ABSTRACT
Spin-lattice relaxation times T1 and T1d as well as NMR second moment were employed to study molecular dynamics of pyridoxine (vitamin B6) in the temperature range 10-350 K. The T1 minimum observed at low temperatures at 200 MHz is attributed to a motion of methyl group. The motion is interpreted in terms of Haupt's theory, which takes into account the tunneling assisted relaxation. At low temperatures, where T1 is temperature independent, occupation of the ground state only is assumed. A motion of proton of the hydroxyl groups or CH2OH groups probably provides additional mechanism of relaxation, in the high-temperature region.
Subject(s)
Crystallization/methods , Crystallography/methods , Motion , Pyridoxine/chemistry , Kinetics , Protein Conformation , Protein Denaturation , Protons , TemperatureABSTRACT
Rheometry, 13C CP/MAS NMR spectra and 1H spin-lattice relaxation times T1 and T1rho have been employed to study the structure and molecular dynamics in composites of polyethylene (LDPE) with calcium carbonate filler. It has been found that the addition of the filler into the polymer leads to an increase in composite rigidity and a decrease in mobility in its crystalline regions. The presence of the filler affects the crystallization process making the crystal structure less perfect and reduces the size of the crystallites.
Subject(s)
Calcium Carbonate/chemistry , Magnetic Resonance Spectroscopy/methods , Manufactured Materials/analysis , Materials Testing/methods , Polyethylene/chemistry , Rheology/methods , Carbon Isotopes , Elasticity , Molecular Conformation , Protons , Shear Strength , Temperature , ViscosityABSTRACT
Spin-lattice relaxation times T1 in solid pregnenolone have been studied over a wide range of temperatures, from 77 up to 417 K. The dynamic processes arising from C3 motion of the three methyl substituents are separated, and their activation parameters are determined.
Subject(s)
Magnetic Resonance Spectroscopy , Pregnenolone/chemistry , Humans , Progesterone/chemistry , TemperatureABSTRACT
Spin-lattice relaxation times Tl and Tld as well as NMR second moment were employed to study the molecular dynamics of riboflavin (vitamin B2) in the temperature range 55-350 K. The broad and flat Tl minimum observed at low temperatures is attributed to the motion of two nonequivalent methyl groups. The motion of the methyl groups is interpreted in terms of Haupt's theory, which takes into account the tunneling assisted relaxation. An additional mechanism of relaxation in the high temperature region is provided by the motion of a proton in one of the hydroxyl groups. The Davidson-Cole distribution of correlation times for this motion is assumed.
Subject(s)
Magnetic Resonance Spectroscopy , Riboflavin/chemistry , Hydrogen , TemperatureABSTRACT
Spin-lattice relaxation times T1 and nuclear Overhauser effect (NOE) enhancement factors for the individual ring carbons in di-n-butyl phthalate (DBF) show that the reorientational correlation function corresponding to the global dynamics in supercooled liquid can be described by a Davidson-Cole distribution. Measurements of proton spin-lattice relaxation times T1 and T1p, as well as 1H NMR spectra at temperatures below the glass transition temperature, Tg, reveal that the same distribution holds also for description of local dynamics in glassy DBF. The activation parameters of the motions detected are derived.
Subject(s)
Dibutyl Phthalate/chemistry , Glass/chemistry , Magnetic Resonance Spectroscopy , Carbon Isotopes , Chemical Phenomena , Chemistry, Physical , Cold Temperature , Electron Spin Resonance Spectroscopy , Hydrogen , Molecular Conformation , ProtonsABSTRACT
Spin-lattice relaxation times T1 and T1p as well as 1H NMR spectra have been employed to study the dynamics of the glass-forming di-isobutyl phthalate in the temperature range extending from 100 K, through the glass transition temperature Tg, up to 340 K. Below Tg NMR relaxation is governed by local dynamics and may be attributed to rotation of methyl groups at low temperatures and to motion of isobutyl groups in the intermediate temperature interval. Above Tg the main relaxation mechanism is provided by overall molecular motion. The observed relaxation behavior is explained by motional models assuming asymmetrical distributions of correlation times. The motional parameters obtained from Davidson-Cole distribution, which yields the best fit of the data at all temperatures are given.
Subject(s)
Dibutyl Phthalate/analogs & derivatives , Dibutyl Phthalate/chemistry , Glass , Magnetic Resonance SpectroscopyABSTRACT
Temperature dependences of proton and fluorine second moments and spin-lattice relaxation time T1 below glass transition were measured in glassy "I-Do,Pip-Me-BF4" ionene. The existence of motions of methyl groups and segments linking the cationic centers, namely piperidinium rings and trimethylene groups, for the polymeric part of ionene were established. Isotropic rotation of the counter-ion was evidenced and its limited diffusion suggested. To interpret the proton and fluorine relaxation data, a Davidson-Cole distribution of correlation times was assumed.
