NIRS Institute of Water, Yuyamadai 2-7-10, Kawanishi, Hyogo Pref., Japan.
J Phys Chem A. 2010 Jul 15;114(27):7398-407. doi: 10.1021/jp102479t.
Hydration property of amide C=O was investigated from the OH stretching fundamentals and the first combinations of the water in the hydrate, formed in hydrophobic solution of an N,N-dialkyl amide ((CH(3)CH(2))(2)NCO(CH(2))(10)CH(3)) in heptane. The property was also examined for ester C=O of an alkyl ester (CH(3)(CH(2))(8)COOCH(3)) for comparison. The hydrates of C=O...H-O-H (I) and C=O...H-O-H...O=C (II) occur, the latter emerging above 5% concentration only and increasing in relative population with increasing concentration. The free OH of the water in I shows a sharp stretching band (nu(1)(OH(f))) at about 3690 cm(-1) and the bonded OH shows a much broader stretching band (nu(1)(OH(b))) of a significantly lower frequency. The difference Deltanu(fb) (= nu(1)(OH(f))-nu(1)(OH(b))), which is used as an indicator of hydration ability, is much larger for amide C=O (205 cm(-1)) than for ester C=O (134 cm(-1)). Equilibrium constant k(H) for the hydration process [C=O + (H(2)O) <--> C=O...H-O-H] is larger by about ten times for amide C=O than for ester C=O. Factors Deltanu(fb) and k(H) demonstrate that amide C=O has a strong hydration ability, implying that amide C=O of peptide linkage has an important contribution to high hydration ability of proteins.
酰胺羰基的水合性质是通过研究水在水合物中的 OH 伸缩基本振动和第一组合得到的，这些水合物是在正构烷烃中疏水缔合的 N,N-二烷基酰胺（(CH(3)CH(2))(2)NCO(CH(2))(10)CH(3)）形成的。为了进行比较，还研究了烷基酯（CH(3)(CH(2))(8)COOCH(3)）的酯羰基 C=O 的水合性质。C=O…H-O-H（I）和 C=O…H-O-H…O=C（II）两种水合物都会形成，后一种仅在 5%以上浓度时才会出现，并且随着浓度的增加，其相对丰度也会增加。I 中水的游离 OH 在约 3690 cm(-1)处显示出尖锐的伸缩带（nu(1)(OH(f)))，而结合 OH 则显示出频率显著降低的更宽的伸缩带（nu(1)(OH(b)))。酰胺羰基 C=O（205 cm(-1)）的水化能力指示符 Deltanu(fb)（nu(1)(OH(f))-nu(1)(OH(b))）比酯羰基 C=O（134 cm(-1)）大得多。酰胺羰基 C=O 的水化过程[C=O + (H(2)O) <--> C=O…H-O-H]的平衡常数 k(H)比酯羰基 C=O 大约十倍。Deltanu(fb)和 k(H)这两个因素表明酰胺羰基 C=O 具有很强的水合能力，这意味着肽键中的酰胺羰基 C=O 对蛋白质的高水合能力有重要贡献。
