Solvent and temperature dependence of the hyperfine coupling constants in CTPO

Abstract

The hyperfine coupling constant to the proton in the 4 position of the nitroxide spin label 4-protio-3-carbamoyl-2,2,5,5-tetraperdeuteromethyl-3-pyrrohne-1-yloxy ( mHCTPO) has been measured in seven solvents of varying polarities at 259 and 323 K. All of the proton hyperfine coupling constants in 3-carbamoyl-2,2,5,5,-tetramethyl-3-pyrroline-1-yloxyl (CTPO) have been measured by NMR at 500 MHz in CD 3OD at 307 and 323 K. These results together with corrected results in the literature have been fitted to an empirical equation which yields accurate values of the hyperfine coupling constants from measured values of the nitrogen hyperfine coupling constant and the temperature. Gaussian linewidths, necessary to correct for inhomogeneous broadening in unresolved spin-label spectra, may be calculated from an empirical equation involving the nitrogen hyperfine coupling constant and the temperature.