title: Proton concentration jumps and generation of transmembrane pH-gradients by photolysis of 4-formyl-6-methoxy-3-nitrophenoxyacetic acid.
abstract: Proton concentration gradients across membranes are important for many biological energy transducing processes. The kinetics of proton dependent processes can be studied by pH-jump methods in which protons are photochemically released. In the following we describe the synthesis and the properties of photolabile 4-formyl-6-methoxy-3-nitrophenoxyacetic acid, a 'caged proton'. The synthesis is based on vanillin, which is alkylated with chloroacetic acid to give a carboxylic acid (pK = 2.72). In a second step a nitro group ortho to the formyl group is introduced. Photochemical proton release occurs by a reaction mechanism analogous to the well known photochemical formation of 2-nitrosobenzoic acid from 2-nitrobenzaldehyde. The pK values of the photoproduct are 0.75 and 2.76, respectively, thus allowing the use of the compound in a wide pH-range. The quantum yield is 0.18, lower than in the case of the 2-nitrobenzaldehyde/2-nitrosobenzoic acid system (phi = 0.5). The release of the proton in a flash photolysis experiment occurs within less than 1 microseconds. The spectrum of photolabile compound has absorption maxima at 263 nm and 345 nm, respectively. Its permeability across a lipid bilayer membrane is very low (permeability coefficient Pd approximately equal to 10(-9) cm.s-1 at pH 8) so that transmembrane proton concentration gradients can be generated.
authors.affiliation: Fakultät für Biologie, Universität Konstanz, F.R.G.
authors.forename: K
authors.initials: K
authors.lastname: Janko
authors.forename: J
authors.initials: J
authors.lastname: Reichert
mesh_terms: D006016:Glycolates / Q000138:chemical synthesis / Q000528:radiation effects*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007834:Lasers; D008081:Liposomes; D010777:Photochemistry; D011522:Protons
chemical_list: D006016:Glycolates; D008081:Liposomes; D011522:Protons; C054398:4-formyl-6-methoxy-3-nitrophenoxyacetic acid