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71.
Boev VI Pérez-Juste J Pastoriza-Santos I Silva CJ Gomes Mde J Liz-Marzán LM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(23):10268-10272
Hybrid organic-inorganic nanocomposites containing uniform distributions of metal nanoparticles have been prepared by mixing a preformed nanoparticle colloid with the precursors of a ureasil, prior to the sol-gel transition. These nanocomposites possess not only high optical quality and optical features dictated by the size and shape of the nanoparticle dopants but also a high degree of flexibility, which can largely enhance the range of applications in practical devices. The deposition of a uniform silica shell on the nanoparticle surface prior to the sol-gel transition was found to be required to maintain the colloidal stability during the process and, thus, to retain the optical properties in the final nanocomposite material. This method can be readily extended to other materials, such as semiconductor and magnetic nanoparticles. 相似文献
72.
The polarization of interdigitated gold electrodes mounted over a silica thin film formed by oxidation of a Si wafer produces reproducible electrostatic patterns with overall excess negative charge, as observed by scanning electric potential microscopy. Domain charge concentrations as high as 76 charge units per square micrometer are obtained when a 5 V difference is applied to the electrodes thus producing fields in the 10(6) V m(-1) range. These patterns vanish when the electrodes are short-circuited and grounded. Characteristic times for pattern formation and relaxation are in the order of 10 min. The results are consistent with a model based on the discharge of H(+) ions at the negative electrodes, leaving behind immobile surface-bound SiO(-) groups and thus showing that chemisorption phenomena are decisive for electrostatic charging of insulators. 相似文献
73.
A variational method called discrete variable representation is applied to study the energy spectra of two interacting electrons in a quantum dot with a three-dimensional anisotropic harmonic confinement potential. This method, applied originally to problems in molecular physics and theoretical chemistry, is here used to solve the eigenvalue equation to relative motion between the electrons. The two-electron quantum dot spectrum is determined then with a precision of at least six digits. Moreover, the electron correlation energies for various potential confinement parameters are investigated for singlet and triplet states. When possible, the present results are compared with the available theoretical values. 相似文献
74.
VISIBLE CHEMILUMINESCENCE ASSOCIATED WITH THE REACTION BETWEEN METHEMOGLOBIN OR OXYHEMOGLOBIN WITH HYDROGEN PEROXIDE 总被引:1,自引:0,他引:1
Eduardo A. Lissi Jorge Escobar Carlos Pascual Maria del Castillo Tais H. Schmitt Paolo Di Mascio 《Photochemistry and photobiology》1994,60(5):405-411
Abstract Visible chemiluminescence is emitted in the irreversible deactivation of hemoglobin or methemoglobin with excess H2 O2 . The emission takes place in two phases. The most intense one lasts a few seconds and is followed by a second phase of lower intensity that remains for longer periods. This second phase presents chaotic or sustained oscillations. Free radicals are implicated in the luminescent process since the emission can be reduced by free radical scavengers such as 6-hydroxy-2,5,7,8,-tetramethylchroman-2-carboxylic acid (Trolox) or ascorbic acid. These additives lead to a delay in reaching the maximum intensity, which can be related to their consumption, implying substantial recycling of the hemoprotein. Chemiluminescence is also observed in the oxidation of hemin by H2 O2 , suggesting a role for the heme group in the processes leading to the excited state production. The lower intensity observed in the presence of hemin can be related to the contribution of the globin chains. 相似文献
75.
Vanommeslaeghe K Van Alsenoy C De Proft F Martins JC Tourwé D Geerlings P 《Organic & biomolecular chemistry》2003,1(16):2951-2957
Histone deacetylase (HDAC) inhibitors have recently attracted considerable interest because of their therapeutic potential for the treatment of cell proliferative diseases. An X-ray structure of a very potent inhibitor, Trichostatin A (TSA), bound to HDLP (an HDAC analogue isolated from Aquifex aeolicus), is available. From this structure, an active site model (322 atoms), relevant for the binding of TSA and structural analogues, has been derived, and TSA has been minimized in this active site at HF 3-21G* level. The resulting conformation is in excellent accordance with the X-ray structure, and indicates a deprotonation of the hydroxamic acid in TSA by His 131. Also, a water molecule was minimized in the active site. In addition to a similar deprotonation, in accordance with a possible catalytic mechanism of HDAC as proposed by Finnin et al. (M. S. Finnin, J. R. Donigian, A. Cohen, V. M. Richon, R. A. Rifkind and P. A. Marks, Nature, 1999, 401, 188-193), a displacement of the resulting OH- ion in the active site was observed. Based on these results, the difference in energy of binding between TSA and water was calculated. The resulting value is realistic in respect to experimental binding affinities. Furthermore, the mechanism of action of the His 131-Asp 166 charge relay system was investigated. Although the Asp residue in this motif is known to substantially increase the basicity of the His residue, no proton transfer from His 131 to Asp 166 was observed on binding of TSA or water. However, in the empty protonated active site, this proton transfer does occur. 相似文献
76.
Wedin P Martinez CJ Lewis JA Daicic J Bergström L 《Journal of colloid and interface science》2004,272(1):1-9
Stress development during drying of coatings produced from aqueous dispersions of calcium carbonate particles in the presence and absence of organic binders was studied using a controlled-environment stress apparatus that simultaneously monitored drying stress, weight loss, and relative humidity. Specifically, the influence of two organic binders on drying stress evolution was investigated: (1) carboxymethylcellulose, a water-soluble viscosifying aid, and (2) a styrene-butadiene latex emulsion of varying glass transition temperature. The stress histories exhibited three distinct regions. First, a period of stress rise was observed, which reflected the capillary tension exerted by the liquid on the particle network. Second, a maximum stress was observed. Third, it was followed by a period of either stress decay or rise depending on the organic species present. Significant differences in stress histories were observed between coatings containing soluble and nonsoluble binders. Maximum drying stresses (sigmamax) of 0.2-0.5 MPa were observed for coatings produced from pure calcium carbonate or calcium carbonate-latex suspensions, whereas coatings with carboxymethylcellulose exhibited substantially higher sigmamax values of 1-2 MPa. Upon drying, these coatings were quite hygroscopic, such that cyclic variations in relative humidity induced large cyclic changes in residual stress. 相似文献
77.
Rauter AP Martins A Borges C Ferreira J Jorge J Bronze MR Coelho AV Choi YH Verpoorte R 《Journal of chromatography. A》2005,1089(1-2):59-64
The anti-hyperglycemic flavonoid extract obtained from Genista tenera was first studied by liquid chromatography (LC)-diode array detection (DAD) which showed the presence of two major compounds. One of them was identified as genistein-7-O-glucoside. Luteolin-7-O-glucoside was detected as a minor constituent, while luteolin-7,3'-di-O-glucoside and rutin were found in trace amounts. LC-DAD-ESI-MS and NMR were used to confirm the structure of these compounds and allowed the elucidation of the structure of the unknown major compound, which is the flavonoid 5,7,4'-trihydroxyisoflavone-8-C-glucoside. 相似文献
78.
M.G.?CarvalhoEmail author J.M.R.C.A.?Santos A.A.?Martins M.M.?Figueiredo 《Cellulose (London, England)》2005,12(4):371-383
In this work attention has been focused on the effects of papermaking beating, web forming and sizing operations on the physical/chemical
surface properties of bleached Eucalyptus globulus kraft fibres. Inverse gas chromatography (IGC) was used to determine the dispersive component of surface tension (γsd) as well as the acidic/basic character (according to the Lewis concept) of the solid surfaces (pulp fibres and pulp handsheets).
The results have shown that the main effect of beating is to increase the fibre's Lewis acidic character. Web forming caused
a strong decrease in γsd and significant increments in the adhesion works of both acidic and basic probes, lowering the ratio between the two. Nevertheless,
the surface of handsheets still exhibited a dominant acidic character. The sizing operation did not change the dispersive
component of the surface tension significantly but decreased the difference between the adhesion works of the acidic and basic
probes, rendering the handsheet surface less Lewis acidic and more Lewis basic. Thus, although internal sizing is expected
to strongly influence liquid spreading at the paper surface and liquid penetration of the fibre's network, it is concluded
that beating and web forming lead to important changes in the surface energetic properties of the Eucalyptus globulus kraft fibres. 相似文献
79.
Various high levels of theory have been applied to the characterization of two higher lying biradicaloid metastable singlet states of peroxynitrous acid. A singlet minimum (cis-2) was located that had an elongated O-O distance (2.17 A) and was only 12.2 kcal/mol [UB3LYP/6-311+G(3df,2p)+ZPVE] higher in energy than its ground-state precursor. A trans-metastable singlet (trans-2) was 10.9 kcal/mol higher in energy than ground-state HO-ONO. CASSCF(12,10)/6-311+G(d,p) calculations predict the optimized geometries of these cis- and trans-metastable singlets to be close to those obtained with DFT. Optimization of cis- and trans-2 within the COSMO solvent model suggests that both exist as energy minima in polar media. Both cis- and trans-2 exist as hydrogen bonded complexes with several water molecules. These collective data suggest that solvated forms of cis-2.3H(2)O and trans-2.3H(2)O represent the elusive higher lying biradicaloid minima that were recently (J. Am. Chem. Soc. 2003, 125, 16204) advocated as the metastable forms of peroxynitrous acid (HOONO). The involvement of metastable trans-2 in the gas phase oxidation of methane and isobutane is firmly established to take place on the unrestricted [UB3LYP/6-311+G(d,p)] potential energy surface (PES) with classical activations barriers for the hydrogen abstraction step that are 15.7 and 5.9 kcal/mol lower than the corresponding activation energies for producing products methanol and tert-butyl alcohol formed on the restricted PES. The oxidation of dimethyl sulfide and dimethyl selenide, two-electron oxidations, proceeds by an S(N)2-like attack of the heteroatom lone pair on the O-O bond of ground-state peroxynitrous acid. No involvement of metastable forms of HO-ONO was discernible. 相似文献
80.
Bossée A Afonso C Fournier F Tasseau O Pepe C Bellier B Tabet JC 《Journal of mass spectrometry : JMS》2004,39(8):903-912
Peptide metallation with Cu2+ was explored in the negative ESI mode using an ion trap mass spectrometer. Under these conditions, the [(M-3H) + CuII]- species formed were investigated under low-energy collision-induced dissociation conditions. MS2 experiments indicate a very different behavior of CuII metallated complexes compared with [M-H]- species. CuII induces an easy loss of CO2 and specific side-chain cleavages (by radical losses) at the C-terminal residue, as observed previously by prompt 'in source' dissociation experiments. The loss of CO2 yields an unstable carbylide that leads to further dissociations involving the migration of a proton or a hydrogen radical (through the reduction of CuII). Multistage MS3 experiments were carried out to rationalize this behavior. Fragmentation pathways are proposed in order to explain the product ions observed. The side-chain radical loss at the C-terminus was demonstrated to be a consecutive process. Finally, evidence is provided that the specific side-chain cleavages can be used for the differentiation of Leu/Ile and Gln/Lys residues when they are located at the C-terminus. The existence of a zwitterionic form in the case of the anionic YGGFK-CuII complex is proposed. 相似文献