The solubility of (14)C-labelled barium carbonate in aqueous systems

The solubility of (14)C-labelled barium carbonate has been determined in basic aqueous solutions with and without added Ba(2+) present and in aqueous solutions containing no added Ba(2+) or OH(-) ions. By use of activity coefficients from the literature, K(sp) has been determined to be 4.0 x 10(-10) +/- 0.5 x 10(-10) at 25 degrees .     

Photochemistry of neutral isonitrile gold(I) complexes: modulation of photoreactivity by aurophilicity and pi-acceptance ability

This work demonstrates for the first time that aurophilicity and ligand pi-acceptance ability sensitize the photoreactivity of Au(I) complexes. Photolysis of LAu(I)Cl (L = RNC or CO) complexes leads to free L, Au(III), and Au(0) photoproducts. Solutions of (p-tosyl)CH(2)NCAuCl in dichloromethane undergo significant oligomerization leading to dimers and trimers with formation constants of 1.61 x 10(3) and 6.61 x 10(3) M(-1), respectively, representing the highest values reported to date for complexes that exhibit aurophilic association in solution. The photoproduct quantum yield (Phi) varies with the LAu(I)Cl concentration in solution. For (p-tosyl)CH(2)NCAuCl, metallic gold forms with Phi = 0.0065 and 0.032 in 4.0 x 10(-5) and 4.0 x 10(-3) M dichloromethane solutions, respectively. Meanwhile, irradiation of t-BuNCAuCl primarily produces t-BuNCAuCl(3) with Phi = 0.0045 and 0.013 for 5.0 x 10(-5) and 5.0 x 10(-3) M dichloromethane solutions, respectively. For Au(CO)Cl, metallic gold forms with Phi = 0.013 and 0.065 upon irradiation of 8.0 x 10(-5) and 8.0 x 10(-3) M dichloromethane solutions, respectively. Hence, *[LAuX](n) oligomeric species are more photoreactive than monomeric species. The results also demonstrate intuitive control of Phi via modulation of the pi-acceptance ability of L, as both follow CO > (p-tosyl)CH(2)NC > (alkyl)NC in LAuCl, a trend that is also commensurate with the relative long-term photosensitivity of the corresponding solids and solutions. A new method for preparing stable small gold nanoparticles is described based on the fundamental findings above. Thus, photolysis of different concentrations of LAuX in solutions containing a primary amine-terminated dendrimer leads to clear solutions exhibiting tunable visible plasmon absorptions of gold nanoparticles; these solutions maintain their colors and stability indefinitely. TEM measurements for representative samples prepared by photolysis of (p-tosyl)CH(2)NCAuCl solutions give rise to spherical nanoparticles as small as 5 nm.     

Adsorption of sodium dodecyl sulfate onto clathrate hydrates in the presence of salt

This work presents the effect of NaCl on the adsorption of sodium dodecyl sulfate (SDS) at the cyclopentane (CP) hydrate-water interface. The adsorption isotherms and the SDS solubility in NaCl solutions are obtained using liquid-liquid titrations. The solubility data are determined at typical hydrate forming temperatures (274-287K) to ensure that the adsorption isotherms are obtained within SDS solubility limits in NaCl solutions. The isotherms show L-S (Langmuir-Step) type behaviors with 1mM and 10mM NaCl solutions while L type isotherm is determined for 25mM NaCl solutions due to the low SDS solubility in this salt concentration. Zeta potentials of CP hydrate particles in the aqueous solutions support the shape of the adsorption isotherm with the 1mM NaCl solution. The 1mM NaCl case shows the highest SDS adsorption amount among the cases with 0mM, 10mM, and 25mM NaCl solutions. In this case, the competition for adsorption between Cl(-) and DS(-) is not as strong compared to the 10 and 25mM NaCl cases and the presence of Na(+) ions may reduce the repulsion between DS(-) ions, which results in a higher adsorption of DS(-) ions and enhanced enclathration.     

Mass and charge balance in self-assembled multilayer films on gold. Measurements with optical reflectometry and quartz crystal microbalance

This work aimed to the determination of weight uptakes and charge balance in the course of successive deposition of polyelectrolytes, using the so-called self-assembled multilayer technique. Polyelectrolytes were the quaternized polydimethylaminoethyl methacrylate chloride, (MADQUAT) and poly(acrylic acid) (PAA). Experiments were made at pH 5.5 in NaCl solutions between 10(-3) and 10(-1) M. Deposits (5 bilayers) on a gold substrate were monitored using a quartz crystal microbalance (QCM) and optical fixed-angle reflectometry. Analysis of data lead to the determination of the sensitivity factor of the reflectometric output. QCM allowed the direct measurement of weight uptakes in 10(-3) and 10(-2) M solutions, while the viscoelastic properties of the film did not look appropriate for the measurement in 10(-1) M solutions. The layer-by-layer uptakes and charge balances in 10(-3) and 10(-2) M solutions revealed a large contribution of the counterions in the neutralization of the electrical charge in the film, more so for the highly charged MADQUAT polymer. The difference between two successive polymer charge densities increased significantly with the layer number and the electrolyte concentration. The increase of NaCl concentration induced an increase of MADQUAT but reversely a decrease of PAA deposits. The results were consistent with the determining influence of the salt in polyelectrolyte adsorption, both with regards to the concentration and the type of ions that has been well demonstrated in the literature. This work also draws attention to the role of small ions in the structural and application properties of self-assembled multilayer films.     

Potentiometric determination of trace silver based on the use of a carbon paste electrode

A carbon paste electrode used as a sensor for silver has been developed and electrode response characteristics have been investigated. The electrode exhibits linear response to the logarithm of the concentration of silver from 5 x 10(-7)M to 1 x 10(-2)M, with a response slope of 63 +/- 2 mV. The detection limit according to IUPAC recommendations is 1 x 10(-7)M. This electrode has been used to determine trace silver in fixing solutions and waste electroplate solutions with good results.     

Distribution of Pb(II) species in aqueous solutions

Turbidity and zeta potential measurements were made on solid precipitates formed after raising the pH of a 10(-3) mol/l lead nitrate aqueous solutions containing 10(-2) mol/l KCl with KOH. Distribution diagrams of Pb(II) species in aqueous solutions at a total Pb(II) concentration of 10(-3) mol/l and 10(-2) mol/l KCl was constructed to explain the results. Several solubility products for solid Pb(OH)(2) were found from the literature and used to construct the diagrams. It was observed that distribution diagrams constructed using a solubility product of 1.43x10(-20) explained the experimental results better than those with other reported solubility products.     

Solvation dynamics in aqueous anionic and cationic micelle solutions: sodium alkyl sulfate and alkyltrimethylammonium bromide

Solvation dynamics of the fluorescence probe, coumarin 102, in anionic surfactant, sodium alkyl sulfate (C(n)H(2n+1)SO(4)Na; n = 8, 10, 12, and 14), and cationic surfactant, alkyltrimethylammonium bromide (C(n)H(2n+1)N(CH(3))(3)Br; n = 10, 12, 14, and 16), micelle solutions have been investigated by a picosecond streak camera system. The solvation dynamics in the time range of 10(-10)-10(-8) s is characterized by a biexponential function. The faster solvation time constants are about 110-160 ps for both anionic and cationic micelle solutions, and the slower solvation time constants for sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions are about 1.2-2.6 ns and 450-740 ps, respectively. Both the faster and the slower solvation times become slower with longer alkyl chain surfactant micelles. The alkyl-chain-length dependence of the solvation dynamics in both sodium alkyl sulfate and alkyltrimethylammonium bromide micelles can be attributed to the variation of the micellar surface density of the polar headgroup by the change of the alkyl chain length. The slower solvation time constants of sodium alkyl sulfate micelle solutions are about 3.5 times slower than those of alkyltrimethylammonium bromide micelle solutions for the same alkyl-chain-length surfactants. The interaction energies of the geometry optimized mimic clusters (H(2)O-C(2)H(5)SO(4)(-) and H(2)O-C(2)H(5)N(CH(3))(3)(+)) have been estimated by the density functional theory calculations to understand the interaction strengths between water and alkyl sulfate and alkyltrimethylammonium headgroups. The difference of the slower solvation time constants between sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions arises likely from their different specific interactions.     

Quantitative phosphorescence study of interactions of cytosine and cytidine and its nucleotides in frozen aqueous solution: evidence for anomalous heavy-atom effect

Phosphorescence vs. pH titration curves of cytosine, cytidine, cytidine-5'-mono-phosphate (CMP), -diphosphate (CDP) and -triphosphate (CTP) were obtained in methanol/water 10/90 v/v and in various aqueous sodium halide solutions frozen at 77 degrees K. As shown by the shape of the titration curve, molecular aggregates or "puddles" of cytosine and cytidine were shown to occur only in relatively concentrated frozen solution (10(-3)M), these aggregates being dissociated in dilute frozen solutions (相似文献   

Sensitive detection of tetracyclines using europium-sensitized fluorescence with EDTA as co-ligand and cetyltrimethylammonium chloride as surfactant

The determination of tetracyclines (TC) in aqueous solutions, based on europium-sensitized fluorescence, has been improved using EDTA as co-ligand and cetyltrimethylammonium chloride as surfactant. The method involves working in slightly alkaline solutions with the formation of a new chelate where the lanthanide ion is bound to the beta-diketone group. The method is about 6 times more sensitive than that with the Eu-TC-Triton system and LODs are 2.5 x 10(-10), 5 x 10(-10), 1.5 x 10(-9) and 2 x 10(-9) mol l-1 for TC, oxytetracycline, chlortetracycline and doxycycline, respectively. The method has been applied to the determination of TC in calf serum without sample pretreatment. The mean recovery was close to 102% and the lowest concentration attainable in serum samples was better than 0.1 microgram ml-1.     

Diffusion coefficients of C60 and C60- in benzonitrile and dichloromethane solutions containing tetrabutylammonium perchlorate, measured by potential-step chronoamperometry.

The diffusion coefficients of C(60) in dichloromethane and benzonitrile solutions containing 0.1 M tetrabutylammonium perchlorate were determined by single potential-step chronoamperometry at small disk electrodes. The diffusion coefficients of C(60) were obtained by curve fitting of the chronoamperograms to a theoretical equation by Shoup and Szabo. The values were (1.4 +/- 0.3) x 10(-9) and (4.1 +/- 0.3) x 10(-10) m(2) s(-1), respectively (the errors are 95% confidence limits). The diffusion coefficients of C(60)(-) in these solutions were measured by double potential-step chronoamperometry. The ratios of the diffusion coefficients of C(60) to those of C(60)(-) were obtained from theoretical curves of the ratios of the current at the second potential step to the current at the first one. The values of the ratios were 1.2 +/- 0.2 and 1.0 +/- 0.3, respectively.     

Quartz crystal microbalance with dissipation monitoring and surface plasmon resonance studies of carboxymethyl cellulose adsorption onto regenerated cellulose surfaces

Adsorption of anionic polyelectrolytes, sodium salts of carboxymethyl celluloses (CMCs) with different degrees of substitution (DS = 0.9 and 1.2), from aqueous electrolyte solutions onto regenerated cellulose surfaces was studied using quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) experiments. The influence of both calcium chloride (CaCl(2)) and sodium chloride (NaCl) on CMC adsorption was examined. The QCM-D results demonstrated that CaCl(2) (divalent cation) caused significantly greater CMC adsorption onto regenerated cellulose surfaces than NaCl (monovalent cation) at the same ionic strength. The CMC layers adsorbed onto regenerated cellulose surfaces from CaCl(2) solutions exhibited greater stability upon exposure to flowing water than layers adsorbed from NaCl solutions. Both QCM-D and SPR results showed that CMC adsorption onto regenerated cellulose surfaces from CaCl(2) solutions increased with increasing CaCl(2) concentration up to the solubility limit (10 mM). Voigt-based viscoelastic modeling of the QCM-D data indicated that the CMC layers adsorbed onto regenerated cellulose surfaces had shear viscosities of η(f) ≈ 10(-3) N·s·m(-2) and elastic shear moduli of μ(f) ≈ 10(5) N·m(-2). Furthermore, the combination of SPR spectroscopy and QCM-D showed that the CMC layers contained 90-95% water. Adsorption isotherms for CMCs in CaCl(2) solutions were also obtained from QCM-D and were fit by Freundlich isotherms. This study demonstrated that CMC adsorption from CaCl(2) solutions is useful for the modification of cellulose surfaces.     

Primary photochemical processes of the phototoxic neuroleptic cyamemazine: a study by laser flash photolysis and steady-state irradiation

The photophysical and photochemical properties of the UV-A-absorbing phototoxic drug cyamemazine (CMZ) (2-cyano-10-(3-[dimethylamino]-2-methyl-propyl)-phenothiazine) have been investigated in neutral buffered aqueous solutions. The transient absorbances of the hydrated electrons, of the first excited triplet state (3CMZ*) with a characteristic absorption band peaking at 420 nm and of the radical cation (*CMZ+) (maximum absorbance at 500 nm) have been observed by 355 nm laser flash spectroscopy of deaerated solutions. All these transient species are formed by monophotonic processes and react with oxygen. Bimolecular reaction rate constants of *CMZ+ and 3CMZ* with O2 are 2 x 10(7) M(-1) s(-1) and 4 x 10(9) M(-1) s(-1), respectively. The 3CMZ* reacts only sluggishly (reaction rate constant, 9 x 10(6) M(-1) s(-1)) with tryptophan chosen as a Type-I photodynamic substrate. Steady-state irradiations with 365 nm light demonstrate that CMZ is rapidly photolyzed (quantum yield, 0.04) in O2-saturated solutions leading to oxidation of the sulfur atom and of the side-chain nitrogen of CMZ. This photoproduct (2-cyano-10-(3-[dimethylamino, N-oxide]-2-methyl-propyl)-5-oxide-phenothiazine), is a good Type-I and Type-II photodynamic photosensitizer producing singlet oxygen in high yield (approximately 0.45) and could play a major role in the phototoxicity of CMZ.     

Characterization of isopoly metal oxyanions using electrospray time-of-flight mass spectrometry

Electrospray time-of-flight mass spectrometry was used to study dilute (10(-3) M) solutions of tungstate, vanadate and perrhenate oxyanions under acidic and basic conditions. The electrospray mass spectra of tungstate and vanadate solutions indicate the presence of protonated monomeric oxyanions in basic solution (pH approximately 10) and protonated polymeric species in acidic solutions (pH approximately 4). Monomeric perrhenate was the only species detected in both acidic and basic perrhenate solutions. For all three systems, the core metalate species detected by electrospray were consistent with reported speciation in aqueous solutions. Copyright 2000 John Wiley & Sons, Ltd.     

Broadband dielectric spectroscopic, calorimetric, and FTIR-ATR investigations of D-arabinose aqueous solutions

The dielectric relaxation behavior of D-arabinose aqueous solutions at different water concentrations is examined by broadband dielectric spectroscopy in the frequency range of 10(-2) -10(7) Hz and in the temperature range of 120-300 K. Differential scanning calorimetry is also performed to find the glass transition temperatures (T(g)). In addition, the same solutions are analyzed by Fourier transform infrared (FTIR) spectroscopy using the attenuated total reflectance (ATR) method at the same temperature interval and in the frequency range of 3800-2800 cm(-1). The temperature dependence of the relaxation times is examined for the different weight fractions (x(w)) of water along with the temperature dependence of dielectric strength. Two relaxation processes are observed in the aqueous solutions for all concentrations of water. The slower process, the so-called primary relaxation process (process-I), is responsible for the T(g) whereas the faster one (designated as process-II) is due to the reorientational motion of the water molecules. As for other hydrophilic water solutions, dielectric data for process-II indicate the existence of a critical water concentration above which water mobility is less restricted. Accordingly, FTIR-ATR measurements on aqueous solutions show an increment in the intensity (area) of the O-H stretching sub-band close to 3200 cm(-1) as the water concentration increases.     

半导体硅片的电化学研究(英文)

采用电化学直流极化和交流阻抗技术 ,在有光照和黑暗条件下分别研究了半导体硅片在稀释氢氟酸溶液中的电化学特性 .两种电化学技术均对溶液中含有的微量铜 (1 0 - 9wt % -浓度水平 )非常敏感 ,但仅对溶液中的 1 0 - 6 wt % -浓度水平的非离子型表面活性剂敏感 .结果表明 ,有光照条件下在硅 /溶液界面上极易发生电化学反应 ,且该反应对硅表面性质起主导作用 .     

Photochemical behavior of a new long-chain UV absorber derived from 4-tert-butyl-4'-methoxydibenzoylmethane

A new UV filter, the 1-(4-tert-butylphenyl)-2-decanyl-3-(4'-methoxyphenyl)-propane-1,3-dione, called C10-DBM, was prepared by grafting a 10-carbon aliphatic chain to the alpha-carbonyl position of 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM), a well-known and often used UV filter. The UV-A absorption efficiency of organic solutions containing the new filter was tested and compared with identical solutions containing BM-DBM with or without irradiation (xenon lamp). The originality of this new filter is that its UV-A absorbance appeared during irradiation of the molecule. Although the molar absorption coefficient of C10-DBM in the UV-A domain was lower than that of BM-DBM, the solutions absorption exhibited a much more photostable behavior under irradiation. In this study, we first demonstrated that C10-DBM was a precursor of BM-DBM (enol isomer) by means of high-performance liquid chromatography followed by mass spectrometry. Indeed, we showed that the UV-A absorption of C10-DBM solutions appearing during the irradiation of the molecule was due to a Norrish-II reaction (beta-cleavage), which induced the release of the BM-DBM enol form and 1-decene. Then, we established a kinetic model for the photochemistry of C10-DBM and fitted the variation of UV absorption spectra to confirm the proposed mechanism.     

Decamolybdocobaltate heteropolyanions in aqueous solutions: chemistry driving their formation and domains of stability

In the present study, aqueous solutions of decamolybdocobaltate H(4)Co(2)Mo(10)O(38)(6-) heteropolyanions were prepared from molybdenum oxide, cobalt carbonate precursors and hydrogen peroxide used as oxidizing agent. The preparation was optimized adding a consecutive hydrothermal treatment at 150 °C to obtain pure H(4)Co(2)Mo(10)O(38)(6-) aqueous solutions for Co/Mo atomic ratio of 0.5. Combining quantitative Raman and UV-visible measurements and chemometric methods, it was demonstrated that a mixture of H(4)Co(2)Mo(10)O(38)(6-) and octomolybdate Mo(8)O(26)(4-) species is obtained for Co/Mo ratios lower than 0.5, and the relative quantities of H(4)Co(2)Mo(10)O(38)(6-) are determined by the presence of Mo(8)O(26)(4-) species and by the quantity of Co(2+) countercations available in the solutions to ensure the electroneutrality. As these quantities can be predicted for each Co/Mo ratio, this finding allows rationalization of the preparation of heterogeneous catalysts using impregnation by H(4)Co(2)Mo(10)O(38)(6-) aqueous solutions. Parameters relevant of the impregnation step such as the pH, the Co/Mo ratio, and the molybdenum concentration were varied to determine the domains of stability of H(4)Co(2)Mo(10)O(38)(6-) heteropolyanions after formation. Stable from pH 1 to 4.5, this dimeric Anderson species is destabilized above pH 4.5; Co(2+), monomolybdate MoO(4)(2-) ions, and precipitates are then formed. For Co/Mo ratios lower than 0.5, the relative quantity of dimer does not vary with the pH and with a change of the Co/Mo ratio consecutive to the hydrothermal treatment. On the contrary, the coproduced Mo(8)O(26)(4-) species can be transformed into other isopolymolybdates varying the pH according to their domains of stability. For all of the ratios, H(4)Co(2)Mo(10)O(38)(6-) dimers were also shown to be stable in a wide range of molybdenum concentrations.     

Photostability and thermal stability of indocyanine green

The photo-fading of the S0-S1 absorption band of the infrared dye indocyanine green sodium iodide (ICG-NaI) has been studied by cw laser excitation to the S1 band. Monomeric solutions in water, heavy water, aqueous sodium azide, human plasma, methanol and dimethyl sulfoxide (DMSO) as well as J-aggregated solutions in H2O and D2O have been investigated. A leucoform of indocyanine green seems to be formed by photodegradation. The degradation slows down with exposure time. The initial degradation yield, phi D,0, is determined. In monomeric and dimeric water, heavy water and sodium azide solutions the initial photostability is of the order of phi D.0 approximately 10(-3), in the organic solvents methanol and DMSO it is of the order of phi D.0 approximately 10(-5), and in human plasma it is phi D.0 approximately 2 x 10(-6). J-aggregates at high concentration are very stable. The thermal stability of the ICG-NaI solutions at room temperature in the dark is compared with their photostability. The thermal degradation time of monomeric and dimeric ICG-NaI in water, heavy water and sodium azide solutions is t(th) approximately 10 days, while no thermal degradation is observed for ICG-NaI J-aggregates and ICG-NaI in methanol, DMSO and human plasma.     

Nitrogen dioxide multiphase chemistry: uptake kinetics on aqueous solutions containing phenolic compounds

The uptake coefficients of NO2 on aqueous solutions containing guaiacol, syringol and catechol were determined over the pH range from 1 to 13 using the wetted wall flowtube technique. The measured uptake coefficients were used to determine the rate coefficients for the reaction of the physically dissolved NO2 with the neutral and deprotonated forms of phenolic compounds listed above. These organic compounds are ubiquitous not only in biomass burning plumes but also in soils, where they form part of the building blocks of humic acids. The NO2 uptake kinetics on solutions containing guaiacol, syringol or catechol were observed to be strongly pH dependent with uptake coefficients increasing from below 10(-7), under acidic conditions, to more than 10(-5) at pH values above 10. This behaviour illustrates the difference of reactivity between the neutral phenolic species and the phenoxide ions. The corresponding second order rate coefficients were typically observed to increase from 10(5) M(-1) s(-1) for the neutral compounds to a minimum of 10(8) M(-1) s(-1) for the phenoxide ions.     

Spectroscopic evidence of monomeric aluminium phthalocyanine tetrasulphonate in aqueous solutions

Aqueous solutions of aluminium phthalocyanine tetrasulphonate (AlPcS(4)) were investigated by means of absorption and fluorescence spectroscopy. The absorption spectrum of AlPcS(4) is independent of concentration in a wide range (from 10(-8) to 10(-4) M). The fluorescence spectrum measured with a standard setup is strongly dependent on AlPcS(4) concentration, and the fluorescence maximum is gradually red-shifted with increasing concentration. Calculations that take into account reabsorption of fluorescence (inner-filter effect) fit the experimental observations at low concentrations (up to 10(-6) M). Disagreement between the calculations and spectra recorded at higher concentrations (above 10(-5) M) shows that the reabsorbed light may be reemitted as fluorescence. The influence of inner-filter effects on the spectral shape was demonstrated by the experiments where a fibre-optic front-face fluorescence setup was applied: Under such conditions the shape of the fluorescence spectra for a high concentration (10(-3) M) coincided with that of a low concentration (10(-8) M). In conclusion, the present spectroscopic results show that AlPcS(4) does not form aggregates and is a very stable compound in aqueous solutions.