Shadow of a Shadow: Ferrocyanide and Nitroprusside as Sunscreens for Photosensitive Prebiotic Molecules

Stellar irradiation is thought to be a significant contributor to the origin of life. Ultraviolet (UV) light interacting with iron cyanide complexes may play an important role in prebiotic chemistry. The UV-Visible (UV-Vis) spectra of these iron cyanide complexes can be measured by the same source that drives the chemistry, providing a real-time in situ quantitative analysis of prebiotically relevant, UV-driven photochemistry. We measure the UV-Vis absorbances of ferrocyanide and nitroprusside, and relate these absorbances to known concentrations. We show that these absorbances can be combined to accurately predict the concentrations of ferrocyanide-nitroprusside mixtures that could be generated from ferrocyanide and nitroxyl salts irradiated by ultraviolet light. The ferrocyanide molar attenuation coefficients were found to be maximal at the following: εferrocyanide(340nm)=(2.2±0.4)×103dm2mol-1. Nitroprusside peaks show the following values: εnitroprusside(340nm)=(4.1±0.3)×102dm2mol-1, εnitroprusside(400nm)=(1.71±0.05)×102dm2mol-1, and εnitroprusside(500nm)=62.1±1.7dm2mol-1. With the help of our measured absorbances, we consider ferrocyanide and nitroprusside to function as sunscreens. In the absence of continuous ferrocyanide sources, UV-sensitive compounds could be protected on timescales of months. This would allow for compounds like nicotinamide adenine dinucleotide, NADH, to survive for over a year at depths of 5 m, compared to a lifetime of 6 months when unprotected. Our toy model constrains the photochemical survival of compounds of interest to the origin of life community across a comprehensive spectral range and can be used to constrain the survival using different exoplanetary irradiative conditions; thus, we are able to explore the UV environment with the presence of ferrocyanide and nitroprusside and contribute to the wider discussion surrounding the prevalence of the origin of life in the Universe.