Preparation of benzyne complexes of group 10 metals by intramolecular suzuki coupling of ortho-metalated phenylboronic esters: molecular structure of the first benzyne-palladium(0) complex

A series of nickel(II) and palladium(II) aryl complexes substituted in the ortho position of the aromatic ring by a (pinacolato)boronic ester group, [MBr[o-C(6)H(4)B(pin)]L(2)] (M = Ni, L(2) = 2PPh(3) (2a), 2PCy(3) (2b), 2PEt(3) (2c), dcpe (2d), dppe (2e), and dppb (2f); M = Pd, L(2) = 2PPh(3) (3a), 2PCy(3) (3b), and dcpe (3d)), has been prepared. Many of these complexes react readily with KO(t)Bu to form the corresponding benzyne complexes [M(eta(2)-C(6)H(4))L(2)] (M = Ni, L(2) = 2PPh(3) (4a), 2PCy(3) (4b), 2PEt(3) (4c), dcpe (4d); M = Pd, L(2) = 2PCy(3) (5b)). This reaction can be regarded as an intramolecular version of a Suzuki cross-coupling reaction, the driving force for which may be the steric interaction between the boronic ester group and the phosphine ligands present in the precursors 2 and 3. Complex 3d also reacts with KO(t)Bu, but in this case disproportionation of the initially formed eta(2)-C(6)H(4) complex (5d) leads to a 1:1 mixture of a novel dinuclear palladium(I) complex, [(dcpe)Pd(mu(2)-C(6)H(4))Pd(dcpe)] (6), and a 2,2'-biphenyldiyl complex, [Pd(2,2'-C(6)H(4)C(6)H(4))(dcpe)] (7d). Complexes 2a, 3b, 3d, 4b, 5b, 6, and 7d have been structurally characterized by X-ray diffraction; complex 5b is the first example of an isolated benzyne-palladium(0) species.     

Photo-triggered hydrogen atom transfer from an iridium hydride complex to unactivated olefins

Many photoactive metal complexes can act as electron donors or acceptors upon photoexcitation, but hydrogen atom transfer (HAT) reactivity is rare. We discovered that a typical representative of a widely used class of iridium hydride complexes acts as an H-atom donor to unactivated olefins upon irradiation at 470 nm in the presence of tertiary alkyl amines as sacrificial electron and proton sources. The catalytic hydrogenation of simple olefins served as a test ground to establish this new photo-reactivity of iridium hydrides. Substrates that are very difficult to activate by photoinduced electron transfer were readily hydrogenated, and structure–reactivity relationships established with 12 different olefins are in line with typical HAT reactivity, reflecting the relative stabilities of radical intermediates formed by HAT. Radical clock, H/D isotope labeling, and transient absorption experiments provide further mechanistic insight and corroborate the interpretation of the overall reactivity in terms of photo-triggered hydrogen atom transfer (photo-HAT). The catalytically active species is identified as an Ir(ii) hydride with an Ir^II–H bond dissociation free energy around 44 kcal mol⁻¹, which is formed after reductive ³MLCT excited-state quenching of the corresponding Ir(iii) hydride, i.e. the actual HAT step occurs on the ground-state potential energy surface. The photo-HAT reactivity presented here represents a conceptually novel approach to photocatalysis with metal complexes, which is fundamentally different from the many prior studies relying on photoinduced electron transfer.

Upon irradiation with visible light, an iridium hydride complex undergoes hydrogen atom transfer (HAT) to unactivated olefins in presence of a sacrificial electron donor and a proton source.     

Adsorption of cationic cellulose derivative/anionic surfactant complexes onto solid surfaces. II. Hydrophobized silica surfaces

The effect of the anionic surfactant SDS (sodium dodecyl sulfate) on the adsorption behavior of cationic hydroxyethyl cellulose (Polymer JR-400) and hydrophobically modified cationic cellulose (Quatrisoft LM-200) at hydrophobized silica has been investigated by null ellipsometry and compared with the previous data for adsorption onto hydrophilic silica surfaces. The adsorbed amount of LM-200 is found to be considerably larger than the adsorbed amount of JR-400 at both surfaces. Both polymers had higher affinity toward hydrophobized silica than to silica. The effect of SDS on polymer adsorption was studied under two different conditions: adsorption of polymer/SDS complexes from premixed solutions and addition of SDS to preadsorbed polymer layers. Association of the surfactant to the polymer seems to control the interfacial behavior, which depends on the surfactant concentration. For the JR-400/SDS complex, the adsorbed amount on hydrophobized silica started to increase progressively from much lower SDS concentrations, while the adsorbed amount on silica increased sharply only slightly below the phase separation region. For the LM-200/SDS complex, the adsorbed amounts increased progressively from very low SDS concentrations at both surfaces, and no large difference in the adsorption behavior was observed between two surfaces below the phase separation region. The complex desorbed from the surface at high SDS concentrations above the critical micelle concentration. The reversibility of the adsorption of polymer/SDS complexes upon rinsing was also investigated. When the premixed polymer/SDS solutions at high SDS concentrations (>5 mM) were diluted by adding water, the adsorbed amount increased due to the precipitation of the complex. The effect of the rinsing process on the adsorbed layer was determined by the hydrophobicity of the polymer and the surface.     

Self-assembly of amphiphilic hexapyridinium cations at the air/water interface and on HOPG surfaces.

Mono- and multilayers of a novel amphiphilic hexapyridinium cation with six eicosyl chains (3) are spread at the air/water interface as well as on highly ordered pyrolytic graphite (HOPG). On water, the monolayer of 3 is investigated by recording surface pressure/area and surface potential/area isotherms, and by Brewster angle microscopy (BAM). Self-organized tubular micelles with an internal edge-on orientation of molecules form at the air/water interface at low surface pressure whereas multilayers are present at high surface pressure, after a phase transition. Packing motifs suggesting a tubular arrangement of the constituting molecules were gleaned from atomic force microscopy (AFM) investigations of Langmuir-Blodgett (LB) monolayers being transferred on HOPG at different surface pressures. These LB film structures are compared to the self-assembled monolayer (SAM) of 3 formed via adsorption from a supersaturated solution, which is studied by scanning tunnelling microscopy (STM). On HOPG the SAM of 3 consists of nanorods with a highly ordered edge-on packing of the aromatic rings and an arrangement of alkyl chains which resembles the packing of molecules at the air/water interface at low surface pressure. Additional details of the molecular packing were gleaned from single-crystal X-ray structure analysis of the hexapyridinium model compound 2b, which possesses methyl instead of eicosyl residues.     

Elektronenstoss-induzierter zerfall von benzol-tricarbonyl-chrom- und -wolfram-derivaten; ein vergleich

The Electron impact mass spectra of (CO)₃ MC₆H₅—X complexes (M = Cr, W; X = OCH₃, OC₄H₉, CO₂CH₃, CO₂C₄H₉) were recorded. From metastable transitions and by high-resolution measurements complete fragmentation diagrams were obtained; in some cases comparative structure determinations of fragment ions were carried out by collisional activation. The fragmentation of the tungsten complexes considerably differs from that of the chromium compounds. The differences may be attributed to the stronger-electrophilic character as well as to the more pronounced tendency of tungsten to attain higher oxidation states.     

Multiple-locus variable number tandem repeats analysis for genetic fingerprinting of pathogenic bacteria

DNA fingerprinting has attracted considerable interest as means for identifying, tracing and preventing the dissemination of infectious agents. Various methods have been developed for typing of pathogenic bacteria, which differ in discriminative power, reproducibility and ease of interpretation. During recent years a typing method, which uses the information provided by whole genome sequencing of bacterial species, has gained increased attention. Short sequence repeat (SSR) motifs are known to undergo frequent variation in the number of repeated units through cellular mechanisms most commonly active during chromosome replication. A class of SSRs, named variable number of tandem repeats (VNTRs), has proven to be a suitable target for assessing genetic polymorphisms within bacterial species. This review attempts to give an overview of bacterial agents where VNTR-based typing, or multiple-locus variant-repeat analysis (MLVA) has been developed for typing purposes, together with addressing advantages and drawbacks associated with the use of tandem repeated DNA motifs as targets for bacterial typing and identification.     

Synthesis and supramolecular properties of molecular clips with anthracene sidewalls

Novel molecular clips with anthracene sidewalls (1 a-c) were synthesized; they form stable host-guest complexes with a variety of electron-deficient aromatic and quinoid molecules. According to single-crystal structure analyses of clip 1 c and 1,2,4,5-tetracyanobenzene (TCNB) complex 14@1 b, the clips' anthracene sidewalls have to be compressed substantially during the complex formation to provide attractive pi-pi interactions between the aromatic guest molecule and the two anthracene sidewalls in the complex. The compression and expansion of aromatic sidewalls are calculated by molecular mechanics to be low-energy processes, so the energy required for compression of the anthracene sidewalls during complex formation is apparently overcompensated by the gain in energy resulting from the attractive pi-pi interactions. The finding that complexes of the clips 1 a-c are more stable than those of the corresponding clips 2 a-c can be explained in terms of the larger van der Waals contact surfaces of the anthracene sidewalls in 1 a-c (relative to the naphthalene sidewalls in 2 a-c). Color changes resulting from charge-transfer (CT) bands are observed in complex formation by 1 a-c: from colorless to red or purple with TCNB (14), and from yellow to green with 2,4,7-trinitro-9-fluorenone TNF (17). Independently, the host 1 b and guest 14 fluoresce from their respective excited singlet states, whilst in the complex 14@1 b the charge-transfer state quenches the higher-energy singlet states of the two components, and as a result luminescence is only observed from this new CT state. To the best of our knowledge, complex 14@1 b is the first example of CT luminescence from a host-guest complex. The binding constant determined for the formation of the TCNB complex 14@1 b from a UV/Vis titration experiment (Ka = 12 400 m(-1)) agrees well with the value (K(a) = 12 800 m(-1)) obtained by 1H NMR titration.     

Explorative data analysis of two-dimensional electrophoresis gels

Methods for classification of two-dimensional (2-DE) electrophoresis gels based on multivariate data analysis are demonstrated. Two-dimensional gels of ten wheat varieties are analyzed and it is demonstrated how to classify the wheat varieties in two qualities and a method for initial screening of gels is presented. First, an approach is demonstrated in which no prior knowledge of the separated proteins is used. Alignment of the gels followed by a simple transformation of data makes it possible to analyze the gels in an automated explorative manner by principal component analysis, to determine if the gels should be further analyzed. A more detailed approach is done by analyzing spot volume lists by principal components analysis and partial least square regression. The use of spot volume data offers a mean to investigate the spot pattern and link the classified protein patterns to distinct spots on the gels for further investigation. The explorative approach in analysis of 2-D gels makes it possible, in a fast and convenient way, to screen many gels in order to determine the protein patterns that form clusters and could be selected for further examination.     

Investigations of a novel process to the framework of benzo[c]cinnoline

A novel synthetic process leading to the framework of benzo[c]cinnoline has been discovered and investigated. The process is composed of two separate reactions, the first of which is a partial reduction of the nitro groups of the 2,2'-dinitrobiphenyl, a process that we believe proceeds via a SET mechanism to yield the hydroxyamino and nitroso groups. In the following step the cyclization takes place under formation of the -N=N- bond. We believe that this process take place via a radical mechanism through the nitroso radical anion. The novel process affords either benzo[c]cinnoline or benzo[c]cinnoline N-oxide, both in high yields, 93% and 91%, respectively. To obtain benzo[c]cinnoline, the reaction is conducted with an alcohol as solvent and an alkoxide as the base, while for benzo[c]cinnoline N-oxide, water is used as solvent with sodium hydroxide as the base. To establish the latter procedure, statistical experimental design and multivariate modeling were utilized to reveal the response surface for the reaction and to determine the optimal conditions for the reaction. A proposal for the complex reaction mechanism is given. During the corroboration of the mechanism, a new deoxygenation reaction for converting benzo[c]cinnoline N-oxide into benzo[c]cinnoline was discovered. The reaction is conducted by treating the N-oxide with sodium ethoxide at elevated temperature to achieve near-quantitative conversion into benzo[c]cinnoline in a yield of 96%.     

HPLC Method for Determination of Rosiglitazone in Plasma

A fast and sensitive high performance liquid chromatography method for quantitative determination of rosiglitazone in human plasma has been developed. The extraction from plasma was performed using solid-phase extraction (SPE) on C4 silica (100 mg) disposable extraction cartridges (DEC). The separation of rosiglitazone and two metabolites was achieved on a Phenomenex® Synergi 4 µm MAX-RP (150 × 4.6 mm) column, protected by a guard column. The mobile phase was 0.01 M ammonium acetate, pH 7.0 - acetonitrile (65:35, v/v). (3S)-3-OH-quinidine was used as internal standard. The analytes were detected using fluorescence detection. The method was validated. The limit of quantitation was 1 ng mL⁻¹ and the detection limit was 0.25 ng mL⁻¹ for rosiglitazone in human plasma. The recovery was 90% for rosiglitazone. Linearity was observed over a range of 1-1000 ng mL⁻¹ (r²=0.9959). The intra- and inter-day precision (C.V.) did not exceed 8.7 %. Applicability of the method was demonstrated by a clinical pharmacokinetic study. A healthy volunteer received in two separate phases 4 mg and 8 mg rosiglitazone maleate as a single oral dose. Plasma concentrations were measured for 24 h in both phases.