Comparative Adsorption of Saturated and Unsaturated Fatty Acids at the Iron Oxide/Oil Interface.

A detailed comparison of the adsorption behavior of long straight chain saturated and unsaturated fatty acids at the iron oxide/oil interface has been considered using a combination of surface study techniques. Both depletion isotherms and polarized neutron reflectometry (PNR) show that the extent of adsorption decreases as the number of double bonds in the alkyl chains increases. Sum frequency generation spectroscopic measurements demonstrate that there is also an increase in chain disorder within the adsorbed layer as the unsaturation increases. However, for the unsaturated analogues, a decrease in peak intensity is seen for the double bond peak upon heating, which is thought to arise from isomerization in the surface-bound layer. The PNR study of oleic acid adsorption indicates chemisorbed monolayer adsorption, with a further diffuse reversible adsorbed layer formed at higher concentrations.

Adsorption of Bovine Serum Albumin (BSA) at the Oil/Water Interface: A Neutron Reflection Study.

The structure of the adsorbed protein layer at the oil/water interface is essential to the understanding of the role of proteins in emulsion stabilization, and it is important to glean the mechanistic events of protein adsorption at such buried interfaces. This article reports on a novel experimental methodology for probing protein adsorption at the buried oil/water interface. Neutron reflectivity was used with a carefully selected set of isotopic contrasts to study the adsorption of bovine serum albumin (BSA) at the hexadecane/water interface, and the results were compared to those for the air/water interface. The adsorption isotherm was determined at the isoelectric point, and the results showed that a higher degree of adsorption could be achieved at the more hydrophobic interface. The adsorbed BSA molecules formed a monolayer on the aqueous side of the interface. The molecules in this layer were partially denatured by the presence of oil, and once released from the spatial constraint by the globular framework they were free to establish more favorable interactions with the hydrophobic medium. Thus, a loose layer extending toward the oil phase was clearly observed, resulting in an overall broader interface. By analogy to the air/water interface, as the concentration of BSA increased to 1.0 mg mL(-1) a secondary layer extending toward the aqueous phase was observed, possibly resulting from the steric repulsion upon the saturation of the primary monolayer. Results clearly indicate a more compact arrangement of molecules at the oil/water interface: this must be caused by the loss of the globular structure as a consequence of the denaturing action of the hexadecane.

Structural studies of surfactants at the oil-water interface by neutron reflectometery.

We report information regarding the structure at the interface between hexadecane and an aqueous solution of trimethyl tetradecyl ammonium bromide (C14TAB) with appropriate deuterium labeling. We also report the role of the headgroup size and the charge on structures at the oil-water interface by comparing the data for C14TAB to that for a deuterated trimethyl tetradecyl ammonium sulfate (C14TAS) solution at the oil-water interface. As the charge on the counterion increases, this results in a reduction in the limiting area per molecule and an increase in the adsorbed amount at the oil-water interface.

Neutron reflectivity study of alkylated azacrown ether at the air-liquid and the liquid-liquid interfaces.

We report the neutron reflectometry study of partially deuterated di-hexadecyl-diaza-18-crown-6 ether (d-ACE-16) at the air-water and the oil-water interfaces. At the air-water interface, the thickness of the monolayer is smaller than that for a fully stretched d-ACE-16 molecule, suggesting a tilt of the alkyl chains with respect to the normal. At the oil-water interface, the same molecules were found to form a more diffuse layer distribution stretching across both sides of the interface. On the oil side, the molecules are densely packed within a thickness of 17 A, the hydrophilic part of the molecule with the azacrown ether ring being immersed in the adjacent aqueous side of the interface. The latter consists of a thick 38 A layer comprising staggered, loosely adsorbed d-ACE-16 molecules. With increasing spread amount, the adsorbed layer density increases at the oil side until saturation at ca. 2.25 x 10(-6) mol m(-2), above which the layer collapses.

New guideline for tramadol usage following adverse drug reactions reported to the Iranian Pharmacovigilance Center.

BACKGROUND: Tramadol was introduced as injection and oral form to Iranian Pharmaceutical Market in 2002. Shortly after, the injection form of the drug was observed at the top of suspected drug list of Adverse Drug Reactions (ADRs) received monthly by Iranian Pharmacovigilance Center (IPC). OBJECTIVES: To detect, assess and report total number of Tramadol-induced ADRs received by IPC. To assess the frequency of reported Tramadol-induced ADRs before and after interventions. To design a guideline for prevention of probable ADRs due to Tramadol injection. METHODS: A descriptive study was conducted on spontaneous reporting received by IPC from April 2002 to February 2005. All ADRs suspected to be induced by Tramadol registered in the database during mentioned period were analysed. To assess the effect of different interventions based on Spontaneous Reporting System, the trend of reporting frequency of Tramadol-induced ADRs was evaluated before and after interventions. RESULTS: There were 337 cases of Tramadol-induced ADRs describing 939 reactions, reported to IPC during the study period. Although causal relationship had not been established, three cases of deaths appeared among the reports. The severity of reactions led to implementation of limitations on injectable Tramadol distribution to community pharmacies and the restriction of its use to hospitals only. Since most adverse reactions were dose-dependent, the drug potency of injectable Tramadol available in the country changed from 100 mg to 50 mg. The assessment of ADR reports received by IPC showed that the frequency of adverse reactions registered in the centre was reduced considerably following these interventions. CONCLUSION: Designing a detailed programme by Pharmacovigilance Centres and closely monitoring of newly marketed pharmaceutical products is highly recommended.