Isotopic study of the mechanism of ozone formation

The mechanism of ozone formation has been studied using ¹⁶O and ¹⁸O₂. High-resolution microwave spectroscopy was used to measure the amounts of the isotopomeric ozone species formed. The study is hampered by the very rapid exchange process between the reactants, that tends to scramble the isotopes and hence give a 2:1 statistical ratio between the two possible isotopomers. We have found a strategy to come around this difficulty and conclude that the mechanism is a simple end-on-addition.     

The determination of coal combustion kinetics with thermogravimetry

This investigation concerns the determination of the kinetics of coal combustion. It is not well possible to use an exact analytical formula for the rate equation. For that reason a stepwise method is proposed, giving the activation energy as function of the reaction parameter , without assumption of any specific rate equation.

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Zusammenfassung Diese Arbeit beschäftigt sich mit der Kinetik der Kohleverbrennung. Für die Reaktionsgeschwindigkeit ist es jedoch nicht möglich, eine exakte analytische Gleichung anzuwenden. Aus diesem Grunde wird ein schrittweises Vorgehen vorgeschlagen, das die Aktivierungsenergie ohne Voraussetzung jeglicher spezifischer Geschwindigkeitsgleichungen als Funktion des Reaktionsparameters liefert.

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The authors wish to thank Mr. L. J. M. van der Valk for doing a lot of the experiments and Mr J. J. B. van, Hoist for making the drawings.     

Determination of purines including 2,8-dihydroxyadenine in urine using capillary electrophoresis

For the purpose of rapid drug monitoring, methods have been developed for the determination of 2,8-dihydroxyadenine, allopurinol, oxypurinol, adenine, hypoxanthine, hippuric acid and xanthine in urine with and without sodium dodecyl sulfate as additive in sodium tetraborate running buffer. No sample preparation is necessary. 6-methylmercaptopurine and etofylline have been used as the internal standards. The limit of detection is 5 microM and the range of quantification stretches from 20 to 2000 microM. The capillary electrophoresis methods are simple, fast and robust.     

Hole Migration in Telomere-Based Oligonucleotide Anions and G-Quadruplexes

Vacuum ultraviolet photoionization of a gas-phase oligonucleotide anion leads to the formation of a valence hole. This hole migrates towards an energetically favorable site where it can weaken bonds and ultimately lead to bond cleavage. We have studied Vacuum UV photoionization of deprotonated oligonucleotides containing the human telomere sequence dTTAGGG and G-quadruplex structures consisting of four dTGGGGT single strands, stabilized by NH₄⁺ counter ions. The oligonucleotide and G-quadruplex anions were confined in a radiofrequency ion trap, interfaced with a synchrotron beamline and the photofragmentation was studied using time-of-flight mass spectrometry. Oligonucleotide 12-mers containing the 5'-TTAGGG sequence were found to predominantly break in the GGG region, whereas no selective bond cleavage region was observed for the reversed 5'-GGGATT sequence. For G-quadruplex structures, fragmentation was quenched and mostly non-dissociative single and double electron removal was observed.     

Synthetic α,β(1→4)-Glucan Oligosaccharides as Models for Heparan Sulfate

Abstract

α,β-(1→4)-Glucans were devised as models for heparan sulfate with the simplifying assumptions that carboxyl-reduction and sulfation of heparan sulfate does not decrease the SMC antiproliferative activity and that N-sulfates in glucosamines can be replaced by O-sulfates. The target oligo-saccharides were synthesized using maltosyl building blocks. Glycosylation of methyl 2,3,6,2′,3′,6′-hexa-O-benzyl-β-maltoside (1) with hepta-O-acetyl-α-maltosyl bromide (2) furnished tetrasaccharide 3 which was deprotected to α-D-Glc-(1→4)-β-D-Glc-(1→4)-α-D-Glc-(1→4)-β-D-Glc-(1→OCH₃) (5) or, alternatively, converted to the tetrasaccharide glycosyl acceptor (8) with one free hydroxyl function (4?′-OH). Further glycosylation with glucosyl or maltosyl bromide followed by deblocking gave the pentasaccharide [β-D-Glc-(1→4)-α-D-Glc-(1→4)]₂-β-D-Glc-(1→OCH₃) (11) and hexasaccharide [α-D-Glc-(1→4)-β-D-Glc-(1→4)₂-α-D-Glc-(1→4)-β-D-Glc-(1→OCH₃) (14). The protected tetrasaccharide 3 and hexasaccharide 12 were fully characterized by ¹H and ¹³C NMR spectroscopy. Assignments were possible using 1D TOCSY, T-ROESY, ¹H,¹H 2D COSY supplemented by ¹H-detected one-bond and multiple-bond ¹H,¹³C 2D COSY experiments.     

Novel deoxygenation reaction of epoxides by indium

[reaction: see text] A novel, mild, ecofriendly protocol for the deoxygenation of epoxides to alkenes using indium metal and indium(I) chloride or ammonium chloride in alcohol has been developed. It was necessary for the presence of good radical-stabilizing groups adjacent to the oxirane ring for the deoxygenation reaction to occur. It is proposed that this reaction occurs through an SET process with indium as an electron donor.