Role of conformational isomerism in solvent-mediated charge transfer in chiral (S) 1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM): condensed-phase to jet-cooled spectroscopic studies

Intramolecular charge-transfer reaction in chiral (S) 1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM) has been investigated in the condensed phase and in jet-cooled conditions by means of laser-induced fluorescence, dispersed emission, resonance-enhanced two-photon ionization, and IR-UV double resonance experiments, as well as quantum chemical calculations. In the condensed phase, THIQM only shows local emission in nonpolar and protic solvents and dual emission in aprotic polar solvents, where the solvent-polarity dependent Stokes shifted emission is ascribed to a state involving charge transfer from the nitrogen lone pair to the benzene π-cloud. Ab initio calculations reveal two low-energy conformers, which are observed in jet-cooled conditions. In the most stable conformer, THIQM(I), the CH(2)OH substituent acts as a hydrogen bond donor to the nitrogen lone pair in the equatorial position, while the second most stable conformer, THIQM(II), corresponds to the opposite NH···O hydrogen bond, with the nitrogen lone pair in the axial position. The two low-energy jet-cooled conformers of THIQM evidenced from the laser-induced fluorescence and dispersed emission spectra only show structured local emission. Complexes with usual solvents reproduce the condensed phase properties. The jet-cooled complex with aprotic polar solvent acetonitrile shows both local emission and charge transfer emission as observed in solution. The jet-cooled hydrate mainly shows local emission due to the unavailability of the nitrogen lone pair through intermolecular hydrogen bonding.     

Electro-active silver oxide nanocubes for label free direct sensing of bisphenol A to assure water quality

This research, for the first time, demonstrates a direct electrochemical detection of bisphenol A (BPA) using silver oxide (Ag₂O) nanocubes (NCs) modified platinum electrode. The Ag₂O NCs, size ranging from 60 to 100 nm utilized in this research as a smart electro-active sensing platform were pure and synthesized using a cost-effective, affordable, and facile chemical route. The Ag₂O NCs modified electrochemical sensor exhibited a low limit of detection (LOD) as 20 nmol dm^?3, high sensitivity as 95 μA (μmol dm^?3)^?1 cm^?2, and linear dynamic range (LDR) varies from 80 nmol dm^?3- 4.8 μmol dm^?3. This sensor also showed good selectivity, reproducibility, and reusability for BPA detection. The practical application of developed sensor was also tested using real water samples. The outcomes of this research suggested that Ag₂O NCs based sensor can be useful for effective and efficient electrochemical BPA sensing in both real and lab samples.     

Combined Photoredox and Iron Catalysis for the Cyclotrimerization of Alkynes

Successful combinations of visible‐light photocatalysis with metal catalysis have recently enabled the development of hitherto unknown chemical reactions. Dual mechanisms from merging metal‐free photocatalysts and earth‐abundant metal catalysts are still in their infancy. We report a photo‐organo‐iron‐catalyzed cyclotrimerization of alkynes by photoredox activation of a ligand‐free Fe catalyst. The reaction operates under very mild conditions (visible light, 20 °C, 1 h) with 1–2 mol % loading of the three catalysts (dye, amine, FeCl₂).     

Bi3+‐Er3+ and Bi3+‐Yb3+ Codoped Cs2AgInCl6 Double Perovskite Near‐Infrared Emitters

Bi³⁺ and lanthanide ions have been codoped in metal oxides as optical sensitizers and emitters. But such codoping is not known in typical semiconductors such as Si, GaAs, and CdSe. Metal halide perovskite with coordination number 6 provides an opportunity to codope Bi³⁺ and lanthanide ions. Codoping of Bi³⁺ and Ln³⁺ (Ln=Er and Yb) in Cs₂AgInCl₆ double perovskite is presented. Bi³⁺‐Er³⁺ codoped Cs₂AgInCl₆ shows Er³⁺ f‐electron emission at 1540 nm (suitable for low‐loss optical communication). Bi³⁺ codoping decreases the excitation (absorption) energy, such that the samples can be excited with ca. 370 nm light. At that excitation, Bi³⁺‐Er³⁺ codoped Cs₂AgInCl₆ shows ca. 45 times higher emission intensity compared to the Er³⁺ doped Cs₂AgInCl₆. Similar results are also observed in Bi³⁺‐Yb³⁺ codoped sample emitting at 994 nm. A combination of temperature‐dependent (5.7 K to 423 K) photoluminescence and calculations is used to understand the optical sensitization and emission processes.     

A Systems Approach to a One-Pot Electrochemical Wittig Olefination Avoiding the Use of Chemical Reductant or Sacrificial Electrode

An unprecedented one-pot fully electrochemically driven Wittig olefination reaction system without employing a chemical reductant or sacrificial electrode material to regenerate triphenylphosphine (TPP) from triphenylphosphine oxide (TPPO) and base-free in situ formation of Wittig ylides, is reported. Starting from TPPO, the initial step of the phosphoryl P=O bond activation proceeds through alkylation with RX (R=Me, Et; X=OSO₂CF₃ (OTf)), affording the corresponding [Ph₃POR]⁺X⁻ salts which undergo efficient electroreduction to TPP in the presence of a substoichiometric amount of the Sc(OTf)₃ Lewis acid on a Ag-electrode. Subsequent alkylation of TPP affords Ph₃PR⁺ which enables a facile and efficient electrochemical in situ formation of the corresponding Wittig ylide under base-free condition and their direct use for the olefination of various carbonyl compounds. The mechanism and, in particular, the intriguing role of Sc³⁺ as mediator in the TPPO electroreduction been uncovered by density functional theory calculations.     

No collective neutrino flavor conversions during the supernova accretion phase

We perform a dedicated study of the supernova (SN) neutrino flavor evolution during the accretion phase, using results from recent neutrino radiation hydrodynamics simulations. In contrast to what was expected in the presence of only neutrino-neutrino interactions, we find that the multiangle effects associated with the dense ordinary matter suppress collective oscillations. The matter suppression implies that neutrino oscillations will start outside the neutrino decoupling region and therefore will have a negligible impact on the neutrino heating and the explosion dynamics. Furthermore, the possible detection of the next galactic SN neutrino signal from the accretion phase, based on the usual Mikheyev-Smirnov-Wolfenstein effect in the SN mantle and Earth matter effects, can reveal the neutrino mass hierarchy in the case that the mixing angle θ(13) is not very small.     

Magneto-resistance, thermal conductivity, thermo-electric power and specific heat of superconductor Gd0.95Pr0.05Ba2Cu2.94M0.06O7−δ (M=Fe, Ni, Zn and Mn)

In the present paper, we present thermal and electrical transport properties of pristine and co-doped samples of high temperature superconductors Gd_0.95Pr_0.05Ba₂Cu_2.94M_0.06O_7−δ. It is found that all the samples, except the Mn co-doped sample, show metallic behavior in the normal state. It is observed that the upper critical field has a correlation with the substituent site of the co-dopant. Thermal conductivity κ(T) of all the samples, except the one with Zn co-doping, exhibits a hump like structure around their respective transition temperatures. A negative sign of the measured thermo-power (S) in Gd-123 indicates that electron-like carriers dominate the heat transport in the pristine sample; whereas a sign reversal in S, as a consequence of the change of dominant carrier upon doping, is observed. Specific heat (C_P) measurements show a jump around the transition temperature (T_C) for the pristine sample, however, such a jump in C_P is strongly suppressed for the doped samples.     

An evolutionary game-theoretic model for ethno-religious conflicts between two groups

Ethno-religious conflict in multi-cultural societies has been one of the major causes of loss of life and property in recent history. In this paper, we present and analyze a multi-agent game theoretic model for computational study of ethno-religious conflicts in multi-cultural societies. Empirical fact-based research in sociology and conflict resolution literature have identified (a) ethno-religious identity of the population, (b) spatial structure (distribution) of the population, (c) existing history of animosity, and (d) influence of leaders as some of the salient factors causing ethno-religious violence. It has also been experimentally shown by Lumsden that multi-cultural conflict can be viewed as a Prisoner’s Dilemma (PD) game. Using the above observations, we model the multi-cultural conflict problem as a variant of the repeated PD game in graphs. The graph consists of labeled nodes corresponding to the different ethno-religious types and the topology of the graph encodes the spatial distribution and interaction of the population. We assume the structure of the graph to have the statistical properties of a social network with the high degree nodes representing the leaders of the society. The agents play the game with neighbors of their opponent type and they update their strategies based on neighbors of their same type. This strategy update dynamics, where the update neighborhood is different from the game playing neighborhood, distinguishes our model from conventional models of PD games in graphs. We present simulation results showing the effect of various parameters of our model to the propensity of conflict in a population consisting of two ethno-religious groups. We also compare our simulation results to real data of occurrence of ethno-religious violence in Yugoslavia.     

Emergent Universe with Exotic Matter in Brane World Scenario

In this work, we have examined the emergent scenario in brane world model for phantom and tachyonic matter. For tachyonic matter field we have obtained emergent scenario is possible for closed, open and flat model of the universe with some restriction of potential. For normal scalar field the emergent scenario is possible only for closed model and the result is identical with the work of Ellis et al. (Class. Quantum Gravity 21:223, 2004), but for phantom field the emergent scenario is possible for closed, open and flat model of the universe with some restriction of potential.