In-situ identification of various structural features of vanadyl porphyrins in crude oil by high-field (3.4 T) ENDOR spectroscopy combined with DFT calculations

TL;DR

This study employs high-field ENDOR spectroscopy combined with DFT calculations to identify and characterize vanadyl porphyrins directly in crude oil without sample treatment, revealing detailed structural information.

Contribution

It introduces a novel in-situ approach using 3.4 T ENDOR spectroscopy with DFT to analyze metalloporphyrins in native crude oil environments.

Findings

Identification of specific vanadyl porphyrin structures in crude oil.

Correlation of ENDOR features with DFT-predicted structures.

Demonstration of in-situ analysis without sample preparation.

Abstract

Structural characterization of metalloporphyrins in complex systems such as native hydrocarbons is in the focus of scientific and industrial interests since 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 radiofrequency pulses at near the proton Larmor frequencies of 144 MHz to probe the paramagnetic vanadyls. By means of density functional theory (DFT) calculations, ENDOR features are explained and ascribed to certain vanadyl porhyrin structural forms known to be present in crude oil.