Spectral Properties of Thioflavin T and Its Complexes with Amyloid Fibrils

Comparative analysis of the absorption and fluorescence spectra and fluorescence excitation spectra of thioflavin T (ThT) in various solvents and in the composition of amyloid fibrils has shown that ThT, when excited in the region of the long-wavelength absorption band, fluoresces in the spectral region with a maximum at 478–484 nm. The appearance in aqueous and alcohol solutions of a fluorescence band with a maximum near 440 nm has been attributed to the presence in the composition of the ThT preparations of an impurity with an absorption band in the 340–350-nm range. The literature data showing that in glycerol ThT has a wide fluorescence spectrum with two maxima are due to the artifact connected with the use of a high concentration of the dye. It has been suggested that the cause of the low quantum yield of ThT aqueous and alcohol solutions is the breakage of the system of conjugated bonds due to the reorientation of the benzothiozole and benzaminic rings of ThT in the excited state with respect to one another. The main factor determining the high quantum yield of fluorescence of ThT incorporated in fibrils is the steric restriction of the rotation of the rings about one another under these conditions. The suggestions made have been verified by the quantum-chemical calculation of the ThT molecule geometry in the ground and excited states

Резонансное усиление флуоресценции квантовых точек у поверхности плазмонных пленок

Effective enhancement of the fluorescence signal of chromophores adsorbed directly onto plasmonic films can be observed under conditions of strong spectral resonance between plasmon and chromophore absorptions. This effect seems to contradict the established mechanisms of complete quenching of the fluorescence of chromophores under their adsorbtion directly onto the metal surface. However, under certain conditions, enhancement of the fluorescence signal is observed for both inorganic and organic chromophores. To understand the effect and conditions of its observation, we propose to use the quantum concept of virtual photon exchange in the near optical field - dressed photons. This concept is borrowed from the physics of elementary particles and is already well adapted to the problems of nanophotonics by M. Otsu. In this paper, we discuss exclusively the key factors responsible for enhancement of fluorescence of CdSe/ZnS nanocrystals and the effective dressed photons exchange: the size of nanoparticles, the distance between them, and the presence of spectral overlap indicating the possibility of resonant interactions between plasmons and chromophores.Communicated by Academician Sergei V. GaponenkoЭффективное усиление сигнала флуоресценции хромофоров, адсорбированных непосредственно на плазмонные пленки (ПП), можно наблюдать в условиях сильного спектрального резонанса между плазмонным поглощением и поглощением хромофора. Указанный эффект, на первый взгляд, противоречит установленным механизмам полного тушения флуоресценции хромофоров при их адсорбции непосредственно на поверхность металла. Однако при определенных условиях усиление сигнала флуоресценции наблюдается как для неорганических, так и органических хромофоров. Для понимания эффекта и условий, при которых он может наблюдаться, мы предлагаем исходить из двух основополагающих факторов, определяющих вероятности квантовых переходов, - матричного элемента перехода, ответственного за наблюдаемое излучение, и плотности конечных состояний. Однако при определении матричного элемента перехода необходимо учитывать наличие нескольких хромофорных систем (адсорбированные хромофоры и локализованные плазмоны), способных поглощать возбуждающее излучение и еще одной плазмон-поляритонной системы, имеющей светоподобную природу и способной к излучению световых квантов, а также взаимодействие между ними, которое может быть описано в рамках обмена виртуальными фотонами. Учитывая, что расстояния между наночастицами намного меньше длины волны света и дипольное приближение не работает, мы предлагаем использовать квантовую концепцию обмена виртуальными фотонами в ближнем оптическом поле - «одетыми» фотонами. Эта концепция заимствована из физики элементарных частиц и уже хорошо адаптирована к проблемам нанофотоники М. Отсу. Второй фактор, который также может давать значительный вклад в усиление, - это модификация плотности как электронных, так и фотонных состояний - эффект, который предложен С. В. Гапоненко в качестве модели, ответственной за усиление гигантского комбинационного рассеяния света хромофоров в стоксовой и антистоксовой области вблизи наночастиц с плазмонными свойствами. В данной работе обсуждаются такие ключевые факторы, ответственные за усиление флуоресценции наночастиц CdSe/ZnS и эффективный обмен виртуальными фотонами, как размер наночастиц, расстояния между ними и наличие спектрального перекрытия, указывающего на возможность резонансных взаимодействий между плазмонами и хромофорами.Представлено академиком С.В. Гапоненк

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

Application of X-Ray Fluorescence Analysis to Determine the Elemental Composition of Tissues from Different Ovarian Neoplasms

x-ray fluorescence analysis, endometrioid cancer, mucinous cancer, serous carcinoma, ovarian tissues, microelements.We present the results of x-ray fluorescence analysis of tissues from healthy ovaries and from ovaries with different pathologies: benign and borderline tumors, mucinous and endometrioid cancers, serous carcinomas. We determine the average copper, zinc, calcium, selenium, cadmium, lead, and mercury levels. We observed that in the benign ovarian tumors, we see a significant decrease in the cadmium, mercury, and lead levels compared with healthy tissues. In the borderline neoplasms, the copper level is reduced relative to zinc (Cu/Zn), cadmium, mercury, and lead, and also the zinc concentration is increased. In the ovarian carcinomas, we observed changes in the ratio of the chemical elements in the tumor tissues, depending on the histologic type. The results obtained can be used for differentiation, diagnosis, and adjustment of treatment for different ovarian neoplasms

Formation of trans-2-[4-(dimethylamino)styryl]-3-ethyl-1,3-nzothiazolium perchlorate dimers in the presence of sodium polystyrene sulfonate formation of trans-2-[4-(dimethylamino)styryl]-3-ethyl-1,3-benzothiazolium perchlorate dimers in the presence of sodium polystyrene sulfonate

The spectral properties of a novel thiofl avin T derivative, trans-2-[4-(dimethylamino)styryl]-3-ethyl-1,3- benzothiazolium perchlorate (DMASEBT), were studied in aqueous solutions in the presence of sodium polystyrene sulfonate (SPS). It was shown that SPS either could interact with dye monomers or initiate the formation of non-fl uorescent dye dimers depending on the concentration ratio of dye and polyelectrolyte. DMASEBT dimer formation in the presence of SPS produced a hypsochromic shift by 40 nm in the absorption spectrum and quenched fl uorescence. A bathochromic shift of the absorption spectrum and an increase of the fl uorescence intensity by an order of magnitude were observed if DMASEBT monomers interacted with SPS. Quantum-chemical analysis found that sandwich dimers (H-aggregates) were most stable. A comparison of DMASEBT spectra in the presence of SPS and amyloid fi brils showed that DMASEBT molecules were incorporated into amyloid fi brils as monomers. The spectral changes associated with this incorporation could not be explained by the formation of dye aggregates

Photophysical properties of trans-2-[4-(dimethylamino)styryl] 3-ethyl-1,3-benzothiazolium perchlorate, a new structural analog of thioflavin T

Spectral properties of a newly synthesized thiofl avin T (ThT) derivative, trans-2-[4-(dimethylamino)styryl]-3-ethyl-1,3-benzothiazolium perchlorate (DMASEBT) with absorption and fl uorescence spectra shifted to longer wavelengths (than ThT), were studied. Quantum-chemical calculations established that DMASEBT is planar in the ground state. The energy minimum of the excited molecule corresponded to a twisted conformation (TICT-state) with a 90° angle between the planar fragments. Charge in the molecule redistributed and a non-fl uorescing TICT-state was formed if the fragments rotated. Fluorescence occurred from the non-equilibrium excited state (LE-state). It was shown that limited torsional rotation of the molecular fragments and; therefore, a decreased probability of transitioning into the non-fl uorescing TICT-state, were responsible for the signifi cantly increased quantum yield and fluorescence lifetime of DMASEBT upon increasing the solvent viscosity and incorporating it into amyloid fi brils

Aggregation of thioflavin T and its new derivative in the presence of anionic polyelectrolyte

Spectral properties of aqueous solutions of thioflavin T (ThT) and its new derivative, trans-2-[4-(dimethylamino) styryl]-3-ethyl-1,3-benzothiazolium perchlorate (DMASEBT) were studied in the presence of anionic polyelectrolyte sodium polystyrene sulfonate (PSS). It was shown that PSS promote the dye dimerization process. Quantum–chemical analysis of DMASEBT in monomer and dimer forms allowed to suggest that the dimers have a sandwich-like structure, i.e. H-aggregates can be formed. DMASEBT dimer formation in the presence of PSS leads to a 40 nm hypsochromic shift of the dye absorption spectrum and to quenching of its fluorescence. The PSS interaction with the monomeric dye leads to a 26 nm bathochromic shift of the absorption spectrum and to one order of magnitude increase in its fluorescence

Aggregation of thioflavin T and its new derivative in the presence of anionic polyelectrolyte

Spectral properties of aqueous solutions of thioflavin T (ThT) and its new derivative, trans-2-[4-(dimethylamino) styryl]-3-ethyl-1,3-benzothiazolium perchlorate (DMASEBT) were studied in the presence of anionic polyelectrolyte sodium polystyrene sulfonate (PSS). It was shown that PSS promote the dye dimerization process. Quantum–chemical analysis of DMASEBT in monomer and dimer forms allowed to suggest that the dimers have a sandwich-like structure, i.e. H-aggregates can be formed. DMASEBT dimer formation in the presence of PSS leads to a 40 nm hypsochromic shift of the dye absorption spectrum and to quenching of its fluorescence. The PSS interaction with the monomeric dye leads to a 26 nm bathochromic shift of the absorption spectrum and to one order of magnitude increase in its fluorescence