Catalytic asymmetric desymmetrization approaches to enantioenriched cyclopentanes

Catalytic asymmetric desymmetrization represents an excellent strategy for accessing highly functionalized chiral building blocks. However, the application of desymmetrization for the synthesis of enantio-enriched cyclopentane derivatives remained limited, when compared to chiral cyclohexanes. We have recently developed a desymmetrization protocol for prochiral 2,2-disubstituted cyclopentene-1,3-diones by direct catalytic asymmetric vinylogous nucleophilic addition of deconjugated butenolides. In this perspective, we give an overview of asymmetric desymmetrization reactions leading to enantioenriched cyclopentanes and their derivatives. The focus is kept confined to the diverse nature of reactions used for this purpose. A brief discussion on the potential future directions is also provided.

Nature of the activation of succinate dehydrogenase byvarious effectors and in hypobaria and hypoxia

Hepatic mitochondrial succinate dehydrogenase (succinate:(acceptor)oxidoreductase, EC 1.3.99.1) was activated by preincubation of mitochondria with four diverse classes of compounds, the dicarboxylic acids, nitrophenols, quinols (and ubiquinols) and pyrophosphates. Of the various compounds tested malonate, oxaloacetate and pyrophosphate, well-known competitive inhibitors of the enzyme, and also hydroquinone and ubiquinols were effective even at low concentrations and showed maximal stimulation in 2 min.

Functional Corannulene: Diverse Structures, Enhanced Charge Transport, and Tunable Optoelectronic Properties

Chemical functionalization of various hydrocarbons, such as coronene, corannulene, and so forth, shows good promise in electronics applications because of their tunable optoelectronic properties. By using quantum chemical calculations, we have investigated the changes in the corannulene buckybowl structure, which greatly affect its electronic and optical properties when functionalized with different electron-withdrawing imide groups. We find that the chemical nature and position of functional groups strongly regulate the stacking geometry, -stacking interactions, and electronic structure. Herein, a range of optoelectronic properties and structure-property relationships of various imide-functionalized corannulenes are explored and rationalized in detail. In terms of carrier mobility, we find that the functionalization strongly affects the reorganization energy of corannulene, while the enhanced stacking improves hopping integrals, favoring the carrier mobility of crystals of pentafluorophenylcorannulene-5-monoimide. The study shows a host of emerging optoelectronic properties and enhancements in the charge-transport characteristics of functionalized corannulene, which may find possible semiconductor and electronics applications.

Multichannel-Emissive V-Shaped Boryl-BODIPY Dyads: Synthesis, Structure, and Remarkably Diverse Response toward Fluoride

Three new V-shaped boryl-BODIPY dyads (1-3) were synthesized and structurally characterized. Compounds 1-3 are structurally close molecular siblings differing only in the number of methyl substituents on the BODIPY moiety that were found to play a major role in determining their photophysical behavior. The dyads show rare forms of multiple-channel emission characteristics arising from different extents of electronic energy transfer (EET) processes between the two covalently linked fluorescent chromophores (borane and BODIPY units). Insights into the origin and nature of their emission behavior were gained from comparison with closely related model molecular systems and related photophysical investigations. Because of the presence of the Lewis acidic triarylborane moiety, the dyads function as highly selective and sensitive fluoride sensors with vastly different response behaviors. When fluoride binds to the tricoordinate borane center, dyad 1 shows gradual quenching of its BODIPY-dominated emission due to the ceasing of the (borane to BODIPY) EET process. Dyad 2 shows a ratiometric fluorescence response for fluoride ions. Dyad 3 forms fluoride-induced nanoaggregates that result in fast and effective quenching of its fluorescence intensity just for similar to 0.3 ppm of analyte (i.e., 0.1 equiv 0.26 ppm of fluoride). The small structural alterations in these three structurally close dyads (1 - 3) result in exceptionally versatile and unique photophysical behaviors and remarkably diverse responses toward a single analyte, i.e., fluoride ion.

Diamond-Graphite Hybrids And The Nature Of Amorphous-Carbon And Diamond-Like Carbon

The nature of amorphous carbon has been explored by molecular mechanics by examining the structures of species such as C84Hx and C150Hx, wherein the percentage of sp(3) carbons is progressively increased in a graphitic network. The nature of diamond-like carbon has been similarly investigated by examining the structures of C84Hx and C102Hx where the percentage of sp(2) carbons is varied in an sp(3) network. The dependence of the average coordination number as well as the sp(3)/sp(2) atom ratio on the atom fraction of hydrogen has been investigated in light of the random covalent network model.

Thermopower and nature of the hole-doped states in LaMnO3 and related systems showing giant magnetoresistance

We have measured the thermopower (S) of hole-doped LaMnO3 systems in order to see its dependence on the Mn4+ content as well as to investigate other crucial factors that determine S. We have carried out hole doping (creation of Mn4+ by two distinct means, namely, by the substitution of La by divalent cations such as Ca and Sr and by self-doping without aliovalent substitution). The thermopower is sensitive not only to the hole concentration but also to the process employed for hole doping, which we explain as arising from the differences in the nature of the hole-doped states. We also point out a general trend in the dependence of S on hole concentration at high temperatures (T> T-c), similar to that found in the normal-state thermopower of the cuprates.

The nature of the charge-ordered state in Y0.5Ca0.5MnO3 with a very small average radius of the A-site cations

A detailed investigation of Y0.5Ca0.5MnO3 with a very small radius of the A-site cations ([r(A)] approximate to 1.13 Angstrom reveals the occurrence of a charge-ordering transition in the paramagnetic state, at a relatively high temperature of 260 K. The orthorhombic lattice distortion, as measured by the dimensionless index D, is large (similar to 1.75%) over the entire 300-100 K range, but the antiferromagnetic interactions become prominent only at low temperatures (< 160 K). The charge-ordering gap in Y0.5Ca0.5MnO3, measured by low-temperature vacuum tunnelling spectroscopy, is large (similar to 0.5 eV) and the charge-ordered state is unaffected by the application of a magnetic field of 6 T. The study indicates that the nature of charge-ordering in Y0.5Ca0.5MnO3 which is dominated by the cooperative Jahn-Teller effect and the associated lattice distortion is distinctly different from analogous manganates with larger [r(A)].

PocketMatch: A new algorithm to compare binding sites in protein structures

Recognizing similarities and deriving relationships among protein molecules is a fundamental requirement in present-day biology. Similarities can be present at various levels which can be detected through comparison of protein sequences or their structural folds. In some cases similarities obscure at these levels could be present merely in the substructures at their binding sites. Inferring functional similarities between protein molecules by comparing their binding sites is still largely exploratory and not as yet a routine protocol. One of the main reasons for this is the limitation in the choice of appropriate analytical tools that can compare binding sites with high sensitivity. To benefit from the enormous amount of structural data that is being rapidly accumulated, it is essential to have high throughput tools that enable large scale binding site comparison. Results: Here we present a new algorithm PocketMatch for comparison of binding sites in a frame invariant manner. Each binding site is represented by 90 lists of sorted distances capturing shape and chemical nature of the site. The sorted arrays are then aligned using an incremental alignment method and scored to obtain PMScores for pairs of sites. A comprehensive sensitivity analysis and an extensive validation of the algorithm have been carried out. A comparison with other site matching algorithms is also presented. Perturbation studies where the geometry of a given site was retained but the residue types were changed randomly, indicated that chance similarities were virtually non-existent. Our analysis also demonstrates that shape information alone is insufficient to discriminate between diverse binding sites, unless combined with chemical nature of amino acids. Conclusion: A new algorithm has been developed to compare binding sites in accurate, efficient and high-throughput manner. Though the representation used is conceptually simplistic, we demonstrate that along with the new alignment strategy used, it is sufficient to enable binding comparison with high sensitivity. Novel methodology has also been presented for validating the algorithm for accuracy and sensitivity with respect to geometry and chemical nature of the site. The method is also fast and takes about 1/250(th) second for one comparison on a single processor. A parallel version on BlueGene has also been implemented.

Identification of the nature of platinum related midgap state in silicon by deep level transient spectroscopy

In this article, we present the detailed investigations on platinum related midgap state corresponding to E-c -0.52 eV probed by deep level transient spectroscopy. By irradiating the platinum doped samples with high-energy (1.1 MeV) gamma rays, we observed that the concentration of the midgap state increases and follows a square dependence with irradiation dose. However, the concentration of the acceptor corresponding to E-c -20.28 eV remained constant. Furthermore, from the studies on passivation by atomic hydrogen and thermal reactivation, we noticed that the E-c -0.52 eV level reappears in the samples annealed at high temperatures after hydrogenation. The interaction of platinum with various defects and the qualitative arguments based on the law of mass action suggest that the platinum related midgap defect might possibly correspond to the interstitial platinum-divacancy complex (V-Pt-V).

Socio-environmental impact of idol immersion: dimensions and directions

India possesses a diverse and rich cultural heritage and is renowned as a 'land of festivals'. These festivals attract massive community involvement paving way to new materials such as 'Plaster of Paris' being used for 'modernizing' the representation of idols with very little thought given to the issues of toxicity and environmental impacts. Another dimension to the whole issue is the plight of the artisans and the workers involved in the trade. Owing to the unorganized nature of the industry there is minimal or no guidelines pertaining-to the worker safety and health risks of the people involved. This paper attempts to address the complexities of the inherent hazards as a consequence of these socio-environmental issues and trace the scientific rationale in addressing them in a practical and pragmatic way.

On the nature of power flow equations in security analysis

The power system network is assumed to be in steady-state even during low frequency transients. However, depending on generator dynamics, and toad and control characteristics, the system model and the nature of power flow equations can vary The nature of power flow equations describing the system during a contingency is investigated in detail. It is shown that under some mild assumptions on load-voltage characteristics, the power flow equations can be decoupled in an exact manner. When the generator dynamics are considered, the solutions for the load voltages are exact if load nodes are not directly connected to each other

The nature of non-equilibrium solidification of undercooled Agsingle bondCu alloys in contact with primary copper dendrites

Liquids of silver-copper alloys with near eutectic compositions embedded in a copper matrix were undercooled. The structural and microstructural investigations of these alloys solidified from undercooled temperature indicated the absence of both the eutectic reaction and diffusionless transformation below the equal free energy curve (T0). Instead the liquid maintained local equilibrium with the copper dendrites continuously until it intersected the extended solidus of the silver rich solid solution.

A combined XPS-UPS-EELS study of nitrogen adsorbed on clean and barium-promoted iron surfaces: The nature of the precursor to dissociation

For N2 on a clean Fe surface, the adsorbed precursor in a parallel orientation becomes predominant around 110 K, while at lower temperatures it coexists with a weakly adsorbed species. On a Ba-promoted Fe surface, however, N2 is present exclusively in the precursor state in the temperature range 80–150 K following moderate exposure. Besides exhibiting a low N-N stretching frequency of 1530 cm−1, the precursor shows a clear separation between the 5σ and 1π levels in the UPS; the precursor dissociates to give a nitridic species around 160 K.