Synthesis, characterization and antibacterial activity of a new silver(I) complex based on a flexible dicarboxylic acid ligand

Accepted Manuscript Synthesis, characterization and antibacterial activity of a new silver(I) complex based on a flexible dicarboxylic acid ligand Jie Sun, Qing-rong Huang, Ju-hua Zhou PII:

S0022-2860(15)30426-9

DOI:

10.1016/j.molstruc.2015.11.021

Reference:

MOLSTR 21971

To appear in:

Journal of Molecular Structure

Received Date: 2 September 2015 Revised Date:

6 November 2015

Accepted Date: 11 November 2015

Please cite this article as: J. Sun, Q.-r. Huang, J.-h. Zhou, Synthesis, characterization and antibacterial activity of a new silver(I) complex based on a flexible dicarboxylic acid ligand, Journal of Molecular Structure (2015), doi: 10.1016/j.molstruc.2015.11.021. 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 Synthesis, characterization and antibacterial activity of a new silver(I)

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complex based on a flexible dicarboxylic acid ligand

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Synthesis, characterization and antibacterial activity of a new silver(I) complex based on a flexible dicarboxylic acid ligand

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Jie Sun*, Qing-rong Huang, Ju-hua, Zhou

School of Life Science Ludong University, Yantai, 264025, Shandong, People’s Republic of China.

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Abstract

A novel silver(I) complex sustained by a flexible dicarboxylic acid ligand, [Ag2(L)]n

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(1, H2L = 2,2’-{[1,2-phenylenebis(methylene)]-bis(sulfanediyl)}dibenzoic acid), has been synthesized and structurally characterized. In 1, four anti conformation L2ligands bind three silver(I) ions to form a trinuclear subunit through S···Ag and Ag···Ag interactions, and then those trinuclear subunits are further extended to an infinite 1D silver(I) chain through the anti L2- ligands. Thus, the thermal stability,

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luminescent behavior and antibacterial activity of 1 were also discussed. Keywords: Silver(I) chain; Flexible dicarboxylic acid ligand; Ag···Ag interaction;

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Crystal structure; Antibacterial activity

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1. Introduction The past decade have witnessed the boom of metal-organic coordination complexes(MOCCs), due to their intriguing topologies and potential functional

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applications in the fields of storage and separation, magnetism, catalysis, luminescence and membrane [1-6]. As we know that much attention has been focused on the assembly of MOCCs based on a rigid carboxylate and N-containing ligands, however, the systemic research of flexible carboxylate ligand in the construction of

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metal–organic coordination systems is somewhat rare[7]. Flexible counterparts can

transform their conformations to match the coordination requirements of the metal

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centre. This can give a richer variety of structures than found for a rigid-ligand equivalent. Among various flexible ligands, multicarboxylates containing –CH2–O– or –CH2–S– arms have attracted great interests[8]. Recently, Sun’s group have reported four metal–organic complexes based on three flexible dicarboxylic acid ligands and copper paddlewheel SBU[9], our group have also reported a mononuclear copper

complex

Cu(NH3)3(L6)]·(H2O)0.66

(1)

(H2L6

=

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2,2’-(1,2-phenylenebis(methylene))bis(sulfanediyl)-dibenzoic acid) and the complex could be dimerized to form a binuclear complex with an altered copper coordination geometry through thermal SCSC transformation or solid state reaction under dry grinding conditions[10].

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On the other hand, compared to wildly used Zn, Cd, Cu transition and rare earth element during construction of MOCCs, silver-centered metal-organic coordination

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systems are also rarely investigated. Silver-containing complex appeared as antimicrobial agents since the middle age[11]. Because of their multi-targeting mechanism, silver-based antimicrobial agents are often applied to overcome bacterial resistance[12]. Silver(I) has shown to be able to inactivate proteins, bind to thiol groups and form stable Ag–S bonds. Silver ions are also able to change the structure of the bacteria cell wall, leading to changes in its mobility and stability and to a subsequent bacterial death, the mechanisms of action and resistance of silver ions have been intensively study by recent reviews[13]. It is reported that silver-centred

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complexes show higher antibacterial activity than silver ions, because of their synergistic effects between silver ions and organic ligands. Based on the considerations above, herein we reported a silver(I) complex based on a flexible

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dicarboxylic acid ligand(H2L), and studied the photo- and biological properties of final complex.

[Please insert: Scheme1 The synthesis procedures of the H2L in complex 1]

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2. Experimental procedure 2.1. Materials and methods

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All the reagents and solvents employed were commercially available and used as received without further purification. H2L was synthesized according to the procedure of Dai et al[9]. Infrared spectra were recorded on a Bruker VERTEX-70 spectrometer as KBr pellets in the frequency range 4000-400 cm-1. The elemental analyses (C, H contents)

were

determined

on

a

CE

instruments

EA

1110

analyzer.

Photoluminescence measurements were performed on a Hitachi F-7000 fluorescence

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spectrophotometer with solid powder on a 1 cm quartz round plate with a dewar flask apparatus. TG curves were measured from 30 to 600 °C on a SDT Q600 instrument at a heating rate 10 °C/min under the N2 atmosphere (100 mL/min).

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2.2. Synthesis of [Ag2(L)]n

Three drops of NaOH (0.1 mL, 0.8M) was added to a suspension of H2L (0.015 g,

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0.037 mmol) in H2O (1 mL) to give a clear solution. AgNO3 (0.030 g, 0.170 mmol) in MeOH (9 mL) was added to the clear solution, upon which lots of brown precipitate formed immediately. After three drops of NH3·H2O (0.1 mL, 25–28%) was added, a

colorless solution was generated after 10 minutes stirring, which was filtered and transferred to a test tube. After slow evaporation at room temperature for two months, large stick colorless crystals of 1 were formed (yield: 45%). Elemental analysis calcd

(%) for 1: C 42.30, H 2.56, N 10.25; found: C 42.02, H 2.52, N 10.11%. Selected IR peaks (cm-1): 3395 (m), 2963 (m), 1590 (s), 1546 (s), 1399 (s), 1361 (m), 854 (w), 788 (m), 725 (w), 713 (m). 3

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2.3. X-ray crystallography Single crystals of the complex 1 was collected on a SuperNova diffractometer equipped with a molybdenum micro-focus X-ray source (λ = 0.71073 Å) and an Eos

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CCD detector under 293 K. The data were collected with a ω-scan technique and an arbitrary φ-angle. Data reduction was performed with the CrysAlisPro package, [14]

and an analytical adsorption correction was performed. The structures were solved by direct methods and refined by full-matrix least-squares on F2 with anisotropic

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displacement using the SHELXTL software package. [15] The non-H atoms were treated anisotropically, whereas the aromatic and hydroxy hydrogen atoms were

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placed in calculated, ideal positions and refined as riding on their respective carbon or oxygen atoms. The structures were examined using the Addsym subroutine of PLATON [16] to assure that no additional symmetry could be applied to the models. For 1, crystal data and collection and parameters are summarized in Table 1, and selected bond lengths and angles are given in Table 2.

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[Insert Table 1 and 2 here]

Table 1. Crystallographic data for 1

Table 2. Selected bond lengths and angles for 1

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3. Results and discussion

3.1. Crystal structure of [Ag2(L)]n 1.

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The molecular structure of 1 was determined by single-crystal X-ray diffraction analysis. Complex 1 crystallizes in monoclinic space group of C2/c and the asymmetric unit contains one independent and two halves Ag ions, and one H2L

ligand. As shown in Fig. 1, when the Ag⋯Ag interactions are not taken into account, the coordination number of three Ag are all four, but they adopt three different coordination environments, indicating the rich coordination mode of Ag. Ag1 in complex 1 adopt four-coordinated tetrahedral geometry, completed by four O atoms from four different H2L ligands; Ag2 is bonded to two O, two S atoms of three H2L ligands, and Ag2 atom forming distorted tetrahedral geometry; the Ag3 is located in a 4

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square geometry and coordinated by four O atoms from three different H2L ligands. The Ag-O bond lengths range from 2.238(3) to 2.501(2) Å and the maximum bond angle is 119.91(9)o and the Ag-S bond lengths are located in 2.5333(8) to 2.9161(8) Å.

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Both the Ag-S and Ag-O bond lengths fall in the normal ranges as the reported complexes [17-20]. As depicted in Fig.2, the H2L ligand in 1 has an anti conformation, as shown by the distribution of the two substituted 2-mercaptobenzoate

groups with respect to the plane of the central aromatic ring. The anti L2- ligands bind to seven Ag(I) centres, the planes of the aromatic rings of the 2-mercaptobenzoate

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arms make dihedral angles of 84.8 (3) and 77.8 (3)o. The dihedral angles between the

carboxylic groups and adjacent phenyl ring planes for one crystallographic

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independent L2- ligands are ca. 5.59 and 54.58°, respectively. The neighboring subunits were further to an infinite zigzag chain (Fig. 3) through Ag···Ag interactions (Ag1···Ag2i = 3.2769(2), Ag1···Ag3 = 3.4258(3) and Ag2ii···Ag3= 3.8754(2) Å) and Ag···S interactions(Ag2···S1 = 2.533(8), Ag2···S2ii = 2.5428(8) and Ag3···S1 = 2.9161(8) Å). [ symmetry code: (i) 1-x, 2-y, 1-z; (ii) 1-x, y, 0.5-z; (iii) x, 2-y, 0.5+z;

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(iv) 1-x, y, 1.5-z]

[Please insert: Figure 1. The coordination environment around Ag(I) ions in 1, all hydrogen atoms are omitted for clarity and Ag···Ag interactions highlighted by purple

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dashed lines][ symmetry code: (i) 1-x, y, 0.5-z; (ii) 1-x, 2-y, 1-z]. [Please insert: Figure 2. The coordination environment H2L ligand in 1, all hydrogen

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atoms are omitted for clarity and Ag···Ag interactions highlighted by purple dashed lines] [ symmetry code: (i) 1-x, 2-y, 1-z; (ii) 1-x, y, 0.5-z; (iii) x, 2-y, 0.5+z; (iv) 1-x, y,

1.5-z].

[Please insert: Figure 3. The 1D chain structure of 1 supported by Ag···Ag and

Ag···S interactions] In complex 1, the silver chains are aligned parallel to one another in the crystalline phase. There are abundant secondary interactions between adjacent silver 5

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wires(Fig.4). [Please insert: Figure 4. The packing structure of 1 view along (a) a and (b) c

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direction]

3.2. X-ray Power Diffraction Analyses and Thermogravimetric Analyses.

Phase purity of 1 is sustained by the X-ray powder diffraction pattern (Fig.

S1). The dissimilarities in intensity may be due to the preferred orientation of the

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crystalline powder samples. The solid FT-IR spectrum (Fig. S2) of 1 shows that

the asymmetric and symmetric stretching vibrations of deprotonated carboxyl

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group are in ~1592 and ~1388 cm-1, respectively [21-23]. These results are in good agreement with solid state crystal structure. To study the thermal stablity of complex 1, the thermal gravimetric analyse (TGA) of 1 was measured from 40 to 800 °C at a heating rate 10 °C/min under the N2 atmosphere. As shown in Fig. S3, the frame of complex 1 shows high thermal stability and almost no weight loss was observed until 248 °C, after that, the frame of complex 1 began to decompose,

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accompanying the release of the H2L ligand. [Please insert: Figure 5. The photoluminescence of free ligands and complex 1 in

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solid state]

3.3. Photoluminescence Properties.

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The photoluminescence of H2L and complex 1 were measured in solid state at

room temperature (Fig. 5). The free ligand H2L displays photoluminescence with emission maximum at 416 nm (λex = 330 nm). It can be presumed that this emission

peak originates from the π→π* transition. For complex 1, at room temperature it displays an emission band at 438 nm, upon excitation at 330 nm. Compared with the emission of free H2L ligand, the emission band of 1 is red-shifted by 22 nm, which may contribute to ligand-to-metal charge transfer (LMCT) transition perturbed by Ag···Ag interactions from the electronic transition between coordinated O atoms p

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orbitals and Ag(I) ion 5s orbital[24-25]. 3.4. Antibacterial Activity. The method of Oxford-cup tests were used to evaluated the antibacterial activity

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of AgNO3, H2L and complex 1. The antibacterial activity was estimated by monitoring the growth of certain Gram-positive (B. subtilis, S. aureus) and Gram-negative (E. coli) bacterial strains in the presence of different concentrations of

these complexes ranging from 1, 5 and 10 mg·mL−1. As presented in Table S1, it

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showed the results of in vitro activity determination based on the diameter of the

inhibition zone (in mm). H2L did not show antibacterial activity, however, complex 1

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and AgNO3 have some antibacterial activity to three model bacterial strains, which means that the antibacterial activity have relations with silver ions. As shown in Fig.6, with the increasing of complex 1 and AgNO3 content of antibacterial activity increased. Complex 1 resulted to have bigger antibacterial activity to E. coli bacterial strains than the original compound (H2L) and AgNO3 solutions, the diameter of the inhibition zone is 28 mm when the concentration of complex 1 is up to 10 mg·mL−1.

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These results suggested that the combination of H2L with the silver(I) may represent an additional advantage for its use in the management of infections caused by S. aureus, B. subtilis and especially E. coli.

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[Please insert: Figure 6. The antibacterial activity of complex 1 against B. subtilis(a), S. aureus(b) and E. coli(c) ]

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4. Conclusions

In summary, we utilized the flexible dicarboxylic acid ligand to synthesize and

characterize a novel 1D silver chain sustained by Ag···Ag and Ag···S interactions. The thermal stability, photoluminescence behavior and antibacterial activity of 1 were

also discussed. Compare with free ligand and silver, complex 1 shows higher antibacterial activity against E. coli.

Acknowledgments

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This work was financially supported by the National Natural Science Foundation of China (No. 21401096). Appendix A. Supplementary material

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CCDC 1035701 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/

retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge

CB

21EZ,

UK;

fax:

(+44)

1223-336-033;

or

e-mail:

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[email protected]. Supplementary data associated with this article can be found, in the online version.

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TableÅ1Å TableÅ1ÅCrystalÅdataÅandÅstructureÅrefinementÅforÅcomplexÅ1.Å CrystalÅdataÅandÅstructureÅrefinementÅforÅcomplexÅ1.Å IdentificationÅcodeÅ complexÅ1Å EmpiricalÅformulaÅ C22H16Ag2O4S2Å FormulaÅweightÅ 624.21Å Temperature/KÅ 273.15Å CrystalÅsystemÅ monoclinicÅ SpaceÅgroupÅ C2/cÅ a/ Å 20.2580(16)Å b/ Å 15.6777(13)Å c/ Å 13.6916(11)Å α/°Å 90.00Å β/°Å 106.7530(10)Å γ/°Å 90.00Å 3 Volume/ Å 4163.9(6)Å ZÅ 8Å 3 ρcalcg/cm Å 1.991Å -1 μ/mm Å 2.109Å F(000)Å 2448.0Å 3 CrystalÅsize/mm Å 0.2Å×Å0.13Å×Å0.11Å RadiationÅ MoKαÅ(λÅ=Å0.71000)Å 2ΘÅrangeÅforÅdataÅ 4.96ÅtoÅ55.1Å collection/°Å -25Å ÅhÅ Å26,Å-20Å ÅkÅ Å20,Å-17Å ÅlÅ Å IndexÅrangesÅ 17Å ReflectionsÅcollectedÅ 17457Å IndependentÅreflectionsÅ 4806Å[RintÅ =Å0.0276,ÅRsigmaÅ =Å0.0280]Å Data/restraints/parametersÅ 4806/0/273Å Goodness-of-fitÅonÅF2Å 1.021Å FinalÅRÅindexesÅ[I>=2σÅ(I)]ÅR1Å =Å0.0317,ÅwR2Å =Å0.0664Å FinalÅRÅindexesÅ[allÅdata]Å R1Å =Å0.0453,ÅwR2Å =Å0.0716Å -3 LargestÅdiff.Åpeak/holeÅ/ÅeÅ Å0.65/-0.60Å

(2) Table 2 Selected bond distances (Å) and angles (°) for 1

Ag1—O1 Ag1—O1i Ag1—O3ii Ag1—O3iii Ag2—S1 Ag2—S2ii

2.393 (2) 2.393 (2) 2.238 (3) 2.238 (3) 2.5333 (8) 2.5428 (8)

Ag2—O2i Ag3—S1 Ag3—S1iii Ag3—O1 Ag3—O1iii Ag3—O1iv

2.280 (2) 2.9161 (8) 2.9161 (8) 2.501(2) 2.501(2) 2.244(2)

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O1i—Ag1—O1 82.18 (10) O3iii—Ag1—O1 119.91 (9) O3iii—Ag1—O1i 106.65 (9) O3iii—Ag1—O1i 119.91 (9) O3iii—Ag1—O1 106.65 (9) O3ii—Ag1—O3iii 117.22 (18) ii i S1—Ag2—S2 135.84 (3) O2 —Ag2—S1 120.02 (9) O2i—Ag2—S2ii 101.21 (8) S1—Ag3—S1iii 180.0 O4ii—Ag3—O1 97.89 (9) O4iv—Ag3—O1iii 97.89 (9) iv ii iv O4 —Ag3—O1 82.11 (9) O4 —Ag3—O4 180.000 (1) Symmetry codes: (i) −x+1, y, −z+1/2; (ii) x, −y+2, z−1/2; (iii) −x+1, −y+2, −z+1; (iv) −x+1, y, −z+3/2; (v) x, −y+2, z+1/2.

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Scheme1 The synthesis procedures of the H2L in complex 1

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Figure 1. The coordination environment around Ag(I) ions in 1, all hydrogen atoms are omitted for clarity and Ag···Ag interactions highlighted by purple

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dashed lines][ symmetry code: (i) 1-x, y, 0.5-z; (ii) 1-x, 2-y, 1-z].

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Figure 2. The coordination environment H2L ligand in 1, all hydrogen atoms are

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omitted for clarity and Ag···Ag interactions highlighted by purple dashed lines] [ symmetry code: (i) 1-x, 2-y, 1-z; (ii) 1-x, y, 0.5-z; (iii) x, 2-y, 0.5+z; (iv) 1-x, y,

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1.5-z]

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Figure 3. The 1D chain structure of 1 supported by Ag···Ag and Ag···S interactions

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Figure 4. The packing structure of 1 view along (a) a and (b) c direction

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[Please insert: Figure 5. The photoluminescence of free ligands and complex 1 in

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solid state]

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[Please insert: Figure 6. The antibacterial activity of complex 1 against B.

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subtilis(a), S. aureus(b) and E. coli(c) ]

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Reserach Highlights Title: Synthesis, characterization and antibacterial activity of a new silver(I)

Authors: Jie Sun*, Qingrong, Huang, Juhua, Zhou

(i)

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complex based on a flexible dicarboxylic acid ligand

A novel silver(I) complex sustained by a flexible dicarboxylic acid ligand has

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been synthesized and structurally characterized.

The silver(I) wire was sustained by S···Ag and Ag···Ag interactions.

(iii)

Compare with free ligand and silver, complex 1 shows higher antibacterial

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activity against E. coli

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(ii)