Potassium carbonate as a base for the N-alkylation of indole and pyrrole in ionic liquids

The methodology for the N-alkylation of indole and pyrrole using potassium carbonate in 1-n-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF₄] as the sustainable reaction media with acetonitrile as the cosolvent is described herein. Our approach provides good yields with alkyl halides as well as sulfonates as the electrophiles. Cesium carbonate was also found to be a consistent base in the N-alkylation. The proposed methodology is simple and mild with easy workup.     

Preparation and low field magnetoresistance of double layered manganite La1.4Ca1.6Mn2O7

Double layered manganite of La_1.4Ca_1.6Mn₂O₇ (DLCMO) was prepared using solid state reaction method and had a metal-insulator transition temperature (T_MI) of 125 K. The short range 2D-feerromagnetic ordering (T_C2) starts growing when T<168 K and it gets converted into 3D-ferromagnetic ordering (T_C1) at 114 K. Low field magnetoresistance (MR) behaviour of the DLCMO was investigated and compared with an infinite layered manganite La_0.7Ca_0.3MnO₃ (LCMO). For DLCMO, in the temperature range between T_C1 and T_C2, the MR showed a gradual increase with the magnetic field. The observed MR and R-T behaviour of double layered manganite for T_C1<T<T_C2 has been explained in the frame work of the two phase model [ferromagnetic (FM) domains and paramagnetic (PM) regions] and percolative behaviour of transport in FM-PM mixture.     

Glycosides, depression and suicidal behaviour: the role of glycoside-linked proteins

Nowadays depression and suicide are two of the most important worldwide public health problems. Although their specific molecular mechanisms are still largely unknown, glycosides can play a fundamental role in their pathogenesis. These molecules act presumably through the up-regulation of plasticity-related proteins: probably they can have a presynaptic facilitatory effect, through the activation of several intracellular signaling pathways that include molecules like protein kinase A, Rap-1, cAMP, cADPR and G proteins. These proteins take part in a myriad of brain functions such as cell survival and synaptic plasticity. In depressed suicide victims, it has been found that their activity is strongly decreased, primarily in hippocampus and prefrontal cortex. These studies suggest that glycosides can regulate neuroprotection through Rap-1 and other molecules, and may play a crucial role in the pathophysiology of depression and suicide.     

Ratiometric detection of Hg2+ ions: an allosterically synchronized Hg2+/Li+ switch based on thiacalix[4]crown

A new heteroditopic chemosensor based on the 1,3-alternate conformation of thiacalix[4]crown shows a ratiometric fluorescence response towards Hg(2+) ions. Further, a negative allosteric behaviour between Hg(2+)/Li(+) ions is observed. Thus, metal ion exchange triggers a Hg(2+)/Li(+) switchable fluorescent chemosensor.     

Carbene-based ruthenium photosensitizers

A new series of N-heterocyclic carbene (NHC)-pyridine ruthenium complexes incorporating a carbene unit as an ancillary ligand were designed and successfully synthesized by using simple synthetic methods. The photophysical, electrochemical and photovoltaic properties of these NHC-pyridine based ruthenium complexes were investigated. These complexes showed photoelectric conversion efficiencies in the range of 6.43 ～ 7.24% under the illumination of AM 1.5 (100 mW cm(-2)). Interestingly, the modifications on the ancillary ligand of these sensitizers by removal of an alkoxyl group and replacement of the octyl chain with a 3,5-difluorobenzyl group showed a 13% increase in the conversion efficiency for the CifPR dye. These results demonstrated that structural modifications on the NHC-pyridine ancillary ligand of ruthenium complexes results in dye-sensitized solar cells exhibiting a comparable cell performance to that obtained using the standard N719 dye.     

Antifungal activity of plumericin and isoplumericin

This study evaluated the in vitro antifungal activity of the chloroform extract of Plumeria bicolor and its phytoconstituents plumericin and isoplumericin against Candida species and Cryptococcus neoformans by measuring the Minimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (MFC). Plumericin's consistently high activity against Candida albicans, C. krusei, C. glabrata, C. tropicalis and Cryptococcus neoformans was more potent than isoplumericin and the standard antifungal drug nystatin suggesting its potential as a drug candidate for candidiasis and cryptococcosis.     

Antibacterial potential of citral derivatives

Nine conjugated acid derivatives from monoterpene citral have been synthesized using ester, amide condensations, Wittig, Knoevenagel, Baylis-Hillman reactions and their antimicrobial activities were evaluated through disc diffusion and serial dilution methods. Several derivatives displayed interesting antimicrobial activity. Particularly, the Baylis-Hillman adducts 8-10 were found to have more potent antibacterial and antifungal activities than standard drugs namely chloramphenicol and nystatin respectively.     

Electronic structure description of a [Co(III)3Co(IV)O4] cluster: a model for the paramagnetic intermediate in cobalt-catalyzed water oxidation

Multifrequency electron paramagnetic resonace (EPR) spectroscopy and electronic structure calculations were performed on [Co(4)O(4)(C(5)H(5)N)(4)(CH(3)CO(2))(4)](+) (1(+)), a cobalt tetramer with total electron spin S = 1/2 and formal cobalt oxidation states III, III, III, and IV. The cuboidal arrangement of its cobalt and oxygen atoms is similar to that of proposed structures for the molecular cobaltate clusters of the cobalt-phosphate (Co-Pi) water-oxidizing catalyst. The Davies electron-nuclear double resonance (ENDOR) spectrum is well-modeled using a single class of hyperfine-coupled (59)Co nuclei with a modestly strong interaction (principal elements of the hyperfine tensor are equal to [-20(±2), 77(±1), -5(±15)] MHz). Mims (1)H ENDOR spectra of 1(+) with selectively deuterated pyridine ligands confirm that the amount of unpaired spin on the cobalt-bonding partner is significantly reduced from unity. Multifrequency (14)N ESEEM spectra (acquired at 9.5 and 34.0 GHz) indicate that four nearly equivalent nitrogen nuclei are coupled to the electron spin. Cumulatively, our EPR spectroscopic findings indicate that the unpaired spin is delocalized almost equally across the eight core atoms, a finding corroborated by results from DFT calculations. Each octahedrally coordinated cobalt ion is forced into a low-spin electron configuration by the anionic oxo and carboxylato ligands, and a fractional electron hole is localized on each metal center in a Co 3d(xz,yz)-based molecular orbital for this essentially [Co(+3.125)(4)O(4)] system. Comparing the EPR spectrum of 1(+) with that of the catalyst film allows us to draw conclusions about the electronic structure of this water-oxidation catalyst.     

Designer peptide dendrimers using click reaction

We designed and synthesized various peptide dendrimers using a 1,3-dipolar cycloaddition (Click) reaction. The dendritic structures reported here include symmetrical, asymmetrical, and cationic dendrimers with triazole, cystine, aromatic, aliphatic, and Lys-Asp dipeptide cores. The high chemoselectivity of the click reaction allowed us to synthesize good yields of high-purity protected and unprotected dendritic structures. Triazole is an excellent peptide bond mimic, which remains hydrolytically stable. Dendrimer 15a and the core unit 21 gelate in a mixture of organic solvents. We also demonstrated the versatility of the design by synthesizing various carbohydrate-based dendrimers.     

Fluoride-induced cyclization of pentacenequinone to higher quinones

Novel pentacenequinone derivatives 3, 7, and 10 have been synthesized via Suzuki-Miyaura coupling. Derivatives 3 and 7 having OTBS groups undergo irreversible fluoride-induced cyclization to substituted higher quinones in the presence of TBAF in dry THF using one-pot, two-step strategies in moderate yields. These functionalized higher quinone derivatives are freely soluble in THF and DMSO and can be used as precursors for the synthesis of higher acene derivatives.