Development of New Linking Chemistry with the fac-{Re(CO)3}+ Core for Eventual Applications in Radiopharmaceuticals in Imaging and Therapy

The facile labeling of biomolecules with a radionuclide is a key goal in radiopharmaceutical development. This study explores two different ligand systems for fac-[Re(CO)3L]+ complexes, that could be used in bioconjugation. The first approach uses a tridentate ligand having a sulfonamide linkage and modeled on previously evaluated fac-[Re(CO)3(N(SO2R)dpa)]PF6 complexes. The present goal was to develop new related sulfonamide complexes with more hydrophilic ligands designed to avoid the bioavailability problems that would plague the N(SO2R)dpa ligand system. A series of fac-[Re(CO)3(N(SO2R)dien)]PF6 complexes with different R groups linked to the central nitrogen of a symmetric tridentate sulfonamides were synthesized with the aim of improving the favorable in vivo bioavailability. These compounds are characterized by NMR spectroscopy and by X-ray crystallography. The second approach using monodentate ligands led to the synthesis of several amidine complexes. The challenge of avoiding isomers of amidine complexes was overcome by using C2-symmetrical heterocyclic secondary amines with 6-membered and larger rings to create an amidine substituent bulkier than the amidine CCH3 group. Treatment of fac-[Re(CO)3(Me2bipy)(CH3CN)] BF4 with these amines in organic solvents yielded novel fac-[Re(CO)3(Me2bipy)(HNC(CH3)N(CH2)2Y)]BF4 complexes having only one isomer with the E configuration as established by solid-state and 1H NMR spectroscopic data. The combination of the high steric bulk and the C2-symmetry of the amidine substituents favors the E configuration exclusively. I extended the chemistry to smaller heterocyclic amines with 4- and 5-membered rings and found amidine formation reactions were faster. Moreover, I also showed that the amidine formation reactions were faster when the methyl group of fac-[Re(CO)3(Me2bipy)(CH3CN)]BF4 was replaced by a phenyl group. A series of fac-[Re(CO)3(Me2bipy)(HNC(C6H5)N(CH2)x)]+ complexes were synthesized, characterized and used in the comparison with the analogous fac-[Re(CO)3(Me2bipy)(HNC(CH3)N(CH2)x)]+ complexes in order to understand the properties of amidine complexes and to correlate the structural features with their behavior in solution. Furthermore, a new method employing the fac-[Re(CO)3(H2O)3]+ precursor successfully demonstrated the synthesis of fac-[Re(CO)3(Me2bipy)(amidine)]+ complexes in more aqueous conditions. This new method holds promise for use in biomedical studies

Cyclohepta[de]naphthalenes and the Rearranged Abietane Framework of Microstegiol via Nicholas Reaction Chemistry

Nicholas reactions on 2,7-dioxygenated naphthalenes give C-1 monosubstitution and C-1/C-8 disubstitution in most cases. From gamma-carbonyl cation monocondensation product 3b or alkyne-unsubstituted dicondensation product 4a, cyclohepta[de]naphthalenes bearing no substituents, gem-dimethyl substituents, and a ketone function, and the rearranged abietane framework of microstegiol may be prepared

Nucleic-acid recognition interfaces: How the greater ability of RNA duplexes to bend towards the surface influences electrochemical sensor performance

The influence of RNA versus DNA on the performance of electrochemical biosensors where redox-labelled nucleic acid duplexes bend towards the electrode surface has been assessed. Faster electron transfer was observed for duplexes containing RNA, suggesting duplexes with RNA are more flexible. These data are of particular importance for microRNA biosensors

The rapid formation of functional monolayers on silicon under mild conditions

We report on an exceedingly mild chemical functionalization of hydrogen-terminated Si(100) with unactivated and unprotected bifunctional α,ω-dialkynes. Monolayer formation occurs rapidly in the dark, and at room temperature, from dilute solutions of an aromatic-conjugated acetylene. The method addresses the poor reactivity of p-type substrates under mild conditions. We suggest the importance of several factors, including an optimal orientation for electron transfer between the adsorbate and the Si surface, conjugation of the acetylenic function with a π-system, as well as the choice of a solvent system that favors electron transfer and screens Coulombic interactions between surface holes and electrons. The passivated Si(100) electrode is amenable to further functionalization and shown to be a viable model system for redox studies at non-oxide semiconductor electrodes in aqueous solutions

Synthesis and electron transfer studies of anthraquinones

Bibliography: p. 185-18

Ta-Based Nanostructured Materials for Proton Exchange Membrane Fuel Cells

The focus of this work has been to assess the suitability of nanostructured TaOxNy, primarily as nanotubes (NTs), as a catalyst and/or catalyst support material for proton exchange membrane fuel cell (PEMFC) applications. It was found that this n-type material could be switched between an insulating state at > 0.6 V vs RHE to a conducting state at < 0.6 V in both aqueous and organic media. In the conducting state, the redox activity was proposed to be due to the Ta4+/5+ reaction, along with insertion/de-insertion of solution cations. The conductivity switching behavior was correlated with electrochromism, with the NTs being yellow-orange in the oxidized state and blue-black when reduced. TaOxNy was then tested for its activity in catalyzing hydrogen oxidation (HOR) and oxygen reduction (ORR) in acidic medium. Although TaOxNy alone is inactive towards these reactions, the presence of Pt nanoparticles (NPs) changed its behaviour. When deposited on a thin compact TaOxNy film, normal Pt electrochemistry was seen with a ~60 mV⋅decade-1 ORR Tafel slope. When Pt NPs were deposited on TaOxNy NTs, a 105 mV⋅decade-1 ORR Tafel slope was seen attributed to porosity or resistance of the TaOxNy. Both the TaOxNy NTs alone and the Pt NPs/TaOxNy NTs material were found to be very resistant to corrosion under PEMFC operating conditions, evaluated through an in-house accelerated durability test. Further, due to its conductivity switching characteristics, the HOR showed better performance than the ORR, but not as good as for state-of the art Pt/Carbon. Interestingly, some hydrogen oxidation was seen even when TaOxNy is non-conducting, attributed to stabilization of the Ta4+ state in H2. TaOxNy was also anchored on colloid imprinted carbon (CIC) to improve its conductivity and durability. Although the CIC improved the conductivity, all CIC-based materials failed the corrosion accelerated durability tests (ADT). The presence of TaOxNy or N-doping of CIC (N is doped during synthesis) also did not improve the corrosion resistance. Overall, TaOxNy was shown to be a very durable material, resistant to corrosion even at very high anodic potentials. It is also a promising support material for Pt NPs for the catalysis of the HOR, but its conductivity likely needs to be improved further in order to catalyze the ORR