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Journal ArticleDOI

Thioflavin T as a molecular rotor: fluorescent properties of thioflavin T in solvents with different viscosity.

TL;DR: The photophysical model successfully explains the fluorescent properties of ThT in solvents with different viscosities and supports the idea that the reason for the characteristic increase in the ThT fluorescence intensity accompanying its incorporation into the amyloid fibrils is determined by the rigidity of the dye environment.
Abstract: The effect of solvent viscosity on thioflavin T (ThT) fluorescent properties is analyzed to understand the molecular mechanisms of the characteristic increase in ThT fluorescence intensity accompanying its incorporation into the amyloid-like fibrils. To this end, the dependencies of the ThT quantum yield and fluorescence lifetime on temperature and glycerol content in the water−glycerol mixtures are studied. It has been found that fluorescent properties of ThT are typical for the specific class of fluorophores known as molecular rotors. It has been established that the low ThT fluorescence intensity in the solvents with low viscosity is caused by the nonradiative deactivation of the excited state associated with the torsional motion of the ThT benzthiazole and aminobenzene rings relative to each other, which results in the transition of ThT molecule to nonfluorescent twisted internal charge transfer (TICT) state. The rate of this process is determined by the solvent viscosity, whereas the emission does oc...
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Journal ArticleDOI
TL;DR: Increased understanding of present molecular probes as well as development of new probes are of utmost importance for development of strategies to control amyloid formation and overcome neurodegenerative disorders.
Abstract: Because understanding amyloid fibrillation in molecular detail is essential for development of strategies to control amyloid formation and overcome neurodegenerative disorders, increased understanding of present molecular probes as well as development of new probes are of utmost importance. To date, the binding modes of these molecular probes to amyloid fibrils are by no means adequately described or understood, and the large number of studies on Thioflavin T (ThT) and Congo Red (CR) binding have resulted in models that are incomplete and conflicting. Different types of binding sites are likely to be present in amyloid fibrils with differences in binding modes. ThT may bind in channels running parallel to the long axis of the fibril. In the channels, ThT may bind in either a monomeric or dimeric form of which the molecular conformation is likely to be planar. CR may bind in grooves formed along the β-sheets as a planar molecule in either a monomeric or supramolecular form.

551 citations

Journal ArticleDOI
TL;DR: The application of a water-soluble fluorogenic dye, Thioflavin T (ThT), in a dual role of exclusively inducing quadruplex folding in the 22AG human telomeric DNA, both in the presence and absence of Tris buffer/salt, is demonstrated.
Abstract: The quest for a G-quadruplex specific fluorescent sensor among other DNA forms under physiological salt conditions has been addressed in this article We demonstrate for the first time the application of a water-soluble fluorogenic dye, Thioflavin T (ThT), in a dual role of exclusively inducing quadruplex folding in the 22AG human telomeric DNA, both in the presence and absence of Tris buffer/salt, and sensing the same through its fluorescence light-up having emission enhancement of the order of 2100-fold in the visible region Appropriate conditions allow an apparent switch over of the parallel quadruplex structure in 22AG–ThT (50 mM Tris, pH 72) solution to the antiparallel form just by the addition of K+ ions in the range 10–50 mM Moreover, addition of ThT cooperatively stabilizes the K+ induced antiparallel quadruplexes by a ΔTm ∼11 °C The distinction of ThT as a quadruplex inducer has been contrasted with the erstwhile used structurally related dye, Thiazole Orange (TO), which did not induce any q

503 citations

Journal ArticleDOI
TL;DR: The advantages and disadvantages of the various nonradiative models while focusing on the model that was initially proposed by Glasbeek and co-workers for auramine-O to be the best suited for ThT are discussed.
Abstract: Thioflavin-T (ThT) can bind to amyloid fibrils and is frequently used as a fluorescent marker for in vitro biomedical assays of the potency of inhibitors for amyloid-related diseases, such as Alzheimer's disease, Parkinson's disease, and amyloidosis. Upon binding to amyloid fibrils, the steady-state (time-integrated) emission intensity of ThT increases by orders of magnitude. The simplicity of this type of measurement has made ThT a common fluorescent marker in biomedical research over the last 50 years. As a result of the remarkable development in ultrafast spectroscopy measurements, researchers have made substantial progress in understanding the photophysical nature of ThT. Both ab initio quantum-mechanical calculations and experimental evidence have shown that the electronically excited-state surface potential of ThT is composed of two regimes: a locally excited (LE) state and a charge-transfer (CT) state. The electronic wave function of the excited state changes from the initial LE state to the CT state as a result of the rotation around a single C-C bond in the middle of the molecule, which connects the benzothiazole moiety to the dimethylanilino ring. This twisted-internal-CT (TICT) is responsible for the molecular rotor behavior of ThT. This Account discusses several factors that can influence the LE-TICT dynamics of the excited state. Solvent, temperature, and hydrostatic pressure play roles in this process. In the context of biomedical assays, the binding to amyloid fibrils inhibits the internal rotation of the molecular segments and as a result, the electron cannot cross into the nonradiative "dark" CT state. The LE state has high oscillator strength that enables radiative excited-state relaxation to the ground state. This process makes the ThT molecule light up in the presence of amyloid fibrils. In the literature, researchers have suggested several models to explain nonradiative processes. We discuss the advantages and disadvantages of the various nonradiative models while focusing on the model that was initially proposed by Glasbeek and co-workers for auramine-O to be the best suited for ThT. We further discuss the computational fitting of the model for the nonradiative process of ThT.

305 citations

Journal ArticleDOI
TL;DR: These efforts fundamentally extend existing understanding about the origins of amyloid-induced photophysical changes by preventing the fluorophore from adopting its preferred excited state configuration, nonradiative relaxation pathways are minimized and quantum yield is increased.
Abstract: The small molecule thioflavin T (ThT) is a defining probe for the identification and mechanistic study of amyloid fiber formation. As such, ThT is fundamental to investigations of serious diseases such as Alzheimer’s disease, Parkinson disease, and type II diabetes. For each disease, a different protein undergoes conformational conversion to a β-sheet rich fiber. The fluorescence of ThT exhibits an increase in quantum yield upon binding these fibers. Despite its widespread use, the structural basis for binding specificity and for the changes to the photophysical properties of ThT remain poorly understood. Here, we report the co-crystal structures of ThT with two alternative states of β-2 microglobulin (β2m); one monomeric, the other an amyloid-like oligomer. In the latter, the dye intercalates between β-sheets orthogonal to the β-strands. Importantly, the fluorophore is bound in such a manner that a photophysically relevant torsion is limited to a range of angles generally associated with low, not high, quantum yield. Quantum mechanical assessment of the fluorophore shows the electronic distribution to be strongly stabilized by aromatic interactions with the protein. Monomeric β2m gives little increase in ThT fluorescence despite showing three fluorophores, at two binding sites, in configurations generally associated with high quantum yield. Our efforts fundamentally extend existing understanding about the origins of amyloid-induced photophysical changes. Specifically, the β-sheet interface that characterizes amyloid acts both sterically and electronically to stabilize the fluorophore’s ground state electronic distribution. By preventing the fluorophore from adopting its preferred excited state configuration, nonradiative relaxation pathways are minimized and quantum yield is increased.

294 citations


Cites background from "Thioflavin T as a molecular rotor: ..."

  • ...fibrils of the Alzheimer’s disease Abeta(16-22) peptide probed by molecular dynamics simulations....

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  • ...This can be compared to observations that show increased quantum yield for ThT in viscous solvents such as glycerol (21)....

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  • ...Wu C, et al. (2008) The binding of thioflavin T and its neutral analog BTA-1 to protofibrils of the Alzheimer’s disease Abeta(16-22) peptide probed by molecular dynamics simulations....

    [...]

Journal ArticleDOI
10 Apr 2017-Amyloid
TL;DR: A conceptual instruction manual, covering appropriate considerations and pitfalls related to the use of ThT, and recommendations for complementary techniques to address shortcomings in the ThT assay.
Abstract: Thioflavin T (ThT) has been widely used to investigate amyloid formation since 1989. While concerns have recently been raised about its use as a probe specific for amyloid, ThT still continues to be a very valuable tool for studying kinetic aspects of fibrillation and associated inhibition mechanisms. This review aims to provide a conceptual instruction manual, covering appropriate considerations and pitfalls related to the use of ThT. We start by giving a brief introduction to amyloid formation with focus on the morphology of different aggregate species, followed by a discussion of the quality of protein needed to obtain reliable fibrillation data. After an overview of the photochemical basis for ThT's amyloid binding properties and artifacts that may arise from this, we describe how to plan and analyze ThT assays. We conclude with recommendations for complementary techniques to address shortcomings in the ThT assay.

235 citations


Cites background from "Thioflavin T as a molecular rotor: ..."

  • ...Decreasing solvent temperatures will increase the inherent ThT fluorescence due to increased solvent viscosity [89,91]....

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References
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Journal ArticleDOI
TL;DR: A description of the ab initio quantum chemistry package GAMESS, which can be treated with wave functions ranging from the simplest closed‐shell case up to a general MCSCF case, permitting calculations at the necessary level of sophistication.
Abstract: A description of the ab initio quantum chemistry package GAMESS is presented. Chemical systems containing atoms through radon can be treated with wave functions ranging from the simplest closed-shell case up to a general MCSCF case, permitting calculations at the necessary level of sophistication. Emphasis is given to novel features of the program. The parallelization strategy used in the RHF, ROHF, UHF, and GVB sections of the program is described, and detailed speecup results are given. Parallel calculations can be run on ordinary workstations as well as dedicated parallel machines. © John Wiley & Sons, Inc.

18,546 citations

BookDOI
25 Apr 2012
TL;DR: In this article, the effects of intermolecular photophysical processes on fluorescence emission are discussed and an analysis of the effect of polarity of fluorescence emissions is presented.
Abstract: Preface. Prologue. Introduction. Absorption of UV--visible light. Characteristics of Fluorescence Emission. Effects of Intermolecular Photophysical Processes on Fluorescence Emission. Fluorescence polarization: Emission Ansotropy. Principles of steady--state and time--resolved fluorometric techniques. Effect of polarity of fluorescence emission. Polarity probes. Microviscosity, fluidity, molecular mobility. Estimation by means of fluorescent probes. Resonance energy transfer and its applications. Fluorescent molecular sensors of ions and molecules. Advanced techniques in fluorescence spectroscopy. Epilogue. Index.

4,261 citations

Journal ArticleDOI
Harry LeVine1
TL;DR: Thioflavine T associates rapidly with aggregated fibrils of the synthetic β/A4‐derived peptides β( 1–28) and β(1–40), giving rise to a new excitation maximum at 450 nm and enhanced emission at 482 nm, as opposed to the 385 nm and 445 nm of the free dye.
Abstract: Thioflavine T (ThT) associates rapidly with aggregated fibrils of the synthetic beta/A4-derived peptides beta(1-28) and beta(1-40), giving rise to a new excitation (ex) (absorption) maximum at 450 nm and enhanced emission (em) at 482 nm, as opposed to the 385 nm (ex) and 445 nm (em) of the free dye. This change is dependent on the aggregated state as monomeric or dimeric peptides do not react, and guanidine dissociation of aggregates destroys the signal. There was no effect of high salt concentrations. Binding to the beta(1-40) is of lower affinity, Kd 2 microM, while it saturates with a Kd of 0.54 microM for beta(1-28). Insulin fibrils converted to a beta-sheet conformation fluoresce intensely with ThT. A variety of polyhydroxy, polyanionic, or polycationic materials fail to interact or impede interaction with the amyloid peptides. This fluorometric technique should allow the kinetic elucidation of the amyloid fibril assembly process as well as the testing of agents that might modulate their assembly or disassembly.

2,188 citations