UV-Vis Absorption and Fluorescence in Bioanalysis

Endogenous Photosensitizers in Human Skin

“…214 In fact, the molar absorption coefficient of proteins at 280 nm (ε 280nm , in L mol −1 cm −1 ) can be determined with an accuracy of ±5% based solely on the individual ε 280nm of Trp (∼5,500), Tyr (∼1,490) and cystine (Cys-Cys, 125) scaled by the number of residues. 215,216 The oxidation of amino acids in neutral/acidic solutions involves an overall hydrogen atom transfer, generally requiring the formation of inner-sphere complexes that impose kinetic barriers. The oxidation of proteins is closely related to redox processes and signaling networks and can be promoted by various other oxidized products, including lipid aldehydes.…”

“…The most important side chains are those of tyrosine (Tyr), phenylalanine (Phe), tryptophan (Trp), histidine (His), and cysteine (Cys), which shift the absorption of peptides and proteins from around 190–220 nm, attributed to the combination of ππ* (ε 190nm ∼ 7,000 L mol –1 cm –1 ) and nπ* (ε 215nm ∼ 100 L mol –1 cm –1 ) transitions of peptide bonds, to longer wavelengths, 230–310 nm . In fact, the molar absorption coefficient of proteins at 280 nm (ε 280nm , in L mol –1 cm –1 ) can be determined with an accuracy of ±5% based solely on the individual ε 280nm of Trp (∼5,500), Tyr (∼1,490) and cystine (Cys-Cys, 125) scaled by the number of residues. , The oxidation of amino acids in neutral/acidic solutions involves an overall hydrogen atom transfer, generally requiring the formation of inner-sphere complexes that impose kinetic barriers. The oxidation of proteins is closely related to redox processes and signaling networks and can be promoted by various other oxidized products, including lipid aldehydes .…”

“…Thymine (T), adenine (A), cytosine (C), guanine (G), and uracil (U), the canonical nitrogenous bases of nucleic acids, absorb UVR effectively 215,427 and models of photocarcinogenesis raise the possibility that a combination of direct and photosensitized DNA lesions (see Box 4) may be involved in the development of malignant skin cancer. 68,88 Despite the high photostability of these nucleobases, as mentioned, direct UV-B DNA photolesions are represented by the formation of two main photoproducts CPD and 6−4PPs.…”

“…Thymine (T), adenine (A), cytosine (C), guanine (G), and uracil (U), the canonical nitrogenous bases of nucleic acids, absorb UVR effectively , and models of photocarcinogenesis raise the possibility that a combination of direct and photosensitized DNA lesions (see Box ) may be involved in the development of malignant skin cancer. , Despite the high photostability of these nucleobases, as mentioned, direct UV-B DNA photolesions are represented by the formation of two main photoproducts CPD and 6–4PPs. ,,− CPDs also accumulate during and after UV-A exposure, even in the absence of photosensitizers, because the DNA double-strand structure can increase the capacity of nucleobases to absorb radiation in this relatively long wavelength range. , CPDs can also be formed by photosensitization, as the pyrimidone ring of 6–4PP can form thymine/thymine-based CPDs via triplet–triplet energy transfer (see further discussion below) . Xenobiotics (e.g., fluoroquinolones, psoralen, and carprofen) interacting noncovalently with DNA can also engage in triplet–triplet energy transfer to form CPDs .…”