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<i>In Situ</i> Identification of Various Structural Features of Vanadyl Porphyrins in Crude Oil by High-Field (3.4 T) Electron–Nuclear Double Resonance Spectroscopy Combined with Density Functional Theory Calculations
Structural
characterization of metalloporphyrins in complex systems, such as
native hydrocarbons, has been the focus of scientific and industrial
interests for many years. We describe electron–nuclear double
resonance (ENDOR) of crude oil from the well without any additional
sample treatment (i.e., in the native environment) in the magnetic
field of about 3.4 T and temperature of 50 K by applying microwave
pulses at 94 GHz (W band) and radio frequency pulses at near the proton
Larmor frequencies of 144 MHz to probe the paramagnetic vanadyls.
By means of density functional theory calculations, ENDOR features
are explained and ascribed to certain vanadyl porhyrin structural
forms known to be present in crude oil