Optimized intermolecular potential for aromatic hydrocarbons based on anisotropic united atoms. III. Polyaromatic and naphthenoaromatic hydrocarbons

In this third article of the series, a new anisotropic united atoms (AUA) intermolecular potential parameter set has been proposed for the carbon force centers connecting the aromatic rings of polyaromatic hydrocarbons to predict thermodynamic properties using both the Gibbs ensemble and NPT Monte Carlo simulations. The model uses the same parameters as previous AUA models used for the aromatic CH force centers. The optimization procedure is based on the minimization of a dimensionless error criterion incorporating various thermodynamic data of naphthalene at 400 and 550 K. The new model has been evaluated on a series of polyaromatic and naphthenoaromatic hydrocarbons over a wide range of temperatures up to near-critical conditions. Vaporization enthalpy, liquid density, and normal boiling temperature are reproduced with good accuracy. The new potential parameters have also been tested successfully on toluene, 1,3,5-trimethylbenzene, styrene, m-xylene, n-hexylbenzene, and n-dodecylbenzene to demonstrate their transferability to alkylbenzenes.     

Characterization of lactosylated proteins of infant formula powders using two-dimensional gel electrophoresis and nanoelectrospray mass spectrometry

Infant formula powders were analyzed by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) to assess the whey proteins quality, which may be altered by the heat treatment used during the processing conditions. Lactosylation was found to be the major chemical modification occurring in whey proteins. In parallel, a two-dimensional (2-D) gel electrophoresis was performed on the milk sample and the entire protein patterns were analyzed by nano-ESI-MS after cutting the different gel spots and in-gel trypsin digestion. A highly selective and specific tandem MS technique has been developed to characterize and localize up to ten lactosylation sites in beta-lactoglobulin (beta-Lg) and alpha(S2)-casein. alpha-Lactalbumin (alpha-La), with five lactosylated peptides, was found to be an interesting protein marker in the milk powder sample to detect chemical modification induced by the processing/storage conditions.     

Synthesis of branched oxime-linked peptide mimetics of the MUC1 containing a universal T-helper epitope

Our goal was to develop mimics of MUC1, highly immunogenic to induce an efficient immune response against the tumor-associated form of MUC1, and sufficiently different from the natural antigen to bypass the tolerance barrier in humans. With the aim of obtaining a well-defined peptide construct as a means of evoking the precise immune responses required in immunotherapy, we synthesized artificial mimics of the MUC1 protein composed of two MUC1 repeat units of inverse orientation and a universal T-helper epitope. To synthesize these heteromeric peptide constructs, we followed a convergent approach using chemoselective ligation based on oxime chemistry. A stem peptide was first synthesized bearing two orthogonally masked aldehydes. After successive deprotection, two oxime bonds can be specifically generated. The proposed strategy proved to be concise and robust, and allowed the synthesis of the tri-branched protein in a very satisfactory yield. The different constructs were tested for their ability to generate antibodies able to recognize the MUC1 protein.     

Gibbs states of the Hopfield model with extensively many patterns

We consider the Hopfield model withM(N)=N patterns, whereN is the number of neurons. We show that if is sufficiently small and the temperature sufficiently low, then there exist disjoint Gibbs states for each of the stored patterns, almost surely with respect to the distribution of the random patterns. This solves a provlem left open in previous work. The key new ingredient is a self-averaging result on the free energy functional. This result has considerable additional interest and some consequences are discussed. A similar result for the free energy of the Sherrington-Kirkpatrick model is also given.     

Rigorous results on the thermodynamics of the dilute Hopfield model

We study the Hopfield model of an autoassociative memory on a random graph onN vertices where the probability of two vertices being joined by a link isp(N). Assuming thatp(N) goes to zero more slowly thanO(1/N), we prove the following results: (1) If the number of stored patternsm(N) is small enough such thatm(N)/Np(N) 0, asN, then the free energy of this model converges, upon proper rescaling, to that of the standard Curie-Weiss model, for almost all choices of the random graph and the random patterns. (2) If in additionm(N) < ln N/ln 2, we prove that there exists, forT< 1, a Gibbs measure associated to each original pattern, whereas for higher temperatures the Gibbs measure is unique. The basic technical result in the proofs is a uniform bound on the difference between the Hamiltonian on a random graph and its mean value.     

Arsenite oxidation and arsenate determination by the molybdene blue method

Based on the similarity in properties of arsenate and phosphate, the colorimetric method using the molybdene blue complex was tested in order to determine low As(V) concentration in waters. The influence of complex formation time, daylight, temperature and competitive anions (silicate and sulphate) upon complex formation was determined. Optimal complex formation was reached in 1 h at 20±1 °C and was slightly favoured when developed in daylight. The formation rate declined with decreasing reaction temperature and no influence of any of the competitive anions tested (at concentrations usually found in natural waters of granitic areas) was noted. The detection limit of this method was 20 μg As(V) l⁻¹. This simple, fast and sensitive arsenic determination method is suitable for field analysis, especially for waters containing low levels of phosphate and organic matter. Through arsenate determination, this colorimetric method allowed the arsenite oxidation efficiency of five common industrial oxidants to be compared. H₂O₂ and MnO_2(s) were not considered as effective oxidants as a high excess was necessary to ensure As(III) oxidation. NaOCl and KMnO₄ were promising oxidants as they allowed complete arsenite oxidation with a small excess for NaOCl or even less than the electron stoichiometric ratio in the case of KMnO₄. FeCl₃ was the most effective oxidant among the reagents tested here.     

Synthesis of new crosslinkable co-polymers containing a push-pull zinc porphyrin for non-linear optical applications

In this paper, the synthesis of a crosslinkable co-polymer containing new push-pull arylethynyl zinc porphyrins is described. The synthesis of porphyrin chromophores, analogous to Therien's porphyrin (J. Am. Chem. Soc.1996, 118, 1497-1503) functionalized with a methacrylic polymerizable group and a carboxylic acid crosslinking group was achieved with a new synthetic procedure leading to a higher overall yield compared to what was previously reported in the literature for similar and simpler structures. Radical copolymerization of the porphyrin chromophore with glycidyl methacrylate has then been carried out with success. This work opens a perspective on the possibility to integrate porphyrinic chromophore with high first-order molecular quadratic hyperpolarizability coefficient in opto-electronic devices.     

Diastereoselective ring-closing metathesis: synthesis of P-stereogenic phosphinates from prochiral phosphinic acid derivatives

[reaction: see text] The preparation of phosphorus-containing trienes featuring two diastereotopic vinyl moieties followed by a diastereoselective ring-closing metathesis is described. This methodology allowed for the synthesis of novel highly functionalized P-stereogenic heterocycles featuring both an exo- and an endocyclic double bond. An investigation into the factors influencing the diastereochemical outcome of the ring-closing metathesis is also presented, revealing that the geometry of the double bonds conjugated to phosphorus is important and that 1,3-stereoinduction is superior to 1,4-stereoinduction for these reactions.     

Palladium-catalyzed oxidative cyclizations: synthesis of dihydropyranones and furanones

A boron-mediated syn- and anti-stereoselective aldol reaction giving rise to various beta-hydroxyenones was coupled to a Pd((II))-mediated oxidative cyclization to give 2,3,6-trisubstituted syn- and anti-dihydropyranones in good yields. The Pd((II))-mediated oxidative cyclization was expanded to alpha-hydroxyenones leading to furan-3(2H)-one derivatives, which include natural product bullatenone and a known precursor of geiparvarin. The sole product of the oxidative cyclization of alpha,beta-dihydroxyenone was a five-membered furan-3(2H)-one derivative, suggesting that the ring closure of these diols is both chemo- and regioselective.     

Photoelectron spectra of vinyl- and 1-alkynylgermanes and stannanes

Primary vinylic and acetylenic germanes and stannanes, synthesized by a chemoselective reduction of the corresponding trichloro derivatives, were investigated by ab initio quantum chemical methods and photoelectron spectroscopy. In particular, the PE spectra display very well-resolved bands which show the increasing destabilizing effect of 14 group heteroatom α-substitution of double or triple carbon–carbon bonds.