Emile Perez

Self-assembly of regular hollow icosahedra in salt-free catanionic solutions

Self-assembled structures having a regular hollow icosahedral form (such as those observed for proteins of virus capsids) can occur as a result of biomineralization processes, but are extremely rare in mineral crystallites. Compact icosahedra made from a boron oxide have been reported, but equivalent structures made of synthetic organic components such as surfactants have not hitherto been observed. It is, however, well known that lipids, as well as mixtures of anionic and cationic single chain surfactants, can readily form bilayers that can adopt a variety of distinct geometric forms: they can fold into soft vesicles or random bilayers (the so-called sponge phase) or form ordered stacks of flat or undulating membranes. Here we show that in salt-free mixtures of anionic and cationic surfactants, such bilayers can self-assemble into hollow aggregates with a regular icosahedral shape. These aggregates are stabilized by the presence of pores located at the vertices of the icosahedra. The resulting structures have a size of about one micrometre and mass of about 1010 daltons, making them larger than any known icosahedral protein assembly or virus capsid. We expect the combination of wall rigidity and holes at vertices of these icosahedral aggregates to be of practical value for controlled drug or DNA release.

Understanding the Fragmentation Pattern of Marine Plastic Debris

The global estimation of microplastic afloat in the ocean is only approximately 1% of annual global plastic inputs. This reflects fundamental knowledge gaps in the transformation, fragmentation, and fates of microplastics in the ocean. In order to better understand microplastic fragmentation we proceeded to a thorough physicochemical characterization of samples collected from the North Artlantic subtropical gyre during the sea campaign Expedition seventh Continent in May 2014. The results were confronted with a mathematical approach. The introduction of mass distribution in opposition to the size distribution commonly proposed in this area clarify the fragmentation pattern. The mathematical analysis of the mass distribution points out a lack of debris with mass lighter than 1 mg. Characterization by means of microscopy, microtomography, and infrared microscopy gives a better understanding of the behavior of microplastic at sea. Flat pieces of debris (2 to 5 mm in length) typically have one face that is more photodegraded (due to exposure to the sun) and the other with more biofilm, suggesting that they float in a preferred orientation. Smaller debris, with a cubic shape (below 2 mm), seems to roll at sea. All faces are evenly photodegraded and they are less colonized. The breakpoint in the mathematical model and the experimental observation around 2 mm leads to the conclusion that there is a discontinuity in the rate of fragmentation: we hypothesized that the smaller microplastics, the cubic ones mostly, are fragmented much faster than the parallelepipeds.

A comparative physical study of two different hydrophilic synthetic latex matrices for the construction of a glucose biosensor.

Two different biodegradable latex polymers functionalised by hydroxy (1) or gluconamide (2) groups proved to be good immobilisation matrixes for glucose oxidase. The responses of these biosensors to glucose additions were measured by potentiostating the modified electrodes at 0.6 V/SCE in order to oxidise the hydrogen peroxide generated by the enzymatic oxidation of glucose in the presence of oxygen. The response of such electrodes was evaluated as a function of film thickness, pH and temperature. Rotating disk electrode experiments showed the influence of the enzyme on the structure of both latex films, namely a marked improvement in matrix permeability. The high permeability of the latex 1 based enzyme sensor (bilayer, P(m)=8.10x10(-4) cm s(-1)) resulted in a high dynamic range. Furthermore, the activation energy for a latex 1 sensor was determined to be 44.55 and 18.03 kJ mol(-1), respectively depending on the conformation of the enzyme.

A rapid and easy procedure of biosensor fabrication by micro-encapsulation of enzyme in hydrophilic synthetic latex films. Application to the amperometric determination of glucose

Novel enzyme electrodes based on synthetic hydrophilic latex matrices are described for the detection of glucose. Glucose oxidase was immobilised through micro-encapsulation, by the simple adsorption of enzyme–latex suspensions on the surface of a platinum electrode. Two latex films functionalised by a hydroxy or a gluconamide group were used. The response of these biosensors to glucose additions was measured by potentiostating the modified electrodes at 0.6 V/SCE in order to oxidise the hydrogen peroxide generated by the enzymatic oxidation of glucose in the presence of dioxygen. The response of such electrodes was evaluated as a function of film thickness and temperature. The sensitivity for a two-layer latex-based biosensor was found to be 38.78 mA M−1 cm−2 with a response time of 3–5 s. Moreover, a marked improvement of the thermal stability of the biosensor was observed. Only at temperatures higher than 65°C the enzyme started to be denatured and being inactive.

Functionalized Vesicles Based on Amphiphilic Boronic Acids: A System for Recognizing Biologically Important Polyols

We report on a new approach for creating water-soluble functionalized vesicles employing N-alkyl-3-boronopyridinium triflates (alkyl = Me, C12H25, C16H33) as sensors for monosaccharides. The nanoaggregate properties were studied by means of DLS, TEM, high-resolution (1)H NMR, and the solvatochromic dyes Reichardts betaine and Methyl Orange. The vesicles were shown to have 30-200 nm diameters depending on the amphiphile chain length. Diol binding to the vesicles was studied by steady-state fluorescence and UV-vis using Alizarin Red S as a probe in the solution at pH 7.4 in the presence and in the absence of D-glucose and D-fructose. Strong sensing ability of boronic acid functional moieties in the order D-fructose > D-glucose was demonstrated, and apparent binding constants were estimated.

FIRST EXAMPLE OF HIGH ASYMMETRIC INDUCTION AT THE PSEUDO-MICELLAR INTERFACE OF A CHIRAL AMPHIPHILIC DENDRIMER

Abstract Sodium borohydride reduced, at the chiral interface of an amphiphilic dendrimer, prochiral ketones to the corresponding chiral alcohols in high yields (>90%) with enantioselectivities over 95% in THF (ex: ee of 99.4% was obtained in reduction of acetophenone).

First example of latices synthesis via oligomerization of norbornene in aqueous emulsions, catalyzed by palladium chloride

Polymerization of norbornene using PdCl2 as catalyst is generally carried out at high temperatures in the absence of solvent. Low yields of polymer with relatively undefined molecular weights are obtained under these conditions. We describe the first example of polymerization of norbornene in water dispersion or aqueous emulsions catalyzed by PdCl2. Good yields of polymers and oligomers were obtained. Furthermore, in aqueous emulsions, novel microlatex which cannot be obtained by radical or ionic routes were synthesized, with particles sizes (≈10 nm.) generally only observed in microemulsion polymerizations.The stereochemistry of the polymers of low molecular weight was partially elucidated by13C NMR.

Spectroscopic detection of carbon nanotube interaction with amphiphilic molecules in epoxy resin composites

Incorporation of carbon nanotubes into epoxy resin composites has the effect of increasing electrical conductivity at low percolation levels. An amphiphilic molecule such as palmitic acid has been used to increase the surface contact area and to improve the dispersion of the carbon nanotube bundles in the prepolymer. The chemical environment of the dispersed nanotubes has been probed using vibrational Raman spectroscopy. Spectroscopic Raman maps on sample surfaces (60×60μm2) with ratios of nanotubes to palmitic acid varying from 1:2 to 2:1 by weight, have been recorded to test the uniformity of the dispersion. Substantial spatial inhomogeneities have been observed in the G-band shift and an additional spectral band at 1450cm−1. The 1450cm−1 band has been attributed to the CH3 group of the amphiphilic molecules adsorbed onto the nanotube surface. The maps are correlated with the measured electrical conductivity values. The highest conductivity has been observed for the best dispersed nanotubes and nanotube...

Synthesis and anti-HIV activity of catanionic analogs of galactosylceramide

Two-chain and gemini catanionic analogs of galactosylceramide were easily prepared in quantitative yields, affording high anti-HIV activities with low cytotoxicities on human cells (e.g. for gemini 4b an EC50 of 0.5 µM with a CC50 of >100 µM were obtained).

New polymer and latex prepared by vinyl polymerization of derivatives of norbornene catalyzed by PdCl2, or PdCl2(TPPTS)2 in water

Abstract We developed a new method of preparation of latex by polymerization of norbornene in aqueous emulsion with SDS, catalyzed by PdCl2. The preparation of small sized latex has been also extended to latex bearing functional groups as alcohol or sugar residues. Two types of catalysts were used: PdCl2 and PdCl2(TPPTS)2. The latex were characterized by light scattering and electron microscopic examination.