A carbon-13 nuclear magnetic resonance relaxation study of the reentrant 60CB–80CB

1991 ◽  
Vol 69 (12) ◽  
pp. 1454-1458 ◽  
Author(s):  
J. S. Lewis ◽  
E. Tomchuk ◽  
E. Bock
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Smectic A ◽  
Relaxation Study ◽  
Pairing Model ◽  
Nematic Phases ◽  
Resonance Relaxation ◽  
Experimental Values

The carbon-13 spin-lattice relaxation times of the protonated ring carbons of octyloxycyanobiphenyl (80CB) in a 26 wt.% mixture of perdeuterated hexyloxycyanobiphenyl (60CB–d21) in 80CB are measured as a function of temperature at 22.63 MHz in the nematic (N), smectic A(SA), and reentrant nematic (RN) phases. The deuterium spectral densities of the ring deuterons of 60CB–d21 in the same sample were studied previously, and the diffusion coefficients [Formula: see text] and [Formula: see text] found in that study are used to calculate the theoretical carbon-13 relaxation times of the protonated ring carbons of 60CB. The general agreement of the theoretical values for 60CB with the experimental values for 80CB demonstrates that the two constituent molecules of the reentrant have similar motions. Small differences, similar in nature to those encountered in other studies of this interesting reentrant, however, do exist in the nematic and reentrant nematic phases and are discussed in terms of the molecular pairing model proposed by Cladis. (Phys. Rev. Lett. 35, 48 (1975).)

A133Cs NMR Spin-Lattice Relaxation Study in Incommensurate Cs2CdI4

2000 ◽  
Vol 55 (1-2) ◽  
pp. 339-342 ◽  
Author(s):  
Koh-ichi Suzuki ◽  
Shin'ichi Ishimaru ◽  
Ryuichi Ikeda
Keyword(s):  
Critical Exponent ◽  
Relaxation Times ◽  
Three Dimensional ◽  
Lattice Relaxation ◽  
Normal Phase ◽  
Incommensurate Phase ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Relaxation Study ◽  
Good Agreement

133Cs NMR spin-lattice relaxation times(T1) in crystalline Cs2CdI4 were measured at 225 - 373 K. The critical exponent ( of T\ observed near the normal-incommensurate transition in the normal phase was determined to be 0.62 ± 0.03, in good agreement with the predicted value for three-dimensional XK-model. The frequency dependent T1 in the incommensurate phase could be explained by the fluctuation of amplitudon and small gap phason.

A proton magnetic resonance relaxation study of molecular motions in trimethylamine-borane

1976 ◽  
Vol 54 (7) ◽  
pp. 1087-1091 ◽  
Author(s):  
T. T. Ang ◽  
B. A. Dunell
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Solid Phase ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Free Induction ◽  
Resonance Spin ◽  
Resonance Relaxation

Proton magnetic resonance spin–lattice relaxation times T1 have been measured for trimethylamine-borane from 120 to 380 K, a few degrees above the melting point. Minima in T1 at 157 and 259 K are attributed to threefold reorientation of each of the three methyl groups and the borane group and to threefold reorientation of the whole molecule about the B—N axis, respectively. Activation energies for these processes were found to be 3.3 and 6.7 kcal/mol. Abrupt changes in T1 at 350 and 360 K correspond exactly with heat capacity transitions observed by other workers. The time constant for the decay of the free induction signal (FID curve) changes by two orders of magnitude at 360 K. Having a value of some 3 ms above 360 K, it shows that there must be rapid diffusion as well as molecular tumbling in the highest temperature solid phase.

14N Nuclear Magnetic Resonance Relaxation of the Nitrate Ion and Ion Pairing in Aqueous Solution

1995 ◽  
Vol 48 (2) ◽  
pp. 207 ◽  
Author(s):  
G Owens ◽  
P Guarilloff ◽  
BJ Steel ◽  
T Kurucsev
Keyword(s):  
Aqueous Solution ◽  
Ion Pairs ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Metal Nitrate ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Fast Exchange ◽  
Resonance Relaxation ◽  
Two State Model

14 N n.m.r. spin-lattice relaxation times of four metal nitrate salts were measured as a function of concentration in aqueous solution. The concentration dependence of T1 was attributed to the formation of ion pairs with increasing concentration in these solutions. The T1 data, allowing for viscosity corrections, were treated by a two-state model of 'free' and 'bound' nitrate ions and to both possibilities of slow and fast exchange between the two states. In the equilibrium expressions estimates of the relevant activity coefficients were included. The slow nitrate exchange mechanism was favoured and the values obtained for this particular mechanism compared well with those derived from alternative measurements.

A proton relaxation study of the conformations of some purine mononucleotides in aqueous solution

1982 ◽  
Vol 60 (23) ◽  
pp. 2976-2983 ◽  
Author(s):  
C. F. G. C. Geraldes ◽  
H. Santos ◽  
A. V. Xavier
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Proton Relaxation ◽  
Spin Lattice ◽  
Population Distributions ◽  
Anti Conformation ◽  
Relaxation Study ◽  
Interproton Distances

A method is described by which conformationally averaged interproton distances in mononucleotides are obtained from measured proton spin-lattice relaxation times and published crystal coordinates of selected mononucleotides. The glycosil conformations of adenosine in D2O and DMSO-d6 and of 5′-AMP, 5′-GMP, 3′-AMP, and 2′-AMP in D2O are examined by quantitative analysis of the conformationally averaged interproton distances in terms of population distributions obtained from potential energy calculations. 5′-AMP strongly prefers a single glycosyl conformation in the anti range. Besides the anti conformation, 5′-GMP has a secondary minimum in the syn region. 3′-AMP, 2′-AMP, and adenosine have more latitude in their glycosyl torsion angle values, with both the syn and anti regions highly populated.

Proton spin–lattice relaxation study of a partial bilayer smectic A phase

1988 ◽  
Vol 3 (6-7) ◽  
pp. 937-945 ◽  
Author(s):  
A. C. Ribeiro ◽  
P. J. Sebastião ◽  
M. Vilfan
Keyword(s):  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Smectic A ◽  
Smectic A Phase ◽  
Relaxation Study

scholarly journals Permeation of small molecules into the cavity of ferritin as revealed by proton nuclear magnetic resonance relaxation

1995 ◽  
Vol 307 (1) ◽  
pp. 253-256 ◽  
Author(s):  
D Yang ◽  
K Nagayama
Keyword(s):  
Relaxation Times ◽  
Nmr Relaxation ◽  
Maximum Size ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Proton Nuclear Magnetic Resonance ◽  
Ferric Ions ◽  
Spin Lattice ◽  
Resonance Relaxation ◽  
Pass Through

The NMR relaxation technique was used to investigate the permeation of molecules into the cavity of ferritin. Spin-lattice relaxation times in the rotating frame of various probe molecules were measured for solutions of recombinant horse L-apoferritin without iron and horse spleen apoferritin with very small amounts of ferric ions. The results show that molecules larger than the size of the ferritin channels can pass through the channels into the ferritin interior, and that the maximum size of molecules for the permeation is smaller than maltotriose.

Deuteron Relaxation Study of the Reorienting Methyl Groups in p-Azoxyanisole

1974 ◽  
Vol 52 (12) ◽  
pp. 2294-2295 ◽  
Author(s):  
M. Wiszniewska ◽  
Ronald Y. Dong ◽  
E. Tomchuk ◽  
E. Bock
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Quadrupole Coupling Constant ◽  
Spin Lattice Relaxation ◽  
Isotropic Phase ◽  
Coupling Constant ◽  
Spin Lattice ◽  
Quadrupole Coupling ◽  
Relaxation Study ◽  
Deuteron Spin

The deuteron spin-lattice relaxation times were measured in the nematic and isotropic phases of p-azoxyanisole(CD3)2. An apparent activation energy for the methyl group reorientation in the isotropic phase is obtained. The quadrupole coupling constant along the C—D bond is found to be 147 ± 8 kHz.

Nuclear magnetic resonance relaxation and anisotropic reorientation in liquid dimethylmercury

1977 ◽  
Vol 55 (8) ◽  
pp. 1303-1313 ◽  
Author(s):  
Claude R. Lassigne ◽  
E. J. Wells
Keyword(s):  
Molecular Diffusion ◽  
Symmetry Axis ◽  
Chemical Shift Anisotropy ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Rotation ◽  
Spin Lattice Relaxation ◽  
Methyl Group ◽  
Spin Lattice ◽  
Resonance Relaxation

Spin–lattice relaxation times of 1H, D, and 199Hg have been measured between 234 and 333 K in liquid dimethylmercury and its isotopic modifications. These measurements have allowed the relaxation mechanisms to be separated. It was found that the spin–rotation interaction is the dominating mechanism for the 199Hg relaxation at 14.1 kG even at low temperatures. We have estimated the spin–rotation constants, [Formula: see text] along with the chemical shift anisotropy [Formula: see text]It is concluded that reorientation about the symmetry axis is not well described by molecular diffusion. Reorientation of the methyl group about its symmetry axis is found to be approximately forty times faster than the reorientation about the perpendicular axis.

A Proton Spin–Lattice Relaxation Study of Molecular Motion in Several Addition Complexes of Trimethylamine and Trimethylphosphine

1974 ◽  
Vol 52 (10) ◽  
pp. 1840-1847 ◽  
Author(s):  
T. T. Ang ◽  
B. A. Dunell
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Methyl Groups ◽  
Threefold Axis ◽  
Spin Lattice ◽  
Relaxation Study ◽  
Boron Tribromide ◽  
Thermal Stability Of

The spin–lattice relaxation times of the solid complexes of trimethylamine with I2, ICl, Br2, BCl3, and BBr3 and the relaxation null times of trimethylphosphine – boron trichloride and – boron tribromide have been measured over a range of temperature by pulsed proton magnetic resonance. A minimum in T1 corresponding to reorientation of the methyl groups about the C—N bonds is observed in each complex, although in the case of Me3, NBr2 the minimum corresponds to a combination of methyl group reorientation and reorientation of the whole Me3N moiety. The complexes with the boron trihalides show a second minimum in T1. These minima have been analyzed in terms of either of two possible motions, reorientation of NMe3 about its threefold axis, or that same motion combined with isotropic molecular tumbling. We favor the interpretation involving the simpler motion. Activation energies have been measured for all the motions. The barriers to reorientation of methyl groups about the C—N bond in the moiety Me3N appear to increase as the thermal stability of the complex decreases.

Mercury-199 nuclear magnetic resonance relaxation in some mercury(II) compounds

1982 ◽  
Vol 60 (16) ◽  
pp. 2113-2117 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Robert E. Lenkinski ◽  
Charles Rodger
Keyword(s):  
Nuclear Magnetic Resonance ◽  
High Field ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Nuclear Magnetic Resonance Relaxation ◽  
Chemical Shielding ◽  
Nmr Studies ◽  
Spin Lattice ◽  
Resonance Relaxation

Mercury-199 spin-lattice relaxation times are reported for several mercury(II) compounds at 5.875 and 9.40 T. From the field dependence of T1, in Hg(CN)2, Hg(CH3)2, and Hg(C6H5)2, 199Hg chemical shielding anisotropies of 3800, 5820, and 5800 ppm are calculated. The errors in these of estimates of Δσ are at least 10%. Some implications of the large Δσ(199Hg) values in high field nmr studies are discussed.

Sign in / Sign up

Export Citation Format

Share Document