Author/Editor		Kristl, J; Pečar, S; Šmid-Korbar, J; Schara, M
Title		Molecular motion of drugs in hydrocolloids measured by electron paramagnetic resonance
Type		članek
Source		Pharm Res
Vol. and No.		Letnik 8, št. 4
Publication year		1991
Volume		str. 505-7
Language		eng
Abstract		The effects of a polymer, the Li-salt copolymer of methylmethacrylic acid, and its methyl ester on the motion of drug molecules in hydrocolloids were studied. The investigation was carried out by means of electron paramagnetic resonance (EPR) using the model nitroxide tempol, and the spin-labeled drugs lidocaine (sl-lid) and dexamethasone (sl-dex). Synthesis of sl-dex was performed. Spin-labeled molecules dissolved in hydrocolloids undergo a fast reorientation motion. The decreasing order of rotational correlation times (tau)--sl-dex greater than sl-lid greater than tempol--suggests that the size and the shape of the molecules strongly affect their motion. The inhibition of motion of larger molecules depends also on their flexibility. The tau values indicate proportionality of the microviscosity of hydrocolloids to the polymer concentration. Rotational motion is dependent on the local environment conditioned by the free spaces between polymer molecules.
Descriptors		COLLOIDS DEXAMETHASONE ELECTRON SPIN RESONANCE SPECTROSCOPY METHYLMETHACRYLATES MOTION SPIN LABELS THERMODYNAMICS VISCOSITY