New pH-sensitive aminoxyls: application to the study of biomembrane transport processes

Abstract

An EPR method for studying transmembrane proton transport using pH-sensitive aminoxyl radicals has been developed for applications in the pH region 4–7. To this end pH-sensitive spin-labelled dextran (pK= 6.1) and sulfonic acid (pK= 5.25), which do not penetrate phospholipid membranes, were synthesized. Using EPR spectroscopy these probes were used to measure the kinetics of pH variations inside large unilamellar phospholipid vesicles after creation of a transmembrane proton gradient. Membrane permeability coefficients for H+(5 × 10–4 cm s–1), Cl–(10–10 cm s–1) and Tl+(10–8 cm s–1) were estimated.