ENERGETICS OF THE INTERACTION BETWEEN WATER, MEMBRANES AND MACROMOLECULES

我们用平衡电喷雾电离-平衡气相离子分子反应测定了一族烷基铵离子CnH_2n+_1NH_3~+的水化热力学：DELTA H(STD，298)，DELTA(STD，298)和DELTAG(STD，298)。在离子源水分压为0-100mtorr，相当于总源压的0-1%，离子源温度为5-65℃的条件下，根据测得的平衡常数计算了水化热力学数值。在涵盖实验变量范围的60种水分压和温度组合的每一种情况下，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。我们的测量结果与公布的一些烷基铵物种的水合状态的数据非常一致，其中存在共同的数据。更重要的是，我们首次能够建立单个分子间氢键的熵强度的测量。增量(STD)的值足够精确，以至于我们能够得出结论，在将第二水添加到已经存在一个水的离子中时，平均净熵损失为3卡/度摩尔，即，在p&lt；0.04时显著的增量-增量(STd)=3卡/度摩尔。熵的净减少与分子间有序性的增加是一致的，即水-水-N+氢键的形成。此外，我们的研究清楚地表明：1)第一水加到裸离子中比加入第三水放热略大；2)第一水加到单烷基铵离子中比单丁基离子加水约2千卡/摩尔，并且随着烷基链长的进一步增加变化相对较小；3)第一水加到单甲基铵离子中约3千卡/摩尔更有利于三甲基的情况。此外，在丙基铵中加入第一水比在三甲基铵中加入第一水更有利，约为1.5千卡/摩尔。-热力学、水化热、疏水性、平衡、质谱学

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