex. The binding energy difference between acetate and nitrite complexes has observed to be 2 kcal/mol (See table 2).
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Both nitrite and acetate anions are quantitatively competitive regards of binding with the naphthalene receptor. The halide anions binds with the host2+ four type of C-H…X- (X= Br- , Cl-, I-) type of hydrogen bonds. The bromide anion binding is weaker than the acetate and nitrite anions as observed from Table 2 and Figure S21 (supporting information). All C-H…Br- type hydrogen bond lengths for bromide is observed to be more than 2.5 Å (Figure S21 See supporting information). Similarly, the Chloride and iodide binding also observed to be weaker 15
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as the binding energy and hydrogen bond lengths shown in Table 2 and Figure S22-S23 (See supporting information) respectively. The hydrogen bonding strengths are in good agreement with the experimental NMR results.
Mulliken atomic charges (e)
cx
Host
0.239
0.218
H44
0.253
0.266
H42
0.257
H64
0.252
C33…O1
3.209
3.140
C32…O1 H-bond distances (Å)
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H59…O1
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C11…O1
3.231
2.271 2.121 2.050 2.138
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H64…O1
0.162
3.295
C12…O1
H42…O1
0.217
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Heavy atom distances (Å)
H44…O1
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H59
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Table 3. Mulliken charges and hydrogen bond distances of Host2+and their CH3OO− complex (cx).
Table 3 shows the hydrogen bonding lengths, heavy atom distances and charges of the host2+ and host2+.CH3COO- of the most stable complex. The order of hydrogen bonding strengths are CH2…O > CH3…O.
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TD-DFT Results To further support the experimental observations of the host-anion interactions and to provide a better insight into fundamental H-bonded cavity and anions binding interaction, TD-DFT
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calculations were carried out.
Table 4. Calculated HOMO, LUMO, HOMO-LUMO Gap (HLG), Wavelength (λabs) and Oscillator Strength (f) for Host2+…X- (CH3COO-, NO2-, Br-, Cl-, I-) complexes at B3LYP/6-31g(d) level in gas phase.
(eV) Host2+
-10.984
Host2+.CH3COO- -7.711
Host2+.Br
Host2+.I-*
a
-
-7.345
(eV)
(eV)
-6.656
4.33
-4.102
-4.052
-3.910
-7.683
-3.932
AC C
Host2+.Cl
-
-7.031
HLGa
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-
Host2+.NO2
LUMO
-6.985
3.61
E
-4.288
λabs,calb (nm)
fc
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HOMO
2.98
S1
327.74
0.005
S2
326.39
0.003
S1
394.75
0.015
S2
356.06
0.016
S1
516.15
S2
3.43
3.75
2.70
Confd
Weight (%)
HL
68
HL
70
0.017
HL
70
469.8
0.003
H L+2
66
S1
436.29
0.025
HL
63
S2
434.81
0.010
S1
391.76
0.013
HL
66
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Complex
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TD-DFT calculated data
S2
388.32
0.002
S1
573.99
0.009
HL
68
S2
561.18
0.004
H-1 L
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HOMO, LUMO, and HOMO-LUMO gaps (HLG) are calculated with the B3LYP/6-31G(d) method. bAbsorption energies are calculated with the TD-DFT method at the B3LYP/6-31G(d) level. cOscillator strength. dH and L stands for the predicted HOMO and LUMO, respectively.e*HOMO-LUMO and TD-DFT results are obtained for the iodine complex at B3LYP/LANL2DZ level of theory.
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The frontier molecular orbital diagrams (FMOs), HOMO-LUMO gap, λ values have also been calculated and reported in Table 4 -.
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The corresponding HOMO-LUMO structures are shown in Figure 10. The HOMOLUMO structures for NO2-, Br-, Cl- and I- anion complexes are shown in supporting information Figure S24, S25, S26, and S27, respectively. As shown in Figure 10, the HOMO is located on
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one of the N-methylated 2-methyl benzimidazole. On the other hand the LUMO are located on
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the anion and one of the N-methylated 2-methyl benzimidazole.
(b)
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(a)
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Figure 10. Molecular orbital distribution plots of HOMO (a) and LUMO (b) states in the ground state for Host2+…CH3COO- complex in gas phase.
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Figure S28 (see supporting information) shows the Electrostatic potential surface diagram of Host2+ and Host2+.CH3COO- complex. Figure S28 suggests that significantly enhance the electropositive character of the cavity for the anion interactions have been created between the
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two arms of 2-methyl benzimidazole groups. The blue region between the two arms of Nmethylated 2-methyl benzimidazole shows the possible site for the anion binding. Interestingly, the CH3COO- anion complex in acetonitrile with presently reported naphthalene containing
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host2+ via C-H…O type of H-bonding only. Moreover, the nitrite anion also competitively formed CH2…O > CH3…O type hydrogen bonding complex with the naphthalene receptor
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produced a second highest binding energy due to the presence of oxygen. In addition to this CH…O type H-bonds are appeared to be responsible for strong binding and participate in the molecular recognition.
In Summary, CH2…O and CH3…O type hydrogen bonding appears to be the most significant
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because of this naphthalene containing receptor shows a strong binding affinity towards acetate
Conclusion
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and nitrile anions competitively. The TD-DFT results are consistent with the experimental results.
We have successfully developed a novel 2-methyl benimidazole-based receptor 1. The 1H NMR,
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UV–vis and fluorescence studies show that the receptor is particularly efficient for recognizing acetate. The (CH3)+ --- X- type ionic hydrogen and naphthalene benzylic C-H hydrogen are key hydrogen bond donors for acetate recognition. The binding cavity formed in receptor 1 prefers to accommodate small negatively charged atom such as oxygen. Therefore, acetate and nitrite show strong affinity for receptor 1 in acetonitrile due to negatively charged oxygen in them. Inaddition, 1H NMR titration show that the order of binding affinity for halides are Br- > Cl- > I-. 19
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These results reflect size and basicities of halides. Modeling from the density functional theory supports all of experimental results.
Therefore introducing aliphatic methyl groups as
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recognition element could be a useful moiety for host–guest chemistry.
Experimental Section
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Materials
tetra-n butylammonium hydroxide (TBAOH), tetra-n-butylammonium fluoride (TBAF), tetra-ndihydrogen
phosphate
(TBACH3COO-),
tetra-n-butylammonium
(TBAH2PO4-),
tetra-n-butylammonium
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butylammonium
nitrite
(TBANO2-),and
acetate
tetra-n-butylammonium
bromide (TBABr-), tetra-n-butylammonium chloride (TBACl-) and tetra-n butylammonium
Measurements
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iodide (TBAI-) were purchased from Sigma-Aldrich Chemical Co., Inc., and used as received.
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Absorption spectra were recorded using a biochrom Libra S70 spectrophotometer (Biochrom Ltd, England). NMR spectra were recorded using a BRUKER spectrometer operated at 500
AC C
MHz. ESI MS spectra were obtained using a JMS 700 (Jeol, Japan) double focusing magnetic sector mass spectrometer. All measurements were carried out at room temperature (298 K).
Synthesis
1,8-bis(bromomethyl)naphthalene and 2-methyl-1H-benzo[d]imidazole are available commercially from Sigma Aldrich.
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Receptor 1 To a solution of 2-methybenzimidazole (0.42g, 3.2 mmol) in CH3CN (50 mL), NaOH (25%, 5 mL) aqueous solution was added and the mixture was stirred under N2 for 4 h. Then, 1,8-
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bis(bromomethyl)naphthalene (0.5 g, 1.6 mmol) was added in one portion and the reaction mixture was stirred at rt for 72 h. After completion of the reaction, the precipitate was filtered off, washed thoroughly with CH3CN (3X50 mL) to give the 1,8-bis((2-methyl-1Hbenzo[d]imidazol-1-yl)methyl)naphthalene (0.9 g, 75.6%). Then it was proceeded to next step
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without further purification.
1,8-bis((2-methyl-1H-benzo[d]imidazol-1-yl)methyl)naphthalene (0.9g, 2.2 mmol) was stirred in
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CH3CN (10 mL) at 90 ⁰C under N2 for 10 min, and then methyl iodide (1.22g, 8.6 mmol in 6 mL CH3CN was added in one portion. The mixture was stirred at 90⁰ C under N2 for 72 h. After completion of the reaction, the precipitated solid was filtered off, washed thoroughly with CH3CN (3X50 mL) and diethyl ether (3X50 mL) to give the iodide salt. On treatment of the aqueous solution of the iodide salt with a saturated aqueous solution of NH4PF6, the precipitate formed. The precipitate was collected, washed thoroughly with water, and dried to give the
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hexafluorophosphate salt of the sensor 1 (1.1g, 93%) as white powder. receptor 1:, 1H NMR (500 MHz, ACN-d3), δ 7.97 (m, 4H), 7.73 (m, 4H), 7.70 (t, 2H, J = 1.9 Hz), 7.62 (d, 2H, J = 8.6 Hz), 7.35 (d, 2H, J = 7.0 Hz), 6.63 (d, 2H, J = 8.3 Hz), 6.42 (s, 4H), 4.06 (s, 6H), 2.84 (s, 6H). 13C NMR (500 MHz, ACN-d3): δ 153.66, 137.04, 133.30, 132.22, 131.54, 130.66, 130.58, 127.95, 126.84,
AC C
591.21 [M-PF6]+
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125.41, 118.40, 114.15, 50.93, 33.24, 11.49 mass: calcd for C30H30F12N4P2 m/z = 736.51, found
Acknowledgments
This research was supported by the Basic Science Research Program of the Korean National Research Foundation funded by the Korean Ministry of Education, Science and Technology (2010-0021333). 21
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1. (a) Caltagirone, C. ; Gale, P. A. Chem. Soc. Rev., 2009, 38, 520-563; (b) Wenzel, M. ;
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Campbell, T. ; Pfefferkorn, R. ; Rounsaville, J. F. Ullmann’s Encyclopedia Industrial Chemistry,
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R.; Loeb, S. J. Coord. Chem. Rev., 2003, 240, 77- 99; (e) Kubik, S. Chem. Soc. Rev. 2009, 38,
5. (a) Xu, Z. ; Kim, S.; Yoon, J. Chem. Soc. Rev., 2010, 39, 1457-1466; (b) Yoon, J.; Kim,
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S.K. ; Singh,; N.J.& Kim, K.S., Chem. Soc. Rev.,35, 2006,355–360 ; (c) Niu, H. T.; Yin, Z.; Su, D.;
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Niu, D. ; He, J. ; Cheng, J. P. Dalton Trans., 2008, 3694- 3700 ; (d) Mesquida, N. Dinares, I. ; Ibanez , A. ; Alcalde, E. Org. Biomol. Chem., 2013, 11, 6385- 6396. 6. (a) Shang , J.; Gallagher, N. M.; Bie, F. ; Li, Q. ; Che, Y. ; Wang, Y. ; Jiang, H. J. Org. Chem., 2014, 79, 5134–5144 ; (b) Wang, L. ; Fang, G. ; Ye, D. ; Cao, D. Sensors. and Actuators. B., 2014, 195, 572–580; (c) Benjamin. S ; Schubert, U. S .Chem. Soc. Rev., 2014, 43, 2522-2571 (d) Liu , Y-H.; Zhang. L. ; Xu.X-N. ; Li. Z-M . ; Zhang . D-W.; Zhao.X. ; Li , Z.T. Org. Chem. Front., 2014, 1, 494-500; (e) Haridas, V.; Sahu, S. ; P.P.; Sapala. A .R , 22
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A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.Stratmann, O.
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Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg,S. Dapprich, A. D. Daniels, O. Farkas, J.
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B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian Inc., Wallingford CT, 2009.
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Supporting information
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A selective acetate anion binding receptor: participation via cationic CH3 donors
Thiravidamani Senthil Pandiana, Venkatesan Srinivasadesikanb, M. C. Linb
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Jongmin Kang*a
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b.
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Department of Chemistry, Sejong University, Seoul, 143-747, South Korea Center for Interdisciplinary Molecular Science, Department of Applied Chemistry, National Chiao Tung University, Hsinchu 300, Taiwan
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Email: [email protected]; [email protected]
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4. Fig S4 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium acetate-------------------S8
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5. Fig S5 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium acetate-----S8
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6. Fig S6 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium nitrite--------------------S9 7. Fig S7 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium nitrite-------S9
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8. Fig S8 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium bromide ----------------S10 9. Fig S9 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium bromide---S10
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10. Fig S10 A family of UV-vis spectra recorded over the course of titrating a 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium chloride-----------------------------------------------------------------------------------------S11 11. Fig S11 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium chloride------------------S11 12. Fig S12 A family of fluorescence spectra recorded over the course of titrating a 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium chloride-----------------------------------------------------------------------------------------S12 13. Fig S13 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium chloride----S12
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14. Fig S14 A family of UV-vis spectra recorded over the course of titrating a 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium iodide------------------------------------------------------------------------------------------S13 15. Fig S15 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium chloride----------------S13 16. Fig S16A family of fluorescence spectra recorded over the course of titrating a 20
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µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium iodide-------------------------------------------------------------------------------------------S14
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17. Fig S17 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium iodide------S14 18. Fig S18 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium chloride (0 –78 equiv.) in ACN –d3------------------------------S15
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19. Fig S19 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium ioddie (0 –90 equiv.) in ACN –d3--------------------------------S15
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20. Fig S20 Optimized geometry for Host2+.NO2- complex in solvent phase (ACN as a solvent) at B3LYP/6-31g(d) level in Gaussian 09. Dashed lines denote the hydrogen bonds (strong and weak). --------------------------------------------------------------------S16
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21. Fig S21 Optimized geometry for Host2+.Br- complex in solvent phase (ACN as a solvent) at B3LYP/6-31g(d) level in Gaussian 09. Dashed lines denote the hydrogen bonds (strong and weak). --------------------------------------------------------------------S16 22. Fig S22 Optimized geometry for Host2+.Cl- complex in solvent phase (ACN as a solvent) at B3LYP/6-31g(d) level in Gaussian 09. Dashed lines denote the hydrogen bonds (strong and weak). --------------------------------------------------------------------S17 23. Fig S23 Optimized geometry for Host2+.I- complex in solvent phase (ACN as a solvent) at B3LYP/LANL2DZ level in Gaussian 09. Dashed lines denote the hydrogen bonds (strong and weak). ------------------------------------------------------S17 S3
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25. Fig S25. Molecular orbital distribution plots of HOMO,HOMO-1, LUMO and LUMO+1 states in the ground state of Host2+-Br- complex.----------------------------S19 26. Fig S26. Molecular orbital distribution plots of HOMO,HOMO-1, LUMO and LUMO+1 states in the ground state of Host2+-Cl- complex.----------------------------S20
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27. Fig S27. Molecular orbital distribution plots of HOMO,HOMO-1, LUMO and LUMO+1 states in the ground state of Host2+-I- complex.------------------------------S21
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28. Fig 28. Electrostatic potential of a) Host2+ and b) Host2+.CH3COO- complex at B3LYP/6-31g(d) level in solvent phase using Acetonitrile as a solvent---------------S22
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29. Table S1: The binding energies of host2+-halides- complex in gas phase and solvent phase (Unit:kcal/mol) calculated at B3LYP/6-31G(d)--------------------------S22
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Fig S1. 1H NMR spectrum of compound 1
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Fig S2. 13C NMR spectrum of compound 1
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Fig S3. HRMS(FAB) spectrum of compound 1
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Fig S4 Benesi-Hildebrand plot for the UV-vis titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium actate
Fig S5 Benesi-Hildebrand plot for the fluorescence titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium acetate
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Fig S6 Benesi-Hildebrand plot for the UV-vis titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium nitrite
Fig S7Benesi-Hildebrand plot for the fluorescence titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium nitrite
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Fig S8 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium bromide
Fig S9 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium bromide
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Fig S10. A family of spectra recorded over the course of titrating a 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium chloride
Fig S11 Benesi-Hildebrand plot for the UV-vis titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium chloride
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Fig S12 A family of fluorescence spectra recorded over the course of titrating a 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium chloride
Fig S13 Benesi-Hildebrand plot for the fluorescence titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium chloride
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Fig S14 A family of UV-vis spectra recorded over the course of titrating a 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium iodide
Fig S15 Benesi-Hildebrand plot for the UV-vis titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium iodide
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Fig S16 A family of fluorescence spectra recorded over the course of titrating a 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium iodide
Fig S17 Benesi-Hildebrand plot for the fluorescence titration of 20 µM DMSO solution of receptor 1 with increased amounts of tetrabutylammonium iodide
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Fig S18. 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium chloride (0 –77.8 equiv.) in DMSO-d6
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Fig S19. 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium ioddie (0 –90equiv.) in DMSO-d6
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Figure S20: Most stable structure of Host 2+…NO2- complex in acetonitrile phase using PCM solvation model at B3LYP/6-31g(d) level of theory. Hydrogen bond lengths are noted (Å).
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Figure S21: Most stable structure of Host 2+…Br- complex in acetonitrile phase using PCM solvation model at B3LYP/6-31g(d) level of theory. Hydrogen bond lengths are noted (Å).
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Figure S22: Most stable structure of Host 2+…Cl- complex in acetonitrile phase using PCM solvation model at B3LYP/6-31g(d) level of theory. Hydrogen bond lengths are noted (Å).
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Figure S23: Most stable structure of Host 2+…I- complex in acetonitrile phase using PCM solvation model at B3LYP/LANL2DZ level of theory. Hydrogen bond lengths are noted (Å).
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LUMO+1
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Figure S24: Frontier Molecular Orbital diagram of Host 2+…NO2- complex in gas phase at B3LYP/6-31g(d) level. HOMO: Highest Occupied Molecular Orbital; LUMO: Lowest Un-occupied Molecular Orbital.
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Figure S25: Frontier Molecular Orbital diagram of Host 2+…Br- complex in gas phase at B3LYP/6-31g(d) level. HOMO: Highest Occupied Molecular Orbital; LUMO: Lowest Un-occupied Molecular Orbital.
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Figure S26: Frontier Molecular Orbital diagram of Host 2+…Cl- complex in gas phase at B3LYP/6-31g(d) level. HOMO: Highest Occupied Molecular Orbital; LUMO: Lowest Un-occupied Molecular Orbital.
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Figure S27: Frontier Molecular Orbital diagram of Host 2+…I- complex in gas phase at B3LYP/LANL2DZ level. HOMO: Highest Occupied Molecular Orbital; LUMO: Lowest Un-occupied Molecular Orbital.
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a)
b)
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Figure S28. Electrostatic potential of a) Host2+ and b) Host2+.CH3COO- complex at B3LYP/6-31g(d) level in solvent phase using Acetonitrile as a solvent. Table S1: Experimental and Computational Binding Energies (BEs) for Host2+ with X-complexes in gas and solvent phase (acetonitrile).a
System -
Host.NO2 -
Host.Br Host.Cl -
a
-5.47
Solvent -19.98
-5.38
-157.23
-17.96
-4.29
-155.33
-14.86
-4.15
-151.63
-9.09
-3.94
-135.73
-5.94
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Host.I
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-
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Host.CH3COO
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Exp
Binding Energy Theory Gas -162.72
Units are in kcal/mol. Experimental binding energies are derived from UV binding constants. DFT calculations are performed at B3LYP/6-31G(d) level in gas and solvent phase (acetonitrile) using a polarizable continuum model. (Zero point corrections are included). bBinding energy of Iodine complex is calculated at the B3LYP/ LANL2DZ level of theory.
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S0040-4020(15)01207-7
DOI:
10.1016/j.tet.2015.08.015
Reference:
TET 27037
To appear in:
Tetrahedron
Received Date: 17 June 2015 Revised Date:
3 August 2015
Accepted Date: 5 August 2015
Please cite this article as: Pandian TS, Srinivasadesikan V, Lin MC, Kang J, A selective acetate anion binding receptor: participation via cationic CH3 donors, Tetrahedron (2015), doi: 10.1016/ j.tet.2015.08.015. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Graphical Abstract
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A selective acetate anion binding receptor: participation via cationic CH3 donors
a.
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Thiravidamani Senthil Pandiana, V. Srinivasadesikanb, M. C. Linb, Jongmin Kang*a
Department of Chemistry, Sejong University, Seoul, 143-747, South Korea [email protected]
Center for Interdisciplinary Molecular Science, Department of Applied
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Chemistry, National Chiao Tung University, Hsinchu 300, Taiwan
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Email: [email protected] Abstract
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A novel receptor 1 which has only C-H hydrogen bonds as recognition element has been designed and synthesized. The receptor 1 utilizes cationic CH3 in 2-methyl benzimidazole and naphthalene benzylic C-H as hydrogen bonding donor. The binding cavity formed in receptor 1
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prefers to accommodate small negatively charged atom such as oxygen. Therefore, acetate and nitrite show strong affinity for receptor 1 in acetonitrile due to negatively charged oxygen in
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them. In addition, the order of binding affinity for halides are Br- > Cl- > I-. These results reflect the size and basicities of halides. Further, 1H NMR titration of halide clearly indicates the anionπ interaction. The experimental data from UV-vis, fluorescence and 1H NMR titration are consistent with DFT results. Key words: anion receptor, C-H hydrogen bonds, acetate, nitrite, anion-π interaction
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Introduction
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Carboxylate anion sensor has been thriving area of research getting much attraction from all over the supramolecular groups because of enormous applications in pharmaceutical, biological areas.1 In addition, carboxylates are the most fundamental importance in nature and in chemical
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technology.2 Recent physiological studies evidenced that the anions of weak aliphatic acids such as acetate transiently inhibits myocardial contraction by increasing mitochondrial calcium
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uptake.3. For these logical reasons selective detection of acetate is an impressive facet of anion receptor chemistry. Generally, as the recognition unit for anions, N-H hydrogen such as urea, thiourea, and amide has been utilized.4 However, various polarized C-H groups are proven to be effective hydrogen bond donors. For example, imidazolium5, triazolium6, perimidium7 groups are successfully utilized for anion recognition elements. In addition, aliphatic hydrogen bond
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donor units such as benzylic8 and pure aliphatic9 have been shown to be effective hydrogen bonding element in anion recognition. Further, there have been many detailed studies of C-H
anions.
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level as well as solution level for the diverse
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hydrogen bonding in gas phase10 and solid state
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In addition, Sensors for nitrite anion based on gas phase reactions, electrochemical, colorimetric determination of paper micro fluidic devices and gelators have been developed. However, nitrite sensors generally have developed by using Griess reaction because of its high selectivity. Still, a simple probe for detection of NO2- anion is challenging among the field of supramolecular analytical chemistry. Besides, the primary source of nitrite in our diets is processed (cured) meat or fish, and nitrites are considered a potential reactant precursor for nitrosamines. The serious
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health risks caused by high nitrite exposure are blue baby syndrome, spontaneous abortion, and birth defects in the central nervous system. Because of these reasons determination of nitrite anion has received great interest.12
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Anion - π interactions are usually restricted to aryl derivatives bearing electron-withdrawing substituents. The aryl rings are electron-deficient π center. This phenomenon is ascribed to Coulombic attraction between a negatively charged anion and electron-deficient aromatic ring.
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Even though the numerous solid-state examples, theoretical experiments, few solution-phase examples recognize the anion–π interaction.13
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As an effort to develop a new anion receptor which utilizes only C-H hydrogen bonding, we designed and synthesized a new anion receptor 1 which has naphthalene spacer and 2-methyl benzimidazole as anionic recognition element. Here we’d like to report the synthesis and binding properties of receptor 1. The binding phenomena of receptor 1 could be monitored by UV-vis,
Results and Discussion
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Synthesis
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fluorescence and 1H NMR spectra and the results are consistent with DFT analysis.
1) CH3CN,NaOH
N H
2) CH3I, CH3CN
N
3) aq. NH4PF6
PF6-
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Br
N
Br
N
N N PF61
Receptor 1 was synthesized by the reaction between 2 equivalents of 2-methybenzimidazole and 1,8-bis(bromomethyl)naphthalene. Then, anion exchange with ammonium hexafluorophosphate
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gave receptor 1 bearing two 2-methybenzimidazole arms on naphthalene in 49% overall yield. Receptor 1 was characterized by 1H NMR, 13C NMR, and high-resolution mass spectrometry
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Interactions with acetate The ability of receptor 1 to recognize acetate was studied in acetonitrile using UV–vis titration spectra. The receptor 1 displayed strong absorption band at 226 nm in acetonitrile. Figure 1a
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shows the family of UV-vis spectra obtained over the course of the titration of solution 1 with tetrabutylammonium acetate in acetonitrile. As acetate ions were added to the 20 µM acetonitrile
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solution of 1, the absorbance peak at 279 nm was gradually decreased with small bathochromic shift. In addition, there were well-defined isosbestic points at 223nm, 231nm, 238nm, which indicated that new species were formed by the interaction of 1 and acetate. In addition, the receptor 1 displayed strong fluorescence emission in acetonitrile as shown in Figure 1b. The excitation and emission wavelength were 271 and 347nm, respectively. The intensity of emission
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spectrum from 20 µM solution of the receptor 1 gradually decreased as the concentration of tetrabutylammonium acetate was increased (1–26 equiv), which also indicates the association
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between the receptor 1 and acetate.
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Figure 1. Family of UV–vis spectra (a) and fluorescence spectra (b) recorded over the course of titration of 20 µM acetonitrile solutions of the receptor 1 with the standard solution tetrabutylammonium acetate
The complexation abilities of receptor 1 to acetate was also measured by standard 1H NMR titration experiments in CD3CN using a constant host concentration (2 mM) and increasing
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concentrations of acetate anions. The addition of tetrabutylammonium acetate salts to the solution of receptor 1 in CD3CN resulted in large downfield shifts of benzimdazole C2-CH3 and benzylic C-H. (Figure 2) For example, addition of tetrabutylammonium acetate moved
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benzimdazole C2-CH3 from 2.84 to 2.89 ppm and benzylic C-H from 6.41 to 6.70 ppm. The downfield shifts of these protons indicate the presence of a hydrogen bond interaction between
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these C-H hydrogens and acetate ion.
6
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Figure 2. 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium acetate (0 –2.5 equiv.) in CD3CN
AC C
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The stoichiometry between receptor 1 and acetate was determined to be 1:1 using a UV Job plot in acetonitrile (Figure 3).
Figure 3. Job plots of receptor 1 with tetrabutylammonium acetate, nitrate and bromide obtained by UV-vis in acetonitrile.
A Benesi–Hildebrand plot 14 by use of change at 279 nm in UV–vis spectrum and 347 nm in fluorescence spectrum gave the association constants. The association constants calculated were
7
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1.0 X 104 M-1 from UV–vis titration and 1.0 X 104 M-1 from fluorescence titration, respectively. In addition, analysis of chemical shift utilizing EQNMR15 gave the association constant of
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1.1 X 104 M-1 which is similar to the values obtained from UV–vis and fluorescence titrations.
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Interactions with nitrite
The abilities of receptor 1 to recognize with nitrite were also studied in acetonitrile using UV–vis
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titration spectra. The receptor 1 in acetonitrile exhibits absorption band at 226nm, 271nm and 279nm. When the amount of nitrite was increased, small bathochromic shift of λmax observed with an isosbestic point at 254 nm (Figure 4a). The existence of isosbestic point for UV-vis titrations of receptor 1 with nitrite suggests a 1:1 complexation, and this binding stoichiometry
AC C
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was confirmed by UV –vis Job’s plot analysis (Figure 3)
(a)
(b)
Figure 4. Family of UV–vis spectra (a) and fluorescence spectra (b) recorded over the course of titration of 20 µM acetonitrile solutions of the receptor 1 with the standard solution tetrabutylammonium nitrite
8
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In addition, the intensity of emission spectrum from the receptor 1 gradually decreased as the concentration of tetrabutylammonium nitrite salts was increased (1 –30 equiv), which also indicates the association between the receptor 1 and nitrite (Figure 4b). From these experiments,
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association constants for nitrite were calculated as 8.8 X 103 M-1and 8.7 X 103 M-1 from the UV– vis and fluorescence titrations, respectively.
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Hydrogen bond formation was confirmed by 1H NMR titration. When nitrite was added, benzimdazole C2-CH3 and benzylic C-H moved to downfield (Figure 5). For example,
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benzimdazole C2-CH3 moved from 2.84 to 2.87ppm and benzylic C-H from 6.41ppm to 6.66ppm respectively. The association constants calculated for nitrite were calculated as 9.2 X 103 for 1H NMR titration. Surprisingly, the resulting association constant for nitrite anion is much
AC C
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comparable with acetate anion complex with receptor 1.
Figure 5. 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium nitrite (0 –5.1 equiv.) in CD3CN
9
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Interactions with halides
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The receptor 1 showed similar titration behaviors for halides. For example, when the amount of bromide was increased, small bathochromic shift of λmax along with sharp isosbestic points at 223 and 236 nm were observed (Figure 6a). The stoichiometry between receptor 1 and bromide was confirmed by Job’s plot analysis (Figure 3). In addition, the intensity of emission spectrum
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from the receptor 1 gradually decreased as the concentration of tetrabutylammonium bromide
M AN U
salts was increased (10–190 equiv), which also indicates the association between the receptor 1 and bromide (Figure 6b). From these experiments, association constants for bromide were calculated as 1.4 X 103 M-1and 1.5 X 103 M-1 from the UV–vis and fluorescence titrations,
AC C
EP
TE D
respectively.
(a)
(b)
Figure 6. Family of UV–vis spectra (a) and fluorescence spectra (b) recorded over the course of titration of 20 µM acetonitrile solutions of the receptor 1 with the standard solution tetrabutylammonium bromide
10
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Hydrogen bond formation was also confirmed by 1H NMR titration. For example, addition of tetrabutylammonium bromide moved benzimdazole C2-CH3 from 2.84 to 3.04 ppm and benzylic C-H from 6.42 to 7.09 ppm (Figure 7). The downfield shifts of these protons indicate the
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presence of a hydrogen bond interaction between these C-H hydrogens and bromide ion, whereas the upfield shift of benzimidazole’s aromatic CH proton from xx ppm to xx ppm could be ascribed to charge transfer interaction of bromide with electron deficient aromatic ring, namely
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anion-π interaction16 (Figure 7). These anion-π interactions are pronounced with halide anions. Therefore, Chloride and bromide showed similar 1H NMR spectral changes with receptor 1. (see
AC C
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Figure S18 and S19). Calculated binding constants for other anions are summarized in Table 1.
Figure 7. 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium bromide (0 – 66 equiv.) in CD3CN
We also tried dihydrogen phosphate and hydrogen sulfate However, dihydrogen phosphate only gave precipitation with receptor 1 and hydrogen sulfate did not bind to receptor 1 at all. 11
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From the experiment we concluded that the selectivity of halide anions were in the order of Br>Cl->I1
UV
H NMRa
Fluorescence
1.0 X104
1.1X104
1.0X104
NO2-
8.8 X 103
9.2X 103
8.7 X 103
Br-
1.4 X103
1.5 X103
1.5 X103
Cl-
1.2 X 103
1.2 X 103
1.3 X 103
I-
7.8X 102
7.9X 102
7.4X 102
Errors are less than 15 %
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a.
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CH3COO-
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TBA-Anions
Table 1 Association constants (M-1) of receptors 1 with various anions in Acetonitrile
Deprotonation of C2-CH3 was observed with highly basic fluoride 17 and it was confirmed through titration with hydroxide ion. Changes in the absorbance spectra in the presence of
AC C
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other anions. (Figure 8)
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hydroxide and fluoride were almost identical and were clearly different from those observed for
12
(b)
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(a)
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AC C
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Figure 8. Family of UV-vis spectra recorded over the course of titrating a 20 µM Acetronitrile solution of receptor 1 with increasing amounts of tetrabutylammonium fluoride (a) and tetrabutylammonium hydroxide (b).
13
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Binding Energy Studies
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Figure 9. Most stable structure for Host2+.CH3COO- complex in solvent phase (Acetonitrile as a solvent) optimized using B3LYP/6-31g(d) in Gaussian 09. Dashed lines denote the hydrogen bonds (strong and weak). See Table 3 for geometrical parameters and Mulliken charges. Atom numbering included. Atom colors: Grey- Carbon; Red- Oxygen; Blue- Nitrogen; White- Hydrogen.
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To corroborate the experimental results of anion binding with naphthalene receptor the state-of-the-art density functional theory (DFT) calculations have been performed at B3LYP18 level of theory in gas and solvent (acetonitrile) phase. In this study naphthalene containing
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receptor binding with CH3COO-, NO2-, Br-, Cl- and I- anions have been investigated. The proton NMR results show the downfield shifting of naphthalene benzylic CH2 and cationic CH3 peaks for the formation of H-bonding with host2+. anion (CH3COO-, NO2-, Br-, Cl-, I-) complexes. Therefore, we have investigated the binding poses more accurately using the computational methods. All the calculations are carried out using the Gaussian 09 suit of program.19 Figure 9 shows the structure of host2+ and their CH3COO- complex optimized at the B3LYP level using the 6- 31g (d) basis set. The binding energies estimated by experiment and theory are presented in Table 2. 14
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Table 2.Experimental and Computational Binding Energies (BEs) for Host2+ with X-complexes in acetonitrile solvent.a Binding Energies calc
Host2+.CH3COO-
-5.47
-19.98
Host2+.NO2-
-5.38
-17.96
Host2+.Br-
-4.29
-14.86
Host2+.Cl-
-4.15
-9.09
Host2+.I-*
-3.94
-5.94b
a
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Exp
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Complex
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Units are in kcal/mol. Experimental binding energies are derived from UV binding constants. DFT calculations are performed at B3LYP/6-31G(d) level using a polarizable continuum model in solvent phase (acetonitrile) (Zero point corrections are included). bBinding energy of Iodine complex is calculated at the B3LYP/ LANL2DZ level of theory.
The present receptor seems to be formed four C-H…O type H-bonding with acetate anion. On
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the other hand, six C-H…O type hydrogen bonds has been observed in nitrite complex as shown in Figure S20 (see supporting information). The nitrite anion is located between the two arms of N-methylated 2-methylbenzimidazole groups of naphthalene receptor and the nitrite anion
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complex’s hydrogen bonding length is comparable to acetate complex. The binding energy difference between acetate and nitrite complexes has observed to be 2 kcal/mol (See table 2).
AC C
Both nitrite and acetate anions are quantitatively competitive regards of binding with the naphthalene receptor. The halide anions binds with the host2+ four type of C-H…X- (X= Br- , Cl-, I-) type of hydrogen bonds. The bromide anion binding is weaker than the acetate and nitrite anions as observed from Table 2 and Figure S21 (supporting information). All C-H…Br- type hydrogen bond lengths for bromide is observed to be more than 2.5 Å (Figure S21 See supporting information). Similarly, the Chloride and iodide binding also observed to be weaker 15
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as the binding energy and hydrogen bond lengths shown in Table 2 and Figure S22-S23 (See supporting information) respectively. The hydrogen bonding strengths are in good agreement with the experimental NMR results.
Mulliken atomic charges (e)
cx
Host
0.239
0.218
H44
0.253
0.266
H42
0.257
H64
0.252
C33…O1
3.209
3.140
C32…O1 H-bond distances (Å)
EP
H59…O1
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C11…O1
3.231
2.271 2.121 2.050 2.138
AC C
H64…O1
0.162
3.295
C12…O1
H42…O1
0.217
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Heavy atom distances (Å)
H44…O1
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H59
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Table 3. Mulliken charges and hydrogen bond distances of Host2+and their CH3OO− complex (cx).
Table 3 shows the hydrogen bonding lengths, heavy atom distances and charges of the host2+ and host2+.CH3COO- of the most stable complex. The order of hydrogen bonding strengths are CH2…O > CH3…O.
16
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TD-DFT Results To further support the experimental observations of the host-anion interactions and to provide a better insight into fundamental H-bonded cavity and anions binding interaction, TD-DFT
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calculations were carried out.
Table 4. Calculated HOMO, LUMO, HOMO-LUMO Gap (HLG), Wavelength (λabs) and Oscillator Strength (f) for Host2+…X- (CH3COO-, NO2-, Br-, Cl-, I-) complexes at B3LYP/6-31g(d) level in gas phase.
(eV) Host2+
-10.984
Host2+.CH3COO- -7.711
Host2+.Br
Host2+.I-*
a
-
-7.345
(eV)
(eV)
-6.656
4.33
-4.102
-4.052
-3.910
-7.683
-3.932
AC C
Host2+.Cl
-
-7.031
HLGa
EP
-
Host2+.NO2
LUMO
-6.985
3.61
E
-4.288
λabs,calb (nm)
fc
M AN U
HOMO
2.98
S1
327.74
0.005
S2
326.39
0.003
S1
394.75
0.015
S2
356.06
0.016
S1
516.15
S2
3.43
3.75
2.70
Confd
Weight (%)
HL
68
HL
70
0.017
HL
70
469.8
0.003
H L+2
66
S1
436.29
0.025
HL
63
S2
434.81
0.010
S1
391.76
0.013
HL
66
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Complex
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TD-DFT calculated data
S2
388.32
0.002
S1
573.99
0.009
HL
68
S2
561.18
0.004
H-1 L
67
HOMO, LUMO, and HOMO-LUMO gaps (HLG) are calculated with the B3LYP/6-31G(d) method. bAbsorption energies are calculated with the TD-DFT method at the B3LYP/6-31G(d) level. cOscillator strength. dH and L stands for the predicted HOMO and LUMO, respectively.e*HOMO-LUMO and TD-DFT results are obtained for the iodine complex at B3LYP/LANL2DZ level of theory.
17
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The frontier molecular orbital diagrams (FMOs), HOMO-LUMO gap, λ values have also been calculated and reported in Table 4 -.
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The corresponding HOMO-LUMO structures are shown in Figure 10. The HOMOLUMO structures for NO2-, Br-, Cl- and I- anion complexes are shown in supporting information Figure S24, S25, S26, and S27, respectively. As shown in Figure 10, the HOMO is located on
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one of the N-methylated 2-methyl benzimidazole. On the other hand the LUMO are located on
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the anion and one of the N-methylated 2-methyl benzimidazole.
(b)
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(a)
AC C
Figure 10. Molecular orbital distribution plots of HOMO (a) and LUMO (b) states in the ground state for Host2+…CH3COO- complex in gas phase.
18
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Figure S28 (see supporting information) shows the Electrostatic potential surface diagram of Host2+ and Host2+.CH3COO- complex. Figure S28 suggests that significantly enhance the electropositive character of the cavity for the anion interactions have been created between the
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two arms of 2-methyl benzimidazole groups. The blue region between the two arms of Nmethylated 2-methyl benzimidazole shows the possible site for the anion binding. Interestingly, the CH3COO- anion complex in acetonitrile with presently reported naphthalene containing
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host2+ via C-H…O type of H-bonding only. Moreover, the nitrite anion also competitively formed CH2…O > CH3…O type hydrogen bonding complex with the naphthalene receptor
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produced a second highest binding energy due to the presence of oxygen. In addition to this CH…O type H-bonds are appeared to be responsible for strong binding and participate in the molecular recognition.
In Summary, CH2…O and CH3…O type hydrogen bonding appears to be the most significant
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because of this naphthalene containing receptor shows a strong binding affinity towards acetate
Conclusion
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and nitrile anions competitively. The TD-DFT results are consistent with the experimental results.
We have successfully developed a novel 2-methyl benimidazole-based receptor 1. The 1H NMR,
AC C
UV–vis and fluorescence studies show that the receptor is particularly efficient for recognizing acetate. The (CH3)+ --- X- type ionic hydrogen and naphthalene benzylic C-H hydrogen are key hydrogen bond donors for acetate recognition. The binding cavity formed in receptor 1 prefers to accommodate small negatively charged atom such as oxygen. Therefore, acetate and nitrite show strong affinity for receptor 1 in acetonitrile due to negatively charged oxygen in them. Inaddition, 1H NMR titration show that the order of binding affinity for halides are Br- > Cl- > I-. 19
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These results reflect size and basicities of halides. Modeling from the density functional theory supports all of experimental results.
Therefore introducing aliphatic methyl groups as
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recognition element could be a useful moiety for host–guest chemistry.
Experimental Section
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Materials
tetra-n butylammonium hydroxide (TBAOH), tetra-n-butylammonium fluoride (TBAF), tetra-ndihydrogen
phosphate
(TBACH3COO-),
tetra-n-butylammonium
(TBAH2PO4-),
tetra-n-butylammonium
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butylammonium
nitrite
(TBANO2-),and
acetate
tetra-n-butylammonium
bromide (TBABr-), tetra-n-butylammonium chloride (TBACl-) and tetra-n butylammonium
Measurements
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iodide (TBAI-) were purchased from Sigma-Aldrich Chemical Co., Inc., and used as received.
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Absorption spectra were recorded using a biochrom Libra S70 spectrophotometer (Biochrom Ltd, England). NMR spectra were recorded using a BRUKER spectrometer operated at 500
AC C
MHz. ESI MS spectra were obtained using a JMS 700 (Jeol, Japan) double focusing magnetic sector mass spectrometer. All measurements were carried out at room temperature (298 K).
Synthesis
1,8-bis(bromomethyl)naphthalene and 2-methyl-1H-benzo[d]imidazole are available commercially from Sigma Aldrich.
20
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Receptor 1 To a solution of 2-methybenzimidazole (0.42g, 3.2 mmol) in CH3CN (50 mL), NaOH (25%, 5 mL) aqueous solution was added and the mixture was stirred under N2 for 4 h. Then, 1,8-
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bis(bromomethyl)naphthalene (0.5 g, 1.6 mmol) was added in one portion and the reaction mixture was stirred at rt for 72 h. After completion of the reaction, the precipitate was filtered off, washed thoroughly with CH3CN (3X50 mL) to give the 1,8-bis((2-methyl-1Hbenzo[d]imidazol-1-yl)methyl)naphthalene (0.9 g, 75.6%). Then it was proceeded to next step
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without further purification.
1,8-bis((2-methyl-1H-benzo[d]imidazol-1-yl)methyl)naphthalene (0.9g, 2.2 mmol) was stirred in
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CH3CN (10 mL) at 90 ⁰C under N2 for 10 min, and then methyl iodide (1.22g, 8.6 mmol in 6 mL CH3CN was added in one portion. The mixture was stirred at 90⁰ C under N2 for 72 h. After completion of the reaction, the precipitated solid was filtered off, washed thoroughly with CH3CN (3X50 mL) and diethyl ether (3X50 mL) to give the iodide salt. On treatment of the aqueous solution of the iodide salt with a saturated aqueous solution of NH4PF6, the precipitate formed. The precipitate was collected, washed thoroughly with water, and dried to give the
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hexafluorophosphate salt of the sensor 1 (1.1g, 93%) as white powder. receptor 1:, 1H NMR (500 MHz, ACN-d3), δ 7.97 (m, 4H), 7.73 (m, 4H), 7.70 (t, 2H, J = 1.9 Hz), 7.62 (d, 2H, J = 8.6 Hz), 7.35 (d, 2H, J = 7.0 Hz), 6.63 (d, 2H, J = 8.3 Hz), 6.42 (s, 4H), 4.06 (s, 6H), 2.84 (s, 6H). 13C NMR (500 MHz, ACN-d3): δ 153.66, 137.04, 133.30, 132.22, 131.54, 130.66, 130.58, 127.95, 126.84,
AC C
591.21 [M-PF6]+
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125.41, 118.40, 114.15, 50.93, 33.24, 11.49 mass: calcd for C30H30F12N4P2 m/z = 736.51, found
Acknowledgments
This research was supported by the Basic Science Research Program of the Korean National Research Foundation funded by the Korean Ministry of Education, Science and Technology (2010-0021333). 21
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AC C
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AC C
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14. Benesi, H.; Hildebrand, H. J. Am. Chem. Soc. 1949, 71, 2703-2707. 15. Hynes, M. J.; EQNMR, J. Chem. Soc. Dalton Trans. 1993, 311-312.
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16. Zapata, F.; Gonzalez, L.; Caballero, A.; Alkorta, I.; Elguero, J. and Molina, P. Chem. Eur. J., 2015, 21, 9797–9808.
17. Amendola, V. ; Boiocchi, M.; Fabbrizzi, L.; Fusco, N. Eur. J. Org. Chem. 2011, 6434–6444. 18. A. D. Becke, Phys. ReV. 1988, A38, 3098-3100. A. D. Becke, J. Chem. Phys. 1993, 98, 5648-5652 ; (b) A. D. Becke, J. Chem. Phys. 1997, 107, 8554-8560 ; (c) H. L. Schmider, A. D. Becke . J. Chem. Phys. 1998, 108, 9624-9631. 24
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19. Gaussian 09, Revision A.02, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M.
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Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari,
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A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.Stratmann, O.
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Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg,S. Dapprich, A. D. Daniels, O. Farkas, J.
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B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian Inc., Wallingford CT, 2009.
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Supporting information
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A selective acetate anion binding receptor: participation via cationic CH3 donors
Thiravidamani Senthil Pandiana, Venkatesan Srinivasadesikanb, M. C. Linb
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Jongmin Kang*a
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Department of Chemistry, Sejong University, Seoul, 143-747, South Korea Center for Interdisciplinary Molecular Science, Department of Applied Chemistry, National Chiao Tung University, Hsinchu 300, Taiwan
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Email: [email protected]; [email protected]
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4. Fig S4 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium acetate-------------------S8
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5. Fig S5 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium acetate-----S8
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6. Fig S6 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium nitrite--------------------S9 7. Fig S7 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium nitrite-------S9
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8. Fig S8 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium bromide ----------------S10 9. Fig S9 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium bromide---S10
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10. Fig S10 A family of UV-vis spectra recorded over the course of titrating a 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium chloride-----------------------------------------------------------------------------------------S11 11. Fig S11 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium chloride------------------S11 12. Fig S12 A family of fluorescence spectra recorded over the course of titrating a 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium chloride-----------------------------------------------------------------------------------------S12 13. Fig S13 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium chloride----S12
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14. Fig S14 A family of UV-vis spectra recorded over the course of titrating a 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium iodide------------------------------------------------------------------------------------------S13 15. Fig S15 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium chloride----------------S13 16. Fig S16A family of fluorescence spectra recorded over the course of titrating a 20
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µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium iodide-------------------------------------------------------------------------------------------S14
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17. Fig S17 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium iodide------S14 18. Fig S18 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium chloride (0 –78 equiv.) in ACN –d3------------------------------S15
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19. Fig S19 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium ioddie (0 –90 equiv.) in ACN –d3--------------------------------S15
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20. Fig S20 Optimized geometry for Host2+.NO2- complex in solvent phase (ACN as a solvent) at B3LYP/6-31g(d) level in Gaussian 09. Dashed lines denote the hydrogen bonds (strong and weak). --------------------------------------------------------------------S16
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21. Fig S21 Optimized geometry for Host2+.Br- complex in solvent phase (ACN as a solvent) at B3LYP/6-31g(d) level in Gaussian 09. Dashed lines denote the hydrogen bonds (strong and weak). --------------------------------------------------------------------S16 22. Fig S22 Optimized geometry for Host2+.Cl- complex in solvent phase (ACN as a solvent) at B3LYP/6-31g(d) level in Gaussian 09. Dashed lines denote the hydrogen bonds (strong and weak). --------------------------------------------------------------------S17 23. Fig S23 Optimized geometry for Host2+.I- complex in solvent phase (ACN as a solvent) at B3LYP/LANL2DZ level in Gaussian 09. Dashed lines denote the hydrogen bonds (strong and weak). ------------------------------------------------------S17 S3
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25. Fig S25. Molecular orbital distribution plots of HOMO,HOMO-1, LUMO and LUMO+1 states in the ground state of Host2+-Br- complex.----------------------------S19 26. Fig S26. Molecular orbital distribution plots of HOMO,HOMO-1, LUMO and LUMO+1 states in the ground state of Host2+-Cl- complex.----------------------------S20
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27. Fig S27. Molecular orbital distribution plots of HOMO,HOMO-1, LUMO and LUMO+1 states in the ground state of Host2+-I- complex.------------------------------S21
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28. Fig 28. Electrostatic potential of a) Host2+ and b) Host2+.CH3COO- complex at B3LYP/6-31g(d) level in solvent phase using Acetonitrile as a solvent---------------S22
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29. Table S1: The binding energies of host2+-halides- complex in gas phase and solvent phase (Unit:kcal/mol) calculated at B3LYP/6-31G(d)--------------------------S22
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Fig S1. 1H NMR spectrum of compound 1
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Fig S2. 13C NMR spectrum of compound 1
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Fig S3. HRMS(FAB) spectrum of compound 1
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Fig S4 Benesi-Hildebrand plot for the UV-vis titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium actate
Fig S5 Benesi-Hildebrand plot for the fluorescence titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium acetate
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Fig S6 Benesi-Hildebrand plot for the UV-vis titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium nitrite
Fig S7Benesi-Hildebrand plot for the fluorescence titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium nitrite
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Fig S8 Benesi-Hildebrand plot for the UV-vis titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium bromide
Fig S9 Benesi-Hildebrand plot for the fluorescence titration of 20 µM ACN solution of receptor 1 with increased amounts of tetrabutylammonium bromide
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Fig S10. A family of spectra recorded over the course of titrating a 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium chloride
Fig S11 Benesi-Hildebrand plot for the UV-vis titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium chloride
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Fig S12 A family of fluorescence spectra recorded over the course of titrating a 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium chloride
Fig S13 Benesi-Hildebrand plot for the fluorescence titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium chloride
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Fig S14 A family of UV-vis spectra recorded over the course of titrating a 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium iodide
Fig S15 Benesi-Hildebrand plot for the UV-vis titration of 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium iodide
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Fig S16 A family of fluorescence spectra recorded over the course of titrating a 20 µM acetonitrile solution of receptor 1 with increased amounts of tetrabutylammonium iodide
Fig S17 Benesi-Hildebrand plot for the fluorescence titration of 20 µM DMSO solution of receptor 1 with increased amounts of tetrabutylammonium iodide
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Fig S18. 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium chloride (0 –77.8 equiv.) in DMSO-d6
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Fig S19. 1H NMR spectra of 2 mM of receptor 1 containing increasing amounts of tetrabutylammonium ioddie (0 –90equiv.) in DMSO-d6
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Figure S20: Most stable structure of Host 2+…NO2- complex in acetonitrile phase using PCM solvation model at B3LYP/6-31g(d) level of theory. Hydrogen bond lengths are noted (Å).
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Figure S21: Most stable structure of Host 2+…Br- complex in acetonitrile phase using PCM solvation model at B3LYP/6-31g(d) level of theory. Hydrogen bond lengths are noted (Å).
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Figure S22: Most stable structure of Host 2+…Cl- complex in acetonitrile phase using PCM solvation model at B3LYP/6-31g(d) level of theory. Hydrogen bond lengths are noted (Å).
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Figure S23: Most stable structure of Host 2+…I- complex in acetonitrile phase using PCM solvation model at B3LYP/LANL2DZ level of theory. Hydrogen bond lengths are noted (Å).
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LUMO+1
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Figure S24: Frontier Molecular Orbital diagram of Host 2+…NO2- complex in gas phase at B3LYP/6-31g(d) level. HOMO: Highest Occupied Molecular Orbital; LUMO: Lowest Un-occupied Molecular Orbital.
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Figure S25: Frontier Molecular Orbital diagram of Host 2+…Br- complex in gas phase at B3LYP/6-31g(d) level. HOMO: Highest Occupied Molecular Orbital; LUMO: Lowest Un-occupied Molecular Orbital.
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Figure S26: Frontier Molecular Orbital diagram of Host 2+…Cl- complex in gas phase at B3LYP/6-31g(d) level. HOMO: Highest Occupied Molecular Orbital; LUMO: Lowest Un-occupied Molecular Orbital.
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Figure S27: Frontier Molecular Orbital diagram of Host 2+…I- complex in gas phase at B3LYP/LANL2DZ level. HOMO: Highest Occupied Molecular Orbital; LUMO: Lowest Un-occupied Molecular Orbital.
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a)
b)
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Figure S28. Electrostatic potential of a) Host2+ and b) Host2+.CH3COO- complex at B3LYP/6-31g(d) level in solvent phase using Acetonitrile as a solvent. Table S1: Experimental and Computational Binding Energies (BEs) for Host2+ with X-complexes in gas and solvent phase (acetonitrile).a
System -
Host.NO2 -
Host.Br Host.Cl -
a
-5.47
Solvent -19.98
-5.38
-157.23
-17.96
-4.29
-155.33
-14.86
-4.15
-151.63
-9.09
-3.94
-135.73
-5.94
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Binding Energy Theory Gas -162.72
Units are in kcal/mol. Experimental binding energies are derived from UV binding constants. DFT calculations are performed at B3LYP/6-31G(d) level in gas and solvent phase (acetonitrile) using a polarizable continuum model. (Zero point corrections are included). bBinding energy of Iodine complex is calculated at the B3LYP/ LANL2DZ level of theory.
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