Protein triplet states

Reevaluating Protein Photoluminescence: Remarkable Visible Luminescence upon Concentration and Insight into the Emission Mechanism

“…[2][3][4] However,t hese experiments have typically been restricted to dilute solutions with a l ex of around 280-300 nm. Few investigations have been devoted to the emission of concentrated solutions or solids with much longer l ex values,p resumably because of the concentration quenching effect of conventional aromatic luminophores and the maximal absorption of 280, 275, and 258 nm for Tr p, Ty r, and Phe, [2][3][4] respectively.T of urther unravel the concentration effect, photophysical properties of aqueous BSA solutions have been investigated. [24] Ford ilute BSA solutions ( 0.1 mg mL À1 ) with a l ex of 300 nm, negligible or faint PL signals are recorded with am aximum at 348 nm, which is assignable to the Tr pr esidues.…”

“…[24] Ford ilute BSA solutions ( 0.1 mg mL À1 ) with a l ex of 300 nm, negligible or faint PL signals are recorded with am aximum at 348 nm, which is assignable to the Tr pr esidues. [2][3][4] Notably,t he PL peak intensity initially increases and then decreases with increasing concentration, with an inflexion point of around 10 mg mL À1 ([Trp] % 0.3 mm ; Figure S2 in the Supporting Information). Thelatter quenching is ascribed to self-absorption and/or exciton interactions.…”

“…Protein photoluminescence has been extensively studied due to its fundamental importance for understanding photochemical reactions in proteins and broad applications in pH sensors,f luorescent bioimaging,a nd protein conformation indicators. [1][2][3][4][5][6][7] Previous works have shown that proteins in aqueous solutions show intrinsic near-ultraviolet (UV) photoluminescence (PL), which is generally believed to have originated from the aromatic amino acid residues of tryptophan (Trp), tyrosine (Tyr), and phenylalanine (Phe;F igure 1A). [2][3][4][5] Meanwhile,g reen fluorescent protein (GFP) from the jellyfish Aequorea victoria [8][9][10] has at remendous impact on life sciences.T he chromophore, p-hydroxybenzylidene-2,3-dimethylimidazolinone (p-HOBDI), which is located within ap rotective b-barrel, is responsible for the unique emission ( Figure 1B).…”

“…In particular,b oth fluorescence and phosphorescence of natural proteins are considered to result from the presence of aromatic amino acid residues. [2][3][4]7] These investigations,however,are generally restricted to solutions without appreciable aggregation, and/or the adoption of relatively short excitation wavelengths (l ex < 300 nm). Recently,b ased on the exploration of nonconventional luminogens devoid of remarkable conjugates with extended delocalization lengths, [11][12][13][14] and aiming to uncover the mechanism of visible emission of nonaromatic peptides and proteins, [15][16][17] we investigated natural nonaromatic amino acids and poly(amino acids) and revealed prevalent intrinsic emission in concentrated solutions and/or solids ( Figure 1C).…”

Hydrogen Atoms Are Produced When Tryptophan within a Protein Is Irradiated with Ultraviolet Light

“…\ 7 n Likewise, the aromatic amino acid tryptophan, which possesses an indole ring as a side group, shares similar diversity in its photochemistry (1-3)-to such a degree that tryptophan photochemistry is implicated in cellular disease states The excited states (singlet and triplet) of the indole chromophore have been extensively probed using a wide array of spectroscopic techniques (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26). Of these, the triplet state of tryptophan has emerged as an important tool for the study of chromophore-protein dynamics (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37). In this communication we probe the photochemistry of the tryptophan residue in a Ca2+-binding protein, cod parvalbumin type 111, through electron paramagnetic resonance (EPR) spectroscopy during UV irradiation at very low temperatures in condensed phase.…”