&ITSyn &ITvs &ITAnti &ITCarboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis

Pal, Rumpa and Reddy, M B Madhusudana and Dinesh, B and Venkatesha, Manjunath A. and Grabowsky, Simon and Jelsch, Christian and Row, Tayur N Guru (2018) &ITSyn &ITvs &ITAnti &ITCarboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis. In: JOURNAL OF PHYSICAL CHEMISTRY A, 122 (14). pp. 3665-3679.

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Abstract

A comparative study of syn vs anti carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the anti form, all three bond angles surrounding of the -COOH group are close to similar to 120 degrees, as expected for a C-sp(2) atom, C-carboxyl whereas in the syn form, the angle C-alpha-C(O)-O-hydroxyl angle is significantly smaller by 5-10 degrees. The oxygen atom in the carboxyl group is more electronegative in the anti form, so the polarity of the acidic O-H bond is higher in the anti form compared to the syn form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated anti carboxylic acid forms the strongest O-H center dot center dot center dot O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp(2) and sp(3) lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds.

Item Type:	Journal Article
Publication:	JOURNAL OF PHYSICAL CHEMISTRY A
Publisher:	AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Additional Information:	Copy right for this article belong to AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	04 May 2018 18:48
Last Modified:	04 May 2018 18:48
URI:	http://eprints.iisc.ac.in/id/eprint/59716

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