Novel co-catalytic activity of zinc metal with classical initiators for the ring opening polymerisation of norbornene

Zinc metal was shown to considerably increase the activity of the metal(III) chloride salts of ruthenium, iridium and osmium as metathesis initiators for the ROMP of norbornene. The stereochemistry of the polymers formed was determined by ¹H and ¹³C NMR. Formation of the initial carbene species is not via the normally accepted vinyl hydride mechanism. An alternative mechanism involving a metallacyclopentane intermediate is postulated.     

The molybdenum blue reaction for the determination of orthophosphate revisited: Opening the black box

The molybdenum blue reaction, used predominantly for the determination of orthophosphate in environmental waters, has been perpetually modified and re-optimised over the years, but this important reaction in analytical chemistry is usually treated as something of a 'black box' in the analytical literature. A large number of papers describe a wide variety of reaction conditions and apparently different products (as determined by UV–visible spectroscopy) but a discussion of the chemistry underlying this behaviour is often addressed superficially or not at all. This review aims to rationalise the findings of the many 'optimised' molybdenum blue methods in the literature, mainly for environmental waters, in terms of the underlying polyoxometallate chemistry and offers suggestions for the further enhancement of this time-honoured analytical reaction.     

A new ring opening reaction of N-aminophthalimide hydrazones

Araldehyde hydrazones III of N-aminophthalimide underwent rapid ring opening reactions initiated by the addition of excess base to their refluxing methanolic solutions. The products were conveniently isolated through liquid-liquid extraction as the stable sodium salts V, and acidification precipitated the resulting phthalic acid congeners VI from aqueous solution. Compounds III readily exchanged one hydrazine moiety for another. For example, IIId reacted with 2,4-dinitrophenylhydrazine to give the 2,4-dinitrophenylhydrazone of 4-chlorobenzaldehyde (VIId, 93%). Nonetheless, IIIg reacted exclusively at the carboxaldehyde function to give products VIIIa and VIIIb.     

Instability and heterogeneity: a new approach needed!

The outcome of routine testing for instability and heterogeneity of materials used in proficiency tests tends to be weakly informative because of the unacceptable cost of obtaining enough data to support a suitably powerful statistical test. A better strategy would be to spend considerably more on a large initial validation of a type of material or a procedure for preparing it, and then to monitor all subsequent batches of material of that type by a much cheaper quality control system. The expense of a powerful validation would be quickly recouped by savings in the longer term. Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher.     

From sulfur-amine solutions to metal sulfide nanocrystals: peering into the oleylamine-sulfur black box

In this Article, we present our findings on the formation of metal sulfide nanocrystals from sulfur-alkylamine solutions. By pulsed field gradient diffusion NMR along with the standard toolbox of 1D and 2D NMR, we determined that sulfur-amine solutions used as a sulfur precursor exist as alkylammonium polysulfides at low temperatures. Upon heating to temperatures used in nanocrystal synthesis, the polysulfide ions react with excess amine to generate H(2)S, which combines with the metal precursor to form metal sulfide. Four different reaction pathways were found, each of which produced H(2)S and the byproducts identified in this Article. Thioamides were identified as an intermediate and were shown to exhibit much more rapid kinetics than sulfur-alkylamine solutions at low temperatures in the synthesis of metal sulfide nanocrystals.     

Towards the understanding of the activity of G9a inhibitors: an activity landscape and molecular modeling approach

In this work, we analyze the structure–activity relationships (SAR) of epigenetic inhibitors (lysine mimetics) against lysine methyltransferase (G9a or EHMT2) using a combined activity landscape, molecular docking and molecular dynamics approach. The study was based on a set of 251 G9a inhibitors with reported experimental activity. The activity landscape analysis rapidly led to the identification of activity cliffs, scaffolds hops and other active an inactive molecules with distinct SAR. Structure-based analysis of activity cliffs, scaffold hops and other selected active and inactive G9a inhibitors by means of docking followed by molecular dynamics simulations led to the identification of interactions with key residues involved in activity against G9a, for instance with ASP 1083, LEU 1086, ASP 1088, TYR 1154 and PHE 1158. The outcome of this work is expected to further advance the development of G9a inhibitors.

     

A new 2-arylbenzofuran with antioxidant activity from the black colored rice (Oryza sativa L.) bran

From the black colored rice bran of Oryza sativa cv. Heugjinjubyeo, a new 2-arylbenzofuran, 2-(3,4-dihydroxyphenyl)-4,6-dihydroxybenzofuran-3-carboxylic acid methyl ester, oryzafuran (1), was isolated. Its structure has been elucidated on the basis of spectral data. This compound showed strong antioxidative activity in a 1,1-diphenyl-2-picrylhydrazyl free radical scavenging assay.     

The interaction of diphosphonates with calcitic surfaces: understanding the inhibition activity in marble dissolution

The rates of dissolution of calcitic Carrara marble have been reported to be significantly reduced in alkaline pH (pH 8.25) at 25 degrees C in the presence of (1-hydroxyethylidene)-1,1 diphosphonic acid (HEDP). The adsorption takes place at the calcite/water interface at the double layer through the interaction of charged surface species with the charged solution species of the adsorbate. The present work focused on obtaining a better understanding of the interaction of the calcite surface with HEDP. Calculations were performed according to the triple layer model, assuming the formation of surface complexes between the charged surface species of calcite and the species of HEDP dominant at pH 8.25. According to the model, the adsorbed species are located at the inner Helmholtz plane of the electrical double layer. Strong lateral interactions between the adsorbed species were suggested and were corroborated from the calculation of the respective energy, which was equal to 69 kJ mol(-1). The adsorption isotherm was consistent with the proposed model at low surface coverage values, while discrepancies between the values experimentally measured and the predicted were found at higher adsorbate concentrations. The deviations from the predicted values were attributed to the fact that HEDP adsorption on calcite resulted in the formation of multiple layers. The model explained adequately the changes in the zeta-potential values of calcite in the presence of HEDP in the solution which resulted in charge reversal upon adsorption.     

The minicellirradiator: A new system for a new market

Since the commissioning of the first industrial Gamma Irradiator design, designers and operators of irradiation systems have been attempting to meet the specific production requirements and challenges presented to them. This objective has resulted in many different versions of irradiators currently in service today, all of which had original charters and many of which still perform very well within even the new requirements of this industry.

Continuing changes in the marketplace have, however, placed pressures on existing designs due to a combination of changing dose requirements for sterlization, increased economic pressures from the specific industry served for both time and location and the increasing variety of product types requiring processing. Additionally, certain market areas which could never economically support a typical gamma processing facility have either not been serviced, or have forced potential gamma users to transport product long distances to one of these existing facilities.

The MiniCell^TM removes many of the traditional barriers previously accepted in the radiation processing industry for building a processing facility in a location. Its reduced size and cost have allowed many potential users to consider in-house processing and its ability to be quickly assembled allow it to meet market needs in a much more timely fashion than the previous designs.

The MiniCell system can cost effectively meet many of the current market needs of reducing total cost of processing and also be flexible enough to process product in a wide range of industries effectively.     

Magnesium monoperoxyphtalate: A new reagent for the oxidative ring opening of furans to cis-enediones

Ring opening of furans can be accomplished with the title reagent to afford cis-enediones stereospecifically, with great advantages over the hazardous MCPBA.     

Mollusk shell formation: a source of new concepts for understanding biomineralization processes

The biological approach to forming crystals is proving to be most surprising. Mollusks build their shells by using a hydrophobic silk gel, very acidic aspartic acid rich proteins, and apparently also an amorphous precursor phase from which the crystals form. All this takes place in a highly structured chitinous framework. Here we present ideas on how these disparate components work together to produce the highly structured pearly nacreous layer of the mollusk shell.     

A ring opening reaction of benzisothiazolones. A new route to unsymmetrical disulfides

A series of unsymmetrical disulfides has been prepared by employing a reaction involving a ring opening, nucleophilic attack of a thiol on a 1,2-benzisothiazol-3-one. The benzisothiazolones were in turn prepared by an intramolecular ring closure of an amide on a sulfenyl thiocarbonate. The sulfenyl esters were synthesized as intermediates for preparing mixed-disulfides, but the benzisothiazolone ring closure occurred spontaneously. It was initially thought that the mixed-disulfides were being formed from the sulfenyl ester, but the isolation and stepwise reaction of the benzisothiazolones provided proof for the reaction mechanism.     

p-Tyrosol: a new synthetic method and new types of pharmacological activity

Russian Chemical Bulletin - A new method for the synthesis of p-tyrosol, i.e., 2-(4-hydroxyphenyl)ethanol, has been developed, which considerably simplified the process of preparation of this...     

Discovery of benthol A and its challenging stereochemical assignment: opening up a new window for skeletal diversity of super-carbon-chain compounds

Super-carbon-chain compounds (SCCCs) are marine organic molecules featuring long polyol carbon chains with numerous stereocenters. Polyol–polyene compounds (PPCs) and ladder-frame polyethers (LFPs) are two major families. It is highly challenging to establish the absolute configurations of SCCCs. In this century, few new SCCC families have been reported. Benthol A, an aberrant SCCC, was obtained from a South China Sea benthic dinoflagellate that should belong to a new taxon. Its planar structure and absolute configuration, containing thirty-five carbon stereocenters, were unambiguously established by a combination of extensive NMR spectroscopic investigations, periodate degradation of the 1,2-diol groups, ozonolysis of the carbon–carbon double bonds, J-based configurational analysis, NOE interactions, modified Mosher''s MTPA ester method, and DFT-NMR ¹³C chemical-shift calculations aided by DP4+ statistical analysis. Benthol A displayed potent antimalarial activity against Plasmodium falciparum 3D7 parasites. This new molecule combines extraordinary structural features, particularly eight scattered ether rings on a C₇₂ backbone chain, which places it within a new SCCC family between PPCs and LFPs, herein termed polyol–polyether compounds. This suggestion was strongly supported by principal component analysis. The discovery of benthol A does not only provide new insights into the untapped biosynthetic potential of marine dinoflagellates, but also opens up a new window for skeletal diversity of SCCCs.

The discovery of benthol A, a marine natural product featuring thirty-five carbon stereocenters and eight scattered ether rings within a C₇₂ backbone chain, inaugurates a new family of super-carbon-chain compounds.     

A new angle on pluronic additives: advancing droplets and understanding in digital microfluidics

Biofouling in microfluidic devices limits the type of samples which can be handled and the duration for which samples can be manipulated. Despite the cost of disposing fouled devices, relatively few strategies have been developed to tackle this problem. Here, we have analyzed a series of eight amphiphilic droplet additives, Pluronic coblock polymers of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO), as a solution to biofouling in digital microfluidics using serum-containing cell culture media as a model fluid. Our analysis shows that species with longer PPO chains are superior for enabling droplet motion and reducing biofouling. Two of the tested species, L92 and P105, were found to lengthen device lifetimes by 2-3 times relative to additives used previously when used at optimal concentrations. Pluronics with low PEO content such as L92 were found to be cytotoxic to an immortalized mammalian cell line, and therefore we recommend that Pluronic additives with greater or equal to 50% PEO composition, such as P105, be used for digital microfluidic applications involving cells. Finally, contact angle measurements were used to probe the interaction between Pluronic-containing droplets and device surfaces. Strong correlations were found between various types of contact angle measurements and the capacity of additives to reduce biofouling, which suggests that contact angle measurements may be useful as a tool for rapidly screening new candidates for the potential to reduce biofouling. We propose that this study will be useful for scientists and engineers who are developing digital microfluidic platforms for a wide range of applications involving protein-containing solutions, and in particular, for applications involving cells.     

A new indole-alkaloid and a new phenolic-glycoside with cytotoxic activity from Strychnos fendleri

A new indole alkaloid strychnosinol (1) and a new phenolic-glycoside (2) were isolated from the bark and leaves of Strychnos fendleri Sprague & Sandwith, together with six known compounds reported for the first time in this species. The structures of these compounds were determined on the basis of spectroscopic data; mainly those obtained by using ¹H and ¹³C NMR (1D and 2D) and mass spectrometry. Strychnosinol (1) and the phenolic glycoside (2) together with compounds 3–8 were evaluated for cytotoxicity against a panel of five tumour cell lines; IC₅₀ values between 0.090 and 0.227 μM for the human tumour cell lines were observed for compound 2.     

Tunneling in green tea: understanding the antioxidant activity of catechol-containing compounds. A variational transition-state theory study

The catechol functionality present in the catechins is responsible for the protective effects exerted by green tea against a wide range of human diseases. High-level electronic structure calculations and canonical variational transition-state theory including multidimensional tunneling corrections have allowed us to understand the key factors of the antioxidant effectiveness of the catechol group. This catechol group forms two hydrogen bonds with the two oxygen atoms of the lipid peroxyl radical, leading to a very compact reactant complex. This fact produces an extremely narrow adiabatic potential-energy profile corresponding to the hydrogen abstraction by the peroxyl radical, which makes it possible for a huge tunneling contribution to take place. So, quantum-mechanical tunneling highly increases the corresponding rate constant value, in such a way that catechins become able to trap the lipid peroxyl radicals in a dominant competition with the very damaging free-radical chain-lipid peroxidation reaction.     

Antimalarial activity of a new family of analogues of manzamine A

Manzamine A represents an important lead structure for the development of novel antimalarial chemotherapies. The synthesis and biological evaluation of a group of simplified analogues of manzamine A, which were designed to examine the roles of the A and D rings and of both the relative stereochemistry and the orientation of the beta-carboline heterocycle on the antimalarial activity of manzamine A, are described. [structure: see text]