ON THE LUMINESCENCE OF _L‐TRYPTOPHANE AND l‐TYROSINE IN AQUEOUS SOLUTION AT 77dK INDUCED BY X‐RAYS AND U.V.‐LIGHT

Abstract

Abstrrtct--rhc lumincscence arising from L-tryptophane and L-tyrosine in aqueous solutions at 77°K during irradiation with u.v.-light and with X-rays has been studied. The spectra obtaincd with the two types of radiation were largely similar, differing only in that the yields of phosphorescence relative to fluorescence were considerably enhanced in thc case of X-irradiation. The decay times observed for the exponentially decaying phosphorescence, being 6.6 sec and 2.7 sec for tryptophane and tyrosine respectively, were the same for both kinds of irradiation. The G-value of the X-ray induced luminescence was about 10 for both tryptophane and tyrosine. Thus, about 30 per cent of the total energy absorbed from X-rays in these compounds was re-emitted as light.It was concluded that the X-ray induced fluorescence and phosphorescence originate from the same levels as does the luminescence caused by u.v.-light, i.e. the lowest excited singlet and the lowest triplet level of the aromatic structure of these compounds. In the case of X-irradiation the enhanced ratios between the yiclds of phosphorescence and fluorescence indicated that some process other than excitation directly from the ground state contributed considerably to the luminescence yields. Assuming this process to be a recombination between the ionized molecule and its electron, it was calculated that the contribution to the luminescence yield from excitations directly from the ground state relative to that from ionizations, was negligible for both compounds.

Solvent-Slaved Dynamic Processes Observed by Tryptophan Phosphorescence of Human Serum Albumin

“…2. The data followed a general pattern where lifetimes are long-lived at T < 170 K and decrease with increasing temperature above 170 K. At 77 K, the t p value for free tryptophan in g/w was 6.33 s, similar to the long tryptophan phosphorescence lifetimes in glassy matrixes at liquid nitrogen temperature reported in the literature (38)(39)(40). At the same temperature, the lifetimes for HSA in g/w (5.65 s) and in trehalose (5.20 s) were notably shorter.…”

“…There is no consensus value in the literature for k RP of tryptophan, but as the longest reported lifetimes range from 6 to 7 s (38)(39)(40), an intermediate value of (k RP ) À1 ¼ 6.5 s was chosen for subsequent calculations of k NR. Any uncertainty in k RP translates into a corresponding uncertainty in the calculated values of k NR at the lowest temperatures only, having no effect on the analysis of k NR at temperatures above T g (as outlined in the Discussion section.)…”

X-ray-excited optical luminescence of protein crystals: a new tool for studying radiation damage during diffraction data collection

“…Cystine yielded a weak XEOL signal with a λ max of 808 nm that is likely to arise from the disulfide bond. The spectral shapes observed are broadly consistent with previously recorded XEOL data for tyrosine, tryptophan and phenylalanine powders and for tryptophan dissolved in 1:1 water:ethylene glycol (Carter et al ., 1965; Steen, 1967, 1968; Nelson et al ., 1967; Nummedal & Steen, 1969). The XEOL spectra bleached after continued exposure to X-rays, as previously observed in other inorganic systems (Rogalev & Goulon, 2002).…”

X‐ray‐ and U.V.‐INDUCED Excitation of Adenine, Thymine and the Related Nucleosides and Nucleotides in Solution at 77°k*

“…The apparatus and the procedure used for irradiation and measurement of the spectra and emission yields have been described in more detail elsewhere [7,8].…”