X-ray studies on crystalline complexes involving amino acids and peptides.XXXVIII. Crystal structures of the complexes of L-arginine and L-histidinewith glutaric acid and a comparative study of amino acid-glutaric acid complexes

The complexes of glutaric acid with l-arginine and l-histidine (two crystal forms) exhibit different stoichiometries and ionization states. The aggreg ation patterns in two of the crystals are remarkably similar to those obser ved earlier in similar structures, while the pattern in the remaining one h as not been seen earlier. The variability in the ionization state and stoic hiometry observed in amino acid-dicarboxylic acid complexes appears to repr esent subtle differences in the response of a molecule to the presence in i ts neighbourhood of another type of molecule. The glutaric acid molecules ( or glutarate or semiglutarate ions) in their complexes and in other crystal s favour a fully extended conformation, albeit with frequent departures fro m it. The change in the chirality of the component molecules in the complex could lead to drastic changes in the aggregation pattern; alternatively, t he effects of the change are accommodated through small adjustments in esse ntially the same pattern.