| The interactions of the active sites of nucleic acid, sugar and protein with metal cations were studied by using the ab initio SCF , DFT, relativistic effective core potentials(RECP) and MP2 approaches employing 6-311+G(d,p) and 6-311G(d) basis sets, the structures and properties of complexes were systemically investigated, and the function with metal cations in organism was testified or forecasted.The structures of DMP'and BMP-Mn+ ( Li+, Na+, K+, Cu+, Mg2+, Be2+, Ca2\ Zn2T)were optimized by HF/6-311+G(d,p) and B3LYP/6-311+G(d,p) in the C2 symmetry. For the structures of all the metal catons (with the except Li+,Be2+)complexes ,the relativistic effective core potentials (RECP)LanL2DZ were used. The structures of Guanine and Guanine-Mn+ ( Li+,Na+, K+,Cu+, Mg2+, Be2,Ca2,Zn2+)were optimized by HF/6-311 G(d) and B3LYP/ 6-311 G(d). For the structures of the metal catons (Cu+,Ag+,Au+,Zn2+,Cd2+,Hg2+)complexes RECP(LanL2DZ) were used. All the nonmetal elements in the RECP calculations were described by the corresponding basis sets in the all-electron calculations. MP2 was employed in calculating single-point energies of the systems whose structure were optimized by HF. All the optimized structures were characterized by the analysis of the harmonic vibratinal frequencies obtained from the diagonalization of force constant matrices. The interaction energies (A E) and the interaction Gibbs energies ( A G) were corrected by ZPVE.The outcome makes clear: RECP can be used with confidence for heavy metal cations. However, in order to ensure the precision of computation, EDEF and A EBSSE should be taken into account. Opening of both Z OPO and Z. COP would correspond to widening and elongation of the helices and therefore ,could make folding of the polynucleotide molecules easier. Metal cations can enhance the C-O hydrolysis in at least two ways: by shielding the negatively charged phosphinyl oxygens to promote attack of the esteric carbons by nucleophilic anions and by alterations of bond length i.e. by weakening the C-O bonding and by strengtheningthe P-O bonding. The optimized C-O esteric bond of the Mg2+ complexes is longer than that of the Ca2+ complexes, so the esteric hydrolysis ability of Mg2~ is superior to that of Ca2". The deformation of the complexes caused by bivalent ions is more serious than those caused by monovalent ions. The A E and A G of the complexes with bivalent ions are smaller than those with monovalent ions . Therefore, the interaction between bivalent ions and the ligands(DMP", Guanine) is stronger than that between monovalent ions and ligands . The stability of different metal cations group complexes is lib group > Ila group > Ib group > la group(except Li+,Be2+,Mg2"). And in the same group the stability of complexes decreases with increasing atomic number of the metal ions(except the Au+, Hg2+complexes), because A E and A G added with increasing atomic number of the metal ions. The highly ionic character between ligands (BMP', Guanine) and Mn" (LiT,Be2"),and increasingly covalent character of bonding when passing from Na+ to Cs", The decreasing ionic character corresponds to A E, the same is to alkaline earth metals. There were both Coulombic interaction via 2+ ,1+ charge and high covalent d-orbital-lone pair bonding interaction in the complexes of group lib, Ib cations, resulting in stronger bond interaction than that of the complexes of group Ila, la cations.The structures of (3-D-ribose(RI) and the complexes composed by M"~ (Na+, K"\ Ca2*. Mg2+) interacting with the different parts of RI were optimized by HF/6-311G(d) and B3LYP/6-311G(d). The structure of the steadiest complexes were optimized by not only HF/6-311+G(d,p) but also RECP employing LanL2DZ basis set (with the exception of Lr,Be2+). MP2 was employed in calculating single-point energies of the systems whose structure were optimized by HF. All the optimized structures were characterized by computing the harmonic vibrational frequencies. The calculated A E and A G were corrected by Z... |
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