Structural Studies of Hydrogen-bonded Peptides and Polypeptides by Solid-state NMR

Abstract

Nuclear magnetic resonance (NMR) chemical shifts are one of the most important parameters for providing information about molecular structure, and high-resolution NMR spectroscopy has been used as one of the most powerful means for obtaining useful information on the details of the hydrogen bond. This chapter describes recent studies on the hydrogen-bonded structures of peptides and polypeptides in the solid state through the observation of NMR chemical shifts and through theoretical calculations of nuclear shieldings (chemical shifts) to get an understanding of the nature and influence of hydrogen bonds. The chemical shifts in the solid state provide direct information about the hydrogen bond present in peptides and polypeptides with a fixed conformation. The 13 C chemical shift obtained from solid-state NMR is closely related to the electronic structure of a molecule, and therefore, includes information about the three-dimensional structure of the molecule. To reveal the correlation between the structures of peptides and the 13 C chemical shifts, 13 C shielding calculations have been discussed in the chapter using finite perturbation theory with intermediate neglect of differential overlap (FPT-INDO) and by the coupled Hartree–Fock method, using ab initio gauge-invariant atomic orbitals (GIAO-CHF). The chapter concludes that solid-state high-resolution NMR spectroscopy combined with quantum–chemical calculation is a useful methodology for elucidating the hydrogen-bonded structure of peptides and polypeptides—including proteins, in the solid state.