Chemical data evaluation: general considerations and approaches for IUPAC projects and the chemistry community (IUPAC Technical Report).

The International Union of Pure and Applied Chemistry (IUPAC) has a long tradition of supporting the compilation of chemical data and their evaluation through direct projects, nomenclature and terminology work, and partnerships with international scientific bodies, government agencies and other organizations. The IUPAC Interdivisional Subcommittee on Critical Evaluation of Data (ISCED) has been established to provide guidance on issues related to the evaluation of chemical data. In this first report we define the general principles of the evaluation of scientific data and describe best practices and approaches to data evaluation in chemistry.

Spectroscopic Study of the Behavior of Mo(VI) and W(VI) Polyanions in Sulfuric-Phosphoric Acid Mixtures.

The solution chemistry of Mo(VI) and W(VI) in mixtures of sulfuric and phosphoric acids is relevant to the development of practicable hydrometallurgical processes for the recovery and separation of these two elements from low-grade scheelite ores. The behavior of Mo(VI) and W(VI) in such mixtures has been studied using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), nuclear magnetic resonance (NMR), and small-angle X-ray scattering (SAXS) spectroscopies, along with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). Where applicable, these techniques have produced a self-consistent picture of the similarities and differences between the chemical speciation of Mo(VI) and W(VI) as functions of solution composition, mostly at a constant phosphorous/metal (P/M; M = Mo(VI) or W(VI)) ratio of ∼1. In dilute acidic media (0.02 mol·kg-1 H+, without H2SO4), Mo(VI) exists mostly (∼60%) as P2Mo5O236- with the remaining ∼40% as ß-Mo8O264-. Under the same conditions, W(VI) is largely present as NaPW11O396- (∼80%) and P2W5O236- (∼10%), with the remainder probably occurring as isopolytungstates such as W12O4212- and some tungstophosphate dimers such as P2W18O626-. At higher acid concentrations (≲5 mol·kg-1 H2SO4), polymeric Mo(VI) anions are broken down to form the oxocations MoO22+ and Mo2O52+ and their protonated forms, with the dimers becoming increasingly dominant at higher acidities (∼80% in 5 mol·kg-1 H2SO4). In stark contrast, W(VI) polyanions do not decompose at higher acidities but instead form (∼70% in 0.6 mol·kg-1 H2SO4) a Keggin ion, PW12O403-. Further acidification with H2SO4 results in the agglomeration of this Keggin ion, forming clusters of about 50 and 100 Å in diameter that ultimately produce crystalline precipitates, which could be identified in part by their X-ray diffraction patterns. Possible application of these findings to the hydrometallurgical separation of Mo and W using acidic solutions is briefly discussed, based on a limited number of batch solvent extractions.

The Fate of Morbidly Obese Patients With Joint Pain: A Retrospective Study of Patient Outcomes.

BACKGROUND: The number of obese patients seeking a total joint arthroplasty (TJA) continues to increase. Weight loss is often recommended to treat joint pain and reduce risks associated with TJA. We sought to determine the effectiveness of an orthopedic surgeon's recommendation to lose weight. METHODS: We identified morbidly obese (body mass index (BMI) 40-49.9 kg/m2) and super obese (BMI ≥50 kg/m2) patients with hip or knee osteoarthritis. Patients with less than 3-month follow-up were excluded. Patient characteristics (age, gender, BMI, comorbidities), disease characteristics (joint affected, radiographic osteoarthritis grading), and treatments were recorded. Clinically meaningful weight loss was defined as weight loss greater than 5%. RESULTS: Two hundred thirty morbid and 50 super obese patients were identified. Super obese patients were more likely to be referred to weight management (52.0% vs 21.7%, P < .001) and were less likely to receive TJA (20.0% vs 41.7%, P = .004). Each 1 kg/m2 increase in BMI decreased the odds of TJA by 10.9% (odds ratio = 0.891, 95% confidence interval: 0.833-0.953, P = .001). Forty (23.0%) of the nonoperatively treated patients achieved clinically meaningful weight loss, and 19 (17.9%) patients who underwent TJA lost weight before surgery. After surgery, the number of patients who achieved a clinically meaningful weight loss grew to 32 (30.2%). CONCLUSION: In morbid and super obese patients, increasing BMI reduces the likelihood that a patient will receive TJA, and when counseled by their orthopedic surgeon, few patients participate in weight-loss programs or are otherwise able to lose weight. Weight loss is an inconsistently modifiable risk factor for joint replacement surgery.

A spectroscopic study of solvent effects on the formation of Cu(ii)-chloride complexes in aqueous solution.

A combination of electronic (UV-vis) and X-ray absorption (EXAFS, XANES) spectroscopies has been used to investigate the formation of copper(ii)/chloride complexes in concentrated aqueous solutions. It is established that lowering the water activity by the addition of Mg(ClO4)2 at a constant Cl-/Cu(ii) ratio results in the replacement of water molecules by Cl- ions in the primary coordination shell of Cu(ii). This behavior closely parallels the effect of increasing the Cl-/Cu(ii) ratio and demonstrates that full understanding of the stoichiometry and structures of the complexes formed in concentrated metal-ion chloride solutions requires explicit consideration of the role of the solvent.

Reference Materials for Phase Equilibrium Studies. 1. Liquid-Liquid Equilibria (IUPAC Technical Report).

This article is the first of three projected IUPAC Technical Reports resulting from IUPAC Project 2011-037-2-100 (Reference Materials for Phase Equilibrium Studies). The goal of that project was to select reference systems with critically evaluated property values for the validation of instruments and techniques used in phase equilibrium studies for mixtures. This Report proposes seven systems for liquid-liquid equilibrium studies, covering the four most common categories of binary mixtures: aqueous systems of moderate solubility, non-aqueous systems, systems with low solubility, and systems with ionic liquids. For each system, the available literature sources, accepted data, smoothing equations, and estimated uncertainties are given.

Systematic Variations of Ion Hydration in Aqueous Alkali Metal Fluoride Solutions.

Aqueous solutions of three alkali metal fluorides-NaF, KF, and CsF-have been studied by dielectric relaxation spectroscopy (DRS) over the frequency range 0.2 ≲ ν/GHz ≤ 89 at 25 °C and at concentrations 0.05 ≲ c/mol L-1 ≲ 1. The combination of these measurements with analogous literature data for RbF(aq) and M'Cl(aq) (M' = Li, Na, K, and Cs) made possible a systematic analysis of the hydration of F- and the alkali metal cations. Unlike the other halide ions, F- was found to have a well-defined hydration shell which contains ∼7 water molecules, consistent with the appearance of a "slow"-water mode at ∼10 GHz in the spectra. Limiting total effective hydration numbers (Zt0) for M'F(aq), obtained from the solvent-related modes, did not follow a simple sequence, varying in the order CsF < NaF < RbF < KF. However, it is shown that this anomalous sequence results from subtle variations in the strength of the M'+-OH2 bonding. Thus, it was established that Zib0(M'+) values, corresponding to the numbers of strongly ("irrotationally") bound (ib) water molecules around the cations, do vary with charge density in the order Li+ ≫ Na+ > K+ > Rb+ > Cs+. It was also found that Zs0(M'+), the number of moderately bound ("slow") water molecules, varied in the same order: K+ > Rb+ > Cs+. However, the presence of ib water molecules in the hydration shells of Li+ and Na+ attenuates their further interaction with surrounding water molecules such that Zs0(M'+) ≈ 0 for both ions.

Enthalpies of Solution of C-Alkylresorcin[4]arenes in Water and Acetonitrile: Hydrophilic and Hydrophobic Effects.

Enthalpies of solution, Δsln H, of six C-alkylresorcin[4]arene ( C-ARA) solids, with alkyl substituents varying systematically from methyl (Me) to hexyl (Hx), have been measured in water, using solubility data, and in acetonitrile, by direct calorimetry. For all of the C-ARAs studied, the values of Δsln H were highly favorable (exothermic) for dissolution into water but were strongly unfavorable (endothermic) for dissolution into acetonitrile (ACN). The differences between the two solvents varied systematically with increasing carbon chain length, from about 100 kJ·mol-1 (for Me) to 140 kJ·mol-1 (for Hx). These extraordinary variances can be attributed to the loss of hydrophilic hydration of the eight -OH groups on the rim of the C-ARAs and also by the loss of (enthalpically favorable) hydrophobic hydration of the alkyl chains upon transfer from the highly structured, strongly H-bonding water to the aprotic, relatively weak donor/acceptor ACN. Although Δsln H values for the present C-ARAs in H2O are strongly favorable, they are more than counteracted by even larger negative changes in the entropy of dissolution, Δsln S. This enthalpy/entropy compensation effect is consistent with the low aqueous solubilities (<10-3 mol·kg-1) of the C-ARAs and their slight increase with increasing carbon chain length, which is opposite to typical behavior of the homologous series of organic molecules.

Nature of Monomeric Molybdenum(VI) Cations in Acid Solutions Using Theoretical Calculations and Raman Spectroscopy.

The composition and structures of the two protonated species formed from uncharged molybdic acid, MoO2(OH)2(OH2)20, in strongly acidic solutions have been investigated using a combination of density functional theory calculations, first-principles molecular dynamics simulations, and Raman spectroscopy. The calculations show that both protonated species maintain the original octahedral structure of molybdic acid. Computed p Ka values indicated that the ═O moieties are the proton acceptor sites and, therefore, that MoO(OH)3(OH2)2+ and Mo(OH)4(OH2)22+ are the probable protonated forms of Mo(VI) in strong acid solutions, rather than the previously accepted MoO2(OH)2- x(OH2)2+ x x+ ( x = 1, 2) species. This finding is shown to be broadly consistent with the observed Raman spectra. Structural details of MoO(OH)3(OH2)2+ and Mo(OH)4(OH2)22+ are reported.

Cation Hydration and Ion Pairing in Aqueous Solutions of MgCl2 and CaCl2.

Broadband dielectric relaxation spectroscopy (DRS) has been used to investigate aqueous solutions of MgCl2 and CaCl2 up to concentrations of about 1.8 mol L-1 at 25 °C over the frequency range 0.07 ≤ ν/GHz ≤ 89. Detailed analysis of the dominant solvent mode centered at ∼20 GHz showed that both Mg2+ and Ca2+ are strongly solvated, each immobilizing ∼20 water molecules on the DRS timescale. This is consistent with the formation of two well-defined hydration layers around both cations. The hydration shell of Ca2+(aq) was found to be slightly more labile compared with Mg2+(aq). Two or three low-intensity solute-related modes were observed at frequencies ≲10 GHz for MgCl2(aq) and CaCl2, respectively. Two of these modes were attributed to the formation of double-solvent-separated and solvent-shared 1:1 ion pairs. The third mode (observed at very low frequencies and only for some CaCl2 solutions) was thought to be due to an ion-cloud relaxation. No evidence was found for "slow" water or, consistent with the strong cation hydration, for contact ion pairs. The overall association constants for MgCl+(aq) and CaCl+(aq) calculated from the ion-pairing constants were very small but in good agreement with literature values obtained from other techniques.

Hydration and ion association of La3+ and Eu3+ salts in aqueous solution.

Aqueous solutions of five lanthanide salts: LaCl3, La(NO3)3, La2(SO4)3, Eu(NO3)3 and Eu2(SO4)3 have been studied at 25 °C by dielectric relaxation spectroscopy over the frequency range 0.05 ≤ ν/GHz ≤ 89. Detailed analysis of the solvent-related modes located at higher frequencies showed that both La3+ and Eu3+ are strongly hydrated, even including partial formation of a third hydration shell similar to that of Al3+(aq). Up to two solute-related modes could be detected at lower frequencies, due to the formation of various types of 1 : 1 ion pairs (IPs). All five salts showed modest levels of association in the order Cl- < NO3- ≪ SO42-, mostly in the form of double-solvent-separated IPs with small amounts of solvent-shared IPs. Overall association constants, , calculated from the stepwise IP formation constants were consistent with literature values.

Formation constants of copper(I) complexes with cysteine, penicillamine and glutathione: implications for copper speciation in the human eye.

Protonation constants for the biologically-important thioamino acids cysteine (CSH), penicillamine (PSH) and glutathione (GSH), and the formation constants of their complexes with Cu(I), have been measured at 25 °C and an ionic strength of 1.00 mol dm(-3) (Na)Cl using glass electrode potentiometry. The first successful characterisation of binary Cu(I)-CSH and Cu(I)-GSH species over the whole pH range was achieved in this study by the addition of a second thioamino acid, which prevented the precipitation that normally occurs. Appropriate combinations of binary and ternary (mixed ligand) titration data were used to optimise the speciation models and formation constants for the binary species. The results obtained differ significantly from literature data with respect to the detection and quantification of protonated and polynuclear complexes. The present results are thought to be more reliable because of the exceptionally wide pH and concentration ranges employed, the excellent reproducibility of the data, the close agreement between the calculated and observed formation functions, and the low standard deviations and absence of numerical correlation in the constants. The present formation constants were incorporated into a large Cu speciation model which was used to predict, for the first time, metal-ligand equilibria in the biofluids of the human eye. This simulation provided an explanation for the precipitation of metallic copper in lens and cornea, which is known to occur as a consequence of Wilson's disease.

Ion hydration and association in aqueous potassium phosphate solutions.

Ionic hydration and ion association in aqueous solutions of KH2PO4, K2HPO4, and K3PO4 at 25 °C up to high concentrations have been investigated using dielectric relaxation spectroscopy (DRS). The three phosphate anions were found to be extensively hydrated, with total hydration numbers at infinite dilution of ~11 (for H2PO4(-)), ~20 (HPO4(2-)), and ~39 (PO4(3-)). These values are indicative of the existence of a second hydration shell around HPO4(2-) and especially PO4(3-). Two types of hydrating water molecules could be quantified: irrotationally bound (ib, H2O molecules essentially "frozen" on the DRS time scale) and "slow" (loosely bound water molecules with identifiably slower dynamics than bulk water). For H2PO4(-) over the entire concentration range and for HPO4(2-) and PO4(3-) at concentrations c ≲ 1 mol L(-1), only "slow" H2O was detected; however, at higher concentrations of the latter two anions, an increasing fraction of ib water appears, making up ~50% of the total hydration number close to the saturation limit of K2HPO4. Contrary to common belief, all three salts showed significant ion pair formation, with standard association constants of the 1:1 species increasing in the order: KH2PO4(0)(aq) < KHPO4(-)(aq) < KPO4(2-)(aq). The main type of ion pair in solution shifted from solvent-shared ion pairs (SIPs) to double-solvent-separated ion pairs (2SIPs) in the same sequence.

Ultra-Broadband Dielectric and Optical Kerr-Effect Study of the Ionic Liquids Ethyl and Propylammonium Nitrate.

Dielectric relaxation (DR) and optical Kerr-effect (OKE) spectra of the archetypal protic ionic liquids ethyl- and propylammonium nitrate (EAN and PAN) have been measured over an unusually large frequency range from 200 MHz to 10 THz at temperatures (mostly) between 5 and 65 °C. Analysis of the low-frequency α-relaxation, associated with the cooperative relaxations of the cations (DR) and anions (OKE) and any clusters present, indicated that ion reorientation in EAN is decoupled from viscosity and occurs via cooperative relaxation involving large-angle jumps rather than rotational diffusion. Detailed consideration of the high-frequency parts of the DR and OKE spectra showed that the observed intensities were a complex combination of overlapping and possibly coupled modes. In addition to previously identified intermolecular H-bond vibrations, there are significant contributions from the librations of the cations and anions. The present assignments were shown to be consistent with the isotopic shifts observed for deuterated EAN.

Solvation and association of 3:1 electrolytes in N,N-dimethylformamide.

A detailed study has been made of the solvation and ion association of the trifluoromethanesulfonate (Tf(-)) salts of aluminum(III), scandium(III), and lanthanum(III) in N,N-dimethylformamide (DMF) at 25 °C using dielectric relaxation spectroscopy over the frequency range of 0.1 ≲ ν/GHz ≤ 89. The spectra of all solutions exhibited either two (for ScTf3 and LaTf3) or three (for AlTf3) relaxation processes, a dominant mode centered at ∼15 GHz due to the solvent and one or (for AlTf3 solutions) two solute-related processes at lower frequencies (νmax ≲ 2 GHz). Effective solvation numbers, Zib, calculated from the solvent relaxation process indicated that all three cations were strongly solvated by DMF with Zib(0) values at infinite dilution in the order (Al(3+) ≈ Sc(3+) ≈ 10) < (La(3+) ≈ 13), consistent with at least partial formation of a second solvation shell around each cation. One solute-related mode for each set of salt solutions was assigned to the rotational diffusion of solvent-shared ion pairs (SIPs) of 1:1 stoicheometry; the additional slower process for AlTf3 solutions in DMF was attributed to the presence of double-solvent-separated IPs. The overall association constants at infinite dilution for the 1:1 IPs, KA°(MTf(2+)), were significant, but as expected from Debye-Hückel considerations, the KA values decreased rapidly with increasing solute concentration.

Hydrophilic and hydrophobic hydration of sodium propanoate and sodium butanoate in aqueous solution.

Aqueous solutions of sodium propanoate (NaOPr) and n-butanoate (NaOBu) have been studied at concentrations of c ~/< 3 M by broadband dielectric relaxation spectroscopy over the frequency range 0.2 ≤ ν/GHz ≤ 89 at 25 °C. Three relaxation modes were resolved, centered at (approximately) 1, 8, and 18 GHz, for both sets of solutions. The two faster modes were assigned to the cooperative relaxation of "slow" and bulk water molecules. Detailed analysis of the spectra indicated that both OPr(-) and OBu(-) were strongly hydrated, with ~23 and ~33 slow water molecules per anion, respectively, at infinite dilution. These effective hydration numbers include ~6 water molecules hydrophilically bound to the carboxylate moiety, with the remainder arising from the hydrophobic hydration of the nonpolar alkyl chains. The latter shows a characteristic rapid decrease with increasing solute concentration, which facilitated the separation of the hydrophobic and hydrophilic contributions. The lowest frequency mode was a composite with contributions from ion-cloud, ion-pair, and anion relaxations. Although this low intensity mode provided specific evidence of weak ion pairing between Na(+)(aq) and the carboxylate anions, reliable estimates of the association constant could not be made because of its composite nature.

Structure and dynamics of 1-N-alkyl-3-N-methylimidazolium tetrafluoroborate + acetonitrile mixtures.

A detailed investigation of the binary mixtures of the ionic liquids (ILs) 1-N-R-3-N-methylimidazolium tetrafluoroborate (R = ethyl, n-butyl, n-hexyl) with the important molecular solvent acetonitrile (AN) over the entire composition range has been made at 25 °C using broadband dielectric spectroscopy. All spectra showed two modes: a Cole-Cole (CC) mode centered at ~2 GHz and a Debye mode centered at ~50 GHz. However, detailed analysis indicated both relaxations were composites. The Debye mode arises from the rotational diffusion of free AN molecules with contributions from ultrafast vibrations and librations of the ILs. The CC mode corresponds to the jump rotation of the imidazolium cations and the hindered rotational diffusion of "slow" AN molecules solvating them. At very low IL concentrations 1:1 contact ion pairs are dominant. Overall, these IL + AN mixtures can be divided into two broad regions: at IL mole fraction (x(IL)) ≲ 0.2 the IL behaves as a rather weakly associated conventional electrolyte while at x(IL) ≳ 0.2 it takes on its IL characteristics, "lubricated" by the AN.

Structure and dynamics in protic ionic liquids: a combined optical Kerr-effect and dielectric relaxation spectroscopy study.

The structure and dynamics of ionic liquids (ILs) are unusual due to the strong interactions between the ions and counter ions. These microscopic properties determine the bulk transport properties critical to applications of ILs such as advanced fuel cells. The terahertz dynamics and slower relaxations of simple alkylammonium nitrate protic ionic liquids (PILs) are here studied using femtosecond optical Kerr-effect spectroscopy, dielectric relaxation spectroscopy, and terahertz time-domain spectroscopy. The observed dynamics give insight into more general liquid behaviour while comparison with glass-forming liquids reveals an underlying power-law decay and relaxation rates suggest supramolecular structure and nanoscale segregation.

Hydration of formate and acetate ions by dielectric relaxation spectroscopy.

Dielectric relaxation (DR) spectra have been measured for aqueous solutions of sodium formate (NaOFm) and sodium acetate (NaOAc) over a wide range of frequencies (0.2 ≤ ν/GHz ≤ 89) up to solute concentrations c is less or approximately equal to 3.2 M and is less or approximately equal to 3.7 M, respectively, at 25 °C. Measurements were also made on NaOAc(aq) at 15 ≤ T/°C ≤ 35. In addition to the usual dominant bulk-water relaxation process at ~20 GHz, one or two further relaxation modes were detected. One process, centered at ~8 GHz and observed for both NaOFm(aq) and NaOAc(aq), was attributed to the presence of slow water in the hydration shells of the anions. A lower-frequency process at ~0.6 GHz, observed only for NaOAc(aq) at c is less or approximately equal to 1 M, was thought to be due to the presence of very small concentrations of ion pairs. Detailed analysis of the spectra indicated that very few (<2 per anion) water molecules were irrotationally bound (frozen) on the DR time scale. Nevertheless, both anions are strongly hydrated, as evidenced by the significant amounts of slow water detected. Such H(2)O molecules with reduced dynamics result from two distinct effects. The first is the relatively strong hydrophilic interaction of water with the -COO(-) moiety, which is similar for the two anions and little affected by increasing solute concentration. The second (for OAc(-) only) is the hydrophobic hydration of the -CH(3) group, which is fragile, decreasing markedly with increasing solute concentration and temperature. The activation parameters for bulk-water relaxation in NaOAc(aq) indicated a breakdown of the bulk water structure at high solute concentrations.

Association of ionic liquids in solution: a combined dielectric and conductivity study of [bmim][Cl] in water and in acetonitrile.

Ion association of the ionic liquid [bmim][Cl] in acetonitrile and in water was studied by dielectric spectroscopy for salt concentrations c ≤ 1.3 M at 298.15 K and by measurement of molar electrical conductivities, Λ, of dilute solutions (c ≤ 0.006 M) in the temperature range 273.15 ≲ T/K ≤ 313.15. Whilst acetonitrile solutions of [bmim][Cl] exhibit moderate ion pairing, with an association constant of K°(A) ≈ 60 M(-1) and increasing with temperature, [bmim][Cl] is only weakly associated in water (K°(A) ≈ 6 M(-1)) and ion pairing decreases with rising temperature. Only contact ion pairs were detected in both solvents. Standard-state enthalpy, entropy and heat capacity changes of ion association were derived, as well as the activation enthalpy of charge transport and the limiting conductivity of the cation, λ(∞) ([bmim](+)). These data, in conjunction with effective solvation numbers obtained from the dielectric spectra, suggest that the solvation of [bmim](+) is much weaker in water than in acetonitrile.

Development of a novel mathematical model using a group contribution method for prediction of ionic liquid toxicities.

A new mathematical model has been developed that expresses the toxicities (EC50 values) of a wide variety of ionic liquids (ILs) towards the freshwater flea Daphnia magna by means of a quantitative structure-activity relationship (QSAR). The data were analyzed using summed contributions from the cations, their alkyl substituents and anions. The model employed multiple linear regression analysis with polynomial model using the MATLAB software. The model predicted IL toxicities with R²=0.974 and standard error of estimate of 0.028. This model affords a practical, cost-effective and convenient alternative to experimental ecotoxicological assessment of many ILs.