Fluorine-19 Nuclear Magnetic Resonance Relaxation Analysis of the Interaction of Fluorocarbon with Oxygen

Abstract

Fluorine-19 nuclear spin relaxation rates for fluorocarbon solutions involving oxygen have been measured over a wide frequency range (10 to 235 MHz) at 25°C. The 19F relaxation of the solvents involving paramagnetic oxygen can be explained by Bipolar electron spin-nuclear spin interaction modulated by both translational diffusion (Td of 2.0X10" and 2.5X10-11 s for C6F6 and C6H4(CF3)2, respectively) and the lifetime of the short-lived complex (th of 7.6X10-13 and 1.3X10-12 s for C6F6 and C6H4(CF3)2, respectively), although the translational contribution is dominant. The translational motions account for 81 and 70% of the relaxation process and are characterized in the present analysis by closest distances of 3.6 and 3.8 A for C6F6 and C6H4(CF3)2, respectively. KeywordsFluorocarbon, oxygen, '9F nuclear magnetic resonance relaxation, nucleus-electron distance molecular interaction correlation timePerfluorinated liquids are known to dissolve significant quantities of molecular oxygen, ca. 30 to 60 cm3 of gaseous oxygen per 100 cm3 of liquid fluorocarbon at 25° C under ordinary pressure.' The solubility of oxygen is in fluorocarbons about three or ten times as large as that observed in the parent hydrocarbons or in water, respectively. The property of those highly fluorinated compounds has suggested a probable utility of fluorinated solvents in artificial blood and liquid breathing.2-4 No evidence has been provided to support assumptions that can reasonably be made to account for this solubility. We may assume charge transfer interaction induced by molecular oxygen within transient encounter complexes with the fluorinated solvent molecules. In the case of a stable association between the oxygen and fluorocarbon molecule, we will show that there is a preferential site in the fluorocarbon molecule to fix oxygen.There exist two 19F nuclear magnetic resonance (NMR) relaxation studies5'6 on the fluorocarbon-oxygen interaction, but the authors were unable to determine the dynamic parameters (correlation times and nucleuselectron distances) from the relaxation analysis. Delpeuch et al.5 suggested that the relaxation mechanism for C6F6 interacting with oxygen can be explained by a discontinuous diffusion through the C6F6 liquid "lattice" with a short residence time (<10-12 s) in privileged positions of the lattice. Parhaml et al.6 showed a preferential approach of oxygen to some parts of the perfluorocarbon (perfluorodecalin, perfluorotripropylamine) over other parts, most likely due to steric effects rather than specific binding.The present study on the frequency dependence of 19F nuclear relaxation times affords informations (relaxation mechanism, correlation times and nucleus-electron distances) on the dynamic aspects of the molecular oxygenfluorocarbons (C6F6 and C6H4(CF3)2) interaction. We, furthermore, describe from a static viewpoint how a downfield 19F scalar shift (positive spin density) induced by paramagnetic oxygen was observed for fluorocarbons. Theoretical BackgroundThe interactions between fluorocarbons and ox...

Towards Determination of Distances Between Nanoparticles and Grafted Paramagnetic Ions by NMR Relaxation

“…The number of paramagnetic ions and oxygen molecules per particle N S , determined by SQUID and EPR measurements [ 11 – 13 , 15 , 18 – 21 , 25 ], as well as the correlation times τ e of the electron spins of these ions and molecules [ 35 – 43 ] are given in Table 2 .…”