Charge Fluctuations and Counterion Condensation

We predict a condensation phenomenon in an overall neutral system, consisting of a single charged plate and its oppositely charged counterions. Based on the ``two-fluid'' model, in which the counterions are divided into a ``free'' and a ``condensed'' fraction, we argue that for high surface charge, fluctuations can lead to a phase transition in which a large fraction of counterions is condensed. Furthermore, we show that depending on the valence, the condensation is either a first-order or a smooth transition.Comment: 16 pages, 1 figure, accepted to be published in PR

Genome-Wide Association Study in BRCA1 Mutation Carriers Identifies Novel Loci Associated with Breast and Ovarian Cancer Risk

BRCA1-associated breast and ovarian cancer risks can be modified by common genetic variants. To identify further cancer risk-modifying loci, we performed a multi-stage GWAS of 11,705 BRCA1 carriers (of whom 5,920 were diagnosed with breast and 1,839 were diagnosed with ovarian cancer), with a further replication in an additional sample of 2,646 BRCA1 carriers. We identified a novel breast cancer risk modifier locus at 1q32 for BRCA1 carriers (rs2290854, P = 2.7×10-8, HR = 1.14, 95% CI: 1.09-1.20). In addition, we identified two novel ovarian cancer risk modifier loci: 17q21.31 (rs17631303, P = 1.4×10-8, HR = 1.27, 95% CI: 1.17-1.38) and 4q32.3 (rs4691139, P = 3.4×10-8, HR = 1.20, 95% CI: 1.17-1.38). The 4q32.3 locus was not associated with ovarian cancer risk in the general population or BRCA2 carriers, suggesting a BRCA1-specific associat

A quantitative characterisation of phospholipid composition and biosynthesis in HeLa cells and nuclei

Nuclei from human cells, stripped of their nuclear envelope by non-ionic detergent, contain a pool of endonuclear phospholipid that is distinct from that of other cellular membranes (Hunt et al., 2001 A. Hunt, G. Clark, G. Attard and A. Postle, J. Biol. Chem. 276 (11) (2001), pp. 8492–8499. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (52)Hunt et al., 2001). The composition dynamics, organisation and role of this endonuclear phospholipid are currently unclear, although there is mounting evidence of its possible involvement in the regulation of nuclear processes such as transcription (Martelli et al., 2004).We have conducted a study that correlates the composition of endonuclear phospholipid to the DNA replication cycle. Using tandem electrospray ionisation mass spectrometry, the phospholipid content of cultured HeLa (human cervical carcinoma) cells and their isolated naked nuclei has been determined quantitatively, both in the presence and absence of cell-cycle blocking agents such as mimosine (Krude, 1999). By harvesting nuclei at different times during the blocking procedure, or after release of the block we were able to monitor the endonuclear phospholipid composition throughout the cell cycle.Preliminary results indicate that the endonuclear lipid pool is enriched in diacyglycerol (DAG) compared with exonuclear lipids. The endonuclear DAG is also found to be enriched in saturated species. The potential implications of these observations on the cell-cycle dependence of lipid biosynthesis and on apoptosis are discussed

An in vivo ratio control mechanism for phospholipid homeostasis: evidence from lipidomic studies

While it is widely accepted that the lipid composition of eukaryotic membranes is under homeostatic control, the mechanisms through which cells sense lipid composition are still the subject of debate. It has been postulated that membrane curvature elastic energy is the membrane property that is regulated by cells, and that lipid composition is maintained by a ratio control function derived from the concentrations of type II and type 0 lipids, weighted appropriately. We assess this proposal by seeking a signature of ratio control in quantified lipid composition data obtained by electrospray ionization mass spectrometry from over 40 independent asynchronous cell populations. Our approach revealed the existence of a universal 'pivot' lipid, which marks the boundary between type 0 lipids and type II lipids, and which is invariant between different cell types or cells grown under different conditions. The presence of such a pivot species is a distinctive signature of the operation in vivo, in human cell lines, of a control function that is consistent with the hypothesis that membrane elastic energy is homeostatically controlled

A lipid mass spectrometry investigation on the effect of non-bilayer forming amphiphiles to the phospholipid metabolism of HeLa cells

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DNA that is dispersed in the liquid crystalline phases of phospholipids is actively transcribed

We report that a 4.3 kbp linearised T7 DNA plasmid is actively transcribed when it is dispersed in the hexagonal liquid crystalline phase of dioleoylphosphoethanolamine (DOPE)

Differences in catalytic properties between mesoporous and nanoparticulate platinum

Conventional Pt/Al2O3 catalysts prepared by wet-impregnation are composed of Pt nanoparticles exposing convex and facetted surfaces deposited on high-surface area ?-Al2O3 supports. A hexagonal phase mesoporous Pt material (denoted H1-Pt) prepared by chemical reduction in the aqueous domains of a lyotropic liquid crystalline template exposes however mainly a concave surface with expected different catalytic properties. A series of Pt/Al2O3 catalysts were prepared using H1-Pt, Pt-black or wet-impregnated Pt, and the samples were characterized by SEM-EDX and TEM, and finally evaluated for CO oxidation. The H1-Pt/Al2O3 catalyst showed an ignition profile for CO oxidation at lower temperatures and thus appeared less sensitive to CO poisoning than the two other types of samples. This difference may be related to the differences in surface curvature

Optical properties of mesoporous II-VI semiconductor compound films

Direct liquid crystal templating from non-ionic polyoxyethylene surfactants has been utilised to produce well-defined birefringent films of nanostructured cadmium telluride films which displayed good optical properties as evidenced by UV/ VIS reflectance spectroscopy

Nanoporous semiconductor-based metamaterials

Growth of periodic nanoporous CdTe and ZnO metamaterials is developed and characterised. We model the induced birefringence and measure the charge transport and density of surface states in the films