1 H– 14 N cross-relaxation spectrum analysis in sildenafil and sildenafil citrate
| Autor: | Tomaž Apih, A. Gregorovič, Janez Seliger |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
Nuclear and High Energy Physics
Radiation 010304 chemical physics Proton Chemistry Analytical chemistry chemistry.chemical_element General Chemistry 010402 general chemistry 01 natural sciences Nitrogen Molecular physics Homonuclear molecule 0104 chemical sciences Dipole Laser linewidth Pairing 0103 physical sciences Quadrupole Spectrum analysis Instrumentation |
| Zdroj: | Solid State Nuclear Magnetic Resonance. 78:16-23 |
| ISSN: | 0926-2040 |
| Popis: | Here we describe a method for the extraction of (14)N quadrupole parameters from a (1)H-(14)N cross-relaxation spectrum by fitting the lineshapes of the (14)N quadrupole transitions. The procedures used typically to fit quadrupole lineshapes are not directly applicable to fit the (1)H-(14)N cross-relaxation spectrum, because the presence of proton homonuclear dipolar interaction broadens the lineshapes considerably and prevents a reliable determination of Cq and η from a single lineshape. Instead, one must fit two or even three lineshapes originating from the same nitrogen site simultaneously. The problem is to identify which lineshapes belong together when many are observed due to the existence of several nitrogen sites. We solve this problem by fitting the spectrum for all possible combinations and find the best-fitting one. This combination then most likely correctly identifies lineshapes belonging to the same nitrogen site. There are two main advantages of our method compared to the typically used method, which relies only on lineshape singularities: (i) the method is "automatic" and does not require knowledge of nitrogen quadrupole parameters in similar environments to aid dip pairing and (ii) the accuracy of quadrupole parameters is better, as proton linewidth is included in the fits. We use sildenafil and sildenafil citrate as model compounds, each with six non-equivalent nitrogen sites. |
| Databáze: | OpenAIRE |
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