ENERGETICS OF THE INTERACTION BETWEEN WATER, MEMBRANES AND MACROMOLECULES

我们用电喷雾电离平衡气相离子分子在平衡状态下的反应，测定了烷基铵离子家族CnH2n+1NH3+的水化热力学δ tah (std,298), δ tas （std,298）和δ tag （std,298）。在离子源水分压为0 ~ 100 mtorr，相当于总源压力的0 ~ 1%，离子源温度为5 ~ 65℃的条件下，通过测量平衡常数计算水化热力学值。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种水合状态，即0到3个与核心离子相关的水分子进行平衡离子强度测量。我们的测量结果与发表的一些烷基铵物种的水化状态的数据密切一致，其中常见的数据存在。更重要的是，我们第一次能够测量单个分子间氢键的熵强。delta （std）的值足够精确，因此我们能够得出这样的结论：熵的平均净损失为3卡/度。摩尔在添加第二个水离子已经有一个存在,也就是说,delta-deltaS (std) = 3卡路里/度。摩尔显著，p < 0.04。熵的净减少与分子间有序的增加是一致的，即水-水- N+氢键的形成。此外，我们的研究清楚地表明：1)向裸离子中加入第一种水比加入第三种水明显更放热；2)单烷基铵离子的第一水加成对单甲基比单丁基有利约2千卡/摩尔，并且随着烷基链长的进一步增加，这一变化相对较小；3)在三甲基的情况下，第一水对单甲基铵离子的加入约为3千卡/摩尔更有利。此外，第一次水加入丙基铵比第一次水加入三甲基铵约有利1.5千卡/摩尔。-热力学，水合焓，疏水性，平衡，质谱

We have determined hydration thermodynamics, deltaH(std,298), deltaS(std,298), and deltaG(std,298), for a family of alkyl ammonium ions, CnH2n+1NH3+ for n between 1 and 8 carbons, using electrospray ionization-equilibrium gas phase ion molecule reactions at equilibrium. The hydration thermodynamic values were calculated from equilibrium constants measured under conditions of ion source water partial pressures ranging between 0 and 100 mtorr, equivalent to 0-1% of total source pressure, and ion source temperatures ranging between 5 and 65C. 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 the 60 combinations of water partial pressures and temperatures covering the ranges of experimental variables. Results of our measurements are in close agreement with published data for some of the alkyl ammonium species for the hydration states where common data are present. Of much greater importance is that we have been able to establish for the first time a measurement of the entropic strength of a single intermolecular hydrogen bond. The values for deltaS(std) are sufficiently precise that we are able to conclude that there is an average net loss in entropy of 3 cal/deg.mole in adding the second water to an ion already having one water present, i.e., delta-deltaS(std) = 3 cal/deg.mole significant at p < 0.04. The net decrease in entropy is consistent with a gain in intermolecular ordering, that is the formation of a water - water - N+ hydrogen bond. Furthermore, our studies clearly show that 1) addition of the first water to a bare ion is apprecibly more exothermic than addition of the third; 2) addition of the first water to monoalkyl ammonium ions is about 2 kcal/mole more favorable for the case of monomethyl than for monobutyl and that there is relatively little change by further increases of alkyl chain length; 3) addition of the first water to monomethyl ammonium ions is about 3 kcal/mole more favorable for the case of trimethyl. Furthermore, addition of the first water to propyl ammonium is about 1.5 kcal/mole more favorable than the addition of the first water to trimethyl ammonium. - Thermodynamics, Hydration Enthalpy, Hydrophobicity, Equilibrium, Mass Spectrometry