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Spectroscopic study of 2-, 4-and 5-substituents on pK(a) values of imidazole heterocycles prone to intramolecular proton-electrons transfer
Eseola, Abiodun O.1,2; Obi-Egbedi, Nelson O.3
2010-02-01
Source PublicationSPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY
ISSN1386-1425
Volume75Issue:2Pages:693-701
AbstractNew 2-(1H-imidazol-2-yl)phenols (L1Et-L8tBuPt) bearing a phenolic proton in the vicinity of the imidazole base were prepared and characterized. Experimental studies of the dependence of their protonation/deprotonation equilibrium on substituent identities and intramolecular hydrogen bonding tendencies were carried Out using electronic absorption spectroscopy at varying pH values. In order to make comparison, 2-(anthracen-10-yl)-4,5-diphenyl-1H-imidazole (L9Anthr) bearing no phenolic proton and 4,5-diphenyl-2-(4,5-diphenyl-1H-imidazol-2-yl)-1H-imidazole(L10BisIm) bearing two symmetrical imidazole base fragments were also prepared and experimentally investigated. DFT calculations were carried out to study frontier orbitals of the investigated molecules. While electron-releasing substituents produced increase in protonation-deprotonation pK(a)s for the hydroxyl group, values for the imidazole base were mainly affected by polarization of the imidazole ring aromaticity across the 2-imidazole carbon and the 4,5-imidazole carbons axis of the imidazole ring. It was concluded that electron-releasing substituents on the phenol ring and/or electron-withdrawing substituents on 4.5-imidazole carbons negatively affects donor strengths/coordination chemistries of 2-(1H-imidazol-2-yl)phenols, and vice versa. Change of substituents on the phenol ring significantly altered the donor strength of the imidazole base. The understanding of pK(a) variation on account of electronic effects of substituents in this work should aid the understanding of biochemical properties and substituent environments of imidazole-containing biomacromolecules. (C) 2009 Elsevier B.V. All rights reserved.
KeywordIonization Constants Uv Spectroscopy Pk(a)s Protonation-deprotonation Substituent Effects
DOI10.1016/j.saa.2009.11.041
Indexed BySCI
Language英语
WOS IDWOS:000274591200031
PublisherPERGAMON-ELSEVIER SCIENCE LTD
Citation statistics
Cited Times:14[WOS]   [WOS Record]     [Related Records in WOS]
Document Type期刊论文
Identifierhttp://ir.iccas.ac.cn/handle/121111/69268
Collection中国科学院化学研究所
Corresponding AuthorEseola, Abiodun O.
Affiliation1.Redeemers Univ, Dept Chem Sci, Redemption City, Nigeria
2.Chinese Acad Sci, Inst Chem, Beijing Natl Lab Mol Sci, Beijing 100190, Peoples R China
3.Univ Ibadan, Dept Chem, Ibadan, Nigeria
Recommended Citation
GB/T 7714
Eseola, Abiodun O.,Obi-Egbedi, Nelson O.. Spectroscopic study of 2-, 4-and 5-substituents on pK(a) values of imidazole heterocycles prone to intramolecular proton-electrons transfer[J]. SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY,2010,75(2):693-701.
APA Eseola, Abiodun O.,&Obi-Egbedi, Nelson O..(2010).Spectroscopic study of 2-, 4-and 5-substituents on pK(a) values of imidazole heterocycles prone to intramolecular proton-electrons transfer.SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY,75(2),693-701.
MLA Eseola, Abiodun O.,et al."Spectroscopic study of 2-, 4-and 5-substituents on pK(a) values of imidazole heterocycles prone to intramolecular proton-electrons transfer".SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 75.2(2010):693-701.
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