NMR Basis for Biomolecular Structure (Theory)

Abstract

Synonyms Coherence transfer; Density matrix formalism; Multidimensional NMR; Nuclear magnetic resonance ; Product operator formalism Synopsis Nuclear magnetic resonance (NMR) is referred to as a nucleus with spin under a magnetic field that will be excited by electromagnetic radiation with specific frequency (Larmor frequency). The resonance frequency variation depends on magnetic field strength, atom type, and the chemical environments the atom exists (chemical shift phenomenon). Chemical shift analysis can provide plenty of structure information of a molecule, but the overcrowd resonance signals in conventional (one-dimensional) spectra restricted its use on biomolecules. The superiority of modern NMR is to disperse the overcrowd resonance signals to multidimension. Density matrix formalism is the core of modern NMR, which mathematically describes the evolution of a nuclear spin system precisely. Product operator formalism, the simplified version of density matrix formalism, is more convenient and practical for NMR pulse program design. There are three types of pathway for coherence transfer: through scalar coupling, through dipolar coupling, and through physical or chemical exchange. Multidimensional NMR pulse program is composed of four different types of period: preparation period, evolution period, mixing period, and acquisition period.