Atomic layer deposition in nanometer-level replication of cellulosic substances and preparation of photocatalytic TiO2/cellulose composites

TiO2 replicas of filter paper with nanometer-level accuracy were prepared by atomic layer deposition of thin conformal TiO2 coating, followed by a removal of the paper by air-anneal at 450 degrees C. Photocatalytic anatase TiO2/cellulose composites were also made by leaving the paper intact. The TiO2 films were deposited from Ti(OMe)4 and H2O at 150-250 degrees C. The photocatalytic activity of the TiO2/cellulose composite was verified by photocatalytic reduction of Ag(I) from an aqueous solution to Ag nanoparticles on the TiO2 surface. The TiO2/cellulose composites are mechanically more stable than the free-standing TiO2 replicas and are therefore potentially suitable as lightweight, high surface area photocatalysts.     

Stereoselective syntheses of 20-epi cholanic acid derivatives from 16-dehydropregnenolone acetate

A stereoselective total synthesis of naturally occurring 20-epi cholanic acid derivatives has been realized, starting from readily available 16-dehydropregnenolone acetate. The key step of these syntheses involves an ionic hydrogenation of a C-20,22-ketene dithioacetal and deoxygenation of steroidal C-20 tert-alcohols, to set up the unnatural C(20R) configuration with 100% stereoselectivity. The unnatural C-22 aldehydes with C(20R) stereocenters thus obtained were elaborated to 20-epi cholanic acid derivatives. Two derivatives of 20-epi cholanic acid were synthesized and their structures have been confirmed by single crystal X-ray analysis. Catalytic hydrogenation of 16-dehydropregnenolone acetate and 16-dehydropregnenolone in ethanol affords C-5,C-16 tetrahydro products. Crystal structure analysis of one of these products revealed C-5α and C-17α configurations of the hydrogen atoms.     

Silver Coated Platinum Core–Shell Nanostructures on Etched Si Nanowires: Atomic Layer Deposition (ALD) Processing and Application in SERS

A new method to prepare plasmonically active noble metal nanostructures on large surface area silicon nanowires (SiNWs) mediated by atomic layer deposition (ALD) technology has successfully been demonstrated for applications of surface‐enhanced Raman spectroscopy (SERS)‐based sensing. As host material for the plasmonically active nanostructures we use dense single‐crystalline SiNWs with diameters of less than 100 nm as obtained by a wet chemical etching method based on silver nitrate and hydrofluoric acid solutions. The SERS active metal nanoparticles/islands are made from silver (Ag) shells as deposited by autometallography on the core nanoislands made from platinum (Pt) that can easily be deposited by ALD in the form of nanoislands covering the SiNW surfaces in a controlled way. The density of the plasmonically inactive Pt islands as well as the thickness of noble metal Ag shell are two key factors determining the magnitude of the SERS signal enhancement and sensitivity of detection. The optimized Ag coated Pt islands on SiNWs exhibit great potential for ultrasensitive molecular sensing in terms of high SERS signal enhancement ability, good stability and reproducibility. The plasmonic activity of the core‐shell Pt//Ag system that will be experimentally realized in this paper as an example was demonstrated in numerical finite element simulations as well as experimentally in Raman measurements of SERS activity of a highly diluted model dye molecule. The morphology and structure of the core‐shell Pt//Ag nanoparticles on SiNW surfaces were investigated by scanning‐ and transmission electron microscopy. Optimized core–shell nanoparticle geometries for maximum Raman signal enhancement is discussed essentially based on the finite element modeling.     

Infrared emission following photolysis of methylisothiocyanate and methylthiocyanate

Methylisothiocyanate (CH(3)NCS) was photolyzed at 193 and 248 nm, and the resulting time-resolved infrared emission was observed. Similar experiments were performed on methylthiocyanate (CH(3)SCN) photolyzed at 193 nm. Previous work suggested that these isomers undergo excited-state isomerization prior to dissociation, but other experiments have contradicted this claim. In the infrared emission experiments, we observed the same products from both starting materials, supporting the theory of excited-state isomerization prior to dissociation. Methylisothiocyanate is the active ingredient in a widely used pesticide and has been observed to form highly toxic methyl isocyanate (CH(3)NCO) under environmental conditions. The mechanism for this formation has been unclear, but must involve some oxygen-containing species. At 248 nm, methylisothiocyanate was photolyzed alone and with three atmospheric oxidizers: O(2), NO, and NO(2). No chemical reaction was observed with O(2), whereas secondary reactions were observed with NO and NO(2). When methylisothiocyanate was photolyzed with NO(2), methyl isocyanate (CH(3)NCO) was observed, suggesting a likely environmental mechanism for methyl isocyanate formation.     

A novel one pot multi-component strategy for facile synthesis of 5-aryl-[1,2,4]triazolidine-3-thiones

We have disclosed an efficient, one pot, novel multi-component approach for the synthesis of 5-aryl-[1,2,4]triazolidine-3-thiones from aldehyde, hydrazine hydrate, and trimethylsilyl isothiocyanate (TMSNCS) in the presence of catalytic amount of sulfamic acid. High yields, easy work-up procedure, no chromatographic separation, and novelty in multi-component strategy are the main merits of the present strategy.     

Effect of β-cyclodextrin complexation on physicochemical properties of zaleplon

The physicochemical properties and dissolution profile of zaleplon (ZPN) β-cyclodextrin (βCD) inclusion complex were investigated. The phase solubility profile of ZPN with β-cyclodextrin was classified as A_L-type. Stability constant with 1:1 molar ratio was calculated from the phase solubility diagram and the aqueous solubility of ZPN was found to be enhanced by 714% (p < 0.001) for β-cyclodextrin. Binary systems of ZPN with βCD were prepared by kneading method. The solid-state properties of complex were characterized by differential scanning calorimetry, Fourier transformation-infrared spectroscopy and powder X-ray diffractometry. It could be concluded that ZPN could form inclusion complex with β-cyclodextrin. The dissolution profile of inclusion complex was determined and compared with those of ZPN alone and its physical mixture. The dissolution rate of ZPN was significantly increased by complexation with βCD, as compared with pure drug and physical mixture.     

Potassium phosphate or silica sulfuric acid catalyzed conjugate addition of thiols to α,β-unsaturated ketones at room temperature under solvent-free conditions

Potassium phosphate and silica sulfuric acid have been found to be useful and highly efficient catalysts for conjugate addition of thiols to α,β-unsaturated ketones under solvent-free conditions, at room temperature. Silica sulfuric acid (SSA) was found to be suitable for electron-deficient enones while potassium phosphate was found to effect thia-Michael addition with both, electron-deficient as well as electron-rich conjugated ketones.