Ullmann diaryl ether synthesis: rate acceleration by 2,2,6,6-tetramethylheptane-3,5-dione

[reaction: see text]. In the copper salt catalyzed ether formation from aryl bromides or iodides and phenols, 2,2,6,6-tetramethylheptane-3,5-dione (TMHD) was found to greatly accelerate the ordinarily difficult reaction, making it occur under more moderate temperatures and reaction times. A series of aryl halides and phenols were shown to form ethers in NMP as the solvent, cesium carbonate as the base, and CuCl and TMHD as the catalysts. The reaction was shown to tolerate electron-rich aryl bromides and electron-neutral phenols.     

Recent highlights in stationary phase design for open-tubular capillary electrochromatography

This review examines the most recent innovations made to achieve high performance in open-tubular capillary electrochromatography (OT-CEC) separations, focusing on the ingenious chemical and physical solutions made to increase the surface area and equip the stationary phase with exploitable selectivity. Among the approaches taken are chemically bonded ligands, etching with chemical bonding, sol-gels, molecularly imprinted polymers, porous layers, physically attached or adsorbed phases, and nanoparticle coatings. Particularly noteworthy are modern developments with macrocyclic receptor ligands, nanoparticles and open channel electrochromatography on-chip.     

Morphological characterization of elastin-mimetic block copolymers utilizing cryo- and cryoetch-HRSEM.

Elastin-mimetic block copolymers were produced by genetic engineering. Genetically driven synthesis permitted control of the final physiochemical characteristics of the block copolymers. We designed BB and BAB block copolymers in which the A-block was hydrophilic and the B-block was hydrophobic. By designing the copolymers in this manner, it was proposed that they would self-assemble into micellar aggregates that, at high concentration, would form thermoreversible hydrogels. To analyze the three-dimensional fine surface morphology of the copolymers, to the resolution level of a few nanometers, we employed cryo-HRSEM. This method provided vast expanses of the specimen in its frozen hydrated state for survey. In our initial cryo-HRSEM studies, we observed the protein filaments and micelles surrounded by lakes of vitreous ice. Upon examination at low and intermediate magnifications, there was an extensive honeycomb-like filamentous network. To delineate the fine morphology of the hydrogel network at high magnification and to greater depths, we cryoetched away unbound water from the sample surface, in high vacuum, prior to chromium deposition. By using this technique, we were able to visualize for characterization purposes the fine fibril networks formed from the micellar aggregates over the surface of the hydrogel.     

Studies on the reactivity of phenyliodonium ylide of 2-hydroxy-1,4-naphthoquinone: reactions with indole derivatives and other C-nucleophiles

[reaction: see text] Thermal decomposition of phenyliodonium ylide of 2-hydroxy-1,4-naphthoquinone (lawsone) in the presence of indole derivatives affords 3-acylated indoles existing in their enol forms, through a ring contraction and alpha,alpha'-dioxoketene formation reaction. The same reactants afford 3-(3-indolyl)-2-hydroxy-1,4-naphthoquinones in a copper-catalyzed reaction. Enamines, among other C-nucleophiles tested, give analogous results.     

Parallelization of three-center electron repulsion integrals

The parallelization of the three-center electron repulsion integrals arising from the variational fitting of the Coulomb potential is presented. A scheme for dynamical load balancing of the corresponding loop structure is discussed. The implementation in the density functional theory program deMon using the message passing interface is described. The efficiency of the parallelization is analyzed by selected benchmark calculations     

Strong solute-solute dispersive interactions in a protein-ligand complex

The contributions of solute-solute dispersion interactions to binding thermodynamics have generally been thought to be small, due to the surmised equality between solute-solvent dispersion interactions prior to the interaction versus solute-solute dispersion interactions following the interaction. The thermodynamics of binding of primary alcohols to the major urinary protein (MUP-I) indicate that this general assumption is not justified. The enthalpy of binding becomes more favorable with increasing chain length, whereas the entropy of binding becomes less favorable, both parameters showing a linear dependence. Despite the hydrophobicity of the interacting species, these data show that binding is not dominated by the classical hydrophobic effect, but can be attributed to favorable ligand-protein dispersion interactions.     

Automatic flow procedure for the determination of glycerol in wine using enzymatic reaction and spectrophotometry

An automatic flow procedure for the determination of glycerol in wines by employing a flow system based on multicommutation and enzymatic reaction is described. Glycerol dehydrogenase was immobilized on aminopropyl glass beads and packed into a column that was coupled to the flow system. The NADH produced by the enzymatic reaction was monitored by spectrophotometry at 340 nm and its radiation absorption presented a relationship with glycerol concentration. The system manifold comprised a set of three-way solenoid valves controlled by a microcomputer, which was furnished with electronic interfaces and runs a software that was designed to carry out on-line sample dilution, reagent addition, and data acquisition. The procedure allows the determination of glycerol in wine samples without any prior pretreatment. The procedure presented as profitable features a linear response range between 2.0 and 10.0 g l⁻¹ glycerol (R=0.998), a detection limit of 0.006 g l⁻¹ glycerol, a relative standard deviation of 1.8% (n=14) for a typical wine sample presenting 5.3 g l⁻¹ glycerol, a sampling throughput of 33 determinations per hour, and a NAD⁺ consumption of 0.8 mg per determination. The results were compared with those obtained using a reference method and no significant difference at 90% confidence level was observed.     

STRUCTURE-ACTIVITY STUDIES OF PHOTOACTIVATED ANTIVIRAL AND CYTOTOXIC TRICYCLIC THIOPHENES

The photoactivated antiviral and cytotoxic activities of the naturally occurring thiophene, alpha-terthienyl (1), and 15 synthetic analogues were evaluated against murine cytomegalovirus and Sindbis virus, and murine mastocytoma cells. After irradiation with near UV light, alpha-terthienyl and most of its analogues had significant toxicity, with minimum inhibitory concentrations in the range of 0.02-40 microM. In the absence of near UV irradiation, only one analogue had antiviral activity and five were cytotoxic. The most active analogues were those containing carboxylic acid, hydroxyl, or cyano substituents. Quantitative structure-activity relationship analysis of thiophene phototoxicity suggested that the rate of singlet oxygen production is the primary determinant of antiviral and cytotoxic activities. For phototoxicity against murine cytomegalovirus, a significant role for hydrophobicity was also demonstrated. Tricyclic thiophenes show significant potential for photochemotherapy of viral infections and cancer, and further evaluation in animal models is recommended.     

Pyridine-substituted oligopeptides as scaffolds for the assembly of multimetallic complexes: variation of chain length

This paper presents the synthesis and characterization of pyridine-substituted artificial oligopeptides with an aminoethylglycine backbone of varying length, which are designed to act as scaffolds for the self-assembly of multimetallic structures. The identities and purities of the oligopeptides are confirmed with mass spectrometry, (1)H NMR, HPLC, and pH titrations. The acid dissociation constants for the oligopeptides were determined and were found to decrease with increasing pyridine units. Titrations of the oligopeptides with Cu(II) and Pt(II) complexes containing the tridentate ligands 2,2':6',2'-terpyridine and pyridine 2,6-dicarboxylic acid were monitored using UV-visible absorption spectroscopy and showed stoichiometric binding based on the number of pyridines on the peptide strand. Metal titrations performed using an analogous oligopeptide with methyl substituents (in place of the pyridine ligands) showed very weak or no binding. In the case of the oligopeptides containing bound Pt(terpyridine)(2+) complexes, cyclic voltammetry reveals two sequential one-electron reductions at formal potentials that do not vary as a function of oligopeptide length. The measured diffusion coefficients were measured with chronoamperometry and were found to decrease with increasing oliopeptide length.     

Packing Measure Analysis of Harmonic Measure

We show that, for any Jordan domain J in R², harmonic measureis supported by a Borel set of packing dimension 1. We alsoobtain incomplete analogs to the results of Makarov, which connectthe almost everywhere behavior of the derivative near the boundaryfor the conformal mapping function from the unit disk J withthe Hausdorff measure properties of sets supporting the harmonicmeasure.