Harald Jancke

Gaschromatographische und 29Si‐NMR‐spektroskopische Untersuchungen an Kieselsäuretrimethylsilylestern

Kieselsauretrimethylsilylester unterschiedlicher Konstitution werden mit Hilfe der Gaschromatographie hinsichtlich ihres Retentionsindex und der Retentionstemperatur charakterisiert. Es wird gezeigt, das die Retentionsdaten der Ester im wesentlichen von der Anzahl der Trimethylsilylgruppen im Molekul abhangen und nur wenig von der Konstitution des Kieselsauregerustes beeinflust werden. Die 29Si-NMR-Spektren von neun Kieselsaure-TMS-Estern unterschiedlicher Konstitution wurden aufgenommen und die Zuordnung der Signale zu den einzelnen Baugruppen der Ester diskutiert. Auf der Grundlage dieser Ergebnisse wurden Konstitutionsuntersuchungen an hexameren Kieselsaure-TMS-Estern durchgefuhrt, die zur Identifizierung von zwei Isomeren des Bicyclohexakieselsaureesters [(CH3)3Si]10[Si6O17] fuhrten.

Fulvic acid composition in degraded fenlands

Fulvic acids (FAs) from topsoil and ground water solutions were investigated to discover effects of land use and peat degradation on their molecular chemical composition and thermal properties. The FAs were extracted from three Gleysols under arable land, intensive and extensive grassland, and from three Histosols under alder forest, extensive grassland, and a natural succession in a long-term (> 200 years) cultivated fen area. Functional groups and molecular subunits of the FAs were investigated by 13C Nuclear Magnetic Resonance (13C NMR) spectroscopy. Thermal properties and structural molecular subunits were investigated by off-line pyrolysis, and Pyrolysis-Field Ionization Mass Spectrometry (Py-FIMS). The 13C NMR spectra showed that the FAs from topsoil solutions had smaller proportions of alkyl C (mean: —8 %) and more aromatic C (mean: + 6 %) than FAs from ground water. This clear differentiation of dissolved FAs in the soil profiles is consistent with Py-FIMS data which have shown enrichments of lipids in ground water FAs. Furthermore, Py-FIMS revealed that the FAs from topsoils were richer in phenols + lignin monomers, carbohydrates, as well as mostly aromatic N-containing compounds. These molecular subunits of FAs, relatively enriched in topsoil, were also the main indicators of land use and peat degradation. For topsoil solutions, the proportions of phenols + lignin monomers and carbohydrates increased stepwise with peat degradation in Gleysols and Histosols. Correspondingly, the thermal properties indicated the incorporation of these compounds into FAs by chemical bonds of larger thermal stability. Statistical evaluation by principal component analysis of Py-FIMS clearly supported the differentiation of FAs according to the origin from topsoils and ground water, different soil types, and land use and peat degradation. Hence, it is concluded that water soluble FAs can be utilized as objective ecological indicators for soil effects on adjacent ground and surface waters. Molekulare Zusammensetzung von Fulvosauren in unterschiedlich genutzten Gleyen und Niedermooren Fulvosauren (FAs) aus Bodenlosung und Grundwasser wurden untersucht, um Veranderungen von Zusammensetzung und thermischen Eigenschaften infolge unterschiedlicher Landnutzung und Torfdegradierung zu erforschen. Dazu wurden die FAs aus drei Gleyen unter Acker, extensivem und intensivem Grasland sowie aus drei Niedermooren unter Erlenbruchwald, Dauergrasland und naturlicher Sukzession in einem bereits seit langer Zeit kultivierten Niedermoorgebiet extrahiert. Funktionelle Gruppen und molekulare Untereinheiten der FAs wurden mit 13C-Kernresonanz-Spektroskopie (13C-NMR), off-line-Pyrolyse und on-line-Pyrolyse-Feldionisation-Massenspektrometrie (Py-FIMS) analysiert. Die 13C-NMR-Spektren zeigten niedrigere Anteile an Alkyl-C (Mittelwert: —8 %) und hohere Anteile an aromatischem C (Mittelwert: + 6 %) der FAs aus Losungen aus Oberboden im Vergleich zu den FAs aus Grundwasser. In Ubereinstimmung damit ergab die Py-FIMS relative Anreicherungen an Lipiden in den FAs aus Grundwasser. Die FAs aus Oberboden waren dagegen reicher an monomeren Ligninbausteinen, Kohlenhydraten und N-Verbindungen. Diese in den FAs aus Oberboden angereicherten, molekularen Untereinheiten waren auch die Hauptindikatoren fur Effekte der Landnutzung und Torfdegradierung. In beiden Gruppen von Boden fuhrte eine erhohte Intensitat der Bodennutzung und damit verbundene Beluftung zu groseren Anteilen an Phenolen + Ligninmonomeren und Kohlenhydraten. Die aus den Py-FI-Massenspektren berechneten Thermogramme zeigen, dass diese Verbindungen nicht nur relativ angereichert, sondern auch durch chemische Bindungen mit groserer thermischer Stabilitat charakterisiert sind. Die Ergebnisse belegen, dass geloste FAs als schnell wirksame und objektive Indikatoren fur mogliche Auswirkungen von Landnutzungsanderungen auf benachbarte Oberflachengewasser genutzt werden konnen.

New Evidence For The Molecular Composition Of Soil Organic Matter In Vertisols

The distribution of soil organic matter (SOM) in particle-size fractions and the molecular composition of SOM were investigated for five FAO/UNESCO reference Vertisols. Throughout the soil profiles, more than 80% of SOM was associated with clay-size fractions. The remaining proportions were distributed in silt (mean: 15%) and sand (mean < 1%). The uniform depth distribution of organic carbon (C org ) and total nitrogen (N t ) in size fractions distinguished the Vertisols from other major soil groups. The composition of SOM in the surface horizons was studied by solid-state 13 C nuclear magnetic resonance ( 13 C-NMR) spectroscopy, analytical pyrolysis, and wet chemical analyses of organic N forms. The 13 C-NMR spectra showed low signal-to-noise ratios and indicated the predominance of alkyl C in four of the samples. In contrast to the general low extractability of SOM in Vertisols, unexpectedly large proportions of C and N (61-95%) could be pyrolyzed and analyzed by field-ionization mass spectrometry (Py-FIMS) and Curie-point gas chromatography/mass spectrometry (Py-GC/MS). Signals of nitrogen-containing compounds were pronounced in the FI mass spectra, and carbohydrates also contributed significantly to the total ion intensity (TII). Quantitative evaluation showed that the large proportions of heterocyclic N-containing compounds and peptides (up to 20% of TII) distinguished these Vertisols from Regosols, Cambisols, Podzols, Chernozems, and Histosols which were analyzed by Py-FIMS. Derivatives of pyrrole and pyridine as well as aromatic nitriles were observed in the GC/mass spectra of all samples. Hydrolysis and fractionation of organic N forms yielded large proportions of hydrolyzable N (84-98% of total N) and NH 3 -N (32-53% of total N), adding further evidence to the importance of N-containing molecules in Vertisols. These results suggest that recent concepts regarding the molecular composition of SOM in Vertisols should be revised because they overemphasize long-chain aliphatics and neglect aromatic and aliphatic N-containing molecules, which were unequivocally identified by analytical pyrolysis.

Control of the specific surface area of silica by a sol–gel process using 2-methylpentane-2,4-diol

An improved method for the preparation of porous silica xerogels is described. Tetraethoxysilane (TEOS) as the starting alkoxide is modified by transesterification with 2-methylpentane-2,4-diol (MPD) prior to hydrolysis. The specific surface area and the pore size distribution of the calcined gels can be easily controlled by variation of the preparation parameters. Thus, a xerogel exhibiting a specific surface area of 1108 m2 g–1 was obtained after calcination at 450 °C for 4 h. The species formed by the transesterification of tetramethoxysilane (TMOS) with MPD were studied by 29Si NMR spectroscopy and chemical ionisation mass spectroscopy (CI MS).

The early stages of the sol-gel processing of TEOS

The reactivity of tetraethoxysilane (TEOS) used in many sol-gel syntheses can be increased by prehydrolysis. In contrast to one-step prehydrolysis acidic two-step prehydrolysis causes an increase of the reactivity of the low molecular species provided the total water/TEOS ratios are the same in both cases. By choice of the processing conditions of the hydrolysis—shown on variation of water content, hydrolysis steps and heat treatment—the degree of condensation, the ratio of hydrolyzable (-OC2H5) and hydrolyzed groups (-OH) and the structure of the low molecular species (short chains, 3-membered and 4-membered rings) can be influenced systematically. The development of the building units formed in the early reaction stages is ascertained by molybdate method and 29Si NMR measurements.

Über die Reaktion des käfigartigen Kieselsäurederivats [(CH3)2HSi]8Si8O20 mit ungesättigten organischen Verbindungen

29Si-, 1H- und 13C-NMR-Untersuchungen zeigen, das das Doppelvierring-kieselsaurederivat [(CH3)2HSi]8Si8O20 mit seinen acht HSiGruppen pro Molekul Additionsreaktionen mit den einfach ungesattigten Verbindungen Vinylcyclohexen, Allylglycidylether, Methacrylsauremethylester, Octadecen-1 und Styren eingeht. Die Addition erfolgt uberwiegend entgegen der Markovnikov-Regel. Als Reaktionsprodukte werden meist olartige, in organischen Losungsmitteln losliche Verbindungen der Formeln [C6H9(CH2)2Si(CH3)2]8Si8O20, [CH3OOCCH(CH3)CH2Si(CH3)2]8Si8O20, CH3(CH2)17Si([CH3)2]8Si8O20 und [C6H5(CH2)2Si(CH3)2]8Si8O20 bzw. [C6H5CH(CH3)Si(CH3)2]8Si8O20 erhalten, die durch die chemischen Verschiebungen der 29Si-, 1H- und 13C-NMR-Signale charakterisiert werden. Reaction of the Cage-like Silicic Acid Derivative [(CH3)2HSi]8Si8O20 with Unsaturated Organic Compounds By 29Si, 1H, and 13C NMR investigations were shown that the eight HSigroups of the double four-ring silicic acid derivative [(CH3)2HSi]8Si8O20 react with the following unsaturated compounds: vinylcyclohexene, allyl glycidyl ether, methyl methacrylate, octadecene-1, and styrene. The resulting oily products are soluble in organic solvents. The compounds were characterized by the chemical shifts of the 29Si, 1H, and 13C NMR signals. Their formulae are [C6H9(CH2)2Si(CH3)2]8Si8O20, [CH3OOCCH(CH3)CH2Si(CH3)2]8Si8O20, [CH3(CH2)17Si(CH3)2]8Si8O20 and [C6H5(CH2)2Si(CH3)2]8Si8O20, and [C6H5CH(CH3)Si(CH3)2]8 Si8O20, respectively. Mainly the addition reactions do not follow the Markovnikov rule.

Microscopic vs. macroscopic structural evolution of SiO2 sols and gels employing a tailor-made fluorescent reporter dye

The short- and long-term structural evolution and aging of sol–gel materials prepared under mild conditions are studied by fluorometry, dynamic light scattering (DLS), 29Si NMR and gravimetry. In combination with the first, a newly developed donor–acceptor-substituted fluorescent probe with two acidophilic sites of different strength and topology is introduced. Its performance in detecting changes in parameters such as polarity, proticity, and pore volume on the microscopic scale is compared to two other dyes and to the macroscopic changes revealed by DLS, NMR and gravimetry. At early stages of the sol–gel process, fluorometry, DLS and NMR reveal similar changes which are typical of the structural evolution of SiO2 sols having different synthesis parameters. During later times of sol aging, DLS and NMR reflect the growth of the network and indicate that all sols approach similar structural equilibria. Fluorometry supports these findings by signalling a gradual decrease in mobile species with high proton activity. The formation of the spanning cluster upon gelation is strongly evident only from DLS results while the local environment of the fluorophore remains largely unchanged. However, the fluorescent dye is able to report microscopic changes even during long-term aging. Drying of the gels with a pronounced contraction of solvated pores is readily observable by fluorometry and gravimetry. During the late reaction stages, the fluorescence properties of the tailor-made dye are still sensitive toward the environment.

On reasons of 29Si NMR chemical shift/structure relations for silicon oxides, nitrides, and carbides: An individual-gauge-for-localized-orbitals study

For alpha-quartz, monoclinic ZSM-5, alpha- and beta-Si3N4 and SiC-6H polytype, the silicon chemical shifts have been calculated using the IGLO (individual gauge for localized orbitals) method and models of different size in real crystal geometry. The result is a theoretical chemical shift scale, which is very similar to the corresponding experimental scale from 29Si MAS NMR experiments. It is shown that the assignment of isotropic silicon chemical shifts of crystallized solids based on theory is a method of practical applicability, also in cases where experimental methods or empirical relations fail. The two NMR spectral lines of alpha-Si3N4 are for the first time assigned to the crystallographic positions. The partition of the silicon chemical shifts into localized contributions from different parts of the model allows insight into the interactions around the resonance nucleus due to substituent and geometry variations leading to silicon chemical shifts.

Non-selective signal loss in the 13C CPMAS NMR spectra of soil organic matter. Investigations of particle size fractions

In 13C cross-polarisation magic angle spinning (CPMAS) spectra of soil samples, the paramagnetic soil constituents partially discriminate against the signal intensity of the 13C atoms. The aim of the present study was to check to what extent this signal depression depends on the paramagnetic ion content and if it is selective for a certain kind of carbon species. The spectra of a variety of particle size fractions of five quite different soils were recorded. A procedure was developed to compare quantitatively the relative carbon content of the different spectra. It was found that iron ions differ in their efficiency to discriminate against the carbon signals. Nevertheless a strong linear correlation between the detectability of carbon and cube root(wt.%Fe) was observed for both the total signal and the signal of the different carbon species as well. This underlines that iron ions mainly influence the depression of the 13C signal in soil spectra. Furthermore we found, that for C: Fe ratios of 1.5 to 20 non-selective signal losses dominate. Despite a high percentage of non-detectable carbon (up to 90%), the 13C CPMAS spectra of our soil samples correctly reflect the relative composition of soil organic matter.

Investigations of Structure and Stability of the Tetrachlorinedecaoxide Anion Complex (TCDO)

Raman spectroscopic and 35Cl-NMR scans of Hydro-Xan®, a preparation containing the biocatalytically effective Tetrachlorinedecaoxide anion (TCDO), are described. The spectroscopic analyses showed that HydroXan® does not contain chlorite initially used in the preparation anymore. Furthermore, a structure of four equal chlorate-like ClO3-groups was indicated for TCDO by the scans. Such a structure is supported by the long-term stability of HydroXan® found at tests over 267 days. Untersuchungen zur Struktur und Stabilitat des Tetrachlordecasauerstoff-Anions (TCDO) Es werden raman- und 35Cl-NMR-spektroskopische Untersuchungen am HydroXan®, einem Praparat, das das biokatalytisch wirksame Tetrachlordecaoxid-Anion (TCDO) enthalt, beschrieben. Die Untersuchungen zeigen, dass HydroXan® das Ausgangsprodukt Chlorit nicht mehr enthalt. Untersuchungen des Depolarisationsgrades der Ramanbanden legen fur das TCDO eine Struktur nahe, in der vier gleichwertige chloratahnliche ClO3-Gruppen vorhanden sind. Langzeituntersuchungen uber 267 Tage liefern Anhaltspunkte zur Stabilitat des HydroXans®.