Visible Spectrophotometric Measurements Research Articles

Chemical relevance of the copper(II)— l-carnosine system in aqueous solution: A thermodynamic and spectrophotometric study

The copper(II)— l-carnosine (L −) system has been re-investigated in aqueous solution, at I = 0.1 mol dm −1, different temperatures (5⩽ t⩽45°C) and with metal to ligand ratios ranging from 3:1 to 1:3. Both potentiometry and visible spectrophotometry were employed. From an overall consideration of all experiments, [CuLH] 2+, [CuL] +, [CuLH −1]°, [Cu 2L 2H −2]° and [Cu 2LH −1] 2+ were recognized as the species which provide the best interpretation of experimental data. The complex formation constants, determined at different temperatures, allowed us to obtain reliable values of Δ H° and good estimates of Δ C° p. From visible spectrophotometric measurements, carried out at different pH and metal to ligand ratios, it was possible to calculate the electronic spectrum of each complex formed in solution. A structure is also proposed for each species, on the basis of thermodynamic and spectral results.

Potentiometric and spectroscopic study of copper(II) complexes with glycyl-glycyl- l-histidyl- l-alanine in aqueous solution

The complex formation between copper(II) and the tetrapeptide glycyl-glycyl- l-histidyl- l-alanine ([H 3L] 2+) has been studied in aqueous solution at t = 25°C and I = 0.1 mol dm −3 by potentiometric, visible spectrophotometric and circular dichroism measurements. All the experimental techniques show that the complex [CuLH −2] − is predominant over a wide pH range, while the monodentate [CuLH] 2+ is formed in the acidic region and a further deprotonated [CuLH −3] 2− species exists at pH higher than 10. The formation constants of the three above complexes are reported and a structure is proposed on the basis of spectroscopic results. The structure of [CuLH −2] − species very probably involves four nitrogen donors in the plane, excluding coordination by the l-alanine residue, while it seems likely that [CuLH −3] 2− is formed by simple dissociation of the N-1 pyrrole hydrogen.

Investigation of the interactions between humic substances and a cationic detergent (Cetiltrimethylammonium bromide)

Visible spectrophotometric measurements were used to study binding of cetltrimethylammonium to humic molecules. Detergent molecules appeared to bind to ionized carboxyl and phenolic groups. Complete neutralization of negative charges caused quantitative precipitation of humic substances at low ionic strength. Detergent amounts higher than the stoichiometric ratio caused salting in of precipitate. The influence of organic carbon concentration, ionic strength and pH of the solution on the complex composition at minimum solubility was investigated.

The inclusion of tropaeolin 000 no. 2 by permethylated β-cyclodextrin. A kinetic and equilibrium study

Temperature-jump visible spectrophotometric studies show the monoanionic form of the dye tropaeolin (TR) to be included by permethylated β-cyclodextrin (βPCD) in a fast step to form a 1:1 complex (TR·βPCD), which is followed by the slower formation of the 2:1 complex (TR)2·βPCD, in which tropaeolin dimerizes: [graphic omited] At 298.2 K K1=(1.24 ± 0.05)× 102 dm3 mol–1, K2=(4.82 ± 0.42)× 104 dm3 mol–1, k2=(1.68 ± 0.09)× 108 dm3 mol–1 s–1 and k–2=(3.48 ± 0.11)× 103 s–1 in aqueous solutions buffered at pH 5.50 by 0.100 mol dm–3 phosphate and 0.200 mol dm–3 K2SO4 supporting electrolyte. U.v.–visible spectrophotometric equilibrium measurements yield K1=(1.36 ± 0.11)× 102 dm3 mol–1 and K2=(2.29 ± 0.38)× 104 dm3 mol–1. A similar study of inclusion of the dye pyronine B was attempted, but the u.v.–visible spectral changes were too small for a quantitative study. These results are compared with those obtained from the analogous β- and γ-cyclodextrin systems.

Estimation of acidic and physical properties of solid acids based on adsorption of basic molecules in non-polar solvents

The adsorption equilibrium among a solid acid having both acidic and physically adsorptive sites, a base and a Hammett indicator have been investigated theoretically to derive a new surface acidity function SA and a physical adsorptivity function SP. A system composed of silica–alumina as a solid acid, pyridine as a base and each Hammett indicator have been experimentally treated for application of SA and SP. SA and SP are defined by SA=–log (Σmi= 1αi[Ai]) where αi and [Ai] are the strength and amount of the ith group of vacant acid sites, respectively, and SP=–log (Σnj= 1µj and [Pj]), where µj and [Pj] are the strength and amount of the jth group of vacant physical adsorptive sites, respectively. Silica–alumina dispersed in benzene or benzene–cyclohexane was neutralized to various degrees with pyridine in the presence of one of five Hammett indicators and the solid and liquid phases were subjected to u.v.–visible spectrophotometric measurements. A data analysis based on SA has revealed that the silica–alumina contains 0.11 m mol g–1 acid sites of –log α=–3.9 ± 0.6 as referenced to –logβ= 1.5, assigned as a standard for 4-(phenylazo)diphenylamine, a Hammett indicator, where β is the strength of a base in a similar sense to α. Relative strengths have been evaluated for the five Hammett indicators as basic and physical adsorbates to the silica-alumina. An experimental criterion has been set up for the application of SA to the determination of the strength–amount distribution for a solid acid.

A kinetic and equilibrium study of the inclusion of pyronine B by β- and γ-cyclodextrin

Temperature-jump visible spectrophotometric studies show the dye pyronine B (PB) in its monovalent cationic form to be included by γ-cyclodextrin (γCD) in a fast step to form a 1:1 complex (PB·γCD), which is followed by the slower formation of the 2:1 complex (PB)2·γCD, in which pyronine B dimerises: PB +gamma;CD [graphic omitted] PB·gamma;CD (K1)(fast)(1), PB + PB·γCD [graphic omitted] (PB)2·γCD (K2)(slow)(2) where, in aqueous 1.00 mol dm–3 NaCl at pH 5.70 and 298.2 K, K1=(4.3 ± 0.1)× 102 dm3 mol–1, K2=(1.28 ± 0.04)× 105 dm3 mol–1, k2=(8.2 ± 0.2)× 108 dm3 mol–1 s–1 and k–2=(6.40 ± 0.05)× 103 s–1. In the presence of βCD only the formation of PB·βCD is detected and is characterised by k1=(1.1 ± 0.1)× 108 dm3 mol–1 s–1 and k–1=(1.5 ± 0.5)× 104 s–1. Equilibrium u.v.–visible spectrophotometric measurements are consistent with these kinetic data. No inclusion of PB by αCD was detected. These data are compared with those characterising related systems. The dimerisation of PB in the absence of γCD is fast, an observation which forms the basis for some of the mechanistic deductions concerning the formation of (PB)2·γCD, and also for a reassessment of some mechanistic interpretion in earlier studies.

Interaction en milieu eau–dioxane des ions Cu2+, Ni2+ et Ag+ avec les acides furannecarboxylique-2 et tetrahydrofurannecarboxylique-2

The protonation constants of furan-2 carboxylic (HFC) and tetrahydrofuran-2 carboxylic (THFC) acids and the stability constants of their copper, nickel and silver 1:1 complexes have been measured in water containing 50% dioxane (I = 0.1 (NaNO3); t = 25 °C). Treatment of the potentiometric data has been completed by uv–visible spectrophotometric measurements. The results are discussed and a chelate structure is displayed for the Cu – tetrahydrofuran-2 carboxylic acid system.

Errors in ultraviolet and visible spectrophotometric measurements caused by multiple reflections in the cell

Errors in ultraviolet and visible spectrophotometric measurements caused by multiple reflections in the cell

Preparation, Absorption Spectra and Electronic Configuration of some amino complexes of nickel (II) acetate

AbstractThree hexaco‐ordinated complexes of nickel (II) acetate with ammonia, ethylenediamine and propylenediamine have been prepared. Conductivity measurements indicate the complexes to be non‐electrolytes. Molecular weight measurements confirm this. The visible absorption spectrophotometric measurements show a number of bands corresponding to the various permitted transitions of the metal and a discussion of the structure in the light of these transitions is presented.

Synergism in the solvent extraction of di, tri and tetravalent metal ions—IV: Absorption spectral studies of the synergistic complexes

In previous work with radioactive tracers in this series, formulae have been assigned to the metal complexes synergistically extracted from aqueous solution by an organic phase containing thenoyl trifluoracetone (HTTA) and neutral organophosphorous compounds. Stable solid complexes have now been isolated and are shown to have the same formulae. These formulae have been confirmed by ultra-violet and visible absorption spectrophotometric measurements of dilute solutions of uranyl, thorium and neodymium complexes.