Ram S. Shukla

Biological and clinical aspects of Lanthanide coordination compounds.

The coordinating chemistry of lanthanides, relevant to the biological, biochemical and medical aspects, makes a significant contribution to understanding the basis of application of lanthanides, particularly in biological and medical systems. The importance of the applications of lanthanides, as an excellent diagnostic and prognostic probe in clinical diagnostics, and an anticancer material, is remarkably increasing. Lanthanide complexes based X-ray contrast imaging and lanthanide chelates based contrast enhancing agents for magnetic resonance imaging (MRI) are being excessively used in radiological analysis in our body systems. The most important property of the chelating agents, in lanthanide chelate complex, is its ability to alter the behaviour of lanthanide ion with which it binds in biological systems, and the chelation markedly modifies the biodistribution and excretion profile of the lanthanide ions. The chelating agents, especially aminopoly carboxylic acids, being hydrophilic, increase the proportion of their complex excreted from complexed lanthanide ion form biological systems. Lanthanide polyamino carboxylate-chelate complexes are used as contrast enhancing agents for Magnetic Resonance Imaging. Conjugation of antibodies and other tissue specific molecules to lanthanide chelates has led to a new type of specific MRI contrast agents and their conjugated MRI contrast agents with improved relaxivity, functioning in the body similar to drugs. Many specific features of contrast agent assisted MRI make it particularly effective for musculoskeletal and cerebrospinal imaging. Lanthanide-chelate contrast agents are effectively used in clinical diagnostic investigations involving cerebrospinal diseases and in evaluation of central nervous system. Chelated lanthanide complexes shift reagent aided 23Na NMR spectroscopic analysis is used in cellular, tissue and whole organ systems.

Chiral Mn(III) salen complex-catalyzed enantioselective epoxidation of nonfunctionalized alkenes using urea–H2O2 adduct as oxidant

AbstractEnantioselective epoxidation of chromenes, indene, and styrene mediated by manganese salen complexes 1a–b, 2a–b (1 mol%) as catalystswith urea–H 2 O 2 adduct as an oxidant is observed to give excellent epoxide yield ( > 99%) in 0.5–4 h with enantiomeric excess (ee) in therange 56–99% except for styrene in which case 23–39% ee was obtained in 20 h. Even with a catalyst loading of 0.4 mol%, the system worksefficiently with retention of enantioselectivity, albeit with an increase in reaction time. Kinetic investigations of a representative substrate,indene, with these catalysts indicated a kinetic profile having first-order dependence with respect to the concentrations of the catalyst andoxidant and independent of-initial concentration of the substrate. Based on kinetic, catalytic and experimental evidence, the mechanism ofthe epoxidation reaction is suggested.  2003 Elsevier Inc. All rights reserved. Keywords: Enantioselective; Chiral; Manganese; Nonfunctionalized alkenes; Catalysis; Urea–H

One-pot synthesis of C8 aldehydes/alcohols from propylene using eco-friendly hydrotalcite supported HRhCO(PPh3)3 catalyst

A multi-functional catalyst [HF/HT] containing a rhodium complex, HRh(CO)(PPh3)3 [HF] and a solid base, hydrotalcite Mg1−xAlx(OH2)x+(CO32−)x/n·mH2O [HT], synthesized by impregnation of [HF] onto the surface of [HT], was investigated for the one-pot synthesis of C8 aldol derivatives (aldehydes or alcohols) from propylene. The catalyst was found to be efficient to carry out hydroformylation, aldol condensation and hydrogenation reactions in one pot. The catalytic activity of [HF/HT(X)] was studied in detail as functions of Mg/Al molar ratio (X) of [HT], amount of [HF] complex and [HT], and reaction temperature. The selectivity for 2-ethylhexanal was observed to increase upon increasing X and amount of [HT]. The highest selectivity for 2-ethylhexanol was observed for [HT] Mg/Al molar ratio of 3.5 at 250 °C. The kinetic profiles of the various products obtained were in agreement with the reaction pathway proposed to understand the role of the [HF/HT] catalyst on the formation of C8 aldol derivatives. Thermal stability of the [HF/HT] catalyst system was also investigated.

Absorption Spectral Studies Involving 4f–4f Transitions as Structural Probe in Chemical and Biochemical Reactions and Compositional Dependence of Intensity Parameters

Abstract Absorption spectral studies on lanthanides are described, dealing with 4f–4f transitions as structural probe in chemical and biochemical reactions, and compositional dependence of intensity parameters in order to understand the structure and nature of lanthanide bimolecular interaction. This review is basically addressed to the suitable application of solution absorptional spectral spectroscopy: (i) in probing the binding characteristics and multimetal simultaneous coordination of biomolecules, (ii) following the different steps involved n complex sol-gel processes involving heterometallic alkoxides as precursors fore generation of suitable materials for future computing devices, and (iii) in pursuing the progress of some organic synthesis, specially Meerwin-Ponndorf-Verley reaction and Diels-Alder cycloaddition reaction, homogeneously catalysed by lanthanides. Solution kinetics of interactions of lanthanides involved in the reactions is presented.

Kinetic and mechanistic investigations on reductions of aflatoxins by lactic acid.

The kinetics of reduction of AFB(1) to AFB(2) and AFG(1) to AFG(2) by lactic acid has been investigated in dilute aqueous acidic solutions (pH 3.35-4.50) as a function of the concentrations of lactic acid, AFB(1), AFG(1) and hydrogen ion at 37 degrees C. The rate of the reaction was found to be first order with respect to the concentrations of lactic acid and aflatoxins and independent on hydrogen ion concentration. The experimental results are interpreted in terms of mechanisms involving an initial formation of transient oxonium intermediate, which tends to polarize the olefinic (C=C) carbon, which in turn causes the hydride abstraction from alpha-carbon atom of lactic acid in rate determining step. The proposed mechanisms involve an overall transfer of two protons and two electrons from lactic acid to AFB(1) and AFG(1) to give the corresponding reduced less toxic products AFB(2) and AFG(2) and the oxidised product pyruvic acid.

Amelioration of cytotoxic effects of aflatoxin by vitamin A : an in vitro study on erythrocytes

We have evaluated the ameliorative role of vitamin A on aflatoxin-induced cytotoxicity in vitro. Aflatoxin (1.95 microM)-induced hemolysis was found to be significantly reduced on addition of vitamin A (125--1250 IU/ml) in incubation medium. The decrease in hemolysis was almost dose dependent. The kinetics of reduction of AFB(1) to B(2) and AFG(1) to G(2) by vitamin A has been investigated in dilute aqueous solution at 37 degrees C. The rate of the reduction was found to be first order with respect to the concentration of vitamin A and aflatoxin concentration.

Kinetic, mechanistic, and thermodynamic investigations on ferrofluid-catalyzed oxidation of L-ascorbic acid by hydrogen peroxide in acidic aqueous solution

The reduction of ferrofluid (FF) by L-ascorbic acid (H(2)A) and the reoxidation of the reduced FF to its original form by hydrogen peroxide have been investigated in aqueous acidic medium. The rate of reduction of FF was found to be first order with respect to [H(2)A] and [FF] and independent with respect to [H(2)O(2)] and ionic strength. The rate of reduction of FF increased with increasing pH (2.5-4.0), having an inverse first order dependence in [H(+)]. With increasing temperature (15-45 degrees C), the rate of reduction was increased in line with the Arrhenius equation. Based on experimental evidence and results a mechanism, operative to reduce FF and reoxidize the reduced FF by H(2)O(2), which makes the system catalytic, is suggested. Thermodynamic quantities associated with FF-catalyzed oxidation of H(2)A by H(2)O(2) were determined and compared with other closely related systems.

Interaction of aflatoxin with L-ascorbic acid: a kinetic and mechanistic approach.

Aflatoxins containing B(1), B(2), G(1) and G(2) obtained by growing Aspergillus parasiticus on SMKY liquid medium were tested for cytotoxicity (hemolysis) on RBC suspension in the presence and absence of L-ascorbic acid (AA). The results revealed that hemolysis was significantly increased on increasing the concentration of aflatoxin (0.5-3 microg ml(-1)). It was also found that pretreatment with AA (5-100 microg ml(-1)) significantly decreased aflatoxin-induced hemolysis. The solution chemistry of the interaction of aflatoxin with AA in aqueous solutions showed enhanced conversion of AFB(1) and AFG(1) to AFB(2) and AFG(2), respectively. Hemolytic, kinetic and mechanistic aspects of the interactions of aflatoxins and AA are discussed.

An elegant synthesis of chitosan grafted hydrotalcite nano-bio composite material and its effective catalysis for solvent-free synthesis of jasminaldehyde

A novel nano-bio composite of chitosan and a layered double hydroxide was elegantly synthesized by a co-precipitation method. The nano-bio composite material (CMA) was thoroughly characterized by FTIR, TGA, XRD, SEM and TEM. The composite material CMA showed efficient catalytic activity for selective synthesis of jasminaldehyde under solvent free conditions by condensation of benzaldehyde and 1-heptanal. In typical employed conditions, 39.5 mmol benzaldehyde, 7.9 mmol 1-heptanal, 100 mg catalyst, 160 °C and 700 rpm, a maximum selectivity of 89% with 99% conversion was obtained. The investigations were performed in detail as a function of the amount of catalyst, temperature and molar ratio of 1-heptanal to benzaldehyde to observe the effect of these reaction parameters on the conversion, selectivity and rate of the formation of the condensation products. All these parameters were found to influence the performance of the catalyst. The initial rate of formation of jasminaldehyde was found to be ∼20% more than the rates with individual chitosan and hydrotalcite. The rate of formation of 2-pentyl-2-nonenal with CMA was found to be lower in comparison with individual catalysts, chitosan and hydrotalcite. The determined activation energy was 16.3 kJ mol−1. The catalyst was elegantly separated, washed and dried, and found to be effectively recycled six times without any substantial loss in its activity.

Praseodymium(III)-substituted bismuth titanate thin-film generation using metallo-organic precursors with an M-O-C skeleton and sol-gel technique and employing 4f-4f transition spectra as a probe to explore kinetic performance.

A hetero-trimetallic lanthanide-substituted bismuth titanate (BLT, where lanthanide is praseodymium) with stoichiometry Pr(0.75)Bi(3.25) Ti(3)O(12) has been obtained as both highly homogenized crystalline and amorphous thin films using three different BLT precursors: (i). precursor A-(Pr(OC(3)H(7)(i))(3),Bi(OOCCH(3))(3),Ti(OC(3)H(7)(i))(4)); (ii). precursor B-(Pr(OC(3)H(7)(i))(2)(acac),Bi(OOCCH(3))(3),Ti(OC(3)H(7)(i))(3)(acac)); and (iii). precursor C-(Pr(OC(3)H(7)(i))(2)(acac),Bi(OOCCH(3))(3),Ti(OC(3)H(7)(i))(2)(acac))(2). These three BLT precursors (A, B, C) are prepared by reacting constituent monometallic precursors in the desired stoichiometry and by employing controlled acidic hydrolysis via the sol-gel method. Paramagnetic Pr(III), being a f(2) ion, gives characteristic 4f-4f transition bands (3H(4)-->3P(2), 3H(4)-->3P(1), 3H(4)-->3P(0), and 3H(4)-->1D(2)) in the visible region, the intensities of which have been found to be highly sensitive to even minor changes in the immediate coordination around Pr(III), occurring as a result of the progress of polycondensation reactions of three multicomponent BLT sols. We have used the changes with time in the intensities (represented by oscillator strengths of these four 4f-4f bands) and the magnitude and variation of the spectral parameters evaluated from the observed spectra with a view toward monitoring the sol-gel reactions of BLT precursors A, B, and C. 4f-4f transition spectra of the aliquots, withdrawn from the hydrolyzing A, B, and C sols at different time intervals, represent the changes occurring in the Pr(III) environment with the progress of sol-gel hydrolysis of BLT, and are used to investigate the kinetic performance in hydrolysis of the three precursors. Kinetics of hydrolysis of precursors A, B, and C indicate that all four f-f transition bands of Pr are almost equally sensitive to precursor hydrolysis in the order A>B>C.