Energetics Of The Interaction Between Water, Membranes A

本工作的目的是确定溶液中分子和离子之间形成非共价键所需的能量。这种非共价键的能量需求的知识，特别是那些涉及水和生物重要分子，是理解分子相互作用和构象的变化，是不可或缺的。本研究涉及使用平衡离子-分子反应化学方法确定热力学量Δ H（std）298、Δ S（std）298和Δ G（std）298。水合热力学值由在0-136摄氏度的温度范围内在0和100毫托之间的离子源水分压下测量的平衡常数计算。对至少4种水合状态进行平衡离子强度测量，在覆盖实验变量范围的至少60种水分压和温度组合中的每一种下，与核心离子相关联的0至3个水分子。在25- 60 ℃的温度范围之外，这些测量在实验上变得非常具有挑战性，并且需要在每个新的温度点平衡几个小时。该项目的最初目标是确定一系列烷基铵离子CnH（2n+1）NH3+的溶剂化焓。虽然这些离子显然是一个模型系统，但它们提供了深入了解烃链长度和溶剂化以及脂质和膜的水合作用之间关系的可能性。以前的工作者已经确定了约25%的水化，我们已经研究和我们的测量结果与这些公布的数据非常一致的热力学参数。在过去的一年里，我们已经完成了我们在这个系统中的测量。此外，我们已经开始将这项工作扩展到更具生物学意义的系统。几位研究人员的观察表明，1，2-（OH）2-丙烷和1，3-（OH）2-丙烷对膜融合和胶原自组装的影响不同。有人假设，这些差异效应可能归因于这两种分子周围水的组织差异。我们对这两种简单二元醇的平衡离子分子研究表明，它们的水合热力学有很大差异。逐步向质子化的1，2-（OH）2-丙烷中加入水显示出每次加入的疏水性减小的趋势。虽然我们无法获得第一次加水的直接测量值，但我们能够根据水分压和温度估计该过程的渗透性上限。我们的结论是，这第一个水合步骤是积极的非常有利的。对于1，3-（OH）2-丙烷添加前两个水分子观察到1，2-（OH）2-丙烷的能量下降趋势，但对于添加第三个水分子没有保持。第三个水添加到复合物中被确定为比第二个水的添加在能量上更有利，并且另外发现该过程的熵大幅降低。这两个观察导致我们的结论，1，3-（OH）2-丙烷三水合物是一个充满活力和熵的有利状态。这种有利的水合状态的存在与1，3-二醇掺入并破坏原本稳定的生物分子结构一致。

The purpose of this work is the determination of the energies required for the formation of non-covalent bonds between molecules and ions in solution. Knowledge of the energetic requirements of such non-covalent bonds, particularly those involving water and biologically significant molecules, is fundamental to understanding molecular interactions and the changes in conformations that are integral to them. This research involves determining the thermodynamic quantities deltaH(std)298, deltaS(std)298, and deltaG(std)298 using the approach of equilibrium ion-molecule reaction chemistry. Hydration thermodynamics values were calculated from equilibrium constants measured over a temperature range of 0-136 degrees C at ion source water partial pressures ranging between zero and 100 mtorr. Equilibrium ion intensity measurements were made for at least 4 hydration states, i.e., zero through 3 water molecules associated with a core ion, at each of at least 60 combinations of water partial pressures and temperatures covering the ranges of experimental variables. Outside of the 25-60C temperature range, these measurements become very challenging experimentally and require several hours of equilibration at each new temperature point. The initial goal of the project is determining the enthalpy of solvation of a series of alkylammonium ions, CnH(2n+1)NH3+. While these ions are clearly a model system, they offer the possibility of providing insights into the understanding of the relationship between hydrocarbon chain length and solvation as well as the hydration of lipids and membranes. Previous workers have determined thermodynamic parameters for about 25% of the hydrations we have studied and results from our measurements are in close agreement with those published data. In the past year we have completed our measurements in this system. In addition, we have begun extending this work to more biologically significant systems. Observations by several investigators have shown differing effects of 1,2-(OH)2-propane and 1,3-(OH)2-propane on membrane fusion and collagen self-assembly. It has been hypothesized that these differential effects might be attributed to differences in the organization of water around these two molecules. Our equilibrium ion molecule studies of these two simple diols points to substantial differences in their hydration thermodynamics. The stepwise addition of water to protonated 1,2-(OH)2-propane shows a trend of diminishing exothermicity for each addition. While we were unable to obtain a direct measurement for the addition of the first water, we were able to estimate a upper limit on the exothermicity for this process based on the water partial pressure and temperature. We conclude that this first hydration step is energetically very favorable. The decreasing trend in energetics seen for 1,2-(OH)2-propane was observed for the addition of the first two water molecules to 1,3-(OH)2-propane, but was not maintained for the addition of the third water molecule. The addition of the third water to the complex was determined to be energetically more favorable than the addition of the second, and in addition was found to have a substantial decrease in the entropy for the process. These two observations lead to our concluding that the 1,3-(OH)2-propane trihydrate is an energetic and entropic favorable state. The existence of such a favorable state of hydration is consistent with the 1,3-diol incorporating into and disrupting otherwise stable biomolecular structures.