Adsorption of a tripeptide on platinum electrodes: II. Kinetics and isotherms

Changes in the capacitance of a platinum electrode due to adsorption of the tripeptide Bz-Phe-Val-Arg-pNA have been measured and analyzed. The experimental isotherm can be described with a Langmuir isotherm if changes in molecular conformation are taken into account. The desorption and adsorption kinetics both exhibit two time constants which are proposed to reflect that the molecules are adsorbed in at least two different conformations. Measurements of the initial rate of adsorption are consistent with the isotherm and the desorption kinetics. The difference between the electrically determined isotherm and one determined by ellipsometry is also explained by a change in conformation of the molecules on the surface.     

Scandium: Thermodynamic properties,chemical equilibria,and standard potentials

We have gathered, critically evaluated, calculated, and tabulated thermodynamic properties and related equilibrium constants and standard potentials for compounds and aqueous species of scandium. We have been explicit about sources of data so that interested readers can check the steps leading to tabulated thermodynamic quantities and thus form their own opinions about reliability and accuracy.     

Hydrogen induced interfacial polarization at PdSiO2 interfaces

Internal photoemission experiments were performed to study the polarization layer induced by hydrogen at PdSiO₂ interfaces. It was found that this polarization layer behaves like a true dipole layer where one monolayer of hydrogen atoms at the interface corresponds to a barrier lowering of 0.5 eV in accordance with earlier measurements on threshold voltage shifts of Pd-SiO₂ -Si field effect transistors. Furthermore experiments on AlSiO₂ structures indicate that the catalytic dissociation of H₂ on metals like Pd and Pt is necessary for the introduction of a hydrogen polarization layer at a metal-SiO₂ interface.     

Further evidence for reflection asymmetry in the Ra region — The decoupling parameter and the magnetic moment

Decoupling parameters and magnetic moments are calculated for octupole deformed shapes in the strong coupling approximation. Comparisons to experimental values give strong evidence for stable octupole deformation in ²²⁷Ra and especially ²²⁵Ra.     

Anatomy of glycosynthesis: structure and kinetics of the Humicola insolens Cel7B E197A and E197S glycosynthase mutants

The formation of glycoconjugates and oligosaccharides remains one of the most challenging chemical syntheses. Chemo-enzymatic routes using retaining glycosidases have been successfully harnessed but require tight kinetic or thermodynamic control. "Glycosynthases," specifically engineered glycosidases that catalyze the formation of glycosidic bonds from glycosyl donor and acceptor alcohol, are an emerging range of synthetic tools in which catalytic nucleophile mutants are harnessed together with glycosyl fluoride donors to generate powerful and versatile catalysts. Here we present the structural and kinetic dissection of the Humicola insolens Cel7B glycosynthases in which the nucleophile of the wild-type enzyme is mutated to alanine and serine (E197A and E197S). 3-D structures reveal the acceptor and donor subsites and the basis for substrate inhibition. Kinetic analysis shows that the E197S mutant is considerably more active than the corresponding alanine mutant due to a 40-fold increase in k(cat).     

A novel fragmentation of trimethylsilyl ethers of 3β-hydroxy-Δ5-steroids

An ion formed by loss of 56 mass units from the molecular ion is often seen in mass spectra of trimethylsilyl ethers of C₁₉ and C₂₁ steroids having a 3β-hydroxy-Δ⁵ structure and an oxo group at C-17 or C-20. The nature of this fragment was investigated by the use of perdeuteriotrimethylsilyl ether derivatives and of [4-¹⁴C], [3-¹⁸O], [4,4-²H₂] and [2,2,4,4-²H] labelled derivatives of 3β-hydroxy-5-androsten-17-one and 3β-hydroxy-5-pregnen-20-one. Evidence is presented to show that the neutral fragment of mass 56 is composed of carbon atoms 1, 2 and 3, the oxygen at C-3 and four hydrogen atoms. During the fragmentation process, the trimethylsilyl group and one of the hydrogens at C-2 are transferred to the fragment that carries the charge.     

Argon ion laser-induced BaS BΣ-AΣ, A′Π, aΠ, and XΣ fluorescence spectra: Analysis of A A′, A a, and A′ a perturbations

The 333.6-, 351.1-, and 363.8-nm lines of a cw argon ion laser are found to coincide with the BaS B¹Σ⁺-X¹Σ⁺ (12, 0) R(17), (6, 0) P(35), and (3, 0) R(125) transitions, respectively. Fluorescence transitions from the laser-prepared upper levels terminating in X¹Σ⁺ V = 0–28, A¹Σ⁺ V = 1–3, A′¹Π V = 1–13, and a³Π₁ V = 3–12 are assigned. These results are combined with a previous analysis of the extensively perturbed BaS A¹Σ⁺-X¹Σ⁺ system [R. F. Barrow, W. G. Burton, and P. A. Jones, Trans. Farad. Soc.67, 902–906 (1971)]. Every observed perturbation of the BaS A¹Σ⁺ state is electronically and vibrationally assigned. The levels a³Π₀ V = 10–13, a³Π₁ V = 12–14, a³Π₂ V = 15, and A′¹Π V = 10–13 are sampled via their perturbations of A¹Σ⁺ V = 0–2. Although the mutual interactions of the a³Π, A′¹Π, and A¹Σ⁺ states approach Hund's case (c) limit, a complete deperturbation is performed from a case (a) starting point. Of the five lowest energy electronic states of BaS, only b³Σ⁺ remains uncharacterized. Principal deperturbed molecular constants are (in cm⁻¹, 1σ uncertainties in parentheses):

Full-size image

     

Argon ion laser-induced BaS B1Σ+-A1Σ+, A′1Π, a3Π, and X1Σ+ fluorescence spectra: Analysis of A ∼ A′, A ∼ a,and A′ ∼ a perturbations

The 333.6-, 351.1-, and 363.8-nm lines of a cw argon ion laser are found to coincide with the BaS B¹Σ⁺-X¹Σ⁺ (12, 0) R(17), (6, 0) P(35), and (3, 0) R(125) transitions, respectively. Fluorescence transitions from the laser-prepared upper levels terminating in X¹Σ⁺v = 0–28, A¹Σ⁺v = 1–3, A′¹Π v = 1–13, and a³Π₁v = 3–12 are assigned. These results are combined with a previous analysis of the extensively perturbed BaS A¹Σ⁺-X¹Σ⁺ system [R. F. Barrow, W. G. Burton, and P. A. Jones, Trans. Farad. Soc.67, 902–906 (1971)]. Every observed perturbation of the BaS A¹Σ⁺ state is electronically and vibrationally assigned. The levels a³Π₀v = 10–13, a³Π₁v = 12–14, a³Π₂v = 15, and A′¹Π v = 10–13 are sampled via their perturbations of A¹Σ⁺v = 0–2. Although the mutual interactions of the a³Π, A′¹Π, and A¹Σ⁺ states approach Hund's case (c) limit, a complete deperturbation is performed from a case (a) starting point. Of the five lowest energy electronic states of BaS, only b³Σ⁺ remains uncharacterized. Principal deperturbed molecular constants are (in cm^?1, 1σ uncertainties in parentheses):

     

99.

In memoriam     

Ingemar Wadsö  Giovanni Rialdi 《Journal of Thermal Analysis and Calorimetry》2007,90(3):959-959

     

100.

Aggregation-induced folding of a de novo designed polypeptide immobilized on gold nanoparticles     

Aili D  Enander K  Rydberg J  Lundström I  Baltzer L  Liedberg B 《Journal of the American Chemical Society》2006,128(7):2194-2195

This communication reports the first steps in the construction of a novel, nanoparticle-based hybrid material for biomimetic and biosensor applications. Gold nanoparticles were modified with synthetic polypeptides to enable control of the particle aggregation state in a switchable manner, and particle aggregation was, in turn, found to induce folding of the immobilized peptides.     

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	$\text{T}{}_{\mathrm{e}}$	$\text{ω}{}_{\mathrm{e}}$	$\text{ω}{}_{\mathrm{e}}\text{x}{}_{\mathrm{e}}$	$\text{B}{}_{\mathrm{e}}\text{× 10}{}^2$	$\text{α}{}_{\mathrm{e}}\text{× 10}{}^4$	$\text{R}{}_{\mathrm{e}}\text{(}\text{A}\text{?}\text{)}$
$\text{A}{}^1\text{Σ}{}^{\mathrm{+}}$	14 498.6(1)	287.7(1)	1.15(5)	9.365(5)	5.0(10)	2.633
$\text{A′}{}^1\text{Π}$	12 095(6)	258.9(5)	0.7	8.21(5)	3.6(5)	2.813
$\text{a}{}^3\text{Π}{}_{\mathrm{i}}$	11 835(6)	259.6(5)	0.7	8.21	3.6	2.813
$\text{X}{}^1\text{Σ}{}^{\mathrm{+}}$	0	379.50(4)	0.91(1)	10.334(1)	3.4(2)	2.507

Aggregation-induced folding of a de novo designed polypeptide immobilized on gold nanoparticles

This communication reports the first steps in the construction of a novel, nanoparticle-based hybrid material for biomimetic and biosensor applications. Gold nanoparticles were modified with synthetic polypeptides to enable control of the particle aggregation state in a switchable manner, and particle aggregation was, in turn, found to induce folding of the immobilized peptides.