DQFA-Artículos

URI permanente para esta colecciónhttps://hdl.handle.net/10953/276

Examinar

Mostrando 1 - 20 de 59

Control of the geometry and anisotropy driven by the combination of steric and anion coordination effects in CoII complexes with N6-tripodal ligands: the impact of the size of the ligand on the magnetization relaxation time
(Royal Society of Chemistry, 2024) Landart-Gereka, Aritz; Quesada-Moreno, María Mar; Palacios-López, María Ángeles; Li, Yanling; Ozerov, Mykhaylo; Krzystek, Jurek; Colacio, Enrique
Four mononuclear CoII complexes of formula [Co(L)(SCN)2(CH3OH)0.5(H2O)0.5]·1.5H2O·0.75CH3OH (1), [Co(L1)Cl2]·H2O·2CH3CN (2), [Co(L1)(SCN)2]·1.5H2O·CH3OH (3) and [Co(L1)]ClO4·2CH3OH (4) were prepared from the N6-tripodal Schiff base ligands (S)P[N(Me)N=C(H)2-Q]3 (L) and (S)P[N(Me)N=C(H)1-ISOQ]3 (L1), where Q and ISOQ represent quinolyl and isoquinolyl moieties, respectively. In 1, the L ligand does not coordinate to the CoII ion in a tripodal manner but using a new N,N,S tridentate mode, which is due to the fact that the N6-tripodal coordination promotes a strong steric hindrance between the quinolyl moieties. However, L1 can coordinate to the CoII ions either in a tripodal manner using CoII salts with poorly coordinating anions to give 4 or in a bisbidentate fashion using CoII salt-containing medium to strongly coordinating anions to afford 2 and 3. In the case of L1, there is no steric hindrance between ISOQ moieties after coordination to the CoII ion. The CoII ion exhibits a distorted octahedral geometry for compounds 1–3, with the anions in cis positions for the former and in trans positions for the two latter compounds. Compound 4 shows an intermediate geometry between an octahedral and trigonal prism but closer to the latter one. DC magnetic properties, HFEPR and FIRMS measurements and ab initio calculations demonstrate that distorted octahedral complexes 1–3 exhibit easy-plane magnetic anisotropy (D > 0), whereas compound 4 shows large easy-axis magnetic anisotropy (D < 0). Comparative analysis of the magneto-structural data underlines the important role that is played not only by the coordination geometry but also the electronic effects in determining the anisotropy of the CoII ions. Compounds 2–3 show a field-induced slow relaxation of magnetization. Despite its large easy-axis magnetic anisotropy, compound 4 does not show significant slow relaxation (SMR) above 2 K under zero applied magnetic fields, but its magnetic dilution with ZnII triggers SMR at zero field. Finally, it is worth remarking that compounds 2–4 show smaller relaxation times than the analogous complexes with the tripodal ligand bearing in its arms pyridine instead of isoquinoline moieties, which is most likely due to the increase of the molecular size in the former one.
Large easy-axis magnetic anisotropy in a series of trigonal prismatic mononuclear cobalt(ii) complexes with zero-field hidden single-molecule magnet behaviour: the important role of the distortion of the coordination sphere and intermolecular interactions in the slow relaxation
(Royal Society of Chemistry, 2022) Landart-Gereka, Aritz; Quesada-Moreno, María Mar; Díaz-Ortega, Ismael; Nojiri, Hiroyuki; Ozerov, Mykhaylo; Krzystek, Jurek; Palacios-López, María Ángeles; Colacio, Enrique
The complexes [Co(L)]X·S (X = CoCl42−, S = CH3CN (1); X = ZnCl42−, S = CH3OH (2)), [Co(L)]X2·S (X = ClO4−, S = 2CH3OH (3) and X = BF4− (4)) and [Co(L)(NCS)2] (5), where L = the N6-tripodal ligand tris(pyridylhydrazonyl)phosphorylsulfide, were prepared and studied by X-ray crystallography, ac and dc magnetic data, FIRMS and HFEPR spectra, and theoretical calculations. On passing from 1 to 4, the change of the counteranion decreases slightly the distortion of the CoN6 coordination polyhedron from trigonal prismatic to octahedral, with a parallel increase of the easy-axis magnetic anisotropy. Compound 1 does not show slow magnetic relaxation, even in the presence of a dc magnetic field, due to fast QTM triggered by dipolar interactions. Although the complexes 2–4 show a weak frequency and temperature dependence of the ac susceptibility below 10 K at zero field, they exhibit slow relaxation and single-molecule magnet (SMM) behaviour under the corresponding optimal field. The relaxation of the magnetization takes place mainly through a Raman relaxation process above 4 K, whereas below this temperature QTM and/or direct processes dominate. The relaxation time increases with the parallel increase of the uniaxial anisotropy on passing from 1 to 4. The width of the hysteresis for the trigonal prismatic complexes at 0.4 K decreases in the order 3 > 2 > 4 > 1, which is due to combined effects of QTM relaxation and axial anisotropy. Magnetic dilution of complexes 3 and 4 with ZnII triggers the slow relaxation of the magnetization at zero-field, so that these complexes can be considered as “hidden mononuclear SMMs”. Compound 5, with a compressed octahedral geometry, exhibits easy-plane magnetic anisotropy (D = +34.7 cm−1), and it is a field-induced mononuclear SMM with magnetization relaxation faster than compounds 2–4 and a smaller hysteresis loop.
Unlocking the Water Trimer Loop: Isotopic Study of Benzophenone-(H2O)1–3 Clusters with Rotational Spectroscopy
(Wiley, 2021) Li, Weixing; Quesada-Moreno, María Mar; Pinacho, Pablo; Schnell, Melanie
Examined here are the structures of complexes of benzophenone microsolvated with up to three water molecules by using broadband rotational spectroscopy and the cold conditions of a molecular jet. The analysis shows that the water molecules dock sideways on benzophenone for the water monomer and dimer moieties, and they move above one of the aromatic rings when the water cluster grows to the trimer. The rotational spectra shows that the water trimer moiety in the complex adopts an open-loop arrangement. Ab initio calculations face a dilemma of identifying the global minimum between the open loop and the closed loop, which is only solved when zero-point vibrational energy correction is applied. An OH⋅⋅⋅π bond and a Bürgi-Dunitz interaction between benzophenone and the water trimer are present in the cluster. This work shows the subtle balance between water–water and water–solute interactions when the solute molecule offers several different anchor sites for water molecules.
Analysis of thyme essential oils using gas-phase broadband rotational spectroscopy
(Royal Society of Chemistry, 2019) Quesada-Moreno, María Mar; Krin, Anna; Schnell, Melanie
A semi-quantitative analysis of the components of two natural essential oils has been carried out using broadband rotational spectroscopy, which is inherently molecule specific. The samples under study were two thyme essential oils from Spain with different compositions: (a) with thymol as the most abundant species (thyme I) and (b) with linalool and 4-carvomenthenol being the most abundant ones (thyme II). Relative intensity measurements of selected rotational transitions were carried out to estimate the abundances of the different species present in these complex mixtures, taking into account the square of the respective dipole moment components. One strength of rotational spectroscopy is its structure sensitivity. Here, we also re-investigated the microwave spectrum of linalool and determined the accurate experimental gas-phase structures of thymol and linalool through the assignment of all 13C isotopologues of their lowest energy conformers. A characteristic splitting pattern of the rotational transitions due to internal rotation of two non-equivalent methyl groups of linalool was observed in the thyme II spectrum. Their internal rotation barriers were experimentally determined to 4.7703(96) kJ mol−1 and 9.2581(74) kJ mol−1, respectively.
Determining the Zero-Field Cooling/ Field Cooling Blocking Temperature from AC-Susceptibility data for Single-Molecule Magnets
(Royal Society of Chemistry, 2025) Gil, Yolimar; Quesada-Moreno, María Mar; Palacios-López, María Ángeles; Gómez-Coca, Silvia; Colacio, Enrique; Ruiz, Eliseo; Aravena, Daniel
We present a general relationship between the magnetisation blocking temperature (TB) measured using the zero-field cooling/field cooling technique (ZFC/FC) and the temperature-dependent spin relaxation time obtained from AC susceptibility and magnetisation decay measurements. The presented mathematical approach supplies ZFC/FC blocking temperatures at any heating rate (RH), providing comparable values to those obtained experimentally, as demonstrated by testing 107 examples for reported single-molecule magnets (SMMs) where the ZFC/FC curve has been measured. This procedure is examined in further detail for a new single-molecule magnet, [Dy(OPAd2Bz)2(H2O)4Br]Br2·4THF (1) (OPAd2Bz: di(1-adamantyl)benzylphosphine oxide). For this compound, ZFC/FC measurements were made over a broad range of heating rates (0.01–5 K min−1), which agreed with the general behaviour predicted from AC susceptibility data. We discuss how the demagnetisation mechanism determines the sensitivity of TB with respect to the heating rate: TB is mostly insensitive to RH for Orbach relaxation, while there is a larger sensitivity for Raman-limited systems. Our conclusions provide a clear physical interpretation of ZFC/FC blocking temperatures, aiding in the proper contextualization of this figure of merit.
Simultaneous Testing of Multiclass Organic Contaminants in 4 Food and Environment by Liquid Chromatography/ Dielectric 5 Barrier Discharge Ionization- Mass Spectrometry
(RSC, 2012) Gilbert-López, Bienvenida; García-Reyes, Juan Francisco; Meyer, Cordula; Michels, Antje; Franzke, Joachim; Molina-Díaz, Antonio; Hayen, Heiko
A Dielectric Barrier Discharge Ionization (DBDI) LC/MS interface is based on the use of a lowtemperature helium plasma, which features the possibility of simultaneous ionization of species with a wide variety of physicochemical properties. In this work, the performance of LC/DBDI-MS for trace analysis of highly relevant species in food and environment has been examined. Over 75 relevant species including multiclass priority organic contaminants and residues such as pesticides, polycyclic aromatic hydrocarbons, organochlorine species, pharmaceuticals, personal care products, and drugs of abuse were tested. LC/DBDI-MS performance for this application was assessed and compared with standard LC/MS sources (electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)). The used benchtop Orbitrap mass spectrometer features a 10 Hz polarity switching mode, so that both positive and negative ion mode acquisitions are possible with acquisition cycles matching the requirements of fast liquid chromatography. Both polar and nonpolar species (including those typically analyzed by GC/electron ionization-MS) can be tested in a single run using polarity switching mode. The methodology was found to be effective in detecting a wide array of organic compounds at concentration levels in the low ng L-1 to mg kg-1 range in wastewater and food matrices, respectively. The linearity was evaluated in an olive oil extract, obtaining good correlation coefficients in the studied range. Additionally, minor matrix effects (<=15% of signal suppression or enhancement) were observed for most of the studied analytes in this complex fatty matrix. The results obtained were compared with data from both ESI and APCI sources, obtaining a merged coverage between ESI and APCI in terms of analyte ionization and higher overall sensitivity for the proposed ion source based on the DBD principle. The use of this approach further extends the coverage of current LC/MS methods towards an even larger variety of chemical species including both polar and nonpolar (non-ESI amenable) species and may find several applications in fields such as food and environment testing or metabolomics where GC/MS and LC/MS are combined to cover as many different species as possible.
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 Jesús
This 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.
Gold-Nanoparticles-based Solid-Phase Microextraction Coatings for Determining Organochlorine Pesticides in Aqueous Environmental Samples
(wiley, 2017-03) Gutiérrez-Serpa, Adrián; Rocío-Bautista, Priscilla; Pino, Verónica; Jiménez-Moreno, Francisco; Jiménez-Abizanda, Ana Isabel
The use of solid-phase microextraction coatings based on gold nanoparticles was investigated, focusing the attention on the preparation of nanoparticles with nonclassical reduction agents of HAuCl4 such as gallic acid and H2O2, rather than the conventional sodium citrate. All nanoparticles were characterized by diode array spectroscopy, whereas novel nanoparticles prepared with gallic acid and H2O2 were also characterized by microscopic techniques. Solid-phase microextraction coatings were prepared with a layer-by-layer approach. Gallic acid permitted the preparation of stable nanoparticles with milder experimental conditions (1 min, room temperature) and provided the most uniform coatings (thickness ∼3 μm). Seven organochlorine pesticides were determined in different environmental waters using gas chromatography with electron capture detection. Despite the low thickness of the coatings, limits of detection of the entire method down to 0.13 μg/L were obtained. A comparison with the commercial polyacrylate in terms of the partition coefficients of the analytes to the coatings gave logarithm of the partition coefficient values two times higher with gallic acid than polyacrylate (although the commercial fiber is 28 times thicker). Interfiber relative standard deviation values ranged from 8.67 to 21.3%. Optimum fibers also presented an adequate lifetime (>100 extractions).
Microfluidic water-assisted trap focusing method for ultra-large volume injection in reversed-phase nano-liquid chromatography coupled to electron ionization tandem-mass spectrometry
(Elsevier, 2020-09) Termopoli, Veronica; Famiglini, Giorgio; Vocale, Palma; Morini, Gian Luca; Palma, Pierangela; Rocío-Bautista, Priscilla; Mansoor, Saeed; Perry, Simon; Cappiello, Achille
Herein we present an efficient, column-switching method that relies on a custom-made T-union passive diffusion micromixer to assist water dilution and promote trap solute focusing of a high sample volume dissolved in pure organic solvent using a 0.075 mm i.d. nano-LC column. This method allows injecting 20 μL (or higher) of sample volume, speeding up the analysis time, with a 400-fold increase of the limits of quantitation for selected compounds. Five pesticides in different media were used as model compounds, and the analyses were carried out with a triple quadrupole mass spectrometer equipped with a Liquid Electron Ionization (LEI) LC-MS interface working in multiple reaction monitoring (MRM) mode. The system microfluidics were investigated using COMSOL modeling software. Robustness of the entire system was evaluated using a post-extraction addition soil extracts with limits of detection values spanning from 0.10 to 0.45 µg/L. Reproducible results in terms of peak area, peak shape, and retention times were achieved in soil matrix. Repeatability test on peak area variations were lower than 10%.
Solid-phase microextraction coatings based on the metal-organic framework ZIF-8: Ensuring stable and reusable fibers
(Elsevier, 2020-08) Rocío-Bautista, Priscilla; Gutiérrez-Serpa, Adrián; Cruz, Alexander John; Ameloot, Rob; Ayala-Díaz, Juan; Afonso, Ana M.; Pasán, Jorge; Rodríguez-Hermida, Sabina; Pino, Verónica
Chemical vapor deposition of MOFs (MOF-CVD) has been used to coat solid-phase microextraction (SPME) fibers with ZIF-8, by exposing ZnO layers to the linker vapor (2-methylimidazole). This ZIF-8 coating has been used as a seed layer in a following solvothermal MOF growth step in order to increase the ZIF-8 thickness. The combined MOF-CVD and solvothermal growth of ZIF-8 on the fibers result in a thickness of ~3 μm, with adequate thermal stability, and mechanical integrity when tested with methanol and acetonitrile ultrasonic treatments. The fibers have been evaluated in direct immersion mode using gas chromatography and flame ionization detection (GC-FID), for a group of target analytes including three polycyclic aromatic hydrocarbons (PAHs) and five personal care products (PCPs). The optimized conditions of the SPME-GC-FID methods include low amount of aqueous sample (5 mL), stirring for 45 min at 35 °C, and desorption at 280 °C for 5 min. The method presents limits of detection down to 0.6 μg L−1; intra-day, inter-day and inter-batch relative standard deviation values lower than 16%, 19%, and 23%, respectively; and a lifetime higher than 70 cycles.
Influence of ligand functionalization of UiO-66-based metal-organic frameworks when used as sorbents in dispersive solid-phase analytical microextraction for different aqueous organic pollutants
(MDPI, 2018-11) Taima-Mancena, Iván; Rocío-Bautista, Priscilla; Pasán, Jorge; Ayala-Díaz, Juan; Ruiz-Pérez, Catalina; Afonso, Ana M.; Lago, Ana B.; Pino, Verónica
Four metal-organic frameworks (MOFs), specifically UiO-66, UiO-66-NH2, UiO-66-NO2, and MIL-53(Al), were synthesized, characterized, and used as sorbents in a dispersive micro-solid phase extraction (D-µSPE) method for the determination of nine pollutants of different nature, including drugs, phenols, polycyclic aromatic hydrocarbons, and personal care products in environmental waters. The D-µSPE method, using these MOFs as sorbents and in combination with high-performance liquid chromatography (HPLC) and diode-array detection (DAD), was optimized. The optimization study pointed out to UiO-66-NO2 as the best MOF to use in the multi-component determination. Furthermore, the utilization of isoreticular MOFs based on UiO-66 with the same topology but different functional groups, and MIL-53(Al) to compare with, allowed us for the first time to evaluate the influence of such functionalization of the ligand with regards to the efficiency of the D-µSPE-HPLC-DAD method. Optimum conditions included: 20 mg of UiO-66-NO2 MOF in 20 mL of the aqueous sample, 3 min of agitation by vortex and 5 min of centrifugation, followed by the use of only 500 µL of acetonitrile as desorption solvent (once the MOF containing analytes was separated), 5 min of vortex and 5 min of centrifugation. The validation of the D-µSPE-HPLC-DAD method showed limits of detection down to 1.5 ng·L−1, average relative recoveries of 107% for a spiked level of 1.50 µg·L−1, and inter-day precision values with relative standard deviations lower than 14%, for the group of pollutants considered.
A green metal–organic framework to monitor water contaminants
(RSC Advance, 2018-09) Rocío-Bautista, Priscilla; Pino, Verónica; Pasán, Jorge; Ayala-Díaz, Juan; Ruiz-Pérez, Catalina; Afonso, Ana M.
The CIM-80 material (aluminum(III)-mesaconate) has been synthetized in high yield through a novel green procedure involving water and urea as co-reactants. The CIM-80 material exhibits good thermal stability with a working range from RT to 350 °C with a small contraction upon desolvation. Moreover, this material is stable in water at different pH values (1–10) for at least one week, and shows a LC50 value higher than 2 mg mL−1. The new material has been tested in a microextraction methodology for the monitoring of up to 22 water pollutants while presenting little environmental impact: only 20 mg of CIM-80 and 500 μL of acetonitrile are needed per analysis. The analytical performance of the CIM-80 in the microextraction strategy is similar to or even better for several pollutants than that of MIL-53(Al). The average extraction efficiencies range from ∼20% for heavy polycyclic aromatic hydrocarbons to ∼70–100% for the lighter ones. In the case of the emerging contaminants, the average extraction efficiency can reach values up to 70% for triclosan and carbamazepine.
Insights in the analytical performance of neat metal-organic frameworks in the determination of pollutants of different nature from waters using dispersive miniaturized solid-phase extraction and liquid chromatography
(Elsevier, 2018-03) Rocío-Bautista, Priscilla; Pino, Verónica; Pasán, Jorge; López-Hernández, Irene; Ayala-Díaz, Juan; Ruiz-Pérez, Catalina; Afonso, Ana M.
Five metal-organic frameworks (MOFs), specifically HKUST-1, MOF-5(Zn), MIL-53(Al), UiO-64 and MOF-74(Zn) are synthesized, characterized, and utilized in a miniaturized solid-phase extraction method under dispersive mode (D-µSPE) for the determination of six pollutants of different nature, including one polycyclic aromatic hydrocarbon, two hormones, two drugs, and one disinfectant, from environmental waters (tap water and wastewater). A discussion of possible interactions justifying the partitioning of target analytes to the MOFs is included, considering not only the analytes’ physicochemical characteristics but also those of MOFs: metal nature, structural environment of MOF pores, pore size and pore aperture widths, among others. MIL-53(Al) is selected for its versatility and high extraction efficiency for the target compounds. The D-µSPE method using MIL-53(Al) is optimized and used in combination with high-performance liquid chromatography (HPLC) with diode array detector (DAD) or liquid-chromatography with time-of-flight mass spectrometric detector (LC-TOF). Under optimum conditions, only 5 mg of MIL-53(Al) are required for 10 mL of water, with the aid of 5 min of vortex and 5 min of centrifugation. Elution is accomplished with 200 µL of acetonitrile (3 times), and evaporation down to 100 µL before LC injection. Detection limits down to 0.040 μg L−1 for triclosan and 0.013 μg L−1 for atrazine are obtained for the entire method using HPLC-DAD and LC-TOF, respectively. The method, operating at low spiked levels (2 µg L−1 for HPLC-DAD and 0.7 µg L−1 for LC-TOF), is also characterized for average relative recoveries of 109% and 105%; relative standard deviation values lower than 8.7% and 7.5%; and average extraction efficiencies of 41.2% and 49.1%; using HPLC-DAD and LC-TOF, respectively; while demonstrating adequate analytical performance with complex samples such as wastewaters.
A magnetic-based dispersive micro-solid-phase extraction method using the metal-organic framework HKUST-1 and ultra-high-performance liquid chromatography with fluorescence detection for determining polycyclic aromatic hydrocarbons in waters and fruit tea infusions
(Elsevier, 2016-03) Rocío-Bautista, Priscilla; Pino, Verónica; Ayala-Díaz, Juan; Pasán, Jorge; Ruiz-Pérez, Catalina; Afonso, Ana M.
A hybrid material composed by the metal-organic framework (MOF) HKUST-1 and Fe3O4 magnetic nanoparticles (MNPs) has been synthetized in a quite simple manner, characterized, and used in a magnetic-assisted dispersive micro-solid-phase extraction (M-d-μSPE) method in combination with ultra-high-performance liquid chromatography (UHPLC) and fluorescence detection (FD). The application was devoted to the determination of 8 heavy polycyclic aromatic hydrocarbons (PAHs) in different aqueous samples, specifically tap water, wastewaters, and fruit tea infusion samples. The overall M-d-μSPE-UHPLC-FD method was optimized and validated. The method is characterized by: its simplicity in both the preparation of the hybrid material (simple mixing) and the magnetic-assisted approach (∼10 min extraction time), the use of low sorbent amounts (20 mg of HKUST-1 and 5 mg of Fe3O4 MNPs), and the low organic solvent consumption in the overall M-d-μSPE-UHPLC-FD method (1.5 mL of acetonitrile in the M-d-μSPE method and 2.8 mL of acetonitrile in the UHPLC-FD run). The resulting method has high sensitivity, with LODs down to 0.8 ng L−1; adequate intermediate precision, with relative standard deviation values (RSD) always lower than 6.3% (being the range 5.9–9.0% in tap water for a spiked level of 45 ng L−1, 6.1–14% in wastewaters for a spiked level of 45 ng L−1, and 7.2–17% in fruit tea infusion samples for a spiked level of 45 ng L−1); and adequate relative recoveries, with average values of 82% in tap water, and 94% and 75% in wastewater and fruit tea infusion samples, respectively, if using the proper matrix-matched calibration.
Conformational Flexibility of Limonene Oxide Studied By Microwave Spectroscopy
(Wiley, 2017) Loru, Donatella; Quesada-Moreno, María Mar; Avilés-Moreno, Juan Ramón; Jarman, Natasha; Huet, Thérèse R.; López-González, Juan Jesús; Sanz, María Eugenia
Monoterpenoids are biogenic volatile organic compounds (BVOCs) that play a major role in atmospheric chemistry, participating in the formation of aerosols. In this work, the monoterpenoid R-(+)-limonene oxide (C10H16O) has been characterized in the gas phase by Fourier transform microwave spectroscopy in a supersonic jet. Five conformers of limonene oxide, four equatorial and one axial considering the configuration of the isopropenyl group, have been unambiguously identified from the analysis of the rotational spectrum. The observed conformers include cis and trans forms, and are stabilised by a subtle balance of hydrogen bonds, dispersive interactions and steric effects. Estimated conformational relative abundances surprisingly reveal that the axial conformer has an abundance similar to some equatorial conformers. In addition, the potential energy surface was extensively explored using density functional theory and ab initio methods.
Structure Determination, Conformational Flexibility, Internal Dynamics, and Chiral Analysis of Pulegone and Its Complex with Water
(Wiley, 2018) Krin, Anna; Pérez-Cuadrado, Cristóbal; Pinacho, Pablo; Quesada-Moreno, María Mar; López-González, Juan Jesús; Avilés-Moreno, Juan Ramón; Blanco-Rodríguez, Susana; López-Alonso, Juan Carlos; Schnell, Melanie
In the current work we present a detailed analysis of the chiral molecule pulegone, which is a constituent of essential oils, using broadband rotational spectroscopy. Two conformers are observed under the cold conditions of a molecular jet. We report an accurate experimentally determined structure for the lowest energy conformer. For both conformers, a characteristic splitting pattern is observed in the spectrum, resulting from the internal rotation of the two non-equivalent methyl groups situated in the isopropylidene side chain. The determined energy barriers are 1.961911(46) kJ/mol and 6.3617(12) kJ/mol for one conformer, and 1.96094(74) kJ/mol and 6.705(44) kJ/mol for the other one. Moreover, a cluster of the lowest energy conformer with one water molecule is reported. The water molecule locks one of the methyl groups via a hydrogen bond and some secondary interactions, so that we only observe internal rotation splittings from the other methyl group with an internal rotation barrier of 2.01013(38) kJ/mol. Additionally, the chirality-sensitive microwave three-wave mixing technique is applied for the differentiation between the enantiomers, which can become of further use for the analysis of essential oils.
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).
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 Jesús
The 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.
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, José
1H-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.
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, José
For 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.

RUJA: Repositorio Institucional de Producción Científica

Examinar

Envíos recientes