Structural and electrochemical comparison of trinuclear ruthenium oxo clusters [Ru(OAc)O(L)]and [Ru(OAc)O(L)(CO)] (L = imidazole, benzimidazole, and 4-phenylpyridine).

The triruthenium oxo clusters [Ru(OAc)O(L)] and [Ru(OAc)O(L)(CO)] possess unique electronic characteristics that vary based on the ligands L. Here we report an investigation of the structural, electrochemical, and optical properties of clusters with imidazole, benzimidazole, and 4-phenylpyridine ligands. The complexes [Ru(OAc)O(L)] [1: L = imidazole (im); 2: L = benzimidazole (benzim); 3: L = 4-phenylpyridine (4PP)] and [Ru(OAc)O(L)(CO)] (1-CO and 3-CO) were synthesized by reaction of either [Ru(OAc)O(MeOH)] or [Ru(OAc)O(MeOH)(CO)], respectively, with the corresponding heterocycle.

Nanodiscs as a Modular Platform for Multimodal MR-Optical Imaging.

Nanodiscs are monodisperse, self-assembled discoidal particles that consist of a lipid bilayer encircled by membrane scaffold proteins (MSP). Nanodiscs have been used to solubilize membrane proteins for structural and functional studies and deliver therapeutic phospholipids. Herein, we report on tetramethylrhodamine (TMR) tagged nanodiscs that solubilize lipophilic MR contrast agents for generation of multimodal nanoparticles for cellular imaging.

Modulation of amyloid-β aggregation by histidine-coordinating Cobalt(III) Schiff base complexes.

Oligomers of the Aβ42 peptide are significant neurotoxins linked to Alzheimer's disease (AD). Histidine (His) residues present at the N terminus of Aβ42 are believed to influence toxicity by either serving as metal-ion binding sites (which promote oligomerization and oxidative damage) or facilitating synaptic binding. Transition metal complexes that bind to these residues and modulate Aβ toxicity have emerged as therapeutic candidates.

Axial ligand exchange of N-heterocyclic cobalt(III) Schiff base complexes: molecular structure and NMR solution dynamics.

The kinetic and thermodynamic ligand exchange dynamics are important considerations in the rational design of metal-based therapeutics and therefore, require detailed investigation. Co(III) Schiff base complex derivatives of bis(acetylacetone)ethylenediimine [acacen] have been found to be potent enzyme and transcription factor inhibitors. These complexes undergo solution exchange of labile axial ligands.

Cobalt derivatives as promising therapeutic agents.

Inorganic complexes are versatile platforms for the development of potent and selective pharmaceutical agents. Cobalt possesses a diverse array of properties that can be manipulated to yield promising drug candidates. Investigations into the mechanism of cobalt therapeutic agents can provide valuable insight into the physicochemical properties that can be harnessed for drug development.

Synapse-binding subpopulations of Aβ oligomers sensitive to peptide assembly blockers and scFv antibodies.

Amyloid β42 self-assembly is complex, with multiple pathways leading to large insoluble fibrils or soluble oligomers. Oligomers are now regarded as most germane to Alzheimer's pathogenesis. We have investigated the hypothesis that oligomer formation itself occurs through alternative pathways, with some leading to synapse-binding toxins.

Analytical methods for characterizing magnetic resonance probes.

The efficiency of Gd(III) contrast agents in magnetic resonance image enhancement is governed by a set of tunable structural parameters. Understanding and measuring these parameters requires specific analytical techniques. This Feature describes strategies to optimize each of the critical Gd(III) relaxation parameters for molecular imaging applications and the methods employed for their evaluation.

Trinuclear ruthenium clusters as bivalent electrochemical probes for ligand-receptor binding interactions.

Despite their popularity, electrochemical biosensors often suffer from low sensitivity. One possible approach to overcome low sensitivity in protein biosensors is to utilize multivalent ligand-receptor interactions. Controlling the spatial arrangement of ligands on surfaces is another crucial aspect of electrochemical biosensor design.

A Three-Channel Spectrometer for Wide-Field Imaging of Anisotropic Plasmonic Nanoparticles.

A three-channel spectrometer (3CS) based on a commercial digital camera was developed to distinguish among tens of large (>100 nm), anisotropic plasmonic particles with various shapes, orientations, and compositions on a surface simultaneously. Using band pass filters and polarizers, the contrast of 3CS images could be enhanced to identify specific orientation and composition characteristics of gold and gold-silver nanopyramids and as well as the direction of the longest arm of gold nanostars.

Probing the Chemical Stability of Mixed Ferrites: Implications for MR Contrast Agent Design.

Nanomaterials with mixed composition, in particular magnetic spinel ferrites, are emerging as efficient contrast agents for magnetic resonance imaging (MRI). Many factors, including size, composition, atomic structure, and surface properties are crucial in the design of such nanoparticle-based probes due to their influence on the magnetic properties. Silica-coated iron oxide (IO-SiO(2)) and cobalt ferrite (CoIO-SiO(2)) nanoparticles were synthesized using standard high temperature thermal decomposition and base-catalyzed water-in-oil microemulsion techniques.

A modular system for the synthesis of multiplexed magnetic resonance probes.

We have developed a modular architecture for preparing high-relaxivity multiplexed probes utilizing click chemistry. Our system incorporates azide bearing Gd(III) chelates and a trialkyne scaffold with a functional group for subsequent modification. In optimizing the relaxivity of this new complex, we undertook a study of the linker length between a chelate and the scaffold to determine its effect on relaxivity.

Electrochemistry of redox-active self-assembled monolayers.

Redox-active self-assembled monolayers (SAMs) provide an excellent platform for investigating electron transfer kinetics. Using a well-defined bridge, a redox center can be positioned at a fixed distance from the electrode and electron transfer kinetics probed using a variety of electrochemical techniques. Cyclic voltammetry, AC voltammetry, electrochemical impedance spectroscopy, and chronoamperometry are most commonly used to determine the rate of electron transfer of redox-activated SAMs.

Highly dispersible, superparamagnetic magnetite nanoflowers for magnetic resonance imaging.

A one-pot reaction process was developed to synthesize highly dispersible, superparamagnetic Fe(3)O(4) nanoflowers; the potential of these nanoflowers as MRI contrast agents was investigated.

Ultrasmall, Water-Soluble Magnetite Nanoparticles with High Relaxivity for Magnetic Resonance Imaging.

Ultrasmall (3, 4, 5, and 6 nm), water-soluble FeO magnetic nanoparticles were synthesized in diethylene glycol (DEG) via a facile one-pot reaction. Hydrodynamic size and relaxation time measurements did not show particle aggregation when FeO nanoparticles were dispersed in phosphate buffered saline, fetal bovine serum, or calf bovine serum for 1 week. Furthermore, the new FeO nanoparticles tolerated high salt concentrations (≤1 M NaCl) and a wide pH range from 5 to 11.

Kinetic dispersion in redox-active dithiocarbamate monolayers.

Dithiocarbamates (dtcs) have been implicated as important gold-binding groups in molecular electronics. Dtcs have two alkane branches connected at a single anchoring point that has a bidentate resonance structure. Forming readily in situ by the combination of secondary amines and CS(2), dtcs adsorb quickly onto gold surfaces.

Protein binding and the electronic properties of iron(II) complexes: an electrochemical and optical investigation of outer sphere effects.

Metalloenzymes and electron transfer proteins influence the electrochemical properties of metal cofactors by controlling the second-sphere environment of the protein active site. Properties that tune this environment include the dielectric constant, templated charge structure, van der Waals interactions, and hydrogen bonds. By systematically varying the binding of a redox-active ligand with a protein, we can evaluate how these noncovalent interactions alter the electronic structure of the bound metal complex.

Electroactive self-assembled monolayers on gold via bipodal dithiazepane anchoring groups.

Novel dithiazepane-functionalized ferrocenyl-phenylethynyl oligomers 1 and 2 have been synthesized. Self-assembled monolayers (SAMs) of these ferrocene derivatives have been studied by X-ray photoelectron spectroscopy, ellipsometry, and cyclic voltammetry. It has been shown by XPS that monolayers of the dithiazepane-anchored molecules on gold electrodes contain gold-thiolate species.

Mechanistic investigation of beta-galactosidase-activated MR contrast agents.

We report a mechanistic investigation of an isomeric series of beta-galactosidase-activated magnetic resonance contrast agents. Our strategy focuses on the synthesis of macrocyclic caged-complexes that coordinatively saturate a chelated lanthanide. Enzyme cleavage of the complex results in an open coordination site available for water that creates a detectable MR contrast agent.

Synthesis and characterization of ruthenium and rhenium nucleosides.

We report the synthesis and characterization of new ruthenium and rhenium nucleosides [Ru(tolyl-acac)2(IMPy)-T] (tolyl-acac=di(p-methylbenzonatemethane), IMPy=2'-iminomethylpyridine, T=thymidine) (5) and [Re(CO)3(IMPy)-T]Cl (9), respectively. Structural analysis of 9 shows that the incorporation of this metal complex causes minimal perturbation to the sugar backbone and the nucleobase. Eletrochemical (5, E1/2=0.

Synthesis and electrochemical characterization of a transition-metal-modified ligand-receptor pair.

The energetics of weak interactions (van der Waals forces, hydrogen bonding) are difficult to quantify in biological ligand-receptor pairs. Insight into the biochemical role these forces play is critical to an understanding of signal transduction events and the drug discovery process. Ruthenium pentaammine and iron tetracyano complexes modified with either biotin or desthiobiotin have been synthesized and characterized.

Syntheses of the 47 electron clusters [(Cp*Fe)3(mu3-X)2] (X = S, Se) and the First Fe/Sn/Se Heterocubane Cluster [(CpFe)3(SnCl3)(mu3-Se)4] x DME by the use of chalcogenostannate salts.

By reacting 1-aminoethylammonium (H2NCH2CH2NH3+ = enH+) salts of [Sn2E6]4- anions (E = S, Se), [enH]4[Sn2S6] (1) and [enH]4[Sn2Se6] x en (2), with FeCl2/LiCp, three novel (partly) oxidized, Cp* ligated iron chalcogenide clusters were synthesized. Two of them, [(CpFe)3(mu3-S)2] (3) and [(Cp*Fe)3(mu3-Se)2] (4), contain formally 47 valence electrons. [(Cp*Fe)3(SnCl3)(mu3-Se)4] x DME (5) represents the first known mixed metal Fe/Sn/Se heterocubane type cluster.

New class of ruthenium sulfide clusters: Ru(4)S(6)(PPh(3))(4), Ru(5)S(6)(PPh(3))(5), and Ru(6)S(8)(PPh(3))(6).

Reaction of RuCl(2)(PPh(3))(3) with S(2)(-) sources yields a family of phosphine-containing Ru-S clusters which have been characterized crystallographically and by MALDI-MS. Ru(4)S(6)(PPh(3))(4) (Ru-Ru(av) = 2.94 A) has idealized T(d)() symmetry whereas Ru(6)S(8)(PPh(3))(6) (Ru-Ru(av) = 2.