| Summary: | 碩士 === 國立成功大學 === 化學系 === 90 === We used the AM1 and ab initio methods to calculate phosphorus oxides P4On (n=6-10), phosphate, polyphosphates, and ATP molecule. According to the results of P4On (n=6-10), we found that the PO bonds in P4On will couple each other. The increased terminal P=O bonds will make other bridged P-O bonds stronger than before and cause its structure distorted.
The un-dissociated poly-phosphoric acids are cyclic by the intra-molecular hydrogen bonds. The polyphosphates are linear because of the repulsions between the negative charges on terminal oxygen atoms. As for the polyphosphates which their degree of polymerization is above three, the bond orders of the bridged P-O bonds are symmetrical: the outer bridged P-O bonds are weakest, and near the weakest bridged P-O bonds are strongest. The bond orders of those middle bridged P-O bonds are at the moderate range compared to the outer ones. The result shows that the resonance modes of polyphosphates have two kinds of situations: the electrons on the terminal oxygen atoms at two extremities of polyphosphates would delocalize in the area of PO3 group, and the electrons on the terminal oxygen atoms at middle parts of polyphosphates would delocalize in the area of PO2 group. Thus it can be seen, polyphosphates are constituted by two PO3 groups as two end points and a few PO2 groups as the middle parts linked by bridged oxygen atoms.
The bond order distributions of bridged P-O bonds in AMP, ADP, and ATP molecules are some how different from polyphosphates and exhibits the order of “weak-strong-weak- strong” phenomena. The differences of the bond orders of the bridged P-O bonds in AMP, ADP, and ATP molecules are larger than that in polyphosphates. Hence the bridged P-O bonds in AMP, ADP, and ATP molecules are broken more easily during the hydrolysis reaction. Also, the results provide proofs of the experiments of hydrolysis reaction mechanism for such molecules.
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