Low‐frequency ESR studies on permeable and impermeable deuterated nitroxyl radicals in corn oil solution

Abstract

Low-frequency electron spin resonance studies were performed for 2 mM concentration of deuterated permeable and impermeable nitroxyl spin probes, 3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl and 3-carboxy-2,2,5,5,-tetramethyl-1-pyrrolidinyloxy in pure water and various concentrations of corn oil solution. The electron spin resonance parameters such as the line width, hyperfine coupling constant, g factor, rotational correlation time, permeability, and partition parameter were estimated. The broadening of line width was observed for nitroxyl radicals in corn oil mixture. The rotational correlation time increases with increasing concentration of corn oil, which indicates the less mobile nature of spin probe in corn oil mixture. The membrane permeability and partition parameter values were estimated as a function of corn oil concentration, which reveals that the nitroxyl radicals permeate equally into the aqueous phase and oil phase at the corn oil concentration of 50%. The electron spin resonance spectra demonstrate the permeable and impermeable nature of nitroxyl spin probes. From these results, the corn oil concentration was optimized as 50% for phantom studies. In this work, the corn oil and pure water mixture phantom models with various viscosities correspond to plasma membrane, and whole blood membrane with different hematocrit levels was studied for monitoring the biological characteristics and their interactions with permeable nitroxyl spin probe. These results will be useful for the development of electron spin resonance and Overhauser-enhanced magnetic resonance imaging modalities in biomedical applications.

Solvent Effects on Skin Penetration and Spatial Distribution of the Hydrophilic Nitroxide Spin Probe PCA Investigated by EPR

“…It means that PCA in the viable skin layer was of high mobility and in a hydrophilic microenvironment (Table 2 ). PCA is generally considered as a cell membrane-impermeable probe due to its hydrophilicity [ 40 ]. However, several studies showed that PCA could enter cells, even though the intracellular amount was much lower than the intercellular one [ 48 , 54 ].…”

“…This is different from many published findings, which stated that the PBS-ethanol cosolvent was better than the pure solvents, e.g., ethanol or PBS [ 26 – 29 ]. PCA is a small hydrophilic molecule (186 g/mol) with a natural logarithmic partition coefficient of −1.8 [ 40 ]. With the hydration of the SC by PBS [ 41 , 42 ], possibly the solubility of PCA in the SC was increased, and hence the penetration of PCA into the SC could be enhanced.…”