Bestimmung der Extraktionskonstanten der Tellur-Pyrasolindithiocarbaminate

Abstract

In this work the exchange reactions between the ion Te(IV) in the aqueous phase and the aryl substituted pyrasolindithiocarbaminates of zinc into chloroform have been investigated. The equilibrium (exchange) constants of these reactions have been determined experi mentally. The extraction constants and two-phase stability constants of Te(PDTC)₄ have been calculated.     

Electrochemical Studies of Ternary Complexes of Cd(II) with Promethazine and Glutamic Acid

Abstract

The ternary complexes of Cd(II) with promethazine and glutamic acid have been studied polarographically. The stability constants of the formed complexes have been calculated using the suitable methods. The results reveal the formation of two ternary complexes, Cd(Glu) (Pro), and Cd(Clu)₂ (Pro) with stability constants of 7.4 and 9.22 (log K), respectively.     

The Stability Constants of Some Benzo-15-Crown-5 And Naphtho-15-Crown-5 Derivatives

Abstract

The stability constants for the complexes of several benzo-15-crown-5 and naphtho-15-crown-5 derivatives containing various substituents in the aromatic ring have been determined in methanol. The potentiometric method with glass ion-selective electrodes has been employed. The stability constants have been compared to the selectivity coefficients (log k^pot _K,Na ) of membrane electrodes based on the mentioned compounds. No significant relationship has been stated.     

Free radical reactions of pyridoxal (vitamin B6): a pulse radiolysis study

Redox reactions of pyridoxal (P-OH) with e¯_aq, ^. OH, N ^. ₃, SO ^. ₄¯ and various organo-haloperoxyl radicals have been studied using pulse radiolysis technique. The rate constants for the reaction of P-OH or P-O¯ with the above-mentioned radicals and the transient absorption spectra have been measured. The transients formed in the reaction of hydrated electron and oxidizing radicals with pyridoxal have been assigned. An attempt has been made to find a correlation between the rate constants and Taft parameter for the reactions with the organo-haloperoxyl radicals. It has also been observed that the one-electron oxidized radical of pyridoxal is repaired by uric acid. The reduction potential for the P-OH ^.+/P-OH couple at pH 7, as measured by cyclic voltammetry, has been found to be +1.11 V vs. NHE.     

A new type of pseudorotaxanes based on cucurbit[6]uril and bis-cyanopyridyl alkane compounds

Using bis-cyanopyridyl alkane compounds as guests, three cucurbit[6]uril-based new pseudorotaxanes (2a, 2b and 2c) were synthesised and characterised. The crystal structures for 2a and 2c have been determined and discussed. In addition, formation constants and thermodynamic parameters in aqueous solution, as well as thermal decomposition behaviour in solid state, have been studied by ¹H NMR and TGA techniques, respectively.     

Synthesis and thermodynamic studies of the dinuclear adducts between dimethyltin(IV) dichloride with SalenH2 and MII(Salen) complexes in chloroform

A UV-Vis spectrophotometric study of adduct formation of SalenH₂ (1) and M^II(Salen), where M?=?Mn (2), Fe (3), Co (4), Ni (5) and Cu (6) as donors with Me₂SnCl₂ as acceptor have been investigated in chloroform. Adducts (1a–6a) have been characterized by ¹H, ¹³C and ¹¹⁹Sn NMR, IR and electronic spectroscopy and microanalysis. Formation constants and thermodynamic parameters were measured for 1 : 1 and 2 : 1 adducts at various temperatures (T?=?278 to 308 K). The data refinement was carried out with the SQUAD 84 program. The trend of formation constants of M^II(Salen) complexes with Me₂SnCl₂ follows the order: Mn>Fe>Cu>Co>Ni. The formation constants for the free 1 and M^II(Salen) with Me₂SnCl₂ changes according to the following trend: M^II(Salen)>SalenH₂     

Correlation Between Chromatographic Behaviour and Stability Constant of Metal Ions on Diethylenetriamine Thin Layer

Abstract

The stability constants of the complexes formed between diethylenetriamine and the metal ions -V, Th, As, Pb, Zr and Se have been determined by pH metric method and these values, together with the stability constants for the metal ions -Co, Zn, Cd, Hg, Cu, Ni and Ag already reported, have been utilised to show their correlation with chromatographic behaviour of these metal ions on silica gel G plates impregnated with diethylenetriamine.     

Investigation of the Metal Cation Binding Properties of Macrocyclic EDTA–Bis(Amide) Complexes by Potentiometry and Stopped-Flow Spectrophotometry

The protonation constants of macrocyclic EDTA–bis(amide), EDTA–EAM (1), EDTA–PAM (2), EDTA–BAM (3), and EDTA–PenAM (4), and the stability constants of theirLn³⁺and Cu²⁺complexes have been determined by potentiometric titration at 25.0 ± 0.1°C andI= 0.10M(KCl). The dissociation rates of someLn³⁺complexes have been measured by stopped-flow and conventional spectrophotometry at 25.0 ± 0.1°C andI= 0.10M(NaClO₄). The first protonation constants of the ligands were lower than that of EDTA, reflecting the strong electron-withdrawing ability of the carbonyl group. The stability constants and dissociation rates ofLn³⁺complexes followed the orderLn(1)⁺〈Ln(2)⁺〉Ln(3)⁺〉Ln(4)⁺. An increase in ring size from 13 (2) to 15 (4) by addition of the carbon chain between two amide nitrogens of the ligands leads to an increase in the thermodynamic and kinetic stability of the complexes. However,1shows a different behavior in the complexes because of its greater rigidity and basicity.     

Spectrophotometric Evaluation of Acidity Constants of Diprotic Acids: Errors Involved as a Consequence of an Erroneous Choice of the Limit Absorbances

Abstract

The erroneous choice of the limit absorbances of a diprotic acid leads to the inaccurate acidity constants to be evaluated. The errors thus implied are calculated for two hypothetical systems. In addition, two practical systems, isonicotinic acid and 1,3-bis [(2-pyridyl)methyleneamino]guanidine have also been the subject of study having had their acidity constants evaluated accurately.     

Donnan Exclusion Chromatography Application to Complex Formation Studies

Abstract

A new method for the evaluation of stability constants of complex species has been proposed, based on the principle of Donnan exclusion chromatography. The stability constants for trimetaphosphate complexes of magnesium and calcium ions have been evaluated to be log β₁ = 1.50 and 1.64 (I=1.00, 25° ± 2°C), respectively.     

Synthesis,Potentiometric and 1H NMR Study of Protonation and Complex Formation of 1,4,7-Triazacyclononane-1,4-Diacetate

Abstract

Protonation constants and the protonation scheme of 1,4,7-triazacyclononone-1,4-diacetate (NO2A) have been determined by pH potentiometry and ¹H NMR techniques; shielding constants valid for the entire pH range have been calculated. It has been pointed out that the most basic site in the molecule is the unsubstituted secondary amino group. The first two protonation steps belong to ring nitrogens, the third and fourth ones to the carboxylates; the last nitrogen is protonated in very acidic solutions only. Stability constants of complexes of NO2A with selected divalent and trivalent metal ions were determined; with them no indication of kinetic inertness was found. In NO2A complexes the relative contribution of the triazacyclononane ring to the log K _ML values is greater for soft than for hard metal ions, compared to corresponding values for 1,4,7-triazacyclononane-1,4,7-triacetate.     

Synthesis,crystal structure,stability studies,DNA/albumin interactions,and antimicrobial activities of two Cu(II) complexes with amino acids and 5-nitro-1,10-phenanthroline

One-dimensional (1-D) coordination polymer and mononuclear copper(II) complexes, ([Cu(nphen)(asn)]ClO₄)_n (1) and [Cu(nphen)(gln)(H₂O)]ClO₄·H₂O (2) (nphen = 5-nitro-110-phenanthroline, asn = asparagine, gln = glutamine), have been synthesized and characterized by IR spectroscopy, ESI-MS, CHN analysis, and single-crystal X-ray diffraction. These binary and ternary complexes of copper(II) with nphen, asn, and gln have been investigated using potentiometric methods in 0.1 M KCl aqueous ionic media at 298.2 K. The protonation constants of the ligands and the stability constants of 1 and 2 have been calculated from the potentiometric data using the “BEST” software package. The potentiometric results have been analyzed using the “SPE” software package, and the distribution curves for the copper-containing species have been determined for the ternary systems. The CT-DNA-binding properties of these complexes have been investigated by thermal denaturation measurements and both absorption and emission spectroscopy. Further, the interaction of these complexes with bovine serum albumin (BSA) and human serum albumin (HSA) has been investigated using absorption and emission spectroscopy. The thermodynamic parameters, free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) were calculated by the van’t Hoff equation and discussed. The distances between the serum albumins and 1 and 2 have been obtained according to fluorescence resonance energy transfer (FRET). Conformational changes of serum albumins have been observed from synchronous fluorescence technique. The antimicrobial activity of the complexes has also been tested on some bacteria. The effect of different amino acids on the copper(II) complexes are discussed.     

Calorimetric Investigations of Complex Formation of 2,3,4,5,6-Pentafluoroaniline with Proton Acceptors in CCl4

Abstract

Solution enthalpies of 2,3,4,5,6-pentafluoraniline in CCl₄ as well as in the solutions of tetrahydrofuran and hexamethylphosphoric triamide have been measured. From the obtained data and spectroscopically determined equilibrium constants the enthalpies of the complex formation of 2,3,4,5,6-pentafluoroaniline with one and two molecules of tetrahydrofuran and hexamethylphosphoric triamide have been calculated. The results yielded from the combination of calorimetric and spectroscopic data have been compared with those obtained using the i.r. method only.     

Analytical Study of a Picrate Ion Selective Membrane Electrode Using Chloride as Reference Anion

Abstract

A series of anion selective electrodes of the liquid membrane type have been examined with respect to selectivity characteristics. The resulting selectivity data are examined in terms of theory of liquid membrane electrodes and correlations are made with extraction constants.     

Elastic properties of bent-core nematic liquid crystals: the role of the bend angle

ABSTRACT

The nematic phase formed from bent-core liquid crystals has been the focus of intensive research for more than a decade. With the potential of biaxial nematic phase and other interesting features, such as high Kerr constants, large flexoelectric coefficients and anomalous elastic constants, these bent-core materials have been in the limelight of research. This paper presents a mini-review of the interesting elastic behaviour reported in various bent-core compounds. The review further focusses on two different types of bent-core compounds as exemplars: one derived from an oxadiazole and other a thiadiazole, highlighting the importance of bend angle in bent-core compounds. The universality of the unique behaviour of bend elastic constants via molecular field theory and atomistic modelling has also been summarised.     

Preparation and Properties of Some Poly-aluminum Organosiloxanes with Cyclonetwork Structures

Abstract

Poly condensation of aluminum butoxide with α, ω -dihydroxydi-methylsiloxanes having varied polymerization coefficients has been studied. Some kinetic dependencies in the generation of cyclonetwork poly(aluminum dim ethylsiloxanes) have been investigated and the rate constants of cross-linking reaction, depending on the chain length of initial α, ω-dihydroxypolydimethylsiloxanes, have been calculated.     

Spektrophotometrische Untersuchung Der Wechselwirkung Zwischen Rh(III) und 1-(2-Thiazolylazo)-Resorzin

Abstract

It has been shown, that depending on the ratio of the concentration of Rh(III) and 1-(2-thiazolylazo)-resorcin and the pH there will be formed in solution at least two substances with different chemical and light absorption properties. The optimum conditions for the existence of each substance have been determined in addition to molar absorbtivities of the colored substances, the equilibrium constants for their formation, and their stability constants.     

NMR-spektroskopische und massenspektrometrische Untersuchung der Struktur und Lösungsgleichgewichte von Hydroxyethylaminotoluchinonen

Summary The constitution of hydroxyethylaminotoluquinones have been assigned by means of modern NMR-techniques. The solution equilibria constants have been determined by recording¹H-NMR spectra at different temperatures. The reaction of compounds2a ₁ and2c ₁ with acetic anhydride leads to the corresponding acetyl derivatives with quinone skeleton. The mass spectra of2a ₁ –c ₁ are discussed on basis of the fragmentation pattern.

     

Differential Pulse Polarographic Investigation of Copper (II) - Cephalexin Complex

Abstract

It has been found by dp polarography that cephalexin forms a complex Cu(CEF)₂, at pH = 8.7, ionic strength μ = 0.2 and room temperature. The stoichiometric ratio and stability constant values have been evaluated by Lingane's and De Ford and Hume's methods. The overall stability constants, logβ₂ = 9.44 and 9.13, have been determined with methods applied.     

The EPR Spectra of Tetradentate Schiff-Base Complexes of Copper II V. N,N′-bis(1,1,1-trifluoro 2,4-hexanedione)1,2-propanediimine

Abstract

Complex formation between lead(II) ions and some N-substituted iminodiacetic acids has been studied at 25° in aqueous sodium perchlorate with ionic strength 0.50 M. Measurements have been carried out with glass and lead amalgam electrodes. For all the ligands 1:1 mononuclear complexes form, one of which monoprotonated. The stability constants have been evaluated.