Metal supported on dendronized magnetic nanoparticles: highly selective hydroformylation catalysts

A method for homogenizing heterogeneous catalyst is described. The method is based on growing polyaminoamido (PAMAM) dendrons on silica-coated magnetic nanoparticles. After the dendronizing process, the silica-coated magnetic nanoparticles are more stable and more soluble in organic solvents. The dendronized particles are phosphonated, complexed with [Rh(COD)Cl]2, and applied in catalytic hydroformylation reactions. These new catalysts are proven to be highly selective and reactive.     

Photochemical Transformation of Colchicine: A Kinetic Study

Spectroscopic methods and theoretical calculations were used to study the photophysical properties of colchicine (1). The characteristic bands of colchicine (1) transitions occurring at ∼245 nm and 350 nm arise from n–π ^* and π–π ^* transitions, and were found to be blue shifted with increasing polarity index of the solvent and red shifted (bathocrhomic) with increasing acidity of the media. Solvent type and polarity were found to affect both the rate constant and photo conversion yield. Excitation of colchicine (1) at 366 nm populates the S1 orbital, from which the photoreaction of colchicine (1) initially produces lumicolchicine directly in its ground state by a concerted disrotatory electrocyclization (i.e., 4π electrocyclization involving the tropolone ring). The acidity of the media affects both rate constants and conversion yield; both of these were inversely proportional to the acid concentration. The presence of acid decreases the photo conversion yield of colchicine (1) from 90% to 40%. The ionic strength affects both the rate constants and the photo conversion yield; rate constants are inversely related to the ionic strength. The photochemistry of colchicine (1) is explained on the basis of the initial formation of a solvation complex in the ground state.     

Light-driven tyrosine radical formation in a ruthenium-tyrosine complex attached to nanoparticle TiO2

We demonstrate a possibility of multistep electron transfer in a supramolecular complex adsorbed on the surface of nanocrystalline TiO(2). The complex mimics the function of the tyrosine(Z)() and chlorophyll unit P(680) in natural photosystem II (PSII). A ruthenium(II) tris(bipyridyl) complex covalently linked to a L-tyrosine ethyl ester through an amide bond was attached to the surface of nanocrystalline TiO(2) via carboxylic acid groups linked to the bpy ligands. Synthesis and characterization of this complex are described. Excitation (450 nm) of the complex promotes an electron to a metal-to-ligand charge-transfer (MLCT) excited state, from which the electron is injected into TiO(2). The photogeneration of Ru(III) is followed by an intramolecular electron transfer from tyrosine to Ru(III), regenerating the photosensitizer Ru(II) and forming the tyrosyl radical. The tyrosyl radical is formed in less than 5 micros with a yield of 15%. This rather low yield is a result of a fast back electron transfer reaction from the nanocrystalline TiO(2) to the photogenerated Ru(III).     

Hydrogenation of arenes, alkenes and alkynes catalyzed by a sol–gel entrapped mixture of [Rh(cod)Cl]2 and Na[HRu3(CO)11]

A sol–gel entrapped 1:3 mixture of [Rh(cod)Cl]₂ and Na[HRu₃(CO)₁₁] catalyzes the hydrogenation of various unsaturated substrates by two distinguishable mechanisms. Under 13.8 bar H₂ and 20 °C methylated arenes react rapidly to give cycloalkane derivatives. XRD and TEM studies showed that under these conditions the hydrogenation proceeds without the generation of free metal particles. The hydrogenation of non-methylated arenes, as well as that of alkenes and alkynes, require a temperature of 80–120 °C at which the entrapped complexes form metallic nano-particles of 3–5 nm. Chloroarenes are also hydrodechlorinated at 120 °C, but require a hydrogen pressure of ≥25 bar. At both temperature ranges the catalysts are reusable at least four times. The high efficiency of the hydrogenation process at 20 °C is rationalized by a synergistic effect between the two different metal atoms of the combined catalyst. This may be related to a remote control model through a hydrogen spillover mechanism.     

Diastereoselective Synthesis of Camptothecin-like Scaffolds: Construction of a New Class of Pseudo-natural Products

The discovery of novel small molecules endowed with high 3D-content remains a powerful tool for interrogating underrepresented biological space. To this end, the pseudo-natural products (pseudo-NP) strategy has become one of the most important tools to deliver biologically significant chemical probes. In this article, we describe the development of a new class of pseudo-NP collection, through connecting tryptamines with a furanose derivative followed by subjecting the product from this operation to a ring distortion strategy that led to diastereoselective synthesis of camptothecin-like compounds. This process is driven by a cascade that unites Pictet–Spengler reaction with Michael addition reaction, followed by oxidative-ring enlargement and subsequent transannular aldol cyclization delivering camptothecin-like architectures. The obtained diastereoselectivity was verified using density functional theory (DFT) calculations.     

Modified cellulose morphologies and its composites; SEM and TEM analysis

The complex, multi-level super molecular architecture of cellulose has been the subject of interest for several decades. The mechanical, physical, and environmental properties of cellulose depend on the molecular, supramolecular and morphological structure of the cellulose. This paper gives a brief overview to micro structural analysis of cellulose, as studied using transmission electron microscopy and scanning electron microscopy. The application of these techniques to study the diverse morphology of cellulose and its composites is illustrated using several examples.     

Enhancement of Haloperidol Binding Affinity to Dopamine Receptor via Forming a Charge-Transfer Complex with Picric Acid and 7,7,8,8-Tetracyanoquinodimethane for Improvement of the Antipsychotic Efficacy

Haloperidol (HPL) is a typical antipsychotic drug used to treat acute psychotic conditions, delirium, and schizophrenia. Solid charge transfer (CT) products of HPL with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and picric acid (PA) have not been reported till date. Therefore, we conducted this study to investigate the donor–acceptor CT interactions between HPL (donor) and TCNQ and PA (π-acceptors) in liquid and solid states. The complete spectroscopic and analytical analyses deduced that the stoichiometry of these synthesized complexes was 1:1 molar ratio. Molecular docking calculations were performed for HPL as a donor and the resulting CT complexes with TCNQ and PA as acceptors with two protein receptors, serotonin and dopamine, to study the comparative interactions among them, as they are important neurotransmitters that play a large role in mental health. A molecular dynamics simulation was ran for 100 ns with the output from AutoDock Vina to refine docking results and better examine the molecular processes of receptor–ligand interactions. When compared to the reactant donor, the CT complex [(HPL)(TCNQ)] interacted with serotonin and dopamine more efficiently than HPL only. CT complex [(HPL)(TCNQ)] with dopamine (CTtD) showed the greatest binding energy value among all. Additionally, CTtD complex established more a stable interaction with dopamine than HPL–dopamine.     

A needle-like Cu2CdSnS4 alloy nanostructure-based integrated electrochemical biosensor for detecting the DNA of Dengue serotype 2

Microchimica Acta - The authors describe an integrated biosensor for amperometric DNA detection of Dengue virus in real time. Cu2CdSnS4 (CCTS) quaternary alloy nanostructures were successfully...     

Three-phase microemulsion/sol-gel system for aqueous catalysis with hydrophobic chemicals

A facile three-phase transport process is described that allows to carry out catalytic reactions in water, whereby all components are hydrophobic. According to this process a hydrophobic substrate is microemulsified in water and subjected to an organometallic catalyst, which is entrapped within a partially hydrophobized sol-gel matrix. The surfactant molecules, which carry the hydrophobic substrate, adsorb/desorb reversibly on the surface of the sol-gel matrix breaking the micellar structure, spilling their substrate load into the porous medium that contains the catalyst. A catalytic reaction then takes place within the ceramic material to form the desired products that are extracted by the desorbing surfactant, carrying the emulsified product back into the solution. The method is general and versatile and has been demonstrated with the catalytic hydrogenations of alkenes, alkynes, aromatic C=C bonds, and nitro and cyano groups.     

Heck vinylation of aryl iodides by a silica sol-gel entrapped Pd(II) catalyst and its combination with a photocyclization process

[reaction: see text] Silica sol-gel encaged PdCl(2)(PPh(3))(2) is a recyclable catalyst for the Heck vinylation of aryl iodides. It is possible to couple the Heck reaction with photocyclization in a one-pot process.