Shape-tunable polymer nodules grown from liposomes via ring-opening metathesis polymerization

A new inisurf (acting as surfactant and initiator) molecule for ring-opening metathesis polymerization (ROMP) was synthesized and used in aqueous solution in order to control the size and shape of polymer nodules grown from liposomes. Nodules were observed to grow in size with conversion of monomer, and depending on the monomer used, they adopted either a spherical or comet-like shape. Here, we investigate polymer production from a liposome surface. We use a hydrophobic derivative of the Grubbs catalyst positioned at the liposome surface to allow for ROMP of monomers dissolved in the aqueous outer phase. We obtain nodules of polymer that can grow up to tens of micrometers, unveiling new efficient possibilities of polymerization from a membrane in an aqueous solution.     

Multichannel digital transmission in an optical network of communicating molecules

In present telecommunication networks, information transfer relies on the interplay of optical and electrical signals. Data are communicated optically but processed electronically. Methods to maintain the propagating signals solely at the optical level must be developed to overcome the transmission capacities and speed limits imposed by the electronic components. We have demonstrated that molecular switches can be used to gate optical signals in response to optical signals. We have realized a simple optical network consisting of three light sources, one cell containing a solution of three fluorescent molecules, one cell containing a solution of a three-state molecular switch and a detector. The light emitted by the three fluorophores is absorbed by the three states of the molecular switch. Using this simple operating principle, we have shown that multichannel digital transmission can be implemented on an ensemble of communicating molecules relying exclusively on the interplay of optical inputs and optical outputs.     

Anilinepropylsilica xerogel used as a selective Cu (II) adsorbent in aqueous solution

The metal ion adsorption properties of the microporous hybrid anilinepropylsilica xerogel were studied using divalent copper, zinc, and cadmium ions in aqueous solutions in concentrations ranging from 10(-4) up to 5x10(-3) moll(-1). At low concentrations the surface of the solid phase presents selectivity for Cu (II), even in competitive conditions. This preferential sorption ability for copper in relation to zinc and cadmium ions was interpreted by considering the xerogel morphology.     

Adsorption and thermal condensation mechanisms of amino acids on oxide supports. 1. Glycine on silica

Glycine was adsorbed on the surface of a well-defined silica from aqueous solutions of variable concentrations and pHs. The adsorbed molecules were characterized using middle-IR and UV-vis-NIR spectroscopies. Except at the lowest pH (2.0), they were predominantly present on the surface as zwitterions. Two successive deposition mechanisms were evidenced with increasing glycine concentration. At low concentrations, glycine is specifically adsorbed on silica surface sites, probably through its NH3+ moiety. The pH dependence suggests that these sites may be silanolate groups (approximately equal to Si-O-). At higher concentrations, specific adsorption sites are saturated and surface-induced precipitation of beta-glycine is observed. The thermal reactivity of adsorbed/deposited glycine was then investigated by thermogravimetric analysis, in situ diffuse reflectance IR spectroscopy, and thermoprogrammed desorption coupled with mass spectrometry. Adsorbed glycine molecules react to form peptide bonds at a temperature considerably lower than that for bulk crystalline alpha-glycine. The main reaction product is the cyclic dimer diketopiperazine, with no evidence of the linear dimer. The activation mechanism is not diffusionally limited; the formation of "surface acyls", previously proposed for related systems, has not been evidenced here. These findings are of relevance for the evaluation of prebiotic peptide synthesis scenarios.     

Very general formation of tetrahydropterin cation radicals during reaction of iron porphyrins with tetrahydropterins: model for the corresponding NO-synthase reaction

Electron transfer from tetrahydropterins to iron porphyrins, with formation of intermediate tetrahydropterin cation radicals, is a very general reaction that was shown to occur not only with tetrahydrobiopterin, as originally found in NO-synthases, but also with another important biological cofactor, tetrahydrofolate, and various iron porphyrins, either in their ferric state, or in the Fe(II)O(2) state, as in the first model of the corresponding NO-synthase reaction described in this paper.     

Asymmetric [2,3]-rearrangement of glycine-derived allyl ammonium ylids

The first examples of highly enantioselective [2,3]-sigmatropic rearrangements of acyclic allylic ammonium ylids are reported. Thus, a range of N-{2'-[(N'-allyl-N',N'-dialkyl)ammonium]}acetyl camphor sultams undergo rearrangement at 0 degrees C in DME solution with high diastereofacial control (up to 99:1 dr) to give allylglycines in generally high yield. The power of the method has been demonstrated in a rapid and efficient synthesis of (R)-allyl glycine.     

Adding water to sugar: a spectroscopic and computational study of alpha- and beta-phenylxyloside in the gas phase

The gas phase structures of phenyl alpha- and beta-d-xylopyranoside (alpha- and beta-pXyl) and their mono-hydrates have been investigated using a combination of resonant two-photon ionization (R2PI), ultra-violet hole-burning and resonant infrared ion dip spectroscopy, coupled with density functional theory (DFT) and ab initio computation. The hole-burning experiments indicate the population of a single conformer only, in each of the two anomers. Their experimental and calculated infrared spectra are both consistent with a conformational assignment corresponding to the computed global minimum configuration. All three OH groups are oriented towards the oxygen atom (O1) on the anomeric carbon atom to form an all trans(ttt) counter-clockwise chain of hydrogen bonds. The mono-hydrates, alpha- and beta-pXyl(H(2)O) each populate two distinct structures in the molecular beam environment, with the water molecule inserted between OH4 and OH3 or between OH3 and OH2 in alpha-pXyl(H2O), and between OH2 and O1 in either of two alternative orientations, in beta-pXyl(H2O). In all of the mono-hydrated xyloside complexes, the water molecule inserts into the weakest link of the sugar molecules' hydrogen-bonded chain of hydroxy groups, creating a single extended chain, strengthened by co-operativity. The all-trans configuration of the xylose moiety is retained and the mono-hydrate structures correspond to those calculated to lie at the lowest relative energies.     

Wavelength dependence of the hyper Rayleigh scattering response from gold nanoparticles

The wavelength dependence of the quadratic hyperpolarizability of 11 nm diam gold nanoparticles, is reported as measured by hyper Rayleigh scattering. An important photoluminescence background underlying the hyper Rayleigh signal is observed, a contribution attributed to radiative electron-hole recombinations following multiphoton excitation favored by adsorbed organic compound like citrate on the surface of the nanoparticles. The absolute value of the quadratic hyperpolarizability of gold spherical nanoparticles is determined and a strong enhancement is observed for harmonic frequencies in resonance with the dipolar surface plasmon excitation. No contribution of the interband transition is observed. The absolute values reported, beta(C)=5.1x10(-26) esu at the second harmonic energy 2.39 eV, have been measured with femtosecond long laser pulse, and are 1 order of magnitude weaker that the one previously reported with nanosecond long pulses. This difference can be related to similar measurements performed on the second order hyperpolarizability of gold nanoparticles and may be attributed to different electronic relaxation regimes. Finally, the spectrum of the quadratic hyperpolarizability is compared to the theoretically expected one.     

Intrinsic folding of small peptide chains: spectroscopic evidence for the formation of beta-turns in the gas phase

Laser desorption of model peptides coupled to laser spectroscopic techniques enables the gas-phase observation of genuine secondary structures of biology. Spectroscopic evidence for the formation of beta-turns in gas-phase peptide chains containing glycine and phenylalanine residues establishes the intrinsic stability of these forms and their ability to compete with other stable structures. The precise characterization of local minima on the potential energy surface from IR spectroscopy constitutes an acute assessment for the state-of-the-art quantum mechanical calculations also presented. The observation of different types of beta-turns depending upon the residue order within the sequence is found to be consistent with the residue propensities in beta-turns of proteins, which suggests that the prevalence of glycine in type II and II' turns stems essentially from an energetic origin, already at play under isolated conditions.     

The Antiepileptic Lamotrigine and Its Analogues: Comparative Theoretical Electronic Properties

Electronic properties of lamotrigine (LTG) and two analogues (A1 and A2) are compared through MOPAC-AM1 calculations. Two stable conformers of LTG are calculated to exist in agreement with X-ray crystallography. In the three compounds and the two conformers for each of them, the more favorable protonation sites are N₂ and N₄; these should then be the sites appropriate for interaction with a receptor, and group valence reinforces the supposition. The molecular electrostatic potentials show that a region between the two chlorine atoms in LTG could be the site for an electrostatic interaction with a corresponding site in the receptor. The fluorine atom in A1 would play an equivalent role. A simple model for LTG-receptor interaction is proposed.