G. Barone et al., EXCESS-ENTHALPIES OF N-ACETYLGLYCINEAMIDE AND N-ACETYL-L-LEUCINEAMIDEIN CONCENTRATED AQUEOUS-SOLUTIONS OF TETRAMETHYLUREA, Thermochimica acta, 227, 1993, pp. 67-73
A comparison has been made among the values of the enthalpic pairwise
interaction coefficients of two N-acetylamides of the amino acids glyc
ine (NAGA) and leucine (NALA) in concentrated aqueous solutions of tet
ramethylurea (TMU) and urea, in pure water, and in pure liquid amides.
The second virial coefficients of the excess enthalpies are found to
be negative for both the model peptidic molecules in 4M TMU, as in liq
uid amides, dimethylformamide (DMF) and fused N-methylacetamide (NMA),
substances assumed to mimic the core of globular proteins. This is th
e reverse of what was found for concentrated aqueous solutions of urea
(U), where ail the enthalpic second virial coefficients were positive
. This suggests a completely different mechanism for the denaturation
of protein in the presence of urea and TMU, due to different protein-d
enaturant interactions.