Acidic zeolites like H-Y, H-ZSM-5, H-MCM-22 and H-MOR zeolites were found to be the selective adsorbents for the removal of thiophene from toluene or n-heptane as solvent. The competitive adsorption of toluene is found to influence the adsorption capacity for thiophene and is more predominant when high-alumina zeolites are used as adsorbents. This behaviour is also reflected by the results of the adsorption of thiophene on H-ZSM-5 zeolites with varied nSi/nAl ratios (viz. 13, 19 and 36) from toluene and n-heptane as solvents, respectively. UV-Vis spectroscopic results show that the oligomerization of thiophene leads to the formation of dimers and trimers on these zeolites. The oligomerization in acid zeolites is regarded to be dependent on the geometry of the pore system of the zeolites. The sulphur-containing compounds with more than one ring viz. benzothiophene, which are also present in substantial amounts in certain hydrocarbon fractions, are not adsorbed on H-ZSM-5 zeolites. This is obvious, as the diameter of the pore aperture of zeolite H-ZSM-5 is smaller than the molecular size of benzothiophene. Metal ion-exchanged FAU-type zeolites are found to be promising adsorbents for the removal of sulphur-containing compounds from model solutions. The introduction of Cu+-, Ni2+-, Ce3+-, La3+- and Y3+- ions into zeolite Na+-Y by aqueous ion-exchange substantially improves the adsorption capacity for thiophene from toluene or n-heptane as solvent. More than the absolute content of Cu+-ions, the presence of Cu+-ions at the sites exposed to supercages is believed to influence the adsorption of thiophene on Cu+-Y zeolite. It was shown experimentally for the case of Cu+-Y and Ce3+-Y that the supercages present in the FAU zeolite allow for an access of bulkier sulphur-containing compounds (viz. benzothiophene, dibenzothiophene and dimethyl dibenzothiophene). The presence of these bulkier compounds compete with thiophene and are preferentially adsorbed on Cu+-Y zeolite. IR spectroscopic results revealed that the adsorption of thiophene on Na+-Y, Cu+-Y and Ni2+-Y is primarily a result of the interaction of thiophene via pi-complexation between C=C double bond (of thiophene) and metal ions (in the zeolite framework). A different mode of interaction of thiophene with Ce3+-, La3+- and Y3+-metal ions was observed in the IR spectra of thiophene adsorbed on Ce3+-Y, La3+-Y and Y3+-Y zeolites, respectively. On these adsorbents, thiophene is believed to interact via a lone electron pair of the sulphur atom with metal ions present in the adsorbent (M-S interaction). The experimental results show that there is a large difference in the thiophene adsorption capacities of pi-complexation adsorbents (like Cu+-Y, Ni2+-Y) between the model solution with toluene as solvent and the model solution with n-heptane as solvent. The lower capacity of these zeolites for the adsorption of thiophene from toluene than from n-heptane as solvent is the clear indication of competition of toluene in interating with adsorbent in a way similar to thiophene. The difference in thiophene adsorption capacities is very low in the case of adsorbents Ce3+-Y, La3+-Y and Y3+-Y, which are believed to interact with thiophene predominantly by direct M3+-S bond (thiophene interacting with metal ion via a lone pair of electrons). TG-DTA analysis was used to study the regeneration behaviour of the adsorbents. Acid zeolites can be regenerated by simply heating at 400 °C in a flow of nitrogen whereas thiophene is chemically adsorbed on the metal ion. By contrast, it is not possible to regenerate by heating under idle inert gas flow. The only way to regenerate these adsorbents is to burn off the adsorbate, which eventually brings about an undesired emission of SOx. The exothermic peaks appeared at different temperatures in the heat flow profiles of Cu+-Y, Ce3+-Y, La3+-Y and Y3+-Y are also indicating that two different types of interaction are present as revealed by IR spectroscopy, too. One major difficulty in reducing the sulphur content in fuels to value below 10 ppm is the inability in removing alkyl dibenzothiophenes, viz. 4,6 dimethyl dibenzothiophene, by the existing catalytic hydrodesulphurization technique. Cu+-Y and Ce3+-Y were found in the present study to adsorb this compound from toluene to a certain extent. To meet the stringent regulations on sulphur content, selective adsorption by zeolites could be a valuable post-purification method after the catalytic hydrodesulphurization unit.
Within this thesis a series of molecular species has been studied, with focus on hydrogen bonded species and on (solvated) transition metal complexes. Experimental techniques such as FT-ICR-MS and IRMPD were combined with ab initio calculations for the determination of structure and reactivity of the aforementioned types of systems. On the basis of high level electronic structure calculations of neutral water clusters (H2O)n with n = 17-21 a transitional size regime has been determined, where a structural stabilization between all-surface and interior configurations alternates with the addition or removal of a single water molecule. Electronic structure calculations suggested that for n = 17 and 19 the interior configuration would be energetically more stable than the all-surface one. The gas phase infrared spectrum of the singly hydrated ammonium ion, NH4+(H2O), had previously been recorded by photodissociation spectroscopy of mass selected ions and interpreted by means of ab initio calculations. The present work provides additional information on the shape of the potential energy curves of NH4+(H2O) along the N-H distance on MP2/aug-cc-pVDZ level of theory yielding an anharmonic potential shape. Calculation of potential energy curves of the O-H mode of the intramolecular hydrogen bond of various dicarboxylic acids (oxalic to adipic acid) revealed that the shapes of the potentials directly correlate to the size of the system and the resulting ring strain The shape of the potential is also influenced by the charge of the system. Calculation of anharmonic frequencies based on the VPT2 approach lead to reasonable results in all systems with narrow potentials. IRMPD spectra of complexes in the gas phase have been recorded for a series of cationic vanadium oxide complexes when reacted with acetonitrile, methanol and ethanol. The experimental spectra are compared to calculated absorption spectra. The systematic DFT study identifies potential candidates for reductive nitrile coupling in cationic transition metal acetonitrile complexes. On the basis of the calculations, the formation of metallacyclic structures in group 3 through 7 complexes can be ruled out. Solvation of the transition metal cation by five acetonitrile ligands leads to a reductive nitrile coupling reaction in three types of complexes, namely those containing either niobium, tantalum or tungsten.
Colorectal cancer is the second most prevalent cancer form in both men and women in the Europe. In 2002, alimentary cancer (oesophagus, stomach, intestines) made up 26% of the annual incident cases of cancer amongst males in Europe, whereby about half of those were cancers of the colon and rectum (Eurostat 2002). Epidemiological evidence accumulating over the last decades indicates that besides a genetic disposition, diet plays a strong epigenetic role in the genesis of cancer. It is generally assumed that diet is causal for up to 80% of colorectal cancer (Bingham 2000). With the prospect of an approximated 50% rise in global cancer incidence over the first two decades of the 21st century, the World Health Organisation (WHO) has emphasized the need for an improvement in nutrition. Indeed there is increasing public health awareness with respect to nutrition. Today, living healthily is associated with less consumption of animal fats and red (processed) meat, moderate or no consumption of alcohol coupled with increased physical activity, and frequent intake of fruits, vegetables and whole grains (Bingham 1999; Johnson 2004). This idealogy partly stems from scientific epidemiological evidence supportive of an inverse correlation between the consumption of fruits and vegetables and the development cancer. Besides fibre and essential micro-nutrients like ascobate, folate, and tocopherols, the anti-carcinogenic properties of fruits and vegetables are generally thought to be rooted in the bioactivity of secondary plant components like flavonoids (Johnson 2004; Rice-Evans and Miller 1996; Rice-Evans 1995). Along with the increased public health awareness, has also come a burgeoning and lucrative dietary supplement industry, which markets products based on polyphenols and other potentially healthy compounds, sometimes with questionable promises of better health and increased longevity. These claims are based on accumulating in vitro and in vivo evidence indicating that flavonoids and polyphenols in fruits and vegetables can hinder proliferation, induce apoptosis of cancerous cells (Kern et al. 2005; Kumar et al. 2007; Thangapazham et al. 2007), act as antioxidants (Justino et al. 2006; Rice-Evans 1995) and influence cell signalling pathways (Marko et al. 2004; Joseph et al. 2007; Granado-Serrano et al. 2007), all of which are potential mechanisms proposed for their anti-carcinogenic activity. However, not only is the vast variety of supplements worrisome, but also problematic, is their easy accessibilty (just a click away on the internet) and the amount that can potentially be consumed. Such supplements are usually offered in pharmaceutical form (tablets, capsules, powder, concentrates) containing concentrations well beyond what is normally comsumable from the diet. For example, quercetin’s recommended intake is about 1g daily. However, estimates portend a possible daily increase of upto 1000 fold of the daily intake of quercetin (Hertog et al. 1995). Mindful of the concept of dose coined from the words of swiss scientist Paracelsus “What is it that is not poison? All things are poison and nothing is without poison. The right dose differentiates a poison and a remedy.” (“Alle Dinge sind Gift und nichts ist ohn’ Gift; allein die Dosis macht, dass ein Ding kein Gift ist”), it is thus conceivable that such high concentrations may not only reverse the acclaimed positive effects of flavonoids and polyphenols but also have negative effects thereby representing a health risk. The fact that direct evidence of the beneficial effects of flavonoids and polyphenols remains wanting, if not entirely lacking, coupled with the afore-mentioned marketing trend demands for a thorough examination of the possible adverse effects that may arise from increased consumption of flavonoids and polyphenols. The genesis and progression of cancer is usually accompanied by dysfunctional signalling of certain cell signalling pathways. Typical for colon carcinogenesis is the malfunctioning of the Wnt-signalling pathway, a pathway, which is crucial for the growth and development of normal colonocytes. The dysfunction of the Wnt-signalling pathway occurs in a manner that culminates in a proliferation stimulus of colonocytes, while differentiation is increasingly minimized. Hence, tumourigenesis is promoted. Interupting the proliferation stumuli by intervening in the actions of components of the Wnt-signalling pathway is one potential mechanism for the anti-carcinogenic action of flavonoids and polyphenols (Pahlke et al. 2006; Dashwood et al. 2002; Park et al. 2005). However, as previously hinted, the indulgence in the consumption of flavonoids and polyphenols based supplements could instead lead to a proliferation stimulus and provoke or promote carcinogenesis in normal cells or pre-cancerous cells respectively. The aim of this work was to