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

Abstract

In a famous experiment Stanley Miller showed that a large number of organic substances can emerge from sparking a mixture of methane, ammonia and hydrogen in the presence of water (Miller, Science 117:528-529, 1953). Among these substances Miller identified different amino acids, and he concluded that prebiotic events may well have produced many of Life's molecular building blocks. There have been many variants of the original experiment since, including different gas mixtures (Miller, J Am Chem Soc 77:2351-2361, 1955; Oró Nature 197:862-867, 1963; Schlesinger and Miller, J Mol Evol 19:376-382, 1983; Miyakawa et al., Proc Natl Acad Sci 99:14,628-14,631, 2002). Recently some of Miller's remaining original samples were analyzed with modern equipment (Johnson et al. Science 322:404-404, 2008; Parker et al. Proc Natl Acad Sci 108:5526-5531, 2011) and a total of 23 racemic amino acids were identified. To give an overview of the chemical variety of a possible prebiotic broth, here we analyze a "Miller type" experiment using state of the art mass spectrometry and NMR spectroscopy. We identify substances of a wide range of saturation, which can be hydrophilic, hydrophobic or amphiphilic in nature. Often the molecules contain heteroatoms, with amines and amides being prominent classes of molecule. In some samples we detect ethylene glycol based polymers. Their formation in water requires the presence of a catalyst. Contrary to expectations, we cannot identify any preferred reaction product. The capacity to spontaneously produce this extremely high degree of molecular variety in a very simple experiment is a remarkable feature of organic chemistry and possibly prerequisite for Life to emerge. It remains a future task to uncover how dedicated, organized chemical reaction pathways may have arisen from this degree of complexity.

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).…”

“…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.…”

Catalysis in the Primordial World

“…Simple molecules (H 2 O, CO, NH 3 , CH 4 ) along with complex ones were available on Earth from the early stages of its formation, but it seems that Earth's collision with a Mars-sized body, about 4.5 billion years ago which formed the Moon, removed its pristine atmosphere. 15 This kind of atmosphere did not easily yield amino acids after being exposed to ionizing agents, like UV radiation or electrical sparkling; 16 however the synthesis could have been much improved by buffering reaction solution (CaCO 3 ) and lowering of its oxidation potential (Fe 2+ ). 17 For the prebiotic synthesis and eventually emergence of life, it was also necessary to provide suitable geological habitat (increased concentration, temperature or pressure etc.)…”

Miller–Urey Spark‐Discharge Experiments in the Deuterium World

“…[1] Since that landmark work, several further studies have explored similar systems and brought more advanced analytical techniques to bear on the complex product mixtures produced, as well as arguing if ar educing atmosphere could be realistic for the early Earth. [2][3][4] As with many such experiments,the Miller-Urey reaction has been typically performed in sealed clean glassware with asmall number of pure reagents,whereas life emerged in afar more complex and heterogeneous environment. [5] However, even this simple system produces alarge and diverse range of products,t hought to be resulting from ac ombinatorial explosion of simple uncontrolled reactions,a nd their study is limited due to their perceived analytical intractability.…”