Associative π−π Interactions of Condensed Aromatic Compounds with Vanadyl or Nickel Porphyrin Complexes Are Not Observed in the Organic Phase

Abstract

Association of vanadium and nickel petroporphyrin compounds with aromatic groups is commonly invoked as an important mechanism for aggregation of asphaltenes. In this study, the interaction of vanadium and nickel octaethylporphyrin with condensed aromatic compounds and bridged aromatic compounds was investigated. Neither UV-vis nor fluorescence spectroscopy detect any interactions between porphyrins and aromatic ring groups in either the ground or excited states. The lack of detectable binding of these model compounds suggests that the association of the majority of the vanadium and nickel petroporphyrins in crude oils with the asphaltene fraction may be due to other functionality appended to the porphyrin ring, rather than favorable π-π stacking interactions of aromatic rings with the porphyrin core itself.

High-Field (3.4 T) ENDOR Investigation of Asphaltenes in Native Oil and Vanadyl Complexes by Asphaltene Adsorption on Alumina Surface

“…Dickie and Yen were the first who proposed an aggregation scheme for the macrostructure of petroleum asphaltenes, within which petroporphyrins could stack to the aromatic sheets of asphaltene [24]. Their opinion as well as the abilities of EPR techniques to shed light on aggregation structure was criticized by authors of [64]. In [64], solutions of porphyrin complexes (i.e., model systems) were investigated by UV-Vis and fluorescence spectroscopy.…”

“…Their opinion as well as the abilities of EPR techniques to shed light on aggregation structure was criticized by authors of [64]. In [64], solutions of porphyrin complexes (i.e., model systems) were investigated by UV-Vis and fluorescence spectroscopy. From the lack of detectable binding of these model compounds, it was suggested that the association of the majority of vanadium and nickel petroporphyrins in crude oils with the asphaltene fraction may be due to other functionalities appended to the porphyrin ring, rather than favorable π − π stacking interactions of aromatic rings with the porphyrin core itself.…”

“…Our ENDOR (i.e., EPRbased) positive experimental results (i.e., based not on the failure of detection but on success of detection) carried out on real (i.e., not model) oil samples are in correspondence with the title and conclusions of ref. [64].…”

Synthesis and Aggregation Behavior of Chiral Naphthoquinoline Petroporphyrin Asphaltene Model Compounds

“…The design and synthesis of complex organic molecules to validate, compare, and illuminate molecular characteristics of the asphaltenes is both time‐consuming and expensive. Thus, more often than not, researchers rely on commercially available metalloporphyrins (e.g., Ni II ‐ and V IV O derivatives of octaethyl‐ and tetraphenylporphyrin) as simplified probes for intermolecular aggregation, often coupled with the use UV/Vis and fluorescence spectroscopy to monitor the process . Unfortunately, the limited range of commercial porphyrin compounds in turn limits, and even biases, analytical results and conclusions.…”

“…Thus, more often than not, researchers rely on commercially available metalloporphyrins (e.g.,N i II -a nd V IV Od erivatives of octaethyl-a nd tetraphenylporphyrin)a ss implified probesf or intermolecular aggregation,o ften coupled with the use UV/Vis and fluorescences pectroscopy to monitor the process. [26] Unfortunately,t he limited range of commercialp orphyrin compounds in turn limits,a nd even biases, analytical resultsa nd conclusions. As ar esult,w eh ave workedt od evelop efficient protocols for the synthesis of larger and more diverses tructural representatives of the asphaltenes.…”