Interaction of drug molecules with carrier systems as studied by parelectric spectroscopy and electron spin resonance

According to recent investigations of nanoparticular carrier systems the mode of drug-particle interaction appears to influence drug penetration into the skin. For a more detailed insight into the molecular structure of drug loaded particles the two independent analytical methods, namely the parelectric spectroscopy (PS) and the electron spin resonance (ESR) have been applied to 4,5,5,-trimethyl-1-yloxy-3-imidazoline-2-spiro-3′-(5′⁎-cholestane) as a model drug. Spectra have been analyzed in dependence on the concentration of the spin label. Changes in the concentration-dependent dipole mobility and dipole density given by PS and the concentration-dependent rotational correlation time (ESR) which are a measure of the vicinity of carrier and/or the surfactant and guest molecule were studied with cholestane-labeled solid lipid nanoparticles (SLN), nanoparticular lipid carriers (NLC) and nanoemulsions (NE). The spin probes were attached to the SLN surface which consists of two distinct sub-compartments: the rim and the flat surface of the disk-like shapes. The shape could be observed by freeze-fraction electron microscopy. Spin probes, however, were incorporated into the carrier matrix in the cases of NLC and NE. Results of PS are verified by ESR which allows a more detailed insight. Taking the results together a detailed new model of ‘drug’-particle interaction could be established.