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Influence of methanol on the rotational diffusion of poly( L ‐lysine) in the helix–coil transition
Author(s) -
Hanssum H.,
Rüterjans H.
Publication year - 1980
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1980.360190902
Subject(s) - chemistry , aqueous solution , solvent , random coil , methylene , helix (gastropod) , rotational diffusion , methanol , crystallography , diffusion , electromagnetic coil , relaxation (psychology) , polymer , side chain , polymer chemistry , organic chemistry , thermodynamics , molecule , circular dichroism , psychology , physics , snail , biology , electrical engineering , engineering , ecology , social psychology
13 C spin‐lattice relaxation times of poly( L ‐lysine) have been obtained at 67.9 MHz in aqueous solution and in a mixed solvent (40% methanol/60% water). A concomitant determination of the conformation by CD permits the correlation of conformation and rotational diffusion of the polymer. The dependence on pH of the spin‐lattice relaxation times of the 13 C α and the side‐chain carbon resonances reflects the diffusional motion in the random‐coil conformation, in the helix–coil transition, and in the conformation of the α‐helix. In the mixed solvent the reorientational correlation time of the C α ‐H α vector increases from τ = 0.37 nsec (random coil) to τ = 12.0 nsec (α‐helix). In aqueous solution the correlation time of this vector increases from τ = 0.33 nsec (random coil) to τ ≫ 11 nsec. The reorientation rates of the side‐chain methylene groups in the two solvents are markedly different. The reorientation of all methylene groups is reduced in the mixed solvent.