Theoretical Study of Comb-Polymers Adsorption on Solid Surfaces

We propose a theoretical investigation of the physical adsorption of neutral comb-polymers with an adsorbing skeleton and non-adsorbing side-chains on a flat surface. Such polymers are particularly interesting as "dynamic coating" matrices for bio-separations, especially for DNA sequencing, capillary electrophoresis and lab-on-chips. Separation performances are increased by coating the inner surface of the capillaries with neutral polymers. This method allows to screen the surface charges, thus to prevent electro-osmosis flow and adhesion of charged macromolecules (e.g. proteins) on the capillary walls. We identify three adsorption regimes: a "mushroom" regime, in which the coating is formed by strongly adsorbed skeleton loops and the side-chains anchored on the skeleton are in a swollen state, a "brush" regime, characterized by a uniform multi-chains coating with an extended layer of non-adsorbing side-chains and a non-adsorbed regime. By using a combination of mean field and scaling approaches, we explicitly derive asymptotic forms for the monomer concentration profiles, for the adsorption free energy and for the thickness of the adsorbed layer as a function of the skeleton and side-chains sizes and of the adsorption parameters. Moreover, we obtain the scaling laws for the transitions between the different regimes. These predictions can be checked by performing experiments aimed at investigating polymer adsorption, such as Neutron or X-ray Reflectometry, Ellipsometry, Quartz Microbalance, or Surface Force Apparatus.Comment: 30 pages, 7 figures, to be published in Macromolecule

Birhythmicity in a model for the cyclic AMP signalling system of the slime mold Dictyostelium discoideum

AbstractWe demonstrate the coexistence of two simultaneously stable periodic regimes in a model based on receptor desensitization for the cyclic AMP signalling system of the slime mold Dictyostelium discoideum. These results provide the first example of autonomous birhythmicity in a biochemical model closely related to experimental observations. Whereas the transition from one stable mode of oscillations to the other can be elicited by suprathreshold stimuli, the two periodic regimes differ in their sensitivity to perturbations. That multiple oscillations occur in a model based on a single feedback loop suggests that the conditions for birhythmicity are widely satisfied in biological systems

The failure of the League of Nations to provide collective security in the Italo-Ethiopian war, 1935-1936

Thesis (M.A.)--Boston University, 1946. This item was digitized by the Internet Archive

Peptide dendrimer/lipid hybrid systems are efficient DNA transfection reagents: structure--activity relationships highlight the role of charge distribution across dendrimer generations.

Efficient DNA delivery into cells is the prerequisite of the genetic manipulation of organisms in molecular and cellular biology as well as, ultimately, in nonviral gene therapy. Current reagents, however, are relatively inefficient, and structure-activity relationships to guide their improvement are hard to come by. We now explore peptide dendrimers as a new type of transfection reagent and provide a quantitative framework for their evaluation. A collection of dendrimers with cationic and hydrophobic amino acid motifs (such as KK, KA, KH, KL, and LL) distributed across three dendrimer generations was synthesized by a solid-phase protocol that provides ready access to dendrimers in milligram quantities. In conjunction with a lipid component (DOTMA/DOPE), the best reagent, G1,2,3-KL ((LysLeu)8(LysLysLeu)4(LysLysLeu)2LysGlySerCys-NH2), improves transfection by 6-10-fold over commercial reagents under their respective optimal conditions. Emerging structure-activity relationships show that dendrimers with cationic and hydrophobic residues distributed in each generation are transfecting most efficiently. The trigenerational dendritic structure has an advantage over a linear analogue worth up to an order of magnitude. The success of placing the decisive cationic charge patterns in inner shells rather than previously on the surface of macromolecules suggests that this class of dendrimers significantly differs from existing transfection reagents. In the future, this platform may be tuned further and coupled to cell-targeting moieties to enhance transfection and cell specificity

E box motifs as mediators of proviral latency of human retroviruses

The palindromic sequence motifs (CANNTG) known as E boxes are considered as binding sites for the basic helix-loop-helix (bHLH) class of DNA-binding proteins. Their presence has been reported in the long terminal repeats (LTR) of the HIV-1 and HTLV-1 proviruses. Their close proximity with the TATA region of both LTRs indicates that the bHLH proteins may act as important regulators of the function of proviral transcription. Indeed, observations on HIV-1 and recent results on HTLV-1 underline that these E boxes may be critically involved in the regulation of the proviral transcription of these human retroviruses. Indeed, of the two E boxes flanking the TATA sequences of the HIV-1 provirus, the 3' E box has been implicated in the transcriptional inhibition of viral gene expression. Such a role might also be played by the unique 5' E box present in the HTLV-1 LTR. In both cases, the expression of tissue-specfic bHLH proteins, like TAL1 might counteract the inhibitory effect exerted by E box proteins, thereby increasing proviral transcription. Finally, a phylogenetic study encompassing several subtypes of these two human retroviruses underlines that these E box motifs have recently appeared in the proviral LTRs and may be considered as potential mediators in the establishment of proviral latency

0254: Updated reference levels for radiation doses to patients undergoing coronary angiography and coronary percutaneous interventions: the RAY’ACT2 study

PurposeThe RAY’ACT project is a nationwide, multicentre survey program aimed at evaluating patient radiation protection (RP) during coronary angiography (CA) and percutaneous coronary interventions (PCI) in French non-university public hospitals, which represent>30% of the national activity for PCIs, and 60% of the emergency cases. We present the updated reference levels based on the results of the second survey conducted in 2013 (RAY’ACT2).MethodsRP parameters from 48,547 CAs and 40,026 PCIs performed at 61 centres during 2013 and routinely registered in professional software were extracted and analysed retrospectively. Kerma-area product (KAP), fluoroscopy time (FT), number of acquired frames (Nb F) and runs (NR), and total Air Kerma at interventional reference point (KA, r) were analysed separately for CAs and PCIs (elective and ad hoc pooled). All procedures of the year were included.ResultsThe table shows the medians (Q1-Q3) of the RP parameters, updated RLs based on the 75th percentiles of the values for CA and PCI (bold), and previous RLs (RAY’ACT1, 2010).ConclusionsBetween 2010 and 2013, a 20 to 30% decrease was observed in medians and Reference Levels (Q3) for main RP parameters, including KAP and total Air Kerma.Abstract 0254 – Table: Results2013 (RAY’ACT2) 61 centres2010 (RAY’ACT1) 44 centresCAN=48,547N=31,066KAP (Gy.cm²)20.9 (11.8-35.7)27.2 (15.5-45.2)FT (min)3.3 (2.1-5.7)3.7 (2.3-6.3)Nb Frames404 (284-566)553 (388-769)KA,r (mGy)294 (164-498)421 (240-695)PCIN=40,026N=25,356KAP (Gy.cm²)45.2 (25.6-77.6)56.8 (32.8-94.6)FT (min)9.8 (6.3-15.4)10.3 (6.7-16.2)Nb Frames676 (465-960)837 (578-1193)KA,r (mGy)747 (421-1285)1052 (589-1788

Reptilia, Amphisbaenidae, Monopeltis schoutedeni de Witte, 1933: first record from Gabon, with an updated key to Gabonese worm lizards

The amphisbaenian Monopeltis schoutedeni is reported for the first time from Gabon based on a single individual from the extreme southeastern part of the country. The species was formerly known only from the Republic of Congo and the Democratic Republic of Congo. It is the 4th amphisbaenian and the 123rd reptile species recorded from Gabon. An identification key to Gabon amphisbaenians is provided