Room temperature luminescence of 1,N2-etheno-2-aminopurine in poly (vinyl alcohol) films.

We studied spectral properties of 1,N2-etheno-2-aminopurine after immobilization in poly (vinyl alcohol) films. The absorption spectrum of 1,N2-ε2APu consists of two peaks centered at 300 and 370 nm, and the fluorescence spectrum has maximum at about 460 nm. The fluorescence quantum efficiency is 62%. The fluorescence anisotropy reaches a value of 0.3 at longer wavelengths, while it is low at shorter wavelengths (corresponding to the second single excited state). The 1,N2-ε2APu has a relatively long fluorescence lifetime of about 16 ns and a noticeable room temperature phosphorescence with a lifetime of about 220 ms. A broad phosphorescence emission band (425-675 nm) is centered at about 530 nm and markedly overlaps with fluorescence at shorter wavelengths. Surprisingly, the phosphorescence excitation spectrum of 1,N2-ε2APu-doped poly (vinyl alcohol) film differs from the absorption and fluorescence excitation spectra. The strongest room temperature phosphorescence excitation is about 335 nm. At longer excitation wavelengths, above 450 nm, where fluorescence cannot be excited, a triplet excitation is still possible. The 1,N2-ε2APu phosphorescence anisotropy spectra confirm direct triplet state excitation. The ability to excite molecules at long wavelengths can find applications in the study of biological molecules that are unstable when excited at high energies.

Chemo-Enzymatic Generation of Highly Fluorescent Nucleoside Analogs Using Purine-Nucleoside Phosphorylase.

Chemo-enzymatic syntheses of strongly fluorescent nucleoside analogs, potentially applicable in analytical biochemistry and cell biology are reviewed. The syntheses and properties of fluorescent ribofuranosides of several purine, 8-azapurine, and etheno-purine derivatives, obtained using various types of purine nucleoside phosphorylase (PNP) as catalysts, as well as α-ribose-1-phosphate (r1P) as a second substrate, are described. In several instances, the ribosylation sites are different to the canonical purine N9. Some of the obtained ribosides show fluorescence yields close to 100%. Possible applications of the new analogs include assays of PNP, nucleoside hydrolases, and other enzyme activities both in vitro and within living cells using fluorescence microscopy.