Electrochemical and Spectroscopic Characteristics of Artemisinin Antimalarial Drug: Charge Transfer Redox Process

Artemisinin is a plant extract and popular in treating many diseases including malaria. It is a sesquiterpene lactone with several binding modes to several molecules. Oxidation and reduction of this molecule at different electrode materials was studied in tetrabutyl ammonium bromide in acetonitrile solution. The apparent standard heterogeneous rate constant for electron transfer (k_h) was found to be 23 cm s^?1. The value of the electron transfer coefficient (αn_a) was found to be 0.496. The diffusion coefficient (D) was found to be 3.34 × 10^?6 cm s^?1. Gold (Au), glassy carbon, and pyrolytic graphite electrodes exhibited distinguishable current densities. A value of E _1/2 = –0.81 V versus Ag/AgCl was obtained, and a value of n = 1.52 (2) was estimated.     

Nickel ferrocyanide modified electrodes as active cation-exchange matrices: real time XRD evaluation of overlayer structure and electrochemical behavior

The dynamic variations in the structure of nickel ferrocyanide modified electrodes was determined using in situ diffractoelectrochemical techniques. X-ray powder diffraction peaks from the nickel ferrocyanide modified electrode were recorded during electrochemical oxidation/reduction of the surface overlayer and reversible changes in the unit cell lattice parameter observed. The electrochemical changes that occur during oxidation/reduction in various alkali cation electrolytes are correlated with changes in the lattice parameter. It is postulated that micro-domains form when two cations having markedly different radii such as cesium and potassium are intercalated into the nickel ferrocyanide structure so that distinct regions of the nickel ferrocyanide layer containing cesium exist separated from regions with the lighter alkali cations.     

Phorboxazole Synthetic Studies: Design, Synthesis and Biological Evaluation of Phorboxazole A and Hemi-Phorboxazole A Related Analogues

The design, synthesis and biological evaluation of a new phorboxazole analogue, comprising an acetal replacement for the C-ring tetrahdropyran of the natural product and carrying a potency-enhancing C(45-46) vinyl chloride side chain, is described. In addition, the synthesis of (+)-hemi-phorboxazole A and a series of related hemi-phorboxazole A analogues has been achieved. The new acetal ring replacement analogue displayed activity comparable to that of the parent natural product against HCT-116 (colon) cells (IC(50) 2.25 ng/mL). Equally important, the phorboxazole analogue and two related hemiphorboxazole A congeners exhibited significant antifungal activity when assayed against pathogenic Candida albicans strains.     

Real meromorphic functions and linear differential polynomials

We determine all real meromorphic functions f in the plane such that f has finitely many zeros, the poles of f have bounded multiplicities, and f and F have finitely many non-real zeros, where F is a linear differential polynomial given by F = f (k) +Σk-1j=0ajf(j) , in which k≥2 and the coefficients aj are real numbers with a0≠0.     

Functional film of ethylene vinyl acetate and co‐polyamide compound containing “Nisin” active substance

This study deals with flexible films incorporating nisin for antibacterial active packaging purposes. A novel approach was used to gain control over nisin release profile from a thermoplastic film in order to enhance its antibacterial efficiency. This approach involves polymer blends of ethylene vinyl acetate copolymer and co‐polyamide at various ratios. It was shown that the release profile of an antibacterial substance from active packaging to foodstuff is a key factor concerning the antibacterial efficiency. Samples of 400[μm] were produced by using a laboratory twin screw compounder and a laboratory hot press. Samples were characterized for their migration kinetics, molecular interactions, mechanical properties, and water swelling properties. Antibacterial activity tests show that nisin incorporated films reduced bacterial count by different extents. Listeria ATCC 33090 was used as target bacteria (data not shown). Nisin migration profile to water medium was determined by Lowry's protocol. Scanning electron microscopy images and thermal analysis indicated that no significant molecular interactions occurred. Furthermore, droplet and co‐continues like morphology were seen at different polymer blend ratios. Osmotic pressure driven release mechanism appears to be the dominant migration mechanism, and diffusion kinetics was dominant. Results show that morphology of the polymer blend matrix alters the diffusion coefficient. In addition, water swelling characterization of different samples was done in order to reveal the relations with the diffusion coefficient. It seems that there is an inverse resemblance between water swelling and the diffusion coefficient trends.     

Conjugated Addition to 2,2-Dimethyl-3(2h)-furanone: Support for the Baldwin Rules for Ring Closure

In connection with our exploratory studies directed at devising a total synthetic approach to jatro-phone¹ and related antitumor agents,² we have recently explored conjugate addition of organocuprates³ to the 3 (2H)-furanone ring system. In this letter we document the results of that study.     

Unification of anion relay chemistry with the Takeda and Hiyama cross-coupling reactions: identification of an effective silicon-based transfer agent

The unification of Anion Relay Chemistry (ARC) with the Takeda and Hiyama palladium-mediated cross-coupling processes to provide aryl-aryl, alkenyl-aryl, and alkenyl-alkenyl coupled products by exploiting a common silicon-based transfer agent has been achieved. These results provide a practical solution for intermolecular cross-coupling of organolithium reagents without the problematic lithium-halogen exchange and/or undesired homocoupling that has kept organolithium cross-couplings from achieving the same level of utility asother palladium-mediated methods (e.g., Suzuki organoboron, Negishi organozinc, Stille organotin, Kumada organomagnesium, etc.).     

Spongipyran synthetic studies. Total synthesis of (+)-spongistatin 2

Evolution of a convergent synthetic strategy to access (+)-spongistatin 2 (2), a potent cytotoxic marine macrolide, is described. Highlights of the synthesis include: development of a multicomponent dithiane-mediated linchpin union tactic, devised and implemented specifically for construction of the spongistatin AB and CD spiro ring systems; application of a Ca^II ion controlled acid promoted equilibration to set the thermodynamically less stable axial-equatorial stereogenicity in the CD spiroketal; use of sulfone addition/Julia methylenation sequences to unite the AB and CD fragments and introduce the C(44)-C(51) side chain; and fragment union and final elaboration to (+)-spongistatin 2 (2) exploiting Wittig olefination to unite the advanced ABCD and EF fragments, followed by regioselective Yamaguchi macrolactonization and global deprotection. Correction of the CD spiro ring stereogenicity was subsequently achieved via acid equilibration in the presence of Ca^II ion to furnish (+)-spongistatin 2 (2). The synthesis proceeded with a longest linear sequence of 41 steps.     

Studies on Electronic Effects in O‐, N‐ and S‐Chelated Ruthenium Olefin‐Metathesis Catalysts

A short overview on the structural design of the Hoveyda–Grubbs‐type ruthenium initiators chelated through oxygen, nitrogen or sulfur atoms is presented. Our aim was to compare and contrast O‐, N‐ and S‐chelated ruthenium complexes to better understand the impact of electron‐withdrawing and ‐donating substituents on the geometry and activity of the ruthenium complexes and to gain further insight into the trans–cis isomerisation process of the S‐chelated complexes. To evaluate the different effects of chelating heteroatoms and to probe electronic effects on sulfur‐ and nitrogen‐chelated latent catalysts, we synthesised a series of novel complexes. These catalysts were compared against two well‐known oxygen‐chelated initiators and a sulfoxide‐chelated complex. The structures of the new complexes have been determined by single‐crystal X‐ray diffraction and analysed to search for correlations between the structural features and activity. The replacement of the oxygen‐chelating atom by a sulfur or nitrogen atom resulted in catalysts that were inert at room temperature for typical ring‐closing metathesis (RCM) and cross‐metathesis reactions and showed catalytic activity only at higher temperatures. Furthermore, one nitrogen‐chelated initiator demonstrated thermo‐switchable behaviour in RCM reactions, similar to its sulfur‐chelated counterparts.     

Use of the quartz crystal microbalance to monitor ligand-induced conformational rearrangements in HIV-1 envelope protein gp120

We evaluated the potential of a quartz crystal microbalance with dissipation monitoring (QCM-D) to provide a sensitive, label-free method for detecting the conformational rearrangement of glycoprotein gp120 upon binding to different ligands. This glycoprotein is normally found on the envelope of the HIV-1 virus and is involved in viral entry into host cells. It was immobilized on the surface of the sensing element of the QCM-D and was exposed to individual solutions of several different small-molecule inhibitors as well as to a solution of a soluble form of the host cell receptor to which gp120 binds. Instrument responses to ligand-triggered changes were in qualitative agreement with conformational changes as suggested by other biophysical methods.