Mesoscopic properties of semiflexible amyloid fibrils

We have determined the contour length, persistence length, bending rigidity, and critical percolation concentration for semiflexible amyloid fibrils formed from the globular proteins beta-lactoglobulin, bovine serum albumin, and ovalbumin. The persistence length was estimated using an adjusted random contact model for highly charged semiflexible chains. We have found contour lengths in the range of 50 nm to 10 microm and persistence lengths in the range of 16 nm to 1.6 microm. This wide range of contour and persistence lengths and the ease of preparation of these amyloid fibrils make them ideal model systems for the study of semiflexible polymers.     

2-O-Substituted-3,6-per-anhydro-α-Cyclodextrin as Potential Biocompatible Agents for the Selective Complexation of Heavy Metal Ions with Special Attention to Lead

We report on the synthesis,characterization and ionic complexation properties ofhexakis (2-O-acetyl-3,6-anhydro)cyclomaltohexaose and hexakis (2-O-methyl-3,6-anhydro) cyclomaltohexaose usingthin-layer chromatography and Nuclear MagneticResonance spectroscopy. The selectivity towardscations depends on chemical modification of thehydroxyl groups and a very high specificity can beobtained in the case of lead for methylatedderivatives.     

On the first polyarsenic organic compound from nature: arsenicin A from the New Caledonian marine sponge Echinochalina bargibanti

Reported here is the first polyarsenic compound ever found in nature. Denominated arsenicin A, it was isolated along a bioassay-guided fractionation of the organic extract of the poecilosclerid sponge Echinochalina bargibanti collected from the north-eastern coast of New Caledonia. In defining an adamantine-type polyarsenic structure for this compound, deceptively simple NMR spectra were complemented by extensive mass spectral analysis. However, it was only the synthesis of a model compound that provided the basis to discriminate structure 4 from other spectrally compatible structures for arsenicin A; to this end, a comparative ab initio simulation of IR spectra for the natural and the synthetic compounds was decisive. Arsenicin A is endowed with potent bactericidal and fungicidal activities on human pathogenic strains. All this may revive pharmacological interest in arsenic compounds while prompting us to rethink the arsenic cycle in nature.     

The Kv2.1 K<Superscript>+</Superscript> channel targets to the axon initial segment of hippocampal and cortical neurons in culture and <Emphasis Type="Italic">in situ</Emphasis>

Background  

The Kv2.1 delayed-rectifier K⁺ channel regulates membrane excitability in hippocampal neurons where it targets to dynamic cell surface clusters on the soma and proximal dendrites. In the past, Kv2.1 has been assumed to be absent from the axon initial segment.     

Synthesis of 0-(2-0-α-D-glucopyranosyl)-β-D-galactopyranoside of optically pure δ-hydroxyl-L-lysyl-glycine: a glycopeptide of the glomerular basement membrane

The synthesis of the glycopeptide Glu-Gal-Hyl-Gly, which forms an essential part of the Glomerlar Basement Membrane, is presented. The use of the levulinyl group as a protective group and the availability of the optically pure and fully-protected lactone of δ-hydroxy-L-Lysine (Hyl) will be put forward.     

Aided self-assembly of porphyrin nanoaggregates into ring-shaped architectures

The formation of micrometer-sized, highly ordered porphyrin rings on surfaces has been investigated. The porphyrin-based nanoarchitectures are formed by deposition from evaporating solutions through a surface dewetting process which can be tuned by variations in the substitution pattern of the molecules used, the coating of the surface and the conditions under which the evaporation takes place. Control over the combined self-assembly and surface dewetting results in nanorings possessing a defined internal architecture. The ordering of the molecules within the rings has been studied by a variety of microscopy techniques (TEM, AFM, fluorescence microscopy) and the exact ordering of the porphyrins within the rings has been quantified.     

Printed Dielectrophoretic Electrode-Based Continuous Flow Microfluidic Systems for Particles 3D-Trapping

Inkjet-printing is used to fabricate dielectrophoretic electrodes able to trap polystyrene (PS) microparticles as well as model planktonic cells. The possibility of rapid prototyping offered by inkjet-printing allows the rational design of microchannels with tailored electric field distributions experienced by the suspended particles, which in turn provides a handle to drive them towards target regions. Specifically, this goal is achieved using two facing substrates constituting the bottom and the top walls of the channel, with a pair of interdigitated electrodes previously patterned by inkjet-printing on each side. Influence of electrode polarization (magnitude and frequency of the input signal) is investigated both theoretically, by modeling the electric field distribution inside the channel, and experimentally using confocal fluorescence microscopy. The printed device is able to sort circulating PS particles as a function of their size, with diameters ranging from 0.5 to 5 µm, as well as to separate planktonic species according to their composition (Alexandrium minutum versus Prorocentrum micans). This work paves the way for the development of large-area, microstructured dielectrophoretic electrodes able to separate the constituents of samples at flow rates up to 150 µL mn⁻¹.     

Electrostatic interactions of colloidal particles in nonpolar solvents: role of surface chemistry and charge control agents

We study the electrostatic and hydrodynamic interactions of colloidal particles in nonpolar solvents. Using blinking optical tweezers, we can extract the screening length, kappa-1, the effective surface potential, |ezeta*|, and the hydrodynamic radius, ah, in a single measurement. We apply this technique to suspensions of polystyrene and poly(methyl methacrylate) particles in hexadecane with soluble charge control agents, aerosol sodium di-2-ethylhexylsulfosuccinate (AOT) and polyisobutylene succinimide (OLOA-1200). We find that the electrostatic interactions of these particles depend sensitively on surface composition as well as on the concentration and chemistry of the charge control agent.