Anju Chadha

Covalent Bonding of Bay-Region Diol Epoxides to Nucleic Acids

Although the solution chemistry of diol epoxides is now fairly well understood, a great deal remains to be elucidated regarding their reaction in the presence of DNA. Not only DNA but also small molecules are capable of sequestering diol epoxides in aqueous solutions with equilibrium constants on the order of 10(2)-10(4) M-1. In the case of DNA, at least two major families of complexes are presently recognized, possibly the result of groove binding vs. intercalation. As is the case for diol epoxides free in solution, the complexed diol epoxides undergo solvolysis to tetraols and in some cases possibly to keto diols as well. Fractionation between covalent bonding and solvolysis from within the complex(s) is determined more by the nature of the parent hydrocarbon from which the diol epoxide is derived than any other factor. Studies of a wide variety of alkylating and arylating agents have show that practically every potentially nucleophilic site on DNA can serve as a target for modification. In the case of the diol epoxides, practically all of the modification occurs at the exocyclic amino groups of the purine bases. In contrast to the diol epoxides, other epoxides such as those derived from aflatoxin B1, vinyl chloride, propylene, 9-vinylanthracene, and styrene preferentially bind to the aromatic ring nitrogens N-7 in guanine and N-3 in adenine (cf. Chadha et al., 1989). Molecular modeling as well as the spectroscopic evidence suggests that the hydrocarbon portion of the diol epoxides lies in the minor groove of DNA when bound to the exocyclic 2-amino group of guanine and in the major groove when bound to the exocyclic 6-amino group of adenine. Detailed conformational analysis of adducted DNA should prove to be extremely valuable in developing mechanistic models for the enzymatic processing of chemically altered DNA. At present, the critical lesion or lesions responsible for induction of neoplasia remains obscured by the large number of apparently noncritical adducts which form when polycyclic hydrocarbon diol epoxides bond to DNA.

Biocatalytic deracemisation of α-hydroxy esters: high yield preparation of (S)-ethyl 2-hydroxy-4-phenylbutanoate from the racemate

Abstract Biocatalytic deracemisaton of the racemic ethyl ester of 2-hydroxy-4-phenylbutanoic acid gives the ( S )-enantiomer exclusively in >99% e.e. and 85–90% yield. Ethyl and methyl esters of mandelic acid and the methyl ester of 2-hydroxy-4-phenylbutanoic acid also gave the ( S )-enantiomer exclusively. Whole cells of Candida parapsilosis (ATCC 7330) were used to effect this biotansformation.

Asymmetric reduction of 2-oxo-4-phenylbutanoic acid ethyl ester by Daucus carota cell cultures

Abstract A novel method to produce (R)-(−)-2-hydroxy-4-phenylbutanoic acid ethyl ester 1b has been developed. 2-Oxo-4-phenylbutanoic acid ethyl ester 1a is reduced to 1b by the cell cultures of Daucus carota in high enantiomeric excess and yield.

Enzymatic resolution of 2-hydroxy-4-phenylbutanoic acid and 2-hydroxy-4-phenylbutenoic acid

Abstract Racemic 2-hydroxy-4-phenylbutanoic acid and 2-hydroxy-4-phenyl-butenoic acid have been resolved using a lipase. In each case, the (R)-2-hydroxy and the (S)-2-acetoxy acids were isolated with high enantiomeric excess and yield.

Synthesis of hydrocinnamic esters by Pseudomonas cepacia lipase

Abstract Lipase from Pseudomonas cepacia was used to prepare esters of hydrocinnamic acid by direct esterification of the carboxylic acid in good yields (70–83%). For some esters, transesterification gave better yields (92%). Optimization of the reaction conditions resulted in a dramatic increase in the yield of the product ester. The role of solvents was studied. Notably, cinnamic acid esters are not formed under these conditions.

Comparison of a potentiometric and a micromechanical triglyceride biosensor

Sensitive biosensors for detection of triglyceride concentration are important. In this paper we report on two types of silicon based triglyceride sensors: an electrolyte-insulator-semiconductor capacitor (EISCAP) which is a potentiometric device and a polysilicon microcantilever. The detection principle for both sensors is based on the enzymatic hydrolysis of triglyceride though the sensing mechanisms are different: electronic for the EISCAP and mechanical for the microcantilever. The characteristics and performances of the two sensors are critically compared. The EISCAP sensor necessitates the presence of a buffer for stable measurements which limits the sensitivity of the sensor at low concentrations of the bioanalyte to 1mM. The cantilever sensor works without a buffer which improves the lower level of sensitivity to 10 microm. Both sensors are found to give reproducible and reliable results.

MEMS Composite Porous Silicon/Polysilicon Cantilever Sensor for Enhanced Triglycerides Biosensing

A novel composite porous silicon/polysilicon microcantilever for biosensing applications with enhanced sensitivity is reported. It is fabricated by surface micromachining of polysilicon cantilevers followed by the formation of the surface porous layer after release by Reaction Induced Vapor Phase Stain Etch. The microcantilevers with porous surface layer are characterized by their morphology that exhibits a dual macro and nanostructure for very effective immobilization of biomolecules. The current work focuses on the fabrication of composite porous silicon/polysilicon microcantilevers, characterization of their morphology and demonstration of improved immobilization of enzymes resulting in enhanced sensing of triglycerides.

Simplified Procedure for TEMPO-Catalyzed Oxidation: Selective Oxidation of Alcohols, α-Hydroxy Esters, and Amides Using TEMPO and Calcium Hypochlorite

Abstract A wide range of primary and secondary multifunctional alcohols, α-hydroxyamides, and α-hydroxyesters were oxidized to their corresponding aldehydes, ketones, α-ketoamides, and α-ketoesters under mild reaction conditions using 2,2,6,6-tetramethylpiperidine-1-oxyl as a catalyst with calcium hypochlorite as an oxidant [TEMPO-Ca(OCl)2]. This simplified method does not require any transition metals, acids, or bases and demonstrates controlled and selective oxidation of structurally diverse alcohols, affording moderate to excellent yields at room temperature. GRAPHICAL ABSTRACT

Structures of covalent nucleoside adducts formed from adenine, guanine, and cytosine bases of DNA and the optically active bay-region 3,4-diol 1,2-epoxides of benz[a]anthracene

Chemical structures of the principal covalent adducts formed from DNA upon reaction in vitro with the four optically active 3,4-diol 1,2-epoxides of benz[a]anthracene have been elucidated at the nucleoside level. In addition to adducts formed by cis and trans addition of the exocyclic amino groups of deoxyadenosine (dA) and deoxyguanosine (dG) and a trans deoxycytidine (dC) adduct, chemical characterization of a deglycosylated N-7 dG adduct formed in DNA by trans opening of the (4S,3R)-diol (2R,IS)-epoxide isomer is reported. Relative stereochemistries of the adducts (cis versus trans opening of the epoxides by the exocyclic amino groups) were deduced from the coupling constants of the methine protons of the tetrahydro benzo rings of the acetylated derivatives

BSA binding to silica capped gold nanostructures: effect of surface cap and conjugation design on nanostructure–BSA interface

This paper presents a detailed and systematic study of amine functionalization of silica coating of gold nanostructures and the electrostatic and covalent binding of the prepared silica capped gold nanostructures to BSA. The involvement of a Tryptophan residue in the hydrophobic pocket of BSA and its interaction with nanostructures was established. Fluorescence studies of tryptophan residues of the protein molecules after conjugation revealed that the method of crosslinking did not bring about major changes to the binding constant (1012 M−1) of BSA to nanostructures. Electrostatic binding indicated a larger number of binding sites (2.56) on the protein. Nanoparticle binding brought about a reduction in the characteristic negative ellipticity of BSA, indicating a change in the helical content. The reduction in the elliptical path of BSA was influenced by both nanoparticle curvature and crosslinker, such as in the case of glutaraldehyde or by the nanoparticle curvature alone as in the case of zero length crosslinker – EDC–NHS. Though not a subject matter of this study, the results obtained in this study could have implications in the design of nanobiomaterials, biosafety concerns and their cellular responses.