Liquid chromatographic isolation of coplanar PCB congeners on an activated carbon stationary phase

A rapid and uncomplicated method for the fractionation of PCBs leading to an isolation of the highly toxic non-ortho substituted PCBs is described. The liquid chromatographic separation was achieved on a stationary phase consisting of activated carbon and Celite 545. Using eluents with different polarity, isolation of the non-ortho substituted PCBs in a single fraction was achieved. The fractions were analysed by GC/MS. The method was tested by the determination of non-ortho substituted PCBs in technical mixtures (Aroclor 1254 and Aroclor 1242). The results were compared with those obtained by using an HPLC fractionation on a porous graphitic carbon column. Finally, the micro-column fractionation was used for the determination of non-ortho substituted PCBs in native soil samples. Received: 5 March 1997 / Revised: 4 June 1997 / Accepted: 6 June 1997     

Formal total synthesis of β-pipitzol

(±)-$\text{O}$-methylperezone ($\text{1b}$) was obtained by selective oxidative demethylation of (±)-leucoperezone trimethyl ether ($\text{4a}$). Compound ($\text{4a}$) was prepared by condensation of 2,3,5-trimethoxytoluene ($\text{5e}$) with 6-methyl-5-hepten-2-one, followed by reductive removal of the tertiary alcohol. The aromatic precursor $\text{5e}$ was prepared in four steps from 2,3-dimethoxytoluene ($\text{5a}$) and, alternatively, in three steps from 5-bromoveratraldehyde ($\text{6a}$). Racemic $\text{1b}$ and $\text{4a}$ were directly compared with the optically active molecules prepared from natural R(-)-perezone ($\text{1a}$).     

Measurements and Utilization of Consistent Gibbs Energies of Transfer of Single Ions: Towards a Unified Redox Potential Scale for All Solvents

Utilizing the “ideal” ionic liquid salt bridge to measure Gibbs energies of transfer of silver ions between the solvents water, acetonitrile, propylene carbonate and dimethylformamide results in a consistent data set with a precision of 0.6 kJ mol⁻¹ over 87 measurements in 10 half-cells. This forms the basis for a coherent experimental thermodynamic framework of ion solvation chemistry. In addition, we define the solvent independent - and the values that account for the electronating potential of any redox system similar to the value of a medium that accounts for its protonating potential. This scale is thermodynamically well-defined enabling a straightforward comparison of the redox potentials (reducities) of all media with respect to the aqueous redox potential scale, hence unifying all conventional solvents′ redox potential scales. Thus, using the Gibbs energy of transfer of the silver ion published herein, one can convert and unify all hitherto published redox potentials measured, for example, against ferrocene, to the scale.     

Palladium salicylaldimine complexes containing boronate esters

Reactions of salicylaldehydes with boronate ester derivatives of aniline have been examined. Addition of these Schiff base ligands to palladium acetate or Na₂PdCl₄ afforded novel boron-containing trans-bis(N-arylsalicylaldiminato) palladium complexes.Condensation of salicylaldehyde (2-HOC₆H₄C(O)H) with H₂NC₆H₄Bpin (pin=1,2-O₂C₂Me₄) afforded the boron-containing Schiff bases, 2-HOC₆H₄C(H)=NC₆H₄Bpin (1–3a). Similar reactivity with 2-hydroxy-5-nitrobenzaldehyde and 2-hydroxy-1-naphthaldehyde gave the corresponding Schiff bases (1-3b) and (1-3c), respectively. Reaction of Schiff bases (2) and (3) with palladium acetate or Na₂PdCl₄ afforded complexes of the type PdL₂ (4,5), where L=deprotonated Schiff base. The molecular structure of the nitro-salicylaldehyde 4-Bpin palladium complex (5b) was characterized by an X-ray diffraction study. All new palladium compounds have been characterized fully and tested for their antifungal activity against Aspergillus niger and Aspergillus flavus.     

Thiacalix[4]arene derivatives with proximally bridged lower rim

New types of lower rim proximally bridged thiacalix[4]arenes have been prepared by direct aminolysis of starting tetraacetate derivative in the cone conformation using aliphatic α,ω-diamines. X-ray crystallography revealed the highly preorganized array of -C(O)NH- bonds resulting in strong intramolecular hydrogen bonding between amide groups of both bridges. The length of the corresponding diamine was found to have an essential influence on the yield of these bridged molecules.     

Potentiometric and spectrophotometric titration of Cu2+ complexes with N-isopropyl-2-methyl-1,2-propanediamine

The complexation of Cu²⁺ by N-isopropyl-2-methyl-1,2-propanediamine (L) has been studied by potentiometric and spectrophotometric titration. The dominant complexes formed in this system are [CuL]²⁺, [CuL₂]²⁺, [Cu₂L₂(OH)₂]²⁺, and [CuL(OH)₂]. The data were thoroughly tested for different models with [CuL(OH)]⁺, [CuL(OH)]⁺, [Cu(OH)]⁺, and [Cu₂(OH)₂]²⁺ as additional species. The importance of steric factors is indicated by the d-d* spectra: for [CuL₂]²⁺, (λ_max = 499 nm) the absorption maximum is shifted by 50 nm to high energies relative to [Cu(en)₂]²⁺, (λ_max = 549 nm), whereas the opposite is true for the 1:1 complexes ([CuL]²⁺ : λ_max = 712 nm,s [Cu(en)]²⁺ : λ_max = 660 nm).     

Drying dissipative structures of the aqueous suspensions of monodisperse bentonite particles

Macroscopic and microscopic dissipative structural patterns formed in the course of drying the fractionated and monodisperse bentonite particles (plate-like in their shape) in aqueous deionized suspension and in the presence of NaCl have been studied on a cover glass. The patterns coexisted with the broad ring of the hill accumulated with the particles and with the round hills are formed around the outside edges of the film and in the center, respectively, in the macroscopic scale. By the addition of NaCl the pattern shifts from the broad ring to the round hill in the center. The spoke-like cracks, which have been observed for the suspensions of the spherical particles so often hitherto, are not observed at all for the bentonite suspensions. The characteristic convection flow of the particles and the interactions among the particles and substrate are important for the macroscopic pattern formation. Wrinkled, branch-like and/or star-like fractal patterns are observed in the microscopic scale. These patterns are determined mainly by the electrostatic and polar interactions between the particles and/or between the particle and the substrate in the course of drying.