Infrared multiple photon dissociation （IRMPD） spectroscopic and theoretical studies of protonated homodimers of amino acids generated by electrospray ionization in the gas phase have been reviewed. Results show that...Infrared multiple photon dissociation （IRMPD） spectroscopic and theoretical studies of protonated homodimers of amino acids generated by electrospray ionization in the gas phase have been reviewed. Results show that proton affinity （PA） may be applied as a probe to predict their structural type： salt- bridged or charge-solvated. Proline can be viewed as a reference. For an amino acid with a PA value higher than that of proline, the most stable conformation of its protonated homodimer tends to prefer salt- bridged conformation; otherwise, charge-solvated conformation is expected to be the most stable. However, side chain effects may cause the inaccuracy in structural determination due to the strong interactions with the charge, which makes the charge-solvated structure more stable even for species with high PA values. Temperature effect on distribution of different isomers is also very important. In lots of cases, the coexistence of multiple isomers is general, which makes the explanation of an overall IRMPD spectrum difficult. So a statistical view on the distribution of optimized isomers is very helpful.展开更多
It is well-known that nucleoside-derived radicals play crucial roles in cellular activity.However,due to the instability of the radicals and their widespread isomerization,experimental research on their generation and...It is well-known that nucleoside-derived radicals play crucial roles in cellular activity.However,due to the instability of the radicals and their widespread isomerization,experimental research on their generation and structural characterization has been a challenge for a long time.Herein,we provide a unique approach to selectively generate the isomers of nucleoside radicals in the gas phase.Through the process of ultraviolet photodissociation(UVPD)at 285 and 245 nm,we were able to selectively produce O_(2) and C5 isomers of cytidine radicals from a single precursor ion of protonated 5-I-cytidine.These radical isomers were structurally characterized by a combination of infrared multiphoton dissociation(IRMPD)spectroscopy of the mass-selected ions and systematic computations.The structural characteristics of cytidine radical isomers such as the anti/syn glycosidic link and the North/South sugar ring conformation were disclosed.The key to selectivity lay in whether the excess energy of the precursor ions after absorbing one ultraviolet photon and undergoing the homo-cleavage of the C–I bond could overcome the corresponding energy barrier of the isomerization.This method provides an effective way for the selective generation of radical isomers with rich flexibility by wavelength-regulated UVPD and reasonable introductions of C–I bonds in the precursors.展开更多
Researches in laser separation of carbon isotopes have made considerable advances as regards theory and experimental methods in the recent decade. Many working molecules, such as CCl4, CF3I, CF3Cl and CF3COCF3, have b...Researches in laser separation of carbon isotopes have made considerable advances as regards theory and experimental methods in the recent decade. Many working molecules, such as CCl4, CF3I, CF3Cl and CF3COCF3, have been studied. In 1982, Gauthier and coworkers in Canada investigated carbon isotope enrichment in the IRMPD of CF2HCl （Freon-22）.展开更多
基金supported by the National Natural Science Foundation of China(Nos.21475065,21627801 and 11704280)
文摘Infrared multiple photon dissociation （IRMPD） spectroscopic and theoretical studies of protonated homodimers of amino acids generated by electrospray ionization in the gas phase have been reviewed. Results show that proton affinity （PA） may be applied as a probe to predict their structural type： salt- bridged or charge-solvated. Proline can be viewed as a reference. For an amino acid with a PA value higher than that of proline, the most stable conformation of its protonated homodimer tends to prefer salt- bridged conformation; otherwise, charge-solvated conformation is expected to be the most stable. However, side chain effects may cause the inaccuracy in structural determination due to the strong interactions with the charge, which makes the charge-solvated structure more stable even for species with high PA values. Temperature effect on distribution of different isomers is also very important. In lots of cases, the coexistence of multiple isomers is general, which makes the explanation of an overall IRMPD spectrum difficult. So a statistical view on the distribution of optimized isomers is very helpful.
基金supported financially by the National Natural Science Foundation of China(NSFCgrant nos.22174076 and 21627801).
文摘It is well-known that nucleoside-derived radicals play crucial roles in cellular activity.However,due to the instability of the radicals and their widespread isomerization,experimental research on their generation and structural characterization has been a challenge for a long time.Herein,we provide a unique approach to selectively generate the isomers of nucleoside radicals in the gas phase.Through the process of ultraviolet photodissociation(UVPD)at 285 and 245 nm,we were able to selectively produce O_(2) and C5 isomers of cytidine radicals from a single precursor ion of protonated 5-I-cytidine.These radical isomers were structurally characterized by a combination of infrared multiphoton dissociation(IRMPD)spectroscopy of the mass-selected ions and systematic computations.The structural characteristics of cytidine radical isomers such as the anti/syn glycosidic link and the North/South sugar ring conformation were disclosed.The key to selectivity lay in whether the excess energy of the precursor ions after absorbing one ultraviolet photon and undergoing the homo-cleavage of the C–I bond could overcome the corresponding energy barrier of the isomerization.This method provides an effective way for the selective generation of radical isomers with rich flexibility by wavelength-regulated UVPD and reasonable introductions of C–I bonds in the precursors.
基金Project supported by the National Natural Science Foundation of China
文摘Researches in laser separation of carbon isotopes have made considerable advances as regards theory and experimental methods in the recent decade. Many working molecules, such as CCl4, CF3I, CF3Cl and CF3COCF3, have been studied. In 1982, Gauthier and coworkers in Canada investigated carbon isotope enrichment in the IRMPD of CF2HCl （Freon-22）.
