Dipole Dipole Coupling
Mostrando 13-24 de 31 artigos, teses e dissertações.
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13. Attenuated T2 relaxation by mutual cancellation of dipole–dipole coupling and chemical shift anisotropy indicates an avenue to NMR structures of very large biological macromolecules in solution
Fast transverse relaxation of 1H, 15N, and 13C by dipole-dipole coupling (DD) and chemical shift anisotropy (CSA) modulated by rotational molecular motions has a dominant impact on the size limit for biomacromolecular structures that can be studied by NMR spectroscopy in solution. Transverse relaxation-optimized spectroscopy (TROSY) is an approach for suppre
The National Academy of Sciences of the USA.
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14. Magnetic Dipole-Dipole Coupled Cu(II) Pairs in Nitric Oxide-Treated Tyrosinase: A Structural Relationship Between the Active Sites of Tyrosinase and Hemocyanin
The Tr and T[unk] states of tyrosinase were treated with NO. EPR spectra of the products observed at 14°K and at 113°K showed mixtures of two signals. One had components in the region of g = 2, about 1200 G wide, and in the region of g = 4, showing hyperfine splitting. The other signal was similar to that arising from isolated Cu(II) ions in an axially sym
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15. Direct observation of dipolar couplings between distant protons in weakly aligned nucleic acids
Under conditions where macromolecules are aligned very weakly with respect to an external magnetic field, Brownian diffusion no longer averages internuclear dipole–dipole interactions to zero. The resulting residual dipolar coupling, although typically 3 orders of magnitude weaker than in a fully aligned sample, can readily be measured by solution NMR meth
National Academy of Sciences.
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16. Magnetic order and energetics of dipolar coupling in magnetic superconductors
The exact (not just nearest-neighbor) dipolar coupling energy densities for the observed structures of the rare earth Chevrel compounds are calculated by the method of Luttinger and Tisza. The dipolar coupling energy density for the most probable spin configuration is comparable to the observed magnetic transition temperature, TM, but the most probable groun
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17. Fretting about FRET: Failure of the Ideal Dipole Approximation
With recent growth in the use of fluorescence-detected resonance energy transfer (FRET), it is being applied to complex systems in modern and diverse ways where it is not always clear that the common approximations required for analysis are applicable. For instance, the ideal dipole approximation (IDA), which is implicit in the Förster equation, is known to
The Biophysical Society.
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18. The origin of vibrational mode couplings in various secondary structural motifs of polypeptides
Electrostatic (through-space) and covalent (through-bond) contributions to couplings involving the CO and C—N vibrational stretching modes of the amide group in the α-helix and the parallel and antiparallel β-sheet structures of alanine polypeptides are analyzed. Coupling constants computed at the density functional theory level are compared with the tra
National Academy of Sciences.
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19. 31P nuclear magnetic relaxation studies of phosphocreatine in intact muscle: determination of intracellular free magnesium.
31P nuclear magnetic relaxation rates for phosphocreatine in intact frog gastrocnemius were compared with those observed in model solutions at 4 degrees, a temperature at which muscle maintains its physiological state for at least 5 hr. Both nuclear Overhauser effect and spin-lattice relaxation rate (1/T1) experiments indicate that dipole-dipole interactions
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20. Oriented properties of the chlorophylls: Electronic absorption spectroscopy of orthorhombic pyrochlorophyllide a-apomyoglobin single crystals
The orientations of the transition dipole moments in chlorophyll (Chl) are among the most useful spectroscopic properties for determining macromolecular architecture in photosynthetic complexes; however, the relationships between these orientations and the Chl molecular geometry are unknown. In order to solve this problem, we have prepared single crystals of
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21. Interaction of ubisemiquinone with a paramagnetic component in heart tissue.
The origin of most of the electron paramagnetic resonances obtained at low temperature and low microwave power from heart tissue and subcellular fractions derived therefrom is now understood. A signal that emerges on partial reduction with characteristic lines at 3227 G (0.3227 tesla) and 3309 G (0.3309 tesla) (at 9.2 GHz) and disappears again on full reduct
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22. Polarization transfer by cross-correlated relaxation in solution NMR with very large molecules
In common multidimensional NMR experiments for studies of biological macromolecules in solution, magnetization transfers via spin–spin couplings [insensitive nuclei enhanced by polarization transfer (INEPT)] are key elements of the pulse schemes. For molecular weights beyond 100,000, transverse relaxation during the transfer time may become a limiting fact
The National Academy of Sciences.
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23. Coherent infrared multidimensional spectra of the OH stretching band in liquid water simulated by direct nonlinear exciton propagation
The two-dimensional vibrational response of the disordered strongly fluctuating OH exciton band in liquid water is investigated using a new simulation protocol. The direct nonlinear exciton propagation generalizes the nonlinear exciton equations to include nonadiabatic time dependent Hamiltonian and transition dipole fluctuations. The excitonic picture is re
American Institute of Physics.
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24. Role of backbone solvation and electrostatics in generating preferred peptide backbone conformations: Distributions of phi
The “coil library,” consisting of the φ, ψ values of residues outside secondary structure in high-resolution protein structures, has chiefly the β, αR, αL, and polyproline II backbone conformations. In denatured proteins, the 20 aa have different average values of the 3JHNα coupling constant, related to the backbone angle φ by the Karplus relation
The National Academy of Sciences.