Synthesis of unsymmetrical and regio-defined 2,3,6-quinoxaline and 2,3,7-pyridopyrazine derivatives

Differential reactivity of the amine functionality in a number of common 1,2-diamine starting materials is exploited to undertake an expedient synthesis of unsymmetrical 2,3,6-trisubstituted quinoxaline and unsymmetrical 2,3,7-trisubstituted pyridopyrazine derivatives.     

Enzymatic assembly of the bis-indole core of rebeccamycin

Rebeccamycin is a member of the family of indolocarbazole antibiotics with broad spectrum antitumor activity. The indolocarbazole framework is derived from two molecules of tryptophan, but very little is known about the enzymes involved in rebeccamycin biosynthesis. Here, we show that RebD is responsible for all catalytic steps forming the central pyrrole ring of chlorochromopyrrolic acid from two molecules of chloroindolepyruvic acid. This transformation does not require any additional cofactors and constitutes the first step of bis-indole formation in the biosynthesis of rebeccamycin.     

Anomalous electronic Raman scattering in NaxCoO2.yH2O

Raman scattering experiments on NaxCoO2.yH2O single crystals show a broad electronic continuum with a pronounced peak around 100 cm(-1) and a cutoff at approximately 560 cm(-1) over a wide range of doping levels. The electronic Raman spectra in superconducting and nonsuperconducting samples are similar at room temperature, but evolve in markedly different ways with decreasing temperature. For superconducting samples, the low-energy spectral weight is depleted upon cooling below T* approximately 150 K, indicating the opening of a pseudogap that is not present in nonsuperconducting materials. Weak additional phonon modes observed below T* suggest that the pseudogap is associated with charge ordering.     

Empirtical estimates with minimal <Emphasis Type="Italic">d</Emphasis>-risk for discrete exponential families

We develop an empirical d-a posteriori approach to estimations with uniformly minimal d-risk, when the a priori distribution is completely unknown. For a scalar parameter of a discrete exponential family we construct empirical estimates based on archive data and prove the convergence of the empirical d-risk to the true one. As an example we adduce the estimation of the Poisson distribution parameter. We numerically study the accuracy of the estimates by a statistical modeling technique.     

DEA model with shared resources and efficiency decomposition

Data envelopment analysis (DEA) has proved to be an excellent approach for measuring performance of decision making units (DMUs) that use multiple inputs to generate multiple outputs. In many real world scenarios, DMUs have a two-stage network process with shared input resources used in both stages of operations. For example, in hospital operations, some of the input resources such as equipment, personnel, and information technology are used in the first stage to generate medical record to track treatments, tests, drug dosages, and costs. The same set of resources used by first stage activities are used to generate the second-stage patient services. Patient services also use the services generated by the first stage operations of housekeeping, medical records, and laundry. These DMUs have not only inputs and outputs, but also intermediate measures that exist in-between the two-stage operations. The distinguishing characteristic is that some of the inputs to the first stage are shared by both the first and second stage, but some of the shared inputs cannot be conveniently split up and allocated to the operations of the two stages. Recognizing this distinction is critical for these types of DEA applications because measuring the efficiency of the production for first-stage outputs can be misleading and can understate the efficiency if DEA fails to consider that some of the inputs generate other second-stage outputs. The current paper develops a set of DEA models for measuring the performance of two-stage network processes with non splittable shared inputs. An additive efficiency decomposition for the two-stage network process is presented. The models are developed under the assumption of variable returns to scale (VRS), but can be readily applied under the assumption of constant returns to scale (CRS). An application is provided.     

Electrochemical and structural characterization of lithium titanate electrodes

Lithium titanate (LTO) materials of different particle size, surface area, and morphology were characterized by constant current cycling and cyclic voltammetry. By examining the particles and electrodes with scanning electron microscopy, we show that particle morphology, in addition to particle size, has important implications for high-rate performance. Large agglomerates, even when porous and made of small crystallites, cannot effectively form homogenous electrodes with the polymer binder and carbon conducting diluents; hence, low power performance results. Another nanostructured LTO of very high surface area was found to have poor electrochemical performance most likely due to its high concentration of structural defects. We recommend further development in nanoparticles of LTO of optimal crystallinity as well as improved electrode homogeneity through the use of more compatible binders and conducting diluents and better electrode processing techniques. Simultaneous realization of these imperatives should facilitate the development of LTO-based high-power batteries for automotive applications.     

Novel guanosine-cytidine dinucleoside that self-assembles into a trimeric supramolecule

[reaction: see text] Synthesis and assembly studies of a guanosine-cytidine dinucleoside 1 that self-assembles into a trimeric supramolecule (I) are presented. Dinucleoside 1 was obtained by utilizing two consecutive palladium-catalyzed cross-coupling reactions. Ensemble I was analyzed by ESI-MS, NMR spectroscopies, size exclusion chromatography (SEC), and vapor pressure osmometry (VPO).     

Ketonization of incarcerated acetophenone enol

A free-standing simple enol has been generated inside a carceplex. Rates of ketonization under various conditions were determined; ketonization is extremely slow as compared to the rate in solution. Complexed water is required, and the mechanism proceeds via formation of an enolate followed by protonation at carbon by the same molecule of water that removed the proton from the enol. Acid or base retards ketonization by removing water from the cavity.