Conformation of hydroxy-L-proline in aqueous solution. Comparison of results from lanthanide ion probe measurements and proton coupling constants

Abstract

The conformation of hydroxy-L-proline in D₂O solution has been studied by analysing its ¹H chemical shifts and spin-lattice relaxation times perturbed by the binding of lanthanide(^III) ion. Spin couplings, including a large long-range coupling constant (2.22 Hz) between the protons bonded to the β- and δ-carbons, remain unaltered by the binding of La^III. Thus, conformational changes upon complex formation are absent. The assignment of protons in this study which utilizes the lanthanide probe is in agreement with previous result from analysis of the coupling constants. The conformations estimated independently by these two approaches are similar, although from a more quantitative point of view the puckering angles ω₁, (between the planes formed by C_α, C_β, and N and by C_β, C_δ, and N) and ω₂(between the planes formed by C_β, C_δ, and N and by C_β, C_γ, and C_δ) differ by ca. 20 and 15°, respectively, between the two conformations.