Действие ультрафиолетового излучения на тиамин и дисульфиды тиамина

In a neutral medium, the exposure of thiamine disulfide to the ultraviolet of solar radiation (as well as to the ultraviolet radiation of mercury lamp with λ > 300 nm) results in the formation of a thiamine molecule with closed thiazole ring and a molecule of thiamine thiazolone. Asymmetric thiamine disulfides, e.g., thiamine propyl disulfide, on exposure to ultraviolet (UVA range) produced thiamine and propyl disulfides. Thiamine and thiazolone of thiamine are stable upon exposure to light of 320-400 nm (UVA range). UV irradiation within spectral range of 200-300 nm results in further photodestruction of thiamine and thiamine thiazolone and production of 2-methyl-4-amino-5aminomethyl-pyrimidine as the main photoproduct. The possibility to use thiamine disulfide derivatives as a promising class of anti-cataract drugs as well as drugs to decrease the toxic effect of ultraviolet radiation on human retina is discussed. Под действием ультрафиолетового солнечного излучения (а также ультрафиолетового излучения ртутной лампы с λ > 300 нм) на тиамин дисульфид в нейтральной водной среде образуются молекулы тиамина с закрытым тиазоловым циклом и молекулы тиазолона тиамина. Асимметричный дисульфид тиамина, например тиаминпропил дисульфид, под действием ультрафиолетового излучения (UVA диапазон) образует тиамин и пропилдисульфид соответственно. Тиамин и тиазолон тиамина устойчивы к действию излучения 320-400 нм (UVA диапазон). При воздействии ультрафиолетового излучения с λ от 200 до 300 нм происходит фотодеструкция тиамина и тиазолона тиамина и образуется 2-метил4-амино-5-аминометил-пиримидин в качестве основного продукта. Обсуждается возможность использования дисульфидных производных тиамина как перспективного класса антикатарактальных препаратов, а также препаратов для снижения токсического действия ультрафиолетового излучения на сетчатку глаза

Extrinsic Fluorescent Dyes as Tools for Protein Characterization

Noncovalent, extrinsic fluorescent dyes are applied in various fields of protein analysis, e.g. to characterize folding intermediates, measure surface hydrophobicity, and detect aggregation or fibrillation. The main underlying mechanisms, which explain the fluorescence properties of many extrinsic dyes, are solvent relaxation processes and (twisted) intramolecular charge transfer reactions, which are affected by the environment and by interactions of the dyes with proteins. In recent time, the use of extrinsic fluorescent dyes such as ANS, Bis-ANS, Nile Red, Thioflavin T and others has increased, because of their versatility, sensitivity and suitability for high-throughput screening. The intention of this review is to give an overview of available extrinsic dyes, explain their spectral properties, and show illustrative examples of their various applications in protein characterization

Solvent Polarity Effect on Nonradiative Decay Rate of Thioflavin T

It has been established earlier that fluorescence quantum yield of thioflavin T (ThT)a probe widely used for amyloid fibrils detectionis viscosity-dependent, and photophysical properties of ThT can be well-described by the fluorescent molecular rotor model, which associates twisted internal charge transfer (TICT) reaction with the main nonradiative decay process in the excited state of the dye. Solutions of ThT in a range of polar solvents were studied using steady-state fluorescence and sub-picosecond transient absorption spectroscopy methods, and we showed that solvent effect on nonradiative transition rate <i>k</i>_nr cannot be reduced to the dependence on viscosity only and that ∼3 times change of <i>k</i>_nr can be observed for ThT in aprotic solvents and water, which correlates with solvent polarity. Different behavior was observed in alcohol solutions, particularly in longer <i>n</i>-alcohols, where TICT rate was mainly determined by rotational diffusion of ThT fragments. Quantum-chemical calculations of S₀ → S₁ transition energy were performed to get insight of polar solvent contribution to the excited-state energy stabilization. Effect of polar solvent on electronic energy levels of ThT was simulated by applying homogeneous electric field according to the Onsager cavity model. Static solvent effect on the excited-state potential energy surface, where charge transfer reaction takes place, was not essential to account for experimentally observed TICT rate differences in water and aprotic solvents. From the other side, nonradiative decay rate of ThT in water, ethylene glycol, and aprotic solvents was found to follow dynamics of polar solvation <i>k</i>_nr ∼ τ_<i>S</i>^–1, which can explain dependence of the TICT rate on both polarity and viscosity of the solvents