Examinando por Autor "Alkorta, Ibon"
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Ítem Conformational preference and chiroptical response of Carbohydrates D-Ribose and 2-Deoxy-D-ribose in aqueous and solid phases(American Chemical Society, 2013) Quesada-Moreno, María del Mar; Azofra, Luis Miguel; Avilés-Moreno, Juan Ramón; Alkorta, Ibon; Elguero, José; López-González, Juan JesúsThis work targets the structural preferences of D-ribose and 2-deoxy-D-ribose in water solution and solid phase. A theoretical DFT (B3LYP and M06-2X) and MP2 study has been undertaken considering the five possible configurations (open-chain, α-furanose, β-furanose, α-pyranose, and β-pyranose) of these two carbohydrates with a comparison of the solvent treatment using only a continuum solvation model (PCM) and the PCM plus one explicit water molecule. In addition, experimental vibrational studies using both nonchiroptical (IR-Raman) and chiroptical (VCD) techniques have been carried out. The theoretical and experimental results show that α-and β-pyranose forms are the dominant configurations for both compounds. Moreover, it has been found that 2-deoxy-D-ribose presents a non-negligible percentage of open-chain forms in aqueous solution, while in solid phase this configuration is absent.Ítem Self-assembly structures of 1H-indazoles in solution and solid phases: A vibrational (IR, FarIR, Raman and VCD) and computational study(Wiley, 2013) Avilés-Moreno, Juan Ramón; Quesada-Moreno, María del Mar; López-González, Juan Jesús; Claramunt, Rosa M.; López-García, Concepción; Alkorta, Ibon; Elguero, José1H-indazoles are good candidates to study phenomena of molecular association and spontaneous resolution of chiral compounds. Thus, because the 1H-indazoles can crystallize forming dimers, trimers or catemers, depending on their structure and the phase where they are, the difficulty of the experimental analysis of the structure of the family of 1H-indazoles is clear. This lead to contemplate several questions: How can we determine the presence of different structures of a determined molecular species if they change according to the phase? Could these different structures be present in the same phase simultaneously? How can it be determined? In order to shed light on these questions, we outline a very complete strategy by using different techniques of vibrational spectroscopy sensitive (VCD) and not sensitive (IR, FarIR and Raman) to the chirality together with quantum chemical calculations.Ítem Supramolecular organization of perfluorinated 1H-indazoles in the solid state using X-ray crystallography, SSNMR and sensitive (VCD) and non sensitive (MIR, FIR and Raman) to chirality vibrational spectroscopies(Royal Society of Chemistry, 2017) Quesada-Moreno, María del Mar; Avilés-Moreno, Juan Ramón; López-González, Juan Jesús; Jacob, Kane; Vendier, Laure; Etienne, Michel; Alkorta, Ibon; Elguero, José; Claramunt, Rosa M.1H-Indazole derivatives exhibit a remarkable property since some of them form chiral supramolecular structures starting from achiral monomers. The present work deals with the study of three perfluorinated 1H-indazoles that resolve spontaneously as conglomerates. These conglomerates can contain either a pure enantiomer (one helix) or a mixture of both enantiomers (both helices) with an enantiomeric excess (e.e.) of one of them. The difficulty of the structural analysis of these types of compounds is thus clear. We outline a complete strategy to determine the structures and configurations (M or P helices) of the enantiomers (helices) forming the conglomerates of these perfluorinated 1H-indazoles based on X-ray crystallography, solid state NMR spectroscopy and different solid state vibrational spectroscopies that are either sensitive (VCD) or not (FarIR, IR and Raman) to chirality, together with quantum chemical calculations (DFT).Ítem Understanding the Aldo-Enediolate Tautomerism of Glycolaldehyde in Basic Aqueous Solutions(Wiley, 2015) Azofra, Luis Miguel; Quesada-Moreno, María del Mar; Alkorta, Ibon; Avilés-Moreno, Juan Ramón; Elguero, José; López-González, Juan JesúsThe biochemically important interconversion process between aldoses and ketoses is assumed to take place via 1,2-enediol or 1,2-enediolate intermediates, but such intermediates have never been isolated. The current work was undertaken in an attempt to detect the presence of the 1,2-enediol structure of glycolaldehyde in alkaline medium, actually a 1,2-enediolate, and to try to clarify the scarce data existing about both the formation of the deprotonated enediol and the aldo-enediolate equilibrium. The Raman spectra of neutral and basic solutions were recorded as a function of time for eleven days. Several bands associated with the presence of the enediolate were observed in alkaline medium. Glycolaldehyde exists as three different structures in aqueous solution at neutral pH, i.e. hydrated aldehydes, aldehydes and dimers, with a respective ratio of approximately 4:0.25:1. Additionally, the formation of Z-enediolate forms takes place at basic pH, together with the increase of aldehyde species, as 2-oxoethan-1-olate, and the decrease of hydrated aldehyde and dimeric forms. The theoretical ratio ~1.5:1 aldehyde:Z-enediolate reproduces the experimental Raman spectrum in basic medium, with the additional contribution of the previously mentioned ratio between hydrated aldehyde and dimeric forms. Finally, Raman spectroscopy allowed us to monitor the enolization of this carbohydrate model and to conclude that the aldo-enediol tautomerism, formally aldo-enediolate, happens when a suitable amount of basic species is added.Ítem Vibrational circular dichroism (VCD) methodology for the measurement of enantiomeric excess in chiral compounds in solid phase and for the complementary use of NMR and VCD techniques in solution: the camphor case(Royal Society of Chemistry, 2018) Quesada-Moreno, María del Mar; Virgili, Albert; Monteagudo, Eva; Claramunt, Rosa M.; Avilés-Moreno, Juan Ramón; López-González, Juan Jesús; Alkorta, Ibon; Elguero, JoséFor the first time, the success of a methodology for the determination of enantiomeric excesses (% ee) in chiral solid samples by vibrational circular dichroism (VCD) spectroscopy is reported. We have used camphor to determine the % ee in a blind sample constituted by a mixture of its two enantiomers as a test of the validity of our approach. IR and VCD spectra of different enantiomeric mixtures of R/S-camphor in nujol mulls were recorded and linear regressions of VCD intensities (ΔAbs.) vs. % ee for selected bands were found. Finally, the VCD intensities of a blind sample were interpolated in these linear regressions, obtaining its % ee with a rms of 2.4. These results in the solid phase were complemented with the determination of % ee in the liquid phase by VCD and NMR techniques, which are proved to be complementary techniques to carry out this kind of analysis. In the same way as in the VCD solid phase, linear regressions of ΔAbs. vs. % ee for selected bands were established, obtaining a rms of 1.1 in the % ee determination of a blind sample. 1H NMR experiments at 600 MHz using the chiral solvating agent, (S,S)-ABTE, allow to determine in CD2Cl2 solution the proportions of enantiomers with great accuracy. 13C CPMAS NMR spectra prove that this technique cannot be used for conglomerates and/or solid solutions.