Nanoparticles: the future or ancient past?

Hot spring Grand Prismatic Spring, Yellowstone, illustrative picture.
author: Jim Peaco, source: Wikipedia

Minerals are essential to life and they weren´t any less important when life arose – that much has been known since the 1950s. In 1966 chemist Cairns-Smith even presented a hypothesis that the whole beginning of life depended solely on clay minerals. Current scientific knowledge corrects his hypothesis a little as it wasn´t only clay minerals that were important but the geochemical environment of early Earth as a whole. The planet must have been a paradise for early life but how did the paradise look like and what processes were essential? The importance of minerals is undeniable. Together with crystals, the mineral surface plays an incredibly important role because it facilitates the concentration and selection of various substances, enabling the creation of much more complicated compounds. Current scientific theories talk about the so-called kinetic trap – trapping of suitable chemical substances during reactions. Hot springs could have been an excellent environment for this thanks to strong volcanic activity on early Earth. Hot places where asteroids fell could also be suitable. According to Czech scientists, it is very likely that these were the places where life came into existence. 

What do nanoparticles have to do with all of this? This study focuses on one type of nanoparticles – so-called quantum dots, specifically on those made of zinc and cadmium (ZnCd). Quantum dots are rather a subject of technological research considering their wide range of industrial applications. Usually, they are prepared artificially from two types of metal. Their small proportions give them completely different properties than the original material. It is also possible to “tune” their properties by changing their size. However, quantum dots aren´t only industrial. Nature itself can create them. For example, they arise in hydrothermal springs or biomass combustion and are also an important part of our surroundings. Quantum dots could also play a very important role in the creation of life thanks to their universal catalytic properties. 

The research group focused on three main aspects of ZnCd quantum dots’ significance. ZnCd dots served as a model system for the research of their origin under early Earth conditions. The synthesis from a solution of relevant metal ions in the form of their salts, sulfur alcohols, and formamide, which is a very important molecule in prebiotic chemistry, is easy. In such a solution, quantum dots emerge solely thanks to UV radiation simulating the early Sun rays coming to Earth´s surface which lacked the ozone layer then. The environment for the creation of quantum dots is thus the same as the one needed for the beginning of life.

Further, the study focused on the function of ZnCd quantum dots. The first important application is catalysis. Dots can support the synthesis of RNA nucleic bases in the presence of formamide. The synthesis then yields more of the molecules essential to life as we know it. The difference is especially noticeable in pyrimidine bases which usually have lower yields than purine bases when formamide is present. However, if the synthesis is facilitated by ZnCd quantum dots, the yield of pyrimidine bases is suddenly larger than of the purine ones. The second function of the nanoparticles in question is the nanozyme function. Nanozymes are tiny (nano)particles that act as enzymes. ZnCd quantum dots can mimic an enzyme called peroxidase thus acting as an oxidation agent in the presence of hydrogen peroxide. Besides that, they can imitate another group of enzymes essential to the creation of life and the functioning of basic processes in genetic expression – restriction endonucleases. These enzymes cleave DNA strands in precise places.

Scientists managed to prove that formamide, which is an important component of so-called prebiotic soup (the chemical mix that was present before life began), provides a suitable environment for ZnCd quantum dots´ creation using UV radiation. The peroxidase activity of those nanoparticles has been proven by experiments mimicking the conditions of early Earth. Quantum dots surely could have had their place in prebiotic chemistry. However, other types of quantum dots and their complex nanozymatic activity remains to be explored.

Nejdl, L.; Petera, L.; Šponer, J.; Zemánková, K.; Pavelicová, K.; Knížek, A.; Adam, V.; Vaculovičová, M.; Ivanek, O.; Ferus, M. Quantum Dots in Peroxidase-like Chemistry and Formamide-Based Hot Spring Synthesis of Nucleobases. Astrobiology 2022, 22 (5), 541–551.

Magda Křelinová