Synthesis, characterization, thermal and antibacterial studies of organosilicon (IV) and organotin (IV) complexes derived from Schiff base ligand
Jai Devi,* Suman Devi
Department of Chemistry, Guru Jambheshwar University of Science & Technology, Hisar-125001, Haryana
*Corresponding Author E-mail: jaidevi_gju@yahoo.com
ABSTRACT:
The aim of the present work is to evaluate the biological activities of silicon and tin complexes with Schiff base ligand derived from 4-nitro-o-phenylenediamine and dehydroacetic acid in 1:1 molar ratio. Schiff base and their complexes have been characterized by elemental analysis, FT-IR and NMR (1H, 13C, 29Si, 119Sn) spectral techniques. On the basis of analysis penta-coordinated geometry around silicon and tin atom in 1:1 molar ratio was proposed. Thermal studies of all the synthesized complexes have been carried out using thermogravimetry (TG) technique under a nitrogen atmosphere. The thermal decompositions occurred in two steps and resulted into the formation of pure SiO2 and SnO2 residue. The biological activity of Schiff base ligand as well as their complexes has been carried out by minimum inhibitory concentration of tested compounds against various bacterial strains (S.epidermidis, S.hominis, P.aeruginosa and K.pneumoniae) which was later compared with standard drug ciprofloxacin. The antibacterial data revealed that complexes shows superior biological activity as compared to their respective ligand.
KEYWORDS: Schiff base, antibacterial, spectral techniques, dehydroacetic acid, complexes.
1. INTRODUCTION:
Metal complexes belonging to azomethine class of compounds have attracted the attention of many chemists owing to their wide spectrum of pharmacological activity profile with structural flexibility and ligational behavior. Organosilicon and organotin complexes of Schiff bases have received much interest during the last few years. The study of these complexes has been significant area of current research. Silicon and tin complexes have variety of industrial and medicinal applications in biological system as antibacterial, antifungal, anticancer, anti-HIV[1-6], anticonvulsant, anti malarial and anti inflammatory activity.
Metal complexes of Schiff bases have been used for catalysis, molecular recognition and in biological process. Hence in the quest for biologically more potent antimicrobial agents, we envisioned to synthesize the Schiff base derived from 4-nitro-o- phenylenediamine and dehydroacetic acid and further their silicon and tin complexes have been synthesized. All these compounds have been characterized with the help of conductance measurements, elemental analyses, IR, 1H, 13C, 29Si and 119Sn NMR spectroscopy. Further these were screened for antibacterial activity to examine the biological effect of these complexes on microbes.
2. EXPERIMENTAL:
All of the chemicals were of reagent grade (supplied by Sigma-Aldrich and Qualigen) and used as received without further purification. The IR spectra were recorded using a Spectrum BX Series FT-IR spectrophotometer in the range 400-4000 cm-1, using KBr pellets. The NMR (1H, 13C, 29Si and 119Sn) spectra were recorded on a Bruker Avance II 300 MHz NMR Spectrometer and all chemical shifts (δ) were reported in parts per million (ppm) downfield from the internal standard tetramethylsilane (TMS) in CDCl3 and DMSO-d6. Elemental analyses were carried out on a Perkin Elmer 2400 analyzer. Molar conductance was measured with conductivity bridge type model-306, Systronics in DMSO solvent.
Biology
Two Gram positive bacteria viz. Staphylococcus epidermidis [MTCC 3086], Staphylococcus hominis [MTCC 4435] and two Gram negative bacteria viz. Pseudomonas aeruginosa [MTCC 7453] and Klebsiella pneumoniae [MTCC 4030] were used for antibacterial activity. All the bacterial strains were procured from Microbial Type Culture Collection (MTCC), Institute of Microbial Technology (IMTECH), Chandigarh. The strains were cultured at 370C on nutrient agar medium in aerobic conditions for 24 h.
Minimum Inhibitory Concentration (MIC) of the organosilicon and organotin complexes was determined by microdilution technique using 96-well microtiter plates[7]. The bacteria inoculums were prepared in 5 mL nutrient broth and incubated at 370C for 48 h. The final inoculums were of approximately 1.5 × 106 CFU/mL (Mcfarland standard). Controls with 0.5 mL of culture medium without the test samples compounds and other without microorganisms were used in the tests. Tubes were incubated at 370C for 24 h. The activity was measured as a function of turbidity. Lack of turbidity was further confirmed by pouring suspension aliquot of 0.1 mL into pre-sterilized Petri dishes with nutrient agar medium.
3. RESULTS AND DISCUSSION:
Chemistry
The Schiff base ligand H2L was synthesized by reaction of 4-nitro-o- phenylenediamine and dehydroacetic acid in ethanol as solvent and its silicon and tin complexes were synthesized by refluxing it with dichlorodiorganosilane/dichlorodiorganotin in the presence of sodium metal in dry methanol. The mode of bonding and the geometry of these complexes were determined with the help of different spectral techniques. The resulting solid complexes were soluble in MeOH, EtOH, CDCl3 and DMSO (Table 1). Molar conductance values of these compounds were in the range of 07-19 ohm-1 cm2 mol-1, revealed non electrolytic nature of complexes[8].
Table-1: Physicochemical characterization and elemental analyses of Schiff base ligand and its complexes
|
Comp. No. |
Compounds |
Molecular formula |
m/z |
Yield (%) |
Anal. Found (Calc) (%) |
|||
|
|
||||||||
|
C |
H |
N |
Si/Sn |
|||||
|
1. |
H2L |
C14H13N3O5 |
303.27 |
91 |
55.43(55.45) |
4.28(4.32) |
13.84(13.86) |
- |
|
2. |
Me2SiL |
C16H17SiN3O5 |
349.41 |
87 |
53.48(53.47) |
4.80(4.77) |
11.71(11.69) |
7.78(7.81) |
|
3. |
Et2SiL |
C18H21SiN3O5 |
387.46 |
82 |
55.78(55.80) |
5.43(5.46) |
10.80(10.84) |
7.22(7.25) |
|
4. |
Bu2SiL |
C22H29SiN3O5 |
443.57 |
83 |
59.54(59.57) |
6.54(6.59) |
9.45(9.47) |
6.35(6.33) |
|
5. |
Ph2SiL |
C26H21SiN3O5 |
483.13 |
85 |
54.54(64.58) |
4.43(4.38) |
8.67(8.69) |
5.84(5.81) |
|
6. |
Me2SnL |
C16H17SnN3O5 |
450.03 |
82 |
42.66(42.70) |
3.85(3.81) |
9.30(9.34) |
26.35(26.38) |
|
7. |
Et2SnL |
C18H21SnN3O5 |
478.09 |
86 |
45.26(45.22) |
4.40(4.43) |
8.82(8.79) |
24.80(24.83) |
|
8. |
Bu2SnL |
C22H29SnN3O5 |
534.19 |
80 |
49.49(49.46) |
5.41(5.47) |
7.82(7.87) |
22.26(22.22) |
|
9. |
Ph2SnL |
C26H21SnN3O5 |
574.17 |
81 |
54.36(54.39) |
3.65(3.69) |
7.35(7.32) |
20.65(20.67) |
|
|
|
|
|
|
|
|
|
|
IR spectra
On comparison of IR spectra of Schiff base ligand and its complexes, it was observed that disappearance of a broad band due to v (O-H) of ligand at 3207 cm-1, indicated the coordination of hydroxyl oxygen with the central metal atom[9]. Another sharp band due to azomethine v (C=N) group of Schiff base appeared at 1621 cm-1 and this was shifted in the complexes by ± 15 cm-1 which indicated the participation of the azomethine nitrogen in coordination[10]. The band due to v (N-H) at 3075 cm-1 of ligand was moved slightly towards lower wavelength in the complexes suggesting the attachment of imino nitrogen in complexation[11]. The formation of the target compounds were further supported by appearance of some new bands at 560-503 cm-1 and 490-434 cm-1 due to v (M-O) and v (M-N) modes, respectively.
1H NMR Spectra
The 1H NMR spectra of the Schiff base and its complexes were recorded in CDCl3 and DMSO-d6 using tetramethylsilane as internal standard. The OH proton of free ligand displayed signal at 15.80 ppm, which disappeared in the complexes indicating the coordination of the hydroxyl oxygen to the silicon and tin atom after deprotonation. The C-H proton of dehydroacetic acid ring appeared as a sharp singlet at 6.56 ppm and methyl protons of DHA appeared at 2.23-2.37 ppm for the ligands and remained almost unchanged in the complexes. A multiplet due to aromatic protons of ligand appeared in the range 7.01-6.63 ppm. The formation of silicon and tin complexes were further confirmed by the appearance of new signals at 1.30-1.36 ppm, 2.09-2.43 ppm, 1.86-2.57 ppm and 7.45-7.59 ppm due to methyl, ethyl, butyl, and phenyl protons directly attached to the central atom.
|
Comp No. |
Compounds |
-OH |
-N=C-CH3 |
-CH |
Aromatic-H |
C6-CH3 |
-NH2 |
M-R |
|
|
|
|
|
|
|
|
|
|
|
1. |
H2L |
15.80 |
2.23 |
6.56 |
7.01-6.63(m,4H) |
2.37 |
5.43(2H) |
- |
|
2. |
Me2SiL |
- |
2.11 |
6.83 |
7.50-7.29(m, 4H) |
2.59 |
6.30(1H)
|
1.30(s,6H) |
|
3. |
Et2SiL |
- |
2.15 |
6.80 |
7.50-7.33(m, 4H) |
2.55 |
6.41(1H)
|
2.40(q,4H), 2.10(t,6H) |
|
4. |
Bu2SiL |
- |
2.10 |
6.79 |
7.53-7.32(m, 4H) |
2.61 |
6.27(1H)
|
2.57 (t,4H), 2.31(t,6H), 2.11-1.86(m,8H)
|
|
5. |
Ph2SiL |
- |
2.14 |
6.85 |
7.56-7.43(m, 4H) |
2.58 |
6.39(1H)
|
7.59-7.51(m, 4H), 7.48-7.45(m, 6H)
|
|
6. |
Me2SnL |
- |
2.17 |
6.80 |
7.55-7.36(m, 4H) |
2.60 |
6.40(1H)
|
1.36(s,6H) |
|
7. |
Et2SnL |
- |
2.19 |
6.78 |
7.57-7.39(m, 4H) |
2.63 |
6.31(1H)
|
2.43(q,4H), 2.09(t,6H) |
|
8. |
Bu2SnL |
- |
2.16 |
6.69 |
7.58-7.39(m, 4H) |
2.59 |
6.37(1H)
|
2.53 (t,4H), 2.21(t,6H), 2.17-1.97(m,8H)
|
|
9. |
Ph2SnL |
- |
2.17 |
6.84 |
7.56-7.33(m, 4H) |
2.61 |
6.35(1H) |
7.59-7.54(m, 4H), 7.51-7.49(m, 6H) |
|
|
|
|
|
|
|
|
|
|
13C NMR Spectra
On comparison of the 13C NMR spectra of ligand and its complexes, it was observed that signal due to azomethine carbon (C-7) appeared at 156.20 ppm and was shifted in the complexes, which revealed the coordination of azomethine nitrogen with the central atom. The signal due to C-H carbon of dehydroacetic acid ring appeared at 111.68 ppm in ligand and remained almost unaltered in complexes, confirmed its non involvement in coordination. Signals due to carbons of methyl group in the DHA ring appeared at 19.70 and 20.85 ppm, which remained same in the complexes. The signals of methyl group carbon attached to silicon and tin atom appeared at 35.46-35.50 ppm and the carbon of ethyl group appeared at 12.45- 16.23 ppm. The signals of carbon due to n-butyl and phenyl group appeared at 20.09-29.09 ppm and 135.04-137.02 ppm, respectively. The carbon of substituted aromatic ring appeared in the range of 120.54-135.59 ppm.
|
Comp No. |
Compounds |
C-2 |
C-3 |
C-4 |
C-5 |
C-6 |
C-7 |
C-CH3 |
Aromatic carbon |
M-R |
|
|
|
|
|
|
|
|
|
|
|
|
|
1. |
H2L |
145.10 |
99.70 |
173.86 |
111.68 |
137.45 |
156.20 |
19.70, 20.85 |
135.59-120.54
|
- |
|
2. |
Me2SiL |
145.50 |
98.46
|
175.60 |
111.11
|
138.31
|
169.98
|
19.10, 20.69 |
133.89-125.50
|
35.46
|
|
3. |
Et2SiL |
145.55 |
97.96
|
175.32 |
110.19
|
136.91
|
169.32
|
19.42, 20.73 |
133.60-124.20
|
12.45, 15.29
|
|
4. |
Bu2SiL |
146.05 |
97.99
|
175.54 |
111.08
|
136.96
|
169.54
|
19.21, 20.82 |
133.38-124.80
|
20.09, 21.55, 25.78, 28.99 |
|
5. |
Ph2SiL |
146.26 |
98.91
|
174.97 |
111.01
|
138.16
|
170.04
|
18.91, 20.37 |
134.08-124.23
|
136.98,135.97, 135.52, 135.04 |
|
6. |
Me2SnL |
146.30 |
98.40
|
175.23 |
110.23 |
138.37
|
169.99
|
19.48, 21.00 |
133.34-124.90
|
35.50
|
|
7. |
Et2SnL |
145.68 |
98.16
|
176.02 |
110.26
|
136.92
|
170.12
|
19.47, 20.23 |
133.12-125.56
|
12.64, 16.23
|
|
8. |
Bu2SnL |
146.32 |
97.59
|
175.05 |
111.00
|
136.46
|
169.20
|
20.14, 21.62 |
133.58-124.844
|
20.34, 21.89, 26.76, 29.09 |
|
9. |
Ph2SnL |
145.39 |
97.95
|
175.27 |
110.31
|
138.00
|
170.39
|
19.99, 20.57 |
134.53-124.59
|
137.02,136.00, 135.49, 135.54 |
|
|
|
|
|
|
|
|
|
|
|
|
29Si and 119Sn NMR Spectra
In order to find out the geometry of the complexes, 29Si and 119Sn NMR spectra were recorded in CDCl3 and DMSO-d6. The appearance of sharp signals at δ −93 to −106 ppm and δ − 153 to – 160 ppm[12, 13] are assigned to R2SiL and R2SnL complexes respectively, which have penta-coordinated environment around the central atom The spectra displayed a sharp singlet for each complex proves the formation of single compound.
Thermal analysis of organosilicon (IV) and organotin (IV) complexes
The thermogravimetric (TG) analysis of compounds were obtained in the inert atmosphere. The decomposition of all the studied complexes ended with SiO2 and SnO2 formation. All the complexes show a gradual loss in weight due to decomposition by fragmentation with increasing temperature. The thermogravimetric curves shows two successive steps, first step of decomposition match to the loss of R (Me, Et, Bu and Ph) groups attached to Si/Sn and second step of decomposition related to the loss of ligand moiety along with the formation of SiO2 and SnO2 as final residue.
Antimicrobial Evaluation
The newly synthesized compounds were subjected to in vitro antibacterial activity against Gram-positive bacteria (S.epidermidis, S.hominis) and Gram negative bacteria (P.aeruginosa, K.pneumoniae) and activity was evaluated by calculating Minimum Inhibitory Concentraions using micro dilution technique (Table 4 and Figure I). Ciprofloxacin was used as positive control and DMSO was used as negative control.
Antibacterial data revealed that-
§ Schiff base ligand possesses considerable activity against different bacterial strains, which might be due to azomethine linkage[14].
§ Biological activity of Schiff base improved on coordination with central atom. This enhanced activity might be due to chelation effect in which polarity reduces on coordination with metal ion, because of the partial sharing of its positive charge with the donor[15, 16]. Hence improved lipophilic character of these complexes favors the penetration of these compounds in the lipid cell membrane.
§ Among all the complexes phenyl derivatives were found to be highly active as compared to other derivatives (Me, Et and Bu) against all the bacterial strains. This may be due to the electron releasing ability of phenyl group[17].
Table-4: Minimum Inhibitory Concentrations (MICs) value of ligands and its complexes
|
Comp No. |
Compounds |
S.epidermidis |
S.hominis |
P.aeruginosa |
K.pneumoniae |
|
Gram +ve bacteria |
|
Gram -ve bacteria |
|||
|
1. |
H2L |
30 |
30 |
- |
- |
|
2. |
Me2SiL |
30 |
30 |
15 |
- |
|
3. |
Et2SiL |
15 |
15 |
15 |
30 |
|
4. |
Bu2SiL |
7.5 |
7.5 |
15 |
15 |
|
5. |
Ph2SiL |
3.75 |
7.5 |
7.5 |
7.5 |
|
6. |
Me2SnL |
15 |
15 |
30 |
30 |
|
7. |
Et2SnL |
15 |
15 |
15 |
30 |
|
8. |
Bu2SnL |
7.5 |
7.5 |
15 |
15 |
|
9. |
Ph2SnL |
7.5 |
3.75 |
7.5 |
7.5 |
|
|
|
|
|
|
|
|
|
|||||
Figure- I: In vitro antibacteria activity of ligand and its complexes
4. CONCLUSION:
Compounds 1-9 were synthesized and characterized by various spectral techniques. The spectral and analytical data were in good agreement with the proposed penta coordinated structures. Compounds were screened for their in vitro antibacterial activity against Gram positive and Gram negative bacteria and data exposed that all compounds displayed excellent activity and activity of Schiff base got enhanced on complexation with silicon and tin atom.
5. ACKNOWLEDGEMENT:
Suman Devi is thankful to the Department of Science and Technology, Panchkula, Haryana (India) for the financial support.
6. ETHICAL STATEMENT:
This article does not contain any studies with human participants or animals performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
7. REFERENCES:
1. Jain M and Singh RV. Synthesis, Characterization, and Biotoxicity of NN⌢ Donor Sulphonamide Imine Silicon(IV) Complexes. Bioinorganic Chemistry Application. 1; 2006: 1-10.
2. Chaudhary A, Phor A, Gaur S, Singh RV. Isolation, characterization and anti-tumour properties of novel chiral organotin(IV) complexes of phenanthrolines. Heterocyclic Communications. 10; 2004: 181-186.
3. Gielen M, Tiekink ERT, Bouhdid A, Dde Vos, Biesemans M, Verbruggen I, William R. Synthesis, characterization and in-vitro antitumour activity of dibutyltin carboxylates involving the perfluorophenyl moiety: Crystal structure of the dimeric bis[(4-fluoro- and pentafluoro-benzoato)di-n-butyltin] oxides. Appllied Organometalllic Chemistry. 9; (1995): 639-648. DOI:10.1002/00c.590090720.
4. Casas J, Castineiras A, Condori F, Couce MD, Russo U, Sanchez A, Seoane R, Sordo J, Varela JM. Diorganotin(IV)-promoted deamination of amino acids by pyridoxal: SnR2+2 complexes of pyridoxal 5′-phosphate and of the Schiff base pyridoxal-pyridoxamine (PLPM), and antibacterial activities of PLPM and [SnR2 (PLPM-2H)] (R = Me, Et, Bu, Ph). Polyhedron. 22; 2003: 53-65.
5. Maurya MR, Khurana S, Schulzke C and Rehder D. Dioxo- and Oxovanadium(V) Complexes of Biomimetic Hydrazone ONO Donor Ligands: Synthesis, Characterization, and Reactivity. European Journal of Inorganic Chemistry. 2001; 2001: 779- 787.
6. Parrilha GL, Vieira RP, Rebolledo AP, Mendes IC, Lima LM, Barreiro EJ, Piro OE, Castellano EE, Beraldo H. Binuclear zinc(II) complexes with the anti-inflammatory compounds salicylaldehyde semicarbazone and salicylaldehyde-4-chlorobenzoyl hydrazone (H 2LASSBio-1064). Polyhedron, 30; 2011: 1891-1898. DOI:10.1016/j.poly.2011.04.024.
7. NCCLS (National Committee for Clinical Laboratory Standards). Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically, Approved Standard. M7-A5. 2000. Das S, Choudhury MD. Antimicrobial Activity of Stem Bark Extracts from the Plant Oroxylum indicum Vent. Assam University Journal of Science and Technology: Biological and Environmental Sciences, 5; 2010: 95–99.
8. Devi J, Devi S and Kumar A. Synthesis, spectral, and in vitro antimicrobial studies of organosilicon(IV) complexes with Schiff bases derived from dehydroacetic acid. Monatshefte Fur Chemie, 2016. DOI:10.1007/s00706-016-1720-z.
9. Devi J, Kumari S and Malhotra R. Synthesis, Spectroscopic Studies, and Biological Activity of Organosilicon(iv) Complexes of Ligands Derived from 2-Aminobenzothiazole Derivatives and 2-Hydroxy-3 Methoxy Benzaldehyde. Phosphorus Sulfur Silicon Related Elements. 187; 2012: 587-597.
10. Adeola N A, Gabriel KA and Ayorinde NO. Synthesis, characterization, antibacterial, and thermal studies of unsymmetrical Schiff-base complexes of cobalt(II). Journal Coordination Chemistry. 63; 2010: 4398-4410.
11. Manan MF, Kassim K and Manan MAFA. Synthesis, characterization and conductivity studies of schiff base ligand derived from isatin and o-phenylenediamine with its cobalt(II) metal complex and lithium-schiff base compound. Malaysian Journal Analytical Science. 16; 2012: 318-324.
12. Singh K, Dharampal, Parkash V. Synthesis, spectroscopic studies, and in vitro antifungal activity of organosilicon(IV) and organotin(IV) complexes of 4-amino-5-mercapto-3-methyl-S- triazole Schiff bases. Phosphorus Sulfur Silicon Related Elements, 183; 2008: 2784-2794. DOI:10.1080/10426500802013577.
13. Devi J, Devi S and Kumar A. Synthesis, antibacterial evaluation and QSAR analysis of Schiff base complexes derived from [2,2′-(ethylenedioxy)bis(ethylamine)] and aromatic aldehydes. Medicinal Chemical Communications DOI: 10.1039/c5md00568j.
14. Chilwal A, Malhotra P and Narula AK. Synthesis, characterization, thermal, and antibacterial studies of organotin(IV) complexes of indole-3-butyric acid and indole-3-propionic acid. Phosphorus. Sulfur Silicon Related Elements. 189; 2014: 410-421.
15. Tweedy BG. Plant extracts with metal ions as potential antimicrobial agents. Phytopathology. 55; 1964: 910-914.
16. Mohini Y, Prasad RBN and Karuna MSL. Synthesis of fatty acid Schiff base esters as potential antimicrobial and chemotherapeutic agents. Medicinal Chemistry Research. 22; 2013: 4360–4366.
17. Hall HI, Wong OT and Chapman JM. Cytotoxicity of imides-N-alkyl semicarbazones, thiosemicarbazones, acetylhydrazones and related derivatives. Anticancer Drugs. 6; 1995: 147-153.
Received on 08.07.2016 Modified on 16.08.2016
Accepted on 22.08.2016 © AJRC All right reserved
Asian J. Research Chem. 2016; 9(9): 419-424.
DOI: 10.5958/0974-4150.2016.00063.8