Near-IR laser-induced and spontaneous conformational transformations in monomers of 9-methylhypoxanthine.
This study reveals how UV and near-infrared light can induce specific conformational changes in 9-methylhypoxanthine, but its physiological relevance remains unclear.
Where it sits
this study against the rest of the cerebrolysin corpusSummary and findings
The study investigates the conformational transformations of 9-methylhypoxanthine monomers in low-temperature Ar and Ne matrices. UV light converts the oxo tautomer into the hydroxy form, which exists in two conformers. Near-infrared light selectively interconverts these hydroxy conformers.
Abstract
Monomers of 9-methylhypoxanthine isolated in low-temperature Ar and Ne matrices adopt nearly exclusively the oxo tautomeric form. Upon excitation with UV (λ = 278 nm) light, the oxo tautomer converts into the hydroxy form. There are two conformational structures of the hydroxy tautomer of 9-methylhypoxanthine. These conformers differ in the orientation of the OH group, with the hydrogen atom pointing either toward the N1 or toward the N7 atom of the purine frame. We have demonstrated that, upon irradiation with narrowband near-infrared light tuned to the spectral position of the 2νOH overtone absorption, the two hydroxy conformers can be selectively converted into each other. Exposure of the matrix to the broadband mid-infrared and near-infrared radiation also results in conformational transformations involving the two OH rotamers. Finally, when the matrix is kept in the dark and at low temperature, the higher-energy hydroxy conformer (with OH group oriented toward the N7 atom) spontaneously converts into the lower-energy counterpart (with OH group oriented toward the N1 atom). The last process must be governed by the H-atom tunneling. The above isomerizations enabled the reliable separation and assignment of the infrared spectra of the two hydroxy conformers. The presence of multiple isosbestic points is a strong evidence that the observed transformations involve only the two OH rotamers. Interpretation of the experimental observations was supported by theoretical prediction of infrared spectra and calculations of isomerization barriers.
Background
This study addresses the conformational dynamics of 9-methylhypoxanthine, a derivative of hypoxanthine, which is relevant for understanding tautomeric shifts in nucleic acid components. Prior research has focused on tautomeric forms in biological systems, but this study explores these transformations under controlled spectroscopic conditions. Understanding these shifts is crucial for insights into molecular stability and reactivity.
Methods
The study used low-temperature argon and neon matrices to isolate 9-methylhypoxanthine monomers. UV light at 278 nm was used to convert the oxo tautomer to the hydroxy form. Near-infrared light was applied to selectively interconvert the hydroxy conformers. Spectroscopic analysis and theoretical predictions supported the observations.
Results
Upon UV excitation, the oxo tautomer converted to the hydroxy form, which exists in two conformers distinguished by OH orientation. Near-infrared light facilitated selective interconversion between these conformers. Spontaneous conversion from the higher-energy to the lower-energy hydroxy conformer occurred in the dark, suggesting H-atom tunneling. Isosbestic points confirmed the involvement of only the two OH rotamers.
Interpretation
The study provides detailed insights into the conformational dynamics of 9-methylhypoxanthine under specific conditions. While the transformations were significant, they were observed in a non-biological setting, limiting direct clinical relevance. The findings align with theoretical predictions, but the lack of biological context suggests limited immediate applicability to human health.
Key findings
- UV light at 278 nm converts oxo tautomer to hydroxy form.
- Two hydroxy conformers differ by OH orientation toward N1 or N7.
- Near-IR light tuned to 2νOH overtone selectively interconverts hydroxy conformers.
- Spontaneous conversion from N7 to N1 orientation occurs in the dark at low temperature.
- Isosbestic points indicate transformations involve only the two OH rotamers.
Limitations
- Conducted in low-temperature matrices.
- Non-biological setting.
- Based on spectroscopic analysis.
- Theoretical predictions used.
- No biological assays conducted.