ENERGETICS OF THE INTERACTION BETWEEN WATER, MEMBRANES AND MACROMOLECULES

这项工作的目的是确定溶液中分子和离子之间的非共价键形成和断裂所需的能量。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学上重要的分子，是理解分子相互作用和构象的变化是必不可少的。本研究涉及使用平衡离子-分子反应化学和电喷雾电离产生的离子的方法来确定热力学量 *H（std）298、*S（std）298和 *G（std）298。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之间关系的可能性。在过去的一年中，我们改进了我们以前的测定，特别是通过减少与第一和第三水合步骤的值相关的方差。这是通过进一步扩大我们研究的温度范围来实现的，因此我们现在的温度范围是从0 ° C到90 ° C。亚环境温度和高温都需要对用于这些研究的质谱仪进行重大修改，并且还需要在确保温度测定的可靠值方面做出相当大的努力。从在各种离子源水分压下在整个温度范围内测量的平衡常数计算水合热力学值。对至少4种水合状态进行平衡离子强度测量，在60种水分压和温度的组合下，每一种组合都覆盖了实验变量的范围。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上进行几个小时的平衡。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那些公布的数据是非常一致的热力学参数。除了改进以前的实验量，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。我们已经产生了这两个二醇的水合质谱，并观察到除了四个水分子到每个物种。然而，相对于未水合形式，1，3-丙二醇的每种水合形式的强度约为1，2-丙二醇中相同水合水平的强度的两倍。这很可能是1，3-丙二醇形成内部氢键的固有能力的结果，这种能力是1，2-丙二醇由于空间位阻而缺乏的。

The purpose of this work is the determination of the energy required for non-covalent bonds between molecules and ions in solution to form and break. Knowledge of the energetic requirements of such non-covalent bonds, particularly those involving water and biologically signifcant molecules, is fundamental to understanding molecular interactions and the changes in conformations that are integral to them. This research involves determining the thermodynamic quantities *H(std)298, *S(std)298, and *G(std)298 using the approach of equilibrium ion-molecule reaction chemistry and ions produced by electrospray ionization. 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. In the past year we have refined our previous determinations, particularly by decreasing the variance associated with the values for the first and third hydration steps. This has been accomplished by further extending the temperature range of our studies so that we now span the temperature from 0o to 90o C. Both the sub-ambient and high temperatures have required substantial modifications to the mass spectrometer used for these studies and have also required an apprecible effort in assuring reliable values for the temperture determinations. The hydration thermodynamics values were calculated from equilibrium constants measured over the full temperature range at a variety of ion source water partial pressures. Equilibrium ion intensity measurements were made for at least 4 hydration states, i.e., zero through 3 water molecules associated with the core ion, at each of 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 equilbration at each new temperature point. Previous workers have determined thermodyanamic parameters for about 25% of the hydrations we have studied and results for our measurements are in close agreement with those published data. In addition to refining previous experimental quantities, 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. We have generated hydration mass spectra spectra of both of these diols and have observed addition of four water molecules to each species. However, the intensity of each of the hydrated forms of the 1,3-propanediol, relative to the unhydrated form, is about twice as great as those same levels of hydration in the 1,2-propanediol. This may very well be a consequnce of the inherent ability of the 1,3-propoanediol to form internal hydrogen bonds, a capability that is lacking in the 1,2- due to steric hinderances.