Photophysics of aminoxanthone derivatives and their application as binding probes for DNA

Xanthones with amino substituents were synthesized to diminish the photoreactivity of the xanthone chromophore with DNA, with the objective of using these molecules to study their binding dynamics with DNA. The aminoxanthones showed a strong solvatochromic effect on their singlet and triplet excited-state photophysics, where polar solvents led to a decrease of the energies for the excited states. Quenching of the triplet excited states by nitrite anions was used to determine the binding dynamics, and a residence time in the microsecond time domain was estimated for the bound 2-aminoxanthone with DNA. The quenching experiments performed showed that this methodology will not be applicable to study the binding dynamics of a wide variety of guests with DNA.     

Stereoselective synthesis of both enantiomers of trans-2-(diphenylmethylideneamino)cyclopropanecarboxylic acid using a chiral pool approach and their incorporation in dipeptides

The stereoselective synthesis of (1R,2R)- and (1S,2S)-trans-2-(diphenylmethylideneamino)cyclopropanecarboxylic acid has been accomplished in six steps starting from (2S)- and (2R)-β-benzyl N-(tert-butoxycarbonyl)aspartate, respectively. The key-step in the reaction sequence is a stereoselective base-induced ring closure with a good trans diastereoselectivity. These novel trans-β-ACC derivatives could be incorporated in dipeptides employing a standard peptide coupling technique.     

The reaction of red phosphorus with 1‐bromonaphthalene in the KOH–DMSO system: Synthesis of tri(1‐naphthyl)phosphane

Red phosphorus reacts with 1‐bromonaphthalene in the KOH–DMSO system upon heating (47–70°C, 3 h) to give tri(1‐naphthyl)phosphane in 10% yield. Microwave activation (600 W, 6 min) of the reaction affords the above‐mentioned phosphane in 25% yield. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:198–203, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20671     

Ramsey’s theorem for trees: the polarized tree theorem and notions of stability

We formulate a polarized version of Ramsey’s theorem for trees. For those exponents greater than 2, both the reverse mathematics and the computability theory associated with this theorem parallel that of its linear analog. For pairs, the situation is more complex. In particular, there are many reasonable notions of stability in the tree setting, complicating the analysis of the related results.     

Natural convection mass transfer behavior of serially connected cylindrical electrodes

Natural convection mass transfer rates at both vertical and horizontal serially connected tubes were reported using the electrochemical technique involving the measurement of limiting currents for the deposition of copper on copper cylinders from acidified cupric sulphate solutions. Measurements were carried out with: (a) one tube active; (b) two tube surfaces active; (c) three tube surfaces active.

The electrolyte concentration and a number of serial connections of tubes were varied to provide a range of GrSc extending from 5.3×10⁸ to 9.5×10¹¹. The mass transfer rates at serially connected horizontal cylinders were in good agreement with mass transfer data in the literature. Correlation of results covered both laminar and turbulent conditions separately. The mass transfer rates at serially connected vertical cylinders were controlled by the boundary layer development at the multi-electrodes. The results for vertical electrodes, which are single, serially connected two and three electrodes, were separately correlated in the turbulent region.

The results illustrate the important effect of boundary layer development in determining current distribution in multi-electrode electrochemical cells.     

Dinitrogen activation by titanium sandwich complexes

The activation of dinitrogen by titanium sandwich complexes of the general form (eta5-C5Me4R)2Ti (R = CHMe2, CMe3, SiMe3) has been systematically investigated. Low-temperature, in situ, solution infrared spectroscopy has allowed detection of monomeric bis-dinitrogen complexes of titanium that are isostructural with more familiar dicarbonyl derivatives. One example, (eta5-C5Me4CHMe2)2Ti(N2)2, has also been characterized by X-ray diffraction and reveals weakly activated dinitrogen ligands. From the solution IR data, the relative azophilicity of the titanium sandwich complexes has been established and increases with smaller cyclopentadienyl substituents.     

Diazotrifluoropropionamido-containing prenylcysteines: syntheses and applications for studying isoprenoid-protein interactions

Photoaffinity-labeled prenylcysteines (1 and 2) incorporating a diazotrifluoropropionamide-based photophore have been prepared. Photolyses of 2 in the presence of RhoGDI, a protein that interacts with prenylated proteins, and prenylcysteine-containing competitors demonstrate the effectiveness of this photoaffinity-labeled analogue as a tool for studying isoprenoid binding sites.     

Kinetics of radical polymerization, LVI. Investigation of the effect of molecular inhibitors on the radical polymerization of p-methyl-styrene. c-nitroso compounds

The inhibitive effect of p-nitroso aniline derivatives was studied for the bulk polymerization of p-methyl styrene (pMS). The compounds p-nitros-N,N-dimethyl-aniline (p-NDMA), p-nitroso-N,N-diethyl-aniline (p-NDEA) and p-nitrosodiphenyl-amine (p-NDPA) are strong inhibitors of pMS polymerizations. The inhibition period is directly proportional to the initial concentration of the inhibitor; thus, no side reaction takes place. After the inhibition period the polymerization with p-NDMA and with p-NDEA proceeds at a rate equal to that of the sample without inhibitor, while p-NDPA causes a slight secondary retardation. The value of the stoichiometric coefficient (μ) is lower than the theoretical one. This stoichiometric anomaly can be interpreted in terms of the hot radical theory.     

Evolution of the Cu/ZnO methanol synthesis catalyst during its reduction and re-oxidation

Summary Cu K EXAFS studies of the structure of Cu-Zn oxide catalyst were performed for the as prepared samples, those after its activation by hydrogen and after its subsequent re-oxidation. It was found that during the primary formation of the CuZnO solid solution, the copper ions are dissolved in the extended stacking faults of the ZnO lattice as ultra-small oxide clusters. Activation by hydrogen at 473 K leads to the reduction of most copper cations to Cu⁰with the formation of nanoparticles with the characteristic size of ca. 1.6 nm. The copper metal particles were re-oxidized to Cu²⁺at 523 K in<span lang=EN-US style='mso-ansi-language:EN-US'>ahelium flow containing 0.05 vol. % oxygen. The re-oxidized cations do not form a CuO phase. Instead, they return to the extended stacking faults of ZnO. However, this time they form stripe-like clusters of square-planar coordinated copper cations.     

Long-lived lanthanide emission via a pH-sensitive and switchable LRET complex

Lanthanide-based luminescence resonance energy transfer (LRET) can be used as a tool to enhance lanthanide emission for time-resolved cellular imaging applications. By shortening lanthanide emission lifetimes whilst providing an alternative radiative pathway to the formally forbidden, weak lanthanide-only emission, the photon flux of such systems is increased. With this aim in mind, we investigated energy transfer in differently spaced donor–acceptor terbium–rhodamine pairs with the LRET “on” (low pH) and LRET “off” (high pH). Results informed the design, preparation and characterisation of a compound containing terbium, a spectrally-matched pH-responsive fluorophore and a receptor-targeting group. By combining these elements, we observed switchable LRET, where the targeting group sensitises lanthanide emission, resulting in an energy transfer to the rhodamine dye with an efficiency of E = 0.53. This strategy can be used to increase lanthanide emission rates for brighter optical probes.

A pH-sensitive luminescence resonance energy transfer (LRET) was explored as a method to increase photon flux in a terbium-rhodamine-receptor targeting group construct. At low pH, long-lived dye emission and shorter terbium lifetimes were observed.