Is chemical evolution a part of evolution?

Chemical evolution: in the beginning there was sugar

The origin of all life lies in organic molecules. But how did these come about from inorganic substances? LMU chemist Oliver Trapp reports on a reaction path in which sugar is formed on minerals without water.

A trip back in time: more than four billion years ago, the earth was anything but a blue planet. It began to cool slowly, and the shell of various mineral layers formed. Strong volcanism shaped the picture. And the atmosphere was made up of carbon dioxide, nitrogen, methane, ammonia, hydrogen sulfide and gaseous water. In this hostile environment all life began, only what steps were required?

Researchers have been dealing with this question for decades. As early as 1953, Stanley Miller and Harold C. Urey, like US chemists, had a breakthrough. In the experiment they simulated the primordial atmosphere of the earth including spark discharge as a model for thunderstorms. In fact, in addition to other substances, they also found amino acids in their reaction that build proteins. Today we know that the reaction conditions did not correspond to the original situation. Nonetheless, the Miller-Urey experiment was a breakthrough.

How other important molecules, such as sugar, fats or nucleic acids, could have originated remained open. Without this complex construction kit, an evolution that primarily led to cyanobacteria would be inconceivable. Oliver Trapp, Professor of Organic Chemistry at LMU, deals with this central question.

Formaldehyde sugar

The search for clues begins in 1861. Alexander Butlerow, a Russian chemist, discovered that various sugars are formed from formaldehyde in the so-called formose reaction. Miller and Urey found formic acid in their experiments. When they are reduced, formaldehyde is produced. Butlerow found out that various minerals catalyze the formose reaction. These included oxides and hydroxides of calcium, barium, thallium and lead. Calcium in particular is abundant in the upper layers of the earth.

However, the hypothesis that sugars could have originated in this way has two flaws. The formose reaction creates a mixture of different compounds. In addition, this path only takes place in aqueous systems. However, sugars can also be detected on meteorites.

Trapp, together with colleagues from the LMU and the Max Planck Institute for Astronomy in Heidelberg, investigated another possibility. The researchers carried out their experiments under mechanochemical conditions. That means: All reagents and minerals were put into a ball mill. The aim of the working group was to simulate mechanical forces as they occurred in the history of the earth. This happened without the addition of solvents.

In fact, the formose reaction proceeded under the reaction conditions. Numerous minerals were suitable to catalyze the process. They adsorbed formaldehyde. Together with glycolaldehyde, this resulted in the sugar ribose. Among other things, it occurs in ribonucleic acids, which store the genetic information of living things. But higher sugars were also produced in the experiment. At the same time, only a few by-products such as lactic acid or methanol were formed.

"Our results provide a plausible explanation for the formation of sugars in the solid phase, but also in an extraterrestrial environment in which no water is available," says Trapp. This results in new pieces of the puzzle that slowly fit into a comprehensive picture and show important ways in which life comes into being. “But we are also convinced that the knowledge gained will open up completely new perspectives for research,” adds the LMU chemist.

Scientific contact:

Prof. Dr. Oliver Trapp
LMU, Department of Chemistry
+49 (0)89 2180-77461
[email protected]

Original publication:

Maren Haas, Saskia Lamour, Sarah Babette Christ & Oliver Trapp
Mineral-mediated carbohydrate synthesis by mechanical forces in a primordial geochemical setting
Communication Chemistry - Nature, 2020
https://www.nature.com/articles/s42004-020-00387-w

https://www.uni-muenchen.de/forschung/news/2020/trapp_formose.html

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