cell1b dft from Molecular interactions in nanocellulose assembly

The contribution of hydrogen bonds and the London dispersion force in the cohesion of cellulose is discussed in the light of the structure, spectroscopic data, empirical molecular-modelling parameters and thermodynamics data of analogue molecules. The hydrogen bond of cellulose is mainly electrostatic, and the stabilization energy in cellulose for each hydrogen bond is estimated to be between 17 and 30 kJ mol−1. On average, hydroxyl groups of cellulose form hydrogen bonds comparable to those of other simple alcohols. The London dispersion interaction may be estimated from empirical attraction terms in molecular modelling by simple integration over all components. Although this interaction extends to relatively large distances in colloidal systems, the short-range interaction is dominant for the cohesion of cellulose and is equivalent to a compression of 3 GPa. Trends of heat of vaporization of alkyl alcohols and alkanes suggests a stabilization by such hydroxyl group hydrogen bonding to be of the order of 24 kJ mol−1, whereas the London dispersion force contributes about 0.41 kJ mol−1 Da−1. The simple arithmetic sum of the energy is consistent with the experimental enthalpy of sublimation of small sugars, where the main part of the cohesive energy comes from hydrogen bonds. For cellulose, because of the reduced number of hydroxyl groups, the London dispersion force provides the main contribution to intermolecular cohesion.This article is part of a discussion meeting issue ‘New horizons for cellulose nanotechnology’.

本文结合类似物分子的结构、光谱数据、经验分子建模参数及热力学数据，探讨了氢键（hydrogen bonds）与伦敦色散力（London dispersion force）在纤维素凝聚力形成中的作用。纤维素中的氢键主要呈静电特性，单条氢键的稳定能估算值介于17至30 kJ·mol⁻¹之间。平均而言，纤维素的羟基所形成的氢键与其他简单醇类的氢键水平相当。伦敦色散相互作用可通过分子建模中的经验吸引项，对所有组分进行简单积分来估算。尽管该相互作用在胶体系统中可延伸至相对较大的距离，但短程相互作用对纤维素的凝聚力起主导作用，其等效压缩压强可达3 GPa。烷基醇与烷烃的汽化热变化趋势表明，羟基氢键带来的稳定能约为24 kJ·mol⁻¹，而伦敦色散力的贡献约为0.41 kJ·mol⁻¹·Da⁻¹。将这些能量进行简单算术求和后，结果与小分子糖类的实验升华焓相符——这类糖类的凝聚力主要来自氢键。对于纤维素而言，由于其羟基数量减少，伦敦色散力成为分子间凝聚力的主要贡献来源。本文属于‘纤维素纳米技术的新视野’专题讨论会议议题的一部分。