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157 p.(eng.) 153 p. (eusk.), La espectroscopía rotacional es la técnica de mayor resolución que proporciona datos estructurales de las moléculas y pequeños agregados en fase gas, así como información sobre sus dinámicas moleculares. Esta tesis está mayoritariamente focalizada al estudio de azucares utilizando la combinación de la espectroscopia rotacional y los cálculos químico cuánticos. En la tesis se presentan varios estudios, partiendo del estudio de la eritrulosa en la que combinamos los datos obtenidos en el laboratorio con los datos de los radio-telescopios para su intento de detección en el medio interestelar y continuamos con varios estudios de azucares derivados de glucosa, galactosa y manosa. Nuestros resultados muestran como las pequeñas mutaciones en los azucares (de oxidaciones, lactonizaciones, oxidaciones) producen grandes cambios estructurales de la estructura intrínseca de los monosacáridos en fase gas.Por último, se presentan varios estudios de procesos químicos de relevante interés en la biología. Entre ellos la transferencia de protones en el dimero de ácido furoico y la micro-solvatación del metil benzoato.En general demostramos como la espectroscopia de rotación permite el estudio de las estructuras y de varios procesos de importancia en la biología.

El objetivo del presente trabajo es el estudio de las interacciones intermoleculares que estabilizan los confórmeros del complejo indol-prolinamida mediante la espectroscopía de rotación y cálculos computacionales. Gracias a estos últimos, hemos podido observar que hay cuatro confórmeros del complejo indol-prolinamida que se estabilizan mediante enlaces de hidrógeno. Por este motivo, se ha pretendido llevar a cabo un estudio de las transiciones de rotación del complejo indol-prolinamida con un espectrómetro de microondas de banda ancha con transformada de Fourier y pulso ‘chirped’. Como solo ha sido posible estudiar sus transiciones teóricamente ya que dicho complejo no se ha formado o no ha sido detectado, hemos decidido llevar a cabo un estudio de las transiciones de rotación del indol y del complejo indol-agua. Además, como las transiciones más intensas son las del indol, se ha llevado a cabo otro estudio, esta vez solo de las transiciones del indol, con un espectrómetro de rotación de ondas milimétricas. De este modo, hemos podido realizar un ajuste completo de sus constantes de rotación, de distorsión centrífuga y de sus momentos cuadrupolares, el cual recoge transiciones cuyas frecuencias pertenecen a las regiones 2-8 GHz y 75-110 GHz. Por el contrario, no ha sido posible estudiar las transiciones de la prolinamida y las del complejo prolinamida-agua por su baja intensidad en el espectro de rotación., The aim of the present work is the study of the intermolecular interactions that stabilize the indol-prolinamide complex’s structures with rotational spectroscopy and computational work. Thanks to this computational work, we have observed that there are four indol-prolinamide complex’s structures that are stabilized by hydrogen bonds. For this reason, we have pretended to make a study of the rotational transitions of indole-prolinamide complex with a chirped pulse Fourier transform broadband microwave espectrometer. By the fact that it has only been possible to study its transitions theoretically because the complex has not formed or has not been detected, we have decided to make a study of the rotational transitions of indole and indole-water complex. In addition, we have made a study of the transitions of indole, this time with a millimeter wave rotational espectrometer, because their intensities are the highest. By this way, we have made a complete study of its rotational and centrifugal distorsion constants and quadrupole moments, in which appear transitions whose frequencies belong to regions 2-8 GHz and 75-110 GHz. By the other hand, it has not been possible to study the transitions of prolinamide and prolinamide-water complex because of their very low intensity in the rotational spectrum., Departamento de Química Física y Química Inorgánica, Grado en Química

The role of non-covalent interactions (NCIs) has broadened with the inclusion of new types of interactions and a plethora of weak donor/acceptor partners. This work illustrates the potential of chirped-pulse Fourier transform microwave technique, which has revolutionized the field of rotational spectroscopy. In particular, it has been exploited to reveal the role of NCIs' in the molecular self-aggregation of difluoromethane where a pentamer, two hexamers and a heptamer were detected. The development of a new automated assignment program and a sophisticated computational screening protocol was essential for identifying the homoclusters in conditions of spectral congestion. The major role of dispersion forces leads to less directional interactions and more distorted structures than those found in polar clusters, although a detailed analysis demonstrates that the dominant interaction energy is the pairwise interaction. The tetramer cluster is identified as a structural unit in larger clusters, representing the maximum expression of bond between dimers.

157 p.(eng.) 153 p. (eusk.), La espectroscopía rotacional es la técnica de mayor resolución que proporciona datos estructurales de las moléculas y pequeños agregados en fase gas, así como información sobre sus dinámicas moleculares. Esta tesis está mayoritariamente focalizada al estudio de azucares utilizando la combinación de la espectroscopia rotacional y los cálculos químico cuánticos. En la tesis se presentan varios estudios, partiendo del estudio de la eritrulosa en la que combinamos los datos obtenidos en el laboratorio con los datos de los radio-telescopios para su intento de detección en el medio interestelar y continuamos con varios estudios de azucares derivados de glucosa, galactosa y manosa. Nuestros resultados muestran como las pequeñas mutaciones en los azucares (de oxidaciones, lactonizaciones, oxidaciones) producen grandes cambios estructurales de la estructura intrínseca de los monosacáridos en fase gas.Por último, se presentan varios estudios de procesos químicos de relevante interés en la biología. Entre ellos la transferencia de protones en el dimero de ácido furoico y la micro-solvatación del metil benzoato.En general demostramos como la espectroscopia de rotación permite el estudio de las estructuras y de varios procesos de importancia en la biología.

The conformational space of methacrylamide was explored by quantum mechanical modeling and surveyed in the 59.6–104.0 GHz frequency range using a millimeter-wave Stark-modulated free-jet absorption spectrometer. According to the relative orientation of the two unsaturated bonds, two conformers were observed, namely s-trans (A=5234.360(1), B=3364.9717(8) and C=2173.099(1) MHz) and s-cis (A=5207.292(1), B=3470.930(1) and C=2113.496(1) MHz). The s-trans conformation is the global minimum, with relative energy 4(2) kJ mol−1 and calculated isomerization barrier 15 kJ mol−1. Except for the methyl hydrogen atoms, s-cis-methacrylamide is planar and its methyl internal rotation barrier is 10.2(1) kJ mol−1. In s-trans-methacrylamide the allyl and amino frames form a dihedral angle of about 30° and the methyl internal rotation barrier is 7.4 kJ mol−1. This different behaviour is explained in terms of attractive and repulsive intramolecular interactions between groups: CH2/CO and CH3/NH2 for s-cis, CH2/NH2 and CH3/CO for s-trans. The tunneling splitting related to the double-well potential describing the interconversion between the two equivalent s-trans forms is 837.97(2) MHz and was reproduced by a one-dimensional flexible model using a 3.6 kJ mol−1 interconversion barrier.

One of the most fascinating questions in chemistry is why nature chose CGAT as the alphabet of life. Very likely, such selection was the result of multiple factors and a long period of refinement. Here, we explore how the intermolecular interactions influenced such process, by characterizing the formation of dimers between adenine, theobromine and 4-aminopyrimidine. Using a combination of mass-resolved excitation spectroscopy and DFT calculations, we determined the structure of adenine-theobromine and 4-aminopyrimidine-theobromine dimers. The binding energy of these dimers is very close to the canonical adenine-thymine nucleobases. Likewise, the dimers are able to adopt Watson-Crick conformations. These findings seem to indicate that there were many options available to build the first versions of the informational polymers, which also had to compete with other molecules, such as 4-aminopyrimidine, which does not have a valid attaching point for a saccharide. For some reason, nature did not select the most strongly-bonded partners or if it did, such proto-bases were later replaced by the nowadays canonical CGAT.

Broadband microwave spectra were recorded over the 2-18 GHz frequency range for a series of four model aromatic components of lignin; namely, guaiacol (ortho-methoxy phenol, G), syringol (2,6-dimethoxy phenol, S), 4-methyl guaiacol (MG), and 4-vinyl guaiacol (VG), under jet-cooled conditions in the gas phase. Using a combination of 13C isotopic data and electronic structure calculations, distortions of the phenyl ring by the substituents on the ring are identified. In all four molecules, the rC(1)-C(6) bond between the two substituted C-atoms lengthens, leading to clear bond alternation that reflects an increase in the phenyl ring resonance structure with double bonds at rC(1)-C(2), rC(3)-C(4) and rC(5)-C(6). Syringol, with its symmetric methoxy substituents, possesses a microwave spectrum with tunneling doublets in the a-type transitions associated with H-atom tunneling. These splittings were fit to determine a barrier to hindered rotation of the OH group of 1975 cm−1, a value nearly 50 % greater than that in phenol, due to the presence of the intramolecular OH⋅⋅⋅OCH3 H-bonds at the two equivalent planar geometries. In 4-methyl guaiacol, methyl rotor splittings are observed and used to confirm and refine an earlier measurement of the three-fold barrier V3=67 cm−1. Finally, 4-vinyl guaiacol shows transitions due to two conformers differing in the relative orientations of the vinyl and OH groups.

La espectroscopía rotacional es la técnica de mayor resolución que proporciona datos estructurales de las moléculas y pequeños agregados en fase gas, así como información sobre sus dinámicas moleculares. Esta tesis está mayoritariamente focalizada al estudio de azucares utilizando la combinación de la espectroscopia rotacional y los cálculos químico cuánticos. En la tesis se presentan varios estudios, partiendo del estudio de la eritrulosa en la que combinamos los datos obtenidos en el laboratorio con los datos de los radio-telescopios para su intento de detección en el medio interestelar y continuamos con varios estudios de azucares derivados de glucosa, galactosa y manosa. Nuestros resultados muestran como las pequeñas mutaciones en los azucares (de oxidaciones, lactonizaciones, oxidaciones) producen grandes cambios estructurales de la estructura intrínseca de los monosacáridos en fase gas.Por último, se presentan varios estudios de procesos químicos de relevante interés en la biología. Entre ellos la transferencia de protones en el dimero de ácido furoico y la micro-solvatación del metil benzoato.En general demostramos como la espectroscopia de rotación permite el estudio de las estructuras y de varios procesos de importancia en la biología.

The qualitative determination of small molecules that reach the gas phase after the thermal decomposition of solar cell materials, have been carried out by means of microwave spectroscopy (MW). In this case, the evidence of small molecule tracers after the thermal decomposition of pervoskites (CH3NH3PbI3) has been proved thanks to the combination between rotational spectroscopy and supersonic expansion. The results are in good agreement with those previously obtained from other techniques, and this demostrates the ability of microwave spectroscopy to perform satisfactorly as analytical tool.; Mikrouhin-espektroskopiaren (MW) oinarriak eta sistema esperimentalen oinarrizko funtsak emanez, materialen deskonposizio termikoetan gas eran igortzen diren molekula txikien determinazio kualitatiboa burutu daitekeela frogatu da. Adibide modura, errotazio-espektroskopiaren eta hedapen supersonikoaren konbinaketaren bidezko etorkizuneko eguzki-zeluletan erabil daitekeen metilamonio berun triioduroa (CH3NH3PbI3) perovskiten deskonposizio termikoan sortzen diren molekula txikien determinazio zehatza egin da. Lortutako emaitzak aurretik bestelako teknikekin lortutako emaitzekin bat datozela ikusi da, prozedura honen baliagarritasuna erakutsiz eta mikrouhin-espektroskopia teknika analitiko moduan erabil daitekeela erakutsiz.

The role of non-covalent interactions (NCIs) has broadened with the inclusion of new types of interactions and a plethora of weak donor/acceptor partners. This work illustrates the potential of chirped-pulse Fourier transform microwave technique, which has revolutionized the field of rotational spectroscopy. In particular, it has been exploited to reveal the role of NCIs' in the molecular self-aggregation of difluoromethane where a pentamer, two hexamers and a heptamer were detected. The development of a new automated assignment program and a sophisticated computational screening protocol was essential for identifying the homoclusters in conditions of spectral congestion. The major role of dispersion forces leads to less directional interactions and more distorted structures than those found in polar clusters, although a detailed analysis demonstrates that the dominant interaction energy is the pairwise interaction. The tetramer cluster is identified as a structural unit in larger clusters, representing the maximum expression of bond between dimers.

The interaction between carbon dioxide and planar carboxylic acids has been investigated through the analysis of the microwave spectrum of the acrylic acid·CO2 complex and quantum chemical modeling of the R-COOH·(CO2)1,16 clusters, where R = H, CH2CH. As regards the 1 : 1 compounds, two species, involving the s-cis and s-trans conformers of acrylic acid were observed. For both of them, a similar bidentate interaction arises between the carbonyl group of CO2 and the carboxylic group of the organic acid, leading to the formation of a planar six-membered ring. The binding energy is estimated to be De ≃ 21 kJ mol-1, 1/3 being the energy contributions of the tetrel to hydrogen bonds, respectively. In the 1 : 16 clusters, the ring arrangement is broken, allowing for the interaction of the acid with several CO2 molecules. The CO2 molecules completely surround formic acid, whereas, in the case of acrylic acid, they tend to avoid the allyl chain.

Rotational spectroscopy provides the most powerful means of identifying molecules of biological interest in the interstellar medium (ISM), but despite their importance, the detection of carbohydrates has remained rather elusive. Here, we present a comprehensive Fourier transform rotational spectroscopic study of elusive erythrulose, a sugar building block likely to be present in the ISM, employing a novel method of transferring the hygroscopic oily carbohydrate into the gas phase. The high sensitivity of the experiment allowed the rotational spectra of all monosubstituted isotopologue species of 13C-12C3H8O4 to be recorded, which, together with quantum chemical calculations, enabled us to determine their equilibrium geometries (reSE) with great precision. Searches employing the new experimental data for erythrulose have been undertaken in different ISM regions, so far including the cold areas Barnard 1, the pre-stellar core TMC-1, Sagittarius B2. Although no lines of erythrulose were found, this data will serve to enable future searches and possible detections in other ISM regions.

The hydrogen-bonded complex between acrylonitrile (CH2=CHCN) and methanol has been characterized spectroscopically in the millimeter wave range (59.6-74.4 GHz) using a free jet absorption millimeter wave spectrometer. Precise values of the rotational and centrifugal distortion constants were obtained from the measured frequencies of the complex of acrylonitrile with CH3OH and CD3OD. The analysis of the splittings of the rotational lines due to the hindered internal rotation of the methanol methyl group led to the determination of a V-3 value of 221.9(7) and 218(5) cm(-1) for the complexes of CH3OH and CD3OD, respectively, and these values are about 40% lower than that of free methanol. The structure of the observed conformation is in agreement with the global minimum determined at the MP2/aug-cc-pVTZ level of calculation, and the counterpoise corrected intermolecular binding energy, obtained at the same theoretical level, is D-e = 26.3 kJ mol(-1)

The hydrogen-bonded complex between acrylonitrile (CH2=CHCN) and methanol has been characterized spectroscopically in the millimeter wave range (59.6-74.4 GHz) using a free jet absorption millimeter wave spectrometer. Precise values of the rotational and centrifugal distortion constants were obtained from the measured frequencies of the complex of acrylonitrile with CH3OH and CD3OD. The analysis of the splittings of the rotational lines due to the hindered internal rotation of the methanol methyl group led to the determination of a V-3 value of 221.9(7) and 218(5) cm(-1) for the complexes of CH3OH and CD3OD, respectively, and these values are about 40% lower than that of free methanol. The structure of the observed conformation is in agreement with the global minimum determined at the MP2/aug-cc-pVTZ level of calculation, and the counterpoise corrected intermolecular binding energy, obtained at the same theoretical level, is D-e = 26.3 kJ mol(-1).

We recorded the rotational spectra of six isotopologues of the most stable conformer of 1,2-butanediol in the 59.6–74.4 GHz frequency region. The observed species are the four monosubstituted 13C, the OD···OH and the OD···OD, and the measurements were performed using a Free-Jet Absorption Millimeter Wave spectrometer. The analysis of the 18 experimental rotational constants determined for all the isotopologues together with those of the parent species, lead to the determination of the coordinates in the principal axis system for the substituted atoms. From the theoretical structure, calculated at the B3LYP-D3/aug-cc-pVTZ level of theory, a refinement of the structural parameters led to a partial r0 geometry, which reproduced all the rotational constants within 1.3 MHz.

Understanding the molecular basis of the appearance of life on Earth is an exciting research field. Many factors may have influenced the election of the molecules used by living beings and evolution may have modified those original compounds. In an attempt to understand the role played by intermolecular interactions in the election of CGAT as the alphabet of life, we present here a thorough experimental and computational study on the interaction of theobromine with water. Theobromine is a xanthine derivative, structurally related to the nucleobases, and also present in many living beings. The experimental results demonstrate that the most stable isomer of theobromine-water was formed and detected in supersonic expansions. This isomer very well resembles the structure of the dimers between nucleobases and water, offering similar values of binding energy. A comparison between the results obtained for theobromine-water with those reported in the literature for monohydrates of nucleobases is also offered.

We studied the impact of aliphatic side chains on the stability and conformational landscape of the local anaesthetics benzocaine, butamben and isobutamben, combining high-resolution rotational spectroscopy in the microwave and millimetre regions and molecular modelling. The study reveals the connections between alkyl chain flexibility and molecular conformations.

Direct spectroscopic evidence of a reaction occurring between acrolein and water and involving the exchange of an oxygen atom has been obtained by characterizing the non-covalently bound water complexes and their isotopic forms, via rotational spectroscopy. The experimental geometries of the binary and ternary water complexes have been determined, and other stationary points on the reaction path have been characterized using ab initio quantum chemical methods at the MP2/6-311++G(d,p) level. These results can enhance the understanding of the water-mediated atmospherically important reactions involving acrolein.