Growth of single crystals of copper and their thermal profile estimation

Copper crystals have been grown by Czochralski technique in a 6-bar argon gas environment. X-ray analysis shows that these are single crystals and are strain-free. A slight pressure environment that is truly hydrostatic seems to improve the quality of the crystals. Thermal profile estimation results show that the values of temperature which decrease upto the neck region are same in magnitude as those measured during the experiments and that necking improves the thermal profile and, consequently, the crystal quality. No facet formation has been observed in these crystals.     

Synthesis, structural and magnetic properties of spin ladder compound Ca1−xCoxCu2O3

MCu₂O₃ (M=Ca and Co) system has two-leg spin ladder structure similar to that of the prototype SrCu₂O₃ system except that the rungs are buckled with an angle of 123° and 105° for CaCu₂O₃ and CoCu₂O₃ compounds, respectively. We have synthesized powder samples of (Ca_1−xCo_x)Cu₂O₃ (x=0.00-1.00) by the solid state reaction method and their structural and magnetic properties have been investigated. All the synthesized compounds crystallize in orthorhombic structure with space group Pmmn. Lattice parameters of (Ca_1−xCo_x)Cu₂O₃ decrease with the increase in Co content. DC magnetic susceptibility χ(T) results of the end products CaCu₂O₃ and CoCu₂O₃ show antiferromagnetic transition (T_N) at 27 and 215 K, respectively. Co doping into (Ca_1−xCo_x)Cu₂O₃ enhances its T_N systematically with increasing Co concentration. The χ(T) of CoCu₂O₃ shows a broad transition with the peak temperature around 215 K and it was found to be field independent up to 90 kOe. The ambiguity concerning the transition was ruled out by recording the temperature dependent X-ray diffraction pattern on CoCu₂O₃ system, which indicated that there is no structural transition in the investigated temperature range of 115-300 K. Further, specific heat measurement on CoCu₂O₃ confirms the magnetic phase transition by the appearance of a sharp peak at 215 K.     

ProSTRIP: A method to find similar structural repeats in three-dimensional protein structures

The occurrence of similar structural repeats in a protein structure has evolved through gene duplication. These repeats act as a structural building block and form more than one compact structural and functional unit called a repeat domain. The protein families comprising similar structural repeats are mainly involved in protein–protein interactions as well as binding to other ligand molecules. The identification of internal sequence repeats in the primary structure is not sufficient for the analysis of structural repeats. Thus, a new method called ProSTRIP has been developed using dynamic programming to find the similar structural repeats in a three-dimensional protein structure. The detection of these repeats is made by calculating the protein backbone Cα angles. An internet computing server is also created by implementing this method and enables graphical visualization of the results. It can be freely accessed at http://cluster.physics.iisc.ernet.in/prostrip/.     

Halogenative kinetic resolution of β-aryloxy cyclic alcohols: chiral BINAP-mediated SN2 displacement of hydroxy groups by chlorides with inversion of stereochemistry

A series of optically active cyclic trans-β-aryloxy alcohols have been obtained by non-enzymatic kinetic resolution of the corresponding racemic aryloxy cyclic alcohols using commercially available (S)-BINAP and NCS by S_N2 halogenation of a hydroxy group. The product, cis-β-aryloxy chlorides, was also obtained in optically active form with inversion of the stereochemistry.     

Fiber-optic Singlet Oxygen [1O2 (1Δg)] Generator Device Serving as a Point Selective Sterilizer

Traditionally, Type II heterogeneous photo-oxidations produce singlet oxygen via external irradiation of a sensitizer and external supply of ground-state oxygen. A potential improvement is reported here. A hollow-core fiber-optic device was developed with an “internal” supply of light and flowing oxygen, and a porous photosensitizer-end capped configuration. Singlet oxygen was delivered through the fiber tip. The singlet oxygen steady-state concentration in the immediate vicinity of the probe tip was ca 20 f m by N-benzoyl- dl -methionine trapping. The device is portable and the singlet oxygen-generating tip is maneuverable, which opened the door to simple disinfectant studies. Complete Escherichia coli inactivation was observed in 2 h when the singlet oxygen sensitizing probe tip was immersed in 0.1 mL aqueous samples of 0.1–4.4 × 10⁷ cells. Photobleaching of the probe tip occurred after ca 12 h of use, requiring baking and sensitizer reloading steps for reuse.     

Synthesis,Characterization, and Antibacterial Activity of Novel (1H‐Benzo[d]imidazole‐2‐yl)‐6‐(diethylamino)‐3H‐one‐xanthene,Phenoxazine, and Oxazine

A series of novel (1H‐benzo[d]imidazole‐2‐yl)‐6‐(diethylamino)‐3H‐one‐xanthene, phenoxazine, and oxazine derivatives have been synthesized from 2‐(2′,4′‐dihydroxyphenyl) benzimidazole intermediate. Synthesized compounds 8a , 8b , 8c , 8d are fluorescent in solution, photophysical properties of compounds were studied and results revealed that compounds absorb and emit in UV–visible region with good fluorescence quantum yield. Synthesized compounds are thermally stable up to 300°C. The antibacterial activities of the synthesized compounds were studied by the well‐diffusion method. Escherichia coli (ATTC‐25922), Staphylococcus aureus (ATCC‐25923), Micrococcus (ATCC‐4698), and Bacillus subtilis (ATCC‐55422) were used to investigate the antibacterial activities.     

Enantioselective Synthesis of α‐Hydroxy Amides and β‐Amino Alcohols from α‐Keto Amides

Synthesis of enantiomerically enriched α‐hydroxy amides and β‐amino alcohols has been accomplished by enantioselective reduction of α‐keto amides with hydrosilanes. A series of α‐keto amides were reduced in the presence of chiral Cu^II/(S)‐DTBM‐SEGPHOS catalyst to give the corresponding optically active α‐hydroxy amides with excellent enantioselectivities by using (EtO)₃SiH as a reducing agent. Furthermore, a one‐pot complete reduction of both ketone and amide groups of α‐keto amides has been achieved using the same chiral copper catalyst followed by tetra‐n‐butylammonium fluoride (TBAF) catalyst in presence of (EtO)₃SiH to afford the corresponding chiral β‐amino alcohol derivatives.     

Synthesis of polyethylene glycol (PEG) assisted tungsten oxide (WO3) nanoparticles for L-dopa bio-sensing applications

Nanocrystalline tungsten oxides (WO_3−δ) are currently receiving a lot of attention because of their interesting electrical, magnetic, optical and mechanical properties. In this report, we present the synthesis of PEG assisted tungsten oxide (WO₃) nanoparticles by simple household microwave irradiation (2.45 GHz) method. The samples were characterized using powder X-ray diffraction (XRD), thermal analysis (TG/DTA), transmission electron microscopy (TEM), UV-visible diffusion reflectance spectroscopy (UV-VIS-DRS), cyclic voltammetry and electrochemical impedance spectroscopy. Powder XRD results revealed that both the samples prepared with and without surfactant crystallize in the orthorhombic structure corresponding to WO₃·H₂O phase. Subsequent annealing under identical conditions (600 °C/air/6 h) led to significantly different products i.e. monoclinic W₁₇O₄₇ from surfactant free sample and orthorhombic WO₃ from PEG assisted sample. Blue emission was observed through UV-VIS-DRS with blue shift and the band gap energy was estimated as 2.7 and 3.28 eV for PEG assisted as prepared (WO₃·H₂O) and annealed samples (WO₃) respectively. Electrochemical measurements have been performed on all the samples deposited on the surface of glassy carbon (GC) electrode which showed high sensitivity and good selectivity for PEG assisted sample (WO₃·H₂O) for the direct detection of l-dopa.     

Cu-catalyzed one-pot synthesis of unsymmetrical diaryl thioethers by coupling of aryl halides using a thiol precursor

An efficient Cu-catalyzed one-pot approach for the synthesis of unsymmetrical diaryl thioethers using potassium ethyl xanthogenate as a thiol surrogate is developed. This new protocol avoids usage of intricate thiols and makes use of its easily available xanthate as a precursor, and thiol will be generated in situ to prepare the diaryl thioethers through a Cu-catalyzed double arylation. This strategy was further successfully utilized for the synthesis of symmetrical diaryl thioethers, aryl alkyl thioethers, and benzothiazoles.