Kenneth W. Jolley

Diffusion of fat and water in cheese as studied by pulsed field gradient nuclear magnetic resonance

Abstract Pulsed field gradient nuclear magnetic resonance was used to measure water and fat self-diffusion coefficients in Cheddar and Swiss cheeses. The water diffusion coefficients are about one-sixth that of bulk water at the same temperature and there is strong evidence to suggest that water diffusion is confined to surfaces within the protein matrix. The echo attenuation for the fat indicates restricted diffusion consistent with the fat being present in the form of small droplets within the cheese. The theory of restricted diffusion has been extended to allow for a spread of droplet size. The data conform to a gaussian distribution of molecular numbers (sphere volume) over droplet radius. A small attenuation approximation is used in the theory but consistent values of droplet radii and standard deviations in droplet size are obtained over a large echo attenuation range.

Nuclear magnetic resonance studies of wheat starch pastes

Nuclear magnetic resonance measurements have been made on wheat starch pastes with contrasting rheological properties. Carbon-13 measurements indicate that about 60% of the polysaccharide in the pastes exists as mobile liquid-like polymer while the remaining 40% is in an immobile crystalline form. The ratio of mobile to crystalline polymer is the same for all pastes. Proton (1H) relaxation measurements show that in contrast to other gel systems the observed water relaxation times are not related to rheological properties and are governed by exchange between bulk and mobile polymer-associated water. Exchange at crystalline polymer sites is either nonexistent or too slow to be of significance on the NMR time scale. Measurements have also been made of water diffusion coefficients for pastes and for amylopectin-water systems. The modified Wang equation when fitted to the diffusion data gives shape factors that are consistent with an oblate ellipsoidal shape for the amylopectin molecule in solution.

A pulsed field gradient system for a fourier transform spectrometer

Abstract The construction and performance of a pulsed field gradient system for use with a commercial high-resolution pulse-Fourier transform NMR spectrometer is described. The diffusion coefficient of benzene as measured by the system lies within 0.9% of the current literature value. The use of an external 2 H lock in conjunction with signal averaging facilitates the measurement of diffusion coefficients for solution components present in small concentrations and data are presented for a 0.5% (w/v) solution of polystyrene ( M r = 110,000) in carbon tetrachloride. The ability of the system to investigate slow diffusion is demonstrated by measurements made on a 10% (w/v) solution of polystyrene ( M r = 230,000) in carbon tetrachloride. Homogeneity coils in the 1 H probe enable the self-diffusion of single components in multicomponent systems to be investigated, and results for the binary system butanol-benzene are presented.

31P-NMR studies of bovine β-casein

Abstract Highly resolved 31P nuclear magnetic resonance spectra of the phosphoprotein bovine β-casein and one of its phosphopeptides (residues 1–25) have been obtained with samples treated to remove paramagnetic metal ions. Spin-lattice (T1) and spin-spin (T2) relaxation times indicate little or no restriction to the segmental motion in the phosphoserine cluster region for both β-casein and its phosphopeptide. The spectrum Of β-casein consists of four peaks over the pH range 5.7–8.0. The low-field peak has been assigned to Ser(P)-35 by comparison of the β-casein and the phosphopeptide spectra. Interpretation of the NMR titration curves of 31P chemical shifts against pH in terms of a simple proton dissociation model is unsatisfactory. A two-site model in which it is assumed that the ionization of a phosphoserine residue is affected by the ionization of neighbouring residues gives excellent fits to the titration data. The phosphoserine cluster residues (residues 15–19) have been assigned according to this interactive model.

Nematic–lamellar tricritical behavior and structure of the lamellar phase in the ammonium pentadecafluorooctanoate (APFO)/water system

2H NMR spectroscopy has been used to map a high‐resolution (±0.04 K) phase diagram for the ammonium pentadecafluorooctanoate(APFO)/heavy water system. It is qualitatively similar to that for the CsPFO/heavy water system. In particular, it exhibits a discotic micellar nematic phase N+D intermediate to an isotropic micellar solution phase I and a lamellar phase for weight fractions of APFO between 0.395 (φ=0.278) and 0.589 (φ=0.455) and temperatures between 292.10 and 338.10 K. The N+D to lamellar transition crosses over from second to first order behavior at a tricritical point similar to the superfluid transition in 3He/4He mixtures. X‐ray scattering experiments shows there to be no dramatic change in the structure of the micelle at the I to N+D and the N+D to lamellar transitions. Nematic order parameters (orientational order parameters of the discoidal micelles) have been calculated from electrical conductivity measurements. Their variation with temperature in the nematic phase and across the nematic to...

Sample cell for high-precision temperature-dependence NMR experiments

Abstract A simple sample temperature control system is described which minimizes temperature gradients and provides for accurate and precise control of sample temperature. The sample is confined in a standard 5 mm o.d. NMR tube, supported in a standard 10 mm o.d. tube, through which a fluid, whose temperature is regulated in an external thermostat, is rapidly circulated by way of a double-pass liquid-flow arrangement. The device can be readily used in any standard 10 mm NMR probe. When water is used as the cryogenic fluid, sample temperatures in the range 273 to 370 K, with an accuracy, precision, and resolution (settability) of ±0.005 K, are accessable. We have extensively used the system to study phase transitions and phase behavior of liquid crystals, although many other applications may be envisaged. Herein, the performance characteristics of the device are demonstrated by 2H and 133Cs experiments on the cesium pentadecafluorooctanoate (CsPFO)/water liquid-crystal system.

Anomalous effects in experiments on monodomain nematic and lamellar phases of the caesium pentadecafluorooctanoate(CsPFO)/water system

Abstract The effects of defects on a variety of experiments on monodomain nematic and lamellar phases of the CsPFO/water system are described. In NMR experiments the observed anomalous behaviour depends on whether the sample tube is oriented with its long axis perpendicular or parallel to the direction of the applied magnetic field. In the former case, focal domains are shown to lead to a distortion of the spectra on heating, but not on cooling the sample; whereas, in the latter case, dislocations (possibly of the edge variety) are generated on cooling and focal domains on heating. Similar defects can lead to anomalous effects in measurements of bulk properties such as the electrical conductivity, as demonstrated here. In density measurements on unoriented samples using a vibrating capillary densitometer, anomalous decreases in density are observed at the isotropic-to-nematic and nematic-to-lamellar phase transitions. These anomalies are absent in density measurements using a classical dilatometer.

Location of the discotic lamellar-nematic tricritical point and isotope effects in the caesium pentadecafluorooctanoate (CsPFO)/water system as established by 133 Cs N.M.R. spectroscopy

Abstract 133Cs N.M.R. spectroscopy has been used to locate the discotic lamellar (smectic A)-nematic tricritical point in the CsPFO/H2O and CsPFO/2H2O systems. In both systems this occurs at the same volume fraction of 0·25, but at different temperatures (302·05 and 304·80 K, respectively). The phase diagram for the CsPFO/H2O system has also been studied for the first time and a comparison of the corresponding fixed points shows there to be large isotope effects.

Towards functionalized poly(terthiophenes): regioselective synthesis of oligoether-substituted bis(styryl)sexithiophenes

A variety of new bis(oligo(oxyethylene)styryl)sexithiophenes have been prepared by chemical oxidation of ether-substituted styrylterthiophenes with FeCl3. In all cases dimers are formed in high yields, rather than the expected polymers. In addition, although three different regioisomers can potentially be formed from such an oxidation, the isolable products are shown to consist of only the head-to-head regioisomer. Theoretical calculations on alkoxystyrylterthiophenes show that this can be understood in terms of an uneven electron spin density distribution at the two alpha-positions available for polymerization. Electron density calculations on the resulting head-to-head alkoxystyrylsexithiophenes show that the spin density is concentrated in the core of the molecule rather than at the alpha-positions, a result that explains the absence of significant amounts of higher oligomers.

Magnetic-field-induced deuterium quadrupole splitting in a solution of discotic micelles approaching an isotropic-to-nematic transition

Abstract 2 H NMR of 2 H 2 O has been used to monitor magnetic-field-induced order in an isotropic solution of discotic micelles of caesium pentadecafluorooctanoate (CsPFO) on approaching a transition to a nematic phase. This is revealed as a quadrupole splitting of the isotropic signal which is first observed, at the field strength of the experiment (6.34 T), at a temperature approximately 80 mK higher than the upper boundary of the transition ( T IN ). This splitting increases rapidly with decreasing temperature and diverges as a hypothetical second-order transition to the nematic phase is approached at a temperature T *. The divergence follows a ( T - T *) −1 dependence as predicted by molecular field theory. At T IN the divergence is quenched and in the biphasic region the quadrupole splitting is constant. This facilitates the precise determination of T IN and T IN - T *. For a sample with a weight fraction of CsPFO of 0.302 a value 0.016 ± 0.002 K is obtained for T IN - T *.