Ultrasonic absorption and permeability for liposomes near phase transition

Abstract

The specific ultrasonic absorption coefficient per wavelength as a function of temperature in the vicinity of the phase transition of liposomes, composed of a 4 : 1 mixturc of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglyeerol (DPPG), of different sizes was determined using an acoustic interferometer. Small unilamellar vesicles {,SUV) and multilamellar vesiclcs (MLV) yielded results similar to those in the literature, viz., an absorption maximum at the transition temperature. Seven intermediate sizes including several size distributions of large unilamellar vesicles (LUV) were studied, yielding information on size dependencies of the temperatures at which the peaks occur, the widths at half peak amplitude, and the peak amplitudes. All liposome sizes except the SUV exhibited approximately the same transition temperature as did the largest MLV. The widths of the peaks were inversely related to liposome size, with a strong dependence for the smallest vesicles and an approach to independence for the largest vesicles. The amplitudes of the peaks exhibited a general increase with size with two exceptions, viz., the SUV and the vesicles with average diameters of 90-100 nm. It was also found that the membrane permeability increased near the transition temperature. The temperature dependencies of ultrasonic absorption and membrane permeability are compared.

Fluid-gel interphase line tension and density fluctuations in dipalmitoylphosphatidylcholine multilamellar vesicles: an ultrasonic study

“…The backward rate constants are assumed to be proportional to the number of external molecules in the cluster, because the larger the number of external molecules, the larger the probability of one of them to leave the cluster bi = boncxt,r (18) where 6, serves as an adjusting parameter (the physical meaning of bo is the probability of a single molecule pair to leave the cluster during a unit of time). The forward rate constants are determined from the equilibrium condition,ft = bixi/xi-,, where the concentrations of the clusters, xi, are calculated by eqs [12][13][14][15][16].…”

“…This is why the computations in our work were performed under three arbitrary assumptions about the contribution of the external molecules•, the contribution is (i) the same as that of internal ones, (ii) half that of the internal molecules, and ( ) zero. Therefore, MV = ncííAH(T-T0)/T0 = neífAS(T-Ta) (13) where AH and AS are partial molar transition enthalpy and entropy, respectively, in an infinitesimal system; T0is the transition temperature; and is the effective number of "internal" pairs of molecules, which is determined by the formula nett = n-(l-Q)nexl (14) where n is the number of pairs of lipid molecules in a cluster; next is the number of external lipid pairs (see below); and is equal to 1, '/2, or 0, respectively, depending on the assumption of the contribution of external molecules adopted.…”

Structural Modifications of DMPC Vesicles upon Interaction with Poly(amidoamine) Dendrimers Studied by CW-Electron Paramagnetic Resonance and Electron Spin−Echo Techniques

“…To investigate interactions occurring between n SBDs and the cell membrane, we have recently analyzed the continuous wave (CW)- and pulsed-electron paramagnetic resonance (EPR) spectra of spin-labeled n SBDs in the presence of phosphatidylcholine curved bilayers or multilayers, termed vesicles and liposomes. , These prototypes are widely used as model membranes. − The SBDs undergo fast exchange between the vesicle surface and the bulk solution; however, when the exchange rate is decreased, a physical interaction which depends on the dendrimer size (generation) and the protonation of the dendrimer surface groups is evident . Since the labels are attached to the dendrimer in this previous study, no information are obtained concerning eventual modification of the vesicle structure upon interaction with the dendrimers.…”

Characterization of Starburst Dendrimers and Vesicle Solutions and Their Interactions by CW- and Pulsed-EPR, TEM, and Dynamic Light Scattering

“…Curved bilayers and multilayers, termed vesicles and liposomes, , are widely employed as models of biological membranes. − In this study, we explore interactions between liposomes formed by dimyristoylphosphatidylcoline (DMPC) and dendritic macromolecules , termed starburst dendrimers …”