Hydrogen-bonding dynamics in aqueous solutions of amides and acids: monomer, dimer, trimer, and polymer.
Hydrogen-bonding dynamics in aqueous solutions of amides and acids: monomer, dimer, trimer, and polymer.
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DOI：
10.1021/jp803627u
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发表时间：
2008-10
期刊：
影响因子：
--
通讯作者：
H. Shirota;H. Ushiyama
中科院分区：
文献类型：
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作者：
H. Shirota;H. Ushiyama
利用飞秒拉曼诱导克尔效应光谱和从头计算量子化学方法研究了一系列酰胺类和酸类水溶液中的氢键动力学。本文研究的酰胺和酸有：乙酰胺、1,3-丙二羧酸、1,3,5-戊三羧酸、分子量为1500的聚丙烯酰胺、醋酸、1,3-丙二羧酸、1,3,5-戊三羧酸和分子量为2000的聚丙烯酸。酰胺水溶液的飞秒阻尼瞬态特征是由酰胺和水的分子间氢键引起的，随着酰胺分子量的增大，飞秒阻尼瞬态特征变得更加明显。在约100 cm（-1）处的一个特征振动带被指定为氢键振动模式，从头算量子化学计算结果表明，该模式至少需要两个水组成与酰胺的氢键网络。由于酰胺与水之间的分子间相互作用更强，酰胺水溶液中约100 cm（-1）处的氢键振动模式随着酰胺分子量的增大而向更高频率转移。证据可能来自于聚合物比低聚物和单体更强的疏水相互作用。在皮秒时间范围内，聚合物水溶液出现了一个时间常数约为60ps的超慢弛豫过程。通过与单体和低聚物的比较，弛豫被指定为聚合物的结构重复单元的局部运动。
Hydrogen-bonding dynamics in aqueous solutions of series of amides and acids have been investigated by means of femtosecond Raman-induced Kerr effect spectroscopy and ab initio quantum chemistry calculation. The amides and acids studied here are acetamide, 1,3-propanedicarboxamide, 1,3,5-pentanetricaroxamide, polyacrylamide with Mw=1500, acetic acid, 1,3-propanedicarboxylic acid, 1,3,5-pentanetricarboxylic acid, and poly(acrylic acid) with Mw=2000. The femtosecond damped transient feature for aqueous amide solutions, which arises from the intermolecular hydrogen bonds of amide and water, becomes clearer with the larger molecular weight of amide. A characteristic vibrational band at about 100 cm(-1) is assigned as the hydrogen-bonding vibrational mode and the ab initio quantum chemistry calculation result indicates that at least two waters, which make up the hydrogen-bonding network with amide, are necessary for this mode. The hydrogen-bonding vibrational mode at about 100 cm(-1) in aqueous amide solutions shifts to the higher frequency with the larger molecular weight amide in consequence of the stronger intermolecular interaction between amide and water. The evidence likely comes from the stronger hydrophobic interaction for polymer than oligomers and monomer. In the picosecond time region, an extra slow relaxation process with a time constant of about 60 ps has been found in the aqueous polymer solutions. The relaxation is assigned as a local motion of the constitutional repeat unit of polymers from comparison with monomer and oligomers.