- Spatially controlled Suzuki and Heck catalytic molecular coupling
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The initiation and control of chemical coupling has the potential to offer much within the context of "bottom up" nanofabrication. We report herein the use of a palladium-modified, catalytically active, AFM probe to initiate and spatially control surface-
- Davis, Jason J.,Bagshaw, Claire B.,Busuttil, Katerina L.,Hanyu, Yuki,Coleman, Karl S.
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- External stimulus-responsive supramolecular structures formed by a stilbene cyclodextrin dimer
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Cyclodextrin (CD) based supramolecular complexes have been prepared using a stilbene bis(β-CD) dimer and a ditopic adamantyl guest. The conformation of the stilbene bis(β-CD) dimer in aqueous solutions could be photochemically controlled. The ROESY spectra of the β-CD dimer with the adamantyl dimer showed NOE between the protons of adamantyl moieties and the inner protons of the CD. When the host cyclodextrin dimer was in trans conformation, supramolecular dimers or small assemblies are formed in solutions, whereas in its cis conformation supramolecular linear polymers with high molecular weight were observed. Thus the structure of the supramolecular polymers could be controlled by an external stimulus. Copyright
- Kuad, Paul,Miyawaki, Atsuhisa,Takashima, Yoshinori,Yamaguchi, Hiroyasu,Harada, Akira
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- Mechanochemical ruthenium-catalyzed olefin metathesis
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We describe the development of a mechanochemical approach for Ru-catalyzed olefin metathesis, including cross-metathesis and ring-closing metathesis. The method uses commercially available catalysts to achieve high-yielding, rapid, room-temperature metathesis of solid or liquid olefins on a multigram scale using either no or only a catalytic amount of a liquid.
- Do, Jean-Louis,Mottillo, Cristina,Tan, Davin,trukil, Vjekoslav,Frii, Tomislav
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- Dual-colored 4,4′,4′′,4′′′-(cyclobutane-1,2,3,4-tetrayl)-tetrabenzoate electrochromic materials with large optical contrast and coloration efficiency
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Nine 4,4′,4′′,4′′′-(cyclobutane-1,2,3,4-tetrayl)tetrabenzoate derivative electrochromic materials have been designed, synthesized, and characterized. Seven compounds displayed dual-colored electrochromism. The required potential and colored states were markedly influenced by substitution. When the substituent was alkyl, colored states of purple and blue were obtained at an applied voltage of -2.3 and -2.6 V, respectively; when the substituent was phenyl with an electron-donating group, colored states of purple bluish and bright blue were obtained at an applied voltage of -2.1 and -2.3 V, respectively; when the substituent was phenyl with an electron-withdrawing group, monocolored state and bad electrochromic properties were obtained. Moreover, electrochromic devices based on most of these compounds show large optical contrast, fast response time, and high coloration efficiency.
- Zhu, Chun-Rong,Xie, Jia-Ping,Mou, Hong-Rong,Huang, Zhen-Jie,Tang, Qian,Gong, Cheng-Bin,Fu, Xiang-Kai
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- Variation of formal hydrogen-bonding networks within electronically delocalized π-conjugated oligopeptide nanostructures
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This photophysical study characterizes the generality of intermolecular electronic interactions present within nanomaterials derived from self-assembling oligopeptides with embedded π-conjugated oligophenylenevinylene (OPV) subunits stilbene and distyrylbenzene that in principle present two distinct β-sheet motifs. Two different synthetic approaches led to oligopeptides that upon self-assembly are expected to self-assemble into multimeric aggregates stabilized by β-sheet-like secondary structures. The target molecules express either two C-termini linked to the central OPV core (symmetric peptides) or the more common N-termini to C-termini polarity typical of natural oligopeptides (nonsymmetric peptides). Both peptide secondary structures were shown to form extended 1-D peptide aggregates with intimate intermolecular π-electron interactions. Differences in length of the π-conjugated OPV segments resulted in differing extents of intermolecular interactions and the resulting photophysics. The peptides containing the shorter stilbene (OPV2) units showed little ground state interactions and resulted in excimeric emission, while the longer distyrylbenzene (OPV3) peptides had different ground state interactions between adjacent π-conjugated subunits resulting in either perturbed electronic properties arising from exciton coupling or excimer-like excited states. Molecular dynamics simulations of nascent aggregate formation predict peptide dimerization to be a spontaneous process, possessing thermodynamic driving potentials in the range 2-6 kcal/mol for the four molecules considered. Antiparallel stacking of the peptides containing an OPV3 subunit is thermodynamically favored over the parallel orientation, whereas both arrangements are equally favored for the peptides containing an OPV2 subunit. This study validates the generality of peptide-π-peptide self-assembly to provide electronically delocalized supramolecular structures and suggests flexibility in peptide sequence design as a way to tune the material properties of π-conjugated supramolecular polymers.
- Wall, Brian D.,Zhou, Yuecheng,Mei, Shao,Ardoa, Herdeline Ann M.,Ferguson, Andrew L.,Tovar, John D.
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p. 11375 - 11385
(2015/01/08)
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- Mechanistic studies on the Pd-catalyzed vinylation of aryl halides with vinylalkoxysilanes in water: The effect of the solvent and NaOH promoter
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The mechanism of the Pd-catalyzed vinylation of aryl halides with vinylalkoxysilanes in water has been studied using different catalytic precursors. The NaOH promoter converts the initial vinylalkoxysilane into a highly reactive water-soluble vinylsilanolate species. Similarly, deuterium-labeling experiments have shown that, irrespective of the catalytic precursor used, vinylation occurs exclusively at the CH vinylic functionality via a Heck reaction and not at the C-Si bond via a Hiyama cross-coupling. The involvement of a Heck mechanism is interpreted in terms of the reduced nucleophilicity of the base in water, which disfavors the transmetalation step. The Heck product (β-silylvinylarene) undergoes partial desilylation, with formation of a vinylarene, by three different routes: (a) hydrolytic desilylation by the aqueous solvent (only at high temperature); (b) transmetalation of the silyl olefin on the PdH Heck intermediate followed by reductive elimination of vinylarene; (c) reinsertion of the silyl olefin into the PdH bond of the Heck intermediate followed by β-Si syn-elimination. Both the Hiyama and Heck catalytic cycles and desilylation mechanisms b and c have been computationally evaluated for the [Pd(en)Cl2] precursor in water as solvent. The calculated Gibbs energy barriers support the reinsertion route proposed on the basis of the experimental results.
- Gordillo, Alvaro,Ortuno, Manuel A.,Lopez-Mardomingo, Carmen,Lledos, Agusti,Ujaque, Gregori,De Jesus, Ernesto
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supporting information
p. 13749 - 13763
(2013/10/01)
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- Consecutive palladium-catalyzed Hiyama-Heck reactions in aqueous media under ligand-free conditions
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Symmetric and asymmetric (E)-1,2-diarylethenes are synthesized from aryl bromides by consecutive one-pot Hiyama-Heck reactions carried out in water and under air; the only additives required are sodium hydroxide, palladium acetate and poly(ethylene glycol), and the products are isolable in many cases by simple filtration of the water solution. The Royal Society of Chemistry.
- Gordillo, Alvaro,De Jesus, Ernesto,Lopez-Mardomingo, Carmen
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p. 4056 - 4058
(2008/03/14)
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- Crossover from superexchange to hopping as the mechanism for photoinduced charge transfer in DNA hairpin conjugates
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The mechanism and dynamics of photoinduced charge separation and charge recombination have been investigated in synthetic DNA hairpins possessing donor and acceptor stilbenes separated by one to seven A:T base pairs. The application of femtosecond broadband pump-probe spectroscopy, nanosecond transient absorption spectroscopy, and picosecond fluorescence decay measurements permits detailed analysis of the formation and decay of the stilbene acceptor singlet state and of the charge-separated intermediates. When the donor and acceptor are separated by a single A:T base pair, charge separation occurs via a single-step superexchange mechanism. However, when the donor and acceptor are separated by two or more A:T base pairs, charge separation occurs via a multistep process consisting of hole injection, hole transport, and hole trapping. In such cases, hole arrival at the electron donor is slower than hole injection into the bridging A-tract. Rate constants for charge separation (hole arrival) and charge recombination are dependent upon the donor-acceptor distance; however, the rate constant for hole injection is independent of the donor-acceptor distance. The observation of crossover from a superexchange to a hopping mechanism provides a "missing link" in the analysis of DNA electron transfer and requires reevaluation of the existing literature for photoinduced electron transfer in DNA.
- Lewis, Frederick D.,Zhu, Huihe,Daublain, Pierre,Fiebig, Torsten,Raytchev, Milen,Wang, Qiang,Shafirovich, Vladimir
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p. 791 - 800
(2007/10/03)
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- Optimized liquid-phase oxidation
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Disclosed is an optimized process and apparatus for more efficiently and economically carrying out the liquid-phase oxidation of an oxidizable compound. Such liquid-phase oxidation is carried out in a bubble column reactor that provides for a highly effic
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Page/Page column 43-45
(2008/06/13)
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- Optimized liquid-phase oxidation
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Disclosed is an optimized process and apparatus for more efficiently and economically carrying out the liquid-phase oxidation of an oxidizable compound. Such liquid-phase oxidation is carried out in a bubble column reactor that provides for a highly effic
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Page/Page column 43-45
(2008/06/13)
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- Optimized liquid-phase oxidation
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Disclosed is an optimized process and apparatus for more efficiently and economically carrying out the liquid-phase oxidation of an oxidizable compound. Such liquid-phase oxidation is carried out in a bubble column reactor that provides for a highly effic
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Page/Page column 39-40
(2008/06/13)
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- The synthesis of some head to head linked DNA minor groove binders
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A series of head to head linked dimers of heterocyclic amino acids has been prepared for investigation of affinity and selectivity in binding to the minor groove of DNA. The selection of targets for synthesis was led by computer based design. Several novel dicarboxylic acid linkers including indoles, phenanthrenes, a fluorenone, and a bisbenzothiophene have been included. Analysis of binding to DNA by footprinting showed high affinity for compounds derived from 2,7-dihydrophenanthrene dicarboxylic acid and a predominant selectivity for AT rich regions containing at least 4 AT pairs but with the ability to span up to two CG base pairs. (C) 2000 Elsevier Science Ltd.
- Khalaf, Abedawn I.,Pitt, Andrew R.,Scobie, Martin,Suckling, Colin J.,Urwin, John,Waigh, Roger D.,Fishleigh, Robert V.,Young, Steven C.,Wylie, William A.
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p. 5225 - 5239
(2007/10/03)
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