Time-resolved Fluorescence Spectroscopy Research Articles

Probing lithium-ion induced micro-environment changes in pyrrolidinium-based mono-cationic and di-cationic ionic liquids.

Recent advancements in lithium-ion battery technology have focused on integrating lithium salts into ionic liquid (IL) electrolytes to overcome some of the limitations associated with traditional organic liquid electrolytes. However, this proposition brings complexities because lithium salts can have a profound impact on the microscopic structural organization of ILs. In this work, we investigate the structural organization and diffusion dynamics of pyrrolidinium-based monocationic ionic liquids (MILs) and dicationic ionic liquids (DILs) in the absence and presence of lithium salt by employing time-resolved fluorescence spectroscopy (TRFS), nuclear magnetic resonance (NMR) spectroscopy, and molecular dynamics (MD) simulation studies. Our findings reveal that the coordination of Li+ ions with the anions of both MILs and DILs leads to a change in the structural arrangement of the nonpolar regions of the given media. Quite interestingly, a significantly more pronounced perturbation in the nano-structural organization of MILs as compared to DILs upon the introduction of Li+ ions has been observed in the current investigations. Through meticulous data analysis, it has been elucidated that the differential impact of lithium salt on the DIL as compared to the MIL stems from the unique structural organization of the DIL. The findings of this study are expected to provide valuable insights into the design and formulations of optimized electrolytes for lithium-ion battery applications.

Deprotonation-Induced Large Fluorescence Turn ON in a 2,4-Bis(benzo[d]thiazol-2-yl)phenol (HBT-BT) Derivative.

2-(2'-Hydroxyphenyl)benzothiazole (HBT) is an interesting candidate that has been used to develop fluorescent probes with large Stokes' shifts (Δλ > 100 nm) by utilizing excited-state intramolecular proton transfer (ESIPT). The efficiency of the ESIPT process in HBT is dependent on the acidity of the central phenolic group. The possible deprotonation of the enol form of HBT (PhOH → PhO- + H+) can generate anionic form in solution that exhibits a noticeable hypsochromic effect in emission (λem ≈ 475). By introduction of an appropriate substituent to the central phenolic ring, the ESIPT efficiency of the HBT can be controlled by modulating enol to anionic dynamic equilibrium. In this work, we extensively studied the solvent-dependent equilibrium of the 2-enol, 2-keto, and 2-anoinic species of the HBT derivative 2,4-bis(benzo[d]thiazol-2-yl)phenol (2) by steady-state and time-resolved fluorescence spectroscopy. Probe 2 was synthesized by attaching a second benzothiazole unit via a para phenylene linkage and was found to be significantly acidic. In comparison to parent HBT (1), probe 2 produced a highly emissive (λem ≈ 475) 2-anionic species in solution by deprotonation. The 2-anionic was dominated in polar aprotic solvents such as DMF and DMSO and much weakly observed in nonpolar to moderately polar solvents. The solvent-dependent equilibrium was studied by 1H NMR spectroscopy in different solvents. The formation of 2-anionic was found to be dependent on (a) the type of solvent and (b) the presence of basic anionic species (i.e., fluoride). The photophysical properties (absorbance and emission) of probe 2 were investigated in different solvent environments and in the presence of different anionic species to understand the dynamic equilibrium that leads to the generation of 2-anionic in solution. The fluorescence lifetime measurements of 2 in different solvents revealed the existence of 2-enol, 2-keto, and 2-anionic species. Also, the fluoride-induced transformation of 2-enol to 2-anionic was studied by fluorescence lifetime measurements. The density functional theory (DFT)-based computational calculations were performed to evaluate the electronic nature of the dynamic equilibrium that produced 2-anionic. Computational studies, employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT), confirmed that the 2-enol species is stable in the ground state, while upon excitation, 2-enol species undergoes ESIPT spontaneously. Computed absorption and emission wavelengths showed good agreement with the experimental results.

Fluorescence Quenching and Electron Transfer Dynamics of a Thiophene-Substituted 1,3,4-Oxadiazole Derivative with Nitroaromatic Compounds.

This study investigates the fluorescence quenching behavior of a newly synthesized thiophene-substituted 1,3,4-oxadiazole derivative, 2-(4-(4-vinyl phenyl)phenyl)-5-(5-(4-vinyl phenyl)thiophene-2-yl)-1,3,4-oxadiazole (TSO), in the presence of various nitroaromatic compounds (NACs), including 2-nitrotoluene, 4-nitrotoluene, nitrobenzene, and picric acid (2,4,6-trinitrophenol). The interactions were examined in an ethanol medium at room temperature using steady-state and time-resolved fluorescence spectroscopy. Steady-state fluorescence analysis revealed a non-linear Stern-Volmer (SV) plot exhibiting positive deviation, while time-resolved measurements displayed a linear relationship. To interpret these findings, ground-state complex formation and the sphere-of-action static quenching models were applied. The study determined key quenching parameters, including the Stern-Volmer constant, quenching rate constant, static quenching constant, and sphere-of-action radius. Notably, fluorescence quenching efficiency increased with the number of NO2 groups in the NACs.Electrochemical analysis, complemented by Density Functional Theory (DFT) calculations, confirmed that electron transfer was the primary quenching mechanism. Furthermore, binding site analysis demonstrated a 1:1 binding stoichiometry between TSO and NACs, with picric acid exhibiting the highest binding affinity. Given the growing interest in fluorescence-based sensing approaches, these findings contribute valuable insights into the development of advanced sensors for detecting nitroaromatic pollutants and explosive residues.

Effect of Bile Salt on the Self‐Assembled Architecture of Pluronic P123 Micelles: A Chemometric and Fluorescence Study

AbstractIn our present work the effect of bile salt namely sodium cholate (NaC) on the thermotropic microenvironment of Pluronic P123 (PEO20‐PPO70‐PEO20) block co‐polymer is investigated by using steady state and time resolved fluorescence spectroscopy in combination with multivariate curve resolution and alternate least square (MCR‐ALS) technique. 1‐Naphthol (1‐NaP) is used as an excited state proton transfer (ESPT) fluorescent molecular probe to gain insight into the microenvironment of Pluronic P123‐NaC system. We observed that effective interaction of NaC in Pluronic P123 at different temperatures (2–25 °C) reduces the overall fluorescence intensity of 1‐NaP. However, the sol to gel transition temperature remains unaffected in presence NaC at low concentration. MCR‐ALS analysed fluorescence spectra of 1‐NaP indicated that the relative contribution of anionic peak increases and neutral peak decreases in presence of NaC in Pluronic P123. This is due to the fact that hydration in the Pluronic P123 microenvironment increases by the charged interfacial region of NaC. Fluorescence life time data suggested that 1‐NaP is distributed mostly in polymer‐water interface and core region of Pluronic P123 experiencing relatively polar microenvironment with restricted diffusive motion.

Exploring Time-Resolved Fluorescence Data: A Software Solution for Model Generation and Analysis

Time-resolved fluorescence techniques, such as fluorescence lifetime imaging microscopy (FLIM), fluorescence correlation spectroscopy (FCS), and time-resolved fluorescence spectroscopy, are ideally suited for investigating molecular dynamics and interactions in biological and chemical systems. However, the analysis and interpretation of these datasets require advanced computational tools capable of handling diverse models and datasets. This paper presents a comprehensive software solution designed for model generation and analysis of time-resolved fluorescence data with a strong focus on fluorescence for quantitative structural analysis and biophysics. The software supports the integration of multiple fluorescence techniques and provides users with robust tools for performing complex model analysis across diverse experimental data. By enabling global analysis, model generation, data visualization, and sampling over model parameters, the software enhances the interpretability of intricate fluorescence phenomena. By providing flexible modeling capabilities, this solution offers a versatile platform for researchers to extract meaningful insights from time-resolved fluorescence data, aiding in the understanding of dynamic biomolecular processes.

Comparative interaction of silver nanoparticles with diverse classes of proteins: Selectivity toward silk sericin protein from Antheraea assama.

Comparative interaction of silver nanoparticles with diverse classes of proteins: Selectivity toward silk sericin protein from Antheraea assama.

Tuning Excited-State Charge Transfer Character in Cofacial Core-Substituted Perylenediimide Dimers.

Understanding the interplay between excimer formation and symmetry-breaking charge separation is important for optimizing charge separation in organic photovoltaic materials. To explore this connection, we synthesized four 1,6,7,12-tetrakis(p-X-phenoxy)perylene-(3,4:9,10)-bisdicarboximide cofacially stacked dimers, where X = MeO, tert-butyl, Br, and CF3. Steady-state spectroscopy reveals H-type aggregation and excimer formation in all four dimers, while transient absorption spectroscopy shows relatively small changes in their excited-state absorptions. However, time-resolved fluorescence (TRF) spectroscopy shows that relaxation occurs from an initial Frenkel exciton-dominated excimer state to one in which charge transfer (CT) character contributes. Relaxation to the lower-lying state with CT character is attributed to a combination of structural and charge distribution changes elicited by varying the substituents. This study illustrates how subtle changes in charge distribution and structure can combine to influence the excited state dynamics that influence charge separation in molecular dimers.

Role of growth conditions and physicochemical factors controlling the removal and biomineralization of U(VI) by Stenotrophomonas bentonitica BII-R7.

Role of growth conditions and physicochemical factors controlling the removal and biomineralization of U(VI) by Stenotrophomonas bentonitica BII-R7.

Amyloid capture and aggregation inhibition by human serum albumin.

Amyloid capture and aggregation inhibition by human serum albumin.

Insight into sequestration and release characteristics of uranium(VI) on phlogopite in the presence of humic acid.

Insight into sequestration and release characteristics of uranium(VI) on phlogopite in the presence of humic acid.

Spectroscopic Visualization of Drug-Biomolecules Interactions: An Insight to Fluorescence Quenching as Tool in Drug Discovery.

Fluorescence quenching, a process where the intensity of fluorescence is diminished by various molecular interactions, has emerged as a critical tool in drug discovery. This review delves into the underlying mechanisms of fluorescence quenching, including static and dynamic quenching, Förster resonance energy transfer (FRET), and photoinduced electron transfer (PET). Each mechanism offers unique insights into molecular interactions, binding affinities, and conformational changes of drug candidates, enabling researchers to dissect complex biological systems with precision. The application of fluorescence quenching in high-throughput screening (HTS) is particularly emphasized, highlighting its role in identifying lead compounds and optimizing drug-target interactions. Furthermore, the review explores the integration of advanced fluorescence techniques, such as time-resolved fluorescence and single-molecule spectroscopy, in elucidating the quenching phenomena at a molecular level. These techniques provide a deeper understanding of drug-receptor interactions, allosteric modulation, and protein dynamics, which are pivotal in the drug development pipeline. The potential of fluorescence quenching in probing the pharmacokinetics and pharmacodynamics of novel therapeutics is also discussed, underscoring its versatility and effectiveness. By offering a comprehensive analysis of fluorescence quenching mechanisms and their applications, this review aims to inform future drug discovery endeavors, fostering the development of more effective and targeted therapies.

Nanosecond-pulsed electroluminescence from high current-driven quantum-dot light-emitting diodes.

Ultrashort optical emission, with pulse duration ranging from nanoseconds to femtoseconds, is usually obtained from lasers. In this work, we achieve nanosecond-pulsed electroluminescence (EL) from a solution-processed fast-response quantum dot light-emitting diode (QLED). By modeling the QLED with a resistor-capacitor equivalent circuit and analyzing the transient current of the circuit, the dynamic of the carrier injection and transport process that fundamentally affects the transient EL of QLED is revealed, which helps to guide the optimization of fast-response QLED. Driven by a high current source, the optimized QLED can output stable and repeatable ultrashort EL with a pulse duration of 20 nanoseconds, a repetition rate of 50 kilohertz, and a high radiant exitance of 5.4 watts per square centimeter. Enabled by the nanosecond-pulsed EL, the developed QLED can be directly used as an instantaneous excitation source for time-resolved fluorescence spectroscopy. Meanwhile, its use as an exposure flash for high-speed imaging is also demonstrated.

Photophysics of a Nucleoside Analogue: 4-Cyanoindole-2'-deoxyribonucleoside.

It has been shown that 4-cyanoindole-2'-deoxyribonucleoside (4CNI-NS) is a versatile spectroscopic probe of DNA structure and dynamics, as it can pair with all four natural DNA bases. However, its photophysics have not been examined in detail. Herein, we employed multiple techniques, including static fluorescence spectroscopy, time-resolved fluorescence spectroscopy, transient infrared spectroscopy, and theoretical calculations, to assess the photophysical properties of this nucleoside analogue in a series of solvents. We found that (1) its fluorescence has a large quantum yield (0.85 ± 0.10) and a relatively long decay lifetime (10.3 ± 1.0 ns) in H2O, both of which become smaller in other solvents examined, (2) its maximum fluorescence emission frequency exhibits a linear dependence on the relative polarity index of the solvent, (3) the oscillator strength of its C≡N stretching vibration is increased by a factor of >10 upon transition to its excited electronic state (S1), (4) besides solvent relaxation, a rotational motion around the single bond connecting the pentose group and the indole ring is also present in the S1 state, and (5) in aprotic solvents both processes lead the C≡N stretching frequency (νESA) to shift toward higher frequencies, whereas in protic solvents the effects of these processes are more complex. Taken together, these findings provide a molecular basis for interpreting the spectroscopic signals of this nucleoside analogue in practical applications.

Structures of complete HIV-1 TAR RNA portray a dynamic platform poised for protein binding and structural remodeling

The HIV-1 TAR RNA plays key roles in viral genome architecture, transcription and replication. Previous structural analyses focused on its upper stem loop, which has served as a paradigm to study RNA structural dynamics. However, an imperfectly paired lower stem immediately abuts and stacks with the upper half, both of which are required for efficient HIV replication. Here, we report crystal structures of the full-length HIV-1 TAR which reveal substantial conformational mobility in its three conserved bulges and in its lower stem, which coordinately maintain the structural fluidity of the entire RNA. We find that TAR RNA is a robust inhibitor of PKR, and primarily uses its lower stem to capture and sequester PKR monomers, preventing their dimerization and activation. The lower stem exhibits transient conformational excursions detected by a ligation assay. Time-resolved fluorescence spectroscopy reveals local and global TAR structural remodeling by HIV-1 nucleocapsid, Tat, and PKR. This study portrays the structure, dynamics, and interactions of a complete TAR RNA, uncovers a convergent RNA-based viral strategy to evade innate immunity, and provides avenues to develop antivirals that target a dynamic, multifunctional viral RNA.

U(VI) sorption onto rutile surface in the presence or absence of EDTA: A combined macroscopic and spectroscopic study.

U(VI) sorption onto rutile surface in the presence or absence of EDTA: A combined macroscopic and spectroscopic study.

Synthesis of Nonadentate Ligand Diethylene Glycol-Bis(3-Aminopropyl Ether)-N,N,N',N'-Tetraacetic Acid DEGTA and Its Complexation Behavior toward Trivalent Lanthanides and Actinides.

A new nonadentate ligand, DEGTA (diethylene glycol-bis(3-aminopropyl ether)-N,N,N',N'-tetraacetic acid), from the polyaminopolycarboxylate family, was synthesized in a two-step reaction. The ligand's pH-dependent behavior (structure and pKa values) was determined by nuclear magnetic resonance (NMR) spectroscopy. The complexation ability of the ligand toward trivalent lanthanides and actinides was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) using Eu(III) and Cm(III) as representatives. For Eu(III), two species occurring at different pH values were observed and corroborated by concentration- and pD-dependent NMR-titration series, viz. [EuH2(DEGTA)]+ and [Eu(DEGTA)]-. The latter is shown to be nine-coordinate, forming isostructural complexes with Cm(III) and Sm(III) as inferred from TRLFS and 2D NMR experiments, respectively. Since DEGTA can be seen as a consecutive derivative of EDTA and EGTA with an elongated backbone, the structures of their Eu(III) complexes were calculated using density functional theory (DFT) and the same aminoacetate binding motif proven by Fourier-transform infrared (FT-IR) spectroscopy. Upon comparison of structure-property relationships (denticity and chain length vs coordination geometry and complex stability) one can draw conclusions on DEGTA's complexation behavior in particular, and some generalizable trends in complexation properties within the complexone series are discussed. Looking further ahead, this knowledge will help in further developing decontamination, decommissioning, and decorporation strategies.

Application of phage surface display for the identification of Eu3+-binding peptides.

Europium as one of the rare earth elements (REE) has outstanding properties in terms of its application for high-tech and renewable energy products. The high supply risk of REE, coupled with their low recovery rates from secondary sources, necessitates innovative recycling approaches. We introduce a phage display-based peptide biosorbent recycling technology that offers a cost-effective and environmentally friendly solution for recovering metal ions, supporting circular economy goals. In this study, we used phage surface display to screen for peptides with high affinity for europium (III) ions (Eu3+). Performing several independent biopanning experiments with the Ph.D.-12 Phage Display Peptide Library and different elution methods as well as combining them with next-generation sequencing, we identified eight peptides with moderate to good affinities for Eu3+ ions, verified by time-resolved laser fluorescence spectroscopy. The peptides EALTVNIKREME as well as DVHHVDGNDLQPFEGGGS and DSIHSDVTKDGRYPVEGGGS, the latter are variants of enriched dodecamers, proved to be the best candidates for future biosorption and selectivity studies. This study underscores the potential of phage surface display for peptide-based REE recovery, laying the foundation for selective recycling technologies from secondary raw materials.

Location of 7-Aminoactinomycin D in Micellar Medium Depends on Ionic Nature of the Surfactant Head Group.

7-Aminoactinomycin D (7AAMD) is the fluorescent analogue of the anticancer drug actinomycin D (AMD). In order to overcome toxic side effects and enhanced bioavailability of 7AAMD, micellar drug carrier systems could be useful. We have used cationic (hexadecetyltrimethylammonium bromide [CTAB]), anionic (sodium dodecyl sulphate [SDS]) and non-ionic (t-octylphenoxypolyoxyethanol, Triton-X100 [TX 100]) surfactants to prepare micelle. We have explored the mechanism of the interaction of 7AAMD with micelles using steady-state and time-resolved fluorescence spectroscopy. Our results revealed that the Stokes' shift values of 7AAMD were decreased in all three micellar medium compared to that in the absence of any micelle. Thus, 7AAMD is localized in less polar microenvironment of micelles than bulk water. In addition, from the time-resolved fluorescence study of 7AAMD, we found that the relative contribution of the conformers of 7AAMD depended on the surfactant head group. Furthermore, acrylamide induced fluorescence quenching study shows differential accessibility of the quencher molecules towards 7AAMD depending on the ionic nature of the surfactant head group. In the presence of acrylamide, 7AAMD was expelled out from the non-ionic TX 100 micelle but not in CTAB and SDS micelle. Thus, our results are valuable to design new drug delivery system for AMD-like antitumor agents.

Perspective: fluorescence lifetime imaging and single-molecule spectroscopy for studying biological condensates

Abstract Biological condensates, often formed via liquid-liquid phase separation (LLPS), are membraneless compartments organizing biochemical reactions. Recent advances have shifted the focus from identifying condensates to elucidating their dynamic biological functions, such as buffering concentrations, mediating reactions, and regulating signaling. These are critical for cellular processes and implicated in diseases like cancer and neurodegeneration. Advanced microscopy techniques, including fluorescence lifetime imaging microscopy (FLIM), FLIM-FRET, and fluorescence correlation spectroscopy (FCS), enable quantitative, real-time investigations of condensate composition, dynamics, material properties, and their responses to environmental stimuli in live cells. This perspective highlights the utility of time-resolved fluorescence and single-molecule spectroscopy techniques for shedding light on condensate functions, properties, and interactions with membranes, offering insights into cellular physiology and pathology.

Excited-State Proton Transfer Dynamics of Cyanonaphthol in Protic Ionic Liquids: Concerted Effects of Basicity of Anions and Alkyl Carbons in Cations.

Excited-state proton transfer (ESPT) reactions of 5-cyano-2-naphthol (5CN2) and 5,8-dicyano-2-naphthol (DCN2) were investigated in protic ionic liquids (PILs) composed of quaternary ammonium (NnnnH+) (n = 2, 4, or 8) and hexanoate (C5H11COO-) using time-resolved fluorescence spectroscopy. The effects of the number of alkyl carbons in the cation and the basicity of the anion on the reaction yield and dynamics were examined. In a series of [NnnnH][C5H11COO], fluorescence from the hydrogen-bonding complex (AHBX-*) of a proton-dissociated form (RO-*) with a solvent acid in the electronic excited state was observed between the fluorescence bands of an acidic form (ROH*) and an anionic form (RO-*) as in the case of [N222H][CF3COO] (Fujii et al., J. Phys. Chem B, 2017, 121, 6042). The yield, formation rate, and decay rate of AHBX-* were assessed by the steady-state fluorescence intensity ratio of AHBX-* to RO-* and by analysis of the time-resolved fluorescence spectra within several tens of nanoseconds. The stability of AHBX-* was significantly different from that in [N222H][CF3COO] and depended on the number of alkyl carbons in the cation. The formation of AHBX-* was quite fast compared to the case in [N222H][CF3COO] and almost close to the excitation pulse width. Excitation wavelength dependence of the fluorescence dynamics was observed within several hundred picoseconds for the series of [NnnnH][C5H11COO]. The origin was ascribed to the complex with solvent IL formed in the electronic ground state, as suggested by the density-functional theory (DFT) calculations.