Model of peripheral protein adsorption to the water/lipid interface

Two models have been developed to describe the adsorption of a model peripheral protein, colipase, to phospholipid/diacylglycerol (PL/DG) monolayers. One model is applicable at monolayer collapse pressure and at any composition that exceeds the DG mole fraction of PL/DG lateral complexes (Sugár, I. P.; Mizuno, N. K.; Momsen, M. M.; Brockman, H. L. Biophys. J. 2001, 81, 3387-3397). The other model is applicable at any lateral pressure but only below the mole fraction of DG in the complex (Sugár, I. P.; Mizuno, N. K.; Brockman, H. L. Biophys. J. 2005, 89, 3997-4005). Both models assume that initiation of colipase adsorption to the water/lipid interface requires an area of water-exposed hydrophobic surface that exceeds a critical value. In the first model, accessible surface is provided by the head groups of the uncomplexed DG molecules. This surface area follows a binomial distribution. In the second model, accessible area is created by hydrocarbon chains becoming exposed at the water/lipid interface as total lipid packing density of monolayers of PL and/or PL/DG complexes is decreased. This surface area follows a Poisson distribution. The model described in this paper is a unification, extension, and improvement of these models that is applicable at any lateral pressure and any PL/DG mole fraction. Calculated normalized initial colipase adsorption rates are compared with the available experimental values, and predictions of the adsorption rates are made for currently unmeasured compositions and lateral pressure regimes.     

Selenium and nutrition: The accuracy and variability of the selenium content in commercial supplements

Summary Selenium is a required trace-element that has been found to be protective against serious chronic diseases such as cancer and cardiovascular disease in some, but not all, epidemiological studies using both case-control and intervention designs. As a result, the fraction of the adult U.S. population now taking a daily selenium supplement is steadily increasing. In this study, we analyzed 10 or more replicate Se supplement tablets, from each of 15 different products representing 12 different brand names with most being sampled at two different times separated by approximately 30 months. Two chemical forms, seleno-yeast and selenate were tested in 50, 100 and 200 µg/tablet dosages (seleno-yeast) and 25 and 200 µg/tablet dosages (selenate). Variations in contemporary lots were evaluated at both sampling periods. The Se content provided on the product label is generally understated. One tablet contained 2.5 times more selenium than the stated dose. Selenate supplements are less accurately labeled and more highly variable compared to yeast supplements. One popular multivitamin, labeled at 200 µg/tablet, contained tablets in excess of 300 µg. Many subjects using this supplement will exceed the 400 µg/day tolerable upper limit of intake, recently established, for Se by the Institute of Medicine’s Food and Nutrition Board.     

Analysis of the toenail as a biomonitor of supranutritional intake of Zn,Cu, and Mg

The toenail was examined as a biological monitor of Mg, Zn, and Cu intake using an observational case control model. The One Source Cohort matched 63 individuals in Columbia Missouri who took the One Source multivitamin with 63 control individuals. The matching criteria were based on age, sex, ethnicity, smoking status, and body mass index. The multivitamin contained supra-nutritional levels of Se, Mg, Cu, and Zn. The toenail clippings were examined for these elements using instrumental neutron activation analysis (INAA). A statistical analysis did not indicate a significant difference for Mg, Cu, or Zn between the nails of One Source supplement users and control subjects (p<0.76, 0.55, and 0.85, respectively). The trace nutrient Se was used as an internal control. Previous studies have consistently demonstrated that toenail Se is positively correlated with Se supplement use and the analysis did result in a significant correlation in the toenails of One Source users and control subjects (p<1·10⁻⁴). This internal Se control suggests that the One Source Cohort is largely free from misclassification errors that could interfere with the biomonitor response for the supranutritional intake of Mg, Cu, and Zn.     

Preliminary study of the thermally stimulated blue luminescence of ulexite

In this paper, novel results on the blue thermally stimulated luminescence (TSL) emission of ulexite (NaCaB₅O₆(OH)₆·5H₂O) have been studied. The four maxima appearing at 60, 110, 200 and 240°C on the TSL glow curves of this borate could be respectively associated to: (i) the first dehydration (NaCaB₅O₆(OH)₆·5H₂O→NaCaB₅O₆(OH)₆·3H₂O), (ii) the creation-annihilation of the three-hydrated phase, (iii) the Na-coordinated chains dehydroxylation and the starting point of the alkali self-diffusion through the lattice and (iv) the amorphisation of the lattice. These results are fairly well correlated with the differential thermal analyses (DTA), in situ thermal observations under environmental scanning electron microscope (TESEM) and thermal X-ray diffraction (TXRD) techniques.     

The bulk viscoelastic properties of poly(styrene-co-sodium styrene-p-carboxylate)

The effect of up to 7.82 mol % ionic groups on the stress relaxation and dynamic mechanical (torsion pendulum) properties of poly(styrene-co-sodium styrene-p-carboxylate) was studied. The results obtained were compared with those reported elsewhere for polymers containing the same ionic groups at a different position on the polystyrene backbone (styrene-sodium methacrylate copolymers) and with polymers containing different ionic groups at the same position (styrene-sodium styrene-p-sulfonate copolymers). The results of these comparisons showed that positioning of ionic groups affects the size of ionic aggregates formed, while their type dictates the strength of the forces within the aggegrates.