Catalyst-Controlled C-H Allylation and Annulation of 2-Aryl Quinazolinones with 2-Methylidene Cyclic Carbonate.

The site-selective modification of quinazolinone as a privileged bicyclic N-heterocycle is an attractive topic in medicinal chemistry and material science. We herein report the ruthenium(II)-catalyzed C-H allylation of 2-aryl quinazolinones with 2-methylidene cyclic carbonate. In addition, tandem C-H allylation and annulation are achieved under rhodium(III) catalysis, resulting in the formation of tetracyclic quinazolinones including a tertiary carbon center. Post-transformations of the synthesized products demonstrate the potential of the developed methodology. A series of mechanistic investigations were also performed.

Strategy to probe multimodal light emissions from Eu3+/Yb3+ activated garnet nanophosphors for LED devices and solar cell applications.

This study investigates multimodal light emission from an Eu3+/Yb3+ activated Y3Ga5O12 (YGG) nanophosphor synthesized using a low temperature solution combustion method. The prepared sample possesses a cubic phase and an Ia3̄d space group and this is confirmed with X-ray diffraction and Rietveld refinement analysis. The synthesized sample shows orange-red emission bands because of the f-f transitions of Eu3+ under UV (393 nm) and NIR (980 nm) excitations via downshifting (DS) and upconversion (UC) processes, respectively. Upon UV (393 nm) excitation of the sample, the Eu3+ ions absorb this energy and then transfer it to a neighboring pair of Yb3+ ions giving NIR emission (900-1100 nm) corresponding to the 2F5/2 → 2F7/2 transition of Yb3+. The energy transfer from a single Eu3+ ion to a pair of Yb3+ ions is possible because of the quantum cutting (QC) process and this energy transfer efficiency is found to increase with the increasing concentration of the Yb3+. The quantitative estimation of energy transfer and internal quantum cutting efficiency is determined by measuring the decay kinetics. An activation energy of 0.25 eV indicates the good thermal stability of the sample. Furthermore, samples are suitable for use in practical applications in lighting devices by combining them with the near-ultraviolet (NUV; InGaN) chip. The fabricated LED device shows stability with the driving current flow values. Studies indicate that the present nanophosphor could be useful for display devices, and in enhancing the spectral conversion efficiency of the solar cells.

Probing multimodal light emission from Tb3+/Yb3+-doped garnet nanophosphors for lighting applications.

Herein we report the solution-combustion-method-synthesized Tb3+- and Tb3+/Yb3+-doped Gd3Ga5O12 nanophosphors, which possess luminescent and magnetic properties. The phase formation/crystal structure, and morphology of the prepared nanophosphors are studied using X-ray diffraction (XRD)/Raman spectroscopy and a field emission scanning electron microscope (FE-SEM), respectively. Tb3+/Yb3+-doped phosphor samples exhibit green emission with an intense band around 544 nm through downshifting (DS) and upconversion (UC) processes because of the 5D4 → 7F5 transition of Tb3+. In addition to this visible emission, these samples also show a NIR emission band around 1024 nm via the quantum cutting (QC) process due to the 2F5/2 → 2F7/2 transition of Yb3+. Emission decay measurements of the 5D4 → 7F5 transition of Tb3+ are performed to obtain the rate of energy transfer from Tb3+ to nearby Yb3+. Furthermore, using this energy transfer, the quantum cutting efficiencies were estimated. For their practical application, a selected sample was used to fabricate a LED device by combining the sample with a UV-C LED (274 nm). The obtained results, such as the activation energy (∼0.20 eV) and the high CRI value (78), suggest that the prepared sample can be utilized as a green-light-emitting agent in phosphor-coated (pc) WLEDs.

Structural and Functional Characterization of Mycobacterium tuberculosis Homoserine Transacetylase.

Mycobacterium tuberculosis (Mtb) lacking functional homoserine transacetylase (HTA) is compromised in methionine biosynthesis, protein synthesis, and in the activity of multiple essential S-adenosyl-l-methionine-dependent enzymes. Additionally, deficient mutants are further disarmed by the toxic accumulation of lysine due to a redirection of the metabolic flux toward the lysine biosynthetic pathway. Studies with deletion mutants and crystallographic studies of the apoenzyme have, respectively, validated Mtb HTA as an essential enzyme and revealed a ligandable binding site. Seeking a mechanistic characterization of this enzyme, we report crucial structural details and comprehensive functional characterization of Mtb HTA. Crystallographic and mass spectral observation of the acetylated HTA intermediate and initial velocity studies were consistent with a ping-pong kinetic mechanism. Wild-type HTA and its site-directed mutants were kinetically characterized with a panel of natural and alternative substrates to understand substrate specificity and identify critical residues for catalysis. Titration experiments using fluorescence quenching showed that both substrates─acetyl-CoA and l-homoserine─engage in a strong and weak binding interaction with HTA. Additionally, substrate inhibition by acetyl-CoA and product inhibition by CoA and O-acetyl-l-homoserine were proposed to form the basis of a feedback regulation mechanism. By furnishing key mechanistic and structural information, these studies provide a foundation for structure-based design efforts around this attractive Mtb target.

Light-induced dissolution and concomitant crystallization of a Keggin-type polyoxometalate mimicking a naturally occurring phenomenon.

A suspension of a yellow polycrystalline compound [PPh4]3[PMoVI12O40] in N-methylformanilide (NMF) (in which it is not soluble), on irradiation with sunlight, initiates dissolution via its reduction followed by its crystallization leading to the isolation of single crystals of compound [PPh4]4[PMoVMoVI11O40]·3CH3(C6H5)NCHO (1). Compounds [PPh4]3[PMoVI12O40]·1.75 CH3(C6H5)NCHO (2) and [PPh4]3[PMoVI12O40]·2CH3(C6H5)NCHO (3), each containing an oxidized Keggin anion, are obtained at two different temperatures when the corresponding mother liquor is kept in the dark.

Rhodium(III)-Catalyzed Conjugate Addition of ß-CF3-Enones with Quinoline N-Oxides.

The site-selective incorporation of a trifluoromethyl group into biologically active molecules and pharmaceuticals has emerged as a central topic in medicinal chemistry and drug discovery. Herein, we demonstrate the rhodium(III)-catalyzed conjugate addition of ß-trifluoromethylated enones with quinoline N-oxides, which result in the generation of ß-trifluoromethyl-ß'-quinolinated ketones. The reaction proceeds under mild conditions with complete functional group tolerance. The synthetic applicability was showcased by successful gram-scale experiments and valuable synthetic transformations of coupling products.

Comparative study of upconversion and photoacoustic measurements of Er3+/Yb3+doped La2O3phosphor under 980 nm.

The Er3+/Yb3+doped La2O3phosphor samples were synthesized by the combustion method and then photoluminescence and photoacoustic spectroscopic studies were done. Prepared samples were annealed at 800 °C, 1000 °C and 1300 °C and all samples were found in pure hexagonal phase as confirmed by XRD analysis. From FE-SEM images it is found that particle size increases with increase in annealing temperature. The frequency upconversion emission spectra of samples were recorded by exciting the sample with 980 nm diode laser and maximum emission intensity is obtained for the sample annealed at 1000 °C for 2 h. A photoacoustic cell was designed and wavelength dependent photoacoustic spectra were measured. The effect of sample storage time on radiative and non-radiative emission properties of sample was checked by measuring upconversion emission and photoacoustic spectra, simultaneously. It is observed that the emission intensity and photoacoustic signal both decreases with time. The maximum photoacoustic signal is obtained around 974 nm wavelength and it indicates its potential for photo-thermal therapy using infrared excitation.

Methylene Thiazolidinediones as Alkylation Reagents in Catalytic C-H Functionalization: Rapid Access to Glitazones.

The straightforward and rapid incorporation of a thiazolidinedione scaffold into prefunctionalized (hetero)aromatic compounds is in demand for the development of antidiabetic glitazones and other pharmaceuticals. Herein, we report the unprecedented N- and O-directed C-H alkylation of various (hetero)arenes with methylene thiazolidinediones under rhodium(III) catalysis. The applicability of the developed protocol in challenging contexts is exhibited by the late-stage installation of a methylene thiazolidinedione moiety on the C-H bond of commercially available drug molecules. Combined mechanistic investigations aided the elucidation of a plausible reaction mechanism.

Perovskite La1-xKxCoO3-δ (0 ≤ x ≤ 0.5): a novel bifunctional OER/ORR electrocatalyst and supercapacitive charge storage electrode in a neutral Na2SO4 electrolyte.

The as-prepared La1-xKxCoO3-δ (0 ≤ x ≤ 0.5) showed superior pseudocapacitive charge storage capacity in a neutral 0.5 M Na2SO4 electrolyte and superior electrocatalytic activities for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in a 1 M KOH electrolyte. 30% K doped p-type La0.7K0.3CoO3-δ presents superior OER activity with an overpotential of ∼335 mV at 10 mA cm-2 current rate in a 1 M KOH electrolyte. Additionally, La1-xKxCoO3-δ (0 ≤ x ≤ 0.5) presents an excellent charge-storage capacitance in a neutral 0.5 M Na2SO4 electrolyte resulting in a gravimetric capacitance of the La0.5K0.5CoO3-δ electrode equivalent to 378 F g-1, 282 F g-1, 221 F g-1, 163 F g-1, and 74 F g-1 at a current density of 1 A g-1, 2 A g-1, 3 A g-1, 5 A g-1, and 10 A g-1, respectively. After 2500 continuous cycles of charge/discharge, the La0.5K0.5CoO3-δ//AC cell exhibits higher stability, capacitive retention (94%) and coulombic efficiency (97%). The gravimetric charge storage capacity of ASCs (La0.5K0.5CoO3-δ//AC) in the full cell mode showed capacitance equivalent to 308 F g-1, 287 F g-1, 238 F g-1, 209 F g-1 and 162 F g-1 at current densities of 1 A g-1, 2 A g-1, 3 A g-1, 5 A g-1 and 10 A g-1 in a neutral 0.5 M Na2SO4 electrolyte respectively. Maximum specific power equivalent to ∼6884 W kg-1 was observed at a current density of 10 A g-1 when the specific energy reached ∼57 W h kg-1 for the full cell. The double exchange mechanism coupled with stoichiometric oxygen defects present in the perovskite lattice seems to be operative behind the enhanced electrocatalytic OER properties, and additionally, it improves the charge storage kinetics of the La1-xKxCoO3-δ (0 ≤ x ≤ 0.5) electrode in a neutral Na2SO4 electrolyte for supercapacitor application. This work presents a rational strategy for introducing facile oxygen ion defects into perovskite structured La1-xKxCoO3-δ (0 ≤ x ≤ 0.5) to develop multifunctional electrode materials for a supercapacitor and energy conversion (OER/ORR) electrode of metal-air batteries.

C-H amidation of 2-aryl azlactones under iridium(III) catalysis: access to chiral amino acids.

In this study, we examine the site-selctive iridium(III)-catalyzed C-H amidation between 2-aryl azlactones and acyl azides. This transformation produces a range of ortho-amidated azlactones, which act as precursors for the synthesis of chiral amino acids via organocatalyzed ring-opening reactions. To test its effectiveness, the method developed is applied to the late-stage C-H amidation of complex drug molecules. The isolation of an iridacycle species supports a proposed reaction pathway.

Ruthenium(II)-Catalyzed Tandem C-H Allylation and [3 + 2] Dipolar Cycloaddition to Construct Bridged Tetracycles.

The ruthenium(II)-catalyzed tandem C-H allylation and intramolecular dipolar cycloaddition between azomethine imines and 2-methylidenetrimethylene carbonate is described herein. The initially formed ß-substituted allyl fragment could trigger the exotype [3 + 2] cycloaddition with the polar azomethine group, resulting in the formation of bridged tetracycles bearing a hydroxymethylene group at a bridgehead carbon center. A wide substrate scope and broad functional group compatibility were observed. The gram-scale synthesis and synthetic transformations demonstrate the synthetic utility of this process.

Polyoxometalate-Supported Copper(I)-Pyrazole Complex: Unusual Stability, Geometrical Isomers, Organic Transformation, and Computation.

We have described the synthesis and characterization of a polyoxometalate (POM)-supported copper(I)-pyrazole complex, [CuI(C15H12N2)2] [PW12O40{CuI(C15H12N2)2}2]·CH3OH (1). There are three Cu(I)-pyrazole coordination complexes in compound 1, out of which two are supported by the {PW12O40}3- Keggin POM by coordinate covalent bonds from the POM surface through oxygen donors to the Cu(I) centers of two Cu(I) complexes and one remains uncoordinated to the POM surface, acting as a cationic complex species in the crystals of 1. The POM-coordinated Cu(I) complexes have a T-shaped geometry, and the uncoordinated Cu(I) complex is a linear one. During the solvothermal synthesis of compound 1, remarkably, the associated 1,5-diphenylpyrazole ligand is formed from cinnamaldehyde phenylhydrazone through oxidative cyclization at the cost of Cu(II) reduction to Cu(I), and then, these two (copper(I) and pyrazole ligand) form the coordination complex. Compound 1 undergoes desolvation on heating the single crystals of compound 1 at 55 °C in the aerial atmosphere with the formation of the desolvated compound [CuI(C15H12N2)2][PW12O40{CuI(C15H12N2)2}2] (2). Interestingly, when an aqueous suspension of compound 1 is bubbled with O2 gas at room temperature, it undergoes solid-to-solid transformation, resulting in the formation of the compound [CuI(C15H12N2)2]3[PW12O40] (3). Compounds 1, 2, and 3 have been characterized by routine spectral analyses (including cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) studies) and unambiguously by single-crystal X-ray crystallography. We have performed density functional theory (DFT) calculations on compound 1 to understand the rationale of its unusual stability toward oxidation.

Polymer-Induced Emission-Active Fluorine-Embedded Carbon Dots for the Preparation of Warm WLEDs with a High Color Rendering Index.

Exploration of many strategies has continuously contributed to producing aggregation-induced red-emissive carbon dots (CDs). In this work, we designed fluorine-embedded (F-embedded) CDs from 1,2,4-triaminobenzene, thiourea, and ammonium fluoride (NH4F) exhibiting polymer-induced emission (PIE). The PIE phenomenon of fluorescent CDs is obtained in poly(vinyl alcohol) (PVA), showing emissions at 611 and 617 nm in the dispersed and solid states, respectively. The CDs exhibited a red shift of 28 nm in the PVA solution because PVA hydroxyl groups formed a robust bridge-like H-bonding network between CDs. The fluorine embedded in CDs enhanced the H-bond affinity toward PVA. It showed that this H-bond restricted the coupling of CDs' surface states and inhibited the nonirradiation transfer. For the solid state, surface PVA chains eliminated the π-π interaction of the conjugated core and constructed a self-quenching resistance polymeric system around CDs. As a result, CDs showed an unexpected red shift of fluorescence emission in PVA. Furthermore, white light-emitting diodes (WLEDs) have a correlated color temperature (CCT) of 5232 K, and a high color rendering index of 95 has been fabricated by integrating the red- and green-emissive films over the UV LEDs. Interestingly, the as-synthesized CDs showed room temperature phosphorescence (RTP), which enabled us to employ the CDs in double-security protection. Simultaneously, CDs have been used in fingerprint detection.

KOtBu-promoted C3-homocoupling of quinoxalinones through single electron transfer from an sp2 carbanion intermediate.

The C3-selective homodimerization of quinoxalinones is described. A C3-sp2 carbanion species generated through deprotonation of quinoxalinone using potassium tert-butoxide (KOtBu) transfers an electron (single electron transfer mechanism) to a second quinoxalinone, affording a radical-anion intermediate. The radical scavenging and electron paramagnetic resonance (EPR) experiments support the plausible radical reaction pathway. A mild reaction temperature and a short reaction time were attained under cost-effective conditions, which reveal the amenability of this protocol to pharmaceutical and chemical industries.

Synthesis of Succinimide-Linked Indazol-3-ols Derived from Maleimides under Rh(III) Catalysis.

The structural modification of N-aryl indazolols as tautomers of N-aryl indazolones has been established as a hot topic in pharmaceutics and medicinal chemistry. We herein disclose the rhodium(III)-catalyzed 1,4-addition reaction of maleimides with N-aryl indazol-3-ols, which provides the succinimide-bearing indazol-3-ol scaffolds with complete regioselectivity and a good functional group tolerance. Notably, the versatility of this protocol is demonstrated by the use of drug-molecule-linked and fluorescence-probe-linked maleimides.

NASICON-structured Na3Fe2PO4(SO4)2: a potential cathode material for rechargeable sodium-ion batteries.

The cost-effective and abundant availability of sodium offers an opportunity for rechargeable Na-ion batteries as an ideal replacement for rechargeable Li-ion batteries. However, the larger size and strong Na+-Na+ interaction create multidimensional phase instability and transformation problems, especially in layer-structured NaxMO2 (Mn, Co, Fe, and Ni) that inhibit the direct transformation of rechargeable Li-ion battery technology to Na-ion batteries. However, framework structures offer superior structural stability due to the interconnection of polyanions or polyhedra forming cationic octahedra. Sodium superionic conductor (NASICON)-type structures are well known for their superior Na+ ion transport and are identified as intercalative hosts as electrodes for rechargeable Na-ion batteries. Here, we report the synthesis of Na3Fe2PO4(SO4)2 in a NASICON framework structure and its investigation as a cathode in a Na/Na3Fe2PO4(SO4)2 cell working on the Fe3+/Fe2+ redox couple. The cell provides a single-phase reaction having a capacity approaching 70 mA h g-1 at 0.1 C after 50 cycles in the voltage range of 2 to 4.2 V, with a columbic efficiency approaching 100%. The large availability of Na and Fe with the stable redox and charge/discharge performance of NASICON-type Na3Fe2PO4(SO4)2 make it a possible cathode candidate for next-generation rechargeable sodium-ion batteries.

Synthesis, Characterizations, and Electrochemical Performances of Highly Porous, Anhydrous Co0.5Ni0.5C2O4 for Pseudocapacitive Energy Storage Applications.

Electrochemical energy storage relies essentially on the development of innovative electrode materials with enhanced kinetics of ion transport. Pseudocapacitors are excellent candidates to bridge the performance gap between supercapacitors and batteries. Highly porous, anhydrous Ni0.5Co0.5C2O4 is envisaged here as a potential electrode for pseudocapacitor applications, mainly because of its open pore framework structure, which poses inherent structural stability due to the presence of planar oxalate anions (C2O4 2-), and active participation of Ni2+/3+ and Co2+/3+ results in high intercalative charge storage capacity in the aqueous KOH electrolyte. The Ni0.5Co0.5C2O4 electrode shows specific capacitance equivalent to 2396 F/g at 1 A/g in the potential window of 0.6 V in the aqueous 2 M KOH electrolyte by galvanostatic charge/discharge experiments. Predominant pseudocapacitive mechanism seems to operative behind high charge storage due to active participation of Ni2+/3+ and Co2+/3+ redox couple as intercalative (inner) and surface (outer) charges stored by porous anhydrous Co0.5Ni0.5C2O4 were close to high 38 and 62% respectively. Further, in full cell asymmetric supercapacitors (ASCs) in which porous anhydrous Co0.5Ni0.5C2O4 was used as the positive electrode and activated carbon (AC) was utilized as the negative electrode, in the operating potential window 1.6 V, the highest specific energy of 283 W h/kg and specific power of ∼817 W/kg were achieved at 1 A/g current rates. Even at a very high power density of 7981 W/kg, the hybrid supercapacitor still attains an energy density of ∼75 W h/kg with high cyclic stability at a 10 A/g current rate. The detailed electrochemical studies confirm higher cyclic stability and a superior electrochemical energy storage property of porous anhydrous Co0.5Ni0.5C2O4, making it a potential pseudocapacitive electrode for large energy storage applications.

Novel anti-adipogenic effect of CF3-allylated indole in 3T3-L1 cells.

Indole derivatives from various plants are known to have health benefits because of their anti-cancer, anti-oxidant, anti-inflammatory, and anti-tubercular effects. However, their effects on adipogenesis have not been fully elucidated yet. Herein, we show that a newly synthesized indole derivative, CF3-allylated indole, [(E)-1-(pyrimidin- 2-yl)-2-(4,4,4- trifluorobut-2-enyl)-1H-indole], effectively inhibits adipogenesis. We found that CF3-allylated indole inhibited lipid accumulation and suppressed the expression of CCAAT/enhancer-binding protein α (C/EBPα) and peroxisome proliferator activated receptor γ (PPARγ) in 3T3-L1 cells. The inhibitory effect of CF3-allylated indole primarily occurred at the early phase of adipocyte differentiation by increasing intracellular cyclic adenosine monophosphate (cAMP) levels and enhancing protein kinase A (PKA) and adenosine monophosphate-activated protein kinase (AMPK) signaling. Conversely, depletion of PKA or treatment with a protein kinase A inhibitor (H89) reversed such inhibitory effects of CF3-allylated indole on adipogenesis and PPARγ expression. These results suggest that CF3-allylated indole inhibits early stages of adipogenesis by increasing phosphorylation of PKA/AMPK, leading to decreased expression of adipogenic genes in 3T3-L1 cells. These results indicate that CF3-allylated indole has potential for controlling initial adipocyte differentiation in metabolic disorders such as obesity.

La1-x K x FeO3-δ: An Anion Intercalative Pseudocapacitive Electrode for Supercapacitor Application.

The green energy alternative to a fossil fuel-based economy can be provided only by coupling renewable energy solution solutions such as solar or wind energy plants with large-scale electrochemical energy storage devices. Enabling high-energy storage coupled with high-power delivery can be envisaged though high-capacitive pseudocapacitor electrodes. A pseudocapacitor electrode with multiple oxidation state accessibility can enable more than 1e - charge/transfer per molecule to facilitate superior energy storage. K-doped LaFeO3 (La1-x K x FeO3-δ) is presented here as an electrode having a high pseudocapacitance storage, equivalent to 1.32e - charge/transfer per molecule, resulting in a capacity equivalent of 662 F/g at 1 mV/s scan rate by introduction of a layered potential over the Fe-ion octahedral to utilize higher redox state energies (Fe4+→ Fe2+). La/K ordering in orthorhombic perovskite (La1-x K x FeO3-δ) made the Fe4+ oxidation state accessible, and a systematic shift in the redox energies of Fe4+/3+ and Fe3+/2+ redox couples was observed with K+ ion doping in the A site of the LaFeO3 perovskite, which resulted in a high faradic contribution to the capacitance, coupled with anionic intercalation of H2O/OH- in the host perovskite lattice. The surface capacitive and diffusion control contributions for capacitance are about 42 and 58%, respectively, at -0.6 V, with a scan rate of 1  mV/s. A high gravimetric capacitance, equivalent to 619, 347, 188, 121, and 65 F/g, respectively, at 1, 2, 3, 5, and 10 A/g constant current, was observed for the La0.5K0.5FeO3-δ electrode. Up to 88.9% capacitive retention and 97% Coulombic efficacy were obtained for continuous 5000 cycles of charge/discharge for the La0.5K0.5FeO3-δ electrode. The gravimetric capacitance values of ASCs (activated carbon//La0.5K0.5FeO3-δ) are 348, 290, 228, and 147 F/g at current densities of 1, 2, 3, and 5 A/g, respectively. A maximum specific power of ∼3594 W/kg was obtained when the specific energy reached ∼117 Wh/kg at 5 A/g of current density.