Syed Ahmed Tirmizi

A spectroscopic and viscometric study of the metal ion-induced gelation of the biopolymer chitosan

Abstract The gelation of the biopolymer chitosan in solution through crosslinking reactions with Pt( II ) has been investigated by simultaneously monitoring both the viscosity of the system and the number of metal-amine bonds formed per chitosan chain, as probed spectroscopically. The variables studied in the investigations included the chitosan to Pt( II ) concentration ratio, the pH of the reaction solution, and the concentration, molecular weight and degree of deacylation of chitosan. A kinetic model for the time dependence of the formation of crosslinks and a spectral model for the time evolution of the spectra were developed for the gelation process. These models included the effects of light scattering, steric hindrance, pH and variation of pKa as a function of the fraction of monomer units charged, and they were tested successfully against the experimental spectra. The time of gelation was found to decrease with increases in the following experimental parameters while holding all the other parameters constant: (1) concentration of Pt( II ), (2) pH of the reaction solution, (3) molecular weight of chitosan, and (4) concentration of chitosan in solution. In accordance with percolation theory, the calculated crosslink/chain ratios at the time of gelation were found to be quite consistent for the various reaction conditions and to be consistent also with predictions of thresholds for percolation of rigidity by network theories.

Chitaline materials: soluble chitosan-polyaniline copolymers and their conductive doped forms

Abstract Graft copolymers of polyaniline and chitosan have been synthesized. They are soluble in aqueous solution and form self-supporting materials, including thick films and fibers. Upon protonic doping, their conductivities rise from less than ∼10−7 S/cm to the 10−2 to 10−5 S/cm range, depending on the initial chitosan-to-aniline ratio. Spectroscopic studies show the grafting and demonstrate that the electronic states are similar to those of the emeraldine and protonically doped emeraldine forms of polyaniline.

Statistical apportionment and risk assessment of selected metals in sediments from Rawal Lake (Pakistan)

The present study was carried out in order to evaluate the statistical apportionment and risk assessment of selected metals (Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Pb, Sr, and Zn) in freshly deposited sediments in Rawal Lake, Pakistan. Composite sediment samples were collected, oven-dried, grounded, homogenized, and processed to assess the water-soluble and acid extractable concentrations of the metals in the water extract and acid extract of the sediments using flame atomic absorption spectrophotometer. Statistical methods were used to identify the possible sources of the metals. Sediment quality guidelines and potential acute toxicity were used to evaluate the ecotoxicological sense of selected metals. Non-carcinogenic health risk assessment was also carried out to determine the potential adverse health risks to the inhabitants. Relatively higher concentration was noted for Ca, Fe, Mg, Na, K, Mn, and Sr in the sediment samples. Principal component analysis and cluster analysis revealed anthropogenic contributions of Cd, Pb, Cr, Mn, Fe, and Li in the sediments. Enrichment factors of the metals in sediments showed severe to moderate enrichment of Cd, Pb, Ca, Fe, Li, Mn, and Sr. Geoaccumulation indices and contamination factors evidenced significant contamination by Cd and Pb, although, on the whole, low degree of contamination was noted. The levels of some metals exceeded the sediment quality guidelines, which revealed frequently adverse biological effects to the dwelling biota in the aquatic ecosystem. The sediments were found to be significantly contaminated by Cd, Pb, Cr, Mn, Fe, and Li.

Synthesis, spectral characterization and antibacterial studies of palladium(II) complexes of heterocyclic thiones

Reactions of K2[PdCl4] with heterocyclic thiones in molar ratios of 1:2 and 1:4 in water-methanol medium yielded the palladium(II) complexes with the general formula of either [Pd(L)Cl2], [Pd(L)2]Cl2 or [Pd(L)4]Cl2 where L ═ Imidazolidine-2-thione (Imt), 2-Mercaptopyridine (Mpy), 2-Mercaptopyrimidine (Mpm), 6-Mercaptopurine (6-Mp) and Thionicotinamide (Tna). The complexes were characterized by elemental analysis and spectroscopic (IR, 1H and 13C NMR) methods. An upfield shift in the >C═S resonance of thiones in 13C NMR and downfield shift in N–H or aromatic proton resonances in 1H NMR are consistent with the sulfur coordination to palladium(II). The complexes were screened for antibacterial activity, and the results showed that the complexes exhibited moderate activities as compared to that of a standard drug.

Tetrakis(thiourea-κS)palladium(II) dithio­cyanate

The title compound, [Pd(CH4N2S)4](SCN)2, consists of complex [Pd(TU)4]2+ [TU = thiourea, SC(NH2)2] cations and thiocyanate counter-anions. The PdII cation is situated on an inversion centre and exhibits an almost square-planar coordination by the S atoms of the TU ligands. The complex cations are connected through the thiocyanate ions via N—H⋯N [2.922 (3)–3.056 (3) Å] and N—H⋯S [3.369 (2)–3.645 (2) Å] hydrogen bonds.

Synthesis, spectroscopic characterization, biological screenings, DNA binding study and POM analyses of transition metal carboxylates.

This article contains the synthesis of a novel carboxylic acid derivative, its transition metal complexes and evaluation of biological applications. Six carboxylate complexes of transition metals, Zn(II) and Hg(II), have been successfully synthesized and characterized by FT-IR and NMR (1H, 13C). The ligand, HL, (4-[(2,6-Diethylphenyl)amino]-4-oxobutanoic acid) was also characterized by single crystal X-ray analysis. The complexation occurs via oxygen atoms of the carboxylate moiety. FT-IR date show the bidentate nature of the carboxylate moiety of the ligand as the Δν value in all complexes is less than that of the free ligand. The ligand and its complexes were screened for antifungal and antileishmanial activities. The results showed that the ligand and its complexes are active with few exceptions. UV-visible spectroscopy and viscometry results reveal that the ligand and its complexes interact with the DNA via intercalative mode of interaction. A new and efficient strategy to identify the pharmacophores and anti-pharmacophores sites in carboxylate derivatives for the antibacterial/antifungal activity using Petra, Osiris and Molinspiration (POM) analyses was also carried out.

Synthesis, spectral characterization and in vitro antibacterial evaluation and Petra/Osiris/Molinspiration analyses of new Palladium(II) iodide complexes with thioamides

Abstract The paper emphasizes on the synthesis of Palladium(II) iodide complexes containing based ligands. The new compounds of general formulae [Pd(L)4]I2 where L = Thiourea (Tu), Methylthiourea (Metu), Dimethylthiourea (Dmtu), Tetramethylthiourea (Tmtu), Imidazolidine-2-thione (Imt), Mercaptopyridine (Mpy), Mercaptopyrimidine (Mpm), and Thionicotinamide (Tna) were prepared simply by reacting K2[PdCl4] with the corresponding thioamides in 1:2 M ratio and then with 2 equivalents Potassium iodide. The complexes were characterized by elemental analysis and spectroscopic techniques (IR, 1H and 13C NMR). All the synthesized complexes were screened for antibacterial activity and some of compounds have shown good activities against both gram positive and gram negative bacteria. POM analyses reveal that the compounds are only slightly toxic and present a potential for antibacterial activity. Moreover, they have 16–23% drug score which is an important parameter for the compound possessing the drug properties.

A method optimization study for atomic absorption spectrophotometric determination of total zinc in insulin using direct aspiration technique

Abstract A sensitive, reliable and relative fast method has been developed for the determination of total zinc in insulin by atomic absorption spectrophotometer. This designed study was used to optimize the procedures for the existing methods. Spectrograms of both standard and sample solutions of zinc were recorded by measuring the absorbance at 213.9 nm for determination of total zinc. System suitability parameters were evaluated and were found to be within the limits. Linearity was evaluated through graphical representation of concentration versus absorbance. Repeatability (intra-day) and intermediate precision (inter-day) were assessed by analyzing working standard solutions. Accuracy and robustness were experimented from the standard procedures. The percentage recovery of zinc was found to be 99.8%, relative standard deviation RSD 1.13%, linearity of determination LOD 0.0032 μg/mL, and limit of quantization LOQ 0.0120 μg/mL. This developed and proposed method was then validated in terms of accuracy, precision, linearity and robustness which can be successfully used for the quantization of zinc in insulin.

3-Carbamothioylpyridinium iodide

In the crystal of the title salt, C6H7N2S+·I−, inversion-related cations form an R 2 2(8) dimer linked by a pair of N—H⋯S hydrogen bonds. Pairs of iodide anions are located between adjacent cation dimers and are linked to them by way of N—H⋯I hydrogen bonds. This results in zigzag chains propagating in [001] lying parallel to the bc plane.

SYNTHESIS, CRYSTAL STRUCTURE, AND ANTIMICROBIAL STUDIES OF TRANS-[PD(PPH3)2(IMIDAZOLIDINE-2-THIONE)2]CL2 · 3.5H2O

The palladium(II) complex, [Pd(PPh3)2(Imt)2]Cl2 · 3.5H2O (I) (Imt = imidazolidine-2-thione), has been synthesized and characterized by IR, NMR, and X-ray crystallography. An upfield shift in the >C=S resonance of Imt in the 13C NMR spectrum and a downfield shift in the N-H resonance in 1H NMR are consistent with the sulfur coordination of Imt to palladium(II). In the crystal structure of I, the central palladium atom is coordinated to two thione sulfur atoms of Imt and to two phosphorus atoms possessing a square-planar environment with the average cis and trans bond angles of 89.60° and 167.31°, respectively. The title complex was screened for antimicrobial effects, and the results showed that it exhibits moderate activities against gram-negative bacteria (E. coli, P. aeruginosa). The complexes also exhibited significant activities against yeast (C. albicans, S. serevisaiae).