A Study of Life-type Processes in Liquid Ammonia

Liquid ammonia (LNH3) has a number of properties similar to water, such as the ability to dissolve a diverse range of chemical compounds and, based on the variety of chemical reactions in this non-aqueous solvent, speculation has arisen about the possibility of life processes in liquid ammonia.
"Life" is difficult to define, but the general consensus is that it is comprised of a variety of individual process that could be regarded as "processes of life", some of which can be modelled within the laboratory. This project is primarily concerned with looking at some of these life processes and attempting to model them in liquid ammonia. This may give rise to the notion that life in liquid ammonia is plausible which could be of great interest to those searching for extra-terrestrial life as ammonia is found in our solar system and very likely in many other parts of the vast universe.
One of life's fundamental processes is compartmentalisation, which is the aggregation of molecules into a protective cellular microenvironment, allowing life to survive and develop. Simple cell models in water and some other solvents have been studied widely allowing for a greater understanding of how the cell membrane works and they also have many commercial applications such as acting as drug delivery systems and as detergents. In this project, the aggregation of a variety of surfactants in liquid ammonia has been studied using a range of detection techniques. The common ionic surfactants, such as sodium dodecyl sulfate (SDS) and perfluorooctanoic acid (PFOA) were found not to aggregate in liquid ammonia, as evidenced by their conductance profiles. The reduced dielectric constant of liquid ammonia (εr = 16) compared with that of water (εr = 80) does not sufficiently decrease the repulsion between adjacent ionic head groups that naturally repel one another, and so micelle formation is not favoured. However, non-ionic, fully fluorinated fatty acid amides have been shown to aggregate into micelles in liquid ammonia using 19F NMR as a detection method. The aggregation of fluorinated amides in liquid ammonia was found to follow trends observed for hydrocarbon surfactants in water, such as the relationship between critical micelle concentration (cmc) and hydrophobic tail length. Additionally, the magnitude of 19F NMR shifts seem to suggest that the monomeric surfactant is surrounded by a relatively polar ammonia environment whereas those molecules in the aggregated micelle are surrounded by the neighbouring fluorine atoms from the adjacent hydrophobic chains, as would be expected deep in a micelle core. There is also some evidence of micelle catalysis in liquid ammonia.
Another major contributor to life‟s processes are enzymes, which are nature‟s catalysts made up of proteins which fold up into a unique structure because of their interactions with water. Although their natural habitat is generally an aqueous environment, within an organism for example, enzyme catalysis in non-aqueous environments, such as organic media, has been widely studied and they have many applications in industrial processes. Enzyme catalysis has never been reported in pure, anhydrous, ammonia. This part of the project explores the extent at which lipases can catalyse the ammonolysis of triglycerides in liquid ammonia. Immobilized forms of Lipase B from Candida antarctica (CALB) were found to catalyse the ammonolysis of a variety of triglycerides in liquid ammonia and appear to be more selective towards larger molecules. The rates of triester conversion to diester for short-medium chain triglycerides were increased moderately with added lipase, whereas the subsequent ammonolysis of diester and monoester from triacetin showed no significant enhancement by the lipase. Conversely, for the longer chain triglyceride, triolein, a significant increase in conversion to oleamide was observed with the addition of the lipase. In addition to the positive implications for the "life in ammonia" proposal, the lipase catalysed ammonolysis of triglycerides in liquid ammonia may have potential industrial applications. Triglycerides are abundant in nature, as fats and oils, and so are very cheap to acquire and the products of their ammonolysis, fatty acid amides, have many applications such as lubricating agents in the plastic industry and even medical uses. Oleamide, which is structurally related to the endogenous cannabinoid anandamide, is currently being examined for its sleep inducing effects.
In addition to the preliminary studies of life-type processes in liquid ammonia, some general reactions have been explored, in particular the ammonolysis of esters and its catalysis by the ammonium cation.
Small scale glassware can be used for the safe study of liquid ammonia at room temperature under approximately 10 bar pressure. Reactions in liquid ammonia have been previously studied generally by using a simple sampling method and analysing by GC or HPLC. Additionally, in this project, a variety of analytical techniques in liquid ammonia have also been developed such as the use of conductance, UV-vis and liquid ammonia NMR.