Integrated in situ monitoring of a metalorganic vapor phase epitaxy reactor for II–VI epitaxy

The focus of this paper is the integrated use of system and wafer monitors to obtain a complete picture of the growth process and to identify the major causes of variance. In situ monitoring of a growing layer of Hg_1-xCd_xTe using laser reflectometry has been compared with the outputs of various system monitors such as pyrometer, organometallic concentration, and flow. Differences between the expected and measured concentrations were corrected by initially adjusting the organometallic flows, and the remaining variance in CdTe interdiffused multilayer process layer thickness was then corrected by increasing the CdTe cycle time. The remainder of the layer gave a homogenized alloy composition of 0.256 for a target value of 0.258. This example shows how different in situ monitors have been integrated to give a comprehensive picture of the growth process, which were then related to known kinetic behavior. As a result of this monitoring, it was possible to identify critical parameters for control.     

Binding energies of wannier excitons in GaAs-Ga1−xAlxAs quantum well structures

Binding energies of Wannier excitons in a quantum well structure consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga_1?xAl_xAs are calculated using a variational approach. Due to reduction in symmetry along the axis of growth of these quantum well structures and the presence of band discontinuities at the interfaces, the degeneracy of the valence band of GaAs is removed leading to two exciton systems, namely, the heavy hole exciton and the light hole exciton. The variations of the binding energies of these two excitons as a function of the size of the GaAs quantum wells for various values of the heights of the potential barrier are calculated and their behavior is discussed.     

Copolymerization of styrene and acrylonitrile with functional silanes

Styrene has been copolymerized to high conversions with vinylmethyl diacetoxysilane (VMDAS) and vinylmethyldiethoxysilane (VMDES) in bulk and in toluene at 60 using azobisisobutyronitrile (AIBN) as initiator. Acrylonitrile has also been copolymerized with VMDAS at 50 in bulk using AIBN. The compositions of the copolymers were determined from the silicon contents; reactivity ratios were calculated by the Kelen-Tüdös method. The reactivity ratio r₁ (styrene) is higher for styrene-VMDES than for styrene-VMDAS, indicating higher reactivity of VMDAS towards polystyryl radical. VMDAS was found to be more reactive towards the polyacrylonitrile than towards the polystyrene radical. The influences of the silicon comonomer on properties such as intrinsic viscosity, solubility, molecular weight distribution and thermal behaviour were also studied.     

Binding energy of a Mott-Wannier exciton in a polarizable medium

A new effective interaction potential between an electron and a hole of a Mott-Wannier exciton in a polarizable medium is derived following a procedure similar to that of Haken. The variational polaron wave functions used are those first proposed by Haga. Using this effective interaction potential the values of the binding energy of an exciton are calculated variationally in several polar crystals. The values thus obtained agree very well with those derived from experimental measurements and are always considerably smaller than those calculated using Haken's potential.     

Symmetry breaking for theBBP-couplings

The B-A system of CP molecule has been reinvestigated. The rotational structures in the (0, 0) and (1, 1) bands have been photographed in the second order of a 10.6 m grating with 25μ slit width. The molecular constants have been determined using a weighted least squares fit computer program. It is found that the spin-splitting constant in the B-state is negative and not positive as reported by previous workers. An accurate value ofα in the A-state could be determined. The present analysis also suggests that the spin-splitting constant in the ground state of CP should be positive, hence the assignment of theR ₁ andR ₂ orP ₁ andP ₂ branches in the B-X system of CP by Barwaldet al should be interchanged.     

Gram‐Scale Synthesis of Chiral Cyclopropane‐Containing Drugs and Drug Precursors with Engineered Myoglobin Catalysts Featuring Complementary Stereoselectivity

Engineered hemoproteins have recently emerged as promising systems for promoting asymmetric cyclopropanations, but variants featuring predictable, complementary stereoselectivity in these reactions have remained elusive. In this study, a rationally driven strategy was implemented and applied to engineer myoglobin variants capable of providing access to 1‐carboxy‐2‐aryl‐cyclopropanes with high trans‐(1R,2R) selectivity and catalytic activity. The stereoselectivity of these cyclopropanation biocatalysts complements that of trans‐(1S,2S)‐selective variants developed here and previously. In combination with whole‐cell biotransformations, these stereocomplementary biocatalysts enabled the multigram synthesis of the chiral cyclopropane core of four drugs (Tranylcypromine, Tasimelteon, Ticagrelor, and a TRPV1 inhibitor) in high yield and with excellent diastereo‐ and enantioselectivity (98–99.9% de; 96–99.9% ee). These biocatalytic strategies outperform currently available methods to produce these drugs.     

Ligand and Linkage Isomers of Bis(ethylthiocarbamato) Copper Complexes with Cyclic C6H8 Backbone Substituents: Synthesis,Characterization, and Antiproliferation Activity

A series of isomeric bis(alkylthiocarbamate) copper complexes have been synthesized, characterized, and evaluated for antiproliferation activity. The complexes were derived from ligand isomers with 3-methylpentyl (H₂L²) and cyclohexyl (H₂L³) backbone substituents, which each yield a pair of linkage isomers. The thermodynamic products CuL^2a/3a have two imino N and two S donors resulting in three five-member chelate rings (555 isomers). The kinetic isomers CuL^2b/3b have one imino and one hydrazino N donor and two S donors resulting in four-, six-, and five-member rings (465 isomers). The 555 isomers have more accessible Cu^II/I potentials (E_1/2=−811/−768 mV vs. ferrocenium/ferrocene) and lower energy charge transfer bands than their 465 counterparts (E_1/2=−923/-854 mV). Antiproliferation activities were evaluated against the lung adenocarcinoma cell line (A549) and nonmalignant lung fibroblast cell line (IMR-90) using the MTT assay. CuL^2a was potent (^A549EC₅₀=0.080 μM) and selective (^IMR-90EC₅₀/^A549EC₅₀=25) for A549. Its linkage isomer CuL^2b had equivalent A549 activity, but lower selectivity (^IMR-90EC₅₀/^A549EC₅₀=12.5). The isomers CuL^3a and CuL^3b were less potent with ^A549EC₅₀ values of 1.9 and 0.19 M and less selective with ^IMR-90EC₅₀/^A549EC₅₀ ratios of 2.3 and 2.65, respectively. There was no correlation between reduction potential and A549 antiproliferation activity/selectivity.     

Room temperature synthesis of protonated layered titanate sheets using peroxo titanium carbonate complex solution

We report the synthesis of peroxo titanium carbonate complex solution as a novel water-soluble precursor for the direct synthesis of layered protonated titanate at room temperature. The synthesized titanates showed excellent removal capacity for Pb(2+) and methylene blue. Based on experimental observations, a probable mechanism for the formation of protonated layered dititanate sheets is also discussed.     

Onion slice shaped assembled ZnS quantum wires

Ultra-narrow wurtzite ZnS quantum wires assembled towards an onion slice shape are synthesized in water using a simple hydrothermal procedure. Wires are formed through an oriented attachment mechanism from wurtzite ZnS spherical particles. Strong confinement effect originated from the narrow width was observed and holds promise for use in broad optoelectronic device application.     

Palladium supported on chitosan as a recyclable and selective catalyst for the synthesis of 2-phenyl ethanol

Two different chitosan supported palladium based catalysts were prepared, wherein dispersed palladium nanoparticles were obtained via chemical reduction supported on chitosan (Pd/CTS) and amine functionalized modified chitosan (Pd/AFCTS). The catalytic activity of the Pd-based catalysts, Pd/CTS and Pd/AFCTS, were assessed in the hydrogenation of styrene oxide to 2-phenyl ethanol. Both Pd-based catalysts enhanced the formation of the desired 2-phenyl ethanol in contrast to a conventional Pd/C catalyst without the assistance of inorganic or organic base. A considerable influence on the conversion and selectivity was observed in the case of Pd/AFCTS, consisting of palladium nanoparticles stabilized and dispersed on amine-functionalized chitosan matrix, affording complete conversion of styrene oxide with 98% selectivity to 2-phenyl ethanol. The catalyst Pd/AFCTS has also been recycled without significant loss of activity and selectivity.