Resonance Raman and DFT studies of tetra-tert-butyl porphine: Assignment of strongly enhanced distortion modes in a ruffled porphyrin

The free-base form of tetra-tert-butyl porphine (TtBP), which has extremely bulky meso substituents, is severely distorted from planarity, with a ruffling angle of 65.5degrees. The resonance Raman spectrum of TtBP (lambda(ex) = 457.9 nm) and its d(2), d(8), and d(10) isotopomers have been recorded, and while the spectra show high-frequency bands similar to those observed for planar meso-substituted porphyrins, there are several additional intense bands in the low-frequency region. Density functional calculations at the B3-LYP/6-31G(d) level were carried out for all four isotopomers, and calculated frequencies were scaled using a single factor of 0.98. The single factor scaling approach was validated on free base porphine where the RMS error was found to be 14.9 cm(-1). All the assigned bands in the high-frequency (> 1000 cm(-1)) region of TtBP were found to be due to vibrations similar in character to the in-plane skeletal modes of conventional planar porphyrins. In the low-frequency region, two of the bands, assigned as nu(8) (ca. 330 cm(-1)) and nu(16) (ca. 540 cm(-1)), are also found in planar porphyrins such as tetra-phenyl porphine (TPP) and tetra-iso-propyl porphine (IPP). Of the remaining three very strong bands, the lowest frequency band was assigned as gamma(12) (pyr swivel, obsd 415 cm(-1), calcd 407 cm(-1) in do). The next band, observed at 589 cm-1 in the do compound (calcd 583 cm(-1)), was assigned as a mode whose composition is a mixture of modes that were previously labeled gamma(13) (gamma(CmCaHmCa)) andy gamma(11) (pyr fold(asym)) in NiOEP. The final strong band, observed at 744 cm(-1) (calcd 746 cm(-1)), was assigned to a mode whose composition is again a mixture of gamma(11) and gamma(13), although here it is gamma(11) rather than gamma(13) which predominates. These bands have characters and positions similar to those of three of the four porphyrin ring-based, weak bands that have previously been observed for NiTPP. In addition there are several weaker bands in the TtBP spectra that are also

Plasma chloriding of thin-film silver - A novel process in silver-silver chloride reference electrode fabrication

Silver thin films were modified using a novel plasma modification process for the development of thin-film silver-silver chloride reference electrodes. The surface, physical, and electrochemical properties of these electrodes were investigated by atomic force microscopy, thickness and resistivity measurement techniques, as well as impedance spectroscopy and potentiometry. After plasma treatment, thin-film growth was observed and the electrodes, in general, exhibited low interface impedance and a roughened surface. Evidence of a complex surface reorganization was found. Correlating plasma conditions with film properties suggested that increasing pressure and exposure duration increased species availability, therefore governing the reaction rates, while input power appeared to influence the type of surface chemical reactions. Results also indicated that Ar/Cl-2 mixtures should be employed rather than pure chlorine plasmas. (C) 2002 The Electrochemical Society.

Electrochemistry in Room-Temperature Ionic Liquids: Potential Windows at Mercury Electrodes

The cathodic and anodic: potential limit of eleven different ionic liquids were determined at a mercury hemisphere electrode. Ionic liquids containing the phosphonium cation (tri(n-hexyl)tetradecylphosphonium, [P-14.6,P-6.6](+)) give the largest potential window, especially When Coupled to a trifluorotris(pentafluoroethyl)- [FAP](-). or bis(trifluoromethanesulfonyl)imide, [NTf2](-), anion.

Electrochemical Oxidation of Hydrogen Sulfide at Platinum Electrodes in Room Temperature Ionic Liquids: Evidence for Significant Accumulation of H2S at the Pt/1-Butyl-3-methylimidazolium Trifluoromethylsulfonate Interface

Electrochemical oxidation of hydrogen sulfide gas (H2S) has been studied at a platinum microelectrode (10 mu m diameter) in five room temperature ionic liquids (RTILs): [C(4)mim][OTf], [C(4)dmim][NTf2], [C(4)mim][PF6],. [C(6)mim][FAP], and [P-14,P-6,P-6,P-6][FAP] (where [C-n mim](+) = 1-alkyl-3-methylimidazolium, [C(n)dmim](+) = 1-alkyl-2,3-dimethylimidazolium, [P-14,P-6,P-6,P-6](+) = tris(p-hexyl)-tetradecylphosphonium, [OTf](-) = trifluoromethlysulfonate, [NTf2](-) = bis(trifluoromethylsulfonyl)imide, [PF6](-) = hexafluorophosphate, and [FAP](-) = trifluorotris(pentafluoroethyl)phosphate). In four of the RTILs ([C(4)dmim][NTf2], [C(4)mim][PF6], [C(6)mim][FAP], and [P-14,P-6,P-6,P-6][FAP]), no clear oxidative signal was observed. In [C(4)mim][OTf], a chemically irreversible oxidation peak was observed on the oxidative sweep with no signal seen on the reverse scan. The oxidative signal showed an adsorptive stripping peak type followed by near steady-state limiting current behavior. Potential step chronoamperometry was carried out on the reductive wave, giving a diffusion coefficient and solubility of 1.6 x 10(-11) m(2) s(-1) and 7 mM, respectively (at 25 degrees C). Using these data, we modeled the oxidation signal kinetically, assuming adsorption preceded oxidation and that adsorption was approximately Langmuirian. The oxidation step was described by an electrochemically fully irreversible Tafel law/Butler-Volmer formalism. Modeling indicated a substantial buildup of H2S in the double layer in excess of the coverage that would be expected for a monolayer of chemisorbed H2S, reflecting high solubility of the gas in [C(4)mim][OTf] and possible attractive interactions with the [OTf](-) anions accumulated at the electrode at potentials positive of the potential of zero charge. Solute enrichment of the double layer in the solution adjacent to the electrode appears a novel feature of RTIL electrochemistry.

Dissolved Argon Changes the Rate of Diffusion in Room Temperature Ionic Liquids: Effect of the Presence and Absence of Argon and Nitrogen on the Voltammetry of Ferrocene

This work explores the effects of argon and nitrogen, two electrochemically and chemically inert gases frequently used in sample preparation of room temperature ionic liquid (RTIL) solutions, on the eelectrochemical characterization of ferrocene (Fc) dissolved in the RTIL 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C(2)mim][NTf2]). Remarkably, chronoamperometrically determined diffusion coefficients of Fc in [C(2)mim][NTf2] are found to increase from 4.8 (+/- 0.2) x 10(-11) m(2) s(-1) under vacuum conditions to 6.6 (+/- 0.5) x 10(-11) m(2) s(-1) in an atmosphere of 1 atm Ar. In contrast, exposing a vacuum-purified sample to an atmosphere of 1 atm N-2 resulted in no significant change in the measured diffusion coefficient of Fc. The effect of dissolved argon on diffusion transport is unexpected and has implications in electrochemistry and elsewhere. Fc was found to volatilize under vacuum conditions. We propose, however, that evacuation of the cell by vacuum prior to electrochemical measurements being carried out is the only way to ensure that no contamination of the sample occurs, and use of an in situ method of determining the diffusion coefficient and concentration of Fc dispells,any ambiguity associated with Fc depletion by vacuum.

Electrochemical Determination of Manganese Solubility in Mercury via Amalgamation and Stripping in the Room Temperature Ionic Liquid n-Hexyltriethylammonium Bis(trifluoromethanesulfonyl)imide, [N-6,N-2,N-2,N-2][NTf2]

The solubility of manganese in mercury was determined electrochemically via amalgamation and stripping in the room temperature ionic liquid n-hexyltriethylammonium bis(trifluoromethanesulfonyl)imide, [N-6,N-2,N-2,N-2][NTf2]. A hemispherical mercury electrode was made by electrodepositing mercury onto a planar platinum microelectrode. Cyclic voltammetry of Mn2+ in [N-6,N-2,N-2,N-2][NTf2] at the mercury microhemisphere electrode was investigated at temperatures of 298, 303 and 313 K. The solubility of Mn in Hg was determined on the basis of the charge under the reduction peak (Mn2+ --> Mn-0) and the corresponding reoxidation.

Speciation of Rare-Earth Metal Complexes in Ionic Liquids: A Multiple-Technique Approach

The dissolution process of metal complexes in ionic liquids was investigated by a multiple-technique approach to reveal the solvate species of the metal in solution. The task-specific ionic liquid betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]) is able to dissolve stoichiometric amounts of the oxides of the rare-earth elements. The crystal structures of the compounds [Eu-2(bet)(8)(H2O)(4)][Tf2N](6), [Eu-2(bet)(8)(H2O)(2)][Tf2N](6)center dot 2H(2)O, and [Y-2(bet)(6)(H2O)(4)][Tf2N](6) were found to consist of dimers. These rare-earth complexes are well soluble in the ionic liquids [Hbet][Tf2N] and [C(4)mim]- [Tf2N] (C(4)mim = 1-butyl-3-methylimidazolium). The speciation of the metal complexes after dissolution in these ionic liquids was investigated by luminescence spectroscopy, H-1, C-13, and Y-89 NMR spectroscopy, and by the synchrotron techniques EXAFS (extended X-ray absorption fine structure) and HEXS (high-energy X-ray scattering). The combination of these complementary analytical techniques reveals that the cationic dimers decompose into monomers after dissolution of the complexes in the ionic liquids. Deeper insight into the solution processes of metal compounds is desirable for applications of ionic liquids in the field of electrochemistry, catalysis, and materials chemistry.

Influence of the anion on the electrodeposition of cobalt from imidazolium ionic liquids

Cyclic voltammetry and absorption spectrophotometry were used to examine the complex formation of cobalt (II) in the ionic liquids 1-butyl-3-methylimidazolium chloride ([C(4)mim] Cl) and 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([C(4)mim][Tf2N]). In [C(4)mim]Cl, cobalt(II) is complexed as [CoCl4](2-) at CoCl2 concentrations less than 33 mol %. Cyclic voltammograms show that cobalt cannot be electrodeposited at these concentrations. However, cobalt metal can be electrodeposited at CoCl2 concentrations above the threshold concentration of 33 mol %. In the ionic liquid [C(4)mim][Tf2N] there is no threshold CoCl2 concentration for electrodeposition due to the absence of [CoCl4](2-). (C) 2007 The Electrochemical Society.

The electrochemical oxidation of catechol and dopamine on platinum in 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(2)mim][NTf2]) and 1-Butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF4]): Adsorption effects in ionic liquid voltammetry

The electrochemical oxidation of catechol and dopamine has been studied at a platinum micro-electrode (10 pm diameter) in two room temperature ionic liquids (RTILs): 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(2)mim][NTf2]) and 1-Butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BE4]). For catechol in [C(2)mim][NTf2], an electrochemically quasi-reversible oxidation peak was observed at 1.1 V vs. Pt with a back peak at 0.4 V vs. Pt. This is assigned to the two-electron oxidation of catechol to doubly protonated o-benzoquinone. Double-step chronoamperometry gave a diffusion coefficient for the catechol and the oxidised species which is 3.8 x 10(-11) m(2) s(-1) for both. For catechol in [C(4)mim][BF4], a two-electron oxidation wave was observed at 1.0 V vs. Pt with no back peak. Another peak at less positive potential was also observed at 0.6 V vs. Pt in [C(4)mim][BF4] but not in [C(2)mim][NTf2] which is assigned to the adsorption of electrochemically formed neutral o-benzoquinone on the platinum electrode. The oxidised protonated o-benzoquinone is suggested to be deprotonated by the [BF4](-) anion, but not by the [NTf2](-) anion: hence adsorption of the neutral species at the platinum electrode, not the charged species. For dopamine in both RTILs, two chemically irreversible oxidation peaks were observed at 0.75 V and 1.1 V vs. Pt, and assigned to the oxidation of dopamine to the corresponding semi-quinone and the quinone. Potential-step chronoamperometry was carried out on the oxidation waves of dopamine in [C(2)mim][NTf2] and the diffusion coefficient of species in solution was calculated to be 6.85 x 10(-12) m(2) s(-1) and confirmed that the waves corresponded to one and two electron processes. A third wave was observed at 1.8 V vs. Pt which is attributed to the oxidation of the amine group to a radical cation with likely subsequent follow up chemistry. In [C(4)mim][BF4] a peak at less positive potential was observed for dopamine, similar to catechol which is assigned to the adsorption of the neutral quinone species on the platinum electrode formed by the reaction of the removal of protons from the oxidised dopamine with the [BF4](-) anion. (C) 2009 Elsevier B.V. All rights reserved.

Using Room Temperature Ionic Liquids as Solvents to Probe Structural Effects in Electro-Reduction Processes. Electrochemical Behavior of Mutagenic Disperse Nitroazo Dyes in Room Temperature Ionic Liquids

The electrochemical reduction of the disperse azo dyes Red1, Red13 and Orange1 (Or1) was investigated in the RTILs [C(4)mim][NTf2] and [C(4)mpyrr][NTf2], and in contrast with their behavior in conventional aprotic solvents, was shown to proceed via a reversible one electron step to form stable radical anion, which is further reduced at more negative potentials to the dianion. In [C(4)mpyrr][NTf2], cleavage of the N-H bond on the secondary amine was inferred for Orange1, and the ease at which this cleavage occurred is rationalized in terms of acidity of the amine moiety. The ease of reduction was observed to decrease in the order Or1 > Red13 > Red1, and is related to the electron delocalization within the molecule and the electron withdrawing power of the substituents.

SpaciMS: spatial and temporal operando resolution of reactions within catalytic monoliths

Monolithic catalysts are widely used as structured catalysts, especially in the abatement of pollutants. Probing what happens inside these monoliths during operation is, therefore, vital for modelling and prediction of the catalyst behavior. SpaciMS is a spatially resolved capillary-inlet mass spectroscopy system allowing for the generation of spatially resolved maps of the reactions within monoliths. In this study SpaciMS results combined with 3D CFD modelling demonstrate that SpaciMS is a highly sensitive and minimally invasive technique that can provide reaction maps as well as catalytic temporal behavior. Herein we illustrate this by examining kinetic oscillations during a CO oxidation reaction over a Pt/Rh on alumina catalyst supported on a cordierite monolith. These oscillations were only observed within the monolith by SpaciMS between 30 and 90% CO conversion. Equivalent experiments performed in a plug-flow reactor using this catalyst in a crushed form over a similar range of reaction conditions did not display any oscillations demonstrating the importance of intra monolith analysis. This work demonstrates that the SpaciMS offers an accurate and comprehensive picture of structured catalysts under operation.

Development of a recombinant Fab-fragment based electrochemical immunosensor for deoxynivalenol detection in food samples

A reliable and cost-effective electrochemical method for the detection of deoxynivalenol (DON) in cereals and cereal-based food samples based on the use of a novel anti-DON Fab fragment is presented. The analytical system employed, Enzyme-Linked-Immunomagnetic-Electrochemical (ELIME) assay, is based on the use of immunomagnetic beads (IMBs) coupled with eight magnetized screen-printed electrodes (8-mScPEs) as electrochemical transducers.