Synthetic Usefulness of the Sugar Cyclopentylidene Ketals

ABSTRACT

Cyclopentylidene ketals, moderately more acid-labile than their isopropylidene analogs, offer an alternative to the latter blocking groups. They have been shown to resist a large variety of reaction conditions commonly encountered in carbohydrate chemistry.     

A low-cost environmentally friendly approach to isolate lignin containing micro and nanofibrillated cellulose from Eucalyptus globulus bark by steam explosion

Cellulose - Micro- and Nano-Fibrillated Cellulose (MNFC) have gained increasing attention due to their remarkable properties, but their production usually requires an intensive multi-step process....     

Analysis of changes in attenuated total reflection FTIR fingerprints of Pseudomonas fluorescens from planktonic state to nascent biofilm state

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy is a useful method for monitoring biofilm in situ, non-destructively, in real time, and under fully hydrated conditions. In this work we focused on changes in Pseudomonas fluorescens ATR-FTIR fingerprint accompanying the very early stages of biofilm formation: initial bacterial adhesion and the very beginning of biofilm development in the presence of nutrients. To help interpreting variations in the ATR-FTIR fingerprint of sessile bacteria, ATR-FTIR spectra of planktonic bacteria in different growth phases were also examined, and the average surface coverage and spatial arrangement of bacteria on the ATR crystal were determined by epifluorescence microscopy. The proteins, nucleic acids and polysaccharides ATR-FTIR spectral data recorded during growth of sessile bacteria were shown to be linked to changes in the physiological state of the bacteria, possibly accompanied by extracellular polymeric substances production. This work clearly showed by spectroscopic method how bacteria change drastically their metabolism during the first hours of biofilm formation.     

Phase behavior, topology, and growth of neutral catanionic reverse micelles

The ternary catanionic system octylammoniumoctanoate/octane/water is studied by combined SANS, light scattering, conductivity, and phase diagram approach in the water-poor microemulsion region. The sphere-to-cylinder growth and branching depends on the concentration, the water-to-surfactant ratio, and the temperature. The unidimensional growth leads to a network of interconnected wormlike micelles. Like most studied linear nonionic surfactants, in this true catanionic system at equimolarity of anionic and cationic surfactant, the curvature toward water increases with temperature, making connections between cylinders less frequent.     

Charge dependent behavior of PNA/DNA/PNA triplexes in the gas phase

Intact noncovalent complexes were studied in the gas phase using negative ion nano-ESI mass spectrometry. Among various noncovalent systems studied in the gas phase, the interaction of DNA strands with peptide nucleic acids (PNAs) presents a strong interest as biologically relevant systems. PNAs originally described by Nielsen are used as DNA mimics as possible medical agents by imprisoning DNA single strands into stable noncovalent complexes. Two types of PNAs were investigated in the PNA/DNA multiplex: the original Nielsen's PNA and a modified backbone PNA by the introduction of syn- and anti-(aminoethyl)thiazolidine rings. We first investigated the stoichiometry of PNA/DNA multiplexes formed in solution and observed them in the gas phase via qualitative kinetics of complementary strand associations. It resulted in observing PNA2/DNA triplexes (ts) as the multiply deprotonated species, most stable in both the solution and gas phase. Second, charge-dependant decompositions of these species were undertaken under low-energy collision conditions. It appears that covalent bond cleavages (base releasing or skeleton cleavage) occur from lower ts charge states rather than ts unzipping, which takes place from higher charge states. This behavior can be explained by considering the presence of zwitterions depending on the charge state. They result in strong salt-bridge interactions between the positively charged PNA side chain and the negatively charged DNA backbone. We propose a general model to clearly display the involved patterns in the noncovalent triplex decompositions. Third, the relative stability of three PNA2/DNA complexes was scrutinized in the gas phase by acquiring the breakdown curves of their ts(6-) form, corresponding to the ts unzipping. The chemical structures of the studied PNAs were chosen in order to evidence the possible influence of backbone stereochemistry on the rigidity of PNA2/DNA complexes. It provided significantly different stabilities via V(m) measurements. The relative gas-phase stability order obtained was compared to that found in solution by Chassaing et al., and shows qualitative agreement.     

Chemical bonding in phosphane and amine complexes of main group elements and transition metals

The geometries and bond dissociation energies of the main group complexes X3B-NX3, X3B-PX3, X3Al-NX3, and X3Al-PX3 (X = H, Me, Cl) and the transition metal complexes (CO)5M-NX3 and (CO)5M-PX3 (M = Cr, Mo, W) have been calculated using gradient-corrected density functional theory at the BP86/TZ2P level. The nature of the donor-acceptor bonds was investigated with an energy decomposition analysis. It is found that the bond dissociation energy is not a good measure for the intrinsic strength of Lewis acidity and basicity because the preparation energies of the fragments may significantly change the trend of the bond strength. The interaction energies between the frozen fragments of the borane complexes are in most cases larger than the interaction energies of the alane complexes. The bond dissociation energy of the alane complexes is sometimes higher than that of the borane analogues because the energy for distorting the planar equilibrium geometry of BX3 to the pyramidal from in the complexes is higher than for AlX3. Inspection of the three energy terms, DeltaE(Pauli), DeltaE(orb), and DeltaE(elstat), shows that all three of them must be considered to understand the trends of the Lewis acid and base strength. The orbital term of the donor-acceptor bonds with the Lewis bases NCl3 and PCl3 have a higher pi character than the bonds of EH3 and EMe3, but NCl3 and PCl3 are weaker Lewis bases because the lone-pair orbital at the donor atoms N and P has a high percent s character. The calculated DeltaE(int) values suggest that the trends of the intrinsic Lewis bases' strengths in the main-group complexes with BX3 and AlX3 are NMe3 > NH3 > NCl3 and PMe3 > PH3 > PCl3. The transition metal complexes exhibit a somewhat different order with NH3 > NMe3 > NCl3 and PMe3 > PH3 > PCl3. The slightly weaker bonding of NMe3 than that of NH3 comes from stronger Pauli repulsion. The bond length does not always correlate with the bond dissociation energy, nor does it always correlate with the intrinsic interaction energy.     

New three-step domino reaction, "thiophilic addition-beta-elimination of fluoride-[3,3] sigmatropic rearrangement": Synthesis of alpha-allylic and alpha,alpha-bis(allylic) alpha-trifluoromethyl dithioesters

The three-step domino reaction, "thiophilic addition of an organomagnesium reagent onto dithioester-beta-elimination of fluoride-[3,3] sigmatropic rearrangement", provides the product of formal regiospecific substitution of a fluorine atom by an allyl group. This mild and versatile methodology was applied to the synthesis of various alpha-allylic and alpha,alpha-bis(allylic) alpha-trifluoromethyl dithioesters.     

In situ characterisation of a microorganism surface by Raman microspectroscopy: the shell of Ascaris eggs

Intestinal nematodes are very common human parasites and a single species, Ascaris lumbricoïdes, is estimated to infect a quarter of the world’s population. A sticky external layer covers their eggs. This work shows that Raman vibrational confocal spectroscopy is able to give information on the biochemical composition of the shell of Ascaris eggs. The biochemical localised characterisation of Ascaris eggs was performed directly on the eggs in their aqueous environment. The studied parasites came from two origins: dissections of adult females and extractions from biosolid sludges. The presence of mucopolysaccharides, proteins and chitin in the shell was demonstrated. The presence of ascaroside compounds was shown particularly via the narrow and intense bands from the organised long CH₂ chains. To the best of our knowledge, this is the first time that the latter have been observed in Raman vibrational spectra of microorganisms. Hydration of the shell was different depending on the intensity of the colour of the sludge eggs. Knowledge of the biochemical structural properties of egg surfaces would be useful to understand the egg adhesion phenomena on vegetables contaminated by reused wastewater.