Correlation of the hydrogen-bonded backbone amide 15N CST principal components with hydrogen bond distance RN…O for A) α-helical and B) β-sheet structure, for the four proteins under investigation, E. coli thioredoxin reassemblies, LC8, and CAP-Gly. The downfield shift of all three 15N CST principal components, notably in δ 11, with decreasing RN…O is indicated by the negative Pearson correlation coefficients (RP) for both α-helical and β-sheet secondary structures.