Luminescent Di‐ and Polynuclear Organometallic Gold(I)–Metal (Au2, {Au2Ag}n and {Au2Cu}n) Compounds Containing Bidentate Phosphanes as Active Antimicrobial Agents

The reaction of new dinuclear gold(I) organometallic complexes containing mesityl ligands and bridging bidentate phosphanes [Au₂(mes)₂(μ‐LL)] (LL=dppe: 1,2‐bis(diphenylphosphano)ethane 1 a , and water‐soluble dppy: 1,2‐bis(di‐3‐pyridylphosphano)ethane 1 b ) with Ag⁺ and Cu⁺ lead to the formation of a family of heterometallic clusters with mesityl bridging ligands of the general formula [Au₂M(μ‐mes)₂(μ‐LL)][A] (M=Ag, A=ClO₄^?, LL=dppe 2 a , dppy 2 b ; M=Ag, A=SO₃CF₃^?, LL=dppe 3 a , dppy 3 b ; M=Cu, A=PF₆^?, LL=dppe 4 a , dppy 4 b ). The new compounds were characterized by different spectroscopic techniques and mass spectrometry The crystal structures of [Au₂(mes)₂(μ‐dppy)] ( 1 b ) and [Au₂Ag(μ‐mes)₂(μ‐dppe)][SO₃CF₃] ( 3 a ) were determined by a single‐crystal X‐ray diffraction study. 3 a in solid state is not a cyclic trinuclear Au₂Ag derivative but it gives an open polymeric structure instead, with the {Au₂(μ‐dppe)} fragments “linked” by {Ag(μ‐mes)₂} units. The very short distances of 2.7559(6) Å (Au? Ag) and 2.9229(8) Å (Au? Au) are indicative of gold–silver (metallophilic) and aurophilic interactions. A systematic study of their luminescence properties revealed that all compounds are brightly luminescent in solid state, at room temperature (RT) and at 77 K, or in frozen DMSO solutions with lifetimes in the microsecond range and probably due to the self‐aggregation of [Au₂M(μ‐mes)₂(μ‐LL)]⁺ units (M=Ag or Cu; LL=dppe or dppy) into an extended chain structure, through Au? Au and/or Au? M metallophilic interactions, as that observed for 3 a . In solid state the heterometallic Au₂M complexes with dppe ( 2 a – 4 a ) show a shift of emission maxima (from ca. 430 to the range of 520‐540 nm) as compared to the parent dinuclear organometallic product 1 a while the complexes with dppy ( 2 b–4 b ) display a more moderate shift (505 for 1 b to a max of 563 nm for 4 b ). More importantly, compound [Au₂Ag(μ‐mes)₂(μ‐dppy)]ClO₄ ( 2 b ) resulted luminescent in diluted DMSO solution at room temperature. Previously reported compound [Au₂Cl₂(μ‐LL)] (LL dppy 5 b ) was also studied for comparative purposes. The antimicrobial activity of 1–5 and Ag[A] (A=ClO₄^?, SO₃CF₃^?) against Gram‐positive and Gram‐negative bacteria and yeast was evaluated. Most tested compounds displayed moderate to high antibacterial activity while heteronuclear Au₂M derivatives with dppe ( 2 a – 4 a ) were the more active (minimum inhibitory concentration 10 to 1 μg mL^?1). Compounds containing silver were ten times more active to Gram‐negative bacteria than the parent dinuclear compound 1 a or silver salts. Au₂Ag compounds with dppy ( 2 b , 3 b ) were also potent against fungi.     

Protein regulators of eicosanoid synthesis: role in inflammation

A variety of factors contribute to the complex course of inflammation. Microbiological, immunological and toxic agents can initiate the inflammatory response by activating a variety of humoral and cellular mediators. In the early phase of inflammation, excessive amounts of cytokines and inflammatory mediators are released. These factors activate, in addition to other signaling pathways, the lipid synthesis pathways, which play a crucial role in the pathogenesis of organ dysfunction. Arachidonic acid (AA), the precursor of pro-inflammatory eicosanoids, is released from membrane phospholipids by the action of phospholipase A(2) (PLA(2)), and is metabolized to prostaglandins (PGs) and leukotrienes (LTs) by the action of cyclooxygenase (COX) and lipoxygenase (LO) enzymes, respectively. Disordered activation of PLA(2), LO and COX enzymes have been implicated in many inflammatory diseases. PLA(2) is activated by phospholipase-A(2)-activating protein (PLAP) and LO by 5-lipoxygenase-activating protein (FLAP). The inducible form of COX-2 enzyme, which is usually not present under basal conditions, is induced in inflammation. In this article the function of these enzymes in eicosanoid synthesis, their regulation, and their implication in inflammatory disorders will be reviewed. The properties, function and regulation of the protein activators PLAP and FLAP will also be discussed.     

Comparative study of separation and determination of triazines by micellar electrokinetic capillary chromatography and nonaqueous capillary electrophoresis: application to residue analysis in natural waters

The separation and determination of a mixture of chloro- and methylthiotriazines in water samples by both micellar electrokinetic capillary chromatography (MEKC) and nonaqueous capillary zone electrophoresis (NA-CZE) were compared. The characteristics of both methods proved to be very similar in terms of separation efficiency and analysis times, but application of these methods for the analysis of triazines in natural waters, with a prior preconcentration step, revealed significant differences. A preconcentration step by solid-phase extraction (SPE) with Oasis HLB cartridges was accomplished for the determination of triazines at sub-ppb levels in drinking and river waters; when NA-CZE was used after this SPE step, electropherograms with fewer interferences and more stable baselines were obtained than when separation was carried out using MEKC. Another aspect related to the application to real samples was the lack of precision encountered upon evaluating the electrophoretic signals generated when using SPE coupled with NA-CZE. Here, we demonstrate the importance of choosing an appropriate internal standard for analyte quantification. It is recommended that a triazine belonging to the same family as that of the triazine to be determined should be used as internal standard.     

Desulfation and rearrangement of tigemonam to an isoxazolidin-5-one and the synthesis of the rearrangement product

The β-lactam antibiotic Tigemonam 2 undergoes desulfation to the N-hydroxyazetidinone 4 , which rearranges to the isoxazolidin-5-one 6 . The structure of the rearrangement product 6 was confirmed by synthesis.     

Studies on accelerated sulphur vulcanization of natural rubber using 1-phenyl-2, 4-dithiobiuret/tertiary butyl benzothiazole sulphenamide

The use of binary accelerators has gained tremendous importance since it increases the production rate of the article made of that elastomer. The authors have analyzed the performance of a novel binary accelerator system in the sulphur vulcanization of natural rubber (NR). The vulcanizates resulting from the binary accelerated process obtained good mechanical properties, ageing and swelling resistance. Network characterization of the mixes was done using swelling measurements, stress-strain analysis etc. The chain entanglement density was measured using dynamic mechanical analysis. However the performance is found to be dependent on the relative proportion of mono, di and polysulphidic linkages in the material. The result of the study points out that the proposed system can be active in NR regardless of the vulcanization recipe and temperature. The performance of the new binary system in filled vulcanizates is also studied. Based on the processing, mechanical and chemical characterization an optimum concentration is suggested for the new system.     

Experimental and theoretical characterization of arsenite in water: insights into the coordination environment of As-O

Long-term exposure to arsenic in drinking water has been linked to cancer of the bladder, lungs, skin, kidney, nasal passages, liver, and prostate in humans. It is therefore important to understand the structural aspects of arsenic in water, as hydrated arsenic is most likely the initial form of the metalloid absorbed by cells. We present a detailed experimental and theoretical characterization of the coordination environment of hydrated arsenite. XANES analysis confirms As(III) is a stable redox form of the metalloid in solution. EXAFS analysis indicate, at neutral pH, arsenite has a nearest-neighbor coordination geometry of approximately 3 As-O bonds at an average bond length of 1.77 A, while at basic pH the nearest-neighbor coordination geometry shifts to a single short As-O bond at 1.69 A and two longer As-O bonds at 1.82 A. Long-range ligand scattering is present in all EXAFS samples; however, these data could not be fit with any degree of certainty. There is no XAS detectable interaction between As and antimony, suggesting they are not imported into cells as a multinuclear complex. XAS results were compared to a structural database of arsenite compounds to confirm that a 3 coordinate As-O complex for hydrated arsenite is the predominate species in solution. Finally, quantum chemical studies indicate arsenite in solution is solvated by 3 water molecules. These results indicate As(OH)3 as the most stable structure existing in solution at neutral pH; thus, ionic As transport does not appear to be involved in the cellular uptake process.     

Elevated-temperature metathesis syntheses of structurally novel alkali-metal tetrakis(3,5-di-tert-butylpyrazolato)lanthanoidate(III) complexes: toluene-coordinated discrete bimetallic complexes and supramolecular chains

Sodium and potassium tetrakis(3,5-di-tert-butylpyrazolato)lanthanoidate(III) complexes [M[Ln(tBu(2)pz)(4)]] have been prepared by reaction of anhydrous lanthanoid trihalides with alkali metal 3,5-di-tert-butylpyrazolates at 200-300 degrees C, and a 1,2,4,5-tetramethylbenzene flux for M=K. On extraction with toluene (or occasionally directly from the reaction tube) the following complexes were isolated: [Na(PhMe)[Ln(tBu(2)pz)(4)]] (1 Ln; 1 Ln=1 Tb, 1 Ho, 1 Er, 1 Yb), [K(PhMe)[Ln(tBu(2)pz)(4)]].2 PhMe (2 Ln; 2 Ln=2 La, 2 Sm, 2 Tb, 2 Ho, 2 Yb, 2 Lu), [Na[Ln(tBu(2)pz)(4)]](n) (3 Ln; 3 Ln=3 La, 3 Tb, 3 Ho, 3 Er, 3 Yb), [K[Ln(tBu(2)pz)(4)]](n) (4 Ln; 4 Ln=4 La, 4 Nd, 4 Sm, 4 Tb, 4 Ho, 4 Er, 4 Yb, 4 Lu), with the last two classes generally being obtained by loss of toluene from 1 Ln or 2 Ln, and [Na(tBu(2)pzH)[Ln(tBu(2)pz)(4)]].PhMe (5 Ln; 5 Ln=5 Nd, 5 Er, 5 Yb). Extraction with 1,2-dimethoxyethane (DME) after isolation of 2 Ho yielded [K(dme)[Ho(tBu(2)pz)(4)]] (6 Ho). X-ray crystal structures of 1 Ln (=1 Tb, 1 Ho; P2(1)/c), 2 Ln (=2 La, 2 Sm, 2 Tb, 2 Yb, 2 Lu; Pnma), 3,4 Ln (=3 La, 3 Er, 4 Sm; P2(1)/m), and 5 Ln (=5 Nd, 5 Er, and 5 Yb; P1) show each group to be isomorphous regardless of the size of the Ln(3+) ion. All complexes contain eight-coordinate [Ln(eta(2)-tBu(2)pz)(4)] units. These are further linked to the alkali metal by bridging through two (1,2,5 Ln) or three (3,4 Ln) tBu(2)pz groups which show striking coordination versatility. Sodium is coordinated by an eta(4)-PhMe, a micro-eta(2):eta(2)-tBu(2)pz, and a micro-eta(4)(Na):eta(2)(Ln)-tBu(2)pz ligand in 1 Ln, and by one eta(1)-tBu(2)pzH and two micro-eta(3)(Na):eta(2)(Ln) ligands in 5 Ln. By contrast, potassium has one eta(6)-PhMe and two micro-eta(5)(K):eta(2)(Ln) ligands in 2 Ln. Classes 3,4 Ln form polymeric chains with the alkali metal bonded by two micro-eta(3)(NNC-M):eta(2)(Ln)-tBu(2)pz ligands within [MLn(tBu(2)pz)(4)] units which are joined together by eta(1)(C)-tBu(2)pz-Na, K linkages.