Determination of lipid‐soluble arsenic species in seaweed‐eating sheep from Orkney

This work is part of an ongoing research study towards an understanding of the complete metabolism of arsenosugars in mammalian organisms when ingesting seaweed, using the North Ronaldsay (NR) sheep as a model organism. We focus on the analysis of only those arsenic species bound to the lipids of the feed (Laminaria digitata), faeces and the tissues of the NR sheep using a novel enzymatic hydrolytic method that is simple and reliable. This rare breed of sheep, found in the remote Orkney Islands in the north of Scotland, live the entire year on the beaches and eat seaweed that is washed ashore (up to 3 kg daily). Previous studies on arsenic fractionation in muscle, kidney and liver tissues revealed that most of the arsenic is concentrated in the fat fractions of these tissues (muscle fat: 61%; liver fat: 66%; kidney fat: 25%) rather than in the non‐lipid fractions. Hence, this study was undertaken in order to determine the arsenic species bound to lipids in the muscle, kidney and faeces of NR sheep and to compare these with the arsenic species bound to the lipids of the L. digitata consumed. The enzymatic hydrolytic procedure has been successfully employed for the first time to cleave the arsenic species cleanly from the rest of the lipid structure. This makes the arsenic species water soluble and enables their direct determination by high‐performance liquid chromatography coupled with inductively coupled plasma mass spectrometry. Dimethylarsinic acid (DMA(V)) and monomethylarsonic acid (MA(V)) were found to be the major hydrolysed arsenic species bound to the kidney and muscle lipids, whereas arsenosugar‐1 was found to be the major hydrolysed arsenic species in L. digitata lipids. On the other hand, DMA(V) was found to be the major arsenical obtained after the enzymatic hydrolysis of the faeces lipids. These results seem to suggest that both direct absorption and biotransformation of the absorbed organoarsenicals are the likely reasons for their occurrence and accumulation in the NR sheep tissues. Copyright © 2003 John Wiley & Sons, Ltd.     

The Synthesis and Crystal Structure of Hg3TeI4

The structure of cubic Hg₃TeI₄ was determined from powder data. The four positions of the cubic closestpacking of the anions are statistically occupied by 0.8 Te-atoms and 3.2 I-atoms. The two types of tetrahedral holes are occupied to the extent of 2/4 and 0.4/4, respectively, by Hg-atoms. With an ordered model of lower symmetry, the stoichiometric composition can be explained and a homogeneous charge distribution can be achieved. The ordered model contains regions of the structure of red HgI₂, which are connected by fragments of the SiS₂-type.     

Mechanism of gain narrowing in conjugated polymer thin films

Received: 19 January 1998     

The conformal structure of space-time in a constructive axiomatics based on elements of quantum mechanics

A constructive axiomatic approach to the geometry of space-time in the domain of classical and quantum physics can be founded on basic experiences made with quantum objects. The corresponding matter fields are described by linear systems of partial differential equations. Their characteristics are studied. Postulates concerning the related jump cones and jump amplitudes lead to a unique conformal structure attributed to the space-time geometry.     

Ropelengths of closed braids

For a link K, let L(K) denote the ropelength of K and let Cr(K) denote the crossing number of K. An important problem in geometric knot theory concerns the bound on L(K) in terms of Cr(K). It is well known that there exist positive constants c₁, c₂ such that for any link K, c₁⋅(Cr(K))^3/4?L(K)?c₂⋅(Cr(K))^3/2. In this paper, we show that any closed braid with n crossings can be realized by a unit thickness rope of length at most of the order O(n6/5). Thus, if a link K admits a closed braid representation in which the number of crossings is bounded by a(Cr(K)) for some constant a?1, then we have L(K)?c⋅(Cr(K))^6/5 for some constant c>0 which only depends on a. In particular, this holds for any link that admits a reduced alternating closed braid representation, or any link K that admits a regular projection in which there are at most O(Cr(K)) crossings and Seifert circles.     

Dye-exchange dynamics in micellar solutions studied by fluorescence correlation spectroscopy

We investigated the dye-exchange dynamics between rhodamine 123 (R123), a mitochondrial fluorescent dye, and micelles as membrane mimetic systems. In the presence of neutral micelles (Triton X-100 and Brij 35) R123 partitions between the aqueous solution and the micellar pseudo-phase, undergoing red shift of the absorption and the emission spectra. Fluorescence correlation spectroscopy (FCS) was used to study the dynamics of these systems over an extremely wide time range and at the single-molecule level, yielding information in one and the same experiment about the diffusional dynamics of free and bound rhodamine and about the dye-exchange dynamics as well as several photophysical properties of the rhodamine bound to the micelles. It was found that the entry rate constants are diffusion-controlled, indicating that there are no geometric or orientational requirements for the association of the dye with the micelle. With respect to the dye-exchange dynamics, micelles are found to behave as soft supramolecular cages in contrast to other rigid supramolecular cavities, such as cyclodextrins. The exit rate constants depend on the surfactant and determine the stability of the binding. Single-molecule multiparameter fluorescence detection (MFD) was used to examine the fluorescence properties of individual molecules in comparison to ensembles of molecules. The MFD histograms confirm the fast dye-exchange dynamics observed by FCS and yield mean values of fluorescence lifetimes and anisotropies in agreement with those obtained in bulk measurements.