Microbial degradation of quadricyclane-derived tricyclo[2.2.1.0^2,6]heptan-3-ol in soil

Abstract

Quadricyclane (tetracyclo[3.2.02,7.04,6]heptane) is a strained, saturated cyclic hydrocarbon and a potential environmental contaminant because of uses in solar energy and optical memory storage devices and as a recently proposed additive to jet fuel. Quadricyclane is very unstable in both soil and water, and in the environment it exists as abiotic transformation products, tricyclo[2.2.1.02,6]heptan-3-ol and bicyclo[2.2.1]hept-5-en-2-ol. In soils, tricyclo[2.2.1.02,6]heptan-3-ol is microbially transformed to a C7H8O intermediate which we postulate to be tricyclo[2.2.1.02,6]heptan-3-one. This compound is subsequently biodegraded over several months. Elevated respiration rates in soils amended with tricyclo[2.2.1.02,6]heptan-3-ol provide evidence that it is mineralized to CO2, while bicyclo[2.2.1]hept-5-en-2-ol concentrations in soil microcosms remained unchanged over a period of 8 months.Key words: quadricyclane, biotransformation, biodégradation, tricyclo[2.2.1.02,6]heptan-3-ol, bicyclo[2.2.1]hept-5-en-2-ol.

Quadricyclane hydration kinetics in natural waters

“…This ketone increased in concentration over 4-months elapsed time. It was presumed to be an indicator of microbial degradation since it is an intermediate formed rapidly in biodegradation of the hydration product nortricyclyl alcohol [2]. Accordingly, all rate data reported below were obtained at elapsed times of less than 3 weeks, during which time bacterial degradation of quadricyclane hydration products was not observed.…”

“…At selected times, sets of three vials were removed from the incubator, extracted, and the extracts analyzed for hydration products to provide data for kinetic calculations. After 3 weeks, preliminary rate experiments in both phosphate and carbonate buffers produced traces of tricyclo[2.2.1.0 2,6 ]heptan-3-one, which was identified by mass spectrometry. This ketone increased in concentration over 4-months elapsed time.…”

“…A hydration reaction mechanism consistent with these experiments is given in Figure 1. Nortricyclyl alcohol (tricyclo[2.2.1.0 2,6 ]heptan-3-ol) and exo-5-norbornen-2-ol (bicyclo[2.2.1]hept-5-en-2-ol) were identified and quantified in all rate measurements. Carbocation intermediates shown are presumed to exist at low concentrations but are postulated structures that were not identified by spectroscopic analysis.…”

“…The density of 0.982 g/ cm 3 and a boiling point of 108ЊC are close to those of water, in which it readily forms small droplet suspensions. This research relates to estimation of the environmental persistence of quadricyclane (quadricyclo[2.2.1.0 2,6 .0 3,5 ]heptane) and investigates the kinetics of its degradation by hydration. The proposed hydration mechanism differs from the published mechanism [1] in kind and number of intermediates.…”

“…There are several implications of quadricyclane hydration for its fate and transport in the environment. Hydration apparently precedes biooxidation [2] and is thus the first step in quadricyclane degradation. Nucleophilic reactions concurrent with hydration may produce compounds of environmental concern.…”