Effect of methyl and hydroxyl substituents on the π-electronic spectra and ionization potential of p-benzoquinone

SCF -LCAO -MO -CI semi-empirical π-electron calculations have been made of the first two singlet transitions and ionization potentials of hydroxy-, methyl- and hydroxy-methyl substituted p-benzoquinone, using a modified Pariser-Parr-Pople method. The various molecules could be divided into two classes on the basis of their first π-electron transition, namely, those in which the 3-position was occupied and others where this position was vacant.     

Photo-induced formation of silver nanoparticles and polymerization of acrylamide derivatives

The effect of silver ions and silver nanoparticles on the rate of polymerization of acrylamide and N-isopropylacylamide was investigated. Composites of silver particles of diameter around 30 nm and polyacrylamide were prepared by the photochemical method in the absence of any photosensitizer. The particles formed were characterized by UV–visible spectrophotometry, XRD, and TEM. It was shown that the presence of metal ions such as Ag⁺, Co²⁺, and Ni²⁺ in the acrylamide monomer is essential for photoinduced polymerization.     

An efficient, catalyst- and solvent-free, four-component, and one-pot synthesis of polyhydroquinolines on grinding

An efficient synthesis of polyhydroquinolines is achieved via a four-component reaction of aldehydes, dimedone, active methylene compounds, and ammonium acetate in one-pot under solvent-free conditions at room temperature on grinding. The present method does not involve any hazardous organic solvent or catalyst. The key advantages are the short reaction time, high yields, simple workup, and purification of products by non-chromatographic methods, i.e., by simple recrystallization from ethanol.     

Graphene oxide: A carbocatalyst for the one-pot multicomponent synthesis of highly functionalized tetrahydropyridines

A simple, straightforward and efficient methodology is described for the synthesis of polysubstituted tetrahydropyridine via one-pot multicomponent reaction of β-ketoester, aldehyde and aniline in presence of catalytic amount of graphene oxide in acetonitrile. Graphene oxide is a versatile carbocatalyst and this is the first report on its application in a five component reaction. Good yield, usage of readily available starting material, operational simplicity, easy work-up and eco-friendly re-usable catalyst are the key features of this protocol.     

Fluorescent zinc-terpyridine complex containing coordinated peroxo counter ion in aqueous medium

We describe a mixed ligand-zinc(d ¹⁰ ) complex containing coordinated peroxo ion and 2,2′2″-terpyridine and exhibiting fluorescence in the visible region (473 nm) on excitation at 390 nm in aqueous medium at room temperature. We also discuss the unusual phenomenon of enhancement of this fluorescence intensity on addition of some transition metal ions(3d ⁵, 3d¹⁰, 4d⁰and3d ⁹electronic configurations).     

A Theorem of Truemper

Received November 5, 1997     

Self-assembly of Ag nanoparticle-biotin composites into long fiberlike microstructures

An end-to-end assembly of spherical Ag nanoparticles takes place in the presence of biotin to form long fiberlike microstructures. These microstructures are about 4 mum long with a thickness of 1 mum, obtained from SEM studies. TEM studies showed the presence of spherical silver nanoparticles having an average size of 20 nm. ATR-FTIR studies revealed that silver ions interact with biotin involving the carboxylate group. A weak binding of the silver particles with the thioether and ureido groups helps in connecting the Ag nanoparticles to form long fiberlike structures. Elucidation of the mechanism of formation of the spherical Ag clusters was done by pulse radiolysis.     

Synthesis, structural and spectroscopic characterization, catalytic properties, and thermal transformations of new cyclic di- and trisiloxanediolato tantalum complexes

The reaction between Ta(OEt)5 and 1,1,3,3-tetramethyl-1,3-disiloxanediol, (HOSiMe2OSiMe2OH), leads to new siloxy complexes in which the dimeric nature of Ta(OEt)5 is maintained with both bridging ethoxide and disiloxanediolato bridges. With equal amounts of the reagents, two terminal OEt groups are replaced to form [Ta(OEt)2]2(mu-OEt)2(mu-OSiMe2OSiMe2O)2, 1, whereas with an excess of diol, the remaining terminal OEt groups are also replaced but with a trisiloxanediolato unit to form [Ta(OSiMe2OSiMe2OSiMe2O)]2(mu-OEt)2(mu-OSiMe2OSiMe2O)2, 2. Complexes 1 and 2 catalyze the transformation of HOSiMe2OSiMe2OH to polysiloxanes. Thermal treatment of 1 results in the formation of a 1:2 mixture of Ta2O5/SiO2; no new phases are observed. The molecular structures of 1 and 2 are confirmed by X-ray crystallography.