Investigating the formation of metal nitride complexes employing a tetradentate bis-carbene bis-phenolate ligand.

The synthesis of Mn and Cr nitride complexes of a pro-radical tetradentate bis-phenol bis-N-heterocyclic carbene ligand H2LC2O2 was investigated. Employing either azide photolysis of the Mn precursor complex MnLC2O2(N3) or a nitride exchange reaction between MnLC2O2(Br) and the nitride exchange reagent Mnsalen(N) failed to provide a useful route to the target nitride MnLC2O2(N). Experimental results support initial formation of the target nitride MnLC2O2(N), however, the nitride rapidly inserts into a Mn-C bond.

Structural and electrochemical properties of mononuclear copper(II) complexes with pentadentate ethylenediamine-based ligands with pyridine/quinoline/isoquinoline/quinoxaline binding sites.

-Monosubstituted ethylenediamine derivatives with three methylene-tethered aromatic groups ((ArCH)NCHCHN(R)CHAr (R-ArArAr), where Ar = 2-pyridyl, 2-quinolyl, 1- and 3-isoquinolyl and 2-quinoxalyl; R = methyl, benzyl and phenyl) were utilized as pentadentate ligands for copper(II) complexation. Fifteen mononuclear copper(II) complexes were synthesized and exhibit differences in cyclic voltammetry, absorption spectroscopy and solid state geometries, depending on the aromatic group (Ar) and the substituent on the aliphatic nitrogen atom (R) of the ligand. Compared with the pyridine and isoquinoline complexes, the quinoline and quinoxaline derivatives exhibit distinct Cu(II)/Cu(I) redox potentials and d-d transition absorption wavelengths.

Unusually short unsupported Au(III)⋯Au(III) aurophilic contacts in emissive lanthanide tetracyanoaurate(III) complexes.

A series of [Au(CN)] salts with lanthanide 2,2'-bipyridine dioxide cations features Au(III) aurophilic interactions between [Au(CN)] groups, with Au⋯Au distances of 3.3603(4) Å and 3.4354(4) Å that are shorter than any previously reported.

Untangling ancillary ligand donation locus of oxidation effects on metal nitride reactivity.

We detail the relative role of ancillary ligand electron-donating ability in comparison to the locus of oxidation (either metal or ligand) on the electrophilic reactivity of a series of oxidized Mn salen nitride complexes. The electron-donating ability of the ancillary salen ligand was tuned the -phenolate substituent (R = CF, H, Bu, OPr, NMe, NEt) in order to have minimal effect on the geometry at the metal center. Through a suite of experimental (electrochemistry, electron paramagnetic resonance spectroscopy, UV-vis-NIR spectroscopy) and theoretical (density functional theory) techniques, we have demonstrated that metal-based oxidation to [Mn(Sal)N] occurs for R = CF, H, Bu, OPr, while ligand radical formation to [Mn(Sal)N]˙ occurs with the more electron-donating substituents R = NMe, NEt.

Targeting misfolding and aggregation of the amyloid-β peptide and mutant p53 protein using multifunctional molecules.

Biomolecule misfolding and aggregation play a major role in human disease, spanning from neurodegeneration to cancer. Inhibition of these processes is of considerable interest, and due to the multifactorial nature of these diseases, the development of drugs that act on multiple pathways simultaneously is a promising approach. This Feature Article focuses on the development of multifunctional molecules designed to inhibit the misfolding and aggregation of the amyloid-β (Aβ) peptide in Alzheimer's disease (AD), and the mutant p53 protein in cancer.

Altering relative metal-binding affinities in multifunctional Metallochaperones for mutant p53 reactivation.

The p53 protein plays a major role in cancer prevention, and over 50% of cancer diagnoses can be attributed to p53 malfunction. p53 incorporates a structural Zn site that is required for proper protein folding and function, and in many cases point mutations can result in loss of the Zn ion, destabilization of the tertiary structure, and eventual amyloid aggregation. Herein, we report a series of compounds designed to act as small molecule stabilizers of mutant p53, and feature Zn-binding fragments to chaperone Zn to the metal depleted site and restore wild-type (WT) function.

Multifunctional metallochaperone modifications for targeting subsite cavities in mutant p53-Y220C.

The p53 protein, known as the 'guardian of the genome', plays an important role in cancer prevention. Unfortunately, p53 mutations result in compromised activity with over 50% of cancers resulting from point mutations to p53. There is considerable interest in mutant p53 reactivation, with the development of small-molecule reactivators showing promise.

Inhibition of p53 protein aggregation as a cancer treatment strategy.

The p53 protein plays a critical role in the prevention of genome mutations in the body, however, this protein is frequently mutated in cancer and almost all cancers exhibit malfunction along the p53 pathway. In addition to a loss of activity, mutant p53 protein is prone to unfolding and aggregation, eventually forming amyloid aggregates. There continues to be a considerable effort to develop strategies to restore normal p53 expression and activity and this review details recent advances in small-molecule stabilization of mutant p53 protein and the design of p53 aggregation inhibitors.

Chromium Nitride Umpolung Tuned by the Locus of Oxidation.

Oxidation of a series of Cr nitride salen complexes () with different -phenolate substituents (R = CF, tBu, NMe) was investigated to determine how the locus of oxidation (either metal or ligand) dictates reactivity at the nitride. -phenolate substituents were chosen to provide maximum variation in the electron-donating ability of the tetradentate ligand at a site remote from the metal coordination sphere. We show that one-electron oxidation affords Cr nitrides (; R = CF, tBu) and a localized Cr nitride phenoxyl radical for the more electron-donating NMe substituent ().

A role for bioinorganic chemistry in the reactivation of mutant p53 in cancer.

Metal ion dysregulation has been implicated in a number of diseases from neurodegeneration to cancer. While defective metal ion transport mechanisms are known to cause specific diseases of genetic origin, the role of metal dysregulation in many diseases has yet to be elucidated due to the complicated function (both good and bad!) of metal ions in the body. A breakdown in metal ion speciation can manifest in several ways from increased reactive oxygen species (ROS) generation to an increase in protein misfolding and aggregation.

Elaboration on the Electronics of Salen Manganese Nitrides: Investigations into Alkoxy-Substituted Ligand Scaffolds.

The ligand electronics of salen manganese nitride complexes directly influence the locus of oxidation and, thus, the reactivity of the resulting oxidized species. This work investigates the influence of -butoxy, isopropoxy, and methoxy substituents on the electronics of salen manganese nitride species and includes the first documentation of the para Hammett value for the -butoxy substituent (σ = -0.13 ± 0.

Exciton Coupling in Redox-Active Salen based Self-Assembled Metallacycles.

The incorporation of a redox-active nickel salen complex into supramolecular structures was explored via coordination-driven self-assembly with homobimetallic ruthenium complexes (bridged by oxalato or 5,8-dihydroxy-1,4-naphthoquinato ligands). The self-assembly resulted in the formation of a discrete rectangle using the oxalato complex and either a rectangle or a catenane employing the larger naphthoquinonato complex. The formation of the interlocked self-assembly was determined to be solvent and concentration dependent.

A balancing act: using small molecules for therapeutic intervention of the p53 pathway in cancer.

Referred to as the "guardian of the genome", p53 is the most frequently mutated protein in cancer and almost all cancers exhibit malfunction along the p53 pathway. As an overexpressed and tumour-specific target, the past two decades have seen considerable dedication to the development of small molecules that aim to restore wild-type function in mutant p53. In this review we collect and communicate the chemical principles involved in small molecule drug design for misfolded proteins in anticancer therapy.

Effect of Distortions on the Geometric and Electronic Structures of One-Electron Oxidized Vanadium(IV), Copper(II), and Cobalt(II)/(III) Salen Complexes.

The ligands '-bis(3--butyl-5-methoxysalicylidene)-1,2-ethanediamine and '-bis(3--butyl-5-methoxysalicylidene)-1,3-propanediamine were chelated to V(IV)═O (, ), Cu(II) (, ), Co(II) (), and Co(III) (). The X-ray crystal structures of - were solved. The vanadium center in - resides in square pyramidal geometry, with an axially bound oxo ligand, whereas the metal ion displays a tetrahedrally distorted square planar geometry in -.

Bifunctional ligand design for modulating mutant p53 aggregation in cancer.

Protein misfolding and aggregation contributes to the development of a wide range of diseases. In cancer, over 50% of diagnoses are attributed to p53 malfunction due to missense mutations, many of which result in protein misfolding and accelerated aggregation. p53 mutations also frequently result in alteration or loss of zinc at the DNA-binding site, which increases aggregation nucleation with zinc-bound p53.

Modification of Aβ Peptide Aggregation via Covalent Binding of a Series of Ru(III) Complexes.

Alzheimer's disease (AD) is the most common form of dementia, leading to loss of cognition, and eventually death. The disease is characterized by the formation of extracellular aggregates of the amyloid-beta (Aβ) peptide and neurofibrillary tangles of tau protein inside cells, and oxidative stress. In this study, we investigate a series of Ru(III) complexes () derived from NAMI-A in which the imidazole ligand has been substituted for pyridine derivatives, as potential therapeutics for AD.

Stabilization of different redox levels of a tridentate benzoxazole amidophenoxide ligand when bound to Co(iii) or V(v).

A tridentate benzoxazole-containing aminophenol ligand NNO was coordinated to Co and V metal centers and the electronic structure of the resultant complexes characterized by both experimental and theoretical methods. The solid state structure of the Co complex exhibits a distorted octahedral geometry with two tridentate ligands bound in meridional fashion, and coordination-sphere bond lengths consistent with a Co(iii) oxidation state. EPR and magnetic data support a S = 1/2 ground state, and a formal electronic description of Co(iii)(NNO)(NNO) where NNO corresponds to an amidophenoxide and NNO to the iminosemiquinone redox level.

Coordination-driven assembly of a supramolecular square and oxidation to a tetra-ligand radical species.

The design and synthesis of a supramolecular square was achieved by coordination-driven assembly of redox-active nickel(ii) salen linkers and (ethylenediamine)palladium(ii) nodes. The tetrameric geometry of the supramolecular structure was confirmed via MS, NMR, and electrochemical experiments. While oxidation of the monomeric metalloligand Schiff-base affords a Ni(iii) species, oxidation of the coordination-driven assembly results in ligand radical formation.

A catalytic antioxidant for limiting amyloid-beta peptide aggregation and reactive oxygen species generation.

Alzheimer's disease (AD) is a multifaceted disease that is characterized by increased oxidative stress, metal-ion dysregulation, and the formation of intracellular neurofibrillary tangles and extracellular amyloid-β (Aβ) aggregates. In this work we report the large affinity binding of the iron(iii) 2,17-bis-sulfonato-5,10,15-tris(pentafluorophenyl)corrole complex to the Aβ peptide ( ∼ 10) and the ability of the bound to act as a catalytic antioxidant in both the presence and absence of Cu(ii) ions. Specific findings are that: (a) an Aβ histidine residue binds axially to ; (b) that the resulting adduct is an efficient catalase; (c) this interaction restricts the formation of high molecular weight peptide aggregates.

Electronic Structure and Reactivity Studies of a Nonsymmetric One-Electron Oxidized Cu Bis-phenoxide Complex.

The tetradentate mixed imino/amino phenoxide ligand (N-(3,5-di-tert-butylsalicylidene)-N'-(2-hydroxyl-3,5-di-tert-butylbenzyl))-trans-1,2-cyclohexanediamine (salalen) was complexed with Cu, and the resulting Cu complex () was characterized by a number of experimental techniques and theoretical calculations. Two quasi-reversible redox processes for , as observed by cyclic voltammetry, demonstrated the potential stability of oxidized forms, and also the increased electron-donating ability of the salalen ligand in comparison to the salen analogue. The electronic structure of the one-electron oxidized [] was then studied in detail, and Cu K-edge X-ray Absorption Spectroscopy (XAS) measurements confirmed a Cu-phenoxyl radical complex in solution.

Multifunctional Compounds for Activation of the p53-Y220C Mutant in Cancer.

The p53 protein plays a major role in cancer prevention, and over 50 % of cancer diagnoses can be attributed to p53 malfunction. The common p53 mutation Y220C causes local protein unfolding, aggregation, and can result in a loss of Zn in the DNA-binding domain. Structural analysis has shown that this mutant creates a surface site that can be stabilized using small molecules, and herein a multifunctional approach to restore function to p53-Y220C is reported.

Evaluation of Tc-sulfonamide and sulfocoumarin derivatives for imaging carbonic anhydrase IX expression.

With the aim to prepare hypoxia tumor imaging agents, technetium(I) and rhenium(I) tricarbonyl complexes with dipyridylamine (L1 = N-{[1-(2,2-dioxido-1,2-benzoxathiin-6-yl)-1H-1,2,3-triazol-4-yl]methyl}-N-(2-pyridinylmethyl)-2-pyridinemethanamine; L3 = N-{[1-[N-(4-aminosulfonylphenyl)]-1H-1,2,3-triazol-4-yl]methyl}-N-(2-pyridinyl-methyl)-2-pyridinemethanamine), and iminodiacetate (HL2 = N-{[1-(2,2-dioxido-1,2-benzoxathiin-6-yl)-1H-1,2,3-triazole-4-yl]methyl}-N-(carboxy-methyl)-glycine; HL4 = N-{[1-[N-(4-aminosulfonylphenyl)]-1H-1,2,3-triazole-4-yl]methyl}-N-(carboxymethyl)-glycine) ligands appended to sulfonamide or sulfocoumarin carbonic anhydrase inhibitors were synthesized. The Re(I) complexes were characterized using H/C NMR, MS, EA, and in one case the X-ray structure of [EtNH][Re(CO)(L2)] was obtained. As expected, the Re coordination geometry is distorted octahedral, with a tridentate iminodiacetate ligand in a fac arrangement dictated by the three strong-field CO ligands.

Exploiting exciton coupling of ligand radical intervalence charge transfer transitions to tune NIR absorption.

We detail the rational design of a series of bimetallic bis-ligand radical Ni salen complexes in which the relative orientation of the ligand radical chromophores provides a mechanism to tune the energy of intense intervalence charge transfer (IVCT) bands in the near infrared (NIR) region. Through a suite of experimental (electrochemistry, electron paramagnetic resonance spectroscopy, UV-vis-NIR spectroscopy) and theoretical (density functional theory) techniques, we demonstrate that bimetallic Ni salen complexes form bis-ligand radicals upon two-electron oxidation, whose NIR absorption energies depend on the geometry imposed in the bis-ligand radical complex. Relative to the oxidized monomer [] ( = 4500 cm, = 27 700 M cm), oxidation of the cofacially constrained analogue to [] results in a blue-shifted NIR band ( = 4830 cm, = 42 900 M cm), while oxidation of to [], with parallel arrangement of chromophores, results in a red-shifted NIR band ( = 4150 cm, = 46 600 M cm); the NIR bands exhibit double the intensity in comparison to the monomer.

Electronic Structure and Reactivity of One-Electron-Oxidized Copper(II) Bis(phenolate)-Dipyrrin Complexes.

The sterically hindered bis(phenol)-dipyrrin ligands LH and LH were reacted with 1 equiv of copper(II) under ambient conditions to produce the copper radical complexes [Cu(L)] and [Cu(L)]. Their X-ray crystal structures show relatively short C-O bond distances (mean bond distances of 1.287 and 1.