13C NMR studies of conformational dynamics in α-tocopherol esters in solution and solid state

Witkowski, Stanisław; Wawer, Iwona

doi:10.1039/b110734h

Cited by 10 publications

(3 citation statements)

References 14 publications

(10 reference statements)

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“…It is not very easy in general to know the population and structural details of such conformers that are equilibrated with each other in solution by using conventional spectroscopic techniques such as UV−vis, electron paramagnetic resonance (EPR), or NMR measurements. For example, the conformational dynamics of α-tocopherol in solution have recently been studied in detail by 13 C NMR spectroscopy . However, this elegant methodology cannot be applied to the radical cation species.…”

Section: Resultsmentioning

confidence: 99%

Chiroptical Properties of Organic Radical Cations. The Electronic and Vibrational Circular Dichroism Spectra of α-Tocopherol Derivatives and Sterically Hindered Chiral Hydroquinone Ethers

2004

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Qualitatively and quantitatively reliable electronic and vibrational circular dichroism (ECD and VCD) spectra of chiral organic radical cations were obtained for the first time with R-tocopherol derivatives and sterically hindered chiral hydroquinone ethers. The isolation and spectral measurements of chiral radical cation salts were made possible by using nitrosonium or antimony derivatives as electron-transfer oxidants, which can cleanly oxidize the substrate donors without giving any byproducts in the sample solution. Such reliable ECD spectra enabled us to fully examine the chiroptical properties of organic radical cations and also compare them with those of the corresponding neutral compounds. The observed VCD spectra of neutral and radical cationic species of chiral hydroquinone ether were nicely simulated by density functional theory (DFT) calculations, from which the relative contribution of each radical cation conformer in solution was evaluated. Thus, the combined synthetic, spectroscopic, and theoretical protocol, composed of chiral modification, clean oxidation to form stable radical cations, ECD/VCD spectral analyses, and DFT calculations, was demonstrated to be a powerful, indispensable tool for elucidating a comprehensive picture of radical cationic species in solution.

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Section: Resultsmentioning

confidence: 99%

Chiroptical Properties of Organic Radical Cations. The Electronic and Vibrational Circular Dichroism Spectra of α-Tocopherol Derivatives and Sterically Hindered Chiral Hydroquinone Ethers

2004

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“…The conformational and dynamic effects occurring in chroman derivatives have recently been discussed elsewhere. 22 The stereochemistry of the chiral centers of flavanones and isoflavanones is a matter which has received considerable attention and is still a challenge in structural chemistry. 23 In our calculations, for 1a we assumed S absolute configuration at the C2 chiral center by analogy with other flavanones with known stereochemistry.…”

Section: Dft Giao Calculationsmentioning

confidence: 99%

Structural studies of 2-(3′,4′-dihydroxyphenyl)-7-β-D-glucopyranos-1-O-yl-8-hydroxychroman-4-one in the liquid and solid states by means of 2D NMR spectroscopy and DFT calculations

Olejniczak

Ganicz

Tomczykowa

et al. 2002

J. Chem. Soc., Perkin Trans. 2

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Homo-and heteronuclear correlated spectroscopy in the liquid phase and the PASS-2D NMR technique in the solid state were applied to the identification and structural studies of the flavanone 2-(3Ј,4Ј-dihydroxyphenyl)-7-β-glucopyranos-1-O-yl-8-hydroxychroman-4-one 1. The principal elements of the 13 C chemical shift tensor were established and verified by DFT GIAO calculations. Analysis of the 13 C δ ii and comparison with the theoretical shielding parameters calculated for different conformers of 1 in a vacuum were carried out to choose the most reliable geometry in the solid state.

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“…The Gibbs free energy of the activation (Δ G # ) of the process was successfully achieved using 13 C NMR techniques in a solution [ 13 , 14 ] and solid state [ 8 , 15 , 16 ]. The resulting data regarding the α-tocopherol nicotinate, acetate and succinate indicated that for interconverted methyl groups (2a and 2b) the coalescence temperature ( T c ) occurs at 304, 296 and 288K with Δ G # values of 62.6, 61.0 and 58.0 kJ mol −1 , respectively [ 17 ]. In the case of chromanol-6-ol acetate, the calculated values were slightly lower and reached T c = 293K and Δ G # = 59.5 kJ mol −1 [ 12 , 14 ].…”

Section: Introductionmentioning

confidence: 99%

13C CP MAS NMR and DFT Studies of 6-Chromanyl Ethereal Derivatives

et al. 2022

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Vitamin E consists of a group of compounds including α- β- γ- and δ-tocopherols and α- β- γ- and δ-tocotrienols, containing the chroman-6-ol system. The recognition of the structural and dynamic properties of this system, present in all vitamers, seems to be important for the full explanation of the mechanism of the biological activity of vitamin E. This paper presents results of the structural analysis of the chosen 6-chromanyl ethereal derivatives using experimental (13 C NMR-in solution and solid state, as well as variable temperature experiments; single crystal X-ray diffraction) and theoretical (DFT) methods. For one of the studied compounds, 2,2,5,7,8-pentamethyl-6-((tetrahydro-2H-pyran-2-yl)oxy) chroman, the splitting of some signals was observed in the 13C dynamic NMR spectra. This observation was explained by the application of a conformational analysis and subsequent DFT optimization, followed by the calculation of NMR properties.

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13C NMR studies of conformational dynamics in α-tocopherol esters in solution and solid state

Cited by 10 publications

References 14 publications

Chiroptical Properties of Organic Radical Cations. The Electronic and Vibrational Circular Dichroism Spectra of α-Tocopherol Derivatives and Sterically Hindered Chiral Hydroquinone Ethers

Chiroptical Properties of Organic Radical Cations. The Electronic and Vibrational Circular Dichroism Spectra of α-Tocopherol Derivatives and Sterically Hindered Chiral Hydroquinone Ethers

Structural studies of 2-(3′,4′-dihydroxyphenyl)-7-β-D-glucopyranos-1-O-yl-8-hydroxychroman-4-one in the liquid and solid states by means of 2D NMR spectroscopy and DFT calculations

13C CP MAS NMR and DFT Studies of 6-Chromanyl Ethereal Derivatives

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