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Binding of 9-N-Butyladenine by Carboxylic Acids: Evidence that Hoogsteen Binding Can Dominate in Solution

Rao, Photon and Ghosh, Suhrit and Maitra, Uday (1999) Binding of 9-N-Butyladenine by Carboxylic Acids: Evidence that Hoogsteen Binding Can Dominate in Solution. In: Journal Of Physical Chemistry B, 103 (21). pp. 4528-4533.

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H-1 NMR titration of 9-N-butyladenine (1) with a series of 1 1 rt presentative carboxylic acids has been carried out in CDCl3 by following the chemical shifts of delta(H-2) and delta(H-8) of 1 to determine the association constants for the Watson-Crick and the Hoogsteen modes of binding. Compound 1 has been found to bind carboxylic acids through the Watson-Crick (WC) site or the Hoogsteen (I-IG) site. The binding of carboxylic acids from the WC site shifts the delta(H-2) signal upfield, whereas the binding from the HG site shifts the delta(H-8) Signal downfield. Analyses of binding-induced shifts of delta(H-2) and delta(H-8) of 1 in the presence of the carboxylic acids have indicated a distinct preference Sor the HG site by aromatic carboxylic acids, such as benzoic acid and monobenzyl isophthalate. On the other hand, aliphatic acids such as 4-nitrophenylacetic acid and propanoic acid are found to prefer the WC site for complexing 1. Binding affinities of a few alkenoic and alkynoic acids were also determined. In addition to the complexes (1/acid) of I:I stoichiometry, the possibility of a 1:2 complexation between 1 and the carboxylic acids is addressed. A possible rationale for the upfield shift of H-2 (of 1) upon binding by a carboxylic acid is discussed. The K-a's were found to increase in general with enhanced acidity of the carboxylic acids. However, the pK(a) values of the acids do not appear to determine the site-specificity of the binding of 1.

Item Type: Journal Article
Publication: Journal Of Physical Chemistry B
Publisher: American Chemical Society
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Chemical Sciences > Organic Chemistry
Date Deposited: 27 Feb 2009 10:51
Last Modified: 19 Sep 2010 04:59
URI: http://eprints.iisc.ac.in/id/eprint/18040

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