The dissociation constants (pKa) for sparingly soluble phenothiazines (promazine, chlorpromazine, trifluoropromazine) in water were measured by second-derivative spectrophotometry. The intense background signals in the absorption spectra due to the turbidity caused by the precipitation of insoluble free base of the phenothiazine derivatives were eliminated in the second-derivative spectra, and the solubilities of the phenothiazine derivatives could be easily determined from the peak-to-trough lengths (D values) of the second-derivative signals. The pKa values were calculated from the pH dependence of the D values. The pKa values obtained agreed well with reported values and the standard deviations for 6–10 determinations were ? 0.02. The solubilities of the free bases of the phenothiazines were also determined. 相似文献
In exploring the capability of nuclear magnetic resonance (NMR) spectroscopy for pomegranate juice analysis, the eight aromatic singlet resonances of α- and β-punicalagin were clearly identified in the 1H NMR spectra of juice samples. The four downfield resonances were found to be sensitive to small pH changes around pH 3.50 where the NMR spectra of the juice samples were recorded. To understand this unusual behavior, the 1H and 13C resonance assignments of the punicalagin anomers were determined in aqueous solution and pH titrations with UV and 1H NMR detection carried out to characterize the acid–base properties of punicalagin over the pH range 2–8. Simultaneous fitting of all of the pH-sensitive 1H NMR signals produced similar but significantly different pKa values for the first two deprotonation equilibria of the gallagic acid moiety of the punicalagin α- (pKa1?=?4.57?±?0.02, pKa2?=?5.63?±?0.03) and β- (pKa1?=?4.36?±?0.01, pKa2?=?5.47?±?0.02) anomers. Equivalent pKa values, (α?:?6.64?±?0.01, β?:?6.63±?0.01) were measured for the third deprotonation step involving the ellagic acid group, in good agreement with a prior literature report. The punicalagin anomer equilibrium readjusts in parallel with the proton dissociation steps as the pH is raised such that β-punicalagin becomes the most abundant anomer at neutral pH. The unusual upfield shifts observed for the glucose H3 and H5 resonances with increasing pH along with the shift in the α/β anomer equilibrium are likely the consequence of a conformational rearrangement.
Figure
Titration of the punicalagin phenolate protons over the pH range 2–8 results in changes in the aromatic proton chemical shifts and a readjustment of the anomer equilibrium. 相似文献
To contribute to the understanding of Eu(III) interaction preperties on hydrous alumina particles in the absence and presence of fulvic acid (FA), the complexation properties of Eu(III) with hydrous alumina, FA and FA-alumina hybrids are studied by batch and time-resolved laser fluorescence spectroscopy (TRLFS) techniques. The continuous increase in the fluorescence lifetime of Eu-alumina and Eu-FA with increasing pH indicates that the complexation is accompanied by decreasing number of hydration water in the first coordination sphere of Eu(III). Eu(III) is adsorbed onto alumina particles as outer-sphere surface complexes of ≡(Al?O)?Eu· (OH)· 7H2O and ≡(Al?O)?Eu· 6H2O at low pH values, and as inner-sphere surface complexes as ≡(Al?O)2?Eu+· 4H2O at high pH. In FA solution, Eu(III) forms complexes with FA as (COO)2Eu+(H2O)x and the hydration water number in the first coordination sphere decreases with pH increasing. The formation of ≡COO?Eu?(O?Al≡)· 4H2O is observed on FA-alumina hybrids, suggesting the formation of strong inner-sphere surface complexes in the presence of FA. The surface complexes are also characterized by their emission spectra [the ratio of emission intensities of 5D0→7F1 (λ=594 nm) and 5D0→7F2 (λ=619 nm) transitions] and their fluorescence lifetime. The findings is important to understand the contribution of FA in the complexation properties of Eu(III) on FA-alumina hybrids that the clarification of the environmental behavior of humic substances is necessary to understand fully the behavior of Eu(III), or its analogue trivalent lanthanide and actinide ions in natural environment. 相似文献
EPR and electronic absorption spectra of chrome alum solutions in sulphuric and phosphoric acids have been studied. Broadening of the EPR lines and shifts in the positions of the electronic spectra absorption bands were observed at low acid concentrations. In concentrated acids the 4T2g band splits into several well resolved components and the EPR spectra show two resolved areas of fine structure. Each structure may be described by a spinHamiltonian of the form where D is the zero-field splitting parameter due to the action of the axial crystal fields. The changes in the spectra as the acid concentration is increased are explained by changes in the internal environment of the CrIII complexes as a result of the substitution of H2O by anions of the acid residue. The symmetry of the complexes predominating at particular acid concentrations and the parameters D, g and Dt have been determined from an analysis of the EPR and optical absorption spectra. The character of the bond of the CrIII ion with the surrounding ligands has also been estimated. 相似文献
Nitrogen dioxide (?NO2), one of the oxidizing radicals formed in vivo is suspected to play a role in various pathophysiological processes. The reactions of ?NO2 with dietary catechins, the group of flavonoids present in high amounts in green tea and red wine, have been investigated by pulse radiolysis method. The kinetics of the reaction of ?NO2 with gallic acid have been also studied for comparison. The spectra of transient intermediates are presented. The rate constants of the reaction of ?NO2 with catechin, epigallocatechin, epigallocatechin gallate and gallic acid determined by the competition method with 2,2’-azinobis-(3-ethylbenzthiazoline-6-sulfonate) at pH 7.0 and room temperature have been found to be 0.9, 1.0, 2.3 and 0.5×108 M?1 s?1, respectively. The values for catechins are among the highest reported for the reactions of ?NO2 with non-radical compounds. 相似文献
The CL spectra of the title reactions and their pressure dependences have been studied over the 5 × 10?6 ? 5 × 10?3 torr range in a beam-gas experiment. In the Sm + N2O, O3 and Yb + O3 reactions simple bimolecular formation of the short lived (radiative lifetime τR < 3 × 10?6 s) MO* emitters dominates the entire pressure range. In the other systems Sm + (F2, Cl2), Yb + (F2, Cl2) the CL spectra are strongly pressure dependent, indicating extensive energy transfer from long-lived intermediates. Reaction mechanisms are suggested. The quantum yields Φ, obtained by calibrating relative quantum yields with Dickson and Zare's absolute value for Sm + N2O [Chem. Phys. 7 (1975) 367], range from Φ = 2.3% (for Sm + F2, the most efficient reaction) down to Φ = 0.005% for Yb + Cl2. The following lower limit estimates were obtained for the product dissociation energies from the short wavelength CL cutoffs: D00(SmF) ? 121.3 ± 2.4 kcal/mole, D00(SmCl) ? ? 100 ± 3 kcal/mole, D00(YbO) ? 94.2 ± 1.5 kcal/moie, D00(YbF) ? 123.7 ± 2.3 kcal/mole. 相似文献
A parametric analysis of the Stark-split spectra of Nd3+ in frozen dilute aqueous solutions of neodymium chloride has been carried out.The similarity of the spectra of Nd3+ in frozen dilute solutions and in crystals, where the ion is nine-fold coordinated and of approximate D3h symmetry (Nd3+: LaCl3, neodymium ethylsulfate and bromate), was used to obtain initial parameter values. Simultaneous diagonalization of the free ion and crystal field hamiltonians resulted in a r.m.s. deviation σ of 11 cm?1 for 50 levels. The resulting crystal field parameters are B20 = 278 ± 19, B40 = ?201 ± 39, Bb0 = ?946 ± 55 and B66 = 663 ± 43 cm?1. Selection rules for D3h are approximately obeyed. The small value of σ, the number of levels accounted for and the fact that the final parameters are not very different from those in the crystals indicate a nine-fold coordination of approximate D3h symmetry for Nd3+ in frozen aqueous solutions. The spectra of liquid solutions show by their similarity to the spectra of frozen solutions that the same surroundings exist in the liquid. 相似文献
The solubility of ethylmethylglyoxime (EMG) was studied as a function of pH. The solubility Ksl in 0.1 M aqueous solution is 0.0132 ±0.0006 M. The distribution constants KDl of EMG between various organic solvents and 0.1 M aqueous solution were found to be —0.47 for chloroform, —0.51 for benzene, —1.10 for carbon tetrachloride and —1.83 for hexane. The acid dissociation constants were determined from potentiometric titrations; the values pKa1=10.51 and pKa2=12.02 were obtaining by fitting the experimental data to normalized curves. The UV spectra of 5·10-5M EMG solutions of varying pH were measured between 210 and 290 nm. It is shown that H2A has an absorption maximum at 226 nm and HA-and A2- have absorption maxima at nearly the same wavelengths, i.e. 258 and 266 nm, respectively. The spectra of HA- and A2- have approximately the same form. The data are compared with those of dimethylglyoxime (DMG). The distribution constants (org/aq) are 4–5 times higher for EMG. The acid dissociation constants are about the same for EMG and DMG, but EMG is more soluble in water than DMG (13.2 and 5.0 mmoles/l, respectively). The UV spectra of EMG and DMG are very similar. 相似文献
Synthesis and characterization of five arylazo derivatives of 1-amino-2-hydroxy-4-naphthalenesulfonic acid (H2L1) are reported. The UV/Vis absorption spectra of the parent compound (H2L1) and its arylazo derivatives (H2L2–H4L6) have been measured at room temperature in seven solvents of different polarities and with variable parameters. The electronic transitions were analyzed using SPSS program, linear regression technique and Kamlet–Taft’s equation to permit a good understanding of solvent-induced spectral shifts. The electronic absorption spectra of the prepared compounds containing different substituents were studied in aqueous solutions at different pH values. The pK values of the investigated compounds were evaluated spectrophotometrically. The prevailing acid species present at any pH range are judged from the constructed distribution diagrams. 相似文献
The infrared spectra of the isotopically isolated NH3D+ and HDO species have been examined in seven ammonium Tutton salts. The observed spectra are in good agreement with predictions based on the known crystallographic features of these salts. Linear regression of the ND stretching frequencies v1(NH3D+) of the isotopically isolated NH3D+ ion on hydrogen-bonded distance d(N ? O) indicated the existence of a correlation ; subsequent fitting of the data to a more plausible empirical function v1(NH3D+) = v1,∞,-k1 exp(-k2,d) resulted in a coefficient of determination of 0.94 and a standard deviation of 10 cm?1 for the goodness of fit. The structural differences caused by the distortion of the metal coordination octahedron in the copper(II) Tutton salts are discussed. For this purpose the spectra of isotopically dilute HDO in the salts M2i[Cu(H2O)6](SO4)2 (Mi = K, Rb, Cs) have also been measured. No evidence of phase transformations between room and liquid-nitrogen temperatures was detected in the spectra of any of the saltri studied in this work. 相似文献
The proton NMR in single crystals of malonic acid has been studied by multiple pulse line narrowing techniques. The nuclear magnetic shielding tensors σ(i) of all protons in malonic acid could be determined from the spectra. There are two magnetically distinct carboxyl protons. The principal components of their shielding tensors are found to be σ(1)ZZ= ?0.8 ppm, σ(1)YY = ?19.2 ppm, σ(1)XX = ?21.8 ppm, and σ(2)ZZ = ?1.0 ppm, σ(2)ZZ = ?21.3 ppm relative to adamantane. The error limits are estimated to be ± 1 ppm. The most shielded directions lie along the hydrogen bond directions to within 8 degrees. The least shielded directions are essentially perpendicular to the plane of the carboxyl groups. Within experimental accuracy the shielding of the aliphatic protons is axially symmetric about the CH bond axes. The anisotropy Δσ = σ? ? σ⊥ is (4 ± 1) ppm. The gross features of the anisotropy of the carboxyl protons are shown to be governed by the diamagnetic effect. 相似文献
Voltammetry of silicotungstic acid (STA), H4SiW12O40, that was encapsulated in silica was performed in the absence of a contacting liquid phase. Two one-electron reductions that are separated by 200?mV were observed, which is the same behavior as in aqueous solution. At scan rates, v, below 10?mV s?1 with a 10?μm dia. carbon fiber indicator electrode, plateaus with limiting currents which are independent of v were observed, which is indicative of spherical diffusion from a field that is much larger than the electrode area. At v?>?20?V?s?1, peaks were observed with currents directly proportional to v½. For a gel aged for 2 days, an effective diffusion coefficient, Deff, of 3?×?10?7?cm2 s?1 was estimated by voltammetry and chronoamperometry; the concentration of the redox sites thereby determined was about 0.5?M. The Deff values that were obtained in this study were larger than expected for a solid electrolyte, which suggests an important role of residual water. In support of this model, gels that were aged in a humidistat at 33% humidity at room temperature for 2 and 5 days lost 16% and 13%, respectively, of their mass when dried at 120°. 相似文献
Some inconsistency has existed in the assignment of the vibrational spectra of the Cr(CN)63? ion, and the crystal structure of K3Cr(CN)6 has been described both as monoclinic C2h5 and as orthorhombic D2h14. The solution and single crystal Raman spectra were recorded at room temperature. On the basis of these data a new assignment was made and the crystal structure was determined to be orthorhombic. 相似文献
The acid dissociation constant of the imidazolium ring of the decapeptide luliberin has been determined by 1H NMR-followed titration in D2O. The normal procedure for the analysis of the titration curve, i.e. direct use of the Henderson-Haselbalch equation, is still applicable in this case, but for more complex peptides a modified calculation procedure is proposed. Results obtained when both methods were applied to luliberin are compared. The influence of D2O when used as the solvent in this type of determination has been studied using Nα-acetyl-L -histidine methyl ester as a model compound. The difference between the acid dissociation constant of this molecule determined in H2O and in D2O implies that a correction of ?.25 unit is needed for those pKa values calculated by plotting the chemical shifts in D2O vs the apparent pH meter readings. The pKa found for Nα-acetyl-L-histidine methyl ester, 6.30 ± 0.04, can be taken as a standard value for histidine-containing peptides. 相似文献
The vibrational spectra (IR and Raman) of CH2ClPO3H2 and of its anions in solutions of H2O and D2O are reported. The IR spectra of the solid dibasic sodium and potassium salts, the solid normal and O-deuterated monobasic sodium and potassium salts and of the solid normal and O-deuterated acid are discussed. Symmetry and internal stretching force constants, stretch-stretch interactions and potential energy distributions are obtained from normal coordinate analysis of CH2C1PO3H2, CH2ClPO3H? and CH2C1PO32?, and the calculated and observed frequencies for O-deuterated acid and monobasic anion are compared. 相似文献
Reference value standards, pH (RVS), for 0.05 mol kg?1 potassium hydrogenphthalate (KHPh) reference buffer solutions in 5, 15 and 30% (w/w) acetonitrile/water mixed solvents at temperatures from 288.15 to 308.15 K are determined from reversible e.m.f. measurements of the cell Pt¦H2¦KHPh + KCl¦AgCl|Ag|Pt. Values of the first ionisation constant of o-phthalic acid (H2Ph; benzene-1,2-dicarboxylic acid) in these mixed solvents are also determined from analogous measurements. The consistency of the results is analysed by multilinear regression of the quantity p(aHγCl) as a function of both solution composition and temperature. The standard pH (RVS) values determined are given by the equation pH (RVS) = 4.0080 + 6.330x + 16.177x2 ? 115.3x3 + 0.3089u ? 201.0ux2 + 909ux3 + 13.04v, where x is the mole fraction of acetonitrile in the mixed solvent, u = z/(1 + z), v = [ln(1 + z) ? u], z = (T ? θ)/θ, and θ = 298.15 K. 相似文献
The values of the thermodynamic second dissociation constant, pK2, and related thermodynamic quantities of N-(2-hydroxyethyl)piperazine-N′-2-hydroxypropanesulfonic acid (HEPPSO) have already been reported from 5 to 55?°C, including 37?°C, by the emf method. This paper reports the results for the pH of one chloride-free buffer solution containing the composition: (a) HEPPSO (0.08 mol?kg?1)+NaHEPPSO (0.04 mol?kg?1). The remaining seventeen buffer solutions contain a saline medium of ionic strength I=0.16 mol?kg?1, matching closely that of physiological fluids. Conventional pH values, denoted as paH, for all eighteen buffer solutions from 5 to 55?°C have been calculated. The operational pH values, designated as pH, with residual liquid-junction corrections for five buffer solutions, one without NaCl, and four with buffer solutions in saline media of I=0.16 mol?kg?1 are recommended as pH standards in the range of physiological application. These are based on the NBS/NIST standard scale for pH measurements. 相似文献
The mechanism of lithium ion intercalation/de-intercalation into LiNi1/3Mn1/3Co1/3O2 cathode material prepared by reactions under autogenic pressure at elevated temperatures method is investigated both in aqueous and non-aqueous electrolytes using electrochemical impedance spectroscopy (EIS) technique. In accordance with the results obtained an equivalent circuit is used to fit the impedance spectra. The kinetic parameters of intercalation/de-intercalation processes are evaluated with the help of the same equivalent circuit. The dependence of charge transfer resistance (Rct), exchange current (I0), double layer capacitance (Cdl), Warburg resistance (Zw), and chemical diffusion coefficient (DLi+) on potential during intercalation/de-intercalation is studied. The behavior of EIS spectra and its potential dependence is studied to get the kinetics of the mechanism of intercalation/de-intercalation processes, which cannot be obtained from the usual electrochemical studies like cyclic voltammetry. The results indicate that intercalation and de-intercalation of lithium ions in aqueous solution follows almost similar mechanism in non-aqueous system. DLi+ values are in the range of 10?8 to 10?14?cm2?s?1 in aqueous 5?M LiNO3 and that in non-aqueous 1?M LiAsF6/EC+DMC electrolyte is in the order of 10?12?cm2?s?1 during the intercalation/de-intercalation processes. A typical cell LiTi2 (PO4)3/5?M LiNO3/LiNi1/3Mn1/3Co1/3O2 is constructed and the cycling stability is compared to that with an organic electrolyte. 相似文献
Emulsions of n-tetradecane in water (0.1%v/V) homogenized by ultrasounds (1 5 min) were stabilized by 0.5 or 1.0 M ethanol and in the presence of lysozyme (4 mg 100 ml−1) or 1 mM lysine monohydrochloride (14.6 mg 100 ml−1). The zeta potentials and multimodal size distributions of the droplets after 5, 15, 30, 60, 120 min, and 1 and 2 days were determined by dynamic light scattering technique using ZetaPlus apparatus (Brookhaven Instr., USA). Both parameters were determined on the same sample subsequently without any mixing. The effect of pH [4, 6.8 (natural), and 11] was also investigated. The most stable emulsions in 1 M ethanol solutions alone were at pH 6.8 and 11 (the effective diameter Deff and 350 nm, respectively), while in 0.5 M at pH 4 (Deff nm). The most stable emulsions with lysozyme were obtained at pH 4 and 1 M ethanol (Deff nm), and with lysine at pH 6.8 and 0.5 M ethanol (Deff nm). Except for the emulsions with lysozyme at pH 4 and 6.8, in the rest systems the zeta potentials were negative and ranged between −5 and −85 mV as a function of time and pH. The changes of zeta potential indicate that H+ ions are not much potential determining, while OH− ions increase the negative zeta potentials. However, H+ ions affect functional groups of lysozyme molecules adsorbed on the alkane droplet, what appears in essential changes of zeta potential and even reversed sign of it in some systems. The results point that stability of these emulsions may also be determined by hydrogen bonding. 相似文献
Temperature dependences of the heat capacity of G-3(D4) and G-6(D4) carbosilanecyclosiloxane dendrimers are studied for the first time by precision adiabatic vacuum and differential scanning calorimetry in the range of 6 to 350–450 K. Physical transformations in the investigated temperature range are observed and their standard thermodynamic characteristics are determined and discussed. Standard thermodynamic functions for a mole unit are calculated from the experimental data: Cp○(T), H○(T), ? H○(0), S○(T) ? S○(0), and G○(T) ? H○(0) in the range of T → 0 to (350–449) K and standard entropies of formation at 298.15 K. Low-temperature (T ≤ 50 K) heat capacity is analyzed using the Debye theory of heat capacity of solids and the multifractal model. The values of fractal dimensionality D are determined and some conclusions on the topology of the investigated structures are drawn. The corresponding thermodynamic properties of the investigated carbosilanecyclosiloxane dendrimers under study are compared. 相似文献