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Properties of 2,6-diamino-8-azapurine, a highly fluorescent purine analog and its N-alkyl derivatives: Tautomerism and excited-state proton transfer reactions

Paper ID Volume ID Publish Year Pages File Format Full-Text
26968 43990 2013 9 PDF Available
Title
Properties of 2,6-diamino-8-azapurine, a highly fluorescent purine analog and its N-alkyl derivatives: Tautomerism and excited-state proton transfer reactions
Abstract

•2,6-Diamino-8-azapurine is strongly fluorescent in water, maximum at 365 nm.•Upon acidification, a new emission band appears at 410 nm.•The 410 nm fluorescence is characteristic for the neutral N8-methyl derivative.•The cation of N8-methyl derivative deprotonates in the excited state, pK* ∼ −2.•Interpretation: 2,6-diamino-8-azapurine undergoes N(9)H ↔ N(8)H phototautomerism via cation.

Fluorescence emission properties of 2,6-diamino-8-azapurine (2-amino-8-azaadenine) in aqueous medium were examined. The title compound exhibits strong fluorescence centered at 365 nm, with quantum yield 0.40 and bi-exponential decay with lifetimes of ∼7.5 and ca. 0.2 ns. The spectral properties of 2,6-diamino-8-azaapurine are very similar to those of its 9-alkoxyphosphonate, suggesting that the protomer responsible for the emission of the former must be identified as N(9)H form. In acidic media (pH ∼ 2.5), fluorescence of the title compound is shifted to 410 nm, and is very similar to that of the neutral form of the N8-methyl derivative, the latter emitting at 410 nm with yield 0.85 and lifetime 12.7 ns. The N8-methyl derivative in the moderately acidic media undergoes rapid excited-state deprotonation, with pK* calculated to be as low as −2, compared to pKa 4.8 in the ground state, and resulting in the presence of the 410 nm fluorescence band well below the ground-state pKa. We therefore propose that the 410 nm band observed in the fluorescence of 2,6-diamino-8-azapurine cation is the consequence of (a) shift in tautomerism upon protonation from N(9)H toward N(8)H form and (b) rapid excited-state deprotonation of the latter. This conclusion is supported by the study of solvent, isotope and buffer concentration effects.

Keywords
8-Azapurines; Fluorescence; Purine analogs; Tautomerism; Excited-state proton transfer; PhototautomerismDaaPur, 2,6-diamino-8-azapurine, 2-amino-8-azaadenine (IUPAC name: 3H-[1,2,3]-triazolo[4,5-d]pyrimidine-5,7-diamine); PMP-DaaPur, 9-(2-phosphonylmethox
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Properties of 2,6-diamino-8-azapurine, a highly fluorescent purine analog and its N-alkyl derivatives: Tautomerism and excited-state proton transfer reactions
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 265, 1 August 2013, Pages 49–57
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
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