Hydroalumination of Thioacetylenes: A Versatile Generation and Reactions of α-Aluminate Sulfides Intermediates

Hydroalumination of thioacetylenes using DIBAL-H and lithium di-(isobutyl)-n-(butyl)-aluminate hydride (Zweifel's reagent), followed by addition of water, furnished exclusively the (Z)- and ( E )-vinyl sulfides, respectively. The regio- and stereochemistry of the intermediates generated, (Z)- and ( E )-phenylthio vinyl alanates, were determined by capture with iodine, which afforded the corresponding ( E )- and (Z)-1-iodo-1-phenylthio-2-organoyl ethenes. Reactions of the ( E )-iodo(thio)ketene acetals with n-BuLi followed by addition of hexanal afforded the (Z)-phenylthio allylic alcohol, while the (Z)-iodo(thio)ketene acetals under similar reactions conditions gave the ( E )-phenylthio allylic alcohol exclusively.     

A carbohydrate based chiron approach to the lactone intermediate employed in the synthesis of BC-ring fragment of (+)-spirastrellolide A

A concise and stereoselective synthesis of the key intermediate used for constructing the BC-ring fragment of (+)-spirastrellolide A is described. The synthetic sequence represents a chiron approach that employs readily available and inexpensive l-arabinose and sets up the stereochemical triad at C20–C22 all from the sugar. This lactone can be used to assemble the spiroketal in the Southern Half through a cyclic acetal-tethered ring-closing metathesis strategy, and is poised for connecting with the Northern Half at C24–C25.     

Stylissatin A,a cyclic peptide that inhibits nitric oxide production from the marine sponge Stylissa massa

A new cyclic heptapeptide, stylissatin A (1), was isolated from the Papua New Guinean marine sponge Stylissa massa. Through the use of 1D and 2D NMR spectroscopic analysis, Marfey’s method, and MS/MS analysis, its structure was determined to be cyclo-[Tyr¹–Ile²–Phe³–Pro⁴–Ile⁵–Pro⁶–Phe⁷]. Stylissatin A inhibited nitric oxide production in LPS-stimulated murine macrophage RAW264.7 cells with an IC₅₀ value of 87 μM.     

A test procedure for separating viscous recovery and accumulated unrecoverable deformation of polymer under cyclic loading

After uniaxial tension and creep tests, asymmetric stress cycle tests have been performed on two polycarbonate (PC) materials with different molecular weights at room temperature. The effects of stress level (mean stress and stress amplitude) and time-dependent factors (stress rate and peak hold time) on ratcheting were studied. To separate the contributions of viscous recovery and accumulated unrecoverable deformation, a new test procedure has been proposed and performed on polycarbonate. The results demonstrate that the proposed test procedure is suitable for separating the viscous recovery and accumulated unrecoverable deformation. The study clearly shows that, for PC, both the viscous recovery and the accumulated unrecoverable deformation cannot be neglected for cyclic loading; previous viscous deformation has significant influence on the following cyclic accumulated deformation.     

Determination of bromadiolone in pheasants and foxes by differential pulse voltammetry

Bromadiolone, a commercially used anticoagulant rodenticide, was determined in tissues of various animals by differential pulse voltammetry with a carbon-paste electrode. Under the most suitable experimental conditions (step potential of 25?mV?s^?1 and 0.2?mol?L^?1 acetate buffer, pH 4.2), the limit of detection was 0.5?ng?mL^?1. The electroanalytical method was consequently used to investigate the bromadiolone transport within the food chain. Pheasants were exposed to bromadiolone and then used as feed for a fox. The average levels were 528 and 198?ng of bromadiolone per gram of fresh weight of liver of pheasant and fox, respectively. Due to the surprisingly lower content of bromadiolone in the latter, a basic biochemical analysis, particularly blood coagulation, was performed. Among the parameters studied (thrombin time, prothrombin time, activated partial thromboplastin time, and fibrinogen), there was prolongation of the prothrombin time and activated partial thromboplastin time.     

Synthesis,Characterization, Solution Stability Studies,Electrochemistry, and DNA‐Binding Behavior of Cu(II) Complexes of D‐Gluconic Acid

The chemistry of saccharides has emerged as a new subarea of pharmaceuticals. Condensation reactions of D‐gluconic acid with [M(en)₂]Cl₂/[M(ea)₂]Cl₂ where M=Cu, Ni, en=ethylenediamine, and ea=ethanolamine were carried out and a new series of chiral complexes have been isolated and characterized. Molar conductance measurements show that the complexes are ionic, and the spectral data are indicative of octahedral geometry of the complexes [Cu(D‐GlcCO₂H en*)₂ (H₂O)₂] · Cl₂ (1b), [Cu(D‐GlcCO₂H ea*) (H₂O)₂] · Cl₂ (3b) and [Ni(D‐GlcCO₂H ea*) (H₂O)₂] · Cl₂ (4), and the square planar geometry of complex [Ni(D‐GlcCO₂H en*)₂] · Cl₂ (2b). Polarimetric data along with CD spectra establish the chiral nature of complexes. Solution stabilities of these complexes were evaluated by cyclic voltammetric techniques as a function of pH. Electrochemical behavior of the complexes was studied in aqueous solution and showed an irreversible Cu^II/Cu^I couple. Kinetic studies of complex 1b and 3b with calf thymus DNA have been investigated spectrophotometrically under pseudo‐first order conditions, and k _obs values have been evaluated. Circular dichroism, cyclic voltammetry determinations, and viscosity measurements have also been carried out to authenticate the binding of DNA with metal complexes. Complexes 1b and 3b bind to DNA by covalent bond formation.     

Tethering for Selective Synthesis of 2,2′‐Biphenols: The Acetal Method

2,2'‐Biphenols are a large and diverse group of compounds with exceptional properties both as ligands and bioactive agents. Traditional methods for their synthesis by oxidative dimerisation are often problematic and lead to mixtures of ortho‐ and para‐connected regioisomers. To compound these issues, an intermolecular dimerisation strategy is often inappropriate for the synthesis of heterodimers. The ‘acetal method’ provides a solution for these problems: stepwise tethering of two monomeric phenols enables heterodimer synthesis, enforces ortho regioselectivity and allows relatively facile and selective intramolecular reactions to take place. The resulting dibenzo[1,3]dioxepines have been analysed by quantum chemical calculations to obtain information about the activation barrier for ring flip between the enantiomers. Hydrolytic removal of the dioxepine acetal unit revealed the 2,2′‐biphenol target.     

Copolymer Formation Between Two N‐Substituted Anilines—Electrochemical and Spectroelectrochemical Studies

Abstract

Electrochemical polymerization of diphenylamine, DPA with N‐methyl aniline, NMA was performed using cyclic voltammetry in a 4?M sulfuric acid medium. The electrochemical parameters representing the polymer deposition showed a strong dependence on the molar concentration ratios of DPA or NMA in the feed. In situ spectroelectrochemical studies were performed during the electropolymerization with different molar concentration feed ratios of DPA. The results reveal the formation of intermediates together with DPA and NMA units. Derivative cyclic voltabsorptograms (DCVAs) were deduced at the wavelength of absorbance corresponding to the intermediates and explained with redox characteristics in cyclic voltammogram. Results from cyclic voltammetry and spectroelectrochemical studies favor copolymer formation between DPA and NMA. Copolymers were prepared for different molar concentrations feed ratios of DPA and the composition of the monomer units in the copolymers were determined. Reactivity ratios of DPA and NMA were deduced using Fineman–Ross and Kelen–Tudos methods and correlated with the results from cyclic voltammetry and spectroelectrochemical studies.     

Redox Properties of Novel Dinuclear Ni(II) Bis - Tetraazamacrocyclic Complex

Abstract

Dinuclear Ni(II) bis-tetraazamacrocyclic complex 1 with conjugated double bonds at deprotonated β-diimine linking group was characterized by ¹H NMR and cyclic voltammetry. Electrochemical studies indicated high stability of the mixed-valence (Ni^II- Ni^III) and (Ni^II- Ni^I) species, respectively. The main factor contributing to the stabilization of the mixed-valence states is the electronic delocalization through the system of the conjugated double bonds at the deprotonated β-diimine linking group. Complex 1 is the first example of dinuclear Ni(II) tetraazamacro-cyclic complex exhibiting two one-electron oxidation and two one electron reduction steps.     

Spectral and Electrochemical Characterization of Dibenzotetraaza[14]annulenes

The UV/Vis absorption spectra and cyclic voltammograms (CV) of the Cu(II) and Ni(II) complexes of γ,γ'-alkoxycarbonyl derivatives of α,α'- diphenyldibenzo-tetraaza[14]annulene are analyzed and compared. The observed ratio of absorption intensities at the peaks of π-π* transitions is linearly correlated with the difference of HOMO and LUMO energy levels of the substituents. Moreover, the measured values of the mid-peak potential of metal redox reactions on a Pt electrode in DMF are linearly correlated with the ionization potential values of the appropriate substituents.