Are the changes in the lifetime of the excited uranyl ion of chemical or physical nature?

By use of time-resolved laser-induced fluorescence and of basic spectrophotometric methods, we have studied the effects of water/perchloric acid mixtures (up to 12 M), NaClO₄ in water/perchloric acid mixtures and triflic acid (diluted or pure) on the absorption and emission spectra and on the lifetime of the uranyl ion in liquid solutions. Models proposed in order to explain similar results in the case of various elements are discussed. It is shown that the main effect remains largely unexplained, as none of the previously proposed models is able to recover the data without severe contradictions. The two best models, chemical equilibrium or energy transfer, were tentatively modified in order to unravel the inconsistencies pointed out; however, it was not possible to reconcile our data with models based on chemical reactions including ionic strength effects. A model of internal conversion leads to an approximative mathematical treatment, and the quality of the fit is not perfect. Finally, the data may indicate that a complexation of uranyl with perchlorate ion occurs above 4.5 M. The association of HClO₄ and triflic acid are observed at very high concentrations.     

Diffusion of ionic species labeled with35S in various aqueous electrolyte solutions at 25°C

Composite diffusion coeffcients have been measured for the various species labeled with³⁵S which are present in a number of aqueous solutions due to the introduction of the labeled material as³⁵SO ₄ ^2– . The solutions were of two components consisting of water and either sodium sulfate. The diffusion coeffcient measured for sodium chloride solutions is similar to literature data for the corresponding diffusion in sodium sulfate solutions. The results for sulfuric acid and ammonium hydrogen sulfate have been interpreted using literature data for the relative concentrations of the hydrogen sulfate and sulfate ions to obtain estimates for the diffusion coefficents of those ions. The results for perchloric acid, regarded as representing the diffusion coefficient of the hydrogen sulfate ion, have a much different concentration dependence to that observed for the estimates for that ion in sulfuric acid and ammonuim hydrogen sulfate. The difference is attributed to the effect of the perchlorate ion on the water structure.     

Ion solvation and association in LiClO4/sulfolane solution: a vibrational spectroscopic and molecular orbital study

Solvation interaction and ion association in solutions of lithium perchlorate/sulfolane have been studied by using infrared and Raman spectra as a function of concentration of lithium perchlorate. The band changes of antisymmetric OSO stretch, antisymmetric CSC stretch, -SO2 wag and twist suggest that there is an interaction between Li+ and sulfolane molecules, and the site of solvation is the oxygen atom of -SO2 group. The molecular orbital calculation supports this suggestion. On the other hand, the apparent solvation number was calculated, and the band fitting for the ClO4- band reveals the presence of contact ion pair, solvent separated ion pair and free ClO4- anion in the concentrated solutions.     

分光光度法测定水溶液中的有机酸含量

利用水溶液中的有机酸在高氯酸羟胺(HAP)和N,N′-二环己基碳酰亚胺(DCC)存在的条件下生成的羟肟酸,以及羟肟酸在酸性高氯酸铁溶液中显色的性质,建立了一种分光光度测定水中有机酸含量的方法。对显色剂的酸度、浓度、加入体积、HAP和DCC的浓度、加入体积以及显色反应的温度、反应时间对吸光度的影响进行了考察。结果表明,该显色反应在反应条件:0.0687mol/LHAP1.0mL、0.6mol/LDCC0.5mL、震荡均匀后室温下放置反应15min、0.02mol/L酸性高氯酸铁溶液(高氯酸浓度0.3mol/L)显色条件下具有最大的吸光度;并对正丁酸、正戊酸、苯甲酸进行了线性关系考察。结果表明,该检测方法具有仪器简单、操作方便、线性范围较宽、准确度高等优点,可用于那些不易从水溶液中萃取的有机酸的测定,也可用于液相色谱洗脱液中有机酸的测定。     

Vibrational spectral studies of solutions at elevated temperatures and pressures. IX. Acetic acid

Raman spectra of glacial acetic acid from 350 to 3700 cm^–1 have been measured at temperatures up to 275°C and at a pressure of 9 MPa. Raman spectra of aqueous solutions of acetic acid from 3.9 to 16 molar have been measured up to 200°C at a pressure of 7 MPa. The spectral region 800 to 1850 cm^–1 for both glacial acetic acid and its aqueous solutions have been studied in detail since this region is significantly affected by variations in temperature and concentration. An interpretation of the bands in this spectral region was made with the aid of factor analysis, difference spectroscopy, band resolution techniques and the existing extensive literature. The results suggest that the major equilibrium in glacial acetic acid is between cyclic and linear dimers; however, in aqueous solutions in the concentration range studied, mono- and di-hydrated dimers and cyclic dimers are the predominant species.     

Enhanced and normal Raman scattering from pyridine adsorbed on rough and smooth silver electrodes

A multiplex spectrograph has been used to record potential difference and modulation Raman spectra of pyridine adsorbed on silver electrodes in an electrochemical cell. Spectra have been obtained from rough silver surfaces which give SERS and from surfaces where SERS has been diminished by prolonged cathodic polarisation (DSERS). Raman scattering from pyridine at smooth silver surfaces in potassium perchlorate and fluoride solutions has been distinguished from solution scatter by a potential modulation technique. The results show that the enhanced scattering caused by silver atom or cluster sites is respresentative of the surface as a whole as similar Raman spectra are obtained on smooth surfaces at a count rate as low as ?1.4 photons s^?1 (incident laser power 500 mW).Correlation of simultaneous differential capacitance data and “snapshot” SER spectra indicate that pyridine molecules in aqueous chloride ion solutions adsorb on silver in a flat π-bonded configuration at potentials markedly positive to the point of zero charge and exhibit specific reorientation at ?0.3 V and ?0.45 V (vs. SCE) to become N-bonded, perpendicular to the surface. Results also show that the adsorption behaviour of pyridine in chloride and fluoride ion solutions is largely similar.     

Extraction of scandium ions by 1-alkyl-3-methyl-2-pyrazolin-5-ones from perchlorate solutions

The extraction of perchloric acid and the two-phase partition of 1-alkyl-3-methyl-2-pyrazolin-5-ones (AMPs) in the system water-chloroform-perchloric acid are studied. These reagents can extract scandium cations from weak acid solutions in the presence of perchlorate ions. 1-Alkyl-3-methyl-2-pyrazolin-5-ones separate aqueous perchloric acid solutions into a pair of liquid phases. Scandium ions concentrate in the lower phase, which has a small volume.     

Hydration of the hydrogen ion in aqueous solutions from intensity of the OD band of HDO

The OD band of HDO has been studied in partly deuterated aqueous solutions of acids: hydrochloric, sulfuric, nitric, trifluoroacetic, and perchloric. Composition of the hydrogen ion is determined. Observations are made on hydration of the perchlorate and trifluoroacetate ions.     

Ion Association and Solvation Behavior of Some Lithium Salts in Tetrahydrofuran. A Conductivity and Raman Spectroscopic Study

Accurate measurements of electrical conductivities and laser Raman spectra of solutions of lithium chloride (LiCl), lithium bromide (LiBr), lithium tetrafluoroborate (LiBF₄) and lithium perchlorate (LiClO₄) in tetrahydrofuran are reported. The conductivity data have been analyzed by the Fuoss-Krauss theory, yielding values for the ion-pair and triple-ion formation constants. The Raman spectra suggest the presence of a new signal of perchlorate ClO₄⁻ ions in solution, whereas there is no such evidence for the other investigated anions. The observed processes have been interpreted by an Eigen multistep mechanism. For each salt, the predominant portion is found to remain in the form of ion pairs, leaving only a small fraction of triple ions.     

Non-resonance micro-Raman spectroscopic studies on crystalline domoic acid and its aqueous solutions

Domoic acid (DA) is a neurotoxin naturally present in the marine ecosystem. Since DA's toxicity has been explained by its molecular structure and particularly because of its ethylenic double bond, spectroscopic investigation of this molecule is of importance. We carried out Raman spectroscopy on crystalline DA and on DA in aqueous solutions (28,000-25 ng DA/mL) and assigned Raman modes in comparison with the Raman spectra of its substructures. Noise-free, clear Raman signal from the solutions containing low concentrations of DA were obtained by applying the drop coating deposition Raman (DCDR) technique. Raman spectra reveal that crystalline DA exists in the zwitterionic form. The Raman spectra of the DA aqueous solutions were analysed in the light of their pH whereas the variation in the spectra was attributed to the hydration, the degree of protonation and crystallinity of the solid film. We show that DCDR can be applied for the rapid detection of domoic acid down to 25 ng DA/mL (0.025 ppm).     

Structural Inhomogeneity in Electrolyte Solutions: The Calcium Perchlorate–Water System

A new approach has been proposed to study the structure of aqueous electrolyte solutions. NIR, Raman and attenuated total reflectance, Fourier transform infra-red (ATR FTIR) spectra have been measured for aqueous calcium perchlorate solutions in the 0.22–4.3 mol·L^?1 (0.22–7.46 mol·kg^?1) concentration range at 25 °C. By the methods of principal component analysis (PCA) and multivariate curve resolution—alternating least squares (MCR-ALS) the number, spectra and concentration profiles have been determined for spectroscopically distinguishable forms of water and ClO ₄ ^? ion in solutions. The results have been analyzed using a phenomenological model, establishing thereby: concentration ranges for structural rearrangements of the solution, the nature of structural microirregularities and different states of the ClO ₄ ^? ion in the areas of domination of the natural water structure, and of cybotactic groups of calcium perchlorate hexa and tetra hydrates.     

Vibrational Spectroscopic Study on Ion Solvation and Association of Lithium Perchlorate in 4-Methoxymethyl-ethylene Carbonate

Solvation interaction and ion association in solutions of lithium perchlorate/4-methoxymethyl-ethylene carbonate （MEC） have been studied by using Infrared and Raman spectra as a function of concentration of lithium perchlorate. The splitting of ring deformation band and ring ether asymmetric stretching band, and the change of carbonyl stretching band suggest that there should be a strong interaction between Li^＋ and the solvent molecules, and the site of solvation should be the oxygen atom of carbonyl group. The apparent solvation number of Li^＋ was calculated by using band fitting technique. The solvation number was decreased from 3.3 to 1.1 with increasing the concentration of LiClO4/MEC solutions. On the other hand, the band fitting for the ClO4^- band revealed the presence of contact ion pair, and free ClO4^- anion in the concentrated solutions.     

Standard enthalpies of the formation of malonic acid and products of its dissociation in an aqueous solution

Enthalpies of the dissolution of malonic acid in aqueous solutions of perchloric acid and sodium perchlorate were measured at ionic strength I = 1.0; 1.5; 2.0; 2.5 mol/l and T = 298.15 K by calorimetry. The standard enthalpies of the formation of malonic acid and the products of its dissociation in a aqueous solution were calculated.     

Comparative analysis of structural parameters of the nearest surrounding of nitrate and perchlorate ions in aqueous solutions of electrolytes

Data on structural parameters of the nearest surrounding of nitrate and perchlorate ions in aqueous solutions under standard conditions have been generalized. Hydration numbers, interparticle distances, and ionic association types have been discussed and compared. The major difference between the ions is that nitrate ion tends to form ion pairs, whereas perchlorate ion does not.     

Bathophenanthrolinedisulphonic acid and bathocuproinedisulphonic acid, water soluble reagents for iron and copper

Bathophenanthrolinedisulphonic acid and bathocuproinedisulphonic acid have been isolated in solid form as sodium salts and characterised. Both materials retain the high sensitivity of the parent materials as spectrophotometric reagents, for iron and copper respectively. They are water soluble and unlike the parent reagents may be used in aqueous perchlorate solutions. Interferences are about the same as with the parent reagents, but the pH range for maximum colour formation extends two pH units further into the alkaline region. Iron^II tribathophenanthrolinedi-sulphonic acid is an excellent oxidation-reduction indicator, changing sharply from red to green in the cerate titration of iron^II; it may be used in solutions containing perchloric acid.     

Thallium(I) iodate solubility product and iodic acid dissociation constant from 2 to 75°C

Using methods of potentiostatic coulometry, the solubility of thallium(I) iodate in 0.1m sodium perchlorate and in 0.1m perchloric acid was determined over the temperature range 2–75°C. Thermodynamic functions were calculated for the dissociation of thallium(I) iodate into its aqueous ions. From the solubilities in the acid solutions the dissociation constant of iodic acid was calculated over the temperature range, along with the value of –1.83±0.07 kcal-mol^–1 for the standard enthalpy change for the dissociation.     

The Acid-Catalyzed Hydrolysis of Anomeric Alkyl Fructofuranosides

Abstract

The rate constants for the hydrolysis of some al-kyl α- and β-d-fructofuranosides in aqueous perchloric acid have been determined at various temperatures. The effects of varying the aglycon structure on the hydrolysis rate suggest, together with the markedly positive entropies of activation, that the substrate, protonated on the glycosidic oxygen atom, undergoes a rate-limiting unimolecular heterolysis to form a glycosyl oxocar-benium ion. The rate variations in mixtures of aqueous perchloric acid and dimethyl sulfoxide are interpreted as lending further support for the proposed mechanism.     

Intradiffusion coefficients in perchloric acid solutions: Water at 5°C; water and perchlorate ion at 25°C

Intradiffusion coefficients for tritiated water (³HHO) and perchlorate ion (³⁶ClO ₄ ^- ) were measured in perchloric acid solutions. At 5°C the diffusion coefficient measured for the tritiated species increases to a maximum near 1.3 mol-dm^–3. The data at 25°C have been used to calculate distinct diffusion coefficients, D _ij ^d . As a precursor for those calculations, new estimates were made of the Onsager phenomenological coefficients, l _ij . The l _ij and D _ij ^d are similar to the respective coefficients in hydrochloric acid solutions.     

Infrared study of anion—solvent hydrogen bonding in formamide electrolyte solutions

A splitting of the ND stretching band of partly deuterated formamide has been found in perchlorate and tetrafluoroborate solutions. A continuous shift to lower frequencies has been observed for halide solutions. These effects are discussed in terms of the solvent separated ion pair model previously proposed for aqueous solutions.     

Solvation of the bismuth(III) ion by water, dimethyl sulfoxide, N,N'-dimethylpropyleneurea, and N,N-dimethylthioformamide. An EXAFS, large-angle X-ray scattering, and crystallographic structural study

The structure of the solvated bismuth(III) ion in aqueous, dimethyl sulfoxide, N,N'-dimethylpropyleneurea, and N,N-dimethylthioformamide solution has been studied by means of EXAFS and large-angle X-ray scattering (LAXS). The crystal structures of the solid compounds octakis(dimethyl sulfoxide)bismuth(III) perchlorate, [Bi(OS(CH3)2)8](ClO4)3, hexakis(N,N'-dimethylpropyleneurea)bismuth(III) perchlorate, [Bi(OCN2(CH2)3(CH3)2)6](ClO4)3, and nonaaquabismuth(III) trifluoromethanesulfonate, [Bi(H2O)9](CF3SO3)3 (redetermination), have been determined. The aqueous solutions must be strongly acidic, since the hydrated bismuth(III) ion starts to hydrolyze into Bi6O4(OH)4(6+) complexes already at an excess of strong acid at 1.0 mol.dm-3. For very acidic aqueous perchlorate solutions, the LAXS and EXAFS data gave a satisfactory fit for eight-coordination of the bismuth(III) ion, with a mean Bi-O bond distance of 2.41(1) A. The crystal structure of octakis(dimethyl sulfoxide)bismuth(III) perchlorate shows that the bismuth(III) ion coordinates eight dimethyl sulfoxide molecules via the oxygen atoms in a distorted square antiprismatic configuration. The mean Bi-O bond distance is 2.43 A and the mean Bi...S distance 3.56 A. For the dimethyl sulfoxide solution, the corresponding mean distances were found to be 2.411(6) and 3.535(12) A. The N,N'-dimethylpropyleneurea-solvated bismuth(III) ion is octahedrally coordinated in both solid state and solution with the Bi-O bond distances of 2.324(5) and 2.322(3) A, respectively. The bismuth(III) ion is six-coordinated in the sulfur donor solvent N,N-dimethylthioformamide with a mean Bi-S bond distance of 2.794(8) A. A comparison with the structure of the solvated lanthanum(III) ion shows that the bismuth(III) ion is smaller for all coordination numbers. New effective ionic radii for the bismuth(III) ion in different coordination numbers are proposed, based on results in this study and in the literature.