Asymmetric Diels-Alder reactions with 5-menthyloxy-2-(5H)-furanone

A new class of chiral dienophiles, 5-alkoxy-2(5H)-furanones, has been developed. Both enantiomers of 5-menthyloxy-2(5H)-ftiranone are readily available in enantiomerically pure form, starting from furfural and d- or l-menthol. Excellent diastereoselectivities (d.e. β99%) are obtained in thermal Diels-Alder reactions with several cyclic and acyclic dienes. The use of silyl dienol ethers has resulted in new routes to enantiomerically pure cyclohexanones in a highly regioselective manner.     

Local elevation: A method for improving the searching properties of molecular dynamics simulation

Summary The concept of memory has been introduced into a molecular dynamics algorithm. This was done so as to persuade a molecular system to visit new areas of conformational space rather than be confined to a small number of low-energy regions. The method is demonstrated on a simple model system and the 11-residue cyclic peptide cyclosporin A. For comparison, calculations were also performed using simulated temperature annealing and a potential energy annealing scheme. Although the method can only be applied to systems with a small number of degrees of freedom, it offers the chance to generate a multitude of different low-energy structures, where other methods only give a single one or few. This is clearly important in problems such as drug design, where one is interested in the conformational spread of a system.     

Chemiluminescence immunoassay for the detection and quantification of methyltestosterone residues in muscle tissue

Chemiluminescence as a detection method for immunoassay has successfully been applied to the measurement of methyltestosterone (MT) residues in muscle tissue. The sample is digested enzymatically, extracted with diethyl ether and purified on a Lipidex-5000 column. An optional clean-up utilized disposable C18 columns. As the luminescent label the N-(4-aminobutyl)-N-ethylisoluminol conjugate of MT was used. The antiserum was raised in a rabbit against MT-3-carboxymethyloxime-bovine serum albumin. The detection limit of the assay was 14 +/- 7 pg (n = 13), with a limit of quantification in muscle tissue of 0.125 ppb.     

Synthetically defined oligomers ofL-lysine as model compounds for adsorption studies

For investigations of adsorption of polymers onto surfaces, lysine oligomers of defined lengths were synthesized using standard methods of peptide chemistry. By repeated coupling of peptide derivatives of the same length, peptide chains up to 32 lysine residues were obtained. To suppress end effects theN-terminalα-amino group and the carboxyl group of each peptide were blocked with?-aminocaproyl- andN-methylamide functions respectively. Measurements of the optical rotation of blocked and charged deblocked oligo-L-lysines indicated that ordered structures are present in both forms.     

Non-linearity with metal-metal indicator complex reactions in flow-injection analysis

The linearity of the standard calibration curve in a flow-injection system involving a calcium-cresolphthalein complexone reaction was improved by replacing the organic base, 2-amino-2-methylpropan-1-ol, with the weak inorganic acid-conjugate base, boric acid-borate system as buffer. This was done after a theoretical study done on the relationship between the amount of coloured complex, Ca(2)(CPC)(2-), as major chromophore formed and the total amount of calcium added at different pH values, and employing the knowledge obtained via proton side-reactions. It was shown that a linear calibration curve between 150 and 1000 mg l(-1) of standard Ca(2-) solutions was obtained with a buffer solution containing 0.05 mol l(-1) boric acid, 0.05 mol l(-1) KCl and 35 g l(-1) sodium acetate at a pH of 8.5.     

Investigating the interface of superhydrophobic surfaces in contact with water

Neutron reflectivity (NR) is used to probe the solid, liquid, vapor interface of a porous superhydrophobic (SH) surface submerged in water. A low-temperature, low-pressure technique was used to prepare a rough, highly porous organosilica aerogel-like film. UV/ozone treatments were used to control the surface coverage of hydrophobic organic ligands on the silica framework, allowing the contact angle with water to be continuously varied over the range of 160 degrees (superhydrophobic) to <10 degrees (hydrophilic). NR shows that the superhydrophobic nature of the surface prevents infiltration of water into the porous film. Atomic force microscopy and density functional theory simulations are used in combination to interpret the NR results and help establish the location, width, and nature of the SH film-water interface.     

Urinary excretion of methylated purines in man and in the rat after the administration of theophylline

Chromatographic characteristics of urinary metabolites of theophylline were studied by two-dimensional thin-layer chromatography, high-performance liquid chromatography and gas chromatography--mass spectrometry. Quantitative date for the urinary metabolites of theophylline in asthmatic children are given. It was shown that 1,3-dimethyluric acid is the predominant excretory product. In addition, smaller amounts of 1-methyluric acid, 3-methylxanthine and unchanged theophylline were found. Excretory patterns after theophylline ingestion before and during the administration of allopurinol in asthma patients and in rats suggest the existence of three metabolic pathways of theophylline. The administration of this drug to a patient with xanthine oxidase of theophylline. The administration of this drug to a patient with xanthine oxidase deficiency resulted in the excretion of 1-methyluric acid in addition to 1,3-dimethyluric acid, 3-methylxanthine, 1-methylxanthine and unchanged theophylline. It was concluded that in man the oxidation of theophylline is not catalysed by xanthine oxidase.     

Gas phase ion/molecule reactions in laser desorption mass spectrometry

The desorption of neutrals, alkali ions and quasimolecular ions of sucrose was studied as function of substrate temperature in laser desorption mass spectrometry. These phenomena were also investigated in thermal desorption experiments. It was concluded that in these experiments gas phase cationization is the major ionization process.     

Lattice dynamics of tetracyanoethylene

Lattice dynamics calculations for both crystalline forms of tetracyanoethylene are presented. The comparison of the calculated static and dynamical properties with the experimental data, leads us to suggest an improved parameter set for the “6-exp” potential function for crystals with cyano groups.