Isotope effects on chemical shifts in the study of hydrogen bonded biological systems

This review deals with biological systems and with deuterium isotope effects on chemical shifts caused by the replacement of OH, NH or SH protons by deuterons. Hydrogen bonding is clearly of central importance. Isotope effects on chemical shifts seems very suitable for use in studies of structures and reactions in the interior of proteins, as exchange of the label can be expected to be slow. One-bond deuterium isotope effects on 15N chemical shifts, and two-bond effects on 1H chemical shifts for N(D)Hx systems can be used to gauge hydrogen bond strength in proteins as well as in salt bridges. Solvent isotope effects on 19F chemical shifts show promise in monitoring solvent access. Equilibrium isotope effects need in some cases to be taken into account. Schemes for calculation of deuterium isotope effects on chemical shifts are discussed and it is demonstrated how calculations may be used in the study of complex biological systems.