Emulsion copolymerization of vinyl acetate and butyl acrylate in the presence of fluorescent dyes

This article describes our first experiments for preparing dye‐labeled latex particles by the emulsion copolymerization of a 4/1 (w/w) mixture of vinyl acetate‐butylacrylate (VAc‐BA). We discuss the synthesis of acrylate derivatives of phenanthrene, anthracene, and pyrene [9‐acryloxymethyl phenanthrene ( 7 ), 9‐acryloxymethyl‐10‐methyl anthracene ( 8 ), and 1‐acryloxymethyl pyrene ( 10 )] and an allyl ether derivative of anthracene [9‐allyoxymethyl‐10‐methyl anthracene ( 9 )]. Although the phenanthrene derivative 7 gave latex particles with high monomer conversion and good dye incorporation, the pyrene acrylate and both anthracene comonomers strongly inhibited the free‐radical reaction. To assist our search for a dye that would serve as a useful energy acceptor for phenanthrene and without suppressing VAc‐BA polymerization, we also examined batch emulsion polymerization in the presence of a variety of dye derivatives—substituted anthracenes, acridines, a coumarin, and two benzophenone derivatives. All of the anthracene derivatives, as well as acridine, strongly inhibited monomer polymerization. The coumarin dye 7‐hydroxy‐4‐methyl coumarin ( 22 ) that had only limited solubility allowed more than 90% monomer conversion. Most promising were 2‐hydroxy‐5‐methyl benzophenone ( 23 ) and 4‐N,N‐dimethylamino benzophenone ( 24 ) that at 1 mol % in the monomer mixture permitted virtually quantitative monomer conversion to latex. 4′‐Dimethylamino‐2‐acryloxy‐5‐methyl benzophenone ( 25 ) copolymerized well with the VAc‐BA mixture, yielding latex particles in high yield and with a narrow size distribution. These dyes appear to be useful acceptor dyes for energy‐transfer experiments with phenanthrene. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1594–1607, 2002     

Solid-phase synthesis of a combinatorial array of 1,3-bis(acylamino)-2-butanones, inhibitors of the cysteine proteases cathepsins K and L

To more rapidly prepare members of the 1,3-bis(acylamino)-2-butanone class of cysteine protease inhibitors, a solid-phase synthesis was developed. 1-Azido-3-amino-2,2-dimethoxybutane (4), which has the two amino groups differentiated and the ketone protected as a a ketal, served as a surrogate for the 1,3-diamino-2-butanone core. Amine (4) was coupled to the BAL-resin-linked carboxylic acids derived from alpha-amino acid esters. Evaluation of a small combinatorial array by measuring inhibition constants (Ki,appS) against cathepsins K, L, and B provided some structure-activity relationship trends with respect to selectivity and potency. Novel, potent inhibitors of cathepsins K and L were identified.     

Effect of Organic Additive on the Preparation of Rutile TiO2 by Steam Treatment

Low temperature phase transformation of alkoxide-derived titania was studied under an oxygen flow containing water vapor. The addition of hexylene glycol to the titanium alkoxide solution was effective in transforming rutile phase at low temperature (300°C). Hexylene glycol seems to form a bidentate ligand structure with TEOT in solution state. This bidentate structure promoted the rutile phase at low temperature, under O₂-steam treatment. This modification of TiO₂ gel structure could be monitored by FT-IR and XANES.     

Effect of calcination conditions on MoO3/SiO2 catalysts for synthesis of methylphenyl carbonate

The effect of calcination conditions on MoO₃/SiO₂ catalysts for the synthesis of methylphenyl carbonate was investigated in terms of catalytic activities and surface properties. The calcination temperature was varied in the range of 300 to 800^oC. These calcination conditions have shown a close relationship with the catalyst activities. The optimal calcination temperature of MoO₃/SiO₂was found to be around 550-600^oC. The catalysts were characterized by XRD, SEM, FT-IR and XPS analysis.     

The photochemistry of polydonor-substituted phthalimides: Curtin-Hammett-type control of competing reactions of potentially interconverting zwitterionic biradical intermediates

The results of studies designed to obtain information about the factors that control the chemical efficiencies/regioselectivities and quantum yields of single electron transfer (SET)-promoted reactions of acceptor-polydonor systems are reported. Photochemical and photophysical investigations were carried out with bis-donor tethered phthalimides and naphthalimides of general structure N-phthalimido- and N-naphthalimido-CH2CH2-D-CH2CH2-NMsCH2-E (E = SiMe3 or CO2NBu4 and D = NMs, O, S, and NMe). These substrates contain common terminal donor groups (NMsCH2SiMe3 or NMsCH2CO2NBu4) that have known oxidation potentials and cation radical fragmentation rates. Oxidation potentials and fragmentation rates at the other donor site in each of these substrates are varied by incorporating different heteroatoms and/or substituents. Photoproduct distribution, reaction quantum yield, and fluorescence quantum yield measurements were made. The results show that photocyclization reactions of alpha-trimethylsilylmethansulfonamide (E = SiMe3)- and alpha-carboxymethansulfonamide (E = CO2NBu4)-terminated phthalimides and naphthalimides that contain internal sulfonamide, ether, and thioether donor sites (D = NMs, O, or S) are chemically efficient (80-100%) and that they take place exclusively by a pathway involving sequential photoinduced SET (zwitterionic biradical desilylation or decarboxylation) biradical cyclization. In contrast, photoreactions of alpha-trimethylsilylmethansulfonamide- and alpha-carboxymethansulfonamide-terminated phthalimides and naphthalimides that that contain an internal tertiary amine donor site (D = NMe) are chemically inefficient and follow a pathway involving alpha-deprotonation at the tertiary amine radical cation center in intermediate, iminium radical-containing, zwitterionic biradicals. In addition, the quantum efficiencies for photoreactions of alpha-trimethylsilylmethansulfonamide- and alpha-carboxymethansulfonamide-terminated phthalimides are dependent on the nature of the internal donor (eg., phi = 0.12 for D = NMs, E = SiMe3; phi = 0.02 for D = S, E = SiMe3; phi = 0.04 for D = NMe, E = SiMe3). The results of this effort are discussed in terms of how the relative energies of interconverting zwitterionic biradical intermediates and the energy barriers for their alpha-heterolytic fragmentation reactions influence the chemical yields and quantum efficiencies of SET promoted photocyclization reactions of acceptor-polydonor substrates.     

A one-step synthesis of 2,3-dihydro-4H-pyran-4-ones from 3-ethoxy alpha,beta-unsaturated lactones

[reaction: see text] Addition of diverse nucleophiles to the unsaturated lactone 2 that results from hetero Diels-Alder reaction of Brassard's diene 1 with aldehydes leads to an efficient and general approach to the synthesis of 2,3-dihydro-4H-pyran-4-ones 3.     

Neutral diamide ionophores — Phenylenedioxydiacetamides

The preparation of a series of neutral ligands containing ether and amide groups is described. These ligands as well as related ones bearing other diamide groups are shown to selectively chelate Group II A cations by picrate extraction from water to methylene dichloride. This result was also confirmed by atomic absorption measurement. The changes in UV absorption of aromatic rings and amide groups in the ligands upon titration with metal salts in methanol allow the estimation of the ordering of cation binding.

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Neutrale Diamid-Ionophore — Phenylendioxyacetamide

Zusammenfassung Die Darstellung einer Reihe von neutralen Liganden mit Ether- und Amidgruppen wird beschrieben. Sowohl diese Liganden — als auch verwandte mit anderen Diamidgruppen — bilden mit Kationen der Gruppe II A selektiv Chelate, wie durch Pikratextraktion aus wäßriger Lösung gezeigt wurde. Dieses Ergebnis wurde auch durch Messungen der Atomabsorption bestätigt. Die Änderungen in der UV-Absorption der aromatischen Ringe und der Amidgruppen in Methanol erlauben eine Abschätzung der Größenordnung der Kationenbindung.

     

Peak Height Precision in Hadamard Transform Time-of-Flight Mass Spectra

Hadamard transform (HT) time-of-flight mass spectrometry (TOFMS) is a multiplexing technique that offers high duty cycle for the mass analysis of continuous ion sources. The multiplexing advantage is maximized when spectral noise is independent of signal intensity. For conditions in which shot noise predominates, the variance in each peak is a function of the population of all measured species. We develop expressions for the performance of a HT-TOF mass spectrometer based on Poissonian statistics for the arrival times of ions at the detector. These expressions and complementary probabilistic simulations are used to estimate the magnitude of the baseline noise as a function of mass spectral features and acquisition conditions. Experiment validates the predictions that noise depends on the total number of ions in the acquired spectrum, and the achieved signal-to-noise ratio for a given species depends on its relative population. We find that for HT-TOFMS experiments encoded with an n-order binary off-on sequence that contains N=2 ⁿ −1 elements, the peak height precision, which is the peak intensity divided by its standard deviation, is greater than that of an equivalent conventional TOF experiment by a factor of √N/2 times the square root of the fractional abundance of the peak of interest. Thus, HT-TOFMS is superior to conventional TOF for all species whose fractional abundance F _i exceeds 2/N, which for a typical N value of 2047 corresponds to F _i > 0.001. HT-TOF mass spectra collected at 2500 per second demonstrates the method’s capability of monitoring transient processes not possible by conventional means.     

Differential modulation of zinc-stimulated p21(Cip/WAF1) and cyclin D1 induction by inhibition of PI3 kinase in HT-29 colorectal cancer cells

Activation of the extra cellular signal regulated kinase (ERK) pathway is involved in both proliferation and growth arrest of cells depending on intensity and duration of stimuli. In this study, we have elucidated differential regulation of the zinc-stimulated p21(CiP/WAF1) and cyclin D1 activation by inhibition of phosphoinositide 3-kinase (PI3K). In HT-29 colorectal cancer cells, the ERK activities were increased by zinc, which was accompanied by the induction of p21(Cip/WAF1) and cyclin D1. However, in the HT-29 cells pre-treated with PI3K inhibitor, LY294002, zinc induced further the p21(CiP/WAF) induction whereas abrogated cyclin D1 induction. In addition, the induction of p21(Cip/WAF1) expression completely inhibited the incorporation of bromodeoxyuridine (BrdU) into the nucleus, indicating that p21(CiP/WAF1) is an important indicator for ERK-dependent growth arrest. These studies suggest presence of an inter-related regulatory mechanism of cell proliferation by ERK and PI3K pathways.