The primary goal of the Center for Laboratory Astrophysics is to design, construct, and launch a new generation experimental facility capable of studying the formation and functionalization of (nitrogen containing) polycyclic aromatic hydrocarbons (PAHs) – among them functionalized aromatics relevant to RNA and DNA – on interstellar icy surfaces. This represents a hitherto unsolved key enigma relevant to the origins of life theme. This endeavor is carried out in combination with electronic structure calculations, astrochemical modeling, and astronomical observations. During the life time of cold molecular clouds, (nitrogen-bearing) polycyclic aromatic hydrocarbons ((N)PAHs) co-condense onto interstellar icy grains and become embedded within icy matrices at temperatures as low as 10 K. PAHs are organic molecules featuring laterally fused benzene rings; in NPAHs, the CH moiety is replaced by an isoelectronic nitrogen atom. (N)PAH-like molecules are omnipresent in the interstellar medium (ISM) and may account for up to 30 % of the galactic interstellar carbon. (N)PAHs are considered as key prebiotic molecules and are found at the center of life discussion as precursors to nucleobases in ribonucleic acid (RNA) – the molecule responsible for storage, transcription and translation of genetic information. Nucleotides present the main building blocks of RNA and contain a sugar (ribose), a phosphate group, and a nucleobase (adenine (C5H5N5), cytosine (C4H5N3O), guanine (C5H5N5O), uracil (C4H4N2O2)); these nucleobases have also been found in carbonaceous meteorites such as Murchison. Cytosine (C4H5N3O) and uracil (C4H4N2O2) can be derived from pyrimidine (C4N2H4), whereas adenine (C5H5N5) and guanine (C5H5N5O) are linked to purine (C5N4H4). Pyrimidine (C4N2H4) and purine (C5N4H4) in turn can be formally associated with benzene (C6H6) and indene (C9H8) by replacing two and four CH groups by isoelectronic nitrogen atoms (N). As such, NPAHs can be seen as a crucial intermediate between PAHs and nitrogen bases as found in RNA.
A photo processing of (N)PAH-doped interstellar ices may lead to an incorporation of organic side groups in (N)PAHs. Organic extracts from the Murchison meteorite also contained these substituted (N)PAHs and formed membrane-like boundary structures - the first indication of a cell type structure, which are requisite to the origin of life. The compounds that are water soluble form non-soluble vesicles, constituting molecules that possess both polar and non-polar components. The hollow droplets formed by this lipid multilayer are essential for the origin of life process since they provide an environment in which the functionalized PAHs can evolve by isolating and protecting them from the surrounding medium. Here, (N)PAHs own a functionality not identified in great proportions in the interstellar ice component, that of aromaticity. Biological functionality often uses aromaticity along with bond conjugation for redox processes, where aromatic ketones are widely used to transport electrons across cell membranes. Also, nucleic acids are polycyclic and form the backbone for information coding in DNA and RNA. The purine and pyrimidine bases are essentially functionalized single and double ring aromatics, owning carboxyl, hydroxyl and amino groups with adenine and guanine recently being identified in the Murchison meteorite. However, the elementary mechanisms and kinetics leading to (biorelevant) functionalized (N)PAHs are far from being understood, but imperative to rationalize the Origin of Life. This requires the design of a novel experimental setup embedded in the Center for Laboratory Astrophysics.
The centerpiece of the Center for Laboratory Astrophysics is a novel ultra high vacuum (UHV) surface science machine cable of mimicking the chemical evolution of extraterrestrial ices in deep space. This setup is one of its kind and allows a systematic investigation of the formation of functionalized aromatics connected to the Origin of Life theme on line and in situ in low temperature ices. The center structure breaks down the barriers and cultivates new collaborations that would not be possible otherwise with the pooled innovations and complementary research expertise being considerably more than just the sum of the parts. This project represents a collaboration between the University of Hawai’i (UH), Florida International University (FIU), and the Lebedev Physical Institute of the Russian Academy of Sciences – Samara Branch (LPI RAS). This project is defined by a Memorandum of Understanding between the University of Hawaii and the Lebedev Physical Institute of the Russian Academy of Sciences (Samara).