A general method for convergent synthesis of functionalized exo-glycals based on halogenation and Suzuki cross-coupling of 1-exo-methylene sugars

Functionalized exo-glycals can be readily obtained by palladium catalyzed Suzuki cross-coupling of halo-exo-glycals with boronic acids.     

The influence of patterned nanofiber meshes on human mesenchymal stem cell osteogenesis

A specially designed electroconductive collector enables the electrospinning of P-NFM composed of areas of parallel/uniaxially aligned fibers and areas of random/orthogonal nanofiber distribution. The biological relevance of P-NFM is demonstrated using hBMSCs as an autologous cell source. The structures induce cell orientation along the uniaxially aligned fibers, mainly during earlier culturing periods under basal and osteogenic differentiation conditions. The microtopography of the P-NFM also controls the deposition of mineralized extracellular matrix along the pre-defined fiber direction. Genotypic characterization confirms the successful differentiation into the osteogenic lineage.     

Fibers and 3D mesh scaffolds from biodegradable starch-based blends: production and characterization

The aim of this work is the production of fibers from biodegradable polymers to obtain 3D scaffolds for tissue engineering of hard tissues. The scaffolds required for this highly demanding application need to have, as well as the biological and mechanical characteristics, a high degree of porosity with suitable dimensions for cell seeding and proliferation. Furthermore, the open cell porosity should have adequate interconnectivity for a continuous flow of nutrients and outflow of cell metabolic residues as well as to allow cell growth into confluent layers. Blends of corn starch, a natural biodegradable polymer, with other synthetic polymers (poly(ethylene vinyl alcohol), poly(epsilon-caprolactone), poly(lactic acid)) were selected for this work because of their good balance of properties, namely biocompatibility, processability and mechanical properties. Melt spinning was used to produce fibers from all the blends and 3D meshes from one of the starch-poly(lactic acid) blends. The experimental characterization included the evaluation of the tensile mechanical properties and thermal properties of the fibers and the compression stiffness, porosity and degradation behavior of the 3D meshes. Light microscopy picture of 3D meshes.     

Coupled-column liquid chromatography combined with postcolumn photochemical derivatization and fluorescence detection for the determination of herbicides in groundwater

This study examines the application of coupled-column LC-photochemically induced fluorimetry-fluorescence detection (LC-LC-PIF-FD), demonstrating its potential for the quantitative and selective detection of six herbicides, including propanil and the phenylureas monuron, monolinuron, chlorotoluron, diuron and neburon in groundwater samples. An AQUASIL C18 50 x 4.6 mm(2) id column coupled to an AQUASIL C18 150 x 4.6 mm(2) id column for analyte clean-up and determination were used, respectively. A simple SPE with Cl8 cartridges was carried out, yielding average recoveries between 80 and 112% (n = 6) with RSDs between 0.5 and 9%. The LODs ranged from 0.0083 to 0.0833 microg/L in the groundwater samples.     

Interpretation of unusual absorption bandwidths and resonance Raman intensities in excited state mixed valence

Excited state mixed valence (ESMV) occurs in molecules in which the ground state has a symmetrical charge distribution but the excited state possesses two or more interchangeably equivalent sites that have different formal oxidation states. Although mixed valence excited states are relatively common in both organic and inorganic molecules, their properties have only recently been explored, primarily because their spectroscopic features are usually overlapped or obscured by other transitions in the molecule. The mixed valence excited state absorption bands of 2,3-di-p-anisyl-2,3-diazabicyclo[2.2.2]octane radical cation are well-separated from others in the absorption spectrum and are particularly well-suited for detailed analysis using the ESMV model. Excited state coupling splits the absorption band into two components. The lower energy component is broader and more intense than the higher energy component. The absorption bandwidths are caused by progressions in totally symmetric modes, and the difference in bandwidths is caused by the coordinate dependence of the excited state coupling. The Raman intensities obtained in resonance with the high and low energy components differ significantly from those expected based on the oscillator strengths of the bands. This unexpected observation is a result of the excited state coupling and is explained by both the averaging of the transition dipole moment orientation over all angles for the two types of spectroscopies and the coordinate-dependent coupling. The absorption spectrum is fit using a coupled two-state model in which both symmetric and asymmetric coordinates are included. The physical meaning of the observed resonance Raman intensity trends is discussed along with the origin of the coordinate-dependent coupling. The well-separated mixed valence excited state spectroscopic components enable detailed electronic and resonance Raman data to be obtained from which the model can be more fully developed and tested.     

Rh(II) catalysed intramolecular C-H insertion of diazo substrates in water: a simple and efficient approach to catalyst reuse

Water is an efficient solvent for the Rh2(OAc)4 catalysed intramolecular C-H insertion of a range of diazo substrates without competitive water insertion. Due to the high solubility and stability of the catalyst in water, the catalyst can be efficiently reused.     

Influence of the tannin structure on the disruption effect of carbohydrates on protein-tannin aggregates

The disrupting effect of three different ionic carbohydrates (xanthan, pectin and gum arabic) on the formation of tannin-protein insoluble aggregates was assessed by nephelometry using bovine serum albumin (BSA) and several procyanidin fractions previously extracted from grape seeds. The presence in solution of any of the carbohydrates studied was found to restrain the formation of insoluble protein-tannin aggregates for every procyanidin fraction used. Xanthan was the most effective carbohydrate, whereas gum arabic was the least effective. The present work has revealed that the disrupting effect of carbohydrates is quite different depending on the procyanidin structure complexity. In general, the three carbohydrates studied revealed a similar trend in that their disrupting effect on tannin-BSA aggregate formation decreased with increase of the procyanidin degree of polymerization.     

Mechanism of formation of the internal aldimine in pyridoxal 5'-phosphate-dependent enzymes

In this paper we studied the mechanism of formation of the internal aldimine, a common intermediate to most pyridoxal 5'-phosphate (PLP)-dependent enzymes. A large model based on the crystal structure from the human ornithine decarboxylase (ODC) enzyme was constructed and in total accounts for 504 atoms. The reaction mechanism was investigated using the ONIOM methodology (B3LYP/6-31G(d)//AM1), and the final energies were calculated with the M06/6-311++G(2d,2p)//B3LYP/6-31G(d) level of theory. It was demonstrated that the reaction is accomplished in three sequential steps: (i) the nucleophilic attack of Lysine69 to PLP, (ii) the carbinolamine formation, and (iii) a final dehydration step. For the carbinolamine formation, several mechanistic hypotheses were explored, and the preferred pathway assigns a key role for the conserved active site Cys360. The overall reaction is exergonic in -9.1 kcal/mol, and the rate-limiting step is the dehydration step (E(a) = 13.5 kcal/mol). For the first time, we provide an atomistic portrait of this mechanism in an enzymatic environment. Moreover, we were able to assign a novel role to Cys360 in the ODC reaction mechanism that was never proposed.     

Determination of nine pyrethroid insecticides by high-performance liquid chromatography with post-column photoderivatization and detection based on acetonitrile chemiluminescence

An HPLC method was developed to determine pyrethroids, including fenpropathrin, beta-cyfluthrin, lambda-cyhalothrin, deltamethrin, fenvalerate, permethrin, acrinathrin, tau-fluvalinate, and bifenthrin, by coupling HPLC, post-column irradiation with UV light and chemiluminescence detection of the resulting photoproducts. It is based on the observation that photolyzed pyrethroids take part in a chemiluminescent reaction in presence of K3Fe(CN)6 and NaOH, whose signal increases with the percentage of acetonitrile in the reaction medium. As the yield of the photoderivatization process and the chemiluminescent signals depend on the percentage of acetonitrile, the chromatographic column (a Gemini C18, Phenomenex 150 mm x 4.6 mm, 5 microm particle size) was chosen with the aim of using high percentages of this organic solvent in the mobile phase. Previous studies showed that the rate of the chemiluminescent reaction was very fast. Therefore, a modification was carried out in the detector in order to mix the analytes and reactives as near as possible to the measure cell. The optimised method was validated with respect to linearity, precision, limits of detection and quantification accuracy. Under the optimised conditions, linear working range extends three orders of magnitude with the relative standard deviation on intra-day precision below 10% and detection limits between 0.013 and 0.049 microg mL(-1), according to the compound. The proposed method has been successfully applied to the determination of pyrethroids in tomato with good results.