Effects of homonuclear scalar couplings during multiple refocusing sequences in nuclear magnetic resonance

Abstract

Multiple refocusing cycles can be used to extract transverse relaxation rates, R2, while homonuclear scalar couplings do not interfere. In this work, I have demonstrated the usefulness of a hybrid sequence, which is a compromise between single and multiple refocusing sequences, in order to investigate homonuclear scalar coupled spin systems, and to find a regime where the decays used to extract transverse relaxation rates are not modulated by cosine functions due to J-couplings. It was possible to measure the transverse relaxation rates of carbon-13 in doubly-enriched glycine and compare them with those of carbon-13 in singly-enriched glycine samples, which were in good agreement, and confirmed the feasibility of extracting R2 rates in coupled spin systems. I also investigated spin systems with more than one J-coupling interaction, and showed by experiments and numerical simulations that the increased complexity of the system reduces the possibilities of extracting unmodulated decays.