Nuclear Magnetic Spin-lattice Relaxation Rate Research Articles

Dynamics of water in and around proteins characterized by 1H-spin-lattice relaxometry

Abstract Nuclear magnetic spin-lattice relaxation rate constants measured as a function of the magnetic field strength over wide ranges of Larmor frequency map the noise spectrum that drives spin relaxation. For water in and around protein systems, the spin relaxation reports on the average local translational mobility at the interface which is reduced by approximately factor of three from the bulk and there is anisotropy induced in the motions caused by the excluded volume created by the presence of the protein. Water also penetrates the protein and relatively few bound water sites provide a strong coupling between the protein dynamics and the water-proton-spin relaxation.

Mapping Oxygen Accessibility to Ribonuclease A Using High-Resolution NMR Relaxation Spectroscopy

Paramagnetic contributions to nuclear magnetic spin-lattice relaxation rate constant induced by freely diffusing molecular oxygen measured at hundreds of different protein proton sites provide a direct means for characterizing the exploration of the protein by oxygen. This report focuses on regions of ribonuclease A where the rate constant enhancements are either quite large or quite small. We find that there are several regions of enhanced oxygen affinity for the protein both on the surface and in interior pockets where sufficient free volume permits. Oxygen has weak associative interactions with a number of surface crevices that are generally between secondary structural elements of the protein fold. Several regions near the surface have higher than expected accessibility to oxygen indicating that structural fluctuations in the protein provide intermolecular access. Oxygen penetrates part of the hydrophobic interior, but affinity does not correlate simply with hydrophobicity indices. Oxygen is excluded from regions of high interior packing density and a few surface sites where x-ray diffraction data have indicated the presence of specific hydration with high occupancy.

Magnetic properties of chains in cuprate superconductors studied by the Luttinger-liquid model

Mapping the one-dimensional Hubbard model into the Luttinger-Tomonaga model, we have calculated the temperature dependencies of the chain copper nuclear magnetic spin-lattice relaxation rate and Knight shift for the normal state of the superconducting materials ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ and ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{4}{\mathrm{O}}_{8}.$ The dynamic spin susceptibility has been obtained by using a bosonization technique and results of the renormalization group analysis for one-dimensional quantum systems. A comparison of our results with experiment shows that the model is able to reproduce the main features of the spin dynamics in both materials.

Magnetic cross-relaxation and chemical exchange between microporous solid and mobile liquid phases

Nuclear magnetic spin-lattice relaxation rates are reported as a function of magnetic field strength, pH, and temperature for water protons in Sephadex gels. The water proton rates report the relaxation profile characteristic of the solid at high pH values. At lower pH values, the relaxation rate is limited by a slow chemical exchange process that makes the relaxation rate independent of magnetic field at low field strengths. In cases where the proton exchange rate does not limit the total relaxation rate, the magnetic field dependence of the relaxation rate is given by a power law of the type R = Aν − B , where B is 0.75 except at pH 11 where the data are better represented with B = 0.5. The exchange events important for the water proton relaxation are represented as a two-stage process in which water within the pores of the gel exchanges protons and magnetization with the solid spin system rapidly compared with the rate at which the water within the pores exchanges with the bulk water phase.

Nuclear magnetic spin-lattice relaxation of water protons caused by metal cage compounds.

The nuclear magnetic spin-lattice relaxation rates of water protons are reported for solutions of manganese(II), copper(II), and chromium(III) cage complexes of the sarcophagine type. As simple aqueous solutions, the complexes are only modest magnetic relaxation agents, presumably because they lack protons on atoms in the first-coordination-sphere protons that are sufficiently labile to mix the large relaxation rate at the metal complex with that of the bulk solvent. The relaxation is approximately modeled using spectral density functions derived for translational diffusion of the interacting dipole moments with the modification that the electron spin relaxation rate is directly included as a contribution to the correlation time. In all cases studied, the electron spin relaxation rate is sufficiently large that it contributes directly to the water-proton spin relaxation process. The poor relaxation efficiency of the cage compound may, however, be improved dramatically by binding the complex to a protein. The efficiency is improved even further if the rotational motion of the protein is reduced drastically by an intermolecular cross-linking reaction. The relaxation efficiency of the cross-linked protein-cage complexes rivals that of the best first-coordination-sphere relaxation agents like [Gd(DTPA)(H2O)]2- and [Gd(DOTA)(H2O)]-.

Proton magnetic relaxation of manganese(II) tetrakis(4-sulfophenyl)porphine ion in water

Water proton nuclear magnetic spin-lattice relaxation rates are reported as a function of magnetic field strength for aqueous solutions of manganese tetrakis(4-sulfophenyl)porphine complexes. The manganese(III) complex displays relaxation that is remarkably independent of temperature at low magnetic field and a magnetic field dependence that is characteristic of the electron spin relaxation rates, making a contribution to the correlation time that dominates the electron-nuclear coupling. The manganese(II) complex is much more effective in relaxing water protons, but the usual models of first coordination sphere and outer-sphere relaxation fail to account for the magnitude and the magnetic field dependence of the relaxation rates. The data suggest that the delocalization of the electron density into the ligand system provides an increase in the effectiveness of what may be called the outer-sphere paths for water proton relaxation.

Nuclear relaxation and molecular motions in liquid trifluoroacetonitrile

1 9F and 14N nuclear magnetic spin-lattice relaxation rates in liquid CF3CN have been measured at 14.1 kG. From 14N relaxation rates, the correlation times of the tumbling motion were directly determined. By separating 19F relaxation rates into terms contributed from the dipolar and the spin-rotational interactions, the correlation times of the spinning motion were also obtained. Spin-rotational relaxation rates were used to estimate the angular momentum correlation times. Gordon’s J diffusion model was found to be appropriate to describe the molecular reorientations of this molecule. Some 13C spin-lattice relaxation rates have also been measured and used to estimate the magnitude of 13C spin-rotational constants and chemical shielding anisotropies.