Palladium-catalyzed decarboxylative aza-Michael addition-allylation reactions between allyl carbamates and activated olefins. Generation of quaternary carbon adjacent to secondary amine carbon center

The reaction of allyl carbamates with activated olefins in the presence of Pd(PPh3)4 catalyst in THF proceeded smoothly at room temperature to give the corresponding beta,alpha-bisadducts, beta-amino-alpha-allylated products, in high yields. Not only highly activated olefins containing two cyano groups but also 2-cyano enones underwent facile aza-Michael addition--allylation with various allylic carbamates giving the corresponding products in high yields and with high diastereoselectivities. The stereochemistry of the singly formed product was confirmed with the help of X-ray crystallographic technique. It is an excellent method for creating beta-amino alpha-allyl ketones having two contiguous stereocenters: quaternary carbon adjacent to secondary amine carbon center.     

Beta-alkyl-alpha-allylation of Michael acceptors through the palladium-catalyzed three-component coupling between allylic substrates, trialkylboranes, and activated olefins

The palladium-catalyzed three-component beta-alkyl-alpha-allylation reaction of activated olefins has been achieved. For example, in the presence of 5 mol % of Pd(PPh3)4, the reaction of benzylidenemalononitrile 1a with Et3B and allyl acetate 2a in THF proceeded smoothly at 40 degrees C to give the corresponding beta-ethyl-alpha-allylated product 3a in 81% yield.     

Polyaniline–Prussian blue hybrid: synthesis and magnetic behaviour

We report the synthesis of an organic–inorganic hybrid material composed of a conducting polyaniline (PANI) matrix and Prussian blue (PB) network, the latter formed in situ in the polymer matrix. The hybrid was prepared by treating FeCl₄ ^?-doped PANI with K₃Fe(CN)₆ unlike the previously reported method of potential cycling to obtain alternate layers of PANI and PB. Cyclic voltammetry and X-ray photoelectron spectroscopy investigations confirmed the formation of a network typical of PB inside the PANI matrix. Infrared spectroscopy points to the formation of an extended network between Fe in PANI matrix and Fe from K₃Fe(CN)₆. Magnetization studies of the hybrid material showed ferromagnetic ordering with a T _c of about 6?K.     

Experimental observations on the scaling of adsorption isotherms for nonionic surfactants at a hydrophobic solid-water interface

The self-assembly of nonionic surfactants in bulk solution and on hydrophobic surfaces is driven by the same intermolecular interactions, yet their relationship is not clear. While there are abundant experimental and theoretical studies for self-assembly in bulk solution and at the air-water interface, there are only few systematic studies for hydrophobic solid-water interfaces. In this work, we have used optical reflectometry to measure adsorption isotherms of seven different nonionic alkyl polyethoxylate surfactants (CH3(CH2)I-1(OCH2CH2)JOH, referred to as CIEJ surfactants, with I = 10-14 and J = 3-8), on hydrophobic, chemically homogeneous self-assembled monolayers of octadecyltrichlorosilane. Systematic changes in the adsorption isotherms are observed for variations in the surfactant molecular structure. The maximum surface excess concentration decreases (and minimum area/molecule increases) with the square root of the number of ethoxylate units in the surfactant (J). The adsorption isotherms of all surfactants collapse onto the same curve when the bulk and surface excess concentrations are rescaled by the bulk critical aggregation concentration (CAC) and the maximum surface excess concentration. In an accompanying paper we compare these experimental results with the predictions of a unified model developed for self-assembly of nonionic surfactants in bulk solution and on interfaces.     

Evaluation of enzymatic activity on nanoscale polystyrene-block-polymethylmethacrylate diblock copolymer domains

Understanding structural and functional changes of polymeric surface-bound proteins is extremely important as polymers play an increasingly significant role as arrays and substrates in proteomics applications. We carried out, for the first time, quantitative activity measurements of horseradish peroxidase (HRP) enzymes immobilized selectively on the polystyrene domains of microphase-separated polystyrene-block-polymethylmethacrylate ultrathin films. The specific enzymatic activity of HRP adsorbed on the diblock copolymer surface was evaluated and compared to that of HRP in free solution. We demonstrate that the polymeric surface-bound HRP molecules maintain approximately 85% of their activity in free solution. The unique advantages of diblock copolymer templates, involving nanoscale self-assembly and largely retained protein functionality, make the spontaneously constructed enzyme nanoarrays highly suitable as proteomics substrates. Our novel assembly method of providing functional enzymes on diblock copolymer thin films can be greatly beneficial for high-throughput and high-density protein assays.     

Palladium catalyzed three component coupling reaction between chromones, alcohols, and allylic acetates: diversity-oriented synthesis of highly substituted chromones

This paper describes the palladium catalyzed highly efficient three component coupling (TCC) reactions between chromones, allylic acetates, and alcohols, which lead to a library of multiply substituted chromones. The activity of various palladium catalysts, such as Pd(PPh₃)₄ and Pd₂dba₃·CHCl₃ and their combination with various bisphosphine ligands, was investigated by using THF as a solvent, which revealed that Pd(PPh₃)₄ catalyst was the best one. The reaction most probably proceeds via the formation of benzopyrilium cation, generated from the reaction between chromones and allyl acetate, in the presence of palladium catalyst. The subsequent trapping of the benzopyrilium cation by alcohols would give the corresponding products in excellent yields. This alkoxy-allylation reaction was highly diastereoselective and only one diastereomer was obtained in all the cases.     

Wilson Quotients for Composite Moduli

An analogue for composite moduli of the Wilson quotient is studied. Various congruences are derived, and the question of when these quotients are divisible by is investigated; such an will be called a ``Wilson number". It is shown that numbers in certain infinite classes cannot be Wilson numbers. Eight new Wilson numbers up to 500 million were found.

     

Photophysical study of 3-acetyl-4-oxo-6,7-dihydro-12H-indolo[2,3-a]quinolizine in biomimetic reverse micellar nanocavities: a spectroscopic approach

Photophysical properties of 3-acetyl-4-oxo-6,7-dihydro-12H-indolo[2,3-a]quinolizine (AODIQ), a bioactive molecule, has been investigated in well-characterized, monodispersed biomimicking nanocavities formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in heptane using steady-state and picosecond time resolved fluorescence and fluorescence anisotropy. The emission behavior of AODIQ is very much dependent upon the water/surfactant mole ratio (W), i.e., on the water pool size of the reverse micellar core. AODIQ exhibits a sharp decrease in fluorescence anisotropy with increasing W, implying that the overall motional restriction experienced by the molecule is decreased with increased hydration. Some of the depth-dependent relevant fluorescence parameters, namely, fluorescence maxima and fluorescence anisotropy (r), have been monitored for exploiting the distribution and microenvironment around the probe in the reverse micelles. Fluorescence spectral position and fluorescence quenching studies suggest that the probe does not penetrate into the reverse micellar core; rather it binds at the interfacial region. Quantitaive estimates of the micropolarity and microviscosity at the binding sites of the probe molecule have been determined as a function of W.     

Direct allylic substitution of allyl alcohols by carbon pronucleophiles in the presence of a palladium/carboxylic acid catalyst under neat conditions

The reaction of allylic alcohols with carbon pronucleophiles in the presence of the Pd(PPh₃)₄/carboxylic acid combined catalytic system, under neat conditions (without an organic solvent or without water as the solvent) enabled the direct allylation of the pronucleophiles, giving the corresponding allylated products in high yields.