On the roles of solid-bound ligand scavengers in the removal of palladium residues and in the distinction between homogeneous and heterogeneous catalysis

We have studied the roles and behavior of typical resin- and silica-bound thiol scavengers in the removal of palladium (Pd) residues and in the determination of the true catalytic species in the Heck coupling of bromobenzene and styrene. The results of Pd scavenging and catalyst poisoning by elemental analysis (EA) and transmission electron microscopy (TEM) indicate that silica-bound thiols have an advantage over resin-bound thiols in residual Pd removal from a Heck reaction solution and that all of these scavengers poison effectively the catalytic species but hardly scavenge Pd clusters, even as small as 1 nm from solution presumably because of the steric barrier. Because of a smaller proportion of soluble Pd clusters, using a molecular Pd precatalyst results in a much higher Pd scavenging efficiency than using a supported Pd particle precatalyst. With the aid of catalyst poisoning by the scavengers, filtration testing and TEM studies further illustrate that Pd clusters are inactive for the Heck reaction over Pd(0)/SiO(2), with molecular Pd(0) being solely active. Studies through EA and thermogravimetric analysis suggest that the bound thiols are leached from the scavengers to a different extent at reaction temperatures of 90-135 °C, probably owing to base-catalyzed decomposition or based-promoted dissociation of functional groups from the surfaces, leading to interaction between leached thiols and a solid Pd precatalyst. Meanwhile, the effect of solid-bound thiol binding to soluble Pd on the efficiency of Pd scavenging and the impact of a scavenger on the Pd leaching from supported Pd particles are discussed.     

Synthesis of fullerene@gold core-shell nanostructures

A "direct encapsulation" method was developed for the synthesis of highly stable water-soluble fullerene@gold core-shell nanostructures, with gold nanoshells showing either closed or porous morphology. This gold nano-shell coating formed a "nano-oven", capable of decomposing encapsulated fullerene molecules rapidly when irradiated by laser. We envisaged this being a useful tool for chemical reactions as well as a novel scaffold for nano-material synthesis.     

Occurrence and estimation of trans-resveratrol in one-year-old canes from seven major Chinese grape producing regions

The concentration of trans-resveratrol in 165 grape cane samples from three major grape production regions and four large distribution centers of Chinese wild Vitis species were determined by reversed-phase high-performance liquid chromatography (HPLC). Among the different genotype groups and purpose of uses, cultivars of V. vinifera had much higher amounts of trans-resveratrol than did the cultivars of both V. labrusca or V. labrusca and V. vinifera hybrids, and within the V. vinifera species, significantly higher amounts of trans-resveratrol were found in wine grapes compared to table ones. No significant differences were observed between V. labrusca and its hybrids from crosses with V. vinifera, and between red cultivars and white ones (P < 0.05 or P < 0.01). The contents of trans-resveratrol, as a normal constituent occurring in grape canes, in Chinese wild species of V. amurensis, V. pentagona, and V. davidii from their native habitats were also relatively high.     

Mixed-ligand complex formation of (2,2′,2″-terpyridine)copper(I) and (2,2′2″-terpyridine)copper(II) with some sulfur-containing amino acids

Summary Mixed-ligand complex formation of copper(I) with 2,2,2-terpyridine (terpy) and various biologically significant sulfurcontaining amino acids, L [L = cysteine, penicillamine,N-acetylcysteine andN-acetylpenicillamine] was investigated. WithN-acetylcysteine andN-acetylpenicillamine, copper(I) complexes [Cu(terpy)L]HCl have been isolated and characterised. The amino acid in each case bonds to the copper(I) through the sulfur atom only. These complexes are readily oxidised to the corresponding copper(II) complexes which contain a Cu^II-S(mercaptide) bond as demonstrated by the (S)Cu^II LMCT at 420 nm. The e.p.r. and electronic spectroscopic results are consistent with a distorted octahedral structure. Reactions of copper(I) with terpy and cysteine/ penicillamine in weakly acidic medium produce complexes containing two different copper(II) centres. From a strongly acidic medium, a binary copper(I) terpyridine complex is obtained instead and is shown from i.r. spectral absorptions to contain a protonated pyridyl ring.     

The electrolytic efficiency of amperometric detection in normal-phase high-performance liquid chromatography

The electrolytic efficiency of the wall-jet detector in normal-phase high-performance liquid chromatography (between 0.1 and 5%) is significantly less than its efficiency in reversed-phase separations. A large-volume wall-jet cel with a Ag/Ag⁺ reference serves as the detector system in evaluating the effects of various chromatographic conditions on efficiency. Anthraquinone, phenanthrenaquinone (both at 10^-3–10^-4 M) and three estrogen gen steroids (at 10^-2–10^-3 M) are used as samples with ethanol/ hexane eluents. The effect of pH depends on the sample; increased ethanol concentrations and lower flow rates improve the efficiency.     

Rational design of platinum(IV) compounds to overcome glutathione-S-transferase mediated drug resistance

A rationally designed Pt(IV) anticancer compound is described, employing the novel concept of tethering an inhibitor of glutathione-S-transferase, an enzyme associated with Pt-based drug-resistance, to cisplatin. Its enzyme inhibition activity, investigated using spectrophotometric and mass spectrometry-based techniques, and cytotoxic profile in resistant cancer cells are described.     

Symmetric Weighing Matrices Constructed using Group Matrices

A weighing matrix of order n and weight m² is a square matrix M of order n with entries from {-1,0,+1} such that MM^T=m²I where I is the identity matrix of order n. If M is a group matrix constructed using a group of order n, M is called a group weighing matrix. Recently, group weighing matrices were studied intensively, especially when the groups are cyclic and abelian. In this paper, we study the abelian group weighing matrices that are symmetric, i.e.M^T=M. Some new examples are found. Also we obtain a few exponent bounds on abelian groups that admit symmetric group weighing matrices. In particular, we prove that there is no symmetric abelian group weighing matrices of order 2p^r and weight p² where p is a prime and p≥ 5.Communicated by: K.T. Arasu     

Microwaves make hydroformylation a rapid and easy process

[reaction: see text] Hydroformylation of alkenes can be carried out in a few minutes under microwave activation at a relatively low pressure (40 psi) using commercially available catalysts and ligands. The 80 mL vial of a Discover microwave oven was connected to a cylinder of CO and H2, and after filling the reactor at 40 psi, a mixture of an alkene, the Wilkinson catalyst, and XANTPHOS was submitted to microwave irradiation giving, after 4 min, high conversion into the corresponding aldehyde without formation of the isomerized alkene.