Pattern dynamics in cellular perception

By using a giant amoeboid cell of the Physarum plasmodium, changes in the intracellular distribution of chemical components are studied in relation to information processing in cell behavior. Various kinds of metabolites oscillate, and so the protoplasm should be a collection of chemical oscillators. Spatially, characteristic chemical patterns are self-organized for different cell shapes, and hence cell behavior. New phase waves propagate throughout the cell upon local stimulation, their direction being opposite for attraction and repulsion. Locomotion is inhibited when the coherence of the oscillators breaks. Thus, pattern dynamics is correlated with information processing in the amoeboid cell.     

Synthesis of novel side‐chain triphenylamine polymers with azobenzene moieties via RAFT polymerization and investigation on their photoelectric properties

Two novel and well‐defined polymers, poly[6‐(5‐(diphenylamino)‐2‐((4‐methoxyphenyl)diazenyl)phenoxy)hexyl methacrylate] (PDMMA) and poly[6‐(4‐((3‐ethynylphenyl)diazenyl) phenoxy)hexyl methacrylate] (PDPMMA), which bear triphenylamine (TPA) incorporated to azobenzene either directly (PDMMA) or with an interval (PDPMMA) as pendant groups were successfully prepared via reversible addition‐fragmentation chain transfer polymerization technique. The electrochemical behaviors of PDPMMA and PDMMA were investigated by cyclic voltammograms (CV) measurement. The hole mobilities of the polymer films were determined by fitting the J‐V (current‐voltage) curve into the space‐charge‐limited current method. The influence of photoisomerization of the azobenzene moiety on the behaviors of fluorescence emission, CV and hole mobilities of these two polymers were studied. The fluorescent emission intensities of these two polymers in CH₂Cl₂ were increased by about 100 times after UV irradiation. The oxidation peak currents (I_OX) of the PDMMA and PDPMMA in CH₂Cl₂ were increased after UV irradiation. The photoisomerization of the azobenzene moiety in PDMMA had significant effect on the electrochemical behavior, compared with that in PDPMMA. The changes of the hole mobility before and after UV irradiation were very small for both polymers. The HOMO energies (E_HOMO, HOMO: the highest occupied molecular orbital) of side chain moieties of TPA incorporated with cis‐isomer and trans‐isomer of azobenzene in PDMMA and PDPMMA were obtained by theoretical calculation, which are basically consistent with the experimental results. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Efficient polymer passivation of ligand‐stripped nanocrystal surfaces

Water‐dispersible, polymer‐wrapped nanocrystals are highly sought after for use in biology and chemistry, from nanomedicine to catalysis. The hydrophobicity of their native ligand shell, however, is a significant barrier to their aqueous transfer as single particles. Ligand exchange with hydrophilic small molecules or, alternatively, wrapping over native ligands with amphiphilic polymers is widely employed for aqueous transfer; however, purification can be quite cumbersome. We report here a general two‐step method whereby reactive stripping of native ligands is first carried out using trialkyloxonium salts to reveal a bare nanocrystal surface. This is followed by chemically directed immobilization of a hydrophilic polymer coating. Polyacrylic acids, with side‐chain grafts or functional end groups, were found to be extremely versatile in this regard. The resulting polymer‐wrapped nanocrystal dispersions retained much of the compact size of their bare nanocrystal precursors, highlighting the unique role of monomer side‐chain functionality to serve as effective, conformal ligation motifs. As such, they are well poised for applications where tailored chemical functionality at the nanocrystal's periphery or improved access to their surfaces is desirable. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Visualization of arborescent architecture of polystyrenes prepared by raft‐based initiator‐monomer polymerization using atomic force microscopy

This article presents the utilization of “molecular amplification” to visualize the molecular architecture of “arborescent” (tree‐like) polystyrenes (arbPSs) using atomic force microscopy (AFM). arbPSs with M_n > 80,000 g/mol were synthesized via initiator‐monomer‐type (inimer) RAFT polymerization of styrene mediated by 4‐vinylbenzyl dithiobenzoate in bulk. These arbPS were then used as macrochain transfer agents for polymerization of vinylbenzyl chloride (VBCl) to give arborescent poly(styrene‐block‐vinylbenzyl chloride) (arbPS‐b‐VBCl). Poly(styryl) diphenylethyl lithium (M_n = 11,000 g/mol) was then grafted onto the VBCl units of the arbPS‐b‐VBCl. The M_n of the amplified arbPSs increased over >10 million g/mol, exceeding the exclusion limit of our size exclusion chromatography equipment. AFM confirmed the proposed branches on branches architecture in the samples, together with lesser branched species. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Structures of oxaliplatin‐oligonucleotide adducts from DNA

Oxaliplatin, [(1R,2R)‐cyclohexane‐1,2‐diamine](ethanedioato‐O,O')platinum(II) shows a great efficiency against colorectal cancer. Although the mode of action of oxaliplatin is not yet understood, it is commonly accepted that binding of oxaliplatin to DNA prevents DNA synthesis and alters protein to DNA binding. In order to elucidate the modified DNA–protein interaction and thus to understand the mechanisms leading to cellular misinterpretation of DNA information and apoptosis, we have identified the preferential binding sites and the dynamics of the oxaliplatin‐DNA intrastrand and interstrand adducts at the oligomer level using high‐performance liquid chromatography/electrospray ionization‐tandem mass spectrometry (HPLC/ESI‐MS/MS) and HPLC/inductively coupled plasma‐MS for quantitative studies. We used a combination of benzonase, alkaline phosphatase and Nuclease S1 for digestion. This digestion procedure allows the study of platinated oligomeric nucleotides and more complex interstrand adducts. The digestion products were mostly chromatographically separated and characterized using HPLC/ESI‐ion trap MS/MS experiments. We could show that the adducts to guanine and adenine are quite dynamic; that is, the ratios are changing for several days. In addition, the resulting adducts provide evidence for the action of the digesting enzymes and indicate that the adduct spectrum at the oligomeric level is different to that at the commonly studies dinucleotide level. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and characterization of polymethacrylates containing conjugated oligo(phenylene ethynylene)s as side chains

In order to form suitable systems designed for resonance energy transfer, a series of monodisperse methacrylate‐based monomers containing rigid π‐conjugated oligo(phenylene ethynylenes) with different sizes of the conjugated systems ( M1 – M3 ), and therefore different optoelectronic properties, were synthesized and subsequently polymerized using the reversible addition–fragmentation chain transfer polymerization technique ( P1 – P3 ). In addition, these oligomers were also copolymerized with methyl methacrylate. The obtained polymers were characterized by ¹H NMR spectroscopy, size exclusion chromatography, and analytical ultracentrifugation. The photophysical properties of the polymers were studied by UV–vis absorption and emission spectroscopy in diluted solutions as well as in thin films and compared to the photophysics of the corresponding monomers. Thereby, changes going from monomeric to polymeric systems could be detected in fluorescence quantum yields and lifetimes pointing to energy trapping, e.g., energy transfer. Donor–acceptor copolymers containing different numbers of monomeric units within the side chain exhibit differences in the emission spectra, indicating that energy trapping in polymers is very sensitive to structural properties such as the chain length. UV–vis absorption spectroscopy as well as time‐resolved lifetime studies indicate intrapolymer and interpolymer energy transfer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Radical addition fragmentation chain transfer (RAFT) polymerization of ferrocenyl (Meth)acrylates

We report on the controlled free radical homopolymerization of 1‐ferrocenylethyl acrylate as well as of three new ferrocene bearing monomers, namely 4‐ferrocenylbutyl acrylate, 2‐ferrocenylamido‐2‐methylpropyl acrylate, and 4‐ferrocenylbutyl methacrylate, by the RAFT technique. For comparison, the latter monomer was polymerized using ATRP, too. The ferrocene containing monomers were found to be less reactive than their analogues free of ferrocene. The reasons for the low polymerizability are not entirely clear. As the addition of free ferrocene to the reaction mixture did not notably affect the polymerizations, sterical hindrance by the bulky ferrocene moiety fixed on the monomers seems to be the most probable explanation. Molar masses found for 1‐ferrocenylethyl acrylate did not exceed 10,000 g mol^?1, while for 4‐ferrocenylbutyl (meth)acrylate molar masses of 15,000 g mol^?1 could be obtained. With PDIs as low as 1.3 in RAFT polymerization of the monomers, good control over the polymerization was achieved. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

RAFT polymerization of alternating styrene‐pentafluorostyrene copolymers

Reversible addition‐fragmentation chain‐transfer (RAFT) polymerization was used to control the alternating copolymerization of styrene and 2,3,4,5,6‐pentaflurostyrene. The RAFT polymerization yields a high degree of control over the molecular weight of the polymers and does not significantly influence the reactivity ratios of the monomers. The controlled free‐radical polymerization could be initiated using AIBN at elevated temperatures or using a redox couple (benzoyl peroxide/N,N‐dimethylaniline) at room temperature, while maintaining control over molecular weight and dispersity. The influence of temperature and solvent on the molecular weight distribution and reactivity ratios were investigated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1555–1559