Catalytic Light-Triggered Reduction Promoted by a Dithienylethene Derivative

A pyridinium substituted dithienylethene derivative was used for the first time as an efficient photoreducing agent of two different substrates. This reaction exhibits high catalytic yields due to the continuous regeneration of the initial state of the photochromic molecule.     

Metaheuristic methods based on Tabu search for assigning judges to competitions

Two metaheuristic methods based on Tabu search are introduced to assign judges to individual competitions in a tournament. The complexity of the mathematical formulation accounting for the assignment rules, leads us to use such an approach. The first metaheuristic includes two different Tabu searches that are combined with a diversification strategy. The second metaheuristic is applied to a penalized version of the original model formulated as an assignment problem. This metaheuristic is also based on a Tabu search procedure including a diversification strategy driven by the constraints violated. Numerical results are provided to indicate the efficiency of the methods to generate very good solutions.     

Hydrolysis of mefenpyrdiethyl: an analytical and DFT investigation

The hydrolysis of the herbicide safener mefenpyrdiethyl (1-(2, 4-dichlorophenyl)-4, 5-dihydro-5-methyl-1H-pyrazole-3,5-dicarboxylic acid diethyl ester) was investigated in aqueous solutions in the pH range from 2 to 9 and the temperature range from 298 to 323 K. The kinetics of hydrolysis were pseudo first order and were found to be strongly pH and temperature dependent. While near-constant in acidic medium, the hydrolysis rates strongly increased in alkaline pH, and total hydrolysis was observed at pH 11. Two main hydrolysis products, mefenpyrethyl (monoester) and mefenpyr (dicarboxylic acid) were isolated by ultrahigh-pressure liquid chromatography (UHPLC) and characterized using high-resolution Fourier transform ion cyclotron resonance mass spectroscopy (ICR-FT/MS) as well as ¹H, ¹³C and 2D NMR analyses. Additionally, a density functional theory (DFT) investigation explained the stability of the pesticide at pH 7 and the high reactivity of the pesticide in alkaline medium. The key nucleophilic reaction partner is hydroxyl ions instead of neutral water molecules. Furthermore, the calculated activation barrier for hydrolysis in alkaline medium is in agreement with the extrapolated and experimentally determined activation barrier at pH 14.     

Synthesis,characterization, magnetic,thermal and electrochemical studies of oxidovanadium (IV) picolyl hydrazones as functional catechol oxidase models

The picolyl hydrazone ligands derived from picolonic acid hydrazide and α-pyridyle ketone (L¹, L² and L³), α-acetyl thiophene (L⁴), α-formyl or α-acetyl phenol (L⁵ and L⁶ respectively) and 2-hydroxy-1-naphthaldehyde (L⁷) react with equimolecular amount of vanadyl sulfate in refluxing methanol to yield oxidovanadium (IV) complexes. The structure of the obtained ligands and their oxidovanadium (IV) complexes were characterized by various physicochemical techniques, viz. elemental analysis, molar conductance, magnetic susceptibility measurements, thermal analysis (TGA & DTG), IR, electronic absorption and ESR spectral studies. Cyclic voltammeteric behavior of the complexes has also been discussed. Five-coordinate square-pyramidal structure was proposed for all complexes. A monomeric nature was reported for complexes (2), (3), (6), and (7), while dimeric structures were suggested for complexes (1), (4) and (5). The ability of the complexes to catalyze the aerobic oxidation of catechol to the light absorbing o-quinone has been investigated. The results obtained show that all complexes catalyze this oxidation reaction and large variations in the rate were observed. Electrochemical data for most complexes show that there is a linear relationship between their ability to oxidize catechole and their E_1/2 potentials. The most effective catalysts were those complexes which exhibited E_1/2 values approached to the E° value of the natural tyrosinase enzyme isolated from mushroom, while those that largely deviated from that potential exhibited lower oxidase catalytic activity. The probable mechanistic implications of the catalytic oxidation reactions are discussed.     

Spectrophotometric Determination of Some Fluoroquinolone Antibacterials by Ion‐pair Complex Formation with Cobalt (II) Tetrathiocyanate

A new simple extractive spectrophotometric method has been developed for the determination of levofloxacin (I), norfloxacin (II), and ciprofloxacin (III) in pure form and tablets. The method is based on the formation of blue‐colored ion‐pair associates between the drugs and the inorganic complex, cobalt (II) thiocyanate, at pH 2.5. Those ion‐pair associates are readily extracted into an n‐butanol‐dichloromethane solvent mixture (3.5:6.5) and determined spectrophotometrically at 623 nm. The concentration range is 20–240 μg mL^?1 for the three studied drugs. The proposed method was successfully applied to determine these drugs in their tablet formulations, and the results are in good agreement with those obtained by the reference methods.     

Designed alpha-helical barrels for charge-selective peptide translocation

Synthetic alpha-helix based pores for selective sensing of peptides have not been characterized previously. Here, we report large transmembrane pores, pPorA formed from short synthetic alpha-helical peptides of tunable conductance and selectivity for single-molecule sensing of peptides. We quantified the selective translocation kinetics of differently charged cationic and anionic peptides through these synthetic pores at single-molecule resolution. The charged peptides are electrophoretically pulled into the pores resulting in an increase in the dissociation rate with the voltage indicating successful translocation of peptides. More specifically, we elucidated the charge pattern lining the pore lumen and the orientation of the pores in the membrane based on the asymmetry in the peptide-binding kinetics. The salt and pH-dependent measurements confirm the electrostatic dominance and charge selectivity in controlling target peptide interaction with the pores. Remarkably, we tuned the selectivity of the pores to charged peptides by modifying the charge composition of the pores, thus establishing the molecular and electrostatic basis of peptide translocation. We suggest that these synthetic pores that selectively conduct specific ions and biomolecules are advantageous for nanopore proteomics analysis and synthetic nanobiotechnology applications.

Synthetic alpha-helix based pores for selective sensing of peptides have not been characterized previously.     

6α,7α-epoxy-5α,17α,dihydroxy-1-oxo-22R-witha-2,24-dienolide in leaves of Withania somnifera: Isolation and its crystal structure

6α,7α-epoxy-5α,17α,dihydroxy-1-oxo-22R-witha-2,24-dienolide (C₂₈H₃₈O₆) was isolated from Withania somnifera leaves. The structure of the withanolide was established by spectral analysis and X-ray diffraction studies as withanone. The compound crystallizes in the orthorhombic space group P2₁2₁2₁ with unit cell parameters: a = 9.191(10) Å, b = 12.858(6) Å, c = 21.400(16) Å, Z = 4. The crystal structure was solved by direct methods and refined to R = 0.0603 for 1742 observed reflections. There is positional disorder of the H atom in a hydroxy group (O5), resulting in two possible hydrogen-bond linkages. All the rings of the steroid skeleton are trans connected. Ring A exists in a half-chair conformation, ring B is intermediate between a half-chair and a sofa, ring C a distorted chair, and five-membered ring D is intermediate between a half-chair and an envelope. The δ-lactone ring E adopts a sofa conformation. The twist along the length of the steroid nucleus is negligible [C19–C10…C13–C18=1.8°]. Both the hydroxy groups are involved in hydrogen bonding.     

Direct tissue analysis of phospholipids in rat brain using MALDI-TOFMS and MALDI-ion mobility-TOFMS

After water, lipids are the most common biomolecules found in the brain (12%). A brief perusal of the physiology, anatomy, and pathophysiology of the brain illustrates the importance of lipids. Recent advances in mass spectrometry have allowed the direct probing of tissues. However, most studies have focused on proteins. In the present work, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and MALDI-ion mobility (IM)-TOFMS were employed for direct analysis of phospholipids in rat brain tissue. Molecular ions (MH⁺) corresponding to phosphatidylcholines, phosphatidylethanolamines, and sphingomyelin, were recorded. When studying pharmacology, we learn that many therapeutic compounds are stored in the body’s adipose tissue. MALDI-TOFMS and MALDI- IM-TOFMS were thus used to analyze rat brain tissue with chlorisondamine added directly onto the tissue slice. With both techniques, noncovalent complexes between the tissue phospholipids and chlorisondamine were detected. In addition, MALDI-IM-TOFMS of noncovalent complexes between phospholipids and chlorisondamine displayed a mobility between that of an isobaric lipid and peptide.