Due to their N-glycosidase activity, ribosome-inactivating proteins (RIPs) are attractive candidates as antitumor and antiviral agents in medical and biological research. In the present study, we have successfully cloned two different truncated gelonins into pET-28a(+) vectors and expressed intact recombinant gelonin (rGel), recombinant C-terminally truncated gelonin (rC3-gelonin) and recombinant N- and C-terminally truncated gelonin (rN34C3-gelonin). Biological experiments showed that all these recombinant gelonins have no inhibiting effect on MCF-7 cell lines. These data suggest that the truncated-gelonins are still having a specific structure that does not allow for internalization into cells. Further, truncation of gelonin leads to partial or complete loss of N-glycosidase as well as DNase activity compared to intact rGel. Our data suggest that C-and N-terminal amino acid residues are involved in the catalytic and cytotoxic activities of rGel. In addition, the intact gelonin should be selected as a toxin in the immunoconjugate rather than truncated gelonin.
In the second part, an immunotoxin composed of gelonin, a basic protein of 30 kDa isolated from the Indian plant Gelonium multiflorum and the cytotoxic drug MTX has been studied as a potential tool of gelonin delivery into the cytoplasm of cells. Results of many experiments showed that, on the average, about 5 molecules of MTX were coupled to one molecule of gelonin. The MTX-gelonin conjugate is able to reduce the viability of MCF-7 cell in a dose-dependent manner (ID50, 10 nM) as shown by MTT assay and significantly induce direct and oxidative DNA damage as shown by the alkaline comet assay. However, in-vitro translation toxicity MTX-gelonin conjugates have IC50, 50.5 ng/ml which is less toxic than that of gelonin alone IC50, 4.6 ng/ml. It can be concluded that the positive charge plays an important role in the N-glycosidase activity of gelonin. Furthermore, conjugation of MTX with gelonin through α- and γ- carboxyl groups leads to the partial loss of its anti-folate activity compared to free MTX. These results, taken together, indicate that conjugation of MTX to gelonin permits delivery of the gelonin into the cytoplasm of cancer cells and exerts a measurable toxic effect.
In the third part, we have isolated and characterized two ribosome-inactivating proteins (RIPs) type I, gelonin and GAP31, from seeds of Gelonium multiflorum. Both proteins exhibit RNA-N-glycosidase activity. The amino acid sequences of gelonin and GAP31 were identified by MALDI and ESI mass spectrometry. Gelonin and GAP31 peptides - obtained by proteolytic digestion (trypsin and Arg-C) - are consistent with the amino acid sequence published by Rosenblum and Huang, respectively. Further structural characterization of gelonin and GAP31 (tryptic and Arg-C peptide mapping) showed that the two RIPs have 96% similarity in their sequence. Thus, these two proteins are most probably isoforms arisen from the same gene by alternative splicing. The ESI-MS analysis of gelonin and GAP31 exhibited at least three different post-translational modified forms. A standard plant paucidomannosidic N-glycosylation pattern (GlcNAc2Man2-5Xyl0-1 and GlcNAc2Man6-12Fuc1-2Xyl0-2) was identified using electrospray ionization MS for gelonin on N196 and GAP31 on N189, respectively. Based on these results, both proteins are located in the vacuoles of Gelonium multiflorum seeds.
The scientific intention of this work was to synthesize and characterize new bidentate, tridentate and multidentate ligands and to apply them in heterogenous catalysis. For each type of the ligands, new methods of synthesis were developed. Starting from 1,1'-(pyridine-2,6-diyl)diethanone and dimethylpyridine-2,6-dicarboxylate different bispyrazolpyridines were
synthesized and novel ruthenium complexes of the type (L)(NNN)RuCl2 could be obtained. The complexes with L = triphenylphosphine turned out to be highly efficient
catalyst precursors for the transfer hydrogenation of aromatic ketones. Introduction of a butyl group in the 5-positions of the pyrazoles leads to a pronounced increase of catalytic activity.
To find a method for the synthesis of bispyrimidinepyridines, different reactants and condition were applied and it was found that these tridentate ligands can be obtained by mixing and grinding the tetraketone with guanidinium carbonate and silica, which plays the role of a catalyst in this ring closing reaction.
The bidentate 2-amino-4-(2-pyridinyl)pyrimidines were synthesized from different substrates according to the desired substituent on the pyrimidine ring.
Reacting these bidentate ligands with the ruthenium(II) precursor [(η6-cymene)Ru(Cl)(μ
2-Cl)]2 gave cationic ruthenium(II) complexes of the type [(η6-cymene)Ru(Cl)(adpm)]Cl (adpm = chelating 2-amino-4-(2-yridinyl)pyrimidine ligand). Stirring the freshly prepared complexes with either NaBPh4, NaBF4 or KPF6, the chloride anion was exchanged against other coordinating anions (BF4-, PF6-, BPh4-).Some of these ruthenium complexes have shown very special activities in the transfer hydrogenation of ketones by reacting them in the absence of the base. This led to detailed investigations on the mechanism of this reaction. According to the activities and with the help
of ESI-MS experiments and DFT calculations, a mechanism was proposed for the transfer hydrogenation of acetophenone in the absence of the base. It shows that in the absence of the base, a C-H bond activation at the pyrimidine ring should occur to activate the catalyst.
The palladium complexes of bidentate N,N ligands were examined in coupling reactions. As expected, they did not show very special activities.
Multidentate ligands, having pyrimidine groups as relatively soft donors for late transition metals and simultaneously possessing a binding position for a hard Lewis-acid, could be obtained using the new synthesized bidentate and tridentate ligands.
Mechanisms underlying the biological effects of coffee and its constituents are incompletely understood. Many effects have been attributed solely to caffeine, neglecting that coffee is a mixture of many chemical substances. Some authors suggest that the main mechanism of action of caffeine is to antagonize adenosine receptors (AR); a second effect is the inhibition of phosphodiesterases with the subsequent accumulation of cAMP and an intensification of the effects of catecholamines. Although the inhibition of phosphodiesterases may contribute to the actions of caffeine, there is growing evidence that most pharmacological effects of this xanthine result from antagonism of AR.
One of the main objectives of this work was to investigate whether substances other than caffeine in coffee may influence the homeostasis of intracellular cyclic nucleotides in vitro and in vivo. The influence of selected coffee compounds, extracts and brews on key elements involved in the adenosine receptor-mediated signaling pathway have been investigated.
A further aim of this work was also to determine if coffee or some coffee constituents may have a stimulatory effect on the cellular heme oxygenase activity (HO-activity). Two coffee extracts, a slightly (AB1) and an intensively roasted coffee (AB2), were studied along with selected individual compounds. Caffeine and low substituted pyrazines showed no effect on the HO-activity, while NMP, pyrazines with a greater substitution pattern such as Tetramethylpyrazine (TMP) and 2-Ethyl-3,5(6)-dimethylpyrazine (2-E-3,5-DMP) and both coffee extracts significantly induced the HO-activity in liver hepatocellular carcinoma (HepG2), intestinal colo-rectal adenocarcinoma (Caco-2) and in some instances in monocytic leukemia (MM6) cells.
It was found that caffeine, theophylline, coffee extracts from conventional or functional coffees, pyrazines (2,3-DE-6-MP, 2-Isobutyl-3-methoxyP), 5-CQA and caffeic acid all significantly inhibited the basal cytoplasmatic PDE activity in lysates of lung tumour xenograft cells (LXFL529L) and human platelets. To a somewhat lesser extent, PDE inhibition was also found in experiments performed with paraxanthine and other pyrazines (2-E-3,5-DMP, TMP and 2-E-5-MP). Thus the degree of roasting has a considerable impact on constituents of influence for PDE activity. Caffeine, coffee polyphenols and some pyrazines and further, as yet unknown roasting products appear to represent the main modulating constituents.
In two coffee intervention studies, a short-term (8 weeks) and a long-term study (24 weeks), comprising 8 and 84 healthy volunteers respectively, we examined extracellular key elements of the adenosine pathway including plasma adenosine levels and adenosine deaminase activity. Additionally, we studied the intracellular cAMP concentration and the PDE activity in platelets as surrogate biomarkers of adipocytes.
Results of in vitro experiments had suggested that the concentrations of caffeine and coffee extracts required to obtain a half maximal inhibition were in the upper range of physiological conditions. Yet, it was demonstrated for the first time in vivo that moderate consumption of coffee can modulate the activity of platelet phosphodiesterases in humans in long and short term. In both studies, the first exposure to coffee showed a strong inhibition (p<0.001) of the PDE activity in the platelet lysates of the participants while the second coffee phase showed no or a slight effect when compared with the first coffee intervention.
In both studies a significant increase (p<0.001) in intraplatelet cAMP concentrations during the wash-out phase (after the first coffee phase) was observed. This response could be due to inhibition of the PDE activity in the previously phase extending in to the wash out phase. However, the behavior of cAMP in the following study phases cannot be easily explained. It may be hypothesized that this effect is attributable to adaptive effects to allow PDE inhibition. One possibility is the modulation of the expression of membrane-bound adenosine receptors in platelet precursors, which still have a nucleus. This may potentially influence adenylate cyclase activity in mature platelets. For the observed effects, in addition to caffeine other ingredients of coffee appear to play a role. The findings suggest that monitoring of cAMP homeostasis in platelets is not a useful surrogate biomarker for effects in other tissues.
Neither the activity of adenosine deaminase nor the adenosine concentrations in plasma were markedly modulated by the coffee consumption in both trials. This may reflect the fact that adenosine is subject to quick and effective enzymatic turnover by phosphorylation (adenosine kinase) or deamination (adenosine deaminase) allowing keep its concentration within a well balanced homeostasis. However, it is also well known, that considerable variability exists in the responses to coffee drinking. In part, such variability is due to caffeine tolerance, but there is also evidence for a genetic background.
Altogether the data reported here provide further evidence for the perception that coffee consumption is associated with beneficial health effects demonstrated for the cAMP enhancement in platelets, known to counteract platelet aggregation. The effects observed for the influence of cellular heme oxygenase (HO) are in line with the well documented antioxidative activity of coffee and its constituents.
In the 1st project, successful development of 2nd generation of a palladium catalyst for the selective hydrogenation of carboxylic acids to aldehydes was accomplished. This project was done in cooperation with Dipl. Chem. Thomas Fett from Boeringer Ingelheim, Austria. The new catalyst is highly effective for the conversion of diversely functionalized aromatic, heteroaromatic and aliphatic carboxylic acids to the corresponding aldehydes in the presence of pivalic anhydride at 5 bar hydrogen pressure, which was otherwise achieved either at 30 bar of hydrogen pressure or by using waste intensive hypophosphite bases as reducing agent. Our method has increased the synthetic importance of this valuable transformation. Selective hydrogenation of carboxylic acids to the corresponding aldehydes is now possible with industrial hydrogenation equipment as well as laboratory scale glass autoclaves. It might also convince the synthetic organic chemists to use this transformation for routine aldehyde synthesis in the laboratories.
In the 2nd project, a microwave assisted Cu-catalyzed protodecarboxylation of arenecarboxylic acids to arenes is achieved. This work was done in collaboration with Dipl. Chem. Filipe Manjolinho under the supervision of Dr. Nuria Rodríguez. In the presence of 1-5 mol% of inexpensive CuI/1,10-phenanthroline catalyst generated in situ under microwave radiations, diversely functionalized arenes and heteroarene carboxylic acids have been decarboxylated to the corresponding arenes in good yields at 190 °C in 5-15 min. The loss of volatile arenes with the release of CO2 is controled by the use of sealed high pressure resistant microwave vessels. These reactions are highly beneficial for parallel synthesis in drug discovery due to their short reaction time. Microwave technology will also help in the future to develop more effective catalysts for protodecarboxylation rections.
Based on the microwave assisted protodecarboxylation strategy, decarboxylative coupling of arenecarboxylic acids with aryl triflates and tosylates was also conducted under microwave radiation which provided higher yields of the corresponding biphenyls from deactivated substrates in short reaction time compared to the conventional heating.
In the 3rd project, crystalline, potassium (trifluoromethyl)trimethoxyborate was successfully applied for the synthesis of benzotrifluorides under the oxidative conditions. This project was done in cooperation with Dipl. Chem. Annette Buba. In the presence of Cu(OAc)2 and molecular oxygen, arylboronates were coupled with K+[CF3B(OMe)3] in DMSO at 60 °C. A variety of benzotriflurides was synthesized in good yields under the optimized reaction conditions. This protocol for the oxidative trifluoromethylation of arylboronates is the base for the development of decarboxylative trifluoromethylation reaction of arenecarboxylic acids.
The 4th project discloses the simple and straightforward synthesis of trifluoromethylated alcohols by nucleophilic addition of potassium (trifluoromethyl)trimethoxyborate to carbonyl compounds. This project was done in cooperation with Dr. Thomas Knauber and Dipl. Chem. Annette Buba. In the presence of K+[CF3B(OMe)3] in THF at 60 °C, diversely functionalized aldehydes and ketones were successfully converted into the corresponding trifluoromethylated alcohols.
The 3rd and 4th projects demonstrate the successful establishment of crystalline and shelf stable potassium (trifluoromethyl)trimethoxyborate as highly versatile CF3-source in nucleophilic trifluoromethylation reactions. These new protocols are characterized by their user-friendliness and broad applicability under mild reaction conditions, thus they are beneficial for late stage introduction of CF3-group into organic molecules.
The present PhD thesis is mainly focused on synthesis, characterization and catalytic application of functionalized triphenylphosphine (TPP) ligands and their complexes. We developed a simple and effective strategy to immobilize TPP: A methylester group attached to one of the phenyl rings of TPP allowes the derivatization of the ligand with 3-trimethoxysilylpropylamine, a typical silane coupling agent used for the covalent immobilization of organic compounds on silica surfaces. The resulting functionalized TPP was further coordinated to Pd, Rh and Ru precursors to achieve homogeneous complexes which can be tethered on silica by the post synthetic grafting method and co-condensation method. The obtained heterogeneous catalysts exhibited excellent activity, selectivity and reusability in Suzuki, hydrogenation and transfer hydrogenation reactions. In order to investigate the stability of the catalysts, different types of characterizations such as TEM, solid state NMR of the used catalysts as well as AAS of filtrate and leaching tests were carried out. The results prove the practicability and efficiency of our method. This strategy was further modified to generate an anionic side chain linked to the TPP core by simply replacing the trimethoxysilylpropylamine group by sodium(3-amino- 1-propanesulfonate), which allowes the immobilization on imidazolium modified SBA-15 through electrostatic interaction. The obtained material was further reacted with PdCl2(CNPh)2 and the resulting hybrid material was used for the hydrogenation of olefins allowing mild reaction conditions. The catalyst shows excellent activity, selectivity and stability and it can furthermore be reused for at least ten times without any loss of activity. TEM images of the used catalyst clearly show the absence of palladium nanoparticles, proving the high stability of the palladium compound. By AAS no palladium could be detected in the products and further leaching tests very- fied the reaction to be truly heterogeneous. This concept of non-covalent immobili- zation guarantees a tight bonding of the catalytically active species to the surface in combination with a high mobility, which should be favorable for other catalyses.
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic and persistent organic pollutant, which is ubiquitously found in the environment. The prototype dioxin compound was classified as a human carcinogen by the International Agency for Research on Cancer. TCDD acts as a potent liver tumor promoter in rats, which is one of the major concerns related to TCDD exposure. There is extensive evidence, that TCDD exerts anti-estrogenic effects via arylhydrocarbon receptor (AhR)-mediated induction of cytochromes P450 and interferes with the estrogen receptor alpha (ERalpha)-mediated signaling pathway. The present work was conducted to shed light on the hypothesis that enhanced activation of estradiol metabolism by TCDD-induced enzymes, mainly CYP1A1 and CYP1B1, leads to oxidative DNA damage in liver cells. Furthermore, the possible modulation by 17beta-estradiol (E2) was investigated. The effects were examined using four different AhR-responsive species- and sex-specific liver cell models, rat H4II2 and human HepG2 hepatoma cell lines as well as rat primary hepatocytes from male and female Wistar rats. The effective induction of CYP1A1 and CYP1B1 by TCDD was demonstrated in all liver cell models. Basal and TCDD-induced expression of CYP1B1, which is a key enzyme in stimulating E2 metabolism via the more reactive formation of the genotoxic 4-hydroxyestradiol, was most pronounced in rat primary hepatocytes. CYP-dependent induction of reactive oxygen species (ROS) was only observed in rodent cells. E2 induced ROS only in primary rat hepatocytes, which was associated with a weak CYP1B1 mRNA induction. Thus, E2 itself was suggested to induce its own metabolism in primary rat hepatocytes, resulting in the redox cycling of catechol estradiol metabolites leading to ROS formation. In this study the role of TCDD and E2 on oxidative DNA damage was investigated for the first time in vitro in the comet assay using liver cells. Both TCDD and E2 were shown to induce oxidative DNA base modifications only in rat hepatocytes. Additionally, direct oxidative DNA-damaging effects of the two main E2 metabolites, 4-hydroxyestradiol and 2-hydroxyestradiol, were only observed in rat hepatocytes and revealed that E2 damaged the DNA to the same extent. However, the induction of oxidative DNA damage by E2 could not completely be explained by the metabolic conversion of E2 via CYP1A1 and CYP1B1 and has to be further investigated. The expression of low levels of endogenous ERalpha mRNA in primary rat hepatocytes and the lack of ERalpha in hepatoma cell lines were identified as crucial. Therefore, the effects of interference of ERalpha with AhR were examined in HepG2 cells, which were transiently transfected with ERalpha. The over-expression of ERalpha led to enhanced AhR-mediated transcriptional activity by E2, suggesting a possible regulation of E2 levels. In turn, TCDD reduced E2-mediated ERalpha signaling, confirming the anti-estrogenic action of TCDD. Such a modulation of the combined effects of TCDD with E2 was not observed in any of the other experiments. Thus, the role of low endogenous ERalpha levels has to be further investigated in transfection experiments using rat primary hepatocytes. Overall, rat primary hepatocyte culture turned out to be the more adaptive cell model to investigate metabolism in the liver, reflecting a more realistic situation of the liver tissue. Nevertheless, during this work a crosstalk between ERalpha and AhR was shown for the first time using human hepatoma cell line HepG2 by transiently transfecting ERalpha.
A number of natural products are known that contain an enamide as a key structural feature. This functionality is a very important subunit in various biologically active products and pharmaceutical drug lead compounds. In addition, enamides serve as highly versatile synthetic intermediates, particularly in the pericyclic reaction, formation of heterocycles, cross-coupling and in asymmetric synthesis. As a result, several protocols have been devised for the preparation of enamides. Traditional syntheses include condensation of aldehydes and ketones with amides or from hydroxylamines and acetic anhydride, require harsh conditions and yield mixtures of E/Z products. Several metal catalyzed approaches have been also investigated, such as isomerization of N-allylamides and catalytic cross-coupling of amides with vinyl halides or pseudohalides. These protocols proceed under milder conditions but suffer from the limited availability of these starting materials. The research described in this dissertation focuses on efficient and atom-economic preparation of enamides and thioenamides, using readily available starting materials. We developed catalyst systems generated in situ from bis(2-methallyl)-cycloocta-1,5-diene-ruthenium(II), phosphines and Lewis acid or base, efficiently catalyze the addition of primary amides and thioamides to terminal alkynes with exclusive formation of the anti-Markovnikov products in high yield and stereoselectivity under mild reaction conditions. The generality of the newly developed methodologies is demonstrated by common functional group tolerance. Furthermore, Markovnikov products were formed via phosphine-catalyzed addition of cyclic amides to phenylacetylene derivatives. The hydroamidation protocol of primary amides was successfully used in the synthesis of naturally occurring compounds, such as alatamide, lansiumamide A, botryllamides C and E, and the key intermediate in the synthesis of aristolactam. In order to investigate the reaction mechanism, the addition of various amides and carboxylic acids to terminal alkynes was performed using deuterium labeled starting materials and followed by in situ NMR and GC-MS studies.
The main focus of this dissertation is the synthesis and characterization of more recent zeolites with different pore architectures. The unique shape-selective properties of the zeolites are important in various chemical processes and the new zeolites containing novel internal pore architectures are of high interest, since they could lead to further improvement of existing processes or open the way to new applications. This dissertation is organized in the following way: The first part is focused on the synthesis of selected recent zeolites with different pore architectures and their modification to the acidic and bifunctional forms. The second part comprises the characterization of the physicochemical properties of the prepared zeolites by selected physicochemical methods, viz. powder X-ray diffractometry (XRD), N2 adsorption, thermogravimetric analysis (TGA/DTA/MS), ultraviolet-visible (UV-Vis) spectroscopy, atomic absorption spectroscopy (AAS), infrared (IR) spectroscopy, scanning electron microscopy (SEM), 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, temperature-programmed reduction (TPR), temperature-programmed desorption of pyridine (pyridine TPD) and adsorption experiments with hydrocarbon adsorptives. The third part of this work is devoted to the application of test reactions, i.e., the acid catalyzed disproportionation of ethylbenzene and the bifunctional hydroconversion of n-decane, to characterize the pore size and architecture of the prepared zeolites. They are known to be valuable tools for exploring the pore structure of zeolites. Finally, an additional test, viz. the competitive hydrogenation of 1-hexene and 2,4,4-trimethyl-1-pentene, has been applied to probe the location of noble metals in medium pore zeolite. The synthesis of the following zeolite molecular sieves was successfully performed in the frame of this thesis (they are ranked according to the largest window size in the respective structure): • 14-MR pores: UTD-1, CIT-5, SSZ-53 and IM-12 • 12-MR pores: ITQ-21 and MCM-68 • 10-MR pores: SSZ-35 and MCM-71 All of them were obtained as pure phase (except zeolite MCM-71 with a minor impurity phase that is hardly to avoid and also present in samples shown in the patent literature). The synthesis conditions are very critical with respect to the formation of the zeolite with a given structure. In this work, the recommended synthesis recipes are included. Among the 14-MR zeolites, the aluminosilicates UTD-1 (nSi/nAl = 28), CIT-5 (nSi/nAl = 116) and SSZ-53 (nSi/nAl = 55) with unidimensional extra-large pore opening formed from 14-MR rings exhibit promising catalytic properties with high thermal stability and they possess strong Brønsted-acid sites. By contrast, the germanosilicate IM-12 with a structure containing 14-MR channels intersecting with 12-MR channels is unstable toward moisture. It was found that UTD-1 and SSZ-53 zeolites are highly active catalysts for the acid catalyzed disproportionation of ethylbenzene and n-decane hydroconversion due to their high Brønsted acidity. To explore their pore structures, the applied two test reactions suggest that UTD-1, CIT-5 and SSZ-53 zeolites contain a very open pore system (12-MR or larger pore systems) because the product distributions are not hampered by too small pores. ITQ-21, a germanoaluminosilicate zeolite with a three-dimensional pore system and large spherical cages accessible through six 12-MR windows, can be synthesized with nSi/nAl ratios between 27 and >200. It possesses a large amount of Brønsted-acid sites. The aluminosilicate zeolite MCM-68 (nSi/nAl = 9) is an extremely active catalyst in the disproportionation of ethylbenzene and in the n-decane hydroconversion. This is due to the presence of a high density of strong Brønsted-acid sites in its structure. The disproportionation of ethylbenzene suggests that MCM-68 is a large pore (i.e., at least 12-MR) zeolite, in agreement with its crystallographic structure. In the hydroconversion of n-decane, the presence of tribranched and ethylbranched isomers and a high isopentane yield of 58 % in the hydrocracked products suggest the presence of large (12-MR) pores in its structure. By contrast, a relatively high value for CI* (modified constraint index) of 2.9 suggests the presence of medium (10-MR) pores in its structure. As a whole, the results are in-line with the crystallographic structure of MCM-68. SSZ-35, a 10-MR zeolite, can be synthesized in a broad range of nSi/nAl ratios between 11 and >500. This zeolite is interesting in terms of shape selectivity resulting from its unusual pore system having unidimensional channels alternating between 10-MR windows and large 18-MR cages. This thermally very stable zeolite contains both, strong Brønsted- and strong Lewis-acid sites. The disproportionation of ethylbenzene classifies SSZ-35 as a large pore zeolite. In the hydroconversion of n-decane, the suppression of bulky ethyloctanes and propylheptane clearly suggests the presence of 10-MR sections in the pore system. By contrast, the low CI* values of 1.2-2.3 and the high isopentane yields of 56-60 % in the hydrocracked products suggest that SSZ-35 also possesses larger intracystalline voids, i.e., the 18-MR cages. The results from the catalytic characterization are in good agreement with the crystallographic structure of zeolite SSZ-35. It was also found that the nSi/nAl ratio influences the crystallite size and therefore the external surface area. As a consequence, product selectivities are also influenced: The lowest nSi/nAl ratio or the smallest crystallite size sample produces larger amounts of the relatively bulky products. The formation of these products probably results from the higher conversion or they are preferentially formed on the external surface area of the catalyst. Zeolite MCM-71 (nSi/nAl = 8) possesses an extremely thermally stable structure and contains a high concentration of Brønsted-acid sites. Its structure allows for the separation of n-alkanes from branched alkanes by selective adsorption. MCM-71 exhibits unique shape-selective properties towards the product distribution in ethylbenzene disproportionation, which is different to those obtained in the medium pore SSZ-35 zeolite. All reaction parameters are fulfilled to classify MCM-71 as medium pore zeolite and this is in good agreement with its reported structure consisting of two-dimensional network of elliptical 10-MR channels and an orthogonal sinusoidal 8-MR channels. The competitive hydrogenation of 1-hexene and 2,4,4-trimethyl-1-pentene was exploited to probe that the major part of the noble metal is located inside the intracrystalline void volume of the medium pore zeolite SSZ-35.
Photochemical reactions are of great interest due to their importance in chemical and biological processes. Highly sensitive IR/UV double and triple resonance spectroscopy in molecular beam experiments in combination with ab initio and DFT calculations yields information on reaction coordinates and Intersystem Crossing (ISC) processes subsequent to photoexcitation. In general, molecular beam experiments enable the investigation of isolated, cold molecules without any influence of the environment. Furthermore, small aggregates can be analyzed in a supersonic jet by gradually adding solvent molecules like water. Conclusions concerning the interactions in solution can be derived by investigating and fully understanding small systems with a defined amount of solvent molecules. In this work the first applications of combined IR/UV spectroscopy on reactive isolated molecules and triplet states in molecular beams without using any messenger molecules are presented. Special focus was on excited state proton transfer reactions, which can also be described as keto enol tautomerisms. Various molecules such as 3-hydroxyflavone, 2-(2-naphthyl)-3-hydroxychromone and 2,5-dihydroxybenzoic acid have been investigated with regard to this question. In the case of 3-hydroxyflavone and 2-(2-naphthyl)-3-hydroxychromone, the IR spectra have been recorded subsequent to an excited state proton transfer. Furthermore the dihydrate of 3-hydroxyflavone has been analyzed concerning a possible proton transfer in the excited state: The proton transfer reaction along the water molecules (proton wire) has to be induced by raising the excitation energy. However, photoinduced reactions involve not only singlet but also triplet states. As an archetype molecule xanthone has been analysed. After excitation to the S2 state, ISC occurs into the triplet manifold leading to a population of the T1 state. The IR spectrum of the T1 state has been recorded for the first time using the UV/IR/UV technique without using any messenger molecules. Altogether it is shown that IR/UV double and triple resonance techniques are suitable tools to analyze reaction coordinates of photochemical processes.
The enamide moiety is an important substructure often encountered in biologically active compounds and synthetic drugs. Furthermore, enamides and their derivatives are versatile synthetic intermediates for polymerization, [4+2] cycloaddition, crosscoupling, Heck-olefinination, Halogenation, enantioselective addition or asymmetric hydrogenation. Traditional syntheses of this important substrate class involve rather harsh reaction conditions such as high temperatures and/or the use of strong bases. In continuation of our work on the addition of secondary amides to alkynes, we have developed a broadly applicable protocol for the catalytic addition of N-nucleophiles such as primary amides, imides and thioamides to terminal alkynes. The choice of ligands and additives determines the regiochemical outcome so that with two complementary catalyst systems, both the E-anti-Markovnikov products and the Z-anti-Markovnikov products can be synthesized highly regio- and stereoselectively.