Potassium Fluoride on Alumina (KF/Al2O3)(KF/Al_2O_3)

(A) Sawyer et al. have demonstrated the use of $KF/Al_2O_3$ and 18- Crown-6 to synthesize diaryl ethers, diarylthio ethers, and diaryl amines via $S_NAr$ type addition reaction of phenol, thiophenol, and aniline to 2-fluorobenzonitrile respectively. The optimization of the above reaction conditions led to the synthesis of compounds, which were unachievable using Ullman coupling. For example, electronically unfavorable 3-chloro benzonitrile can be condensed with 3-methylphenol to give corresponding diaryl ether in 66% yields using $KF/Al_2O_3,$ 18-Crown-6 in DMSO at 140 °C. (B) Glaser coupling reactions to generate diacetylenes using $KF/ Al_2O_3$ with $CuCl_2$ and solvent free conditions under microwave irradiation have been optimized by Kabalka et al. The use of two different alkynes, however gives a mixture of products. (C) Silveira et al. have reported the use of $KF/Al_2O_3$ for the synthesis of 3,4-dihydroisoquinolines and isoquinolines by desulfonylation of N-sulfonyltetrahydroisoquinone derivatives. Microwave irradiation (490 W) of the solid-state reaction mixture containing the substrate and base for 10–20 s gives 3,4-dihydroisoquinoline, which on increasing the time leads to the formation of corresponding isoquinoline. (D) $KF/Al_2O_3$ selectively desilylates the tert-butyldimethylsilyl protected phenol at room temperature. Acetonitrile as the solvent eliminates the need for an aqueous work up and the use of ultrasound accelerates the reaction thereby reducing reaction times. (E) Selective O-demethylation of arylalkyl ethers has also been accomplished using $KF/Al_2O_3$ and dry ethylene glycol in 3–5 h at 210–215 °C in moderate to high yields

How pantothenol intervenes in Coenzyme-A biosynthesis of Mycobacterium tuberculosis

Coenzyme A is an indispensable cofactor for all organisms and holds a central position in a number of pathways. Prokaryotic enzymes involved in the synthesis of CoA are quite different from their mammalian counterparts; hence, they are good targets for the development of antimicrobials to treat many diseases. There are antimicrobials that act by inhibiting CoA biosynthesis. It has been suggested that pantothenol exhibits antibacterial activity by competitively inhibiting pantothenate kinase, a key regulatory enzyme for CoA synthesis. Contrary to these suggestions, in this paper, we demonstrate that pantothenol acts as a substrate for Mycobacterium tuberculosis and Escherichia coli pantothenate kinases. The product, 4'-phosphopantothenol, thus formed inhibits competitively the utilization of 4'-phosphopantothenate by CoaBC. Thus, it is the failure of CoaBC to utilize 4'-phosphopantothenol as a substrate that accounts for the bactericidal activity of pantothenol. (C) 2007 Elsevier Inc. All rights reserved

Acyclic Arylamine-Based Ionophores as Potentiometric Sensors for Zn2+ and Ni2+ Ions

Two receptor molecules N-(2-nitrophenyl)benzene-1,2-diamine (DPA) and N,N-bis(2-nitrophenyl)benzene-1,2-diamine (TPA) are proposed as Zn2+ and Ni2+-selective electrodes, respectively. The two electrodes respond to Zn2+ and Ni2+ ions with the detection limits of 1.3 × 10−6 M and 2.8 × 10−6 M, respectively. Both the electrodes have a life time of four months and respond within 15 s and 20 s, respectively, for Zn2+ and Ni2+ over a wide pH range (3–9). The electrodes show very good selectivity towards the primary ions in presence of some alkali, alkaline earth, and transition metal ions

Solvent and Substituent Effect on Selectivity of Triphenylether-Based Ionophores: A Voltammetric Study

The past two decades have seen considerable attention given to chemical sensing due to its quick, reproducible, and accurate results. These are extensively used for the detection of cations and anions in different environmental matrices. Organic-molecule-based sensors have proved to be a great promising tool in determining target species. This communication demonstrates the use of triphenylether derivatives (L1–L4) as receptors for the sensing of cations and anions, using voltammetry as a sensing tool. The effect of the oxidative/reductive nature of the ionophores and, hence, their selectivity behavior was studied in MeCN and MeOH solvents. Three receptors (L2–L4) responded selectively towards cyanide ions following the intramolecular charge-transfer mechanism, while sensing in the case of L1 was not studied because it lacked a proper cavity size

Design of mechanism-based inhibitors of transthyretin amyloidosis: Studies with biphenyl ethers and new structural templates

Transthyretin (TTR), a tetrameric thyroxine (T4) carrier protein, is associated with a variety of amyloid diseases. In this study, we explore the potential of biphenyl ethers (BPE), which are shown to interact with a high affinity to its T4 binding site thereby preventing its aggregation and fibrillogenesis. They prevent fibrillogenesis by stabilizing the tetrameric ground state of transthyretin. Additionally, we identify two new structural templates (2-(5-mercapto-[1,3,4]oxadiazol-2-yl)-phenol and 2,3,6-trichloro-N-(4H-[1,2,4]triazol-3-yl) represented as compounds 11 and 12, respectively, throughout the manuscript) exhibiting the ability to arrest TTR amyloidosis. The dissociation constants for the binding of BPEs and compound 11 and 12 to TTR correlate with their efficacies of inhibiting amyloidosis. They also have the ability to inhibit the elongation of intermediate fibrils as well as show nearly complete (> 90%) disruption of the preformed fibrils. The present study thus establishes biphenyl ethers and compounds 11 and 12 as very potent inhibitors of TTR fibrillization and inducible cytotoxicity

Synthesis and Anti-Staphylococcal Activity of 2,4-Disubstituted Diphenylamines

Infections caused by Staphylococcus aureus are ubiquitous and life threatening. Evolution of resistant strains has necessitated the need to continuously discover new drugs to combat such organisms. Diphenyl ethers, such as triclosan, have recently shown potential as antibacterial agents. In this study, a series of diphenyl amines were synthesized and evaluated for in vitro antibacterial activity against Gram-positive (Staphylococcus aureus, Bacillus subtilis, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Pseudomonas putida) bacteria. Preliminary results showed that six of the twelve synthesized molecules were active against Staphylococcus aureus. Most notable amongst them were compounds 2(2,4-dinitrophenylamino)phenol and 2(2-dinitrophenylamino)phenol having minimum inhibitory concentration (MIC) in the range of 7.8-15.6 µg mL-1 and 7.8-62.5 µg mL-1respectively for all the eight selected organisms. Five active compounds from the preliminary results were further screened against resistant S. aureus cultures where compounds 2(2,4-dinitrophenylamino)phenol, 2(2-dinitrophenylamino)phenol and 2-chloro-N-(2-(2,4-dichlorophenylamino)phenyl)acetamide gave encouraging results having MIC in the range 3.9-7.8 µg mL-1for most of the organisms. Results obtained above for the selected organisms and the resistant S. aureus strains conclude that hydroxyl group at 2-position of ring B potentiates the antibacterial activity and overcomes the antibiotic resistance

Mild Wet Torrefaction and Characterization of Woody Biomass from Mozambique for Thermal Applications

Mozambique has vast forestry resources and also considerable biomass waste material such as bagasse, rice husks, sawdust, coconut husks and shells, cashew nut shell and lump charcoal waste. The potential of the total residues from the agricultural sector and the forest industry is estimated to be approximately 13 PJ. This amount of energy covers totally the production of charcoal which amounted to approximately 12.7 PJ in 2006. Although biomass is an attractive renewable source of energy, it is generally difficult to handle, transport, storage and use due to its lower homogeneity, its lower energy density and the presence of non-combustible inorganic constituents, which leads to different problems in energy conversion units such as deposition, sintering, agglomeration, fouling and corrosion. Therefore, a pretreatment of the biomass to solve these problems could lead to a change of current biomass utilization situation. The aim of this study is to convert Mozambican woody biomass residue into a solid biochar that resembles low-grade coal. In this work the current energy situation in Mozambique has been reviewed, and the available and potential renewable sources including residues from agricultural crops and forest industry as energy have been assessed. It was found that the country is endowed with great potential for biofuel, solar, hydro and wind energy production. However, the production today is still far from fulfilling the energy needs of the country, and the majority of people are still not benefiting from these resources. Charcoal and firewood are still the main sources of energy and will continue to play a very important role in the near future. Additionally, enormous amounts of energy resources are wasted, especially in the agricultural sector. These residues are not visible on national energy statistics. The chemical composition and the fuelwood value index (FVI) showed that by failing to efficiently utilise residues from Afzelia quanzensis, Millettia stuhlmannii and Pterocarpus angolensis, an opportunity to reduce some of the energy related problems is missed. An evaluation of effect of a mild wet torrefaction pretreatment showed that the chemical composition of the biochar is substantially different than the feedstock. The use of diluted acid as catalysts improves the biochar quality, namely in terms of the energy density and ash characteristics; however, the increment of the S content in the final product should be considered for market acceptance (because the fuels have a maximum allowance for S concentration). The thermal behaviour of the untreated and treated biomass was also investigated. The pyrolytic products of umbila and spruce were affected by the treatment and catalyst in terms of yield and composition of the vapours.QC 20150202</p

Location and conformation of pantothenate and its derivatives in Mycobacterium tuberculosis pantothenate kinase: insights into enzyme action

Previous studies of complexes of Mycobacterium tuberculosis PanK (MtPanK) with nucleotide diphosphates and non-hydrolysable analogues of nucleoside triphosphates in the presence or the absence of pantothenate established that the enzyme has dual specificity for ATP and GTP, revealed the unusual movement of ligands during enzyme action and provided information on the effect of pantothenate on the location and conformation of the nucleotides at the beginning and the end of enzyme action. The X-ray analyses of the binary complexes of MtPanK with pantothenate, pantothenol and N-nonylpantothenamide reported here demonstrate that in the absence of nucleotide these ligands occupy, with a somewhat open conformation, a location similar to that occupied by phosphopantothenate in the `end' complexes, which differs distinctly from the location of pantothenate in the closed conformation in the ternary `initiation' complexes. The conformation and the location of the nucleotide were also different in the initiation and end complexes. An invariant arginine appears to play a critical role in the movement of ligands that takes place during enzyme action. The work presented here completes the description of the locations and conformations of nucleoside diphosphates and triphosphates and pantothenate in different binary and ternary complexes, and suggests a structural rationale for the movement of ligands during enzyme action. The present investigation also suggests that N-alkylpantothenamides could be phosphorylated by the enzyme in the same manner as pantothenate