No description available.

It has been found that the herbicide 2,4-D has the ability to increase the rate of transport of positive ions of several kinds and inhibit the transport of negatively charged tetraphenylborate ions in lipid bilayer membranes. Only the neutral molecules of 2,4-D are transport active. The ionized 2,4-D molecules do not modify the transport of ions, and do not by themselves permeate through lipid membranes. The results suggest that the enhancement of transport of positively charged ions is dominated by the increase of the ion translocation rate constant. It has been shown that membrane transport of negatively charged tetraphenylborate ions is suppressed by 2,4-D. The effect is dominated by the suppression of translocation of these ions across membrane interior, rather than by the decrease of their adsorption at the membrane surface. It has been shown that the enhancement of nonactin-mediated transport of potassium ions by 2,4-D can be accounted for by a simple carrier model. From the changes of kinetic parameters of nonactin-K('+) transport, membrane conductance due to positively charged tetraphenylarsonium ions and also from the changes of membrane conductance and relaxation time constant due to transport of negatively charged tetraphenylborate ions, the changes of the electric potential of the membrane interior have been estimated. The potential of the membrane interior becomes more negative in the presence of 2,4-D and its change is proportional to the aqueous concentration of 2,4-D. The effect of 2,4-D on ion transport was explained by the hypothesis that a layer of 2,4-D molecules is absorbed within the membrane/water interfacial region, and that the 2,4-D molecules are oriented in such a way that their dipole moment is directed toward the aqueous medium. The results suggest that this layer is located in the hydrocarbon side of the interface. The hypothesis has been confirmed by the measurements of changes of electric potential difference across air/water and air/lipid monolayer/water interfaces. It has been found that the electric potential of the nonpolar side of the interface decreases in the presence of neutral molecules of 2,4-D, which is in agreement with the conclusions drawn from the results of membrane experiments. The effect of the other auxin-type phenoxy herbicides, 2,4,5-T and 2,4-DB on lipid bilayer membranes has been found to be similar to that of 2,4-D. In contrast, the phenoxy acid 2,4,6-T, has very little or no herbicidal activity, and at the same time has small effect on ion transport in membranes. Biologically active 2,4-D derivatives, amino acid conjugates of 2,4-D (isoleucine, leucine and valine conjugates) have been found to be also transport active in a manner similar to 2,4-D. Similar conclusions have been drawn from experiments with natural auxin indole acetic acid. The results obtained in this work suggest the existence of correlation between the biological activity of herbicides acting as plant growth regulators and their ability to enhance transport of positively charged ions across lipid membranes. This work provides insight into the physical origin of such activity.

No description available.

In this study, parameters for the adsorption of several halogenated phenolate ions to egg-phosphatidylcholine vesicles have been determined by microelectrophoresis.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references. Available also in a digital version from Dissertation Abstracts.

The self-assembled complex (Pden)4(bipy)4+8 is potentially suited as a portal for synthetic ion channels (Pden = (1, 2-ethylenediamine) Pd(II), bipy = 4, 4'-bipyridine). This thesis examines the solution speciation of mixtures of Pden and bipy and the ion channel activity of the proposed channel. A model which describes the concentration of the species in solution as a function of pH and Pden:bipy ratio was developed. The method determines the solution speciation by solving the mass balance equation for each species using the total concentration of Pden, bipy and H+ and the cumulative formations constants for species in solution. This model is general and can be applied to other systems provided that the cumulative macroscopic formation constants (logßpbh) of the species are either known or can be estimated. The cumulative macroscopic formation constant for a species is determined by an additive free energy process as the sum of the logarithms of a microscopic formation constant (logß'pbh) and a statistical factor (logY). Values for logß'pbh were estimated using stepwise formation constants (logK) for model systems which were determined by potentiometric titration. Values for logY were calculated from the symmetries of the species. The model calculates the concentration of each species as a function of pH and Pden:bipy ratio to give a map of the species and their relative concentrations. The model shows that (Pden)4(bipy)4 is the single most abundant species between pH = 4 and 7 and a Pden:bipy ratio of 1:0.4 to 1:6. Under optimum conditions, (Pden)4(bipy)4 holds a maximum of -80 % of the total Pd in solution when the total [Pd] = 1 x 10-5 M. The apparent equilibrium constants for 2.(Pden)(bipy)2 = (Pden)2(bipy)3+bipy and 4.(Pden)(bipy) = (Pden)4(bipy)4 were -0.6 and --106, respectively, at Pden:bipy = 1:1 and pH = 7. The model also permits analysis of the relative rates of formation of (Pden)4(bipy)4 from a number of different precursors. The dominant stepwise processes for the formation of (Pden)4(bipy)4 are dimerization of (Pden)2(bipy)2, addition of Pden to (Pden)3(bipy)4 and addition of (Pden)2(bipy) to (Pden)2(bipy)3. Other possible pathways to (Pden)4(bipy)4 involve less abundant species so are disfavored. Lipophilic derivatives of Pden (PdenR) were synthesized from 1-bromodecane or 1-bromohexadecane and solketal in 30 % and 23 % overall yield, respectively. The complex PdenR was reacted with bipy in acetonitrile and the resultant solution was then tested for ion channel activity using the bilayer clamp experiment. The decyl derivative (R = C10H21) was inactive but a range of activity which include erratic behaviors, short openings and Iong openings were observed for the hexadecyl derivative (R = C16H33) using the bilayer clamp technique. Erratic openings were observed before all short and long openings, but were also observed independently. Hille pore radii, calculated from the observed conductances, were between ˜ 1 and 6.5 Å for the rare short openings. The Hille radii for long opening pores were between ˜1 and 14 Å and these pores did not show any ion selectivity. Channels that exhibit long opening activity were also observed in the absence of Pden:bipy. The large Hille radii and activity in the absence of bipy indicate that the proposed (PdenR)4(bipy)4 channel did not form possibly because the local concentration of bipy was not high enough to compete with the lipid for coordination sites on PdenR. The implications of these findings for self-assembly of ion channels in lipid bilayer membranes are discussed.

Thesis (Ph.D.) -- McMaster University, 1997 / Includes bibliographical references (leaves 151-167) Also available via World Wide Web.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 128-145).

Thesis (M. Sc.)--Memorial University of Newfoundland, 1998. / Bibliography: leaves 68-75.

Thesis (Ph.D.)--Memorial University of Newfoundland, 2004. / Bibliography: leaves 157-167.