https://uvadoc.uva.es/handle/10324/1404 Dpto. Química Física y Química Inorgánica - Artículos de revista 2026-04-13T12:43:56Z https://uvadoc.uva.es/handle/10324/82695 The gas transport properties of mixed matrix membranes (MMMs), prepared by dispersing nanoparticles of MOFs MIL-101(Cr) or MIL-177(Ti) into highly permeable Polymers of Intrinsic Microporosity PIM-EA-TB or PIM-TMN-Trip, were investigated. The homogeneity of the dispersion was confirmed by means of Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray (EDX) mapping analysis. Single gas time-lag measurements provided the permeability and ideal selectivity of different gas pairs, both after treatment of the MMMs with methanol and after natural aging over an extended period (up to 2000 days). This data demonstrated that the gas size-sieving pores of MIL-101(Cr) and MIL-177(Ti) and their good dispersion into the PIM matrix results in MMMs with enhanced gas separation performance, as compared to films composed solely of the polymer. The comparison of actual permeability with the Maxwell model for PIM-EA-TB with both MOFs confirmed the good dispersion and the absence of anomalies, whereas the inconsistency of permeability with prediction data for PIM-TMN-Trip suggests that the MOFs improved the polymer properties, stiffening or occupying the polymer free volume. In particular, the incorporation of MIL-101(Cr) into PIM-EA-TB significantly enhances the H2 permeability from ∼6000 to 13,000 Barrer, with a concurrent increase of the H2/N2 selectivity from 14 to 21. MIL-177(Ti) also enhances the H2/N2 selectivity to 20 due to a slight reduction of the N2 permeability. The addition of MIL-101(Cr) and MIL-177(Ti) into the ultra-permeable PIM-TMN-Trip showed more modest increases in H2 permeability and H2/N2 selectivity from 4.6 to ∼ 10. Hence the data for some of the MMMs surpass the 2008, and even approach the 2015/2019 Robeson’s upper bounds, particularly for gas pairs including H2. 2024-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82694 Overheating in miniaturized electronic devices can reduce their useful life, where conventional heat sinks are insufficient. The utilization of ionenes as solid–solid phase change materials is proposed to enhance thermal dissipation without the risk of leakage. In this work, a series of imidazolium ionenes with structural modifications in their aromatic core and aliphatic chain length were synthesized. The synthesis was carried out using the respective monomers diimidazole and alkyl dibromide, followed by counterion bromide exchange using lithium bis(trifluoromethanesulfonyl)imide, with yields over 90% in all cases. Thermal characterizations showed that all ionenes are heat-resistant, with degradation temperatures between 421 °C and 432 °C; moreover, they all presented only a solid–solid transition (Tg) as a phase change, between 59 °C and 28 °C, which varied depending on the aromatic core used and the length of the aliphatic chain. The obtained ionenes were introduced into an experimental device with an operating temperature of 40 °C, to be evaluated as solid–solid phase change materials in heat sinks. These demonstrated an average decrease in operating temperature of 9 °C compared to the device without ionenes. On the other hand, the stability of the ionenes was analyzed over 10 thermal cycles at 40 °C at a heating rate of 5 °C/min. This analysis demonstrated that the ionenes did not present changes or degradation during the evaluated cycles. These findings demonstrate that imidazolium ionenes are promising solid–solid phase change materials for use as efficient and self-repairing heat sinks in compact electronic devices. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/82690 Previously, it has been reported that amine-PIM-1, a polymer of intrinsic microporosity obtained by reduction of nitrile groups of PIM-1 to primary amine groups, shows enhanced CO2 selectivity during mixed gas permeation studies with respect to single gas measurements for gas pairs involving CO2. This distinct and potentially useful behaviour was ascribed to the affinity of CO2 for the polymer amine groups. Here, we demonstrate that enhanced selectivity originates from both CO2 physisorption and chemisorption. A combination of 13C and 15N solid-state NMR spectroscopic analyses of a CO2-loaded amine-PIM-1 membrane allowed the identification and quantitative determination of both chemisorbed and physisorbed species and the characterization of polymer-CO2 interactions. Experiments with 13C isotopically enriched CO2 unequivocally demonstrated the conversion of 20% of the NH2 groups into carbamic acids at 298 K and a CO2 pressure of 1 bar. Chemisorption was supported by the strong heat of CO2 adsorption for amine-PIM-1 that was estimated as 50 kJ mol−1. Molecular dynamics simulations with models based on the experimentally determined polymer structure gave a detailed description of intra- and interchain hydrogen bond interactions in amine-PIM-1 after chemisorption, as well as of the effect of chemisorption on polymer porosity and physisorption. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/81579 For all the amides detected in the interstellar medium (ISM), the corresponding nitriles or isonitriles have also been detected in the ISM, some of which have relatively high abundances. Among the abundant nitriles for which the corresponding amide has not yet been detected is cyanoacetylene (HCCCN), whose amide counterpart is propiolamide (HCCC(O)NH ). With the aim of supporting searches for this amide in the ISM, we provide a complete rotational study of propiolamide from 6 GHz to 440 GHz using rotational spectroscopic techniques in the frequency and time domain. We identified and measured more than 5500 distinct frequency lines of propiolamide and obtained accurate sets of spectroscopic parameters for the ground state and the three low-lying excited vibrational states. We used the ReMoCA spectral line survey performed with the Atacama Large Millimeter/submillimeter Array toward the star-forming region Sgr B2(N) to search for propiolamide. We report the nondetection of propiolamide toward the hot cores Sgr B2(N1S) and Sgr B2(N2). We find that propiolamide is at least 50 and 13 times less abundant than acetamide in Sgr B2(N1S) and Sgr B2(N2), respectively, indicating that the abundance difference between both amides is more pronounced by at least a factor of 8 and 2, respectively, than for their corresponding nitriles. Although propiolamide has yet to be included in astrochemical modeling networks, the observed upper limit to the ratio of propiolamide to acetamide seems consistent with the ratios of related species as determined from past simulations. 2021-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/81567 Tiopronin, an N-substituted glycine derivative bearing a thiol group, is structurally related to HS-peptides, species of increasing interest in prebiotic chemistry. These thiol-terminated peptides, plausibly formed through abiotic dry-down reactions of mercaptoacids and amino acids, represent viable alternatives to classical peptide formation pathways. In this work, we investigate the conformational landscape of tiopronin by combining high-resolution microwave spectroscopy with quantum-chemical calculations. The Pisa composite schemes (PCS) were employed to locate low-energy conformers and to compute their ground-state rotational constants, which are directly comparable with experimental values. The accuracy of the theoretical results enables an unambiguous spectral assignment and a reliable structural interpretation, demonstrating the usefulness of an integrated experimental/theoretical approach, provided that the underlying quantum-chemical description captures accurate equilibrium values and vibrational averaging effects. More broadly, this strategy is well suited for the reliable characterization of other flexible prebiotic and biochemical building blocks. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/81565 We present an efficient semiexperimental protocol for determining spectroscopically accurate molecular structures from limited isotopologue data with a focus on medium-sized organic molecules. The availability of all monosubstituted isotopologues of norbornadiene enabled the determination of a complete semiexperimental (reqSE) equilibrium structure, establishing a reference for validating reduced-dimensionality approaches that avoid deuterium substitution. The rotational spectrum of norcamphor is reported here for the first time, providing a critical benchmark for assessing the method’s accuracy. By combining composite quantum-chemical calculations with a cost-effective vibrational correction scheme, the protocol achieves near-spectroscopic accuracy while substantially reducing the computational effort. This approach enables the structural characterization of large systems where extensive isotopic substitution is impractical, thereby broadening the applicability of semiexperimental methods in modern molecular spectroscopy. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/81564 This work reports a complete conformational analysis of caffeic acid, an exceptionally versatile pharmacophore, using laser ablation chirped-pulse Fourier transform microwave spectroscopy. The whole conformational space consisting of eight distinct species has been fully deciphered based on the trend of the rotational constants supported by theoretical computations. We show how rotational spectroscopy can be confidently used to distinguish between conformers even when the structural differences are minimal, such as those involved in the conformational panorama of caffeic acid. Additionally, the structural information here provided, such as the planarity observed in all the conformers, could help to elucidate the mechanisms underlying the biological and pharmacological activity of hydroxycinnamic acids. 2023-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/81563 Sulfanilamide, a widely used antibacterial drug, has been brought into the gas phase using laser ablation techniques, and its structure has been characterized in the isolated conditions of a supersonic expansion using Fourier transform microwave techniques. A single conformer stabilized by an N–H⋯O[double bond, length as m-dash]S intramolecular interaction in an equatorial disposition has been unequivocally characterized. To emulate the microsolvation process, we studied its hydrated cluster. The results show that a single water molecule alters the conformational preference and forces sulfanilamide to switch from its initial eclipsed configuration to a staggered disposition. The observed hydrated cluster adopts a structure in which water forms three hydrogen bonds with sulfanilamide stabilizing the molecule. 2022-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/81538 The conformational landscape of β-D-allose, a rare sugar, was investigated using laser ablation in combination with high-resolution rotational spectroscopy. Altogether, three species are identified, exhibiting a counter-clockwise intramolecular hydrogen bond network. The effect of epimerization on the main aldohexose is also studied and, despite the main conformers being very similar, the position of the hydroxyl groups in allose allows the formation of considerably stronger intramolecular hydrogen bonds than in glucose, and this could explain the low abundance of β-D-allose in Nature. 2022-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/81534 Recent developments in attosecond technology led to table-top x-ray spectroscopy in the soft x-ray range, thus uniting the element- and state-specificity of core-level x-ray absorption spectroscopy with the time resolution to follow electronic dynamics in real-time. We describe recent work in attosecond technology and investigations into materials such as Si, SiO2, GaN, Al2O3, Ti, and TiO2, enabled by the convergence of these two capabilities. We showcase the state-of-the-art on isolated attosecond soft x-ray pulses for x-ray absorption near-edge spectroscopy to observe the 3d-state dynamics of the semi-metal TiS2 with attosecond resolution at the Ti L-edge (460 eV). We describe how the element- and state-specificity at the transition metal L-edge of the quantum material allows us to unambiguously identify how and where the optical field influences charge carriers. This precision elucidates that the Ti:3d conduction band states are efficiently photo-doped to a density of 1.9 × 1021 cm−3. The light-field induces coherent motion of intra-band carriers across 38% of the first Brillouin zone. Lastly, we describe the prospects with such unambiguous real-time observation of carrier dynamics in specific bonding or anti-bonding states and speculate that such capability will bring unprecedented opportunities toward an engineered approach for designer materials with pre-defined properties and efficiency. Examples are composites of semiconductors and insulators like Si, Ge, SiO2, GaN, BN, and quantum materials like graphene, transition metal dichalcogens, or high-Tc superconductors like NbN or LaBaCuO. Exiting are prospects to scrutinize canonical questions in multi-body physics, such as whether the electrons or lattice trigger phase transitions. 2021-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/81530 Laser spectroscopy in jets is one of the main sources of structural data from molecular aggregates. Consequently, numerous and sophisticated experimental systems have been developed to extract precise information, which is usually interpreted in the light of quantum mechanical calculations. However, even with the most sophisticated experiments, it is sometimes difficult to interpret the experimental results. We present here the example of water dimer and how after almost 70 years, the assignment of its mass-resolved IR spectrum still generates controversy that extends toward the mechanism of ionization of water aggregates. 2021-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/81528 Herein, we present the first rotational study of the AlaAla dipeptide, brought into the gas phase by laser ablation. Two different structures have been unveiled in the isolated environment of a supersonic expansion by Fourier transform microwave spectroscopy. These structures have been identified through their rotational and 14N quadrupole coupling constants. The flexibility of the –NH2 and –COOH ends allows the formation of strong intramolecular interactions giving rise to five- and seven-membered ring configurations. 2020-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/80777 Herein, for the first time, solid samples of Pro–Gly have been vaporized by laser ablation (LA), and a chirped pulse Fourier transform microwave spectrometer (CP-FTMW) has been employed to explore the broadband rotational spectrum in the 3.0–8.0 GHz range. By integrating experimental data with quantum-chemical computations, we accurately characterized the conformational landscape of this flexible dipeptide, identifying up to five distinct conformers. The N–H⋯N–H hydrogen bond between the amine group of the glycine residue and the amine in the proline ring is highly stabilizing and is present in all conformers. Furthermore, the four most stable conformers exhibit additional stabilizing O–H⋯O[double bond, length as m-dash]C hydrogen bonds between the hydroxyl group and the carbonyl group of proline. We analyzed the key differences between Pro–Gly and Gly-Pro, providing insights into Pro–Gly dipeptide's greater tendency to form β-turn configurations in proteins, in contrast to the Gly-Pro dipeptide's preference for extended conformations. We have illustrated how collisional relaxation distorts the equilibrium conformational distribution, giving rise to missing conformers in the conformational landscape. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/80127 Context. Many complex organic molecules (COMs) observed in the interstellar medium (ISM) are probably not formed in the gas phase. A large consensus has developed that it could be related to the icy surfaces in this environment. Aims. We investigate the process of building N-substituted formamides in the ISM by successive additions of atomic hydrogen to isocyanates. The key point is to see whether the pre-adsorption of the atomic hydrogen on the ice surface is a driving vector as it is for the formation of CH3OH from CO. Methods. We use quantum numerical simulations, namely density functional theory (DFT) and post Hartree–Fock (p-HF) methods derived from coupled-cluster implementations. Several chemical models are presented: the addition of H directly to the isocyanate in the gas phase, the addition of H to the isocyanate pre-adsorbed on ices, the addition of the isocyanate to the hydrogen pre-adsorbed on ices. These ices are successively simulated by a few water molecules up to full bi-layers of them. Results. The formation of formamide (NH2CHO) from the isocyanic acid (HNCO) is taken as a case study. Whatever the level of the calculation and the size of the water cluster supporting the adsorbed isocyanate, the addition of the incoming atomic hydrogen reveals no opportunity to eliminate the energy barrier found in the gas phase. By contrast, the formation of H2NCHO, as well as CH3NHCHO or C2H5NHCHO, is possible without any barrier on the same ice surfaces, with the express condition that the H atom to be added is already attached to the ice, prior to the attack by the isocyanate species. Conclusions. There is a way for the N-substituted formamides to be easily built by two successive hydrogenations on ices starting from the isocyanates HNCO, CH3NCO, and C2H5NCO. Some of those species are already detected; if not, they appear as strong candidates worth considering for future observation campaigns. Moreover, this suggests that other hydrogenation processes neglected to date, could be considered when similar pre-conditions are satisfied. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/80100 Context. The recent interstellar detection of the high-energy O-protonated carbonyl sulfide isomer (HOCS+) toward the molecular cloud G+0.693-0.027 contrasts with the non-detection of its lower-energy S-protonated counterpart, HSCO+, the global minimum in energy. This raises questions regarding the occurrence of selective formation pathways of these [H,C,S,O]+ isomers in space. Aims. In this work, we aim to explore the most likely gas-phase formation routes for both HOCS+ and HSCO+ beyond the direct protonation of OCS (i.e., HCS+ + OH, HCO+ + SH, HOC+ + SH, and HCO + SH+) to help rationalize previous observational results. Methods. We first explored the thermodynamic feasibility of the aforementioned reactions using high-level double-hybrid B2PLYPD3/aug-cc-pVTZ and CCSD(T)-F12/cc-pVTZ-F12 computations. For the reaction HCS+ + OH, found to be the most ther modynamically favorable, we characterized the stationary points on its corresponding potential energy surface (PES). In addition, we also used a composite approach to refine relative energies and employed the statistical rate theory and master equation simulations to estimate rate constants and branching ratios. Results. We show that HOCS+ is preferentially formed through the reaction of HCS+ with OH, providing a plausible chemical explanation for its interstellar presence and the non-detection of the low energy isomer. Nevertheless, while the branching ratio computed at a T Tkin(G+0.693) = 70-140 K is qualitatively consistent with the observations, its value is two orders of magnitude larger than the derived HOCS+/HSCO+ lower limit observational ratio (of 2.3). This suggests that if the upper limit of HSCO+ is close to the real abundance, additional formation pathways may also play a significant role in shaping the isomeric ratio. Conclusions. These results highlight that including all isomers in a given family, along with their isomer-preferential formation pathways, in astrochemical models, which are in many cases isomer-insensitive, is essential to understand their formation routes. 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/80097 Phosphorus is a crucial biogenic element, yet its astrochemical role remains poorly understood due to its low cosmic abundance and the limited number of detected P-containing molecules in the interstellar medium. Given its significance for prebiotic chemistry, PCO-bearing molecules, such as the phosphorus analogs of isocyanates, are promising candidates for laboratory and interstellar studies. Herein, we present a comprehensive theoretical study on the isomeric landscape of the C 2 H 3 PO system, identifying and characterizing 24 low-lying isomers through high-level quantum chemical calculations. The study employs double-hybrid DFT and coupled-cluster methods to refine energy values and structural parameters, while topological analysis of electronic density characterizes chemical bonding. Vinylphosphinidene oxide (CH 2 CHPO) emerges as the most stable isomer, followed by methylphosphaketene (CH 3 PCO), with oxygen-bound structures playing a crucial role in stability. Comparisons with the C 2 H 3 NO system reveal structural parallels, reinforcing the importance of oxygen-bound species. Cyclic structures were also explored, with three- and four-membered P- and O-heterocycles identified, although they are generally less stable than open-chain isomers. These results provide insights into the chemical behavior and stability of C 2 H 3 PO isomers, which could help future spectroscopic studies and detection efforts in the interstellar medium. 2025-01-01T00:00:00Z