NHC-Au(i) complexes bearing trispyrazolyl borate (Tp) ligands: efficient platforms for bimetallic species.

Treatment of NHC-AuCl (NHC = IPr and IMes) complexes with equimolar amounts of KTpR2 (R = Me, H) salts in tetrahydrofuran produces in high yields the heteroleptic complexes 3-6 with the general formula NHC-Au-TpR2. As the TpR ligand in complexes 3-6 features a k1-N type coordination toward the gold(i) center, the subsequent addition of group 10 and 11 metal precursors (NiII, PtII, CuII) results in the isolation of heterobimetallic Au/M complexes supported by TpR platforms. All new metal complexes have been fully characterized by elemental analysis and NMR spectroscopy, and in the case of 3, 4 and 6 by X-ray crystallography.

Hydroxyl-functionalized triazolylidene-based PEPPSI complexes: metallacycle formation effect on the Suzuki coupling reaction.

We report the preparation and full characterization of a series of hydroxyl functionalized 1,2,3-triazolylidene-based PEPPSI complexes 2a-c and their catalytic application in the Suzuki cross coupling reaction of aryl chlorides/amides with boronic acids. Under basic reaction conditions, complexes 2a-c show a notable increase in their catalytic efficiency compared with two ether-wingtip functionalized PEPPSI analogues (3 and 4) and a commercially available NHC-Pd complex (5). The catalytic results suggest that deprotonation of the hydroxyl group in complexes 2a-c plays an important role in the overall process. Deprotonation of the alcohol moiety of complexes 2a-b with sodium tert-butoxide allows for the isolation of metallacycles 6a-b, which are proposed as the active species of cross coupling reactions.

Expedient Synthesis of Highly Functionalized Abnormal Carbenegold(I) Complexes.

The reaction of 4-substituted imidazol-2-ylidenes with various electrophiles produces a series of 2,4-functionalized imidazolium salts. Subsequent metalation of these precursors using AuCl(SMe2) provides the first examples of highly functionalized abnormal carbenegold(I) complexes. The present protocol introduces a new strategy for the synthesis of metallic abnormal carbenes featuring diverse functional groups.

Bridged N-Heterocyclic/Mesoionic (NHC/MIC) Heterodicarbenes as Ligands for Transition Metal Complexes.

Following a copper catalyzed alkyne azide cycloaddition (CuAAC) and N-alkylation protocols, we report the preparation of a hybrid N-heterocyclic/mesoionic [NHC(H+)-MIC(H+)][2I]2- salt (1) in high yields. The treatment of salt 1 with Cu2O and KI yields a second hybrid NHC/MIC proligand featuring a tetraiodocuprate anion [NHC(H+)-MIC(H+)][Cu2I4]2- (2). Through selective deprotonation and metalation, both salts 1 and 2 can generate either the chelate heterodicarbene complexes (3) with the rare [NHC·(M)·MIC]+[MX2]- general formula (M = PdII, RhI) or NHC-anchored/pendent triazolium species (4) [NHC·(M)-MIC(H+)]. If the triazolium moiety of type 4 complexes is deprotonated with KHMDS in the presence of a second metal center, a series of heterobimetallic complexes of the type [NHC·(M)-MIC·(M')] (5) are achieved. Interestingly, the reaction of salt 2 with KHMDS yields the bimetallic copper heterodicarbene (6) which can be a useful transfer reagent for the preparation of type 3 complexes. A variety of synthetic routes for the preparation of complexes 3-5 and their full characterization in solution and in the solid state will be discussed.

Visible-Light-Promoted AuI to AuIII Oxidation in Triazol-5-ylidene Complexes.

Reaction of triazolium precursors [MIC(CH2 )n - H+ ]I- (n=1-3) with potassium hexamethyldisilazane (KHMDS) and AuCl(SMe2 ) generates the gold(I) complexes of the type MIC(CH2 )n ⋅AuI. Visible light exposure of the latter complexes promotes a spontaneous disproportionation process rendering gold(III) complexes of the type [{MIC(CH2 )n }2 ⋅AuI2 ]+ I- . Both the AuI and AuIII complex series were tested in the catalytic hydrohydrazination of terminal alkynes using hydrazine as nitrogen source.

Evaluation of natural materials as exogenous carbon sources for biological treatment of low carbon-to-nitrogen wastewater.

In the bacterial processes involved in the mitigation of nitrogen pollution, an adequately high carbon-to-nitrogen (C : N) ratio is key to sustain denitrification. We evaluated three natural materials (woodchips, barley grains, and peanut shells) as carbon sources for low C : N wastewater. The amount of organic matter released from these materials to aqueous media was evaluated, as well as their pollution swapping potential by measuring the release of total Kjeldahl nitrogen, N-NH4 (+), NO2 (-), and NO3 (-), and total phosphorous. Barley grains yielded the highest amount of organic matter, which also showed to be the most easily biodegradable. Woodchips and peanut shells released carbon rather steadily and so they would not require frequent replenishment from biological reactors. These materials produced eluates with lower concentrations of nutrients than the leachates from barley grains. However, as woodchips yielded lower amounts of suspended solids, they constitute an adequate exogenous source for the biological treatment of carbon-deficient effluents.

Copper(II) complexes supported by click generated mixed NN, NO, and NS 1,2,3-triazole based ligands and their catalytic activity in azide-alkyne cycloaddition.

The preparation and characterization of four new copper(ii) complexes supported by click generated mixed NN, NO, and NS 1,2,3-triazoles are reported. The four complexes display a 1 : 2 copper/ligand ratio and give monomeric units in the solid state. Crystal structures demonstrate that depending on the flexibility of the ligand NX (X = O, N, S) pendant arm, the coordination environment around the metal center can feature square planar or octahedral geometries. All four complexes are catalytically active at room temperature in a copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction using sodium ascorbate as a reducing agent and water-ethanol as a solvent mixture. Complex 8 supported by the NS ligand displayed the best catalytic performance of the series allowing for the easy and high yielding preparation of a variety of mono-, bis- and tris-1,2,3-triazoles under low catalyst loadings.

Resistance and inactivation kinetics of bacterial strains isolated from the non-chlorinated and chlorinated effluents of a WWTP.

The microbiological quality of water from a wastewater treatment plant that uses sodium hypochlorite as a disinfectant was assessed. Mesophilic aerobic bacteria were not removed efficiently. This fact allowed for the isolation of several bacterial strains from the effluents. Molecular identification indicated that the strains were related to Aeromonas hydrophila, Escherichia coli (three strains), Enterobacter cloacae, Kluyvera cryocrescens (three strains), Kluyvera intermedia, Citrobacter freundii (two strains), Bacillus sp. and Enterobacter sp. The first five strains, which were isolated from the non-chlorinated effluent, were used to test resistance to chlorine disinfection using three sets of variables: disinfectant concentration (8, 20 and 30 mg·L(-1)), contact time (0, 15 and 30 min) and water temperature (20, 25 and 30 °C). The results demonstrated that the strains have independent responses to experimental conditions and that the most efficient treatment was an 8 mg·L(-1) dose of disinfectant at a temperature of 20 °C for 30 min. The other eight strains, which were isolated from the chlorinated effluent, were used to analyze inactivation kinetics using the disinfectant at a dose of 15 mg·L(-1) with various retention times (0, 10, 20, 30, 60 and 90 min). The results indicated that during the inactivation process, there was no relationship between removal percentage and retention time and that the strains have no common response to the treatments.

DMD mediated formal synthesis of (+/-)-coerulescine.

A highly efficient method for the formal synthesis of the natural product (+/-)-coerulescine 1 from tetrahydro-beta-carboline 3, mediated by dimethyldioxirane (DMD), is described. Compound 15, the N9-demethylated precursor of 1, was prepared from 3 in 4 steps with an overall yield of 95%. The effect of electron withdrawing groups at the N2,N9 atoms of 3 was explored for the oxidative rearrangement step.

Synthesis of bromoindole alkaloids from Laurencia brongniartii.

A regioselective synthesis of N-carbomethoxy-2,3,5-tribromoindole (6) via a sequential one-pot bromination-aromatization-bromination of N-carbomethoxyindoline (2) is described. The process for the transformation of 2 into 6 permitted the isolation of stable reaction intermediates N-carbomethoxy-5-bromoindoline (3), N-carbomethoxy-5-bromoindole (4), and N-carbomethoxy-3,5-dibromoindole (5). Compound 6 was used to complete the total synthesis of the natural products 1b and 1c. In addition, bromination of N-carbomethoxyindole (11) afforded N-carbomethoxy-2,3,6-tribromoindole (13), from which the natural product 1a was synthesized.

Structure-activity relationships for inhibition of cysteine protease activity and development of Plasmodium falciparum by peptidyl vinyl sulfones.

The Plasmodium falciparum cysteine proteases falcipain-2 and falcipain-3 appear to be required for hemoglobin hydrolysis by intraerythrocytic malaria parasites. Previous studies showed that peptidyl vinyl sulfone inhibitors of falcipain-2 blocked the development of P. falciparum in culture and exerted antimalarial effects in vivo. We now report the structure-activity relationships for inhibition of falcipain-2, falcipain-3, and parasite development by 39 new vinyl sulfone, vinyl sulfonate ester, and vinyl sulfonamide cysteine protease inhibitors. Levels of inhibition of falcipain-2 and falcipain-3 were generally similar, and many potent compounds were identified. Optimal antimalarial compounds, which inhibited P. falciparum development at low nanomolar concentrations, were phenyl vinyl sulfones, vinyl sulfonate esters, and vinyl sulfonamides with P(2) leucine moieties. Our results identify independent structural correlates of falcipain inhibition and antiparasitic activity and suggest that peptidyl vinyl sulfones have promise as antimalarial agents.