MOLECULAR VIBRATIONS IN PHOSPHOENOLPYRUVATE CRYSTALS FROM X-RAY-DIFFRACTION DATA

The anisotropic mean-square atomic displacement parameters from 18 pre viously determined crystal structures representing 26 crystallographic ally independent phosphoenolpyruvate species, ranging from the tribasi c free-acid molecule [(HO)(2)O-POC(CH2)CO2H] to the fully ionized mole cular trianion, have been analyzed in terms of external, rigid-body la ttice vibration modes coupled with low-frequency modes of internal mol ecular torsion and bending vibrations. The results indicate that there tends to be more torsional flexibility about the (H2C)C-CO2 enolcarbo xylate bonds than about the C-O(P) and (C)O-P phosphate ester bonds, a pparently because hydrogen bonding or counterion binding interactions in the crystals restrict the phosphate groups more than the carboxylat e groups. The analysis provides an example that shows that thermal vib ration parameters from crystal structure analyses of good, but not nec essarily extraordinary, accuracy are a rich source of molecular dynami cal information. (C) 1998 Elsevier Science B.V. All rights reserved.