Proefschrift Rijksuniversiteit Groningen. / Auteursnaam op omslag: Arjan van Oeveren.

Proefschrift Rijksuniversiteit Groningen. / Met lit.opg. - Met samenvatting in het Nederlands.

The present study was focused to develop an analytical method to analyse â-lactam antibiotics present in aqueous solutions and able to be applied directly in the fields. The method here presented is based on the chemical reaction between â-lactam antibiotics with phosphomolybdic acid, a heteropolyacid able to be reduced by the thiols obtained after the acid hydrolysis of the â-lactam antibiotics. The blue product obtained, which is proportional to the antibiotic amount, is adsorbed on polyurethane foam, and the intensity of color is directly evaluated on the solid material by means of diffuse reflectance spectroscopy. For all six evaluated â-lactam antibiotics (amoxicillin, ampicillin, penicillin V, penicillin G, cefotaxime, cefuroxime), the analytical parameters achieved were: LOD = 0.03 µg/ml, LOQ = 0.1 µg/ml, RSD = 4.0 %. The study of possible interferences showed that using solid phase extraction is possible to eliminate even strong interferences as ascorbic acid, cysteine and reducing salts like stannous chloride. The present method has avoided, as much as possible, the use of expensive and contaminating solvents and chemical reagents. The method presents the possibility to be applied using only a desktop scanner and a personal PC for measuring the color of the adsorbed material on the PUF.

Both series of monoglyceride gels samples with different monoglyceride concentration of two monoglycerides C14 and C16/18 and series of water-in-oil emulsions that differ from flocculation, water concentration and biopolymer have been investigated by means of PFG NMR. Aim of the measurements was to determine microstructural parameters characterising such heterogenous systems. For the monoglyceride gels a return-to-the-origin probability, the average surface-to-volume ratio of the pore space as well as the tortuosity and dimensionality of the network could be calculated on the basis of echo attenuation and diffusion curves. Additionally pore size distributions have been determined for the monoglyceride gels. The results verify a postulated crystallisation process for monoglyceride gels and were validated by CryoSEM images and image analysis. The PFG NMR findings of the water-in-oil emulsions have been fitted with four various models which were developed in the context of this thesis and assume different diffusion behaviour of the water molecules. All models show individual deficits as the real movement of water molecules in the water-in-oil emulsions is more complex than assumed. Non flocculated and flocculated emulsions could be characterised and the droplet and aggregate size as well as the effective diffusion coefficient could be calculated. The results have been corroborated by CSLM images and image analysis.

A new detector for gas chromatography based on a microwave induced plasma has been developed. In order to record chromatograms emission spectra of diatomics are detected. Also a new method to obtain qualitative information on the analysed organic compound has been developed. The new detection method allows to get information about the atomic composition. In some cases the detector signals can be correlated with the constitution of the analysed substance. The detection method is based on the simultaneous detection of the spectral density of molecular bands of different diatomics as CC, CH, CN, NH, OH and an atomic hydrogen line. The resulting peak areas and the offset of the OH band are correlated with the analysed compounds by multivariate linear regression.

The electrocatalytic characteristics of N4-chelatele electrodes is well known for several redox reactions. The N4-chelate can function thereby according to the principle of the heterogeneous redox catalysis as an intermediate fixed at the electrode surface. The main problem is the limited service life of such electrodes which prohibits the practical application in organic electrosyntheses. The electrochemical properties of N4-chelate electrodes and specially of copper phthalocyanine electrodes were investigated using several electrochemical methods. The results of these measurements lead into a significant refinement of the models of heterogenous redox reaction at N4-chelates. Furthermore models for the degradation process of N4-chelate electrodes could be derived. Finally, quite stable electodes were produced and tested.

The central topic if this work was the comparative assessment of two analytical techniques: Pulsed Field Gradient Nuclear Magnetic Resonance (PFG-NMR) Spectroscopy and the Dynamic Nanosizing Microscopy (DNM). They are focused on the same physical parameter: the self diffusion, for determination of diffusion coefficients and particle sizes. With the methods introduced above nanocapsule dispersions are investigated with regard to their use in pharmaceutical applications. In this work especially the long time stability of dispersions, the dynamic of molecules like surfactants, oil and ethanol as well as the molecular exchange between the capsules and the environment were studied.

The photocycloadditions of 2-(dialkylamino)propenenitriles to 1-acetylnaphthalene in d6 benzene as solvent proceed with high directional selectivity by fast and photoreversible formation of [2+2]-cycloadducts (tetrahydrocyclobuta[a]naphthalenes) followed by a slower and photoirreversible formation of [4+2]-cycloadducts (1,4-dihydro-1,4-ethanonaphthalenes). With increasing duration of irradiation the product pattern is shifted towards a mixture of diastereomeric [4+2]-adducts in which the isomer with endo-orientation of the dialkylamino group in the ethano bridge is predominating. The endo-[4+2]-adduct of 2-(dipropylamino)-propenenitrile to 1-acetylnaphthalene was isolated in pure form, and its configuration was unambiguously corroborated by a single crystal X-ray structure analysis. Upon thermal activation it is converted in a small fraction via an intermediate biradical to the thermodyna-mically more stable exo-epimer before it is decomposed to the educts. Methyl 1-naphthoate reacts in the same way as 1-acetylnaphthalene but less efficiently.

The use of ICP-OES to determinate Rare Earth Elements in different matrices often fails because of high spectral interferences. To achieve an correct result the use of a sample preparation is advisable. In this work Extractionchromatography is used as sample preparartion. Three different substances were used as stationary phase. These are Triazaheptan-1,4,7,7-tetraaceticacid (DETATA), Tetraphenylmethylendiphosphineoxide. (TPMDPO) und Tri-n-octylphosphineoxide (TOPO). If DETATA is used as staionaric phase the recovery of REE in the final solution is reduced to 40-60% when bivalent ions such as Ni2+ and Fe2+ are present in the sample. So this substance is not reliable in the use as stationaric phase if the sample is a steelmatrix. In highly concentrated KCl-solution as matrix the recovery of REEs increases to 98%. In the second part the results of the experiments with TPMDPO are presented. In the presence of Cr3+, Ni2+ oder Mn2+ the recovery decrease significantly. So this substance is also unusable if the matrix is steel. The third examined organic substance is TOPO. If NH4NO3 is added as salting-out material and after reducing the solution with hydrazine the recovery of REEs is qunatitative. The improvement of the detection limit exceeds the factor of 10 if ICP-OES is the used analysing method.

The active site of the NiFe-hydrogenase from <i>Desulfovibrio vulgaris</i> Miyazaki F was investigated by means of X-ray Absorption Spectroscopy (XAS). Using the Extended X-ray Absorption Fine Structure (EXAFS) the active site was structurally characterized to determine differences between four different catalytic states of the enzyme. The nature of an additional ligand which is present in the oxidized forms of the enzyme was revealed and the distance between both metal atoms of the heterobinuclear site was calculated. Suitable data analyzation techniques were developed using simulated spectra. For the verification of these techniques, spectra from model compounds structurally characterized by other methods were used. To ensure sufficient quality of the spectra a newly developed quality control system using statistical criteria was employed.