The kinetics of alkaline hydrolysis of tris(1,10-phenanthroline)Fe(II) has been explored spectrophotometrically in the presence of cyclodextrins (CDs), quaternary amphiphile (CTAB), and their mixed systems. All kinetics run in pseudo-first order conditions with excess concentration of alkali at 298 K (+/- 0.1 K). The reaction rate accelerates in the presence of CTAB. However, in the presence of CDs, the observed rate constant decreases continuously and also the catalytic properties of amphiphile diminishes, indicating the inclusion of both tris(1,10-phenanthroline)Fe(II) and surfactant into the CD cavity in the hydrolysis reaction. The cavity size of gamma-CD among all of the CDs favors the incorporation of both Fe(II) complex and CTAB, which significantly reduces the micellar surface catalysis of CTAB. The decreasing sequence of the rate in CTAB-CDs mixed systems is observed as gamma-CD > beta-CD > alpha-CD. All the experimental kinetic results have been well explained based on the pseudo-phase model (PP model) of micelles and CD-inhibited model of CD systems. The calculated theoretical rate constant values are well consistent with the experimental data. In the absence and presence of CTAB, the calculated values of equilibrium binding constant between Fe(phen)(3)(2+) and gamma-CD (KFe(II)CD) are 109.17 (+/- 1.03) and 414.74 (+/- 3.63) (L mol(-1)), respectively, which support the diminishing of the catalytic properties of CTAB in the presence of gamma-CD in the hydrolysis reaction. The experimental results also corroborate that fact. Finally, the effect of temperature on the reaction rate has been observed and the thermodynamic activation parameters have been evaluated. The linear plot of standard activated enthalpy with standard activated entropy reveals an iso-kinetic relationship that confirms a common mechanism for the reaction in different environments.

Structural alteration and regeneration of myoglobin.

The detailed characterizations of the binding interactions between food additive tartrazine (TZ) and β-lactoglobulin (β-LG) have been investigated through spectroscopic techniques combined with a molecular modeling study. A series of analyses, such as hyperchromic change in the UV-visible spectra, temperature-dependent quenching constant, time-resolved fluorescence, and Rayleigh scattering measurements, show that quenching of β-LG proceeds by a static quenching mechanism. TZ specifically binds with β-LG in a stoichiometry ratio of 1:1, and the observed binding constants (104, K) are 7.64, 9.13, 9.72, and 10.79 at 293, 298, 303, and 308 K, respectively. However, the curious results of binding constants (K) with temperature, encountered in the static quenching, have been well explained on the basis of Le Chatelier's principle. Thermodynamic data and pH-dependent studies along with the surface hydrophobicity binding displacement assay reveal that the durable mode of binding is chiefly entropy-driven, revealing noteworthy interactions of such ionic molecules with the hydrophobic part of β-LG. The modulation of protein conformation has been investigated through steady-state absorption spectroscopy, synchronous emission spectroscopy, circular dichroism, and dynamic light scattering studies. TZ acts as a potential inhibitor in fibrillogenesis. Furthermore, the molecular docking study offers accurate insights about the binding of TZ with β-LG, in consistence with the experimental results. This study would be helpful in pharmaceutical, food, and industrial engineering chemistry research.

We decipher the mode of binding of surfactants with hemoglobin and their release by β-cyclodextrin.

The binding interaction of a well known alkaloid strychnine (STN) with the mammalian milk protein β-lactoglobulin and human lysozyme has been explored by using several spectroscopic techniques along with computational studies.

Microenvironments consisting of surfactants are capable of either inhibiting or catalyzing the reaction rate depending on the specific interaction between surfactant and the reactant species. In this context, micellar catalyzed electron transfer reaction between methylene blue (MB) and ascorbic acid (AA) have been studied in presence of three cationic surfactants (TTAB, CTAB & CPC) at different temperatures under pseudo-first order condition. The kinetic data have been analyzed with different models (i.e., pseudo-phase model, Piszkiewicz's model and Raghavan-Srinivasan's model). The micellar binding constant evaluated from the three models are in good agreement with each other. Out of three surfactants, the lower standard enthalpy of activation (∆‡H°) and higher negative standard entropy of activation (∆‡S°) of CPC have been ascribed to the planar structure of the pyridinium head group which provides less steric hindrance to the attacking ascorbate ions. The formation of catalytic sub micellar aggregates between dye and micelle in the reaction medium in a ratio of 1:1 and 1:2 have been well justified by TEM measurements and the result of positive co-operative values. The catalytic activity of surfactants as well as micellar binding constant increases in the following order: CPC>CTAB>TTAB.

The kinetic investigations on the alkaline hydrolysis of tris-(1,10-phenanthroline)iron(II) has been explored spectrophotometrically in microheterogeneous environment at 301K and ionic strength of 0.13molL(-1). Guar gum, cationic amphiphiles, and their mixtures are used as the reaction environments to carry out the reaction. Guar gum decreases the rate of reaction, which indicates that Fe(II) complex may be trapped in the hydrophobic region of gum. Cationic amphiphile decreases the rate in the presence of guar gum. The extent of interaction between guar gum and amphiphile increases with the hydrophobic carbon chain length. The critical aggregation concentration (CAC) and critical micelle concentration (CMC) of the amphiphiles (cetyl trimenthyl ammonium bromide (CTAB), tetradecyl trimenthyl ammonium bromide (TTAB), dodecyl trimenthyl ammonium bromide (DTAB)) in the presence of guar gum have been determined with conductometry and tensiometry. All observations support either weak or strong interaction of cationic amphiphiles with guar gum. Activation parameters of the reaction in different environments have been determined which corroborate the rate data. [GRAPHICS] .

The biomolecular interaction of a potential prototype drug phenolphthalein (PN) with the transport protein bovine serum albumin (BSA) has been investigated at physiological pH employing various spectroscopic techniques along with computational study. The effect of β-cyclodextrin (β-CD) on PN-bound protein has also been investigated. The interesting phenomenon of all findings is the spontaneous exothermic binding of PN with serum albumin through static quenching mechanism. The thermodynamic parameters (ΔS°, ΔH° & ΔG°) have been justified by the detailed understanding of the binding affinity of PN with protein. The binding displacement measurements and Auto Dock-based docking simulation unravels the probable binding location of PN within the hydrophilic sub-domain IB close to Sudlow site I of BSA where Trp-134 is housed. Although β-CD induces a marginal structural loss of protein, it have played dominant roles to stripping of denaturant from PN-BSA assembles. This study has undertaken to unravel the effect of drug binding of protein so as to rationalize the applicability of the drug molecule as a therapeutic agent and drug delivery.

The interaction between a synthesized dye with proteins, bovine, and human serum albumin (BSA, HSA, respectively) under physiological conditions has been characterized in detail, by means of steady-state and time-resolved fluorescence, UV-vis absorption, and circular dichroism (CD) techniques. An extensive time-resolved fluorescence spectroscopic characterization of the quenching process has been undertaken in conjugation with temperature-dependent fluorescence quenching studies to divulge the actual quenching mechanism. From the thermodynamic observations, it is clear that the binding process is a spontaneous molecular interaction, in which van der Waals and hydrogen bonding interactions play the major roles. The UV-vis absorption and CD results confirm that the dye can induce conformational and micro-environmental changes of both the proteins. In addition, the dye binding provokes the functionality of the native proteins in terms of esterase-like activity. The average binding distance (r) between proteins and dye has been calculated using FRET. Cytotoxicity and antiviral effects of the dye have been found using Vero cell and HSV-1F virus by performing MTT assay. The AutoDock-based docking simulation reveals the probable binding location of dye within the sub-domain IIA of HSA and IB of BSA.

Interaction of toluidine blue (TB), a biologically potent cationic phenothiazinium dye, with anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) have been thoroughly studied employing absorption and emission spectroscopy. A completely distinct spectral behavior of TB has been observed corresponding to pre-micellar and post-micellar region of AOT. Steady-state fluorescence anisotropy measurement has been carefully undertaken to rationalize the spectroscopic results. Effect of γ-cyclodextrin (γ-CD) on the spectral properties of TB has also been encountered for understanding of binding interaction between them. Molecular docking study has been accomplished to enlighten the probable orientation of TB inside the γ-CD core. Here particular interest has been focused on a mixed system, composed of AOT pre-micelles and γ-CD. A remarkable diminution of both absorption and emission intensities of TB has been observed in AOT pre-micelle with a simultaneous colorimetric change of TB solution from dark blue to lavender, and subsequent addition of γ-CD results in enhancement of intensities with dramatic reversal of the lavender colored solution to the original dark blue color. The emission characteristics of TB in the presence of AOT and γ-CD may prove as promising for an ‘IMPLICATION’ logic gate which may perform a significant role in the field of molecular electronics.

Nanocrystalline HgS thin films were synthesized by using an electrochemical route under galvanostatic conditions. Quantum size effects have resulted in the change of the semi-metallic behavior of bulk β-HgS (Eg=-0.5 eV) to semiconducting behavior with an absorption onset around 1.4 eV as confirmed from optical absorption studies. Glancing angle X-ray diffraction analysis confirms the presence of β-HgS (zinc-blend structure) with prominent crystallographic planes of (200), (220) and (311) in the deposit. This is consistent with results obtained from transmission electron diffraction studies. The Raman scattering measurements identified a broad 1LO confined phonon mode at 247 cm-1 which suggests that the crystalline sizes are small.

Nanocrystalline Si has been prepared by anodic etching of Si in an electrolyte consisting of ethanol and HF. The structure and surface morphology have been studied using transmission electron microscopy which reveal the cubic structure and porous morphology of Si nanocrystals (NCs). Electrochemical etching has resulted in surface oxidation of Si NCs as confirmed from X-ray photoelectron spectroscopic measurements. The average size of the Si NCs has been estimated from the line broadening analysis of the Raman scattering. Unique optical transitions associated with porous Si/SiO2 quantum well (QW) like structure has been investigated by surface photovoltage (SPV) measurements.

Thep-Si/HF-electrolyte interface was characterized by capacitance–voltage (C–V) and current–voltage (I–V) studies. At low frequency, the measured capacitance exhibits two maxima: one in the weak accumulation regime (around 0.8 V [SCE]) and the other in the strong accumulation regime (around 2.6 V [SCE]), both of which disappear at high frequency. The disappearance of the two capacitance maxima is attributed to the slow response of interface traps to high frequencies. The flat-band potential, VFB, is found to be frequency dependent. The surface state densities corresponding to the two capacitance maxima are estimated to be 3.2×1011 cm-2 and 2.4×1011 cm-2, respectively. The in situ I–V characteristics distinguish pore formation, transition and electropolishing regions. Porous Si synthesized at 50 mA cm-2 gives a broad photoluminescence peak around 2.04 eV at 300 K.

A low energy cluster beam deposition (LECBD) technique has been used to prepare the Sb cluster films on different substrates and are characterized using a variety of probes. Proton induced X-ray emission (PIXE) analysis shows the absence of any foreign trace elemental impurity even at ppm level. Glancing angle X-ray diffraction (GXRD) and transmission electron diffraction (TED) studies reveal the presence of single crystalline feature of Sb with hexagonal symmetry along with Sb-oxides. The transmission electron micrograph (TEM) of the cluster films of thickness 20 A and 100 A show size distribution which is more for the 100 A film compared to that of the 20 A one. The photoluminescence (PL) studies at 300 K show red shifted peaks along with the one possibly due to HOMO-LUMO transition around 2.4 eV. X-ray photoelectron spectroscopy (XPS) of Sb cluster Films show shoulders to the core level peaks of the Sb corresponding to 3d(3/2) and 3d(5/2) which are shifted by 1.0 to 2.0 eV suggesting the formation of Sb-oxide. Raman scattering studies show the shift of A(1g) and E-g vibrational modes from their bulk value.

In situ current (I)–(V) voltage studies were carried out to get a better understanding of the mechanism of formation of porous silicon (PS). It is observed that on decreasing the anodization current density below a critical value (∼75mAcm−2) the size of the PS crystallites increases while for its values above 75mAcm−2 electropolishing occurs. Raman spectroscopic studies show that the sizes of the Si crystallites are small and change from 4.7 to 3.8nm when the current densities are increased from 20 to 50mAcm−2. Transmission electron micrographs show preferential propagation of pores whereas transmission electron diffraction (TED) patterns show typical crystalline Si with the cubic structure.

Unembeded clusters deposited over different substrates are known to yield size distribution. Hence, with a motivation to arrest the size distribution and explore the novel properties, Se clusters have been deposited on porous Si (PS) matrix. Se clusters have been synthesized by a low energy cluster beam deposition (LECBD) technique on different substrates viz. PS, Si and conducting glass (ITO). PIXE analysis revealed the absence of any foreign impurity in the cluster deposit. TEM micrographs and glancing angle XRD of Se cluster films identify size distribution and presence of a-monoclinic and trigonal phases of Se. PS has been synthesized by anodic etching of p-Si in HF and ethanol mixture. The TEM micrographs and the diffraction patterns of the PS identify the pore morphology and streaking in Bragg spot. A broad red PL band observed in PS was found to be quenched when Se clusters were prepared in PS matrix. No Raman signal could be detected from Se clusters when prepared on ITO or Si substrate. However Raman line could be observed from Se clusters when prepared in PS matrix and found to shift by 2 to 7 cm(-1) from its bulk value.

The porous Si/HF-electrolyte junction has been studied by capacitance (C)–voltage (V) and current (I)–voltage (V) measurements. The observed current under forward bias shows an exponential increase like a Schottky diode with two oscillations around 1.0 and 2.4 V (SCE), respectively, whereas the reverse bias current shows negligible contribution. The low-frequency capacitance spectrum exhibits a peak structure in forward bias regime, which can be ascribed to the charge trapping/detrapping at Fermi level of porous Si under forward bias. The potential and charge distribution for a p-semiconductor/electrolyte junction is discussed

Antimony cluster thin films have been synthesized by the newly-developed low energy cluster beam deposition technique. Proton-induced X-ray emission analysis shows absence of any foreign impurity even at ppm level. Structural analysis by glancing angle X-ray diffraction indicates presence of rhombohedral Sb along with Sb-oxides. Transmission electron microscopy micrographs for 20 Angstrom and 100 Angstrom films respectively show the size distribution along with isolated aggregates. The size distribution for 100 Angstrom thick film is found to be large compared to the 20 Angstrom one. Transmission electron diffraction studies reveal hexagonal symmetry.

Nano-phase Mercury Sulphide is being prepared by an electrodeposition technique. The glancing angle X-ray diffraction (GXRD) and Transmission electron Microscopic (TEM) studies reveal that the deposited nano-phase material is Cubic Mercury Sulphide (beta-HgS) crystallized in Zincblende structure. The impurity, thickness and stoichiometry have been analyzed using Proton induced X-ray emission (PIXE) and Rutherford back scattering spectroscopic (RBS) studies. Optical absorption of nano-crystalline HgS samples shows a blue shift in their absorption threshold with decreasing crystalline size/decreasing electrolysis current density. Blue shift of the optical band gap at the zone center (Gamma-point) in the range of 1.0-2.0 eV from its bulk value (Eg = E(Gamma(1c)) - E(Gamma(15v)) = 0.5 eV) has been detected from the optical absorption studies. The transition from the bulk semimetal to semiconducting behavior is the interesting report of the present work.

. Porous silicon (PS) has been synthesized by anodic etching in HF and ethanol electrolyte. The in situ current–voltage characteristic clearly identify the pore formation, transition and electropolishing regimes. The experimentally observed impedance and phase as a function of frequency (Bode plots) reasonably agree with theoretically simulated Bode plots drawn by considering the equivalent circuit for PS/electrolyte.