Synthon transferability probed with IR spectroscopy: cytosine salts as models for salts of lamivudine

Co-crystal screening of the anti-HIV drug lamivudine was carried out with dicarboxylic acids as co-formers, and three of the resulting crystalline solids, two salts and a co-crystal, were studied with SCXRD, PXRD and FTIR spectroscopy. Salts of cytosine, a molecule that incorporates critical structural features of lamivudine, with the same co-formers, were taken as model systems for IR spectroscopic studies of the synthons in the salts of lamivudine. It is shown that different systems with the same synthon show very similar spectral signatures in the regions corresponding to the synthon absorptions. This reveals again the modular nature of the supramolecular synthon.

The morphology dependent electrocatalytic activity of Ir nanostructures towards oxygen reduction

Iridium nanostructures with different morphologies are synthesized by a simple, environmentally friendly approach in aqueous media under mild conditions. The morphology dependent electrocatalytic activity of Ir nanochains and nanoparticles towards oxygen reduction reaction (ORR) has been demonstrated in both acidic and alkaline media. Comparative electrochemical studies reveal that nanochains exhibit significantly enhanced ORR activities in both acidic and alkaline media as compared with nanoparticles, as a result of the continuous structure of interconnected particles. The mechanism of oxygen reduction on Ir nanostructures predominantly follows a four-electron pathway in alkaline and acidic solutions. Excellent stability and good selectivity towards methanol tolerance are reported.

Graded IR Filters: Distinguishing Between Single and Multipoint NO2 center dot center dot center dot I Halogen Bonded Supramolecular Synthons (P, Q, and R Synthons)

The NO2 center dot center dot center dot I supramolecular synthon is a halogen bonded recognition pattern that is present in the crystal structures of many compounds that contain these functional groups. These synthons have been previously distinguished as P, Q, and R types using topological and geometrical criteria. A five step IR spectroscopic sequence is proposed here to distinguish between these synthon types in solid samples. Sets of known compounds that contain the P, Q, and R synthons are first taken to develop IR spectroscopic identifiers for them. The identifiers are then used to create graded IR filters that sieve the synthons. These filters contain signatures of the individual NO2 center dot center dot center dot I synthons and may be applied to distinguish between P, Q, and R synthon varieties. They are also useful to identify synthons that are of a borderline character, synthons in disordered structures wherein the crystal structure in itself is not sufficient to distinguish synthon types, and in the identification of the NO2 center dot center dot center dot I synthons in compounds with unknown crystal structures. This study establishes clear differences for the three different geometries P, Q, and Rand in the chemical differences in the intermolecular interactions contained in the synthons. Our IR method can be conveniently employed when single crystals are not readily available also in high throughput analysis. It is possible that such identification may also be adopted as an input for crystal structure prediction analysis of compounds with unknown crystal structures.

IR spectroscopy as a probe for C-H center dot center dot center dot X hydrogen bonded supramolecular synthons

Weak hydrogen bonds of the type C-H center dot center dot center dot X (X: N, O, S and halogens) have evoked considerable interest over the years, especially in the context of crystal engineering. However, association patterns of weak hydrogen bonds are generally difficult to characterize, and yet the identification of such patterns is of interest, especially in high throughput work or where single crystal X-ray analysis is difficult or impossible. To obtain structural information on such assemblies, we describe here a five step IR spectroscopic method that identifies supramolecular synthons in weak hydrogen bonded dimer assemblies, bifurcated systems, and p-electron mediated synthons. The synthons studied here contain C-H groups as hydrogen bond donors. The method involves: (i) identifying simple compounds/cocrystals/salts that contain the hydrogen bonded dimer synthon of interest or linear hydrogen bonded assemblies between the same functionalities; (ii) scanning infrared (IR) spectra of the compounds; (iii) identifying characteristic spectral differences between dimer and linear; (iv) assigning identified bands as marker bands for identification of the supramolecular synthon, and finally (v) identifying synthons in compounds whose crystal structures are not known. The method has been effectively implemented for assemblies involving dimer/linear weak hydrogen bonds in nitrobenzenes (C-H center dot center dot center dot O-NO), nitro-dimethylamino compounds (NMe2 center dot center dot center dot O2N), chalcones (C-H center dot center dot center dot O=C), benzonitriles (C-H center dot center dot center dot N C) and fluorobenzoic acids (C-H center dot center dot center dot F-C). Two other special cases of C-H center dot center dot center dot pi and N-H center dot center dot center dot pi synthons were studied in which the band shape of the C-H stretch in hydrocarbons and the N-H deformation in aminobenzenes was examined.

Spatio-temporal correlations in aqueous systems: computational studies of static and dynamic heterogeneity by 2D-IR spectroscopy

Local heterogeneity is ubiquitous in natural aqueous systems. It can be caused locally by external biomolecular subsystems like proteins, DNA, micelles and reverse micelles, nanoscopic materials etc., but can also be intrinsic to the thermodynamic nature of the aqueous solution itself (like binary mixtures or at the gas-liquid interface). The altered dynamics of water in the presence of such diverse surfaces has attracted considerable attention in recent years. As these interfaces are quite narrow, only a few molecular layers thick, they are hard to study by conventional methods. The recent development of two dimensional infra-red (2D-IR) spectroscopy allows us to estimate length and time scales of such dynamics fairly accurately. In this work, we present a series of interesting studies employing two dimensional infra-red spectroscopy (2D-IR) to investigate (i) the heterogeneous dynamics of water inside reverse micelles of varying sizes, (ii) supercritical water near the Widom line that is known to exhibit pronounced density fluctuations and also study (iii) the collective and local polarization fluctuation of water molecules in the presence of several different proteins. The spatio-temporal correlation of confined water molecules inside reverse micelles of varying sizes is well captured through the spectral diffusion of corresponding 2D-IR spectra. In the case of supercritical water also, we observe a strong signature of dynamic heterogeneity from the elongated nature of the 2D-IR spectra. In this case the relaxation is ultrafast. We find remarkable agreement between the different tools employed to study the relaxation of density heterogeneity. For aqueous protein solutions, we find that the calculated dielectric constant of the respective systems unanimously shows a noticeable increment compared to that of neat water. However, the `effective' dielectric constant for successive layers shows significant variation, with the layer adjacent to the protein having a much lower value. Relaxation is also slowest at the surface. We find that the dielectric constant achieves the bulk value at distances more than 3 nm from the surface of the protein.

High Catalytic Activity of Amorphous Ir-Pi for Oxygen Evolution Reaction

Large-scale production of hydrogen gas by water electrolysis is hindered by the sluggish kinetics of oxygen evolution reaction (OER) at the anode. The development of a highly active and stable catalyst for OER is a challenging task. Electrochemically prepared amorphous metal-based catalysts have gained wide attention after the recent discovery of a cnbalt-phosphate (Co-Pi) catalyst: Herein, an amorphous iridium-phosphate (Ir-Pi) is investigated as an oxygen evolution catalyst. The catalyst is prepared by the anodic polarization of carbon paper electrodes in neutral phosphate buffer solutions containing IrCl3. The Ir-Pi film deposited on the substrate has significant amounts of phosphate and It centers in an oxidation state higher than +4. Phosphate plays a significant role in the deposition of the catalyst and also in its activity toward OER. The onset potential of OER on the Ir-Pi is about 150 mV lower in comparison with the Co-Pi under identical experimental conditions. Thus, Ir-Pi is a promising catalyst for electrochemical oxidation of water.

Ir nanoparticles-anchored reduced graphene oxide as a catalyst for oxygen electrode in Li-O-2 cells

Iridium nanoparticles-anchored reduced graphene oxide (Ir-RGO) was prepared by simultaneous reduction of graphene oxide and Ir3+ ions and its catalytic activity for oxygen electrode in Li-O-2 cells was demonstrated. Ir particles with an average size of 3.9 nm were uniformly distributed on RGO sheets. The oxygen reduction reaction (ORR) was studied on an Ir-RGO catalyst in non-aqueous electrolytes using cyclic voltammetry and rotating disk electrode techniques. Li-O-2 cells with Ir-RGO as a bifunctional oxygen electrode catalyst were subjected to charge-discharge cycling at several current densities. A discharge capacity of 9529 mA h g(-1) (11.36 mA h cm(-2)) was obtained initially at a current density of 0.5 mA cm(-2) (393 mA g(-1)). A decrease in capacity was observed on increasing the current density. Although there was a decrease in capacity on repeated discharge-charge cycling initially, a stable capacity was observed for about 30 cycles. The results suggest that Ir-RGO is a useful catalyst for rechargeable Li-O-2 cells.

Determinantes de la intención del consumidor de ir a un destino turístico. Aplicación al caso de "Mundo Maya-México"

[ES] Cada destino turístico tiene una marca que puede elegir el consumidor a la hora de viajar. Este trabajo examina, a través de un modelo causal que contrastamos empíricamente para el caso de Mundo Maya-México, el papel que desempeña la reputación, las emociones y la confianza en la intención de compra de los consumidores de un destino turístico.

Human LDL Structural Diversity Studied by IR Spectroscopy

Lipoproteins are responsible for cholesterol traffic in humans. Low density lipoprotein (LDL) delivers cholesterol from liver to peripheral tissues. A misleading delivery can lead to the formation of atherosclerotic plaques. LDL has a single protein, apoB-100, that binds to a specific receptor. It is known that the failure associated with a deficient protein-receptor binding leads to plaque formation. ApoB-100 is a large single lipid-associated polypeptide difficulting the study of its structure. IR spectroscopy is a technique suitable to follow the different conformational changes produced in apoB-100 because it is not affected by the size of the protein or the turbidity of the sample. We have analyzed LDL spectra of different individuals and shown that, even if there are not big structural changes, a different pattern in the intensity of the band located around 1617 cm 21 related with strands embedded in the lipid monolayer, can be associated with a different conformational rearrangement that could affect to a protein interacting region with the receptor.

O ir-remediável da invenção autobiográfica: desdobramentos do eu na escrita de Caio Fernando Abreu

O trabalho envereda pelos modos e artifícios de construção da subjetividade nos gêneros autobiográficos e nos textos ficcionais, investigando como se dá a escrita que versa sobre o eu. Dos textos abertamente autobiográficos de Caio Fernando Abreu, como a correspondência, passa-se às formas tênues como a crônica e o conto, nos quais se entrecruzam ficção e subjetividade, experiência e invenção. Nesse sentido, estudamos como o sujeito torna-se o centro dos acontecimentos e passa a escrever sobre aquilo que lhe acomete o espírito, o corpo, os sentimentos e pensamentos, seja no registro pontual e objetivo dos acontecimentos ou no floreamento do vivido e do inventado. A intenção é explorar, nos espaços biográficos e literários de Caio Fernando Abreu, o entrelaçamento de vida e grafia, e as possibilidades de escritura de si mesmo em sua correspondência, organizada por Ítalo Moriconi, em Cartas (2002), na coletânea de crônicas Pequenas Epifanias (2006), e nos contos de Ovelhas negras (1995)

O impacto das variáveis Cultura e Clima Organizacional na gestão do Capital Intelectual: Um estudo comparativo entre Brasil, Canadá, Irã e Líbano

Este estudo se propôs verificar, o impacto da cultura e clima organizacional na gestão do Capital Intelectual no Brasil, comparativamente com o Canadá, Irã e Líbano. Para isso, realizou-se uma pesquisa descritiva através de questionário, com escala Likert, com trabalhadores em empresas brasileiras e comparou-se com os dados obtidos, em outra pesquisa, para o Canadá, Irã e Líbano. Deste modo, o estudo procura analisar, comparativamente entre os países, os impactos dos componentes de Cultura e Clima e verifica, em quais deles, há impacto mais favorável ou desfavorável para a gestão do Capital Intelectual. Constatou-se que os níveis dos componentes culturais e de clima organizacional atingiram patamares mais elevados no Brasil que no Canadá, Irã e Líbano, indicando que as variáveis Cultura e Clima têm impacto mais favorável para a gestão do Capital Intelectual nas empresas brasileiras. Sugere-se que estudos posteriores possam verificar impactos e influência de outras variáveis como burocracia, educação, etc.