In Situ Total X‐Ray Scattering Study of WO3 Nanoparticle Formation under Hydrothermal Conditions

Pair distribution function analysis of in situ total scattering data recorded during formation of WO₃ nanocrystals under hydrothermal conditions reveal that a complex precursor structure exists in solution. The WO₆ polyhedra of the precursor cluster undergo reorientation before forming the nanocrystal. This reorientation is the critical element in the formation of different hexagonal polymporphs of WO₃.     

Plane symmetric supergravity solutions

Plane symmetric supergravity solutions given in arecent paper are generalized.     

Weak Ion Acoustic Double Layers in a Warm Plasma

The analytic solutions of the weak ion acoustic double layers in warm unmagnetized and magnetized plasma have been presented with the fluid equation for ions and an arbitrary equation of state for the hot electrons. It has been shown that double layers solutions exist for both magnetized and unmagnetized plasmas when two Boltzmann model for electrons are considered. The potential, the thickness and the velocity of such type of double layers have been calculated and compared with those for the cold plasma.     

Double layers in a field-aligned current driven plasma

The solutions of small amplitude ion acoustic double layers in current-carrying plasma in the presence of the magnetic field have been presented. The electron beam along the magnetic field has only been considered and the drift velocity assumed to be less than the electron thermal velocity. The velocity, the width and the potential of such DLs are calculated.     

Synthesis,characterization, and crystal structure of [Ni(dap(A)<Subscript>2</Subscript>)]<Subscript>2</Subscript> (dap(AH)<Subscript>2</Subscript>: 2,6-diacetylpyridine bis(anthraniloyl hydrazone))—a molecule possessing an infinite double helical chain in the solid state

Anthraniloyl hydrazide (AH) contains two −NH₂ groups, one of them is attached to the aromatic ring and the other is the hydrazinic, −NH₂. It is found that only the later reacts with the carbonyl compounds to form Schiff bases, while the former remains inert. The reasons behind this difference in reactivity are analyzed on the basis of semi-empirical calculations, which show that the lone pair of the ring −NH₂ is considerably delocalized over the ring, resulting in an accumulation of a positive charge on this particular nitrogen. Ni(II) complex of 2,6-diacetylpyridine bis(anthraniloyl hydrazone) has been prepared and characterized by various physico-chemical methods. The structure of the complex was determined by X-ray crystallography. It was found that in the solid state, the compound exist as a dimer, and two coordinated ligand moieties form a double helix around the two metal ions. H-bonding then results in extension of double helix to an infinite chain.     

Indirect spectrofluorimetric determination of arsenic at nanotrace levels in alloys, underground water, industrial waters and sewage sludge

An inexpensive and virtually specific nonextractive Spectrofluorimetric method for the determination of As(III) (1 ng/ml-1 g/ml) in 0.18–1.08N H₂SO₄ has been developed. A known excess of Cr(VI) is allowed to quantitatively oxidize As(III) in the essential presence of a mixture of iodide and chloride as catalyst, followed by the addition of excess 2-(-pyridyl) thioquinaldinamide and measurement of the fluorescence intensity (_em(max) = 488 nm _ex(max) = 360 nm) caused by Cr(VI) remaining after As(III) oxidation. The measurement is repeated without As(III) addition and the decrease in fluorescence intensity gives the As(III) concentration with the help of a calibration graph. The method is very precise and accurate (S. D. = ± 0.474, R. S. D. = 0.95%, for the analysis of 50ng/ml As(III), 11 replicates). The detection limit is 0.3ng/ml As(III). Large excesses of over fifty cations, anions and some complexing agents do not interfere. The method has been successfully applied for arsenic determination in various complex matrices: environmental waters, sewage sludges and several certified reference materials (alloys). This method has also been extended to determine As(V), after its reduction to As(III), in water samples, waste discharge water and sewage sludges.Presented at International Conference Arsenic in Ground Water: Cause, Effect and Remedy, Calcutta, India, February, 1995     

Formation of a DNA layer on Langmuir-Blodgett films and its enzymatic digestion

Here, we report a system we have developed where long double-stranded DNAs (dsDNAs) are immobilized on a monolayer of Zn-arachidate. We have applied the Langmuir-Blodgett technique to form the monolayer of Zn-arachidate where Zn(II) is bound to arachidic acid through charge neutralization. Because tetrahedral Zn(II) participates in DNA recognition through coordination, we have been able to layer DNA over the Zn-arachidate monolayer. The DNA layer shows a typical compression and expansion cycle in a concentration-dependent fashion. Interestingly, the DNA monolayer is available for enzymatic degradation by DNaseI. The detection of DNA and its accessibility towards biological reaction is demonstrated by imaging through fluorescence microscopy. The conformation of the DNA, immobilized on the monolayer, was studied with the help of atomic force microscopy (AFM). We observed that the dsDNAs were aligned in a stretched manner on the surface. To investigate further, we also demonstrate here that the small single-stranded DNA (ssDNA) immobilized on the air-water interface can act as a target molecule for the complementary ssDNA present in the subphase. The study of DNA hybridization done with the help of fluorescence spectroscopy clearly supports the AFM characterization.     

Two-Photon Fluorescence Tracking of Colloidal Clusters

In situ dynamics of colloidal cluster formation from nanoparticles is yet to be addressed. Using two-photon fluorescence (TPF) that has been amply used for single particle tracking, we demonstrate in situ measurement of effective three-dimensional optical trap stiffness of nanoparticles and their aggregates without using any position sensitive detector. Optical trap stiffness is an essential measure of the strength of an optical trap. TPF is a zero-background detection scheme and has excellent signal-to-noise-ratio, which can be easily extended to study the formation of colloidal cluster of nanospheres in the optical trapping regime. TPF tracking can successfully distinguish colloidal cluster from its monomer.     

Discrete Molecular Copper(II) Complex for Efficient Piezoelectric Energy Harvesting Above Room-Temperature

Developing robust, wearable, and biocompatible energy harvesting devices with bulk oxides (ceramics and perovskites) is extremely hard to achieve due to their zero mechanical flexibility, heavy metal toxicity, and tunability of properties. Alternatively, discrete inorganic complexes can be an excellent choice to overcome the above-stated issues, thanks to appropriate molecular engineering. Herein, we report an above-room-temperature ferroelectric discrete molecular complex [Cu(L-phe)(bpy)(H₂O)]PF₆⋅H₂O ( 1 ) which is suitable for piezoelectric energy harvesting due to its large values of piezoelectric co-efficient (d₃₃=10 pm V⁻¹) and spontaneous polarization (P_s=1.3 μC cm⁻²). Among the devices prepared with the composite films of polyvinyl alcohol (PVA) and various weight % composition of 1 , the 10 Wt % composite shows the highest output voltage of 8 V, a power density of 0.85 μW cm⁻², and output current of 5 μA, which is highest for any discrete inorganic complex reported to date.     

Cyanometallate incorporated supramolecular networks based on a nitroalkyl-substituted CuN4 precursor: Synthesis, crystal structure, thermal and electrochemical studies

Two new copper(II) complexes, viz. [Cu(nelin)(H₂O)₂]₂[Fe(CN)₆] · 6H₂O (2) and [{Cu(nelin)}₂Ni(CN)₄](ClO₄)₂ · 2H₂O (3), have been synthesized using [Cu(nelin)](ClO₄)₂ (1) (nelin = 1,9-diamino-5-methyl-5-nitro-3,7-diazanonane) as a nitroalkyl-substituted Cu^IIN₄ precursor, and their structures and supramolecular networks have been fully explored using the single crystal X-ray diffraction technique. The H-bonded 1D chains of 2 run along the a-axis, being generated from supramolecular synthons using cations and anions, and are further propagated into a 3D array to form irregular honeycomb-like channels which are divided into two halves, with each half accomodating a helical water chain running in opposite directions to each other. In complex 3, the trinuclear units are arranged in successive rows in a herringbone fashion and bifurcated hydrogen bonding through the uncoordinated terminals of the [Ni(CN)₄]²⁻ units give rise to a supramolecular (4,4) network. A comparison of the PXRD pattern of complex 2 and its dehydrated form indicate marked changes in the diffraction pattern with the development of a quasi glassy nature in the dehydrated form. The electrochemical properties of 1, 2 and 3 have been investigated in comparative ways using the cyclic voltammetric technique in aqueous and MeCN solutions with Ag/AgCl as a reference electrode. Electrochemical reduction generates the one-electron reduced nitro-radical anion. In water–alcohol glass at 77 K complex 2 exhibits a typical four-line hyperfine EPR spectra with g_|| = 2.11, g = 2.02, A_|| = 150 Oe and A = 5 Oe at ν = 9.45 MHz.