New highlights on degradation process of verdigris from easel paintings

Verdigris is a green copper organometallic pigment, widely used in paintings during the fifteenth and sixteenth centuries. With ageing, chromatic modifications like browning or darkening can be observed on those green painted layers. An original but crucial approach has been developed based on the characterization of a reference neutral verdigris pigment—anhydrous copper acetate—and model samples, made of verdigris and linseed oil. Samples have undergone artificial ageing (temperature, light) to reproduce the color change effect. They were analysed before and after accelerated ageing tests by a complementary set of classical techniques: colorimetry, electron paramagnetic resonance, X-ray absorption spectroscopy, and UV–visible absorption. Our experiments revealed that the incorporation of the verdigris pigment in linseed oil induces a transformation of the copper acetate bimetallic structure, with the formation of monomeric species. These monomers, however, are not directly responsible for the darkening. The chromatic alteration seems instead linked to the transient formation of Cu(I) in the copper complexes of the pigment/oil system. This formation could be initiated by ambient light absorption through ligand-to-metal charge transfer, which favors the decarboxylation of the copper complexes leading to the reduction of Cu(II) into Cu(I). Moreover, dioxygen can react with partially decarboxylated dimers to form peroxy-Cu dimer complexes that can be responsible for the darkening.     

Ferroelectric Mott-Hubbard phase of organic (TMTTF)2X conductors

We present experimental evidence and a corresponding theory for the ferroelectric transition in the family of quasi-one-dimensional conductors (TMTTF)2X. We interpret this new transition in the frame of the combined Mott-Hubbard state taking into account the double action of the spontaneous charge disproportionation on the TMTTF molecular stacks and of the X anionic potentials.     

Simultaneous analysis of cadmium, lead, mercury, and arsenic content in foodstuffs of animal origin by inductively coupled plasma/mass spectrometry after closed vessel microwave digestion: method validation

A method validation of the total analysis of cadmium (Cd), lead (Pb), arsenic (As), and mercury (Hg) in foodstuffs by inductively coupled plasma/mass spectrometry (ICP/MS) after closed vessel microwave digestion is presented. Due to the lack of reference method for ICP/MS techniques in food and, based on the project of the European Committee of Normalization (CEN/TC 275/WG 10), the Agence Fran?aise de Normalisation (AFNOR) guidelines NF V03-110 were used for the evaluation of this method based on 2 steps, sample preparation and multielement detection. Several criteria considered as compulsory (linearity, specificity, precision under repeatability conditions, and trueness) have been estimated and discussed, in addition to intermediate precision reproducibility, the limit of detection, and the limit of quantification. Furthermore, a comparison with in-house methods using electrothermal atomic absorption was performed using an external proficiency testing scheme and food samples. The results indicated that this method could be used in the laboratory for the routine determination of these 4 cumulative toxic metals in foodstuffs with acceptable analytical performance.     

Synthesis of branched poly(butylene succinate): Structure properties relationship

A series of branched poly(butylene succinate) (PBS) were synthesized with several branching agents namely trimethylol propane (TMP), malic acid, trimesic acid, citric acid and glycerol propoxylate. The structure of the branched polymers was analyzed by SEC and ¹H-NMR. The effect of branching agent structure on crystallization was also investigated and played a significant role. Isothermal studies showed that glycerol propoxylate could act as a nucleating agent. By contrast high content of TMP disturbed the regularity of the chain and hindered the crystallization of PBS. From the non-isothermal kinetic study, it was found that glycerol propoxylate increased noticeably the crystallization rate due to the flexible structure of the branching agent. A secondary nucleation was observed with glycerol propoxylate attributed to the crystallization of amorphous fraction included between crystallites formed at the primary crystallization. Chain topology was obtained through rheological investigations and the synthesized polymers showed a typical behavior of a mixture of linear and randomly branched PBS. The incorporation of branches improved the processability of PBS for film blowing application and the modulus and the stress at break of the resulting film were significantly increased.     

Dispersion Laws of a Highly Excited Three-Level Atom with an Equidistant Energy Spectrum

A dispersion law for the system of three-level atoms with an equidistant energy spectrum interacting with resonant laser radiation has been obtained taking into account two successive optically allowed one-photon transitions and an optically allowed two-photon transition between the lower and upper levels. It has been shown that the dispersion law consists of three polariton branches. The effects of repulsion and attraction of branches of the dispersion law and their intersection, as well as the self-consistent variation of the photon–atom coupling constant, have been predicted.     

Synthesis of alkynes and alkynyl iodides bearing a protected amino alcohol moiety as functionalized amino acids precursors

Amino acid precursors in protected amino alcohol form are important synthons that can be used as building-blocks for the hemisynthesis of non-natural amino acids. Serine can be used as a common starting material for the synthesis of such compounds differently protected. Particularly, protected amino alcohols bearing an ethynyl and/or an iodoethynyl group can be used in cross-couplings, in 1,3-dipolar cycloadditions and/or in Nozaki-Hiyama-Kishi type reactions. We thus demonstrated that the efficiently protected amino alcohols derived from serine can be coupled to a sugar derivative by an indium mediated alkynylation reaction. The conditions of this coupling are compatible with such functionalized derivatives and allow envisaging an access to C-glycosylated amino acids.     

Chemical Synthesis of Native S-Palmitoylated Membrane Proteins through Removable-Backbone-Modification-Assisted Ser/Thr Ligation

The preparation of native S-palmitoylated (S-palm) membrane proteins is one of the unsolved challenges in chemical protein synthesis. Herein, we report the first chemical synthesis of S-palm membrane proteins by removable-backbone-modification-assisted Ser/Thr ligation (RBM^GABA-assisted STL). This method involves two critical steps: 1) synthesis of S-palm peptides by a new γ-aminobutyric acid based RBM (RBM^GABA) strategy, and 2) ligation of the S-palm RBM-modified peptides to give the desired S-palm product by the STL method. The utility of the RBM^GABA-assisted STL method was demonstrated by the synthesis of rabbit S-palm sarcolipin (SLN) and S-palm matrix-2 (M2) ion channel. The synthesis of S-palm membrane proteins highlights the importance of developing non-NCL methods for chemical protein synthesis.     

Light Reflection from the end of a semi-infinite semiconductor under conditions of two-photon excitation of biexcitons

It is shown that reflectivity of the end of a semi-infinite semiconductor under conditions of twopulse two-photon excitation of biexcitons from the ground state of the crystal is characterized by a multistable behavior as a function of amplitudes of the incident pulse fields.     

Quantitation of triacylglycerols in plant oils using HPLC with APCI-MS, evaporative light-scattering, and UV detection

The main constituents of plant oils are complex mixtures of TGs differing in acyl chain lengths, number and positions of double bonds, and regioisomerism. A non-aqueous reversed-phase HPLC method with acetonitrile-2-propanol gradient and 30 + 15 cm NovaPak C18 columns makes possible an unambiguous identification of the highest number of TGs ever reported for these oils, based on positive-ion APCI mass spectra. A new approach to TG quantitation is based on the use of response factors with three typical detection techniques for that purpose (APCI-MS, evaporative light-scattering detection, and UV at 205 nm). Response factors of 23 single-acid TGs (saturated TGs from C7 to C22, 7 unsaturated TGs), 4 mixed-acid TGs, diolein and monoolein are calculated from their calibration curves and related to OOO. Due to differences between saturated and unsaturated acyl chains, the use of response factors significantly improves the quantitation of TGs. 133 TGs containing 22 fatty acids with 8-25 carbon atoms and 0-3 double bonds are identified and quantified in 9 plant oils (walnut, hazelnut, cashew nut, almond, poppy seed, yellow melon, mango, fig, date) using HPLC/APCI-MS with a response factor approach. Average parameters and relative fatty acid concentrations are calculated with both HPLC/APCI-MS and GC/ FID.