Energetics Of The Interaction Between Water, Membranes A

水、膜 A 之间相互作用的能量学

• 批准号: 6671875
• 负责人: ALFRED L YERGEY
• 金额: --
• 依托单位: EUNICE KENNEDY SHRIVER NATIONAL INSTITUTE OF CHILD HEALTH & HUMAN DEVELOPMENT
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6671875
• 关键词: angiotensin II; bioenergetics; chemical hydration; electrospray ionization mass spectrometry; intermolecular interaction; macromolecule; membrane; propane; thermodynamics; water

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 water partial pressures in the ion source 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, and include at least 60 combinations of water partial pressures and temperatures covering the ranges of experimental variables. Results have been obtained for three different classes of molecules. First, an exhaustive study of the equilibrium clustering of 1-3 waters around n-alkylammonium, CnH(2n+1)NH3+, and the di- and tri-methyl ammonium ions, has shown a pattern of behavior consistent with water clusters forming around the charged portion of the ion and being influenced by the nature of the attached hydrophobic groups. Detailed analysis of the entropy values derived from these measurements is consistent with detecting the entropy change associated with the formation of an internal hydrogen bond. Second, the concepts of water organizing around a charge site and the formation of internal hydrogen bonds detected by substantial entropy decreases have been explored further with the investigation of the hydration energetics of simple alkyl-diols: 1,2-(OH)2-propane , 1,3-(OH)2-propane, 1,3-(OH)2- butane and 1,4-(OH)2-butane. 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 an 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 energetically and entropically favorable state. On the other hand, both of the butane diols behave in a manner consistent with the 1,2-propane diol. Third, are very recent results from studies of the hydration of several amino acids. Results from the equilibrium clustering of water with the neutral amino acids, glycine, valine and leucine, show behavior that is quite similar to that observed with the alkylammonium ions for the first two water molecules. The addition of the third water however is associated with a decrease in both enthalpy and entropy, suggesting the formation of intramolecular hydrogen bonds as seen in the 1,3-propane diol. in On the other hand, the results obtained to date in studies of the basic amino acids, arginine and lysine, are quite different. That is, while one might expect the energetics of adding the first water to these molecules to be highly favorable, we have determined that it is less energetically favorable than the addition of the first water to the neutral amino acids. This suggests the presence of internal hydrogen bonding being present before any water clusters are formed.

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。了解此类非共价键的能量需求，特别是那些涉及水和生物重要分子的非共价键，对于理解分子相互作用及其不可或缺的构象变化至关重要。这项研究涉及使用平衡离子-分子反应化学方法确定热力学量 deltaH(std)298、deltaS(std)298 和 deltaG(std)298。水合热力学值是根据在 0-136 摄氏度的温度范围内、离子源中的水分压范围在 0 到 100 毫托之间测量的平衡常数来计算的。平衡离子强度测量针对至少 4 种水合状态（即与核心离子相关的 0 到 3 个水分子）进行，并且包括覆盖实验变量范围的至少 60 种水分压和温度组合。已经获得了三种不同类别的分子的结果。首先，对 n-烷基铵、CnH(2n+1)NH3+、二甲基铵离子和三甲基铵离子周围 1-3 个水的平衡聚集进行了详尽的研究，显示了一种与在离子带电部分周围形成的水聚集一致的行为模式，并受到所连接的疏水基团性质的影响。对从这些测量得出的熵值的详细分析与检测与内部氢键形成相关的熵变化是一致的。其次，通过对简单烷基二醇（1,2-(OH)2-丙烷、1,3-(OH)2-丙烷、1,3-(OH)2-丁烷和1,4-(OH)2-丁烷）的水合能量学的研究，进一步探讨了水在电荷位点周围组织和通过显着熵降低检测到的内部氢键形成的概念。向质子化的 1,2-(OH)2-丙烷中逐步添加水显示出每次添加放热性减弱的趋势。虽然我们无法直接测量第一批水的添加量，但我们能够根据水的分压和温度来估计该过程的放热上限。我们得出的结论是，第一个水合步骤在能量上非常有利。在将前两个水分子添加到 1,3-(OH)2-丙烷中时观察到 1,2-(OH)2-丙烷的能量下降趋势，但在添加第三个水分子时并未保持这种趋势。确定向复合物中添加第三种水在能量上比添加第二种水更有利，此外还发现该过程的熵显着降低。这两个观察结果使我们得出结论：1,3-(OH)2-丙烷三水合物是一种能量和熵有利的状态。另一方面，两种丁二醇的行为方式与1,2-丙二醇一致。第三，是几种氨基酸水合研究的最新结果。水与中性氨基酸（甘氨酸、缬氨酸和亮氨酸）的平衡聚类结果显示，前两个水分子的行为与烷基铵离子观察到的行为非常相似。然而，第三种水的添加与焓和熵的降低相关，这表明形成了分子内氢键，如 1,3-丙二醇中所见。另一方面，迄今为止对碱性氨基酸精氨酸和赖氨酸的研究所获得的结果却截然不同。也就是说，虽然人们可能期望将第一批水添加到这些分子中的能量非常有利，但我们已经确定其在能量上不如将第一批水添加到中性氨基酸中有利。这表明在任何水簇形成之前就存在内部氢键。