Search

Photosystem I in most organisms contains long-wavelength or "Red" chlorophylls (Chls) absorbing light beyond 700 nm. At cryogenic temperatures, the Red Chls become quasi-traps for excitations as uphill energy transfer is blocked. One pathway for de-excitation of the Red Chls is via transfer to the oxidized RC (P700+), which has broad absorption in the near-infrared region. This study investigates the excitation dynamics of Red Chls in Photosystem I from the cyanobacterium Thermostichus vulcanus at cryogenic temperatures (77 K) and examines the role of the oxidized RC in modulating their fluorescence kinetics. Using time-resolved fluorescence spectroscopy, the kinetics of Red Chls were recorded for samples with open (neutral P700) and closed (P700+) RCs. We found that emission lifetimes in the range of 710–720 nm remained unaffected by the RC state, while more red-shifted emissions (>730 nm) decayed significantly faster when the RC was closed. A kinetic model describing the quenching by the oxidized RC was constructed based on simultaneous fitting to the recorded fluorescence emission in Photosystem I with open and closed RCs. The analysis resolved multiple Red Chl forms and variable quenching efficiencies correlated with their spectral properties. Only the most red-shifted Chls, with emission beyond 730 nm, are efficiently quenched by P700+, with rate constants of up to 6 ns−1. The modeling results support the notion that structural and energetic disorder in Photosystem I can have a comparable or larger effect on the excitation dynamics than the geometric arrangement of Chls. [ABSTRACT FROM AUTHOR]

A general one-step lateral flow immunochromatographic assay (LFIA) for the quantitative detection of triadimefon (TDF) and triadimenol (TDN) in fruit and vegetable samples was developed using time-resolved fluorescence microspheres (TRFM) as labels. A specific anti-triadimefon monoclonal antibody (mAb) was conjugated with TRFM to fabricate LFIA test strips. A time-resolved fluorometer as an LFIA reader was applied to obtain quantitative results and assess risk ranges for the LFIA test strips. Under the optimized experimental conditions, the limits of detection (LODs) in buffer/cucumbers/tomatoes/oranges were 0.046 ng/mL, 0.135 µg/kg, 1.047 µg/kg, and 5.811 µg/kg, respectively, which are ca. 1000 times lower than that of colloidal gold-labeled strips. The recovery in cucumber/tomato/orange samples was 109.4–116.7%, 87.7–110.9%, and 88.0–111.9%, respectively, indicating that the test strips had good reliability. Coupled with the easily customizable pretreatment procedures for various samples, the LFIA results were obtained within 18 min without the need for professional personnel or complicated equipment. TRFM-LFIA for TDF and TDN also shows remarkable specificity and precision. The test strips were also low-cost, portable, and convenient to use. These results indicate the test strips could be utilized as a novel strategy for on-site detection of TDF and TDN, which has the potential to expand and detect other pesticide or insecticide residues in food. [ABSTRACT FROM AUTHOR]

A novel series of homoconjugated oligomers of azapentacene, linked via the rigid connecting unit bicyclo[2.2.2]octane bridge is presented. The investigation delves into intramolecular singlet fission (iSF) within these dimeric and trimeric frameworks, employing various time‐resolved spectroscopies and quantum chemical calculations. Combining the merits of both through‐space and through‐bond couplings between the constituent chromophores within these rigid homoconjugated structures, iSF proceeds within a few picoseconds, exhibiting a 2–3 orders of magnitude acceleration compared to traditional covalently linked oligomers and achieving an iSF efficiency approaching unity. In the homoconjugated trimer, the larger interplanar angle between neighboring chromophores leads to a relatively slower iSF rate compared to that of the homoconjugated dimer. Furthermore, the active involvement of the charge transfer state is demonstrated to accelerate the iSF process in the trimer, while exerting no influence on the iSF process in the dimer. The study provides novel avenues for investigating the influence of molecular geometry on singlet fission and reveals the crucial role of the interplay between spatial and covalent coupling in facilitating intramolecular singlet fission. [ABSTRACT FROM AUTHOR]

Digital histogram generation for time-resolved measurements with single-photon avalanche diode (SPAD) sensors requires the storage of many timestamp signals. This work presents a mixed-signal time-to-digital converter (TDC) that uses analog storage to achieve an area-efficient design that can be integrated in large SPAD arrays. Fabricated using a 150 nm CMOS process, the prototype occupies an area of only 18.3 µm × 36.5 µm, a notable size reduction compared to conventional designs. The experimental results demonstrated high performance, with an integral nonlinearity (INL) of 0.35/0.14 least significant bit (LSB) and a differential nonlinearity (DNL) of 0.14/−0.12 LSB. In addition, the proposed TDC can support the construction of histograms comprising up to 512 bins, making it an effective solution to accommodate a wide range of resolution requirements. Validated in a point-of-care (PoC) device for fluorescence lifetime measurements, it distinguished between lifetimes of approximately 4.1 ns, 3.6 ns and 80 ns with the Alexa Fluor (AF) 546 and 568 dyes and Quantum Dot (QD) 705, respectively. The analog storage design and area-efficient architecture offer a novel approach to integrating TDCs in SPAD-based systems, with potential applications in medical diagnostics and beyond. [ABSTRACT FROM AUTHOR]

A fully quantum, numerically accurate methodology is presented for the simulation of the exciton dynamics and time-resolved fluorescence of cavity-tuned two-dimensional (2D) materials at finite temperatures. This approach was specifically applied to a monolayer WSe2 system. Our methodology enabled us to identify the dynamical and spectroscopic signatures of polaronic and polaritonic effects and to elucidate their characteristic timescales across a range of exciton–cavity couplings. The approach employed can be extended to simulation of various cavity-tuned 2D materials, specifically for exploring finite temperature nonlinear spectroscopic signals. [ABSTRACT FROM AUTHOR]

The spectral and luminescent properties of the styryl derivative of thioflavin T (ThT) 2-{(1E,3E)-4-[4-(dimethylamino)-2,6-dimethylphenyl]buta-1,3-dien-1-yl}-3-ethyl-1,3-benzothiazolium-3 tosylate (Th-C23) were studied. The fluorescence decay kinetics of Th-C23 incorporated into amyloid fibrils (AF) were not exponential and could be represented as a unimodal distribution of fluorophores over duration α(t). ThT and Th-C23 were shown to form an effective donor–acceptor (D–A) pair when incorporated into the AF structure. The degree of polarization of the acceptor fluorescence was high (~0.4) within the entire spectrum, despite the energy transfer, and was explained by the special orientation of D–A pairs, parallel and antiparallel. The measured fluorescence spectrum of the donor (ThT) and absorption spectrum of the acceptor (Th-C23) were used to calculate the critical energy-transfer radius R0, which could take values from 54 to 68 Å depending on the mutual orientation and quantum yield of the donor and acceptor. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases (CVDs), especially arterial hypertension, stand as prominent contributors to global mortality. Regrettably, individuals with diabetes encounter a two-fold increase in the risk of mortality associated with CVDs. Hydrochlorothiazide (HCTZ) represents a primary intervention for hypertension, particularly in diabetic patients. Nevertheless, there has not yet been a comprehensive assessment of the biophysical characteristics regarding the impact of glucose levels on its binding affinity with human serum albumin (HSA). Thus, the present work reports the interactive profile of HSA/HCTZ in nonglycemic, normoglycemic (80 mg/dL), and hyperglycemic (320 mg/dL) conditions by time-resolved fluorescence, saturation transfer difference–nuclear magnetic resonance (STD-NMR), and surface plasmon resonance (SPR). There was a moderate ground state association of HSA/HCTZ with subdomain IIA that was affected in the presence of different glucose levels. The hyperglycemic condition decreased the binding affinity of HCTZ to subdomain IIA and increased the possibility of subdomain IB also being considered as a secondary binding site due to cooperativity and/or alterations in the protein's structure. Overall, the glucose level under hyperglycemic conditions led to the cavities being more likely to receive more ligands, offering insights into the necessity of glucose control in the human bloodstream to not impact the residence time (pharmacokinetic profile) and pharmacotherapeutic potential of HCTZ. [ABSTRACT FROM AUTHOR]

Plants and algae are faced with a conundrum: harvesting sufficient light to drive their metabolic needs while dissipating light in excess to prevent photodamage, a process known as nonphotochemical quenching. A slowly relaxing form of energy dissipation, termed qH, is critical for plants' survival under abiotic stress; however, qH location in the photosynthetic membrane is unresolved. Here, we tested whether we could isolate subcomplexes from plants in which qH was induced that would remain in an energy-dissipative state. Interestingly, we found that chlorophyll (Chl) fluorescence lifetimes were decreased by qH in isolated major trimeric antenna complexes, indicating that they serve as a site for qH-energy dissipation and providing a natively quenched complex with physiological relevance to natural conditions. Next, we monitored the changes in thylakoid pigment, protein, and lipid contents of antenna with active or inactive qH but did not detect any evident differences. Finally, we investigated whether specific subunits of the major antenna complexes were required for qH but found that qH was insensitive to trimer composition. Because we previously observed that qH can occur in the absence of specific xanthophylls, and no evident changes in pigments, proteins, or lipids were detected, we tentatively propose that the energy-dissipative state reported here may stem from Chl-Chl excitonic interaction.

Coordination polymer nanoparticles (CPNs) are a unique class of nanoparticles designed via the self-aggregation of a metal ion and a polydentate ligand. Among them, lanthanide-based CPNs are considered to be the most promising due to their intrinsic luminescent properties, stability in different oxidation states, and high coordination flexibility. In the present study, cerium-based coordination polymer nanoparticles (Ce-CPNs) have been synthesized using adenosine triphosphate (ATP) as a cross-linking ligand. A weakly emissive molecular-rotor-type dye, Thioflavin-T (ThT), was incorporated into the porous polymeric network of CPNs, which led to a drastic enhancement in the emission intensity of ThT. The emission intensity of ThT-Ce-(III)-ATP-Tris CPNs is severely quenched in the presence of Cu-(II) ions, which has been utilized for the detection of Cu-(II). The sensing mechanism was established by using photophysical techniques such as absorbance, emission, excited-state lifetime, and particle size measurements. The selectivity of this methodology for Cu-(II) ions was checked by studying the interference of several metal ions, anions and biomolecules. The limit of detection (LOD) obtained for Cu-(II) in the present methodology was about 660 nM (42 ppb), which is far below the U.S. EPA prescribed limit (20 μM) in water. The present methodology was successfully demonstrated to determine the Cu-(II) concentration in e-waste leachate and also in spiked human serum samples. The LOD of Cu-(II) in diluted e-waste leachate was found to be marginally higher (730 nM) compared to that in the case of water, whereas the LOD in 10% (v/v) serum was to be 5 μM (320 ppb). [ABSTRACT FROM AUTHOR]

Phycobilisomes serve as a light-harvesting antenna of both photosystem I (PSI) and II (PSII) in cyanobacteria, yet direct energy transfer from phycobilisomes to PSI is not well documented. Here we recorded picosecond time-resolved fluorescence at wavelengths of 605–760 nm in isolated photosystem I (PSI), phycobilisomes and intact cells of a PSII-deficient mutant of Synechocystis sp. PCC 6803 at 77 K to study excitation energy transfer and trapping. By means of a simultaneous target analysis of the kinetics of isolated complexes and whole cells, the pathways and dynamics of energy transfer in vitro and in vivo were established. We establish that the timescale of the slowest equilibration between different terminal emitters in the phycobilisome is ≈800 ps. It was estimated that the terminal emitter in about 40% of the phycobilisomes transfers its energy with a rate constant of 42 ns−1 to PSI. This energy transfer rate is higher than the rates of equilibration within the phycobilisome – between the rods and the core or between the core cylinders – and is evidence for the existence of specific phycobilisome-PSI interactions. The rest of the phycobilisomes remain unconnected or slowly transferring energy to PSI. [ABSTRACT FROM AUTHOR]

Circular permutation (CP) is a technique by which the primary sequence of a protein is rearranged to create new termini. The connectivity of the protein is altered but the overall protein structure generally remains unperturbed. Understanding the effect of CP can help design robust proteins for numerous applications such as in genetic engineering, optoelectronics, and improving catalytic activity. Studies on different protein topologies showed that CP usually affects protein stability as well as unfolding rates. Though a significant number of proteins contain metals or other cofactors, reports of metalloprotein CPs are rare. Thus, we chose a bacterial metalloprotein, azurin, and its CP within the metal-binding site (cpF114). We studied the stabilities, folding, and unfolding rates of apo- and Zn2+-bound CP azurin using fluorescence and circular dichroism. The introduced CP had destabilizing effects on the protein. Also, the folding of the Zn2+-CP protein was much slower than that of the Zn2+-WT or apo-protein. We compared this study to our previously reported azurin-cpN42, where we had observed an equilibrium and kinetic intermediate. cpF114 exhibits an apparent two-state equilibrium unfolding but has an off-pathway kinetic intermediate. Our study hinted at CP as a method to modify the energy landscape of proteins to alter their folding pathways. WT azurin, being a faster folder, may have evolved to optimize the folding rate of metal-bound protein compared to its CPs, albeit all of them have the same structure and function. Our study underscores that protein sequence and protein termini positions are crucial for metalloproteins. TOC Figure. (Top) Zn2+-azurin WT structure (PDB code: 1E67) and 2-D topology diagram of Zn2+-cpF114 azurin. (Bottom) Cartoon diagram representing folding (red arrows) and unfolding (blue arrows) of apo- and Zn2+- WT and cpF114 azurins. The width of the arrows represents the rate of the corresponding processes. [ABSTRACT FROM AUTHOR]

Fluorescence quenching of 3,3,11,11-tetramethyl-8,16-diphenyl-3,4,8,10,11,12,13,16-octahydroacridino[4,3-c]acridine-1,9(2H,5H)dione in liquid mixtures of methanol and acetonitrile have been studied using fluorescence spectroscopy methods. The results obtained are interpreted in terms of nonradiative deactivation of the excited state of the fluorophore due to interaction with a protic solvent. A theoretical analysis of experimental data was carried out, its results were compared with data obtained previously in similar studies in mixtures of methanol and dimethylformamide. The values of a number of model parameters were determined, in particular, the rate constant for the formation of "fluorophore–methanol cluster" complexes and the equilibrium constant of this reaction. The mechanisms of the influence of the aprotic cosolvent on the cluster structure of the mixture and the quantum yield of fluorescence have been analyzed. [ABSTRACT FROM AUTHOR]

The fluorescence assay is one of the popular methods that is applied for detection of different targets. However, this method may show low sensitivity and high background in biological samples due to the natural fluorescence of different compounds in complicated samples. In addition, it inevitably affects the detection results accuracy. A fundamental solution to this problem is the use of the time-resolved fluorescence technique (TRF). The main component of this technique is the use of long fluorescence lifetime reagents. In this review, various time-resolved fluorescent reagents such as complexes of lanthanide ions, lanthanide-doped inorganic nanoparticles; Mn-doped ZnS quantum dots (QDs) and pyrene excimer are introduced. Moreover, TRF sensors, especially TRF aptasensors (DNA-based sensors) are discussed. This review will give new ideas for researchers to develop novel high-sensitive TRF sensors that can remove or decrease background fluorescence and use them for the detection of various targets in complicated samples without treatment. [ABSTRACT FROM AUTHOR]

Variations in the fluorescence lifetimes of Radachlorin photosensitizers in HeLa and A549 cells, caused by photodynamic treatment, were studied using fluorescence lifetime imaging microscopy (FLIM). An analysis of FLIM images of the cells demonstrated a substantial decrease in the mean Radachlorin fluorescence lifetime and intensity as a result of UV irradiation of the photosensitized cells at different doses, with higher doses causing a more pronounced decrease in the mean fluorescence lifetime in cells. The post-treatment decrease in Radachlorin fluorescence intensity was accompanied by the appearance of an additional rapidly decaying fluorescence component and a nonlinear decrease in the weighted fluorescence lifetime obtained from double-exponential fits of time-resolved fluorescence signals. Experiments performed in the aqueous solutions of the photosensitizer revealed similar irreversible changes in the Radachlorin fluorescence lifetime and intensity. Therefore, the observed phenomena occurred most likely due to the photodegradation of the photosensitizer molecules and can be applied for dosimetry and monitoring of irradiation doses in different areas of malignant tissues in the course of photodynamic treatment. [ABSTRACT FROM AUTHOR]

The fusion of tetrapyrroles with aromatic heterocycles constitutes a useful tool for manipulating their opto‐electronic properties. In this work, the synthesis of naphthodithiophene‐fused porphyrins was achieved through a Heck reaction‐based cascade of steps followed by the Scholl reaction. The naphthodithiophene‐fused porphyrins display a unique set of optical and electronic properties. Fusion of the naphtho[2,1‐b:3,4‐b']dithiophene to porphyrin (F2VTP) leads to a ~20% increase in the fluorescence lifetime, which is accompanied, unexpectedly, by a more than two‐fold drop in the emission quantum yield (ϕ=0.018). In contrast, fusion of the isomeric naphtho[1,2‐b:4,3‐b']dithiophene to porphyrin (F3VPT) results in a ~1.5‐fold increase in the fluorescence quantum yield (ϕ=0.13) with a concomitant ~30 % increase in the fluorescence lifetime. This behavior suggests that fusion of the porphyrin with the naphthodithiopheno‐system mainly affects the radiative rate constant in the Q‐state deactivation pathway, where the effects of the isomeric naphtho[2,1‐b:3,4‐b']dithiophene‐ versus naphtho[1,2‐b:4,3‐b']dithiophene‐fusion are essentially the opposite. Interestingly, nucleus‐independent chemical shifts analysis revealed a considerable difference between the aromaticities of these two isomeric systems. Our results demonstrate that subtle structural differences in the fused components of the porphyrin can be reflected in rather significant differences between the photophysical properties of the resulting systems. [ABSTRACT FROM AUTHOR]

Monitoring the quality of food products is very important, due to the fact that substances potentially harmful to consumers may be formed during production and storage. In addition, vegetal oils are subject to falsification, which is based mainly on mixing and adding other, usually cheaper equivalents or providing false data on the composition and origin. In this way, the path from a very healthy product to a product that has a negative impact on the human body is very short. In this study fluorescence spectra and fluorescence decay kinetics of selected cold-pressed oils were characterized and the origin of the observed fluorescence bands was discussed. The obtained fluorescence characteristics were found to be the unique fingerprints of the individual oils and showed evident differences which arise from specific qualitative and quantitative compositions of the oils. The most apparent differences in the shape of fluorescence bands were observed in the emission spectrum at excitation wavelength 350 nm and in the excitation spectrum recorded at emission wavelength 500 nm. The obtained results show the utility of the applied steady-state and time –resolved fluorescence measurements in the identification of the tested vegetal oils. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases (CVDs), especially arterial hypertension, stand as prominent contributors to global mortality. Regrettably, individuals with diabetes encounter a two-fold increase in the risk of mortality associated with CVDs. Hydrochlorothiazide (HCTZ) represents a primary intervention for hypertension, particularly in diabetic patients. Nevertheless, there has not yet been a comprehensive assessment of the biophysical characteristics regarding the impact of glucose levels on its binding affinity with human serum albumin (HSA). Thus, the present work reports the interactive profile of HSA/HCTZ in nonglycemic, normoglycemic (80 mg/dL), and hyperglycemic (320 mg/dL) conditions by time-resolved fluorescence, saturation transfer difference–nuclear magnetic resonance (STD-NMR), and surface plasmon resonance (SPR). There was a moderate ground state association of HSA/HCTZ with subdomain IIA that was affected in the presence of different glucose levels. The hyperglycemic condition decreased the binding affinity of HCTZ to subdomain IIA and increased the possibility of subdomain IB also being considered as a secondary binding site due to cooperativity and/or alterations in the protein’s structure. Overall, the glucose level under hyperglycemic conditions led to the cavities being more likely to receive more ligands, offering insights into the necessity of glucose control in the human bloodstream to not impact the residence time (pharmacokinetic profile) and pharmacotherapeutic potential of HCTZ.

The modulation of kinetics and pathways in the ESIPT process of proton transfer probes holds significant potential for advancing applications in bio-imaging, drug delivery, and OLEDs. One effective approach for achieving this modulation is altering the H-bonding donating capability of the surrounding medium. To investigate this, we conducted a comprehensive study on the excited state intramolecular double proton transfer process of [2,2′-bipyridyl]-3,3′-diol (BP(OH)2) within the confined spaces of silica nanochannels, namely, MCM-41. MCM-41, known for its versatile properties, has emerged as a promising host in various fields, such as drug delivery and heterogeneous catalysis. Upon encapsulation within the MCM-41, the double proton transfer process of BP(OH)2 is significantly modulated, which is reflected in both steady-state and time-resolved photophysical experiments. We have observed an almost 100 times increment in emission intensity and a 30 nm blue-shift in the emission maxima when the probe gets encapsulated inside the silica nanopores. Most importantly, the femtosecond up-conversion profile exhibits an interesting feature. The rise component of 10 ps, which was attributed to MK→DK conversion in bulk acetonitrile (MeCN), is not observed when the probe resides inside the MCM-41, suggesting the proton transfer is concerted rather than sequential, like in the case of bulk MeCN. This anomalous proton transfer mechanism inside the nanochannel was attributed to the weak H-bonding donating ability of the silanol groups, which could not stabilize the MK form, and thus favoured the concerted pathway over sequential. Moreover, DFT calculations corroborate the concerted pathway observed in the MCM-41 with the gas-phase calculations and the sequential mechanism observed in bulk MeCN with the solution-phase calculations.

Phycobilisomes serve as a light-harvesting antenna of both photosystem I (PSI) and II (PSII) in cyanobacteria, yet direct energy transfer from phycobilisomes to PSI is not well documented. Here we recorded picosecond time-resolved fluorescence at wavelengths of 605–760 nm in isolated photosystem I (PSI), phycobilisomes and intact cells of a PSII-deficient mutant of Synechocystis sp. PCC 6803 at 77 K to study excitation energy transfer and trapping. By means of a simultaneous target analysis of the kinetics of isolated complexes and whole cells, the pathways and dynamics of energy transfer in vitro and in vivo were established. We establish that the timescale of the slowest equilibration between different terminal emitters in the phycobilisome is ≈800 ps. It was estimated that the terminal emitter in about 40% of the phycobilisomes transfers its energy with a rate constant of 42 ns−1 to PSI. This energy transfer rate is higher than the rates of equilibration within the phycobilisome – between the rods and the core or between the core cylinders – and is evidence for the existence of specific phycobilisome-PSI interactions. The rest of the phycobilisomes remain unconnected or slowly transferring energy to PSI.

Titanium‐based catalysis in single electron transfer (SET) steps has evolved into a versatile approach for the synthesis of fine chemicals and first attempts have recently been made to enhance its sustainability by merging it with photo‐redox (PR) catalysis. Here, we explore the photochemical principles of all‐Ti‐based SET‐PR‐catalysis, i.e. in the absence of a precious metal PR‐co‐catalyst. By combining time‐resolved emission with ultraviolet‐pump/mid‐infrared‐probe (UV/MIR) spectroscopy on femtosecond‐to‐microsecond time scales we quantify the dynamics of the critical events of entry into the catalytic cycle; namely, the singlet‐triplet interconversion of the do‐it‐all titanocene(IV) PR‐catalyst and its one‐electron reduction by a sacrificial amine electron donor. The results highlight the importance of the PR‐catalyst's singlet‐triplet gap as a design guide for future improvements. [ABSTRACT FROM AUTHOR]

Die titanbasierte Katalyse mit Ein‐Elektronentransfer‐Schritten (SET) hat sich zu einem vielseitigen Ansatz für die Synthese von Feinchemikalien entwickelt. Kürzlich wurden erste Versuche unternommen, ihre Nachhaltigkeit zu verbessern, indem sie mit der Photoredox (PR) Katalyse kombiniert wird. Hier untersuchen wir die photochemischen Prinzipien der SET‐PR‐Katalyse auf Basis von Ti und in Abwesenheit eines Edelmetall PR−Co‐Katalysators. Durch Kombination von zeitaufgelöster Emissionsspektroskopie mit Ultraviolett‐Anregungs‐/Infrarot‐Abfrage‐Spektroskopie auf Zeitskalen von Femtosekunden bis Mikrosekunden quantifizieren wir die Dynamik der kritischen Ereignisse bei der Initiierung des Katalysezyklus, nämlich die Singulett‐Triplett‐Umwandlung des Titanocen(IV) PR‐Universalkatalysators und seine Ein‐Elektronen‐Reduktion durch einen Amin‐Elektronendonator. Die Ergebnisse unterstreichen die Bedeutung der Singulett‐Triplett‐Energielücke des PR‐Katalysators als Leitfaden für künftige Verbesserungen. [ABSTRACT FROM AUTHOR]

Benzo[a]pyrene is a widespread environmental pollutant and a strong carcinogen. It is important to understand its bio-toxicity and degradation mechanism. Herein, we studied the excited state dynamics of benzo[a]pyrene by using time-resolved fluorescence and transient absorption spectroscopic techniques. For the first time, it is identified that benzo[a]pyrene in its singlet excited state could react with oxygen, resulting in fluorescence quenching. Additionally, effective intersystem crossing can occur from its singlet state to the triplet state. Furthermore, the interaction between the excited benzo[a]pyrene and ct-DNA can be observed directly and charge transfer between benzo[a]pyrene and ct-DNA may be the reason. These results lay a foundation for further understanding of the carcinogenic mechanism of benzo[a]pyrene and provide insight into the photo-degradation mechanism of this molecule. [ABSTRACT FROM AUTHOR]

Excited-state chemistry relies on the communication between molecules, making it a crucial aspect of the field. One important question that arises is whether intermolecular communication and its rate can be modified when a molecule is confined. To explore the interaction in such systems, we investigated the ground and excited states of 4′-N,N-diethylaminoflavonol (DEA3HF) in an octa acid-based (OA) confined medium and in ethanolic solution, both in the presence of Rhodamine 6G (R6G). Despite the observed spectral overlap between the flavonol emission and the R6G absorption, as well as the fluorescence quenching of the flavonol in the presence of R6G, the almost constant fluorescence lifetime at different amounts of R6G discards the presence of FRET in the studied systems. Steady-state and time-resolved fluorescence indicate the formation of an emissive complex between the proton transfer dye encapsulated within water-soluble supramolecular host octa acid (DEA3HF@(OA)2) and R6G. A similar result was observed between DEA3HF:R6G in ethanolic solution. The respective Stern–Volmer plots corroborate with these observations, suggesting a static quenching mechanism for both systems. [ABSTRACT FROM AUTHOR]

Excited state intramolecular proton transfer (ESIPT) dynamics of the o-hydroxy analogs of the green fluorescent protein (GFP) chromophore have been investigated by time-resolved spectroscopies and theoretical calculations. These molecules comprise an excellent system to investigate the effect of electronic properties on the energetics and dynamics of ESIPT and to realize applications in photonics. Time-resolved fluorescence with high enough resolution was employed to record the dynamics and the nuclear wave packets in the excited product state exclusively in conjunction with quantum chemical methods. The ESIPT are ultrafast occurring in 30 fs for the compounds employed in this work. Although the ESIPT rates are not affected by the electronic properties of the substituents suggesting barrierless reaction, the energetics, their structures, subsequent dynamics following ESIPT, and possibly the product species are distinct. The results attest that fine tuning of the electronic properties of the compounds may modify the molecular dynamics of ESIPT and subsequent structural relaxation to achieve brighter emitters with broad tuning capabilities. [ABSTRACT FROM AUTHOR]

The co-facially stacked dyes on semiconductor films serve as an alternative model to elucidate the photo-driven exciton dynamics occurring in a molecular assembly. In this study, we report the unique emission properties of coumarin dye adsorbed on the surface of the semiconductor film, measured by ultrafast time-resolved fluorescence. When a rigid coumarin derivative, 7-hydroxycoumarin-3-carboxylic acid (OHCCA), is anchored on the Al2O3 film, the dye manifests dual emissions from the two lowest excited states. Various anchoring modes of a carboxylic acid group on the Al2O3 surface are invoked to account for the unusual emission process. Additionally, we identified characteristic transition dipole interactions in the well-stacked dye aggregates, which leads to discernible excitonic splitting in the electronic transitions. Femtosecond time-resolved fluorescence reveals that the excimer formation in the aggregate occurs with the time constant of 550 fs. Picosecond time-resolved emission spectra confirm the subsequent structural relaxations of the nascent excimer. The enhanced transition dipole via the electronic coupling between OHCCA and metal oxide can be responsible for the dual emission and the ultrafast excimer formation. [ABSTRACT FROM AUTHOR]

• The molecular mechanism of interaction between Pexidartinib and mammalian serum albumins is governed by static quenching. • The binding locus is site II' in the interface between subdomain IIA and IIB of the serum albumins. • The interaction involves an interplay of hydrogen bonding and hydrophobic interactions in stabilising the binding. • PEX binds more effectively with human serum albumin. Binding of biologically important molecules with plasma proteins highly influence its availability, distribution, and metabolism, and thus has great significance in determining its therapeutic efficiency. Hence, studying its interaction with plasma proteins is prime and inevitable. Herein, we have investigated the molecular interaction of Pexidartinib, a novel, primitive and highly selective therapeutical agent against CSF-1R overexpression, with human serum albumin (HSA) and bovine serum albumin (BSA) using various spectroscopic methods, docking and simulations. The intrinsic fluorescence of the proteins considerably quenched on PEX addition accompanied by a slight blue shift. The complex formation between PEX and BSA/HSA induced some alterations in the molecular milieu of the tryptophan residues. The active binding locus was found to be within the hydrophobic cavity of Sudlow site I of both BSA and HSA. The binding dynamics suggest the interplay of hydrogen bonding and hydrophobic interactions in complex stabilisation. MD simulations provides valuable insights into the dynamic facets of the molecular recognition processes involved and governs the stability factor of protein post ligand complexation. [ABSTRACT FROM AUTHOR]

Variations in the fluorescence lifetimes of Radachlorin photosensitizers in HeLa and A549 cells, caused by photodynamic treatment, were studied using fluorescence lifetime imaging microscopy (FLIM). An analysis of FLIM images of the cells demonstrated a substantial decrease in the mean Radachlorin fluorescence lifetime and intensity as a result of UV irradiation of the photosensitized cells at different doses, with higher doses causing a more pronounced decrease in the mean fluorescence lifetime in cells. The post-treatment decrease in Radachlorin fluorescence intensity was accompanied by the appearance of an additional rapidly decaying fluorescence component and a nonlinear decrease in the weighted fluorescence lifetime obtained from double-exponential fits of time-resolved fluorescence signals. Experiments performed in the aqueous solutions of the photosensitizer revealed similar irreversible changes in the Radachlorin fluorescence lifetime and intensity. Therefore, the observed phenomena occurred most likely due to the photodegradation of the photosensitizer molecules and can be applied for dosimetry and monitoring of irradiation doses in different areas of malignant tissues in the course of photodynamic treatment.

Vibrio parahaemolyticus is a common foodborne pathogen in seafood, which often causes seafood borne bacterial gastroenteritis or food poisoning. Thermostable direct hemolysin (TDH) is considered to be one of the main virulence factors involved in this pathogen. The most clinical V. parahaemolyticus isolates produce TDH. Therefore, high sensitivity and specificity detection of TDH are of great significance for food safety and early diagnosis of diseases caused by V. parahaemolyticus. In this study, we developed a rapid, sensitive immunochromatographic test paper assay for the quantitative detection of TDH in seafood samples using time-resolved fluorescence techniques. First, we completed the preparation of fluorescent detection antibodies by coupling lanthanide fluorescent nanospheres with homemade high-affinity polyclonal antibodies based on the principle of the double-antibody sandwich. The lanthanide fluorescent nanospheres used in this study are characterized by a large stokes shift and a long fluorescence lifetime, which effectively reduces background noise and improves detection sensitivity. In addition, the method can be completed within 15 min for the detection of TDH, has a detection limit below 50 ng/mL and good linearity in the range of 50–5000 ng/mL. Moreover, it has good specificity and no cross-reactivity with Vibrio vulnificus hemolysin (VVH), Clostridium perfringens α toxin (CPA) or C. perfringens ε toxin (ETX). Finally, the sensitivity of this method was unchanged when the three simulated samples of Patinopecten yessoensis, Ruditapes philippinarum, and Scapharca broughtonii tested, indicating that the method is not affected by samples in a complex matrix. In conclusion, this study establishes a practical new method for on-site rapid detection of TDH, which is easy to operate, fast response, easy to carry and can be implemented under the field conditions without expensive equipment and professional person.

Histamine produced via the secretion of histidine decarboxylase by the bacteria in fish muscles is a toxic biogenic amine and of significant concern in food hygiene, since a high intake can cause poisoning in humans. This study proposed a fluorometric and colorimetric dual-mode specific method for the detection of histamine in fish, based on the fluorescence labeling of a histamine specific aptamer via the quenching and optical properties of gold nanoparticles (AuNPs). Due to the fluorescence resonance energy transfer phenomenon caused by the proximity of AuNPs and NaYF4:Ce/Tb, resulting in the quenching of the fluorescence signal in the detection system, the presence of histamine will compete with AuNPs to capture the aptamer and release it from the AuNP surface, inducing fluorescence recovery. Meanwhile, the combined detection of the two modes showed good linearity with histamine concentration, the linear detection range of the dual-mode synthesis was 0.2–1.0 μmol/L, with a detection limit of 4.57 nmol/L. Thus, this method has good selectivity and was successfully applied to the detection of histamine in fish foodstuffs with the recoveries of 83.39~102.027% and 82.19~105.94% for Trichiurus haumela and Thamnaconus septentrionalis, respectively. In addition, this method was shown to be simple, rapid, and easy to conduct. Through the mutual verification and combined use of the two modes, a highly sensitive, rapid, and accurate dual-mode detection method for the analysis of histamine content in food was established, thereby providing a reference for the monitoring of food freshness. [ABSTRACT FROM AUTHOR]

Many proteins form amyloid fibrils only under conditions when the probability of transition from a native (structured, densely packed) to an intermediate (labile, destabilized) state is increased. It implies the assumption that some structural intermediates are more convenient for amyloid formation than the others. Hence, if a mutation affects the protein folding pathway, one should expect that this mutation could affect the rate of amyloid formation as well. In the current work, we have compared the effects of amino acid substitutions of bovine carbonic anhydrase II on its unfolding pathway and on its ability to form amyloids at acidic pH and an elevated temperature. Wild-type protein and four mutant forms (L78A, L139A, I208A, and M239A) were studied. We analyzed the change of the protein unfolding pathway by the time-resolved fluorescence technique and the process of amyloid formation by thioflavin T fluorescence assay and electron microscopy. It was revealed that I208A substitution accelerates amyloid formation and affects the structure of the late (molten globule-like)-intermediate state of carbonic anhydrase, whereas the other mutations slow down the growth of amyloids and have either no effect on the unfolding pathway (L78A, L139A) or alter the conformational states arising at the early unfolding stage (M239A). [ABSTRACT FROM AUTHOR]

Despite the enormous environmental damage caused by plastic waste, it makes up over one-third of globally produced plastics. Polyethylene (PE) wastes have low recycling but high production rates. Towards the construction of ionic solar cells from PE, the present work describes the loading of a bioactive photoacid phycocyanobilin (PCB) dye from the pigment of Spirulina blue–green algae (as a natural resource) on low-density polyethylene (LDPE) plastic film. Dyeing was confirmed by X-ray photoelectron spectroscopy (XPS). Upon excitation of the Soret-band (400 nm), the photoluminescence (PL) spectra of PCB in neat solvents revealed two prominent emission peaks at 450–550 and 600–700 nm. The first band assigned to bilirubin-like (PCBBR) species predominated the spectral profile in the highly rigid solvent glycerol and upon loading 0.45 % (w/w) of the dye on plastic. The photoluminescence excitation (PLE) spectra of PCB for the second region (Q-band) at 672 nm in the same solvents confirmed the ground state heterogenicity previously associated with the presence of PCBA (neutral), PCBB (cationic), and PCBC (anionic) conformers. Time-resolved photoluminescence (TRPL) measurements induced via excitation of all PCB species at 510 nm in methanol revealed three-lifetime components with τ1 = ~0.1 ns and τ2 = ~2 ns associated with PCBBR species and τ3 = ~5 ns pertinent to the long-living photoproduct X*. Decay-associated spectra (DAS) analysis of the photoluminescence transient spectra of the final dyed films in the solid-state confirmed the improved generation of the long-living photoproduct as manifested in a significant increase in the PL intensity (~100-fold) and lifetime value (~90 ns) in the Q-region upon loading 6.92 % (w/w) of the dye on plastic. The photoproduct species were presumably assigned to the deprotonated PCB species, suggesting improved ionic mobility. The potential implementation of the PCB-sensitized PE solid wastes for the fabrication of ionic solar cells is discussed. [ABSTRACT FROM AUTHOR]

Light-harvesting antennas in photosynthesis capture light energy and transfer it to the reaction centers (RCs) where photochemistry takes place. The sustainable growth of the reef-building corals relies on a constant supply of the photosynthates produced by the endosymbiotic dinoflagellate, belonging to the family of Symbiodiniaceae. The antenna system in this group consists of the water-soluble peridinin-chlorophyll a-protein (PCP) and the intrinsic membrane chlorophyll a-chlorophyll c2-peridinin protein complex (acpPC). In this report, a nonameric acpPC is reported in a dinoflagellate, Fugasium kawagutii (formerly Symbiodinium kawagutii sp. CS-156). We found that extensive biochemical purification altered the oligomerization states of the initially isolated nonameric acpPC. The excitation energy transfer pathways in the acpPC nonamer and its variants were studied using time-resolved fluorescence and time-resolved absorption spectroscopic techniques at 77 K. Compared to the well-characterized trimeric acpPC, the nonameric acpPC contains an 11 nm red-shifted terminal energy emitter and substantially altered excited state lifetimes of Chl a. The observed energetic overlap of the fluorescence terminal energy emitters with the absorption of RCs is hypothesized to enable efficient downhill excitation energy transfer. Additionally, the shortened Chl a fluorescence decay lifetime in the oligomeric acpPC indicate a protective self-relaxation strategy. We propose that the highly-oligomerized acpPC nonamer represents an intact functional unit in the Symbiodiniaceae thylakoid membrane. They perform efficient excitation energy transfer (to RCs), and are under manageable regulations in favor of photoprotection. [ABSTRACT FROM AUTHOR]

Excitation energy transfer between the photochemically active protein complexes is key for photosynthetic processes. Phototrophic organisms like cyanobacteria experience subtle changes in irradiance under natural conditions. Such changes need adjustments to the excitation energy transfer between the photosystems for sustainable growth. Spectroscopic assessments on purified photosystems usually fail to capture these subtle changes. In this study, we examined whole cells from two model cyanobacteria, Synechocystis sp. PCC 6803 and Synechococcus elongatus UTEX 2973, grown under high and low light conditions to decode the high light tolerance of the latter. This allowed us to study photosynthetic machinery in the native state and in this work we particularly focused on the excitation energy transfer within PSII and PSI manifold. Understanding the high-light tolerance mechanism is imperative as it can help design strategies for increasing the light tolerance of cyanobacteria used for carbon neutral bioproduction. Our observations suggest that Synechococcus 2973 employs an uncommon photoprotection strategy, and the absence of hydroxy-echinenone pigment in this strain opens the possibility of an orange carotenoid protein homolog utilizing zeaxanthin as a scavenger of reactive oxygen species to provide photoprotection. Furthermore, the adjustments to the high-light adaptation mechanism involve downregulating the phycobilisome antenna in Synechococcus 2973, but not in Synechocystis 6803. Additionally, the stoichiometric changes to PSII/PSI are more tightly regulated in Synechococcus 2973., Competing Interests: Declarations. Competing interest: H.B.P. reports financial support was provided by Washington University in St Louis. D.M.N. acknowledges the Center for Solar Energy and Energy Storage at McKelvey School of Engineering at Washington University in St Louis for financial support., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

The main protease (M pro ) is an attractive drug target for inhibiting the coronavirus. Lots of research has focused on the static viewpoint of the M pro , such as the X-ray crystal structure, inhibitors design, and the transition between monomer and dimer. However, the attention to the dynamical features of M pro is limited, which is essential for a deeper determination of the properties of the target protein. In our research, we constructed three single-tryptophan mutants (W31IN, W207IN, and W218IN) of M pro from SARS-CoV-2 and SARS-CoV to monitor the motion of M pro at the nano-second timescale using the time-resolved fluorescence assay. We found that the temperature-dependent Stokes shift results show various behaviors among the three single-tryptophan mutants: the microenvironment around the Trp207 residue is more temperature-sensitive compared to that in residues Trp31 and Trp218. The molecular dynamic simulation results further support that M pro SARS is more flexible than that of M pro SARS2 . This difference is directly related to the distinct perturbations of residues Phe185 to Gln192, a loop that connects domain II and domain III. For the first time, we were able to reveal the different motions between M pro SARS2 and M pro SARS , although the static structures of these two are not distinguished. The differences in dynamics would be an essential step towards understanding the evolving trend of coronavirus, providing a comprehensive view of the properties of M pro , and offering perspectives for designing inhibitors for further research., Competing Interests: Declaration of competing interest The authors declare that they have no competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Objectives: One of the widely used optical biopsy methods for monitoring cellular and tissue metabolism is time-resolved fluorescence. The use of this method in optical liver biopsy has a high potential for studying the shift in energy-type production from oxidative phosphorylation to glycolysis and changes in the antioxidant defense of malignant cells. On the other hand, machine learning methods have proven to be an excellent solution to classification problems in medical practice, including biomedical optics. We aim to combine time-resolved fluorescence measurements and machine learning to automate the division of liver parenchyma and tumors (primary malignant, metastases and benign tumors) into classes., Materials and Methods: An optical biopsy was performed using a developed setup with a fine-needle optical probe in clinical conditions under ultrasound control. Fluorescence decays were recorded in a conditionally healthy liver and lesions during percutaneous needle biopsy. The labeled data set was created on the basis of the recorded fluorescence results and the histopathological classification of the biopsies obtained. Several machine learning methods were trained using different separation strategies of the training test set, and their respective accuracy was compared., Results: Our results show that each of the tumor types had its own characteristic metabolic shifts recorded by the time-resolved fluorescence spectroscopy. The application of machine learning demonstrates a reliable separation of the liver and all tumor types into cancer and noncancer classes with sensitivity, specificity and corresponding accuracy greater than 0.91, 0.79 and 0.90, using the random forest method. We also show that our method is capable of giving a preliminary diagnosis of the type of liver tumor (primary malignant, metastases and benign tumors) with a sensitivity, specificity and accuracy of at least 0.80, 0.95 and 0.90., Conclusions: These promising results highlight its potential as a key tool in the future development of diagnostic and therapeutic strategies for liver cancers. Lasers Surg. Med. 00:00-00, 2024. 2024 Wiley Periodicals LLC., (© 2024 The Author(s). Lasers in Surgery and Medicine published by Wiley Periodicals LLC.)

Phycobilisome (PBS) is a pigment-protein complex utilized by red algae and cyanobacteria in photosynthesis for light harvesting. A cyanobacterium Synechocystis sp. PCC 6803 contains PBS with a tricylindrical core built of allophycocyanin (APC) disks where six phycocyanin (PC) rods are attached. The top core cylinder is seemingly involved in attaching four PC rods and binding orange carotenoid protein (OCP) to quench excess of excitation energy. In this study, we have deleted the third linker domain (LD3) of ApcE subunit of PBS which assembles four APC discs into the top core cylinder. The mutation resulted in PBS with bicylindrical core, structurally comparable to the naturally existing PBS from Synechococcus 7942. Lack of LD3 and the top APC cylinder reduces the excitation energy transfer between PC and APC in the mutant. Moreover, these PBSs are more prone to light induced-photodamage and do not bind to the photoactivated orange carotenoid protein (OCP), a known PBS excitation quencher. These findings highlight the complex and elegant interplay between the PBS architecture and the functional efficiency, suggesting that in PBSs with naturally tri-cylindrical cores, the top cylinder has essential roles in recruiting the rods and proper binding of OCP., (© 2024 Wiley-VCH GmbH.)

Amantadine (AMA), commonly used to treat viral infections in livestock and poultry, has been banned owing to its potential hazards to human well-being. To detect unauthorized AMA usage in livestock, we developed a polyclonal antibody with a high affinity for the specific recognition of AMA through a rational design based on a structure similar to AMA and revealed the availability of the hapten design by computational chemistry analysis. Using this antibody, we established a highly responsive time-resolved fluorescence immunochromatographic assay (TRFICA). The visual detection limit of the assay is 0.6 μg/kg, and the quantitative detection limit is 0.05 μg/kg. The TRFICA also showed good recovery rates ranging from 94.5 to 109.9%, with variability coefficients not exceeding 10%. The outcomes of undisclosed sample examinations aligned with those of HPLC-MS/MS analyses, indicating that this approach can function as an ideal screening and monitoring tool for detecting illegal AMA in chicken muscle.

Benzo[a]pyrene is a widespread environmental pollutant and a strong carcinogen. It is important to understand its bio-toxicity and degradation mechanism. Herein, we studied the excited state dynamics of benzo[a]pyrene by using time-resolved fluorescence and transient absorption spectroscopic techniques. For the first time, it is identified that benzo[a]pyrene in its singlet excited state could react with oxygen, resulting in fluorescence quenching. Additionally, effective intersystem crossing can occur from its singlet state to the triplet state. Furthermore, the interaction between the excited benzo[a]pyrene and ct-DNA can be observed directly and charge transfer between benzo[a]pyrene and ct-DNA may be the reason. These results lay a foundation for further understanding of the carcinogenic mechanism of benzo[a]pyrene and provide insight into the photo-degradation mechanism of this molecule.

The ultrafast dynamics of triplet excitons and polarons in hexaphenyl film was investigated by time-resolved fluorescence and femtosecond transient absorption techniques under various excitation photon energies. Two distinct pathways of triplet formation were clearly observed. Long-lived triplet states are populated within 4.5 ps via singlet fission-intersystem crossing, while the short-lived triplet states (1.5 ns) are generated via singlet fission from vibrational electronic states. In the meantime, polarons were formed from hot excitons on a timescale of <30 fs and recombined in ultrafast lifetime (0.37 ps). In addition, the characterization of hexaphenyl film suggests the morphologies of crystal and aggregate to wide applications in organic electronic devices. The present study provides a universally applicable film fabrication in hexaphenyl system towards future singlet fission-based solar cells. [ABSTRACT FROM AUTHOR]

Photosystem I (PSI) is a large membrane photosynthetic complex that harvests sunlight and drives photosynthetic electron transport. In both green algae and higher plants, PSI's ultrafast energy transfer and charge separation kinetics have been characterized. In contrast, it is not yet clear in Physcomitrella patens , even though moss is one of the earliest land plants and represents a critical stage in plant evolution. Here, we measured the time-resolved fluorescence of purified Pp PSI-LHCI at both room temperature (RT) and 77 K. Compared to the PSI kinetics of Arabidopsis thaliana at RT, we found that although the overall trapping time of Pp PSI-LHCI is nearly identical, ∼46 ps, their lifetimes at different wavelength regions differ. Specifically, Pp PSI-LHCI is slower in energy trapping below 720 nm but faster beyond. The slow-down of energy transfer between bulk chlorophylls (Chls, <720 nm) in Pp PSI-LHCI is probably because of the larger spatial gap between the PSI core and LHCI belt, and the acceleration of trapping at longer wavelength is most likely due to the lack of low-energy red-shifted Chls (red Chls). Indeed, time-resolved fluorescence results at 77 K revealed only three types of red Chls of 702 nm, 712 nm, and 720 nm in Pp PSI-LHCI but failed to detect the red Chls of 735 nm that present in LHCI in higher plants. Finally, we briefly discussed the evolutionary adaptations of PSI-LHCI in the context of red Chls from green algae to mosses and to land plants. • Ultrafast energy trapping kinetics of PSI-LHCI in moss were determined. • PSI-LHCI in moss has a similar overall trapping time to the one in Arabidopsis. • The reddest forms of Chls in PSI-LHCI in moss is at ∼720 nm. [ABSTRACT FROM AUTHOR]

In this response we underscore that the instrumentation described in the original publication (Liu et al 2012 Phys. Med. Biol. 57 843-65) was based on pulse-sampling technique, while the comment by Zhang et al is based on the assumption that a time-correlated single photon counting (TCSPC) instrumentation was used. Therefore the arguments made in the comment are not applicable to the noise model reported by Liu et al. As reported in the literature (Lakowicz 2006 Principles of Fluorescence Spectroscopy (New York: Springer)), while in the TCSPC the experimental noise can be estimated from Poisson statistics, such an assumption is not valid for pulse-sampling (transient recording) techniques. To further clarify this aspect, we present here a comprehensive noise model describing the signal and noise propagation of the pulse sampling time-resolved fluorescence detection. Experimental data recorded in various conditions are analyzed as a case study to demonstrate the noise model of our instrumental system. In addition, regarding the statement of correcting equation (3) in Liu et al (2012 Phys. Med. Biol. 57 843-65), the notation of discrete time Laguerre function in the original publication was clear and consistent with literature conventions (Marmarelis 1993 Ann. Biomed. Eng. 21 573-89, Westwick and Kearney 2003 Identification of Nonlinear Physiological Systems (Hoboken, NJ: Wiley)). Thus, it does not require revision.

Excited-state chemistry relies on the communication between molecules, making it a crucial aspect of the field. One important question that arises is whether intermolecular communication and its rate can be modified when a molecule is confined. To explore the interaction in such systems, we investigated the ground and excited states of 4′-N,N-diethylaminoflavonol (DEA3HF) in an octa acid-based (OA) confined medium and in ethanolic solution, both in the presence of Rhodamine 6G (R6G). Despite the observed spectral overlap between the flavonol emission and the R6G absorption, as well as the fluorescence quenching of the flavonol in the presence of R6G, the almost constant fluorescence lifetime at different amounts of R6G discards the presence of FRET in the studied systems. Steady-state and time-resolved fluorescence indicate the formation of an emissive complex between the proton transfer dye encapsulated within water-soluble supramolecular host octa acid (DEA3HF@(OA)2) and R6G. A similar result was observed between DEA3HF:R6G in ethanolic solution. The respective Stern–Volmer plots corroborate with these observations, suggesting a static quenching mechanism for both systems.

Phycobilisome (PBS) is a large pigment-protein complex in cyanobacteria and red algae responsible for capturing sunlight and transferring its energy to photosystems (PS). Spectroscopic and structural properties of various PBSs have been widely studied, however, the nature of so-called complex-complex interactions between PBS and PSs remains much less explored. In this work, we have investigated the function of a newly identified PBS linker protein, ApcG, some domain of which, together with a loop region (PB-loop in ApcE), is possibly located near the PBS-PS interface. Using Synechocystis sp. PCC 6803, we generated an ApcG deletion mutant and probed its deletion effect on the energetic coupling between PBS and photosystems. Steady-state and time-resolved spectroscopic characterization of the purified ΔApcG-PBS demonstrated that ApcG removal weakly affects the photophysical properties of PBS for which the spectroscopic properties of terminal energy emitters are comparable to those of PBS from wild-type strain. However, analysis of fluorescence decay imaging datasets reveals that ApcG deletion induces disruptions within the allophycocyanin (APC) core, resulting in the emergence (splitting) of two spectrally diverse subgroups with some short-lived APC. Profound spectroscopic changes of the whole ΔApcG mutant cell, however, emerge during state transition, a dynamic process of light scheme adaptation. The mutant cells in State I show a substantial increase in PBS-related fluorescence. On the other hand, global analysis of time-resolved fluorescence demonstrates that in general ApcG deletion does not alter or inhibit state transitions interpreted in terms of the changes of the PSII and PSI fluorescence emission intensity. The results revealed yet–to–be discovered mechanism of ApcG-docking induced excitation energy transfer regulation within PBS or to Photosystems. • Time-resolved fluorescence unveiled the photophysical characteristics of ΔApcG-PBS. • Mutation induces very minor disruptions within the allophycocyanin (APC) core. • Distinct spectral subgroups of short-lived APC identified in ΔApcG-PBS • Small linker protein causes altered energy transfer from PBS to RC. • Deletion of ApcG subunit does not impede state transitions in mutant cells. [ABSTRACT FROM AUTHOR]

The effect of the chemical structure of selected phenolic acids on the molecular organization of gliadins was investigated with the application of Fourier Transform Infrared (FTIR) technique, steady-state, and time-resolved fluorescence spectroscopy. Hydroxybenzoic (4-hydroxybenzoic, protocatechuic, vanillic, and syringic) and hydroxycinnamic (coumaric, caffeic, ferulic, sinapic) acids have been used as gliadins modifiers. The results indicated that hydroxybenzoic acids due to their smaller size incorporate into spaces between two polypeptide chains and form a hydrogen bond with them leading to aggregation. Additionally, syringic acids could incorporate into hydrophobic pockets of protein. Whereas hydroxycinnamic acids, due to their higher stiffness and larger size, separated polypeptide chains leading to gliadin disaggregation. These acids did not incorporate into hydrophobic pockets. [ABSTRACT FROM AUTHOR]