Uncatalyzed reaction of silyl ketene acetals with oxalyl chloride: a straightforward preparation of symmetrical pulvinic acids

[reaction: see text] Several natural pulvinic acids were synthesized. Silyl ketene acetals derived from methyl arylacetates (4 equiv) reacted with oxalyl chloride at -78 degrees C, without the need of adding a catalyst. After treatment of the crude diketones with DBU and acidification with hydrochloric acid, symmetrical pulvinic acids methyl esters were obtained. Saponification of the methyl esters afforded the corresponding pulvinic acids in 60-70% overall yields from oxalyl chloride.     

Salt removal during Off-Gel electrophoresis of protein samples

The Off-Gel technology was recently described for protein fractionation in a solution placed on top of an immobilized pH gradient gel. In addition, this process was found to remove salts from the biological samples to analyze. This desalting effect is studied experimentally in a conductometric prototype cell. A simplified analytical model is developed to understand this process and a good agreement is found with the conductivity measurements. To illustrate the desalting of a biological sample, a 1 mg.mL(-1) solution of beta-lactoglobulin A in 0.1 M NaCl is subjected to electrophoresis in a single compartment Off-Gel cell. The analysis of the resulting sample by ESI-MS demonstrates the effective removal of salt. A finite element diffusion-migration model is also used to illustrate how the nonuniformity of the electric field in the cell, associated with the salt migration, can slow down the desalting process.     

PHOTOIONIZATION OF TRYPTOPHAN: AN ELECTRON SPIN RESONANCE INVESTIGATION

The photoionization of tryptophan has been studied by ESR spectroscopy using the free radical scavenger 5, 5 dimethyl-1-pyrroline-l-oxide as a spin trap for hydrated electrons. A special set-up has been devised to irradiate more than one aliquot of the bubbled aqueous solutions in the cavity without removing the ESR cell out of the cavity.
Quantum yields of electrons production have been estimated as a function of irradiation wavelength. No photoionization threshold has been observed in these experiments.     

ACID-BASE EQUILIBRIA OF THE EXCITED SINGLET AND TRIPLET STATES AND THE SEMI-REDUCED FORM OF ACRIDINE ORANGE

Abstract— The acid-base equilibria of the excited singlet and triplet states of acridine orange (AO) were studied by flash-photolysis and fluorometric methods. The dye is a stronger base in the first excited singlet state (pK_s= 13.3) than in the triplet and ground states (pK_r= 10.3: pK_c, = 10.2); acridine orange follows the trend observed with some other heterocyclic compounds, viz. pK_s > pK_r= pK,_c. At room temperature, an anomalous fluorescence occurs from the dye in basic media: the assignment of this emission is discussed.
The semi-reduced dye was studied as a function of pH. In a large pH range (3–14), only the protolytic equilibrium between the cationic (AOH₂⁺) and the neutral (AOH) radicals was observed; the pK value corresponding to this equilibrium was found to be in the range of pH 5–6.     

Hemoabzymes different strategies for obtaining artificial hemoproteins based on antibodies

Besides existing models of chemical or biotechnological origin for hemoproteins like peroxidases and cytochromes P450, catalytic antibod ies (Abs) with a metalloporphyrin cofactor represent a promising alter native route to catalysts tailored for selective oxidation reactions. A brief overview of the literature shows that, until now, the first strategy for obtaining such artificial hemoproteins has been to produce antipor phyrin Abs, raised against various free-base, N-substituted, Sn-,Pd-,or Fe-porphyrins. Four of them exhibited, in the presence of the corre sponding Fe-porphyrin cofactor, a significant peroxidase activity, with k_cat/K_m values of 10² to 5 × 10³/M/s. This value remained low when com pared to that of peroxidases, probably because neither a proximal ligand of the Fe, nor amino acid residues participating in the catalysis of the heterolytic cleavage of the O—O bond of H₂O₂, have been induced in those Abs. This strategy has been shown to be insufficient for the elabo ration of effective models of cytochromes P450, because only one set of Abs, raised againstmeso-tetrakis(para-carboxyvinylphenyl)porphyrin, was reported to catalyze the nonstereoselective oxidation of styrene by iodosyl benzene using a Mn-porphyrin cofactor, and attempts to gener ate Abs having binding sites for both the substrate and the metallopor phyrin cofactor, using as a hapten a porphyrin covalently linked to the substrate, were not successful. A second strategy is then proposed, which involves the chemical labeling of antisubstrate Abs with a metallopor phyrin. As an example, preliminary results are presented on the covalent linkage of an Fe-porphyrin to an antiestradiol Ab, in order to obtain semisynthetic catalytic Abs able to catalyze the selective oxidation of steroids.     

Multitrack electrospray chips

Multitrack electrospray chips (MTEC) were fabricated by UV-photoablation of polyethylene terephthalate (PET) substrates. They are composed of an array of up to six microchannels that are successively used as electrospray ionization (ESI) emitters for mass spectrometry (MS). There is no requirement for alignment of the different spraying microchannels with the mass spectrometer orifice. The MTEC is thus fixed in front of the mass spectrometer and the successive MS analyses are performed without moving the chip. The sequential electrospraying by successive application of an identical high voltage in each off-axis microchannel was evaluated for the fast screening of peptides and proteins. The counting of cysteines in peptides through chemical modification and the relative quantification of a peptide in two samples are presented herein as two original strategies based on this new analytical tool.     

Synthesis and radioprotective study of new siladithioacetals and germadithioacetals

A series of organosilicon and organogermanium compounds derived from cysteamine, methylcysteamine and 2‐[1‐(1‐naphthyl)ethyl]‐2‐imidazoline have been prepared and their radiopharmacological properties (radioprotective activity and toxicity) have been determined in mice. A number of these new organometallic derivatives have been found to possess radioprotective activity. We have also noted a notable decrease of the toxicity and a fairly large increase in the radioprotective activity in comparison with the unsubstituted organic molecules. Copyright © 2003 John Wiley & Sons, Ltd.     

OXYDATION ALCALINE PAR L'ACIDE PERPROPIONIQUE D'ARYL MÉTHYL SULFURES EN SULFOXYDES. ETUDES EXPÉRIMENTALES ET THÉORIQUES DE L'OXYDATION NUCLÉOPHILE DE DÉRIVÉS P-SUBSTITUÉS DU THIOANISOLE PAR L'ANION PERPROPIONATE EN MILIEU MICELLAIRE

L'action de l'acide perpropionique CH₃CH₂CO₃H (1) a été étudiée en milieu alcalin micellaire (pH ～ 11; chlorure de cétyl triméthyl ammonium, CTACl) sur le thioanisole (4) et sur ses dérivés p-substitués, le p-méthoxy (2), le p-méthyl (3), le p-bromo (5) et le p-nitro (6). L'oxydation conduit exclusivement aux dérivés sulfoxydes (2a–6a). Les effets du pH, de la substitution et de la température ont permis de mieux comprendre la réaction d'oxydation de ces sulfures en sulfoxydes par l'acide perpropionique. Des calculs ab initio ont montré la cohérence de nos hypothèses. Enfin l'influence du milieu sur la cinétique de la réaction a été évalué en phase aqueuse (pH ～ 11) en présence de CTACl.

The reaction of perpropionic acid CH₃CH₂CO₃H (1) with thioanisole (4) and p-substituted thioanisoles [p-methoxy (2), p-methyl (3), p-bromo (5), and p-nitro (6)] in stoechiometric proportion has been carried out in micellar medium (cetyl trimethyl ammonium chloride, CTACl). Studies of the influence of the pH, the temperature and the substitution of the thioanisole, provide a better understanding of the sulfoxides (2a–6a) formation. Ab initio calculations have been achieved and the oxidation reaction has been studied in detail in aqueous medium (pH = 11).     

A thermodynamic approach to model the caloric properties of semicrystalline polymers

It is well known that the crystallisation and melting behaviour of semicrystalline polymers depends in a pronounced manner on the temperature history. If the polymer is in the liquid state above the melting point, and the temperature is reduced to a level below the glass transition, the final degree of crystallinity, the amount of the rigid amorphous phase and the configurational state of the mobile amorphous phase strongly depend on the cooling rate. If the temperature is increased afterwards, the extents of cold crystallisation and melting are functions of the heating rate. Since crystalline and amorphous phases exhibit different densities, the specific volume depends also on the temperature history. In this article, a thermodynamically based phenomenological approach is developed which allows for the constitutive representation of these phenomena in the time domain. The degree of crystallinity and the configuration of the amorphous phase are represented by two internal state variables whose evolution equations are formulated under consideration of the second law of thermodynamics. The model for the specific Gibbs free energy takes the chemical potentials of the different phases and the mixture entropy into account. For simplification, it is assumed that the amount of the rigid amorphous phase is proportional to the degree of crystallinity. An essential outcome of the model is an equation in closed form for the equilibrium degree of crystallinity in dependence on pressure and temperature. Numerical simulations demonstrate that the process dependences of crystallisation and melting under consideration of the glass transition are represented.