X-ray studies on crystalline complexes involving amino acids. IV. The structure of L-arginine L-ascorbate

Sudhakar, V and Vijayan, M (1980) X-ray studies on crystalline complexes involving amino acids. IV. The structure of L-arginine L-ascorbate. In: Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 36 (1). pp. 120-125.

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Abstract

L-Arginine ascorbate, C6HIsN40+.C6H706, a 1"1 crystalline complex between the amino acid arginineand the vitamin ascorbic acid, crystallizes in the monoclinic space group P21 with two formula units in a cell of dimensions a = 5.060 (8), b = 9.977 (9), c = 15.330 (13) A, fl = 97.5 (2) °. The structure was solved by the symbolic addition procedure and refined to an R of 0.067 for 1501 photographically observed reflec- tions. The conformation of the arginine molecule in the structure is different from any observed so far. The present structure provides the first description of the ascorbate anion unaffected by the geometrical constraints and disturbances imposed by the requirements of metal coordination. The lactone group and the deprotonated enediol group in the anion are planar and the side chain assumes a conformation which appears to be sterically the most favourable. In the crystals, the arginine molecules and the ascorbate anions aggregate separately into alternating layers. The molecules in the arginine layer are held together by interactions involving a-amino and ~t-carboxylate groups, a situation analogous to that found in proteins. The two layers of unlike molecules are interconnected primarily through the interactions of the side-chain guanidyl group of arginine with the ascorbate ion. These involve a specific ion-pair interaction accompanied by two convergent hydrogen bonds and another pair of nearly parallel hydrogen bonds.

Item Type:	Journal Article
Publication:	Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry
Publisher:	International Union of Crystallography
Additional Information:	Copyright of this article belongs to International Union of Crystallography.
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	03 Feb 2010 09:19
Last Modified:	19 Sep 2010 05:45
URI:	http://eprints.iisc.ac.in/id/eprint/23214

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