Reversed phase liquid chromatography of PCBs as a basis for the calculation of water solubility and log Kow for polychlorobiphenyls

Summary Water solubility (S _w) and log K _ow values have been determined for 154 possible polychlorobiphenyls using the retention indices obtained by RP-HPLC and structurally selected PCB congeners with known log K _ow values for the regression lines. The water solubility data are melting point corrected.

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Umkehrphasen-Flüssig-Chromatographie von PCBs als Grundlage zur Berechnung der Wasserlöslichkeit und des log K _ow für Polychlorbiphenyle

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 75th birthday     

The Association Constants of H<Superscript><Emphasis Type="Italic">+</Emphasis></Superscript> and Ca<Superscript><Emphasis Type="Italic">2 +</Emphasis></Superscript> with 2-Keto-D-Gluconate in Aqueous Solutions

2-Keto-D-gluconate (kG) is naturally produced in soils, sediments and rock faces through the microbial oxidation of glucose. Studies have qualitatively shown kG to enhance the dissolution of soil minerals. However, quantitative information, such as the log K values for the formation of metal–kG complexes, are not available. This paper presents the results of potentiometric titration studies that employ H⁺ and Ca²⁺ ion selective electrodes (ISEs) to determine the conditional ion association constants (log Q values) for the protonation and deprotonation of kG and the formation of Ca–kG complexes. The experimentally-determined log Q values were then converted to the corresponding ion association constants (the zero ionic strength condition; log K values) by employing a modified Davies equation for charged species and the Setchenów equation for neutral species. The log K values were determined by potentiometric titrations at constant kG concentration, varied ionic strengths, 25 or 22 ^∘C, and in the absence of CO₂. The computer model GEOCHEM-PC was used to determine the aqueous speciation of ions other than kG and the computer model FITEQL was used to estimate conditional log Q values for reactions in the various chemical models. Based on our evaluations, equilibrium constants for the following reactions were determined: H⁺+ kG^– ⇌ HkG⁰, log K_a1 = (3.00 ± 0.06), kG^–⇌ H_–1kG^2–+ H⁺, log K_a–1 = –(11.97 ± 0.41), and Ca²⁺+ kG^–⇌ CakG⁺, log K₁₀₁ = (1.74 ± 0.04).     

Absorption and electroabsorption spectra of carotenoid cation radical and dication

Radical cations and dications of two carotenoids astaxanthin and canthaxanthin were prepared by oxidation with FeCl₃ in fluorinated alcohols at room temperature. Absorption and electroabsorption (Stark effect) spectra were recorded for astaxanthin cations in mixed frozen matrices at temperatures about 160 K. The D₀→D₂ transition in cation radical is at 835 nm. The electroabsorption spectrum for the D₀→D₂ transition exhibits a negative change of molecular polarizability, Δα=−1.2·10⁻³⁸ C·m²/V (−105 A³), which seems to originate from the change in bond order alternation in the ground state rather than from the electric field-induced interaction of D₁ and D₂ excited states. Absorption spectrum of astaxanthin dication is located at 715–717 nm, between those of D₀→D₂ in cation radical and S₀→S₂ in neutral carotenoid. Its shape reflects a short vibronic progression and strong inhomogeneous broadening. The polarizability change on electronic excitation, Δα=2.89·10⁻³⁸ C·m²/V (260 A³), is five times smaller than in neutral astaxanthin. This value reflects the larger energetic distance from the lowest excited state to the higher excited states than in the neutral molecule.     

Equilibrium Studies of Schiff Bases and Their Complexes with Ni(II), Cu(II) and Zn(II) derived from Salicylaldehyde and Some α-Amino Acids

The acid-base equilibria of Schiff bases derived from salicylaldehyde, glycine, alanine, serine, tyrosine, and phenylalanine, and their Ni(II), Cu(II) and Zn(II) complex formation equilibria were investigated by a potentiometric method in aqueous solution (t = 25^∘C, μ = 0.1 M, KCl). The data from the potentiometric titrations were evaluated by means of the BEST computer program. The order of the formation constant values of the Schiff bases was Sal-Ala > Sal-Gly > Sal-Ser > Sal-Phe > Sal-Tyr, which is the same order as the increasing log K₁ values of amino acids (and the log K₂ values of tyrosine) with the exception of an inversion between serine and phenylalanine. Also, it was seen that the stability constants, log β₁ and log β₂, of Schiff base–metal complexes vary for all the metal ions investigated, viz., Sal-Gly > Sal-Ala > Sal-Ser > Sal-Tyr > Sal-Phe with the exception of Sal-Gly in the copper complex. The effect of the nature of the amino acids on their formation, protonation and stability constants was also discussed.     

Effect of the acyl group and the dodecylsulfonate chain on the inclusion of pyrene inside the cavity of β-cyclodextrin

The solubilization of pyrene in aqueous solution of β-cyclodextrin (β-CD) or its derivatives such as β-CD-hexanoyl, β-CD-benzoyl and β-CD-dodecylsulfonate was investigated by spectrophotometry. Linear and non-linear regression methods were used to estimate the association constants (K₁). A 1:1 stoichiometric ratio and different effects of the hexanoyl, benzoyl and dodecylsulfonate groups on the association constant were observed for the binary inclusion complex between pyrene and β-CD. The formation constant was shown to decrease when β-CD was modified by a dodecylsulfonate chain. The value of K₁ was 190 ± 10 L mol⁻¹ for the [pyrene/β-CD] complex and 145 L mol⁻¹ for the [pyrene/β-CD-dodecylsulfonate] complex. Partitioning of the pyrene molecules between the dodecylsulfonate chains and cyclodextrin cavities can explain the decrease in the association constant value. In the cases of β-CD-hexanoyl and β-CD-benzoyl derivatives, no association constants were detected. Results suggest that the high hydrophobicity of the hexanoyl and benzoyl groups prevents the inclusion of pyrene molecules inside the cyclodextrin cavity.     

Natural abundance C REDOR coupled to a singly N-labeled nucleus: simultaneous determination of interatomic distances in crystalline ammonium [N] -glutamate monohydrate

REDOR technique was applied to natural abundance ¹³C nuclei coupled to a singly labeled ¹⁵N nucleus to determine the ¹³C, ¹⁵N interatomic distances simultaneously in crystalline ammonium [¹⁵N] -glutamate monohydrate (1). Consequently, the interatomic C–N distances between ¹⁵N and ¹³C=O, ¹³C_α, ¹³C_β, ¹³C_γ, and ¹³C_δ carbon nuclei for 1 were determined with a precision of ±0.15 Å, after the experimental conditions such as the location of samples in the rotor, length of π pulse etc. were carefully optimized. ¹³C-REDOR factors for three spin system, (ΔS/S₀)_CN1N2, and the sum of two isolated 2-spin system, (ΔS/S₀)^*=(ΔS/S₀)_CN1+(ΔS/S₀)_CN2, were further evaluated by the REDOR measurements on isotopically diluted 1 in a controlled manner. Subsequently, the intra- and intermolecular C–N distances were separated by searching the minima in the contour map of root mean square deviation (RMSD) between the theoretically and experimentally obtained (ΔS/S₀)^* values against two interatomic distances, r_C–N1 and r_C–N2. When the intramolecular C–N distance (r_C–N1) of the particular carbon nucleus is substantially shorter than the intermolecular one (r_C–N2), C–N distances within a single molecule were obtained with an accuracy of ±0.06 Å as in the cases of C=O, C_α and C_β carbon nuclei. C–N distances between the molecule in question and the nearest neighboring molecules can be also obtained, although accuracy was lower. On the contrary, it was difficult to determine the interatomic distances in the same molecule when the intermolecular dipolar contribution is larger than the intramolecular one as in the case of C_δ carbon nucleus.     

Bio Availability of Polychlorinated Biphenyl Congeners in the Soil to Earthworm (L. rubellus) System

Abstract

The earthworm's (Lumbricus rubellus) uptake of polychlorinated biphenyls (PCBs) from a soil contaminated with a commercial PCB formulation (Askarel at 150 μg g^?1) and their elimination of PCBs into a low contaminated soil (15 μg g^?1) has been studied. 17 individual congeners were monitored. The uptake and the elimination rate were similar for all PCB congeners notwithstanding their different chloro-substitution pattern which suggested that bioaccumulation of PCBs in earthworms is governed by passive, possibly diffusion controlled processes. The equilibrium state in the three-phase system, soil/soil water/earthworm was reached with a half-time around 3–4 days. The soil to earthworm bioconcentration factor ranged from 4 to 20 for tetra- to octa-chlorinated biphenyls and was weakly depending on the octanol-water partition coefficient: BCF = ?(1.3?1.8) × K _OW ^(0.35?0.40).     

Tetrameric O–HO hydrogen-bond systems accompanied by C–HO hydrogen-bonds in the crystal of 1,4-bis(hydroxymethyl)triptycene: an X-ray study

The crystal structure of the title compound was determined (crystal data at 143 K: triclinic, space group P−1, Z=4, a=9.538(2) Å, b=11.638(2) Å, c=14.473(2) Å, α=88.647(3)°, β=89.875(3)°, γ=83.835(3)°, V=1596.9(4) ų). In the crystal there exist two kinds of tetrameric O–HO hydrogen-bond (H-bond) systems that are quite similar to each other. The oxygen atoms accept also intermolecular C–HO H-bonds. The two types of the H-bonds connect the molecules to an infinite two-dimensional supramolecular unit, the stacking of which is aided by an intermolecular C–Hπ H-bond. A phase transition with ΔH_t=4.4±0.1 kJ/mol was found at around 420 K.     

Square-Planar Heteroleptic Complexes of α-Diimine-NiII-Catecholate Type: Intramolecular Ligand-to-Ligand Charge Transfer

Two heteroleptic Ni^II complexes combined the redox-active catecholate and 2,2′- bipyridine ligand platforms were synthesized to observe a photoinduced intramolecular ligand-to-ligand charge transfer (LL’CT, HOMO_catecholate → LUMO_α-diimine). A molecular design of compound [Ni^II(3,6-Cat)(bipy)]∙CH₃CN (1) on the base of bulky 3,6-di-tert-butyl-o-benzoquinone (3,6-DTBQ) was an annelation of the ligand with an electron donor glycol fragment, producing derivative [Ni^II(3,6-Cat^gly)(bipy)]∙CH₂Cl₂ (2), in order to influence the energy of LL’CT transition. A substantial longwave shift of the absorption peak was observed in the UV-Vis-NIR spectra of 2 compared with those in 1. In addition, the studied Ni^II derivatives demonstrated a pronounced negative solvatochromism, which was established using a broad set of solvents. The molecular geometry of both compounds can be ascribed as an insignificantly distorted square-planar type, and the π–π intermolecular stacking of the neighboring α-diimines is realized in a crystal packing. There is a lamellar crystal structure for complex 1, whereas the perpendicular T-motifs with the inter-stacks attractive π–π interactions form the packing of complex 2. The redox-active nature of ligand systems was clearly shown through the electrochemical study: a quasi-reversible one-electron reduction of 2,2′-bipyridine and two reversible successive one-electron oxidative conversations (“catecholate dianion—o-benzosemiquinonato radical anion—neutral o-benzoquinone”) were detected.     

Complexation properties of phosphonocarboxylic acids in aqueous solutions

The concentration formation constants of phosphonoacetic acid (PAA) complexes with the Ca²⁺ and Mg²⁺ ions were determined in aqueous solution at 25°C by potentiometric and coulometric titrations at different ionic strengths and were extrapolated to I=0 in order to obtain thermodynamic values of the formation constants. Complexes were formed by the completely deprotonated K _f (ML) and monoprotonated K _f (MHL) forms of the PAA anion. The respective values for the complexes are: log K _f (CaL)=4.68±0.03, log K _f (CaHL)=2.61±0.08; log K _f (MgL)=5.58±0.09, log K _f (MgHL)=3.0±0.3. The enthalpy and entropy of complexation for the deprotonated Ca²⁺ and Mg²⁺ PAA species, determined from the temperature dependence of the log K _f (ML), are: H⁰(Ca) =0.6±0.2 kcal-mol^–1, S⁰(Ca)=21.4±0.6 cal-mol^–1-K^–1, H⁰(Mg)=3.0±0.7 kcal-mol^–1, and S⁰(Mg)=35±2 cal-mol^–1-K^–1. It is seen there-fore, that the complexes are entropy stabilized but enthalpy destabilized. Formation constants were also determined for Ca²⁺ and Mg²⁺ complexes with PAA analogs, phosphonoformic and 3-phosphonopropionic acids and the complexation of PAA was also studied at a single ionic strength, with Na⁺, Ag⁺, Tl⁺, Sr²⁺, Ba²⁺, Cd²⁺, Cu²⁺, and Pb²⁺ ions.     

Study of ion–solvent interactions of some tetraalkylammonium halides in THF + CCl4 mixtures by conductance measurements

Conductivities of some tetraalkylammonium halides, viz. tetrapentylammonium chloride (Pen₄NCl), tetrahexylammonium chloride (Hex₄NCl), tetraheptylammonium chloride (Hep₄NCl), and tetraoctylammonium chloride (Oct₄NCl) were measured at 298.15 K in THF + CCl₄ mixtures with 40, 60 and 80 mass% of THF. A minimum in the conductometric curves (molar conductance, Λ vs. square root of concentration, √c) was observed at concentrations which is dependent both on the salt and the solvent. The observed molar conductivities were explained by the formation of ion-pairs (M⁺ + X⁻ ↔ MX, K_P) and triple-ions (2M⁺ + X⁻ ↔ M₂X⁺; M⁺ + 2X⁻ ↔ MX₂⁻, K_T). A linear relationship between the triple-ion formation constants [log(K_T/K_P)] and the salt concentrations at the minimum conductivity (log C_min) was given for all salts in THF + CCl₄ mixtures. The formation of triple-ions might be attributed to the ion sizes in solutions in which coulombic interactions and covalent bonding forces act as the main forces between the ions (R₄N⁺X⁻).