Second Harmonic Studies of Ions Crossing Liposome Membranes in Real Time

Abstract

The transport kinetics of the positively charged triphenylmethane dye, malachite green (MG(+)), across liposome bilayers effects the transport of monovalent inorganic cations when ionophores are present in the membrane. Three different types of ionophores characterized by different transport mechanisms have been studied. The ionophores are gramicidin A (gA) (a channel former), valinomycin (VAL) (a lipophilic cyclopeptide that encloses an alkali ion), and carbonyl cyanide-m-chlorophenylhydrazone (CCCP) (a weak acid that functions as a protonophore). The effects of these ionophores on the kinetics and extent of MG(+) crossing into the liposome, investigated using the interface selective second harmonic generation method, were found to be markedly different.

Adsorption and transport of charged vs. neutral hydrophobic molecules at the membrane of murine erythroleukemia (MEL) cells

“…The SH fields generated by the oppositely oriented MG would cancel with one another, resulting in a time dependent attenuation of the SHG signal, where the rate of decay would be proportional to the membrane transport kinetics of MG. Subsequently, whereas MG has been shown to transport across bacterial or purely synthetic lipid membranes [17,18,[20][21][22]24,25], it is unable to transport across the MEL cell membrane. Fig.…”

“…In addition to probing adsorption and transport across living cell membranes [17,18,20], SHG has been applied to other biologically relevant systems including liposomes [21][22][23][24][25], neurons [26], and collagen networks [27,28].…”

Probing the colloidal gold nanoparticle/aqueous interface with second harmonic generation

“…Previous SHG studies on the free adsorption of the triphenyl methane dye, malachite green (MG), to the surface of colloidal polystyrene microparticles has allowed the free energy of adsorption as well as the maximum number of adsorbate sites to be determined [29,30]. This SHG research has since been extended to study the adsorption of molecules to a variety of types and sizes of colloidal polymer microparticles and nanoparticles [31][32][33][34][35], clay [36], TiO 2 [37], and carbon black [38] nanoparticles, oil droplets in water [30], as well as phospholipid liposomes bilayer membranes [39,40]. Related work using SHG to measure the surface electrostatic potential [41] and the surface acidity pK a [42] of nanoparticles has also been achieved.…”

Fluoromodule-based reporter/probes designed for in vivo fluorescence imaging

“…From its similarity to triarylmethane dyes and MG-based fluorogens, we predicted that SC1 would be nonfluorescent in water, but would become fluorescent if bound and rigidized by a compatible FAP. SC1 was expected to be membrane permeant and therefore useful for labeling intracellular FAP-tagged targets due to its compositional and structural similarity to MG (30). Mars1 and Mars1Cy bind and activate fluorescence from MG-based fluorogens such as MG-ester and MG-2p, in addition to SC1, indicating that variation in probe structure, particularly in the form of flexible linkers on the end distal to the diarylmethane group, is tolerated.…”