The proton magnetic
resonance spectroscopy of 11 proteins (molecular weight range 5700-650000) has
been investigated in five denaturing solvents, viz., trifluoroacetic acid-d,
formic acid, dichloroacetic acid, 6M guanidine hydrochloride in D2O,
and 8M urea in D2O. The chemical shifts, line-widths, and
intensities of the resonances have been measured of the histidine C2 protons,
the methionine SCH3 protons and methyl protons of leucine,
isoleucine, and valine, the aromatic protons, and the α-CH protons. ��� It is found that, with some exceptions
delineated below, the line- widths of the methyl resonances are constant for a
particular solvent, independent of the molecular weight of the protein. This
indicates that, in general, the proteins behave as random coil structures in
these solvents, which confirms the conclusion reached by Tanford
and co-workers1-4 for 6M
guanidine hydrochloride. ��� However, methyl line broadening occurs in
dichloroacetic acid for catalase and fibrinogen, in guanidine hydrochloride for
insulin, and in urea for insulin and lysozyme. Furthermore, the C 2 histidine
resonance is absent in dichloroacetic acid solutions of thyroglobulin, catalase,
and fibrinogen; the SCH3 resonance is absent in myoglobin in trifluoroacetic
acid-d and occurs as a doublet for trypsin in guanidine hydrochloride and in
urea. A general line broadening of resonances indicates association and/or incomplete
unfolding of molecules, whereas perturbations of only one particular resonance,
as in the cases detailed above, are probably due to intramolecular non-covalent
interactions which involve the perturbed group and another unspecified group in
the protein. ��
Toward Engineering Intrinsic Line Widths and Line Broadening in Perovskite Nanoplatelets
