Electron Spin Echo Study of Doxyl Spin Probes in Micellar Systems of Ammonium Perfluorooctanoate

Abstract

The two-pulse and three-pulse electron spin echo techniques were applied to investigate the behavior of doxyl stearic acid spin probes in micellar aqueous solutions of ammonium perfluorooctanoate. Three doxyl stearic acids with the nitroxide group in different positions on the alkyl chain were used as spin probes, and deuteriated water was used to study the deuterium modulation of the echo signals. The experimental patterns were interpreted by best-fit spectra calculated by taking into account both the echo decay and the nuclear modulation. The analysis determines the number of deuterium nuclei in the surroundings of the NO groups and the time constant for the electron spin reorientation causing spectral diffusion and echo decay. From these data we conclude that water molecules belonging to the N O solvation sphere were maintained in the micelles and that the long-chain nitroxide probes were tilted in the micelle core in order to occupy regions with relatively easy water accessibility which was slightly higher for 12-DXSA than for 5-and 16-DXSA. The modulation of the hyperfine couplings of the methyl protons due to their rotational motionwas the main mechanism contributing to the echo decay.

Probing the structure of membrane proteins with electron spin echo envelope modulation spectroscopy

“…If the 2 H nucleus and the SL are in close (< 8 Å) proximity, the 2 H modulation can be observed in the time domain data, and a Fourier transformation of the ESEEM data will reveal a peak at or near the 2 H Larmor frequency. ESEEM spectroscopy has been used to probe the ligand coordination sphere of metalloenzymes, protein solvent accessibility, and membrane protein depth 16–18. For the first time, we demonstrate that SDSL ESEEM can be used to directly probe the secondary structure of a protein and/or distances between SLs and amino acid side chains.…”

Interaction between Starburst Dendrimers and SDS micelles studied by continuous-wave and pulsed electron spin resonances

“…Both the continuous-wave Electron Paramagnetic Resonance (cw-EPR) [14][15][16][17][18][19][20][21][22] and the Electron Spin Echo (ESE) [23][24][25][26] techniques have been extensively used to study organized systems, such as micellar solutions. Recently we have applied the cw-EPR technique to investigate the supramolecular structures formed when positively charged surfactants are added to solutions of anionic SBDs [21,22,27].…”

ESR study of aqueous micellar solutions of perfluoropolyether surfactants with the use of fluorinated spin probes

“…The examined TEMPO derivatives, however, were not found suitable for the host CMC determination, because they themselves form micelles at low concentrations (CMC = 1.6 × 10 −6 and 4.7 × 10 −7 mol/dm 3 for C12-and C16-TEMPO, respectively) [13][14][15]. Electron spin echo modulation study of n-DSA probes in APFO micelles [16] indicated that the protiated probe chains do not penetrate deeply into the micellar core but are largely tilted and occupy regions with relatively easy water accessibility.…”