p-tert-Butylcalix[4]arene complexes of molybdenum and tungsten: reactivity of the calixarene methylene C-H bond and the facile migration of the metal around the phenolic rim of the calixarene

p-tert-Butylcalix[4]arene, [CalixBut(OH)4], reacts with Mo(PMe3)6 and W(PMe3)4(eta2-CH2PMe2)H to yield compounds of composition {[CalixBut(OH)2(O)2]M(PMe3)3H2} which exhibit unprecedented use of a C-H bond of a calixarene methylene group as a binding functionality in the form of agostic and alkyl hydride derivatives. Thus, X-ray diffraction studies demonstrate that, in the solid state, the molybdenum complex [CalixBut(OH)2(O)2]Mo(PMe3)3H2 exists as an agostic derivative with a Mo...H-C interaction, whereas the tungsten complex exists as a metallated trihydride [Calix-HBut(OH)2(O)2]W(PMe3)3H3. Solution 1H NMR spectroscopic studies, however, provide evidence that [Calix-HBut(OH)2(O)2]W(PMe3)3H3 is in equilibrium with its agostic isomer [CalixBut(OH)2(O)2]W(PMe3)3H2. Dynamic NMR spectroscopy also indicates that the [M(PMe3)3H2] fragments of both the molybdenum and tungsten complexes [CalixBut(OH)2(O)2]M(PMe3)3H2 migrate rapidly around the phenolic rim of the calixarene on the NMR time scale, an observation that is in accord with incorporation of deuterium into the methylene endo positions upon treatment of the isomeric mixture of [CalixBut(OH)2(O)2]W(PMe3)3H2 and [Calix-HBut(OH)2(O)2]W(PMe3)3H3 with D2. Treatment of {[CalixBut(OH)2(O)2]W(PMe3)3H2} with Ph2C2 gives the alkylidene complex [CalixBut(O)4]W=C(Ph)Ar [Ar = PhCC(Ph)CH2Ph].     

Palladium complexes with Pd-->B dative bonds: analysis of the bonding in the palladaboratrane compound [kappa4-B(mimBut)3]Pd(PMe3)

The dinuclear complex {[mu-kappa(1),kappa(3)-B(mim(Bu(t)))(3)]Pd}(2), which features a Pd-->B dative bond, may be obtained by the reaction of [Tm(Bu(t))]K with Pd(OAc)(2); treatment of {[mu-kappa(1),kappa(3)-B(mim(Bu(t)))(3)]Pd}(2) with PMe(3) affords the mononuclear boratrane derivative [kappa(4)-B(mim(Bu(t)))(3)]Pd(PMe(3)), for which a molecular orbital analysis indicates that the palladium center possesses a d(8) configuration.     

Coordination chemistry of 5,6,7-trimethyl-[1,2,4]triazolo[1,5-a]pyrimidine with first-row transition-metal salts: Synthesis, spectroscopy and single-crystal structures, with counter-anion dependence of the structures

A variety of new coordination compounds with transition-metal salts and the ligand trimethyl[1,2,4]triazolo[1,5-a]pyrimidine (abbreviated as tmtp) is described, together with several of their 3D crystal structures and spectroscopic and magnetic properties. The compounds were selected based on the coordination ability of the counterion, halide, nitrate, sulfate, thiocyanate and perchlorate. The formed coordination compounds and their coordination numbers were found to be strongly dependent on both the cation and the used counter-anion. The several compounds studied have the following structural formulae: [CuCl₂(tmtp)₂], [CuBr₂(tmtp)₂], [ZnBr₂(tmtp)₂], [Cu(NO₃)₂(tmtp)₂], [CuSO₄(tmtp)₂]₂(H₂O)(MeOH), [Cu(H₂O)(NCS)₂(tmtp)₂], [Zn(NCS)₂(tmtp)₂], [Cd(NCS)₂(tmtp)₂] and [M(H₂O)₂(tmtp)₄](BF₄)₂, in which M = Co, Ni, Zn.The new coordination compounds have been further characterized by NMR, (far-)IR and LF spectra, as well as by C, H, N element analyses, and EPR spectra for the Cu(II) compounds. The coordination around the metal varies from 4 (Zn, Cu), via 5 (Cu) to 6 (for Co, Cu and Cd). The anions usually complete the coordination sphere; only the Co and Zn compounds with the tetrafluoridoborate anions have no coordinated anions, but water ligands complete the octahedral coordination sphere. In the 5-coordinated [Cu(H₂O)(NCS)₂(tmtp)₂] water completes the square pyramid geometry.     

Copper perchlorate and tetrafluoridoborate compounds with the ligand 1,4,5-triazanaphthalene. Gradual transformation of mononuclear Cu(II) compounds via polynuclear mixed-valence Cu(II)/Cu(I) species to dinuclear Cu(I); syntheses, characterizations and X-ray structures

When the ligand 1,4,5-triazanaphthalene (abbreviated as tan) is reacted with Cu(II) BF(4)(-) and ClO(4)(-) salts, a variety of mononuclear compounds has been found, all with the [Cu(tan)(4)] unit and varying amounts of weakly coordinating axial ligands and lattice solvents. Reproducible compounds formed include two purple compounds, analyzing as [Cu(tan)(4)](ClO(4))(2)(CH(3)OH)(2)(H(2)O) (1) and [Cu(tan)(4)](BF(4))(2)(CH(3)OH)(1.5)(H(2)O) (3), and two blue compounds, analyzing as [Cu(tan)(4)](ClO(4))(2)(H(2)O)(2) (2) and [Cu(tan)(4)](2)(BF(4))(2)(H(2)O)(2) (4). Upon standing at room temperature, red-coloured, mixed-valence dinuclear-based 3D coordination polymers are formed by conversion of the purple/blue products, of which [Cu(2)(tan)(4)](n)(BF(4))(3n) (5) and the isomorphic methanol-water adduct [Cu(tan)(4)](n)(BF(4))(3n)(CH(3)OH)(n)(H(2)O)(5n) (5A) are presented in this paper. In addition a fully reduced dinuclear Cu(I) compound of formula [Cu(2)(tan)(3)(ClO(4))(2)] (7) has been observed, and structurally characterized, as a rare three-blade propeller structure, with a Cu-Cu distance of 2.504 ?.     

Where organometallics and dendrimers merge: the incorporation of organometallic species into dendritic molecules

This review will describe the ongoing efforts being made to incorporate organometallic fragments into the framework of dendrimers. While purely dendritic organic molecules are well known and well studied, species incorporating organometallic moieties potentially offer many benefits that are not available to only organic containing dendrimers. For example, catalytic or redox active organometallic functions can be included in the dendritic framework and impart these characteristics onto the dendrimer. This report will give an overview of the latest developments in this field by highlighting selected examples that detail novel synthetic strategies or dendrimer construction methodologies, interesting practical applications or address specific problems associated with organometallic dendrimers.     

Enantioselective Artificial Metalloenzymes Based on a Bovine Pancreatic Polypeptide Scaffold

Site creation : Enantioselective artificial metalloenzymes have been created by grafting a new active site onto bovine pancreatic polypeptide through the introduction of an amino acid capable of coordinating a copper(II) ion. This hybrid catalyst gave good enantioselectivities in the Diels–Alder and Michael addition reactions in water (see scheme) and displayed a very high substrate selectivity.

     

Bile UPLC-MS fingerprinting and bile acid fluxes during human liver transplantation

Bile flow restoration is a crucial step in the recovery process post transplantation of the liver. Here, metabolic trajectories based on changes in bile secretion - a known marker of functionality - have been utilised as an approach for discovering bile fluxes during transplantation. A total of ten liver transplants were monitored and from these 68 bile samples from both donors and recipients were collected and analysed using ultra-performance LC-MS in combination with multivariate statistical analysis. Based on the principal component scores constructed from the total bile fingerprint, differentiation of the bile acid concentrations before and after transplantation was detected. A trend was also observed, by constructing metabolic trajectories, whereby the post-transplant profiles approached the position of pre-transplant profiles within 30-60?min of the restoration of bile secretion function. The ten major conjugated bile acid salts were measured and a significant increase in concentrations of taurocholic acid and taurochenodeoxycholic acid were seen after transplantation. In addition, the ratios of secondary bile acids detected in gall bladder and hepatic bile were measured before and after transplantation. This study suggests that bile acid ratios in the donor liver at the pre-transplant and post-transplant stage may be important and that profiling of secreted bile after transplantation may aid clinical assessment and progress post-transplantation.     

Single electron transfer events and dynamical heterogeneity in the small protein azurin from Pseudomonas aeruginosa

Monitoring the fluorescence of single-dye-labeled azurin molecules, we observed the reaction of azurin with hexacyanoferrate under controlled redox potential yielding data on the timing of individual (forward and backward) electron transfer (ET) events. Change-point analysis of the time traces demonstrates significant fluctuations of ET rates and of mid-point potential E₀. These fluctuations are a signature of dynamical heterogeneity, here observed on a 14 kDa protein, the smallest to date. By correlating changes in forward and backward reaction rates we found that 6% of the observed change events could be explained by a change in midpoint potential, while for 25% a change of the donor–acceptor coupling could explain the data. The remaining 69% are driven by variations in complex association constants or structural changes that cause forward and back ET rates to vary independently. Thus, the observed spread in individual ET rates could be related in a unique way to variations in molecular parameters. The relevance for the understanding of metabolic processes is briefly discussed.

Observing electron transfer events in individual azurin molecules, we relate the spread in transfer rates in a unique way to variations in molecular parameters.     

A small molecule discrimination map of the antibiotic resistance kinome

Kinase-mediated resistance to antibiotics is a significant clinical challenge. These enzymes share a common protein fold characteristic of Ser/Thr/Tyr protein kinases. We screened 14 antibiotic resistance kinases against 80 chemically diverse protein kinase inhibitors to map resistance kinase chemical space. The screens identified molecules with both broad and narrow inhibition profiles, proving that protein kinase inhibitors offer privileged chemical matter with the potential to block antibiotic resistance. One example is the flavonol quercetin, which inhibited a number of resistance kinases in vitro and in vivo. This activity was rationalized by determination of the crystal structure of the aminoglycoside kinase APH(2″)-IVa in complex with quercetin and its antibiotic substrate kanamycin. Our data demonstrate that protein kinase inhibitors offer chemical scaffolds that can block antibiotic resistance, providing leads for co-drug design.     

Monomers and polymers from plant oils via click chemistry reactions

As a consequence of the depleting of fossil reserves and environmental issues, today, plant oils and fatty acids derived therefrom have a respectable status within the polymer chemistry community. However, maximizing the benefits of these renewable feedstocks requires the utilization of sustainable and efficient chemical transformations. The emergence of click chemistry concept and especially the renaissance of thiol‐ene addition reaction have had an impact on the way to make plant oil‐derived polymers. This highlight discusses the applicability and success of thiol‐ene addition and other click reactions in the transformation of oleochemicals into monomers and polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013