Complex formation constants and thermodynamic parameters for La(III) and Y(III)L-serine complexes

Summary The stoichiometric stability constants for La(III) and Y(III)L-serine complexes were determined by potentiometric methods at different ionic strengths adjusted with NaClO₄ and at different temperatures. The overall changes in free energy (G ^o), enthalpy (H ^o), and entropy (S ^o) during the protonation ofL-serine and that accompanying the complex formation with the metal ions have been evaluated.

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Komplexbildungskonstanten und thermodynamische Parameter für La(III)- und Y(III)-L-Serin-Komplexe

Zusammenfassung Die stöchiometrischen Komplexbildungskonstanten für La(III)- und Y(III)-L-Serin-Komplexe wurden mittels potentiometrischer Methoden bei verschiedenen Ionenstärken (mit NaClO₄ adjustiert) und bei verschiedenen Temperaturen bestimmt. Die Änderungen in der freien Energie (G ^o), Enthalpie (H ^o) und Entropie (S ^o) während der Protonierung und der Komplexbildung mit den Metallionen wurden ermittelt.

     

Reactivity of tungsten(0) and molybdenum(0) pentacarbonyl thiobenzoate anions: thiobenzoate as a cis-CO labilizing ligand

The [Et₄N][M(CO)₅SCOPh] complexes (1a, M = Mo; 2a, M = W) have been prepared at ambient temperatures by reacting the photogenerated M(CO)₅ THF intermediate with [Et₄N][SCOPh] in THF. Kinetic studies of the reactions of the anions [M(CO)₅SCOPh]^– with the tri(iso-propyl)phosphite (L) ligand under pseudo-first-order conditions indicate that these reactions are first-order in substrate and are independent of the P(OPr-i)₃ concentration. It is thus envisaged that these CO substitutions proceed via a mechanism which involves initial cis-M—CO bond-breaking, followed by fast attack of the incoming nucleophile on the resulting intermediate to give [cis-M(CO)₄{P(O-Pri)₃}SCOPh]^–. This facile displacement of cis-CO indicates the labilizing nature of the thiobenzoate ligand, most probably by virtue of distal oxygen atom participation. Activation parameters for the reactions are: [M(CO)₅SCOPh]^– + L cis-[M(CO)₄(L)SCOPh]^– + CO M = Mo, H = 24.6(2) kcal mol^–1, S = 8.2(6) eu; M = W, H = 28.4(2) kcal mol^–1, S = 11.3(5) eu. Kinetic data and the mechanism of these ligand-substitutions are discussed.     

Elektrometrische Untersuchungen über die Komplexbildung von La(III) mit 3.5-Dinitrosalicylsäure

Zusammenfassung Die Komplexbildung zwischen La(III) und 3.5-Dinitrosalicylsäure in 0.1m-KNO₃ wurde potentiometrisch und konduktometrisch untersucht. Wir erforschten die Bildung von 11- und 12-Komplexen oberhalb pH 3.5. Der 11-Komplex bildet sich in Lösung, während der 12-Komplex ausfällt. Die Stabilitätskonstante des 11-Komplexes wurde durch Anwendung der vonCalvin undMelchior erweiterten Methode vonBjerrum bestimmt. Für logK fand man Werte von 4.92, 5.00 und 5.12 bei 25°, 30°, beziehungsweise 35° C. Die Werte für F, H und S wurden für 30° C berechnet und bestimmt zu–6.97 Kcal/Mol,–7.49 Kcal/Mol, beziehungsweise –1.70 cal/Mol/Grad.

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Electromeric studies on the complex formation between La(III) and 3.5-dinitrosalicylic acid

The complex formation between La(III) and 3.5-dinitrosalicylic acid in 0.1m-KNO₃ medium has been studied potentiometrically and conductometrically. The formation of 11 and 12 complexes beyond 3.5 pH was investigated. 11 complex is formed in solution while 12 complex is precipitated. The stability constant of the 11 complex was determined by applying the Calvin and Melchior's extension ofBjerrum's method. The logK values have been found to be 4.92, 5.00, and 5.12 at 25, 30 and 35°C, respectively. The values of F, H, and S have also been evaluated at 30°C and found to be–6.97 Kcal/mole,–7.49 Kcal/mole, and–1.70 Kcal/mole/degree, respectively.

     

Conductance of iron(III) laurate solutions in binary liquid mixtures

Summary The specific conductivity of iron(III) laurate solutions in binary liquid mixtures shows that the soap aggregates into micelles and CMC is found to be independent of temperature and concentration of benzene, acetone and tetrachloromethane in 1-butanol. The variation of molecular conductance,, with soap concentration, C, is expressed by the equation: = 10^AC^B. Both constants A and B vary with solvent composition but B remains constant with increase in temperature. Several parameters such as molecular conductance at infinite dilution, , dissociation constant, K, heat of dissociation, H, entropy, S and free energy, G of dissociation of soap have been evaluated and the effect of the nature of solvents has been discussed.     

Band structure of even and ions of odd polyenes

The analysis of experimental data for singlet transitions (E _n) of even polyenes (I), cations (II) and anions (III) of odd polyenes show that for infinite chains E (I)/E (II)=E (I)/E (III) = 2:1. It is shown that the energy gap is equal for the three systems. In cases (II) and (III) there is a level (NBMO) in the gap which is vacant in (II) and occupied in (III). That is why the first optical transition in (II) and (III) depends on the semiwidth of the gap.     

The position of plutonium/III/ in the lanthanide series in respect to thermodynamic functions of complex formation with nitrates and thiocyanates

The position of Pu/III/ within lanthanides in respect to G⁰, H⁰ and S⁰ of complex formation with nitrate and thiocyanate ligands was determined by the extraction method. It was found that in respect to G⁰, Pu/III/ is a light pseudolanthanide for nitrate ligands and a heavy pseudolanthanide for thiocyanate ligands. A comparison of the positions of Pu/III/ and Am/III/ in respect to G⁰, H⁰ and S⁰ shows that the radius of plutonium is greater than that of americium in the An/NO₃/ ₅ ^2– complex and smaller in the An/NCS/₃/TBP/_n complex. The increase in the radii between plutonium and americium in the thiocyanate complex points out to a contribution from 5f orbitals to bonding.     

Complexation,solubilities and thermodynamic functions for cerium(III) fluoride-water system

The solubility, solubility product and the thermodynamic functions for the CeF₃–H₂O system have been measured using the radiometric, conductometric and potentiometric techniques. The radiometric values for the solubility and solubility product, the lowest and more acceptable for reasons cited in previous papers, are 3.14·10^–5 M and 2.17·10^–17 respectively. The enthalpy change measured by the conductometric method is almost twice as that obtained by potentiometric method due to abnormal conductances registered at higher temperatures. The average values for H^o and G^o and S^o at 298 K are 53.0±17.4, 91.7±4.0 and –129.7±58.2 KJ·mol^–1 respectively. The positive values for H^o and G^o and the negative value for S^o are indicative of the low solubility of this salt in water. The stability constants for the mono- and difluoride complexes of Ce(III) have been determined potentiometrically using unsaturated solution mixtures of Ce(III) and F^–. These values for CeF⁺ and CeF ₂ ⁺ are 997±98 and (1.03±0.44)·10⁵, respectively. Studies on pH dependence of the solubility shows that the solubility reaches a minimum value at a pH of about 3.2.     

Bildungskonstanten von Komplexen der 3-Hydroxynaphthalin-2-carbonsäure mit Pr(III), Nd(III), Gd(III), Dy(III), Er(III) und Yb(III)

The stability constants of the complexes of 3-hydroxynaphthalene-2-carboxylic acid with some lanthanides have been obtained potentiometrically in aqueous dioxane (50%,V/V) at three temperatures and keeping the ionic strength at 0.1M (KNO₃), usingIrving-Rossotti titration technique. The values of overall changes in G°, H°, and S° have also been evaluated.     

NMR studies of the interaction between tris-acetylacetonates of Fe(III), Cr(III) and diethyldichloride of Sn (IV)

Paramagnetic relaxation rate of CH₂ protons has been found to be higher than that of CH₃ protons of SnEt₂Cl₂ in the presence of tris-acetylacetonate of Cr(III) in chloroform at 298 K, which supports the specific interactions between these compounds. The revealed ligand exchange between Cr(AA)₃, Fe(AA)₃ and SnEt₂Cl₂ takes place with the equilibrium shifted to the side of initial reactants.

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, -CH₂ CH₃- SnEt₂Cl₂ - Cr(III) 298 K, . Cr(AA)₃, Fe(AA)₃ SnEt₂Cl₂, .

     

Kinetics and mechanism of oxidation ofd-xylose by Mn(III) pyrophosphate

The oxidation ofd-xylose by Mn(III) pyrophosphate in sulphuric acid has been found to be first order with respect to [Mn(III)]. Variation of rate with [d-xylose] suggests the rapid formation of reversible cyclic complex between Mn(III) and id-xylose, which further disproportionates in a slow rate determining step. Oxidation rate has been found to increase with [H⁺]. Retardation of rate due to [pyrophosphate] and increase due to [Mn(II)] have been also observed. The value of thermodynamic parameters E, S, and G have been found to be 17.6±0.1 kcal/mole, –10.1±0.1 e.u. and 20.6±0.1 kcal/ mole respectively. A mechanism involving a free radical has been proposed for the reaction under study.     

Ligand-structure effect on electrochemical reduction of copper(II) complexes

Summary Half-wave potentials for a one-electron reduction of copper(II) complexes containing polydentate ligands can be calculated using the equationE _1/2=E ⁰(Cu^2+/+)+ _{i j} E _i where E _i are contributions related to the electronic and steric properties of the ligands. The values of 18 E _i contributions are presented and explained, and the effect of the solvents on the half-wave potentials is exemplified.Dedicated to Prof. Dr. Viktor Gutmann to his 70th birthday     

The Influence of Dimerization of Water-Soluble Metalloporphyrins as Photosensitizers on the Efficiency of Generation of Singlet Oxygen

Quantum yields () for the generation of singlet oxygen sensitized by Pd(II) complexes of water-soluble porphyrins: meso-tetrakis(4-N-methylpyridyl)porphine [PdTMPyP]⁴⁺ ( = 0.9), meso-tetrakis(4-N,N,N-trimethylaminophenyl)porphine [PdTTMAPP]⁴⁺ ( = 0.8), meso-tetrakis(4-carboxyphenyl)porphine [PdTCPP]^4– ( = 0.7), and meso-tetrakis(4-sulfonatophenyl)porphine [PdTSPP]^4– ( = 0.5) were determined using a chemical method. It was found that the dimerization and aggregation of metalloporphyrins greatly influence the value. The quantum yields evaluated for the formation of singlet oxygen sensitized by metalloporphyrin monomeric and dimeric forms are _{, M} 0.9 and _{, D} 0.2, respectively, and do not depend on the porphyrin nature.     

Effect of acid-base equilibria of reactants and the effect of waterorganic mixtures on the kinetics of oxidation of cysteinsulphenatobis(ethylenediamine)cobalt(III) ion by periodate

Summary The kinetics of oxidation of cysteinsulphenatobis(ethylenediamine)cobalt(III) ion by periodate were investigated in mixtures containing up to 40%t-BuOH andi-PrOH. The effect of acid-base equilibria on the rate constants and activation parameters H, S and the effect ionic strength on the rate constant at different concentrations HClO₄ are also reported. The solvent effects on the oxidation at the different pH are interpreted in terms of solvation of the initial and transition states.     

Relativistic perturbation theory of molecular structure

Summary The recently developed relativistic double perturbation theory is extended to handle relativistic changes of molecular structure more easily. This is achieved by simple coordinate scalings. Accurate higher order mixed perturbation energies for H ₂ ⁺ are calculated. The relativistic changes of bond energy,DE, of bond length,R _e , and especially of force constant,k, and of anharmonicity,a, are large, up to 100%·(Z/c)². The dominant contributions tok anda are due to the indirect change of the nonrelativistick anda connected with the relativistic change of bond length. Accordingly the relativistic changes obey Badger's and Gordy's rules (–RDEk).Dedicated to Prof. Klaus Ruedenberg in appreciation of his fundamental contributions to both formal theory and physical explanations in quantum chemistry     

Komplexe von Cu(II), Zn(II), Ni(II) und Mn(II) mit N-m-Tolyl-p-methylbenzhydroxamsäure

The thermodynamic proton ligand and metal ligand stability constants of N-m-tolyl-p-methylbenzohydroxamic acid with Cu(II), Zn(II), Ni(II), and Mn(II) have been determined at 25° and 35° in several dioxane-water media. The pK _a and logK ₁ (logK ₂ or log ₂) varies linearly with the mole fraction of dioxane at a given temperature but not linearly with the reciprocal of dielectric constants of the medium. Values of G ^o, H ^o, and S ^o are tubulated. The stabilities of the complexes mostly follow the order of electron affinities of the metal ions. An attempt has been made to calculate the ligand field stabilization energy of the complexes.

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Mit 2 Abbildungen     

CH Acidity of Di- and Trisubstituted Methanes

It is shown that the CH acidity of di- and trisubstituted methanes can be studied using the ap- proaches consisting in singling out the contributions of physically significant factors from the overall acidification mechanisms in the gas phase and in solution. This procedure implies formal decomposition of the calculated gas-phase deprotonation energy Edeprot into the following terms: electrostatic energy of proton detachment from the acid CH bond, with the state of the remainder of the molecule absolutely unperturbed (E ₁); electronic relaxation energy of the resulting molecular residue and formation of a virtual carbanion therefrom (E ₂); the Edeprot component due to displacement of the atomic nuclei on changing from the virtual to real carbanion E ₃. Relationships between the energy components E ₁, E ₂, E ₃, and the commonly used characteristics of the molecular structure were investigated. The parameter E ₁ is selectively sensitive to the inductive effect of the substituent. Imperfect correlation between E ₁ and the sum of the _I constants can be due to the fact that the contributions to the _I constants from the effective charge on the hydrogen atom of the CH bond being deprotonated and from the polarizabilities of the substituents are not taken into account. In contrast to monosubstituted methanes, in di- and trisubstituted methanes there is no correlation between the E ₂ component and the ¹ J(^13CH) constants. The linear dependence linking the sums of the components E ₁ + E ₂ and the pyramidal angle in the carbanions is responsible for the relaxation nature of the effects associated with the E ₂ + E ₃ sum. Comparison of the data obtained with the calculated patterns of redistribution of the effective charges on atoms accompanying conversion of CH acids to carbanions enabled elucidation of the relative contribution of each of the components, E ₂ and E ₃, to the deprotonation energy of selected groups of substituted methanes. The previously developed technique of separating the energy of protolytic equilibrium in the gas from that of solvation processes in solution enabled assessment of the contributions from electrostatic solvation to pK _a in DMSO. The same technique of singling out the solvation component due to intermolecular hydrogen bonds from pK _a(H₂O) was used in studying the acid-base equilibria for substituted methanes in aqueous solution. It was shown that the solvation effects manifested in the liquid-phase CH acidity can be modeled by the effects revealed for analogous hydrogen bonds of ion-molecule complexes in the gas phase. The relationships between the strength of hydrogen bonds and the CH-acidic properties of compounds in the gas phase and liquid water are similar.     

Preferential solvation of silver(I) acetate in water,methanol and their mixtures with dimethyl sulfoxide

The solvent transport number, , of dimethyl sulfoxide andGibbs solvation energies of silver acetate in the binary solvent systems, water—DMSO and methanol—DMSO, were determined by employingEMF and solubility measurements. While the transfer free energy of the salt increases from water to water—DMSO mixtures (up toX _DMSO =0.7) and then decreases, it continuously decreases from methanol to methanol—DMSO mixtures. In both mixed solvents, G° _t(Ag+) decreases down to pureDMSO and that of acetate ion increases with increasing composition ofDMSO indicating that silver ion is preferentially solvated byDMSO and acetate ion by water or methanol in these mixtures. The solvent transport numbers, , ofDMSO are positive throughout, passing through a maximum atX _DMSO =0.45 (=1.0) in the case of water—DMSO mixtures and atX _DMSO =0.25 (=1.8) in methanol—DMSO mixtures. This observation is shown to be in accord with the conclusions arrived at from the transfer energy data of the salt in the two mixtures.

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Bevorzugte Solvatation von Silber(I) acetat in Wasser, Methanol und deren Mischungen mit Dimethylsulfoxid

Zusammenfassung Es wurde die Lösungsmitteltransportzahl () von Dimethylsulfoxid und dieGibbssche Solvatationsenergie von Silberacetat in den binären Lösungsmittelsystemen Wasser—DMSO und Methanol—DMSO mittelsEMK- und Löslichkeitsmessungen ermittelt. Während die freie Energie des Transfers des Salzes beim Übergang von Wasser zu Wasser—DMSO-Mischungen zunächst ansteigt (bisX _DMSO =0,7) und dann abfällt, ist für das System Methanol bzw. Methanol—DMSO ein kontinuierlicher Anstieg feststellbar. In beiden Mischsystemen fällt G°t(Ag⁺) bis zu reinemDMSO, der entsprechende Wert für Acetat steigt bei großeren Anteilen vonDMSO an. Das zeigt, daß das Silber(I)ion bevorzugt vonDMSO solvatisiert wird, Acetat von der jeweils anderen Komponente (Wasser bzw. Methanol). Die Lösungsmitteltransportzahl fürDMSO ist stets positiv mit Maxima beiX _DMSO =0,45 (=1,0) für Wasser—DMSO undX _DMSO =0,25 (=1,8) für Methanol—DMSO. Diese Beobachtung steht im Einklang mit Rückschlüssen, die aus den Transferenergiedaten des Salzes in den zwei untersuchten Systemen getroffen werden können.

     

Numerische Auswertung von Enzymanalysen

Zusammenfassung Für eine numerische Auswertung von Enzymanalysen erscheint es zunächst naheliegend, in die Meßpunkte eine Ausgleichsgerade einzupassen und deren Steigung als Schätzwert für die gesuchte Anfangsgeschwindigkeit E/t ₀ zu nehmen. Die Steigung der Ausgleichsgeraden liefert aber die mittlere Reaktionsgeschwindigkeit über die gesamte Meßzeit und unterschätzt E/t ₀ immer dann, wenn die Reaktion gegen Ende der Meßzeit etwas langsamer läuft. Bei automatischen Geräten muß das Auswerteverfahren auch in solchen Fällen E/t ₀ richtig schätzen. In der vorliegenden Arbeit wird eine einfache Möglichkeit, die zu diesem Ziel führt, diskutiert, nämlich die Schätzung von E/t ₀ mit einer Ausgleichsparabel, die dem Reaktionsverlauf folgen kann.

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Numerical evaluation of enzyme analyses

To calculate enzyme concentrations numerically, it seems obvious to fit a straight line into the data points and take the slope as an estimate for the starting velocity E/t ₀. This slope, however, is proportional to the average reaction rate over the total measurement interval and always underestimates E/t ₀ when the reaction is slowing down towards the end. Automatic analyzers must correctly estimate E/t ₀ even in such cases. As discussed in this article, this can be achieved by fitting a second order parabola, that can follow the reaction, into the data points.

     

Thermodynamics of Proton Association of Polyacrylates and Polymethacrylates in NaCl(aq)

Enthalpies of protonation of polyacrylates and polymethacrylates with different molecular weights in aqueous NaCl solutions, 0 I 2 mol-L^–1 were determined by titration calorimetry at 25°C. H values are dependent on both the neutralization degree, , and the molecular weight of polyacids. T S of protonation was obtained using pK values already reported and the present H results. Empirical equations for the dependence on I, , and molecular weight are reported for both H and T S.     

Determination of kinetic parameters of the FeCl3/FeCl2 systemvia a novel treatment of chronoamperometric data

Summary Computer based methods for the processing of chronoamperometric datavia convolutions are discussed. On the example of the quasi-reversible Fe³⁺/Fe²⁺ couple, their application for data acquisition and determination of the heterogeneous electrochemical parameters is demonstrated. The plot of Q/i vs. t/i is superior to that employingi/I ₁, being less sensitive to distortions by charging currents once these have died away and by the effects of damping on the initially rapidly varying currents. Cyclic voltammetry is often combined with convolution or deconvolution, and digital simulation studies are also frequently performed to confirm the results.

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Bestimmung kinetischer Parameter des Systems FeCl₃/FeCl₂ mittels einer neuen Verarbeitung chronoamperometrischer Daten

Zusammenfassung Computerunterstützte Verfahren zur Verarbeitung chronoamperometrischer Daten mittels Faltungsintegralen werden diskutiert. Am Beispiel des quasireversiblen Systems Fe³⁺/Fe²⁺ wird die Anwendung der neuen Methoden zur Datenerfassung und zur Bestimmung der heterogenen elektrochemischen Parameter gezeigt. Der Plot von Q/i gegen t/i ist dem voni/I ₁ überlegen, da er durch Ladeströme und Dämpfung der ursprünglich stark variierenden Ströme weniger stark beeinflußt wird. Cyclische Voltammetrie wird häufig im Zusammenhang mit Konvolutions- und Dekonvolutionsmethoden angewandt; digitale Simulation zur Überprüfung der Ergebnisse wird ebenfalls oft eingesetzt.