Synthesis of 3-miktoarm stars and 1st generation mikto dendritic copolymers by "living" radical polymerization and "click" chemistry

The facile synthesis of 3-miktoarm star polymers and 1st generation mikto polymeric dendrimers using atom transfer radical polymerization (ATRP) and "click" chemistry is demonstrated. ATRP was used to synthesize near uniform polymers with Br chain ends, which were easily converted into azido groups. These polymer chains were then attached to a trifunctional alkyne molecule (tripropargylamine) using click reactions in a variety of ways to make the miktoarm stars and miktoarm polymeric dendrimers.     

Decay of the transient Cu(B)-CO complex is accompanied by formation of the heme Fe-CO complex of cytochrome cbb(3)-CO at ambient temperature: evidence from time-resolved Fourier transform infrared spectroscopy

Time-resolved step-scan Fourier infrared spectroscopy has been used to study the CO-bound cbb(3)-type cytochrome c oxidase from Pseudomonas stutzeri at room temperature. We observe a single band in the FTIR spectrum at 1956 cm(-1) (beta-form). The time-resolved data indicate that upon photolysis, CO is transferred from heme b(3) (nu(CO) = 1956 cm(-1)) to CuB (nu(CO) = 2064 cm(-1)). The decay of the 2065 cm(-1) peak (t(1/2) = 120 +/- 16 ms) and the development of the 1956 cm(-1) peak (t(1/2) = 144 +/- 8 ms ) suggest that formation of the Fe-CO complex is concurrent with the decay of the CuB-CO complex. The intensity ratio of the Fe-CO/CuB-CO (2.15) remains constant for all data points, and thus we conclude that no fraction of CO escapes the binuclear center at 293 K.     

Preparation, characterization, resistance to protein adsorption, and specific avidin-biotin binding of poly(amidoamine) dendrimers functionalized with oligo(ethylene glycol) on gold

Protein-resistant films derived from the fifth-generation poly(amidoamine) dendrimers (PAMAM G5) functionalized with oligo(ethylene glycol) (OEG) derivatives consisting of various ethylene glycol units (EG(n), n = 3, 4, and 6) were prepared on the self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid (MUA) on gold substrates. The resulting films were characterized by ellipsometry, contact angle goniometry, and X-ray photoelectron spectroscopy (XPS). About 35% of the peripheral amines of the dendrimers were reacted with N-hydroxysuccinimide-terminated EG(n) derivatives (NHS-EG(n)). The dendrimer films showed improved stability over octadecanethiolate SAMs on gold in hot solvents, attributed to the formation of multiple amide bonds per PAMAM unit with underlying NHS-activated MUA monolayer. The EG(n)-attached PAMAM surfaces with n = 3 reduced the adsorption of fibrinogen to approximately 20% monolayer, whereas 2-3% for n = 4 or 6. The dendrimer films with various densities of EG(n) molecules on PAMAM surfaces were prepared by immersion of the NHS-terminated MUA-functionalized gold substrates in ethanolic solutions containing PAMAM and NHS-EG(n) of various mole ratios. The density (r) of the EG(n) molecules on the PAMAM surfaces is consistent with the mole ratio (r') of NHS-EG(n)/free amine of PAMAM in solutions. The resistance to protein adsorption of the resulting surfaces is correlated with the surface density and the length of the EG chains. At their respective r, the EG(n)-modified dendrimer films resisted approximately 95% adsorption of fibrinogen on gold surfaces. Finally, the specific binding of avidin to the approximately 5% and approximately 40% biotinylated EG3 dendrimers (surface density of biotin with respect to the total number of terminal amino groups on PAMAM G5) gave rise to about 50% and 100% surface coverage by avidin, respectively.     

Emerging Direct Targeting β-Catenin Agents

Aberrant accumulation of β-catenin in the cell nucleus as a result of deregulation of the Wnt/β-catenin pathway is found in various types of cancer. Direct β-catenin targeting agents are being researched despite obstacles; however, specific β-catenin drugs for clinical treatments have not been approved so far. We focused on direct β-catenin targeting of potential therapeutic value as anticancer agents. This review provides recent advances on small molecule β-catenin agents. Structure-activity relationships and biological activities of reported inhibitors are discussed. This work provides useful knowledge in the discovery of β-catenin agents.     

Mechanically driven reorganization of thermoresponsive diblock copolymer assemblies in water

Controlled formation of a variety of 3D structures was observed at high polymer weight fractions in water from a single diblock, consisting of poly(N-isopropylacrylamide), PNIPAM, and polystyrene, PSTY segments. The structures form through a mechanical process driven by swelling of hydrophilic polymer segments upon a change in temperature (see picture, SDS=sodium dodecylsulfate).     

A Constrained and “Inverted” [3+3] Salphen Macrocycle with an ortho-Phenylethynyl Substitution Pattern

A [3+3] Schiff-base salphen macrocycle ( 7 a ) was synthesized by imine condensation between ortho-phenylenediamine and ortho-phenylethynyl-bridged bis(5-salicylaldehyde) precursors. The triangular-shaped macrocycle 7 a has a nonclassical (or “inverted”) design in which the N₂O₂ coordination pockets are located at the sides instead of the corners. Compound 7 a could be synthesized in a reasonably good yield (64 %) considering the steric constraints imposed by the ortho substitution pattern. Subsequent zinc metalation afforded the corresponding Zn metallomacrocycle 7 b . Spectroscopic experiments evidenced weak ( 7 a ) to strong ( 7 b ) self-aggregation behavior in solution. Their ability to self-organize at the supramolecular level was further studied in the solid state by AFM and TEM, which revealed the formation of large bundles of fibers with lengths of several micrometers and widths of nanometers.     

Elucidating heteroatom influence on homonuclear 4J(H,H) coupling constants by DFT/NMR approach

We report the structural dependency of long range scalar J-coupling constant across four bonds as function of the dihedral angles Φ1 and Φ3. The calculated homonuclear coupling constants ⁴J(_H,H), obtained at a density functional theory level, were measured between C(1)─X(2) and X(2)─C(3) bonds in three-term models, where C, N, O, and S were systematically used as the second atom of the alkyl structures ( 1 - 4 ). The ⁴J_(H,H) calculated values, tabulated for variation of 30° for both Φ1 and Φ3, have disclosed an unexpected detectable coupling constant (⁴J(_H,H) ≥ 1 Hz) across heteroatoms, useful to provide valuable structural information. A 2-methyl-1,3-dithiane sulfide ( 5 ) was used as a case study to prove the applicability and reliability of the calculated values to real issues. The ⁴J(_H,H) values obtained at density functional theory for the system 4 have reproduced with good accuracy an unexpected experimental ⁴J(_H2ax-H4ax) = 1.01 Hz of sulfide molecule ( 5 ), suggesting these calculated coupling constant values as a new powerful tool for the organic synthesis and stereochemical analysis.     

The rational LS-category of -trivial fibrations

We provide new upper and lower bounds for the rational LS-category of a rational fibration of simply connected spaces that depend on a measure of the triviality of which is strictly finer than the vanishing of the higher holonomy actions. In particular, we prove that if is -trivial for some and enjoys Poincaré duality, then

     

Oxidation of di-n-propyl ether: Characterization of low-temperature products

The oxidation of di-n-propyl-ether (DPE) was performed in a jet-stirred reactor at 1 and 10 atm, at residence times of 1 and 0.7 s, respectively, and initial fuel concentrations of 5000 and 1000 ppm at 1 and 10 atm, respectively. Atmospheric pressure experiments were used for characterization of cool flame products. The 10 atm experiment provided KHPs profile vs. temperature and mole fraction profiles of stable species which were obtained through sonic probe sampling, gas chromatography, Fourier transform infrared spectrometry analyses. High resolution mass spectrometry analyses (HRMS) with syringe direct injection or ultra-high-pressure liquid chromatography coupling was used to characterize hydroperoxides (C₃H₈O₂, C₆H₁₄O₃), diols (C₆H₁₄O₃), ketohydroperoxides (C₆H₁₂O₄), carboxylic acids, and highly oxygenated molecules (C₆H₁₂O₆, C₆H₁₂O₈) resulting from up to four O₂ additions on fuel's radicals. Heated electrospray and atmospheric pressure chemical ionizations (HESI and APCI) were used in positive and negative mode. Whereas the CH₂ groups neighboring the ether function are the most favorable sites for H-atom abstraction reactions, speciation indicated that other sites can react by metathesis forming a large pool of intermediates. Our kinetic reaction mechanism represents the experimental data for most of the stable species but need to be expended for simulating the formation of newly detected species.