Hydrophobic barrier in liposomes studied by FT-ESEEM.

An improvement of the electron spin echo envelope modulation technique (ESEEM) for studying the hydrophobic barrier in lipid membranes was proposed. Water penetration depth into the lipid bilayer composed of egg-phosphatidylcholine and dicetylphosphate was studied. For this purpose the stearic acid spin probes with nitroxide moiety at different positions on the acyl chain were dissolved in the bilayer of liposomes prepared in buffer solution with D2O. The ESEEM method is based on the deuterium effect to the 14N-hyperfine splitting constant of the spin probe. For the analysis of the spectra we suggested the frequency domain approach (Fourier transform-ESEEM) instead of the time domain. In order to test this approach, the influence of cholesterol and octanol on the water penetration depth into liposomes was measured. FT-ESEEM appeared to be a more sensitive method for the quantitative measurements of the water penetration depth than the time domain. This approach can become one of the most effective methods for studying the influence of surfactants and other biologically active molecules on water penetration depth into membranes.

Paramagnetic molecular centers in gamma-irradiated aluminum hydroxide complexed with glycine or serine.

Paramagnetic molecular centers produced by gamma irradiation at 77 K and at 293 K in Alx(OH)y, when precipitated with glycine or serine, were studied by ESR spectroscopy. Stable paramagnetic centers characteristic for the amino acid were observed only in the complexes with DL-alpha-serine, and only in air. In the absence of air, at 293 K, none of the paramagnetic centers gave ESR spectra characteristic of the amino acids examined. Irradiation at 77 K produced the glycine radical, .CH2COOH, only in the complex prepared at pH 6.8 and not in the complex prepared at pH 9.5. The radical decayed when the sample was warmed. In the serine complexes, at 77 K the radicals characteristic of the amino acid were not observed. Differences in the behavior between glycine and serine in the complexes prepared under similar conditions are probably due to the serine OH group available for hydrogen bonding in the matrix.

Paramagnetic molecular centers in gamma-irradiated precipitates in the system AlCl3-DL-alpha-valine-NaOH.

Formation and stability of paramagnetic molecular centers were studied in AlCl3-NaOH-DL-alpha-valine by ESR spectroscopy. In Al3(OH)9(valine)1 x 3H2O gamma-irradiated at room temperature the valine radical [formula: see text] was detected. The radical was formed by abstraction of a hydrogen atom from the valine molecule coupled to the aluminum hydroxide matrix. Stability of the radical depended critically on structural properties of the aluminum hydroxide matrix. In aluminum hydroxide with the ratio (Al)/(Valine) = 20, either no paramagnetic species were detected (irradiation in air) or a singlet at g = 2.008 of 1.8 mT linewidth was detected (irradiation in vacuum) at room temperature. Primary paramagnetic species (gamma irradiation at 77 K) in Al3(OH)9(Val)1 x 3H2O are chloride paramagnetic centers and the primary neutral valine radical [formula: see text] It was formed by abstraction of the NH2 group from the valine molecule. With warming, this radical was not transformed to the radical (I).