J. V. D. Veen, B. W. Low
Dec 15, 1972
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Journal
Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry
Abstract
Glycyl-L-phenylalaninep-toluenesulfonate, CllH15N203. C7HvOaS, and glycyl-L-phenylalanine p-bromobenzenesulfonate, ClIH~sN203.C6H403SBr, both crystallize in the monoclinic space group C2 with unit-cell dimensions a=35-99 (1), b=6.005 (2), c=9.679 (5) ,~, ,8= 109.12 (5) ° and a=35-91 (l), b= 5"838 (2), c=9.679 (8) A, fl=93.59 (5) ° respectively. There are four molecules in the unit cell with Dm = 1 "297 g.cm -3 for the tosylate and 1.498 g.cm -3 for the brosylate. Preliminary crystallographic data are also reported for glycyl-L-phenylalanine. The structures of the two salts were solved by heavy atom methods using Cu Kc~ peak-height data and refined by least squares to R values of 0.095 (tosylate) and 0-12 (brosylate). Peptide and sulfonate conformations in both structures are nearly identical. Molecular packing is characterized by sheets of peptide extended along a alternating with parallel sheets of benzenesulfonate ions. Within both tosylate (brosylate) and peptide sheets, the hydrophilic regions show extensive hydrogen bonding. The principal difference between the structures arises from the relative positions of the tosylate methyl and brosylate bromine with respect to the screw axes, which leads to different fl angles in the two lattices. The peptide consists of an essentially planar region from the N(1) atom of Gly to the Cfl(2) atom of the Phe with the carboxyl and phenyl groups twisted 74 and 99 ° respectively from this plane.