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81.
[reaction: see text] The enzymatic degradation of starch can be monitored electronically using single-walled carbon nanotubes (SWNTs) as semiconducting probes in field-effect transistors (FETs). Incubation of these devices in aqueous buffer solutions of amyloglucosidase (AMG) results in the removal of the starch from both the silicon surfaces and the side walls of the SWNTs in the FETs, as evidenced by direct imaging and electronic measurements. 相似文献
82.
A simple and effective method of measuring diffusion rates of various acylating reagents in macro beads (in this work diameters greater than 570 microm) of amino-functionalized resins is presented. The extent of diffusion at various points of time was determined by treating beads with a staining reagent ("chloranil", 2,3,5,6-tetrachloro-1,4-benzoquinone) that colored the regions of the beads that had not yet been permeated by reagent (the central part of the beads). The volume of unstained resin (permeated part) was compared with the volume of the stained part, and diffusion rate constants were calculated. Factors influencing diffusion such as reagent concentration, solvent, temperature, resin type, and mechanical effects were investigated. The results showed that diffusion was promoted by increased temperature, good swelling of the resin, small reagents, and high concentrations but not by sonication or mechanical agitation. 相似文献
83.
Wang Q Zakeeruddin SM Cremer J Bäuerle P Humphry-Baker R Grätzel M 《Journal of the American Chemical Society》2005,127(15):5706-5713
We report on cross surface ambipolar charge percolation within a monolayer of a molecular triad adsorbed on semiconducting or insulating mesoscopic metal oxide films. The triad consists of a triphenlyamine (TPA) donor and a perylenemonoimide (PMI) acceptor connected by a bithiophene (T2) bridge. The self-assembled PMI-T2-TPA monolayer exhibits p-type or n-type conduction depending on the potential that is applied to the conducting glass (FTO) electrode supporting the oxide films. Cross surface electron transfer is turned on at around -1.24 V (vs Fc+/Fc) where the PMI moiety is electroactive. The color of the film changes from red to blue during the reduction of the PMI. By contrast, lateral hole transfer is turned on at around 0.8 V (vs Fc+/Fc) where the TPA moiety becomes electroactive. The stepwise oxidation of the T2-TPA units at 0.79 and 1.28 V (vs Fc+/Fc) is associated with a color change of the film from red to black. Cyclic voltammetric as well as chronocoulometric and spectroelectrochemical measurements were applied to determine the percolation threshold for cross surface charge transfer and the diffusion coefficients for the electron and hole hopping process. The effect of oxide surface states on the lateral charge motion was also investigated. 相似文献
84.
Miranda LP Lubell WD Halkes KM Groth T Grøtli M Rademann J Gotfredsen CH Meldal M 《Journal of combinatorial chemistry》2002,4(5):523-529
A novel polymer matrix for solid-phase synthesis, SPOCC(194) resin (1), was designed featuring a backbone of homogeneous tetraethylene glycol (TEG(194)) macromonomer linked by quaternary carbon junctions and terminating in primary alcohol functionality. Beaded SPOCC(194) resin was effectively prepared by suspension polymerization of oxetanylated TEG macromonomer 5 in stirred silicon oil. Mechanically stable and inert to a diverse range of reaction conditions, SPOCC(194) possessed a high hydroxyl group loading (0.9-1.2 mmol/g) for substrate attachment and swelled effectively ( approximately 2-4 mL/g) in a variety of organic and aqueous solvents. Developed for solid-phase synthesis at high reactant concentrations for driving organic and aqueous reactions to completion, SPOCC(194) exhibited high functional group density (mmol/mL) similar to that of low-loaded aminomethylated polystyrene-divinylbenzene copolymer (PS-1%DVB) yet significantly higher than that of PEGA(1900), SPOCC(1500), and TentaGel S. High-resolution MAS NMR spectra of Fmoc-derivatized SPOCC(194) indicate that monitoring of functional group transformation is possible. Moreover, by employment of a nonaromatic resin-linker combination, electrophilic chemistry, such as Lewis acid catalyzed glycosylation and Friedel-Crafts acylation, was selectively performed on substrate bound to SPOCC(194) resin. Such properties make SPOCC(194) resin a promising new polymer matrix for the support-bound construction of small organic molecules by parallel and combinatorial synthesis and the scavenging of solution-phase reactants or byproducts. 相似文献
85.
Cataldo L Dutan C Misra SK Loss S Grützmacher H Geoffroy M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(11):3463-3468
The EPR spectrum of the novel radical Mes*(CH3)P--PMes* (Mes*=2,4,6-(tBu)3C6H2) was measured in the temperature range 100-300 K, and was found to be drastically temperature dependent as a result of the large anisotropy of the 31P hyperfine tensors. Below 180 K, a spectrum of the liquid solution is accurately simulated by calculating the spectral modifications due to slow tumbling of the radical. To achieve this simulation, an algorithm was developed by extending the well-known nitroxide slow-motion simulation technique for the coupling of one electron spin to two nuclear spins. An additional dynamic process responsible for the observed line broadening was found to occur between 180 K and room temperature; this broadening is consistent with an exchange between two conformations. The differences between the isotropic 31P couplings associated with the two conformers are shown to be probably due to an internal rotation about the P--P bond. 相似文献
86.
Let H={a
0, a
1, a
2, b
0, b
1, b
2} be the poset defined by a
0<a
2<a
1, b
0<b
2<b
1, a
0<b
1, and b
0<a
1. For an infinite regular cardinal
, we describe the free
-lattice on H. This continues the work of I. Rival and R. Wille who accomplished the same for
=. In subsequent papers, we show how to apply this result to describe the free
-lattice on a poset for a large class of posets, called slender posets. 相似文献
87.
Pter Molnr Jzsef Deli Zoltn Matus Gyula Tth Andrea Steck Hanspeter Pfander 《Helvetica chimica acta》1997,80(1):221-229
β-Cryptoxanthin ( 1 ) was acetylated and then epoxidized with monoperoxyphthalic acid. After hydrolysis, repeated chromatography, and crystallization, (3S,5R,6S)-5,6-epoxy-β-cryptoxanthin ( 3 ), (3S,5S,6R)-5,6-epoxy-β-cryptoxanthin ( 4 ), (3R,5′R,6′R)-5′,6′-epoxy-β-cryptoxanthin ( 5 ), (3S,5R,6S,5′R,6′S)-5,6:5′,6′-diepoxy-β-cryp-toxanthin ( 6 ), and (3S,5S,6R,5′S,6′R)-5,6:5′,6′-diepoxy-β-cryptoxanthin ( 7 ) were isolated as main products and characterized by their UV/VIS, CD, 1H- and 13C-NMR, and mass spectra. The comparison of the carotenoid isolated from yellow, tomato-shaped paprika (Capsicum annuum var. lycopersiciforme flavum) with 3–5 strongly supports the structure of 3 for the natural product. 相似文献
88.
Electrochemical impedance spectroscopy (EIS) has been performed to investigate electronic and ionic processes in dye-sensitized solar cells (DSC). A theoretical model has been elaborated, to interpret the frequency response of the device. The high-frequency feature is attributed to the charge transfer at the counter electrode while the response in the intermediate-frequency region is associated with the electron transport in the mesoscopic TiO2 film and the back reaction at the TiO2/electrolyte interface. The low-frequency region reflects the diffusion in the electrolyte. Using an appropriate equivalent circuit, the electron transport rate and electron lifetime in the mesoscopic film have been derived, which agree with the values derived from transient photocurrent and photovoltage measurements. The EIS measurements show that DSC performance variations under prolonged thermal aging result mainly from the decrease in the lifetime of the conduction band electron in the TiO2 film. 相似文献
89.
For the first time, the nuclear magnetic resonance (NMR) spin-spin coupling mechanism is decomposed into one-electron and electron-electron interaction contributions to demonstrate that spin-information transport between different orbitals is not exclusively an electron-exchange phenomenon. This is done using coupled perturbed density-functional theory in conjunction with the recently developed J-OC-PSP [=J-OC-OC-PSP: Decomposition of J into orbital contributions using orbital currents and partial spin polarization)] method. One-orbital contributions comprise Ramsey response and self-exchange effects and the two-orbital contributions describe first-order delocalization and steric exchange. The two-orbital effects can be characterized as external orbital, echo, and spin transport contributions. A relationship of these electronic effects to zeroth-order orbital theory is demonstrated and their sign and magnitude predicted using simple models and graphical representations of first order orbitals. In the case of methane the two NMR spin-spin coupling constants result from totally different Fermi contact coupling mechanisms. (1)J(C,H) is the result of the Ramsey response and the self-exchange of the bond orbital diminished by external first-order delocalization external one-orbital effects whereas (2)J(H,H) spin-spin coupling is almost exclusively mitigated by a two-orbital steric exchange effect. From this analysis, a series of prediction can be made how geometrical deformations, electron lone pairs, and substituent effects lead to a change in the values of (1)J(C,H) and (2)J(H,H), respectively, for hydrocarbons. 相似文献
90.
The macrodiolide antibiotic elaiophylin (1) forms stable, long-lasting cation selective ion channels in planar lipid bilayer membranes prepared from soybean phosphatidylcholine. Current of the single ion channel displayed two sublevels corresponding to the two substates of the channel conductance: a slow substate, with about 5 s of mean dwell time in the open state at 40% level of the total amplitude conductance, and a fast substate of higher conductance with dwell times in the open and closed state of about 0.1 s. Amplitude conductances of the single ion channels in 200 mM of LiCl, NaCl, KCl, RbCl and CsCl were 75, 140, 220, 240 and 226 pS, and the conductance was linear function of the electrolyte concentration. Ratios of cation to anion permeabilities of the channel for NaCl and KCl were 8+/-2 and >24, respectively. A molecular model of the channel structure is suggested. 相似文献