Papers by Tuomas Vainikka
International journal of electrochemical science
Electrochimica Acta, 2013
ABSTRACT In this paper we report the properties of the Fe(II)/Fe(III) reaction in a deep eutectic... more ABSTRACT In this paper we report the properties of the Fe(II)/Fe(III) reaction in a deep eutectic solvent based on choline chloride and ethylene glycol. This reaction is shown to be facile using a wall-jet electrode and rotating disc electrode. The deposition and stripping of iron exhibits equally slow kinetics as in aqueous systems. Using these two reactions an all-iron redox flow battery based on ionic liquids is reported for the first time. An energy efficiency of 37% is attained at a current density of 0.5 mA cm−2. A Zn(II)–Fe(II)complex is shown to form when zinc is oxidized by Fe(III). When this complex is applied in a redox flow battery energy efficiencies of 78% are achieved at a current density of 0.5 mA cm−2.
Journal of Pharmaceutical Sciences, 2013
The affinity of a drug to a biological membrane can affect the distribution and the availability ... more The affinity of a drug to a biological membrane can affect the distribution and the availability of the active compound to its target. Adsorption is usually determined with in vitro distribution studies based on partitioning of the drug between buffer and tissue, which have limitations such as the high variability of the uptake data and the need for high accuracy in the measurement of drug concentration. Furthermore, distribution studies yield solute concentrations in the bulk of the tissue, whereas electrokinetic phenomena such as streaming potential and electroosmosis reflect the electric charge density on a membrane surface. Streaming potential thus can be used in studying the conditions, by which the charge sign and density can be regulated. That, in turn, has significance to electroosmotic transport mechanism during iontophoresis. In this communication, the adsorption of model compounds methylprednisolone sodium succinate, propranolol, and cytochrome C on bovine and porcine sclera is determined as a function of their concentration by measuring streaming potential. Both membranes had negative streaming potential, proving that they carry negative charge, but had different values at negative and positive pressure differences, which is addressed to the structural asymmetry of these membranes. Bovine sclera had a clearly higher value of streaming potential, ca. −26 nV/ Pa, than porcine sclera, ca. −7 nV/Pa (10 mM NaCl solution). All the model compounds were adsorbed on bovine and porcine sclera already in the millimolar concentration range and can have an impact to electroosmosis during transscleral iontophoresis. The results obtained help to better elucidate the phenomena involved in transscleral transport, both in passive diffusion and in iontophoresis, supporting the future application of iontophoresis to the noninvasive delivery of drugs to the posterior segment of the human eye.
Electrochimica Acta, 2013
The electrochemistry of copper(I) and copper(II) chloride complexes in the RTIL 1-butyl-1methylpy... more The electrochemistry of copper(I) and copper(II) chloride complexes in the RTIL 1-butyl-1methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, BMPTf 2 N, has been studied with constant current electrolysis and cyclic staircase voltammetry at temperatures between 21.0 and 96.0 • C and in different concentrations of chloride. The chloride concentration was controlled by addition of 1-butyl-1-methylpyrrolidinium chloride, BMPCl. An important finding is the evidence of a three-coordinated complex, Cu(I)Cl 3 2− which has not been found in organic chloroaluminates without a significant increase in temperature. Two Cu(I) species were found at molar ratios of [Cl − ]/[Cu] < 4. The kinetic parameters for the quasi-reversible Cu(I)-Cu(II) electron transfer were obtained with non-linear fitting. Successful fits required that the charge transfer coefficients for the reduction of Cu(II) (˛) and oxidation of Cu(I) (ˇ) did not sum up to unity, i.e. ˛ + ˇ / = 1. This result was interpreted using Tsallis non-extensive thermostatistics.
Electrochimica Acta, 2012
In this work, simultaneous characterisation of conductivity, viscosity and heterogeneous kinetics... more In this work, simultaneous characterisation of conductivity, viscosity and heterogeneous kinetics is demonstrated in a deep eutectic solvent based on choline chloride and ethylene glycol, using concurrent steady state voltammetric and impedance measurements at a rotating disc electrode. A theoretical treatment based on post-experimental correction of ohmic losses is shown to be reliable. The parameters determined at 25 • C are: standard rate constant of electron transfer k 0 = 10 ± 1 × 10 −4 cm s −1 , charge transfer coefficient ˛ = 0.39 ± 0.03, formal potential E 0 = 0.430 ± 0.005 V vs. Ag/AgCl, conductivity Ä = 10.1 ± 0.3 mS cm −1 , dynamic viscosity Á = 37 ± 3 mPa s, diffusion coefficient of Cu 2+ D O = 1.32 ± 0.5 × 10 −7 cm 2 s −1 and Stokes radius of the Cu 2+ complex R H = 0.33 nm.
Electrochimica Acta, 2011
Kinetics of electron transfer of the Cu(I)/Cu(II) redox couple at a platinum electrode has been s... more Kinetics of electron transfer of the Cu(I)/Cu(II) redox couple at a platinum electrode has been studied with chronoamperometry, cyclic voltammetry and impedance spectroscopy in a deep eutectic solvent consisting of choline chloride and ethylene glycol. At 25 • C, the reaction was found to be quasi-reversible with a relatively high rate constant k 0 of 9.5 ± 2 × 10 −4 cm s −1 , and a charge transfer coefficient˛of 0.25 ± 0.05. Diffusion coefficients for the Cu(I) and Cu(II) complexes were determined to be 2.7 ± 0.1 × 10 −7 and 1.5 ± 0.1 × 10 −7 cm 2 s −1 , respectively. The viscosity of the electrolyte was 41 ± 3 mPa s. The temperature dependency was also investigated. The activation energy of mass transfer was found to be 27.7 ± 1 kJ mol −1 and that of electron transfer 39 ± 7 kJ mol −1 . Speciation of the Cu(I) and Cu(II) complexes was determined using UV-VIS spectroscopy, and the prevailing Cu(I) complex was found to be [CuCl 3 ] 2− and that of Cu(II) [CuCl 4 ] 2− .
Chemical Communications, 2014
Lithium cations are shown to have a significant role in catalyzing oxygen and proton reduction al... more Lithium cations are shown to have a significant role in catalyzing oxygen and proton reduction along with S N 1 reactions in biphasic systems. We propose that this catalytic effect is due to the surprising acidity of the hydrated cations; interactions between the cation and its surrounding solvation shell will make the constituent water molecules more acidic.
Electrochimica Acta, 2015
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Papers by Tuomas Vainikka