AMINO ACID/PEPTIDE TRANSFER THERMODYNAMICS

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Our two groups will collaborate to develop chromatography methods to measure amino acid partitioning, to better understand protein stabilities. Current experiments involve liquid oil/water partitioning or crystal diketopiperazine dissolution. But protein cores are neither like liquid oils nor like crystalline dipeptides. We propose 3 chromatographic methods: (1) Ordered-Oil/Water Partitioning Chromatography, in which we will have independent control over the steric constraints and the degree of "liquidness-solidness" in the oil. (2) Reversed-Phase Hydrogen Bonding Chromatography, in which we will have independent control over the hydrogen bonding capacity in oil and aqueous phases. (3) Peptide Phase Chromatography, in which we will covalently attach peptides, rather than alkyl chains, to silica supports for the partitioning of amino acids from aqueous solvents. We will measure transfer free energies, enthalpies, entropies, and heat capacities for amino acids and peptides. Our goals are: (i) to develop partitioning media that more closely resemble protein cores than current experimental models, and (ii) to dissect hydrogen-bonding and stearic components from the transfer thermodynamics. A (4) Theoretical Component will attempt to interpret protein stabilities in terms of these and other model experiments. A theory effort will also assess the importance of solute and cavity shape for partitioning thermodynamics in constrained media, such as proteins and chromatography columns. Our ultimate goal is to use these partitioning studies of amino acids and peptides to help unravel the driving forces underlying protein stabilities.