Structure of vesicles formed from non-ionic dialkylglycerol poly(oxyethylene) ether surfactants: effect of electrolyte and cholesterol.

Five non-ionic dialkylglycerol poly(oxyethylene) ether surfactants, designated 2C(m)E(n) (where m, the number of carbons in each alkyl chain=16 or 18, and n, the number of oxyethylene units=12, 16 or 17) have been examined for their ability to form vesicles when dispersed in water or in an aqueous solution of 154 mM NaCl, alone or in the presence of 50 mol% cholesterol. Freeze fracture electron microscopy and light scattering showed that regardless of the hydrating fluid, all the non-ionic surfactants, with the exception of 2C(16)E(17) and 2C(18)E(17), formed vesicles in the absence of cholesterol - 2C(16)E(17) and 2C(18)E(17) instead formed micellar aggregates. All surfactants, however, formed vesicles in the presence of 50 mol% cholesterol. Small angle neutron scattering studies of the surfactant vesicles enabled the bilayer thickness and repeat distance (d-spacing) to be determined. The bilayers formed by all the non-ionic surfactants in the absence of cholesterol were surprisingly thin (∼50 Å for the E(12) containing surfactants and ∼64 Å for 2C(18)E(16)) most likely due to the intrusion of oxyethylene groups into the hydrophobic core of the bilayers. In contrast, however, the non-ionic surfactants exhibited a relatively large d-spacing of around ∼130-150 Å. The addition of 50 mol% cholesterol had a dramatic effect on the thickness of the vesicle bilayer, increasing its size by 10-20 Å, most probably because of an extrusion of oxyethylene from the hydrophobic region of the bilayer and/or a reduction in the tilt on the surfactant alkyl chains. Additionally the presence of cholesterol in a vesicle tended to reduce slightly both the d-spacing and the thickness of the water layer separating the bilayers. The presence of NaCl, even at the low concentrations used in the study, did affect the properties of the bilayer such that it reduced the d-spacing and, in the case of cholesterol-containing systems, also reduced bilayer thickness.

One step back in understanding racial differences in birth weight.

In recognition of the biological and social connections in demographic processes, demographers have integrated biological factors into their models of population variation. This new effort has tended to focus on the analysis of fertility and mortality. Edwin J.C.G. van den Oord and David C. Rowe's article, "Racial Differences in Birth Health Risk: A Quantitative Genetic Approach," published in the August 2000 issue of Demography, is part of this effort. These authors use race as a proxy for genetic variation, which subverts even the most positive attempts to understand the impact of genetic variation on demographic processes. The authors' statistical results restate their anachronistic theory of race using latent variables that are not open to empirical testing. Although new data increase the opportunities for the examination of the relationship between biology and demographic processes researchers must be vigilant not to commit the errors of the past by misusing race as a variable.

Physicochemical and solubilization properties of N, N-dimethyl-N-(3-dodecylcarbonyloxypropyl)amineoxide: a biodegradable nonionic surfactant.

The physicochemical characteristics of N,N-dimethyl-N-(3-dodecylcar- bonyloxypropyl)amineoxide (DDCPNO), a biodegradable analogue of a N, N-dimethylalkylamine-N-oxide, are compared with those of N, N-dimethyldodecylamine-N-oxide (DDNO) to establish the effect on the properties of DDNO of inserting a propoxy linker between the hydrophobic tail and hydrophilic head region. Surface tension measurements gave a critical micelle concentration of 0.33 mM for DDCPNO compared with a value of 1.57 mM for DDNO, suggesting that the former was the more hydrophobic surfactant. This result was confirmed by laser light scattering studies in which total intensity light scattering indicated the presence of DDCPNO micelles of aggregation number 85.0. Photon correlation spectroscopy studies yielded a limiting hydrodynamic diameter of 4.0 nm in comparison with values of 57.5 and 3.3 nm obtained for the aggregation number and the limiting hydrodynamic size, respectively, of DDNO micelles. Studies demonstrated that neither a dilute aqueous solution of DDCPNO or DDNO exhibited a cloud point within the temperature range 293-373 K. Solubilization studies showed that the capacity of DDCPNO micelles for a range of drugs of varying size and polarity was less than that observed with DDNO micelles at an equivalent surfactant concentration. As a further measure of solubilization, the ability of DDCPNO to form oil-in-water microemulsions with a range of ethyl ester oils was investigated and found to be slightly higher than that achieved with DDNO. Together these studies suggest that the presence of the semipolar linker significantly alters the properties of this low molecular weight surfactant.

Recanalization of a portal-vein thrombosis and partial resolution of biliary cirrhosis following cholecystectomy for cholelithiasis in an infant.

Cholelithiasis in infants and children is unusual and is reputedly associated with underlying hemolytic disorders, total parenteral nutrition, ileal disease, and congenital anomalies of the biliary tree. We report a case of cholecystitis with pigmented stones in a 3-month-old infant associated with portal vein thrombosis (PVT) and biliary cirrhosis without the above-mentioned causes. Recanalization of the PV and partial resolution of the cirrhosis was observed following cholecystectomy. To our knowledge, cholelithiasis associated with PVT and cirrhosis in an infant has not been reported in the literature.

Identification of a ferryl intermediate of Escherichia coli cytochrome d terminal oxidase by resonance Raman spectroscopy.

The 680-nm-absorbing "peroxide state" of the Escherichia coli cytochrome d terminal oxidase complex, obtained by addition of excess hydrogen peroxide to the enzyme, is shown to be a ferryl intermediate in the catalytic cycle of the enzyme. This ferryl intermediate is also created by aerobic oxidation of the fully reduced enzyme. Resonance Raman spectra with 647.1-nm excitation show an FeIV = O stretching band at 815 cm-1, a higher frequency than noted in any other ferryl-containing enzyme to date. The band shows an 16O/18O frequency shift of -46 cm-1, larger than that observed for any porphyrin ferryl species. The FeIV = O formulation was unambiguously established by oxidations of the reduced enzyme with 16O2, 18O2, and 16O18O. Only the use of a mixed-isotope gas permitted discrimination between a ferryl and a peroxo structure. A catalytic cycle for the cytochrome d terminal oxidase complex is proposed, and possible reasons for the high v(Fe = O) frequency are discussed.