Teeth of the red fox Vulpes vulpes (L., 1758) as a bioindicator in studies on fluoride pollution

An examination was made of fluoride content in the mandibular first molars of the permanent teeth of the red fox Vulpes vulpes living in north-west (NW) Poland. The teeth were first dried to a constant weight at 105°C and then ashed. Fluorides were determined potentiometrically, and their concentrations were expressed in dry weight (DW) and ash. The results were used to perform an indirect estimation of fluoride pollution in the examined region of Poland. The collected specimens (n = 35) were classified into one of the three age categories: immature (im, 6–12 months), subadult (subad, from 12 to 20 months) and adult (ad, >20 months). The mean concentrations (geometric mean) of fluoride were similar in the im and subad groups (230 and 296 mg/kg DW and 297 and 385 mg/kg ash, respectively), and significantly smaller than in the ad group (504 and 654 mg/kg, respectively, in DW and ash). Basing on other reports that the ∼400 mg/kg DW concentration of fluoride in bones in the long-lived wild mammals generally reflects the geochemical background, it was found that 57% of the foxes in NW Poland exceeded this value by 9% to 170%. This indirectly reflects a moderate fluoride contamination in the tested region

On the nature of hydrogen bonding between the phosphatidylcholine head group and water and dimethylsulfoxide

Molecular dynamics simulations are used to provide a detailed investigation of the hydrogen bond networks around the phosphatidylcholine (PC) head group in 1,2-dipropionyl-sn-glycero-3-phosphocholine in pure water, 10 mol.% and 30 mol.% dimethylsulfoxide (DMSO)-water solutions. Specifically, it is observed that DMSO replaces those water molecules that are within the first solvation shell of the choline, phosphate and ester groups of the PC head group, but are not hydrogen-bonded to the group. The effect of the presence of DMSO on the hydrogen bond network around the PC head groups of the lipid changes with the concentration of DMSO. In comparison to the hydrogen bond network observed in the pure water system, the number of hydrogen-bonded chains of solvent molecules increases slightly for the 10 mol.% DMSO system, while, in the 30 mol.% DMSO system, the number of hydrogen-bonded chains of solvent molecules decreases. © 2012 Elsevier B.V. All rights reserved

On the solvation structure of dimethylsulfoxide/water around the phosphatidylcholine head group in solution.

The solution structure of the phosphocholine (PC) head group in 1,2-dipropionyl-sn-glycero-3-phosphocholine (C(3)-PC) in 30 mol. % dimethylsulfoxide (DMSO)-water solutions has been determined by using neutron diffraction enhanced with isotopic substitution in combination with computer simulation techniques. By investigating the atomic scale hydration structure around the PC head group, a unique description of the displacement of water molecules by DMSO molecules is detailed around various locations of the head group. Specifically, DMSO molecules were found to be the most prevalent around the onium portion of the head group, with the dipoles of the DMSO molecules being aligned where the negatively charged oxygen can interact strongly with the positively charged lipid group. The phosphate group is also partially dehydrated by the presence of the DMSO molecules. However, around this group the bulkier positive end of the DMSO dipole is interacting with negatively charged groups of the lipid head group, the DMSO layer shows no obvious ordering as it cannot form hydrogen bonds with the oxygen atoms in the PO(4) group such as water molecules can. Interestingly, DMSO-water contacts have also increased in the presence of the lipid molecule relative to DMSO-water contacts observed in pure DMSO/water solutions at similar concentrations

Calcium mediated interaction of calf-thymus DNA with monolayers of distearoylphosphatidylcholine: a neutron and X-ray reflectivity study

X-ray and neutron reflection studies, the latter in conjunction with contrast variation, have been combined to study the interaction of calf thymus DNA (ctDNA) with monolayers of distearoylphosphatidylcholine (DSPC) in the presence of 20 mM Ca2+ ions, at the air-liquid interface as a function of surface pressure (10, 20, 30 and 40 mN m-1). Analysis of the X-ray and neutron reflection data showed that, regardless of the surface pressure of the monolayer, a layer of ctDNA was present below the DSPC lipid head groups and that this ctDNA-containing layer (thickness [similar]12.5 to 15 A) was separated from the DSPC head groups by a layer of water of [similar]9 A thickness. The thickness of the ctDNA-containing layer was thinner than that reported for monolayers of cationic lipid at the air-water interface (18-25 A) although in these monolayers no water layer separating the lipid head groups from the layer containing ctDNA has been reported. At all surface pressures the amount of ctDNA present in the layer was in the range 30-40% by volume. As no significant re-arrangement of the DSPC film was required to accommodate the presence of the ctDNA, this suggests that the distribution of charges in the lipid film matches well the charge spacing of ctDNA. Brewster angle microscopy measurements of DSPC on water in the absence of Ca2+ showed the presence of a continuous film containing small, regular shaped domains at all four surface pressures examined. When Ca2+ ions were present in the sub-phase, although the film was still continuous, the domains comprising the film were more irregular in appearance while the presence of Ca2+ ions and ctDNA resulted in the domains becoming smaller and more regularly packed on the surface. © 2013, Royal Society of Chemistry