Energetics Of The Interaction Between Water, Membranes A

这项工作的目的是确定在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，特别是涉及水和具有生物意义的分子的那些键，是理解分子相互作用和它们所必需的构象变化的基础。本研究采用平衡离子-分子反应化学的方法确定了热力学参数deltaH(Std)298、deltaS(Std)298和deltaG(Std)298。根据在0-136摄氏度温度范围内、离子源水分压在0-100mtorr范围内测量的平衡常数计算水化热力学数值。在实验变量范围内的至少60种水分压和温度组合中的每一种下，对至少4种水化状态，即与核心离子相关的0到3个水分子进行了平衡离子强度测量。在25-60摄氏度的温度范围之外，这些测量在实验上变得非常具有挑战性，需要在每个新的温度点上进行几个小时的平衡。该项目的最初目标是确定一系列烷基铵离子CNH(2n+1)NH3+的溶剂化能。虽然这些离子显然是一个模型体系，但它们为理解碳氢链长度与溶剂化以及脂类和膜的水化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所研究的大约25%的水合物的热力学参数，我们的测量结果与已发表的数据非常一致。在过去的一年里，我们已经完成了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。几个研究人员的观察显示，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，这些不同的影响可能归因于这两个分子周围水组织的不同。我们对这两个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的差异。在质子化的1，2-(OH)2-丙烷中逐步加水，每次加成放热都有减小的趋势。虽然我们无法获得第一次加水的直接测量，但我们能够根据水的分压和温度估计这个过程的放热上限。我们得出结论，这第一个水化步骤在能量上是非常有利的。在1，3-(OH)2-丙烷中加入前两个水分子后，1，2-(OH)2-丙烷的能级有下降的趋势，但第三个水分子的加入不能保持这一趋势。向络合物中加入第三个水在能量上比加入第二个水更有利，此外，还发现该过程的熵显著降低。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高能的和熵有利的状态。这种良好水合状态的存在与1，3-二醇结合并破坏了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.