No abstract

Determination of the molecular structures of petroporphyrins has been crucial to understand the diagenetic pathways and maturation of petroleum. However, these studies have been hampered by their structural complexity and the challenges associated with their isolation. In comparison to the skeletal macrocyclic structures, much less is known about the substitutions, which are more sensitive to the maturation and diagenesis pathways. While these isolated vanadyl petroporphyrins largely consist of etioporphyrin and deoxophylloerythroetioporphyrin as expected, surprisingly, we find evidence that one or a few β hydrogens are present in petroporphyrins of low carbon numbers using a combination of ultraviolet–visible spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry, and non-contact atomic force microscopy. Petroporphyrins with β hydrogens were not anticipated on the basis of their biological precursors. The data support dealkylation under catagenesis but not transalkylation or random alkylation of the β and meso positions, despite the fact that more complex porphyrin structures are formed.

No abstract

The initial thermal reactions of aromatic hydrocarbons are relevant to many industrial applications. However, tracking the growing number of heavy polycyclic aromatic hydrocarbon (PAH) products is extremely challenging because many reactions are unfolding in parallel from a mixture of molecules. Herein, we studied the reactions of 2,7-dimethylpyrene (DMPY) to decipher the roles of methyl substituents during mild thermal treatment. We found that the presence of methyl substituents is key for reducing the thermal severity required to initiate chemical reactions in natural molecular mixtures. A complex mixture of thermal products including monomers, dimers, and trimers was characterized by NMR, mass spectrometry, and noncontact atomic force microscopy (nc-AFM). A wide range of structural transformations including methyl transfer and polymerization reactions were identified. A detailed mechanistic understanding on the roles of H radicals during the polymerization of polycyclic aromatic hydrocarbons was obtained.

No abstract

We investigated some specially designed model compounds as proxies for archipelago structures in asphaltenes and heavy oils using noncontact atomic force microscopy (nc-AFM). Various adsorption conformations of three different kinds of linkers including aryl−aryl, aryl−CH 2 −aryl, and aryl−(CH 2 ) 3 −aryl were identified. By focusing on the nature of linkages or bridges between aromatic cores, this work directly addresses the long-standing question on petroleum molecular structures by validating detailed features in images and overcoming challenges of nonplanar structures and conformations, providing a foundation to apply nc-AFM to unknown structures in petroleum.

No abstract

The initial thermal reactions of aromatic hydrocarbons are relevant to many industrial applications. However, tracking the growing number of heavy polycyclic aromatic hydrocarbon (PAH) products is extremely challenging because many reactions are unfolding in parallel from a mixture of molecules. Herein, we studied the reactions of 2,7-dimethylpyrene (DMPY) to decipher the roles of methyl substituents during mild thermal treatment. We found that the presence of methyl substituents is key for reducing the thermal severity required to initiate chemical reactions in natural molecular mixtures. A complex mixture of thermal products including monomers, dimers, and trimers were characterized by NMR, mass spectrometry and non-contact atomic force microscopy (nc-AFM). A wide range of structural transformations including methyl transfer and polymerization reactions were identified. A detailed mechanistic understanding was obtained on the roles of H radicals during the polymerization of polycyclic aromatic hydrocarbons.