Inclusion complexation of novel synthesis amino acid based ionic liquids with β-cyclodextrin

Journal Pre-proof Inclusion complexation of novel synthesis amino acid based ionic liquids with β-cyclodextrin

Manoj Kumar Banjare, Ramesh Kumar Banjare, Kamalakanta Behera, Siddharth Pandey, Prashant Mundeja, Kallol K. Ghosh PII:

S0167-7322(19)34558-1

DOI:

https://doi.org/10.1016/j.molliq.2019.112204

Reference:

MOLLIQ 112204

To appear in:

Journal of Molecular Liquids

Received date:

13 August 2019

Revised date:

21 November 2019

Accepted date:

23 November 2019

Please cite this article as: M.K. Banjare, R.K. Banjare, K. Behera, et al., Inclusion complexation of novel synthesis amino acid based ionic liquids with β-cyclodextrin, Journal of Molecular Liquids(2018), https://doi.org/10.1016/j.molliq.2019.112204

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© 2018 Published by Elsevier.

Journal Pre-proof

Inclusion Complexation of Novel Synthesis Amino Acid Based Ionic Liquids with β-Cyclodextrin Manoj Kumar Banjarea,b* and Ramesh Kumar Banjareb, Kamalakanta Beherac, Siddharth Pandeyd, Prashant Mundejab and Kallol K. Ghosha* a

School of Studies in Chemistry, Pt. Ravishankar Shukla University, Raipur, 492 010, Chhattisgarh, India.

b

MATS School of Sciences, MATS University, Pagariya Complex, Pandari, Raipur (C.G.), 492001, India.

c

Centre for Interdisciplinary Research in Basic Sciences, JMI, Jamia Nagar, New Delhi, 110025, India.

d

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Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India.

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Graphical Abstract

Inclusion complexation ( IC ) between amino acid based ionic liquids i .e., 1-(2(octylamino)-2-oxoethyl)pyridin-1-ium

bromide

and

4-((hydroxyimino)methyl)-1-(2-

(octylamino)-2-oxoethyl)pyridin-1-ium bromide with β-cyclodextrin have been investigated by UV-Vis, FT-IR and 1H NMR spectroscopy. 1:1 stoichiometry of IC has been observed using Job plot method and confirmed by FT-IR and 1H NMR.

1

Journal Pre-proof Abstract Inclusion complex formation between amino acid based ionic liquids (AAILs) i.e., 1-(2(octylamino)-2-oxoethyl)pyridin-1-ium

bromide

and

4-((hydroxyimino)methyl)-1-(2-

(octylamino)-2-oxoethyl)pyridin-1-ium bromide into β-cyclodextrin have been investigated in solution. The inclusion complexes (ICs) of AAILs with β-CD were synthesized through the co-precipitation method. The solid IC formation is characterized by numerous analytical techniques, primarily by UV-vis spectroscopy and secondary by major techniques i.e., FT-IR and 1H-NMR. The binding constant and 1:1 stoichiometric of ICs nature of the complex between AAILs and β-CD in solution were determined by Job’s plot method using UV-vis

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spectroscopy. As results suggest, the binding constants of ICs are higher for OAOEPB- β-CD as compared to HIMOAOEPB-β-CD. The different thermodynamic parameters such as

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change in standard Gibbs free energy (ΔG0), standard enthalpy changes (ΔH0) and standard entropy change (ΔS0) have been estimated with the help of van’t Hoff equation. Noteworthy

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changes of IR stretching frequency also support the IC formation. 1H-NMR results suggest

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that the tail part of AAILs is more suitably included inside the hydrophobic cavity of β-CD

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and it shows 1:1 stoichiometric ICs formation.

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Keywords: Ionic liquids, Cyclodextrin, Inclusion complex, FTIR and NMR

* Author for correspondence Mobile No: +91-98277-68119 E-mail: [email protected]; [email protected]

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Journal Pre-proof 1. Introduction In recent years biocompatible and biodegradable ionic liquids (ILs) have been synthesized for biomedical and biochemical applications [1]. ILs have been used to solubilize biomaterials such as cellulose [2-3], inhibit or enhance enzyme activities [4-5], enhance antibiotic effectiveness or act as novel antimicrobial compounds and act as drug delivery system [6-7]. An attractive feature of ILs is the ability to fine-tune the structure, to tailor the properties for a particular purpose. Their toxicity and bio-degradation assessment plays very significant role for the design and development of IL [8]. AAILs have numerous potential applications includes heterogeneous catalysis, electrochemical and biosensors, CO2 capture, analytic

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devices and solvents for chemical transformation, cellulose dissolution, extraction and separation processes etc. [9-11].

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Cyclodextrins are macro cyclic oligosaccharides molecules which consists of α-(1,4)linked D-(+)-glucopyranose units and are known as α-, β- and γ-cyclodextrins, respectively

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[12-14]. Cyclodextrin contain three dimensional molecular configurations (i) the upper/wider

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rim containing secondary hydroxyl groups and (ii) the lower/narrower rim having primary hydroxyl groups [15-18]. Through the alkyl chain and other non covalent interaction of the

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ILs, they can form various self-assembly structures in aqueous solution, including host molecules (α-, β- and γ-cyclodextrins) which have found many applications in the fields of

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cosmetic, drug delivery and material science etc [19-23]. Considerable interests have been centered on the nature of the interaction during the host-guest complexation as well as the

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structure of the CD complexes [24-25]. Molecular modeling, simulation, X-ray crystallography, NMR, FTIR spectroscopy, optical spectroscopy (UV-Vis, fluorescence, circular dichroism) and thermal characterization methods have been frequently used to determine the molecular structure of ICs [26-30]. Amino acids ILs were introduced just 15 years ago. Ohno and coworkers31 have synthesized the amino acid ILs for the first time in 2005. They prepared these ILs using 20 natural amino acids. In the preparation of AAILs the anion exchange method has been used [31]. This procedure includes the preparation of imidazolium hydroxide to neutralize a series of amino acids. 1-ethyl-3-methylimidazolium cation has been chosen for the study having excellent ability to form RTILs with amino acids. This easy method of preparation has become the standard procedure to produce AA anion ILs [32]. Shen et al.[33] have studied the interaction between 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide [C4mim][NTf2], 1-hexyl-2,3-dimethylimidazolium chloride [C6mmim][Cl] and 1-dodecyl-3methylimidazolium bis-(trifluoromethylsulfonyl)imide [C12mim][NTf2] with β-cyclodextrin (β-CD). Different 1:1 stochiometric ICs derivatives were obtained with the ILs 3

Journal Pre-proof [C4mim][NTf2] and [C6mmim][Cl] and the association constants were estimated by 19

fluorescence, conductivity and

F-NMR methods. Zheng et al. [34] studied the ILs i.e.,

1-dodecyl-3-methylimidazolium methylimidazolium

hexafluorophosphate

hexafluorophosphate

(C12mimPF6),

(C14mimPF6),

and

1-tetradecyl-31-hexadecyl-3-

methylimidazolium hexafluorophosphate (C16mimPF6), for the formation of ICs with βcyclodextrin (β-CD). The surface tension measurements revealed that there were 1:1 stoichiometry ICs for β-CD-[C12mimPF6] and β-CD-[C16mimPF6] and 1:2 stoichiometry ICs for β-CD-[C14mim][PF6] ICs. These ICs were characterized by XRD, 1

13

C CP/MAS NMR,

H-NMR, rotating frame nuclear Over Hauser effect spectroscopy (ROESY), and

thermogravimetry (TGA). Tran et al.[35] used near-infrared spectroscopy to determine constants

between

phenol

and

β-

and

γ-cyclodextrins

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[butylmethylimidazolium] [chloride] RTIL.

α-,

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binding

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The aim of this work is to synthesize of inclusion complexes (ICs) between amino based

ionic

liquids

i.e.,

1-(2-(octylamino)-2-oxoethyl)pyridin-1-ium

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acid

bromide

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(OAOEPB), 4-((hydroxyimino)methyl)-1-(2-(octylamino)-2-oxoethyl)pyridin-1-ium bromide (HIMOAOEPB) within β-CD. The UV-vis spectroscopy method revealed 1:1 stoichiometry

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ICs for OAOEPB-β-CD and HIMOAOEPB-β-CD systems. These ICs were further

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characterized by using FTIR and 1H-NMR spectral results.

4-((hydroxyimino)methyl)-1-(2-(octylamino)-

ium bromide

2-oxoethyl)pyridin-1-ium bromide

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1-(2-(octylamino)-2-oxoethyl)pyridin-1OH

O

HO

O

O OH

HO

O

OHO HO

OH O

O

OH O OH

HO

N

OH O OH

-CDs

HO

O

O

OH

HO

N

N

OH OH OH O

OH OOH

S O O Na +

O

O OH

β-cyclodextrin

methyl orange

Scheme 1 Structures of AAILs, β-cyclodextrin and methyl orange

2. Experimental Section 2.1. Materials Amino acid based ionic liquids i.e., 4-((hydroxyimino)methyl)-1-(2-(octylamino)-2-oxoethyl) 4

Journal Pre-proof pyridin-1-ium bromide and 1-(2-(octylamino)-2-oxoethyl)pyridin-1-ium bromide were obtained from

Prof. Yevgen Karpichev (Chair of Green Chemistry, Department of

Chemistry, Tallinn University of Technology, 12618 Tallinn, Estonia) and used as received. β-cyclodextrin and methyl orange were purchased from Sigma-Aldrich Pvt. Ltd., Banglore, India and deuterium oxide was purchased from Merck KGaA, 64271, Darmstadt, Germany. All the solutions have been prepared using double distilled water. 2.3 Methods a) Preparation of inclusion complex The inclusion complexes were prepared using the co-precipitation method [36]. The β-CD (1.14 g) was dissolved in 10 mL distilled water at 353K in a water bath. The AAILs (0.2 g) in

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5 mL methanol was slowly added to the β-CD solution with continuous stirring. The molar

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ratio of AAIL to β-CD was 1:1. The vessel was covered with aluminum foil and stirred continuously for 48 h at 353K before refrigerating overnight at 278K. The precipitated IC un-complexes AAILs and β-CD. b) UV-vis absorption spectroscopy

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was recovered by filtration and washed with a small amount of methanol and water to remove

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The absorption spectra were recorded on Varian Cary 60 UV-visible spectroscopy. UV–vis absorption spectrum of methyl orange (MO) was measured from 200 nm to 600 nm. UV–vis

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absorption spectra of AAILs, β-CD as well as AAILs-β-CD systems were taken in the wavelength range of 200-600 nm in MO (4.60 x 10-5 M) at 298K.

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c) FTIR

FTIR spectra were taken by Nicolate iS-150 (Thermo-Fisher) DRS-FTIR spectrometer by KBr plate technique. For preparation of KBr plate, 1 mg of the solid IC and 100 mg KBr were mixed. IR spectra were scanned between 4000-400 cm-1 at room temperature. d) NMR measurements 1

H-NMR spectra were recorded on a Brüker at 400 MHz. All the NMR measurements were

recorded using D2O as solvent. The NMR experiments were carried out by β-cyclodextrin (βCD) with amino acid based ILs OAOEPB and HIMOAOEPB solutions. Scale is used in order to represent the chemical shifts of various protons of β-cyclodextrin and AAILs. Signals are mentioned as δ values in ppm. Data are cited as chemical shift. 3. Results and Discussion 3.1 Inclusion complexes formation AAILs-β-CD complexes were obtained by co-precipitation method [36]. AAIL is watersoluble at 298K and its resulting complex with the CD increased the water solubility. UV-Vis spectroscopy studies of the Job’s Plots method were carried out to evaluate the host:guest 5

Journal Pre-proof interaction between AAILs and β-CD [37]. Ghosh et al. [38] studied the interaction between α and β-CD and imidazolium based IL in the presence of methyl orange. These data demonstrated that a 1:1 stoichiometry of complexes between 1-butyl3methylimidazolium octylsulphate [Bmim][OS] was obtained. The binding constants (K) of [Bmim][OS]-β-CD complexes were calculated using Benesi-Hildbland equation (5) [39]. UV-vis spectroscopy, FT-IR and 1H-NMR, can give information about the influence of the AAILs structures on the AAILs : β-CD ICs formed [40]. UV-vis spectroscopic data were systematically analyzed. Linear graphical methods apply the changes in absorbance of AAILs/β-CD due to its molecular recognition into the apolar cavities of β-CD and the binding constants (K) were

formation of 1:1 ICs. Ka

IC

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[AAILs]f + [CD]

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obtained [41]. There should be equilibrium between host and the guest molecules in the

(1)

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The expression for the association constant (K) can be obtained from the above equation as follows: [IC] (2) 𝐾𝑎 = [AAILs]f [CD]f

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Here, [IC], [AAILs]f and [CD]f represent the equilibrium concentration of IC, free AAILs molecule and free CD, respectively. According to the binding isotherm, the association

[IC] [Aobs − A0 ] or [A − Aobs ] [CD]f [AAILs]f [CD]f

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𝐾𝑎 =

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constant (K) for the formation of IC may be expressed as

[CD]f = [CD]ad –

[AAILs]f

[Aobs −A0 ]

(3) (4)

[A −Aobs ]

Here, A0, Aobs and A are the absorbance of AAILs molecule at initial state, during addition of CD and final state, respectively. [AAILs]ad and [CD]ad are the concentrations of AAILs and the added CD, respectively. Thus, the values of K for the ICs were estimated from the binding isotherm by applying non-linear program. The binding constants (K), obtained from the binding isotherm with the application of linear plot are listed in the Table 1. 3.2 Stoichiometry Earlier to the calculation of the equilibrium binding constants of the ICs, the binding stoichiometry of the β-CD : AAILs host-guest complexes has to be feasible and it is calculated using Job’s method [42]. The UV-visible absorption spectra show that the absorbance value increases with increasing AAILs (OAOEPB/HIMOAOEPB) concentration while keeping the concentration of β-CD constant. It signifies that the solubility of AAILs is 6

Journal Pre-proof enhanced within the aqueous β-CD system leading formation of the ICs. This observed change in absorbance behavior (Fig. 1 and 2) can be ascribed to the formation of 1:1 stoichiometry of CD:AAILs ICs. Fig. 1 and 2, show some of the Job’s plots obtained for the different AAILs in presence of β-CD. The UV-vis absorption peaks of the AAILs and β-CD with changes in the absorbance can provide sufficient information for the result of the ICs [43]. For this reason; 1H-NMR measurement can be used in order to get conformational information about AAILs/β-CD interaction. In all cases only 1:1 complexes with β-CD are formed under the working conditions. 3.3 Job’s plot: stoichiometry of the host-guest inclusion complex The efficient and successful method to identify the stoichiometry of the host-guest

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inclusion complex is the Job’s method, popularly known as the continuous variation method.

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This technique was applied here using UV-vis spectroscopy by measuring the absorbance of a set of solutions for amino acid based ionic liquids i.e., 1-(2-(octylamino)-24-((hydroxyimino) methyl)-1-(2-(octylamino)-2-

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oxoethyl)pyridin-1-ium bromide and

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oxoethyl)pyridin-1-ium bromide with β-CD having their mole fractions in the range 0-1. Job’s plot were generated by plotting absorbance against R, R = [AAIL]/([AAIL]+[CD]).

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Absorbance were calculated at λmax = 256 nm for all the solutions at 297, 293 and 301 K. The value of R at the maxima on the curve provides the stoichiometry of IC, thus, the ratio of

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guest and host is 1:2, R ≈ 0.33; 1:1, R ≈ 0.5; 2:1, R ≈ 0.66 etc. In the present work maxima for each of the plots were found at R ≈ 0.5, which indicate 1:1 stoichiometry of the host-guest

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inclusion complexes (Fig. 1 and 2).

3.4 UV-Vis Spectroscopic Analysis of the Inclusion Complexation of β-Cyclodextrin in the Presence of Amino Acid-Based ILs The literature reveals that the changes in the cyclodextrin structure inserted by the tail part in the hydrophobic region of cyclodextrin molecule are followed with the shift in the wavelength in the near-UV region [44]. The absorption spectra of sodium 4-[(4dimethylamino) phenyldiazenyl]benzenesulfonate (methyl orange) in aqueous solutions containing ILs in the presence of β-CD with increasing the concentration of CD at different temperatures are displayed in Fig. 1 and 2. The main characteristics of the absorption spectra peaks are clearly observable from Fig. S1 at λmax 432 nm. As shown in Fig. S1, the absorption of MO in a β-CD aqueous solution is increased on increasing β-CD concentration from 0.186 mM to 3.36 mM in aqueous AAIL [OAOEPB] solution. UV-vis absorption spectroscopy is a significant technique to determine not only the absorbance of ICs but also we obtain the comparative binding stability of the AAILs with β-CD. The UV-vis spectra show that the absorbance increases with increasing the β-CD 7

Journal Pre-proof concentration while the concentration of OAOEPB (0.099 mM) remains constants (Fig. S1). It indicates that the solubility of AAIL (guest molecule) increase upon forming the IC. The binding constants (K) were obtained from the altered Benesi-Hildebrand equation (5) for the 1:1 inclusion complexes between AAILs and β-CD as shown below;

1 ∆A

=

1 ∆∈

+

1 (5)

K[AAILs]0 [CD]0

This equation is suitable in case of 1:1 host-guest IC only. A good linear equation is observed and the K values are gained from double-reciprocal plots and shown in Table 1. The binding

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constants (K) for the IC formation obtained from the slope of the Benesi-Hildebrand plot according to equation, is found to be AAIL HIMOAOEPB is lower compared to AAIL

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OAOEPB. Binding constants values observed in our case are larger compared to

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imidazolium, pyridinium, morpholinium based ionic liquids and surfactants system [45-49].

313.55

-24.88

5.81

-17.58

3.10

-24.26

5.31

-11.20

297

85.78

-24.60

5.47

-14.45

300

131.20

-24.81

4.02

-15.10

300 293

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HIMOAOEPBβ-Cyclodextrin

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Table 1. Binding constants (K) and thermodynamic parameters ΔH0, ΔS0, ΔG0 of AAILs inclusion complexes. Inclusion Temperature K x104 ΔH0 ΔS0 ΔG0 Complex (in Kelvin) (M-1) (kJmol-1) (J mol-1K-1.) (kJmol-1) 9.85 -24.28 6.46 -12.33 293 OAOEPBβ-Cyclodextrin 165.54 -24.64 4.46 -16.20 297

Standard uncertainties in temperature u are: u(T) = ±0.01 K. Mean errors in K = ± 0.03 M-1; ΔHo = ± 0.02 kJ mol-1; ΔSo = ±0.02 J mol-1K-1.

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[A] [B] [C] Fig 1. Job’s plots of OAOEPB-β-CD system at λmax = 256 nm at 650 298.15 K. R = [AAIL]/([AAIL] + [β-CD]), A = absorbance difference concentration of host and guest molecules at [A] 293 K , [B] 297K and [C] 301K temperature.

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n r u

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[A] [B] [C] Fig 2. Job’s plots of HIMOAOEPB-β-CD system at λmax = 256 nm at 650 298.15 K. R = [AAIL]/([AAIL] + [β-CD]), A = absorbance difference concentration of host and guest molecules at [A] 293 K , [B] 297K and [C] 301K temperature. 9

Journal Pre-proof The thermodynamic parameters i.e., change in standard Gibbs free energy (ΔG0), standard enthalpy changes (ΔH0) and standard entropy change (ΔS0) for the formation of IC of IL and β-CD can be determined using Van’t Hoff equation (6) with the help of association constant (K). ∆H

InK = − RT +

∆S

(6)

R

∆G0 = ∆H − T∆S

(7)

In Eq. (3), lnK varies linearly with 1/T. The ΔH0 value depends upon the equilibrium constant at three different temperatures. The different thermodynamic parameters (standard Gibbs free energy (ΔG0), standard enthalpy changes (ΔH0) and standard entropy change (ΔS0)) for the formation of two

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ICs were mentioned in Table 1. The ΔG0 and ΔH0 values were established negative in both the cases, which indicate that the two ICs form spontaneously and it is an exothermic process. Although the

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process is more favored by entropy since the value of ΔS0 is positive. In general method the formation of IC is thermodynamically favorable.

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3.5 FTIR studies

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Amino acid based ILs like guest molecules and β-CD as host molecule can form the ICs which have been determined by FT-IR spectroscopic investigation. The FT-IR absorption peaks of the AAIL or

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β-CD with changes in the shape, shift and intensity can provide sufficient information for the result of the ICs [50]. Analysis of the FTIR data of the ICs as well as the pure cyclodextrin as a host and

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AAILs as a guest molecule too reveals the truth about the way by which the ICs are formed and supports the same status of host:guest interaction as achieved from the 1H-NMR spectroscopic study.

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All the FTIR spectra of the IC and the pure β-CD and pure AAILs molecules were recorded by preparing potassium bromide plate. The significant changes in the IR spectra of the pure β-CD and AAILs to the ICs which are shown in the Fig. 3 and 4, suggests the formation of ICs exploring the binding mode of the Guests to the host molecules. The FT-IR results significantly give information for the stretching frequencies (cm-1) of AAILs, β-CD and its ICs as listed in the Tables 2 to 5. Table 2 Comparison between the intensity of β-Cyclodextrin and inclusion complex OAOEPB β-cyclodextrin. Wavenumber (cm-1)

Functional Group β-CD

OAOEPB -β-CD

ν [OH]

3380

3320

ν [C-H]

2916.35

2920.30

ν [-C-H] bending

1412.27

1488

10

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Fig.3 DRS-FTIR spectra of (A) β-cyclodextrin, (B) 1-(2-(octylamino)-2-oxoethyl)pyridin-1-ium bromide (OAOEPB), (C) inclusion complex (1:1) of β-cyclodextrin with AAIL 1-(2-(octylamino)-211

Journal Pre-proof oxoethyl)pyridin-1-ium bromide (OAOEPB+β-CD). Table 3 Comparisons between the intensity of OAOEPB and inclusion complex OAOEPB-βcyclodextrin. Functional Wavenumber (cm-1) Group OAOEPB OAOEPB-β-CD -O-H and -N-H stretching 3221.54 3280.14 frequencies ν [-O-H] carboxylic acid 2920.30 2923.78 Aromatic C=C Bending 1670.59 1673.59 ν [C-O-] stretching vibration 1256.01 1331.76 C-H in-plane-bending 778.79 852.41

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a) Significant interactions of the AAILs and β-CD in the [OAOEPB+β-CD] IC were evaluated as follows: (i) The signal for -O-H stretching of β-CD was at 3380 cm-1 and the -O-H

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and -N-H stretching frequencies of OAOEPB were at 3406.46 cm-1 and the region of 3221.54 cm-1

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respectively, whereas in the IC these signals shifted to 2933.18 and 3320.14 cm -1 correspondingly. This is possibly due to the formation of H-bonding between OAOEPB and β-CD. (ii) The peaks for

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-C-O (carboxylic acid –O-H group) at 2920.30, 2854.68 cm-1, aromatic C=C bending stretching 1670.59, 1557.25 cm-1, C-O- stretching vibration is 1256.01 cm-1 of OAOEPB, which shifted to

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2923.78, 1673.59 and 1151.78 cm-1 respectively. This is possibly remaining to the formation of H-bond between OAOEPB and β-CD. (iii) The signals at 2916.35 cm-1 and 1412.27 cm-1

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corresponding to -C-H stretching and -C-H bending of β-CD, shifted to 2920.30 cm-1 and 1488 cm-1 respectively. On the other hand, -C-H out-of-plane bending for OAOEPB molecule were

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observed at 778.79 cm-1 which shifted to 852.41 cm-1 correspondingly. This may because of the various interactions taking place while the formation of the complex assembly between OAOEPB and β-CD (Fig. 3).

b) The shifting of the following IR signals satisfactorily explicates the formation of [HIMOAOEPB+β-CD] IC. (i) The -O-H signal for β-CD was at 3380 cm-1 which are shifted to 3320 cm-1 for IC. This is probably due to the formation of H-bond by HIMOAOEPB with β-CD. (ii) The peaks at the 2924.19 cm-1 (asymmetric –CH2-, symmetric –CH3, -CH2 stretching vibration frequency) and 1648.36 cm-1 (=C-H stretching vibration), 1450.68 cm-1 (C-N bending/C=C stretching vibration frequency), 1152.62 cm-1 (C-O stretching vibration) for the HIMOAOEPB were shifted to the frequencies 2920.30, 1658.66, 1414.08 and 1205.30 cm-1 of HIMOAOEPB towards the formation of H-bond with β-CD. (iii) The -C-H stretching and bending mode of frequencies of β-CD were at 2916 and 1412 cm-1 respectively and peaks for the aromatic out-ofplane -C-H bending frequencies for HIMOAOEPB were at 938.30 cm-1 respectively, are now shifted to 2920.30, 1414.08 and 933.89 cm-1 respectively. Thus, FTIR spectral analysis also indorses the same as obtained from the 1H NMR spectra (Fig.5 to 7). 12

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Fig.4 DRS-FTIR spectra of (A) β-cyclodextrin, (B) 4-((hydroxyimino)methyl)-1-(2-(octylamino)-2-oxoethyl) pyridin-1-iumbromide (HIMOAOEPB) (C) inclusion complex (1:1) of β-cyclodextrin with amino acid based ionic liquids 4-((hydroxyimino)methyl)-1-(2-(octylamino)-2-oxoethyl)pyridin-1-iumbromide (HIMOAOEPB + β-CD).

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Table 4 Comparisons between the intensity of β-Cyclodextrin and inclusion complex HIMOAOEPB -β-cyclodextrin. Functional Group Wave number (cm-1) β-CD

HIMOAOEPB -β-CD

3380

3320

ν [C-H]

2916.35

2920.30

ν [-C-H] bending

1412.27

1414.08

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ν [OH]

-O-H and -N-H stretching frequencies

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asymmetric –CH2-, symmetric –CH3, -CH2 stretching vibration frequency =C-H stretching vibration C-N bending/C=C stretching vibration frequency C-O stretching vibration aromatic out-of-plane - C-H bending frequencies

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Table 5 Comparisons between the intensity of HIMOAOEPB and inclusion complex HIMOAOEPB -β- cyclodextrin. Functional Wave number (cm-1) Group HIMOAOEPB HIMOAOEPB-β-CD 3258.13

3299.09

2924.19

2920.30

1648.36 1450.68

1658.66 1414.08

1152.62 938.89

1205.30 933.89

3.6 Proton nuclear magnetic resonance studies 1

H-NMR is the most useful method to obtain information about inclusion complex

formation and their geometries [51]. It is very useful to provide information on host:guest ICs, since the proton (1H) environment in both the CD and ILs molecules will be affected by their interactions and will hence be reflected by chemical shift variations of protons from both species [52-53]. NMR spectroscopy was employed in our study to obtain information on the ICs of both AAILs with β-CD and the 1H-NMR spectral response is presented in Fig. 5-7 and S2-S3. In Fig.5 to 7, comparing β-CD and their ICs, it is nice to observe the special peaks of β-CD in the spectra of ICs, clearly showing improvement of the spectra (Fig. 6 and 7, ppm: 0-4). NMR study on the formation of ICs between AAILs and β-CD in D2O are shown in Fig.5 to 7. As the results obtained for the formation of ICs, the chemical shifts values are shown to change for β-CD molecule. As 14

Journal Pre-proof shown in Fig.6 and 7, the peaks of H1 to H6 have clear displacements of the chemical shifts with the formation of ICs. The β-CD molecule contains three protons (H1, H2 and H4) that are cited in the outer surface of the cavity and the other two protons (H3 and H5) are cited in the inner cavity. Our results demonstrate that the proton H5 shows upfield shifts after formation of the ICs with AAILs OAOEPB-β-CD (δ=3.537ppm) and HIMOAOEPB-β-CD (δ=3.612ppm) and chemical shifts of proton H3 are also shifted to the upfield after formation of complexes with AAILs OAOEPB-β-CD (δ=3.788ppm) and HIMOAOEPB-β-CD (δ = 3.808ppm). It was earlier shown that the extent of upfield shifts of H5 and H3 protons of cyclodextrin after complex formation can be taken as a

of

measure of the depth of inclusion as well as the complex stability [54-55]. Therefore, the 1H NMR results obtained for β-CD could provide a clue on the stability of the ICs formed with the two

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different AAILs.

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Fig. 6 1H NMR spectra of β-CD-1-(2-(octylamino)-2-oxoethyl)pyridin-1-ium bromide ICs in D2O at 300K temperature.

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Fig.7 1H NMR spectra of β-CD- 4-((hydroxyimino)methyl)-1-(2-(octylamino)-2-oxoethyl)pyridin-1-iumbromide ICs in D2O at 300K temperature.

18

Journal Pre-proof First, ICs with AAILs formed affect on the δ values of the H1, H2, H3, H4, H5, and H6 protons of the β-CD shows comparatively weak. While the change in shift values for β-CD complexes with AAIL HIMOAOEPB (0.08-0.09 ppm) is observed to be slightly less as compared to that for AAIL OAOEPB (0.1-0.2 ppm). It is a significant contribution to the formation of IC from both H3 and H5 protons because these are present in wide side and narrow side of the β-CD cavity [56]. The chemical shift values of pure β-CD and its ICs are listed in Table 6. Table 6 clearly shows the chemical shift values of H3 protons (3.905 ppm) are larger as compared to H5 protons (3.77 ppm) and after inclusion complexation with both AAILs, the changes of δ values are larger for OAOEPB than HIMOAOEPB. It can be deduced from the 1H NMR data that AAILs were entered into the β-

of

CD cavity. The AAILs could be inserted into the β-CD cavity from the two sides of the cavity of β -CD. By comparing the integration area of these protons with that of the H1 protons of β-CD, we

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determined that the inclusion stoichiometry of the AAILs/β-CD complexes was 1:1, which was

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closely related to the results obtained through Job's plot.

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Table 6 Change in chemical shift (δ ppm) of the protons of β-cyclodextrin host molecules when complexes with ionic liquids guest molecules in D2O at 300K. H1

Proton (ppm) β-cyclodextrin OAOEPB +β-CD

4. Conclusion

H4

H5

H6

3.770

3.794

3.905, 3.881,

3.556,

4.991

3.573

3.857

3.548

5.006, 4.998

3.514

3.788

3.210

3.537

3.606

3.540

3.808

3.185

3.612

3.786

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HIMOAOEPB+β-CD

H3

3.581

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4.981

H2

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Chemical shift of

5.006, 4.999

The results obtained from UV-vis spectroscopy, FTIR-DRS and 1H-NMR experiments provided significant information to explain the complexation mechanism of the ICs of AAILs with β-CD. In conclusion, AAILs were able to form ICs with β-CD in the stoichiometric ratio of 1:1, resulting in Job's plots and characterized by the spectral results of the UV-Vis, FTIR and NMR spectroscopy. The binding constant values were obtained as follows: OAOEPB > HIMOAOEPB. A quantitative analysis was performed in the C=O stretching wave number range of the DRS-FTIR spectra of the AAILs-β-CD ICs, according to a well-established model. 1H NMR analysis approved the formation of the ICs between AAILs and β-CD. 5. Supporting information (S) Fig. S1 Absorption spectra of MO ([MO] = 4.60 × 10-5 moldm-3) containing different concentrations of β-CD in OAOEPB AAIL solution. Fig. S2 19

1

H NMR spectra of 1-(2-(octylamino)-2-

Journal Pre-proof oxoethyl)pyridin-1-ium bromide ICs in D2O at 300K temperature. Fig. S3 1H NMR spectra of 4((hydroxyimino) methyl)-1-(2-(octylamino)-2-oxoethyl)pyridin-1-ium bromide

in D2O at 300K

temperature. 6. Acknowledgements The authors are grateful to Prof. Yevgen Karpichev (Chair of Green Chemistry, Department of Chemistry, Tallinn University of Technology, 12618 Tallinn, Estonia) and National Center for Natural Resources (NCNR), Pt. Ravishankar Shukla University, Raipur (C.G.) for providing the nuclear magnetic resonance (NMR). Dr. Kamalakanta Behera is thankful to the Science and Engineering Research Board (SERB), New Delhi, India, for providing a research grant

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(YSS/2015/001997).

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Journal Pre-proof

Authors Statements Authors

Author statement

Dr. Manoj Kumar Banjare

Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data Curation, Writing - Original Draft, Writing - Review & Editing, Visualization

Mr. Ramesh Kumar Banjare

Methodology, Formal analysis, Data Curation, Investigation

Dr. Kamalakanta Behera

Writing - Original Draft, Writing - Review & Editing, Visualization, Project administration Conceptualization, Supervision, Writing - Original Draft,

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Prof. Siddharth Pandey

Writing - Review & Editing, Visualization, Project

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administration

Data Curation, Investigation

Prof. Kallol K. Ghosh

Conceptualization, Supervision, Project administration, Funding

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Mr. Prashant Mundeja

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acquisition. Writing - Original Draft, Writing - Review &

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Editing, Visualization, Project administration

25

Journal Pre-proof Highlight: 1. The binding constants of β-CD are higher for OAOEPB as compared to HIMOAOEPB. 2. IR data give information about the functional groups concerned the Stoichiometry ICs. 3. AAILs was clever to form ICs with β-CD in the 1:1 stoichiometric ICs by Job's plots.

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4. UV-Vis spectroscopy, FT-IR and 1H NMR were carried out to confirm ICs formation.

26