Refine
Has Fulltext
- no (297) (remove)
Year of publication
- 2008 (297) (remove)
Document Type
- Article (198)
- Doctoral Thesis (67)
- Monograph/Edited Volume (28)
- Review (3)
- Other (1)
Language
- English (297) (remove)
Is part of the Bibliography
- yes (297)
Institute
- Institut für Chemie (65)
- Institut für Biochemie und Biologie (61)
- Department Psychologie (28)
- Institut für Anglistik und Amerikanistik (24)
- Wirtschaftswissenschaften (17)
- Institut für Informatik und Computational Science (13)
- Institut für Umweltwissenschaften und Geographie (12)
- Department Linguistik (11)
- Institut für Physik und Astronomie (9)
- Institut für Mathematik (8)
Spatio-temporal patterns of throughfall and solute deposition in an open tropical rain forest
(2008)
A series of 9,10-diarylanthracenes with various substituents at the ortho positions have been synthesised by palladium-catalysed cross-coupling reactions. Such compounds exhibit interesting physical properties and can be applied as molecular switches. Despite the high steric demand of the substituents, products were formed in moderate-to-good yields. In some cases, microwave conditions further improved yields. Bis-coupling afforded two isomers (syn and anti) that do not interconvert at room temperature. These products were easily separated and their relative stereochemistries were unequivocally assigned by NMR spectroscopy and X-ray analysis. The syn and anti isomers exhibit different physical properties (e.g., melting points and solubilities) and interconversion by rotation around the aryl-aryl axis commences at <100 °C for fluoro-substituted diarylanthracenes and at >300 °C for alkyl- or alkoxy-substituted diarylanthracenes. The reactions with singlet oxygen were studied separately and revealed different reactivities and reaction pathways. The yields and reactivities depend on the size and electronic nature of the substituents. The anti isomers form the same 9,10-endoperoxides as the syn species, occasionally accompanied by unexpected 1,4-endoperoxides as byproducts. Thermolysis of the endoperoxides exclusively yielded the syn isomers. The interesting rotation around the aryl-aryl axis allows the application of 9,10-diarylanthracenes as molecular switches, which are triggered by light and air under mild conditions. Finally, the oxygenation and thermolysis sequence provides a simple, synthetic access to a single stereoisomer (syn) from an unselective coupling step.
This study presents an application of an innovative sampling strategy to assess soil moisture dynamics in a headwater of the Weißeritz in the German eastern Ore Mountains. A grassland site and a forested site were instrumented with two Spatial TDR clusters (STDR) that consist of 39 and 32 coated TDR probes of 60 cm length. Distributed time series of vertically averaged soil moisture data from both sites/ensembles were analyzed by statistical and geostatistical methods. Spatial variability and the spatial mean at the forested site were larger than at the grassland site. Furthermore, clustering of TDR probes in combination with long-term monitoring allowed identification of average spatial covariance structures at the small field scale for different wetness states. The correlation length of soil water content as well as the sill to nugget ratio at the grassland site increased with increasing average wetness and but, in contrast, were constant at the forested site. As soil properties at both the forested and grassland sites are extremely variable, this suggests that the correlation structure at the forested site is dominated by the pattern of throughfall and interception. We also found a strong correlation between average soil moisture dynamics and runoff coefficients of rainfall-runoff events observed at gauge Rehefeld, which explains almost as much variability in the runoff coefficients as pre-event discharge. By combining these results with a recession analysis we derived a first conceptual model of the dominant runoff mechanisms operating in this catchment. Finally, long term simulations with a physically based hydrological model were in good/acceptable accordance with the time series of spatial average soil water content observed at the forested site and the grassland site, respectively. Both simulations used a homogeneous soil setup that closely reproduces observed average soil conditions observed at the field sites. This corroborates the proposed sampling strategy of clustering TDR probes in typical functional units is a promising technique to explore the soil moisture control on runoff generation. Long term monitoring of such sites could maybe yield valuable information for flood warning. The sampling strategy helps furthermore to unravel different types of soil moisture variability.
Tuning of the excited-state properties and photovoltaic performance in PPV-based polymer blends
(2008)
Aliens, intregration
(2008)
Xenophobia
(2008)
Linking elements in German are generally assumed to have developed either from suffixes indicating the genitive singular or from plural markers. In this paper it is argued that only the linking element -(e)s- evolved from an inflectional suffix, that of the genitive case, but not the syllabic linking elements -e-, -er- and -(e)n- homophonous with plural markers. For these linking elements the explanation is doubtful for a number of reasons. The present paper proposes an alternative explanation for the development of such interfixes, according to which both linking elements and plural markers have been grammaticalized from the same old Indo-European stem suffixes which indicated the declension class of the noun.. Their homophony is due to the fact that they both evolved from the same source. After the decline of the original endings, the indicators of moribund inflectional classes became afunctional 'junc' and were then reanalysed either as plural markers or as linking elements. This development of linking elements can thus be shown as a case of exaptation or regrammaticalization.
Background: There is an increased need to replace materials derived from fossil sources by renewables. Sugar- cane derived carbohydrates are very abundant in Brazil and are the cheapest sugars available in the market, with more than 400 million tons of sugarcane processed in the year 2007. The objective of this work was to study the prepn. of sugar acrylates from free sugars and free acrylic acid, thus avoiding the previous prepn. of protected sugar derivs., such as glycosides, or activated acrylates, such as vinyl acrylate. Results: Lipase catalyzed esterification of three mono- and two disaccharides with acrylic acid, in the presence or absence of mol. sieves was investigated. The reactions were monitored by high-performance liq. chromatog. (HPLC) and the products were analyzed by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. The main products are mono- and diacrylates, while higher esters are formed as minor products. The highest conversion to sugar acrylates was obsd. for the D-glucose and D- fructose, followed by D-xylose and D-maltose. Mol. sieves had no pronounced effect on the conversion. Conclusions: A feasible method is described to produce and to characterize sugar acrylates, including those contg. more than two acrylate groups. The process for prodn. of these higher esters could potentially be optimized further to produce mols. for crosslinking in acrylate polymn. and other applications. The direct enzymic esterification of free carbohydrates with acrylic acid is unprecedented. [on SciFinder (R)].
The late Cenozoic climate of East Africa is punctuated by episodes of short, alternating periods of extreme wetness and aridity, superimposed on a regime of subdued moisture availability exhibiting a long-term drying trend. These periods of extreme climate variability appear to correlate with maxima in the 400-thousand-year (kyr) component of the Earth's eccentricity cycle. Prior to 2.7 Ma the wet phases appear every 400 kyrs, whereas after 2.7 Ma, the wet phases appear every 800 kyrs, with periods of precessional-forced extreme climate variability at 2.7-2.5 Ma, 1.9-1.7 Ma, and 1.1-0.9 Ma before present. The last three major lake phases occur at the times of major global climatic transitions, such as the onset of Northern Hemisphere Glaciation (2.7-2.5 Ma), intensification of the Walker Circulation (1.9-1.7 Ma), and the Mid-Pleistocene Revolution (1.0-0.7 Ma). High-latitude forcing is required to compress the Intertropical Convergence Zone so that East Africa becomes locally sensitive to precessional forcing, resulting in rapid shifts from wet to dry conditions. These periods of extreme climate variability may have provided a catalyst for evolutionary change and driven key speciation and dispersal events amongst mammals and hominins in East Africa. (C) 2007 Elsevier Ltd. All rights reserved.
A series of terbium- and europium-exchanged microporous-mesoporous zeolite Socony Mobil Five (MFI)-type materials such as Zeotile-1 and Zeogrid with varying Si/Al ratios was investigated using FTIR, PXRD, adsorption- desorption isotherms of N-2 at 77 K and time-resolved luminescence spectroscopy. Silylation of the lanthanides-exchanged Zeotile-1 and Zeogrid with hexadecyl trimethoxysilanes via post-synthesis grafting was also studied. The results showed that the lanthanide's photoluminescence spectra and decays were modified due to silylation. The different silylation effects in Zeotile-1 and Zeogrid were correlated with the textural properties of the investigated materials. (C) 2007 Elsevier B.V. All rights reserved.
In this paper, we present an approach to recover the dynamics from recurrences of a system and then generate (multivariate) twin surrogate (TS) trajectories. In contrast to other approaches, such as the linear-like surrogates, this technique produces surrogates which correspond to an independent copy of the underlying system, i.e. they induce a trajectory of the underlying system visiting the attractor in a different way. We show that these surrogates are well suited to test for complex synchronization, which makes it possible to systematically assess the reliability of synchronization analyses. We then apply the TS to study binocular fixational movements and find strong indications that the fixational movements of the left and right eye are phase synchronized. This result indicates that there might be only one centre in the brain that produces the fixational movements in both eyes or a close link between the two centres.
Empirical studies of text coherence often use tree-like structures in the spirit of Rhetorical Structure Theory (RST) as representational device. This paper identifies several sources of ambiguity in RST-inspired trees and argues that such structures are therefore not as explanatory as a text representation should be. As an alternative, an approach toward multi-level annotation (MLA) of texts is proposed, which separates the information into distinct levels of representation, in particular: referential structure, thematic structure, conjunctive relations, and intentional structure. Levels are conceptually built upon each other, and human annotators can produce them using a dedicated software environment. We argue that the resulting multi-level corpora are descriptively more adequate, and as a resource are more useful than RST-style treebanks.
The electron ionization (EI) mass spectra of a variety of stereoisomeric tricyclic 1,3,2-oxazaphosphino[4,3- a]isoquinolines (1-4), 1,2,3-oxathiazino[4,3-a]isoquinoline-4-oxides (5-7) and the -4,4-dioxides (8-10) of oxazaphospholo- and oxathiazolo[4,3-a]- (11, 12, 15 and 16) and -[3,4-b]isoquinolines (13, 14 and 17) were recorded. Ring size and fusion, the different heteroatoms (P and S) and substituents on the ring systems strongly influence the mass spectra. In addition, mass spectra of the stereoisomers of compounds 1, 2 and 13, 14 revealed stereochemically relevant differences which are not observed for the other pairs of isomers. Copyright © 2008 John Wiley & Sons, Ltd.
The complex formation of the ligands 1,12-diazaperylene (dap), 1,1-bisisoquinoline (bis), 2,2-bipyridine (bpy) and 1,10-phenanthroline (phen) with transition metal ions (M = Fe, Co, Ni, Cu, Zn, Ru, Os, Re, Pd, Pt, Ag and Cd) in the gas phase has been studied by electrospray ionization mass spectrometry. With the exception of Ru, Os, Fe, Ni and Cu, singly charged complexes [MLn]+ (n = 1,2) were observed. The complexes of dap and bis with Ru, Os, Fe and Ni ions, and the mixed ligand complexes with bpy and phen, are preferably of the doubly charged type [ML3]2+. In addition, collision- induced dissociation (CID) measurements were employed to evaluate the relative stabilities of these complexes. The CID experiments of mixed-ligand complexes which contain both dap and phen or dap and bpy exhibit preferential elimination of bpy, indicating that bpy is a weaker ligand than phen and dap.
From a series of pentanuclear, heterobimetallic complexes of the general composition [{Ln(H2O)n}2{Ni(dto)2}3] · xH2O, four complexes (Ln = Gd(III) with n = 4; Ln = Dy(III), Ho(III), or Er(III), with n = 5; x = 9-12; dto = 1,2- dithiooxalate) were studied due to their large magnetic moments (up to 14.65 B.M.). The magnetic properties of these complete series were measured at room temperature and the temperature dependent magnetic properties of the complexes Gd2Ni3, Dy2Ni3, Ho2Ni3, and Er2Ni3 were studied at room temperature down to 1.8 K. Whereas the intramolecular metal- metal distances were rather long (Ni1-Ni2: 11.0-11.5 Å; Ln-Ni: 6.0-6.3 Å), relatively short intermolecular metal-metal distances (Ni1-Ni2;: 3.5 Å; Er-Er;: 6.0 Å) were found in the crystal lattice, giving rise to weak intermolecular metal-metal interactions. These weak spin interactions were also supported by the EPR spectrum of a powdered sample of the diamagnetically undiluted Gd2Ni3 complex.
The stereodynamic behaviour of 1-(trifluoromethylsulfonyl)piperidine 1, 4-(trifluoromethylsulfonyl)morpholine 2, 1,4-bis(trifluoromethylsulfonyl)piperazine 3 and 4-(trifluoromethylsulfonyl)thiomorpholine 1,1-dioxide 4 was studied by low-temperature 1H, 13C and 19F NMR spectroscopies. In acetone solution, compounds 1, 2 and 4 were found to exist as mixtures of two conformers in the ratio of 4:1, 4:1 and 8:1, respectively, differing by orientation of the CF3 group with respect to the ring. Compound 3 exists as a mixture of three conformers in the ratio of 3:28:69 also differing by the orientation of the two CF3 groups. Unlike the previously studied N-trifyl substituted 1,3,5-triheterocyclohexanes, the preferred conformers of compound 1 and of 1,4-diheterocyclohexanes 2-4 are those with the CF3 group directed outward from the ring, which is caused by intramolecular interactions of the oxygen atoms of the CF3SO2N groups with the equatorial hydrogens in the ;-position. B3LYP/6-311+G(d,p) calculations of the energy, geometry and NMR parameters corroborate the experimental data. The calculated Perlin effects for all conformers of compounds 1-4 as well as those measured for the major conformers of compounds 3 and 4 were analyzed by the use of the NBO analysis.
Multinuclear dynamic NMR spectroscopy of 5-trifluoromethylsulfonyl-1,3,5-dioxaazinane (4) revealed the existence of two close in energy chair conformers with differently oriented CF3 groups with respect to the ring. Of the two alternative routes for their interconversion, the ring inversion path with intermediate formation of the corresponding 2,5-twist-conformer is preferred, with the energy barrier of 11.2 kcal/mol in excellent agreement with the experimental value (11.7 kcal/mol). The Perlin effect is studied experimentally and calculated theoretically for all CH2 groups and found to be subject to the nature of the adjacent heteroatoms O and N, respectively.
The crystal and molecular structures of trans-2,4,4-trimethyl-4-silathiane 1-oxide 1 and 4,4-dimethyl-4- silathiane 1,1-dioxide 2 were determined by single crystal X-ray diffraction. Both compounds have the chair conformation with the 2-Me and the S=O group in compound 1 occupying the equatorial positions. The DFT (B3LYP/6-311G(d,p)) and MP2 (MP2/6-311G(d,p)) theoretical calculations nicely reproduce the X-ray experimental geometry. The obtained results are discussed in connection with the electronic and structural properties of the compounds.
Reduction of 4-nitro-1-ethyl-1H-1,2,3-triazole with aluminum in alkaline medium resulted in a syn-isomer of 1,2- bis(1-ethyl-1H-1,2,3-triazol-4-yl)diazene 1-oxide. The latter according to the data of X-ray diffraction analysis existed in the crystal as the most stable s-cis,s-trans-conformer, and in solution, as showed NMR data, as a mixture of s-cis,s-trans- and s-trans,s-trans-conformers. The data of quantum-chemical calculations are in agreement with the results of the structural studies.
Vinylogs of fulvalenes with cyclopropenyl and cyclopentadienyl moieties attached either to different carbon atoms (c-C3H2-CH-CH=C5H4-c, 7) or to the same carbon atom [X=C(c-C3H2)(c-C5H4), 10] [X = CH2; C(CN)2; C(NH2)2; C(OCH2)2; O; c-C3H2; c-C5H4; SiH2; CCl2] of the double bond inserted between the two rings are examined theoretically at the B3LYP/ 6;311G(d,p) level. Both types of compounds are shown to possess aromaticity, which was called "push;pull" and "captodative" aromaticity, respectively. For the captodative mesoionic structures X=C(c-C3H2)(c-C5H4), the presence of both the two aromatic moieties and the C=C double bond is the necessary and sufficient condition for their existence as energetic minima on the potential energy surface. Aromatic stabilization energy (ASE) was assessed by the use of homodesmotic reactions and heats of hydrogenation. Spatial magnetic criteria (through space NMR shieldings, TSNMRS) of the two types of vinylogous fulvalenes 7 and 10 have been calculated by the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept of Paul von Ragué; Schleyer, and visualized as iso-chemical-shielding surfaces (ICSS) of various sizes and directions. TSNMRS values can be successfully employed to visualize and quantify the partial push;pull and captodative aromaticity of both the three- and five-membered ring moieties. In addition, the push;pull effect in compounds 7 and 10 could be quantified by the occupation quotient ;*C=C/;C=C of the double bond inserted between the two rings.
This paper describes the principle of a homogeneous indirect fluorescence quenching immunoassay that uses monoclonal antibodies. It is a carrier-free assay system that is performed completely in solution. The assay system was established for the determination of a low molecular weight substance (hapten), the herbicide diuron, used as a model analyte. A fluorescein-monuron conjugate together with a fluorescence-quenching monoclonal anti-fluorescein antibody and an anti-analyte antibody (here an anti-diuron/monuron monoclonal antibody) were used as central components of the assay. The fluorescein-monuron conjugate can be bound either by the anti-fluorescein monoclonal antibody or by the anti-diuron/ monuron monoclonal antibody. Due to steric hindrance, binding of both antibodies to the conjugate was not possible at the same time. By selecting the antibody concentrations appropriately, a dynamic equilibrium can be established that permits the preferential binding of the anti-diuron/monuron antibody to the conjugate, which allows the fluorescein in the conjugate to fluoresce. This equilibrium can be easily altered by adding free analyte (diuron), which competes with the conjugate to bind to the anti-diuron/monuron antibody. A reduction of anti-diuron/monuron antibody binding to the conjugate results in an increase in the binding of the anti-fluorescein antibody, which leads to a decrease in the fluorescence of the conjugate. The fluorescence is therefore a direct indicator of the state of equilibrium of the system and thus also the presence of free unconjugated analyte. The determination of an analyte based on this test principle does not require any washing steps. After the test components are mixed, the dynamic equilibrium is rapidly reached and the results can be obtained in less than 5 min by measuring the fluorescence of the fluorescein. We used this test principle for the determination of diuron, which was demonstrated for concentrations of approximately 5 nM.
We present an approach to the correlated dynamics of many-electron systems. We show, that the two-electron reduced density matrix (2RDM) can provide a suitable description of the real time evolution of a system. To achieve this, the hierarchy of equations of motion must be truncated in a practical way. Also, the computational effort, given that the 2RDM is represented by products of two-electron determinants, is discussed, and numerical model calculations are presented.
The mutual dependencies of characteristic quantities for an isotope selective photoionization, namely optimization efficiency, target state population, and wave packet dephasing are presented for the NaK dimer. A pre- optimized pulse shape obtained from the maximization of the isotopomer ratio 23Na39K/23Na41K for the first excited electronic state serves as an initial guess for the subsequent optimization. For the ionization it provides almost vanishing population of the heavier ionic isotopomer and an ionic isotopomer ratio which is significant higher than the findings obtained from former investigations. The wave packet motions on the first excited state of the neutral molecule are in phase for both isotopomers. The optimization procedure, i.e. the simultaneous maximization of the 23Na39K+ photoionization yield and the minimization of the 23Na41K+ photoionization yield for the electronic ground state is based on optimal control theory and leads to a rise of ionic ground state population for both isotopomers related to a significant wave packet dephasing. Upon optimization the isotopomer ratio of the yields falls due to incidental resonances of vibronic transitions. The interplay of the observables are discussed and compared with the values obtained from an optimization which was started from a pure Gaussian pulse shape.
The cyclizations of tetrahydroisoquinoline 1,2-amino alcohols with phenylphosphonic dichloride, bis(2- chloroethyl)phosphoramidic dichloride, thionyl chloride and sulfuryl chloride were utilized to synthesize 1,5,6,10b- tetrahydro-1,3,2-oxazaphospholo[4,3-a]isoquinolines (2, 3), 1,5,10,10a-tetrahydro-1,3,2-oxazaphospholo[3,4- b]isoquinolines (8, 9), 1,5,6,10b-tetrahydro-1,2,3-oxathiazolo[4,3-a]isoquinolines (4-6) anda 1,5,10,10a-tetrahydro- 1,2,3-oxathiazolo[3,4-b]isoquinoline (11), which are the first representatives of these ring systems. NMR spectroscopic analysis revealed the existence of conformational equilibria that are fast on the NMR timescale. Theoretical DFT calculations pointed to the participation of generally two preferred conformers in the conformational equilibria; the positions of the equilibria were indicated by the experimental NMR spectroscopic parameters, and they are in good agreement with the theoretically calculated energy differences of the participating conformers. For two compounds, which could be not isolated (10, 12), both the preferred conformers and the stereochemistry could be concluded from the DFT calculation results.
Olfactory performance of patients with anorexia nervosa and healthy subjects in hunger and satiety
(2008)
The aim of this study was to compare the olfactory performance of anorectic patients and healthy controls with regard to the state of satiety. Using the Sniffin" Sticks, sensitivity to a nonfood odor (n-butanol) and to a food- related odor (isoamyl acetate) was assessed in 12 anorectic females and compared with 24 healthy controls. Threshold tests were performed in a hungry as well as in a satiated state, odor discrimination and odor identification only when satiated. Pleasantness of the odors was recorded. In terms of the non-food odor n-butanol, the olfactory sensitivity of anorectic patients and controls did not differ. Patients with anorexia nervosa had a significantly lower detection threshold for the food-related odor, but only in the hungry condition. Anorectic patients showed significant deficits in odor discrimination and identification, and under-evaluated the pleasantness of isoamyl acetate. Our results suggest an impaired projection from secondary to tertiary olfactory structures in anorexia nervosa, based upon the dichotomy of performance between detection threshold and odor discrimination/dentification. The reduced pleasantness of isoamyl acetate indicates a decreased olfactory responsiveness to food stimuli in anorexia nervosa.
We calculate the perihelion precession for nearly circular orbits in a central potential V(r). Differently from other approaches to this problem, we do not assume that the potential is close to the Newtonian one. The main idea in the deduction is to apply the underlying symmetries of the system, and to use the transformation behaviour in a rotating system of reference. This is equivalent to say, that the effective potential can be written in a one-parameter set of possibilities as sum of centrifugal potential and potential of the central force.
KEPI is a protein kinase C-potentiated inhibitory protein for type 1 Ser/Thr protein phosphatases. We found no or reduced expression of KEPI in breast cancer cell lines, breast tumors and metastases in comparison to normal breast cell lines and tissues, respectively. KEPI protein expression and ubiquitous localization was detected with a newly generated antibody. Ectopic KEPI expression in MCF7 breast cancer cells induced differential expression of 95 genes, including the up-regulation of the tumor suppressors EGR1 (early growth response 1) and PTEN (phosphatase and tensin homolog), which is regulated by EGR1. We further show that the up-regulation of EGR1 in MCF7/KEPI cells is mediated by MEK-ERK signaling. The inhibition of this pathway by the MEK inhibitor UO126 led to a strong decrease in EGR1 expression in MCF7/KEPI cells. These results reveal a novel role for KEPI in the regulation of the tumor suppressor gene EGR1 via activation of the MEK-ERK MAPK pathway.
Two sesquiterpenes, corymbolone and mustakone, isolated from the chloroform extract of the rhizomes of Cyperus articulatus, exhibited significant anti-plasmodial properties. Mustakone was approximately ten times more active than corymbolone against the sensitive strains of the Plasmodium falciparum.