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Biomedical subjects

J Anwar

Publications and source records attributed to J Anwar.

8 recordsLinked to original sources
PubMed1996

Dielectric analysis of phosphorylcholine head group mobility in egg lecithin liposomes.

PURPOSE: A knowledge of the interfacial properties of lecithin underpins our understanding of many of the physicochemical characteristics of drug delivery systems such as liposomes and lecithin stabilized microemulsions. In order to further this understanding, a high frequency dielectric study of the interfacial properties of egg lecithin liposomes was undertaken. METHODS: The effect of temperature, lecithin concentration and probe sonication on the interfacial dielectric properties of liposomal suspensions was investigated by high frequency dielectric relaxation spectroscopy between 0.2-6 GHz. RESULTS: The frequency dependent permittivity of each suspension exhibited a dielectric dispersion centred around 100 MHz, corresponding to the relaxation of zwitterionic head groups. The activation energy for head group reorientation was estimated as delta H = 6.3 kJ mol-1. There was an increase in extent of inter-head group interactions on increasing the liposome volume fraction, whereas the effect of probe sonication showed that: (i) head groups in both the outer and inner lamellae contribute to the dielectric response; (ii) the head groups may be less restricted in liposomes of high surface curvature with few lamellae; (iii) the high frequency permittivity of the suspension increased on sonication, as a result of a reduction in the amount of (depolarized) interlamellar water following a reduction in the number of lamellae per liposome. CONCLUSIONS: Dielectric analysis of the zwitterionic head groups of lecithin therefore provides a means for investigating the surface of lecithin liposomes, and may be used to investigate the effect of drugs and other solutes on membranes.

Eggs↗
PubMed1996

Computer simulation of crystal-liquid interface: application to wettability of solids.

PURPOSE: This study describes the development and application of a molecular simulation technique for investigating the solid-liquid interface. It attempts to relate the molecular and crystal structure to the observed wettability of solids. METHODS: Molecular simulations have been carried out for the crystal-water interface of a series of N-n-alkyl-D-gluconamide crystals using the Monte Carlo technique. The molecular system simulated consisted of a layer of water bounded by two crystal slabs. The interfacial potential energies were calculated for the crystal-water interactions and compared with experimental enthalpy values obtained from contact angle measurements. RESULTS: The simulations clearly reveal the distinct hydrophilic and hydrophobic nature of the respective (010) and (010) faces of these compounds. The distribution of water at the interface observed in the simulations is in accord with the nature of the crystal faces. The calculated interfacial potential energies are in the right ball park, but consistently higher than the experimental values. The disparity, however, is justifiable, resulting from the highly simplified model simulated. CONCLUSIONS: Using the developed molecular simulation technique one can calculate the wettability of a solid given the crystal structure. This approach represents an important step towards the goal of engineering crystals with desired wettability characteristics.

Gluconates↗
PubMed1991

Determination of chloride at picogram levels by molecular fluorescence in a graphite furnace.

Chloride was determined at nanogram levels by adding excess of indium to the sample introduced into a graphite furnace and measuring the laser induced molecular fluorescence of indium chloride. The diatomic molecules of indium chloride were excited by a pulsed dye laser at 267 nm and fluorescence was measured at 359 nm. The effects of various parameters including amount of indium added, furnace thermal conditions and presence of concomitants were also studied. A linear calibration in the range of 0.025-1.25 ng and a detection limit of 17 pg of chloride were obtained under optimum conditions. The analytical usefulness of the method was checked by determining the chloride content in National Institute of Standards and Technology, Standard Reference Materials 1571a and 1571b Orchard Leaves.

Chlorides↗
PubMed1989

Polymorphism of sulfathiazole.

The polymorphism of sulfathiazole has been reexamined. The issue of the separate existence of two of the forms, forms III and IV, has now been definitively resolved: both forms exist. Single crystals were used to generate X-ray diffraction patterns, equivalent to those normally obtained from polycrystalline samples, using the ingenious Gandolfi camera. The patterns obtained were distinct and in agreement with the theoretical powder patterns calculated from the reported structures of the two forms, thus confirming the separate existence. Disagreement between the results of previous workers has been traced to two main causes: characterization techniques are not very discriminating for the two forms (III and IV), and the samples examined have invariably been mixtures of III and IV, since the two forms usually crystallize together. Furthermore, crystals of form III exhibit marked preferred orientation, which complicates powder X-ray diffraction (PXRD) analysis. The IR, Raman, and 13C NMR spectra, and PXRD patterns are reported for all four forms. These distinct fingerprints should now enable one to isolate pure samples and to study the properties and the relationships between these forms with full confidence.

Calorimetry, Differential Scanning↗