From interstellar systems to terrestrial organic and biomolecules: a synergetic theoretical and experimental rotational study

The hunt for new complex organic molecules (COMs) in the interstellar medium (ISM) based on the synergy between radio astronomy and rotational spectroscopy is among the most coveted targets in current Astronomy and Astrophysics. Recent improvements in sensitivity, bandwidth, and spatial resolution in instrumentation at existing telescopes, together with the construction of new observational facilities, have opened a new window of possibilities for studying rich astronomical sources, awaiting the detection of entirely new species. Furthermore, understanding their formation pathways and their corresponding intricate chemical networks remains some of the key challenges for Astrochemistry. In this context, the scientific community is constantly pushing the limits of the complexity of interstellar chemistry, highlighting the recent detection of systems of unparalleled degrees of complexity, such as cyanonaftalene or ethanolamine. Nevertheless, many molecules that are reasonable interstellar candidates remain unexplored even in the laboratory because they are solid and labile molecules with very low vapor pressure, which usually decompose during conventional experiments. To overcome the urgent need for rotational data, in the first part of the present Thesis, we have carried out a combinational theoretical and laboratory rotational study of several COMs as a prerequisite to search for them in the ISM. Hence, we have used a battery of state-of-the-art rotational spectroscopic techniques to characterize the rotational spectrum of several relevant glycine isomers: acetohydroxamic acid and glycolamide; two cyano bearing compounds: cyanoacetamide and cyanoacetic acid; as well as two aldehydes: n- and i-butyraldehyde, together with a purely computational study of amino acetaldehyde. Moreover, we have explored the potential energy surfaces (PES) on the gas-phase formation of several protonated glycine isomers along with protonated cyanoacetamide, finding for each case a feasible interstellar formation process. Our precise laboratory measurements have been subsequently used to search for some of the studied molecular systems toward the giant molecular cloud complex Sagittarius B2 (Sgr B2) using different ALMA line surveys and toward the cold molecular cloud G+0.693-0.027 employing IRAM 30-m and Yebes 40-m observations. Regardless of the differences in their physical-chemical properties, both astronomical sources stand among the richest chemical inventories in the ISM. To date, we have not achieved any positive identification of the studied molecules. Nevertheless, the experimental data reported in this thesis will also enable eventual searches for the yet undetected species in the ISM using new and more sensitive astronomical line surveys. These future identifications in space should establish a road map that will help to understand the levels of chemical complexity reached in the ISM, as well as to decipher the link between interstellar chemistry and the rich chemical reservoir found in comets and meteorites. In the second part of this Thesis, we have taken advantage of the excellent sensitivity and specificity of our laser ablation Fourier transform microwave techniques to unleash the conformational panorama and molecular shape of several organic and biomolecules for the first time. Herein, we report a comprehensive microwave study of the amino acid L-DOPA and unveil the three-dimensional structure of two organic synthons of significant relevance: squaric acid and its water clusters and a “shape-shifting” (fluxional) substituted barbaralone. The latest exhibit an interesting valence tautomerism, which has been conclusively deciphered in the gas phase using rotational spectroscopy. We also analyze the role of the intramolecular interactions that modulate the conformational behavior of these systems using a combination of precise experimental data, such as the analysis of the 14N hyperfine structure in the case of N-bearing species (i.e., L-DOPA) and quantum chemical computations.Departamento de Química Física y Química InorgánicaDoctorado en Químic

Amino acetaldehyde conformers: structure and spectroscopic properties

Producción CientíficaWe present a computational study of the different conformers of amino acetaldehyde. This molecule is a precursor of glycine and also an isomer of the detected molecules acetaldehyde and methylformamide. In addition, a previous theoretical result shows that amino acetaldehyde could be formed from the gas phase reaction of formamide with CH+5⁠. Different computational approaches, going from density functional theory (DFT) to coupled cluster (CC) calculations, are employed for the characterization of the amino acetaldehyde conformers. We locate four low-lying conformation on the singlet potential energy surface (PES), two with a synperiplanar arrangement of the carboxylic oxygen atom and the NH2 group, and the other two conformers with an anticlinal disposition. All levels of theory predict the conformer with a synperiplanar arrangement and the H atoms of the NH2 group pointing in the direction of the oxygen, denoted as in-sp-amino acetaldehyde, as the most stable. The viability of the interconversion processes between the four conformers in space is analysed. Relevant spectroscopic parameters to rotational spectroscopy with ‘spectroscopic’ accuracy at the composite level are reported. Vibrational frequencies and infrared intensities are also computed at the CC with single and double excitations (CCSD) level including anharmonic corrections. This information could help in the experimental characterization of amino acetaldehyde that could be considered as a good candidate molecule to be searched for in space.Ministerio de Economía, Industria y Competitividad (Grant AYA2017-87515-P)Junta de Castilla y León (Ref. project VA010G18

Unveiling the shape of N-Acetylgalactosamine: A cancer-associated sugar derivative

Producción CientíficaIn the present work, we report the first rotational study of N-acetylgalactosamine, a cancer-associated sugar derivative, by means of high-resolution rotational spectroscopy. Two different conformers have been conclusively characterized using broadband Fourier transform microwave spectroscopy coupled with a laser ablation vaporization system. Additionally, we performed a comprehensive analysis of the intramolecular interactions that govern these structures, which allowed us to both characterize the existence of intramolecular hydrogen bond networks that drive the intrinsic conformation panorama of N-acetylgalactosamine and further rationalize the biological role of this aminosugar derivative as part of the Tn antigen.Ministerio de Ciencia, Innovación y Universidades (project PID2019-111396GB-I00)Junta de Castilla y León (project VA244P20)European Union’s Seventh Framework Programme (FP/2007-2013)/ERC-2013-SyG (grant 610256 NANOCOSMOS

Shape‐shifting molecules: unveiling the valence tautomerism phenomena in bare barbaralones

Producción CientíficaWe report a state-of-the-art spectroscopic study of an archetypical barbaralone, conclusively revealing the valence tautomerism phenomena for this bistable molecular system. The two distinct 1- and 5-substituted valence tautomers have been isolated in a supersonic expansion for the first time and successfully characterized by high-resolution rotational spectroscopy. This work provides irrefutable experimental evidence of the [3,3]-rearrangement in barbaralones and highlights the use of rotational spectroscopy to analyze shape-shifting mixtures. Moreover, this observation opens the window toward the characterization of new fluxional systems in the isolation conditions of the gas phase and should serve as a reference point in the general understanding of valence tautomerism.Ministerio de Ciencia e Innovación y Agencia Estatal de Investigación (grants MCIN/A EI/10.13039/ 501100011 033, PID2019-111396GB-I00, PID2019-104815GB-I00, CEX2019-000925-S)Junta de Castilla y Leon (projects VA077U16 and VA244P20)Agencia de Gestión de Ayudas Universitarias y de Investigación y el Programa CERCA/Generalitat de Catalunya de apoyo financiero (2017 SGR 1257)Ministerio de Ciencia, Innovación y Universidades (grant FPU17/02987

Formation of Protonated Glycine Isomers in the Interstellar Medium

Producción CientíficaA computational study of protonated glycine isomers with [H6C2O2N]+ molecular formula has been carried out. All of them are possible products of the reaction between protonated hydroxylamine and acetic acid. All reaction processes that could form the [H6C2O2N]+ isomers considered in this work are exothermic except for those initiated by the most stable isomer of protonated hydroxylamine which give CH3CONH2+OH and CH3COHNOH2+ isomers. The analysis of the potential energy surfaces corresponding to the reaction of protonated hydroxylamine and acetic acid has been focused on the most abundant products, namely, CH3CONH2+OH, CH3COONH3+, and CH3C(OH)+ONH2, obtained from a previous chemical dynamics simulations study. From this analysis we found that even if the reactions of formation of the CH3COONH3+ and the CH3C(OH)+ONH2 isomers are exothermic processes, significant activation barriers were found in the paths leading to these products. The only exothermic process (ΔE = −23.9 kcal mol–1 at the CCSD(T) level) with no net activation barrier was initiated by the high-energy isomer of protonated hydroxylamine, which leads to the CH3CONH2+OH isomer. Therefore, the formation of this isomer could be feasible under interstellar conditions from the reaction of the less stable isomer of protonated hydroxylamine and acetic acid. In addition, an analysis of their neutral counterparts, with [H5C2O2N] molecular formula, has been carried out. The relevant spectroscopic parameters for [H6C2O2N]+ and [H5C2O2N] isomers that could help in their laboratory or astronomical detection, by radioastronomy or infrared spectroscopy, are reported.Ministerio de Economía, Industria y Competitividad ( grant AYA2017-87515-P)Junta de Castilla y León (Grant VA010G18)Ministerio de Ciencia, Innovación y Universidades (Predoctoral FPU Grant FPU17/02987

Formation of interstellar cyanoacetamide: a rotational and computational study

Producción CientíficaContext. Cyanoacetamide is a –CN bearing molecule that is also an amide derivative target molecule in the interstellar medium. Aims. The aim of our investigation is to analyze the feasibility of a plausible formation process of protonated cyanoacetamide under interstellar conditions and to provide direct experimental frequencies of the ground vibrational state of the neutral form in the microwave region in order to enable its eventual identification in the interstellar medium. Methods. We used high-level theoretical computations to study the formation process of protonated cyanoacetamide. Furthermore, we employed a high-resolution laser-ablation molecular beam Fourier transform spectroscopic technique to measure the frequencies of the neutral form. Results. We report the first rotational characterization of cyanoacetamide, and a precise set of the relevant rotational spectroscopic constants have been determined as a first step to identifying the molecule in the interstellar medium. We fully explored the potential energy surface to study a gas-phase reaction on the formation process of protonated cyanoacetamide. We found that an exothermic process with no net activation barrier is initiated by the high-energy isomer of protonated hydroxylamine, which leads to protonated cyanoacetamide.Ministerio de Ciencia, Innovación y Universidades (Project CTQ2016-76393-P)Ministerio de Economía, Industria y Competitividad (Grant AYA2017-87515-P)Junta de Castilla y León (Grants VA077U16 and Grant VA010G18)European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC-2013- SyG, Grant Agreement no. 610 256 NANOCOSMO

A journey across dopamine Metabolism: A rotational study of DOPAC

Producción CientíficaDOPAC, a relevant scaffold in dopamine metabolism, was probed in the gas phase and interrogated by high-resolution rotational spectroscopy. Herein, three distinct conformers were isolated in a supersonic jet and identified for the first time through an examination of the trend of the rotational constants and the dipole moment selection rules. Additionally, we examined the plausible relaxation pathways of the low-energy conformers of DOPAC, which helped us to claim the indirect detection of two additional conformers, providing conclusive experimental evidence of the flexible nature of this biomolecule. The current investigation sheds some light on the differences between jet-cooled rotational experiments and matrix-isolation infrared spectroscopy.Ministerio de Ciencia e Innovación (CTQ2016-76393-P and PID2019- 111396 GB-I00)Junta de Castilla y León (VA077U16 and VA244P20)European Research Council under the European Union’s Seventh Framework Programme (FP/2007- 2013)/ERC-2013-SyG, Grant Agreement n. 610256 NANOCOSMO

The nicotinic agonist cytisine: The role of the NH···N interaction

Producción CientíficaWe report a detailed structural study of cytisine, an alkaloid used to help with smoking cessation, looking forward to unveiling its role as a nicotinic agonist. High-resolution rotational spectroscopy has allowed us to characterize two different conformers exhibiting axial and equatorial arrangements of the piperidinic NH group. Unexpectedly, the axial form has been found as the predominant configuration, in contrast to that observed for related molecules, such as piperidine. This anomalous behavior has been justified in terms of an intramolecular NH···N hydrogen bond. Moreover, this interaction justifies the overstabilization of the axial conformer over the equatorial one and is crucial for the mechanism of action of cytisine over the nicotinic receptor, further rationalizing its behavior as a nicotinic agonist.Ministerio de Ciencia, Innovación y Universidades (project PID2019-111396GB-I00)Junta de Castilla y León (project VA244P20)European Research Council under the European Union’s Seventh Framework Programme (FP/2007- 2013)/ERC-2013-SyG (grant 610256 NANOCOSMOS

Definición del potencial ecológico en aguas fuertemente modificadas: aplicación en el tramo medio del río Tajo

El objetivo de este trabajo es doble, por un lado medir el grado de alteración hidrológica al que se ven sometidas las masas de agua del tramo medio del río Tajo, debido a la regulación de caudales, lo que las clasifica como masas hidrológicamente alteradas. En segundo lugar tratar de relacionar el grado de alteración hidrológica, con el estado ambiental definido por varios indicadores hidrobiológicos: bentos, macrófitas, peces y estado de las riberas

Discovery of the elusive carbonic acid (HOCOOH) in space

After a quarter century since the detection of the last interstellar carboxylic acid, acetic acid (CH$_3$COOH), we report the discovery of a new one, the cis-trans form of carbonic acid (HOCOOH), toward the Galactic Center molecular cloud G+0.693-0.027. HOCOOH stands as the first interstellar molecule containing three oxygen atoms and also the third carboxylic acid detected so far in the interstellar medium. Albeit the limited available laboratory measurements (up to 65 GHz), we have also identified several pairs of unblended lines directly in the astronomical data (between 75-120 GHz), which allowed us to slightly improve the set of spectroscopic constants. We derive a column density for cis-trans HOCOOH of $N$ = (6.4 $\pm$ 0.4) $\times$ 10$^{12}$ cm$^{-2}$, which yields an abundance with respect to molecular H$_2$ of 4.7 $\times$ 10$^{-11}$. Meanwhile, the extremely low dipole moment (about fifteen times lower) of the lower-energy conformer, cis-cis HOCOOH, precludes its detection. We obtain an upper limit to its abundance with respect to H$_2$ of $\leq$ 1.2 $\times$10$^{-9}$, which suggests that cis-cis HOCOOH might be fairly abundant in interstellar space, although it is nearly undetectable by radio astronomical observations. We derive a cis-cis/cis-trans ratio $\leq$ 25, consistent with the smaller energy difference between both conformers compared with the relative stability of trans- and cis-formic acid (HCOOH). Finally, we compare the abundance of these acids in different astronomical environments, further suggesting a relationship between the chemical content found in the interstellar medium and the chemical composition of the minor bodies of the Solar System, which could be inherited during the star formation process.Comment: Accepted for publication in The Astrophysical Journa