prebiotic nucleobases Dotaz Zobrazit nápovědu
The photoinduced isomerization of diaminomaleonitrile (DAMN) to diaminofumaronitrile (DAFN) was suggested to play a key role in the prebiotically plausible formation of purine nucleobases and nucleotides. In this work we analyze two competitive photoisomerization mechanisms on the basis of state-of-the-art quantum-chemical calculations. Even though it was suggested that this process might occur on the triplet potential-energy surface, our results indicate that the singlet reaction channel should not be disregarded either. In fact, the peaked topography of the S1 /S0 conical intersection suggests that the deexcitation should most likely occur on a sub-picosecond timescale and the singlet photoisomerization mechanism might effectively compete even with a very efficient intersystem crossing. Such a scenario is further supported by the relatively small spin-orbit coupling of the S1 and T2 states in the Franck-Condon region, which does not indicate a very effective triplet bypass for this photoreaction. Therefore, we conclude that the triplet reaction channel in DAMN might not be as prominent as was previously thought.
- Klíčová slova
- isomerization, nucleobases, nucleotides, photochemistry, quantum chemistry,
- MeSH
- fotochemie MeSH
- fumaráty chemie MeSH
- kvantová teorie MeSH
- molekulární modely MeSH
- nitrily chemie MeSH
- nukleotidy chemie MeSH
- prebiotika MeSH
- puriny chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- diaminofumaronitrile MeSH Prohlížeč
- diaminomaleonitrile MeSH Prohlížeč
- fumaráty MeSH
- nitrily MeSH
- nukleotidy MeSH
- prebiotika MeSH
- purine MeSH Prohlížeč
- puriny MeSH
Synthesis of nucleobases in nonaqueous environments is an alternative way for the emergence of terrestrial life, which could solve the fundamental problem connected to the hydrolytic instability of nucleic acid components in an aqueous environment. In this contribution, we present a plausible reaction route for the prebiotic synthesis of nucleobases in formamide, which does not require participation of the formamide trimer and aminoimidazole-carbonitrile intermediates. The computed activation energy of the proposed pathway is noticeably higher than that of the HCN-based synthetic route, but it is still feasible under the experimental conditions of the Saladino synthesis. We show that, albeit both the pyrimidine and purine ring formation utilizes the undissociated form of formamide, the dehydration product of formamide, HCN, may also play a key role in the mechanism. The rate determining step of the entire reaction path is the cyclization of the diaza-pentanimine precursor. The subsequent formation of the imidazole ring proceeds with a moderate activation energy. Our calculations thus demonstrate that the experimentally suggested reaction path without the involvement of aminoimidazole-carbonitrile intermediates is also a viable alternative for the nonaqueous synthesis of nucleobases.
- MeSH
- chemické modely MeSH
- cyklizace MeSH
- formamidy chemie MeSH
- imidazoly chemie MeSH
- katalýza MeSH
- kinetika MeSH
- kvantová teorie MeSH
- nukleové kyseliny chemie MeSH
- puriny chemie MeSH
- pyrimidiny chemie MeSH
- termodynamika MeSH
- voda chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Názvy látek
- formamide MeSH Prohlížeč
- formamidy MeSH
- imidazoly MeSH
- nukleové kyseliny MeSH
- puriny MeSH
- pyrimidiny MeSH
- voda MeSH
Synthesis of RNA nucleobases from formamide is one of the recurring topics of prebiotic chemistry research. Earlier reports suggest that thymine, the substitute for uracil in DNA, may also be synthesized from formamide in the presence of catalysts enabling conversion of formamide to formaldehyde. In the current paper, we show that to a lesser extent conversion of uracil to thymine may occur even in the absence of catalysts. This is enabled by the presence of formic acid in the reaction mixture that forms as the hydrolysis product of formamide. Under the reaction conditions of our study, the disproportionation of formic acid may produce formaldehyde that hydroxymethylates uracil in the first step of the conversion process. The experiments are supplemented by quantum chemical modeling of the reaction pathway, supporting the plausibility of the mechanism suggested by Saladino and coworkers.
Besides delivering plausible prebiotic feedstock molecules and high-energy initiators, extraterrestrial impacts could also affect the process of abiogenesis by altering the early Earth's geological environment in which primitive life was conceived. We show that iron-rich smectites formed by reprocessing of basalts due to the residual post-impact heat could catalyze the synthesis and accumulation of important prebiotic building blocks such as nucleobases, amino acids and urea.
- MeSH
- aminokyseliny chemie MeSH
- evoluce chemická MeSH
- jíl chemie MeSH
- katalýza MeSH
- meteoroidy * MeSH
- mimozemské prostředí chemie MeSH
- močovina chemie MeSH
- původ života MeSH
- silikáty chemie MeSH
- železo chemie MeSH
- Země (planeta) MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- aminokyseliny MeSH
- basalt MeSH Prohlížeč
- jíl MeSH
- močovina MeSH
- silikáty MeSH
- Smectite MeSH Prohlížeč
- železo MeSH
The Miller-Urey experiments pioneered modern research on the molecular origins of life, but their actual relevance in this field was later questioned because the gas mixture used in their research is considered too reducing with respect to the most accepted hypotheses for the conditions on primordial Earth. In particular, the production of only amino acids has been taken as evidence of the limited relevance of the results. Here, we report an experimental work, combined with state-of-the-art computational methods, in which both electric discharge and laser-driven plasma impact simulations were carried out in a reducing atmosphere containing NH3 + CO. We show that RNA nucleobases are synthesized in these experiments, strongly supporting the possibility of the emergence of biologically relevant molecules in a reducing atmosphere. The reconstructed synthetic pathways indicate that small radicals and formamide play a crucial role, in agreement with a number of recent experimental and theoretical results.
- Klíčová slova
- asteroid impact, life origins, reducing atmosphere,
- MeSH
- amoniak chemie MeSH
- atmosféra MeSH
- chemické modely MeSH
- evoluce chemická MeSH
- formamidy chemie MeSH
- oxid uhelnatý chemie MeSH
- oxidace-redukce MeSH
- původ života MeSH
- RNA chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- amoniak MeSH
- formamide MeSH Prohlížeč
- formamidy MeSH
- oxid uhelnatý MeSH
- RNA MeSH
Chemical environments of young planets are assumed to be significantly influenced by impacts of bodies lingering after the dissolution of the protoplanetary disk. We explore the chemical consequences of impacts of these bodies under reducing planetary atmospheres dominated by carbon monoxide, methane, and molecular nitrogen. Impacts were simulated by using a terawatt high-power laser system. Our experimental results show that one-pot impact-plasma-initiated synthesis of all the RNA canonical nucleobases and the simplest amino acid glycine is possible in this type of atmosphere in the presence of montmorillonite. This one-pot synthesis begins with de novo formation of hydrogen cyanide (HCN) and proceeds through intermediates such as cyanoacetylene and urea.
- Klíčová slova
- Extraterrestrial objects impacts, Hydrogen cyanide, Origin of life, Primitive Earth atmosphere,
- MeSH
- atmosféra MeSH
- glycin * MeSH
- kyanovodík * MeSH
- mimozemské prostředí MeSH
- nukleotidy * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- glycin * MeSH
- kyanovodík * MeSH
- nukleotidy * MeSH
One of the most controversial questions of the RNA world theory is the formation of nucleosides through the reaction of nucleobases with ribose. The study presented herein discusses the thermodynamics of nucleoside formation under prebiotic conditions through the classical reaction route, which involves ribose and cytosine, as well as through the novel pathway suggested by Powner et al. [Nature 2009, 459, 239-242]. Our computations show that, in contrast to the classical pathway, the route proposed by Powner et al. perfectly satisfies all conditions of a typical metabolic pathway that occurs in living organisms. In addition, we reveal the reasons that render the reaction of ribose with nucleobases endothermic and, thereby, less plausible under prebiotic conditions. We show that phosphates may play an indispensable role in the glycosylation of nucleobases by making this endothermic reaction step exothermic. In addition, we describe the catalytic role of phosphate anions in the formation of 2-aminooxazole, which is one of the key steps of the synthetic route reported by Powner et al.
- MeSH
- anionty chemie MeSH
- chemické modely MeSH
- fosfáty chemie MeSH
- glykosylace MeSH
- katalýza MeSH
- kvantová teorie MeSH
- nukleosidy chemie MeSH
- oxazoly chemie MeSH
- prebiotika MeSH
- ribonukleosidy chemie MeSH
- RNA chemie MeSH
- termodynamika MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Názvy látek
- 2-aminooxazole MeSH Prohlížeč
- anionty MeSH
- fosfáty MeSH
- nukleosidy MeSH
- oxazoly MeSH
- prebiotika MeSH
- ribonukleosidy MeSH
- RNA MeSH
High-yielding and selective prebiotic syntheses of RNA and DNA nucleotides involve UV irradiation to promote the key reaction steps and eradicate biologically irrelevant isomers. While these syntheses were likely enabled by UV-rich prebiotic environment, UV-induced formation of photodamages in polymeric nucleic acids, such as cyclobutane pyrimidine dimers (CPDs), remains the key unresolved issue for the origins of RNA and DNA on Earth. Here, we demonstrate that substitution of adenine with 2,6-diaminopurine enables repair of CPDs with yields reaching 92%. This substantial self-repairing activity originates from excellent electron donating properties of 2,6-diaminopurine in nucleic acid strands. We also show that the deoxyribonucleosides of 2,6-diaminopurine and adenine can be formed under the same prebiotic conditions. Considering that 2,6-diaminopurine was previously shown to increase the rate of nonenzymatic RNA replication, this nucleobase could have played critical roles in the formation of functional and photostable RNA/DNA oligomers in UV-rich prebiotic environments.
- MeSH
- 2-aminopurin analogy a deriváty farmakologie MeSH
- adenin MeSH
- DNA účinky léků účinky záření MeSH
- nukleotidy MeSH
- nukleové kyseliny MeSH
- oprava DNA účinky léků MeSH
- pyrimidinové dimery MeSH
- RNA chemie MeSH
- simulace molekulární dynamiky MeSH
- ultrafialové záření škodlivé účinky MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- 2-aminopurin MeSH
- 2,6-diaminopurine MeSH Prohlížeč
- adenin MeSH
- DNA MeSH
- nukleotidy MeSH
- nukleové kyseliny MeSH
- pyrimidinové dimery MeSH
- RNA MeSH
2,6-Diaminopurine (2,6-dAP) is an alternative nucleobase that potentially played a role in prebiotic chemistry. We studied its excited state dynamics in the gas phase by REMPI, IR-UV hole burning, and ps pump-probe spectroscopy and performed quantum chemical calculations at the SCS-ADC(2) level of theory to interpret the experimental results. We found the 9H tautomer to have a small barrier to ultrafast relaxation via puckering of its 6-membered ring. The 7H tautomer has a larger barrier to reach a conical intersection and also has a sizable triplet yield. These results are discussed relative to other purines, for which 9H tautomerization appears to be more photostable than 7H and homosubstituted purines appear to be less photostable than heterosubstituted or singly substituted purines.
- Klíčová slova
- excited state dynamics, gas phase spectroscopy, prebiotic nucleobases, quantum computations,
- Publikační typ
- časopisecké články MeSH
50 years after the historical Miller-Urey experiment, the formamide-based scenario is perhaps the most powerful concurrent hypothesis for the origin of life on our planet besides the traditional HCN-based concept. The information accumulated during the last 15 years in this topic is astonishingly growing and nowadays the formamide-based model represents one of the most complete and coherent pathways leading from simple prebiotic precursors up to the first catalytically active RNA molecules. In this work, we overview the major events of this long pathway that have emerged from recent experimental and theoretical studies, mainly concentrating on the mechanistic, methodological, and structural aspects of this research.
- Klíčová slova
- RNA, formamide, nucleobases, nucleotides, origin of life,
- MeSH
- formamidy chemie MeSH
- katalýza MeSH
- oligonukleotidy chemie metabolismus MeSH
- původ života MeSH
- RNA chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
- Názvy látek
- formamidy MeSH
- oligonukleotidy MeSH
- RNA MeSH
