Study on the conformation and dynamics of amphoteric polymers and the theoretical hydration of alanine dipeptide

Abstract

Part A The effects of the structural variation and the relative stability by the hydration of Alanine dipeptide in $C_7^eq$, $C_7^ax$, $C_5$, $α_R$, and $P_Ⅱ$ conformations were investigated by the method of SUMSL(Secant-type Unconstrained Minimization Solver) energy minimization technique with the empirical potential energy function of the solute, and ST2 water model. The binding sites of water molecules in the solute were selected from spherical interaction energy maps. As a function of the number of added water molecules, we traced the structural variations mainly in the (φ, ψ) torsion angle space, and calculated the total internal energies of each solute-water systems to evaluate the relative probabilities between those five conformers. The results indicate that the conformers having no intramolecular hydrogen-bondings, such as $α_R$, $C_5$, and $P_Ⅱ$, show larger structural variations than the conformers of $C_7^ax$, and $C_7^eq$ that have intramolecular hydrogen-bondings. The torsion angle of ψ fluctuated more than φ for all the examined conformers. The energetically dominant conformation is shifted from $C_7^eq$to (R as the hydration is preceded. Part B Solution conformations and dynamic mobilities of novel amphoteric copolymers were studied for aqueous solutions of P(sodium 2-methacryloyloxyethanesulfonate-co-2-methacryloyloxyethyltrimethyl- ammonium iodide) [P(NaMES-co-METMAI)] as a function of composition, concentration, addition of HCl and addition of KCl. As HCl or KCl was added successively to the 5 w/v% copolymer solutions, the reduced viscosities of the solutions were reduced except the 1:1 copolymer solution. The dynamic mobility of the cationic side chain was estimated with the quadrupolar $^14N$-NMR relaxation technique. The motion of the interacting counterion, $Na^+$, was studied by Poisson- Boltzmann electrostatic theories and the quadrupolar $^23Na$-NMR. Since the intramolecular 1:1 ion pair between MES- and $METMA^+$ acts as an effective ...