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Search Results: 1 - 10 of 615 matches for " Heiko Ihmels "
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Synthesis of cationic dibenzosemibullvalene-based phase-transfer catalysts by di-π-methane rearrangements of pyrrolinium-annelated dibenzobarrelene derivatives
Heiko Ihmels,Jia Luo
Beilstein Journal of Organic Chemistry , 2011, DOI: 10.3762/bjoc.7.17
Abstract: Dibenzobarrelene derivatives, that are annelated with a pyrrolinium unit [N,N-dialkyl-3,4-(9',10'-dihydro-9',10'-anthraceno-3-pyrrolinium) derivatives], undergo a photo-induced di-π-methane rearrangement upon triplet sensitization to give the corresponding cationic dibenzosemibullvalene derivatives [N,N-dialkyl-3,4-{8c,8e-(4b,8b-dihydrodibenzo[a,f]cyclopropa[cd]pentaleno)}pyrrolidinium derivatives]. Whereas the covalent attachment of a benzophenone functionality to the pyrrolinium nitrogen atom did not result in an internal triplet sensitization, the introduction of a benzophenone unit as part of the counter ion enables the di-π-methane rearrangement of the dibenzobarrelene derivative in the solid-state. Preliminary experiments indicate that a cationic pyrrolidinium-annelated dibenzosemibullvalene may act as phase-transfer catalyst in alkylation reactions.
Effects of anion complexation on the photoreactivity of bisureido- and bisthioureido-substituted dibenzobarrelene derivatives
Heiko Ihmels,Jia Luo
Beilstein Journal of Organic Chemistry , 2011, DOI: 10.3762/bjoc.7.37
Abstract: Bisureido- and a bisthioureido-substituted dibenzobarrelene derivative were synthesized and the photoreactivity of two representative examples were studied. Direct irradiation of the ureido-substituted derivative induces a di-π-methane rearrangement to the corresponding dibenzosemibullvalene derivative, whereas the thioureido-substituted derivative is almost photoinert. Complexes of the latter derivative with chloride, carboxylates, or sulfonate anions, however, are efficiently transformed to the dibenzosemibullvalene product upon irradiation, presumably by suppressing the self-quenching of the thiourea units in the complex. The association of the ureido-substituted dibenzobarrelene derivative with (S)-mandelate and irradiation of this complex led to the formation of the dibenzosemibullvalene with moderate stereoselectivity (68:32 er). In contrast, the thioureido derivative showed no such effect upon complexation of chiral anions.
Photochemistry of Styrene Oxide: A Triplet Pathway in the Singlet Excitation of a Monoaryl Oxirane  [PDF]
Benny E. Aney, Heiko Ihmels, Rick C. White
International Journal of Organic Chemistry (IJOC) , 2017, DOI: 10.4236/ijoc.2017.73020
Abstract: Direct photolysis and quenching experiments with styrene oxide support the existence of an efficient triplet photochemical pathway to benzyl radical formation. Similar photolytic behavior for styrene glycol carbonate strongly supports the 1,3-diradical, resulting from the scission of the benzylic C-O bond, as the geometric source of the triplet pathway. Primary photoproducts were determined by both NMR and HPLC analysis and we observed that toluene and bibenzyl were both primary photoproducts, not secondary photoproducts.
Photoreactions of cyclic sulfite esters: Evidence for diradical intermediates
Rick C. White,Benny E. Arney Jr.,Heiko Ihmels
Beilstein Journal of Organic Chemistry , 2012, DOI: 10.3762/bjoc.8.134
Abstract: The photochemistry of a phenyl and 1,2-diphenyl substituted sulfite ester is reported. The performance of photoreactions under relatively mild reaction conditions enables the detection of products that have not been observed in previous studies. It is concluded that, complementary to the initially proposed carbene intermediates, diradicals may also be considered.
Ethyl 1,6-dimethyl-2-oxo-4-(quinolin-4-yl)-1,2,3,4-tetrahydropyrimidine-5-carboxylate
Roman I. Zubatyuk,Oleg V. Shishkin,Heiko Ihmels,Iryna A. Lebedyeva
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810023482
Abstract: In the title compound, C18H19N3O3, the tetrahydropyrimidone ring adopts a distorted boat conformation. In the crystal structure, intermolecular N—H...O hydrogen bonds link the molecules into centrosymmetric dimers, which are further linked via intermolecular C—H...π interactions. In addition, an intramolecular C—H...O hydrogen bond occurs.
Where Do We Stand on Locating the Self?  [PDF]
Jakub Limanowski, Heiko Hecht
Psychology (PSYCH) , 2011, DOI: 10.4236/psych.2011.24049
Abstract: The subjective location of the Self in the body is a traditionally problematic question, and it can only be addressed from the first-person perspective. However, this does not preclude an empirical approach to the question. In the present study, we examined whether a large sample of participants would be willing and able to determine the perceived location of their Self. The main goal was to assess current beliefs about the nature of the Self and its assumed relation to specific bodily organs. Eighty-seven participants indicated the center of their Self by placing crosshairs on human silhouettes and abstract, non-human silhouettes with varying anatomy. Results show a clearly dominant role of the brain and the heart for Self-location in humans, but only of the brain for Self-location in abstract creatures. Moreover, results reveal that people believe there is one single point inside the human body where their Self is located.
A High-Performance Cellular Automaton Model of Tumor Growth with Dynamically Growing Domains  [PDF]
Jan Poleszczuk, Heiko Enderling
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.51017
Abstract:

Tumor growth from a single transformed cancer cell up to a clinically apparent mass spans many spatial and temporal orders of magnitude. Implementation of cellular automata simulations of such tumor growth can be straightforward but computing performance often counterbalances simplicity. Computationally convenient simulation times can be achieved by choosing appropriate data structures, memory and cell handling as well as domain setup. We propose a cellular automaton model of tumor growth with a domain that expands dynamically as the tumor population increases. We discuss memory access, data structures and implementation techniques that yield high-performance multi-scale Monte Carlo simulations of tumor growth. We discuss tumor properties that favor the proposed high-performance design and present simulation results of the tumor growth model. We estimate to which parameters the model is the most sensitive, and show that tumor volume depends on a number of parameters in a non-monotonic manner.

Similarities and Differences in Genome-Wide Expression Data of Six Organisms
Sven Bergmann,Jan Ihmels,Naama Barkai
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.0020009
Abstract: Comparing genomic properties of different organisms is of fundamental importance in the study of biological and evolutionary principles. Although differences among organisms are often attributed to differential gene expression, genome-wide comparative analysis thus far has been based primarily on genomic sequence information. We present a comparative study of large datasets of expression profiles from six evolutionarily distant organisms: S. cerevisiae, C. elegans, E. coli, A. thaliana, D. melanogaster, and H. sapiens. We use genomic sequence information to connect these data and compare global and modular properties of the transcription programs. Linking genes whose expression profiles are similar, we find that for all organisms the connectivity distribution follows a power-law, highly connected genes tend to be essential and conserved, and the expression program is highly modular. We reveal the modular structure by decomposing each set of expression data into coexpressed modules. Functionally related sets of genes are frequently coexpressed in multiple organisms. Yet their relative importance to the transcription program and their regulatory relationships vary among organisms. Our results demonstrate the potential of combining sequence and expression data for improving functional gene annotation and expanding our understanding of how gene expression and diversity evolved.
Similarities and Differences in Genome-Wide Expression Data of Six Organisms
Sven Bergmann,Jan Ihmels,Naama Barkai
PLOS Biology , 2004, DOI: 10.1371/journal.pbio.0020009
Abstract: Comparing genomic properties of different organisms is of fundamental importance in the study of biological and evolutionary principles. Although differences among organisms are often attributed to differential gene expression, genome-wide comparative analysis thus far has been based primarily on genomic sequence information. We present a comparative study of large datasets of expression profiles from six evolutionarily distant organisms: S. cerevisiae, C. elegans, E. coli, A. thaliana, D. melanogaster, and H. sapiens. We use genomic sequence information to connect these data and compare global and modular properties of the transcription programs. Linking genes whose expression profiles are similar, we find that for all organisms the connectivity distribution follows a power-law, highly connected genes tend to be essential and conserved, and the expression program is highly modular. We reveal the modular structure by decomposing each set of expression data into coexpressed modules. Functionally related sets of genes are frequently coexpressed in multiple organisms. Yet their relative importance to the transcription program and their regulatory relationships vary among organisms. Our results demonstrate the potential of combining sequence and expression data for improving functional gene annotation and expanding our understanding of how gene expression and diversity evolved.
On technically solving an effective QCD-Hamiltonian
S. Bielefeld,J. Ihmels,H. C. Pauli
Physics , 1999,
Abstract: By their very nature, field-theoretical Hamiltonians are derived in momentum representation. To solve the corresponding integro-differential equations is more difficult than to solve the simpler differential equations in configuration space (`Schr\"odinger equation'). For the latter many different and very effective methods have been developed in the past. But rather than to Fourier-transform to configuration space - which is not always easy - the equations are solved here directly in momentum space, by using Gaussian quadratures. Special attention is given to the case where the potential in configuration space is linear and where the corresponding momentum-space kernel has an almost intractable 1/(\vec k - \vec k')^4 -singularity. Its regularization requires a certain technical effort, introducing suitable counter terms. The method is numerically reliable and fast, faster than other methods in the literature. It should be useful to and also applicable in other approaches, including phenomenological Schr\"odinger-type equations.
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