A theoretical approach to the hydration of phosphodiesters in the presence of protons

Abstract

Hydration of the dimethylphosphate anion (DMP-) and dimethylphosphoric acid (DMPH) and of DMP-in the presence of a proton has been studied by the C N D 0 / 2 molecular-orbital method. The hydration energies of the (DMP--H,O) and ( DMPH-H20) complexes and the stabilization energies of ( DMP-.H+-H20) systems of different structures have been found, and additionally Wiberg indices and bond energies (together with their three components) have been computed. Regardless of the type of structure considered, for the trihydrate of dimethylphosphate in the presence of a proton only one water molecule in the first hydration shell is characterized by the lowest bond energy, which is about twice as low as energies of the two remaining water molecules. For the trihydrate of DMP-two water molecules at two equivalent positions, E , , and E3,, are characterized by the lowest hydrogenbond energy and are CQ. 20 kcalmol-' lower in energy than the most stable sites in acid structures. The results of theoretical studies support the experimental data obtained in investigations of the hydration of synthetic poly( dialkylphosphate) by the pulsed n.m.r. method. c v, h) P

Hydration of synthetic polypropylenephosphate (PPP) ? a simplified model for natural teichoic acids Part 3. Bound (nonfreezing) water in PPP gels by the pulsed Fourier transform NMR method

“…For the trihydrate of a DMP anion the hydrogen bond energies are ca. 20 kcal/mole lower than those at the hydration sites of DMP acid structures [9].…”

“…T1 of hydrate water protons below phase transition of weakly bound water is about three orders of magnitude lower than T1 of ice protons. The distribution of correlation times of hydrate water is a consequence of the presence of nonequivalent sites on the phosphate group at which water molecules reside [9] and of nonequivalent groups in PPP gels such as end groups and the groups appearing in repeated units of different conformations. The temperature region of "apparent" phase transition effect is shifted to a higher temperature (-20 ~ for hydrates of PPP in magnesium salt form.…”

Thoeretical analysis of conformational transitions in model compounds of natural teichoic acids

“…Geometric parameters (bond lengths and angles) for dimethylphosphodiesters were used as in our previous paper. 15 The structure of the 2DMPH complex was established by searching for a minimum in the energy. E was optimized as a function of r, with the stepwise increment in r being 0.05 A in the vicinity of the minimum in E. The optimum structure of 2DMPH complex, the C N D 0 / 2 partial charges and Wiberg indices are shown in fig.…”