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A Thermodynamic and Kinetic Study on the Stability of the Conformational States of N‐Acetyl‐proline‐methylamide by IR. spectroscopy and chemical relaxation
Author(s) -
Hopmann Rudolf
Publication year - 1974
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19740570634
Subject(s) - chemistry , enthalpy , reaction rate constant , hydrogen bond , equilibrium constant , atmospheric temperature range , spectroscopy , chemical shift , amide , relaxation (psychology) , crystallography , kinetics , thermodynamics , molecule , organic chemistry , psychology , social psychology , physics , quantum mechanics
N‐Acetyl‐proline‐methylamide (APMA) was synthesized by the mixed anhydride method and investigated by IR. spectroscopy and chemical relaxation measurements. The temperature‐induced variation of the IR. absorption bands of the internally hydrogen bonded (b) and of the extended, unbonded (e) species at 3330 and 3450 cm −1 respectively, were used to evaluate the molar absorptivities, a(b) = 280 and a(e) = 50 l/mol · cm, the equilibrium constant K = 0.70, and the molar enthalpy of reaction Δ H = − 2280 ± 60 cal/mol. The entropy was estimated to be in the range − 8 to − 9 e.u. The reaction rates of this conformational transition were measured by the chemical dipole field effect. The relaxation time of the rate process is τ = 2.7 · 10 −9 s, the rate constant for the formation of the hydrogen bond k (b) is 2.2 · 10 8 s −1 , and that for the unfolding accompanied by the breakage of the amide hydrogen bond k (e) is 1.5 · 10 8 s −1 .