Optical, vibrational, spectroelectrochemical and HPLC studies of petroleum porphyrins, partitioning of crude oil transition metals into water, and monitoring of anticorrosion inhibitors in commercial antifreeze coolants

Petroleum porphyrins occur mainly as nickel (Ni) and vanadyl (VO) complexes of cycloalkanoporphyrin (CAP), deoxophylloerythroetioporphyrin (DPEP), etioporphyrin (Etio), and mesoporphyrin (Meso) in crude oils, tar balls, coals, and organic-rich sediments. Their electrochemical, bonding, spectroscopic, and chromatographic properties, along with their partitioning into aquatic environments, are investigated. The construction of cyclic voltammetry (CV) and Raman spectroelectrochemical cells allows acquisition of their redox and bonding characteristics. The CVs indicate reversible one- and two-electron oxidations with electron abstraction from the porphyrin ring and are classified a1u bonding type by resonance Raman (RR) spectroelectrochemistry. RR is further exploited in the vibrational identification of Ni(DPEP) as compared to Ni(Etio-III) and Ni(OEP) (OEP = octaethylporphyrin) using variable excitation wavelengths of 406.7/413.1 (Soret), 530.9 (Q1), and 568.2 (Q0) nm in the high (1200--1700 cm-1), mid (660--1200 cm-1), and low (100--600 cm-1) regions. The characterization of Ni(DPEP) includes its six-(CAP6) and seven-(CAP7) exocyclic derivatives with RR, UV-VIS, and HPLC studies. The UV-VIS absorption red-shifts and the Raman marker downshifts are caused by exocylic non-planar distortions. HPLC separated the DPEP series and sets potentiality for HPLC-RR separation-detection system. Similar studies are applied in VO(CAP)s: metal ion effect and exocyclic ring influences as compared to Ni(CAP)s. Both IR and RR spectra show a band ∼ 990 cm-1 attributed to VO stretching, a useful marker of vanadyl petroporphyrins. These petroporphyrins were examined for their partitioning into water samples containing surfactant/humic acids exposed to Boscan crude. ICP confirmed metal content at parts-per-billion. Ion chromatography indicated negligible ionic content. RR fingerprinted both Ni(DPEP) and VO(DPEP) and established their relative abundance and multiple speciated forms. The petroporphyrin set includes identification of Ni(Meso-IX) isomers. The in-phase and out-of-phase nu(CC)-Et Raman vibrations become useful since the UV-VIS spectra are indistinguishable. The detection/quantification of triazole inhibitors branches out into the coolant analysis, detected at 276 nm with strong chromophoric dyes detected at 495 nm.