The Lithium (Li) Doping Effect for Enhancing Thermoelectric and Optoelectronic Performances of Co2NbAl

Cobalt -rich Heusler compounds represent a very interesting family among Heusler alloys due to their performance in the field of spintronics and magnetic devices. The quaternary Heusler created by swapping of an anti-atom site by an alkali element improves the performance of physical properties for new applications. In this study, the electronic structures and magnetic properties before and after swapping cobalt (Co) by lithium (Li) in the Co2NbAl compound have been investigated using first-principle computational calculations. Our findings revealed that the swapping Co antisite by Li keeps the half-metallic character in the CoLiNbAl. Analysis of band structures show that ternary Heusler compound is ferromagnetic half-metallic with half metallic gap (band gap in minority channel ) equal 0.134 eV but the swapping Co with Li leads the material to change its behavior and becomes a semiconductor with a gap equal 1.043 eV using HSE06 approach. The results of optical and thermoelectric properties such as absorption coefficient, reflectivity or thermopower and figure of merit are very interesting in the optoelectronic field and encourages the researchers to realize photovoltaic cell and thermoelectric generator with a higher efficiency. These interesting features suggest that Co2NbAl and LiNbAlCo Heusler compounds could be good candidates for applications of antiferromagnetic spintronics and optoelectronics in commercial semiconductor industry.

Dynamics and mechanism of dimer dissociation of photoreceptor UVR8

Photoreceptors are a class of light-sensing proteins with critical biological functions. UVR8 is the only identified UV photoreceptor in plants and its dimer dissociation upon UV sensing activates UV-protective processes. However, the dissociation mechanism is still poorly understood. Here, by integrating extensive mutations, ultrafast spectroscopy, and computational calculations, we find that the funneled excitation energy in the interfacial tryptophan (Trp) pyramid center drives a directional Trp-Trp charge separation in 80 ps and produces a critical transient Trp anion, enabling its ultrafast charge neutralization with a nearby positive arginine residue in 17 ps to destroy a key salt bridge. A domino effect is then triggered to unzip the strong interfacial interactions, which is facilitated through flooding the interface by channel and interfacial water molecules. These detailed dynamics reveal a unique molecular mechanism of UV-induced dimer monomerization.

DABCO-promoted photocatalytic C–H functionalization of aldehydes

Herein we present a direct application of DABCO, an inexpensive and broadly accessible organic base, as a hydrogen atom transfer (HAT) abstractor in a photocatalytic strategy for aldehyde C–H activation. The acyl radicals generated in this step were arylated with aryl bromides through a well stablished nickel cross-coupling methodology, leading to a variety of interesting aryl ketones in good yields. We also performed computational calculations to shine light in the HAT step energetics and determined an optimized geometry for the transition state, showing that the hydrogen atom transfer between aldehydes and DABCO is a mildly endergonic, yet sufficiently fast step. The same calculations were performed with quinuclidine, for comparison of both catalysts and the differences are discussed.

Molecular Interactions between Methylene Blue and Sodium Alginate Studied by Molecular Orbital Calculations

A methylene blue (MB) indicator embedded in sodium alginate (SA) film was previously examined for detecting active oxygen species. In a previous study, spectrometry was used to identify and characterize the MB/SA complex. However, the decolorization mechanism was not fully assessed. In this study, our aim is to conduct computational calculations at the B3LYP/6-31G(d) level to clarify the exact types and positions of the interaction that cause the decolorization in MB. The results demonstrate that MB/SA interacts with carboxylates (-COO(superscript)-(superscript)) of SA and the N, C, and S atoms of MB, confirming previous experimental observations.

Rational Design of Simple Organocatalysts for the HSiCl3 Enantioselective Reduction of (E)-N-(1-Phenylethylidene)aniline

Prolinamides are well-known organocatalysts for the HSiCl3 reduction of imines; however, custom design of catalysts is based on trial-and-error experiments. In this work, we have used a combination of computational calculations and experimental work, including kinetic analyses, to properly understand this process and to design optimized catalysts for the benchmark (E)-N-(1-phenylethylidene)aniline. The best results have been obtained with the amide derived from 4-methoxyaniline and the N-pivaloyl protected proline, for which the catalyzed process is almost 600 times faster than the uncatalyzed one. Mechanistic studies reveal that the formation of the component supramolecular complex catalyst-HSiCl3-substrate, involving hydrogen bonding breaking and costly conformational changes in the prolinamide, is an important step in the overall process.

Photophysical Approach of Biological Active Benzofuran Derivatized Pyrrole with Green Synthesized Silver NPs Using C. Roseus Leaves: Computational and Spectroscopic Study

The electronic absorption and fluorescence emission spectra of N-(2,5-dimethyl-pyrrol-1-yl)-2-(5-methoxybenzofuran-3-yl)acetamide (DPMA) molecule were recorded in various solvents at room temperature with the aim of estimation of ground state (\({\mu }_{g}\)) and excited states (\({\mu }_{e}\)) dipole moments using Lippert’s, Bakshiev’s and Kawski-Chamma-Viallete’s equations. The results were signified that, the excited state dipole moment is greater than the ground state dipole moment, which indicates the excited state dipole moment is more polar than the ground state dipole moment. Ecofriendly green synthesis of silver nanoparticles (Ag NPs) were synthesized using catharanthus roseus (C.R) leaf extract was done. These synthesized Ag NPs were used as fluorescence quenchers. Fluorescence lifetime measurement is carried out using time correlated single photon counting technique of DPMA molecule with various concentrations of Ag NPs. A linear Stern-Volmer (S-V) plot was obtained in steady state and transient state method. Furthermore we have estimated computational calculations such as ground state optimized geometry, molecular electrostatic potential (MEP), highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), experimental and theoretical energy band gap, solvent polarity and normalized solvent polarity values. Morphology and sizes of green synthesized silver NPs were characterized by transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDX) and also characterized by UV-Visible absorption.

Phenylisoxazole-3/5-Carbaldehyde Isonicotinylhydrazone Derivatives: Synthesis, Characterization, and Antitubercular Activity

Eight new phenylisoxazole isoniazid derivatives, 3-(2′-fluorophenyl)isoxazole-5-carbaldehyde isonicotinylhydrazone (1), 3-(2′-methoxyphenyl)isoxazole-5-carbaldehyde isonicotinylhydrazone (2), 3-(2′-chlorophenyl)isoxazole-5-carbaldehyde isonicotinylhydrazone (3), 3-(3′-clorophenyl)isoxazole-5-carbaldehyde isonicotinylhydrazone (4), 3-(4′-bromophenyl)isoxazole-5-carbaldehyde isonicotinylhydrazone (5), 5-(4′-methoxiphenyl)isoxazole-3-carbaldehyde isonicotinylhydrazone (6), 5-(4′-methylphenyl)isoxazole-3-carbaldehyde isonicotinylhydrazone (7), and 5-(4′-clorophenyl)isoxazole-3-carbaldehyde isonicotinylhydrazone (8), have been synthesized and characterized by FT-IR, 1H-NMR, 13C-NMR, and mass spectral data. The 2D NMR (1H-1H NOESY) analysis of 1 and 2 confirmed that these compounds in acetone-d6 are in the trans(E) isomeric form. This evidence is supported by computational calculations which were performed for compounds 1–8, using DFT/B3LYP level with the 6-311++G(d,p) basis set. The in vitro antituberculous activity of all the synthesized compounds was determined against the Mycobacterium tuberculosis standard strains: sensitive H37Rv (ATCC-27294) and resistant TB DM97. All the compounds exhibited moderate bioactivity (MIC = 0.34–0.41 μM) with respect to the isoniazid drug (MIC = 0.91 μM) against the H37Rv sensitive strain. Compounds 6 (X = 4′-OCH3) and 7 (X = 4′-CH3) with MIC values of 12.41 and 13.06 μM, respectively, were about two times more cytotoxic, compared with isoniazid, against the resistant strain TB DM97.

Synthesis Luminescent Plasmonic Silver Nanoparticles and The Chemical Affinity towards sulphur atom in Sulphide and Thiourea molecules: Ab-Initio DFT Study

Three different luminescent silver nanoparticles(AgNPs) were synthesized by simple reduction method with the different mole ratios of L-ascorbic/citrate solution and stabilized with CTAB. The prepared three AgNPs were characterized by UV, fluorescence, FTIR, dynamic light scattering measurements and Scanning Electron Microscopy. The plasmon bands of AgNPs- reddish-brown (RB), green (G) and reddish-green (RG) were centered at 565, 587 and 592 nm, respectively. The highly luminescence emission was observed for AgNPs(G). The size diameters of the prepared AgNPs-G, RG and (RB) were measured by dynamic light scattering (DLS) method at 24.3 nm, 66.28 nm and 103.46 nm, respectively. The electrochemical properties of AgNPs-RG was recorded the oxidative part of AgNPs into Ag+ at +0.23 V and the reduction part of Ag+ into Ag0 was recorded at -0.49 V vs. Ag/AgCl). Cetyl trimethylammonium bromide (CTAB) was stabilized AgNPs(RG) which recorded in infrared and scanning electron microscope measurements. The concentration of thiourea, sodium sulphide was detected by the electrochemical sensitivity of AgNPs(RG)-CTAB. A calibration curve between electrochemical sensitivity of AgNPs-CTAB vs concentration of sulphur molecule. The limit of detection (LOD) was founded 2.10 and 1.90 µmole L-1 of sodium sulphide and thiourea, respectively (R2=0.94, n=3). The computational calculations are used to illustrated the chemical affinity of sulphur atom in sodium sulphide or thiourea towards AgNPs(RG).

An Experimental and Theoretical Study of Dye Properties of Thiophenyl Derivatives of 2-Hydroxy-1,4-naphthoquinone (Lawsone)

A prospective study of the dye properties of non-toxic lawsone thiophenyl derivatives, obtained using a green synthetic methodology allowed for the description of their bathochromic shifts in comparison to those of lawsone, a well-known natural pigment used as a colorant that recently also has aroused interest in dye-sensitized solar cells (DSSC). These compounds exhibited colors close to red, with absorption bands in visible and UV wavelength range. The colorimetric study showed that these compounds exhibited a darker color than that of lawsone within a range of colors depending on the substituent in the phenyl ring. Computational calculations employing Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT), showed that the derivatives have lower excitation energies than lawsone, while the alignment of their frontier orbitals regarding the conduction bands of TiO2 and ZnO and the redox potential of the electrolyte I−/I3− suggests that they could be employed as sensitizers. The study of the interactions of the lawsone and a derivative with a TiO2 surface model by different anchoring modes, showed that the adsorption is thermodynamically favored. Natural bond orbital (NBO) analysis indicates a two-center bonding (BD) O-Ti as the main interaction of the dyes with TiO2.