Molecular Recognition, Transient Chirality and Sulfur Hydrogen Bonding in the Benzyl Mercaptan Dimer

The homodimers of transiently chiral molecules offer physical insight into the process of molecular recognition, the preference for homo or heterochiral aggregation and the nature of the non-covalent interactions stabilizing the adducts. We report the observation of the benzyl mercaptan dimer in the isolation conditions of a supersonic jet expansion, using broadband (chirped-pulse) microwave spectroscopy. A single homochiral isomer was observed for the dimer, stabilized by a cooperative sequence of S-H···S and S-H···π hydrogen bonds. The structural data, stabilization energies and energy decomposition describe these non-covalent interactions as weak and dispersion-controlled. A comparison is also provided with the benzyl alcohol dimer.This research was funded by the Spanish Ministerio de Ciencia e Innovación MICINN-FEDER, grants numbers PGC2018-098561-B-C21 and PGC2018-098561-B-C22. The APC were funded by PGC2018-098561-B-C22

Sulfur hydrogen bonding and internal dynamics in the monohydrates of thenyl mercaptan and thenyl alcohol

Producción CientíficaThe monohydrates of thenyl alcohol and thenyl mercaptan have been probed in a supersonic jet expansion using chirped-pulsed and Fabry-Perot Fourier-transform microwave spectroscopy. The rotational spectra revealed a single isomer for each of the dimers. The thenyl alcohol hydrate is stabilized by an O-H···Ow hydrogen bond between the alcohol and water, with water acting as proton acceptor and additionally engaging in a Ow-H···pi interaction with the thenyl ring. Conversely, water behaves as proton donor in the thenyl mercaptan hydrate, linking to the thiol group though a Ow-H···S hydrogen bond and secondary Ow-H··· interactions to the ring. In both dimers water retains internal mobility, as tunneling doublings in the spectrum confirm an internal rotation motion of water inside the cluster. The experimental results have been complemented with density-functional-theory molecular orbital calculations, binding energy decomposition and a topological analysis of the electronic density, providing a comparative description of the effects of hydrogen bonding of water to the alcohol and thiol groups in the dimers, relevant to understand hydrogen bonding to sulfur centers.MICINN-FEDER (PGC2018-098561- B-C22) and JCyL (grant VA056G18

Chirality-Puckering correlation and intermolecular interactions in Sphingosines: Rotational spectroscopy of jaspine B3 and its monohydrate

Producción CientíficaChirality is determinant for sphingosine biofunctions and pharmacological activity, yet the reasons for the biological chiral selection are not well understood. Here, we characterized the intra- and intermolecular interactions at the headgroup of the cytotoxic anhydrophytosphingosine jaspine B, revealing chirality-dependent correlations between the puckering of the ring core and the formation of amino-alcohol hydrogen bond networks, both in the monomer and the monohydrate. Following the specific synthesis of a shortened 3-carbon side-chain molecule, denoted jaspine B3, six different isomers were observed in a jet expansion using broadband (chirped-pulsed) rotational spectroscopy. Additionally, a single isomer of the jaspine B3 monohydrate was observed, revealing the insertion of water in between the hydroxy and amino groups and the formation of a network of O-H···N-H···Oring hydrogen bonds. The specific jaspine B3 stereochemistry thus creates a double-faced molecule where the exposed lone-pair electrons may easily catalyze the formation of intermolecular aggregates and determine the sphingosine biological properties.Ministerio de Ciencia, Innovación y Universidades - Fondo Europeo de Desarrollo Regional (grant PGC2018-098561-B-C22

π-Stacking Isomerism in Polycyclic Aromatic Hydrocarbons: The 2-Naphthalenethiol Dimer

Producción Científicaπ-Stacking is a common descriptor for face-to-face attractive forces between aromatic hydrocarbons. However, the physical origin of this interaction remains debatable. Here we examined π-stacking in a model homodimer formed by two thiol-substituted naphthalene rings. Two isomers of the 2-naphthalenethiol dimer were discovered using rotational spectroscopy, sharing a parallel-displaced crossed orientation and absence of thiol–thiol hydrogen bonds. One of the isomers presents C2 symmetry, structurally analogous to the global minimum of the naphthalene dimer. The experimental data were rationalized with molecular orbital calculations, revealing a shallow potential energy surface. Noncovalent interactions are dominated by dispersion forces according to SAPT energy decomposition. In addition, the reduced electronic density shows a diffuse and extended region of inter-ring interactions, compatible with the description of π-stacking as a competition between dispersion and Pauli repulsion forces

Rotational Spectra of Tetracyclic Quinolizidine Alkaloids: Does a Water Molecule Flip Sparteine?

Producción CientíficaSparteine is a quinolizidine alkaloid used as chiral auxiliary in asymmetric synthesis. We examine whether hydration by a single molecule can flip sparteine from the most stable trans conformation to the bidentate cis arrangement observed in catalytic complexation to a metal center. Sparteine and the dimer sparteine-water were generated in a supersonic jet expansion with H216O and H218O, and characterized by broadband chirped-pulse microwave spectroscopy. Despite the bidentate water dimer was predicted with larger binding energy, a single isomer was observed for the monohydrated cluster, with sparteine retaining the trans conformation observed for the free molecule. The absence of the bidentate dimer is attributed to kinetic control of the cluster formation, favoring the pre-expansion most abundant monomer. The structural properties of the O-H···N hydrogen bond in the dimer are compared with complexes of other secondary and tertiary amines.2018-07-21MINECO-FEDER (CTQ2015-68148-C2-2-P

Caracterizacion del daNado electrico residual tras procesos de implantacion ionica y RTA en silicio y fosfuro de indio

Centro de Informacion y Documentacion Cientifica (CINDOC). C/Joaquin Costa, 22. 28002 Madrid. SPAIN / CINDOC - Centro de Informaciòn y Documentaciòn CientìficaSIGLEESSpai

Elaboración de un libro de texto, CD-ROM y página Web para la asignatura Sistemas Electrónicos para el Tratamiento de la Información, en la Titulación de Ingeniero en Electrónica

Realizado en la Escuela Técnica Superior de Telecomunicaciones de Valladolid, por 3 profesores del centro, para la asignatura de Sistemas Electrónicos para el Tratamiento de la Información I, de cuarto de Ingeniero en Electrónica. El objetivo fundamental era desarrollar un libro de consulta que pretende: la orientación sistemática en el estudio, la información de un contenido con rigor científico y asequible a la exposición y el entrenamiento práctico en la solución de problemas concretos asociados al Tratamiento de la Información. Este material se ha estado usando en la docencia y con una fuerte realimentación por parte del alumnado ha permitido mejorar los recursos de apoyo desarrollados. Los resultados obtenidos han sido satisfactorios habiendo mejorado la compresión de la asignatura gracias al libro de texto desarrollado. El CD y la página Web han sido de gran ayuda para los alumnos al poder disponer de un medio on-line de comunicación y resolución de dudas con el profesor y los propios compañeros.Junta de Castilla y León. Consejería de Educación y CulturaCastilla y LeónJunta de Castilla y León. Consejería de Educación y Cultura; Monasterio de Nuestra Señora de Prado. Autovía Puente Colgante, s. n.; 47071 Valladolid; Tel. +34983411881; Fax +34983411939; [email protected]

Rotational spectroscopy of organophosphorous chemical agents: cresyl and phenyl saligenin phosphates

Cresyl and phenyl saligenin phosphates have been probed in a jet expansion by broadband chirp-excitation microwave spectroscopy, revealing the most stable conformations and their structural properties. The rotational parameters offer a high-resolution univocal route for characterization of organophosphorous agents and a testbed for computational models.We thank MICINN-FEDER (PGC2018-098561-B-C22) and JCyL (VA056G18) for funds.Peer reviewe

A DFT-Based Computational-Experimental Methodology for Synthetic Chemistry: Example of Application to the Catalytic Opening of Epoxides by Titanocene

A novel DFT-based Reaction Kinetics (DFT-RK) simulation approach, employed in combination with real-time data from reaction monitoring instrumentation (like UV–vis, FTIR, Raman, and 2D NMR benchtop spectrometers), is shown to provide a detailed methodology for the analysis and design of complex synthetic chemistry schemes. As an example, it is applied to the opening of epoxides by titanocene in THF, a catalytic system with abundant experimental data available. Through a DFT-RK analysis of real-time IR data, we have developed a comprehensive mechanistic model that opens new perspectives to understand previous experiments. Although derived specifically from the opening of epoxides, the prediction capabilities of the model, built on elementary reactions, together with its practical side (reaction kinetics simulations of real experimental conditions) make it a useful simulation tool for the design of new experiments, as well as for the conception and development of improved versions of the reagents. From the perspective of the methodology employed, because both the computational (DFT-RK) and the experimental (spectroscopic data) components can follow the time evolution of several species simultaneously, it is expected to provide a helpful tool for the study of complex systems in synthetic chemistry