Chemically engineered papain as artificial formate dehydrogenase for NAD(P)H regeneration.

Organometallic complexes of the general formula [(η(6)-arene)Ru(N⁁N)Cl](+) and [(η(5)-Cp*)Rh(N⁁N)Cl](+) where N⁁N is a 2,2'-dipyridylamine (DPA) derivative carrying a thiol-targeted maleimide group, 2,2'-bispyridyl (bpy), 1,10-phenanthroline (phen) or ethylenediamine (en) and arene is benzene, 2-chloro-N-[2-(phenyl)ethyl]acetamide or p-cymene were identified as catalysts for the stereoselective reduction of the enzyme cofactors NAD(P)(+) into NAD(P)H with formate as a hydride donor. A thorough comparison of their effectiveness towards NAD(+) (expressed as TOF) revealed that the Rh(III) complexes were much more potent catalysts than the Ru(II) complexes. Within the Ru(II) complex series, both the N⁁N and arene ligands forming the coordination sphere had a noticeable influence on the activity of the complexes. Covalent anchoring of the maleimide-functionalized Ru(II) and Rh(III) complexes to the cysteine endoproteinase papain yielded hybrid metalloproteins, some of them displaying formate dehydrogenase activity with potentially interesting kinetic parameters.

Decontamination of tetramethylammonium hydroxide (TMAH) splashes: promising results with Diphoterine in vitro.

Tetramethylammonium hydroxide (TMAH), used in microelectronic industries and research and development, has both corrosive properties and systemic toxicity. Two fatal TMAH occupational exposure cases have been published. Studies comparing initial TMAH decontamination with Diphoterine versus tap water were performed: an in vitro pH titration study and an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) in vitro cytotoxicity cell viability assay. For pH normalization, 17 times more tap water than Diphoterine was required. In the cytotoxicity test, two-thirds of the cells remained viable after Diphoterine washing, compared with only one-third after tap water washing (p < .001). Diphoterine washing is a promising TMAH decontamination method.

Coupled sensitizer-catalyst dyads: electron-transfer reactions in a perylene-polyoxometalate conjugate.

Ultrafast discharge of a single-electron capacitor: A variety of intramolecular electron-transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single-electron events. (et=electron transfer, cr=charge recombination, csr=charge-shift reaction, PER=perylene, POM=polyoxometalate).A new strategy is introduced that permits covalent attachment of an organic chromophore to a polyoxometalate (POM) cluster. Two examples are reported that differ according to the nature of the anchoring group and the flexibility of the linker. Both POMs are functionalized with perylene monoimide units, which function as photon collectors and form a relatively long-lived charge-transfer state under illumination. They are reduced to a stable pi-radical anion by electrolysis or to a protonated dianion under photolysis in the presence of aqueous triethanolamine. The presence of the POM opens up an intramolecular electron-transfer route by which the charge-transfer state reduces the POM. The rate of this process depends on the molecular conformation and appears to involve through-space interactions. Prior reduction of the POM leads to efficient fluorescence quenching, again due to intramolecular electron transfer. In most cases, it is difficult to resolve the electron-transfer products because of relatively fast reverse charge shift that occurs within a closed conformer. Although the POM can store multiple electrons, it has not proved possible to use these systems as molecular-scale capacitors because of efficient electron transfer from the one-electron-reduced POM to the excited singlet state of the perylene monoimide.

Braunicetals: acetals from condensation of macrocyclic aldehydes and terpene diols in Botryococcus braunii.

Two series of braunicetals were isolated from the green microalga Botryococcus braunii. Based on spectroscopic and chemical evidence, their structures were determined to be acetals formed by the condensation of C32 and C34 macrocyclic aldehydes with C33 and C34 methylated squalene diols (series I), or a C40 lycopaene diol (series II).

(Eta6-arene) ruthenium(II) complexes and metallo-papain hybrid as Lewis acid catalysts of Diels-Alder reaction in water.

Covalent embedding of a (eta(6)-arene) ruthenium(II) complex into the protein papain gives rise to a metalloenzyme displaying a catalytic efficiency for a Lewis acid-mediated catalysed Diels-Alder reaction enhanced by two orders of magnitude in water.

Investigations of the fragmentation pathways of benzylpyridinium ions under ESI/MS conditions.

Benzylpyridinium ions are often used as 'thermometer ions' in order to evaluate the internal energy distribution of the ions formed in sources of mass spectrometers. However, the detailed fragmentation pathways of these parent ions were not well established. In particular, fragmentation involving a rearrangement (RR) process may be influencing the simulated distribution curves. In a previous study, we suggested that such RR actually occurred under electrospray ionization/mass spectrometry (ESI/MS) and fast atom bombardment/mass spectrometry (FAB/MS) experiments. Here, we present a systematic study of different substituted benzylpyridinium ions. Theoretical calculations showed that RR fragmentation leading to substituted tropylium ions could occur under 'soft ionization' conditions, such as ESI or FAB. Experimental results obtained under gas-phase reactivity conditions showed that some substituted benzylpiridinium compounds actually undergo RR fragmentations under ESI/MS conditions. Mass-analyzed kinetic experiments were also carried out to gain information on the reaction pathways that actually occur, and these experimental results are in agreement with the reaction pathways theoretically proposed.

Suzuki-miyaura cross-coupling of 1,1-dichloro-1-alkenes with 9-alkyl-9-BBN.

We addressed an unexplored application of the Suzuki-Miyaura protocol to the cross-coupling of 1,1-dichloro-1-alkenes with 9-alkyl-9-BBN. The use of bisphosphine ligands with a large P-Pd-P bite angle allowed us to synthesize Z-chlorinated internal alkenes in good yields resulting from a selective monocoupling process, a recurrent challenge with 1,1-dichloro-1-alkenes. Moreover, these monochlorinated olefins could be further transformed providing stereospecifically trisubstituted olefins.

Cysteine-specific, covalent anchoring of transition organometallic complexes to the protein papain from Carica papaya.

Site-directed and covalent introduction of various transition metal-organic entities to the active site of the cysteine endoproteinase, papain, was achieved by treatment of this enzyme with a series of organometallic maleimide derivatives specially designed for the purpose. Kinetic studies made it clear that time-dependent irreversible inactivation of papain occurred in the presence of these organometallic maleimides as a result of Michael addition of the sulfhydryl of Cys25. The rate and mechanism of inactivation were highly dependent on the structure of the organometallic entity attached to the maleimide group. Combined ESI-MS and IR analysis indicated that all the resulting papain adducts contained one organometallic moiety per protein molecule. This confirmed that chemospecific introduction of the metal complexes was indeed achieved. Thus, three novel reagents for heavy-atom derivatization of protein crystals, which include ruthenium, rhenium and tungsten, are now available for the introduction of electron-dense scatterers for phasing of X-ray crystallographic data.

Parameters and mechanistic studies on the oxidative ring cleavage of synthetic heterocyclic naphthoquinones by Streptomyces strains.

Screening of fungal and bacterial strains allowed selection of two Streptomyces strains ( S. platensis and S. cinnamonensis) that oxidatively cleave, in moderate to high yields (up to 65% in 24 h), the quinonic ring of a thiazole fused 1,4-naphthoquinone compound, INO5042, used as a model compound for a series of homologous substituted heterocyclic naphthoquinones. The respective products of these whole-cell biotransformations were identified as isomeric phenol-carboxylic acids resulting from a C-C bond cleavage at a position vicinal to each one of the carbonyl groups. The culture and incubation conditions have been optimised and the mechanism of this biotransformation investigated using oxygen isotope incorporation. The results of 18O2 incorporation indicate a dioxygenase reaction, the mechanism of which is discussed in relation with that of hydroquinone-epoxidases, a family of oxygenating enzymes involved in the biosynthesis of polyketide antibiotics in Streptomyces.