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A stereospecific complex of poly(I) with ammonium ion
Author(s) -
Howard Frank B.,
Miles H. Todd
Publication year - 1982
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360210112
Subject(s) - chemistry , stereospecificity , helix (gastropod) , crystallography , ion , hydrogen bond , ammonium , stereochemistry , metal , molecule , catalysis , organic chemistry , ecology , snail , biology
We describe conditions which lead to complete helix formation of poly(I) in the presence of NH 4 + . Binding of NH 4 +is shown to be specific in the presence of Li + , which does not by itself support helix formation under these conditions. The NH 4 + –poly(I) complex is characterized by uv, CD, and ir spectroscopy. The CD spectrum is strikingly different from those of the Na + or K + complexes, the first extremum being changed from negative for the metal ions to positive for NH 4 + . A stereospecific model is proposed for the NH 4 + –poly(I) helix in which the N of NH 4 +is located on the axis of the four‐stranded helix, midway between planar tetramers formed by the bases. The model is consistent with the tetrahedral symmetry of NH 4 + , the requirement for four acceptable hydrogen bonds, the observed stability of the helix, and the accepted geometry of the backbone.