title: Magnetic field dependent long-lived spin states in amino acids and dipeptides.
abstract: Magnetic field dependence of long-lived spin states (LLSs) of the β-CH2 protons of aromatic amino acids was studied. LLSs are spin states, which are immune to dipolar relaxation, thus having lifetimes far exceeding the longitudinal relaxation times; the simplest example of an LLS is given by the singlet state of two coupled spins. LLSs were created by means of the photo-chemically induced dynamic nuclear polarization technique. The systems studied were amino acids, histidine and tyrosine, with different isotopomers. For labeled amino acids with the α-CH and aromatic protons substituted by deuterium at low fields the LLS lifetime, TLLS, for the β-CH2 protons was more than 40 times longer than the T1-relaxation time. Upon increasing the number of protons the ratio TLLS/T1 was reduced; however, even in the fully protonated amino acids it was about 10; that is, the long-lived mode was still preserved in the system. In addition, the effect of paramagnetic impurities on spin relaxation was studied; field dependencies of T1 and TLLS were measured. LLSs were also formed in tyrosine-containing dyads; a TLLS/T1 ratio of ∼7 was found, usable for extending the spin polarization lifetime in such systems.
authors.affiliation: International Tomography Center SB RAS, Institutskaya 3a, Novosibirsk, 630090, Russia. ivanov@tomo.nsc.ru.
authors.forename: Andrey N
authors.initials: AN
authors.lastname: Pravdivtsev
authors.forename: Alexandra V
authors.initials: AV
authors.lastname: Yurkovskaya
authors.forename: Herbert
authors.initials: H
authors.lastname: Zimmermann
authors.forename: Hans-Martin
authors.initials: HM
authors.lastname: Vieth
authors.forename: Konstantin L
authors.initials: KL
authors.lastname: Ivanov
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D003497:Cyclic N-Oxides / Q000737:chemistry; D003903:Deuterium / Q000737:chemistry; D004151:Dipeptides / Q000737:chemistry*; D060526:Magnetic Fields; D009682:Magnetic Resonance Spectroscopy; D011522:Protons; D011789:Quantum Theory; D013113:Spin Labels
chemical_list: D000596:Amino Acids; D003497:Cyclic N-Oxides; D004151:Dipeptides; D011522:Protons; D013113:Spin Labels; D003903:Deuterium; C001803:tempol