Isothermal titration calorimetry of Ni(II) binding to histidine and to N-2-aminoethylglycine

Isothermal titration calorimetry (ITC) is used to study the complexation thermodynamics of Ni(II) with histidine (His) and with N-2-aminoethylglycine (EDMA). The titrations were performed in HEPES and Tris buffers at various ionic strengths and pH values around 8. The results show the influence of the experimental conditions on the shape and fitting parameters of the calorimetric curves. For the studied systems, the main reaction is concomitant with a number of side reactions which contribute to the global energy measured. From the calorimetric data measured, the formation constants for the species NiHEPES⁺, Tris⁺His⁻, TrisNiHis⁺ and [Ni(EDMA)₂OH]⁻ have been evaluated for the first time and the values obtained properly validated.     

Two flavors of PEPPSI-IPr: activation and diffusion control in a single NHC-ligated Pd catalyst?

Abnormal reactivity has been observed in Negishi, Suzuki-Miyaura, and Kumada-Tamao-Corriu cross-couplings in which PEPPSI-IPr (where PEPPSI stands for pyridine enhanced precatalyst preparation, stabilization, and initiation and IPr refers to the NHC ligand) is employed, implicating the presence of two distinct Pd(0) species in the catalytic cycle. Polybrominated arenes and organometallic reagents react selectively to give the product of exhaustive polysubstitution regardless of the initial reaction stoichiometry. Competition experiments suggest that, after an initial activation controlled oxidative addition, reductive elimination produces an ultrareactive Pd(0) species which consumes all remaining C-Br bonds in the molecule under diffusion control.     

Binaphthyl platform as starting materials for the preparation of electron rich benzo[g,h,i]perylenes. Application to molecular architectures based on amino benzo[g,h,i]perylenes and carborane combinations

Valuable amino benzo[g,h,i]perylenes have been obtained through a one pot electrophilic aromatic substitution--Scholl reaction sequence. Novel molecular architectures combining 3D-o-carborane and planar amino benzo[g,h,i]perylene units are described. Photophysical properties of amino benzo[g,h,i]perylene and the carborane-appended derivatives are discussed.     

Water-dispersible ultrathin Au nanowires prepared using a lamellar template of a long-chain amidoamine derivative

Straight ultrathin Au nanowires (NWs) with diameters less than 2 nm were synthesized using the lamellar structure of C18AA in an organogel and its selective adsorption for specific gold surfaces. In addition, the potential to form a bilayer structure with interdigitated hydrocarbon chains enabled the production of water-dispersible Au NWs without morphological change.     

Quinic acids from Aster caucasicus and from transgenic callus expressing a beta-amyrin synthase

Several different classes of secondary metabolites, including flavonoids, triterpenoid saponins and quinic acid derivatives, are found in Aster spp. (Fam. Asteraceae). Several Aster compounds revealed biological as well as pharmacological activities. In this work, a phytochemical investigation of A. caucasicus evidenced the presence of quinic acid derivatives, as well as the absence of triterpene saponins. To combine in one species the production of different phytochemicals, including triterpenes, an Agrobacterium-mediated transformation of A. caucasicus was set up to introduce A. sedifolius beta-amyrin synthase (AsOXA1)-encoding gene under the control of the constitutive promoter CaMV35S. The quali-quantitative analysis of transgenic calli with ectopic expression of AsOXA1 showed, in one sample, a negligible amount of triterpene saponins combined with higher amount of quinic acid derivatives as compared with the wild type callus.     

Controlling Antibacterial Activity Exclusively with Visible Light: Introducing a Tetra-ortho-Chloro-Azobenzene Amino Acid

The introduction of a novel tetra-ortho-chloroazobenzene amino acid (CEBA) has enabled photoswitching of the antimicrobial activity of tyrocidine A analogues by using exclusively visible light, granting spatiotemporal control under benign conditions. Compounds bearing this photoswitchable amino acid become active upon irradiation with red light, but quickly turn-off upon exposure to other visible light wavelengths. Critically, sunlight quickly triggers isomerisation of the red light-activated compounds into their original trans form, offering an ideal platform for self-deactivation upon release into the environment. Linear analogues of tyrocidine A were found to provide the best photocontrol of their antimicrobial activity, leading to compounds active against Acinetobacter baumannii upon isomerisation. Exploration of their N- and C-termini has provided insights into key elements of their structure and has allowed obtaining new antimicrobials displaying excellent strain selectivity and photocontrol.     

History of Cobaltabis(dicarbollide) in Potentiometry,No Need for Ionophores to Get an Excellent Selectivity

This work is a mini-review highlighting the relevance of the θ metallabis(dicarbollide) [3,3′-Co(1,2-C₂B₉H₁₁)₂]⁻ with its peculiar and differentiating characteristics, among them the capacity to generate hydrogen and dihydrogen bonds, to generate micelles and vesicles, to be able to be dissolved in water or benzene, to have a wide range of redox reversible couples and many more, and to use these properties, in this case, for producing potentiometric membrane sensors to monitor amine-containing drugs or other nitrogen-containing molecules. Sensors have been produced with this monoanionic cluster [3,3′-Co(1,2-C₂B₉H₁₁)₂]⁻. Other monoanionic boron clusters are also discussed, but they are much fewer. It is noteworthy that most of the electrochemical sensor species incorporate an ammonium cation and that this cation is the species to be detected. Alternatively, the detection of the borate anion itself has also been studied, but with significantly fewer examples. The functions of the borate anion in the membrane are different, even as a doping agent for polypyrrole which was the conductive ground on which the PVC membrane was deposited. Apart from these cases related to closo borates, the bulk of the work has been devoted to sensors in which the θ metallabis (dicarbollide) [3,3′-Co(1,2-C₂B₉H₁₁)₂]⁻ is the key element. The metallabis (dicarbollide) anion, [3,3′-Co(1,2-C₂B₉H₁₁)₂]⁻, has many applications; one of these is as new material used to prepare an ion-pair complex with bioactive protonable nitrogen containing compounds, [YH]_x[3,3′-Co(1,2-C₂B₉H₁₁)₂]_y as an active part of PVC membrane potentiometric sensors. The developed electrodes have Nernstian responses for target analytes, i.e., antibiotics, amino acids, neurotransmitters, analgesics, for some decades of concentrations, with a short response time, around 5 s, a good stability of membrane over 45 days, and an optimal selectivity, even for optical isomers, to be used also for real sample analysis and environmental, clinical, pharmaceutical and food analysis.     

Literatur

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