Search

Highlights: [•] Use of polarizability, hardness, electrophilicity as global descriptors for IPT process. [•] Use of IRC as proton transfer co-ordinate supports MPP and MHP principles. [•] Use of O–H distance as PT co-ordinate cannot explain MPP and MHP principle. [•] IRC is the better choice for PT co-ordinate than O–H distance of enol tautomer. [ABSTRACT FROM AUTHOR]

Highlights: [•] Chemical reactivity parameters of some lactum–lactim system have been computed. [•] Computed parameters are polarizability, hyperpolarizability, Hardness and I.P. [•] IRC have been chosen as proton transfer co-ordinate of the titled compounds. [•] Reactivity parameters show their optimum values at TS. [ABSTRACT FROM AUTHOR]

Abstract: A facile one step method for the synthesis of wormlike silver nanoparticles has been carried out in methyl cellulose matrix. Synthesis is based on the reduction of AgNO3 by sodium borohydride (NaBH4) in aqueous methyl cellulose (MC). Synthesized nanoparticles are mostly mono disperse in size and their aggregation is controlled by varying the concentration of AgNO3. Silver nanoparticles are analyzed using transmission electron microscope (TEM), UV–vis spectroscopy and X-ray diffraction (XRD) technique. It has been found that the concentration of AgNO3 has a significant effect on the morphology of Ag nanostructures. Worm like nanostructures showed excellent catalytic activity in the borohydride reduction of p-nitrophenol compared to spherical shaped nanoparticles. [Copyright &y& Elsevier]

Abstract: Monodispersed sodium alginate (SA) stabilized silver nano bar and hydroxyl propyl methyl cellulose (HPMC) stabilized silver nano bar have been synthesized by photochemical method. The nanoparticles are characterized by UV–VIS–NIR spectroscopy, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) study. Catalytic reduction of 4-nitrophenol (4-NP) by sodium borohydride in presence of nanoparticles is also evaluated. The kinetic data obtained by monitoring the change in UV–Vis absorption spectra of 4-NP are explained by Langmuir–Hinshelwood model. It is observed that the rate of reduction is higher in SA stabilized Ag nano bar than the HPMC stabilized Ag nano bar. [Copyright &y& Elsevier]

Abstract: We present here the hybrid DFT level study of a series of dipeptide at 6-31g∗ basis. A rigorous computation has been performed on a series of dipeptide (keeping valine as a fixed component in the N-terminus and the component in the C-terminus are varied with eight different combinations) to investigate various geometrical parameters to understand the effect of amino acid sequence in the dipeptides. Bond lengths, bond angles have been reported. Geometry around α-carbon atom is discussed. The analysis of dihedral angles shows deviations from planarity. This has been explained in terms of the cumulative effect of steric hindrance of –R group and H-bonding. To get an idea about its conformational stability, a rigid potential energy scan has also been performed on valine by rotating –COOH and –CH(CH3)2 groups separately. [Copyright &y& Elsevier]

An Anthracene based fluorescent probe, 1-(Anthracen-2-yliminomethyl)-napthalen-2-ol (AIN), was synthesized via simple one-pot reaction from inexpensive reagents. Intriguingly, it exhibited novel AIE characteristics in H 2 O-THF mixtures at high water content. Size and growth process of particles in different volume percentage of water and THF mixtures were investigated using TRPL, DLS, SEM and optical microscope. The fluorescent aggregates exhibited distinct Hg 2+ -selective “on-off” type fluorescence switching upon binding. Additionally, the fluorescence quenching showed a linear correlation in the Hg 2+ concentration range from 0.3 to 3.6 μM and the limit of detection was estimated as low as ∼3 ppb. The drastic decrease in emission intensity of AIN aggregates was observed in the presence of mercury ions via a complex interplay through the ground state complexation between AIN and Hg 2+ ions and external heavy atom induced perturbation by Hg 2+ ions to the excited states of the AIN. A large Stern–Volmer quenching constant was estimated to be 2.54 × 10 5  M −1 . The proposed analytical system with clear AIE characteristics demonstrates a potential outlook for the on-site visual detection of Hg 2+ in paper strips. Finally, the sensory probe was also applied to determine the concentration of Hg 2+ in real water samples to demonstrate its practical applications. [ABSTRACT FROM AUTHOR]

Aggregate/solid-state fluorescence switching organic material, 4-((pyren-1-yl)methyleneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (PAP) was synthesized via simple one-step synthetic process. It exhibited novel aggregation induced emission (AIE) phenomenon by controlling water ratio in solutions which provide sturdy cyan emissive fluorogenic aggregates with diverse well-defined morphologies, especially tuning the morphologies from 0-D to 1-D microcrystals that show obvious optical waveguide effect. Dynamic light scattering, time-resolved photoluminescence, optical fluorescence microscope and scanning electron microscope were exploited to gain insight into the AIE mechanism and discrimination of the different aggregated morphologies such as 0-D hollow spheres, 1-D hexagonal, hexagonal 1-D growth, rods and wires with distinct emissions tuning in solid state. Intriguingly, triple excitation induced triple emissions of green, yellow and red lights were emanated from microstructures in solid state for the first time which completely covered visible spectral region. By taking the advantage of its attractive AIE feature, the fluorescent hydrosol employed itself as a fluorescent chemosensor with superb selectivity and sensitivity toward explosive TNP through ground state complexation with a detection limit as low as 16 nM and very high Stern–Volmer quenching constant of 4.7 × 10 5 M −1 . An instant ‘naked eye’ response for trace detection of TNP in solid state, we prepared the fluorescent paper strips which make the protocol simple, fast, inexpensive and practical for on-site visualization. [ABSTRACT FROM AUTHOR]

A novel material showing aggregation induced enhanced emission (AIEE) is developed by reprecipitation method using 2,2′ biquinoline (BQN) in aqueous medium. Morphologies of the particles are characterized using optical and scanning electron microscopic (SEM) study. The selective fluorescence and absorbance response of aggregated BQN towards Zn 2+ and H + have been explained due to ground state complexation and protonation of BQN with Zn 2+ and H + respectively. Protonated BQN exhibits charge transfer character in transoid form with yellowish green emission but in BQN-Zn 2+ complex, BQN changes to cis planer conformation and displays considerable intra ligand charge transfer (ILCT) character with sky blue color under UV excitation. A 2:1 BQN-Zn 2+ complex have been confirmed using Job’s plot. Our study revealed that BQN hydrosol act as selective turn-on fluorescence sensor for Zn 2+ ion both in acidic and alkaline medium. Further, the proton induced charge transfer character and the proposed binding modes of the receptor with Zn 2+ have been supported by DFT based computational study. [ABSTRACT FROM AUTHOR]

Pure organic compounds that are also phosphorescent at room temperature are very rare in literature. Here, we report efficient phosphorescence emission from aggregated hydrosol of Benz(a)anthracene (BaA) at room temperature. Aggregated hydrosol of BaA has been synthesized by re-precipitation method and SDS is used as morphology directing agent. Morphology of the particles is characterized using optical and scanning electronic microcopy (SEM). Photophysical properties of the aggregated hydrosol are carried out using UV–vis, steady state and time resolved fluorescence study. The large stoke shifted structured emission from aggregated hydrosol of BaA has been explained due to phosphorescence emission of BaA at room temperature. In the crystalline state, the restricted intermolecular motions (RIM) such as rotations and vibrations are activated by crystal lattice. This rigidification effect makes the chromophore phosphorescent at room temperature. The possible stacking arrangement of the neighboring BaA within the aggregates has been substantiated by computing second order Fukui parameter as local reactivity descriptors. Computational study also reveals that the neighboring BaA molecules are present in parallel slipped conformation in its aggregated crystalline form. [ABSTRACT FROM AUTHOR]

Abstract: Here, we report synthesis of star shape gold nanoparticles using seed mediated growth process. Ag+ ions have been used to catalyze the anisotropic growth of gold particles in the growth solution. Star like gold nanoparticles are characterized using UV–vis and TEM study. Excitation of localized surface plasmon of star shaped gold nanoparticles by the visible radiation results broad and intense localized surface plasmon resonance excitation band. Emission spectra of nanostars upon excitation at 230nm and 480nm has been explained due to localized plasmon at the edge of star like particle and the longitudinal mode of these anisotropically grown gold nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: Potential energy surfaces (PES) for the ground and excited state intramolecular proton transfer (ESIPT) processes in 5-hydroxy-flavone (5HF) were studied using DFT-B3LYP/6-31G(d) and TD-DFT/6-31G(d) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer (GSIPT) in 5HF. Excited states PES calculations support the existence of ESIPT process in 5HF. ESIPT in 5HF has been explained in terms of HOMO, LUMO electron density of the enol and keto tautomer of 5HF. PES scan by phenyl group rotation suggests that the twisted form, i.e., phenyl group rotated by 18.7° out of benzo-γ-pyrone ring plane is the most stable conformer of 5HF. [Copyright &y& Elsevier]

Abstract: DFT calculations has been done applying 6-31G∗ basis set on a series of dipeptides where the N-terminus position is fixed with phenylalanine and the C-terminus is varied with eight different amino acids. Different geometrical parameters (bond angle, bond length, geometry around α-carbon atom) are thoroughly investigated to study the effect of amino acid sequence on dipeptide. Dihedral angle data analysis shows the deviation of amide plane from planarity, which is due to the combined effect of the steric hindrance of –R group and hydrogen bonding. The λ max value for phenylalanine has been calculated, which shows good agreement with the experimental value. A rigid potential energy scan is performed on phenylalanine by rotating –CH2Ph, –COOH and –NH2 groups separately to get some idea about the conformational stability. [Copyright &y& Elsevier]

Abstract: Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of 1-hydroxy-2-naphthaldehyde (1H2NA) and 2-hydroxy-3-naphthaldehyde (2H3NA) were studied using DFT/B3LYP(6-31G) and TD-DFT/B3LYP(6-31G) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer for both the compounds. Excited states PE calculations support the ESIPT process to both 1H2NA and 2H3NA. The wide difference in ESIPT emission process of 1H2NA and 2H3NA have been explained in terms of HOMO and LUMO electron density of the enol and keto tautomer of these two compounds. [Copyright &y& Elsevier]