title: Importance of polarization transfer in reaction products for interpreting and analyzing CIDNP at low magnetic fields.
abstract: The magnetic field dependence of Chemically Induced Dynamic Nuclear Polarization (CIDNP) was studied for the amino acids N-acetyl histidine, N-acetyl tryptophan and N-acetyl tyrosine. It is demonstrated that at low field CIDNP is strongly affected by polarization redistribution in the diamagnetic molecules. Such a polarization transfer is of coherent nature and is due to spin coherences formed together with non-equilibrium population of the spin states. These coherences clearly manifest themselves in an oscillatory time dependence of polarization. Polarization transfer effects are most pronounced at nuclear spin Level Anti-Crossings (LACs), which also result in sharp features in the CIDNP field dependence. Thus, polarization transfer is an important factor, which has to be taken into account in order to interpret low-field CIDNP data on both qualitative and quantitative level. Possible applications of polarization transfer phenomena are also discussed in the paper. In particular, the role of LACs in spin order transfer is highlighted: LACs provide a new tool for precise manipulation of spin hyperpolarization and NMR enhancement of selected target spins.
authors: International Tomography Center, Siberian Branch of the Russian Academy of Science, Institutskaya 3a, Novosibirsk 630090, Russia; Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russia.
authors: Andrey N
authors: AN
authors: Pravdivtsev
authors: International Tomography Center, Siberian Branch of the Russian Academy of Science, Institutskaya 3a, Novosibirsk 630090, Russia; Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russia.
authors: Alexandra V
authors: AV
authors: Yurkovskaya
authors: International Tomography Center, Siberian Branch of the Russian Academy of Science, Institutskaya 3a, Novosibirsk 630090, Russia; Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russia. Electronic address: ivanov@tomo.nsc.ru.
authors: Konstantin L
authors: KL
authors: Ivanov
authors: Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
authors: Hans-Martin
authors: HM
authors: Vieth
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D004574:Electromagnetic Fields; D006639:Histidine / Q000031:analogs & derivatives / Q000737:chemistry; D007202:Indicators and Reagents; D007834:Lasers; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D013113:Spin Labels; D014364:Tryptophan / Q000031:analogs & derivatives / Q000737:chemistry; D014443:Tyrosine / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: D000596:Amino Acids; D007202:Indicators and Reagents; D013113:Spin Labels; D014443:Tyrosine; C006392:N-acetyltryptophan; D006639:Histidine; D014364:Tryptophan; C025787:N-acetyltyrosine; C023495:N-acetylhistidine
keywords: CIDNP; Level anti-crossings; Polarization transfer; Spin hyperpolarization