Coarser connected metrizable topologies

We show that every metric space, X, with w(X)?c has a coarser connected metrizable topology.     

Nanocomposites of TiO 2 and Siloxane Copolymers as Environmentally Safe Flame-Retardant Materials †

Composites of titanium dioxide (TiO₂) nanoparticles and biocatalytically synthesized dimethylsiloxane copolyamides were prepared, and their thermal and flame-retardant properties were investigated. The flammability properties such as heat release capacity and total heat release were measured from microscale cumbustion calorimetry (MCC). The thermal degradation temperatures, char yields, and the heat-release capacities of these nanocomposites were significantly improved over the pure polymers. The heat-release capacities of the siloxane copolymer nanocomposites with 20wt% of TiO₂ were found to be 167 and 129 J/g K, which is a 35% less than the pure polymers (260 and 194 J/g K, respectively). The SEM/EDAX surface-analysis studies on nanocomposite films and their char revealed that nanocrystalline-TiO₂ plays an important role in forming carbonaceous silicate char on the surface as a protective layer.     

Site-specific protein double labeling by expressed protein ligation: applications to repeat proteins

In the last few years, the use of labeled proteins has significantly expanded in the life sciences. Now, labeled proteins are indispensable tools for a wide spectrum of biophysical and chemical biology applications. In particular, the quest for more sophisticated experimental setups requires the development of new synthetic methodology, especially for multiple site-specific labeling. In this paper, we describe a synthetic strategy based on expressed protein ligation to prepare proteins in high purity and homogeneity, in which two different molecular probes are incorporated specifically at any desired position. Proteins are sequentially labeled in solution, with the advantage that a large excess of probes is not required and the labeled fragments are not restricted to peptide synthesis length limitations. This strategy was applied to selectively label a repeat protein with a fluorophores pair in different positions along the protein sequence. The doubly labeled proteins were prepared at high purity and homogeneity, as required for single molecule FRET studies. Remarkably, this approach can be adapted to the introduction of more than two molecular probes.     

Synthesis and evaluation of inhibitors of E. coli PgaB, a polysaccharide de-N-acetylase involved in biofilm formation

Many medically important biofilm forming bacteria produce similar polysaccharide intercellular adhesins (PIA) consisting of partially de-N-acetylated β-(1 → 6)-N-acetylglucosamine polymers (dPNAG). In Escherichia coli, de-N-acetylation of the β-(1 → 6)-N-acetylglucosamine polymer (PNAG) is catalysed by the carbohydrate esterase family 4 deacetylase PgaB. The de-N-acetylation of PNAG is essential for productive PNAG-dependent biofilm formation. Here, we describe the development of a fluorogenic assay to monitor PgaB activity in vitro and the synthesis of a series of PgaB inhibitors. The synthesized inhibitors consist of a metal chelating functional group on a glucosamine scaffold to target the active site metal ion of PgaB. Optimal inhibition was observed with N-thioglycolyl amide (K(i) = 480 μM) and N-methyl-N-glycolyl amide (K(i) = 320 μM) glucosamine derivatives. A chemoenzymatic synthesis of an N-thioglycolyl amide PNAG pentasaccharide led to an inhibitor with an improved K(i) of 280 μM.     

Design,synthesis, and anticancer evaluation of acetamide and hydrazine analogues of pyrimidine

A library of acetamide and hydrazine analogues were generated on the pyrimidine ring through a multistep reaction starting from 5-nitro-pyrimidine-4,6-diol and pyrimidine-4,6-diol, respectively. The synthesized analogues were screened for in vitro cytotoxic activity against various human cancer cell lines like HCT-1 and HT-15 (colon), MCF-7(breast), PC-3 (prostrate), SF268 (CNS) using MTT method. From the bioassay results, it was observed that even though many of the synthesized derivatives exhibited a good potency against various screened cancer cell lines, compound 14a from the acetamide series was found to show potent anticancer activity on all the tested cancer cell lines with IC₅₀ value of 0.36μM on CNS cell line and 1.6μM on HT-21 cell line, and compound 19xxi from hydrazine series of pyrimidine showed potent activity against three tested cancer cell lines with IC₅₀ value of 0.76μM on HT-29 cell line, 2.6μM on HCT-15, and 3.2μM on MCF-7 cell line.     

New 1-alk(en)yl-1,3,5-trihydroxycyclohexanes from the Dufour gland of the African ant Crematogaster nigriceps

The Dufour gland of the African ant Crematogaster nigriceps contains a mixture of at least eight 1-heptadec(en)yl- and 1-nonadec(en)yl-1,3,5-trihydroxycyclohexane derivatives, the mono-unsaturated components being the major ones (about 65%). They are accompanied by small amounts of (Z,Z)-dienic derivatives (<10%). The structures, the relative and absolute configurations, and the preferred conformation of these new compounds have been established by spectroscopic and chemical methods, whereas the positions of the double bond in the alkenyl chains were determined by DMDS derivatisation followed by linked scan EIMS.     

Synthesis of the C1-C16 fragment of the ajudazols

The synthesis of the C1-C16 framework of the ajudazols has been achieved taking advantage of a highly selective isobenzofuran oxidative rearrangement and a key Stille coupling to introduce the key C14-C15 bond.     

Voltammetric determination of arsenic in high iron and manganese groundwaters

Determination of the speciation of arsenic in groundwaters, using cathodic stripping voltammetry (CSV), is severely hampered by high levels of iron and manganese. Experiments showed that the interference is eliminated by addition of EDTA, making it possible to determine the arsenic speciation on-site by CSV. This work presents the CSV method to determine As(III) in high-iron or -manganese groundwaters in the field with only minor sample treatment. The method was field-tested in West-Bengal (India) on a series of groundwater samples. Total arsenic was subsequently determined after acidification to pH 1 by anodic stripping voltammetry (ASV). Comparative measurements by ICP-MS as reference method for total As, and by HPLC for its speciation, were used to corroborate the field data in stored samples. Most of the arsenic (78 ± 0.02%) was found to occur as inorganic As(III) in the freshly collected waters, in accordance with previous studies. The data shows that the modified on-site CSV method for As(III) is a good measure of water contamination with As. The EDTA was also found to be effective in stabilising the arsenic speciation for longterm sample storage at room temperature. Without sample preservation, in water exposed to air and sunlight, the As(III) was found to become oxidised to As(V), and Fe(II) oxidised to Fe(III), removing the As(V) by adsorption on precipitating Fe(III)-hydroxides within a few hours.