Electrochemical studies of vitamin K1 microdroplets: electrocatalytic hydrogen evolution.

The voltammetry of a basal-plane pyrolytic graphite electrode modified with a random ensemble of unsupported microdroplets of vitamin K, is investigated when the electrode is immersed in aqueous electrolytes. It is shown that in dilute acidic solutions, electroreduction occurs in a single two-electron two-proton process to yield the corresponding hydroquinone at the electrode\vitamin K1 microdroplet\aqueous-electrolyte three-phase boundary. On addition of ionic alkali-metal salts to the aqueous acidic phase, the electrochemical reduction of vitamin K1 to the quinol is accompanied by catalytic hydrogen evolution within and alkali-metal-cation insertion into the organic microdroplets. In strongly alkaline solutions, electrochemical reduction of vitamin K1 at the triple-phase junction is proposed as being a single two-electron process with concomitant uptake of alkali-metal cations in order to maintain electroneutrality within the oil phase. Surprisingly, the relative ease of cation insertion into the oil phase is demonstrated to be governed by the degree of ion-pair formation rather than by the Gibbs transfer energy of the cation across the liquid\liquid interface

Photoelectrochemical dechlorination of phenols.

The photoelectrochemical reductions of 4-chlorophenol and 2,4-dichlorophenol are studied in acetonitrile solution at platinum electrodes. The photoelectrochemical reduction follows a CE-type mechanism with the electrochemical step being the formation of dihydrogen. The photochemistry arises from the excitation of the chlorophenolate anion with subsequent loss of chloride, so suggesting green routes based on photons and electricity only, applicable in both aqueous and non-aqueous solution for the dechlorination of chlorophenols

Biphasic sonoelectrosynthesis. A review

Electrosynthesis can be carried out in emulsions formed in situ via sonication of otherwise immiscible liquid/liquid systems. The basic physical principles underlying these experiments are introduced and illustrated via three examples: the electroreduction of liquid olefins, the Kolbe electrooxidation, and the electrogeneration of leuco-methylene green

Voltammetric characteristics of graphite electrodes modified with microdroplets of n-butylferrocene

We report the voltammetry of basal plane pyrolytic graphite electrodes partially covered with immobilised microdroplets of n-butylferrocene and immersed in various aqueous electrolyte solutions. Oxidation of the redox-active oil droplets to form the n-butylferrocinium cation takes place with the expulsion of the cation from the oil phase. The dissolution process is accompanied by the formation of ion pairs between the n-butylferrocinium cation and the counter anion in the aqueous solution; adsorption of the parent compound on the solid electrode surface is also observed. © 2002 Elsevier Science B.V. All rights reserved

Electrochemical probing of photochemical reactions inside femtolitre droplets confined to electrodes.

Random ensembles of femtolitre-volume droplets containing redox active, photosensitive compounds immobilised on an electrode substrate permit photoelectrochemical studies within femtometric environments. Two chemical systems are described; the first is the N,N,N',N'-tetrahexyl-para-phenylenediamine redox-catalysed photochemical debromination of the anaesthetic reagent halothane; the second is the photoinduced electron transfer from excited chlorophyll a to vitamin K1, which has possible potential in the development of solar cells based on photosynthesis

Biphasic redox chemistry of alpha-tocopherol: Evidence for electrochemically induced hydrolysis and dimerization on the surface of and within femtolitre droplets immobilized onto graphite electrodes

The voltammetric behaviour of α-tocopherol, when immobilized as microdroplets on a basal plane pyrolytic graphite electrode and immersed in aqueous electrolyte is reported. Under these biphasic conditions, the electrochemical oxidation is successfully shown to involve two competing pathways initially involving either one or two electrons, the products of which undergo chemical reactions to form electroactive species. One pathway generates a quinone via ring opening hydrolysis at the electrode |α-TOH| aqueous electrolyte three-phase boundary of the femtolitre volume droplets which undergoes reduction on the reverse sweep. The other produces a dimer, via the coupling of α-tocopherol derived radicals, which can be oxidized further to produce cyclized spiro-dimer. Both pathways involve proton expulsion from the redox liquid phase

Low temperature electrochemistry as a mechanistic probe for the partial reduction of heterocycles

The reduction of a series of electron deficient aromatic heterocycles has been examined using electrochemical techniques: the analysis was performed under anhydrous conditions at low temperature, so as to mimic typical synthetic reducing conditions. © 2004 Elsevier Ltd. All rights reserved

Photoelectrochemically driven processes at the N,N,N ',N '-tetrahexylphenylenediamine microdroplet/electrode/aqueous electrolyte triple interface

Novel photoelectrochemical processes are observed upon irradiation of the liquid|liquid|solid triple interface at microdroplets of N,N,N',N'-tetrahexyl-para-phenylenediamine (THPD) deposited onto a basal plane pyrolytic graphite electrode and immersed in aqueous electrolyte solution. In the presence of neutral THPD, cathodic photo responses, and in the presence of THPD+, anodic photo responses with anion-dependent characteristics, are observed. A maximum in the photocurrents observed at intermediate coverage of the electrode surface suggests that the triple interface THPD|electrode|aqueous electrolyte is the reaction zone. This is the first report of photoelectrochemical processes at this type of interface