New insights into the photo-tautomerisation process in β-carboline derivatives revealed by NMR spectroscopy

Reyman, D.; Díaz-Oliva, Cristina; Hallwass, Fernando; Gonçalves, Simone M. C.

doi:10.1039/c1ra00205h

Cited by 5 publications

(4 citation statements)

References 56 publications

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“…On the other hand, the chemical shifts experienced by the HAR hydrogens were greater than those shown for β-CD due to the higher solubility of β-CD in the medium studied. The behavior observed was similar to that shown by HAR in the presence of a hydrogen donor: , H 3 , H 4 , and H 5 (assigned by COSY) were the HAR hydrogens that suffered a greater upfield shift due to the interaction between the pyridine nitrogen and the hydrogen donor (Figure ). The formation of the inclusion complex HAR−β-CD could also explain this behavior by means of an interaction between pyridine nitrogen and the internal hydrogens of β-CD.…”

Section: Resultssupporting

confidence: 62%

“…Recenly, we have proposed 38 an oscillating system between two tautomers to explain this mechanism of Z/Q formation. On the other hand, it is known 39À48 some β-carboline derivatives form inclusion complexes with the β-cyclodextrin (β-CD).…”

Section: ' Introductionmentioning

confidence: 99%

“…Carmona et al , hypothesized that the zwitterionic structure (Z) might also present a quinoid structure (Q). Recenly, we have proposed an oscillating system between two tautomers to explain this mechanism of Z/Q formation.…”

Section: Introductionmentioning

confidence: 99%

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The Impact of Dihydrogen Phosphate Anions on the Excited-State Proton Transfer of Harmane. Effect of β-Cyclodextrin on These Photoreactions

et al. 2011

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Photoinduced proton transfer reactions of harmane (1-methyl-9H-pyrido[3,4-b]indole) (HAR) in the presence of a proton donor/acceptor such as dihydrogen phosphate anions in aqueous solution have been studied by stationary and time-resolved fluorescence spectroscopy. The presence of high amounts of dihydrogen phosphate ions modifies the acid/base properties of this alkaloid. Thus, by keeping the pH constant at pH 8.8 and by increasing the amount of NaH(2)PO(4) in the solution, it is possible to reproduce the same spectral profiles as those obtained in high alkaline solutions (pH >12) in the absence of NaH(2)PO(4). Under these conditions, a new fluorescence profile appears at around 520 nm. This result could be related to the results of a recent investigation which suggests that a high intake of phosphates may promote skin tumorigenesis. The presence of β-cyclodextrin (β-CD) avoids the proton transfer reactions in this alkaloid by means the formation of an inclusion complex between β-CD and HAR. The formation of this complex originates a remarkable enhancement of the emission intensity from the neutral form in contrast to the cationic and zwitterionic forms. A new lifetime was obtained at 360 nm (2.5 ns), which was associated with the emission of this inclusion complex. At this wavelength, the fluorescence intensity decay of HAR can be described by a linear combination of two exponentials. From the ratio between the pre-exponential factors, we have obtained a value of K = 501 M for the equilibrium of formation of this complex.

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Section: Resultssupporting

confidence: 62%

Section: ' Introductionmentioning

confidence: 99%

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The Impact of Dihydrogen Phosphate Anions on the Excited-State Proton Transfer of Harmane. Effect of β-Cyclodextrin on These Photoreactions

et al. 2011

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“…[15] Reports on the photophysical properties of more substituted β-carbolines are rather scarce in the literature. [15][16][17][21][22][23][24][25][26][27][28][29][30] Given the lack of studies of β-carboline absorption and fluorescence, we propose in the present work to explore the impact of the substitution at position 1 on the spectral properties of neutral and protonated β-carboline derivatives. In more details, the substitution by two electron donating groups (methoxy and dimethylamino), one accepting moiety (trifluoromethyl), connected through three different spacers (aryl, styryl and ethynyl) are investigated.…”

Section: Scheme 1 Different β-Carboline Derivates Possessing Bioactiv...mentioning

confidence: 99%

Electron rich substituted β-carboline derivatives: Synthesis and photophysical properties

Maret,

Chebourou,

De Nicola

et al. 2023

Dyes and Pigments

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Solvent‐Assisted Prototopic Switching of Norharmane Along Hydrogen‐Bonded Network: Assessing the Precise Length of Network

Paul,

Dey

2024

J of Physical Organic Chem

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In this article, the proton transfer dynamics along a stable norharmane•(H2O)n (n = 2–4) hydrogen‐bonded cluster on conversion from the neutral to cationic form of norharmane (NHM) in water medium was demonstrated experimentally and theoretically. The distinct absorption and emission bands of different prototropic forms of NHM are well‐known in the literature. Initially, the conversion from neutral to cationic form of NHM on moving from a polar aprotic (acetonitrile) to a polar protic (water) solvent was ensured by steady‐state absorption and fluorescence studies. The analysis of IR spectra and steady‐state anisotropy data of NHM confirmed the possibility of the formation of a hydrogen‐bonded network in the presence of water. The length of the network was explored and assumed by extensive Density Functional Theory (DFT) calculations. Then, by time‐dependent density functional theory (TD‐DFT), the excited state proton transfer (ESPT) pathway was established interrogating the NHM‐water cluster with different numbers of water molecules. The theoretical analysis assured that the NHM•(H2O)2 cluster was incapable of maintaining the stable hydrogen bonding wire in the course of the ESPT mechanism. Rather, NHM•(H2O)3 and NHM•(H2O)4 clusters were simultaneously involved in operating the ESPT mechanism. The NHM•(H2O)4 cluster was more feasible to carry out the proton transfer than the NHM•(H2O)3 cluster. To the best of our knowledge, this was possibly the first theoretical evidence behind the conversion from neutral to cationic form of NHM via the formation of a hydrogen‐bonded network.

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New insights into the photo-tautomerisation process in β-carboline derivatives revealed by NMR spectroscopy

Cited by 5 publications

References 56 publications

The Impact of Dihydrogen Phosphate Anions on the Excited-State Proton Transfer of Harmane. Effect of β-Cyclodextrin on These Photoreactions

The Impact of Dihydrogen Phosphate Anions on the Excited-State Proton Transfer of Harmane. Effect of β-Cyclodextrin on These Photoreactions

Electron rich substituted β-carboline derivatives: Synthesis and photophysical properties

Solvent‐Assisted Prototopic Switching of Norharmane Along Hydrogen‐Bonded Network: Assessing the Precise Length of Network

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