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.
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