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Solvent-modulated ground-state rotamerism and tautomerism and excited-state proton-transfer processes in o-hydroxynaphthylbenzimidazoles.
J Phys Chem A. 2009 Jan 08; 113(1):56-67.JP

Abstract

The ground-state rotamerism and tautomerism and the excited-state proton-transfer processes of 2-(1'-hydroxy-2'-naphthyl)benzimidazole (1) and 2-(3'-hydroxy-2'-naphthyl)benzimidazole (2) have been investigated in various solvents by means of UV-vis absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, and quantum-mechanical ab initio calculations. For both compounds, a solvent-modulated rotameric equilibrium, and also tautomeric for 1, was observed in the ground state. In apolar solvents, both 1 and 2 exist as planar syn normal forms, with the hydroxyl group hydrogen bonded to the benzimidazole N3. In acetonitrile and ethanol, a rotameric equilibrium is established between the syn form and its planar anti rotamer, with the phenyl ring rotated 180 degrees about the C2-C2' bond. In ethylene glycol, glycerol, and aqueous solution with 40% ethanol, a tautomeric equilibrium was detected for 1 between the syn and anti normal forms and the tautomer form, with the hydroxyl proton transferred to the benzimidazole N3. In all of the solvents studied, the syn normal form of 1 and 2 undergoes an ultrafast excited-state intramolecular proton transfer (ESIPT) to yield the excited tautomer. The anti normal forms of 1 and 2, unable to experience ESIPT, give normal form fluorescence. In addition, the anti normal conformer of 2 partly deprotonates at the hydroxyl group in aqueous solution with 40% ethanol, giving the excited anion. The monocations of 1 and 2, protonated at the benzimidazole N3, are strong photoacids that deprotonate completely in aqueous solution with 40% ethanol and to a great extent in ethanol, giving the excited tautomer.

Authors+Show Affiliations

Departamento de Química Física, Facultade de Química, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

19072628

Citation

Brenlla, Alfonso, et al. "Solvent-modulated Ground-state Rotamerism and Tautomerism and Excited-state Proton-transfer Processes in O-hydroxynaphthylbenzimidazoles." The Journal of Physical Chemistry. A, vol. 113, no. 1, 2009, pp. 56-67.
Brenlla A, Rodríguez-Prieto F, Mosquera M, et al. Solvent-modulated ground-state rotamerism and tautomerism and excited-state proton-transfer processes in o-hydroxynaphthylbenzimidazoles. J Phys Chem A. 2009;113(1):56-67.
Brenlla, A., Rodríguez-Prieto, F., Mosquera, M., Ríos, M. A., & Ríos Rodríguez, M. C. (2009). Solvent-modulated ground-state rotamerism and tautomerism and excited-state proton-transfer processes in o-hydroxynaphthylbenzimidazoles. The Journal of Physical Chemistry. A, 113(1), 56-67. https://doi.org/10.1021/jp8076003
Brenlla A, et al. Solvent-modulated Ground-state Rotamerism and Tautomerism and Excited-state Proton-transfer Processes in O-hydroxynaphthylbenzimidazoles. J Phys Chem A. 2009 Jan 8;113(1):56-67. PubMed PMID: 19072628.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Solvent-modulated ground-state rotamerism and tautomerism and excited-state proton-transfer processes in o-hydroxynaphthylbenzimidazoles. AU - Brenlla,Alfonso, AU - Rodríguez-Prieto,Flor, AU - Mosquera,Manuel, AU - Ríos,Miguel A, AU - Ríos Rodríguez,M Carmen, PY - 2008/12/17/entrez PY - 2008/12/17/pubmed PY - 2009/2/20/medline SP - 56 EP - 67 JF - The journal of physical chemistry. A JO - J Phys Chem A VL - 113 IS - 1 N2 - The ground-state rotamerism and tautomerism and the excited-state proton-transfer processes of 2-(1'-hydroxy-2'-naphthyl)benzimidazole (1) and 2-(3'-hydroxy-2'-naphthyl)benzimidazole (2) have been investigated in various solvents by means of UV-vis absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, and quantum-mechanical ab initio calculations. For both compounds, a solvent-modulated rotameric equilibrium, and also tautomeric for 1, was observed in the ground state. In apolar solvents, both 1 and 2 exist as planar syn normal forms, with the hydroxyl group hydrogen bonded to the benzimidazole N3. In acetonitrile and ethanol, a rotameric equilibrium is established between the syn form and its planar anti rotamer, with the phenyl ring rotated 180 degrees about the C2-C2' bond. In ethylene glycol, glycerol, and aqueous solution with 40% ethanol, a tautomeric equilibrium was detected for 1 between the syn and anti normal forms and the tautomer form, with the hydroxyl proton transferred to the benzimidazole N3. In all of the solvents studied, the syn normal form of 1 and 2 undergoes an ultrafast excited-state intramolecular proton transfer (ESIPT) to yield the excited tautomer. The anti normal forms of 1 and 2, unable to experience ESIPT, give normal form fluorescence. In addition, the anti normal conformer of 2 partly deprotonates at the hydroxyl group in aqueous solution with 40% ethanol, giving the excited anion. The monocations of 1 and 2, protonated at the benzimidazole N3, are strong photoacids that deprotonate completely in aqueous solution with 40% ethanol and to a great extent in ethanol, giving the excited tautomer. SN - 1520-5215 UR - https://www.unboundmedicine.com/medline/citation/19072628/Solvent_modulated_ground_state_rotamerism_and_tautomerism_and_excited_state_proton_transfer_processes_in_o_hydroxynaphthylbenzimidazoles_ L2 - https://doi.org/10.1021/jp8076003 DB - PRIME DP - Unbound Medicine ER -