Relaxor Behavior in Ordered Lead Magnesium Niobate (PbMg1/3Nb2/3O3) Thin Films

The local compositional heterogeneity associated with the short‐range ordering of Mg and Nb in PbMg_1/3Nb_2/3O₃ (PMN) is correlated with its characteristic relaxor ferroelectric behavior. Fully ordered PMN is not prepared as a bulk material. This work examines the relaxor behavior in PMN thin films grown at temperatures below 1073 K by artificially reducing the degree of disorder via synthesis of heterostructures with alternate layers of Pb(Mg_2/3Nb_1/3)O₃ and PbNbO₃, as suggested by the random‐site model. 100 nm thick, phase‐pure films are grown epitaxially on (111) SrTiO₃ substrates using alternate target timed pulsed‐laser deposition of Pb(Mg_2/3Nb_1/3)O₃ and PbNbO₃ targets with 20% excess Pb. Selected area electron diffraction confirms the emergence of (1/2, 1/2, 1/2) superlattice spots with randomly distributed ordered domains as large as ≈150 nm. These heterostructures exhibit a dielectric constant of 800, loss tangents of ≈0.03 and 2× remanent polarization of ≈11 µC cm^?2 at room temperature. Polarization–electric field hysteresis loops, Rayleigh data, and optical second‐harmonic generation measurements are consistent with the development of ferroelectric domains below 140 K. Temperature‐dependent permittivity measurements demonstrate reduced frequency dispersion compared to short range ordered PMN films. This work suggests a continuum between normal and relaxor ferroelectric behavior in the engineered PMN thin films.     

Synthesis of three asymmetric N-confused tetraarylporphyrins

Two monosubstituted and one tetrasubstituted N-confused porphyrins (1-3) were prepared in ca. 3-5% yields using a [2 + 2] synthesis. The monosubstituted porphyrins have carbomethoxy (1) or nitro (2) substituents on one of the meso-phenyl groups, while the meso-phenyl groups of the third NCP (3) are substituted with nitro, bromo, and methyl groups in an AB(2)C pattern. The specific regiochemistry of the aryl rings around the macrocycle in each porphyrin was definitively determined using a combination of 1D ((1)H and (13)C) and 2D (gHMBC, gHSQC and ROESY) NMR spectroscopy. The absorption spectra of 1-3 in CH(2)Cl(2) are similar to those of N-confused tetraphenylporphyrin (NCTPP) but have Soret and Q bands that are shifted to lower energies with smaller extinction coefficients in comparison to those for NCTPP.     

Regulating Functions on Partially Ordered Sets

We study the so-called Skorokhod reflection problem (SRP) posed for real-valued functions defined on a partially ordered set (poset), when there are two boundaries, considered also to be functions of the poset. The problem is to constrain the function between the boundaries by adding and subtracting nonnegative nondecreasing (NN) functions in the most efficient way. We show existence and uniqueness of its solution by using only order theoretic arguments. The solution is also shown to obey a fixed point equation. When the underlying poset is a σ-algebra of subsets of a set, our results yield a generalization of the classical Jordan–Hahn decomposition of a signed measure. We also study the problem on a poset that has the structure of a tree, where we identify additional structural properties of the solution, and on discrete posets, where we show that the fixed point equation uniquely characterizes the solution. Further interesting posets we consider are the poset of real n-vectors ordered by majorization, and the poset of n × n positive semidefinite real matrices ordered by pointwise ordering of the associated quadratic forms. We say a function on a poset is of bounded variation if it can be written as the difference of two NN functions. The solution to the SRP when the upper and lower boundaries are the identically zero function corresponds to the most efficient or minimal such representation of a function of bounded variation. Minimal representations for several important functions of bounded variation on several of the posets mentioned above are determined in this paper. A version of this paper was presented at the Applied Probability Workshop, in the Mathematisches Forschungsinstitut Oberwolfach, December 2003 (organized by V. Schmidt, A. Hordijk and F. Baccelli); the authors are grateful for the invitation which gave them the opportunity to make substantial progress in finalizing this work in the uniquely wonderful research atmosphere at Oberwolfach. Research supported by DARPA grant N66001-00-C-8062, ONR grant N00014-1-0637 and NSF grant ECS 0123512. This work was supported in part by NSF grant ANI-9903495, the INTAS-00-265 project, and a Carathéodory research award.     

Gadolinium(III) chloride: a novel and an efficient reagent for the synthesis of homoallylic alcohols

Carbonyl compounds efficiently undergo nucleophilic addition reactions with allylstannanes in the presence of GdCl₃·6H₂O in acetonitrile under extremely mild reaction conditions to give the corresponding homoallylic alcohols in excellent yields and with high chemoselectivity.     

A Novel,Simple and Rapid Regeneration of Alcohols from Their Allylic Ethers Using NaCNBH3 / TMSCl

A Novel, Simple and efficient method for the regeneration of alcohols from their allylic ethers using NaCNBH₃/TMSCl is described.     

A New Novel and Practical One Pot Methodology for Conversion of Alcohols to Amines

A convenient and efficient one pot sequence has been developed for the transformation of alcohols to amines using Sodium azide, triphenylphosphine in CC1₄-DMF.     

Preparation of Paclitaxel-Encapsulated Bio-Functionalized Selenium Nanoparticles and Evaluation of Their Efficacy against Cervical Cancer

The potentiality of nanomedicine in the cancer treatment being widely recognized in the recent years. In the present investigation, the synergistic effects of chitosan-modified selenium nanoparticles loaded with paclitaxel (PTX-chit-SeNPs) were studied. These selenium nanoparticles were tested for drug release analysis at a pH of 7.4 and 5.5, and further characterized using FTIR, DLS, zeta potential, and TEM to confirm their morphology, and the encapsulation of the drug was carried out using UPLC analysis. Quantitative evaluation of anti-cancer properties was performed via MTT analysis, apoptosis, gene expression analysis, cell cycle arrest, and over-production of ROS. The unique combination of phytochemicals from the seed extract, chitosan, paclitaxel, and selenium nanoparticles can be effectively utilized to combat cancerous cells. The production of the nanosystem has been demonstrated to be cost-effective and have unique characteristics, and can be utilized for improving future diagnostic approaches.     

Triphenylphosphine–Iodine: An Efficient Reagent System for the Synthesis of Nitriles From Aldoximes

A wide range of aldoximes were smoothly converted to the corresponding nitriles with triphenylphosphine–iodine.     

Samarium Triflate–Catalyzed Biginelli Condensation: An Improved Method for the Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones

Abstract

A simple and efficient method for multicomponant synthesis of 3,4-dihydropyrimidinones has been reported. All the reactions were carried out using samarium triflate as catalyst (10 mol%) at acetonitrile reflux. This procedure is applicable to a variety of substrates such as aliphatic, aromatic, and heterocyclic aldehydes.