Affiliation: | 1. International Tomography Center, Siberian Branch of the Russian Academy of Sciences, Institutskaya str. 3a, Novosibirsk, 630090 Russia;2. International Tomography Center, Siberian Branch of the Russian Academy of Sciences, Institutskaya str. 3a, Novosibirsk, 630090 Russia Novosibirsk State University, Pirogova str. 1, Novosibirsk, 630090 Russia;3. International Tomography Center, Siberian Branch of the Russian Academy of Sciences, Institutskaya str. 3a, Novosibirsk, 630090 Russia Novosibirsk State University, Pirogova str. 1, Novosibirsk, 630090 Russia Konstantin L'vovich Ivanov passed away on 5th of March 2021. |
Abstract: | Signal Amplification By Reversible Exchange (SABRE) is gaining increased attention as a tool to enhance weak Nuclear Magnetic Resonance (NMR) signals. In SABRE, spin order is transferred from parahydrogen (H2 in its nuclear singlet spin state) to a substrate molecule in a transient Ir-based complex. In recent years, SABRE polarization of biologically active substrates has been demonstrated, notably of metronidazole – an antibiotic and antiprotozoal drug. In this work, we study 15N SABRE polarization of metronidazole at natural isotope abundance. We are able to demonstrate significant 15N polarization reaching 15 %, which corresponds to a signal enhancement of 46,000 at 9.4 T for the nitrogen atom with lone electron pair. Additionally, the other two N-atoms can be polarized, although less efficiently. We present a detailed study of the field dependence of polarization and explain the maxima in the field dependence using the concept of coherent polarization transfer at level anti-crossings in the SABRE complex. A study of spin relaxation phenomena presented here enables optimization of the magnetic field for efficient storage of non-thermal polarization. |