An embryo of protocell membrane: The capsule of graphene oxide

TL;DR

This paper proposes that graphene oxide could have served as an early protocell membrane on Earth, capable of encapsulating biochemical reactions and selectively allowing ion permeation, thus contributing to the origin of life.

Contribution

It introduces a novel theory that graphene oxide may have been an embryo of protocell membranes, supported by experimental evidence of capsule formation and ion selectivity.

Findings

Graphene oxide and phospholipid-graphene oxide can form capsules in acidic, high-salinity solutions.

Graphene oxide exhibits selective permeability for monovalent metal ions similar to biological ion channels.

Capsule formation and ion exchange properties suggest a role in early life development.

Abstract

Many signs indicate that the graphene could widely occur on the early Earth. Here, we report a new theory that graphene might be an embryo of protocell membrane, and found several evidences. Firstly, the graphene oxide and phospholipid-graphene oxide composite would curl into capsules in strongly acidic saturated solution of Pb(NO3)2 at low temperature, providing a protective space for biochemical reactions. Secondly, L-animi acids exhibit higher reactivity than D-animi acids for graphene oxides in favor of the formation of left-handed proteins. Thirdly, monolayer graphene with nanopores prepared by unfocused 84Kr25+ has high selectivity for permeation of the monovalent metal ions (Rb+ > K+ > Cs+ > Na+ > Li+), but does not allow Cl- through, which could be attributed to the ion exchange of oxygen-containing groups on the rim of nanopores. It is similar to K+ channels, which would cause efflux of some ions from capsule of graphene oxides with the decrease of pH in the primitive ocean, creating a suitable inner condition for the origin of life. Consequently, the strongly acidic, high salinity and strong radiation as well as temperature changes in the early Earth, regarded as negative factors, would be indispensable for the origin of protocell. In short, graphene bred life, but digested gradually by the evolution.