Corezzi S, Sassi P, Paolantoni M, Comez L, Morresi A, Fioretto D
Dipartimento di Fisica e Geologia, Università di Perugia, Via Pascoli, I-06123 Perugia, Italy.
Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Via Elce di Sotto 8, I-06123 Perugia, Italy.
J Chem Phys. 2014 May 14;140(18):184505. doi: 10.1063/1.4873575.
Extended frequency range depolarized light scattering measurements of water-levoglucosan solutions are reported at different concentrations and temperatures to assess the effect of the presence and distribution of hydroxyl groups on the dynamics of hydration water. The anhydro bridge, reducing from five to three the number of hydroxyl groups with respect to glucose, considerably affects the hydration properties of levoglucosan with respect to those of mono and disaccharides. In particular, we find that the average retardation of water dynamics is ≈3-4, that is lower than ≈5-6 previously found in glucose, fructose, trehalose, and sucrose. Conversely, the average number of retarded water molecules around levoglucosan is 24, almost double that found in water-glucose mixtures. These results suggest that the ability of sugar molecules to form H-bonds through hydroxyl groups with surrounding water, while producing a more effective retardation, it drastically reduces the spatial extent of the perturbation on the H-bond network. In addition, the analysis of the concentration dependence of the hydration number reveals the aptitude of levoglucosan to produce large aggregates in solution. The analysis of shear viscosity and rotational diffusion time suggests a very short lifetime for these aggregates, typically faster than ≈20 ps.
本文报道了在不同浓度和温度下对水-左旋葡聚糖溶液进行的扩展频率范围去偏振光散射测量，以评估羟基的存在和分布对水合水动力学的影响。与葡萄糖相比，脱水桥使羟基数量从五个减少到三个，这极大地影响了左旋葡聚糖相对于单糖和二糖的水合特性。特别是，我们发现水动力学的平均延迟约为3-4，低于之前在葡萄糖、果糖、海藻糖和蔗糖中发现的约5-6。相反，左旋葡聚糖周围延迟水分子的平均数量为24，几乎是水-葡萄糖混合物中发现数量的两倍。这些结果表明，糖分子通过羟基与周围水形成氢键的能力，在产生更有效延迟的同时，极大地降低了对氢键网络扰动的空间范围。此外，对水合数浓度依赖性的分析揭示了左旋葡聚糖在溶液中形成大聚集体的倾向。对剪切粘度和旋转扩散时间的分析表明，这些聚集体的寿命非常短，通常快于约20皮秒。
