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Synthesis, structural characterization, DFT studies and in-vitro antidiabetic activity of new mixed ligand oxovanadium(IV) complex with tridentate Schiff base
Accepted Manuscript Synthesis, structural characterization, DFT studies and in-vitro antidiabetic activity of new mixed ligand oxovanadium(IV) complex with tridentate Schiff base
R.N. Patel, Yogendra Pratap Singh PII:
S0022-2860(17)31341-8
DOI:
10.1016/j.molstruc.2017.10.010
Reference:
MOLSTR 24381
To appear in:
Journal of Molecular Structure
Received Date:
06 August 2017
Revised Date:
30 September 2017
Accepted Date:
02 October 2017
Please cite this article as: R.N. Patel, Yogendra Pratap Singh, Synthesis, structural characterization, DFT studies and in-vitro antidiabetic activity of new mixed ligand oxovanadium(IV) complex with tridentate Schiff base, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc. 2017.10.010
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ACCEPTED MANUSCRIPT Highlights
Vanadyl complex X-ray structure Supramolecular architectures
ACCEPTED MANUSCRIPT Graphical Abstract The mixed ligand vanadyl complex [VO(L1)(L2)] has been synthesized and structurally characterized. Single crystal diffraction analysis reveals that C-H···π (aryl/metal chelate rings) interactions are contributing to the stabilization of the crystal structure.
ACCEPTED MANUSCRIPT Synthesis, structural characterization, DFT studies and in-vitro antidiabetic activity of new mixed ligand oxovanadium(IV) complex with tridentate Schiff base R. N. Patel*, Yogendra Pratap Singh Department of Chemistry, A. P. S. University, Rewa (M.P.) 486003 India
Abstract The mixed ligand oxovanadium(IV) complex [VO(L1)(L2)] [L1 = N'-[(E)-phenyl(pyridin-2yl)methylidene]benzohydrazide and L2 = Benzhydrazide] has been synthesized in aerobic condition. The complex was characterized by elemental analysis spectroscopic (UV-vis, IR, epr) and electrochemical methods. X-ray diffraction pattern was also used to characterize this complex, which has a distorted octahedral structure. Single crystal diffraction analysis reveals that C-H···π (aryl/metal chelate rings) interactions contribute to the stabilization of the crystal structure in given dimension. The room temperature magnetic susceptibility data shows paramagnetic nature of the complex. The complex was also tested for invitro antidiabetic activity. Moderate α-glucosidase inhibition is shown by this complex, which may be considered as α-glucosidase inhibitors. Keywords: C-H···π (aryl), C-H···π (chelate) interaction, cyclic voltammetry, antidiabetic activity 1. Introduction Crystal structures of transition metal complexes are partially sustained by C-H···π interactions. CH···π interactions are the weakest hydrogen bonds that operate between a soft acid C-H and a soft base system [1-4]. It has been well established that this kind of weaker and softer interactions play significant role in various field of chemistry such as crystal packing [5-12], self-assembly [13,14], host–guest chemistry [15-17] and chiral recognition [18,19]. As it has effect in water and being non-polar, the C-H···π interaction is also important in biological systems. In the domain of metal organic crystal engineering, metalloaromatic character of metal-chelate ring gives rise to the possibility of new generation of π-systems [20]. The concept of “metalloaromaticity” was introduced by Calbin and coworker [21] and C-H···π (metal chelate ring) supramolecular chemistry were reported in the literature [22-24]. However, reports on the bioactivities of such kind of complexes are still rare. Coordination chemistry of vanadium is a topic of interest since the discovery of it being an essential trace element for certain organisms [24,25] and recently as insulin enhancing agents [26,27]. Several oxovanadium(IV) complexes have earlier been studied for their antidiabetic activity [26,28-33]. Search for newer and newer such antidiabetic compounds has become an important area of current biochemical research. Slowing down the digestion and absorption of dietary carbohydrate using α-glucosidase inhibitors has proved to be a promising therapeutic strategy for reducing risk of diabetes and other mediated diseases [34-37]. Acarbose is the first α-glucoside inhibitor approved for treatment of diabetes [38]. A large variety of α-glucosidase inhibitors were extensively studied [39]. There is paucity of data on a α-glucoside inhibition by oxovandium(IV) complexes [33,40,41]. As for present Schiff base, no report on the characterization of its chelate with vanadyl ion appears to exist. The isolated complex was well characterized using various physicochemical techniques. Oxovanadium(IV) complex was studied by single crystal X-ray analysis. DFT calculations and in-vitro antidiabetic activity are also discussed. 2. Experimental 2.1. Synthesis HL (N'-[(E)-phenyl(pyridin-2-yl)methylidene]benzohydrazide) The Schiff base (HL) was prepared by earlier reported procedure [42] and re-crystallized from ethanol. Ligand HL was synthesized by refluxing benzoylhydrazide (1.361 g, 10 mmol) and 2-benzoyl pyridine (1.832 g, 10 mmol) in ethanol for 4 h and allowed to cool. A light yellow precipitate was filtered off, washed with ethanol and dried in CaCl2 desiccator. Yied: 78%. Elem. anal. Calcd. for C19H15N3O (%): C,75.73; H, 5.02; N, 13.94. Found: C, 75.77; H, 5.11; N, 14.03. Selected FT-IR data on KBr (cm−1): ν(C=N), 1624; ν(C=O), 1291 and ν(N-H), 3244. EI-MS: m/z 301.09 (calcd: m/z 301.34).
[VO(L1)(L2)]
ACCEPTED MANUSCRIPT
Vanadyl sulphate (0.163 g, 1 mmol) in 10 mL water and Schiff base (L1) (0.602 g, 2 mmol) in 20 mL methanol were mixed with stirring. The aquamethanol solution (1:2) was stirred for 3 hrs under air at room temperature (28 °C) when the color changed from light yellow to dark burgundy after a few minutes. The serendipitous hydrolysis reaction took place and a new hydrolyzed product L2 was formed. The resulting solution was filtered off and dried under air. After one week, orange plate shaped single crystals, appeared suitable for X-ray diffraction analysis (Yield 65%). Anal. Calcd. (found) for C26H19N5O3V: 62.23, C; 3.88, H; 13.97%, N. Calcd. 62.28, C; 3.73, H; 13.97, N; 9.57, O; 10.16%, V. Selected FT-IR data on KBr (cm−1): ν(C=O), 1575 and ν(V=O) 980. The solid state magnetic moment was (μeff) 1.80 BM. 2.2. Material, instrumentation and analytical method All chemicals used were commercially available and used as received. Elemental analyses were carried out on elemental analyzer Euro–E 3000. Mass spectrum of the ligand (L1) was recorded on an Agilent 6520 Q-Tof (ESI-HRMS & APCI-HRMS). Magnetic susceptibilities at RT, were measured by the Gouy balance using a mercury(II) tetrathiocyanato cobaltate(II) as calibrating agent (χg = 16.44 x 10‾6 c.g.s. units). Diamagnetic corrections were estimated from Pascal tables. Infrared (IR) spectra were recorded on a Bruker α-T spectrophotometer at normal temperature. KBr pellets were prepared by grinding the sample with KBr (IR grade), in the range of 400 to 4000 cm−1. Ligand-field spectra were recorded at 25ºC on a Shimadzu UV-vis recording Spectrophotometer UV-1601 in solution. Cyclic voltammetry measurements were carried out with a BAS-100 Epsilon electrochemical analyzer having an electrochemical cell with a three-electrode system. Ag/AgCl was used as reference electrode, glassy carbon as working electrode and platinum wire as an auxiliary electrode. TBAP (0.1 molLˉ1) was used as the supporting electrolyte in DMSO. All measurements were carried out at 298 K under nitrogen. The solution was deoxygenated by purging nitrogen gas. Electron paramagnetic resonance (epr) spectra were recorded with a Varian E-line Century Series epr spectrometer equipped with a dual cavity and operating at the X-band of the 100 kHz modulation frequency. Tetracyanoethylene (TCNE) was used as a field marker (g = 2.00277). The molar ion exchange was measured using a Systronics digital conductivity meter (TDS-308) using a 10−3 M solution in DMSO. 2.3. X- ray crystallography Diffraction quality block shaped crystal of vanadyl complex was mounted on Rigaku Oxford Diffraction Gemini Eos diffractometer equipped with graphite monochromated CuKα radiation (λ = 1.54182 Å) was used, all operating at 50 kV and 30 mA. Intensity data were collected at 173 K using the ω-2θ scan technique. No significant intensity variation was observed during data collection. Multi-scan absorption corrections were applied empirically to the intensity values (Tmax = 0.793 and Tmin.= 0.395) using SADABS [43]. Data reductions were done by using program Bruker SAINT [44]. The structures were solved by Direct Methods using the program SHELXS-97 [45] and refined with full-matrix least-squares based on F2 using program SHELXL-97 [45]. All non-hydrogen atoms were refined anisotropically. The molecular graphics and crystallographic illustrations was prepared using PLATON [46], ORTEP [47], and WinGX [48] program. All the relevant crystallographic data and structure refinement parameters for the vanadyl complex are summarized in Table 1. CCDC No. 1515813 contain the supplementary crystallographic data for the present paper. 2.4. Theoretical calculation To gain an accurate understanding of the molecular structure of vanadium(IV) complex, full geometry optimizations were carried out using density functional theory (DFT) in the gas phase with the Gaussian 09 suite of programs [49] with the aid of the Gauss View 05 visualization program and the Beck’s three-parameter hybrid method B3LYP with the 6-31G(d,p) basis set [50,51]. Vibrational frequency analyses were also performed at the same level to ensure the structures are local minima. The natural bond orbital (NBO) method on the wave functions was obtained at the same level of theory.
2.5. α-Glucosidase enzymatic activityACCEPTED MANUSCRIPT α-Glucosidase was used as reported in literature [52]. Rat intestinal acetone powder (Sigma chemicals, USA) was sonicated properly in normal saline (100:1 w/v) and after centrifugation at 3000 rpm x 30 mins the supernatant was treated as crude intestinal α-glucosidase. Various dilutions in DMSO (0.1mg/mL solution) were mixed and incubated for 50 µL of enzyme in a 96-well microplate for 5 mins. Reaction mixture was further incubated for another 10 mins with 50 µl substrate (5 mM, p-nitrophenyl-α-Dglucopyranoside) prepared in 100 mM phosphate buffer (pH 6.8) and release of nitrophenol was read at 405 nm spetrophotometrically (MultimodesynergyH4 microplate reader, BioTek instrument, inc.Winoosci, VT, USA). All the samples were run in triplicate and acarbose was taken as standard reference compound. Several dilutions of primary solution (5mg/mL DMSO) were made and assayed accordingly to obtain concentration of the test sample required to inhibit 50% activity (IC50) of the enzyme. Quantification was performed with respect to the standard curve of acarbose (Y = 26.63X + 46.26, R2 = 0.958) results were expressed as microgram of acarbose equivalent per ml of extract. Percent α-Glucosidase inhibition was calculated using (1-B/A) × 100, where A is absorbance of reactants without test samples and B is absorbance of reactants with test samples. 3. Results and discussion 3.1. Synthesis and general characterization The reaction between VOSO4 and L1 in aquamethanol (1:2) ratio in aerobic condition results in formation of new mixed ligand oxovanadyl(IV) complex [VO(L1)(L2)] (eq.1), where L1 is a tridentate ligand and L2 is a bi-dentate hydrolyzed product of L1. VOSO4 + L1
CH3OH
[VO(L1)(L2)]
…………………………(1)
The above state of development has prompted us to undertake the task of mononuclear vanadium(IV) complex [VO(L1)(L2)] using this new Schiff base. However, during the course of synthesis of this complex in aerobic condition reaction of 1:2 vanadyl sulphate and HL (N'-[(E)-phenyl(pyridin-2yl)methylidene]benzohydrazide) in CH3OH serendipitous hydrolysis reactions took place and a new hydrolyzed product L2 was formed. Probably through the metal-assisted hydrolysis of (N'-[(E)phenyl(pyridin-2-yl)methylidene]benzohydrazide) new mixed ligand vanadyl complex was isolated. Orange coloured complex is characterized on the basis of elemental analysis, spectroscopic (IR, UV-vis, CV and epr) data and single crystal X-ray analysis. The complex is non-ionic in nature [53]. The room temperature magnetic moment is 1.80 BM consistent with one unpaired electron (S = 1/2) system ascribed to the paramagnetic species. 3.2. Molecular geometry The complex crystallizes in monoclinic space group Pc. The crystal structure of complex is shown in Fig. 1. The molecular structure of this complex consists of discrete mono-nuclear unit in which VO2+ is coordinated by a enolic oxygen O(1), a amine nitrogen N(2) and one pyridine nitrogen, N(1) from deprotonated Schiff base ligand and a enolic oxygen, O(2) and one amine nitrogen, N(5) of the benzoyl hydrazide. The resulting coordination sphere VO3N3 has a severely distorted octahedral geometry. The tridentate meridionally disposed Schiff base ligand is constituted of two excellently planar segments, OC6H5CNN (mean deviation 0.003 Å) and C5H4N (mean deviation 0.053 Å). The hydrazide chelate ring of co-ligand is enolic and hydrazidic in nature. The V-O(3), 1.619(8) Å is much stronger than V-O(2), 2.151(7) Å being trans to vanadyl oxygen, (O(2). The crystallographic data (CCDC 1515813) and structure refinement summary are presented in Table 1. The major bond lengths and bond angles lengths and bond angles are listed in Table 2. In the neutral complex, the V atom is six coordinated by three nitrogen atoms and two oxygen atoms of L1 and L2 and one vanadyl oxygen. It is a fairly straight forward octahedral structure. The V=O and one O atom of ligand L2 remain axially coordinated with vanadium metal. The V=O distance of 1.619 Å is consistent with vanadyl distances is related complexes [54,55]. Interestingly, although the corresponding distances in each
ACCEPTED ligand (L1 and L2) are not significantly different, theMANUSCRIPT V-O2 (hydroxo) distances (2.004 and 2.151 Å) and VO3 are significantly different from one on other. The systematic analysis of the structural data available for the vanadyl complex revealed that observed C-H···π interactions lead to zero- or one- dimensional aggregations. The zero-demensional aggregats fall in two categories: The first of these features as C-H···π (aryl) interaction (Fig. 2 Top) and second type as C-H···π (metal chelate ring Fig. 2 Bottom). The first type of C-H···π (aryl) interaction occurs a C-H of aryl molecule and a ring (aryl) derived from another species. The second type of C-H···π (metal chelates) interactions was observed in between C-H (aryl) of species and metal chelate of another species. The majority of structures featuring C-H···π interactions utilize these synthons to assemble molecules into 1D supramolecular polymeric chains (Fig. 3). 3.3. DFT calculations The X-ray structure of the complex was used as starting point for the gas phase geometry optimization. The calculated geometrical parameters (bond lengths and bond angles) of the complex are presented in Table 2. The differences in calculated bond lengths and angles of the complex are due to calculation of structural parameter in gas phase. Contour plots of selected molecular orbitals are shown in Fig. 4. The highest energy occupied molecular orbital (HOMO) (α- and β-spin) have 100% π(L) (100%) character. The α-spin low energy unoccupied molecular (LUMO) have been constituted by 100% dπ(V) character while the β-spin LUMO have 100% π(L) character with a HOMO-LUMO energy gap of 0.969 eV (α-spin) and -4.957 eV (β-spin). The presence of paired electron in Schiff base show that diamagnetic character, while in vanadium(IV) complex shows that paramagnetic character with one unpaired electron in HOMO molecular orbital. Spin localization of the complex can be difficult to determine experimentally for intermediated not long-lived enough electron paramagnetic resonance (epr) experiments, however localization of spin density can be determined through computationally generated spin density maps (Fig. 5). Spin density maps were generated to localize the electron density of the unpaired electron. The spin density of the unpaired spin distributed over the 21.21% V, 10.32% O, 68.12% N and 0.35 % C on the coordinated atoms along with a major contribution on vanadium centre. 3.4. Electrochemistry The cyclic voltammograms of complex were measured in DMSO with TBAP as supporting electrolyte recorded as room temperature in the potential window of -0.310 to -1.100 V. The cyclic voltammograms for a 3 mmol solution of the complex exhibits two cathodic waves and two anodic waves. One redox process is irreversible with reduction at -0.80 V and quasi reversible with reduction at -0.60 V (Fig. 6). The reduction waves are larger than oxidation waves, showing that the complex undergoes a chemical change after reduction [56]. The cyclic voltammogram of this complex throw considerable light on the stability of the complex in the presence and absence of an excess of the ethanol. Change in redox waves observed for VO2+ complex treated with ethanol suggested the formation of dioxovanadium(V) complex due to aerial oxidation (eq. 2) [57] Oxovanadium(IV)
EtOH
dioxovanadium(V)
…………….(2)
An initial anodic scan does not include any oxidation peaks possibly the product of a further chemical reaction is electro inactive. The species responsible for the -0.65 V reduction peak is increase. The vanadium(V) complex may have different coordination numbers and consequently quite different electrochemical properties. Similar spectral changes observed when VO2+ treated with EtOH again suggested the conversion of VO2+ with broad and unresolved d-d band to dioxovanadium(V) with clear and resolved band as vanadium(V) complex has 3d0 configuration, d→d band is not expected. After addition of EtOH, there is, however, a strong band at ca. 525 nm for the dioxovandium(V) complex [55], which assigned to LMCT originating from the lone pair in a p-orbital Schiff base oxygen into an empty d-orbital of the vanadium ion (Fig. 7).
3.5. Epr studies
ACCEPTED MANUSCRIPT
The complex was also characterized by epr spectral measurement at liquid nitrogen temperature (Fig. 8). Epr parameters of DMSO solution have been measured for this complex (Table 3). The vanadyl ion has a simple S = 7/2 electron spin and 51V has high natural abundance and an I = 7/2 nuclear spin, it can be used to know the type of sites coordinated to the divalent complex ion. An additivity relationship introduced by Chasteen [58], to estimate the parallel 51V hyperfine constant of vanadyl complexes based on the contribution to Az from each of the four equatorial donor sites. The relationship provides a valid criterion to assess the equatorial donor atoms. The calculations were carried out according to the additivity relationship, using latest listings of the partial contributions of the equatorial ligand functions [59]. Within the limits of errors the experimental Az agrees with the calculated one, suggesting that the solution structure at low temperature does not significantly deviate from the structure in the crystalline solid state (Fig. 1). 3.6. α-Glucosidase inhibition study We have also tested the catalytic activity of the complex to mimic the α-Glucosidase activity. α-glucosidase is responsible for postprandial hyperglycemia. α-glucosidase catalyzes the disaccharides to monosaccharides, which leads to postprandial hyperglycemia [60]. Hence, inhibitor of α-glucosidase is useful in the control of hyperglycemia as this can delay carbohydrate digestions, which consequently reduce risk of diabetics and other carbohydrate mediated diseases [34-37]. Inhibition data (percentage inhibition at 200 μM and IC50 values) for oxovanadium(IV) complex is 14.75 μM. For acarbose as standard percentage inhibition is 18.59 μM. A perusal of the data reveals that the oxovanadium(IV) complex is moderate αglucosidase inhibitor. Various inorganic and organovanadium compounds have been demonstrated to enhance insulin sensitivity in animal models [61]. Organic ligands on vanadium can influence its bioactivity by the bioavailability of the vanadium ion. Careful design of the organic ligands on vanadium could affect their bioactivities significantly, thus making them more suitable for clinical usages in fighting diabetes. These observations suggest that the mixed-ligand oxovanadium complex may be a promising candidate as antidiabetic agent or lead compounds for further development. 4. Conclusion The above state of development has prompted us to undertake the task of mononuclear vanadium(IV) complex [VO(L1)(L2)] using this new Schiff base. In situ new vanadyl complex has been synthesized by an aerial reaction of 1:2 vanadyl sulphate and Schiff base (L1). The systematic analysis of the structural data available for the vanadyl complex revealed that observed C-H···π interactions lead to zero- or onedimensional aggregations. Although this oxovanadium(IV) complex cannot at present be related to specific biological systems, the solvent effects clearly are large both in term of the redox chemistry and coordination chemistry. The complex shows moderate in-vitro α-glucosidase inhibition. As moderate α-glucosidase inhibition is shown therefore this complex may be considered as α-glucosidase inhibitors. Acknowledgements We are grateful to M.P. Council of Science & Technology, Bhopal, India [Scheme No. A/RD/RP2/2015-16/245] for their financial support. RSIC (SAIF) IIT, Bombay for epr measurements and SAIF, Central Drug Research Institute, Lucknow India, are thankfully acknowledged for providing analytical and spectral facilities. Appendix: Supplementary data CCDC 1515813 contains supplementary crystallographic data for the present complex. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033; or email: [email protected]. References 1. 2.
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MANUSCRIPT U. Ashiq, R. A. Jamal, M. ACCEPTED M. Tahir, Z. T. Maqsood, K. M. Khan, I. Omer, M. I. Choudhary, J. Enzyme Inhib. Med. Chem. 24 (2009) 1336. R. N. Patel, Y. Singh, Y. P. Singh, R. J. Butcher, J. Coord. Chem. 69 (2016) 2377. G. M. Sheldrick, SADABS (Version 2.03), University of Gottingen, Germany (2002). SMART (V 5.628) SAINT (V 6.45a), XPREP, SHELXTL, Bruker AXS Inc., Madison,WI (2004). G. M. Sheldrick, Acta Crystallogr Sect. A: Found. Crystallogr. 64 (2008) 112. A. L. Spek, Acta Crystallogr Sect. D Biol. Crystallogr. 65(2009)148. L. J. Farrugia, J. Appl. Crystallogr. 30(1997) 565. L. J. Farrugia, WinGX, J. Appl. Crystallogr. 32 (1999) 837. 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. 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, 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. 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. B. Foresman,J.V. Ortiz, J. Cioslowski and D. J. Fox, Gaussian Inc., Wallingford CT, Gaussian 09, Revision D.01, (2009). A. D. Becke, J. Chem. Phys. 98 (1993) 5648. C. Lee, W. Yang, R. G. Parr, Phys. Rev. 37B (1988) 785. S. Mishra, K. B. Pandeya, A. K. Tiwari, A. Z. Ali, T. Saradamani, J. Indian. Chem. Soc. 88 (2011) 1195. W. J. Garey, Coord. Chem. Rev. 7 (1971) 81. K. Saatchi, K. H. Thompson, B. O. Patrick, M. Pink, V. G. Yuen, J. H. McNeill, C. Orvig, Inorg. Chem. 44 (2005) 2689. R.N. Patel, Y. P. Singh, Y. Singh, R. J. Butcher, J. P. Jasinski, Polyhedron 133 (2017) 102. S. Sujatha, T. M. Rajendiran, R. Kannappan, R. Venkatesan, P. Sambasivarao, Proc. Indian Acad. Sci. (Chem Sci) 112 (2000) 559. C. Orvig, P. Caravan, L. Gelmini, N. Glover, F. G. Herring, H. Li, J. H. McNeill, S. J. Rettig, I. A. Setyawati, J. Am. Chem. Soc. 117 (1995) 12759. N. D. Chasteen, in: L. J. Berliner, J. Reuben (Eds.), Biological Magnetic Resonance, vol. 3, Plenum Press, New York (1981) pp. 53-119. T. S. Smith II, R. LoBrutto, V. L. Pecoraro, Coord. Chem. Rev. 228 (2002) 1. T. Matsui, T. Tanaka, S. Tamura, A. Toshima, K. Tamaya, Y. Miyata, K. Tanaka and K. Matsumoto, J. Agric. Food. Chem. 55 (2007) 99. K. H. Thompson, C. Orvig , J. Inorg. Biochem. 100 (2006) 1925.
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Fig.1. Molecular structure of complex [VO(L1)(L2)].
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Fig. 2. Top: C-H···π (metal chelate) interaction and Bottom: C-H···π (aryl chelate) interaction. Hydrogen atoms are omitted for celerity. Only representative hydrogen atom is shown.
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Fig. 3. One dimensional C-H···π (aryl chelate) interactions to form polymeric chain.
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LUMO = -3.921 eV
HOMO = -2.952 eV
LUMO = -1.661 eV
HOMO = -6.618 eV
LUMO+1 = -3.514 eV
HOMO-1 = -4.073 eV
LUMO+1 = -1.352 eV
HOMO-1 = -6.693 eV
Fig. 4. Contour plots of selected molecular orbitals of vanadium(IV) complex [VO(L1)(L2)].
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Fig. 5. DFT calculated spin density map of complex [VO(L1)(L2)].
Fig. 6. Cyclic valtamograms of vanadium(IV) complex. 1 In DMSO (3 × 10-3 M). 2 after adding 1 mL of ethanol. 3 after adding 2 mL of ethanol.
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Fig. 7. Visible spectral behavior of vanadyl complex [VO(L1)(L2)] with and without ethanol in DMSO.
Fig. 8. Epr spectra of vanadyl complex in DMSO solution at 77K.
ACCEPTED MANUSCRIPT Table 1 Crystal data and structure refinement parameters for complex [VO(L1)(L2)]. Empirical formula C26H19N5O3V Formula weight 500.40 T (K) 173(2) λ (Å) 1.54184 Crystal system Monoclinic Space group Pc a (Å) 7.9279(7) b (Å) 17.9872(19) c (Å) 8.2365(6) α (°) 90 β (°) 96.041(8) γ (°) 90 Volume (Å3) 1168.01(18) Z 2 Density (calculated) (Mg/m3) 1.423 ε (mm-1) 3.874 F(000) 514 3 Crystal size (mm ) 0.47 x 0.23 x 0.06 θ (°) 4.917 to 71.506 Index ranges -4 ≤ h ≤ 9, -22 ≤ k ≤ 20, -9 ≤ l≤9 Reflections collected 2614 Independent reflections 2614 [R(int) = 0.0623] Completeness to theta = 67.500° 99.8 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 1.00000 and 0.35652 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2614 / 38 / 311 2 1.044 Goodness-of-fit on F Final R indices [I>2sigma(I)] R1 = 0.0830, wR2 = 0.2215 R indices (all data) R1 = 0.0947, wR2 = 0.2433 Table 2 Selected interatomic distances [Å] and angles [°] of complex [VO(L1)(L2)]. Bond X-ray DFT Bond X-ray V-O(3) 1.619(8) 1.658 V-N(5) 1.909(8) V-O(1) 2.004(6) 2.125 V-O(2) 2.151(7) V-N(2) 2.089(9) 0.1259 V-N(1) 2.108(8) O(3)-V-N(5) N(5)-V-O(1) N(5)-V-N(2) O(3)-V-N(1) O(1)-V-N(1) O(3)-V-O(2) O(1)-V-O(2) N(1)-V-O(2)
96.2(4) 105.5(3) 150.7(3) 95.0(4) 150.4(3) 168.8(3) 87.4(3) 83.2(3)
96.24 105.92 151.01 95.12 150.82 169.12 87.65 82.35
O(3)-V-O(1) O(3)-V-N(2) O(1)-V-N(2) N(5)-V-N(1) N(2)-V-N(1) N(5)-V-O(2) N(2)-V-O(2)
99.3(4) 112.7(3) 75.3(3) 98.5(3) 75.3(3) 73.2(3) 77.6(3)
DFT 2.015 2.185 2.2145 99.52 113.01 75.38 98.65 75.62 73.25 77.91
Table 3 Spin Hamiltonian parameters of vanadyl complex in frozen DMSO (77K) solution. gz gxy Az × 104 cm-1 Axz Az × 104 cm-1 (calcd.) Donor atom set 1.953 2.010 166 71 162 2Nimine, Npyr, OAro
R.N. Patel, Yogendra Pratap Singh PII:
S0022-2860(17)31341-8
DOI:
10.1016/j.molstruc.2017.10.010
Reference:
MOLSTR 24381
To appear in:
Journal of Molecular Structure
Received Date:
06 August 2017
Revised Date:
30 September 2017
Accepted Date:
02 October 2017
Please cite this article as: R.N. Patel, Yogendra Pratap Singh, Synthesis, structural characterization, DFT studies and in-vitro antidiabetic activity of new mixed ligand oxovanadium(IV) complex with tridentate Schiff base, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc. 2017.10.010
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ACCEPTED MANUSCRIPT Highlights
Vanadyl complex X-ray structure Supramolecular architectures
ACCEPTED MANUSCRIPT Graphical Abstract The mixed ligand vanadyl complex [VO(L1)(L2)] has been synthesized and structurally characterized. Single crystal diffraction analysis reveals that C-H···π (aryl/metal chelate rings) interactions are contributing to the stabilization of the crystal structure.
ACCEPTED MANUSCRIPT Synthesis, structural characterization, DFT studies and in-vitro antidiabetic activity of new mixed ligand oxovanadium(IV) complex with tridentate Schiff base R. N. Patel*, Yogendra Pratap Singh Department of Chemistry, A. P. S. University, Rewa (M.P.) 486003 India
Abstract The mixed ligand oxovanadium(IV) complex [VO(L1)(L2)] [L1 = N'-[(E)-phenyl(pyridin-2yl)methylidene]benzohydrazide and L2 = Benzhydrazide] has been synthesized in aerobic condition. The complex was characterized by elemental analysis spectroscopic (UV-vis, IR, epr) and electrochemical methods. X-ray diffraction pattern was also used to characterize this complex, which has a distorted octahedral structure. Single crystal diffraction analysis reveals that C-H···π (aryl/metal chelate rings) interactions contribute to the stabilization of the crystal structure in given dimension. The room temperature magnetic susceptibility data shows paramagnetic nature of the complex. The complex was also tested for invitro antidiabetic activity. Moderate α-glucosidase inhibition is shown by this complex, which may be considered as α-glucosidase inhibitors. Keywords: C-H···π (aryl), C-H···π (chelate) interaction, cyclic voltammetry, antidiabetic activity 1. Introduction Crystal structures of transition metal complexes are partially sustained by C-H···π interactions. CH···π interactions are the weakest hydrogen bonds that operate between a soft acid C-H and a soft base system [1-4]. It has been well established that this kind of weaker and softer interactions play significant role in various field of chemistry such as crystal packing [5-12], self-assembly [13,14], host–guest chemistry [15-17] and chiral recognition [18,19]. As it has effect in water and being non-polar, the C-H···π interaction is also important in biological systems. In the domain of metal organic crystal engineering, metalloaromatic character of metal-chelate ring gives rise to the possibility of new generation of π-systems [20]. The concept of “metalloaromaticity” was introduced by Calbin and coworker [21] and C-H···π (metal chelate ring) supramolecular chemistry were reported in the literature [22-24]. However, reports on the bioactivities of such kind of complexes are still rare. Coordination chemistry of vanadium is a topic of interest since the discovery of it being an essential trace element for certain organisms [24,25] and recently as insulin enhancing agents [26,27]. Several oxovanadium(IV) complexes have earlier been studied for their antidiabetic activity [26,28-33]. Search for newer and newer such antidiabetic compounds has become an important area of current biochemical research. Slowing down the digestion and absorption of dietary carbohydrate using α-glucosidase inhibitors has proved to be a promising therapeutic strategy for reducing risk of diabetes and other mediated diseases [34-37]. Acarbose is the first α-glucoside inhibitor approved for treatment of diabetes [38]. A large variety of α-glucosidase inhibitors were extensively studied [39]. There is paucity of data on a α-glucoside inhibition by oxovandium(IV) complexes [33,40,41]. As for present Schiff base, no report on the characterization of its chelate with vanadyl ion appears to exist. The isolated complex was well characterized using various physicochemical techniques. Oxovanadium(IV) complex was studied by single crystal X-ray analysis. DFT calculations and in-vitro antidiabetic activity are also discussed. 2. Experimental 2.1. Synthesis HL (N'-[(E)-phenyl(pyridin-2-yl)methylidene]benzohydrazide) The Schiff base (HL) was prepared by earlier reported procedure [42] and re-crystallized from ethanol. Ligand HL was synthesized by refluxing benzoylhydrazide (1.361 g, 10 mmol) and 2-benzoyl pyridine (1.832 g, 10 mmol) in ethanol for 4 h and allowed to cool. A light yellow precipitate was filtered off, washed with ethanol and dried in CaCl2 desiccator. Yied: 78%. Elem. anal. Calcd. for C19H15N3O (%): C,75.73; H, 5.02; N, 13.94. Found: C, 75.77; H, 5.11; N, 14.03. Selected FT-IR data on KBr (cm−1): ν(C=N), 1624; ν(C=O), 1291 and ν(N-H), 3244. EI-MS: m/z 301.09 (calcd: m/z 301.34).
[VO(L1)(L2)]
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Vanadyl sulphate (0.163 g, 1 mmol) in 10 mL water and Schiff base (L1) (0.602 g, 2 mmol) in 20 mL methanol were mixed with stirring. The aquamethanol solution (1:2) was stirred for 3 hrs under air at room temperature (28 °C) when the color changed from light yellow to dark burgundy after a few minutes. The serendipitous hydrolysis reaction took place and a new hydrolyzed product L2 was formed. The resulting solution was filtered off and dried under air. After one week, orange plate shaped single crystals, appeared suitable for X-ray diffraction analysis (Yield 65%). Anal. Calcd. (found) for C26H19N5O3V: 62.23, C; 3.88, H; 13.97%, N. Calcd. 62.28, C; 3.73, H; 13.97, N; 9.57, O; 10.16%, V. Selected FT-IR data on KBr (cm−1): ν(C=O), 1575 and ν(V=O) 980. The solid state magnetic moment was (μeff) 1.80 BM. 2.2. Material, instrumentation and analytical method All chemicals used were commercially available and used as received. Elemental analyses were carried out on elemental analyzer Euro–E 3000. Mass spectrum of the ligand (L1) was recorded on an Agilent 6520 Q-Tof (ESI-HRMS & APCI-HRMS). Magnetic susceptibilities at RT, were measured by the Gouy balance using a mercury(II) tetrathiocyanato cobaltate(II) as calibrating agent (χg = 16.44 x 10‾6 c.g.s. units). Diamagnetic corrections were estimated from Pascal tables. Infrared (IR) spectra were recorded on a Bruker α-T spectrophotometer at normal temperature. KBr pellets were prepared by grinding the sample with KBr (IR grade), in the range of 400 to 4000 cm−1. Ligand-field spectra were recorded at 25ºC on a Shimadzu UV-vis recording Spectrophotometer UV-1601 in solution. Cyclic voltammetry measurements were carried out with a BAS-100 Epsilon electrochemical analyzer having an electrochemical cell with a three-electrode system. Ag/AgCl was used as reference electrode, glassy carbon as working electrode and platinum wire as an auxiliary electrode. TBAP (0.1 molLˉ1) was used as the supporting electrolyte in DMSO. All measurements were carried out at 298 K under nitrogen. The solution was deoxygenated by purging nitrogen gas. Electron paramagnetic resonance (epr) spectra were recorded with a Varian E-line Century Series epr spectrometer equipped with a dual cavity and operating at the X-band of the 100 kHz modulation frequency. Tetracyanoethylene (TCNE) was used as a field marker (g = 2.00277). The molar ion exchange was measured using a Systronics digital conductivity meter (TDS-308) using a 10−3 M solution in DMSO. 2.3. X- ray crystallography Diffraction quality block shaped crystal of vanadyl complex was mounted on Rigaku Oxford Diffraction Gemini Eos diffractometer equipped with graphite monochromated CuKα radiation (λ = 1.54182 Å) was used, all operating at 50 kV and 30 mA. Intensity data were collected at 173 K using the ω-2θ scan technique. No significant intensity variation was observed during data collection. Multi-scan absorption corrections were applied empirically to the intensity values (Tmax = 0.793 and Tmin.= 0.395) using SADABS [43]. Data reductions were done by using program Bruker SAINT [44]. The structures were solved by Direct Methods using the program SHELXS-97 [45] and refined with full-matrix least-squares based on F2 using program SHELXL-97 [45]. All non-hydrogen atoms were refined anisotropically. The molecular graphics and crystallographic illustrations was prepared using PLATON [46], ORTEP [47], and WinGX [48] program. All the relevant crystallographic data and structure refinement parameters for the vanadyl complex are summarized in Table 1. CCDC No. 1515813 contain the supplementary crystallographic data for the present paper. 2.4. Theoretical calculation To gain an accurate understanding of the molecular structure of vanadium(IV) complex, full geometry optimizations were carried out using density functional theory (DFT) in the gas phase with the Gaussian 09 suite of programs [49] with the aid of the Gauss View 05 visualization program and the Beck’s three-parameter hybrid method B3LYP with the 6-31G(d,p) basis set [50,51]. Vibrational frequency analyses were also performed at the same level to ensure the structures are local minima. The natural bond orbital (NBO) method on the wave functions was obtained at the same level of theory.
2.5. α-Glucosidase enzymatic activityACCEPTED MANUSCRIPT α-Glucosidase was used as reported in literature [52]. Rat intestinal acetone powder (Sigma chemicals, USA) was sonicated properly in normal saline (100:1 w/v) and after centrifugation at 3000 rpm x 30 mins the supernatant was treated as crude intestinal α-glucosidase. Various dilutions in DMSO (0.1mg/mL solution) were mixed and incubated for 50 µL of enzyme in a 96-well microplate for 5 mins. Reaction mixture was further incubated for another 10 mins with 50 µl substrate (5 mM, p-nitrophenyl-α-Dglucopyranoside) prepared in 100 mM phosphate buffer (pH 6.8) and release of nitrophenol was read at 405 nm spetrophotometrically (MultimodesynergyH4 microplate reader, BioTek instrument, inc.Winoosci, VT, USA). All the samples were run in triplicate and acarbose was taken as standard reference compound. Several dilutions of primary solution (5mg/mL DMSO) were made and assayed accordingly to obtain concentration of the test sample required to inhibit 50% activity (IC50) of the enzyme. Quantification was performed with respect to the standard curve of acarbose (Y = 26.63X + 46.26, R2 = 0.958) results were expressed as microgram of acarbose equivalent per ml of extract. Percent α-Glucosidase inhibition was calculated using (1-B/A) × 100, where A is absorbance of reactants without test samples and B is absorbance of reactants with test samples. 3. Results and discussion 3.1. Synthesis and general characterization The reaction between VOSO4 and L1 in aquamethanol (1:2) ratio in aerobic condition results in formation of new mixed ligand oxovanadyl(IV) complex [VO(L1)(L2)] (eq.1), where L1 is a tridentate ligand and L2 is a bi-dentate hydrolyzed product of L1. VOSO4 + L1
CH3OH
[VO(L1)(L2)]
…………………………(1)
The above state of development has prompted us to undertake the task of mononuclear vanadium(IV) complex [VO(L1)(L2)] using this new Schiff base. However, during the course of synthesis of this complex in aerobic condition reaction of 1:2 vanadyl sulphate and HL (N'-[(E)-phenyl(pyridin-2yl)methylidene]benzohydrazide) in CH3OH serendipitous hydrolysis reactions took place and a new hydrolyzed product L2 was formed. Probably through the metal-assisted hydrolysis of (N'-[(E)phenyl(pyridin-2-yl)methylidene]benzohydrazide) new mixed ligand vanadyl complex was isolated. Orange coloured complex is characterized on the basis of elemental analysis, spectroscopic (IR, UV-vis, CV and epr) data and single crystal X-ray analysis. The complex is non-ionic in nature [53]. The room temperature magnetic moment is 1.80 BM consistent with one unpaired electron (S = 1/2) system ascribed to the paramagnetic species. 3.2. Molecular geometry The complex crystallizes in monoclinic space group Pc. The crystal structure of complex is shown in Fig. 1. The molecular structure of this complex consists of discrete mono-nuclear unit in which VO2+ is coordinated by a enolic oxygen O(1), a amine nitrogen N(2) and one pyridine nitrogen, N(1) from deprotonated Schiff base ligand and a enolic oxygen, O(2) and one amine nitrogen, N(5) of the benzoyl hydrazide. The resulting coordination sphere VO3N3 has a severely distorted octahedral geometry. The tridentate meridionally disposed Schiff base ligand is constituted of two excellently planar segments, OC6H5CNN (mean deviation 0.003 Å) and C5H4N (mean deviation 0.053 Å). The hydrazide chelate ring of co-ligand is enolic and hydrazidic in nature. The V-O(3), 1.619(8) Å is much stronger than V-O(2), 2.151(7) Å being trans to vanadyl oxygen, (O(2). The crystallographic data (CCDC 1515813) and structure refinement summary are presented in Table 1. The major bond lengths and bond angles lengths and bond angles are listed in Table 2. In the neutral complex, the V atom is six coordinated by three nitrogen atoms and two oxygen atoms of L1 and L2 and one vanadyl oxygen. It is a fairly straight forward octahedral structure. The V=O and one O atom of ligand L2 remain axially coordinated with vanadium metal. The V=O distance of 1.619 Å is consistent with vanadyl distances is related complexes [54,55]. Interestingly, although the corresponding distances in each
ACCEPTED ligand (L1 and L2) are not significantly different, theMANUSCRIPT V-O2 (hydroxo) distances (2.004 and 2.151 Å) and VO3 are significantly different from one on other. The systematic analysis of the structural data available for the vanadyl complex revealed that observed C-H···π interactions lead to zero- or one- dimensional aggregations. The zero-demensional aggregats fall in two categories: The first of these features as C-H···π (aryl) interaction (Fig. 2 Top) and second type as C-H···π (metal chelate ring Fig. 2 Bottom). The first type of C-H···π (aryl) interaction occurs a C-H of aryl molecule and a ring (aryl) derived from another species. The second type of C-H···π (metal chelates) interactions was observed in between C-H (aryl) of species and metal chelate of another species. The majority of structures featuring C-H···π interactions utilize these synthons to assemble molecules into 1D supramolecular polymeric chains (Fig. 3). 3.3. DFT calculations The X-ray structure of the complex was used as starting point for the gas phase geometry optimization. The calculated geometrical parameters (bond lengths and bond angles) of the complex are presented in Table 2. The differences in calculated bond lengths and angles of the complex are due to calculation of structural parameter in gas phase. Contour plots of selected molecular orbitals are shown in Fig. 4. The highest energy occupied molecular orbital (HOMO) (α- and β-spin) have 100% π(L) (100%) character. The α-spin low energy unoccupied molecular (LUMO) have been constituted by 100% dπ(V) character while the β-spin LUMO have 100% π(L) character with a HOMO-LUMO energy gap of 0.969 eV (α-spin) and -4.957 eV (β-spin). The presence of paired electron in Schiff base show that diamagnetic character, while in vanadium(IV) complex shows that paramagnetic character with one unpaired electron in HOMO molecular orbital. Spin localization of the complex can be difficult to determine experimentally for intermediated not long-lived enough electron paramagnetic resonance (epr) experiments, however localization of spin density can be determined through computationally generated spin density maps (Fig. 5). Spin density maps were generated to localize the electron density of the unpaired electron. The spin density of the unpaired spin distributed over the 21.21% V, 10.32% O, 68.12% N and 0.35 % C on the coordinated atoms along with a major contribution on vanadium centre. 3.4. Electrochemistry The cyclic voltammograms of complex were measured in DMSO with TBAP as supporting electrolyte recorded as room temperature in the potential window of -0.310 to -1.100 V. The cyclic voltammograms for a 3 mmol solution of the complex exhibits two cathodic waves and two anodic waves. One redox process is irreversible with reduction at -0.80 V and quasi reversible with reduction at -0.60 V (Fig. 6). The reduction waves are larger than oxidation waves, showing that the complex undergoes a chemical change after reduction [56]. The cyclic voltammogram of this complex throw considerable light on the stability of the complex in the presence and absence of an excess of the ethanol. Change in redox waves observed for VO2+ complex treated with ethanol suggested the formation of dioxovanadium(V) complex due to aerial oxidation (eq. 2) [57] Oxovanadium(IV)
EtOH
dioxovanadium(V)
…………….(2)
An initial anodic scan does not include any oxidation peaks possibly the product of a further chemical reaction is electro inactive. The species responsible for the -0.65 V reduction peak is increase. The vanadium(V) complex may have different coordination numbers and consequently quite different electrochemical properties. Similar spectral changes observed when VO2+ treated with EtOH again suggested the conversion of VO2+ with broad and unresolved d-d band to dioxovanadium(V) with clear and resolved band as vanadium(V) complex has 3d0 configuration, d→d band is not expected. After addition of EtOH, there is, however, a strong band at ca. 525 nm for the dioxovandium(V) complex [55], which assigned to LMCT originating from the lone pair in a p-orbital Schiff base oxygen into an empty d-orbital of the vanadium ion (Fig. 7).
3.5. Epr studies
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The complex was also characterized by epr spectral measurement at liquid nitrogen temperature (Fig. 8). Epr parameters of DMSO solution have been measured for this complex (Table 3). The vanadyl ion has a simple S = 7/2 electron spin and 51V has high natural abundance and an I = 7/2 nuclear spin, it can be used to know the type of sites coordinated to the divalent complex ion. An additivity relationship introduced by Chasteen [58], to estimate the parallel 51V hyperfine constant of vanadyl complexes based on the contribution to Az from each of the four equatorial donor sites. The relationship provides a valid criterion to assess the equatorial donor atoms. The calculations were carried out according to the additivity relationship, using latest listings of the partial contributions of the equatorial ligand functions [59]. Within the limits of errors the experimental Az agrees with the calculated one, suggesting that the solution structure at low temperature does not significantly deviate from the structure in the crystalline solid state (Fig. 1). 3.6. α-Glucosidase inhibition study We have also tested the catalytic activity of the complex to mimic the α-Glucosidase activity. α-glucosidase is responsible for postprandial hyperglycemia. α-glucosidase catalyzes the disaccharides to monosaccharides, which leads to postprandial hyperglycemia [60]. Hence, inhibitor of α-glucosidase is useful in the control of hyperglycemia as this can delay carbohydrate digestions, which consequently reduce risk of diabetics and other carbohydrate mediated diseases [34-37]. Inhibition data (percentage inhibition at 200 μM and IC50 values) for oxovanadium(IV) complex is 14.75 μM. For acarbose as standard percentage inhibition is 18.59 μM. A perusal of the data reveals that the oxovanadium(IV) complex is moderate αglucosidase inhibitor. Various inorganic and organovanadium compounds have been demonstrated to enhance insulin sensitivity in animal models [61]. Organic ligands on vanadium can influence its bioactivity by the bioavailability of the vanadium ion. Careful design of the organic ligands on vanadium could affect their bioactivities significantly, thus making them more suitable for clinical usages in fighting diabetes. These observations suggest that the mixed-ligand oxovanadium complex may be a promising candidate as antidiabetic agent or lead compounds for further development. 4. Conclusion The above state of development has prompted us to undertake the task of mononuclear vanadium(IV) complex [VO(L1)(L2)] using this new Schiff base. In situ new vanadyl complex has been synthesized by an aerial reaction of 1:2 vanadyl sulphate and Schiff base (L1). The systematic analysis of the structural data available for the vanadyl complex revealed that observed C-H···π interactions lead to zero- or onedimensional aggregations. Although this oxovanadium(IV) complex cannot at present be related to specific biological systems, the solvent effects clearly are large both in term of the redox chemistry and coordination chemistry. The complex shows moderate in-vitro α-glucosidase inhibition. As moderate α-glucosidase inhibition is shown therefore this complex may be considered as α-glucosidase inhibitors. Acknowledgements We are grateful to M.P. Council of Science & Technology, Bhopal, India [Scheme No. A/RD/RP2/2015-16/245] for their financial support. RSIC (SAIF) IIT, Bombay for epr measurements and SAIF, Central Drug Research Institute, Lucknow India, are thankfully acknowledged for providing analytical and spectral facilities. Appendix: Supplementary data CCDC 1515813 contains supplementary crystallographic data for the present complex. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033; or email: [email protected]. References 1. 2.
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Fig.1. Molecular structure of complex [VO(L1)(L2)].
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Fig. 2. Top: C-H···π (metal chelate) interaction and Bottom: C-H···π (aryl chelate) interaction. Hydrogen atoms are omitted for celerity. Only representative hydrogen atom is shown.
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Fig. 3. One dimensional C-H···π (aryl chelate) interactions to form polymeric chain.
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LUMO = -3.921 eV
HOMO = -2.952 eV
LUMO = -1.661 eV
HOMO = -6.618 eV
LUMO+1 = -3.514 eV
HOMO-1 = -4.073 eV
LUMO+1 = -1.352 eV
HOMO-1 = -6.693 eV
Fig. 4. Contour plots of selected molecular orbitals of vanadium(IV) complex [VO(L1)(L2)].
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Fig. 5. DFT calculated spin density map of complex [VO(L1)(L2)].
Fig. 6. Cyclic valtamograms of vanadium(IV) complex. 1 In DMSO (3 × 10-3 M). 2 after adding 1 mL of ethanol. 3 after adding 2 mL of ethanol.
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Fig. 7. Visible spectral behavior of vanadyl complex [VO(L1)(L2)] with and without ethanol in DMSO.
Fig. 8. Epr spectra of vanadyl complex in DMSO solution at 77K.
ACCEPTED MANUSCRIPT Table 1 Crystal data and structure refinement parameters for complex [VO(L1)(L2)]. Empirical formula C26H19N5O3V Formula weight 500.40 T (K) 173(2) λ (Å) 1.54184 Crystal system Monoclinic Space group Pc a (Å) 7.9279(7) b (Å) 17.9872(19) c (Å) 8.2365(6) α (°) 90 β (°) 96.041(8) γ (°) 90 Volume (Å3) 1168.01(18) Z 2 Density (calculated) (Mg/m3) 1.423 ε (mm-1) 3.874 F(000) 514 3 Crystal size (mm ) 0.47 x 0.23 x 0.06 θ (°) 4.917 to 71.506 Index ranges -4 ≤ h ≤ 9, -22 ≤ k ≤ 20, -9 ≤ l≤9 Reflections collected 2614 Independent reflections 2614 [R(int) = 0.0623] Completeness to theta = 67.500° 99.8 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 1.00000 and 0.35652 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2614 / 38 / 311 2 1.044 Goodness-of-fit on F Final R indices [I>2sigma(I)] R1 = 0.0830, wR2 = 0.2215 R indices (all data) R1 = 0.0947, wR2 = 0.2433 Table 2 Selected interatomic distances [Å] and angles [°] of complex [VO(L1)(L2)]. Bond X-ray DFT Bond X-ray V-O(3) 1.619(8) 1.658 V-N(5) 1.909(8) V-O(1) 2.004(6) 2.125 V-O(2) 2.151(7) V-N(2) 2.089(9) 0.1259 V-N(1) 2.108(8) O(3)-V-N(5) N(5)-V-O(1) N(5)-V-N(2) O(3)-V-N(1) O(1)-V-N(1) O(3)-V-O(2) O(1)-V-O(2) N(1)-V-O(2)
96.2(4) 105.5(3) 150.7(3) 95.0(4) 150.4(3) 168.8(3) 87.4(3) 83.2(3)
96.24 105.92 151.01 95.12 150.82 169.12 87.65 82.35
O(3)-V-O(1) O(3)-V-N(2) O(1)-V-N(2) N(5)-V-N(1) N(2)-V-N(1) N(5)-V-O(2) N(2)-V-O(2)
99.3(4) 112.7(3) 75.3(3) 98.5(3) 75.3(3) 73.2(3) 77.6(3)
DFT 2.015 2.185 2.2145 99.52 113.01 75.38 98.65 75.62 73.25 77.91
Table 3 Spin Hamiltonian parameters of vanadyl complex in frozen DMSO (77K) solution. gz gxy Az × 104 cm-1 Axz Az × 104 cm-1 (calcd.) Donor atom set 1.953 2.010 166 71 162 2Nimine, Npyr, OAro