Article

Synthesis of a Fluorescent BODIPY-tagged ROMP catalyst and Initial Polymerization-Propelled Diffusion Studies

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Abstract

The synthesis of a Ru-based olefin metathesis catalyst dye-tagged at the N-heterocyclic carbene ligand is reported. Its catalytic activity toward ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene was found to be similar to that of its parent second-generation Hoveyda-Grubbs catalyst. The quantum yield of fluorescence (ΦF = 0.22) makes it a good candidate to explore, by fluorescence correlation spectroscopy, the potential of a ROMP process to provide a molecule with sufficient energy for self-propulsion in solution.

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... Accordingly, synthetic transformations on the hydroxymethyl group in BODIPYs 2, 3 gave access to a "second generation" of BODIPY derivatives comprising formyl-BODIPYs 6a and 6b (a R 1 = H, b R 1 = Et, throughout the series; Scheme 1A) (Dess and Martin, 1983), azidomethyl-BODIPYs 7a and 7b, (Scheme 1B), and bromomethyl-BODIPYs 8a and 8b (Godoy et al., 2015) (Scheme 1C). The latter was also a precursor of azidomethyl BODIPYs 7a and 7b by nucleophilic displacement with sodium azide. ...
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Kinesin is a molecular walking machine that organizes cells by hauling packets of components directionally along microtubules. The physical mechanism that impels directional stepping is uncertain. We show here that, under very high backward loads, the intrinsic directional bias in kinesin stepping can be reversed such that the motor walks sustainedly backwards in a previously undescribed mode of ATP-dependent backward processivity. We find that both forward and backward 8-nm steps occur on the microsecond timescale and that both occur without mechanical substeps on this timescale. The data suggest an underlying mechanism in which, once ATP has bound to the microtubule-attached head, the other head undergoes a diffusional search for its next site, the outcome of which can be biased by an applied load.
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High cis content (81-99%) cis-transoidal polyphenylacetylene (PPA) jacketed with amphiphilic self-assembling dendrons, poly[(3,4-3,5)mG2-4EBn] with m = 8, 10, 12, 14, 16, and (S)-3,7-dimethyloctyl, were synthesized by Rh(C triple bond CPh)(nbd)(PPh(3))(2) (nbd = 2,5-norbornadiene)/N,N-(dimethylamino)pyridine (DMAP) catalyzed polymerization of macromonomers. The resulting cylindrical PPAs self-organize into hexagonal columnar lattices with intracolumnar order (Phi(h)(io)) and without (Phi(h)). The polymers with m = 12, 14, and 16 exhibit also a hexagonal columnar crystal phase (Phi(h,k)). The reversible Phi(h,k)-to-Phi(h)(io)-to- Phi(h) phase transition in these dendronized PPAs was analyzed by a combination of differential scanning calorimetry and small and wide-angle X-ray diffraction experiments performed on powder and oriented fibers. In the Phi(h,k) and Phi(h)(io) phases, the dendronized PPAs form helical porous columns. The helical pore disappears in the Phi(h) phase. This change is accompanied by a decrease of the external column diameter that is induced by stretching of the polymer backbone along the axis of the cylinder. The helix sense of the porous PPA is selected by homochiral alkyl dendritic tails. This transition is generated by an unprecedented conversion of the PPA backbone from the cis-cisoidal conformation in the Phi(h,k) and Phi(h)(io) phases to the cis-transoidal conformation in the Phi(h) phase. Under the same conditions, the pristine cis-PPA undergoes cis-trans isomerization and irreversible intramolecular 6pi electrocyclization of 1,3-cis,5-hexatriene sequences followed by chain cleavage. These processes are eliminated in the dendronized cis-PPA below its decomposition temperature.
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[structure: see text] With the eventual goal of demonstrating a motorized nanocar, the key structure has been synthesized which bears a light-activated unidirectional molecular motor and an oligo(phenylene ethynylene) chassis and axle system with four carboranes to serve as the wheels. Kinetics studies in solution show that the motor indeed rotates upon irradiation with 365 nm light, and the fullerene-free carborane wheel system is an essential design feature for motor operation.
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Alkene metathesis catalyst development has made significant progress over recent years. Research in metathesis catalyst design has endeavoured to tackle three key issues: those of (i) catalyst efficiency and activity, (ii) substrate scope and selectivity--particularly stereoselective metathesis reactions--and (iii) the minimization of metal impurities and catalyst recycling. This article describes a brief history of metathesis catalyst development, followed by a survey of more recent research, with a particular emphasis on ruthenium catalysts.
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The 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene or BODIPY dyes are strongly UV-absorbing small molecules emitting a relatively sharp fluorescence peaks with high quantum yields. The modification of BODIPY framework will lead to probes to be used more effectively for imaging in living cells and whole organisms. In facilitating this process, a summarization of basic chemistry and spectroscopic properties of common BODIPY-derivatives was reviewed and highligting ways in which other interesting probes could be prepared. This review provides the readers particularly interested in applications of BODIPY dyes, a guide to synthesis and spectroscopic properties.
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The design and preparation of model silica nanoparticles bearings dinuclear manganese catalyst and luminophore group was reported. The diacid was prepared by oxidation of 4,4'-dimethyl-2,2'-bipyridine under Jones conditions and purified by conversion to its dimethyl ester. Covalent immobilization of the luminophore onto the silica particles was achieved using a peptide-coupling-type reaction between the carboxylic acid groups of the luminophore. The selected luminophores demonstrated a great robustness towards the highly oxidative H 2O2 environment and resistance to photobleaching. It is believed that ruthenium(II) tris (bipyridine) complexes will have a major role in florescence imaging in the areas of micro- and nanotechnology and molecular devices.