【作者】 张宁；

【导师】 李维仲；

【作者基本信息】 大连理工大学 ， 制冷及低温工程， 2013， 博士

【摘要】 低温生物学是研究生物体在低温环境下表现出的各种生命现象的变化规律及其相互关系,以及实现对细胞、组织、器官乃至整个生物体在低温环境下长期保存的一门涉及生物学、化学、物理学和医学等领域的边缘交叉学科。低温生物学中的低温保存技术已经广泛地应用于工业、农业、医学、畜牧业等诸多领域。低温保存技术是通过人为地制造出低温环境,使具有活性的生物体暂时地减慢细胞代谢速率从而达到长期保存的目的。低温保存技术在发展过程中受到的最大阻碍就是低温损伤,因此研究者采用各种方法来减少或消除低温损伤带来的影响。其中,低温保护剂是最有效且被广泛采用的一种方式。然而,在低温保护剂的使用过程中,如果低温保护剂的使用量不足,则不能达到理想的低温保存效果：而如果低温保护剂的用量过多,则会对生物细胞造成损伤。因此,如何合理地选取低温保护剂的用量是一个始终困扰研究者们的难题。这主要是因为人们对于低温保护剂作用机理的认识还不是很清楚,因此很难设计出合理而有效的低温保护剂配方和使用方法。所以,对低温保护剂作用机理的研究,对于低温保护技术的改进和低温生物学的发展具有深远的意义,同时也是目前低温生物领域的科研人员所面临的重要难题。本文对四种不同类型的低温保护剂(包括：甲醇、乙二醇、甘油和二甲基亚砜)水溶液在不同的浓度和温度条件下进行了分子动力学模拟,并分析了各溶液体系的氢键统计特性和氢键动力学行为。研究发现,低温保护剂分子有助于抑制水分子之间的氢键作用,并且会通过氢键作用束缚越来越多的水分子,使溶液中“束缚水”的比例逐渐增加。这一结果对于解释低温保护剂水溶液在冻结过程中出现的未冻结水现象具有十分重要的意义。此外,研究还发现,随着低温保护剂水溶液浓度的增加,低温保护剂分子与水分子之间的氢键生存周期逐渐延长。这一结果则从另一个侧面说明了低温保护剂分子有助于通过氢键作用将水分子束缚住。这种未冻结水量与保护剂分子-水分子氢键作用之间的相关性,证明了低温保护剂分子通过氢键作用对冰晶抑制的直接原因。本文还进一步分析了溶液浓度和温度对低温保护剂水溶液中水分子自扩散运动的影响。结果显示,随着溶液浓度的增加和温度的降低,水分子的自扩散系数逐渐减小；并且水分子所具有的氢键数越多,它在溶液中的自扩散运动就越缓慢。这些现象都说明了低温保护剂分子通过氢键作用减缓了溶液中水分子的自扩散运动,进而抑制了水分子向晶核的运动趋势,并使其处于保护剂分子的周围,为玻璃化的形成提供了有利的条件。此外,本文还对低温保护剂水溶液的亲水性和疏水性团簇结构进行了分析,并从团簇结构的角度解释了保护剂分子对水分子扩散运动的抑制机理。研究发现,保护剂分子能够通过烃基间疏水性吸引作用形成团簇结构,并且这种团簇尺寸随着浓度的增加而不断增大。这种疏水性团簇结构能够有效地阻碍溶液中水分子的扩散运动,而这种团簇结构的生长又有利于分解水分子间通过氢键作用形成的团簇结构,从而能够有效地削弱水分子形成冰晶的驱动力。根据二甲基亚砜水溶液的氢键分析结果,本文还分析了几何准则和能量准则的合理性。两种氢键准则在氢键统计上都存在一定的不合理性,但是在一般情况下它们对结果的影响是可以接受的。然而,这两种氢键准则在氢键动力学特性的分析上却存在比较大的差异,这主要是因为能量准则缺少对分子间相对取向角的限制。因此,本文建议在对低温保护剂水溶液进行定量的氢键分析时应当采用几何-能量混合型氢键准则。更多还原

【Abstract】 Cryobiology is an inter-and trans-disciplinary subject involving biology, chemistry, physics and medicine, etc., of which the aim is to study various biological phenomenons and their relationships of living organisms, and to preserve cell, tissue, organ and a whole organism at low temperature for a long term. Cryopreservation is a sub-discipline of cryobiology, which is widely applied to industry, agriculture, medicine, livestock, etc. By means of artificial environment of low temperature, the metabolism of the cells in living organism will be slowed down temporarily, resulting in long-term cryopreservation. Cryoinjury is the biggest impediment to the development of cryopreservation. Thus researchers employ several methods to reduce or eliminate the effect of cryoinjury, of which cryoprotectant is the most effective and widely used one. However, for the application of cryoprotectant, too little cryoprotectant will not take enough cryoprotective effect, and too much cryoprotectant will damage to cells. Thus it is difficult to employ proper amount of cryoprotenctant. This is mainly because that the cryoprotective mechanism of cryoprotectant is not well understood, and it is hard to design a reasonable and effective method of using cryoprotectant. Hence, investigation of the cryoprotective mechanism of cryoprotectant is of significant importance to the improvement of cryopreservation technology, and is an major challenge to the researchers in the field of cryobiology.In the present dissertation, the aqueous solutions of four types of cryoprotectants (including methanol, ethylene glycol, glycerol and dimethyl sulfoxide) are studied by molecular dynamics simulation, and the hydrogen bonding statistics and hydrogen bonding dynamics of the solutions are analyzed. The cryoprotectants help to inhibit the interaction of hydrogen bonding between water molecules, and they also constraint water molecules by hydrogen bonds, resulting in the proportion of "bound water" increases with increasing the concentration. This finding is of significant importance to interpret the the emergence of unforzen water in the freezing process. Moreover, the increasing concentration of cryoprotectant will increase the lifetime of the hydrogen bonds between cryoprotectant and water molecules. This is another indication that cryoprotectant molecule contributes to producing "bound water". Unfrozen water is correlated with the cryoprotectant-water hydrogen bond, which proves that the cryoprotectant-water hydrogen bond is directly responsible for the ice inhibition. This dissertation further analyzes the effects of concentration and temperature on the self-diffusion of water in the aqueous solutions of cryoprotectant. It shows that as the concentration increases and temperature decreases, the self-diffusion coefficient of water molecule has a decreasing tendency. The more hydrogen bonds one water molecule has, the slower its self-diffusion is. Thus the cryoprotenctant molecules slow down the self-diffusion motion of water by hydrogen bonding interaction, resulting in the inhibition of the motion of water towards the ice nucleation. The hydrogen bonded water molecules tend to surround the cryoprotectant molecules, which is benefit to achieving vitrification. This dissertation also analyzes the structures of the hydrophilic and hydrophobic clusters in the aqueous solutions of cryoprotectant, and inteprets the mechanism of the inhibition from the cryoprotectant to water self-diffusion in the point of view of cluter. The hydrophobic cluter is resulted from the attraction between intermolecular alkyl groups, and the cluster size increases with increasing the concentration. It is found that the hydrophobic cluster has significant retardation to the diffusion of water moelcules, and the increasing cluster size with concentration tends to break down the hydrogen bonded water cluster, both of which could effectively reduce the driving force of ice formation.On the basis of the hydrogen bonding analysis of the aqueous solution of dimethyl sulfoxide, the dissertation evaluates the geometric and energetic criteria. Both of the hydrogen bonding criteria are found to have deficiency in the hydrogen bonding statistics, but the effect on the hydrogen bonding analysis could be accepted. Nevertheless, the criteria have large distinction in the analysis of hydrogen bonding dynamics due to that energetic criterion is lack of the limitation to the intermolecular angle of relative orientation. Therefore, extended criterion involving both geometric and engetic thresholds is recommended in the hydrogen bonding analysis of aqueous solution of cryoprotenctant.更多还原