A study of polymer-supported bases for the solution phase synthesis of glycosyl trichloroacetimidates

Polystyrene-supported strong organic bases are highly efficient reagents for the solution-phase synthesis of glycosyl trichloroacetimidates, affording quantitative yields of pure products in short reaction times after simple filtration and evaporation. Although efficiency of the different bases varies with substrate structure, polymer-bound 1,8-diazabicyclo[5.4.0]undec-7-ene was found to give the best results for all the substrates tested.     

Experimental study of short- and long-time diffusion regimes of spherical particles in carboxymethylcellulose solutions

The behavior of latex particles in carboxymethylcellulose (CMC) solutions with different probe radii and solution concentrations is investigated. The diffusion processes of probe particles are studied by means of dynamic light scattering experiments. The existence of two diffusion regimes (a short-time regime and a long-time regime) is established for concentrations higher than the threshold value which changes for each probe dimension. Information is also provided about the relative weight of the probe population undergoing the two diffusion processes. This experimental evidence is discussed in connection with the existence of a defined volume (cage) in which short-time diffusion is the characteristic motion, while the long-time diffusion process dominates the motion over all the cages. Furthermore, there was found to be some deviation from Stokes-Einstein behavior.     

Mixing thiols on the surface of silver nanoparticles: preserving antibacterial properties while introducing SERS activity

The purpose of the study was to prepare and characterize nanosuspensions that can maintain high and extended supersaturation to improve the dissolution and absorption of poorly soluble 10-hydroxycamptothecin (10-HCPT). 10-HCPT oral nanosuspensions (HCPT-Nanosuspensions) were produced on a laboratory-scale by microprecipitation- high pressure homogenization method. The particle morphology and the physical state were studied using transmission electron microscopy, X-ray powder diffraction (XRPD), and differential scanning calorimetry (DSC). Supersaturated dissolution tests were carried out with the paddle method. Caco-2 cell experiments were performed to imitate the oral absorption. The in vivo pharmacokinetics studies were undertaken in rats following oral administration. The 10-HCPT nanoparticles were 135 nm in dimension before lyophilization and were claviform or lump in shape. XRPD and DSC both confirmed that a portion of 10-HCPT was present in a crystalline state in nanosuspension. Supersaturated dissolution tests showed HCPT-Nanosuspensions could maintain high supersaturated level for an extended period time. The cell experiment on HCPT-Nanosuspensions showed a significantly higher uptake and greater membrane permeability compared with the other formulations. The pharmacokinetic test exhibited HCPT-Nanosuspensions had a similar pharmacokinetic performance with 10-HCPT solution. In conclusion, highly and extendedly supersaturated HCPT-Nanosuspensions have been prepared which could result in high peak concentration (C _max) and great exposure (AUC) after oral administration.

     

Synthesis of 4-(pyrazol-5-yl)-1,2,4-triazole-3-thiones

Condensation of pyrazolyl isothiocyanates 2 with N-substituted hydrazines provided the 2-methyl/phenyl-4-(pyrazol-5-yl)thiosemicarbazides 3 . Cyclization of 3 with formic acid-acetic anhydride or with triethyl orthoacetate-acetic anhydride provided 4-(pyrazol-5-yl)-l,2,4-triazole-3-thiones 4a-f and 5-methyl-4-(pyrazol-5-yl)-1,2,4-triazole-3-thiones 4g-I respectively.     

GC-MS analytical methods for the determination of personal-care products in water matrices

This article discusses the more recent methods combining gas chromatography and mass spectrometry (GC-MS) for analysis of personal-care products (PCPs) in water matrices. We describe different procedures for sample extraction and preparation as well as different instrumental methods commonly used for these compounds. GC-MS and GC-tandem MS (GC-MS²), which are complementary to liquid chromatography combined with MS (LC-MS), allow identification and quantification of PCPs belonging to different classes with the sensitivity and the selectivity necessary for environmental monitoring. The compounds investigated include fragrances (e.g., nitro and polycyclic musks), antimicrobial compounds (e.g., triclosan), ultraviolet blockers (e.g., methylbenzylidene camphor), antioxidants and preservatives (e.g., phenols and p-hydroxybenzoic acid (parabens)) and insect repellents (e.g., N,N-diethyl-m-toluamide (DEET)). We critically review data in the literature by focusing attention on analytical methods devoted to simultaneous detection and quantification of structurally diverse pharmaceuticals and PCPs.     

Study of the oxidative half‐reaction catalyzed by a non‐heme ferrous catalytic center by means of structural and computational methodologies

Deacetoxycephalosporin C synthase (DAOCS) is a mononuclear ferrous enzyme that catalyzes the expansion of the five‐membered thiazolidine ring of the penicillin nucleus into the six‐membered dihydrothiazine ring of the cephalosporins. In the first half‐reaction with dioxygen and 2‐oxoglutarate, a reactive iron–oxygen species is produced that can subsequently react with the penicillin substrate to yield the cephalosporin. We describe quantum mechanical calculations of the first part of the reaction based on the high‐resolution structures of the active site of DAOCS and its complexes with ligands. These studies are aimed at understanding how the reactive species can be produced and contained in the active site of the enzyme. The results demonstrate the priming of the active site by the co‐substrate for oxygen binding and hint to the presence of a stable iron–peroxo intermediate in equilibrium with a more reactive ferryl species and the formation of CO₂ as a leaving group by decarboxylation of 2‐oxoglutarate. A conclusion from these studies is that substitution of CO₂ by the penicillin substrate triggers the oxidation reaction in a booby‐trap‐like mechanism. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Archaeometric Analysis of Ancient Copper Artefacts by Laser-Induced Breakdown Spectroscopy Technique

Twelve archaeological copper objects from the burial site of “Fontino” cave, near Grosseto, (around 2500–2000 B.C.) were analysed using laser-induced breakdown spectroscopy. Qualitative results and a preliminary study of the samples’ composition are reported and used to make a quantitative estimate; based on these results, the samples were classified using principal components statistical analysis. The perspectives of using laser-induced breakdown spectroscopy for archaeometric analysis are also discussed.     

Ketone-imide versus ketone-oxime reductive cross-coupling promoted by samarium diiodide: new mechanistic insight gained from a failed aminocyclopentitol synthesis

[reaction: see text] The intramolecular 1,6-ketone/imide reductive coupling promoted by samarium diiodide competes favorably with an alternative 1,5-ketone/oxime ether coupling in a keto-oxime substrate derived from D-glucosamine N-protected with a phthalimido group. This pinacol coupling reaction affords new homochiral alpha-hydroxylactam scaffolds that could be useful in diversity-oriented synthesis. A mechanistic proposal for this reaction that explains the experimental results is supported by DFT quantum-mechanical calculations on model compounds.