Chemical Analysis of a “Miller-Type” Complex Prebiotic Broth

Abstract

We have analyzed the chemical variety obtained by Miller-Urey-type experiments using nuclear magnetic resonance (NMR) spectroscopy and coherent anti-Stokes Raman scattering (CARS) spectroscopy, gas chromatography followed by mass spectrometry (GC/MS) and two-dimensional gas chromatography followed by mass spectrometry (GCxGC/MS). In the course of a running Miller-Urey-type experiment, a hydrophobic organic layer emerged besides the hydrophilic aqueous phase and the gaseous phase that were initially present. The gas phase mainly consisted of aromatic compounds and molecules containing C≡C or C≡N triple bonds. The hydrophilic phase contained at least a few thousands of different molecules, primarily distributed in a range of 50 and 500 Da. The hydrophobic phase is characterized by carbon-rich, oil-like compounds and their amphiphilic derivatives containing oxygen with tensioactive properties. The presence of a wide range of oxidized molecules hints to the availability of oxygen radicals. We suggest that they intervene in the formation of alkylated polyethylene glycol (PEG) in the oil/water interface. CARS spectroscopy revealed distinct vibrational molecular signatures. In particular, characteristic spectral bands for cyanide compounds were observed if the broth was prepared with electric discharges in the gaseous phase. The characteristic spectral bands were absent if discharges were released onto the water surface. NMR spectroscopy on the same set of samples independently confirmed the observation. In addition, NMR spectroscopy revealed overall high chemical variability that suggests strong non-linearities due to interdependent, sequential reaction steps.Electronic supplementary materialThe online version of this article (doi:10.1007/s11084-016-9528-8) contains supplementary material, which is available to authorized users.

A Miller–Urey broth mirrors the mass density distribution of all Beilstein indexed organic molecules

“…In previous work (Scherer et al 2017, Wollrab et al 2016 we showed that oxygen reservoirs appear to build up in the broth, likely in form of peroxides, a direct product from oxygen diradicals created in the discharge. These can even release oxygen radicals (Scherer et al 2017). In the positive ionization mode employed here, oxygencontaining molecules are more easily ionized and will preferentially appear in the mass spectra.…”

“…At the end of the experiment (164 h), the remaining liquid was transferred to a sterile flask and stored at 8°C during a few hours until further analysis. The broth contains hydrophobic and hydrophilic components (Scherer et al 2017). Mass spectra of different broths from consecutive Miller-Urey experiments performed under the same experimental conditions, as obtained by direct injection into a Waters Q-Tof Micro mass spectrometer equipped with ESI, did not exhibit any detectable differences.…”

“…The Miller-Urey experiment produces molecules in a way that is subject to a great deal of randomness (Scherer et al 2017). Here we compared the observed molecular mass (i.e.…”

“…While small molecules with elevated vapor pressure essentially remain in the gas phase and remain subject to further discharge, larger and more polar molecules are more likely to dissolve in the liquid phase where they may react further. A previous analysis showed that the Miller-Urey experiment produces many molecules with unsaturated (triple or double) bonds in the gas and in the liquid parts of the broth (Scherer et al 2017, Wollrab et al 2016. These unsaturated bonds tend to react further.…”

“…Over time more substances appeared in the spectra and the distribution shifted towards smaller masses. knowledge there is no experimental work besides (Wollrab et al 2016, Scherer et al 2017 that addresses the enormous molecular variety produced by discharge experiments blindly, that is, without initial bias towards certain molecules or classes of molecules beyond technical limitations of the employed techniques.…”