On- and off column enantiomerization of 4,4′-bisquinolin-2-ones: A comparison of Auto-, DHPLcy2k and DCXplorer calculated thermodynamic data generated by dynamic high,performance liquid chromatography with theoretically calculated data

Fast semipreparative HPLC enantioseparation of four axially chiral biscarbostyrils (4,4′-bisquinoline-2-ones) using ULMO as a π-acidic Pirkle type chiral stationary phase leads to two racemizing pairs (1,2; k_obs 1.6 × 10⁻⁴ and 3.0 × 10⁻⁴ s⁻¹ at 28 °C) and two stable ones (3,4). 3 was stabilized by a crown ether linkage from pos. 6 to 6′, and 4 had sterically demanding bromo substituents in pos. 3 and 3′. On-column generated temperature-dependent chromatograms of 1 and 2 were fitted with Auto-DHPLCy2k and DCXplorer. For cpd 2 both programs delivered similar ΔG values of 90 and 93 kJ/mol, well comparable with the 99 kJ/mol calculated with the B3LYP/6-31G (d) procedure. At temperatures of high conversion DCXplorer delivered inconsistent series of rate constants for the more tailing and less resolved tetramethoxy derivative 1. We connect this problem with an almost impossible halfwidth calculation of tailing peak pairs which are weakly resolved. However, this problem could be observed only in the case of tetramethoxy derivative 1. Stochastic generated data of Auto-DHPLCy2k could be used at a lower percentage of conversion only while the theoretical plate model did not deliver useful data at temperatures of very low conversion but fitted well high conversion chromatogram series of 1 and 2.     

A simple Schiff base as selective and sensitive fluorescent-colorimetric hydrazine chemosensor

ABSTRACT

A new fluorescent-colorimetric chemosensor L has been synthesised by Schiff base condensation reaction between 1,8-diaminooctane and 4-nitro-benzaldehyde in very good yields. Its photo-luminescent properties and selective detection properties for hydrazine have been examined. The synthesised chemosensor exhibited highly selective fluorescence on-off response for hydrazine amongst a wide range of different metal cations, anions and amines, along with the bare eye colour change from colourless to yellow based on intermolecular hydrogen-bond interaction. The limit of detection of the chemosensor L was estimated as 9.77 × 10^?8 M or 3.12 × 10^?6 g L^?1 for hydrazine which is extremely below the limit set by the World Health Organization (WHO) and the binding stoichiometry was proposed to be 1 : 2 based on ¹H NMR spectroscopic techniques and the Job’s plot analysis. The proposed sensing mechanism is the hydrogen-bonding interaction which has further been established by Density Functional Theory (Functional Density Theory (DFT)) studies. This recognition feature of sensor L makes it an efficient chemosensor for hydrazine detection in different water samples.     

Cyclic voltammetry and viscosity measurements of aggregated assemblies of anionic surfactants with nonionic surfactants and triblock copolymers

Cyclic voltammetry (CV) and viscosity measurements have been employed to study the aggregation behavior of mixed micellar systems of anionic surfactant (dioctyl sulfosuccinate sodium salt, AOT) with conventional nonionic surfactants such as Brij 35/TritonX-100/Tween 20/Tween 80/Myrj 45 and two triblock copolymers (L64 and F68). Critical micelle concentration (cmc) values have been determined for various micellar systems from CV measurements using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as an electroactive probe at 25 °C. Diffusion coefficient (D) has been evaluated from Randles–Sevcik equation which showed an overall decrease for most of the binary systems. The negative values of interaction parameters (β) obtained from regular solution theory suggest the synergistic behavior in all the binary systems except AOT + Tween 80 mixtures. The mixed systems of AOT with triblock copolymers showed stronger synergistic interactions than that of mixed systems of AOT with nonionic surfactants. A comparative evaluation of mixed systems of anionic surfactants AOT and sodium dodecyl sulfate with Myrj 45 and AOT + L64 and F68 has been made on the basis of different micellar parameters and structural properties of surfactants. Viscosity measurements also show similar type of interactions in the mixed micelles.     

Synthesis and physico-chemical properties of some Ni(II) complexes with isatin-hydrazones

New Ni(II) complexes with bioactive bishydrazones ligands based on (pyridine-2-carboxaldhyde)-3-isatin, (2-acetylpyridine)-3-isatin, and (2-benzoylpyridine)-3-isatin have been synthesized and characterized by elemental analysis, conductivity measurements, IR and UV-Vis spectroscopy, and thermal analysis. The complexes stoichiometry and formation constants have been determined. The results suggest that isatinbishydrazones act as neutral tridentate ligands with ONN sites coordinating to the metal ion via isatin C=O, azomethine CR=N, and pyridine C=N groups to give [Ni(L)H₂O]Cl₂·2H₂O, (L = neutral tridentate isatin hydrazone ligand). Kinetics and thermodynamic parameters of the complexes thermal decomposition have been elucidated from the thermal data using Coats and Redfern method, which has confirmed the first order kinetics.     

Recent trends in the synthesis of 1,2,3-thiadiazoles

Abstract

1,2,3-Thiadiazoles, structurally active pharmacophores have attracted significant attention of synthetic chemists, medicinal and pharmaceutical researchers because of their versatile biological activities against various diseases such as herbicidal, insecticidal, antiviral, antitumor, antimicrobial, anticancer, plants activator and anti-amoebic activities. A literature survey of the last decade presented in this review article summarizes the major synthetic approaches, methodologies and strategies adopted for the synthesis of 1,2,3-thiadiazole scaffolds which will be help for medicinal chemists and pharmacists in future synthesis and development of novel therapeutic agents.     

Retracted: Acid‐Catalyzed Aquation of Ni(II)‐Hydrazone Complexes: Kinetics and Solvent Effect

Complexes of the type [Ni(L)(H₂O)]Cl₂·nH₂O, where L = 2‐pyridyl‐3‐isatinbishydrazone ligands, have been synthesized and characterized on the bases of elemental analysis, molar conductance, IR, electronic spectra, and thermal analysis (TGA and DTA). Acid‐catalyzed aquation of the Ni(II) isatin‐bishydrazone complexes was followed spectrophotometrically in various water–methanol and water–acetone mixtures at temperature 298 K. Kinetic behavior of the acid aquation is a linear rate law, indicating that the acid‐catalyzed aquation of these complexes in water–methanol and water–acetone mixtures follows a rate law with k_obs = k₂[H⁺]. The effect of the mole fraction of the ganic solvent, i.e., methanol and acetone, on the acid aquation has been analyzed; the decrease in the rate constant values with increasing of the methanol or acetone ratios is attributable to the effect of the co‐organic solvent on the initial states of the acid aquation by the destabilization of the H⁺ ion.     

Development of frozen whale blubber and liver reference materials for the measurement of organic and inorganic contaminants

Summary Fresh frozen homogenates of pilot whale blubber and liver tissue were prepared for use as control materials for the determination of organic and inorganic contaminants in marine mammal tissue analyses. The blubber material was analyzed to determine 30 polychlorinated biphenyl congeners and 16 chlorinated pesticides using gas chromatography with electron capture detection and gas chromatographymass spectrometry. A total of 39 trace elements and methylmercury were determined in the liver homogenate using instrumental neutron activation analysis, voltammetry, and cold vapor atomic absorption spectroscopy. The preparation and analysis of these two tissue materials are part of the development of marine mammal tissue reference materials.