Prebiotic Photoredox Synthesis from Carbon Dioxide and Sulfite

Carbon dioxide (CO2) is the major carbonaceous component of many planetary atmospheres including the Earth throughout its history, and prebiological chemistry that reduces this C1 feedstock to organics has accordingly been sought. Carbon fixation chemistry utilizing hydrogen as stoichiometric reductant tends to require high pressures and temperatures, and yields of products of potential use to nascent biology are low1 . Here we demonstrate efficient ultraviolet (UV) photoredox chemistry between CO2 and sulfite (SO3 2–) that generates organics and sulfate (SO4 2– ). The chemistry is initiated by electron photodetachment from SO3 2– giving sulfite radicals and hydrated electrons, which reduce CO2 to its radical anion. By subjecting individual products and putative intermediates to the reaction conditions and analyzing the resultant mixtures, a network of ensuing reactions that can rationalize the products was revealed. In this way it was further discovered that citrate, malate, succinate, and tartrate can be generated by irradiation of glycolate in the presence of SO3 2– . The simplicity of this carboxysulfitic chemistry and the widespread occurrence and abundance of its feedstocks suggest that it could have readily taken place on the early Earth as well as on the surfaces of many rocky planets. The environmental availability of the carboxylate products on Earth could have driven the development of central carbon metabolism before the advent of biological CO2 fixation.

Prebiotic Photoredox Synthesis from Carbon Dioxide and Sulfite

Carbon dioxide (CO2) is the major carbonaceous component of many planetary atmospheres including the Earth throughout its history, and prebiological chemistry that reduces this C1 feedstock to organics has accordingly been sought. Carbon fixation chemistry utilizing hydrogen as stoichiometric reductant tends to require high pressures and temperatures, and yields of products of potential use to nascent biology are low1 . Here we demonstrate efficient ultraviolet (UV) photoredox chemistry between CO2 and sulfite (SO3 2–) that generates organics and sulfate (SO4 2– ). The chemistry is initiated by electron photodetachment from SO3 2– giving sulfite radicals and hydrated electrons, which reduce CO2 to its radical anion. By subjecting individual products and putative intermediates to the reaction conditions and analyzing the resultant mixtures, a network of ensuing reactions that can rationalize the products was revealed. In this way it was further discovered that citrate, malate, succinate, and tartrate can be generated by irradiation of glycolate in the presence of SO3 2– . The simplicity of this carboxysulfitic chemistry and the widespread occurrence and abundance of its feedstocks suggest that it could have readily taken place on the early Earth as well as on the surfaces of many rocky planets. The environmental availability of the carboxylate products on Earth could have driven the development of central carbon metabolism before the advent of biological CO2 fixation.

Mass-resolved electronic circular dichroism ion spectroscopy

DNA and proteins are chiral: Their three-dimensional structures cannot be superimposed with their mirror images. Circular dichroism spectroscopy is widely used to characterize chiral compounds, but data interpretation is difficult in the case of mixtures. We recorded the electronic circular dichroism spectra of DNA helices separated in a mass spectrometer. We studied guanine-rich strands having various secondary structures, electrosprayed them as negative ions, irradiated them with an ultraviolet nanosecond optical parametric oscillator laser, and measured the difference in electron photodetachment efficiency between left and right circularly polarized light. The reconstructed circular dichroism ion spectra resembled those of their solution-phase counterparts, thereby allowing us to assign the DNA helical topology. The ability to measure circular dichroism directly on biomolecular ions expands the capabilities of mass spectrometry for structural analysis.

Influence of the N atom and its position on electron photodetachment of deprotonated indole and azaindole

Dipole bound state and its vibrational structure observed in deprotonated 7-azaindole by recording the signal of 7-azaindolyl stable neutral radical.

Probing Ligand and Cation Binding Sites in G-Quadruplex Nucleic Acids by Mass Spectrometry and Electron Photodetachment Dissociation Sequencing

ABSTRACTMass spectrometry provides exquisite detail on ligand and cation binding stoichiometries with a DNA target. The next important step is to develop reliable methods to determine the cation and ligand binding sites in each complex separated by the mass spectrometer. To circumvent the caveat of ligand derivatization for cross-linking, which may alter the ligand binding mode, we explored a tandem mass spectrometry (MS/MS) method that does not require ligand derivatization, and is therefore also applicable to localize metal cations. By obtaining more negative charge states for the complexes using supercharging agents, and by creating radical ions by electron photodetachment, oligonucleotide bonds become weaker than the DNA-cation or DNA-ligand noncovalent bonds upon collision-induced dissociation of the radicals. This electron photodetachment (EPD) method allows to locate the binding regions of cations and ligands by top-down sequencing of the oligonucleotide target. The very potent G-quadruplex ligands 360A and PhenDC3 were found to replace a potassium cation and bind close to the central loop of 4-repeat human telomeric sequences.

Probing ligand and cation binding sites in G-quadruplex nucleic acids by mass spectrometry and electron photodetachment dissociation sequencing

Tandem mass spectrometry: native top-down sequencing by electron photodetachment dissociation (EPD) reveals ligand binding sites on DNA G-quadruplexes.