State Fluorescence Research Articles

Cooperativity of ESPT and Aggregation-Induced Emission Effects-An Experimental and Theoretical Analysis of a 1,3,4-Thiadiazole Derivative.

4-[5-(Naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol (NTBD) was extensively studied through stationary UV-vis absorption and fluorescence measurements in various solvents and solvent mixtures and by first-principles quantum chemical calculations. It was observed that while in polar solvents (e.g., methanol) only a single emission band emerged; the analyzed 1,3,4-thiadiazole derivative was capable of producing dual fluorescence signals in low polarity solvents (e.g., n-hexane) and certain solvent mixtures (e.g., methanol/water). As clearly follows from the experimental spectroscopic studies and theoretical modeling, the specific emission characteristic of NTBD is triggered by the effect of enol → keto excited-state intramolecular proton transfer (ESIPT) that in the case of solvent mixture is reinforced by aggregation of thiadiazole molecules. Specifically, the restriction of intramolecular rotation (RIR) due to environmental hindrance suppresses the formation of non-emissive twisted intramolecular charge transfer (TICT) excited keto* states. As a result, this particular thiadiazole derivative is capable of simultaneously producing both ESIPT and aggregation-induced emission (AIE).

Naphthoic Acid Derivatives@Boric Acid Based Fast Photo‐Activated Room‐Temperature Phosphorescence Materials with Dynamic Changed Emission Color

AbstractPhotoactivated dynamic ultralong room‐temperature phosphorescent (PAD‐URTP) materials with changing emission colors are attractive and meaningful but are rarely reported. Herein, a one‐pot heat treatment strategy for embedding 1‐hydroxy‐2‐naphthoic acid (1H2NA) and 2‐hydroxy‐1‐naphthoic acid (2H1NA) into boric acid (BA) matrix (named 1H2NA@BA and 2H1NA@BA) to construct PAD‐URTP materials is developed, which exhibits rapid and reversible photoactivated phosphorescence, as well as photo‐stimulated dynamic change of luminescence color. The luminescent color of 1H2NA@BA could continuously change from blue‐purple to bright cyan‐white upon prolonged 365 nm UV light irradiation, which is attributed to the combined effect of static blue fluorescence and dynamic photoactivated green phosphorescence. Significantly, it could emit over 10 s green afterglow after switching off the UV irradiation. The combination of experiment and theoretical calculation results reveal that their PAD‐URTP behavior is attributed to the energy accumulation of triplet states under UV light irradiation. Finally, a series of information encryption and a complete story of “a mouse and cake” are successfully fabricated by using 1H2NA@BA with other luminescence materials. Thus, this study demonstrates fast PAD‐URTP materials with dynamic color‐changing luminescence and opens up new possibilities as the photo‐responsive luminescent material for further mechanistic understanding and future application.

Computational aptamer design for spike glycoprotein (S) (SARS CoV-2) detection with an electrochemical aptasensor

A new bioinformatic platform (APTERION) was used to design in a short time and with high specificity an aptamer for the detection of the spike protein, a structural protein of SARS-CoV-2 virus, responsible for the COVID-19 pandemic. The aptamer concentration on the carbon electrode surface was optimized using static contact angle and fluorescence method, while specificity was tested using differential pulse voltammetry (DPV) associated to carbon screen-printed electrodes. The data obtained demonstrated the good features of the aptamer which could be used to create a rapid method for the detection of SARS-CoV-2 virus. In fact, it is specific for spike also when tested against bovine serum albumin and lysozyme, competitor proteins if saliva is used as sample to test for the virus presence. Spectrofluorometric characterization allowed to measure the amount of aptamer present on the carbon electrode surface, while DPV measurements proved the affinity of the aptamer towards the spike protein and gave quantitative results. The acquired data allowed to conclude that the APTERION bioinformatic platform is a good method for aptamer design for rapidity and specificity.Key points• Spike protein detection using an electrochemical biosensor• Aptamer characterization by contact angle and fluorescent measurements on electrode surface• Computational design of specific aptamers to speed up the aptameric sequence time

Deciphering the binding behavior and interaction mechanism of apigenin and α-glucosidase based on multi-spectroscopic and molecular simulation studies

This study investigated the molecular mechanism underlying the binding interaction between apigenin (API) and α-glucosidase (α-glu) by a combination of experimental techniques and computational simulation strategies. The spontaneously formation of stable API-α-glu complex was mainly driven by hydrogen bonds and hydrophobic forces, leading to a static fluorescence quenching of α-glu. The binding of API induced secondary structure and conformation changes of α-glu, decreasing the surface hydrophobicity of protein. Computational simulation results demonstrated that API could bind into the active cavity of α-glu via its interaction with active residues at the binding site. The important roles of key residues responsible for the binding stability and affinity between API and α-glu were further revealed by MM/PBSA results. In addition, it can be found that the entrance of active site tended to close after API binding as a result of its interaction with gate keeping residues. Furthermore, the structural basis for the binding interaction behavior of API was revealed and visualized by weak interaction analysis. The findings of our study revealed atomic-level mechanism of the interaction between API, which might shed light on the development of better inhibitors.

Morphophysiology of Punica Granatum L. under microalgae biomass stimulation

The use of microalgae has been proeminent in agricultural scenario, because it is an alternative product considered extremelly productive, which contains essential elements for plants. Thus, this study aimed to evaluate the morphophysiology of Punica granatum L. seedlings treated with Spirulina platensis and Scenedesmus sp. nanoparticles in controlled environment. The research was carried out at the of Federal University of Campina Grande, Pombal-PB, using a completely randomized design with five replications. The factorial scheme (2 x 4) was adopted, represented by two types of microalgae (Spirulina platensis; Scenedesmus sp.) and four doses of application (0, 5, 10 and 15%). Growth evaluations happened at 135 days after planting, verifying the number of leaves and branches and shoot length. The physiological parameters evaluated were gas exchanges, chlorophyll ‘a’ fluorescence, electron transport rate, stationary fluorescence, maximum fluorescence yield after light adaptation and quantum efficiency of PSII. Shoot length and number of branches had rises at doses of 6 and 15%. Number of leaves was induced in seedlings at dose of 8% with Spirulina platensis. Stomatal conductance and internal CO2 concentration increased in seedlings sprayed with Spirulina platensis. extract of Scenedesmus sp. improved the stationary fluorescence and quantum efficiency of PSII in pomegranate seedlings.

Solvent-Dependent Emissions Properties of a Model Aurone Enable Use in Biological Applications.

Fluorophores are powerful visualization tools and the development of novel small organic fluorophores are in great demand. Small organic fluorophores have been derived from the aurone skeleton, 2-benzylidenebenzofuran-3(2H)-one. In this study, we have utilized a model aurone derivative with a methoxy group at the 3' position and a hydroxyl group at the 4' position, termed vanillin aurone, to develop a foundational understanding of structural factors impacting aurone fluorescence properties. The fluorescent behaviors of the model aurone were characterized in solvent environments differing in relative polarity and dielectric constant. These data suggested that hydrogen bonding or electrostatic interactions between excited state aurone and solvent directly impact emissions properties such as peak emission wavelength, emission intensity, and Stokes shift. Time-dependent Density Functional Theory (TD-DFT) model calculations suggest that quenched aurone emissions observed in water are a consequence of stabilization of a twisted excited state conformation that disrupts conjugation. In contrast, the calculations indicate that low polarity solvents such as toluene or acetone stabilize a brightly fluorescent planar state. Based on this, additional experiments were performed to demonstrate use as a turn-on probe in an aqueous environment in response to conditions leading to planar excited state stabilization. Vanillin aurone was observed to bind to a model ATP binding protein, YME1L, leading to enhanced emissions intensities with a dissociation equilibrium constant equal to ~ 30 µM. Separately, the aurone was observed to be cell permeable with significant toxicity at doses exceeding 6.25 µM. Taken together, these results suggest that aurones may be broadly useful as turn-on probes in aqueous environments that promote either a change in relative solvent polarity or through direct stabilization of a planar excited state through macromolecular binding.

Increasing the polarity of β-lapachone does not affect its binding capacity with bovine plasma protein

Despite ortho-quinones showing several biological and pharmacological activities, there is still a lack of biophysical characterization of their interaction with albumin - the main carrier of different endogenous and exogenous compounds in the bloodstream. Thus, the interactive profile between bovine serum albumin (BSA) with β-lapachone (1) and its corresponding synthetic 3-sulfonic acid (2, under physiological pH in the sulphonate form) was performed. There is one main binding site of albumin for both β-lapachones (n ≈ 1) and a static fluorescence quenching mechanism was proposed. The Stern-Volmer constant (KSV) values are 104 M−1, indicating a moderate binding affinity. The enthalpy (−3.41 ± 0.45 and − 8.47 ± 0.37 kJ mol−1, for BSA:1 and BSA:2, respectively) and the corresponding entropy (0.0707 ± 0.0015 and 0.0542 ± 0.0012 kJ mol−1 K−1) values indicate an enthalpically and entropically binding driven. Hydrophobic interactions and hydrogen bonding are the main binding forces. The differences in the polarity of 1 and 2 did not change significantly the affinity to albumin. In addition, the 1,2-naphthoquinones showed a similar binding trend compared with 1,4-naphthoquinones.

Tuning the Absorption, Fluorescence, Intramolecular Charge Transfer, and Intersystem Crossing in Spiro[fluorene]acridinone.

In this work, we prepared a series of electron donor-acceptor systems based on spiro[fluorene-9,7'-dibenzo[c,h]acridine]-5'-one (SFDBAO). Our SFDBAOs consist of orthogonally positioned fluorenes and aromatic ketones. By fine-tuning the substitution of electron-donating pyrenes, the complex interplay among different excited-state decay channels and the overall impact of solvents on these decay channels were uncovered. Placing pyrene, for example, at the aromatic ketones resulted in a profound solvatochromism in the form of a bright charge-transfer (CT) emission spanning from yellow to red-NIR. In contrast, a dark non-emissive CT was noted upon pyrene substitution at the fluorenes. In apolar solvents, efficient triplet-excited state generation was observed for all SFDBAOs. Either charge transfer was concluded to mediate the intersystem crossing (ISC) in the case of pyrene substitution or the El-Sayed rule was applicable when lacking pyrene substitution as in the case of SFABAO. In polar solvents, charge separation is the sole decay upon pyrene substitution. Moreover, competition between ISC and CT lowered the triplet-excited state generation in SFDBAO.

Tuning the Absorption, Fluorescence, Intramolecular Charge Transfer, and Intersystem Crossing in Spiro[fluorene]acridinone

AbstractIn this work, we prepared a series of electron donor‐acceptor systems based on spiro[fluorene‐9,7’‐dibenzo[c,h]acridine]‐5’‐one (SFDBAO). Our SFDBAOs consist of orthogonally positioned fluorenes and aromatic ketones. By fine‐tuning the substitution of electron‐donating pyrenes, the complex interplay among different excited‐state decay channels and the overall impact of solvents on these decay channels were uncovered. Placing pyrene, for example, at the aromatic ketones resulted in a profound solvatochromism in the form of a bright charge‐transfer (CT) emission spanning from yellow to red‐NIR. In contrast, a dark non‐emissive CT was noted upon pyrene substitution at the fluorenes. In apolar solvents, efficient triplet‐excited state generation was observed for all SFDBAOs. Either charge transfer was concluded to mediate the intersystem crossing (ISC) in the case of pyrene substitution or the El‐Sayed rule was applicable when lacking pyrene substitution as in the case of SFABAO. In polar solvents, charge separation is the sole decay upon pyrene substitution. Moreover, competition between ISC and CT lowered the triplet‐excited state generation in SFDBAO.

Rapid X-ray fluorescence analysis as a modern alternative to traditional spectral methods in geochemical prospecting

The purpose of the study is to present the research results of the capabilities of modern portable rapid X-ray fluorescence analyzers when solving problems of geological and geochemical prospecting. On example of the applied SciAps X200 analyzer, the metrological indicators for the analysis results by portable instruments have been studied. The accuracy assessment results of analytical studies according to state standard reference samples are shown. Reproducibility of the analysis results is calculated on the basis of samples from promising gold sites of the Bodaibo synclinorium. The method is proved to be of high precision, and measurement errors in many cases are many times lower than the permissible certified values. The reproducibility is shown as 0,5–20 % depending on the element, which in most cases is significantly lower than the methodology permits. The results of interlaboratory comparative tests confirming the comparability of the analytical results of stationary and portable X-ray fluorescence analyzers are presented. For a number of significant elements, the authors have substantiated the lack of need to refine the results of the field rapid X-ray fluorescence analysis using labor-intensive and expensive methods with acid decomposition - atomic emission and atomic absorption spectroscopy. It has been proved that introduction of portable express equipment into geological prospecting works will make it possible to conduct real-time “on site” analytical studies.

Modulation of Deep-Red to Near-Infrared Room-Temperature Charge-Transfer Phosphorescence of Crystalline "Pyrene Box" Cages by Coupled Ion/Guest Structural Self-Assembly.

Organic cocrystals obtained from multicomponent self-assembly have garnered considerable attention due to their distinct phosphorescence properties and broad applications. Yet, there have been limited reports on cocrystal systems that showcase efficient deep-red to near-infrared (NIR) charge-transfer (CT) phosphorescence. Furthermore, effective strategies to modulate the emission pathways of both fluorescence and phosphorescence remain underexplored. In this work, we dedicated our work to four distinct self-assembled cocrystals called "pyrene box" cages using 1,3,6,8-pyrenetetrasulfonate anions (PTS4-), 4-iodoaniline (1), guanidinium (G+), diaminoguanidinium (A2G+), and hydrated K+ countercations. The binding of such cations to PTS4- platforms adaptively modulates their supramolecular stacking self-assembly with guest molecules 1, allowing to steer the fluorescence and phosphorescence pathways. Notably, the confinement of guest molecule 1 within "pyrene box" PTSK{1} and PTSG{1} cages leads to an efficient deep-red to NIR CT phosphorescence emission. The addition of fuming gases like triethylamine and HCl allows reversible pH modulations of guest binding, which in turn induce a reversible transition of the "pyrene box" cage between fluorescence and phosphorescence states. This capability was further illustrated through a proof-of-concept demonstration in shrimp freshness detection. Our findings not only lay a foundation for future supramolecular designs leveraging weak intermolecular host-guest interactions to engineer excited states in interacting chromophores but also broaden the prospective applications of room-temperature phosphorescence materials in food safety detection.

The differential non-covalent binding of epicatechin and chlorogenic acid to ovotransferrin and the enhancing efficiency of immunomodulatory activity

Seeking safe and environmentally friendly natural immunomodulators is a pressing requirement of humanity. This study investigated the differential binding characteristics of two polar polyphenols (PP), namely epicatechin (EC) and chlorogenic acid (CA), to ovotransferrin (OVT), and explored the relationship between structural transformations and immunomodulatory activity of OVT-PP complexes. Results showed that CA exhibited a stronger affinity for OVT than EC, mainly driven by hydrogen bonds and van der Waals forces. Complexation-induced conformational variations in OVT, including static fluorescence quenching, increased microenvironment polarity surrounding tryptophan and tyrosine residues, and the transition from disordered α-helix to stable β-sheet. Furthermore, the structural conformation transformation of OVT-PP complexes facilitated the enhancement of immunomodulatory activity, with the OVT-CA (10:2) complex demonstrating the best immunomodulatory activity. Principal component analysis (PCA) and Pearson correlation analysis revealed the immunomodulatory activities of the OVT-PP complexes were influenced by surface hydrophobicity (negatively correlated), β-sheet percentage and polyphenol binding constants. It could be inferred that PP complexation increased the surface polarity of OVT, consequently enhancing its immunomodulatory activity by promoting cell membrane affinity and antigen recognition. This study provides valuable guidance for effectively utilizing polyphenol-protein complexes in enhancing immunomodulatory activity.

Lactoferrin docking NIR-II cyanine dye as a potentiated phototheranostic for synchronous multimodal bioimaging and tumor photo-immunotherapy.

Rationale: A promising dye for phototheranostics, IR-1048 is a near-infrared region II (NIR-II) cyanine dye that exhibits exceptional optical characteristics in NIR-II spectrum. Unfortunately, the biological applications of IR-1048 are challenged by its hydrophobic nature, the formation of face-to-face stacked dimeric aggregates (H-aggregates) that result in pronounced spectral blue shifts, and issues related to fluorescence quenching. Method: We present a novel docking strategy involving bovine serum albumin (BSA) and lactoferrin (Lf) to construct BSA@IR-1048 and Lf@IR-1048 nanoprobes. The NIR-II optical characteristics of these nanoprobes have been thoroughly investigated through both theoretical and experimental approaches. In addition, we conducted in vitro and in vivo evaluations of their NIR-II photothermal and photodynamic properties, multimodal imaging capabilities, and effectiveness in photoimmunotherapy. Results: Following the protein docking process, both BSA@IR-1048 and Lf@IR-1048 probes exhibited a red-shifted absorbance peak and an "ON" state in NIR-II fluorescence. Theoretical analyses alongside experimental results indicate that Lf@IR-1048, which has a higher docking binding energy of -10.83 kcal/mol, significantly enhances optical characteristics in the NIR-II region. Notably, when utilizing a single NIR-II light source, Lf@IR-1048 was effective in producing single-linear state oxygen and converting photons into heat energy, achieving a photo-thermal conversion efficiency of 41.9%. The overexpression of transferrin receptors in tumor cells also improved tumor-targeting and enrichment capabilities of Lf@IR-1048, as demonstrated vitro and in vivo studies. Comparatively, Lf@IR-1048 facilitated multimodal imaging-guided NIR-II phototherapy, showing an impressive tumor development inhibition rate of 94.8%. Furthermore, in bilateral CT26 tumor-bearing mice, the Lf@IR-1048-based photo-immunotherapy exhibited significant antitumor activity, attributed to enhanced dendritic cell maturation and infiltration of cytotoxic T lymphocytes. Conclusion: Lf@IR-1048 displays a powerful combination of photothermal therapy, photodynamic therapy, and tumor-targeting potential for effective multimodal imaging-guided NIR-II phototherapy, leading to substantial inhibition of tumor growth.

A novel Salen-based dual channel sensor for easy and selective nanomolar detection of l-cysteine

A Salen-type Schiff base sensor, characterized by XRD, efficiently detects l-cysteine through static and dynamic fluorescence quenching, employing a FRET mechanism. It exhibits remarkable stability, with a low detection limit of 1.52 × 10−9 M.

Photoproperties of favipiravir and its 6-substituted analogues: fluorescence controlled through halogen substitution and tautomerism.

Herein, we have showed the photophysical properties of favipiravir and its 6-substituted analogues. Also, we interpreted the origin of fluorescence of favipiravir and its 6-substituted analogues as a function of tautomerism modulation in ground and excited states. Favipiravir, the 6-fluorine derivative, showed the best photophysical profile, exhibiting a dominant emission wavelength of 430 nm, a high quantum yield (Q.Y.) of 1.0 and a long-lived state (10 ns). Its analogues also showed a maximum emission at 430 nm, but their Q.Y. values were 5-fold lower than that found for favipiravir, decreasing as a function of 6-substitution as follows: F > Cl > Br > I > H. Pyrazines bearing the least electronegative 6-substituent (X = Br, I, H) showed an extra lifetime, which was shorter (0.2-0.3 ns) and less abundant (>15%) than the main lifetime (10 ns, 85%). Further 2D excitation-emission matrix and solvent studies supported that these 3-hydroxy-2-pyrazinecarboxamides present two emissive states. The first of them (λem = 430 nm), which was the most abundant, most fluorescent and long-lived state, was characterized as "locally excited" (LE). Its fluorescence was favored with an increase of the hydrogen-donor nature of the solvent and for pyrazines having a high enolic characteristic. Thus, the high LE-fluorescence of these types of pyrazines depends on the keto-tautomerization of the ground state using a protic solvent and its feasible enol-tautomerization upon excitation. Finally, the second excited state (λem = 536 nm) was suggested as an excited-state intramolecular proton-transfer (ESIPT), and it was observed only, although discretely, for pyrazines bearing the least electronegative 6-substituent.

Coulomb interactions for mediator-enhanced sensitized triplet-triplet annihilation upconversion in solution.

Sensitized triplet-triplet annihilation upconversion offers an attractive possibility to replace a high-energy photon by two photons with lower energy through the combination of a light-harvesting triplet sensitizer and an annihilator for the formation of a fluorescent singlet state. Typically, high annihilator concentrations are required to achieve an efficient initial energy transfer and as a direct consequence the most highly energetic emission is often not detectable due to intrinsic reabsorption by the annihilator itself. Herein, we demonstrate that the addition of a charge-adapted mediator drastically improves the energy transfer efficiency at low annihilator concentrations via an energy transfer cascade. Inspired by molecular dyads and recent developments in nanocrystal-sensitized upconversion, our system exploits a concept to minimize intrinsic filter effects, while boosting the upconversion quantum yield in solution. A sensitizer-annihilator combination consisting of a ruthenium-based complex and 9,10-diphenylanthracene (DPA) is explored as model system and a sulfonated pyrene serves as mediator. The impact of opposite charges between sensitizer and mediator - to induce coulombic attraction and subsequently result in accelerated energy transfer rate constants - is analyzed in detail by different spectroscopic methods. Ion pairing and the resulting static energy transfer in both directions is a minor process, resulting in an improved overall performance. Finally, the more intense upconverted emission in the presence of the mediator is used to drive two catalytic photoreactions in a two-chamber setup, illustrating the advantages of our approach, in particular for photoreactions requiring oxygen that would interfere with the upconversion system.

Chiral Au(III) chelates exhibit unique NCI-60 cytotoxicity profiles and interactions with human serum albumin.

Au(III) bis(pyrrolide-imine) chelates are emerging as a class of versatile, efficacious metallodrug candidates. Here, we synthesised two enantiopure chiral ligands H2L1 and H2L2 (tetradentate cyclohexane-1,2-diamine-bridged bis(pyrrole-imine) derivatives). Metallation of the ligands with Au(III) afforded the chiral cationic complexes AuL1 and AuL2. The in vitro cytotoxicities of AuL1 and AuL2 determined in the NCI-60 single-dose drug screen were 56.5% and 89.1%, respectively. AuL1 was subsequently selected for a five-dose NCI-60 screen, attaining GI50, IC50, and LC50 values of 4.7, 9.3 and 39.8 μM, respectively. Hierarchical cluster analysis of the NCI-60 data indicated that the profile for AuL1 was similar to that of vinblastine sulfate, a microtubule-targeting vinca alkaloid. Reactions of AuL1 with glutathione (GSH) in vitro confirmed its susceptibility to reduction, Au(III) → Au(I), by intracellular thiols. Because human serum albumin (HSA) is responsible for transporting clinically deployed and investigational drugs, we studied the uptake of AuL1 and AuL2 by HSA to delineate how chirality impacts their protein-binding affinity. Steady-state fluorescence quenching data acquired on the native protein and data from site-specific probes showed that the compounds bind at sites close enough to Trp-214 (subdomain IIA) of HSA to quench the fluorophore. The bimolecular quenching rate constants, Kq, were ca. 102 times higher than the maximum diffusion-controlled collision constant of a biomolecule in water (1010 M-1 s-1), confirming that static fluorescence quenching was the dominant mechanism. The Stern-Volmer constants, KSV, were ∼104 M-1 at 37 °C, while the affinity constants, Ka (37 °C), measured ∼2.1 × 104 M-1 (AuL1) and ∼1.2 × 104 M-1 (AuL2) for enthalpy-driven ligand uptake targeting Sudlow's site I. Although far- and near-UV CD spectroscopy indicated that both complexes minimally perturb the secondary and tertiary structure of HSA, substantial shifts in the CD spectra were recorded for both protein-bound ligands. This study highlights the role of chirality in determining the cytotoxicity profiles and protein binding behaviour of enantiomeric Au(III) chelates.

Interactive Profile between 1,4-Naphthoquinone Derivatives and Human Serum Albumin

The interactive profile between four 1,4-naphthoquinone derivatives (1-4) and human serum albumin (HSA) was studied by spectroscopic techniques and in silico calculations. The bimolecular quenching rate constant (kq ca. 1012 L mol-1 s-1) and the time-resolved fluorescence decays indicated a static fluorescence quenching mechanism. Thus, there is a spontaneous ground-state association, and based on both Stern-Volmer, modified Stern-Volmer, and van’t Hoff approaches, the association is moderate mainly driven by hydrophobic forces. The circular dichroism (CD) analysis indicated that until the proportion albumin:compound of 1:8 there is a weak perturbation on the structural content of albumin, while molecular docking results suggested subdomain IIA (site I), a positive electrostatic pocket, as the main binding site. Overall, even though the hydrogen atom replacement by methyl, fluorine, or chlorine atoms in the para position of the aromatic ring in the benzo[g]chromene-5,10-dione moiety changes the lipophilicity, it does not change the binding profile to HSA.

Fluorescence quenching in aggregates of fucoxanthin–chlorophyll protein complexes: Interplay of fluorescing and dark states

Diatoms, a major group of algae, account for about a quarter of the global primary production on Earth. These photosynthetic organisms face significant challenges due to light intensity variations in their underwater habitat. To avoid photodamage, they have developed very efficient non-photochemical quenching (NPQ) mechanisms. These mechanisms originate in their light-harvesting antenna – the fucoxanthin–chlorophyll protein (FCP) complexes. Spectroscopic studies of NPQ in vivo are often hindered by strongly overlapping signals from the photosystems and their antennae. Fortunately, in vitro FCP aggregates constitute a useful model system to study fluorescence (FL) quenching in diatoms. In this work, we present streak-camera FL measurements on FCPa and FCPb complexes, isolated from a centric diatom Cyclotella meneghiniana, and their aggregates. We find that spectra of non-aggregated FCP are dominated by a single fluorescing species, but the FL spectra of FCP aggregates additionally contain contributions from a redshifted emissive state. We relate this red state to a charge transfer state between chlorophyll c and chlorophyll a molecules. The FL quenching, on the other hand, is due to an additional dark state that involves incoherent energy transfer to the fucoxanthin carotenoids. Overall, the global picture of energy transfer and quenching in FCP aggregates is very similar to that of major light-harvesting complexes in higher plants (LHCII), but microscopic details between FCPs and LHCIIs differ significantly.

Effect of π-extension and halogenation on the optical limiting properties of meso-pyrenylBODIPYdyes

The lack of suitable optical limiters that cover the entire UV-visible-NIR region has motivated research to identify novel efficient and stable optical limiting materials. There has been a strong focus on attenuating the second harmonic of Nd:YAG pulsed lasers at 532 nm on the nanosecond timescale. The photophysicochemical processes of a series of mono- and di-(4-dimethylamino)styryl-meso-pyrenylBODIPY and mono- and di-(4-dimethylamino)buta-1,3-dienyl-meso-pyrenylBODIPY dyes were studied by UV-visible absorption and fluorescence emission spectroscopy, and by determining the fluorescence and triplet state lifetimes. Z-scan measurements were carried out at a fixed concentration of 10 [Formula: see text]M so that the effective nonlinear coefficients, third-order susceptibilities, second-order hyperpolarizabilities and limiting fluences of the dyes can be compared and trends in the structure-property relationships for these optical limiting parameters can be identified.