1
|
Ucur B, Shiels OJ, Blanksby SJ, Trevitt AJ. Observation of Solvent-Dependence in the Mechanism of Neutral-Catalyzed Isomerization of para-Aminobenzoic Acid Protomers. J Am Soc Mass Spectrom 2024. [PMID: 38523556 DOI: 10.1021/jasms.3c00433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/26/2024]
Abstract
Proton-transfer reactions are commonplace during electrospray ionization (ESI) mass spectrometry experiments and are often responsible for imparting charge to analyte molecules. Multiple protonation-site isomers (protomers) can arise for polyfunctional molecules and these isomers can interconvert via solvent-mediated proton transfer reactions during various stages of the ESI process. Studying the populations and interconversion of protonation isomers provides key insight into the ESI process, ion-molecule interactions, and ion dissociation mechanisms. An archetype molecule to study protomer interconversion fundamentals in this context is para-aminobenzoic acid (pABA), where both the amino and carboxylic acid protomers are typically formed under ESI and the mechanisms for interconversion are still under refinement. Using ion-trap mass spectrometry reaction kinetics (2.5 mTorr, 300 K), this study examines gas-phase interconversion catalysis of pABA protomers by seven neutral species, which are commen solvents and additives used for ESI: water, formic acid, methanol, ethanol, propanol, ammonia, and acetonitrile. Three distinct reaction cases are reported: (i) formic acid, methanol, ethanol, propanol, and ammonia each catalyze the interconversion between the amino and carboxylic acid protomers via a n = 1 solvent-molecule vehicle mechanism; (ii) for water, however, a n = 6 adduct complex is detected and this suggests that the observed protomer interconversion occurs through a Grotthuss mechanism, in accord with literature reports; (iii) acetonitrile inhibits proton transfer by the formation of particularly stable n = 1 and 2 adduct complexes. The second-order rate constants for the protomer interconversion are observed to increase in the following order: H2O < HCO2H < MeOH < EtOH < PrOH < NH3. Potential energy schemes are reported for all neutral-catalyzed proton transfer reactions using the DSD-PBEP86-D3(BJ)/aug-cc-pVDZ level of theory. A central transition state, which connects the protonation site adducts, is shown to be the key rate-limiting step. The energy of this transition state is sensitive to the proton affinity of the neutral solvent, and this is supported by the correlation between the reaction rate and the solvent proton affinity.
Collapse
Affiliation(s)
- Boris Ucur
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - Oisin J Shiels
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - Stephen J Blanksby
- Central Analytical Research Facility and the School of Chemistry and Physics, Queensland University of Technology, Brisbane 4001, Australia
| | - Adam J Trevitt
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| |
Collapse
|
2
|
Zhang B, Burchill L, Altalhi WAO, Ma HZ, O'Hair RAJ. A fixed-charge model of the N-protomer of 4-aminobenzoic acid to facilitate the study of the unimolecular and bimolecular chemistry of its "neutral" carboxylic acid group. Rapid Commun Mass Spectrom 2024; 38:e9681. [PMID: 38355884 DOI: 10.1002/rcm.9681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Revised: 11/24/2023] [Accepted: 11/25/2023] [Indexed: 02/16/2024]
Abstract
RATIONALE There are a growing number of examples of protomers formed via electrospray ionization (ESI) that do not fragment under mobile proton conditions, giving rise to distinct tandem mass spectra. To model the N-protomer of 4-aminobenzoic acid, here we study the gas-phase unimolecular and bimolecular chemistry of the 4-(carboxyphenyl)trimethylammonium ion. METHODS 4-(Carboxyphenyl)trimethylammonium iodide was synthesized, purified via recrystallization and transferred to the gas phase via ESI. 4-(Carboxyphenyl)trimethylammonium ion, 7, was mass selected and subjected to collision-induced dissociation and ion-molecule reactions in a linear ion trap mass spectrometer. RESULTS The major fragmentation channel for the fixed-charge cation 7 is methyl radical loss, whereas loss of trimethylamine and CO2 represents minor pathways. The free carboxylic acid functional group of 7 is unreactive toward a number of neutral reagents (methanol, acetone, acetonitrile, and N,N'-diisopropylcarbodiimide). 7 reacts very slowly with trimethylborate via addition-elimination, consistent with density functional theory (DFT) calculations that show this reaction is slightly endothermic. The deuterated cation 7(D) undergoes slow D/H exchange with ethanol, and DFT calculations reveal that a flip-flop mechanism operates. CONCLUSIONS The free carboxylic group of 7 is not very reactive toward neutral reagents in the gas phase.
Collapse
Affiliation(s)
- Beiang Zhang
- School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
| | - Laura Burchill
- School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
| | - Weam A O Altalhi
- School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
- Department of Chemistry, Prince Sattam Bin Abdulaziz University, Hotat Bani Tamim, Saudi Arabia
| | - Howard Z Ma
- School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
| | - Richard A J O'Hair
- School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
| |
Collapse
|
3
|
Hirata K, Akasaka K, Dopfer O, Ishiuchi SI, Fujii M. Transition from vehicle to Grotthuss proton transfer in a nanosized flask: cryogenic ion spectroscopy of protonated p-aminobenzoic acid solvated with D 2O. Chem Sci 2024; 15:2725-2730. [PMID: 38404372 PMCID: PMC10882521 DOI: 10.1039/d3sc05455a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Accepted: 01/18/2024] [Indexed: 02/27/2024] Open
Abstract
Proton transfer (PT) is one of the most ubiquitous reactions in chemistry and life science. The unique nature of PT has been rationalized not by the transport of a solvated proton (vehicle mechanism) but by the Grotthuss mechanism in which a proton is transported to the nearest proton acceptor along a hydrogen-bonded network. However, clear experimental evidence of the Grotthuss mechanism has not been reported yet. Herein we show by infrared spectroscopy that a vehicle-type PT occurs in the penta- and hexahydrated clusters of protonated p-aminobenzoic acid, while Grotthuss-type PT is observed in heptahydrated clusters, indicating a change in the PT mechanism depending on the degree of hydration. These findings emphasize the importance of the usually ignored vehicle mechanism as well as the degree of hydration. It highlights the possibility of controlling the PT mechanism by the number of water molecules in chemical and biological environments.
Collapse
Affiliation(s)
- Keisuke Hirata
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- Department of Chemistry, School of Science, Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku Tokyo 152-8550 Japan
- International Research Frontiers Initiative, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
| | - Kyota Akasaka
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- School of Life Science and Technology, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama Kanagawa 226-8503 Japan
| | - Otto Dopfer
- International Research Frontiers Initiative, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- Institut für Optik und Atomare Physik, Technische Universität Berlin Hardenbergstrasse 36 10623 Berlin Germany
| | - Shun-Ichi Ishiuchi
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- Department of Chemistry, School of Science, Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku Tokyo 152-8550 Japan
- International Research Frontiers Initiative, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
| | - Masaaki Fujii
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
- School of Life Science and Technology, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama Kanagawa 226-8503 Japan
- International Research Frontiers Initiative, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku Yokohama 226-8503 Japan
| |
Collapse
|
4
|
Ohshimo K, Sato R, Takasaki Y, Tsunoda K, Ito R, Kanno M, Misaizu F. Highly Efficient Intramolecular Proton Transfer in p-Aminobenzoic Acid by a Single Ammonia Molecule as a Vehicle. J Phys Chem Lett 2023; 14:8281-8288. [PMID: 37677142 DOI: 10.1021/acs.jpclett.3c01996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/09/2023]
Abstract
Proton transfer is classified into two mechanisms: the Grotthuss (proton-relay) and vehicle mechanisms. It has been well studied on gas-phase proton transfer by a proton relay involving multiple molecules. However, a vehicle mechanism in which a single molecule transports a proton has rarely been reported. Here, we have obtained clear evidence that the proton transfers efficiently between the two protonation sites in protonated p-aminobenzoic acid (PABA·H+) by a single ammonia molecule as a vehicle. The gaseous PABA·H+ ions were reacted with NH3 or ND3 under single-collision conditions in a cold ion trap, and the proton-transferred ions were identified by cryogenic ion mobility-mass spectrometry. A reaction intermediate PABA·H+·NH3 was also detected for the first time. The reaction pathway search calculations and ab initio molecular dynamics simulations supported the present experimental finding that intramolecular proton transfer occurs very efficiently by the vehicle mechanism.
Collapse
Affiliation(s)
- Keijiro Ohshimo
- Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
| | - Ryosuke Sato
- Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
| | - Yuya Takasaki
- Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
| | - Kengo Tsunoda
- Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
| | - Ryosuke Ito
- Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
| | - Manabu Kanno
- Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
| | - Fuminori Misaizu
- Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
| |
Collapse
|
5
|
Khuu T, Schleif T, Mohamed A, Mitra S, Johnson MA, Valdiviezo J, Heindel JP, Head-Gordon T. Intra-cluster Charge Migration upon Hydration of Protonated Formic Acid Revealed by Anharmonic Analysis of Cold Ion Vibrational Spectra. J Phys Chem A 2023; 127:7501-7509. [PMID: 37669457 DOI: 10.1021/acs.jpca.3c03971] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/07/2023]
Abstract
The rates of many chemical reactions are accelerated when carried out in micron-sized droplets, but the molecular origin of the rate acceleration remains unclear. One example is the condensation reaction of 1,2-diaminobenzene with formic acid to yield benzimidazole. The observed rate enhancements have been rationalized by invoking enhanced acidity at the surface of methanol solvent droplets with low water content to enable protonation of formic acid to generate a cationic species (protonated formic acid or PFA) formed by attachment of a proton to the neutral acid. Because PFA is the key feature in this reaction mechanism, vibrational spectra of cryogenically cooled, microhydrated PFA·(H2O)n=1-6 were acquired to determine how the extent of charge localization depends on the degree of hydration. Analysis of these highly anharmonic spectra with path integral ab initio molecular dynamics simulations reveals the gradual displacement of the excess proton onto the water network in the microhydration regime at low temperatures with n = 3 as the tipping point for intra-cluster proton transfer.
Collapse
Affiliation(s)
- Thien Khuu
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Tim Schleif
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Ahmed Mohamed
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Sayoni Mitra
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Mark A Johnson
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Jesús Valdiviezo
- Pitzer Theory Center, Department of Chemistry, University of California, Berkeley, California 94720, United States
| | - Joseph P Heindel
- Pitzer Theory Center, Department of Chemistry, University of California, Berkeley, California 94720, United States
| | - Teresa Head-Gordon
- Pitzer Theory Center, Department of Chemistry, University of California, Berkeley, California 94720, United States
| |
Collapse
|
6
|
Hernández HM, Sun Q, Rosati M, Gieseking RLM, Johnson CJ. Bonding and Acidity of the Formal Hydride in the Prototypical Au 9 (PPh 3 ) 8 H 2+ Nanocluster. Angew Chem Int Ed Engl 2023; 62:e202307723. [PMID: 37419865 DOI: 10.1002/anie.202307723] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 07/05/2023] [Accepted: 07/07/2023] [Indexed: 07/09/2023]
Abstract
The role of hydrogen atoms as surface ligands on metal nanoclusters is of profound importance but remains difficult to directly study. While hydrogen atoms often appear to be incorporated formally as hydrides, evidence suggests that they donate electrons to the cluster's delocalized superatomic orbitals and may consequently behave as acidic protons that play key roles in synthetic or catalytic mechanisms. Here we directly test this assertion for the prototypical Au9 (PPh3 )8 H2+ nanocluster, formed by addition of a hydride to the well-characterized Au9 (PPh3 )8 3+ . Using gas-phase infrared spectroscopy, we were able to unambiguously isolate Au9 (PPh3 )8 H2+ and Au9 (PPh3 )8 D2+ , revealing an Au-H stretching mode at 1528 cm-1 that shifts to 1038 cm-1 upon deuteration. This shift is greater than the maximum expected for a typical harmonic potential, suggesting a potential governing cluster-H bonding that has some square-well character consistent with the hydrogen nucleus behaving as a metal atom in the cluster core. Complexing this cluster with very weak bases reveals a redshift of 37 cm-1 in the Au-H vibration, consistent with those typically seen for moderately acidic groups in gas phase molecules and providing an estimate of the acidity of Au9 (PPh3 )8 H2+ , at least with regard to its surface reactivity.
Collapse
Affiliation(s)
- Hanna Morales Hernández
- Department of Chemistry, Stony Brook University, 100 Nicolls Rd., Stony Brook, NY 11794, USA
| | - Qiwei Sun
- Department of Chemistry, Brandeis University, 415 South St., Waltham, MA 02453, USA
| | - Matthew Rosati
- Department of Chemistry, Stony Brook University, 100 Nicolls Rd., Stony Brook, NY 11794, USA
| | | | - Christopher J Johnson
- Department of Chemistry, Stony Brook University, 100 Nicolls Rd., Stony Brook, NY 11794, USA
| |
Collapse
|
7
|
Akasaka K, Hirata K, Haddad F, Dopfer O, Ishiuchi SI, Fujii M. Hydration-induced protomer switching in p-aminobenzoic acid studied by cold double ion trap infrared spectroscopy. Phys Chem Chem Phys 2023; 25:4481-4488. [PMID: 36514975 DOI: 10.1039/d2cp04497h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Para-Aminobenzoic acid (PABA) is a benchmark molecule to study solvent-induced proton site switching. Protonation of the carboxy and amino groups of PABA generates O- and N-protomers of PABAH+, respectively. Ion mobility mass spectrometry (IMS) and infrared photodissociation (IRPD) studies have claimed that the O-protomer most stable in the gas phase is converted to the N-protomer most stable in solution upon hydration with six water molecules in the gas-phase cluster. However, the threshold size has remained ambiguous because the arrival time distributions in the IMS experiments exhibit multiple peaks. On the other hand, IRPD spectroscopy could not detect the N-protomer for smaller hydrated clusters because of broad background due to annealing required to reduce kinetic trapping. Herein, we report the threshold size for O → N protomer switching without ambiguity using IR spectroscopy in a double ion trap spectrometer from 1300 to 1800 cm-1. The pure O-protomer is prepared by electrospray, and size-specific hydrated clusters are formed in a reaction ion trap. The resulting clusters are transferred into a second cryogenic ion trap and the distribution of O- and N-protomers is determined by mid-IR spectroscopy without broadening. The threshold to promote O → N protomer switching is indeed five water molecules. It is smaller than the value reported previously, and as a result, its pentahydrated structure does not support the Grotthuss mechanism proposed previously. The extent of O → N proton transfer is evaluated by collision-assisted stripping IR spectroscopy, and the N-protomer population increases with the number of water molecules. This result is consistent with the dominant population of the N-protomer in aqueous solution.
Collapse
Affiliation(s)
- Kyota Akasaka
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan. .,School of Life Science and Technology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa, 226-8503, Japan
| | - Keisuke Hirata
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan. .,Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.,International Research Frontiers Initiative, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan.
| | - Fuad Haddad
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany
| | - Otto Dopfer
- International Research Frontiers Initiative, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan. .,Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany
| | - Shun-Ichi Ishiuchi
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan. .,Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.,International Research Frontiers Initiative, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan.
| | - Masaaki Fujii
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan. .,School of Life Science and Technology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa, 226-8503, Japan.,International Research Frontiers Initiative, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan.
| |
Collapse
|
8
|
Fu D, Habtegabir SG, Wang H, Feng S, Han Y. Understanding of protomers/deprotomers by combining mass spectrometry and computation. Anal Bioanal Chem 2023:10.1007/s00216-023-04574-1. [PMID: 36737499 DOI: 10.1007/s00216-023-04574-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 01/19/2023] [Accepted: 01/27/2023] [Indexed: 02/05/2023]
Abstract
Multifunctional compounds may form different prototropic isomers under different conditions, which are known as protomers/deprotomers. In biological systems, these protomer/deprotomer isomers affect the interaction modes and conformational landscape between compounds and enzymes and thus present different biological activities. Study on protomers/deprotomers is essentially the study on the acidity/basicity of each intramolecular functional group and its effect on molecular structure. In recent years, the combination of mass spectrometry (MS) and computational chemistry has been proven to be a powerful and effective means to study prototropic isomers. MS-based technologies are developed to discriminate and characterize protomers/deprotomers to provide structural information and monitor transformations, showing great superiority than other experimental methods. Computational chemistry is used to predict the thermodynamic stability of protomers/deprotomers, provide the simulated MS/MS spectra, infrared spectra, and calculate collision cross-section values. By comparing the theoretical data with the corresponding experimental results, the researchers can not only determine the protomer/deprotomer structure, but also investigate the structure-activity relationship in a given system. This review covers various MS methods and theoretical calculations and their devotion to isomer discrimination, structure identification, conformational transformation, and phase transition investigation of protomers/deprotomers.
Collapse
Affiliation(s)
- Dali Fu
- State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum-Beijing, Beijing, 102249, People's Republic of China
| | - Sara Girmay Habtegabir
- State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum-Beijing, Beijing, 102249, People's Republic of China
| | - Haodong Wang
- State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum-Beijing, Beijing, 102249, People's Republic of China
| | - Shijie Feng
- State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum-Beijing, Beijing, 102249, People's Republic of China
| | - Yehua Han
- State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum-Beijing, Beijing, 102249, People's Republic of China.
| |
Collapse
|
9
|
Tammiku-Taul J, Burk P. Nonempirical Prediction of the Relative Electrospray Ionization Efficiencies of Nitroanilines by Combined CBS-QB3 and SCC-DFTB Calculations. J Phys Chem A 2022; 126:8939-8944. [DOI: 10.1021/acs.jpca.2c05420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Jaana Tammiku-Taul
- Institute of Chemistry, University of Tartu, Ravila 14A, Tartu 50411, Estonia
| | - Peeter Burk
- Institute of Chemistry, University of Tartu, Ravila 14A, Tartu 50411, Estonia
| |
Collapse
|
10
|
Sherman SL, Fischer KC, Garand E. Conformational Changes Induced by Methyl Side-Chains in Protonated Tripeptides Containing Glycine and Alanine Residues. J Phys Chem A 2022; 126:4036-4045. [PMID: 35700447 DOI: 10.1021/acs.jpca.2c02584] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
We present a systematic study of the conformational and isomeric populations in gas-phase protonated tripeptides containing glycine and alanine residues using infrared predissociation spectroscopy of cryogenically cooled ions. Specifically, the protonated forms of Gly-Gly-Gly, Ala-Gly-Gly, Gly-Ala-Gly, Gly-Gly-Ala, Ala-Ala-Gly, Ala-Gly-Ala, Gly-Ala-Ala, and Ala-Ala-Ala allow us to sample all permutations of the methyl side-chain position, providing a comprehensive view of the effects of this simple side-chain on the 3-D structure of the peptide. The individual structural populations for all but one of these peptide species are determined via conformer-specific IR-IR double-resonance spectroscopy and comparison with electronic structure predictions. The observed structures can be classified into three main families defined by the protonation site and the number of internal hydrogen bonds. The relative contribution of each structural family is highly dependent on the exact amino acid sequence of the tripeptide. These observed changes in structural population can be rationalized in terms of the electron-donating effect of the methyl side-chain modulating the local proton affinities of the amine and various carbonyl groups in the tripeptide.
Collapse
Affiliation(s)
- Summer L Sherman
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Kaitlyn C Fischer
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Etienne Garand
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| |
Collapse
|
11
|
George MAR, Dopfer O. Infrared spectra and structures of protonated amantadine isomers: detection of ammonium and open-cage iminium ions. Phys Chem Chem Phys 2022; 24:16101-16111. [PMID: 35748364 DOI: 10.1039/d2cp01947g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The protonated form of amantadine (1-C10H15NH2, Ama), the amino derivative of adamantane (C10H16, Ada), is a wide-spread antiviral and anti-Parkinsonian drug and plays a key role in many pharmaceutical processes. Recent studies reveal that the adamantyl cage (C10H15) of Ama can open upon ionization leading to distonic bicyclic iminium isomers, in addition to the canonical nascent Ama+ isomer. Herein, we study protonation of Ama using infrared photodissociation spectroscopy (IRPD) of Ar-tagged ions and density functional theory calculations to characterize cage and open-cage isomers of AmaH+ and the influence of the electron-donating NH2 group on the cage-opening reaction potential. In addition to the canonical ammonium isomer (AmaH+(I)) with an intact adamantyl cage, we identify at least one slightly less stable protonated bicyclic iminium ion (AmaH+(II)). While the ammonium ion is generated by protonation of the basic NH2 group, AmaH+(II) is formally formed by H addition to a distonic bicyclic iminium ion produced upon ionization of Ama and subsequent cage opening.
Collapse
Affiliation(s)
| | - Otto Dopfer
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany.
| |
Collapse
|
12
|
Stropoli SJ, Khuu T, Messinger JP, Karimova NV, Boyer MA, Zakai I, Mitra S, Lachowicz AL, Yang N, Edington SC, Gerber RB, McCoy AB, Johnson MA. Preparation and Characterization of the Halogen-Bonding Motif in the Isolated Cl -·IOH Complex with Cryogenic Ion Vibrational Spectroscopy. J Phys Chem Lett 2022; 13:2750-2756. [PMID: 35315676 DOI: 10.1021/acs.jpclett.2c00218] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
In the presence of a halide ion, hypohalous acids can adopt two binding motifs upon formation of the ion-molecule complexes [XHOY]- (X, Y = Cl, Br, I): a hydrogen (HB) bond to the acid OH group and a halogen (XB) bond between the anion and the acid halogen. Here we isolate the X-bonded Cl-·IOH ion-molecule complex by collisions of I-·(H2O)n clusters with HOCl vapor and measure its vibrational spectrum by IR photodissociation of the H2-tagged complex. Anharmonic analysis of its vibrational band pattern reveals that formation of the XB complex results in dramatic lowering of the HOI bending fundamental frequency and elongation of the O-I bond (by 168 cm-1 and 0.13 Å, respectively, relative to isolated HOI). The frequency of the O-I stretch (estimated 436 cm-1) is also encoded in the spectrum by the weak v = 0 → 2 overtone transition at 872 cm-1.
Collapse
Affiliation(s)
- Santino J Stropoli
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Thien Khuu
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Joseph P Messinger
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Natalia V Karimova
- Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States
| | - Mark A Boyer
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Itai Zakai
- Institute of Chemistry and the Fritz-Haber Center for Molecular Dynamics, The Hebrew University, Jerusalem 91905, Israel
| | - Sayoni Mitra
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Anton L Lachowicz
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Nan Yang
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Sean C Edington
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - R Benny Gerber
- Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States
- Institute of Chemistry and the Fritz-Haber Center for Molecular Dynamics, The Hebrew University, Jerusalem 91905, Israel
| | - Anne B McCoy
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Mark A Johnson
- Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| |
Collapse
|
13
|
Greis K, Kirschbaum C, Fittolani G, Mucha E, Chang R, von Helden G, Meijer G, Delbianco M, Seeberger PH, Pagel K. Neighboring Group Participation of Benzoyl Protecting Groups in C3‐ and C6‐Fluorinated Glucose. European J Org Chem 2022; 2022:e202200255. [PMID: 35915640 PMCID: PMC9321577 DOI: 10.1002/ejoc.202200255] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 03/23/2022] [Indexed: 11/17/2022]
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.
Collapse
Affiliation(s)
- Kim Greis
- Freie Universität Berlin: Freie Universitat Berlin BCP GERMANY
| | | | - Giulio Fittolani
- Max Planck Institute of Colloids and Interfaces: Max-Planck-Institut fur Kolloid und Grenzflachenforschung Carbohydrate Materials GERMANY
| | - Eike Mucha
- Fritz-Haber-Institut der MPG Berlin: Fritz-Haber-Institut der Max-Planck-Gesellschaft MP GERMANY
| | - Rayoon Chang
- Freie Universität Berlin: Freie Universitat Berlin BCP GERMANY
| | - Gert von Helden
- Fritz-Haber-Institut der MPG Berlin: Fritz-Haber-Institut der Max-Planck-Gesellschaft MP GERMANY
| | - Gerard Meijer
- Fritz Haber Institut der Max-Planck-Gesellschaft: Fritz-Haber-Institut der Max-Planck-Gesellschaft MP GERMANY
| | - Martina Delbianco
- Max Planck Institute of Colloids and Interfaces: Max-Planck-Institut fur Kolloid und Grenzflachenforschung Carbohydrate Materials GERMANY
| | - Peter H. Seeberger
- Max Planck Institute of Colloids and Interfaces: Max-Planck-Institut fur Kolloid und Grenzflachenforschung Biomolecular Systems GERMANY
| | - Kevin Pagel
- Freie Universitat Berlin Institute of Chemistry and Biochemistry Arnimallee 22 14195 Berlin GERMANY
| |
Collapse
|
14
|
Kwasigroch B, Khuu T, Perez EH, Denton JK, Schneider EK, Straßner A, Theisen M, Kruppa SV, Weis P, Kappes MM, Riehn C, Johnson MA, Niedner-Schatteburg G. On the Hydrogen Oxalate Binding Motifs onto Dinuclear Cu and Ag Metal Phosphine Complexes. Chemistry 2021; 27:15136-15146. [PMID: 34632659 PMCID: PMC8597048 DOI: 10.1002/chem.202102768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Indexed: 11/23/2022]
Abstract
We report the binding geometries of the isomers that are formed when the hydrogen oxalate ((CO2)2H=HOx) anion attaches to dinuclear coinage metal phosphine complexes of the form [M1M2dcpm2(HOx)]+ with M=Cu, Ag and dcpm=bis(dicyclohexylphosphino)methane, abbreviated [MM]+. These structures are established by comparison of isomer‐selective experimental vibrational band patterns displayed by the cryogenically cooled and N2‐tagged cations with DFT calculations of the predicted spectra for various local minima. Two isomeric classes are identified that feature either attachment of the carboxylate oxygen atoms to the two metal centers (end‐on docking) or attachment of oxygen atoms on different carbon atoms asymmetrically to the metal ions (side‐on docking). Within each class, there are additional isomeric variations according to the orientation of the OH group. This behavior indicates that HOx undergoes strong and directional coordination to [CuCu]+ but adopts a more flexible coordination to [AgAg]+. Infrared spectra of the bare ions, fragmentation thresholds and ion mobility measurements are reported to explore the behaviors of the complexes at ambient temperature.
Collapse
Affiliation(s)
- Björn Kwasigroch
- Department of Chemistry, Technische Universität Kaiserslautern (TUK), Erwin-Schrödinger-Str. 52, 67663, Kaiserslautern, Germany
| | - Thien Khuu
- Sterling Chemistry Laboratory, Yale University, 225 Prospect Str., New Haven, Connecticut, 06520, USA
| | - Evan H Perez
- Sterling Chemistry Laboratory, Yale University, 225 Prospect Str., New Haven, Connecticut, 06520, USA
| | - Joanna K Denton
- Sterling Chemistry Laboratory, Yale University, 225 Prospect Str., New Haven, Connecticut, 06520, USA
| | - Erik K Schneider
- Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT), Fritz-Haber Weg 2, 76131, Karlsruhe, Germany
| | - Annika Straßner
- Department of Chemistry, Technische Universität Kaiserslautern (TUK), Erwin-Schrödinger-Str. 52, 67663, Kaiserslautern, Germany
| | - Marvin Theisen
- Department of Chemistry, Technische Universität Kaiserslautern (TUK), Erwin-Schrödinger-Str. 52, 67663, Kaiserslautern, Germany
| | - Sebastian V Kruppa
- Department of Chemistry, Technische Universität Kaiserslautern (TUK), Erwin-Schrödinger-Str. 52, 67663, Kaiserslautern, Germany
| | - Patrick Weis
- Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT), Fritz-Haber Weg 2, 76131, Karlsruhe, Germany
| | - Manfred M Kappes
- Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT), Fritz-Haber Weg 2, 76131, Karlsruhe, Germany.,Institute for Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
| | - Christoph Riehn
- Department of Chemistry, Technische Universität Kaiserslautern (TUK), Erwin-Schrödinger-Str. 52, 67663, Kaiserslautern, Germany.,Research Center OPTIMAS, Erwin-Schrödinger Str. 46, 67663, Kaiserslautern, Germany
| | - Mark A Johnson
- Sterling Chemistry Laboratory, Yale University, 225 Prospect Str., New Haven, Connecticut, 06520, USA
| | - Gereon Niedner-Schatteburg
- Department of Chemistry, Technische Universität Kaiserslautern (TUK), Erwin-Schrödinger-Str. 52, 67663, Kaiserslautern, Germany.,Research Center OPTIMAS, Erwin-Schrödinger Str. 46, 67663, Kaiserslautern, Germany
| |
Collapse
|
15
|
Batista PR, Penna TC, Ducati LC, Correra TC. p-Aminobenzoic acid protonation dynamics in an evaporating droplet by ab initio molecular dynamics. Phys Chem Chem Phys 2021; 23:19659-19672. [PMID: 34524295 DOI: 10.1039/d1cp01495a] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Protonation equilibria are known to vary from the bulk to microdroplet conditions, which could induce many chemical and physical phenomena. Protonated p-aminobenzoic acid (PABA + H+) can be considered a model for probing the protonation dynamics in an evaporating droplet, as its protonation equilibrium is highly dependent on the formation conditions from solution via atmospheric pressure ionization sources. Experiments using diverse experimental techniques have shown that protic solvents allow formation of the O-protomer (PABA protonated in the carboxylic acid group) stable in the gas phase, while aprotic solvents yield the N-protomer (protonated in the amino group) that is the most stable protomer in solution. In this work, we explore the protonation equilibrium of PABA solvated by different numbers of water molecules (n = 0 to 32) using ab initio molecular dynamics. For n = 8-32, the protonation is either at the NH2 group or in the solvent network. The solvent network interacts with the carboxylic acid group, but there is no complete proton transfer to form the O-protomer. For smaller clusters, however, solvent-mediated proton transfers to the carboxylic acid were observed, both via the Grotthuss mechanism and the vehicle or shuttle mechanism (for n = 1 and 2). Thermodynamic considerations allowed a description of the origins of the kinetic trapping effect, which explains the observation of the solution structure in the gas phase. This effect likely occurs in the final evaporation steps, which are outside the droplet size range covered by previous classical molecular dynamics simulations of charged droplets. These results may be considered relevant in determining the nature of the species observed in the ubiquitous ESI based mass spectrometry analysis, and in general for droplet chemistry, explaining how protonation equilibria are drastically changed from bulk to microdroplet conditions.
Collapse
Affiliation(s)
- Patrick R Batista
- Department of Fundamental Chemistry, Institute of Chemistry - University of São Paulo, Av. Prof. Lineu Prestes, 748, Cidade Universitária, São Paulo, SP, Brazil.
| | - Tatiana C Penna
- Department of Fundamental Chemistry, Institute of Chemistry - University of São Paulo, Av. Prof. Lineu Prestes, 748, Cidade Universitária, São Paulo, SP, Brazil.
| | - Lucas C Ducati
- Department of Fundamental Chemistry, Institute of Chemistry - University of São Paulo, Av. Prof. Lineu Prestes, 748, Cidade Universitária, São Paulo, SP, Brazil.
| | - Thiago C Correra
- Department of Fundamental Chemistry, Institute of Chemistry - University of São Paulo, Av. Prof. Lineu Prestes, 748, Cidade Universitária, São Paulo, SP, Brazil.
| |
Collapse
|
16
|
Wong NK, Rankine CD, Dessent CEH. Measurement of the Population of Electrosprayed Deprotomers of Coumaric Acids Using UV-Vis Laser Photodissociation Spectroscopy. J Phys Chem A 2021; 125:6703-6714. [PMID: 34342453 PMCID: PMC8389988 DOI: 10.1021/acs.jpca.1c04880] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 07/08/2021] [Indexed: 01/05/2023]
Abstract
The measurement of deprotonation sites in multifunctional molecules following electrospray ionization is important to better inform a wide range of spectroscopic and photophysical studies that use electrospray to prepare molecular species for study in the gas phase. We demonstrate that low-resolution UV-vis laser photodissociation spectroscopy can be applied in situ to identify the deprotomers of three coumaric acids, trans-para-coumaric acid (CMA), trans-caffeic acid (CA), and trans-ferulic acid (FA), formed via electrospray. Electronic absorption spectra of the deprotonated coumaric acids are recorded via photodepletion and photofragmentation following electrospray from solutions of ethanol and acetonitrile. By comparing the experimental spectra to wave function theory calculations, we are able to confirm the presence of phenoxide and carboxylate deprotomers upon electrospray for all three coumaric acids, when sprayed from both protic and aprotic solvents. Ratios of the phenoxide:carboxylate deprotomers are obtained by generating summed theoretical absorption spectra that reproduce the experimental spectra. We find that choice of electrospray solvent has little effect on the ratio of deprotomers obtained for deprotonated CMA and CA but has a greater impact for FA. Our results are in excellent agreement with previous work conducted on deprotonated CMA using IR spectroscopy and demonstrate that UV photodissociation spectroscopy of electrosprayed ions has potential as a diagnostic tool for identifying deprotomeric species.
Collapse
Affiliation(s)
- Natalie
G. K. Wong
- Department
of Chemistry, University of York, Heslington, York YO10 5DD, U.K.
| | - Conor D. Rankine
- School
of Natural and Environmental Sciences, Newcastle
University, Newcastle-upon-Tyne NE1 7RU, U.K.
| | | |
Collapse
|
17
|
Gorbachev VM, Miloglyadova L, Tsybizova A, Chen P. Application of continuous wave quantum cascade laser in combination with CIVP spectroscopy for investigation of large organic and organometallic ions. Rev Sci Instrum 2021; 92:083002. [PMID: 34470415 DOI: 10.1063/5.0058625] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Accepted: 07/24/2021] [Indexed: 06/13/2023]
Abstract
Rapidly developing mid-infrared quantum cascade laser (QCL) technology gives easy access to broadly tunable mid-IR laser radiation at a modest cost. Despite several applications of QCL in the industry, its usage for spectroscopic investigation of synthetically relevant organic compounds has been limited. Here, we report the application of an external cavity, continuous wave, mid-IR QCL to cryogenic ion vibrational predissociation spectroscopy to analyze a set of large organic molecules, organometallic complexes, and isotopically labeled compounds. The obtained spectra of test molecules are characterized by a high signal-to-noise ratio and low full width at half-maximum-values, allowing the assignment of two compounds with just a few wavenumber difference. Data generated by cw-QCL and spectra produced by another standard Nd:YAG difference-frequency generation system are compared and discussed.
Collapse
Affiliation(s)
| | | | | | - Peter Chen
- Laboratorium für Organische Chemie, ETH Zürich, CH-8093 Zürich, Switzerland
| |
Collapse
|
18
|
Murashima H, Fujihara A. Gas-Phase Adsorption of N 2 on Protonated Molecules and Its Application to the Structural Elucidation of Small Molecules. Mass Spectrom (Tokyo) 2021; 10:A0096. [PMID: 34136324 PMCID: PMC8188007 DOI: 10.5702/massspectrometry.a0096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 04/21/2021] [Indexed: 11/23/2022] Open
Abstract
The gas-phase adsorption of N2 on protonated serine (Ser, C3H7NO3), threonine (Thr, C4H9NO3), glycine (Gly, C2H5NO2), and 2-aminoethanol (C2H7NO) was investigated using a tandem mass spectrometer equipped with an electrospray ionization source and a cold ion trap. N2 molecules were adsorbed on the free X–H (X=O and N) groups of protonated molecules. Gas-phase N2 adsorption-mass spectrometry detected the presence of free X–H groups in the molecular structures, and was applied to the structural elucidation of small molecules. When the 93 structures with an elemental composition of C3H7NO3 were filtered using the gas-phase N2 adsorption-mass spectrometry results for Ser, the number of possible molecular structures was reduced to 8 via the quantification of the X–H groups. Restricting and minimizing the number of possible candidates were effective steps in the structural elucidation process. Gas-phase N2 adsorption-mass spectrometry combined with mass spectrometry-based techniques has the potential for being useful for elucidating the molecular structures of a variety of molecules.
Collapse
Affiliation(s)
- Hiromori Murashima
- Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Osaka 599-8531, Japan
| | - Akimasa Fujihara
- Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Osaka 599-8531, Japan
| |
Collapse
|