Reliable quantification of copper binding affinities and identification of the binding sites provide a molecular basis for an understanding of the nutritional roles and toxic effects of copper ions. Sets of chromophoric probes are now available that can quantify Cu(i) binding affinities from nanomolar to attomolar concentrations on a unified scale under in vitro conditions. Equivalent probes for Cu(ii) are lacking. This work reports development of a set of four fluorescent dansyl peptide probes (DP1-4) that can quantify Cu(ii) binding affinities from micromolar to femtomolar concentrations, also on a unified scale. The probes were constructed by conjugation of a dansyl group to four short peptides of specific design. Each was characterised by its dissociation constant KD, its pH dependence and the nature of its binding site. One equivalent of Cu(ii) is bound by the individual probes that display different and well-separated affinities at pH 7.4 (log KD = -8.1, -10.1, -12.3 and -14.1, respectively). Intense fluorescence is emitted at λmax ∼ 550 nm upon excitation at ∼330 nm. Binding of Cu(ii) quenches the fluorescence intensity linearly until one equivalent of Cu(ii) is bound. Multiple approaches and multiple affinity standards were employed to ensure reliability. Selected examples of application to well-characterised Cu(ii) binding peptides and proteins are presented. These include Aβ16 peptides, two naturally occurring Cu(ii)-chelating motifs in human serum and cerebrospinal fluid with sequences GHK and DAHK and two copper binding proteins, CopC from Pseudomonas syringae and PcoC from Escherichia coli. Previously reported affinities are reproduced, demonstrating that peptides DP1-4 form a set of robust and reliable probes for Cu(ii) binding to peptides and protein targets.

= H) is reported. This is an isoelectronic variant of CO 2 extrusion−insertion (ExIn) reactions previously developed using heterocumulenes for the synthesis of thioamides (from isothiocyanates, RNCS), amidines (from carbodiimides, RNCNR), and amides (from isocyanates, RNCO). Evidence that the key aryl-palladium intermediate reacts to form a stable allyl-palladium product via insertion of the allene at the C2 position that enables the synthesis of alkenes was provided by a combination of gas-phase multistage mass spectrometry (MS n ) experiments and condensed-phase monitoring using 1 H NMR spectroscopy as well as theoretical computational data. Isolation and X-ray crystallographic analysis of the salt [(phen)Pd(CH 2 CH(Ar)CHPh)] + (CF 3 CO 2 − ) (where Ar = 2,6dimethoxyphenyl) confirmed insertion of the allene at the C2 position and revealed a syn relationship between the two aryl groups. A survey of different hydrogen sources to promote the removal of palladium from the alkene product revealed that NaBH 4 provides the highest yield and with the Z-alkene as the major isomer.

The gas-phase extrusion–insertion (ExIn) reactions of a silver complex [(BPS)Ag(O2CC6H5)]2− ([BPS]2− = 4,7-diphenyl-1,10-phenanthroline-disulfonate), generated via electrospray ionisation was investigated by Multistage Mass Spectrometry (MSn ) experiments in a linear ion trap combined with density functional theory (DFT) calculations. Extrusion of carbon dioxide under collision-induced dissociation (CID) generates the organosilver intermediate [(BPS)Ag(C6H5)]2−, which subsequently reacts with phenyl isocyanate via insertion to yield [(BPS)Ag(NPhC(O)C6H5)]2−. Further CID of the product ion resulted in the formation of [(BPS)Ag(C6H5)]2−, [(BPS)Ag]− and C6H5C(O)NPh−. The formation of a coordinated amidate anion is supported by DFT calculations. Heating a mixture of benzoic acid, phenyl isocyanate, silver carbonate (5 mol%) and phenanthroline (20 mol%) in DMSO and heating by microwave irradiation led to the formation N-phenyl-benzamide in an isolated yield of 89%. The yield decreased to 74% without the addition of phenanthroline, while replacing silver carbonate with sodium carbonate gave an isolated yield of 84%, suggesting that the ExIn reaction may not operate in solution. This was confirmed using benzoic acid with a 13C-isotopic-label at the carboxylate carbon as the starting material, which, under microwave heating in the presence of phenyl isocyanate, silver carbonate (5 mol%) and phenanthroline (20 mol%) gave N-phenyl-benzamide with retention of the 13C isotopic label based on GC-MS experiments under electron ionisation (EI) conditions. DFT calculations using a solvent continuum reveal that the barriers associated with the pathway involving direct attack by the non-coordinated benzoate are below the ExIn pathways for the coordinated silver benzoate.

Alzheimer's disease (AD) is associated with the presence of amyloid plaques in the brain mainly comprised of aggregated forms of amyloid-β (Aβ). Molecules radiolabeled with technetium-99m that cross the blood−brain barrier (BBB) and selectively bind to Aβ plaques have the potential to assist in the diagnosis of AD using single-photon emission computed tomography imaging. In this work, three new tetradentate ligands of pyridyl, amide, amine and thiol donors, featuring a styrylpyridyl group that is known to interact with amyloid plaques, were prepared. The new ligands formed charge-neutral and lipophilic complexes with the [TcO] 3+ and [ReO] 3+ motifs, and two rhenium complexes were characterized by X-ray crystallography. The rhenium(V) complexes interact with synthetic Aβ 1−40 and amyloid plaques on human brain tissue. Two of the new ligands were radiolabeled with 99m Tc using a kit-based approach, and their biodistribution in wild-type mice was evaluated. The presence of amide donors in the tetradentate ligand increased the stability of the respective [TcO] 3+ complexes but reduced brain uptake. While the complexes were able to cross the BBB, the degree of uptake in the brain was not sufficient to justify further investigation of these complexes.