Goodbye to S2- in aqueous solution.

New Raman spectra of Na2S dissolved in hyper-concentrated NaOH(aq) and CsOH(aq) cast serious doubt on the widely-assumed existence of S2-(aq). To avoid conceptual and practical problems with sulfide equilibria in numerous applications, S2-(aq) should be expunged from the chemical literature. Thermodynamic databases involving sulfide minerals also need careful revision.

Quantitative analysis in alkaline solutions by Raman spectroscopy.

A detailed investigation has been made of the analysis of concentrated alkaline aluminate solutions (synthetic Bayer liquors) by Fourier transform (FT) Raman spectroscopy. Satisfactory determinations of Al(OH)4-, SO42- and CO32- were achieved at industrially-relevant concentrations. Possible extensions to a number of other inorganic and organic anions of interest to the alumina refining industry were demonstrated. No significant interferences were observed except for a small but readily correctable contribution of a minor SO42- mode at ∼615 cm-1 to the Al(OH)4- envelope centred at ∼620 cm-1. Hydroxide (OH-) could not be determined with the present FT instrument, due to the low detector sensitivity at high wavenumbers, but might be possible with other spectrometers. Successful extension of the analyses to industrial Bayer process solutions is briefly discussed.

Comment on "Dynamic ion association in aqueous solutions of sulfate" [J. Chem. Phys. 123, 034508 (2005)].

The "dynamic exchange" model of ion association proposed by Watanabe and Hamaguchi, [J. Chem. Phys.123, 034508 (2005)] for aqueous solutions of MgSO4 is shown to be inconsistent with the extensive information available from Raman, relaxation, and thermodynamic studies, all of which can be explained by the Eigen equilibrium model.

An investigation of the lead(II)-hydroxide system.

A detailed investigation of the Pb(II)/OH(-) system has been made in NaClO(4) media at 25 degrees C. Combined UV-vis spectrophotometric-potentiometric titrations at [Pb(II)](T) < or = 10 microM using a long path length cell detected only four mononuclear hydroxide complexes. The values of log beta(1)(q)(), for the equilibria Pb(2+)(aq) + qH(2)O <--> Pb(OH)(q)()((2)(-)(q)()()+)(aq) + qH(+)(aq), were -7.2, -16.1, -26.5, and -38.0 for q = 1-4, respectively, at ionic strength I = 1 M (NaClO(4)). Similar results were obtained at I = 5 M (NaClO(4)). No evidence was found for higher order complexes (q > 4) even at very high [OH(-)]/[Pb(II)] ratios, nor for polynuclear species at [Pb(II)](T) < or = 10 microM. Measurements using (207)Pb-NMR and Raman spectroscopies and differential pulse polarography (DPP) provided only semiquantitative confirmation. The mononuclear Pb(OH)(q)()((2)(-)(q)()()+)(aq) complexes are the only hydrolyzed species likely to be significant under typical environmental and biological conditions.

Complexation of iron(III) and iron(II) by citrate. Implications for iron speciation in blood plasma.

Estimates of the concentrations and identity of the predominant complexes of iron with the low-molecular-mass ligands in vivo are important to improve current understanding of the metabolism of this trace element. These estimates require a knowledge of the stability of the iron-citrate complexes. Previous studies on the equilibrium properties of the Fe(III)-citrate and Fe(II)-citrate are in disagreement. Accordingly, in this work, glass electrode potentiometric titrations have been used to re-determine the formation constants of both the Fe(III)- and Fe(II)-citrate systems at 25 degrees C in 1.00 M (Na)Cl and the reliability of these constants has been evaluated by comparing the measured and predicted redox potentials of the ternary Fe(III)-Fe(II)-citrate system. The formation constants obtained in this way were used in computer simulation models of the low-molecular-mass iron fraction in blood plasma. Redox equilibria of iron are thus included in large models of blood plasma for the first time. The results of these calculations show the predominance of Fe(II)-carbonate complexes and a significant amount of aquated Fe(II) in human blood plasma.

19F NMR study of the equilibria and dynamics of the Al3+/F- system.

A careful reinvestigation by high-field 19F NMR (470 MHz) spectroscopy has been made of the Al3+/F- system in aqueous solution under carefully controlled conditions of pH, concentration, ionic strength (I), and temperature. The 19F NMR spectra show five distinct signals at 278 K and I = 0.6 M (TMACl) which have been attributed to the complexes AlFi(3-i)+(aq) with i < or = 5. There was no need to invoke AlFi(OH)j(3-i-j)+ mixed complexes in the model under our experimental conditions (pH < or = 6.5), nor was any evidence obtained for the formation of AlF6(3-)(aq) at very high ratios of F-/Al3+. The stepwise equilibrium constants obtained for the complexes by integration of the 19F signals are in good agreement with literature data given the differences in medium and temperature. In I = 0.6 M TMACl at 278 K and in I = 3 M KCl at 298 K the log Ki values are 6.42, 5.41, 3.99, 2.50, and 0.84 (for species i = 1-5) and 6.35, 5.25, and 4.11 (for species i = 1-3), respectively. Disappearance of the 19F NMR signals under certain conditions was shown to be due to precipitation. Certain 19F NMR signals exhibit temperature- and concentration-dependent exchange broadening. Detailed line shape analysis of the spectra and magnetization transfer measurements indicate that the kinetics are dominated by F- exchange rather than complex formation. The detected reactions and their rate constants are AlF2(2+) + *F- reversible AlF*F2+ + F- (k02 = (1.8 +/- 0.3) x 10(6) M-1 s-1), AlF3(0) + *F- reversible AlF2*F0 + F- (k03 = (3.9 +/- 0.9) x 10(6) M-1 s-1), and AlF3(0) + H*F reversible AlF2*F0 + HF (kH03 = (6.6 +/- 0.5) x 10(4) M-1 s-1). The rates of these exchange reactions increase markedly with increasing F- substitution. Thus, the reactions of AlF2+(aq) were too inert to be detected even on the T1 NMR time scale, while some of the reactions of AlF3(0)(aq) were fast, causing large line broadening. The ligand exchange appears to follow an associative interchange mechanism. The cis-trans isomerization of AlF2+(aq), consistent with octahedral geometry for that complex, is slowed sufficiently to be observed at temperatures around 270 K. Difference between the Al3+/F- system and the much studied Al3+/OH- system are briefly commented on.

Association constants for the NaSO(4)(-) ion pair in concentrated cesium chloride solutions.

Values of the association constant, beta(NaSO(4)(-)), for the weak ion-pair formed by sodium and sulfate ions in aqueous solution have been determined at 25 degrees C by high precision sodium ion-selective electrode potentiometry in solutions of ionic strength ranging from 0.50 to 7.00 M in CsCl media and in 1.00 M Me(4)NCl. The data in CsCl media were fitted to an extended form of the Debye-Hückel equation which yielded log beta(NaSO(4)(-))(0)=0.834+/-0.005 at infinite dilution. Evidence is also presented for the formation of very weak ion-pairs between Cs(+) and SO(4)(2-).

The ionic product of water in highly concentrated sodium perchlorate solutions.

The ionic product of water, pK(w)=-log[H(+)][OH(-)], has been determined in aqueous solutions of sodium perchlorate over the concentration range of 1.0-8.0 M at 25 degrees C from high-precision potentiometric titrations carried out in cells with liquid junction using both glass and hydrogen electrodes. The glass electrode results are systematically lower probably as a result of interference by Na(+) ions.

Complexation of copper(I) by thioamino acids. Implications for copper speciation in blood plasma.

There is mounting evidence that Cu(I) is the most important oxidation state of copper in many physiological systems. Research into Cu(I)-thioamino acid complex formation serves not only to improve the chelation therapy for treating copper intoxication but may also provide a better understanding of many facets of normal copper metabolism. Formation constants for the ternary mixed ligand complexes of Cu(I) with cysteine (Cys), glutathione (GSH) and penicillamine (Pen) are reported here for the first time. Potentiometric titrations, using techniques specially developed for the stabilization of aqueous Cu(I), were performed at 25 degrees C in 1.00 M (Na)Cl. It was found that precipitation severely limits the experimentally accessible pH range and, consequently, the computer analysis of the binary metal-ligand systems; however, it is also found that this is less of a problem when two different ligands are present. This latter fact permitted better models of the binary systems to be developed. The formation constants of Cu(I)-thioamino acids determined in this work were used in an improved computer simulation of copper speciation in blood plasma which, for the first time, incorporates redox equilibria.

The ionic product of water in concentrated tetramethylammonium chloride solutions.

The ionic product of water, pK(w) = - log[H(+)][OH(-)] has been determined in aqueous solutions of tetramethylammonium chloride over the concentration range of 0.1-5.5 M at 25 degrees C using high-precision glass electrode potentiometric titrations. pK(w) data relating to aqueous potassium and sodium chlorides at ionic strengths up to 5 M are markedly lower than the tetramethylammonium chloride results. These differences are almost certainly due to weak associations between potassium and (especially) sodium and hydroxide ions.

Cyanide thermodynamics 2. Stability constants of copper(I) cyanide complexes in aqueous acetonitrile mixtures.

The stability (formation) constants of the binary Cu(I)-CN(-) complexes have been measured in five aqueous mixtures containing from 10% to 70% v/v acetonitrile (MeCN) by glass electrode potentiometry at 25 degrees C and an ionic strength of l M (NaClO(4)). The constants show monotonic increases with MeCN concentration, the changes being greatest for the higher order complexes, consistent with the unfavourable solvation of CN (-) in these mixtures. The sparing solubility of CuCN(s) prevented determination of the stability constant for CuCN (0) (soln.) at low MeCN concentrations.

Biospeciation, by potentiometry and computer simulation, of Sm-EDTMP, a bone tumor palliative agent.

153Sm-EDTMP (ethylenediaminetetra(methylenephosphonic) acid) is of considerable interest as a bone therapeutic radiopharmaceutical but its properties in solution are not yet well characterized. The protonation constants of EDTMP and the formation constants of the complexes of Sm-EDTMP have accordingly been measured potentiometrically by glass electrode titrations at 25 degrees C in 0.15 M NaCl. Six protonation constants (log beta 011 = 9.638, log beta 012 = 17.330, log beta 013 = 23.597, 10g beta 014 = 28.636, log beta 015 = 31.501, log beta 016 = 32.624) and the formation constants of the [Sm(EDTMP)H-1]6-(log beta 11-1 = 4.865), [SmEDTMP]5-(log beta 110 = 12.018), [Sm(EDTMP)H]4- (log beta 111 = 17.892) and [Sm(EDTMP)H2]3- (log beta 112 = 23.437) complexes were determined. Computer simulations indicate that the [SmEDTMP]5- and the hydroxy [Sm(EDTMP)H-1]6- species are the major Sm(III) complexes formed in blood plasma, which explains the high degree of localization in the kidney and urine observed in biodistribution studies. Calcium ions are probably the major competitor for EDTMP in blood plasma. As the presence of secondary skeletal metastases results in a high rate of bone turnover, it is possible that the high concentration of calcium at these sites encourages localization of 153Sm-EDTMP.

ROLE OF UREA AND METHYLAMINES IN BUOYANCY OF ELASMOBRANCHS

The possible role of urea and trimethylamine oxide (TMAO) in providing positive buoyancy has been examined for elasmobranch fishes. TMAO has a considerably lower density than an equimolar solution of urea, and solutions of both TMAO and urea are considerably less dense than equimolar solutions of most other body fluid solutes. The body fluid composition of three elasmobranchs, the whiskery shark Furgaleus ventralis, the black whaler shark Carcharhinus obscurus and the shovelnosed ray Aptychotremata vincentiana, is typical for marine elasmobranchs, with plasma concentrations of about 260 mmol l-1 Na+, 250 mmol l-1 Cl-, 340 mmol l-1 urea and 70 mmol l-1 trimethylamine oxide. A plasma density of 1.015 was calculated for the whaler shark (from the concentrations, relative molecular masses and absolute molal volumes of plasma solutes), which would contribute a positive lift of 8.45 g l-1. There is a large positive contribution to buoyancy by urea (3.7 g l-1), trimethylamine oxide (1.8 g l-1) and Cl- (4.0 g l-1), whereas slight negative buoyancy is conferred by Na+ (-0.8 g l-1). Divalent cations (Ca2+, Mg2+) contribute minimal negative buoyancy (about -0.1 g l-1 each) despite their rather negative partial molal volumes, because of their low concentrations. Muscle fluids contain about 40 mmol l-1 Cl-, 365 mmol l-1 urea, 160 mmol l-1 trimethylamine oxide, 16 mmol l-1 betaine and 69 mmol l-1 sarcosine. The organic solutes contribute about 12.1 g l-1 lift. Although urea and TMAO act as balancing osmolytes, and TMAO as a counteracting solute, a positive buoyancy role must be considered as a further adaptive function of urea and TMAO accumulation in chondrichthyean fishes.

Iron chelators of the pyridoxal isonicotinoyl hydrazone class. III. Formation constants with calcium(II), magnesium(II) and zinc(II).

Formation constants for the calcium(II), magnesium(II) and zinc(II) complexes of the orally effective iron chelator, pyridoxal isonicotinoyl hydrazone (PIH) and three analogues, pyridoxal benzoyl hydrazone (PBH), pyridoxal p-methoxybenzoyl hydrazone (PpMBH) and pyridoxal m-fluorobenzoyl hydrazone (PmFBH) have been determined by potentiometry at 25 degrees C and I = 0.1 M [KNO3]. The four ligands bind calcium(II) weakly and magnesium(II) only slightly more strongly, as a 1:1 complex which is formed at pH greater than 8. The chelation of zinc(II) for all the ligands studied was greater than that for calcium(II) and magnesium(II), with complexation generally becoming significant at about pH 5. Thus, chelation of zinc(II) but not calcium(II) or magnesium(II) at physiological pH, 7.4 may be expected. Calculated values of the concentration of uncomplexed metal ion indicate that the selectivity of these ligands towards Fe(III) is comparable to that of the clinically used chelator desferrioxamine.