Optical properties of residual shallow donors in GaN epitaxial layers grown by horizontal LP-MOCVD

Received: 1 May 1998/Accepted: 23 June 1998     

Design and synthesis of a 3,4-dehydroproline amide discovery library

The synthesis of a discovery library of 80 3,4-dehydroproline amides was achieved in a four-step reaction sequence from easily accessible 3-aminoallene-3-carboxylate methyl esters. Diversification of these proline mimics was introduced at five different sites: the substituents at the 3-pyrroline unit (R1, R2, R3), at the nitrogen (R4), and the C-terminus (R5). The 3-pyrroline scaffold was synthesized in excellent yields by a silver-catalyzed intramolecular cyclization of aminoallenes, followed by N-functionalization reactions. Maximum diversity was introduced in the final step of the reaction sequence by taking advantage of the carboxylic acid handle of the 3-pyrroline subunit. Amide coupling reactions using polystyrene-carbodiimide (PS-carbodiimide) and 1-hydroxybenzotriazole (HOBt) under microwave irradiation led to 3,4-dehydroproline amides that were obtained in purities greater than 85% by LC/MS/ESLD after scavenging the excess HOBt on a silica-bound carbonate SPE cartridge.     

A quadrupole/time-of-flight mass spectrometry study of trp-cage’s conformation

Trp-cage is a synthetic 20-residue miniprotein that uses tertiary contacts to stabilize its native conformation. NMR, circular dichroism (CD), and UV-resonance Raman spectroscopy were used to probe its energy landscape. In this quadrupole/time-of-flight study, electrospray ionization charge state distribution (CSD) and solution-phase H/D exchange are used to probe Trp-cage's tertiary structure. The CSDs of Trp-cage and its mutant provide spectra showing a pH-dependent conformation change. Solution-phase H/D exchange in 30% deuterated trifluoroethanol solution of the wild type shows increased protection of one labile hydrogen in the native state. Together, CSDs and solution-phase H/D exchange are demonstrated to constitute a simple but effective means to follow conformation changes in a small tertiary protein.     

Pyrrolidine and piperidine formation via copper(II) carboxylate-promoted intramolecular carboamination of unactivated olefins: diastereoselectivity and mechanism

An expanded substrate scope and in-depth analysis of the reaction mechanism of the copper(II) carboxylate-promoted intramolecular carboamination of unactivated alkenes is described. This method provides access to N-functionalized pyrrolidines and piperidines. Both aromatic and aliphatic gamma- and delta-alkenyl N-arylsulfonamides undergo the oxidative cyclization reaction efficiently. N-Benzoyl-2-allylaniline also underwent the oxidative cyclization. The terminal olefin substrates examined were more reactive than those with internal olefins, and the latter terminated in elimination rather than carbon-carbon bond formation. The efficiency of the reaction was enhanced by the use of more organic soluble copper(II) carboxylate salts, copper(II) neodecanoate in particular. The reaction times were reduced by the use of microwave heating. High levels of diastereoselectivity were observed in the synthesis of 2,5-disubstituted pyrrolidines, wherein the cis substitution pattern predominates. The mechanism of the reaction is discussed in the context of the observed reactivity and in comparison to analogous reactions promoted by other reagents and conditions. Our evidence supports a mechanism wherein the N-C bond is formed via intramolecular syn aminocupration and the C-C bond is formed via intramolecular addition of a primary carbon radical to an aromatic ring.     

Triazine‐Based Mesoporous Covalent Imine Polymers as Solid Supports for Copper‐Mediated Chan–Lam Cross‐Coupling N‐Arylation Reactions

The synthesis of a novel mesoporous covalent imine polymeric (MCIPs) material, involving simple Schiff‐base chemistry, is reported. This highly functionalised nitrogen‐rich material acts as a good support for immobilising Cu^II ions, exhibiting excellent catalytic activity in promoting the Chan–Lam cross‐coupling reaction between biologically active amines and arylboronic acids. The performance of this catalyst is also evident from its broad substrate scope, high stability, real heterogeneity, mild reaction conditions and reusability without loss of activity. The observed results will provide additional scope on the design and catalytic applications of this emerging class of materials.     

Synthesis and characterization of side‐chain liquid crystalline polymers bearing cholesterol mesogen

A series of new norbornene carboxylic cholesteryl ester monomers with and without alkyl spacers, NBCh, and NBCh‐n , respectively, were synthesized. New side‐chain liquid crystalline homopolymers, PNBCh and PNBCh‐n , were cleanly prepared using NBCh and NBCh‐n , respectively, with Grubbs 2nd generation catalyst. Molecular and structural characterization of monomers and polymers were carried out by nuclear magnetic resonance, NMR, Fourier transform infrared, FT‐IR, spectroscopy, and gel permeation chromatography, GPC. The thermal and liquid crystalline properties of the homopolymers were investigated by differential scanning calorimetry, DSC, thermogravimetric analysis, TGA, and polarized optical microscopy, POM. Small angle and wide angle X‐ray studies of PNBCh‐n in powder and fiber states not only confirmed the formation of smectic A mesophases, but also established their morphologies. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2690–2701, 2009     

Thickness-dependent orientation evolution in nickel thin films grown on yttria-stabilized zirconia single crystals

Microstructure evolution along with crystallographic orientation change as a function of film thickness was investigated in Ni thin films grown on (100) yttria-stabilized zirconia (YSZ) single crystal substrates. Texture development with two different orientation relationships, OR1: Ni {111}//YSZ {100} and OR2: Ni {100}//YSZ {100}, cube on cube orientation were identified by X-ray diffraction and transmission electron microscopy depending on the film thickness. The observed orientation transition reveals the existence of a critical thickness (～320?nm) favoring two different orientations in sputtered Ni films on YSZ (100) substrate.     

Control Policies for Inventory with Service Time

Abstract

This article introduces an additional control policy—the N-policy–into (s, S) inventory system with positive service time. Under specified interarrival and service time distributions, which are independent of each other, we obtain the necessary and sufficient condition for the system to be stable. We also obtain the optimal values of the control variables s, S, and N; it is seen that the cost function attains the minimum value at s = 0. It is also shown that the cost function is separately convex in the variables S and N. Numerical illustrations are provided. Several measures of performance of the system are evaluated.