Variability in ionization state,stoichiometry and aggregation in histidine complexes with formic acid |
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Authors: | Stephen Suresh M Vijayan |
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Institution: | (1) Molecular Biophysics Unit, Indian Institute of Science, 560 012 Bangalore, India |
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Abstract: | The crystal structures of the complexes of L and DL histidine with formic acid have been determined as part of an effort to
define biologically and evolutionarily important interactions and aggregation patterns. In terms of ionization state and stoichiometry
they may be described as L-histidine formate formic acid and DL-histidine formate monohydrate respectively. In the L-histidine
complex, amino acid molecules arranged in head-to-tail sequences centred around 21 screw axes are interconnected by formic acid molecules and formate ions. Histidine-formate interactions in the structure
gives rise to a characteristic interaction pattern involving a linear array of alternating imidazole groups and formate ions.
In DL-histidine formale monohydrate, head-to-tail sequences involving glide related molecules are interconnected through main
chain-side chain interactions leading to amino acid layers. The layers are held together by formate ions and water molecules
arranged in strings along which the ion and the molecule alternate. The patterns of amino acid aggregation in histidine complexes
exhibit considerably higher variability than those in complexes involving arginine and lysine do.
X-ray studies on crystalline complexes involving amino and peptides Part XXIX. |
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Keywords: | Amino acid complexes molecular aggregation amino acid-carboxylic acid interaction chemical evolution |
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