Investigating the vortex melting phenomenon in BSCCO crystals using magneto-optical imaging technique

Using a novel differential magneto-optical imaging technique we investigate the phenomenon of vortex lattice melting in crystals of Bi₂Sr₂CaCu₂O₈ (BSCCO). The images of melting reveal complex patterns in the formation and evolution of the vortex solid-liquid interface with varying field (H)/temperature (T). We believe that the complex melting patterns are due to a random distribution of material disorder/inhomogeneities across the sample, which create fluctuations in the local melting temperature or field value. To study the fluctuations in the local melting temperature/field, we have constructed maps of the melting landscape T _m(H, r), viz., the melting temperature (T _m) at a given location (r) in the sample at a given field (H). A study of these melting landscapes reveals an unexpected feature: the melting landscape is not fixed, but changes rather dramatically with varying field and temperature along the melting line. It is concluded that the changes in both the scale and shape of the landscape result from the competing contributions of different types of quenched disorder which have opposite effects on the local melting transition.     

Iron-Catalyzed Intermolecular C−H Amination Assisted by an Isolated Iron-Imido Radical Intermediate

Here we report the use of a base metal complex [(^tBupyrpyrr₂)Fe(OEt₂)] ( 1 -OEt₂) (^tBupyrpyrr₂²⁻=3,5-tBu₂-bis(pyrrolyl)pyridine) as a catalyst for intermolecular amination of C_sp3−H bonds of 9,10-dihydroanthracene ( 2 a ) using 2,4,6-trimethyl phenyl azide ( 3 a ) as the nitrene source. The reaction is complete within one hour at 80 °C using as low as 2 mol % 1 -OEt₂ with control in selectivity for single C−H amination versus double C−H amination. Catalytic C−H amination reactions can be extended to other substrates such as cyclohexadiene and xanthene derivatives and can tolerate a variety of aryl azides having methyl groups in both ortho positions. Under stoichiometric conditions the imido radical species [(^tBupyrpyrr₂)Fe{=N(2,6-Me₂-4-tBu-C₆H₂)] ( 1 -imido) can be isolated in 56 % yield, and spectroscopic, magnetometric, and computational studies confirmed it to be an S = 1 Fe^IV complex. Complex 1 -imido reacts with 2 a to produce the ferrous aniline adduct [(^tBupyrpyrr₂)Fe{NH(2,6-Me₂-4-tBu-C₆H₂)(C₁₄H₁₁)}] ( 1 -aniline) in 45 % yield. Lastly, it was found that complexes 1 -imido and 1 -aniline are both competent intermediates in catalytic intermolecular C−H amination.     

Synthesis and characterization of hexa-tailed cryptand based amphiphiles: spontaneous formation of giant vesicular microcapsule with efficient and long-term dye encapsulation

A cryptand with six secondary amino groups has been derivatized by reacting with acid chlorides of different chain lengths (C(7), C(10) and C(18)) to get three cryptand based hexa-tailed neutral amphiphiles (L(1)-L(3)). The cavity of the cryptand head group accommodates two Cu(II) ion giving another set of three amphiphiles. These amphiphiles and its copper complexes can aggregate spontaneously as giant vesicular microcapsules in 10% ethanolic water medium. In all cases vesicles formed are mostly unilamellar in nature. Vesicular microcapsules prepared from L(1)-L(3) can encapsulate hydrophilic dye 5(6)-carboxyfluorescein (CF). Stability of microcapsules, CF encapsulation efficiencies and release rates were dependent on the hydrophobic chain length of the amphiphiles. Results show the permeability of the L(2) and L(3) bilayer is lower than that of phosphatidylcholine vesicles and the loading capacity is approximately 3 times greater. Microcapsules have been characterized by optical microscopy, freeze fracture scanning electron microscopy and confocal fluorescence microscopy.     

Highly porous Co(II)-salicylate metal-organic framework: synthesis, characterization and magnetic properties

A new porous Co(II)-salicylate metal-organic framework material has been synthesized hydrothermally through the reaction of Co(II) chloride with sodium salicylate under mild alkaline pH conditions. To get an idea about the structural aspect of the material from the powder X-ray diffraction (PXRD) pattern, MAUD program has been successfully utilized and the assigned peaks match very well with a new tetragonal phase (space group, P4mm) having the unit cell parameters: a = b = 12.957 (0.042) ?; c = 12.738 (0.019) ?; α = β = γ = 90°, V = 2138.73 ?(3). N(2) adsorption/desorption analyses suggested the material is highly porous in nature having high BET surface area and pore dimensions of 2.0-3.0 nm, which is within the range of small mesopores. Thermogravimetric analysis (TGA) revealed that the H(2)O molecules may be removed from the framework without collapsing the structure and the material is stable up to ca. 573 K. The material is characterized thoroughly by using different characterization tools such as TEM, SEM, UV-visible reflectance spectroscopy, FT IR spectroscopy and photoluminescence spectroscopy. X-Ray photoelectron spectroscopic (XPS) analysis was employed to understand the oxidation state of the cobalt atom and presence of other elements within the framework. The material shows interesting magnetic properties, where the magnetic moments monotonically increase with the decrease in temperature down to 9 K. Below 9 K there is a steep increase in magnetization on further lowering the temperature, thereby suggesting the onset of a long range ferromagnetic transition with ferromagnetic Curie temperature, T(C) = 8.5 K. Furthermore, the M-H curve at 2 K shows a clear hysteresis loop with a coercive field 150 Oe and remnant magnetization 0.8 μ(B)/f.u.     

MCM-41-supported oxo-vanadium(IV) complex: a highly selective heterogeneous catalyst for the bromination of hydroxy aromatic compounds in water

An ecofriendly solid catalyst has been synthesized by anchoring vanadium(IV) into organically modified MCM-41. First, the surface of Si-MCM-41 was modified with 3-aminopropyl-triethoxysilane (3-APTES), the amine group of which upon condensation with ortho-hydroxy-acetophenone affords a N(2)O(2)-type Schiff base moiety in the mesoporous matrix. The Schiff base moieties were used to anchor oxo-vanadium(IV) ions. The prepared catalyst has been characterized by UV-vis, IR spectroscopy, small-angle X-ray diffraction (SAX), nitrogen sorption, and transmission electron microscopy (TEM) studies. It is observed that the mesostructure has not been destroyed in the multistep synthesis procedure, as evidenced by SAX and TEM measurements. The catalyst has shown unprecedented high conversion as well as para selectivity toward the bromination of hydroxy aromatic compounds using aqueous 30% H(2)O(2)/KBr in water. The reaction proceeds according to the stoichiometric ratio, and the monobrominated product was obtained as the major product using a stoichiometric amount of the bromine source. The immobilized complex does not leach or decompose during the catalytic reactions, showing practical advantages over the free metal complex.     

Docking studies of novel pyrazinopyridoindoles class of antihistamines with the homology modelled H(1)-receptor

Histamine is an important neurotransmitter as it controls a multitude of physiological functions by activating specific receptors on target cells. It exerts its effects by binding to four different histamine receptors (H(1)-H(4)), which all belong to the large family of G protein-coupled receptors (GPCRs). Research and development of H(1) ligand has largely focused on antagonists which are used for their anti-allergy effects in the periphery. Recent understanding of the clinical importance of H(1) receptors in brain, however, suggests the pharmacotherapeutic potential of H(1) agonists in neurodegenerative and neuropsychiatric disorders. Despite the therapeutic importance of the H(1) receptor, for many years the molecular features of the H(1) receptor protein had been unknown. In view of the recently reported crystal structure of human H(1) receptor and in continuation of our work on 3D-pharmacophore on antihistamine H(1) and homology model of histamine H(1) receptor, docking studies have been carried out on some promising pyrazinopyridoindole class of antihistamine H(1), including two outliers, to validate our earlier reported models/hypotheses on H(1)-receptor, where a good explanation between estimated and observed activities has been obtained. In addition, the docking study also provided insights about the optimal activity of the outliers, for which no explanation was reported previously.     

A non-volatile memory device consisting of graphene oxide covalently functionalized with ionic liquid

We introduce non-volatile resistive crossbar memory based on ionic liquid covalently functionalized on a partially reduced graphene oxide (PrGO). The write-read-erase-read (WRER) cycles were very stable after several hundred cycles and the retention time of both the ON and OFF states was stable for over 1000 s, indicating that the device we developed can function as a non-volatile memory device.