Excited state proton transfer in di-(2-hydroxy-3-formyl-5-tert butyl phenyl) methane and solvent effect

The proton transfer reaction and the spectroscopic properties of di-(2-hydroxy-3-formyl-5-tert butyl phenyl) methane (HFPM) have been examined in different nonpolar and polar solvents at room temperature and 77 K, by means of absorption, emission and time resolved fluorescence spectroscopy. In the ground state, the primary closed form has been identified in all the nonpolar and polar solvents and the anion is detected only in presence of base in some of the polar solvents. After photoexcitation, the excited state intramolecular proton transfer (ESIPT) is indicated by a large Stokes shifted emission (approximately 10,600 cm-1) in all the nonpolar and polar solvents used, except in water and ethylene glycol (EG). The ESIPT band is likely to be originated from the enol tautomer of the HFPM. Two types of anion and H-bonded complex have been detected in the excited state. In water and EG, only anion and H-bonded complex have been detected in the excited state. At 77 K, HFPM shows phosphorescence in pure ethanol, and in n-hexane in presence of triethylamine. It has been suggested that the appearance of phosphorescence is due to the rotation of the formyl group. The measured nonradiative decay rates have always been found to dominate in the decay processes of the excited state of HFPM. Some semiempirical calculations have been undertaken to rationalize the experimental findings.     

l-Proline-catalyzed one-pot expeditious synthesis of highly substituted pyridines at room temperature

Only 15 mol% of l-proline in ethanol proved to be a very efficient catalyst for the one-pot synthesis of a wide variety of highly substituted pyridines at room temperature. The methodology is mild, efficient, high yielding, and the products can be directly recrystallized from hot ethanol.     

In alkaline media,Fremy’s salt oxidizes alkanols by a hydrogen atom transfer mechanism

In aqueous alkali, Fremy’s salt (potassium nitrosodisulfonate dimer), homolyses nearly exclusively to the monomer radical anion, nitrosodisulfonate (NDS). In this media, NDS almost quantitatively oxidizes benzyl alcohol (PhCH₂OH) to benzaldehyde (PhCHO), itself being reduced to hydroxylamine disulfonate (HNDS). The reaction is very nearly first-order in [NDS], [alkanol] and in [OH⁻]. However, with progressive addition of HNDS, decay kinetics of NDS gradually deviates from first-order. Ultimately, with sufficient excess of HNDS, the reaction becomes second-order in [NDS]. The consumption ratio, (ΔPhCH₂OH]/Δ[NDS]), is ∼2. PhCD₂OH manifests a large primary kinetic isotope effect (k_H/k_D = 11.6). Substituted benzyl alcohols (RBzCH₂OH) with R-groups withdrawing electron density from the O–H bond accelerated the reaction; those with R-groups donating electron density to the O–H bond retarded the reaction. The conversion of 2-propanol to 2-propanone is much slower compared to that of benzyl alcohol to benzaldehyde. An alpha-H atom transfer mechanism seems logical.     

Nanomechanical properties inside the scratch grooves of soda–lime–silica glass

Zn_2?2x Mn_2x GeO₄ (x=0, 0.001, 0.01) phosphors were prepared by conventional solid state reaction technique. X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), diffuse reflection spectra, photoluminescence (PL), and cathodoluminescence (CL) spectroscopy were utilized to characterize the synthesized phosphors. The Mn²⁺-activated Zn₂GeO₄ phosphors exhibit narrow emission band at 532 nm under the excitation of ultraviolet light, which due to the ⁴T₁(⁴G)–⁶A₁(⁶S) transition of Mn²⁺ ions. Also it is observed that there exists energy transfer between the Zn₂GeO₄ host lattice and the activator (Mn²⁺). Under excitation of low-voltage electron beams, Zn₂GeO₄:Mn²⁺ shows strong green emission band dominating at 535 nm, corresponding to the ⁴T₁(⁴G)–⁶A₁(⁶S) emission of Mn²⁺ ions. The emission intensity and chromaticity coordinates of Zn₂GeO₄:Mn²⁺ as a function of accelerating voltage and the filament current were also investigated.     

Sol–gel derived nanocrystalline multiferroic BiFeO3 and R (R=Er and Tm) doped therein: Magnetic phase transitions and enhancement of magnetic properties

Nanocrystalline BiFeO₃ and rare earth ion doped BiFeO₃ (Bi_0.9R_0.1FeO₃, R=Er and Tm) were prepared by sol–gel method. Rietveld analysis of the X-ray diffractograms of the samples revealed that small amount of impurity phase of Bi₂Fe₄O₉ was formed together with the desired phase. In the thermal variation of magnetic mass susceptibility (χ_m) of the samples, one sharp transition below T_M (T_M∼100 K, 50 K and 30 K for BiFeO₃, Bi_0.9Er_0.1FeO₃ and Bi_0.9Tm_0.1FeO₃, respectively) was observed, which clearly hint the change of the domination of the ferromagnetic exchange interaction over the usual antiferromagnetic exchange interaction. Also, static magnetization (M) and susceptibility of each doped sample have been drastically enhanced compared to that of BiFeO₃. The values of χ_m and M measured at different temperatures confirmed that the magnetic behavior of the doped systems has been dominated by the paramagnetic/ferromagnetic clusters below ∼T_M. Another phase transition were observed in the χ_m vs. T curve of the samples at relatively higher temperature T_B (∼260 K for BiFeO₃, ∼220 K for Bi_0.9Er_0.1FeO₃ and ∼180 K for Bi_0.9Tm_0.1FeO₃), which may be attributed to the charge ordering transition. Ferroelectric hysteresis loops of the samples observed at 100 Hz confirmed the presence of ferroelectric ordering of the samples. Measured values of dielectric constants at 1 kHz of each sample in presence and absence of magnetic field confirmed a substantial magnetoelectric coupling of all the samples.     

A new alternative approach of all optical frequency encoded clocked S-R flip-flop exploiting the non-linear character of semiconductor optical amplifiers

In all optical networking and computing system, the role of all-optical flip-flops is very much essential. For signal synchronization with a reference clock and for storage of digital bits the flip-flop has no alternative. In this communication the authors propose a method of developing an all optical frequency encoded clocked R-S flip-flop using the non-linear character of semiconductor optical amplifiers. Frequency is the basic character of light and several encoding/decoding problems in computations and communications can be solved using the frequency encoding principle of optical data. The proposed system is all-optical and therefore it can extend a super fast speed of operation (far above THz limit).     

Strain-tunable band gap in graphene/h-BN hetero-bilayer

Using full-potential density functional calculations within local density approximation (LDA), we predict that mechanically tunable band-gap and quasi-particle-effective-mass are realizable in graphene/hexagonal-BN hetero-bilayer (C/h-BN HBL) by application of in-plane homogeneous biaxial strain. While providing one of the possible reasons for the experimentally observed gap-less pristine-graphene-like electronic properties of C/h-BN HBL, which theoretically has a narrow band-gap, we suggest a schematic experiment for verification of our results which may find applications in nano-electromechanical systems (NEMS), nano opto-mechanical systems (NOMS) and other nano-devices based on C/h-BN HBL.     

Supramolecular Barrel-Rosette Ion Channel Based on 3,5-Diaminobenzoic Acid for Cation-Anion Symport

The structural tropology and functions of natural cation-anion symporting channels have been continuously investigated due to their crucial role in regulating various physiological functions. To understand the physiological functions of the natural symporter channels, it is vital to develop small-molecule-based biomimicking systems that can provide mechanistic insights into the ion-binding sites and the ion-translocation pathways. Herein, we report a series of bis((R)-(−)-mandelic acid)-linked 3,5-diaminobenzoic acid based self-assembled ion channels with distinctive ion transport ability. Ion transport experiment across the lipid bilayer membrane revealed that compound 1 b exhibits the highest transport activity among the series, and it has interesting selective co-transporting functions, i.e., facilitates K⁺/ClO₄⁻ symport. Electrophysiology experiments confirmed the formation of supramolecular ion channels with an average diameter of 6.2±1 Å and single channel conductance of 57.3±1.9 pS. Selectivity studies of channel 1 b in a bilayer lipid membrane demonstrated a permeability ratio of , , and indicating the higher selectivity of the channel towards KClO₄ over KCl salt. A hexameric assembly of a trimeric rosette of 1 b was subjected to molecular dynamics simulations with different salts to understand the supramolecular channel formation and ion selectivity pattern.