NMR Relaxation Enhancement of Water Protons by Gd-Doped Boron Nitride Nanotubes

The longitudinal NMR relaxation rate (<i>R</i>₁) of water protons was measured on aqueous suspensions of Gd@BNNTs (i.e., boron nitride nanotubes doped with 0.4% w/w of Gd) coated with glycol-chitosan in the 0.01–30.0 MHz Larmor frequency range, by using a fast field-cycling relaxometer. The dispersion curve of the relaxivity (<i>r</i>₁) relative to Gd, determined exploiting <i>R</i>₁ data from Gd@BNNT and BNNT suspensions, shows a logarithmic dependence on frequency which is characteristic of a relaxation enhancement dominated by an outer sphere mechanism governed by two-dimensional diffusion of water in proximity of Gd³⁺ ions on the BNNT surface. Quantitative information on water diffusion and affinity for the surface was obtained by analyzing the <i>r</i>₁ NMRD curves in terms of a model for two-dimensional diffusion. The effects of the nanotube assembly in water and of the coating hydrophilicity on the interactions between water molecules and Gd³⁺ ions governing the proton relaxation enhancement at the basis of contrast in magnetic resonance imaging (MRI) are discussed

Interaction of Azole Compounds with DOPC and DOPC/Ergosterol Bilayers by Spin Probe EPR Spectroscopy: Implications for Antifungal Activity

The influence of two antifungal azoles, the newly synthesized compound CPA18 and the commercial drug fluconazole (FLC), on the physical state of 1,2-dioleoyl-<i>sn</i>-glycero-3-phosphocholine (DOPC) and DOPC/ergosterol bilayers was investigated by spin probe electron paramagnetic resonance (EPR) spectroscopy with the aim of ascertaining if direct interactions with the plasma membrane are implied in the mechanism of action against Candida albicans. 5- and 16-Doxyl-stearic acids (5-DSA and 16-DSA, respectively) were employed to this purpose, and EPR spectra were acquired in the 0 to 40 °C temperature range. Spectral line shapes were analyzed within the theory for slow motion EPR using a microscopically ordered macroscopically disordered model to describe the DOPC multilamellar vesicles and an axially symmetric Brownian model for the spin probe motion. For CPA18 remarkable changes in the molecular organization and dynamics of the phospholipid bilayers were found in the region immediately below the polar head groups, probed by 5-DSA, whereas the bilayer core, probed by 16-DSA, was only slightly affected. On the other hand, no effects of FLC on DOPC bilayers were revealed in the regions examined. Small differences were observed between DOPC and DOPC/ergosterol systems. The direct interactions of CPA18 with model membranes here highlighted may contribute to the observed fungicidal properties against both fluconazole-sensitive and -resistant C. albicans strains