ENERGETICS OF THE INTERACTION BETWEEN WATER, MEMBRANES AND MACROMOLECULES

这项工作的目的是确定分子和离子之间非共价键在溶液中形成和断裂所需的能量。了解这种非共价键的能量需求，特别是那些涉及水和具有生物学意义的分子的能量需求，是理解分子相互作用和它们所必需的构象变化的基础。本研究利用平衡离子-分子反应化学的方法和电喷雾电离产生的离子，测定了热力学参数*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和溶剂化之间的关系提供了可能性。在过去的一年里，我们改进了之前的测定，特别是通过减少与第一步和第三步水化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从0摄氏度到90摄氏度。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改进，也需要做出相当大的努力来确保温度测定的可靠数值。根据在不同离子源水分压下测得的全温度范围内的平衡常数，计算了水化热力学数值。在覆盖实验变量范围的60种水分压和温度组合下，对至少4种水化状态，即与核心离子有关的0到3个水分子进行了平衡离子强度测量。在25-60℃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数小时的平衡。以前的工作人员已经确定了我们所研究的大约25%的水合物的热动力学参数，我们的测量结果与那些公布的数据非常一致。除了改进之前的实验量，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。我们生成了这两种二元醇的水合质谱图，并观察到每种物质中添加了四个水分子。然而，每种水合形式的1，3-丙二醇相对于未水合形式的强度大约是1，2-丙二醇中相同水合水平的两倍。这很可能是1，3-丙二醇形成内部氢键的固有能力的结果，而1，2-由于空间位阻而缺乏这种能力。

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.