Association of Model Compounds of Asphaltenes in Organic Solutions

Abstract

The self-association properties of two model compounds of asphaltene, 2,6-bis[2-(pyren-1-yl)ethyl]pyridine (PyPPy, C41H29N) and 2,6-bis[2-(phenanthren-9-yl)ethyl]pyridine (PhPPh, C37H29N), were studied in deuterated chloroform and deuterated methylene chloride. 1H NMR spectroscopy titration experiments showed that both compounds undergo changes in conformation in solution as a function of solvent, concentration, and water concentration. At low concentrations, below 0.1 mM in chloroform, these compounds gave 1H NMR chemical shifts consistent with intra-molecular interaction, likely due to a folding conformation. At concentrations above 10 mM the 1H NMR chemical shifts were consistent with inter-molecular interactions due to aggregation. Results of spin- lattice relaxation time (T1) measurement and diffusion-ordered spectroscopy (DOSY) experiments are consistent with existence of two conformations at low and high concentrations. The addition of water promotes aggregation of these model compounds even at low concentrations of 10-5 M, likely via hydrogen bonds between the pyridyl nitrogens and water.