“To call it a membrane would be to give it too much credit, but it’s at least something [that] kind of encloses and could create a kind of container,” Lunine says. In 2016, he and chemist Martin Rahm (then at Cornell, and currently at Chalmers University of Technology) digitally modeled compounds of hydrogen cyanide, showing they could bind together to form sheets and rolls in a simulated hydrocarbon sea. And then in 2017, another paper published in Science Advances announced the discovery of evidence for vinyl cyanide on Titan, marking a step forward in the search for molecules capable of supporting life on the distant moon.
Back on Earth, Maurer’s experiment is simple. She and her colleagues want to see if they can get compounds to cross that oil-water boundary at all. They’ll start with the familiar genetic molecules DNA and RNA, but these will need some help crossing over. The backbone of nucleic acids like DNA and RNA is a chain of smaller molecules called phosphates, which have a slight negative charge. But negatively charged molecules are less likely to interact with oil than with water, so our familiar genetic molecules may not move into the oil droplets very readily.
However, other molecules might pair with the nucleic acids and help sneak them across the boundary. Biochemical companies have developed molecules called transection agents, which help move nucleic acids through membranes, and one of the team’s goals is to look for combinations of DNA and transection agents that can migrate into the hydrocarbon droplets and remain stable.
“That’s basically saying, ‘Can we tease our biology into functioning at some level in these strange environments?’ ” says Georgia Tech University molecular biologist Loren Williams, who is especially interested in how polymers behave in liquid chloroform.
The team also wants to swap out the nucleic acids’ phosphorus for silicon, creating a molecule that dissolves more easily in hydrocarbons. They also plan to test an alternative genetic molecule using so-called “non-canonical nucleotides,” substituting other chemicals for the familiar adenine, thymine, guanine, and cytosine.
And then there are the really exotic ideas. Bracher’s group at Saint Louis University is working on a completely synthetic molecule that will work like DNA but be made of completely different molecules that form a different type of chemical bond. Instead of the hydrogen bonds that link DNA base pairs, Bracher’s version would use base pairs that share molecules called thioesters.
There’s reason to think it could work. In 2015, Benner, who founded the Foundation for Applied Molecular Evolution in 2001 and is not involved in Bracher’s project, tested a version of DNA with an ether backbone in a solvent of kerosene. He found that this combination wouldn’t work to form life on a place nearly as cold as Titan, but on some so-called “warm Titan” exoplanets, it might be a good option.
“Given how many exoplanets we’re finding around distant stars, chances are there are going to be other worlds like Titan that could have something interesting going on,” says Bracher.