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Nmr studies on complex formation of poly( L ‐lysine HBr) with carbonate ion in aqueous solution
Author(s) -
Kakiuchi Kinji,
Akutsu Hideo
Publication year - 1983
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.360220403
Subject(s) - chemistry , antiparallel (mathematics) , dimer , protonation , crystallography , aqueous solution , ion , carbonate , propylene carbonate , lysine , trimer , stoichiometry , stereochemistry , amino acid , organic chemistry , physics , electrode , quantum mechanics , magnetic field , electrochemistry , biochemistry
Diemer formation of poly( L ‐lysine HBr) in carbonate buffer at pD 10.5 was reported in our previous paper [ Biopolymers (1981) 20 , 345–357]. The mechanism of the dimer formation was investigated employing carbon‐13 and proton nmr. pD dependence of the 13 C‐nmr spectrum of poly( L ‐lysine HBr) in the presence of carbonate ion clearly shows that a complex formation between the CO 3 2−ion and protonated ε‐amino group is involved in the stabilization of the dimer form. The lifetime of the complex is longer than 10 −2 s. A stoichiometric evaluation suggests that CO 3 2−bridges two lysyl side chains. A molecular model of the dimer form designated as a single antiparallel β‐ribbon was proposed and discussed in the light of hydrodynamic and ir spectroscopic properties reported earlier. Concentration change experiments indicate that CO 3 2−binds not only to the dimer formation is inferred as stabilization of the single antiparallel β‐ribbon as an intermediate structure in the conversion between the α‐helix and β‐sheet. The α‐CH proton signal of the lysine residue located in the ordered structure (α‐helix and β‐form) was observed to be separate from that in the random‐coil region.