Vibrational spectroscopic investigation of the phase diagram of a biomimetic lipid monolayer

The phase behavior of a biomimetic monolayer consisting of diphospholipid molecules on water is investigated using vibrational sum-frequency generation and fluorescence microscopy. In addition to the transition from the-molecularly disordered-liquid phase to the highly ordered and oriented con-densed phase, a novel, extremely sharp transition is observed at low compression, which is attributed to the uncurling of the hydrophobic alkane chains upon compression.     

A short path synthesis of [13C/15N] multilabeled pyrimidine nucleosides starting from glucopyranose nucleosides

The synthesis of fully [13C/15N] labeled pyrimidine nucleosides has been achieved from 13C-glucose and labeled nucleobases. The reaction scheme leads directly to the protected nucleosides without the need for the inversion of configuration of C-3 of 13C-glucose. This was achieved by an oxitative ring-opening reaction removing the carbon with the wrong configuration.     

Thermal decomposition of a series of 1,2-diazetines

A homologous series of tricyclic diazetines (6a-c), differing by the number of methylene groups in the saturated bridges of the fused carbon bicycles, was synthesized. The DeltaH++ of decomposition for each of the diazetines to afford N2 and the corresponding alkene was determined experimentally: 6a, 31.7; 6b, 39.3; 6c, 38.8 kcal/mol. The ground-state strain energy of each diazetine was estimated utilizing computationally obtained DeltaHf's for each of the experimentally investigated diazetines as well as several other diazetines whose DeltaH++'s had been previously reported in the literature. The sum of the ground-state strain energies and DeltaH++'s of decomposition for all of the diazetines was nearly constant, with an average value of 59 kcal/mol, suggesting that all of the diazetines decompose via the same mechanism. Generally, the higher the ground-state strain energy of the diazetine, the less the DeltaH++ for decomposition. The decomposition transition states for 6a-c and 7 were modeled computationally at the RB3LYP/6-311+G(3df,2p)//UB3LYP/6-31+G(d,p) level. The agreement of the experimentally determined DeltaH++ values with transition-state energies obtained computationally supports the reaction mechanism originally proposed by Yamabe that the elimination process occurs by an unsymmetrical, yet concerted, transition state with strong biradical character.     

A new paclitaxel prodrug for use in ADEPT strategy

A new paclitaxel prodrug intended for use in Antibody-Directed Prodrug Therapy (ADEPT) or Prodrug Monotherapy (PMT) has been prepared. This prodrug was originally designed to be activated into the drug by human beta-glucuronidase. In order to enhance the liberation rate of paclitaxel, an elongated spacer system including a nitro-aromatic derivative and a N,N'-methylethylenediamine was incorporated between the sugar moiety and the drug. Indeed, this new prodrug proved to be activated significantly faster than a former paclitaxel prodrug containing a conventional spacer.     

Comparison of three sequential extraction procedures used to study trace metal distribution in an acidic sandy soil

On an acid sandy soil contaminated with trace metals (Fe, Mn, Cu, Pb and Zn), three sequential extraction procedures were compared to determine the efficiency of the reagents used and the effects of the step order on the fractionation of metal species. In all cases, a magnesium nitrate solution (MgNIT) was previously used to extract exchangeable forms. In the first procedure (I), the next extraction step was performed with sodium acetate buffer (NaOAc), as used on calcareous soils, to dissolve active calcium carbonate. Then trace metals bound to different forms of oxi-hydroxides (NH(2)OH, TAMOx and TAMAs fractions) were extracted before organic matter/sulfide oxidation with hydrogen peroxide at pH 2.0 in nitric acid medium (OMHyd). Finally, residual bound metals (RESID) in each procedure were extracted with a nitric-hydrofluoric-perchloric acid mixture. The second procedure (II) was the same as I, but without the NaOAc step, because of the absence of carbonate in the study soil. In procedure III, the NaOAc step was omitted and the oxidizable organic/sulfide fraction was extracted with sodium hypochlorite at pH 8.5 (OMOCl) before the reducible fractions. This study first showed that NaOAc may remove considerable amounts of metals (especially Mn and Zn) in other forms than exchangeable ones. Procedures II and III give similar results for Fe, Mn and Zn forms, which were mainly found in fractions of inorganic soil components, but not for Cu and Pb. Copper distribution was affected by the position of the oxidation step in the sequence. In procedure II, where the oxidation step (OMHyd) ended the sequence, Cu was mainly recovered in the TAMOx fraction. However, in procedure III, where the oxidation step (OMOCl) preceded the NH(2)OH, TAMOx and TAMAs steps, Cu was found in both OMOCl and TAMOx fractions. Lead distribution varied with oxidation reagent: it was partly removed in the OMHyd fraction of procedures I and II, and to a much lower extent in the OMOCl fraction of procedure III, probably due to the alkaline pH of the reagent in the latter case.     

Thiolated poly(ε-caprolactone) macroligand with vacant coordination sites on gold substrate: Synthesis and surface characterization

Surface-confined telechelic poly(ε-caprolactone) macroligand with two distinct functional groups per polymeric chain has been synthesized and characterized. The molecular microstructure of the macroligand with regard to the properties of the end-capped functionalities and with those on surface substrate has been studied by solution and surface analytical methods (i.e., X-ray photoelectron spectroscopy (XPS), grazing angle reflectance-Fourier transform IR spectroscopy (GA-FTIR), water contact angle measurements, and atomic force microscopy (AFM)) to elucidate the structure and properties of such multifunctional polymer on gold (1 1 1) substrate.     

Dammarane Triterpenes from Gardenia aubryi Vieill.

Three new dammarane triterpenoids, gardaubryones A–C ( 1 – 3 ), were isolated from the gum collected on the aerial parts of Gardenia aubryi Vieill ., together with the known compounds hydroxydammarenone II ( 4 ), ocotillone ( 5 ), cabraleone, and hollongdione. The structures of the novel compounds were established on the basis of mass spectrometry, NMR experiments, and chemical‐correlation reactions.     

Detection of Frozen–Thawed Duck Fatty Liver by MALDI-TOF Mass Spectrometry: A Chemometrics Study

The marketing of poultry livers is only authorized as fresh, frozen, or deep-frozen. The higher consumer demand for these products for a short period of time may lead to the marketing of frozen–thawed poultry livers: this constitutes fraud. The aim of this study was to design a method for distinguishing frozen–thawed livers from fresh livers. For this, the spectral fingerprint of liver proteins was acquired using Matrix-Assisted Laser Dissociation Ionization-Time-Of-Flight mass spectrometry. The spectra were analyzed using the chemometrics approach. First, principal component analysis studied the expected variability of commercial conditions before and after freezing–thawing. Then, the discriminant power of spectral fingerprint of liver proteins was assessed using supervised model generation. The combined approach of mass spectrometry and chemometrics successfully described the evolution of protein profile during storage time, before and after freezing-thawing, and successfully discriminated the fresh and frozen–thawed livers. These results are promising in terms of fraud detection, providing an opportunity for implementation of a reference method for agencies to fight fraud.     

Bacteria encapsulation in colloidal inorganic matrices: Is it a general method?

Zirconium oxyhydroxide nanoparticles prepared by an aqueous route were evaluated for Escherichia coli bacteria encapsulation. A low viability rate was measured 24 hours after immobilization that could be attributed to nanoparticle cytotoxicity. Moreover, the presence of glycerol, a long-term cell-preserving molecule, hindered gel formation, probably due to its adsorption on the nanoparticle surface. A comparison with boehmite and ferrihydrite gels previously synthesized following a similar aqueous colloidal route suggests that the generalization of this method will rely on a careful control of the nanoparticle surface reactivity and may require surface chemical modification.