Thermodynamics in Conformational Transition of Poly(β-benzyl l-aspartate) As Studied by High-Resolution Solid-State 13C NMR Spectroscopy

Abstract

The thermodynamic characteristics associated with conformational change of poly(β-benzyl l-aspartate) (PBLA) in the solid state are studied by using 13C high-resolution solid-state NMR. PBLA was chosen because four different conformations, i.e., the right-handed (αR-) and left-handed α-helices (αL-helix), left-handed ω-helix (ωL-helix), and antiparallel β-sheet (β-sheet), can be prepared separately, and the thermally induced transition occurs among them. In this work, we analyze spectral changes due to conformational transformation of PBLA and determine the enthalpic and entropic changes associated with the transformation of αR-helix to other conformations; the enthalpic change ΔH per residue becomes ca. 1.4 kJ mol−1, and the entropic change ΔS per residue becomes ca. 3.5 J K−1 mol−1. With using these ΔH and ΔS values, we show that the observed transition curve can be reproduced by a simple statistical model.