Different degrees of hydration in water–oil microemulsions by low-resolution 1H magnetic relaxation analysis

1990 ◽  
Vol 68 (9) ◽  
pp. 1041-1048 ◽  
Author(s):  
Donatella Senatra ◽  
Laura Lendinara ◽  
M. Grazia Giri
Keyword(s):  
Magnetic Relaxation ◽  
Free Water ◽  
Water Concentration ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Exponential Functions ◽  
Scanning Calorimetry ◽  
Experimental Conditions ◽  
Spin Lattice ◽  
Relaxation Curves

The purpose of the research was to establish whether the water configurations, detected by previous differential scanning calorimetry (DSC) analysis, could give rise to different or characteristic nuclear magnetic resonance relaxations. We report the results of a study on water–hexadecane microemulsions at different water contents. The 1H spin–spin and spin–lattice relaxation curves were obtained at 20 MHz and 310 K. The trends of all best-fit relaxation parameters versus water concentration were compared with those obtained for D2O microemulsions with the same experimental conditions and fitting procedures. Two different H2O microemulsion "states" were identified: (i) all the systems without "free water" (defined by DSC as water melting at 273 K) were characterized by 1H spin–spin and spin–lattice relaxation curves well described by two exponential functions and (ii) all the systems with free water were characterized by relaxation curves well described by three exponential functions. The identification of the main phases of the microemulsions interphasal region and continuous medium, besides free water, seems possible on the basis of the 1H magnetic relaxation characteristics.

Phase transitions in solid cycloheptene

1990 ◽  
Vol 68 (4) ◽  
pp. 604-611 ◽  
Author(s):  
Julian Haines ◽  
D. F. R. Gilson
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
Low Temperature Phase

The phase transition behaviour of cycloheptene has been investigated by differential scanning calorimetry, proton spin-lattice relaxation, and vibrational spectroscopy (infrared and Raman). Two solid–solid phase transitions were observed, at 154 and 210 K, with transition enthalpies and entropies of 5.28 and 0.71 kJ mol−1 and 34.3 and 3.4 JK−1, respectively. Cycloheptene melted at 217 K with an entropy of melting of 4.5 JK−1 mol−1. The bands in the vibrational spectra of the two high temperature phases were broad and featureless, characteristic of highly disordered phases. The presence of other conformers, in addition to the chair form, was indicated from bands in the spectra. The ring inversion mode was highly phase dependent and exhibited soft mode type behaviour prior to the transition from the low temperature phase. The low frequency Raman spectra (external modes) of these phases indicated that the molecules are undergoing isotropic reorientation. In the low temperature phase, the vibrational bands were narrow; the splitting of the fundamentals into two components and the presence of nine external modes are consistent with unit cell symmetry of either C2 or Cs with two molecules per primitive unit cell. A glassy state can be produced from the intermediate phase and the vibrational spectra were very similar to those of the high temperature phases, indicating that static disorder was present. The barriers to reorientation, as obtained from proton spin-lattice relaxation measurements, are 9.0 kJ mol−1 in both the high temperature phases, and 15.4 kJ mol−1 in the low temperature, ordered phase. Keywords: cycloheptene, phase transition, differential scanning calorimetry, NMR, vibrational spectroscopy.

Molecular Reorientation in the Plastic Crystalline Phase of Tris

1979 ◽  
Vol 32 (4) ◽  
pp. 905 ◽  
Author(s):  
RE Wasylishen ◽  
PF Barron ◽  
DM Doddrell
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Molecular Reorientation ◽  
Liquid Phase Transition ◽  
X Ray ◽  
Spin Lattice

Carbon-13 N.M.R. spectra of tris(hydroxymethyl)aminomethane (Tris) have been measured between 407 and 461 K. Proton-decoupled 13C N.M.R. spectra of solid Tris between 407 K and its melting point are relatively sharp (v� < 30 Hz) indicating rapid overall molecular reorientation in this temperature range. It was not possible to detect a 13C N.M.R, signal for Tris below 407 K. The observed 13C N.M.R. spin-lattice relaxation times appear continuous across the solid ↔ liquid phase transition. From the temperature dependence of T1, a rotational activation energy of 51.6 � 6 kJ mol-1 is calculated, which indicates that the molecules must expend considerable energy in reorienting. The N.M.R. results are discussed in relation to previous differential scanning calorimetry and X-ray diffraction data which indicate that Tris undergoes a solid ↔ solid transition at 407 K.

Synthesis of sugar-organometallic conjugales: ferrocenyl monosaccharide derivatives

1980 ◽  
Vol 58 (12) ◽  
pp. 1188-1197 ◽  
Author(s):  
Michael J. Adam ◽  
Laurance D. Hall
Keyword(s):  
Group Technology ◽  
Chemical Shifts ◽  
Soluble Sugar ◽  
Free Water ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Water Soluble ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Spin Lattice

Suitably blocked carbohydrates containing free thio 4, amino 5, and hydroxyl 10, 19 nucleophilic functionalities have been treated with (a) ferrocenecarbonyl chlorides 2 and 3, (b) N,N-dimethylaminomethylferrocene methiodide 12, and (c) ferrocenyl tosylate 16 to form the ferrocenyl sugar derivatives 6, 7, 8, 9, 11, 13, 14, 15, and 20. Direct conjugation of a free, water-soluble sugar to ferrocene was achieved by the formation of a Schiff's base between glucosamine hydrochloride 25 and ferrocene carboxaldehyde 24. The synthesis of ferrocenyl sugars using bridging group technology is exemplified by the conjugation of the thio sugar 4 to ferrocene via the versatile coupling reagent cyanuric chloride 21 to form the s-triazine compound 23. These products have been studied by 1H nmr spectroscopy: chemical shifts, coupling constants, and proton spin–lattice relaxation measurements.

Structural Phase Transitions and Ionic Motions in Pyridinium Hexachlorotellurate(IV),Hexachlorostannate(IV), and Hexabromostannate(IV) Crystals as Studied by 1H NMR

1989 ◽  
Vol 44 (4) ◽  
pp. 300-306 ◽  
Author(s):  
Yutaka Tai ◽  
Tetsuo Asaji ◽  
Ryuichi Ikeda ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
H Nmr

Abstract The 1H NMR second moment M2 and the spin-lattice relaxation time T1 are determined for pyridinium hexachlorotellurate(IV), hexachlorostannate(IV), and hexabromostannate(IV) at various temperatures above ca. 140 K. The phase transition temperatures already reported from halogen NQR experiments are determined as 272, 331, and 285 K, respectively, by differential thermal analysis (DTA). The DTA as well as differential scanning calorimetry measurements show that the above phase transitions are of second-order. For pyridinium hexachlorotellurate(IV) and hexa-bromostannate(I V), a sharp 1H T1 dip was observed at the transition temperature. This is interpreted in terms of a phenomenon related to the critical fluctuation of an order parameter. From the measurements of 1H M2, 60° two-site jumps (60° flips) around the pseudo C6 axis of the cation are suggested to occur in the high temperature phases of the complexes. Modulation of X...1H (X = CI, Br) magnetic dipolar interactions due to the reorientational motion of the complex anions is considered as a possible relaxation mechanism in the high temperature phases.

A Discussion on Magnetic Relaxation - Resonance and relaxation in cobalt-doped magnesium oxide

1965 ◽  
Vol 283 (1395) ◽  
pp. 433-444 ◽  
Keyword(s):  
Magnesium Oxide ◽  
Magnetic Relaxation ◽  
Energy Levels ◽  
Lattice Relaxation ◽  
Orbit Interaction ◽  
Spin Lattice Relaxation ◽  
Spin Orbit ◽  
Spin Lattice ◽  
Relaxation Resonance ◽  
Quantitative Calculations

The work I want to describe was started in Bristol in 1959. The purpose was to test theories of spin-lattice relaxation on a system where one could make reasonably quantitative calculations. For this it seemed desirable to study as many aspects of the magnetic properties of one particular system as possible, and to do this both experimentally and theoretically at the same time. The system we chose was cobalt-doped magnesium oxide. This requires some explanation, as at first sight it does not appear to be a particularly simple system. Figure 1 shows how the energy levels of the free cobaltous ion are modified by the crystal field in MgO. The Co 2+ substitutes for Mg 2+ and is surrounded by a regular octahedraon of O 2– ions. The 4 F level splits into three, and these are further split by spin-orbit interaction. The important point is that the lowest level is a Kramers doublet.

scholarly journals Phase Transitions and Molecular Reorientations in Bilayered n-Heptadecylammonium Chloride

1998 ◽  
Vol 51 (3) ◽  
pp. 557 ◽  
Author(s):  
E. C. Reynhardt
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
Heating And Cooling ◽  
Α Phase ◽  
Monium Chloride

An investigation of phase transitions and molecular motions in polycrystalline n-heptadecylam- monium chloride (C17H35NH3Cl), employing differential scanning calorimetry, x-ray powder diffraction and nuclear magnetic resonance techniques, is reported. This compound can occur in two virgin polymorphs at room temperature, one interdigitated and one noninterdigitated. The temperature at which crystallisation occurs determines the polymorph that forms. If these polymorphs are heated transitions to noninterdigitated γ, β and α phases occur. Cooling to room temperature shows the same phase transitions, but the virgin phase is not formed. Instead, a noninterdigitated .epsi; phase is formed. Defect motions of chain-ends play a significant role in the spin-lattice relaxation rates in all the phases. In the α phase a degree of chain melting is present. The molecular dynamics of chains differs during heating and cooling cycles in the .epsi; phase. If the temperature is kept constant during a heating cycle in this phase, fourfold motions of chains are frozen over a period of several hours, but the sample remains noninterdigitated. It seems that the interdigitation process is hampered by the population of defect orientations of chain-ends. The methyl group executes classical threefold reorientations and the NH3 group jumps in an asymmetric threefold potential well.

scholarly journals Spin-lattice Relaxation Rates of Os and Other 5d Elements in Fe

1998 ◽  
Vol 51 (2) ◽  
pp. 281 ◽  
Author(s):  
E. Beck ◽  
W. D. Brewer ◽  
T. Funk ◽  
C. Bobek ◽  
E. Klein
Keyword(s):  
Thermal Cycling ◽  
Nuclear Spin ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Spin Lattice ◽  
Nuclear Spin Lattice Relaxation ◽  
Relaxation Curves ◽  
Comparison Of The Results

We give final results for the nuclear spin-lattice relaxation (SLR) rates of 5d series elements as dilute impurities in iron using the method of thermal cycling on oriented nuclei. In this report, we emphasise some aspects of the analysis of the relaxation curves, especially for Os and Au impurities. A comparison of the results with theory is given.

scholarly journals Order–disorder transitions in adamantane derivatives: vibrational spectroscopic and 13C NMR studies of 1-chloroadamantane

1993 ◽  
Vol 71 (11) ◽  
pp. 1890-1897 ◽  
Author(s):  
Yining Huang ◽  
Ralph M. Paroli ◽  
D.F.R. Gilson ◽  
I.S. Butler
Keyword(s):  
Variable Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Adamantane Derivatives ◽  
Scanning Calorimetry ◽  
Nmr Studies ◽  
Spin Lattice ◽  
Two Phases ◽  
C Nmr

The order–disorder behaviour of 1-chloroadamantane (1-C10H15Cl) has been investigated by differential scanning calorimetry, and variable-temperature vibrational and 13C NMR spectroscopy. The factor group splittings in the vibrational spectra are in accord with the known crystal structures of the two phases. The 13C spin-lattice relaxation times and dipolar dephasing measurements have been analysed to give the barriers to rotation in both phases and to determine the nature of the rotations in each phase. In the ordered phase, the motion is limited to rotation about the molecular axis. In the disordered phase, additional motions occur about axes through the tertiary carbon atoms.

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