Chirp Mixing

TL;DR

This paper introduces chirp mixing, a broadband technique for homonuclear spin coupling in NMR, using adiabatic sweeps to enhance cross polarization and mixing efficiency.

Contribution

We develop the theory of chirp mixing, demonstrating its broadband capabilities and effectiveness in 13C NMR experiments on Alanine.

Findings

Achieves efficient cross polarization between coupled spins.

More broadband than existing methods.

Successfully demonstrated on 13C in Alanine.

Abstract

In this paper, we develop the theory of chirp mixing. The working principle is simple, given coupled homonuclear spins with offsets in range [-B, B], we adiabatically sweep through the resonances. This achieves cross polarization between the z magnetization of the coupled spins. We repeat this basic operation many times with a supercycle to achieve appropriate mixing time. When we sweep through the resonances, midway between the resonances of the coupled spin I and S, the effective field seen by two spins is the same and hence they precess at same frequency around their effective fields. This means the coupling, which normally gets averaged due to the chemical shift difference is no more averaged for a short time and we get mixing. In this paper, we develop these basic ideas. By virtue of its design, the chirp mixing is much more broadband compared to state of the art methods. The proposed methodology is demonstrated on 13C mixing in a sample of Alanine.