A Spin Resonance Investigation of Magnetism and Dynamics in the Charge-transfer Salts β"-(BEDT-TTF)4[(H3O)M(C2O4)3]S

We report a spin resonance study of the family of quasi-two-dimensional organic (super)conductors β”-(BEDT-TTF)₄[(H₃O)M(C₂O₄)₃]S, where M is a 3d transition metal ion and S is a host solvent molecule. The spin systems for M = Cr³⁺ (S = 3/2) and M = Fe³⁺ (S = 5/2) are investigated by means of both resonant and field modulation techniques in the frequency range between 50 and 313 GHz. The role of the different solvent molecules in determining the degree of spin-orbit coupling and the local symmetry at the metal ion site is established. The low temperature behaviour of intensities, positions and widths of the resonant lines shows significant modifications of the spin-orbit coupling, and of the inter-and intra-ionic spin-spin inter actions. Despite the onset of a weak antiferromagnetic internal field at low temperature, the ultimate narrowing of the lines suggests spin-lattice interactions may still be the dominant relaxation process. Diamagnetic screening in the mixed state of the superconducting samples for fields parallel to the quasi-two-dimensional layers induces additional lineshifts only below B = 2.5T and T = 4K, determining the threshold of full field penetration within the anion layers.     

Correlation of thallium uptake with left ventricular wall thickness by cine magnetic resonance imaging in patients with acute and healed myocardial infarcts

Myocardial infarction (MI) is characterized by cellular necrosis which undergoes fibrotic transformation over time. Cine magnetic resonance imaging (MRI) offers high-resolution 3-dimensional images of the left ventricular myocardium, allowing sampling of the myocardial wall thickness over the entire left ventricle. Tomographic (single-photon emission computed tomography [SPECT]) thallium images also provide 3-dimensional information on the location and level of thallium uptake, which has been shown to correlate with myocardial viability. The purposes of this study were: (1) to examine the relation between both end-diastolic and end-systolic wall thickness and normalized thallium-201 uptake over the left ventricle in a group of patients with MI, (2) to examine the relation between regional wall thickening and normalized thallium uptake, and (3) to examine the relation between thallium uptake and wall thickness both early and late after infarction. Twenty-four patients with MI underwent stress, redistribution, and reinjection thallium SPECT imaging and cine MRI within several days. Seventeen patients underwent imaging late after infarction and 7 underwent imaging early after infarction. Normalized thallium activity was correlated with MRI wall thicknesses at both end-diastole and end-systole for 18 segments for each ventricle. In addition, end-diastolic and end-systolic wall thicknesses were grouped by their corresponding thallium activity levels into percentiles. End-systolic wall thickness correlated significantly with normalized thallium uptake in 14 of 18 segments, end-diastolic wall thickness in only 4 of 18 segments, and wall thickening in only 3 of 18 segments. Mean values for end-diastolic and end-systolic wall thicknesses corresponding to severely reduced (<50%) normalized thallium activity were 9.9 +/- 1.1 and 8.5 +/- 0.6, respectively. Using receiver-operating curve analysis, end-systolic wall performed as a better diagnostic parameter than end-diastolic wall for identifying severely reduced thallium activity levels. For all levels of thallium activity, end-diastolic wall thicknesses were all thinner late versus early after MI, whereas end-systolic wall thickness was thinner only in the segments corresponding to severely reduced thallium activity. Based on these results, end-systolic wall thickness is the best noninvasive anatomic parameter of myocardial scar.     

Retention behavior of triglycerides on reverse phase columns using pseudophase liquid chromatography

The use of micellar mobile phases in decreasing the elution time of peanut triglycerides on 10µ reverse phase columns is demonstrated. Both cationic and anionic surfactants were used with “end-capped” and “non-end-capped” reverse phase columns. Surfactants added to both nonaqueous and aqueous organic mobile phases reduced the elution time of all triglyceride peaks when compared to a mobile phase without a surfactant modifier. Sodium dodecyl sulfate (SDS) as the modifier in the mobile phase was the most effective in reducing elution time for triglycerides when an “end-capped” column was used as the stationary medium. Increasing concentrations of surfactant in the mobile phase resulted in corresponding decreases in elution times. A unique feature of micellar phases is that any increase in concentration only alters the concentration of the micelles in the mobile phase. The objective of this study was to investigate the retention behavior of large, non-ionic solute molecules and to elucidate the adsorption mechanism on reverse phase columns.     

Angle-dependent magnetoresistance oscillations and Fermi surface reordering at high magnetic fields is α-(ET)2KHg(SCN)4

Angle dependent magnetoresistance oscillations (AMRO) have been studied in the charge transfer salt α-(ET)₂KHg(SCN)₄ for magnetic fields in the range 0 - 30T. This salt exhibits the onset of antiferromagnetic order at temperatures T_N 8-10 K and the presence below this temperature of a region of sharp negative magnetoresistance at a field around 22 T known as the 'kink'. AMRO have been measured in this salt for a wide range of applied fields since the period, amplitude, and nature of the oscillations can be used to directly infer the character of the Fermi surface (FS) as a function of field. The data indicate that a profound change in the band structure occurs at this kink transition; the high field phase is characterised by quasi-2D oscillations from a closed cylindrical FS which is elongated in the c direction; the low field phase appears to be a spin density wave groundstate, with a FS consisting of a sheet (which is quasi-1D in character and tilted at an angle of 21° to the b^*c plane) and small closed 2D pockets. It is suggested that the breakdown orbits between the pockets and the 1D sheets are able to account for the various Shubnikov-de Haas frequencies observed below the kink.     

The infrared spectra of saturated fatty acids with even number of carbon atoms from caproic,C6 (Hexanoic), to stearic,C18 (Octadecanoic), and of their methyl and ethyl esters

Summary Infrared spectra from 1 to 12 microns have been obtained for 7 of the homologous series of monobasic, straight-chain, saturated fatty acids of even carbon atom content from C₆ to C₁₈ and of their methyl and ethyl esters. Infrared data are presented as plots of the percentage transmission against the wavelength in microns on a linear wavelength scale for each compound, and the exact wavelength positions of maxima of the 11 most prominent bands are tabulated. Correlations of each of these bands with molecular structure are given. Methods for distinguishing the acids from the esters and of differentiating an ethyl ester from a methyl ester by observation of infrared spectra are described. An explanation, supported by earlier work with deuterium-substituted compounds, is given to account for the nonappearance, in the spectra of the fatty acids of any absorption attributable to either the free O—H group or the bonded O—H... O group. Evidence has been accumulated which indicates an association of some sort of the esters and that this association probably involves the carbonyl and the methyl groups. Data are presented to show which of the bands in the infrared spectra do and which do not follow Beer’s law. Presented before the 1950 Fall Meeting of the American Oil Chemists’ Society, San Francisco, California. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

An emulsifier system for experimental intravenous fat emulsions

An emulsifying system for a fat emulsion which has been very satisfactory for intravenous administration to dogs has been developed. The emulsion contained cottonseed oil (15%), polyethylene glycol monopalmitate (1.2%), tartaric acid ester of monoglycerides (0.3%), and polyoxyethylene-polyoxypropylene (0.3%), in isotonic dextrose solution. The polyethylene glycol monopalmitate was isolated from laboratory and commercial esterification reaction mixtures of monoester, diester, and nonreacted polyethylene glycol. Washing with NaCl solution removed nonreacted glycol, and fractionation in acetone separated the mono- and di-esters, the diester separating as a solid. Analytical methods were applied to characterize all fractions, and to determine the reproducibility of composition of successive batches. The monopalmitates from both laboratory and commercial preparations were similar in properties. The tartaric ester of monoglycerides was washed with NaCl solution and fractionated in acetone. The liquid portion was recovered and used for emulsification. Emulsions prepared with the fractionated emulsifiers appear to give satisfactory physiologic results when infused in dogs. This investigation was supported by funds from the Office of the Surgeon General, U. S. Army, Washington, D. C. One of the laboratories of the Southern Utilization Research and Development Division, U. S. Department of Agriculture.     

Modification of vegetable oils

Summary 1. An investigation has been made of low-temperature crystallization from organic solvents as a means of effecting practical separations of the solid and liquid acids of unhydrogenated and hydrogenated cottonseed oils. 2. At any fixed temperature the most efficient separations were obtained in the highly polar solvents, acetone and methyl acetate. However, it was possible in any case to make nonpolar petroleum naphtha (Skellysolve B) fully equivalent to the polar solvents simply by conducting the crystallization at a temperature approximately 10° F. lower than that employed with the polar solvents. Ethyl acetate and methyl ethyl ketone were intermediate between petroleum naphtha and acetone or methyl acetate in their effectiveness. 3. By employing a solvent-fatty acid ratio of 4 to 1 by weight and conducting crystallizations at 5° F. or lower from acetone and −5° F. or lower from petroleum naphtha, the liquid fatty acids from unhydrogenated cottonseed oil could be reduced to below −2° C. in titer and to below about 3 per cent in saturated acid content. Under these conditions there was no appreciable crystallization of oleic acid. 4. At a solvent-fatty acid ratio of 6 to 1 and the same temperatures (5° F. for acetone and − 5° F. for petroleum naphtha) equally good separations could be made of the saturated fatty acids present in the mixed acids from hydrogenated cottonseed oil (I.V.=70). Separation of “iso-oleic” acids from the fatty acids of the hydrogenated oil took place over a wide range of temperatures, beginning at 35° F. in acetone and at 25° F. in petroleum naptha, and being incomplete (according to Twitchell analyses of the liquid acids) in either solvent at −15° F. However, the bulk of the higher melting iso-oleic acids was precipitated as the temperature approached −5° F. in acetone and −15° F. in petroleum naphtha. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Dilatometric investigations of fats

Summary 1. Dilatometric curves betweenca. −38° C. and temperatures representing the liquid state have been determined for a number of pure triglycerides and some commercial fats. 2. From the dilatometric data and density data on the liquid samples, determinations have been made of the density in both the liquid and the solid states, the expansibility of each state with increase in temperature, and the dilation accompanying melting of the samples. From similar comparative data on the three polymorphic forms of tristearin determinations have been made of the volume changes accompanying transformation from one form to another. 3. Certain relationships are pointed out among the various properties of melting point, density, expansibility, melting dilation, specific heat and heat of fusion, and the relation of these properties to chain length and degree of unsaturation in triglycerides is discussed. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.