Scheiner Steve, Kar Tapas
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, USA.
J Phys Chem B. 2005 Mar 3;109(8):3681-9. doi: 10.1021/jp0446736.
The series of CH...O bonds formed between CF(n)H(4-n) (n = 0-3) and water are studied by quantum calculations under vacuum and in various solvents, including aqueous environment. The results are compared with the OH...O bond of the water dimer in the same solvents. Increasing polarity of the solvent leads in all cases to a lessening of the H-bond interaction energy, in a uniform fashion such that the CH...O bonds all remain weaker than OH...O in any solvent. These H-bond weakenings are coupled to a shortening of the inter-subunit separation. The contraction of the covalent CH bond to the bridging proton is reduced as the solvent becomes more polar, and the blue shift of its stretching vibration is likewise diminished. A process is considered that simulates protein folding by starting from a pair of noninteracting subunits in aqueous solvent and then goes to a H-bonded pair within the confines of a protein environment. This process is found to be energetically more favorable for some of the CH...O H-bonds than for the nominally stronger conventional OH...O H-bond. This finding suggests that CH...O bonds can make important energetic contributions to protein folding, on par with those made by traditional H-bonds.
通过量子计算研究了在真空以及包括水环境在内的各种溶剂中，CF(n)H(4 - n)（n = 0 - 3）与水之间形成的一系列CH...O键。将结果与相同溶剂中水二聚体的OH...O键进行了比较。在所有情况下，溶剂极性的增加都会导致氢键相互作用能降低，且方式一致，使得在任何溶剂中CH...O键都比OH...O键弱。这些氢键的减弱与亚基间间距的缩短相关。随着溶剂极性增强，与桥连质子相连的共价CH键的收缩减小，其伸缩振动的蓝移同样减小。考虑了一个过程，该过程从水性溶剂中一对非相互作用的亚基开始，模拟蛋白质折叠，然后在蛋白质环境范围内形成氢键对。发现该过程对于某些CH...O氢键在能量上比名义上更强的传统OH...O氢键更有利。这一发现表明，CH...O键对蛋白质折叠可做出重要的能量贡献，与传统氢键相当。
