Deuteron NMR Relaxation Research Articles

Nuclear magnetic resonance relaxation, permittivity, viscosity and ultrasonic velocity measurements in binary mixtures of methanol and tetrahydrofuran

Proton NMR relaxation rates of CD3OH and proton and oxygen-17 NMR relaxation rates of CD317OH with 6, 11.7 and 26.8%17O enrichment have been measured in binary mixtures with deuteriated tetrahydrofuran ([2H]THF) containing 10, 20, 30, 50, 60, 75, 85 and 95 mol% methanol at 288, 298 and 308 K. Deuteron NMR relaxation rates of CH3OD have also been measured in tetrahydrofuran (THF) at the same compositions and temperatures. From the measured proton relaxation rates, the 17O-induced intramolecular proton relaxation rates have been extracted. Using these values, the rotational correlation time (τOH2) of the OH bond of methanol has been determined at various compositions. The variation of τOH2 with composition indicates that the hydrogen bonding (self-association) of methanol begins to break up after the addition of ca. 25 mol%[2H]THF and at >40 mol%[2H]THF the structure breaking of methanol becomes much more pronounced. Negative values of the excess isentropic compressibility (KEs), excess permittivity (IµE), excess viscosity (ηE) and excess volume (VE) of CH3OH–THF mixtures over the whole composition range also indicate strong structure breaking, especially in the range 30–60 mol% THF, where all these excess parameters pass through a minimum. Proton NMR measurements also confirm that structure breaking of CH3OH by THF is stronger at >40 mol% THF. The deuteron and 17O quadrupole coupling constants of methanol in various CH3OD–THF and CD317OH–[2H]THF mixtures have been evaluated and a strong variation of the deuteron quadrupole coupling constant with composition and temperature as compared to that of 17O is observed.

Molecular Reorientation of Methanol in Mixtures with Carbon Tetrachloride

Abstract Proton and oxygen-17 nmr relaxation rates of CD3 17OH as well as deuteron nmr relaxation rates of CH3OD were measured in mixtures with carbon tetrachloride at different compositions and temperatures. By varying the 170-content different contributions to the proton relaxation rate could be separated and from the 17O-H dipolar interaction contribution the correlation time τ2 OH of the OH bond was determined. Using these correlation times the composition dependence of the deuterium and oxygen-17 quadrupole coupling constants of methanol was derived. A strong variation of the coupling constants over the measured composition range is evident

Deuteron NMR Relaxation Studies of Combined Main‐Chain/Side‐Chain Polymers in the Liquid Crystalline and Glassy State

AbstractCombined main‐chain/side‐chain polymers have been studied by deuteron NMR relaxation techniques. Analysis of the various experiments, employing an appropriate relaxation model, provides detailed information about the molecular organization of these systems. From the dynamic point of view, the primary result is the detection and characterization of the dominant molecular motions above and below the glass transition. Molecular order is characterized by unusually high order parameters of the main‐chain mesogens, exceeding those of the side groups considerably. In addition to molecular biaxiality, observed in all mesophases, there is evidence for phase biaxiality in the smectic A phase.

Field dependence of solvent proton and deuteron NMR relaxation rates of the manganese(II) binding site of chloroplast coupling factor 1

The high-affinity Mn(II) binding site of chloroplast coupling factor 1 (CF{sub 1}), the ATP synthase of higher plants, was studied by field-dependent water proton and deuteron NMR spin-lattice relaxation analysis. Magnetic field dependence of the solvent {sup 1}H relaxation rate (R{sub 1}) contains information about the number (q) and the residence lifetime ({tau}{sub m}) of water molecules within the inner coordination sphere of bound Mn(II) and the spectral density function of the magnetic dipole interaction of the water protons and the Mn(II) ion. Chemical analysis of endogenous nucleotides and metals in the purified enzyme revealed about 1.1-1.3 mol of ADP, 0.1-0.2 mol of ATP, and 1.3 mol of Mg(II) per mole of CF{sub 1}; no Mn(II) was detected. The enzyme bound 0.7 molar equiv of Mn(II) in nonlabile sites and at least 1 additional molar equiv of Mn(II) in a labile site. {sup 1}H NMR relaxation studies were conducted on solutions of purified CF{sub 1} and MnCl{sub 2} at binding ratios of 0.47, 0.89, and 1.3 and {sup 1}H Larmor frequencies between 4 and 62 MHz. The Mn(II) site appears to have approximate tetrahedral symmetry with three protein ligands and one exchangeable water ligand. This Mn(II) binding site is filledmore » when the divalent metal concentration exceeds the substrate concentration, and it appears to have an inhibitory effect on ATPase activity.« less

Integral membrane proteins significantly decrease the molecular motion in lipid bilayers: a deuteron NMR relaxation study of membranes containing myelin proteolipid apoprotein.

The influence of the myelin proteolipid apoprotein on lipid chain order and dynamics was studied by 2H NMR of membranes reconstituted with specifically deuterated dimyristoyl phosphatidylcholines. Quadrupolar echo and saturation recovery experiments were fitted by numerical solution of the stochastic Liouville equation, using a model that includes both inter- and intramolecular motions [Meier, P., Ohmes, E. & Kothe, G. (1986) J. Chem. Phys. 85, 3598-3614]. Combined simulations of both the relaxation times and the quadrupolar echo line shapes as a function of pulse spacing allowed unambiguous assignment of the various motional modes and a consistent interpretation of data from lipids labeled on the C-6, C-13, and C-14 positions of the sn-2 chain. In the fluid phase, the protein has little influence on either the chain order or the population of gauche rotational isomers but strongly retards the chain dynamics. For 1-myristoyl-2-[13-2H2] myristoyl-sn-glycero-3-phosphocholine at 35 degrees C, the correlation time for chain fluctuation increases from 20 nsec to 650 nsec and for chain rotation from 10 nsec to 180 nsec, and the gauche isomer lifetime increases from 0.15 nsec to 1.75 nsec, on going from the lipid alone to a recombinant of protein/lipid ratio 0.073 mol/mol. The results are essentially consistent with spin-label ESR studies on the same system [Brophy, P.J., Horvath, L.I. & Marsh, D. (1984) Biochemistry 23, 860-865], when allowance is made for the different time scales of the two spectroscopies.

Hydrosulfide-ion dynamics in cesium and rubidium hydrosulfide: a deuteron nuclear magnetic resonance study

RbSD and CsSD have a multiplicity of solid-state phase transitions involving changes in the degree of order of the SD− ion. Because the deuteron has a nuclear quadrupole moment, the observed NMR spectrum reflects any changes that take place in the deuteron-site symmetry as a result of a phase change. Furthermore, the magnitude of the observed nuclear quadrupole interaction depends on the time average of the electric-field gradient at the deuteron site; this, in general, is a function of any molecular motion in the crystal. The nuclear spin–lattice relaxation times provide information about the time scale of any molecular reorientation taking place in the crystal structure. Deuteron NMR spectra and relaxation times are presented for RbSD and CsSD over the temperature range from 100 to 400 K. The spin–lattice relaxation time data show that there is reorientation of the SD− ion in the tetragonal phase of CsSD and in the trigonal phase of RbSD. While the correlation time for the reorientation changes from being short compared with the reciprocal of the quadrupole interaction to being the same order of magnitude in the temperature range studied, the deuterium NMR line shapes do not change substantially. It is concluded that the observed reorientation of the SD− ion in both RbSD and CsSD in the low-temperature noncubic phases is end-for-end flipping of the SD− ion since only reorientation by 180° leaves the static quadrupole splitting unchanged.

Oxygen-17 and Deuteron NMR Relaxation Study of Dimethyl Sulfoxide—Water Mixture

Oxygen-17 and Deuteron NMR Relaxation Study of Dimethyl Sulfoxide—Water Mixture

A reinvestigation of the hydration numbers of paramagnetic metalloenzymes by proton and deuteron NMR relaxation times

The analysis of the enhancement of water NMR relaxation rates by paramagnetic metal ions bound to macromolecules is reexamined. By measuring T 1 and T 2 for both protons and deuterons in the same solution and at one high magnetic field it is possible to obtain the hydration number, exchange lifetime, and correlation time of the bound water molecules as well as the magnitude of an additional contribution originating from outer-sphere water molecules. For Mn(II) bovine carboxypeptidase A and Mn(II) bovine carbonic anhydrase B, hydration numbers, q, of unity and exchange lifetimes τ M = 1.0 × 10 −7 and 0.75 X 10 −7 sec at room temperature were found for the two enzymes, respectively. The same q and τ M were obtained in independent measurements at different magnetic fields, and τ M was found to be doubled upon reducing the temperature from 25 to 0°C. The outersphere relaxation could not be explained either by spin diffusion from the protein protons or by dipolar interaction between the Mn(II) ion and freely diffusing water molecules. A good account of this contribution could be obtained by a mechanism involving water molecules which are bound outside the first-hydration sphere and have an average exchange lifetime of about 3 × 10 −10 sec.

Proton dynamics and surface heterogeneity of silica gel with adsorbed benzene below one monolayer coveragea)

Proton and deuteron NMR relaxation times of C6H6, C6D6, and mixtures of these molecules have been measured on a superpure silica gel (SPSG) and a sample of a Matheson silica gel (MSG) both dehydrated at 600° C and rotational (intramolecular) and translational (intermolecular) correlation times have been computed from the relaxation time data at a statistical coverage ϑ=0.6. Three kinds of adsorption sites have been observed: (1) A sites, which are probably oxygen vacancies on the surface, (2) B sites which are assigned to paired hydroxyl groups on the surface, and finally (3) C sites which comprise 80% of the occupied surface and are primarily isolated hydroxyl groups. Rotational and translational motions are highly correlated for the A and B site molecules. The mean number of molecules clustered at the A and B sites are inferred from the intermolecular second moments associated with each of these sites. The surface density of the A sites is 1.1×1012 cm−2 for SPSG and 3.1×1012 cm−2 for MSG.

Deuteron NMR relaxation and molecular motion of polystyrene in solution

AbstractDeuteron relaxation times T1 of polystyrenes deuterated at the backbone (PS‐d3) and the phenyl ring (PS‐d5), respectively, have been measured in solutions of benzene and diethyl malonate as a function of concentration and temperature. We conclude that the motion of the phenyl ring is faster than that of the backbone, the difference being smallest at high temperatures around 180°C. The temperatures dependence is discussed in relation to the activation energies in polystyrene.

Electric field gradient at the deuteron site in liquid DCl

The electric field gradient at the deuteron site in DCl has been estimated as 2.0 × 10 17 V/cm 2 using deuteron and chlorine NMR relaxation time measurements in liquid DCl.