Interaction of Phloretin with Lipid Monolayers: Relationship between Structural Changes and Dipole Potential Change

Abstract

Phloretin is known to adsorb to lipid surfaces and alters the dipole potential of lipid monolayers and bilayers. Its adsorption to biological and artificial membranes results in a change of the membrane permeability for a variety of charged and neutral compounds. In this respect phloretin represents a model substance to study the effect of dipole potentials on membrane permeability. In this investigation we studied the interaction of phloretin with monolayers formed of different lipids in the liquid-expanded and the condensed state. Phloretin integrated into the monolayers as a function of the aqueous concentration of its neutral form, indicated by an increase of the surface pressure in the presence of phloretin. Simultaneous recording of the surface potential of the monolayers allowed us to correlate the degree of phloretin integration and the phloretin-induced dipole potential change. Increasing the surface pressure decreased the phloretin-induced shift of the isotherms, but did not influence the phloretin-induced surface potential change. This means that phloretin adsorption to the lipid surface can occur without affecting the lipid packing. The surface potential effect of phloretin is accompanied by a change of the lipid dipole moment vector dependent on the lipid packing. This means that the relation between the surface potential change and the lipid packing cannot be described by a static model alone. Taking into account the deviations of the surface potential change versus molecular area isotherms of the experimental data to the theoretically predicted course, we propose a model that relates the area change to the dipole moment in a dynamic manner. By using this model the experimental data can be described much better than with a static model.

Dipolar interactions between domains in lipid monolayers at the air–water interface

“…We obtained ∆V LC = (555 ± 12) mV and ∆V LE = (402 ± 8) mV, for the pure LC phase and pure LE phase, respectively. These values are in agreement with previous results for monolayers with the same 34 and different 35 subphase, and for bilayers 36 .…”

Ultrasensitive two-color fluorescence probes for dipole potential in phospholipid membranes

“…In principle, the addition of phloretin and 6-KC may change not only ⌿ d but also the polarity, viscosity, and hydration of the probe-binding site (16)(17)(18)(19). Moreover, these additives also may interact with the probe directly.…”

“…1). It was reported that phloretin, a compound with one carbonyl and four hydroxylic groups, strongly reduces the ⌿ d value (4,(16)(17)(18), whereas sterols including cholesterol increase it. One of the sterol compounds with a strong ⌿ d increasing effect is 6-ketocholestanol (6-KC) (4,19).…”

Electrochemical Properties of Phospholipid Monolayers at Liquid–Liquid Interfaces

“…[7,8,[12][13][14][15] As a result of their unique properties, biomembrane models with variable complexities and can be formed at liquid-liquid interfaces and are well-suited to elucidate structural details of the bilayers membrane and to mimic its functions. [2][3][4] In this context, lipid monolayers at liquid-liquid interfaces have been the basis for numerous technical applications in fields such as biochemistry, electrochemistry, chemistry and biology, and have attracted particular interest for studies of the charge transfer, electroanalysis, drug delivery and membrane activity.…”