Spectrofluorimetric determination of phenyl-<Emphasis Type="Italic">β</Emphasis>-naphthylamine used as rubber antioxidant

Phenyl--naphthylamine (PBN) used as rubber antioxidant was found to have native fluorescence. A spectrofluorimetric method for determination of PBN in multicomponent mixtures of polymer additives is described. The apparent excitation and fluorescence wavelengths used are 348 and 413.5 nm, respectively. Maximum fluorescence intensity is obtained by irradiating PBN dissolved in ethanol, at room temperature. The fluorescence varies linearly with the concentration of PBN in the range of 0.04–4 g mL^–1. The accuracy and precision of the method are reported.     

Landing of size-selected Agn+ clusters on single crystal TiO2 (110)-(1x1) surfaces at room temperature

Mass-selected Ag(n) (+) (n=1,2,3) clusters with impact energy less than 2 eV per atom were deposited from the gas phase onto rutile titania (110)-(1x1) single crystal surfaces at room temperature and imaged using ultra-high vacuum scanning tunneling microscopy. Upon reaching the surface, Ag monomers sintered to form three-dimensional islands of approximately 50 atoms in size, with an average measured height of 7.5 A and diameter of 42 A. This suggests that the monomers are highly mobile on the titania surface at room temperature. Dimers also sintered to form large clusters upon deposition, approximately 30 atoms in size, with an average height of 6.2 A and diameter of 33 A. Clusters formed from monomer deposition appeared approximately three times more frequently at step edges than clusters formed from dimer deposition, indicating that the surface mobility of deposited monomers is higher than that of deposited dimers. In sharp contrast to the deposition of monomers and dimers, the deposition of trimers resulted in a high density of very small clusters on the order of a few atoms in size, indicative of intact trimers on the surface, implying that deposited trimers have very limited mobility on the surface at room temperature.     

Probe molecule spectroscopy of NaCl aerosol particle surfaces

Excited-state absorption spectroscopy and ionization threshold measurements for coumarin 314 (C314) adsorbed to the surface of NaCl aerosols characterize the chemical environment of the particle surface as a function of relative humidity (RH). An atmospheric pressure flow of aerosol passes through an ionization cell where two-photon laser ionization of the adsorbed molecules produces a net charge on the particle. Monitoring this charge as a function of the laser wavelength produces either the absorption spectrum of the S(1) <-- S(0) transition or the ionization threshold. The wavelength of maximum absorption for the S(1) excited-state shifts from 448 nm for RH < 5% to 441 nm for RH = 60%, indicating that adsorbed water decreases the polarity of the surface. Similarly, the ionization threshold increases from 5.10 to 5.27 eV over a similar range of RH. The decrease in polarity is attributable to changes in the local electric field experienced by C314, which is on the order of 1 x 10(7) V/cm, and is correlated with changes in the surface topography. Using a continuum model, we estimate the contributions to the measured thresholds of the polarization response of the surface ions and the electric field and calculate an effective dielectric constant for the adsorbed water film. For a multilayer water coverage (RH = 65%), the effective dielectric constant is approximately 2.4. These results demonstrate that the changes in surface topography with adsorbed water are as important as direct water-solute interactions in determining the solvent character of the surface.     

Cleavage of Carbon Disulfide by n-Propyldiphenylphosphine and Nickel(II) Bromide

Carbon disulfide is cleaved by n-propyldiphenylphosphine and nickel(II) bromide in a one-step process, to form two unprecedented complexes: orange, [Ni(S₂C₂(PⁿPrPh₂)₂)Br(PⁿPrPh₂)]Br⋅CS₂ ( 1 ) and purple [Ni{η²-SC(PⁿPrPh₂)₂}Br(PⁿPrPh₂)]Br⋅0.5CS₂ ( 2 ). Orange ( 1 ) contains a dithiolene-related ligand that results from carbon–carbon bond formation, while purple ( 2 ) contains a remarkable ligand in which two n-propyldiphenylphosphine molecules have added to a carbon atom of a CS unit that is coordinated to nickel.     

A comparison of 3,4,6a,7,10,10a‐hexahydro‐7,10‐epoxypyrimido[2,1‐a]isoindol‐6(2H)‐one and 2‐(2‐aminoethyl)‐3a,4,7,7a‐tetrahydro‐1H‐4,7‐epoxyisoindole‐1,3(2H)‐dione: structural and reactivity differences of two homologous tricyclic imides

The crystal structures of 3,4,6a,7,10,10a‐hexahydro‐7,10‐epoxypyrimido[2,1‐a]isoindol‐6(2H)‐one, C₁₁H₁₂N₂O₂, and 2‐(2‐aminoethyl)‐3a,4,7,7a‐tetrahydro‐1H‐4,7‐epoxyisoindole‐1,3(2H)‐dione, C₁₀H₁₂N₂O₃, two tricyclic imides, show one and two molecules in the asymmetric unit, respectively. Intermolecular hydrogen‐bonding interactions are observed in both compounds.     

Finite time blow-up for radially symmetric solutions to a critical quasilinear Smoluchowski–Poisson system

Finite time blow-up is shown to occur for radially symmetric solutions to a critical quasilinear Smoluchowski–Poisson system provided that the mass of the initial condition exceeds an explicit threshold. In the supercritical case, blow-up is shown to take place for any positive mass. The proof relies on a novel identity of virial type. To cite this article: T. Cie?lak, P. Laurençot, C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Late-Stage Chemoenzymatic Installation of Hydroxy-Bearing Allyl Moiety on the Indole Ring of Tryptophan-Containing Peptides

The late-stage functionalization of indole- and tryptophan-containing compounds with reactive moieties facilitates downstream diversification and leads to changes in their biological properties. Here, the synthesis of two hydroxy-bearing allyl pyrophosphates is described. A chemoenzymatic method is demonstrated which uses a promiscuous indole prenyltransferase enzyme to install a dual reactive hydroxy-bearing allyl moiety directly on the indole ring of tryptophan-containing peptides. This is the first report of late-stage indole modifications with this reactive group.