Hydrogen bonding abilities of hydroxamic acid and its isosteres

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Chapter 3: INTRA- AND INTERMOLECULAR HYDROGEN BONDING IN THIOFORMOHYDROXAMIC ACID:
3.1 INTRODUCTION:
The nature of hydrogen bonds (H-bonds) formed by sulfur is quite different from that formed by oxygen atom and is known further from much familiar examples of H2O and H2S. According to electrostatics, sulfur atoms are usually positive and oxygen is negative, so the fundamental nature of H-bonds is anticipated to be different in them [1]. Though the electronegativity difference between H and S is just 0.38 on the Pauling scale, yet there are reports that the H-bond acceptor ability of thioamide sulfur could surprisingly be equal to or exceed that of amide oxygen [2-4]. There is scarce information available on H-bonding involving sulfur atoms.
The living systems contain a number of sulfur containing molecules including thiopeptides, amino acids e.g. cysteine and methionine etc. Hence understanding biomolecular interactions during protein folding by studying S...H bonding carries prime importance in biochemical research [5]. N-H...S H-bonds are suggested to be present at the active site of various cytochrome P450s and these H-bonds play crucial role in stabilizing the Fe (III) state and protecting the complex against decomposition [6,7]. The influence of N-H...S interactions in regulation of redox potential of the metal-sulfur proteins and other complexes is well known [8,9]. Since the fundamental building block in thiopurines and thiopyrimidines is S=C-NH- and these are H-bonded in the nucleic acids (DANN and RNA), thus thioformohydroxamic acid (TFHA) can serve as a model for studying H-bonds in these systems [10].
The presence of N-methylthioformohydroxamic acid has been recognised in bacterial sources and is commonly termed Thioformin [11]. The antibiotic activity of cupric and ferric complexes of N-methylthioformohydroxamic acid is also reported [12,13]. Thiohydroxamic acids are important in biological and analytical chemistry and are utilized in

Dr. Ruchi Kohli obtained her MSc. in Chemistry (gold medalist) in 2003 from GNDU, Amritsar, Punjab, India and her doctoral degree under guidance of Dr. Damanjit Kaur from the same university in 2012. The broad area of research was theoretical (physical ) chemistry. The topic of research was study of hydroxy amides particularly hydroxamic acids, exploring ist various properties like tautomerism, proton affinities, deprotonation affiniities, solvent effects, substituent effects, hydrogen bonding studies with water and with amino acid side chain model molecules etc.
The author is practising teaching profession for seven years and presently serving as Asst. Prof. at a reputed college. She has nine research papers published in international journals with good impact factors and has presented her work at many conferences and seminars. She also has her name in Marquis Who's Who in the world directory.