Energetics Of The Interaction Between Water, Membranes A

这项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。了解这种非共价键的能量需求，特别是那些涉及水和具有重要生物学意义的分子的能量需求，是理解分子相互作用及其组成部分的构象变化的基础。本研究采用平衡离子-分子反应化学方法确定了δ tah (std)298、δ tas (std)298和δ tag (std)298的热力学量。水合热力学值是根据离子源水分压在0到100 mtorr之间的0-136℃温度范围内测量的平衡常数计算的。在覆盖实验变量范围的至少60种水分压和温度组合下，对至少4种水合状态，即0到3个与一个核心离子相关的水分子进行平衡离子强度测量。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，并且在每个新的温度点需要几个小时的平衡。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，但它们为理解烃链长度与溶剂化以及脂质和膜的水合作用之间的关系提供了可能性。以前的工作人员已经确定了我们研究过的约25%水化反应的热力学参数，我们的测量结果与那些已发表的数据非常吻合。在过去的一年里，我们已经完成了对这个系统的测量。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蛋白自组装的影响不同。据推测，这些不同的影响可能归因于这两种分子周围水的组织不同。我们对这两种简单二醇的平衡离子分子研究指出了它们的水合热力学的实质性差异。将水逐步加成成质子化的1,2-(OH)2-丙烷，其放热性随加成次数的增加而递减。虽然我们无法直接测量第一次水的添加量，但我们能够根据水的分压和温度估计出该过程放热的上限。我们得出结论，第一个水化步骤在能量上是非常有利的。1,2-(OH)2-丙烷在加入前两个水分子时，能量学呈下降趋势，但在加入第三个水分子时，能量学没有保持下降趋势。在配合物中加入第三种水被确定为在能量上比加入第二种水更有利，并且发现该过程的熵大大减少。这两个观察结果使我们得出结论：1,3-(OH)2-丙烷三水合物是一个能量和熵有利的状态。这种有利的水合状态的存在与1,3-二醇结合并破坏其他稳定的生物分子结构是一致的。

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.