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Silica is an important mineral in biology and technology, and many protocols have been developed for the synthesis of complex silica architectures. The current report shows that silsesquioxane nanoparticles carrying polymer arms on their surface are efficient templates for the fabrication of silica particles with a star- or raspberry-like morphology. The shape of the resulting particles depends on the chemistry of the polymer arms. With poly(N,N- dimethylaminoethyl methacrylate) (PDMAEMA) arms, spherical particles with a less electron dense core form. With poly {[2- (methacryloyloxy)ethyl] trimethylammonium iodide} (PMETAI), star- or raspberry-like particles form. Electron microscopy, electron tomography, and small-angle X-ray scattering show that the resulting silica particles have a complex structure, where a silsequioxane nanoparticle carrying the polymer arms is in the center. Next is a region that is polymer-rich. The outermost region of the particle is a silica layer, where the outer parts of the polymer arms are embedded. Time- resolved zeta-potential and pH measurements, dynamic light scattering, and electron microscopy reveal that silica formation proceeds differently if PDMAEMA is exchanged for PMETAI.
Using a regioselective strategy for nucleophilic aromatic substitution on polyfluoropyridines, a nonacoordinating precursor was designed that is adequately suited for complexation of lanthanide cations. Further functionalizations afforded numerous applications for near-IR emission, two-photon absorption spectroscopy, or the formation of luminescent gels.
The epoxy system containing diglycidyl ether of bisphenol A and 4,4'-diaminodiphenyl sulfone is modified with poly(acrylonitrile-butadiene-styrene) (ABS) to explore the effects of the ABS content on the phase morphology, mechanism of phase separation, and viscoelastic properties. The amount of ABS in the blends was 5, 10, 15, and 20 parts per hundred of epoxy resin (phr). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to investigate the final morphology of ABS-modified epoxy blends. Scanning electron microscopic studies of 15 phr ABS-modified epoxy blends reveal a bicontinuous structure in which both epoxy and ABS are continuous, with substructures of the ABS phase dispersed in the continuous epoxy phase and substructures of the epoxy phase dispersed in the continuous ABS phase. TEM micrographs of 15 phr ABS-modified epoxy blends confirm the results observed by SEM. TEM micrographs reveal the existence of nanosubstructures of ABS in 20 phr ABS-modified epoxy blends. To the best of our knowledge, to date, nanosubstructures have never been reported in any epoxy/thermoplastic blends. The influence of the concentration of the thermoplastic on the generated morphology as analyzed by SEM and TEM was explained in detail. The evolution and mechanism of phase separation was investigated in detail by optical microscopy (OM) and small-angle laser light scattering (SALLS). At concentrations lower than 10 phr the system phase separates through nucleation and growth (NG). However, at higher concentrations, 15 and 20 phr, the blends phase separate through both NG and spinodal decomposition mechanisms. On the basis of OM and SALLS, we conclude that the phenomenon of complex substructure formation in dynamic asymmetric blends is due to the combined effect of hydrodynamics and viscoelasticity. Additionally, dynamic mechanical analysis was carried out to evaluate the viscoelastic behavior of the cross-linked epoxy/ABS blends. Finally, apparent weight fractions of epoxy and ABS components in epoxy- and ABS-rich phases were evaluated from T-g analysis.
Simple tripeptides are scaffolds for the synthesis and further assembly of peptide/silver nanoparticle composites. Herein, we further explore peptide-con trolled silver nanoparticle assembly processes. Silver nanoparticles with a pH-responsive peptide coating have been synthesized by using a one-step precipitation/coating route. The nature of the peptide/silver interaction and the effect of the peptide oil the formation of the silver particles have been studied via UV/Vis, X-ray photoelectron, and surface-enhanced Raman spectroscopies as well as through electron microscopy, small angle X-ray scattering and powder Xray diffraction with Rietveld refinement. The particles reversibly form aggregates of different sizes in aqueous solution. The state of aggregation call be controlled by the solution pH value. At low pH values, individual particles are present. At neutral pH values, small clusters form and at high pH values, large precipitates are observed.
The BLUF (blue-light sensing using flavine) domain of the AppA photoreceptor protein from Rhodobacter sphaeroides was modelled by using quantum chemical chromophore plus amino acid models at the (TD-)B3LYP/6-31G* level of theory. The models were based on NMR structures, and further refined by CHARM force field molecular dynamics simulations. The goal is to explain the total redshift by about 10 nm in the UV/Vis spectra of BLUF domains after illumination, and to relate it to structural changes. For this purpose UV/Vis spectra of the available NMR structures were calculated and related to geometrical features. In particular, the hydrogen network embedding the central chromophore is discussed. Specifically, the position of a conserved glutamine, Q63, is found to be important in agreement with findings from previous works. Additionally, however, we find a systematic dependence also on the geometry of a conserved serine, S41. Based on a series of calculations with known structures and with artificial structural models, we argue that indeed the light-induced switching of both Q63 and S41 is necessary to explain the full similar to 10 nm redshift in the light (signalling) state of serine containing BLUF domains. Following or accompanying the double switching, two structurally highly important residues W104 and M106 exchange places, but do not affect the overall UV/ Vis properties of the chromophore.
Mesoporous silica monoliths were prepared by the sol - gel technique and. lled with 1-ethyl-3-methyl imidazolium [Emim]-X (X = dicyanamide [N(CN)(2)], ethyl sulfate [EtSO4], thiocyanate [SCN], and triflate [TfO]) ionic liquids (ILs) using a methanol-IL exchange technique. The structure and behavior of the ILs inside the silica monoliths were studied using X-ray scattering, nitrogen sorption, IR spectroscopy, solid-state NMR, and thermal analysis. DSC finds shifts in both the glass transition temperature and melting points (where applicable) of the ILs. Glass transition and melting occur well below room temperature. There is thus no conflict with the NMR and IR data, which show that the ILs are as mobile at room temperature as the bulk (not confined) ILs. The very narrow line widths of the NMR spectra suggest that the ILs in our materials have the highest mobility reported for confined ILs so far. As a result, our data suggest that it is possible to generate IL/silica hybrid materials (ionogels) with bulk-like properties of the IL. This could be interesting for applications in, e.g., the solar cell or membrane fields.
Films of anthracene carboxylic acids were irradiated through photomasks and oxidized at the exposed regions by singlet oxygen upon sensitization. The efficiency of a photomask to protect the material underneath was investigated by optical and infrared spectroscopy. As the thickness of the film is reduced, the efficiency of the mask drops. This is explained by the migration of singlet oxygen at the solid-air interface, which in turn reacts at the masked area. For films with a thickness of < 15 nm, the efficiency of the mask approaches zero: sufficient efficiency is achieved at thicknesses > 100 nm. From the investigations, it will become clear that the contrast between the irradiated and masked area of an image is affected by reduction of the film thickness. On the other hand, the resolution of an image, which relates to the minimum feature size of an image, is not dependent on the thickness of the film. The contributions of "inside" and "outside" reactions are examined separately, and it quantitative approximation of the spatial range of both modes of the oxygenation is given. We set tip an approximate relation between mask efficiency and experimental conditions comprising internal and external oxygen diffusion, film thickness, and mask dimensions. These results give it deeper insight into the limits of resolution and contrast in singlet oxygen lithography.
Phosphorus meets carbohydrates: Dimethyl phosphite reacts with ceric(IV) ammonium nitrate (CAN) to give phosphonyl radicals that add to glycals 1. The derivatives 2 were isolated in high yields and during a subsequent Horner-Emmons reaction underwent an interesting elimination to give 3,6-dihydro-2H-pyrans 3. The short sequence with simple precursors is applicable to the transformation of hexoses, pentoses, and disaccharides. Bn=benzyl.
Quantum chemical calculations of various azobenzene (AB) derivatives have been carried out with the goal to describe the energetics and kinetics of their thermal cis -> trans isomerization. The effects of substituents, in particular their type, number, and positioning, on activation energies have been systematically studied with the ultimate goal to tailor the switching process. Trends observed for mono- and disubstituted species are discussed. A polarizable continuum model is used to study, in an approximate fashion, the cis -> trans isomerization of azobenzenes in solution. The nature of the transition state(s) and its dependence on substituents and the environment is discussed. In particular for push-pull azobenzenes, the reaction mechanism is found to change from inversion in nonpolar solvents to rotation in polar solvents. Concerning kinetics, calculations based on the Eyring transition state theory give usually reliable activation energies and enthalpies when compared to experimentally determined values. Also, trends in the resulting rate constants are correct. Other computed properties such as activation entropies and thus preexponential rate factors are in only moderate agreement with experiment.
Di-nor-benzofuran neolignan aldehydes, Delta(7)-3,4-methylenedioxy-3'-methoxy-8',9'-dinor- 4',7-epoxy-8,3'-neolignan-7'-aldehyde (ocophyllal A) 1, Delta(7)-3,4,5,3'-tetramethoxy- 8',9'-dinor-4',7-epoxy-8,3'-neolignan-7'-aldehyde (ocophyllal B) 2, and macrophyllin-type bicyclo[3.2.1]octanoid neolignans (7R, 8R, 3'S, 4'S, 5'R)-Delta(8)'-4'-hydroxy-5'- methoxy-3,4-methylenedioxy-2',3'.4',5'-tetrahydro-2'-oxo-7.3',8.5'-neolignan (ocophyllol A) 3, (7R, 8R, 3'S, 4'S, 5'R)-Delta 8'-4'-hydroxy-3,4,5'-trimethoxy- 2',3',4',5'-tetrahydro-2'-oxo-7.3',8.5'-neolignan (ocophyllol B) 4, (7R, 8R, 3'S, 4'S, 5'R)-Delta(8)'-4'-hydroxy-3,4,5,5'-tetramethoxy- 2',3',4',5'-tetrahydro-2'-oxo-7.3',8.5'-neolignan (ocophyllol C) 5, as well as 2'-epi-guianin 6 and (+)-licarin B 7, were isolated and characterized from leaves of Ocotea macrophylla (Lauraceae). The structures and configuration of these compounds were determined by extensive spectroscopic analyses. Inhibition of platelet activating factor (PAF)-induced aggregation of rabbit platelets were tested with neolignans 1-7. Although compound 6 was the most potent PAF-antagonist, compounds 3-5 showed some activity.