The molecular properties of some diesel fuel components and their biodegradation

Abstract

Alkylated polycyclic aromatic hydrocarbons (PAHs) are especially important whenuncombusted fuels are of concern. Bioremediation has become one of the most rapidlydeveloping techniques for cleaning up contaminated soil and aqueous environments and anumber of bacterial species are known to degrade PAHs present in diesel fuels.Pseudomonas has a strong PAH-degrading capacity that remains throughout the wholeprocess of biotreatment. The group of bacterial enzymes responsible for thebiodegradation of PAHs is aromatic hydrocarbon dioxygenase and they catalyze theoxidation of many aromatic compounds. Naphthalene 1,2-dioxygenase (NDO) is one ofthese enzyme systems. Following the finding of Librando and Alparone who proposedaveraged static dipole polarizability ( LT α>) values of dimethylnaphthalenes (DMNs) as apredictor of their biodegradation rates [1], in this chapter are presented the results of thetheoretical investigation of molecular properties of trimethylnaphthalenes (TMNs) [2].The results of the calculations show that values of molecular properties important fordefining the oxidative and reductive routes of TMNs vary little along the series of TMNs.It is assumed that similar to DMNs, the rate-limiting step in the biodegradation kineticsof TMNs is expected to be determined by their polarizabilities. The results of thecalculations show that the average static dipole polarizabilities of TMNs in gas phase aswell as in water solution increase in the order α,α,α-TMN LT α,α,β-TMN LT α,β,β-TMN LT β,β,β-TMN and they can be used as predictors of the biodegradation rates of TMNs.Since naphthalene dioxygenase is capable of degrading PAHs with no more than fourrings, it is interesting to take into consideration other two- and three-rings alkylatedPAHs. The results of calculations of molecular properties of two methylanthracene (MA) isomers have shown that the calculated ionization potential (IP) and electron affinity(EA) values are close for these isomers suggesting that oxidative and reductive pathwaysshould not be critical for the biodegradation of 1-MA and 2-MA. The increase of LT α>values on passing from 1-MA to 2-MA can play an important function in thebiodegradative process of these isomers.