One‐Dimensional,Cofacial Porphyrin Polymers Formed by Self‐Assembly of meso‐Tetrakis(ERE Donor) Zinc(II) Porphyrins

A series of meso‐tetrakis‐(ERE donor) zinc(II) porphyrins n Zn (ERE donor=4‐R‐3,5‐bis[(E)‐methyl]phenyl; 1 Zn: E=NMe₂, R=Br; 2 Zn: E=NMe₂, R=H; 3 Zn: E=OMe, R=Br; 4 Zn: E=OMe, R=H) have been synthesized in excellent yields. As a result of the combination of a Lewis acidic site and eight Lewis basic sites within one molecule, monomeric molecules of n Zn self‐assemble to form one‐dimensional porphyrin polymers [ n Zn]_∞ in the solid state, as confirmed for 1 Zn and 3 Zn by X‐ray crystallography. The coordination environment around the zinc(II) ions in these polymers is octahedral. They are ligated by four equatorial nitrogen atoms of the porphyrin and two apical E atoms (E=N, O) provided by the EBrE donor groups of adjacent n Zn molecules. Complexes 2 Zn and 4 Zn did not form single crystals, but solid‐state UV/Vis analysis points to the formation of similar structures. Solution UV/Vis and ¹H NMR spectroscopy indicated that interactions between 1 Zn and 2 Zn monomers in the polymers are stronger than between 3 Zn and 4 Zn monomers. Interestingly, they also revealed that the presence of a neighboring bromine atom in the EBrE donor groups has a considerable influence on the coordination properties of the benzylic N or O atoms. The zinc(II) ions of the porphyrins most likely adopt only hexacoordination in the solid state, owing to the unique predisposition of Lewis acidic and basic sites in the n Zn molecules. Several parameters of the aggregates, for example, the interplanar separation between porphyrins and the zinc–zinc distances, change as a function of the coordinating E groups. The high degree of modularity in their synthesis makes these zinc(II) porphyrins an interesting new entry in noncovalent multiporphyrin assemblies.     

Reversed-phase high-performance liquid chromatography-thermospray mass spectrometry of radiation-induced decomposition products of thymine and thymidine.

High-performance liquid chromatography-thermospray mass spectrometry was applied to the analysis of various radiation-induced decomposition products of thymidine including N-(2-deoxy-beta-D-erythro-pentofuranosyl)formamide and the various diastereomers of 5,6-dihydroxy-5,6-dihydrothymidine, 5-hydroxy-5,6-dihydrothymidine and 5,6-dihydrothymidine. This method combines high sensitivity and product resolution, rendering it particularly useful for monitoring the formation of radiation-induced base damage within DNA.     

Adsorption of the halogens on cerium dioxide

Summary CeO₂, alone or mixed with La₂O₃, is used as halogen adsorbent in the determination of carbon and hydrogen. Quantitative data are given on the adsorption of the single halogens on various samples of pure CeO₂ and La₂O₃. Retention of CO₂ and the influence of several parameters of special interest in the carbon and hydrogen determination, have been examined. It has been found that the conditions for optimum adsorption of the halogens are a large surface and relatively low adsorption temperature. Unfortunately these conditions cannot be applied in the determination of carbon and hydrogen.

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Zusammenfassung CeO₂ allein oder im Gemisch mit La₂O₃ wurde als Adsorbens für Halogen bei der CH-Bestimmung verwendet. Quantitative Angaben über die Adsorption der einzelnen Halogene an verschiedenen Mustern von reinem CeO₂ und La₂O₃ wurden gebracht. Die Retention von CO₂ und der Einfluß einzelner Parameter, die für die CH-Bestimmung von besonderem Interesse sind, wurden geprüft. Die besten Bedingungen für die Adsorption der Halogene sind große Oberfläche und relativ niedere Temperatur. Beide Bedingungen können leider bei der CH-Bestimmung nicht eingehalten werden.

     

Determination of oxaliplatin in human plasma and plasma ultrafiltrate by graphite-furnace atomic-absorption spectrometry

A method for sensitive determination of the anti-cancer agent oxaliplatin in human plasma and human plasma ultrafiltrate (pUF) is presented. The method is based on the quantification of platinum by graphite-furnace atomic-absorption spectrometry, with Zeeman correction and an atomisation temperature of 2,700°C. Sample pretreatment involves dilution of the samples with a solution containing 0.15 mol L^–1 NaCl and 0.20 mol L^–1 HCl in water. Validation was performed in accordance with the most recent FDA guidelines for bioanalytical method validation. All results were within requirements. The validated ranges of quantification were 0.10–400 mol L^–1 for human pUF and 0.50–400 mol L^–1 for plasma. The assay is now successfully used to support pharmacokinetic studies of cancer patients treated with oxaliplatin.     

Base- and light-assisted synthesis of anthracenes from 3-allylnaphthalene-2-carbaldehydes

The synthesis of substituted anthracenes from naphthalene precursors is described. The key step involved heating ortho-allyl substituted naphthalene-2-carbaldehydes and potassium t-butoxide in DMF with concomitant irradiation from a high pressure mercury lamp to afford anthracenes in yields of 76-98%.     

Light dosimetry: status and prospects

This paper is a report on the state of the art of light dosimetry in photomedicine and photobiology. The basic quantity of interest is the radiant energy fluence rate, which can either be measured using a suitable probe, or calculated theoretically from measured optical constants. First, theoretical models used to analyse experimental transmission and reflection data are briefly discussed. It is shown that a two-flux model derived from the transport equation in the diffusion approximation resembles the Kubelka-Munk and other heuristic models. This illustrates the limitations of these models and suggests their abandonment in favour of transport theory. For theoretical energy fluence rate calculations at least three optical constants are needed, namely the absorption coefficient, the scattering coefficient and the average cosine of the scattering angle. These three constants have been measured for very few tissues. In principle only two of the three constants can be measured directly on thin samples, independent of a theoretical model. The energy fluence rate can be measured quantitatively with a miniature fibre optic probe with isotropic response. Such measurements allow indirect determination of the three optical constants. It appears that we are just beginning to understand the distribution of light energy fluence rate in tissues. Tasks for the near future are comparison of methods to measure optical constants, quantitative checks of calculated and measured energy fluence rates in model tissues and optical phantoms and further development of theoretical models. Particular attention is required for boundary conditions, with and without refractive index matching.     

Kinetics and mechanism of the Co(II)-assisted oxidation of thioureas by dioxygen

Catalytic oxidation of N,N'-dimethylthiourea and thiourea by dioxygen in water using a new cobalt(II) complex of octasulfophenyltetrapyrazinoporphyrazine was performed under mild conditions. The reaction is shown to include the formation of an intermediate anionic five-coordinate complex followed by an unusual two-electron oxidation to produce the corresponding urea and elemental sulfur (S8). Kinetic and thermodynamic parameters for the different reaction steps of the process were determined. Drastic differences in catalytic activity of cobalt and iron octasulfophenyltetrapyrazinoporphyrazines were observed.     

New chiral phosphine-phosphite ligands in the enantioselective palladium-catalyzed allylic alkylation

A series of chiral phosphine-phosphite ligands 1-6 have been synthesized and used in the enantioselective palladium-catalyzed reaction of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate as nucleophile. Ligands 1a, 2, 3, 5a, 6a, and 6b have been synthesized starting from racemic tert-butylphenylphosphinoborane. The use of dynamically resolved Li phosphide (-)-sparteine provided the optically pure ligands. Crystals of the allylpalladium (6a) complex were obtained, suitable for X-ray crystal structure determination. The X-ray crystal structure of the allylpalladium (6a) complex revealed a longer palladium-carbon bond distance trans to the phosphine moiety indicating that the attack of the nucleophile takes place at the carbon trans to the phosphine moiety. This was confirmed by the fact that the phosphine moiety did not affect the enantioselectivity directly. Under mild reaction conditions, enantioselectivities up to 83% were obtained (25 degrees C) with ligand 1e. Systematic variation of the ligand bridge and the phosphite moiety showed that the configuration of the product is controlled by the atropisomerism of the biphenyl substituent at the phosphite moiety. The conformation of the biphenyl group, in turn, is controlled by the substituent at the chiral carbon in the bridge. Ligands with large bite angles yielded higher enantioselectivities.     

Fast sample preparation involving MASE and coupled column normal phase liquid chromatography for the rapid trace analysis of dioxins in air-dust samples from fire catastrophe emissions

A new approach has been developed and tested for the urgent analysis of dioxins in samples of air-dust filters originating from catastrophe emissions. The procedure consists of a fast extraction of the sample with microwave solvent extraction (MASE) and acetone as solvent followed by a fast cleanup of the extract with normal phase coupled column liquid chromatography (LC/LC).

The multi-dimensional LC/LC system employs a 50 mm×4.6 mm i.d. column packed with 3 μm silica and a 150 mm×4.6 mm i.d. column packed with 5 μm PYE as the first and second analytical column, respectively. Iso-hexane is used on both columns to perform cleanup and dichloromethane to perform efficient back-flush elution of the compounds from the second column. The obtained polarity-based separation in the first dimension and molecular-structure based separation in the second dimension provides a fast and powerful cleanup.

Validation was done by analysing samples of homemade RIVM air-dust with aged residues (n=8, spiking level about 15 pg mg⁻¹ per compound) of dioxins/furans and samples of reference Urban Dust SRM 1649a (n=4) with both the new approach and the existing conventional procedure and were instrumentally analyzed with capillary gas chromatography and high resolution mass spectrometric detection (GC/HRMS).

In comparison to the existing conventional procedure, the new approach reduces sample processing from several days to several hours per sample.

As regards the aged-residue air-dust samples, the new method shows a good accuracy, precision and high selectivity providing a performance in good agreement with the existing procedure. In SRM air-dust, the concentration of a few compounds obtained by the new method was below (10–50%) the certified value.     

Facile chemoselective synthesis of dehydroalanine-containing peptides

Useful methodology is described for the synthesis of dehydroalanine residues (II) within peptides. The unnatural amino acid (Se)-phenylselenocysteine (I) can be incorporated into growing peptide chains via standard peptide synthesis procedures. Subsequent oxidative elimination affords a dehydroalanine at the desired position. The oxidation conditions are mild and tolerate functionalities commonly found in peptides, including variously protected cysteine residues. To illustrate its utility, cyclic lanthionines have been synthesized by this method.