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Principles Of Fluorescence Spectroscopy

Because of its fundamental importance in many branches of science, hydrogen bonding is a subject of intense contemporary research interest. The physical and chemical properties of hydrogen bonds in the ground state have been widely studied both experimentally and theoretically by chemists, physicists, and biologists. However, hydrogen bonding in the electronic excited state, which plays an important role in many photophysical processes and photochemical reactions, has scarcely been investigated.Upon electronic excitation of hydrogen-bonded systems by light, the hydrogen donor and acceptor molecules must reorganize in the electronic excited state because of the significant charge distribution difference between the different electronic states. The electronic excited-state hydrogen-bonding dynamics, which are predominantly determined by the vibrational motions of the hydrogen donor and acceptor groups, generally occur on ultrafast time scales of hundreds of femtoseconds. As a result, state-of-the-art femtos...

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Hydrogen Bonding in the Electronic Excited State

There is great need for stand-alone luminescence-based chemosensors that exemplify selectivity, sensitivity, and applicability and that overcome the challenges that arise from complex, real-world media. Discussed herein are recent developments toward these goals in the field of supramolecular luminescent chemosensors, including macrocycles, polymers, and nanomaterials. Specific focus is placed on the development of new macrocycle hosts since 2010, coupled with considerations of the underlying principles of supramolecular chemistry as well as analytes of interest and common luminophores. State-of-the-art developments in the fields of polymer and nanomaterial sensors are also examined, and some remaining unsolved challenges in the area of chemosensors are discussed.

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Supramolecular Luminescent Sensors

High-fidelity mapping of amyloid-β (Aβ) plaques is critical for the early detection of Alzheimer’s disease. However, in vivo probing of Aβ plaques by commercially available thioflavin derivatives (ThT or ThS) has proven to be extremely limited, as evident by the restriction of enrichment quenching effect, low signal-to-noise (S/N) ratio, and poor blood–brain barrier (BBB) penetrability. Herein, we demonstrate a rational design strategy of near-infrared (NIR) aggregation-induced emission (AIE)-active probes for Aβ plaques, through introducing a lipophilic π-conjugated thiophene-bridge for extension to NIR wavelength range with enhancement of BBB penetrability, and tuning the substituted position of the sulfonate group for guaranteeing specific hydrophilicity to maintain the fluorescence-off state before binding to Aβ deposition. Probe QM-FN-SO3 has settled well the AIE dilemma between the lipophilic requirement for longer emission and aggregation behavior from water to protein fibrillogenesis, thus making ...

Rational Design of Near-Infrared Aggregation-Induced-Emission-Active Probes: In Situ Mapping of Amyloid-β Plaques with Ultrasensitivity and High-Fidelity

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.

https://www.tandfonline.com/doi/pdf/10.1080/13506129.2017.1304905

ThT 101: a primer on the use of thioflavin T to investigate amyloid formation

Ultrafast fluorescence spectroscopy reveals a dominant weakly-emissive population of fibril bound thioflavin-T

Using sub-picosecond fluorescence upconversion spectroscopy, the effect of supramolecular confinement on the ultrafast excited state torsional dynamics of an amyloid fibril sensing dye, Thioflavin-T (ThT), is investigated in a novel cyclodextrin derivative, Sulphobutylether β-cyclodextrin (SBE-β-CD). The encapsulation of ThT inside the nanocavity of SBE-β-CD results in a significant increase in the emission intensity and the excited state lifetime of ThT when compared with native β-CD. Detailed analysis of the time-resolved emission spectra (TRES) shows that the time dependent changes in the integrated area, mean frequency and the width of the emission spectra are appreciably slower as compared with bulk water and native β-CD. These features suggest a significant confinement effect on the ultrafast torsional dynamics of ThT. The ionic strength of the medium significantly affects the complexation of ThT with SBE-β-CD, which indicates that the interaction between the host and the guest is predominantly electrostatic in nature. The results further suggest that the hydrophobic interaction in SBE-β-CD, although minor in contribution in the present case, is comparatively stronger than the native β-CD.

Ultrafast torsional dynamics of Thioflavin-T in an anionic cyclodextrin cavity

PicoGreen: a better amyloid probe than Thioflavin-T.

Ultrafast molecular rotor: an efficient sensor for premelting of natural DNA.

The effect of confinement on the ultrafast torsional relaxation dynamics of a well-known ultrafast molecular rotor (UMR) and a recently reported amyloid fibril sensor, Auramine O (AuO), is investigated inside the nanocavity of a novel cyclodextrin derivative, sulphobutylether β-cyclodextrin (SBE-β-CD), using sub-pisosecond fluorescence upconversion spectroscopy. The nanocavity of SBE-β-CD induces a significant increase in the emission intensity and results in a slower transient decay trace of Auramine O when compared to the native β-CD. Detailed analysis of the time-resolved emission spectral features shows that the time-dependent changes in both the mean frequency and the width of the emission spectra are considerably slower as compared to bulk water and native β-CD, which suggests that the excited state torsional dynamics of AuO has been significantly affected in the nanocavity of SBE-β-CD. This effect on the torsional dynamics has been attributed to the perturbation of the water structure inside the nanocavity of SBE-β-CD which suppresses the ability of fast collective solvent reorientation motion to promote the excited-state torsional relaxation of Auramine O. The effect of ionic strength of the medium is invoked to analyze the contribution of electrostatic interactions towards the binding of AuO with SBE-β-CD and is corroborated well by computation of electrostatic potentials for the host molecules. The results also suggest that the hydrophobic interaction provided by the SBE-β-CD is larger than the native β-CD.

Aruna K. Mora

Papers

Ultrafast fluorescence spectroscopy reveals a dominant weakly-emissive population of fibril bound thioflavin-T

Ultrafast torsional dynamics of Thioflavin-T in an anionic cyclodextrin cavity

PicoGreen: a better amyloid probe than Thioflavin-T.

Ultrafast molecular rotor: an efficient sensor for premelting of natural DNA.

Dynamics under confinement: torsional dynamics of Auramine O in a nanocavity