The Experts below are selected from a list of 5772 Experts worldwide ranked by ideXlab platform
Michael T. Bowers - One of the best experts on this subject based on the ideXlab platform.
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molecular structures and ion mobility cross sections analysis of the effects of he and n2 buffer gas
Analytical Chemistry, 2015Co-Authors: Christian Bleiholder, Thomas Wyttenbach, Stephanie Contreras, Nicholas R Johnson, Michael T. BowersAbstract:An empirically observed correlation between ion mobility cross sections in helium and nitrogen buffer gases was examined as a function of temperature, molecular size, and shape. Experimental cross sections were determined for tetraglycine, bradykinin, angiotensin 2, melittin, and ubiquitin at 300 K and in the range from 80 to 550 K on home-built instruments and calculated by the projection Superposition Approximation (PSA) method. The PSA was also used to predict cross sections for larger systems such as human pancreatic alpha-amylase, concanavalin, Pichia pastoris lysyl oxidase, and Klebsiella pneumoniae acetolactate synthase. The data show that the ratio of cross sections in helium and nitrogen depends significantly on the temperature of the buffer gas as well as the size and shape of the analyte ion. Therefore, the analysis of the data indicates that a simple formula that seeks to quantitatively relate the momentum transfer cross sections observed in two distinct buffer gases lacks a sound physical basis.
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a novel projection Approximation algorithm for the fast and accurate computation of molecular collision cross sections iv application to polypeptides
International Journal of Mass Spectrometry, 2013Co-Authors: Christian Bleiholder, Stephanie Contreras, Michael T. BowersAbstract:Abstract One fundamental problem of IMS-MS based structure elucidation is achieving agreement between experimental cross sections and those predicted by theoretical algorithms for candidate structures for the compound of interest. Recently, the projected Superposition Approximation (PSA) was introduced specifically to yield accurate ion mobility cross sections for complex macroscopic systems with great computational efficiency. Here, the PSA method is shown to give cross sections within experimental error over an extended temperature range for short peptide sequences of unknown structure. The method is robust for structures derived from different levels of theory. The existing trajectory method (TJM) and projection Approximation (PA) method were shown sensitive to the level of theory used to derive the candidate structures. The PSA method is much faster than the TJM for the systems measured here. As ion mobility instrumentation improves and becomes increasingly available, cross section measurements and theoretical modeling can become a routine technique for determination of macromolecular structure under a variety of experimental conditions, given the accuracy of the PSA method.
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a novel projection Approximation algorithm for the fast and accurate computation of molecular collision cross sections ii model parameterization and definition of empirical shape factors for proteins
International Journal of Mass Spectrometry, 2013Co-Authors: Christian Bleiholder, Stephanie Contreras, Thanh D Do, Michael T. BowersAbstract:Abstract Parameters for the elements H, C, N, Na, and K for use in conjunction with the projected Superposition Approximation (PSA) method to compute collision cross sections are derived based on experimental collision cross sections in the temperature range from approximately 80 to 550 K. The application of the PSA method to proteins of up to approximately 300 kDa in weight is discussed based on a set of 396 protein structures downloaded from the protein data bank. The general method allows determination of cross sections with essentially the same accuracy as the trajectory method but at several orders of magnitude less computational cost. In addition, we define an empirical shape factor ρ ˜ for proteins that approximates the computationally intensive part of the PSA calculation and can be used to estimate the PSA cross section based on the classical projection Approximation. This empirical method reproduces collision cross sections with an accuracy of approximately 10%.
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factors contributing to the collision cross section of polyatomic ions in the kilodalton to gigadalton range application to ion mobility measurements
Analytical Chemistry, 2013Co-Authors: Thomas Wyttenbach, Christian Bleiholder, Michael T. BowersAbstract:The projected Superposition Approximation (PSA) method was used to theoretically evaluate the factors contributing to the cross section measured in ion mobility experiments and to study how the significance of these factors varies with ion size from diglycine to a 1 μm oil droplet. Thousands of PSA calculations for ∼400 different molecules in the temperature range from 80 to 700 K revealed that the molecular framework made up of atomic hard spheres is, as expected, a major component of the cross section. However, the ion–buffer gas interaction is almost equally important for very small peptides, and although its significance decreases with increasing ion size, interaction is still a factor for megadalton ions. An additional major factor is the ion shape: Fully convex ions drifting in a buffer gas have a minimal frictional resisting force, whereas the resisting force increases with degree of ion surface concaveness. This added resistance is small for peptides and larger for proteins and increases the ion m...
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a novel projection Approximation algorithm for the fast and accurate computation of molecular collision cross sections iii application to supramolecular coordination driven assemblies with complex shapes
International Journal of Mass Spectrometry, 2012Co-Authors: Stanley E Anderson, Christian Bleiholder, Erin R Brocker, Peter J Stang, Michael T. BowersAbstract:Abstract The temperature dependence of the cross sections of rectangular, cyclobis[(2,9-bis[ trans -Pt(PEt 3 ) 2 (PF 6 )]anthracene)(4,4′-dipyridyl)] and triangular cyclotris[(2,9-bis[ trans -Pt(PEt 3 ) 2 (PF 6 )]phenanthrene)(4,4′-dipyridyl)] supramolecular assemblies has been investigated by ion mobility mass spectrometry. Molecular dynamics simulations starting with published X-ray structures of both the rectangle and triangle are used to generate model structures. These model structures are used to generate cross sections for comparison with experiment using the simple projection Approximation, the computer intensive trajectory method and the new projected Superposition Approximation (PSA). It is shown that the PSA method provides the best comparison with experiment for these molecules with unusual topographies but the shape factor needs to use a finer mesh in its calculation than for molecules with more regular shapes like folded proteins. Even so the PSA is nearly a factor of 10 faster than the trajectory method for a “small” system like the triangle with 410 atoms.
S Dietrich - One of the best experts on this subject based on the ideXlab platform.
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electrostatic interaction between colloidal particles trapped at an electrolyte interface
Journal of Chemical Physics, 2014Co-Authors: Arghya Majee, Markus Bier, S DietrichAbstract:The electrostatic interaction between colloidal particles trapped at the interface between two immiscible electrolyte solutions is studied in the limit of small inter-particle distances. Within an appropriate model analytic expressions for the electrostatic potential as well as for the surface and line interaction energies are obtained. They demonstrate that the widely used Superposition Approximation, which is commonly applied to large distances between the colloidal particles, fails qualitatively at small distances, and is quantitatively unreliable even at large distances. Our results contribute to an improved description of the interaction between colloidal particles trapped at fluid interfaces.
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electrostatic interaction between colloidal particles trapped at an electrolyte interface
arXiv: Soft Condensed Matter, 2014Co-Authors: Arghya Majee, Markus Bier, S DietrichAbstract:The electrostatic interaction between colloidal particles trapped at the interface between two immiscible electrolyte solutions is studied in the limit of small inter-particle distances. Within an appropriate model exact analytic expressions for the electrostatic potential as well as for the surface and line interaction energies are obtained. They demonstrate that the widely used Superposition Approximation, which is commonly applied to large distances between the colloidal particles, fails qualitatively at small distances and is quantitatively unreliable even at large distances. Our results contribute to an improved description of the interaction between colloidal particles trapped at fluid interfaces.
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theory of capillary induced interactions beyond the Superposition Approximation
arXiv: Soft Condensed Matter, 2007Co-Authors: Alvaro Dominguez, S Dietrich, M OettelAbstract:Within a general theoretical framework we study the effective, deformation-induced interaction between two colloidal particles trapped at a fluid interface in the regime of small deformations. In many studies, this interaction has been computed with the ansatz that the actual interface configuration for the pair is given by the linear Superposition of the interface deformations around the single particles. Here we assess the validity of this approach and compute the leading term of the effective interaction for large interparticle separation beyond this so-called Superposition Approximation. As an application, we consider the experimentally relevant case of interface deformations owing to the electrostatic field emanating from charged colloidal particles. In mechanical isolation, i.e., if the net force acting on the total system consisting of the particles plus the interface vanishes, the Superposition Approximation is actually invalid. The effective capillary interaction is governed by contributions beyond this Approximation and turns out to be attractive. For sufficiently small surface charges on the colloids, such that linearization is strictly valid, and at asymptotically large separations, the effective interaction does not overcome the direct electrostatic repulsion between the colloidal particles.
Markus Bier - One of the best experts on this subject based on the ideXlab platform.
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electrostatic interaction between dissimilar colloids at fluid interfaces
Physical Review E, 2018Co-Authors: Arghya Majee, Markus Bier, Timo SchmetzerAbstract:The electrostatic interaction between two nonidentical, moderately charged colloids situated in close proximity of each other at a fluid interface is studied. By resorting to a well-justified model system, this problem is analytically solved within the framework of linearized Poisson-Boltzmann density functional theory. The resulting interaction comprises a surface and a line part, both of which, as functions of the interparticle separation, show a rich behavior including monotonic as well as nonmonotonic variations. In almost all cases, these variations cannot be captured correctly by using the Superposition Approximation. Moreover, expressions for the surface tensions, the line tensions and the fluid-fluid interfacial tension, which are all independent of the interparticle separation, are obtained. Our results are expected to be particularly useful for emulsions stabilized by oppositely charged particles.
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electrostatic interaction between colloidal particles trapped at an electrolyte interface
Journal of Chemical Physics, 2014Co-Authors: Arghya Majee, Markus Bier, S DietrichAbstract:The electrostatic interaction between colloidal particles trapped at the interface between two immiscible electrolyte solutions is studied in the limit of small inter-particle distances. Within an appropriate model analytic expressions for the electrostatic potential as well as for the surface and line interaction energies are obtained. They demonstrate that the widely used Superposition Approximation, which is commonly applied to large distances between the colloidal particles, fails qualitatively at small distances, and is quantitatively unreliable even at large distances. Our results contribute to an improved description of the interaction between colloidal particles trapped at fluid interfaces.
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electrostatic interaction between colloidal particles trapped at an electrolyte interface
arXiv: Soft Condensed Matter, 2014Co-Authors: Arghya Majee, Markus Bier, S DietrichAbstract:The electrostatic interaction between colloidal particles trapped at the interface between two immiscible electrolyte solutions is studied in the limit of small inter-particle distances. Within an appropriate model exact analytic expressions for the electrostatic potential as well as for the surface and line interaction energies are obtained. They demonstrate that the widely used Superposition Approximation, which is commonly applied to large distances between the colloidal particles, fails qualitatively at small distances and is quantitatively unreliable even at large distances. Our results contribute to an improved description of the interaction between colloidal particles trapped at fluid interfaces.
Christian Bleiholder - One of the best experts on this subject based on the ideXlab platform.
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molecular structures and ion mobility cross sections analysis of the effects of he and n2 buffer gas
Analytical Chemistry, 2015Co-Authors: Christian Bleiholder, Thomas Wyttenbach, Stephanie Contreras, Nicholas R Johnson, Michael T. BowersAbstract:An empirically observed correlation between ion mobility cross sections in helium and nitrogen buffer gases was examined as a function of temperature, molecular size, and shape. Experimental cross sections were determined for tetraglycine, bradykinin, angiotensin 2, melittin, and ubiquitin at 300 K and in the range from 80 to 550 K on home-built instruments and calculated by the projection Superposition Approximation (PSA) method. The PSA was also used to predict cross sections for larger systems such as human pancreatic alpha-amylase, concanavalin, Pichia pastoris lysyl oxidase, and Klebsiella pneumoniae acetolactate synthase. The data show that the ratio of cross sections in helium and nitrogen depends significantly on the temperature of the buffer gas as well as the size and shape of the analyte ion. Therefore, the analysis of the data indicates that a simple formula that seeks to quantitatively relate the momentum transfer cross sections observed in two distinct buffer gases lacks a sound physical basis.
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a novel projection Approximation algorithm for the fast and accurate computation of molecular collision cross sections iv application to polypeptides
International Journal of Mass Spectrometry, 2013Co-Authors: Christian Bleiholder, Stephanie Contreras, Michael T. BowersAbstract:Abstract One fundamental problem of IMS-MS based structure elucidation is achieving agreement between experimental cross sections and those predicted by theoretical algorithms for candidate structures for the compound of interest. Recently, the projected Superposition Approximation (PSA) was introduced specifically to yield accurate ion mobility cross sections for complex macroscopic systems with great computational efficiency. Here, the PSA method is shown to give cross sections within experimental error over an extended temperature range for short peptide sequences of unknown structure. The method is robust for structures derived from different levels of theory. The existing trajectory method (TJM) and projection Approximation (PA) method were shown sensitive to the level of theory used to derive the candidate structures. The PSA method is much faster than the TJM for the systems measured here. As ion mobility instrumentation improves and becomes increasingly available, cross section measurements and theoretical modeling can become a routine technique for determination of macromolecular structure under a variety of experimental conditions, given the accuracy of the PSA method.
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a novel projection Approximation algorithm for the fast and accurate computation of molecular collision cross sections ii model parameterization and definition of empirical shape factors for proteins
International Journal of Mass Spectrometry, 2013Co-Authors: Christian Bleiholder, Stephanie Contreras, Thanh D Do, Michael T. BowersAbstract:Abstract Parameters for the elements H, C, N, Na, and K for use in conjunction with the projected Superposition Approximation (PSA) method to compute collision cross sections are derived based on experimental collision cross sections in the temperature range from approximately 80 to 550 K. The application of the PSA method to proteins of up to approximately 300 kDa in weight is discussed based on a set of 396 protein structures downloaded from the protein data bank. The general method allows determination of cross sections with essentially the same accuracy as the trajectory method but at several orders of magnitude less computational cost. In addition, we define an empirical shape factor ρ ˜ for proteins that approximates the computationally intensive part of the PSA calculation and can be used to estimate the PSA cross section based on the classical projection Approximation. This empirical method reproduces collision cross sections with an accuracy of approximately 10%.
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factors contributing to the collision cross section of polyatomic ions in the kilodalton to gigadalton range application to ion mobility measurements
Analytical Chemistry, 2013Co-Authors: Thomas Wyttenbach, Christian Bleiholder, Michael T. BowersAbstract:The projected Superposition Approximation (PSA) method was used to theoretically evaluate the factors contributing to the cross section measured in ion mobility experiments and to study how the significance of these factors varies with ion size from diglycine to a 1 μm oil droplet. Thousands of PSA calculations for ∼400 different molecules in the temperature range from 80 to 700 K revealed that the molecular framework made up of atomic hard spheres is, as expected, a major component of the cross section. However, the ion–buffer gas interaction is almost equally important for very small peptides, and although its significance decreases with increasing ion size, interaction is still a factor for megadalton ions. An additional major factor is the ion shape: Fully convex ions drifting in a buffer gas have a minimal frictional resisting force, whereas the resisting force increases with degree of ion surface concaveness. This added resistance is small for peptides and larger for proteins and increases the ion m...
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a novel projection Approximation algorithm for the fast and accurate computation of molecular collision cross sections iii application to supramolecular coordination driven assemblies with complex shapes
International Journal of Mass Spectrometry, 2012Co-Authors: Stanley E Anderson, Christian Bleiholder, Erin R Brocker, Peter J Stang, Michael T. BowersAbstract:Abstract The temperature dependence of the cross sections of rectangular, cyclobis[(2,9-bis[ trans -Pt(PEt 3 ) 2 (PF 6 )]anthracene)(4,4′-dipyridyl)] and triangular cyclotris[(2,9-bis[ trans -Pt(PEt 3 ) 2 (PF 6 )]phenanthrene)(4,4′-dipyridyl)] supramolecular assemblies has been investigated by ion mobility mass spectrometry. Molecular dynamics simulations starting with published X-ray structures of both the rectangle and triangle are used to generate model structures. These model structures are used to generate cross sections for comparison with experiment using the simple projection Approximation, the computer intensive trajectory method and the new projected Superposition Approximation (PSA). It is shown that the PSA method provides the best comparison with experiment for these molecules with unusual topographies but the shape factor needs to use a finer mesh in its calculation than for molecules with more regular shapes like folded proteins. Even so the PSA is nearly a factor of 10 faster than the trajectory method for a “small” system like the triangle with 410 atoms.
Arghya Majee - One of the best experts on this subject based on the ideXlab platform.
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electrostatic interaction between dissimilar colloids at fluid interfaces
Physical Review E, 2018Co-Authors: Arghya Majee, Markus Bier, Timo SchmetzerAbstract:The electrostatic interaction between two nonidentical, moderately charged colloids situated in close proximity of each other at a fluid interface is studied. By resorting to a well-justified model system, this problem is analytically solved within the framework of linearized Poisson-Boltzmann density functional theory. The resulting interaction comprises a surface and a line part, both of which, as functions of the interparticle separation, show a rich behavior including monotonic as well as nonmonotonic variations. In almost all cases, these variations cannot be captured correctly by using the Superposition Approximation. Moreover, expressions for the surface tensions, the line tensions and the fluid-fluid interfacial tension, which are all independent of the interparticle separation, are obtained. Our results are expected to be particularly useful for emulsions stabilized by oppositely charged particles.
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electrostatic interaction between colloidal particles trapped at an electrolyte interface
Journal of Chemical Physics, 2014Co-Authors: Arghya Majee, Markus Bier, S DietrichAbstract:The electrostatic interaction between colloidal particles trapped at the interface between two immiscible electrolyte solutions is studied in the limit of small inter-particle distances. Within an appropriate model analytic expressions for the electrostatic potential as well as for the surface and line interaction energies are obtained. They demonstrate that the widely used Superposition Approximation, which is commonly applied to large distances between the colloidal particles, fails qualitatively at small distances, and is quantitatively unreliable even at large distances. Our results contribute to an improved description of the interaction between colloidal particles trapped at fluid interfaces.
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electrostatic interaction between colloidal particles trapped at an electrolyte interface
arXiv: Soft Condensed Matter, 2014Co-Authors: Arghya Majee, Markus Bier, S DietrichAbstract:The electrostatic interaction between colloidal particles trapped at the interface between two immiscible electrolyte solutions is studied in the limit of small inter-particle distances. Within an appropriate model exact analytic expressions for the electrostatic potential as well as for the surface and line interaction energies are obtained. They demonstrate that the widely used Superposition Approximation, which is commonly applied to large distances between the colloidal particles, fails qualitatively at small distances and is quantitatively unreliable even at large distances. Our results contribute to an improved description of the interaction between colloidal particles trapped at fluid interfaces.