title: Dynamic nuclear polarization properties of nitroxyl radical in high viscous liquid using Overhauser-enhanced Magnetic Resonance Imaging (OMRI).
abstract: The dynamic nuclear polarization (DNP) studies were carried out for (15)N labeled carbamoyl-PROXYL in pure water and pure water/glycerol mixtures of different viscosities (1.8cP, 7cP and 14cP). The dependence of DNP parameters was demonstrated over a range of agent concentration, viscosities, RF power levels and ESR irradiation time. DNP spectra were also recorded for 2mM concentration of (15)N labeled carbamoyl-PROXYL in pure water and pure water/glycerol mixtures of different viscosities. The DNP factors were measured as a function of ESR irradiation time, which increases linearly up to 2mM agent concentration in pure water and pure water/glycerol mixtures of different viscosities. The DNP factor started declining in the higher concentration region (∼3mM), which is due to the ESR line width broadening. The water proton spin-lattice relaxation time was measured at very low Zeeman field (14.529mT). The increased DNP factor (35%) was observed for solvent 2 (η=1.8cP) compared with solvent 1 (η=1cP). The increase in the DNP factor was brought about by the shortening of water proton spin-lattice relaxation time of solvent 2. The decreased DNP factors (30% and 53%) were observed for solvent 3 (η=7cP) and solvent 4 (η=14cP) compared with solvent 2, which is mainly due to the low value of coupling parameter in high viscous liquid samples. The longitudinal relaxivity, leakage factor and coupling parameter were estimated. The coupling parameter values reveal that the dipolar interaction as the major mechanism. The longitudinal relaxivity increases with the increasing viscosity of pure water/glycerol mixtures. The leakage factor showed an asymptotic increase with the increasing agent concentration. It is envisaged that the results reported here may provide guidelines for the design of new viscosity prone nitroxyl radicals, suited to the biological applications of DNP.
authors.affiliation: Department of Physics, NMSSVN College, Nagamalai, Madurai 625 019, Tamil Nadu, India.
authors.forename: M
authors.initials: M
authors.lastname: Kumara Dhas
authors.affiliation: Innovation Center for Medical Redox Navigation, Kyushu University, Fukuoka 812-8582, Japan.
authors.forename: Hideo
authors.initials: H
authors.lastname: Utsumi
authors.affiliation: Department of Chemistry, NMSSVN College, Nagamalai, Madurai 625 019, Tamil Nadu, India.
authors.forename: A
authors.initials: A
authors.lastname: Jawahar
authors.affiliation: Department of Physics, NMSSVN College, Nagamalai, Madurai 625 019, Tamil Nadu, India. Electronic address: miltonfranklin@yahoo.com.
authors.forename: A
authors.initials: A
authors.lastname: Milton Franklin Benial
mesh_terms: D000465:Algorithms; D005990:Glycerol / Q000737:chemistry; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D009587:Nitrogen Isotopes; D009589:Nitrogen Oxides / Q000737:chemistry*; D012997:Solvents; D013113:Spin Labels; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D009587:Nitrogen Isotopes; D009589:Nitrogen Oxides; D012997:Solvents; D013113:Spin Labels; D014867:Water; C039900:nitroxyl; D005990:Glycerol
keywords: Carbamoyl-PROXYL; Dynamic nuclear polarization; ESR; Nitroxyl radical; Overhauser enhancement; Overhauser-enhanced magnetic resonance imaging