Four-atom quantum dynamics, chemical

Quantum reactive scattering calculations on the state-to-state dynamics of gas phase chemical reactions involving four or more atoms can now be carried out. This article describes how the Rotating Bond Approximation (RBA) can be applied to the four-atom reactions OH +... 

This brief summary of the RBA calculations on the reactions of OH with HCl and HBr has aimed to show that quantum treatment of the state-to-state aspects of a four atom reaction can yield new understanding of chemical reaction dynamics and can also provide an insight into useful quantities such as the temperature dependence of rate constants. As the RBA has been applied to reactions with more than four atoms such as OH + CH4 -> H2O + CH3 [16] and Cl + CH3Br CH3CI + Br" [17] this is clearly going to be a useful theoretical tool for the general study of chemical reactions of polyatomic molecules. 

A major challenge in quantum dynamics is to develop quantitatively accurate methods for practical computational study of chemical reactions involving polyatomic molecules. Currently, rigorous quantum dynamics calculations are limited to those systems involving no more than four atoms. In order to perform a quantitatively accurate quantum dynamics study for the vast majority of chemical reactions that are of chemical or biological interest, it is necessary to develop practical computational methods to treat the reaction dynamics of polyatomic molecules. To this end, some reduced dimensionality methods have been proposed to treat polyatomic systems (tetra-atomic systems in particular) by reducing the dynamical degrees of freedom from six to three. 

A similar topic was examined by Ida (Ida and Wu 2008). In this study, molecular dynamics was employed exploring G-quadruplex stabilized by Na and Rb cations, which were found to be tightly bound to a quadruplex structure. Moreover, in d(G(4)T(4)G(4) sequences the Na ions are found to be located in the diagonal T-4 loop region of the G-quadruplex, which is formed by two strands of d(G4T4G4) sequence. The authors proposed that the loop Na ion is located above the terminal G-quartet, coordinating to four guanine 06 atoms from the terminal G-quartet and one 02 atom from a loop thymine base and one water molecule. The Na coordination was also supported by quantum chemical calculations on Na chemical shifts. 

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