Gunnar Stenhagen

Towards an artificial model for Photosystem II: a manganese(II,II) dimer covalently linked to ruthenium(II) tris-bipyridine via a tyrosine derivative

In order to model the individual electron transfer steps from the manganese cluster to the photooxidized sensitizer P680+ in Photosystem II (PS II) in green plants, the supramolecular complex 4 has been synthesized. In this complex, a ruthenium(II) tris-bipyridine type photosensitizer has been linked to a manganese(II) dimer via a substituted L-tyrosine, which bridges the manganese ions. The trinuclear complex 4 was characterized by electron paramagnetic resonance (EPR) and electrospray ionization mass spectrometry (ESI-MS). The excited state lifetime of the ruthenium tris-bipyridine moiety in 4 was found to be about 110 ns in acetonitrile. Using flash photolysis in the presence of an electron acceptor (methylviologen), it was demonstrated that in the supramolecular complex 4 an electron was transferred from the excited state of the ruthenium tris-bipyridine moiety to methylviologen, forming a methylviologen radical and a ruthenium(III) tris-bipyridine moiety. Next, the Ru(III) species retrieved the electron from the manganese(II/II) dimer in an intramolecular electron transfer reaction with a rate constant kET > 1.0 x 10(7) s(-1), generating a manganese(II/III) oxidation state and regenerating the ruthenium(II) photosensitizer. This is the first example of intramolecular electron transfer in a supramolecular complex, in which a manganese dimer is covalently linked to a photosensitizer via a tyrosine unit, in a process which mimics the electron transfer on the donor side of PS II.

A gas phase container for C60; a γ-cyclodextrin dimer

Abstract A molecular complex consisting of two molecules of γ-cyclodextrin and one molecule of C 60 has been identified by negative FAB/LSIMS mass spectroscopy.

A strophanthidin glycoside in siberian wallflower: A contact deterrent for the large white butterfly

Abstract In the greenhouse the Large White butterfly ( Pieris brassicae L.) does not oviposit on the Siberian wallflower ( Cheiranthus x allionii ) or Erysimum scoparium . From the leaves of Cheiranthus x allionii we extracted a strophanthidin glycoside (also present in washings from the leaf surface which when sprayed onto cabbage leaves inhibited egg laying. These extracts were tested in a dual choice chamber. Assayed on the butterflys tarsal receptors the strophanthidin glycoside produced a high, to very high impulse frequency, which is phasi-tonic, with only one cell firing. It appears to be the first natural contact oviposition deterrent recorded for the Lepidoptera.

Direct coupling of packed fused-silica liquid chromatographic columns to a magnetic sector mass spectrometer and application to polar thermolabile compounds

Abstract Fused-silica columns of 0.22 mm I.D. packed with normal small-particle high-performance liquid chromatography packing material were studied. The shape of the column end allows direct connection to a combined electron impact—chemical ionization (EI—CI) ion source. To inject small volumes a syringe-loaded micro-sample injector is used with the time splitting technique. Mass spectra obtained from easily vaporized compounds are similar to, but display less thermal decomposition than, normal EI spectra. Mass spectra of underivatized native mono- and disaccharides give useful structural information. Results from the analysis of cardiac glucosides are also shown. The system provides high-efficiency chromatography with a universal detector, suitable for the analysis of non-volatile and labile compounds.

Water clusters studied by electrospray mass spectrometry

Abstract By a slight modification of the electrospray ionization method, positively charged water clusters H + (H 2 O) n can conveniently be studied by high-resolution mass spectrometry over a large range of masses (from 1 to well over 100 water molecules). Inclusion of an ammonium ion instead of a hydronium ion in the clusters does not lead to a change in the distribution, and this indicates similar structures for the two types of clusters. In small ammonia–water clusters the frequency of ammonia is higher than predicted by statistics, whereas the opposite is true for large ammonia–water clusters. Similarities in the distribution of clusters generated from pure water and from an ammonia–water mixture gives doubt about proton delocalization on the cage surface. Instead, structures which have a central hydronium or ammonium ion are more likely. A new suggestion is made about structures of the well-known clusters H 3 O + (H 2 O) 20 and NH 4 + (H 2 O) 20 .

Resistance in crop species of the genus Brassica to oviposition by the turnip root fly, Hylemya floralis

Root damages, surviving plants, difference in green mass yield between pesticide treated and untreated plants, and egg numbers were used to demonstrate and measure the resistance to the turnip root fly. The relative susceptibility varied both between crops and between cultivars. Resistance to oviposition is concluded to be an attractive possibility of controlling this pest. Tarsal contact with chemical stimuli on the landing surface is the most decisive oviposition factor. The chosen strategy is to facilitate the breeding selection by isolating and visualizing chemical resistance characters on the plant surface with modern chromatographic methods. Condensed surface washings obtained by squirting steam over fresh leaves were applied on leaf dummies. Chemical agents contributing to the difference in egg-laying were in this was washed off from a susceptible cultivar of Chinese cabbage and a resistant cultivar of kale. The difference in eggload between the extracts is caused by accessory oviposition activators in an isolated fraction of Chinese cabbage. These results may be used for a breeding selection of less susceptible Chinese cabbage.

Micro liquid chromatography—mass spectrometry with low flow gradient elution. Studies of electrostatic nebulization and fused-silica column design

Abstract Fused-silica columns (I.D. 0.22 mm), packed with ordinary small-particle HPLC packing material, were directly connected with an electron-impact ion source. A system for micro flow gradient (1–5 μl/min) has been developed. The electrostatic field between the column end and the ion source is the major factor for nebulization. The electrostatic effect was studied with regard to different column tip designs. Experiments with focusing of the solvent spray to increase the sensitivity are also presented. Applications to plant extracts, phenolic acids and other polar compounds are reported.

On tuning the copper(I) coordination number in halocuprate(I) anions: new insights into cation control

Precursors in the crystallisation of selected tetraalkylammonium and tetraalkylphosphonium chlorocuprates(I) and bromocuprates(I) from ethanol solution have been studied by means of electrospray ionisation mass spectrometry. The results are discussed in the context of previous work which indicates that large bulky unipositive cations can be used to tune the copper(I) coordination number in the halocuprate(I) anion with which the cation co-precipitates, Aggregates between quaternary ammonium or phosphonium cations and halide ions, with and without copper(I), have been observed. No evidence is found for the presence of the anions of higher nuclearity observed in the solids, the only halocuprate(I) ions observed in solution being CuX2- (X = Cl, Br).

Developments of micro liquid chromatography—mass spectrometry with gradient elution : Improvements to obtain less thermal decomposition of labile compounds

Abstract Fused-silica columns (I.D. 0.22 mm) packed with ordinary small particle liquid chromatographic material were used in direct connection to an electron impact ion source. The electrostatic field between the column end and an extraction—focusing plate, located close to the ion source inlet, was used for nebulization of the solvent. The ion source was modified to obtain higher efficiency and to reduce the thermal decomposition of labile compouds. A system for micro flow gradients (less than 2 μl/min) has been developed. The flow of a pumping medium (glycerol) is divided into two parallel streams and the flow distribution is controlled using the temperature depedence of the viscosity. The glycerol flow is changed by two “media converters” to the chromatographic solvents. Applications of micro liquid chromatography—mass spectrometry are shown for a plant allelochemical, dhurrin, obtained from Sorghum leaf extract. Mass spectra of glucose, neral, geranial, chlorsulphuron, myoinositol, 3,5,-dinitrobenzoic acid, amtriptyline, 10-hydroxyamitriptyline and omeprazole after liquid chromatography are shown.

Comparison of dynamic fast atom bombardment/liquid secondary ion mass spectrometry and electrospray mass spectrometry coupled to reversed-phase liquid chromatography for the determination of oligosaccharides in seawater

Abstract A method has been developed for determination of non-derivatised oligosaccharides by LC–MS at low concentration levels and in complex matrices of seawater and sediment pore water. Two ionisation techniques, dynamic fast atom bombardment (FAB)/liquid secondary ion (LSI) MS and electrospray ionization (ESI), were investigated and evaluated. The electrospray using Li + ions as adducts proved to be superior to the FAB/LSI-MS for the determination of non-derivatised oligosaccharides. The LC separation was accomplished by the use of a C 18 column and the elution either by a gradient of methanol–acetonitrile–water or pure water, in which latter case the column was held at an elevated temperature. We also report results from measurements of oligosaccharides in pore waters of marine sediment cores. Oligosaccharides of a range from 2 to 6 sugar units were found in a concentration range of 2–100 n M , the smaller sugars being more abundant. The depth profiles in the sediment cores indicate a production in the redox boundary layer and from there, diffusion in both directions to the overlaying water and further down into the sediment.