ABSTRACT
A detailed analysis of nitrogen-15 longitudinal relaxation times in microcrystalline proteins is presented. A theoretical model to quantitatively interpret relaxation times is developed in terms of motional amplitude and characteristic time scale. Different averaging schemes are examined in order to propose an analysis of relaxation curves that takes into account the specificity of MAS experiments. In particular, it is shown that magic angle spinning averages the relaxation rate experienced by a single spin over one rotor period, resulting in individual relaxation curves that are dependent on the orientation of their corresponding carousel with respect to the rotor axis. Powder averaging thus leads to a nonexponential behavior in the observed decay curves. We extract dynamic information from experimental decay curves, using a diffusion in a cone model. We apply this study to the analysis of spin-lattice relaxation rates of the microcrystalline protein Crh at two different fields and determine differential dynamic parameters for several residues in the protein.
Subject(s)
Bacterial Proteins/chemistry , Nuclear Magnetic Resonance, Biomolecular/methods , Phosphoproteins/chemistry , Models, Molecular , Nitrogen Isotopes , Protein Conformation , ThermodynamicsABSTRACT
The order within proton pairs in organic molecules, resulting from hydrogenation with parahydrogen, can be transferred in great part to nearby carbon 13 spins through adequate field manipulations. The molecules with hyperpolarized 13C thus obtained can be used as new contrast agents of high efficiency in MRI. After a brief presentation of the hydrogenation process and apparatus, in relatively low magnetic field, we describe the procedure of order transfer to the 13C spins through a sudden drop from the initial field to zero field followed by an adiabatic remagnetization. The expected final polarizations in the absence of relaxation are given for several compounds. Finally, we show an example of MR images observed in vivo on animals as an illustration of the contrast capacity of this new method.
Subject(s)
Carbon Isotopes , Contrast Media , Magnetic Resonance Imaging , Animals , Guinea PigsABSTRACT
BACKGROUND: Smoking restrictions provide opportunities to modify smoking behavior. A large insurance company implemented a smoke-free grounds policy at two of their office complexes in January, 2000. METHODS: This cohort study evaluated the impact of the smoke-free grounds policy on abstinence among 128 employees who participated in a tobacco dependence treatment program. RESULTS: The overall quit rate at 6 months was 44.5%. The larger complex showed a trend for higher quit rates compared to the smaller complex (46.5 vs. 28.6%). Post-ban participants had higher quit rates than pre-ban participants (52.4 vs. 43.0%). The probability of abstinence at 6 months follow-up was higher for post-ban compared to pre-ban participants (P = 0.03). Post-ban participants were 80% less likely to relapse than pre-ban participants. Non-quitters decreased their consumption by 6.6 cigarettes/day (39.1% decrease). CONCLUSIONS: A "smoke-free grounds" policy encourages abstinence and may play a significant role in harm reduction among continuing tobacco users.
Subject(s)
Occupational Health , Smoking Cessation/methods , Smoking Prevention , Adult , Aged , Confounding Factors, Epidemiologic , Female , Humans , Male , Middle Aged , New Jersey , Proportional Hazards Models , WorkplaceABSTRACT
Mechanical rotation of a sample at 54.7 degrees with respect to the static magnetic field, so-called magic-angle spinning (MAS), is currently a routine procedure in nuclear magnetic resonance (NMR). The technique enhances the spectral resolution by averaging away anisotropic spin interactions thereby producing isotropic-like spectra with resolved chemical shifts and scalar couplings. It should be possible to induce similar effects in a static sample if the direction of the magnetic field is varied, e.g., magic-angle rotation of the B0 field (B0-MAS). Here, this principle is experimentally demonstrated in a static sample of solid hyperpolarized xenon at approximately 3.4 mT. By extension to moderately high fields, it is possible to foresee interesting applications in situations where physical manipulation of the sample is inconvenient or impossible. Such situations are expected to arise in many cases from materials to biomedicine and are particularly relevant to the novel approach of ex situ NMR spectroscopy and imaging.
