Solvatochromic Studies of Fluorescent Azo Dyes: Kamlet-Taft (π*, α and β) and Catalan (Spp, SA and SB) Solvent Scales Approach

A new metal ion-responsive azo-based fluorescent probes have been synthesized and characterized by NMR spectral techniques. Steady-state fluorometric study has been used to analyze the spectroscopic and photophysical characteristics of dye derivatives in various solvents. The fluorescence properties of these dyes are strongly solvent dependent, the wavelength of maximum fluorescence emission shifts to the red. The Kamlet-Taft and Catalan’s solvent scales were found to be the most suitable for describing the solvatochromic shifts of the absorption and fluorescence emission. The hydroxy substituted azo dye formed complexes with several metal ions (Co²⁺, Hg²⁺, Ni²⁺ and Cu²⁺) and fluorescence quenching with metal ions reveal that it can be used as a new fluorescence sensor to detect the Cu²⁺ ion.     

Ultrasound assisted free radical polymerization of glycidyl methacrylate by a new disite phase-transfer catalyst system: A kinetic study

The kinetics of multi-site phase-transfer catalyzed free radical polymerisation of glycidyl methacrylate (GMA) using potassium peroxy disulphate (PDS) as water soluble initiator and newly synthesized 1,4-dihexadecylpyrazine-1,4-diium dibromide as multi-site phase-transfer catalyst (MPTC) has been investigated in ethyl acetate/water two phase system at constant temperature 65±1°C under nitrogen atmosphere and ultrasound irradiation conditions. The rate of polymerization increases with an increase in concentrations of GMA, PDS and MPTC. The order with respect to monomer, initiator and MPTC were found to be 1.0, 0.5 and 1.0, respectively. The comparative study reveals that the Rp of GMA determined in the presence of PTC combined with ultrasound has shown more enhancements in the activity than PTC alone. Based on the observed results a suitable mechanism has been proposed to account for the experimental observations and its significance was discussed.     

Layered double hydroxide-CdSe quantum dot composites through colloidal processing: effect of host matrix-nanoparticle interaction on optical behavior

Layered double hydroxide (LDH)-monodispersed 4-nm CdSe nanoparticle composites were prepared through restacking of layers of colloidally dispersed delaminated LDH in the presence of CdSe nanoparticles in 1-butanol. The composites exhibit a blue shift for CdSe absorption, which increases with a decrease in nanoparticle content. The observed blue shift is due to the interaction of the quantum dots with the LDH layers, which leads to surface modification of the nanoparticles.     

Neutral and Cationic β‐Ketoiminato Bismuth Complexes

The first examples of neutral and cationic bismuth complexes bearing β‐ketoiminato ligands were isolated by employing salt metathesis route. BiCl₃ reacts with [O=C(Me)]CH[C(Me)N(K)Ar] ( 1 ) resulting in a homoleptic β‐ketoiminato bismuth complex Bi[{O=C(Me)}CH{C(Me)NAr}]₃ ( 2 ). The reaction between BiCl₃ and [(CH₂)₂{N(K)C(Me)CHC(Me)=O}₂] ( 3 ) leads to the formation of a cationic bismuth complex [Bi{(CH₂)₂(NC(Me)CHC(Me)=O)₂}]₄[Bi₂Cl₁₀] ( 4 ).     

An alternative route for the preparation of the medical isotope 99Mo from the 238U(γ, f) and 100Mo(γ, n) reactions

The radionuclide ⁹⁹Mo, which has a half-life of 65.94 h was produced from ²³⁸U(γ, f) and ¹⁰⁰Mo(γ, n) reactions using a 10 MeV electron linac at EBC, Kharghar Navi-Mumbai, India. This has been investigated since the daughter product ^99mTc is very important from a medical point of view and can be produced in a generator from the parent ⁹⁹Mo. The activity of ⁹⁹Mo was analyzed by a γ-ray spectrometric technique using a HPGe detector. From the detected γ-rays activity of 140.5 and 739.8 keV, the amount of ⁹⁹Mo produced was determined. For comparison, the amount of ⁹⁹Mo from ²³⁸U(γ, f) and ¹⁰⁰Mo(γ, n) reactions was also estimated using the experimental photon flux from ¹⁹⁷Au(γ, n)¹⁹⁶Au reaction. The amount of ⁹⁹Mo from the detected γ-lines is in agreement with the estimated value for ²³⁸U(γ, f) and ¹⁰⁰Mo(γ, n) reactions. The production of ⁹⁹Mo activity from ²³⁸U(γ, f) and ¹⁰⁰Mo(γ, n) reactions is a relevant and novel approach, which provides alternative routes to ^235,238U(n, f) and ⁹⁸Mo(n, γ) reactions, circumventing the need for a reactor. The viability and practicality of the ⁹⁹Mo production from the ²³⁸U(γ, f) and ¹⁰⁰Mo(γ, n) reactions alternative to ^235,238U(n, f) and ⁹⁸Mo(n, γ) reactions has been emphasize. An estimate has been also arrived based on the experimental data of present work to fulfill the requirement of DOE.     

Phase behavior of lipid-based lyotropic liquid crystals in presence of colloidal nanoparticles

We have investigated the microstructure and phase behavior of monoglyceride-based lyotropic liquid crystals in the presence of hydrophilic silica colloidal particles of size comparable to or slightly exceeding the repeat units of the different liquid crystalline phases. Using small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC), we compare the structural properties of the neat mesophases with those of the systems containing silica colloidal particles. It is found that the colloidal particles always macrophase separate in inverse bicontinuous cubic phases of gyroid (Ia3d) and double diamond (Pn3m) symmetries. SAXS data for the inverse columnar hexagonal phase (H(II)) and lamellar phase (L(α)) suggest that a low volume fraction of the nanoparticles can be accommodated within the mesophases, but that at concentrations above a given threshold, the particles do macrophase separate also in these systems. The behavior is interpreted in terms of the enthalpic and entropic interactions of the nanoparticles with the lamellar and hexagonal phases, and we propose that, in the low concentration limit, the nanoparticles are acting as point defects within the mesophases and, upon further increase in concentration, initiate nucleation of nanoparticles clusters, leading to a macroscopic phase separation.     

Dinaphthoporphycenes: synthesis and nonlinear optical studies

Naphthobipyrrole-derived porphycenes are synthesized for the first time via McMurry coupling of the β-alkylated 2,9-diformylnaphthobipyrrole derivatives, which in turn were prepared easily from 2,3-naphthalene bishydrazine in four steps. Insertion of nickel into the porphycene core results in transformation of the rectangular N4-core into a square type geometry owing to the fusion of naphthalene moiety onto the bipyrrole entities. These porphycenes show large, intensity dependent three-photon absorption.     

Natural convection with surface radiation from a planar heat generating element mounted freely in a vertical channel

Experiments and numerical simulations have been conducted to study the conjugate heat transfer by natural convection and surface radiation from a planar heat generating element placed centrally between two adiabatic vertical plates. The relevant problem dependent parameters considered in this study are modified Rayleigh number, channel aspect ratio, stream-wise location of the heat generating element, and surface emissivities of the heat generating element and the adiabatic side plates. Experiments are conducted for different values of modified Rayleigh number ranging from 3.2 × 10⁵ to 1.6 × 10⁷ and surface emissivities 0.05, 0.55, 0.75 and 0.85. The interdependence between the heat transfer mechanism and the flow field under the influence of surface radiation on natural convection is explored and discussed. Experimental correlations for total and convective Nusselt number, and dimensionless temperature in terms of relevant parameters have been developed. The mathematical model governing the problem has been numerically solved using a commercial computational fluid dynamics package FLUENT 6.3 and the numerical predictions substantiate the experimental observations.     

Mechanistic investigation on binding interaction of bioactive imidazole with protein bovine serum albumin--a biophysical study

The interaction between bioactive imidazole derivative (PPP) and bovine serum albumin (BSA) was investigated using fluorescence and UV-vis spectral studies. The experimental results showed that the fluorescence quenching of BSA by imidazole derivative was the result of the formation of BSA-PPP complex and the effective quenching constants (K(SV)) were 2.66×10(4), 2.56×10(4), and 2.10×10(4) at 301, 310 and 318 K, respectively. Static quenching and non-radiative energy transfer were confirmed to the result in the fluorescence quenching. The binding site number n, apparent binding constant K(A) and corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were measured at different temperatures. The process of binding of PPP molecule on BSA was a spontaneous molecular interaction procedure in which entropy increased and Gibbs free energy decreased.