International Journal of Molecular Sciences

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12 pages, 3368 KiB

Open AccessArticle

Structural Characterization of the Metalized Radical Cations of Adenosine ([Ade+Li-H]^•+ and [Ade+Na-H]^•+) by Infrared Multiphoton Dissociation Spectroscopy and Theoretical Studies

by Min Kou, Luyang Jiao, Shiyin Xu, Mengying Du, Yameng Hou and Xianglei Kong

Int. J. Mol. Sci. 2023, 24(20), 15385; https://doi.org/10.3390/ijms242015385 - 20 Oct 2023

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Abstract

Nucleoside radicals are key intermediates in the process of DNA damage, and alkali metal ions are a common group of ions in living organisms. However, so far, there has been a significant lack of research on the structural effects of alkali metal ions [...] Read more.

Nucleoside radicals are key intermediates in the process of DNA damage, and alkali metal ions are a common group of ions in living organisms. However, so far, there has been a significant lack of research on the structural effects of alkali metal ions on nucleoside free radicals. In this study, we report a new method for generating metalized nucleoside radical cations in the gas phase. The radical cations [Ade+M-H]^•+ (M = Li, Na) are generated by the 280 nm ultraviolet photodissociation (UVPD) of the precursor ions of lithiated and sodiated ions of 2-iodoadenine in a Fourier transform ion cyclotron resonance (FT ICR) cell. Further infrared multiphoton dissociation (IRMPD) spectra of both radical cations were recorded in the region of 2750–3750 cm⁻¹. By combining these results with theoretical calculations, the most stable isomers of both radicals can be identified, which share the common characteristics of triple coordination patterns of the metal ions. For both radical species, the lowest-energy isomers undergo hydrogen transfer. Although the sugar ring in the most stable isomer of [Ade+Li-H]^•+ is in a (South, syn) conformation similar to that of [Ado+Na]⁺, [Ade+Na-H]^•+ is distinguished by the unexpected opening of the sugar ring. Their theoretical spectra are in good agreement with experimental spectra. However, due to the flexibility of the structures and the complexity of their potential energy surfaces, the hydrogen transfer pathways still need to be further studied. Considering that the free radicals formed directly after C-I cleavage have some similar spectral characteristics, the existence of these corresponding isomers cannot be ruled out. The findings imply that the structures of nucleoside radicals may be significantly influenced by the attached alkali metal ions. More detailed experiments and theoretical calculations are still crucial. Full article

(This article belongs to the Special Issue Gas-Phase Transformations: The Mechanisms and Guidances)

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24 pages, 5027 KiB

Open AccessArticle

Activation of Ethanol Transformation on Copper-Containing SBA-15 and MnSBA-15 Catalysts by the Presence of Oxygen in the Reaction Mixture

by Izabela Sobczak, Joanna Wisniewska, Piotr Decyk, Maciej Trejda and Maria Ziolek

Int. J. Mol. Sci. 2023, 24(3), 2252; https://doi.org/10.3390/ijms24032252 - 23 Jan 2023

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Abstract

The aim of this study was to get insight into the pathway of the acetaldehyde formation from ethanol (the rate-limiting step in the production of 1,3-butadiene) on Cu-SBA-15 and Cu-MnSBA-15 mesoporous molecular sieves. Physicochemical properties of the catalysts were investigated by XRD, N [...] Read more.

The aim of this study was to get insight into the pathway of the acetaldehyde formation from ethanol (the rate-limiting step in the production of 1,3-butadiene) on Cu-SBA-15 and Cu-MnSBA-15 mesoporous molecular sieves. Physicochemical properties of the catalysts were investigated by XRD, N₂ ads/des, Uv-vis, XPS, EPR, pyridine adsorption combined with FTIR, 2-propanol decomposition and 2,5-hexanedione cyclization and dehydration test reactions. Ethanol dehydrogenation to acetaldehyde (without and with oxygen) was studied in a flow system using the FTIR technique. In particular, the effect of Lewis acid and basic (Lewis and BrØnsted) sites, and the oxygen presence in the gas reaction mixture with ethanol on the activity and selectivity of copper catalysts, was assessed and discussed. Two different reaction pathways have been proposed depending on the reaction temperature and the presence or absence of oxygen in the flow of the reagents (via ethoxy intermediate way at 593 K, in ethanol flow, or ethoxide intermediate way at 473 K in the presence of ethanol and oxygen in the reaction mixture). Full article

(This article belongs to the Special Issue Gas-Phase Transformations: The Mechanisms and Guidances)

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Review

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23 pages, 3163 KiB

Open AccessReview

Gas Phase Transformations in Carbon-11 Chemistry

by Shuiyu Lu, Sanjay Telu, Fabrice G. Siméon, Lisheng Cai and Victor W. Pike

Int. J. Mol. Sci. 2024, 25(2), 1167; https://doi.org/10.3390/ijms25021167 - 18 Jan 2024

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Abstract

The short-lived positron-emitter carbon-11 (t_1/2 = 20.4 min; β⁺, 99.8%) is prominent for labeling tracers for use in biomedical research with positron emission tomography (PET). Carbon-11 is produced for this purpose with a cyclotron, nowadays almost exclusively by the [...] Read more.

The short-lived positron-emitter carbon-11 (t_1/2 = 20.4 min; β⁺, 99.8%) is prominent for labeling tracers for use in biomedical research with positron emission tomography (PET). Carbon-11 is produced for this purpose with a cyclotron, nowadays almost exclusively by the ¹⁴N(p,α)¹¹C nuclear reaction, either on nitrogen containing a low concentration of oxygen (0.1–0.5%) or hydrogen (~5%) to produce [¹¹C]carbon dioxide or [¹¹C]methane, respectively. These primary radioactive products can be produced in high yields and with high molar activities. However, only [¹¹C]carbon dioxide has some utility for directly labeling PET tracers. Primary products are required to be converted rapidly and efficiently into secondary labeling synthons to provide versatile radiochemistry for labeling diverse tracer chemotypes at molecular positions of choice. This review surveys known gas phase transformations of carbon-11 and summarizes the important roles that many of these transformations now play for producing a broad range of labeling synthons in carbon-11 chemistry. Full article

(This article belongs to the Special Issue Gas-Phase Transformations: The Mechanisms and Guidances)

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