A common antifreeze compound is methanol, the simplest kind of alcohol molecule. Now scientists find that even methanol can get trapped within ice-like cages, findings detailed in the Proceedings of the National Academy of Sciences that could influence what researchers think about the potential for life in Saturn’s moon Titan and other icy celestial bodies.
Methanol is a colorless, flammable, poisonous chemical also known as wood alcohol that can blind or kill if drunk. One of the best-known uses for it is as antifreeze, suppressing the formation of ice when temperatures drop below the normal freezing point of water. The potential existence of methanol on Titan lends credence to the idea that it harbors watery oceans under its icy shell. This in turn raises the possibility that life as we know it might dwell there, since life exists virtually everywhere there is liquid water on Earth.
“Both methanol and ammonia, when mixed with water in the right proportions, can stay liquid down to very low temperatures,” said physical chemist John Ripmeester at the National Research Council of Canada in Ottawa.
Methanol is often used by industry to prevent ice-like lattices known as clathrate hydrates from forming within oil and gas pipelines. Clathrates all serve as cages that entrap molecules — the ones that can block pipelines typically hold methane.
In the roughly 70 years of research of methanol in relation to clathrate hydrates, there was little or no direct evidence that clathrates might cage methanol. Now Ripmeester and his colleagues find methanol can indeed get trapped inside clathrate hydrate structures after all.
The scientists first experimented with clathrates not made of water ice, but rather clathrates made of organic compounds such as tetrahydrofuran hydrate. At temperatures near zero degrees C, X-ray diffraction and nuclear magnetic resonance (NMR) spectroscopy revealed methanol could get incorporated within such clathrate hydrate lattices.
Solutions consisting solely of water and methanol could not be frozen to form clathrate hydrates. However, experiments and molecular dynamics simulations hinted that solutions containing water, methanol and methane could form these ice-like lattices.
Unexpectedly, the researchers discovered that at low temperatures, methanol can actually promote the formation of solid clathrate hydrates instead of preventing it. These findings might influence whether and how methanol is used to help suppress clathrate formation in pipelines in the future, especially in the deep ocean and in polar climates.
“None of the models used to predict hydrate formation conditions in pipelines are accurate as they all assume that methanol will not go into a hydrate,” Ripmeester said.
By spurring the formation of methane clathrate hydrates on icy celestial bodies, methanol could also explain the relatively high concentrations of methane and other hydrocarbons seen on the surface of Saturn’s moon Enceladus, despite predictions that most hydrocarbons should have escaped from its atmosphere long ago. As temperatures fluctuate, clathrate hydrates on these bodies “may anneal giving different compositions, or even may disappear again,” Ripmeester said.
One intriguing aspect of these findings regarding the possibility of life on alien worlds is how clathrate
hydrates can bring together key ingredients of life close together, such as water, methane, ammonia and methanol. “This closeness of these various molecules gives a favorable environment for producing more complex compounds as brought about, for instance, by radiation,” Ripmeester said.