The Experts below are selected from a list of 1251 Experts worldwide ranked by ideXlab platform
Akimitsu Narita - One of the best experts on this subject based on the ideXlab platform.
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synthesis of triply fused porphyrin nanographene conjugates
Angewandte Chemie, 2018Co-Authors: Qiang Chen, Luigi Brambilla, Lakshya Daukiya, Kunal S Mali, Steven De Feyter, Matteo Tommasini, Klaus Mullen, Akimitsu NaritaAbstract:Two unprecedented porphyrin fused nanographene molecules, 1 and 2, have been synthesized by the Scholl reaction from tailor-made precursors based on benzo[m]tetraphene-substituted porphyrins. The chemical structures were validated by a combination of high-Resolution Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (HR MALDI-TOF MS), IR and Raman spectroscopy, and scanning tunnelling microscopy (STM). The UV-vis-near infrared absorption spectroscopy of 1 and 2 demonstrated broad and largely red-shifted absorption spectra extending up to 1000 and 1400 nm, respectively, marking the significant extension of the π-conjugated systems.
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Synthesis of Triply Fused Porphyrin‐Nanographene Conjugates
Angewandte Chemie (International ed. in English), 2018Co-Authors: Qiang Chen, Luigi Brambilla, Lakshya Daukiya, Kunal S Mali, Steven De Feyter, Matteo Tommasini, Klaus Mullen, Akimitsu NaritaAbstract:Two unprecedented porphyrin fused nanographene molecules, 1 and 2, have been synthesized by the Scholl reaction from tailor-made precursors based on benzo[m]tetraphene-substituted porphyrins. The chemical structures were validated by a combination of high-Resolution Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (HR MALDI-TOF MS), IR and Raman spectroscopy, and scanning tunnelling microscopy (STM). The UV-vis-near infrared absorption spectroscopy of 1 and 2 demonstrated broad and largely red-shifted absorption spectra extending up to 1000 and 1400 nm, respectively, marking the significant extension of the π-conjugated systems.
K Habicht - One of the best experts on this subject based on the ideXlab platform.
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generalized Resolution Matrix for neutron spin echo three axis spectrometers
Journal of Applied Crystallography, 2018Co-Authors: Felix Groitl, T Keller, K HabichtAbstract:This article describes the energy Resolution of spin-echo three-axis spectrometers (SE-TASs) by a compact Matrix formalism. SE-TASs allow one to measure the line widths of elementary excitations in crystals, such as phonons and magnons, with an energy Resolution in the µeV range. The Resolution matrices derived here generalize prior work: (i) the formalism works for all crystal structures; (ii) spectrometer detuning effects are included; these arise typically from inaccurate knowledge of the excitation energy and group velocity; (iii) components of the gradient vector of the dispersion surface dω/dq perpendicular to the scattering plane are properly treated; (iv) the curvature of the dispersion surface is easily calculated in reciprocal units; (v) the formalism permits analysis of spin-echo signals resulting from multiple excitation modes within the three-axis spectrometer Resolution ellipsoid.
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Generalized Resolution Matrix for neutron spin‐echo three‐axis spectrometers
Journal of Applied Crystallography, 2018Co-Authors: Felix Groitl, Thomas Keller, K HabichtAbstract:This article describes the energy Resolution of spin-echo three-axis spectrometers (SE-TASs) by a compact Matrix formalism. SE-TASs allow one to measure the line widths of elementary excitations in crystals, such as phonons and magnons, with an energy Resolution in the µeV range. The Resolution matrices derived here generalize prior work: (i) the formalism works for all crystal structures; (ii) spectrometer detuning effects are included; these arise typically from inaccurate knowledge of the excitation energy and group velocity; (iii) components of the gradient vector of the dispersion surface dω/dq perpendicular to the scattering plane are properly treated; (iv) the curvature of the dispersion surface is easily calculated in reciprocal units; (v) the formalism permits analysis of spin-echo signals resulting from multiple excitation modes within the three-axis spectrometer Resolution ellipsoid.
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the Resolution Matrix for neutron spin echo three axis spectroscopy
Physica B-condensed Matter, 2004Co-Authors: K Habicht, T Keller, R GolubAbstract:Abstract The Resolution Matrix, well known in the Resolution theory for neutron three-axis spectrometers, is extended to include the Larmor phase. This adequately describes the Resolution problem for a combination of three-axis and neutron (resonance) spin-echo techniques. A graphical interpretation of the Resolution Matrix in terms of Resolution volumes and Larmor phase diagrams is presented in wavevector-energy space. Integration over wavevector coordinates yields the Resolution function, i.e. the polarization as a function of spin-echo time for an excitation with zero linewidth.
Francesco De Angelis - One of the best experts on this subject based on the ideXlab platform.
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Exploring the frontiers of synthetic eumelanin polymers by high-Resolution Matrix-assisted laser/desorption ionization mass spectrometry.
Journal of mass spectrometry : JMS, 2012Co-Authors: Samantha Reale, Marcello Crucianelli, Alessandro Pezzella, Marco D'ischia, Francesco De AngelisAbstract:New trends in material science and nanotechnologies have spurred growing interest in eumelanins black insoluble biopolymers derived by tyrosinase-catalysed oxidation of tyrosine via 5,6-dihydroxyindole (DHI) and its 2-carboxylic acid (DHICA). Efficient antioxidant and photoprotective actions, associated with peculiar optoelectronic properties, are recognised as prominent functions of eumelanin macromolecules within the human and mammalian pigmentary system, making them unique candidates for the realisation of innovative bio-inspired functional soft materials, with structure-based physical–chemical properties. An unprecedented breakthrough into the mechanism of synthetic eumelanin buildup has derived from a detailed investigation of the oxidative polymerization of DHI and its N-methyl derivative (NMDHI) by linear and reflectron Matrix-assisted laser/desorption ionization mass spectrometry. Regular collections of oligomers of increasing masses, spanning the entire m/z ranges up to 5000 Da (>30-mer) and 8000 Da (> 50-mer) for the two building blocks, respectively, were disclosed. It is the first time that the in vitro polymerisation of dihydroxyindoles to form synthetic eumelanins is explored up to its high mass limits, giving at the same time information on the polymerisation mode, whether it follows a stepwise pattern (being this the conclusion in our case) or a staking sequencing of small-sized entities. It also highlighted the influence of the N-methyl substituent on the polymerization process; this opens the way to the production of N-functionalized, synthetic eumelanin-inspired soft materials, for possible future technological applications. Copyright © 2012 John Wiley & Sons, Ltd.
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exploring the frontiers of synthetic eumelanin polymers by high Resolution Matrix assisted laser desorption ionization mass spectrometry
Journal of Mass Spectrometry, 2012Co-Authors: Samantha Reale, Marcello Crucianelli, Alessandro Pezzella, Marco Dischia, Francesco De AngelisAbstract:New trends in material science and nanotechnologies have spurred growing interest in eumelanins black insoluble biopolymers derived by tyrosinase-catalysed oxidation of tyrosine via 5,6-dihydroxyindole (DHI) and its 2-carboxylic acid (DHICA). Efficient antioxidant and photoprotective actions, associated with peculiar optoelectronic properties, are recognised as prominent functions of eumelanin macromolecules within the human and mammalian pigmentary system, making them unique candidates for the realisation of innovative bio-inspired functional soft materials, with structure-based physical–chemical properties. An unprecedented breakthrough into the mechanism of synthetic eumelanin buildup has derived from a detailed investigation of the oxidative polymerization of DHI and its N-methyl derivative (NMDHI) by linear and reflectron Matrix-assisted laser/desorption ionization mass spectrometry. Regular collections of oligomers of increasing masses, spanning the entire m/z ranges up to 5000 Da (>30-mer) and 8000 Da (> 50-mer) for the two building blocks, respectively, were disclosed. It is the first time that the in vitro polymerisation of dihydroxyindoles to form synthetic eumelanins is explored up to its high mass limits, giving at the same time information on the polymerisation mode, whether it follows a stepwise pattern (being this the conclusion in our case) or a staking sequencing of small-sized entities. It also highlighted the influence of the N-methyl substituent on the polymerization process; this opens the way to the production of N-functionalized, synthetic eumelanin-inspired soft materials, for possible future technological applications. Copyright © 2012 John Wiley & Sons, Ltd.
Andreas Römpp - One of the best experts on this subject based on the ideXlab platform.
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high Resolution Matrix assisted laser desorption ionization imaging of tryptic peptides from tissue
Rapid Communications in Mass Spectrometry, 2012Co-Authors: Yvonne Schober, Sabine Guenther, Bernhard Spengler, Andreas RömppAbstract:RATIONALE The analysis of proteins by mass spectrometry imaging is an important biomedical application as spatial distributions can be used to identify markers for pathological processes. The direct detection and identification of proteins on tissue can be hindered by a number of factors including limited mass range and fragmentation efficiency as well as incompatibility with formalin-fixed samples. METHODS To overcome some of these limitations, on-tissue digestion of proteins was followed by detection of the resulting peptides. Trypsin was applied by a spraying device. Matrix-assisted laser desorption/ionization (MALDI) imaging experiments were performed with a home-built atmospheric-pressure imaging source attached to a LTQ Orbitrap mass spectrometer. The mass accuracy under imaging conditions was better than 3 ppm RMS. This allowed for confident identification of tryptic peptides by comparison with liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) measurements of an adjacent mouse brain section. RESULTS A spatial Resolution of 50 µm was obtained for tryptic peptides on tissue. Several tryptic peptides of myelin showed matching spatial distributions, and numerous tryptic peptides of other proteins were identified. MS images were generated with a bin size (mass range used for image generation) of Δm/z = 0.01 u. Examples demonstrate that MS images with lower selectivity can result in misleading information about the spatial distribution of tryptic peptides. CONCLUSIONS The presented method combines a significantly improved spatial Resolution for tryptic peptides with low-ppm mass accuracy in a single experiment and thus provides highly reliable and specific information. Copyright © 2012 John Wiley & Sons, Ltd.
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High-Resolution Matrix-assisted laser desorption/ionization imaging of tryptic peptides from tissue.
Rapid communications in mass spectrometry : RCM, 2012Co-Authors: Yvonne Schober, Sabine Guenther, Bernhard Spengler, Andreas RömppAbstract:RATIONALE The analysis of proteins by mass spectrometry imaging is an important biomedical application as spatial distributions can be used to identify markers for pathological processes. The direct detection and identification of proteins on tissue can be hindered by a number of factors including limited mass range and fragmentation efficiency as well as incompatibility with formalin-fixed samples. METHODS To overcome some of these limitations, on-tissue digestion of proteins was followed by detection of the resulting peptides. Trypsin was applied by a spraying device. Matrix-assisted laser desorption/ionization (MALDI) imaging experiments were performed with a home-built atmospheric-pressure imaging source attached to a LTQ Orbitrap mass spectrometer. The mass accuracy under imaging conditions was better than 3 ppm RMS. This allowed for confident identification of tryptic peptides by comparison with liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) measurements of an adjacent mouse brain section. RESULTS A spatial Resolution of 50 µm was obtained for tryptic peptides on tissue. Several tryptic peptides of myelin showed matching spatial distributions, and numerous tryptic peptides of other proteins were identified. MS images were generated with a bin size (mass range used for image generation) of Δm/z = 0.01 u. Examples demonstrate that MS images with lower selectivity can result in misleading information about the spatial distribution of tryptic peptides. CONCLUSIONS The presented method combines a significantly improved spatial Resolution for tryptic peptides with low-ppm mass accuracy in a single experiment and thus provides highly reliable and specific information. Copyright © 2012 John Wiley & Sons, Ltd.
Anand Kumar - One of the best experts on this subject based on the ideXlab platform.
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The Resolution Matrix in Tomographic Multiplexing: Optimization of Inter-Parameter Cross-Talk, Relative Quantitation, and Localization
IEEE transactions on bio-medical engineering, 2018Co-Authors: Steven S. Hou, Brian J. Bacskai, Anand KumarAbstract:Objective: We use a Resolution Matrix-based Bayesian framework to compare inversion methods for tomographic fluorescence lifetime multiplexing in a diffuse medium, such as biological tissue. Methods: We consider three inversion methods; an asymptotic time domain (ATD) approach, based on a multiexponential analysis of time domain data, a direct time domain (DTD) approach, which is a minimum error solution, and a cross-talk constrained time domain (CCTD) inversion, which is a solution to an optimization problem that minimizes both error and cross-talk. We compare these methods using Monte Carlo simulations and time domain fluorescence measurements with tissue-mimicking phantoms. Results: The ATD approach provides high accuracy of relative quantitation and spatial localization of two fluorophores embedded in a 18-mm thick turbid medium, with concentration ratios of up to 1:4.25. DTD leads to significant errors in relative quantitation and localization. CCTD provides improved quantitation accuracy over DTD, and better spatial Resolution compared to ATD. We present a rigorous theoretical basis for these results and provide a complete derivation of the CCTD estimator. The Bayesian analysis also leads to a formula for rapid computation of the DTD inverse operator for large-scale tomography measurements. Conclusion: The ATD and CCTD inversion methods provide significant advantages over DTD for accurately estimating multiple overlapping fluorophores. Significance: Time domain fluorescence tomography, using zero cross-talk estimators, can serve as a powerful tool for quantifying multiple fluorescently labeled biological processes. The Bayesian framework presented here can be applied to general multiparameter inverse problems for the quantitative estimation of multiple overlapping parameters.
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Tomographic multiplexing using fluorescence lifetime and spectral contrast
Biomedical Optics 2016, 2016Co-Authors: Steven S. Hou, Brian J. Bacskai, Anand KumarAbstract:We present a Resolution Matrix-based approach to constrain cross-talk in tomographic multiplexing. This approach provides zero cross-talk solutions for lifetime multiplexing and the conditions for achieving zero cross-talk in spectral multiplexing.