A Strategic Design of an Opto-Chemical Security Device with Resettable and Reconfigurable Password Based Upon Dual Channel Two-in-One Chemosensor Molecule.

A simple strategy is proposed to design and develop an intelligent device based on dual channel ion responsive spectral properties of a commercially available molecule, harmine (HM). The system can process different sets of opto-chemical inputs generating different patterns as fluorescence outputs at specific wavelengths which can provide an additional level of protection exploiting both password and pattern recognitions. The proposed system could have the potential to come up with highly secured combinatorial locks at the molecular level that could pose valuable real time and on-site applications for user authentication.

Fabrication, characterization and mosquito larvicidal bioassay of silver nanoparticles synthesized from aqueous fruit extract of putranjiva, Drypetes roxburghii (Wall.).

Highly stable nanoparticles of metallic silver with average dimension of 26.6 nm were synthesized by a simple, cost-effective, reproducible and previously unexploited biogenic source viz. dried green fruits of Drypetes roxburghii (Wall.) (common name putranjiva). The as-synthesized silver nanoparticles (Ag NP) were characterized by their characteristic surface plasmon resonance absorption spectra, X-ray diffraction analysis, energy dispersive X-ray analysis and selected area electron diffraction study. The morphology of the particles was determined by high-resolution transmission electron microscopy. Fourier transform infrared analysis focuses some light on the chemical framework that stabilizes the nanoparticles. The analyses of the phytochemicals present in the fruit extract of the plant were also performed following standard protocol. Mosquito larvicidal bioassay with the Ag NPs was carried out with two mosquitoes, namely Anopheles stephensi Liston and Culex quinquefasciatus Say. The results show impressive mortality rate even at too low concentration of nanoparticle. Toxicity test on non-target organism shows no harmful effect during the study period.

A newly developed highly selective ratiometric fluoride ion sensor: spectroscopic, NMR and density functional studies.

A new easy-to-synthesize chemosensor, 3,3'-bis(indolyl)-4-chlorophenylmethane (hereafter S), was designed, synthesized and employed as a selective optical chemosensor for fluoride ions.(1)H NMR and density functional studies on the system have been carried out to determine the nature of the interaction between S and X(-) (X = inorganic anions) responsible for the significant fluoride-induced changes in the absorption properties of S. The experimental results reveal that abstraction of an acidic proton of S by the fluoride ion, leading to the formation of anionic species, is responsible for the spectral changes. These changes allow signaling for the fluoride ion to detect and estimate the concentration of fluoride ion present even at the submicromolar level, accurate up to 2 µM. Calculations of the transition energies of S, S(-), and S···F(-) (hydrogen bonded complex) show that only S(-) is responsible for the long-wavelength absorption band in the presence of F(-).

Effect of cyclodextrin nanocavity confinement on the photophysics of a beta-carboline analogue: a spectroscopic study.

Interaction of a beta-carboline based biologically active molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with alpha-, beta-, and gamma-cyclodextrins (CDs) in aqueous solution has been studied using steady state and time-resolved fluorescence and steady-state fluorescence anisotropy techniques. Polarity dependent intramolecular charge transfer (ICT) process is responsible for the remarkable sensitivity of this biological fluorophore to the CD environments. Upon encapsulation, the CT fluorescence exhibits hypsochromic shift along with enhancements in the fluorescence yield, fluorescence anisotropy (r), and fluorescence lifetime. The reduction in the nonradiative deactivation rate of the fluorophore within the CD nanocavities leads to an increase in both fluorescence yield and lifetime. Among the three CDs, gamma-CD shows the most spectacular confinement effect. The results establish the formation of 1:1 AODIQ:CD inclusion complexes in alpha- and beta-CDs. In aqueous gamma-CD solutions, however, depending on the concentration of the gamma-CD, formation of both 1:1 and 1:2 complexes have been revealed. Hydrodynamic radii of the 1:1 and 1:2 probe-gamma-CD supramolecular complexes have also been determined.

Surfactant chain-length-dependent modulation of the prototropic transformation of a biological photosensitizer: norharmane in anionic micelles.

A photophysical study of norharmane (NHM), an efficient cancer cell photosensitizer, has been undertaken in well-characterized biomimetic micellar nanocavities formed by anionic surfactants of varying chain length, namely, sodium decyl sulfate (S10S), sodium dodecyl sulfate (S12S), and sodium tetradecyl sulfate (S14S), using steady-state and time-resolved fluorescence spectroscopy. The effect of the hydrophobic chain length on the structural dynamism of the fluorophore has been reported. Experimental results demonstrate that the equilibrium of this dynamism is sensitive to the environment. Variation in the surfactant chain length plays an important role in promoting a specific prototropic form of the probe molecule. A striking feature of the present study is that an increase in the surfactant chain length (hydrophobicity) favors the cationic species of NHM. This has been rationalized on the basis of changes in the local pH and the aggregation number of the micelles. A fluorescence quenching study of the micelle-bound probe using ionic quencher Cu2+ corroborates this.

Binding interaction of a biological photosensitizer with serum albumins: a biophysical study.

A photophysical study on the binding interaction of an efficient cancer cell photosensitizer, norharmane (NHM), with model transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA), has been performed using a combination of steady-state and time-resolved fluorescence techniques. The emission profile undergoes a remarkable change upon addition of the proteins to the buffered aqueous solution of the photosensitizer. The polarity-dependent prototropic transformation is responsible for the remarkable sensitivity of this biological fluorophore to the protein environments. A marked increase in the fluorescence anisotropy in the proteinous environments indicates that the albumin proteins introduce motional restriction on the drug molecule. Light has been thrown on the denaturing action of urea on the probe-bound protein. The probable binding site of the drug in proteins has also been assessed from the combination of denaturation study, micropolarity measurement, and fluorescence resonance energy transfer (FRET) study. The present study suggests that the stability of serum albumins is enhanced upon binding with the drug.

Effect of nanocavity confinement on the rotational relaxation dynamics: 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine in micelles.

In continuation of our recent study on the steady state photophysics of a biologically active beta-carboline derivative, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), in the present article we have investigated the effect of nanocavity confinement on the excited state dynamics and rotational relaxation of the probe using picosecond time resolved fluorescence and fluorescence anisotropy techniques. The polarity dependent intramolecular charge transfer process is responsible for the remarkable sensitivity of this biological fluorophore in micellar environments. The fluorescence anisotropy decay of AODIQ incorporated inside the micelle is biexponential. The rotational motion of the probe was interpreted on the basis of a two step model consisting of a fast restricted rotation of the probe and a slow lateral diffusion of the probe in the micelle; both coupled to the overall rotation of the micelle. Experimental results reveal that micellar environment causes significant retardation of both the wobbling as well as the translational motion of the probe.

Fluorometric and isothermal titration calorimetric studies on binding interaction of a telechelic polymer with sodium alkyl sulfates of varying chain length.

Steady-state fluorescence measurements and isothermal titration calorimetric experiments have been performed to study the interaction between a telechelic polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), and sodium alkyl sulfate surfactants having decyl, dodecyl, and tetradecyl hydrocarbon tails. Fluorometric results suggest polymer-surfactant interaction in the very low range of polymer concentrations. The relative variation in the excimer to monomer pyrene emission intensities with varying surfactant concentration reveals that initial addition of surfactant favors intramolecular preassociation until the surfactant molecules start binding with the ethylene oxide (EO) chain. With the growing number of surfactant aggregates along the EO chain, the association becomes hindered due to the polyelectrolyte effect. The results from microcalorimetric titrations in the low concentration range of PYPY solution (approximately 10(-6) M) with alkyl sulfates suggest two kinds of surfactant-polymer interactions, one with the polymer hydrophobic end groups and the other with the ethylene oxide backbone. The overall polymer-surfactant interaction starts at a much lower surfactant concentration for the hydrophobically modified polymers compared to that in the case of unsubstituted poly(ethylene oxide) homopolymer. From the experiments critical aggregation concentration values and the second critical concentration where free micelles start forming have been determined. An endeavor has been made to unveil the mechanism underlying the corresponding associations of the surfactants with the polymer.

Surfactant-induced modulation of fluorosensor activity: a simple way to maximize the sensor efficiency.

Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-acetyl-4-oxo-6,7-dihydro-12H-indolo-[2,3-a]-quinolizine (AODIQ), is described in a biomimicking micellar nanocage. It has been shown that surfactant concentration dictates the sensing behavior of the fluorophore toward physiologically essential trace metals, such as Cu2+. This is a simple, efficient, and general technique that allows one to utilize the sensor to its maximum efficiency.

Interaction of pyrene-end-capped poly(ethylene oxide) with bovine serum albumin and human serum albumin in aqueous buffer medium: a fluorometric study.

The photophysical behavior of a hydrophobically tailored water-soluble polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), has been studied in aqueous buffered bovine serum albumin (BSA) and human serum albumin (HSA) media. In buffered aqueous solution the polymer shows dual emission corresponding to the monomer and the excimer of pyrene moiety. The relative intensity of the monomer to the excimer emission shows interesting variation with the addition of BSA and HSA and is indicative of significant interaction of these albumin proteins with the polymer. The binding interaction has been shown to have a prominent role on the steady state fluorescence anisotropy of the two emission bands. Attempt has been made to determine the micropolarities of the protein microenvironments from a comparison of the variation of the monomer to excimer relative fluorescence intensities of the probe in water-dioxane mixtures with varying composition.

Encapsulation of norharmane in cyclodextrin: formation of 1:1 and 1:2 inclusion complexes.

Steady state absorption and fluorometric techniques have been used to investigate the photophysics of norharmane (NHM), a bioactive fluorophore, in aqueous as well as aqueous cyclodextrin (CD) environments. The absorption and steady state fluorescence spectral studies reveal the formation of two types of inclusion complexes between the fluorophore and beta-cyclodextrin (beta-CD) depending on the relative population of the two. The stoichiometries and association constants of these complexes have been determined monitoring the fluorescence data. alpha-and gamma-cyclodextrin (alpha-CD, gamma-CD) do not have appreciable effect on the spectral pattern of the fluorophore. The differential fluorimetric behavior of NHM in different CD environments has been rationalized from the variation of the relative dimensions of the probe and the CD cavities.

Photophysical study of 3-acetyl-4-oxo-6,7-dihydro-12H-indolo[2,3-a]quinolizine in biomimetic reverse micellar nanocavities: a spectroscopic approach.

Photophysical properties of 3-acetyl-4-oxo-6,7-dihydro-12H-indolo[2,3-a]quinolizine (AODIQ), a bioactive molecule, has been investigated in well-characterized, monodispersed biomimicking nanocavities formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in heptane using steady-state and picosecond time resolved fluorescence and fluorescence anisotropy. The emission behavior of AODIQ is very much dependent upon the water/surfactant mole ratio (W), i.e., on the water pool size of the reverse micellar core. AODIQ exhibits a sharp decrease in fluorescence anisotropy with increasing W, implying that the overall motional restriction experienced by the molecule is decreased with increased hydration. Some of the depth-dependent relevant fluorescence parameters, namely, fluorescence maxima and fluorescence anisotropy (r), have been monitored for exploiting the distribution and microenvironment around the probe in the reverse micelles. Fluorescence spectral position and fluorescence quenching studies suggest that the probe does not penetrate into the reverse micellar core; rather it binds at the interfacial region. Quantitaive estimates of the micropolarity and microviscosity at the binding sites of the probe molecule have been determined as a function of W.

Spectroscopic investigation on the interaction of ICT probe 3-acetyl-4-oxo-6,7-dihydro-12H Indolo-[2,3-a] quinolizine with serum albumins.

Interaction of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), a biologically active molecule, with model transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA) have been studied using steady state and picosecond time-resolved fluorescence and fluorescence anisotropy. The polarity dependent intramolecular charge transfer (ICT) process is responsible for the remarkable sensitivity of this biological fluorophore to the protein environments. The CT fluorescence exhibits appreciable hypsochromic shift along with an enhancement in the fluorescence yield, fluorescence anisotropy (r) and fluorescence lifetime upon binding with the proteins. The reduction in the rate of ICT within the hydrophobic interior of albumins leads to an increase in the fluorescence yield and lifetime. Marked increase in the fluorescence anisotropy indicates that the probe molecule is located in a motionally constrained environment within the proteins. Micropolarities in the two proteinous environments have been determined following the polarity sensitivity of the CT emission. Addition of urea to the protein-bound systems leads to a reduction in the fluorescence anisotropy indicating the denaturation of the proteins. Polarity measurements and fluorescence resonance energy transfer (FRET) studies throw light in assessing the location of the fluorophore within the two proteinous media.

Constrained photophysics of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine in micellar environments: a spectrofluorometric study.

Photophysical properties of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ) have been studied in different aqueous micellar environments using steady-state and time-resolved emission spectroscopy. The charge transfer (CT) fluorescence exhibits appreciable hypsochromic shift, along with an enhancement in the fluorescence intensity in all the micellar media. This is associated with an increase in the fluorescence anisotropy (r), which suggests that the fluorophore molecule experiences motionally restricted environments upon binding with the micelles. Fluorescence spectral position and fluorescence quenching studies suggest that the fluorescing moiety does not penetrate into the core of the micellar units; rather it binds at the micelle-water interfacial region. The binding constant and free energy change during probe-micelle binding have been evaluated from relevant fluorescence data. Light has been thrown on the mode of action of urea on micelle bound probes. The results are interpreted in terms of the model that urea displaces water molecules from the micellar interface and the consequent destabilization leads to the expulsion of the probe molecules from the interfacial region. Polarity and viscosity of the microenvironments around the probe have been determined in the micellar systems.