James M. van der Veen,' Stevens Institute of Technology, Department of Chemistry and Chemical Engineer-The geometric details and mode of puckering of the five-membered (thiazolidine) ring have been found to be different in two penicillin G salts. In procaine penicillin G monohydrate (aqueous procaine penicillin G or APPG) the penicillin molecule is in an ' extended ' form whereas it is ' coiled ' in potassium penicillin G. The solid-state conformation of penicillin G therefore depends more on local environment than on nature of substitution in the side chain. The procaine molecules in APPG adopt an enlarged (91") torsion angle in the O-C-C-N group and exhibit little quinonoid character in the p-aminobenzoate group.
Proton and 13C n.m.r. and X-ray diffraction evidence has been presented for non-bonded aromatic-arnide attraction leading to a folded structure for hydantoin derivatives of phenylalanine in solution and in the solid state.
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