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Charge pulse relaxation studies were performed on cells of the giant marine alga Valonia utricularis. Two exponential voltage relaxations were recorded as found previously (Benz, R., and U. Zimmermann. 1983. Biophys. J. 43:13-26.). The parameters of the two exponential voltage decays were studied as a function of the chloride concentration in the artificial sea water. Replacement of external chloride by 2(N-morpholino)ethanesulfonate (Mes(-)) had a dramatic influence on the four relaxation parameters. This chloride dependence could not be satisfactorily explained by the simplified model used earlier. Accordingly, additional reaction steps had to be included in the model. Only two relaxation processes could be resolved under all experimental conditions. This means that the heterogeneous complexation reactions, k(R) (association), and k(D) (dissociation) were too fast to be resolved. Therefore a carrier model with equilibrium heterogeneous surface reactions was used to fit the experimental results. From the charge pulse data at different chloride concentrations the translocation rate constants of the free and complexed carriers, k(S) and k(AS), through the membrane, as well as the total surface concentration of carrier systems, N(0), could be evaluated. The results described here indicate that the cell membrane of Valonia utricularis contains an electrogenic transport system for chloride.

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Die nucleophilen Anionen 5a -f greifen Mesityloxid (6) in DME in C-I-und/oder C-3-Position an, wobei in Abhangigkeit vom p-Substituenten in 5 die gesamte Skala von 100% 1,2-Addukt 7 (mit 5a, X = N(CH3)2) zu 100% 1,4-Addukt 9 (mit S f , X = CN) durchlaufen wird. In Ether erhoht sich der Anteil an 9 erheblich. Die Steuerung muR der unterschiedlichen ,,Harte" von 5 a -f zugeschrieben werden, da eine mogliche Ionenpaarbildung gegenlaufig wirkt. Die Oxidationspotentiale von 5 und das Reduktionspotential von 6 schlieRen in DME eine vorgelagerte Elektroneniibertragung bei 1,4-Addition aus, wahrend das leicht reduzierbare Dienon 14 mit 5c radikalisch reagiert .Trimethylsilyl Cyanide -A Reagent for Umpolung, IV') Substituent Effects in the Acylating Nucleophile for Directing 1,2-/1,4-Addition to a,P- Unsaturated KetonesMesityl oxide (6) is attacked by nucleophilic anions 5a -f in DME at the C-I and/or C-3 position. Depending on the p-substituent in 5 the whole scale from 100% 1,2-adduct 7 (with Sa, X = N(CH3)2) to 100% 1,4-adduct 9 (with 5 f , X = CN) is covered. In ether the amount of 9 is strongly enhanced. The control of regiospecificity has to be ascribed to differing "hardness" of 5 a -f , since possible ion pairing produces opposite effects. The oxidation potentials of 5 and the reduction potential of 6 in DME exclude electron transfer before 1,4-addition. The easily reducible dienone 14, however, reacts with 5 c via radicals.