Charge Transport through Self‐Assembled Monolayers of Monoterpenoids

Abstract

The nature of the processes at the origin of life that selected specific classes of molecules for broad incorporation into cells is controversial. Among those classes selected were polyisoprenoids and their derivatives.T his paper tests the hypothesis that polyisoprenoids were early contributors to membranes in part because they (or their derivatives) could facilitate charge transport by quantum tunneling.I tm easures charge transport across self-assembled monolayers (SAMs) of carboxyl-terminated monoterpenoids (O 2 C(C 9 HX)) and alkanoates (O 2 C(C 7 HX)) with different degrees of unsaturation, supported on silver (Ag TS )b ottom electrodes,w ith Ga 2 O 3 / EGaIn top electrodes.M easurements of current density of SAMs of linear length-matched hydrocarbons-both saturated and unsaturated-showthat completely unsaturated molecules transport charge faster than those that are completely saturated by approximately afactor of ten. This increase in relative rates of charge transport correlates with the number of carboncarbon double bonds,b ut not with the extent of conjugation. These results suggest that polyisoprenoids-even fully unsaturated-are not sufficiently good tunneling conductors for their conductivity to have favored them as building blocks in the prebiotic world.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under https://doi.