Thermal and spectral properties of alkali metal complexes of 2-hydroxy-1,4-naphthoquinone

Thermal and spectral studies of reactions between 2-hydroxy-1,4-naphthoquinone (lawsone) and sodium metal (Lw-1, Lw-1A, Lw-1B), CH₃COONa (Lw-2), NaOH (Lw-3), KOH (Lw-4), K₂CO₃ (Lw-5), Tris buffer (Lw-6), ammonia (Lw-7) are studied. Red solids of Lw-1 to Lw-7, Lw-1A, and Lw-1B were isolated and are characterized by elemental analysis, FT-IR, ¹H NMR and UV–Visible spectroscopy. FT-IR spectra of Lw-1A and Lw-1B show, ν _OH of adsorbed as well as coordinated water molecules between 3,600–3,100 cm^?1 and decrease in ν _C=O frequency of lawsone ligand. The benzenoid ring protons C(5)H, C(8)H, C(6)H and C(7)H in Lw-1A and Lw-1B show upfield shift in ¹H NMR spectra. Hypsochromic shift and bathochromic shift is observed to π–π* transition band (~329 nm) and charge transfer band (~455 nm), respectively in UV–Visible spectra of all compounds. Pyrolytic decomposition of all compounds is studied by nonisothermal TG studies in air. Step I in all compounds leads to loss of adsorbed water molecules. Decomposition of lawsone anion in all compounds occurs in two or more steps. Thermodynamically Lw-1 to Lw-7, Lw-1A and Lw-1B are different compounds and their decomposition mechanisms are varied. The respective metal oxide residue viz. (Na₂O or K₂O) obtained after complete decomposition of Lw-1 to Lw-5, Lw-1A, and Lw-1B, is analyzed by powder X-ray diffraction. The adsorbed as well as coordinated water molecules are revealed by DTA and DSC studies as endothermic peak at ~100 °C. Decomposition mechanisms for lawsone anion are proposed based on LC–MS, GC–MS, and TG studies. Thermal and spectral studies reveal the coordination of lawsone ligand in its naphthosemiquinone form with alkali metal ions.     

Synthesis and antimycobacterial screening of new 4-(4-(1-benzyl-1H-1,2,3-triazol-4-yl)-1-phenyl-1H-pyrazol-3-yl)quinoline derivatives

A new series of 4-(4-(1-benzyl-1H-1,2,3-triazol-4-yl)-1-phenyl-1H-pyrazol-3-yl)quinoline ( 6a-t ) have been synthesized by a click reaction of 4-(4-ethynyl-1-phenyl-1H-pyrazol-3-yl)quinoline ( 4a-d ) with a substituted benzyl azide ( 5a-e ). The starting alkyne derivatives 4a-d are obtained from Bestmann-Ohira reaction of 1-phenyl-3-(quinolin-4-yl)-1H-pyrazole-4-carbaldehyde and dimethyl(1-diazo-2-oxopropyl)phosphonate. The newly synthesized compounds are screened against M. tuberculosis H37Ra dormant and active, Escherichia coli, Pseudomonas fluorescence, Staphylococcus aureus and Bacillus subtilis strains at 30 μg/mL concentration. Most of the screened compounds showed good to moderate antibacterial activity against S. aureus, B. subtilis, and Mycobacterium tuberculosis H37Ra strains. The synthesized derivatives of quinolinyl-pyrazole-4-carbaldehyde and quinolinyl-pyrazole-4-ethyne reportd good to moderate activity against both strains of M. tuberculosis H37Ra. Ten derivatives of quinolinyl-pyrazole presented good activity against B. subtilis. These results suggested that further optimization and development of quinolinyl-pyrazolyl-1,2,3-triazole moeity could serve as lead compounds for antimycobacterial activity.     

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.     

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.     

Micelles from PEO-PPO-PEO block copolymers as nanocontainers for solubilization of a poorly water soluble drug hydrochlorothiazide

The effect of molecular characteristics of EO-PO triblock copolymers viz. Pluronic(?) P103 (EO(17)PO(60)PEO(17)), P123 (EO(19)PO(69)EO(19)), and F127 (EO(100)PO(65)EO(100)) on micellar behavior and solubilization of a diuretic drug, hydrochlorothiazide (HCT) was investigated. The critical micellization temperatures (CMTs) and size for empty as well as drug loaded micelles are reported. The CMTs and micelle size depended on the hydrophobicity and molecular weight of the copolymer; a decrease in CMT and increase in size was observed on solubilization. The solubilization of the drug hydrochlorothiazide (HCT) in the block copolymer nanoaggregates at different temperatures (28, 37, 45°C), pH (3.7, 5.0, 6.7) and in the presence of added salt (NaCl) was monitored by using UV-vis spectroscopy and solubility data were used to calculate the solubilization characteristics; micelle-water partition coefficient (P) and thermodynamic parameters of solubilization viz. Gibbs free energy (ΔG(s)°), enthalpy (ΔH(s)°) and entropy (ΔS(s)°). The solubility of the drug in copolymer increases with the trend: P103>P123>F127. The solubilized drug decreased the cloud point (CP) of copolymers. Results show that the drug solubility increases in the presence of salt but significantly enhances with the increase in the temperature and at a lower pH in which drug remains in the non-ionized form.     

Nanoencapsulation and characterization of Albizia chinensis isolated antioxidant quercitrin on PLA nanoparticles

The plant isolated antioxidant quercitrin has been encapsulated on poly-d,l-lactide (PLA) nanoparticles by solvent evaporation method to improve the solubility, permeability and stability of this molecule. The size of quercitrin-PLA nanoparticles is 250 ± 68 nm whereas that PLA nanoparticles is 195 ± 55 nm. The encapsulation efficiency of nanoencapsulated quercitrin evaluated by HPLC and antioxidant assay is 40%. The in vitro release kinetics of quercitrin under physiological condition reveals initial burst release followed by sustained release. Less fluorescence quenching is observed with equimolar concentration of PLA encapsulated quercitrin than free quercitrin. The presence of quercitrin specific peaks on FTIR of five times washed quercitrin loaded PLA nanoparticles provides an extra evidence for the encapsulation of quercitrin into PLA nanoparticles. These properties of quercitrin nanomedicine provide a new potential for the use of such less useful highly active antioxidant molecule towards the development of better therapeutic for intestinal anti-inflammatory effect and nutraceutical compounds.     

Rapid and selective determination of osmium(IV) by UV-visible spectrophotometry using o-methylphenyl thiourea as a chromogenic chelating ligand: sequential separation of osmium(IV), rhodium(III) and platinum(IV)

The objective of this research work was to develop a simple, highly sensitive and precise method for spectrophotometric determination of osmium(IV). O-Methylphenyl thiourea (OMPT) coordinates with osmium(IV) as a 1:1 (osmium(IV)–OMPT) complex in hydrochloric acid media (0.8 mol l^?1). The novelty of the investigated method is instant complex formation at room temperature with no need of heating or standing. The complex is stable for more than 8 days. The method is applicable over a wide linearity range (up to 110 µg ml^?1). A low reagent concentration is required (2 ml, 0.009 mol l^?1 in ethanol). The complex exhibits maximum absorption in the range of wavelength 510–522 nm and 514 nm was selected for further study. The molar absorptivity was 1.864 × 10³ l mol^?1 cm^?1, Sandell’s sensitivity was 0.102 µg of osmium(IV) cm^?2. Proposed method was successfully applied for separation and determination of osmium(IV) from binary and ternary synthetic mixtures containing associated metal ions. A scheme for mutual separation of osmium(IV), rhodium(III) and platinum(IV) is developed.     

Facile radical mediated synthesis of azetidin-2,3-diones: potential synthons for biologically active compounds

Abstract  

An operationally simple and efficient approach for the synthesis of azetidin-2,3-diones is described. The starting substrate 2-(2-bromobenzyloxy)ethanoyl chloride was treated with appropriate Schiff’s bases in triethylamine and dichloromethane to afford 3-(2-bromobenzyloxy)azetidin-2-ones. The synthesis of azetidin-2,3-diones was successfully achieved via radical mediated rearrangement of appropriately substituted 3-(2-bromobenzyloxy)azetidin-2-ones using n-tributyltin hydride and AIBN in refluxing dry benzene.     

Development and applications of single-drop microextraction for pesticide residue analysis: A review

Single-drop microextraction (SDME) has become more popular than other microextraction techniques because it is simple, cost-effective, easy to operate and nearly solvent-free. The technique has been employed successfully for trace analysis in environmental, biomedical and food applications. In view of the increasingly stringent regulatory limits for many pesticides, which are below the LOD of the existing instruments, SDME may provide a cost-effective solution for reducing the LOD of pesticides. The present review focuses on recent development in SDME technique, and its application coupled with various analytical techniques, such as GC-MS, GC and HPLC for pesticide residue analysis in different matrices. The advantages, limitations and outlook on the future of SDME technique for its wider applications are also discussed.     

Cu(II)-azide polymers with various molar equivalents of blocking diamine ligands: synthesis, structures, magnetic properties with DFT studies

Four new neutral copper-azido polymers [Cu(4)(N(3))(8)(Me-hmpz)(2)](n) (1), [Cu(4)(N(3))(8)(men)(2)](n) (2), [Cu(5)(N(3))(10)(N,N-dmen)(2)](n) (3) and [Cu(5)(N(3))(10)(N,N'-dmen)(5)](n) (4) [Me-hmpz = 1-methylhomopiperazine; men = N-methylethylenediamine; N,N-dmen = N,N-dimethylethylenediamine and N,N'-dmen = N,N'-dimethylethylenediamine] have been synthesized by using various molar equivalents of the chelating diamine ligands with Cu(NO(3))(2)·3H(2)O and an excess of NaN(3). Single-crystal X-ray structures show that the basic asymmetric units of 1 and 2 are very similar, but the overall 1D structures were found to be quite different. Complex 3 with a different composition was found to be 2D in nature, while the 1D complex 4 with 1 : 1 metal to diamine ratio presented several new structural features. Cryomagnetic susceptibility measurements over a wide range of temperature were corroborated with density functional theory calculations (B3LYP functional) performed on the complexes 1-3 to provide a qualitative theoretical interpretation of their overall magnetic behavior.