New 19F NMR methodology reveals structures of molecules in complex mixtures of fluorinated compounds.

Although the number of natural fluorinated compounds is very small, fluorinated pharmaceuticals and agrochemicals are numerous. 19F NMR spectroscopy has a great potential for the structure elucidation of fluorinated organic molecules, starting with their production by chemical or chemoenzymatic reactions, through monitoring their structural integrity, to their biotic and abiotic transformation and ultimate degradation in the environment. Additionally, choosing to incorporate 19F into any organic molecule opens a convenient route to study reaction mechanisms and kinetics. Addressing limitations of the existing 19F NMR techniques, we have developed methodology that uses 19F as a powerful spectroscopic spy to study mixtures of fluorinated molecules. The proposed 19F-centred NMR analysis utilises the substantial resolution and sensitivity of 19F to obtain a large number of NMR parameters, which enable structure determination of fluorinated compounds without the need for their separation or the use of standards. Here we illustrate the 19F-centred structure determination process and demonstrate its power by successfully elucidating the structures of chloramination disinfectant by-products of a single mono-fluorinated phenolic compound, which would have been impossible otherwise. This novel NMR approach for the structure elucidation of molecules in complex mixtures represents a major contribution towards the analysis of chemical and biological processes involving fluorinated compounds.

19F-centred NMR analysis of mono-fluorinated compounds.

Addressing limitations of the existing NMR techniques for the structure determination of mono-fluorinated compounds, we have developed methodology that uses 19F as the focal point of this process. The proposed 19F-centred NMR analysis consists of a complementary set of broadband, phase-sensitive NMR experiments that utilise the substantial sensitivity of 19F and its far reaching couplings with 1H and 13C to obtain a large number of NMR parameters. The assembled 1H, 13C and 19F chemical shifts, values of J HF, J HH, and J FC coupling constants and the size of 13C induced 19F isotopic shifts constitute a rich source of information that enables structure elucidation of fluorinated moieties and even complete structures of molecules. Here we introduce the methodology, provide a detailed description of each NMR experiment and illustrate their interpretation using 3-fluoro-3-deoxy-d-glucose. This novel approach performs particularly well in the structure elucidation of fluorinated compounds embedded in complex mixtures, eliminating the need for compound separation or use of standards to confirm the structures. It represents a major contribution towards the analysis of fluorinated agrochemicals and (radio)pharmaceuticals at any point during their lifetime, including preparation, use, biotransformation and biodegradation in the environment. The developed methodology can also assist with the investigations of the stability of fluoroorganics and their pharmacokinetics. Studies of reaction mechanisms using fluorinated molecules as convenient reporters of these processes, will also benefit.

Detection of gas leakage from landfills using infrared thermography--applicability and limitations.

Although landfill gas emission can be greatly reduced by extraction and converting gas to energy, in practice not all gas can be collected and some leaks can still occur. Management of landfill gas can be improved if leaks can be detected and rectified effectively. This paper provides a brief review of methods available for detecting landfill leakage, with a focus on infrared thermography. It then describes a study which was conducted to test if an infrared camera can be used to detect gas leaks accurately by identifying them as anomalies. It examined the applicability and limitations of the technique by investigating fundamental factors such as weather conditions, ground conditions and distance of sensor from source. The paper also describes a test case conducted to reinforce the findings. It concluded that unless all the fundamental factors are clearly understood and addressed, the technique currently can only be used as a screening tool rather than as a precise tool to detect landfill gas leakages. For this reason, it would be difficult to use the technique as a basis for modelling gas emission from landfills.