Aqueous solutions of anionic surfactants Cl(C3F6O)nCF2COOX, consisting of n = 2 and 3 perfluoroisopropoxy units and the counterion X = Na+ or NH4+, were studied by the method of fluorescence quenching with the use of (1-pyrenylbutyl)trimethylammonium bromide as a luminophore, and 1,1'-dimethyl-4,4'bipyridinium dichloride (methyl viologen) as a quencher. From the kinetics of fluorescence decay (time-resolved experiments) micellar aggregation numbers, N, and rate constants of the intramicellar quenching were determined for a wide range of surfactant concentrations, on the basis of the model developed by Infelta and Tachiya. The results are discussed in terms of the shape of the aggregates and the degree of counterion binding. The most important conclusions include: (i) a significant increase of N with increasing surfactant concentration suggests that spherical micelles formed at critical micellar concentration (CMC) transform into ellipsoidal aggregates, (ii) the degree of counterion binding to micelles is higher for NH4+ than for Na+, leading to higher N values in the case of the ammonium salt (n = 2), and (iii) at concentrations close to CMC the longer chain surfactant (n = 3) forms loose aggregates suggesting significant permeation with water molecules. An additional finding of this study is that the micelle-bound luminophore and quencher can form a ground-state complex, and for this reason the N values cannot be evaluated properly from the steady-state fluorescence intensity data using the equation proposed by Turro and Yekta. 相似文献
The reaction of hydrated electron with 9-anthrylmethylammonium cation to form the respective anthracene radical anion in aqueous solution has been studied by the method of pulse radiolysis. The rate constant of the reaction of with is reported. It is demonstrated that the anthracene radical anion is unstable and undergoes further reactions. The spectra of transient intermediates, leading to the final reduction products, are presented. 相似文献
This communication presents the optical studies associated with transition doped (metallic)-neutral (semiconductor or insulator) state for conducting polymers. Special attention is focused on the electronic properties of polyaniline. The interconversion of different oxidation states of polyanilines has been studied by chemical and radiolytic methods. The polyaniline system is described by three sets of chromophores of three different oxidation states: fully reduced leucoemeraldine base (LB), partially oxidized emeraldine base (EB), and fully oxidized pernigraniline (PB). Each oxidation state can exist in its protonated form by treatment with an acid. All members of polyaniline family are spectroscopically distinguishable. The radiolytic study presents evidence that the polyaniline can exist in a continuum of oxidation states. The highly conducting form of polymer, i.e. emeraldine salt can be converted by using ionizing radiation into leucoemeraldine salt. The leucoemeraldine base is the final product of radiolysis of emeraldine base solution. The fully oxidized form of polyaniline can also be obtained by the irradiation of EB in the presence of CCl4 or chlorobenzene. 相似文献
We study the dynamics of an elastic inverted pendulum with amplitude limiters excited horizontally. This particular model corresponds to a class of systems where a clearance is present naturally as an effect of imperfect clamping or it is included to tailor the response. We explore the complex responses of the system for a fixed value of amplitude clearance. The simulation and experimental results are analysed by a 0–1 test, Fourier, and wavelet transforms. The results show that the system can vibrate with subharmonic solution where the main response frequency of a flexible beam is 3 times lower than the excitaion frequency. We claim that an inverted pendulum with imperfect clamping of mechanical resonator can be used in broad frequency band energy harvesting.
Meccanica - This paper deals with nonlinear mechanics of an elevator brake system subjected to uncertainties. A deterministic model that relates the braking force with uncertain parameters is... 相似文献
The reductive release of iron from ferritin by UV light or ionizing radiation has been investigated in separate experiments.
When ferritin is exposed to light, the mineral core is the main photoreceptor for the Fe(III) reduction. In radiolytic studies,
we determined that, in the absence of oxygen, the hydrated electron (eaq−) is the reducing agent triggering redox reactions associated with iron mobilization from ferritin. In an aerobic system,
the superoxide radical anion (O2•−) is also involved in the iron release process. We found that, in photochemical and radiolytical studies, Fe(II) mobilization
from ferritin required an iron chelator. Without a chelator, ferritin is an electron-storage molecule for a long period, on
the order of at least several hours. The reductant or chelator entry into the ferritin core is not necessary for iron release.
The ferrozine is a convenient chelating agent to monitor Fe(II) mobilization, due to a high extinction coefficient of
\textFe ( \textferrozine )34 - {\text{Fe}}\,\left( {\text{ferrozine}} \right)_{3}^{4 - } and a high rate constant of complexation process (2.65 × 104 dm3 mol−1 s−1). 相似文献
Controlled photodeposition of silver nanoparticles (AgNP) on titania coatings using two different sources of UV light is described. Titania (anatase) thin films were prepared by the sol-gel dip-coating method on silicon wafers. AgNPs were grown on the titania surface as a result of UV illumination of titania films immersed in aqueous solutions of silver nitrate. UV xenon lamp or excimer laser, both operating at the wavelength 351 ± 5 nm, was used as illumination sources. The AFM topography of AgNP/TiO2 nanocomposites revealed that silver nanoparticles could be synthesized by both sources of illumination, however the photocatalysis carried out by UV light from xenon lamp illumination leads to larger AgNP than those synthesized using the laser beam. It was found that the increasing concentration of silver ions in the initial solution increases the number of Ag nanoparticles on the titania surface, while longer time of irradiation results the growth of larger size nanoparticles. Antibacterial tests performed on TiO2 covered by Ag nanoparticles revealed that increasing density of nanoparticles enhances the inhibition of bacterial growth. It was also found that antibacterial activity drops by only 10-15% after 6 cycles compared to the initial use. 相似文献
Steady-state and time-resolved fluorescence spectra of 1,3-di(1-pyrenyl)propane (1Py-(3)-1Py) incorporated into macromolecules
of human serum albumin (HSA), into micelles of dodecyltrimethylammo-nium chloride (DTAC), and dissolved in 1,4-dioxane were
compared. The steady-state fluorescence spectra indicated that in all the mentioned environments, upon excitation of 1Py-(3)-1Py,
light was emitted from the single pyrene chromophores (1Py*) and from the 1Py, 1Py* excimers. The time-resolved fluo-rescence emission registered at 480 nm (excimer emission) for 1Py-(3)-1Py in the DTAC micelles
and dissolved in 1,4-dioxane allowed to monitor formation of excimer with time constant τ1=40.0 ns and 9.6 ns, for 1Py-(3)-1Py in the DTAC micelles and in 1,4-dioxane, respectively. However, when the 1Py-(3)-1Py
probe was located inside of the macromolecules of HSA, only the decay of emission was observed for excimer with our set-up
(t>2 ns after excitation). The instantaneous formation of excimer, unrelated to the decay of monomer excitation, indicates that
the considerable fraction of 1Py-(3)-1Py in the hydrophobic pockets of HSA is present as the ground state dimer. The red shift
(Δλ=8 nm) and broadening of UV absorption for 1Py-(3)-1Py in HSA (when compared with absorption 1Py-(3)-1Py in 1,4-dioxane)
and comparison of exci-tation spectra of 1Py-(3)-1Py in HSA and in 1,4-dioxane also indicate that label molecules bound to
some sites of HSA are in the ground state in the dimer conformation. Moreover, the close values of the ratios of intensities
of monomer emission to excimer emission, registered 2 ns (5 ns gate) after excitation pulse with duration 300 ps and at the
steady-state conditions, indicate that the interconversion between conformers of 1Py-(3)-1Py inside of the macro-molecules
of HSA is slow in comparison with the decay time of Py chromophore in the excited state in HSA (two-exponential decay with
decay times τ1=2.41 ns, τ2=69.0 ns). Thus, ratios of the intensities of monomer and excimer emissions of 1Py-(3)-1Py in HSA do not allow to obtain any
information on the local microfluidity inside of the protein macromolecules but could be used for discrimination between different
conformations of the probe, possibly located in different protein pockets.
Received: 29 April 1996 Accepted: 15 August 1996 相似文献
Pulse radiolysis of aqueous solutions of sodium pentacyanonitrosylferrate/II/ Na2[Fe/CN/5NO] /sodium nitroprusside/ was studied in the presence of ethylene glycol as an OH radical scavenger. The rate constants of the one-electron reduction of nitroprusside ion were measured with e
q–
and with radicals derived from some alcohols /ethylene glycol, ethanol, 2-propanol/ as reducing species. The results show that the transition state for the reduction by alcohol radicals is polar. The only observed product of reduction is the Fe/CN/5NO3– ion, which then undergoes a slow dissociation to form Fe/CN/4NO2–. Only a small isotope effect kH/kD=1.08 was observed in D2O solutions for the dissociation reaction. This suggests an intramolecular electron transfer as rate-determining step for the dissociation reaction.Dedicated to Professor Schulte-Frohlinde on the occasion of his 60th birthday. 相似文献