An efficient methodology for the C-C bond forming radical cyclization of hydrophobic substrates in water: effect of additive on radical reaction in water

The combination of the water-soluble radical initiator, 2,2′-azobis[2-(2-imidazolin-2-yl)propane] (VA-061), water-soluble chain carrier, 1-ethylpiperidine hypophosphite (EPHP) and surfactant, cetyltrimethylammonium bromide (CTAB), was found to be the most suitable condition for effective radical cyclization in water for a variety of hydrophobic substrates. The effect of additives and surfactant in the radical cyclization reaction in water was also investigated.     

Hydroxyl-functionalized polyaniline nanospheres: tracing molecular interactions at the nanosurface via vitamin C sensing

Here, we report a synthesis of novel polyaniline nanospheres bearing mono- and bishydroxyl functional groups to trace the molecular interactions at the nanosurfaces through vitamin C sensing. Two new aniline monomers were synthesized via a tailor-made approach and polymerized to produce soluble and uniform polyaniline nanospheres. The structures of the monomers and polymers were characterized by NMR, FT-IR, and MS techniques, and the morphology of the nanomaterials was analyzed by SEM and TEM. The mechanistic aspects of the nanomaterial formations were analyzed by FT-IR and dynamic light scattering techniques. These studies revealed that the hydroxyl-functionalized monomers have strong hydrogen bonding at the monomer level and form spherical aggregates in water, which are templates for the polyaniline nanospheres 600 +/- 100 nm in size. A controlled synthesis was also carried out using aniline hydrochloride as an unsubstituted counterpart, which yields polyaniline nanofibers. WXRD analysis confirmed the presence of a sharp peak at lower angle at 2theta = 7.3 degrees ( d-spacing of 13.4 A) in hydroxyl-substituted nanospheres with respect to enhancement of solid-state ordered crystalline domains, whereas unsubstituted nanofibers were found to be highly amorphous. Vitamin C was employed as an analyte to trace the molecular interaction at the nanosphere surface and study the influence of nanosurface functionalization on the sensing ability of biomolecules. The bishydroxyl-functionalized polyaniline nanospheres were found to show efficient molecular interactions toward vitamin C, whereas nanospheres with a monohydroxyl group or unsubstituted nanofibers failed as sensing materials. In a nut shell, in the present investigation, for the first time, we have proved the importance of surface functionalization of polyaniline nanomaterial, exclusively nanospheres, using hydroxyl groups for studying the molecular interactions at the nanosurfaces with biomolecules such as vitamin C.     

Efficient synthesis of piperidine derivatives using dendrimer based catalytical pockets

The synthesis of highly functionalized piperidine derivatives using amine functionalized maltitol-cored dendritic polymer (MAL-G0) in acetonitrile as the reaction medium is reported. A variety of piperidine derivatives were synthesized and the reaction gave an excellent yield of 89%–95%. The highly functionalized nature of the catalyst provided large number of active sites which resulted in good yield within a short period of time. Maltitol is a carbohydrate polyol system which was chosen here as the core for the synthesis of the dendritic catalyst; it was an effective approach for the preparation of piperidine like medicinal compounds. Maltitol-cored dendritic polymer was effectively synthesized and characterized using GPC, TG, UV–Visible, IR, and NMR techniques and also all the synthesized piperidine derivatives were characterized using LCMS, IR, and NMR techniques.     

Synthetic and Structural Studies on Novel 4,3′-Bicoumarins

Abstract

A series of directly linked 4-3′ bicoumarins have been synthesized by both Knoevenagel and Perkin reactions. This single-step transformation was accomplished by the reaction of coumarin-4-acetates with substituted salicylaldehydes in presence of piperidine using ethanol as solvent and by the reaction of coumarin-4-acetic acids with substituted salicylaldehydes in the presence of sodium hydride in acetic anhydride. Greater yields have been obtained in the sodium hydride and acetic anhydride condition. An intermediate chalcone with an ortho-hydroxyl group, which is a precursor for lactone formation, has been isolated and its structure has been confirmed by x-ray analysis. The nonplanar S-cis arrangement of two C4-C3’ double bonds has been confirmed by nuclear Overhauser spectroscopy (NOE) and x-ray studies. The UV-fluorescence studies support the formation of a conjugated bicoumarin system.     

Fluorous-assisted synthesis of (E)-5-[3-Aminoallyl]-uridine-5′-triphosphate

We describe an efficient method for the synthesis of (E)-5-[3-Aminoallyl]-uridine-5′-triphosphate, AA-UTP that combines the advantage of one-pot triphosphate formation and fluorous solid-phase extraction.     

Solid-phase synthesis of new ribo and deoxyribo BrdU probes for labeling and detection of nucleic acids

A facile and efficient solid-phase synthesis of BrdU-14-UTP and BrdU-14-dUTP is reported. The method involves a nucleophilic addition of CPG-supported Br-dU with a 5′-carboxy modifier amidite, followed by the coupling with AA-UTP or AA-dUTP and finally the solid-support is cleaved under basic conditions. The newly prepared non-radioactive probes may have important applications in immunocytochemistry spatially in labeling and detection assays. BrdU moiety is coupled with nucleotides like dUTP and UTP and incorporated into nucleic acids using generally available polymerase like Taq polymerase or RNA polymerase. The probes thus generated can be used in standard blotting and hybridization procedures including in situ hybridization and detection with anti-BrdU conjugates.     

Carbon nanoparticles as visible-light photocatalysts for efficient CO2 conversion and beyond

Increasing atmospheric CO(2) levels have generated much concern, driving the ongoing carbon sequestration effort. A compelling CO(2) sequestration option is its photocatalytic conversion to hydrocarbons, for which the use of solar irradiation represents an ultimate solution. Here we report a new strategy of using surface-functionalized small carbon nanoparticles to harvest visible photons for subsequent charge separation on the particle surface in order to drive the efficient photocatalytic process. The aqueous solubility of the catalysts enables photoreduction under more desirable homogeneous reaction conditions. Beyond CO(2) conversion, the nanoscale carbon-based photocatalysts are also useful for the photogeneration of H(2) from water under similar conditions.     

New renewable resource amphiphilic molecular design for size-controlled and highly ordered polyaniline nanofibers

We demonstrate here, for the first time, a unique strategy for conducting polyaniline nanofibers based on renewable resources. Naturally available cardanol, which is an industrial waste and main pollutant from the cashew nut industry, is utilized for producing well-defined polyaniline nanofibers. A new amphiphilic molecule is designed and developed from cardanol, which forms a stable emulsion with aniline for a wide composition range in water (1:1 to 1:100 dopant/aniline mole ratio) to produce polyaniline nanofibers. The scanning electron microscopy and transmission electron microscopy analysis of the nanofibers reveals that the dopant/aniline ratio plays a major role in determining the shape and size of polyaniline nanofibers. The nanofiber length increases with the increase in the dopant/aniline ratio, and perfectly linear, well-defined nanofibers of lengths as long as 7-8 muM were produced. The amphiphilic dopant has a built-in head-to-tail geometry and effectively penetrates into the polyaniline chains to form highly organized nanofibers. Wide-angle X-ray diffraction (WXRD) spectra of the nanofibers showed a new peak at 2theta = 6.3 (d spacing = 13.9 A) corresponding to the three-dimensional solid-state ordering of polyaniline-dopant chains, and this peak intensity increases with increase in the nanofiber length. The comparison of morphology and WXRD reveals that high ordering in polyaniline chains results in the formation of long, well-defined nanofibers, and this direct correlation for the polyaniline nanofibers with solid-state ordering has been established. The conductivity of the polyaniline nanofibers also increases with increase in the solid-state ordering rather than increasing with the extent of doping. The polyaniline nanofibers are freely soluble in water and possess high environmental and thermal stability up to 300 degrees C for various applications.     

Ruthenium-catalyzed asymmetric epoxidation of olefins using H2O2, part I: synthesis of new chiral N,N,N-tridentate pybox and pyboxazine ligands and their ruthenium complexes

The synthesis of chiral tridentate N,N,N-pyridine-2,6-bisoxazolines 3 (pybox ligands) and N,N,N-pyridine-2,6-bisoxazines 4 (pyboxazine ligands) is described in detail. These novel ligands constitute a useful toolbox for the application in asymmetric catalysis. Compounds 3 and 4 are conveniently prepared by cyclization of enantiomerically pure alpha- or beta-amino alcohols with dimethyl pyridine-2,6-dicarboximidate. The corresponding ruthenium complexes are efficient asymmetric epoxidation catalysts and have been prepared in good yield and fully characterized by spectroscopic means. Four of these ruthenium complexes have been characterized by X-ray crystallography. For the first time the molecular structure of a pyboxazine complex [2,6-bis-[(4S)-4-phenyl-5,6-dihydro-4H-[1,3]oxazinyl]pyridine](pyridine-2,6-dicarboxylate)ruthenium (S)-2 aa, is presented.     

Ruthenium-catalyzed asymmetric epoxidation of olefins using H2O2, part II: catalytic activities and mechanism

Asymmetric epoxidation of olefins with 30 % H2O2 in the presence of [Ru(pybox)(pydic)] 1 and [Ru(pyboxazine)(pydic)] 2 has been studied in detail (pybox = pyridine-2,6-bisoxazoline, pyboxazine = pyridine-2,6-bisoxazine, pydic = 2,6-pyridinedicarboxylate). 35 Ruthenium complexes with sterically and electronically different substituents have been tested in environmentally benign epoxidation reactions. Mono-, 1,1-di-, cis- and trans-1,2-di-, tri-, and tetra-substituted aromatic olefins with versatile functional groups can be epoxidized with this type of catalyst in good to excellent yields (up to 100 %) with moderate to good enantioselectivies (up to 84 % ee). Additive and solvent effects as well as the relative rate of reaction with different catalysts have been established. It is shown that the presence of weak organic acids or an electron-withdrawing group on the catalyst increases the reactivity. New insights on the reaction intermediates and reaction pathway of the ruthenium-catalyzed epoxidation are proposed on the basis of density functional theory calculation and experiments.