Hydrogen transfer in hydrogen bonded solid state materials

The investigation of strongly hydrogen bonded solid state materials and the hydrogen transfer processes therein are the subject of the present work. Strong hydrogen bonds are found whenever the hydrogen bonded species compete for the hydrogen atom, and are thereby on the verge of showing hydrogen transfer. Consequently, the strongly hydrogen bonded solid state materials investigated in this work are synthesised by co-crystallising chemical compounds which have a similar affinity for the proton. The molecular complexes of isonicotinamide with oxalic acid crystallise in two hydrogenous polymorphs and, upon substituting the acidic hydrogen for deuterium, in two deuterated polymorphs, neither being isostructural to the hydrogenous forms. This phenomenon is known as isotopomeric polymorphism and is rarely observed in molecular materials. The four polymorphic forms are found to exhibit different degrees of hydron transfer. The hydrogenous forms show strong hydrogen bonding between the acid and the pyridine base. The nature of these strong hydrogen bonds is characterised by combined X ray charge density and single crystal neutron diffraction studies and found to be covalent in nature. The covalent hydroxyl bonds are considerably elongated, to an extent that in one polymorph the hydrogen atom occupies a near central position in the strong hydrogen bond. The structural work has been complemented by ab-initio computational studies, using the plane wave and localised atomic orbital methods, to evaluate the nature and the dynamics of the strong hydrogen bonds, and to establish an energy scale for polymorphism. It is found that the atomic orbital calculations yield results in good agreement with the experiment, while the plane wave calculations fail to reproduce the experimental hydrogen bond geometries. A strong electronic delocalisation is observed in the difference electron densities of strong acid – pyridine base hydrogen bonds. The major contribution to the delocalisation is found to originate from the nitrogen lone pair density which in this type of strong hydrogen bond is found to be observed to low experimental resolutions in standard X-ray diffraction experiments. As a consequence, such hydrogen bonds are susceptible to misinterpretation, and can be misinterpreted as hydrogen bonds with a disordered hydrogen, altering the descriptive character of materials significantly from being neutral to being ionic. It is shown that a careful examination of the difference electron densities, with the knowledge of the presence of the nitrogen lone pair density, allows a reasonably accurate determination of nuclear hydrogen positions from X-ray diffraction experiments alone. The hydrogen transfer behaviour in a series of strongly hydrogen bonded materials has been studied. For the molecular complexes of pentachlorophenol with the series of dimethylpyridines, a correlation is established between the dissociation constants determined in solution and the degree of hydrogen transfer from phenol to the pyridine bases in the solid state. The influence of additional strong and weak hydrogen bonding interactions in the vicinity of the strong hydrogen bonds on the hydrogen transfer behaviour is rationalised. Similar studies have been carried out on the molecular complexes of oxalic acid and fumaric acid with the dimethylpyridines, and on the molecular complexes of pentachlorophenol with 1,4-diazabicyclo[2.2.2]octane. The design approach leading to these materials and the hydrogen transfer behaviour observed in these materials is critically analysed

Octahydrocyclopenta[c]pyridine Scaffold – Enantioselective Synthesis and Indole Annulation

An optically active hexahydrocyclopenta[c]pyridine derivative with quaternary stereocenter was prepared as a new heterocyclic scaffold. Key reaction was the Pd‐catalyzed asymmetric allylic alkylation of a piperidine‐based β‐oxoester, which proceeded in very good yield with high level of enantioselectivity (90 %, 95 % ee). The α‐allyl moiety was transformed into a 1,4‐diketone by Pd‐catalyzed Wacker oxidation with molecular oxygen (89 %). This intermediate was cyclized in an intramolecular aldol reaction furnishing the cyclopentenone motif (86 %). Hydrogenation of the C–C double bond gave the cis‐annulated octahydrocyclopenta[c]pyridine (86 %), which was submitted to Fischer indolization (85 %). Although two regioisomers could be expected, only the angular constitution was observed. Relative and absolute configurations were established by X‐ray crystallography of a para‐iodo benzamide derivative. The utility of the title compound as scaffold is further highlighted by a number of synthetically useful transformations, for instance formation of carboxamides, sulfonamides, ureas and reductive aminations with aldehydes

Análisis comparativo del uso de las tecnologías de la información y comunicación (TIC), en la gestión empresarial de los hoteles ubicados en la ciudad de Estelí, Nicaragua entre los años 2008 y 2016

La presente investigación está dirigida al análisis de las Tecnologías de Información y Comunicación (TIC) en la gestión hotelera de los hoteles de la ciudad de Estelí, utilizando como referente un estudio realizado en 2008 y comparando resultados con el año 2016, es un estudio de tipo cuantitativo, se aplicaron 19 encuestas a gerentes, administradores de los hoteles y entrevistas para complementar los análisis estadísticos. Como resultado se encontró que hay cambios significativos en la implementación de nuevas tecnologías como: la incorporación de nuevos equipos tecnológicos (hardware), e incremento de programas (software) específicos para hoteles. El 30% de los encuestados afirmó que la principal limitante es la falta de capacitación y el 28% indica que los altos costos para incorporar las TIC, encontrando diferencia en las dificultades entre los dos años. La hipótesis planteada se acepta en un 84% las TIC han provocado cambios en la gestión empresarial y el uso de tecnología está dirigido al marketing de los hoteles a través del internet. Se proponen seis líneas estratégicas para la mejora del uso de las TIC

Octahydrocyclopenta[c]pyridine Scaffold – Enantioselective Synthesis and Indole Annulation

An optically active hexahydrocyclopenta[c]pyridine derivative with quaternary stereocenter was prepared as a new heterocyclic scaffold. Key reaction was the Pd‐catalyzed asymmetric allylic alkylation of a piperidine‐based β‐oxoester, which proceeded in very good yield with high level of enantioselectivity (90 %, 95 % ee). The α‐allyl moiety was transformed into a 1,4‐diketone by Pd‐catalyzed Wacker oxidation with molecular oxygen (89 %). This intermediate was cyclized in an intramolecular aldol reaction furnishing the cyclopentenone motif (86 %). Hydrogenation of the C–C double bond gave the cis‐annulated octahydrocyclopenta[c]pyridine (86 %), which was submitted to Fischer indolization (85 %). Although two regioisomers could be expected, only the angular constitution was observed. Relative and absolute configurations were established by X‐ray crystallography of a para‐iodo benzamide derivative. The utility of the title compound as scaffold is further highlighted by a number of synthetically useful transformations, for instance formation of carboxamides, sulfonamides, ureas and reductive aminations with aldehydes

Isotopomeric polymorphism in a "doubly-polymorphic" multi-component molecular crystal

Isotopomeric polymorphism is observed in complexes of isonicotinamide with oxalic acid, highly unusual here in that each isotopic complex is itself polymorphic, a situation of “double polymorphism”. The four polymorphic forms exhibit different degrees of hydron transfer.</p

Probing hydrogen positions in hydrous compounds:information from parametric neutron powder diffraction studies

We demonstrate the extent to which modern detector technology, coupled with a high flux constant wavelength neutron source, can be used to obtain high quality diffraction data from short data collections, allowing the refinement of the full structures (including hydrogen positions) of hydrous compounds from in situ neutron powder diffraction measurements. The in situ thermodiffractometry and controlled humidity studies reported here reveal that important information on the reorientations of structural water molecules with changing conditions can be easily extracted, providing insight into the effects of hydrogen bonding on bulk physical properties. Using crystalline BaCl2 center dot 2H(2)O as an example system, we analyse the structural changes in the compound and its dehydration intermediates with changing temperature and humidity levels to demonstrate the quality of the dynamic structural information on the hydrogen atoms and associated hydrogen bonding that can be obtained without resorting to sample deuteration

«Малобюджетний» маркетинг

В умовах сьогоднішньої економічної кризи, яка зачепила всі вітчизняні підприємства, та постійного зниження української національної валюти актуальними стають питання пошуку способів економії коштів. Вирішенням таких проблем може стати «мало бюджетний» маркетинг, який допоможе розвиватися підприємству з використанням мінімальної кількості ресурсів. «Малобюджетний» маркетинг – це маркетингові інструменти залучення й утримання клієнтів, які припускають мінімальні витрати, а іноді можна взагалі обійтися без бюджету

Modular and predictable assembly of porous organic molecular crystals

Nanoporous molecular frameworks are important in applications such as separation, storage and catalysis. Empirical rules exist for their assembly but it is still challenging to place and segregate functionality in three-dimensional porous solids in a predictable way. Indeed, recent studies of mixed crystalline frameworks suggest a preference for the statistical distribution of functionalities throughout the pores rather than, for example, the functional group localization found in the reactive sites of enzymes. This is a potential limitation for 'one-pot' chemical syntheses of porous frameworks from simple starting materials. An alternative strategy is to prepare porous solids from synthetically preorganized molecular pores. In principle, functional organic pore modules could be covalently prefabricated and then assembled to produce materials with specific properties. However, this vision of mix-and-match assembly is far from being realized, not least because of the challenge in reliably predicting three-dimensional structures for molecular crystals, which lack the strong directional bonding found in networks. Here we show that highly porous crystalline solids can be produced by mixing different organic cage modules that self-assemble by means of chiral recognition. The structures of the resulting materials can be predicted computationally, allowing in silico materials design strategies. The constituent pore modules are synthesized in high yields on gram scales in a one-step reaction. Assembly of the porous co-crystals is as simple as combining the modules in solution and removing the solvent. In some cases, the chiral recognition between modules can be exploited to produce porous organic nanoparticles. We show that the method is valid for four different cage modules and can in principle be generalized in a computationally predictable manner based on a lock-and-key assembly between modules