Precursor Of Choice Research Articles

The influence of the molecular weight of polymer on the morphology, functional properties and L929 fibroblasts growth on polylactide membranes for tissue engineering

The main goal of tissue engineering (TE) is supporting the regeneration of damaged tissues that are difficult to regenerate. The experimental results of the preparation of semi-permeable membranes for cell cultures are presented. The effect of the PLA molecular weight and addition of pore precursors on the morphology of the membranes was studied. The pore precursor of choice was polyvinylpyrrolidone (PVP). It was found that semi-permeable membranes for application in tissue engineering can be prepared with polylactides of molecular weight more significant than 37,000 g/mol. Moreover, it was observed that the growth of the molecular weight of the polymer, the porosity, the size of the pores, the Young modulus and maximum tensile increased. Additionally, to obtain a better morphology of the membranes, PVP should be added to the polymeric solution. Positive growth of L929 fibroblast cells on the obtained scaffolds was shown.

Electrodeposition of MoSx Hydrogen Evolution Catalysts from Sulfur-Rich Precursors.

Amorphous molybdenum sulfides (a-MoSx) are known to be active electrocatalysts for the hydrogen evolution reaction (HER), but the role stoichiometry of the sulfur atoms plays in the HER activity remains unclear. In this work, we deposited thin films of a-MoSx from two thiomolybdate deposition baths with different sulfur ratios (MoS42- and Mo2S122-) and showed that the sulfur stoichiometry, as determined by X-ray photoelectron spectroscopy, is controlled by the precursor of choice and the electrochemical method used to deposit the thin films. Using the Mo2S122- precursor allows access to a MoS6 thin film, with a higher S/Mo ratio compared with that of any previously reported electrodeposited films. We also examined the effect of electrochemistry on the resulting S/Mo ratio in the as-prepared a-MoSx thin films. Samples with S/Mo ratios ranging from 2 to 6 were electrodeposited on glassy carbon (GC) substrates by using anodic, cathodic, or cyclic voltammetry deposition. The a-MoSx thin films deposited on GC substrates were tested as HER catalysts in acidic electrolytes. The overpotentials needed to drive current densities of 10 mA/cm2 ranged from 160 mV for MoS6 samples to 216 mV for MoS2 samples, signifying the important role sulfur content plays in HER activity of the prepared films. Furthermore, we characterized the deactivation of the a-MoSx films and found that the sulfur content is gradually depleted over time, leading to a slow deactivation of the a-MoSx thin-film catalysts. We showed a facile procedure that affords a-MoSx films with high sulfur content by using S-rich precursors and highlighted the role of sulfur in the prepared films for HER.

Modification and Functionalization of the Guanidine Group by Tailor-made Precursors

The guanidine group is one of the most important pharmacophoric groups in medicinal chemistry. The only amino acid carrying a guanidine group is arginine. In this article, an easy method for the modification of the guanidine group in peptidic ligands is provided, with an example of RGD-binding integrin ligands. It was recently demonstrated that the distinct modification of the guanidine group in these ligands allows for the selective modulation of the subtype (e.g., between the subtypes αv and α5). Moreover, a formerly unknown strategy for the functionalization via the guanidine group was demonstrated, and the synthetic approach is reviewed in this document. The modifications described here involve terminally (Nω) alkylated and acetylated guanidine groups. For the synthesis, tailor-made precursor molecules are synthesized, which are then subjected to a reaction with an orthogonally deprotected amine to transfer the pre-modified guanidine group. For the synthesis of alkylated guanidines, precursors based on N,N′-Di-Boc-1H-pyrazole-1-carboxamidine are used to synthesize acylated compounds, the precursor of choice being a correspondingly acylated derivative of N-Boc-S-methylisothiourea, which can be obtained in one- and two-step reactions.

Modification and Functionalization of the Guanidine Group by Tailor-made Precursors.

The guanidine group is one of the most important pharmacophoric groups in medicinal chemistry. The only amino acid carrying a guanidine group is arginine. In this article, an easy method for the modification of the guanidine group in peptidic ligands is provided, with an example of RGD-binding integrin ligands. It was recently demonstrated that the distinct modification of the guanidine group in these ligands allows for the selective modulation of the subtype (e.g., between the subtypes αv and α5). Moreover, a formerly unknown strategy for the functionalization via the guanidine group was demonstrated, and the synthetic approach is reviewed in this document. The modifications described here involve terminally (Nω) alkylated and acetylated guanidine groups. For the synthesis, tailor-made precursor molecules are synthesized, which are then subjected to a reaction with an orthogonally deprotected amine to transfer the pre-modified guanidine group. For the synthesis of alkylated guanidines, precursors based on N,N'-Di-Boc-1H-pyrazole-1-carboxamidine are used to synthesize acylated compounds, the precursor of choice being a correspondingly acylated derivative of N-Boc-S-methylisothiourea, which can be obtained in one- and two-step reactions.

ChemInform Abstract: Siloles. Part 2. Silaindenes (Benzosiloles) and Silafluorenes (Dibenzosiloles): Synthesis, Characterization, and Applications

AbstractReview: 170 refs.

Bandrowski’s Base Revisited: Toward a Unprecedented Class of Quinonediimines or New Two-Way Chromophoric Molecular Switches

Temperature-controlled reactivity places Bandrowski's base 3 at the crossroads of a new versatile strategy for the preparation of two different categories of chromophores. We describe the access to a new class of quinonediimines (8) with an extended pi-conjugation owing to the presence of imine functions. Under slightly different conditions, Bandrowski's base appears to be the precursor of choice in the preparation of a novel pH- and light-dependent binary molecular switch. This molecule (11) is constituted of a benzobis(imidazole) core that can be reversibly protonated and a diarylethene unit which can be reversibly converted into its closed form upon irradiation. Triggered by two independent variables, 11 provides four distinct optical states for molecular number processing.

Neural computations underlying action-based decision making in the human brain

Action-based decision making involves choices between different physical actions to obtain rewards. To make such decisions the brain needs to assign a value to each action and then compare them to make a choice. Using fMRI in human subjects, we found evidence for action-value signals in supplementary motor cortex. Separate brain regions, most prominently ventromedial prefrontal cortex, were involved in encoding the expected value of the action that was ultimately taken. These findings differentiate two main forms of value signals in the human brain: those relating to the value of each available action, likely reflecting signals that are a precursor of choice, and those corresponding to the expected value of the action that is subsequently chosen, and therefore reflecting the consequence of the decision process. Furthermore, we also found signals in the dorsomedial frontal cortex that resemble the output of a decision comparator, which implicates this region in the computation of the decision itself.

Synthesis of a Tri- and Tetrasaccharide Fragment Specific for the Shigella flexneri Serotype 5a O-Antigen. A Reinvestigation

ABSTRACT Stereocontrolled, stepwise synthesis of methyl α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside (A(E)B, 1) and methyl 2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside (DA(E)B, 2) is described; these constitute the methyl glycosides of fragments of the O-specific polysaccharide of Shigella flexneri serotype 5a. Two routes to trisaccharide 1 were considered. Route 1 involved the coupling of a precursor to residue A and a disaccharide EB, whereas route 2 was based on the condensation of a precursor to residue E and a disaccharide AB. Rather surprisingly, the latter afforded the β-anomer of 1, namely methyl α-L-rhamnopyranosyl-(1→2)-[β-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside as the major product. Route 1 was preferred. Overall, several observations made during this study suggested that, for the construction of higher fragments, a suitable precursor to rhamnose A would require protecting groups of low bulkiness at position 3 and 4. Therefore, the 2-O-acetyl-3,4-di-O-allyl-α-L-rhamnopyranosyl trichloroacetimidate (35) was the precursor of choice to residue A in the synthesis of the tetrasaccharide 2. The condensation product of 35 and methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl-4-O-benzyl-α-L-rhamnopyranoside was selectively deacylated and condensed to 2-trichloroacetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-glucopyranosyl trichloroacetimidate to afford the corresponding fully protected tetrasaccharide 45. Controlled stepwise deprotection of the latter proceeded smoothly to afford the target 2. It should be emphasised that the preparation of 45 was not straightforward, several donors and coupling conditions that were tested resulted only in the complete recovery of the acceptor. Distortion of several signals in the 13C NMR spectra of the fully or partially protected tetrasaccharide intermediates suggested that steric hindrance, added to the known low reactivity of HO-2 of rhamnosyl acceptors, probably played a major role in the outcome of the glycosidation attempts.

Vanadia–silica aerogels from vanadylacetylacetonate

For the preparation of vanadium pentoxide doped silica gels, vanadium(V) oxide trialkoxides are the precursors of choice [A.E. Stiegman, H. Eckert, G. Plett, S.S. Kim, M. Anderson, A. Yavrouia, Chem. Mater. 5 (11) (1993) 1591; D.C.M. Dutoit, M. Schneider, P. Fabrizioli, A. Baiker, Chem. Mater. 8 (1996) 734] as they possess already the desired oxidation number. In vanadylacetylacetonate, the oxidation number of vanadium is only +4 instead of +5. However, vanadylacetylacetonate is less reactive with water and thus easier to handle, less toxic and cheaper than vanadium(V) oxide triisopropoxide. Gels were prepared using vanadylacetylacetonate, tetramethoxysilane, methanol and water containing HCl or NH 3 as catalyst. After supercritical drying with respect to CO 2 and heat treatment in air, vanadia doped silica aerogels show the same colour change upon adsorption of water molecules as vanadium(V) oxide triisopropoxide doped silica xerogels. Structural properties were investigated by N 2-absorption and SAXS measurements.