A small molecule with osteogenesis-inducing activity in multipotent mesenchymal progenitor cells

Purmorphamine, which is a 2,6,9-trisubstituted purine compound, was discovered through cell-based high-throughput screening from a heterocycle combinatorial library. It differentiates multipotent mesenchymal progenitor cells into an osteoblast lineage. It will serve as a unique chemical tool to study the molecular mechanisms of osteogenesis of stem cells and bone development.     

X-ray photoelectron spectroscopic evidence of distinctive underpotential deposition states of Ag and Cu on Pt substrates

The underpotential deposition (u.p.d.) of copper and silver ions on platinum electrodes has been studied using X-ray photoelectron spectroscopy (x.p.s.). A significant chemical shift of the x.p.s. binding energies of the u.p.d. copper and silver atoms relative to bulk copper and silver metal is obtained. Analogous spectral results are obtained for in situ vapor deposition of copper and silver atoms on clean platinum substrates which reveal the metallic nature of the u.p.d. species.     

The role of intersystem crossing steps in singlet oxygen chemistry and photo-oxidations

Singlet oxygen chemistry and photo-oxidation reactions, in general, often require one or more critical reaction steps that involve an intersystem crossing from a singlet state to a triplet state or vice versa. This paper considers two important intersystem crossing mechanisms, electron spin-electron orbit (spin-orbit) coupling and electron spin-nuclear spin (spin-spin) coupling, and how they may be involved : (1) in the deactivation of ¹O₂ to ³O₂ ; (2) in the thermal catalytic conversion of ³O₂ to ¹O₂; and (3) in the fragmentation of aromatic endoperoxides to yield O₂ and an aromatic substrate.     

Uniform Rice-like CdS Particles Prepared from Water-in-oil Microemulsions

IntroductionNano-sized semiconductors are of great interestdue to their special optical and electronic proper-ties[1,2].As one of the mostimportantⅡ—Ⅵsemicon-ductors,CdS has importantapplications in many fields,such as the solar cell field,non linear o…     

An altered mechanism of hydrolysis for a metal-complexed phosphate diester

Isotope effects in the nucleophile and in the leaving group were measured to gain information about the mechanism and transition state of the hydrolysis of methyl p-nitrophenyl phosphate complexed to a dinuclear cobalt complex. The complexed diester undergoes hydrolysis about 1011 times faster than the corresponding uncomplexed diester. The kinetic isotope effects indicate that this rate acceleration is accompanied by a change in mechanism. A large inverse 18O isotope effect in the bridging hydroxide nucleophile (0.937 +/- 0.002) suggests that nucleophilic attack occurs before the rate-determining step. Large isotope effects in the nitrophenyl leaving group (18Olg = 1.029 +/- 0.002, 15N = 1.0026 +/- 0.0002) indicate significant fission of the P-O ester bond in the transition state of the rate-determining step. The data indicate that in contrast to uncomplexed diesters, which undergo hydrolysis by a concerted mechanism, the reaction of the complexed diester likely proceeds via an addition-elimination mechanism. The rate-limiting step is expulsion of the p-nitrophenyl leaving group from the intermediate, which proceeds by a late transition state with extensive bond fission to the leaving group. This represents a substantial change in mechanism from the hydrolysis of uncomplexed aryl phosphate diesters.     

Evolution of the interface and metal film morphology in the vapor deposition of Ti on hexadecanethiolate hydrocarbon monolayers on Au

The combination of in situ X-ray photoelectron spectroscopy, infrared reflection spectroscopy, atomic force microscopy, and time-of-flight secondary ion mass spectrometry are used to probe the nature of the evolving interface chemistry and metal morphology arising from Ti vapor deposition onto the surface of a CH(3)(CH(2))(15)S/Au{111} self-assembled monolayer (SAM) at ambient temperature. The results show that for a deposition rate of approximately 0.15 Ti atom.nm(-2).s(-1) a highly nonuniform Ti overlayer is produced via a process in which a large fraction of impinging Ti atoms do not stick to the bare SAM surface. The adsorbed atoms form isolated Ti clusters and react with CH(3) groups to form carbide products at the cluster-SAM interfaces. Further growth of Ti clusters appears to be concentrated at these scattered reaction centers. The SAM molecules in the local vicinity are subsequently degraded to inorganic products, progressing deeper into the monolayer as the deposition proceeds to give an inorganic/organic nanocomposite. A continuous overlayer does not form until metal coverage approaches approximately 50 Ti atoms per SAM molecule. These data indicate that for applications such as molecular device contacts the use of Ti may be highly problematic, suffering from both a highly nonuniform contact area and the presence of extensive inorganic products such as nonstoichiometric carbides and hydrides.     

An alternative multipolar expansion for intermolecular potential functions

We have derived a new multipolar expansion for intermolecular potential-energy functions with applications in molecular physics, theoretical chemistry, and mathematical physics. The new formulation employs a separation of radial and angular terms with a simple index structure that leads to computational efficiency and ease of physical interpretation. For the case of the Coulomb interaction, we compare the present formulation with two conventional multipole expansions: the Cartesian tensor and the irreducible spherical tensor expansions. The new formalism leads to efficient numerical algorithms that are useful for general applications beyond intermolecular potentials. In addition to the electrostatic Coulomb interaction, we illustrate the formalism with applications to special function theory and a bipolar expansion involved in potential theory.     

Direct titrations of antibiotics with iodate solutions: Part 2. Some selected cephalosporins

A previous method for the determination of penicillins by direct titration with potassium iodate under strongly acidic conditions has been extended to the assay of some selected cephalosporins. Results are presented, including error and precision analyses, for the determination of cephaloridine, cephalothin and cephalexin. The appropriate stoichiometries are 1 mol cephalosporin to 3 mol iodate for cephalothin and cephaloridine; 1 mol to 2 mol iodate for cephalexin. An irreversible aqueous end-point technique has been compared with the chloroform layer method; the latter gives more precise results for the determination of cephaloridine and cephalothin (0.8% and 1.3% r.s.d. respectively). Comparable precision was obtained by either technique for the determination of cephalexin (1.39% r.s.d.).     

Fullerenes-extracted soot: a new adsorbent for collecting volatile organic compounds in ambient air

Fullerenes-extracted soot (FES) is the by-product of fullerenes production. Retention characteristics at different temperatures for 17 volatile organic compounds (VOCs) on FES are measured. The adsorption and desorption efficiencies for VOCs on FES adsorbent tubes range from 40.8 to 117%, most of them being 100+/-20%. The values are compared with Tenax GR, an adsorbent commonly used in environmental analysis. FES can be used as an adsorbent of low cost to collect VOCs in environmental samples.