Ab Initio Calculations of Deuterium Isotope Effects on Chemical Shifts of Salt-Bridged Lysines

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• 作者：Saif Ullah ; Takayoshi Ishimoto ; Mike P. Williamson ; Poul Erik Hansen
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：March 31, 2011
• 年：2011
• 卷：115
• 期：12
• 页码：3208-3215
• 全文大小：860K
• 年卷期：v.115,no.12(March 31, 2011)
• ISSN：1520-5207

文摘

Deuterium isotope effects measure the change in chemical shift on substitution of a proton by deuterium. They have been calculated by direct treatment of the H/D nuclear quantum effect using a multicomponent ab initio molecular orbital method based on a non-Born鈭扥ppenheimer approximation. This method enables the determination of both the electronic and the protonic (deuteronic) wave functions simultaneously and can directly calculate the geometrical difference induced by H/D isotope effects. The calculations show that the one-bond deuterium isotope effects on ¹⁵N nuclear shielding, ¹螖¹⁵N(D), in ammonium and amines decrease as a counterion or water molecule moves closer to the nitrogen. ¹螖¹⁵N(D) and ²螖¹H(D) of the NH₃⁺ groups of lysine residues in the B1 domain of protein G have been calculated using truncated side chains and also determined experimentally by NMR. Comparisons show that the structures in solution are different from those in the crystal and that solvation plays an important role in weakening the hydrogen bonds.