Investigations into the mechanism of copper-mediated Glaser-Hay couplings using electrochemical techniques.

The mechanism of the copper mediated C-C bond forming reaction known as Glaser-Hay coupling (alkyne dimerization) has been investigated using electrochemical techniques. Applying an oxidative potential to a copper or copper-coated graphite electrode in the presence of the organic base DABCO results in the dimerization of phenylacetylene in good yield. Further mechanistic investigation has shown that this reaction medium results in the assembly of a dinuclear Cu(i) complex which, although previously reported, has never been shown to have catalytic properties for C-C bond formation. The complex is reminiscent of that proposed in the Bohlmann model for the Glaser-Hay reaction and as such lends weight to this proposed mechanism above the alternative proposed mononuclear catalytic cycle.

Electrochemical Fouling of Dopamine and Recovery of Carbon Electrodes.

A significant problem with implantable sensors is electrode fouling, which has been proposed as the main reason for biosensor failures in vivo. Electrochemical fouling is typical for dopamine (DA) as its oxidation products are very reactive and the resulting polydopamine has a robust adhesion capability to virtually all types of surfaces. The degree of DA fouling of different carbon electrodes with different terminations was determined using cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM) approach curves and imaging. The rate of electron transfer kinetics at the fouled electrode surface was determined from SECM approach curves, allowing a comparison of insulating film thickness for the different terminations. SECM imaging allowed the determination of different morphologies, such as continuous layers or islands, of insulating material. We show that heterogeneous modification of carbon electrodes with carboxyl-amine functionalities offers protection against formation of an insulating polydopamine layer, while retaining the ability to detect DA. The benefits of the heterogeneous termination are proposed to be due to the electrostatic repulsion between amino-functionalities and DA. Furthermore, we show that the conductivity of the surfaces as well as the response toward DA was recovered close to the original performance level after cleaning the surfaces for 10-20 cycles in H2SO4 on all materials but pyrolytic carbon (PyC). The recovery capacity of the PyC electrode was lower, possibly due to stronger adsorption of DA on the surface.

In situ spectroscopic monitoring of CO2 reduction at copper oxide electrode.

Copper oxide modified electrodes were investigated as a function of applied electrode potential using in situ infrared spectroscopy and ex situ Raman and X-ray photoelectron spectroscopy. In deoxygenated KHCO3 electrolyte bicarbonate and carbonate species were found to adsorb to the electrode during reduction and the CuO was reduced to Cu(i) or Cu(0) species. Carbonate was incorporated into the structure and the CuO starting material was not regenerated on cycling to positive potentials. In contrast, in CO2 saturated KHCO3 solution, surface adsorption of bicarbonate and carbonate was not observed and adsorption of a carbonato-species was observed with in situ infrared spectroscopy. This species is believed to be activated, bent CO2. On cycling to negative potentials, larger reduction currents were observed in the presence of CO2; however, less of the charge could be attributed to the reduction of CuO. In the presence of CO2 CuO underwent reduction to Cu2O and potentially Cu, with no incorporation of carbonate. Under these conditions the CuO starting material could be regenerated by cycling to positive potentials.

CO2 capture and electrochemical conversion using superbasic [P66614][124Triz].

The ionic liquid trihexyltetradecylphosphonium 1,2,4-triazolide, [P66614][124Triz], has been shown to chemisorb CO2 through equimolar binding of the carbon dioxide with the 1,2,4-triazolide anion. This leads to a possible new, low energy pathway for the electrochemical reduction of carbon dioxide to formate and syngas at low overpotentials, utilizing this reactive ionic liquid media. Herein, an electrochemical investigation of water and carbon dioxide addition to the [P66614][124Triz] on gold and platinum working electrodes is reported. Electrolysis measurements have been performed using CO2 saturated [P66614][124Triz] based solutions at -0.9 V and -1.9 V on gold and platinum electrodes. The effects of the electrode material on the formation of formate and syngas using these solutions are presented and discussed.

Surface redox chemistry and mechanochemistry of insulating polystyrene nanospheres.

Cyclic voltammetry (CV) of polystyrene nanospheres was carried out after immobilisation onto boron-doped diamond electrodes. Although the polystyrene is insulating, a voltammetric response was obtained. This was attributed to the high surface area of the nanospheres, allowing the redox chemistry of the polystyrene surface to be probed despite the non-conducting nature of the bulk. The polystyrene redox response was found to be strongly dependent on prior mechanical agitation. Centrifuged, sonicated and vortexed polystyrene nanospheres all exhibited significantly higher oxidation currents than the non-agitated polystyrene. Mechanical treatment by sonication and centrifugation was found to bring about changes to surface chemistry of the polystyrene spheres, in particular the introduction of oxygen functionalities. For these samples the CV response is attributed to the presence of surface phenol functionalities. On the non-agitated and vortex treated polystyrene surfaces X-ray photoelectron spectroscopy revealed an absence of oxygen functionalities that could explain the redox response. Repetition of the CV experiment in the presence of a solution spin trap suggests that radical species play a role in the observed response. For the vortexed sample the increased oxidation currents were attributed to significant surface roughening and deformation, as revealed by Transmission Electron Microscopy.

Reduction of Carbon Dioxide to Formate at Low Overpotential Using a Superbase Ionic Liquid.

A new low-energy pathway is reported for the electrochemical reduction of CO2 to formate and syngas at low overpotentials, utilizing a reactive ionic liquid as the solvent. The superbasic tetraalkyl phosphonium ionic liquid [P66614][124Triz] is able to chemisorb CO2 through equimolar binding of CO2 with the 1,2,4-triazole anion. This chemisorbed CO2 can be reduced at silver electrodes at overpotentials as low as 0.17 V, forming formate. In contrast, physically absorbed CO2 within the same ionic liquid or in ionic liquids where chemisorption is impossible (such as [P66614][NTf2]) undergoes reduction at significantly increased overpotentials, producing only CO as the product.

Multimetallic complexes and functionalized nanoparticles based on oxygen- and nitrogen-donor combinations.

The versatile precursors [Ru(CH═CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] (BTD = 2,1,3-benzothiadiazole) and [Ru(C(C≡CPh)═CHPh)Cl(CO)(PPh3)2] were treated with isonicotinic acid, 4-cyanobenzoic acid, and 4-(4-pyridyl)benzoic acid under basic conditions to yield [Ru(vinyl)(O2CC5H4N)(CO)(PPh3)2], [Ru(vinyl)(O2CC6H4CN-4)(CO)(PPh3)2], and [Ru(vinyl){O2CC6H4(C5H4N)-4}(CO)(PPh3)2], respectively. The osmium analogue [Os(CH═CHC6H4Me-4)(O2CC5H4N)(CO)(PPh3)2] was also prepared. cis-[RuCl2(dppm)2] was used to prepare the cationic compounds [Ru(O2CC5H4N)(dppm)2](+) and [Ru{O2CC6H4(C5H4N)-4}(dppm)2](+). The treatment of 2 equiv of [Ru(C(C≡CPh)═CHPh)(O2CC5H4N)(CO)(PPh3)2] and [Ru(O2CC5H4N)(dppm)2](+) with AgOTf led to the trimetallic compounds [{Ru(C(C≡CPh)═CHPh)(CO)(PPh3)2(O2CC5H4N)}2Ag](+) and [{Ru(dppm)2(O2CC5H4N)}2Ag](3+). In a similar manner, the reaction of [Ru(O2CC5H4N)(dppm)2](+) with PdCl2 or K2PtCl4 yielded [{Ru(dppm)2(O2CC5H4N)}2MCl2](2+) (M = Pd, Pt). The reaction of [RuHCl(CO)(BTD)(PPh3)2] with HC≡CC6H4F-4 provided [Ru(CH═CHC6H4F-4)Cl(CO)(BTD)(PPh3)2], which was treated with isonicotinic acid and base to yield [Ru(CH═CHC6H4F-4)(O2CC5H4N)(CO)(PPh3)2]. The addition of [Au(C6F5)(tht)] (tht = tetrahydrothiophene) resulted in the formation of [Ru(CH═CHC6H4F-4){O2CC5H4N(AuC6F5)}(CO)(PPh3)2]. Similarly, [Ru(vinyl)(O2CC6H4CN-4)(CO)(PPh3)2] reacted with [Au(C6F5)(tht)] to provide [Ru(vinyl){O2CC6H4(CNAuC6F5)-4}(CO)(PPh3)2]. The reaction of 4-cyanobenzoic acid with [Au(C6F5)(tht)] yielded [Au(C6F5)(NCC6H4CO2H-4)]. This compound was used to prepare [Ru(CH═CHC6H4F-4){O2CC6H4(CNAuC6F5)-4}(CO)(PPh3)2], which was also formed on treatment of [Ru(CH═CHC6H4F-4)(O2CC6H4CN-4)(CO)(PPh3)2] with [Au(C6F5)(tht)]. The known compound [RhCl2(NC5H4CO2)(NC5H4CO2Na)3] and the new complex [RhCl2{NC5H4(C6H4CO2)-4}{NC5H4(C6H4CO2Na)-4}3] were prepared from RhCl3·3H2O and isonicotinic acid or 4-(4-pyridyl)benzoic acid, respectively. The former was treated with [Ru(CH═CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] to yield [RhCl2{NC5H4CO2(Ru(CH═CHC6H4Me-4)(CO)(PPh3)2}4]Cl. As an alternative route to pentametallic compounds, the Pd-coordinated porphyrin [(Pd-TPP)(p-CO2H)4] was treated with 4 equiv of [Ru(CH═CHR)Cl(CO)(BTD)(PPh3)2] in the presence of a base to yield [(Pd-TPP){p-CO2Ru(CH═CHR)(CO)(PPh3)2}4] (R = C6H4Me-4, CPh2OH). Where R = CPh2OH, treatment with HBF4 led to the formation of [(Pd-TPP){p-CO2Ru(═CHCH═CPh2)(CO)(PPh3)2}4](BF4)4. [(Pd-TPP){p-CO2Ru(dppm)2}4](PF6)4 was prepared from [(Pd-TPP)(p-CO2H)4] and cis-[RuCl2(dppm)2]. The reaction of AgNO3 with sodium borohydride in the presence of [Ru(O2CC5H4N)(dppm)2](+) or [RuR{O2CC6H4(C5H4N)-4}(dppm)2](+) provided silver nanoparticles Ag@[NC5H4CO2Ru(dppm)2](+) and Ag@[NC5H4{C6H4CO2Ru(dppm)2}-4](+).

Room-Temperature One-Pot Synthesis of pH-Responsive Pyridine-Functionalized Carbon Surfaces.

Carbon surfaces (glassy carbon, graphite, and boron-doped diamond) were functionalized with layers composed of linked pyridinium and pyridine moieties using simple electrochemical reduction of trifluoroacetylpyridinium. The pyridinium species was generated in situ in solution by the reaction of trifluoroacetic anhydride and pyridine precursors and underwent electrochemical reduction at -1.97 V vs Fc/Fc+, as determined by cyclic voltammetry. The pyridine/pyridinium films were electrodeposited at room temperature, on a timescale of minutes, and were characterized using X-ray photoelectron spectroscopy. The as-prepared films have a net positive charge in aqueous solution at pH 9 and below due to the pyridinium content, confirmed by the electrochemical response of differently charged redox molecules at the functionalized surfaces. The positive charge can be enhanced further through protonation of the neutral pyridine component by controlling the solution pH. Moreover, the nitrogen-acetyl bond can be cleaved through base treatment to purposefully increase the neutral pyridine proportion of the film. This results in a surface that can be "switched" from functionally near neutral to a positive charge by treatment in basic and acidic solutions, respectively, through manipulation of the protonation state of the pyridine. The functionalization process demonstrated here is readily achievable at a fast timescale at room temperature and hence can allow for rapid screening of surface properties. Such functionalized surfaces present a means to test in isolation the specific catalytic performance of pyridinic groups toward key processes such as oxygen and CO2 reduction.

Undoped diamond nanoparticles: origins of surface redox chemistry.

This article discusses some of our recent work on the origins of redox activity of undoped nanodiamond (ND) powders, as well as reviewing some properties and applications of this material. The electrochemical activity is attributed to unsaturated bonding at the ND particle surface; hence the most recent understanding of the surface chemistry of these materials is discussed. The implications of the observed redox activity, especially for use in biological applications, are highlighted, along with future avenues of research.

Astroelectrochemistry: the role of redox reactions in cosmic dust chemistry.

We propose that redox reactions on the surface of interstellar dust grains contribute to the synthesis of some polyatomic species that have been identified by spectroscopic signatures. Most of the dust is found in clouds along with a rich abundance of molecular and atomic species, creating a thermodynamically distinct region in the interstellar medium (ISM) where chemistry can be supported. Using knowledge of redox process at the solid/liquid interface, a hypothesis is presented for processing mechanisms involving electron transfer between surface adsorbed species and the solid dust grains found in the ISM. The hypothesis is based on the interaction of dust grains with electromagnetic radiation and plumes of ionised gas, which electrostatically charge dust grains leading to an adjustment of the Fermi energy of electrons on the surface of individual grains. This process is equivalent to applying an external electrochemical potential to an electrode, to drive redox chemistry on an electrode surface in electrolysis or dynamic electrochemistry. Here the individual grains act as 'single electrode' electrochemical reactors in the gas phase. In this paper we highlight a gap in understanding of redox reactions at the solid/gas interface, which is potentially a very fruitful and interesting area of research.

Electrochemistry of undoped diamond nanoparticles: accessing surface redox states.

The electrochemical response of an electrode-immobilized layer of undoped, insulating diamond nanoparticles is reported, which we attribute to the oxidation and reduction of surface states. The potentials of these surface states are pH-dependent; moreover they are able to interact with solution redox species. The voltammetric response of redox couples Fe(CN)(6)(3-/4-) and IrCl(6)(3-/2-) are compared at bare boron-doped diamond electrodes and electrodes modified with a layer of nanodiamond (ND). In all cases the presence of ND modifies the CV response at slow scan rates if low concentrations of redox couple are used. Enhancements of oxidation currents are noted at potentials at which the ND surface states can also undergo oxidation, and enhancements of reduction currents are likewise observed where ND is also reducible. We attribute these observations to electron transfer occurring between the species generated at the underlying electrode during CV and the ND immobilized in the interfacial region, leading to regeneration of the starting species and hence enhancement in currents due to a feedback mechanism. The magnitude of current enhancement thus depends on the standard potential of the redox couple relative to those of the ND surface states.

Focused ion beam fabrication of boron-doped diamond ultramicroelectrodes.

The fabrication of ultramicroelectrodes (UMEs) for analytical electrochemical applications has been explored, using boron-doped diamond as the active electrode material in an insulating coating formed by deposition of electrophoretic paint. Because of the rough nature of the diamond film, the property of such coatings that is normally exploited in the fabrication of UMEs, namely the tendency to retract automatically from sharp protrusions, cannot be used in the present instance. Instead focused ion beam (FIB) sputtering was employed to controllably produce UMEs with well-defined geometry, critical dimension of a few micrometers, and very thin insulating coatings. If the FIB machining is carried out at normal incidence to the diamond electrode surface, significant ion beam damage reduces the yield of successful electrodes. However, if a parallel machining geometry is employed, high yields of ultramicroelectrodes with a flat disk geometry can be obtained very reliably. The electrochemical properties of diamond UMEs are characterized. They show much lower background currents than the equivalent Pt or carbon fiber electrodes but more varied electrochemical response than macroscopic diamond electrodes.

In Situ Determination of pH at Nanostructured Carbon Electrodes Using IR Spectroscopy.

Changes in pH at electrode surfaces can occur when redox reactions involving the production or consumption of protons take place. Many redox reactions of biological or analytical importance are proton-coupled, resulting in localized interfacial pH changes as the reaction proceeds. Other important electrochemical reactions, such as hydrogen and oxygen evolution reactions, can likewise result in pH changes near the electrode. However, it is very difficult to measure pH changes located within around 100 µm of the electrode surface. This paper describes the use of in situ attenuated total reflectance (ATR) infrared (IR) spectroscopy to determine the pH of different solutions directly at the electrode interface, while a potential is applied. Changes in the distinctive IR bands of solution phosphate species are used as an indicator of pH change, given that the protonation state of the phosphate ions is pH-dependent. We found that the pH at the surface of an electrode modified with carbon nanotubes can increase from 4.5 to 11 during the hydrogen evolution reaction, even in buffered solutions. The local pH change accompanying the hydroquinone-quinone redox reaction is also determined.

Electrochemical synthesis of copper(i) acetylides via simultaneous copper ion and catalytic base electrogeneration for use in click chemistry.

We report an efficient and sustainable electrochemical synthesis of copper(i) acetylides using simultaneous copper oxidation and Hofmann elimination of quaternary ammonium salts. The electrochemically-generated base was also regenerated electrochemically, making it catalytic. A 'Click test' (CuAAC reaction) was performed to assess product purity and an electrochemically-promoted, one-pot CuAAC reaction was performed, which serves as a promising initial demonstration of this approach in a pharmaceutically-relevant reaction.

Models of the iron-only hydrogenase enzyme: structure, electrochemistry and catalytic activity of Fe2(CO)3(µ-dithiolate)(µ,κ1,κ2-triphos).

A series of diiron bis(2-diphenylphosphinoethyl)phenylphosphine (triphos) complexes Fe2(CO)3(µ-dithiolate)(µ,κ1,κ2-triphos) (1-4) [dithiolate = 1 pdt; 2 edt; 3 adt (R = Bz), 4 (SMe)2] have been prepared and investigated as biomimics of the diiron site of [FeFe]-hydrogenases. The triphos ligand bridges the diiron vector whilst also chelating to one iron and 1-3 exist as a mixture of basal-basal-apical (bba) and basal-basal-basal (bbb) isomers which differ in the mode of chelation. In solution the bba and bbb forms do not interconvert on the NMR time scale, but the bba isomers are fluxional, and at low temperature four forms of 1bba are seen as the conformations for the pdt ring and triphos methylene groups are frozen. Crystallographic studies have established bba (pdt) and bbb (adt) ground state conformations and in both there is a significant deviation away from the expected eclipsed conformation (Lap-Fe-Fe-Lap torsion angle 0°) by 49.4 and 24.9° respectively, suggesting that introduction of triphos leads to significant strain and DFT calculations have been used to understand the relative energies of isomers. The electron rich nature of the diiron centre in 1-4 would suggest rapid protonation, but while bridging hydride complexes such as [Fe2(CO)3(µ-pdt)(µ,κ1,κ2-triphos)(µ-H)][BF4] (1H+) can be formed the process is slow. This behavior is likely a result of the high energy barrier in forming the initial (not observed) terminal hydride which requires a significant conformational change in triphos coordination. CV studies show that all starting compounds oxidize at low potentials and the addition of [Cp2Fe][PF6] to 1 affords [Fe2(CO)3(µ-pdt)(µ,κ1,κ2-triphos)][PF6] (1+) which has been characterised by IR spectroscopy. DFT studies suggest a ground state for 1+ with a partially rotated Fe(CO)2P moiety that yields a weak semi-bridging carbonyl with the adjacent Fe(CO)P2 group. No reduction peaks are seen for 1-4 within the solvent window but 1H+ undergoes reduction at -1.7 V. All complexes act as proton-reduction catalysts in the presence of HBF4·Et2O. For 1, three separate processes are observed and their dependence on acid concentration has been probed, and a mechanistic scheme is proposed based on formation via a CECE process of 1(µ-H)H which can either slowly release H2 or undergo further reduction. Relative contributions of the three processes to the total current were found to be highly dependent upon the background electrolyte, being attributed to their relative abilities to facilitate proton transfer processes. While 2 and 4 show similar proton reduction behaviour, the adt complex 3 is quite different being attributed to facile protonation of nitrogen which is followed by addition of a second proton at the diiron centre.

Multimetallic assemblies using piperazine-based dithiocarbamate building blocks.

Treatment of cis-[RuCl2(dppm)2] (dppm = bis(diphenylphosphino)methane) with dithiocarbamates, NaS2CNR2 (R = Me, Et) and [H2NC5H10][S2CNC5H10], yields cations [Ru(S2CNR2)2(dppm)2](+) and [Ru(S2CNC5H10)2(dppm)2](+), respectively. The zwitterions S2CNC4H8NHR (R = Me, Et) react with the same metal complex in the presence of base to yield [Ru(S2CNC4H8NR)(dppm)2](+). Piperazine or 2,6-dimethylpiperazine reacts with carbon disulfide to give the zwitterionic dithiocarbamate salts H2NC4H6(R2-3,5)NCS2 (R = H; R = Me), which form the complexes [Ru(S2CNC4H6(R2-3,5)NH2)(dppm)2](2+) on reaction with cis-[RuCl2(dppm)2]. Sequential treatment of [Ru(S2CNC4H8NH2)(dppm)2](2+) with triethylamine and carbon disulfide forms the versatile metalla-dithiocarbamate complex [Ru(S2CNC4H8NCS2)(dppm)2] which reacts readily with cis-[RuCl2(dppm)2] to yield [{Ru(dppm)2}2(S2CNC4H8NCS2)]. Reaction of [Ru(S2CNC4H8NCS2)(dppm)2] with [Os(CH=CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] (BTD = 2,1,3-benzothiadiazole), [Pd(C6H4CH2NMe2)Cl]2, [PtCl2(PEt3)2], and [NiCl2(dppp)] (dppp = 1,3-bis(diphenylphosphino)propane) results in the heterobimetallic complexes [(dppm)2Ru(S2CNC4H8NCS2)ML(n))](m+) (ML(n) = Os(CH=CHC6H4Me-4)(CO)(PPh3)2](+), m = 1; ML(n) = Pd(C,N-C6H4CH2NMe2), m = 1; ML(n) = Pt(PEt3)2, m = 2; ML(n) = Ni(dppp), m = 2). Reaction of [NiCl2(dppp)] with H2NC4H8NCS2 yields the structurally characterized compound, [Ni(S2CNC4H8NH2)(dppp)](2+), which reacts with base, CS2, and cis-[RuCl2(dppm)2] to provide an alternative route to [(dppm)2Ru(S2CNC4H8NCS2)Ni(dppp)](+). A further metalla-dithiocarbamate based on cobalt, [CpCo(S2CNC4H8NH2)(PPh3)](2+), is formed by treatment of CpCoI2(CO) with S2CNC4H8NH2 followed by PPh3. Further reaction with NEt3, CS2, and cis-[RuCl2(dppm)2] yields [(Ph3P)CpCo(S2CNC4H8NCS2)Ru(dppm)2](2+). Heterotrimetallic species of the form [{(dppm)2Ru(S2CNC4H8NCS2)}2M](2+) result from the reaction of [Ru(S2CNC4H8NCS2)(dppm)2] and M(OAc)2 (where M = Ni, Cu, Zn). Reaction of [Ru(S2CNC4H8NCS2)(dppm)2] with Co(acac)3 and LaCl3 results in the formation of the compounds [{(dppm)2Ru(S2CNC4H8NCS2)}3Co](3+) and [{(dppm)2Ru(S2CNC4H8NCS2)}3La](3+), respectively. The electrochemical behavior of selected examples is also reported.

Insight into the Nature of Iron Sulfide Surfaces During the Electrochemical Hydrogen Evolution and CO2 Reduction Reactions.

Greigite and other iron sulfides are potential, cheap, earth-abundant electrocatalysts for the hydrogen evolution reaction (HER), yet little is known about the underlying surface chemistry. Structural and chemical changes to a greigite (Fe3S4)-modified electrode were determined at -0.6 V versus standard hydrogen electrode (SHE) at pH 7, under conditions of the HER. In situ X-ray absorption spectroscopy was employed at the Fe K-edge to show that iron-sulfur linkages were replaced by iron-oxygen units under these conditions. The resulting material was determined as 60% greigite and 40% iron hydroxide (goethite) with a proposed core-shell structure. A large increase in pH at the electrode surface (to pH 12) is caused by the generation of OH- as a product of the HER. Under these conditions, iron sulfide materials are thermodynamically unstable with respect to the hydroxide. In situ infrared spectroscopy of the solution near the electrode interface confirmed changes in the phosphate ion speciation consistent with a change in pH from 7 to 12 when -0.6 V versus SHE is applied. Saturation of the solution with CO2 resulted in the inhibition of the hydroxide formation, potentially due to surface adsorption of HCO3-. This study shows that the true nature of the greigite electrode under conditions of the HER is a core-shell greigite-hydroxide material and emphasizes the importance of in situ investigation of the catalyst under operation to develop true and accurate mechanistic models.

Nanodiamonds on tetrahedral amorphous carbon significantly enhance dopamine detection and cell viability.

We hypothesize that by using integrated carbon nanostructures on tetrahedral amorphous carbon (ta-C), it is possible to take the performance and characteristics of these bioelectrodes to a completely new level. The integrated carbon electrodes were realized by combining nanodiamonds (NDs) with ta-C thin films coated on Ti-coated Si-substrates. NDs were functionalized with mixture of carboxyl and amine groups NDandante or amine NDamine, carboxyl NDvox or hydroxyl groups NDH and drop-casted or spray-coated onto substrate. By utilizing these novel structures we show that (i) the detection limit for dopamine can be improved by two orders of magnitude [from 10µM to 50nM] in comparison to ta-C thin film electrodes and (ii) the coating method significantly affects electrochemical properties of NDs and (iii) the ND coatings selectively promote cell viability. NDandante and NDH showed most promising electrochemical properties. The viability of human mesenchymal stem cells and osteoblastic SaOS-2 cells was increased on all ND surfaces, whereas the viability of mouse neural stem cells and rat neuroblastic cells was improved on NDandante and NDH and reduced on NDamine and NDvox. The viability of C6 cells remained unchanged, indicating that these surfaces will not cause excess gliosis. In summary, we demonstrated here that by using functionalized NDs on ta-C thin films we can significantly improve sensitivity towards dopamine as well as selectively promote cell viability. Thus, these novel carbon nanostructures provide an interesting concept for development of various in vivo targeted sensor solutions.

Copper complexes with dissymmetrically substituted bis(thiosemicarbazone) ligands as a basis for PET radiopharmaceuticals: control of redox potential and lipophilicity.

Copper(ii) bis(thiosemicarbazone) derivatives have been used extensively in positron emission tomography (PET) to image hypoxia and blood flow and to radiolabel cells for cell tracking. These applications depend on control of redox potentials and lipophilicity of the bis(thiosemicarbazone) complexes, which can be adjusted by altering peripheral ligand substituents. This paper reports the synthesis of a library of new dissymmetrically substituted bis(thiosemicarbazone) ligands by controlling the condensation reactions between dicarbonyl compounds and 4-substituted-3-thiosemicarbazides or using acetal protection. Copper complexes of the new ligands have been prepared by reaction with copper acetate or via transmetallation of the corresponding zinc complexes, which are convenient precursors for the rapid synthesis of radio-copper complexes. Well-defined structure-activity relationships linking ligand alkylation patterns with redox potential and lipophilicity of the complexes are reported.

Electrocatalytic proton reduction catalysed by the low-valent tetrairon-oxo cluster [Fe4(CO)10(κ(2)-dppn)(µ4-O)](2-) [dppn = 1,1'-bis(diphenylphosphino)naphthalene].

The 62-electron oxo-capped tetrairon butterfly cluster, Fe4(CO)10(κ(2)-dppn)(µ4-O) (1) {dppn = 1,8-bis(diphenylphosphino)naphthalene}, undergoes reversible one-electron oxidation and reduction events to generate the 61- and 63-electron radicals [Fe4(CO)10(κ(2)-dppn)(µ4-O)](+) (1+) and [Fe4(CO)10(κ(2)-dppn)(µ4-O)](-) (1-) respectively. Addition of a second electron affords the 64-electron cluster [Fe4(CO)10(κ(2)-dppn)(µ4-O)](2-) (1(2-)) which has more limited stability but is stable within the time frame of the electrochemical experiment. While 1 and 1(-1) are inactive as proton reduction catalysts, dianionic 1(2-) is active for the formation of hydrogen from both CHCl2CO2H and CF3CO2H. This occurs via two separate mechanistic cycles branching at the mono-protonated species [Fe4(CO)10(κ(2)-dppn)(µ4-O)H](-) (1H-) resulting from the rapid protonation of 1(2-). This intermediate then undergoes competing protonation and reduction events leading to EECC and ECEC catalytic cycles respectively with 1- being pivotal to both. In order to understand the nature of [Fe4(CO)10(κ(2)-dppn)(µ4-O)](2-) (1(2-)) and its protonated products density functional theory (DFT) calculations have been employed. Theoretical calculations reveal that the cluster core remains intact in 1(2-), but the two consecutive one-electron reductions lead to an expansion of one of the trigonal-pyramids of this trigonal-bipyramidal cluster. The two-electron reduced cluster 1(2-) protonates at dppn-bound iron, accompanied by a wingtip-hinge iron-iron bond scission, and then reacts with a second proton to evolve hydrogen.