Gaseous Arginine Conformers and Their Unique Intramolecular Interactions
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- 作者：Sanliang Ling ; Wenbo Yu ; Zhijian Huang ; Zijing Lin ; Maciej Harañ ; czyk ; Maciej Gutowski
- 刊名：Journal of Physical Chemistry A
- 出版年：2006
- 出版时间：November 9, 2006
- 年：2006
- 卷：110
- 期：44
- 页码：12282 - 12291
- 全文大小：315K
- 年卷期：v.110,no.44(November 9, 2006)
- ISSN：1520-5215
文摘
Extensive ab initio calculations were employed to characterize stable conformers of gaseous arginine, boththe canonical and zwitterionic tautomers. Step-by-step geometry optimizations of possible single-bond rotamersat the B3LYP/6-31G(d), B3LYP/6-31++G(d,p), and MP2/6-31++G(d,p) levels yield numerous structuresthat are more stable than any known ones. The final electronic energies of the conformers were determinedat the CCSD/6-31++G(d,p) level. The lowest energies of the canonical and zwitterionic structures are lowerthan the existing values by 2.0 and 2.3 kcal/mol, respectively. The relative energies, rotational constants,dipole moments, and harmonic frequencies of the stable conformers remain for future experimental verification.The conformational distributions at various temperatures, estimated according to thermodynamic principles,consist almost exclusively of the newly found structures. One striking feature is the occurrence of blue-shifting hydrogen bonds in all six of the most stable conformers. A unique feature of important conformationsis the coexistence of dihydrogen and blue- and red-shifting hydrogen bonds. In addition to the hydrogenbonds, the stereoelectronic effects were also found to be important stabilization factors. The calculated andmeasured proton affinities agree within the theoretical and experimental uncertainties, affirming the highquality of our conformational search. The theoretical gas-phase basicity of 245.9 kcal/mol is also in goodagreement with the experimental value of 240.6 kcal/mol. The extensive searches establish firmly that gaseousarginine exists primarily in the canonical and not the zwitterionic form.