Mookandi Kanthimathi

Interaction of DNA with [Cr(Schiff base)(H2O)2]ClO4

The binding of Schiff base complexes of chromium(III) of the type [Cr(salen)(H(2)O)(2)](+) and [Cr(salprn)(H(2)O)(2)](+), where salen denotes 1,2-bis(salicylideneamino)ethane and salprn denotes 1,3-bis(salicylideneamino)propane to calf thymus DNA has been investigated by absorption, emission, circular dichroism, melting temperature and viscosity measurements. These chromium(III) complexes showed absorption hyperchromicity accompanied by red shift in charge transfer band, fluorescence enhancement, increase in melting temperature, some structural changes in CD spectra and changes in specific viscosity when bound to calf thymus DNA. The binding constant K(b) has been determined from absorption measurements for both the complexes and found to be (2.5+/-0. 4)x10(3) M(-1) for [Cr(salen)(H(2)O)(2)](+) and (1.7+/-0.3)x10(4) M(-1) for [Cr(salprn)(H(2)O)(2)](+). From the binding stoichiometry of DNA-[Cr(salprn)(H(2)O)(2)](+), the number of binding site size has been determined and found to be ten base pairs per bound complex molecule. The chromium(III) complexes also bring about single strand cleavage in plasmid DNA. The experimental results show that the chromium(III) complexes bind to DNA by non-intercalative mode. Major groove binding is the preferred mode of interaction for these Schiff base complexes of chromium(III).

An improved product-process for cleaner chrome tanning in leather processing

Abstract Severe restrictions imposed by the pollution control authorities on the disposal of chromium, total dissolved solids and chlorides in tannery effluents have forced the tanners to look for low-waste, high exhaust chrome tanning salts. An improved chrome syntan with more than 90% uptake of chrome has been developed. The new product serves both as tanning and retanning agent and can be applied directly to delimed pelts thus eliminating the conventional pickling stage in the leather processing. This modified process helps to reduce the chemical oxygen demand (COD), total dissolved solids (TDS) and chlorides in the spent tan liquor by 51, 81 and 99%, respectively. The product offers full, soft leathers having shrinkage temperature comparable to conventional chrome tanned skins. Since the developed product is highly reactive, it saves time and reduces the water requirement when compared to the conventional chrome tanning method. Thus the novel product/process developed not only has advantages in reducing pollution loads but also seems to be techno-economically viable.

Copper(II) complex of a tridentate ligand: an artificial metalloprotease for bovine serum albumin

A copper(II) complex of 2, 6-bis(benzimidazo-2-yl) pyridine was synthesized and its binding properties with bovine serum albumin (BSA) has been evaluated. The binding plot obtained from the absorption titration data gives a binding constant of 2.4 (+/-0.3) x10(3) M(-1). It was found that the charge transfer band of the metal complex was perturbed in the presence of BSA. The gel electrophoresis pattern of BSA incubated with copper(II) complex shows the metalloproteolytic activity of the metal complex. In the presence of oxygen, protein undergoes site-specific cleavage by binding to the histidine residues of domain III, with the resultant formation of four fragments of molecular weight 49, 45, 22 and 17 kDa. This indicates the presence of two specific binding sites in the protein molecule. In the absence of molecular oxygen, the metal complex was found unable to cleave the protein. The circular dichroism (CD) spectrum of the isolated fragments shows nearly 38% and 32% of alpha helical content in 49 and 45 kDa fragments, respectively, which shows that the cleavage leads to no changes in the secondary structure of the protein fragments.

Development of a force field for some copper(II) Schiff-base complexes

Abstract Molecular mechanics calculations have been performed on Cu(N,N′-ethylenebis(salicylideneimine)) [ Cu ( salen )], Cu(N,N′-propylenebis(salicylideneimine)) [ Cu ( salprn )] and Cu(N,N′-butylenebis(salicylideneimine)) [ Cu ( salbuen) ] after generating a well-balanced force field based on the structural parameters available for Cu(salen) and Cu(salprn). The optimized stretching force constant for CuN and CuO bond types is 2.25 mdyn/A and the bending force constant corresponding to NCuN, OCuO and OCuN types is 0.5 mdyn/A. The stability and structural parameters have been predicted based on the calculations.

Langmuir–Blodgett film properties of a donor–acceptor Schiff base

Abstract A low-molecular weight Schiff base with donor–acceptor substituent on the Schiff base has been synthesized in order to study the Langmuir–Blodgett (LB) film properties. This is the first report wherein we demonstrate a short chain, Schiff base forms stable monolayers which have been transferred onto solid substrates to prepare Langmuir–Blodgett multilayers. Spectroscopic measurements of this Schiff base in chloroform as well as its LB film show changes in the spectral features indicating the changes in the environment around the chromophore.

Effect of molecular association and reactivity on substitution in chromium(III)–salprn complexes

A new chromium(III)–Schiff base complex, [Cr(5-chlorosalprn)(H2O)2]ClO4, where salprn = N,N′-propylenebis(salicylideneimine) has been prepared and characterized by electrospray ionization mass spectrometric (ESIMS) analysis and other spectroscopic techniques. Single crystal X-ray data reveal that the complex assumes a trans-diaquo structure, [Cr(C17H18Cl2N2O4)]ClO4 · H2O. The effect of phenyl ring substituents on the rate of formation of [O=CrV Schiff base]+ has been investigated. The bimolecular rate constant for the formation of O=CrV species by the [Cr(Schiff base)(H2O)2]ClO4, where the Schiff base = salprn, (1) and 5-chlorosalprn, (2) with PhOI was compared. In the case of (2) the rate was found to be faster by an order of magnitude at pH = 4 compared to (1). The introduction of a chloro-substituent on the phenyl ring not only influences the rate of redox reactivity but also the pKa values of aquo ligands of the complexes, indicating the difference in the electronic environment around the metal ion in both (1) and (2).

Synthesis, crystal structure and reactivity of trans-diaquo N,N′-ethylenebis-(3-methoxysalicylideneiminato)chromium(III)

A new chromium(III) Schiff base complex, [Cr(3-methoxysalen)(H2O)2]ClO4, where salen = N,N′-ethylenebis- (salicylideneimine), has been synthesized and characterized by spectroscopic techniques. Single crystal X-ray data reveals that the complex assumes a trans-diaquo structure with formulation [Cr(C18H22N2O6)]ClO4 but, unlike in Cr (salen)(H2O)2+, the two trans-water molecules are equidistant from CrIII. The effect of the substituent on the phenyl ring in respect of redox reactivity has been investigated. The kinetics of the oxidation of [Cr(Schiff base)- (H2O)2]ClO4, where Schiff base = salen, (1) and 3-OMe-salen, (2) by PhOI has been studied. The bimolecular rate constant for the formation of the O=Crv Schiff base in case of (2) was four times faster than that of (1). The introduction of the OMe group substituent on the phenyl ring influences not only the structure and crystal packing, but also the reactivity of the complex and the electronic environment around the metal ion.

Preparation, characterization and reactivities of chromium (III) complexes of a homologous series of Schiff-base ligands

Complexes of general formulation [Cr(Schiff-base)(H2O)2]X, where Schiff-base=1, 2-bis(salicylideneamino)ethane (salen), 1, 3-bis(salicylideneamino) propane (salprn) and 1, 4-bis(salicylideneamino)butane (salbuen) and X=ClO4 or Cl have been prepared and characterised. Single-crystal structure of the complexrans[Cr(salprn)(H2O)2]Cl has been resolved. Evidence for less distorted coordination geometry around chromium in the salprn analogue as compared to that intrans-[Cr(salen)(H2O)2]+ has been presented. The kinetics of the aqua ligand substitution in the complexes Cr(Schiff-base)(H2O)2+ by thiocyanate have been investigated under pseudo-first order conditions with [NCS−]≫[Cr(III)],T=10–50°C, [H+]=10−8−10−1 M,I=1.0M (LiClO4). An attempt has been made to discuss the anomalous lability oftrans-[Cr(salen)(H2O)2]+ reported earlier in comparison to the reactivities of salprn and salbuen analogues. Bimolecular rate constants for the aqua ligand substitution by NCS− in [Cr(Schiff-base)(H2O)2]+ at 25°C vary by more than two orders of magnitude depending on the nature of the Schiff-base ligand. The reactivity order is discussed in terms of the possible steric strain imposed by the equatorially coordinated quadridentate ligand.

Synthesis and photoreaction of Schiff bases derived from p-nitro cinnamaldehyde and diamines in Langmuir and Langmuir-Blodgett films

Abstract Monolayers of Schiff bases derived from ethylene diamine and o -phenylene diamine with p -nitro cinnamaldehyde, (compounds 1 and 2 ) at air/water interface have been studied. Photolysis of 1 in chloroform solution undergoes cis – trans isomerization on irradiation of white light while compound 2 does not undergo isomerization under photolytic conditions. The photolysis of 1 and 2 in Langmuir–Blodgett films (LB films) transferred to quartz plates form dimers. The change in product distribution is attributed to the influence of bridging group of the cinnamaldehyde moieties, molecular configuration and mobility of the compounds in solution, solid state and the aggregation of molecules in monolayer assemblies.

An e.p.r. study of tetradentate Schiff base copper complexes with an N–(CH2)n–N, n = 3–6 backbone

CuII complexes of Schiff-base ligands with a general formulation o-HOC6H4CH=N–(CH2)n–N=CHC6H4OH-o, where n = 3–6 have been prepared and their e.p.r. spectra investigated in order to determine the effect of the flexible methylene backbone length on the structure. The room temperature and 77 K e.p.r. spectra of the compounds, n = 3 and 4, are typical of the axially symmetric ground state with g∥ > g⊥. When n = 5, on the other hand, the complex gives an isotropic spectrum at room temperature. For n = 6, g⊥ appears to be greater than g∥. The giso value increases gradually from n = 3 to n = 6 indicating deviation from planarity. Simulation of the 77 K spectrum for n = 6 shows the presence of two distinct Cu2+ sites of equal probability. The Q-band spectrum of this compound exhibits a narrowed g∥ signal indicative of exchange coupling. The spectrum is a consequence of intermolecular electron exchange giving a pseudo d2z state.