9 results on '"Chang, Rayoon"'
Search Results
2. Cryogenic infrared spectroscopy reveals remarkably short NH+⋯F hydrogen bonds in fluorinated phenylalanines.
- Author
-
Safferthal, Marc, Greis, Kim, Chang, Rayoon, Kirschbaum, Carla, Hoffmann, Waldemar, Meijer, Gerard, von Helden, Gert, and Pagel, Kevin
- Abstract
In past decades, hydrogen bonds involving organic fluorine have been a highly disputed topic. Obtaining clear evidence for the presence of fluorine-specific interactions is generally difficult because of their weak nature. Today, the existence of hydrogen bonds with organic fluorine is widely accepted and supported by numerous studies. However, strong bonds with short H⋯F distances remain scarce and are primarily found in designed model compounds. Using a combination of cryogenic gas-phase infrared spectroscopy and density functional theory, we here analyze a series of conformationally unrestrained fluorinated phenylalanine compounds as protonated species. The results suggest proximal NH
+ ⋯F hydrogen bonds with an exceptionally close H⋯F distance (1.79 Å) in protonated ortho-fluorophenylalanine. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
3. Neighboring Group Participation of Benzoyl Protecting Groups in C3‐ and C6‐Fluorinated Glucose.
- Author
-
Greis, Kim, Kirschbaum, Carla, Fittolani, Giulio, Mucha, Eike, Chang, Rayoon, von Helden, Gert, Meijer, Gerard, Delbianco, Martina, Seeberger, Peter H., and Pagel, Kevin
- Subjects
CHEMICAL properties ,ACYL group ,GLUCOSE ,INFRARED spectroscopy ,RESONANCE effect - Abstract
Fluorination is a potent method to modulate chemical properties of glycans. Here, we study how C3‐ and C6‐fluorination of glucosyl building blocks influence the structure of the intermediate of the glycosylation reaction, the glycosyl cation. Using a combination of gas‐phase infrared spectroscopy and first‐principles theory, glycosyl cations generated from fluorinated and non‐fluorinated monosaccharides are structurally characterized. The results indicate that neighboring group participation of the C2‐benzoyl protecting group is the dominant structural motif for all building blocks, correlating with the β‐selectivity observed in glycosylation reactions. The infrared signatures indicate that participation of the benzoyl group in enhanced by resonance effects. Participation of remote acyl groups such as Fmoc or benzyl on the other hand is unfavored. The introduction of the less bulky fluorine leads to a change in the conformation of the ring pucker, whereas the structure of the active dioxolenium site remains unchanged. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
4. Probing the conformational landscape and thermochemistry of DNA dinucleotide anionsviahelium nanodroplet infrared action spectroscopy
- Author
-
Thomas, Daniel A., Chang, Rayoon, Mucha, Eike, Lettow, Maike, Greis, Kim, Gewinner, Sandy, Schöllkopf, Wieland, Meijer, Gerard, and Von Helden, Gert
- Subjects
basis-sets ,ion mobility ,energy landscape ,cationized arginine ,Physics::Atomic and Molecular Clusters ,mobility-mass spectrometry ,unsolvated peptides ,gas-phase conformations ,Physics::Chemical Physics ,500 Naturwissenschaften und Mathematik::540 Chemie::540 Chemie und zugeordnete Wissenschaften ,photon dissociation spectroscopy - Abstract
Isolation of biomolecules in vacuum facilitates characterization of the intramolecular interactions that determine three-dimensional structure, but experimental quantification of conformer thermochemistry remains challenging. Infrared spectroscopy of molecules trapped in helium nanodroplets is a promising methodology for the measurement of thermochemical parameters. When molecules are captured in a helium nanodroplet, the rate of cooling to an equilibrium temperature ofca.0.4 K is generally faster than the rate of isomerization, resulting in "shock-freezing" that kinetically traps molecules in local conformational minima. This unique property enables the study of temperature-dependent conformational equilibriaviainfrared spectroscopy at 0.4 K, thereby avoiding the deleterious effects of spectral broadening at higher temperatures. Herein, we demonstrate the first application of this approach to ionic species by coupling electrospray ionization mass spectrometry (ESI-MS) with helium nanodroplet infrared action spectroscopy to probe the structure and thermochemistry of deprotonated DNA dinucleotides. Dinucleotide anions were generated by ESI, confined in an ion trap at temperatures between 90 and 350 K, and entrained in traversing helium nanodroplets. The infrared action spectra of the entrained ions show a strong dependence on pre-pickup ion temperature, consistent with the preservation of conformer population upon cooling to 0.4 K. Non-negative matrix factorization was utilized to identify component conformer infrared spectra and determine temperature-dependent conformer populations. Relative enthalpies and entropies of conformers were subsequently obtained from a van't Hoff analysis. IR spectra and conformer thermochemistry are compared to results from ion mobility spectrometry (IMS) and electronic structure methods. The implementation of ESI-MS as a source of dopant molecules expands the diversity of molecules accessible for thermochemical measurements, enabling the study of larger, non-volatile species.
- Published
- 2020
5. Probing the conformational landscape and thermochemistry of DNA dinucleotide anions via helium nanodroplet infrared action spectroscopy.
- Author
-
Thomas, Daniel A., Chang, Rayoon, Mucha, Eike, Lettow, Maike, Greis, Kim, Gewinner, Sandy, Schöllkopf, Wieland, Meijer, Gerard, and von Helden, Gert
- Abstract
Isolation of biomolecules in vacuum facilitates characterization of the intramolecular interactions that determine three-dimensional structure, but experimental quantification of conformer thermochemistry remains challenging. Infrared spectroscopy of molecules trapped in helium nanodroplets is a promising methodology for the measurement of thermochemical parameters. When molecules are captured in a helium nanodroplet, the rate of cooling to an equilibrium temperature of ca. 0.4 K is generally faster than the rate of isomerization, resulting in "shock-freezing" that kinetically traps molecules in local conformational minima. This unique property enables the study of temperature-dependent conformational equilibria via infrared spectroscopy at 0.4 K, thereby avoiding the deleterious effects of spectral broadening at higher temperatures. Herein, we demonstrate the first application of this approach to ionic species by coupling electrospray ionization mass spectrometry (ESI-MS) with helium nanodroplet infrared action spectroscopy to probe the structure and thermochemistry of deprotonated DNA dinucleotides. Dinucleotide anions were generated by ESI, confined in an ion trap at temperatures between 90 and 350 K, and entrained in traversing helium nanodroplets. The infrared action spectra of the entrained ions show a strong dependence on pre-pickup ion temperature, consistent with the preservation of conformer population upon cooling to 0.4 K. Non-negative matrix factorization was utilized to identify component conformer infrared spectra and determine temperature-dependent conformer populations. Relative enthalpies and entropies of conformers were subsequently obtained from a van't Hoff analysis. IR spectra and conformer thermochemistry are compared to results from ion mobility spectrometry (IMS) and electronic structure methods. The implementation of ESI-MS as a source of dopant molecules expands the diversity of molecules accessible for thermochemical measurements, enabling the study of larger, non-volatile species. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
6. An Intrinsic Hydrophobicity Scale for Amino Acids and Its Application to Fluorinated Compounds.
- Author
-
Hoffmann, Waldemar, Langenhan, Jennifer, Huhmann, Susanne, Moschner, Johann, Chang, Rayoon, Accorsi, Matteo, Seo, Jongcheol, Rademann, Jörg, Meijer, Gerard, Koksch, Beate, Bowers, Michael T., von Helden, Gert, and Pagel, Kevin
- Subjects
AMINO acids ,HYDROPHOBIC interactions ,ION mobility spectroscopy - Abstract
More than 100 hydrophobicity scales have been introduced, with each being based on a distinct condensed‐phase approach. However, a comparison of the hydrophobicity values gained from different techniques, and their relative ranking, is not straightforward, as the interactions between the environment and the amino acid are unique to each method. Here, we overcome this limitation by studying the properties of amino acids in the clean‐room environment of the gas phase. In the gas phase, entropic contributions from the hydrophobic effect are by default absent and only the polarity of the side chain dictates the self‐assembly. This allows for the derivation of a novel hydrophobicity scale, which is based solely on the interaction between individual amino acid units within the cluster and thus more accurately reflects the intrinsic nature of a side chain. This principle can be further applied to classify non‐natural derivatives, as shown here for fluorinated amino acid variants. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
7. Eine intrinsische Hydrophobieskala für Aminosäuren und ihre Anwendung auf fluorierte Verbindungen.
- Author
-
Hoffmann, Waldemar, Langenhan, Jennifer, Huhmann, Susanne, Moschner, Johann, Chang, Rayoon, Accorsi, Matteo, Seo, Jongcheol, Rademann, Jörg, Meijer, Gerard, Koksch, Beate, Bowers, Michael T., von Helden, Gert, and Pagel, Kevin
- Abstract
Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2019
- Full Text
- View/download PDF
8. Cryogenic infrared spectroscopy reveals remarkably short NH + ⋯F hydrogen bonds in fluorinated phenylalanines.
- Author
-
Safferthal M, Greis K, Chang R, Kirschbaum C, Hoffmann W, Meijer G, von Helden G, and Pagel K
- Abstract
In past decades, hydrogen bonds involving organic fluorine have been a highly disputed topic. Obtaining clear evidence for the presence of fluorine-specific interactions is generally difficult because of their weak nature. Today, the existence of hydrogen bonds with organic fluorine is widely accepted and supported by numerous studies. However, strong bonds with short H⋯F distances remain scarce and are primarily found in designed model compounds. Using a combination of cryogenic gas-phase infrared spectroscopy and density functional theory, we here analyze a series of conformationally unrestrained fluorinated phenylalanine compounds as protonated species. The results suggest proximal NH
+ ⋯F hydrogen bonds with an exceptionally close H⋯F distance (1.79 Å) in protonated ortho -fluorophenylalanine.- Published
- 2023
- Full Text
- View/download PDF
9. An Intrinsic Hydrophobicity Scale for Amino Acids and Its Application to Fluorinated Compounds.
- Author
-
Hoffmann W, Langenhan J, Huhmann S, Moschner J, Chang R, Accorsi M, Seo J, Rademann J, Meijer G, Koksch B, Bowers MT, von Helden G, and Pagel K
- Abstract
More than 100 hydrophobicity scales have been introduced, with each being based on a distinct condensed-phase approach. However, a comparison of the hydrophobicity values gained from different techniques, and their relative ranking, is not straightforward, as the interactions between the environment and the amino acid are unique to each method. Here, we overcome this limitation by studying the properties of amino acids in the clean-room environment of the gas phase. In the gas phase, entropic contributions from the hydrophobic effect are by default absent and only the polarity of the side chain dictates the self-assembly. This allows for the derivation of a novel hydrophobicity scale, which is based solely on the interaction between individual amino acid units within the cluster and thus more accurately reflects the intrinsic nature of a side chain. This principle can be further applied to classify non-natural derivatives, as shown here for fluorinated amino acid variants., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)
- Published
- 2019
- Full Text
- View/download PDF
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