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991.
We have developed an electrophoretic cell suitable for single-molecule electrophoresis. The setup works for fluorescently labeled macromolecules by direct recording of their motion under an external electric field. The electrophoretic mobility of rodlike, polydisperse actin filaments (F-actin) were measured, as well as its dependence on the orientation of the filaments. A dipping effect is observed and quantitatively accounted for by the difference in hydrodynamic drag between motions along and perpendicular to the long axis of a filament. When averaged over all orientations, the mobility of F-actin in 50 mM KCl and 2 mM MgCl(2) is determined to be -(8.5+/-0.7) x 10(-5) cm(2)(V s). This method is also used to compare the mobility of F-actin and fd virus in a mixture of them. A reliable ratio of 1.26 is measured for fd virus to F-actin. The influence of the orientation dependent drag on electrophoretic mobility is discussed and a strategy for reliable measurement is proposed. 相似文献
992.
Dunn AR Dmochowski IJ Winkler JR Gray HB 《Journal of the American Chemical Society》2003,125(41):12450-12456
We report the synthesis and characterization of Ru-diimine complexes designed to bind to cytochrome p450cam (CYP101). The sensitizer core has the structure [Ru(L(2))L'](2+), where L' is a perfluorinated biphenyl bridge (F(8)bp) connecting 4,4'-dimethylbipyridine to an enzyme substrate (adamantane, F(8)bp-Ad), a heme ligand (imidazole, F(8)bp-Im), or F (F(9)bp). The electron-transfer (ET) driving force (-deltaG degrees ) is varied by replacing the ancillary 2,2'-bipyridine ligands with 4,4',5,5'-tetramethylbipyridine (tmRu). The four complexes all bind p450cam tightly: Ru-F(8)bp-Ad (1, K(d) = 0.077 microM); Ru-F(8)bp-Im (2, K(d) = 3.7 microM); tmRu-F(9)bp (3, K(d) = 2.1 microM); and tmRu-F(8)bp-Im (4, K(d) = 0.48 microM). Binding is predominantly driven by hydrophobic interactions between the Ru-diimine wires and the substrate access channel. With Ru-F(8)bp wires, redox reactions can be triggered on the nanosecond time scale. Ru-wire 2, which ligates the heme iron, shows a small amount of transient heme photoreduction (ca. 30%), whereas the transient photoreduction yield for 4 is 76%. Forward ET with 4 occurs in roughly 40 ns (k(f) = 2.8 x 10(7) s(-)(1)), and back ET (Fe(II) --> Ru(III), k(b) approximately 1.7 x 10(8) s(-)(1)) is near the coupling-limited rate (k(max)). Direct photoreduction was not observed for 1 or 3. The large variation in ET rates among the Ru-diimine:p450 conjugates strongly supports a through-bond model of Ru-heme electronic coupling. 相似文献
993.
Hess CR Juda GA Dooley DM Amii RN Hill MG Winkler JR Gray HB 《Journal of the American Chemical Society》2003,125(24):7156-7157
Diethylaniline-terminated oligo(phenyl-ethynyl)-thiol (DEA-OPE-SH) wires on Au-bead electrodes facilitate electron tunneling to and from the deeply buried topaquinone (TPQ) cofactor in Arthrobacter globiformis amine oxidase (AGAO). Reversible cyclic voltammograms were observed when AGAO was adsorbed onto this DEA-OPE-SAu surface: the 2e-/2H+ reduction potential is -140 mV versus SCE. 相似文献
994.
The monovalent cations of Na(+), K(+), Rb(+), and Cs(+) derived from the highly electropositive alkali metals represent prototypical charged spheres that are mainly subject to relatively simple electrostatic and solvation (hydration) forces. We now find that the largest of these Rb(+) and Cs(+) are involved in rather strong cation...pi(arene) interactions when they are suitably disposed with the ambifunctional hexasubstituted benzene C(6)E(6). The ether tentacles (E = methoxymethyl) allow these cations to effect eta(1)-bonding to the benzene center in a manner strongly reminiscent of the classical sigma-arene complexes with positively charged electrophiles where Z(+) = CH(3)(+), Br(+), Cl(+), Et(3)Si(+), etc. The somewhat smaller potassium cation is involved in a similar M(+)...pi(arene) interaction that leads to eta(2)-bonding with the aromatic center in the pi-mode previously defined in the well-known series of silver(I)/arene complexes. We can find no evidence for significant Na(+)... pi(arene) interaction under essentially the same conditions. As such, the sigma-structure of the Rb(+) and Cs(+) complexes and pi-structure of the K(+) complex are completely integrated into the continuum of sigma-pi bondings of various types of electrophilic (cationic) acceptors with arene donors that were initially identified by Mulliken as charge-transfer. 相似文献
995.
The preparation of a novel series of N-aryl CBI derivatives is detailed in which an aryl para substituent could be used to predictably modulate the reactivity of the resulting CC-1065/duocarmycin alkylation subunit analogue (rho = 0.17). The derivatives were found to be exceptionally stable and to exhibit a well-defined relationship between reactivity and cytotoxic potency. When combined with the results of an extensive series of N-acyl CBI analogues and derivatives assembled over the past 15 years, the studies define a fundamental parabolic relationship between reactivity and cytotoxic potency. 相似文献
996.
Amit Kumar Jay B. Cameron Peter C. Flynn 《Applied biochemistry and biotechnology》2004,113(1-3):27-39
The cost of transporting wood chips by truck and by pipeline as a water slurry was determined. In a practical application
of field delivery by truck of biomass to a pipeline inlet, the pipeline will only be economical at large capacity (>0.5 million
dry t/yr for a one-way pipeline, and >1.25 million dry t/yr for a two-way pipeline that returns the carrier fluid to the pipeline
inlet), and at medium to long distances (>75 km [one-way] and >470 km [two-way] at a capacity of 2 million dry t/yr). Mixed
hardwood and softwood chips in western Canada rise in moisture level from about 50% to 67% when transported in water; the
loss in lower heating value (LHV) would preclude the use of water slurry pipelines for direct combustion applications. The
same chips, when transported in a heavy gas oil, take up as much as 50% oil by weight and result in a fuel that is >30% oil
on mass basis and is about two-thirds oil on a thermal basis. Uptake of water by straw during slurry transport is so extreme
that it has effectively no LHV. Pipeline-delivered biomass could be used in processes that do not produce contained water
as a vapor, such as supercritical water gasification. 相似文献
997.
A combined experimental and theoretical approach has been used to probe the radiolytic decomposition of liquid pyridine. The major single condensed phase product in the gamma-radiolysis of pyridine is dipyridyl with a yield of 1.25 molecules/100 eV total energy absorbed. Scavenging studies suggest that most, if not all, dipyridyl has a radical precursor, but only about 10% of that is due to the pyridyl radical. The remainder of the dipyridyl may be due to reaction of the parent radical cation with pyridine. Iodine scavenging and quantum chemical calculations both show that the ortho-pyridyl radical (2-pyridyl) is far more stable than the other two isomers. 相似文献
998.
Alkyl, aryl, and alkynyl as well as heteroatom derivatives of sym-pentasubstituted corannulenes have been synthesized from sym-pentachlorocorannulene. These units form potential building blocks for future work on superstructures based on corannulene. Absorption/emission properties follow expected trends from the parent 1. sym-Pentasubstitution gives rise to variations in the chemical dynamics of bowl inversion. van der Waals attraction is cited to explain an anomalously high barrier to bowl inversion in 10. 相似文献
999.
Jay A. Labinger 《Journal of organometallic chemistry》1977,136(2):c31-c36
The course of the reaction of (η5-C5H5)Fe(CO)2(η1-C5H5) with phosphorus donor ligands depends strongly on the nature of the ligand; products derived from an Arbuzov-like rearrangement or from reduction have been found as well as the expected simple substitution product. The dynamic PMR behavior of (η5-C5H5)Fe(CO) (P(OPh)3) (η1-C5H5) has been examined. 相似文献
1000.
Polysiloxane acts as a modular scaffold for macromolecular reagent development. Two separate components were covalently integrated into one material, one constituent provided reagent functionality, the other modulated solubility. In particular cinchona alkaloid based ligands used in the osmium tetroxide catalyzed asymmetric dihydroxylation (AD) reaction were covalently attached to commercially available polysiloxane. To enhance the reactivity of these polymeric ligands, multifunctional reagents were designed to include both the cinchona alkaloid and an alkoxyethylester solubilizing moiety providing random co-polymers. While the mono-functional materials led to heterogeneous conditions, the bi-functional polymers resulted in homogeneous reaction mixtures. Although both reagent types provided diol products with excellent yield and selectivity (>99% ee in nearly quantitative yield) the homogeneous analog has nearly twice the reactivity. Every repeat unit in the heterogeneous material was functionalized along the polysiloxane backbone while approximately half of these sites contained ligand in the homogeneous version. This approach led to macromolecular catalysts with high loadings of ligand and therefore materials with very low equivalent weights. Although these polymers are highly loaded they do maintain reactivity on a par with their free ligand counterpart. Using straightforward purification techniques (i.e. precipitation, simple filtration, or ultrafiltration) these polymeric ligands were easily separated from diol product and reused multiple times. Polysiloxane is a viable support for the catalysis of AD reactions and may provide a generally useful backbone for other catalytic systems. 相似文献