A review on synthetic account of 1,2,4-oxadiazoles as anti-infective agents

Molecular Diversity - Most of the currently marketed drugs consist of heterocyclic scaffolds containing nitrogen and or oxygen as heteroatoms in their structures. Several research groups have...     

f-block MOFs: A Pathway to Heterometallic Transuranics

A novel series of heterometallic f-block-frameworks including the first examples of transuranic heterometallic ²³⁸U/²³⁹Pu-metal–organic frameworks (MOFs) and a novel monometallic ²³⁹Pu-analog are reported. In combination with theoretical calculations, we probed the kinetics and thermodynamics of heterometallic actinide(An)-MOF formation and reported the first value of a U-to-Th transmetallation rate. We concluded that formation of uranyl species could be a driving force for solid-state metathesis. Density of states near the Fermi edge, enthalpy of formation, band gap, proton affinity, and thermal/chemical stability were probed as a function of metal ratios. Furthermore, we achieved 97 % of the theoretical maximum capacity for An-integration. These studies shed light on fundamental aspects of actinide chemistry and also foreshadow avenues for the development of emerging classes of An-containing materials, including radioisotope thermoelectric generators or metalloradiopharmaceuticals.     

Fabrication procedures and process sensitivities for CdS/CdTe solar cells

This paper details the laboratory processes used to fabricate CdS/CdTe solar cells at the National Renewable Energy Laboratory. The basic fabrication technique includes low‐pressure chemical vapor deposited SnO₂ , chemical‐bath deposited CdS, close‐spaced sublimated CdTe, solution‐CdCl₂ treatment, and an acid‐contact etch, followed by application of a doped‐graphite paste. This paper also describes the results of a reproducibility study in which cells were produced by multiple operators with an average AM1·5 efficiency of 12·6%. And finally, this paper discusses process sensitivities and alternative cell fabrication procedures and reports the fabrication of a cell with an AM1·5 efficiency of 15·4%. Copyright © 1999 John Wiley & Sons, Ltd.     

High and low-energy proton radiation damage in p/n InP MOCVD solar cells

Indium phosphide p⁺/n/n⁺ solar cells, fabricated by metal organic chemical vapor deposition, were irradiated with 0.2-MeV and 10-MeV protons to a fluence of 10¹³ cm⁻². The power output degradation, 1-V behavior, carrier concentration and defect concentration were observed at intermediate points throughout the irradiations. The 0.2-MeV proton-irradiated solar cells suffered much greater and more rapid degradation in power output than those irradiated wit h 10 MeV protons. The efficiency losses were accompanied by larger increases in the recombination currents in the 0.2-MeV proton-irradiated solar cells. The low-energy proton irradiations also had a larger impact on the series resistance of the solar cell s. Despite the radiation-induced damage, the carrier concentration in the base of the solar cells showed no reduction after 10-MeV or 0.2-MeV proton irradiations and even increased during irradiation with 0.2-MeV protons. In a deep-level transient spectro scopy study of the irradiated samples, the minority carrier defects H4 and H5 at E_v + 0.33 and E_v + 0.52 eV and the majority carrier defects E7 and E10 at E_c − 0.39 and E_c − 0.74 eV were observed. Th e defect introduction rates for the 0.2-MeV proton irradiations were about 20 times higher than for the 10-MeV proton irradiations. The defect E10, observed here after irradiation, has been shown to act as a donor in irradiated n-type InP and may be responsible for obscuring carrier removal. The results of this study are consistent with the much greater damage produced by low-energy protons whose limited range causes them to stop in the active region of the solar cell. © This article is a US Government work and, as such, is in the public domain in the United States of America     

Heteroatoms and substituent effects: The importance of heteroatom hyperconjugation

We have found that the specific rate of α‐sulfonyl carbanion formation in a β‐substituted sulfone shows a sizable dependence on the H C_α C_β X torsion angle. Defining k_N = (k_exch)_X/(k_exch)_model (where the model has X = H or an alkyl group) we observed for a collection of β‐alkoxy sulfones (X = OR) acceptable agreement with the expression log k_N = a + b cos² θ (where a = 1.70 and b = 2.62). Extension to other β‐substituents (X = RS, R₂N, and R₃N⁺) yields the same pattern, with the last showing very large dependence of k_N on the torsion angle (b = 6.3). These observations are ascribed to the presence (in addition to the inductive and field effects) of negative hyperconjugation responsible for accelerations of 1000‐fold and more, deriving from donation of the incipient negative charge on carbon into the σ*_{C X} orbital in the transition state. These observations reflect, and at the same time underline, the importance of the low‐lying antibonding orbitals present in heteroatomic molecules. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:397–405, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10067