Measurements Of Fluorescence Spectra Research Articles

Dose Optimization of Intravenous Indocyanine Green for Malignant Lung Tumor Localization

Background: Intravenously administered indocyanine green (ICG) accumulates in lung tumors, facilitating their detection via a fluorescence spectrum measurement. This method aids in identifying tumor locations that are invisible to the naked eye. We aim to determine the optimal ICG dose and administration method for accurate tumor identification during lung resection surgeries, utilizing a novel ICG fluorescence spectroscopy system for precise tumor localization. Materials and Methods: ICG should be dissolved in the provided solution or distilled water and administered intravenously approximately 24 h before surgery, beginning with an initial dose of 0.5 mg/kg. If the tumor detection rate is insufficient, the dose may be gradually increased to a maximum of 5.0 mg/kg to determine the optimal dosage for effective tumor detection. This fluorescence spectroscopy during surgery may reveal additional lesions that remain undetected in preoperative assessments. The primary endpoint includes the correct diagnostic rate of tumor localization. The secondary endpoints include the measurement of the intraoperative ICG fluorescence spectral intensity in lung tumors, the assessment of the operability and safety of intraperitoneal ICG administrations, the measurement of the ICG fluorescence spectral intensity in surgical specimens, the comparison of the spectral intensity in lung tissues during collapse and expansion, the correlation between ICG camera images and fluorescence spectral intensity, and the comparison of fluorescence analysis results with histopathological findings. The trial has been registered in the jRCT Clinical Trials Registry under the code jRCTs011230037. Results and Conclusions: This trial aims to establish an effective methodology for localizing and diagnosing malignant lung tumors, thereby potentially improving surgical outcomes and refining treatment protocols.

Synthesis of bis-(benzhydryloxy) substituted axially silicon(IV) phthalocyanine: investigation of photophysical, photochemical, and computational electronic properties

Synthesis of axially disubstituted silicon(IV) phthalocyanine bearing benzhydryloxy groups obtained by reaction of SiPcCl2 with diphenylmethanol is reported. Characterization of the compound was performed by 1H and 13C NMR, UV–Vis, mass spectrometry, and FT-IR spectroscopy. Photophysical and photochemical properties were investigated. Fluorescence spectra measurements were performed in DMSO as solvent. A preferred chemical method was used to determine the amount of singlet oxygen production. Optimizations were calculated for the single-molecule Si-Pc with the 6–311 G (d, p) basis set at the B3LYP and B3PW91 levels of density functional theory (DFT). The charge transfer (or) charge delocalization between intramolecular donor–acceptor groups was determined by NBO analysis. Furthermore, molecular electrostatic potential, Fukui functions, electrophilic and nucleophilic character maps were calculated. The electronic structure and energy parameters of the investigated compound were determined to be ΔE calc = 2.19 eV by DFT calculation and ΔE opt = 1.84 by experimental UV spectrum.

Оn the aggregation of polycationic photosensitizer upon binding to Gram-negative bacteria

Polycationic photosensitizers (PS) are not susceptible to aggregation in solutions, but their high local concentrations in Gram-negative bacteria can be sufficient for aggregation and reduced effectiveness of antibacterial photodynamic treatment. By measuring fluorescence spectra and kinetics we were able to evaluate the degree of aggregation of polycationic PS ZnPcChol8 in Gram-negative bacteria E. coli K12 TG1. Binding of ZnPcChol8 to E. coli K12 TG1 leads to an appearance of groups of molecules with shorter PS fluorescence lifetime, a decrease in fluorescence intensity and a shift in the fluorescence spectral maximum. However, we evaluated that about 88% of the fluorescing PS molecules in the bacteria were in an unaggregated state, which indicates only a small reduction in the generation of reactive oxygen species.

Real-time pollen identification using holographic imaging and fluorescence measurements

Abstract. Over the past few years, a diverse range of automatic real-time instruments has been developed to respond to the needs of end users in terms of information about atmospheric bioaerosols. One of them, the SwisensPoleno Jupiter, is an airflow cytometer used for operational automatic bioaerosol monitoring. The instrument records holographic images and fluorescence information for single aerosol particles, which can be used for identification of several aerosol types, in particular different pollen taxa. To improve the pollen identification algorithm applied to the SwisensPoleno Jupiter and currently based only on the holography data, we explore the impact of merging fluorescence spectra measurements with holographic images. We demonstrate, using measurements of aerosolised pollen, that combining information from these two sources results in a considerable improvement in the classification performance compared to using only a single source (balanced accuracy of 0.992 vs. 0.968 and 0.878). This increase in performance can be ascribed to the fact that often classes which are difficult to resolve using holography alone can be well identified using fluorescence and vice versa. We also present a detailed statistical analysis of the features of the pollen grains that are measured and provide a robust, physically based insight into the algorithm's identification process. The results are expected to have a direct impact on operational pollen identification models, particularly improving the recognition of taxa responsible for respiratory allergies.

Study the effect of nano NiCo2O4 doping on the optical and dielectric properties of PMMA/PEO/MWCNTs

In this study, NiCo2O4 nanoparticles were prepared using a hydrothermal process and examined by x-ray diffraction. After that, using the casting technique, blends of polymethyl methacrylate (PMMA)/poly(ethylene oxide) (PEO) were loaded with multi-walled carbon nanotubes (MWCNTs) and different amounts (x) of NiCo2O4 nanoparticles. The obtained blends were characterized using X-ray diffraction and scanning electron microscopy techniques. Utilizing diffuse reflectance measurements, various optical parameters, including energy gap, refractive index, extinction coefficient, optical dielectric constant, optical conductivity, and nonlinear optical parameters, were investigated. Following incorporation of MWCNTs/NiCo2O4 in the blend, the transmittance of the PMMA/PEO blend (90 %) displayed a drop reaching 21 %, the reflectivity and refractive index increased. The direct/indirect optical band gap values of PMMA/PEO (5.07/4.8 eV) decreased attaining 4.96/4.54 eV for the blend with 2.5 wt% NiCo2O4. The optical conductivity greatly enhanced, and the linear and nonlinear optical parameters increased as the amount of NiCo2O4 doping increased. The dispersion parameters for all blends were also calculated. Fluorescence spectra (FL) measurements revealed a reduction in the FL intensity with increasing the NiCo2O4 content (x). Through the dielectric measurements, the impact of increasing NiCo2O4 content on the ac conductivity, dielectric properties, energy density, and electric modulus was analyzed for all blends. Remarkably, a significant increase in AC conductivity was obtained upon loading with 1.5 wt% NiCo2O4. Overall, variation in the dielectric and optical features of the PMMA/PEO/MWCNTs/x wt.% NiCo2O4 blends makes them appropriate for optoelectronic and energy storage applications.

Diphenolic boldine, an aporphine alkaloid: inhibitory effect evaluation on α-glucosidase by molecular dynamics integrating enzyme kinetics

Screening α-glucosidase inhibitors with novel structures is an important field in the development of anti-diabetic drugs due to their application in postprandial hyperglycemia control. Boldine is one of the potent natural antioxidants with a wide range of pharmacological activities. Virtual screening and biochemical inhibition kinetics combined with molecular dynamics simulations were conducted to verify the inactivation function of boldine on α-glucosidase. A series of inhibition kinetics and spectrometry detections were conducted to analyze the α-glucosidase inhibition. Computational simulations of molecular dynamics/docking analyses were conducted to detect boldine docking sites’ details and evaluate the key binding residues. Boldine displayed a typical reversible and mixed-type inhibition manner. Measurements of circular dichroism and fluorescence spectrum showed boldine changed the secondary structure and loosened the tertiary conformation of target α-glucosidase. The computational molecular dynamics showed that boldine could block the active pocket site through close interaction with binding key residues, and two phenolic hydroxyl groups of boldine play a core function in α-glucosidase inhibition via ligand binding. This investigation reveals the boldine function on interaction with the α-glucosidase active site, which provides a new inhibitor candidate. Communicated by Ramaswamy H. Sarma

Excited-state proton transfer based fluorescence in Kaempferol powder and solutions with different concentrations

Kaempferol (KMP) is one of the most common flavonoids, currently being extensively studied for its numerous beneficial health effects. Here we study the fluorescence (FL) emission of KMP powder and of its solutions prepared using different types of solvents (polar and non-polar). In the spectra of KMP powder and KMP solutions with high concentration, the same FL peak with maximum at 1.9 eV is observed. Another FL peak, at higher energy of 2.45 eV, emerges in solutions, its relative intensity increases with decreasing solution concentration. The FL emission of solutions with lowest concentration displays only that peak. To calculate characteristic energies of absorption and emission of KMP molecule in vacuum and in solutions we use time-dependent density functional theory. Comparing the results of computations with measured FL spectra, we associate the FL band at 1.9 eV with the emission due to excited state intramolecular transfer of the proton of –OH5 hydroxyl group. The FL emission at 2.45 eV is related to the –OH3 proton transfer. We measure the FL spectra of KMP powder using two different excitation energies, 3.06 eV and 2.33 eV, and find that its FL spectrum depends on the excitation energy. To understand that dependence, we compare the FL spectra of KMP and Q monohydrate powders. We consider the excited state intermolecular transfer of the proton from –OH3′ hydroxyl group to a neighboring molecule in Q crystal and calculate the energy corresponding to the emission of the resulted anion of Q molecule. The spectral feature at 1.69 eV observed only in the FL spectrum of Q hydrate is attributed to the Q anion FL emission.

Dual-state emission of D-A-D type benzothiadiazole derivatives for the sensitive detection of amine compounds

Organic light-emitting materials with dual-state emission (DSE) in both solution and solid states have attracted widely attention because of their promising applications in diverse areas. In this work, five benzothiadiazole-based D-A-D type luminogens BT2Ph, BT2Na, BT2Pa, BT2An and BT2Py were concisely synthesized by introducing different π–conjugated rigid groups (benzene, naphthalene, phenanthrene, anthracene and pyrene ring). As a result of their twisted conformation and effective conjugation structure, these five dual-state emission molecules exhibit intense photoluminescence in solution and solid state. The reason for these luminogens with DSE behavior was further explained by the twisted intramolecular charge-transfer mechanism based on the variable temperature fluorescence spectrum measurement and theoretical calculation with time-dependent density functional theory (TD-DFT). Moreover, these DSE luminogens which possess excellent photostability and obvious solvatofluorochromic properties were multifunctional fluorescent probes for the visual detection of amine compounds (aniline, cyclohexylamine, and ammonia). A charge transfer mechanism between luminogens and amine compounds was found to be the cause of fluorescence quenching. Thus, these DSE molecules may have applications in anti-counterfeiting and fluorescent sensors.

Spectroscopic and molecular docking study of three kinds of cinnamic acid interaction with pepsin

In this work, under simulated physiological conditions (pH = 2.2, glycine hydrochloric acid buffer solution), the interactions of cinnamic acid (CA), m-hydroxycinnamic acid (m-CA) and p-hydroxycinnamic acid (p-CA) with pepsin were studied by fluorescence spectroscopy, ultraviolet–visible absorption spectroscopy, circular dichroism (CD) spectroscopy, Fourier transform infrared spectroscopy (FTIR), molecular docking and molecular dynamic simulation (MD). The spectrogram results showed that these three kinds of CA had a strong ability to quench the intrinsic fluorescence of pepsin, and the quenching effects were obvious with the increase of concentration of these three kinds of molecules. The quenching mechanism of CA, m-CA and p-CA on the fluorescence of pepsin was static quenching. In addition, a stable complex was formed between three kinds of CA with pepsin. Thermodynamic data and docking information suggested that three kinds of CA combine with pepsin were mainly driven by electrostatic force and hydrogen bond. The binding constant and the number of binding sites were determined. The interaction of CA, m-CA and p-CA with pepsin was spontaneous, and accompanied by non-radiative energy transfer. The results from CD, FTIR, UV–Vis and synchronous fluorescence spectra measurements manifested that the secondary structure of pepsin was changed by the binding of three kinds of CA. The β-sheet of pepsin increased after the interaction with three kinds of CA. The assay results of pepsin activity showed that three kinds of CA led to a decrease in pepsin activity within the investigated concentrations. Molecular docking investigation revealed the formation of polar hydrogen bonds as well as hydrophobic interactions between three kinds of CA with pepsin, and the ligand within the binding pocket of pepsin. MD results implied the formation of a stable complex between three kinds of CA and pepsin. The research suggested that cinnamic acid and its derivatives could be a potential effect on the structure and properties of digestive enzyme.

Theoretical and experimental investigation of novel quinazoline derivatives: synthesis, photophysical, reactive properties, molecular docking and selective HSA biointeraction

Two new quinazoline derivatives (2a and 2b) were successfully synthesized in this work using the condensation technique in excellent yields. Using spectroscopic techniques and elemental analyses, the compounds were completely characterized. Density functional theory (DFT) computations have been used to examine the title compound’s reactive characteristics. Chemical reactivity was predicted using local reactive descriptors and molecule electrostatic potential. Additionally, Time dependent DFT (TD-DFT) simulations were used to examine the impact of solvents on the photophysical characteristics. The affinity of compounds 2a and 2b for human serum albumin (HSA) was further explored using several electronic spectroscopies. Through static mechanisms, both compounds reduce the intrinsic fluorescence of HSA. It is determined that the HSA-2b complex’s binding constant is significantly greater than the HSA-2a complex. The fluorescence spectrum measurements proved that the HSA underwent structural changes after interaction with these compounds. It was demonstrated by site marker competitive displacement studies that compounds 2a and 2b preferred to bind to site I in HSA subdomain IIA. Additionally, synchronised fluorescence spectra were utilized to analyze how HSA’s conformation changed after interacting with various substances. The molecular docking investigations of these compounds with the three critical HSA binding sites, comprising subdomains IIA, IIIA, and IB, further confirmed the experimental findings. The significant contact between the investigated compounds and HSA was supported by the docking simulations. Communicated by Ramaswamy H. Sarma

Impact of site-selective spectroscopy on laser cooling parameter characterization.

From laser design to optical refrigeration, experimentally measured fluorescence spectra are often utilized to obtain input parameters for predictive models. However, in materials that exhibit site-selectivity, the fluorescence spectra depend on the excitation wavelength employed to take the measurement. This work explores different conclusions that predictive models reach after inputting such varied spectra. Here, temperature-dependent site-selective spectroscopy is carried out on an ultra-pure Yb, Al co-doped silica rod fabricated by the modified chemical vapor deposition technique. The results are discussed in the context of characterizing ytterbium doped silica for optical refrigeration. Measurements made between 80 K and 280 K at several different excitation wavelengths yield unique values and temperature dependencies of the mean fluorescence wavelength. For the excitation wavelengths studied here, the variation in emission lineshapes ultimately lead to calculated minimum achievable temperatures (MAT) ranging between 151 K and 169 K, with theoretical optimal pumping wavelengths between 1030 nm and 1037 nm. Direct evaluation of the temperature dependence of the fluorescence spectra band area associated with radiative transitions out of the thermally populated 2F5/2 sublevel may be a better approach to identifying the MAT of a glass where site-selective behavior precludes unique conclusions.

Distinguishing Healthy and Carcinoma Cell Cultures Using Fluorescence Spectra Decomposition with a Genetic-Algorithm-Based Code.

In this paper, we analysed the steady state fluorescence spectra of cell suspensions containing healthy and carcinoma fibroblast mouse cells, using a genetic-algorithm-spectra-decomposition software (GASpeD). In contrast to other deconvolution algorithms, such as polynomial or linear unmixing software, GASpeD takes into account light scatter. In cell suspensions, light scatter plays an important role as it depends on the number of cells, their size, shape, and coagulation. The measured fluorescence spectra were normalized, smoothed and deconvoluted into four peaks and background. The wavelengths of intensities' maxima of lipopigments (LR), FAD, and free/bound NAD(P)H (AF/AB) of the deconvoluted spectra matched published data. In deconvoluted spectra at pH = 7, the fluorescence intensities of the AF/AB ratio in healthy cells was always higher in comparison to carcinoma cells. In addition, the AF/AB ratio in healthy and carcinoma cells were influenced differently by changes in pH. In mixtures of healthy and carcinoma cells, AF/AB decreases when more than 13% of carcinoma cells are present. Expensive instrumentation is not required, and the software is user friendly. Due to these attributes, we hope that this study will be a first step in the development of new cancer biosensors and treatments with the use of optical fibers.

Cross-section spectra and transient characteristics of Er3+ emissions in Gd3(Al, Ga)5O12 garnet single crystal

We measured fluorescence spectra of visible and infrared electronic transitions at 530 (2H11/2 → 4I15/2), 560 (4S3/2 → 4I15/2), 670 (4F9/2 → 4I15/2), 980 (4I11/2 → 4I15/2), 1530 (4I13/2 → 4I15/2) and 2700 nm (4I11/2 → 4I13/2) of Er3+ in Gd3(Al0.4Ga0.6)5O12 garnet single-crystal excited at the wavelength 520 nm (for the 980 nm emission) or 980 nm (for other emissions). From measured fluorescence spectrum, Er3+ emission cross-section spectrum was calibrated for each transition. Absorption cross-section spectra were further derived on the basis of McCumber equation, and compared with those spectra obtained from measured absorption spectrum on the basis of the Beer-Lambert law. The comparison showed that the results given by two methods can be regarded as same within the error. The transient features of visible and infrared emissions were also studied under pulse excitation. The results showed that, while the three IR emissions at 980, 1530 and 2700 nm all follow a mono-exponential function, both green and red 980-nm-upconverted emissions at 560 and 670 nm exhibit non-mono-exponentially decaying feature, and each decaying trace can be fitted by a sum of two exponential functions. The non-mono-exponential feature is related to cross relaxation caused by non-radiative short-distance energy transfer between clustered Er3+ sites.

The choice of spectral ranges of registration for the fluorescent method for detecting leaks in oil pipelines at an excitation wavelength of 355 nm

Mathematical modeling was carried out based on the experimentally measured fluorescence spectra of oil, vegetation and water to select the most effective spectral registration ranges for the fluorescent method for detecting oil leaks at an excitation wavelength of 355 nm. The results of mathematical modeling show that the probabilities of correct detection and false alarms for the problem of detecting oil leaks significantly depend on the type of oil and, accordingly, on the spectral channels selected for monitoring. For reliable detection of oil spills against the background of vegetation or water bodies, two or three spectral channels must be used. The highest probabilities of correct detection (>0.999) and small probabilities of false alarms (<0.04) can be achieved for oils with intensity maxima of laser-induced fluorescent radiation at wavelengths of ~ 420 and 550 nm (when using two spectral channels) and for oils with fluorescence intensity maximum at a wavelength of ~510 nm (when using three spectral channels). For oils with a maximum fluorescence intensity at a wavelength of about 475 nm (when using three spectral channels), the results are worse, although they remain acceptable (at a measurement noise of 10%, the probability of correct detection and false alarms, respectively, 0.94 and 0.11).

CFSA-AGD: An accurate crosstalk fluorescence spectroscopic decomposition method for identifying and quantifying FDOMs in aquatic environments

Fluorescent substances exist in various aquatic environments and other environmental media. It is a critical task to identify the components accurately and quantify their contents precisely. Based on the Crosstalk Fluorescence Spectroscopy Analysis (CFSA) model, a fluorescence spectroscopic decomposition using the Alternating Gradient Descent (AGD) algorithm is developed. By reducing the residual error of the model through alternating iterations, the CFSA-AGD method achieves unsupervised model training and automatic spectroscopic decomposition without extra experimental operations such as dilution or absorbance measurement, exempting from tedious modeling process. The objectives of this work are to validate that the CFSA-AGD method can comprehensively address the decomposition of fluorescence spectral crosstalk. Furthermore, the novel method is applied to the spectroscopic decomposition of natural FDOMs in aquatic environments as a standard tool. The spectral data analyzing the performance of this method is verified and compared with the conventional methods through the experiment on standard samples. The results indicate that CFSA-AGD has higher spectroscopic decomposition accuracy and gives more abundant information on the characteristic spectra with less residual error than parallel factor analysis. This means that the fluorescence spectra of natural FDOMs can be decomposed into the characteristic fluorescence emission spectra of single components with higher accuracy and the characteristic fluorescence absorption spectra that cannot be obtained by the conventional methods. Meanwhile, it improves the analytical precision of the contents (from R2 ≥ 0.9778 to R2 ≥ 0.9920) and reduces the ultimate residual error by two orders of magnitude (from 1.42 × 10−1 to 4.68 × 10−3) when the method is used to estimate the measured fluorescence spectra.

Spectroscopic investigations on fungal aspartic protease as target of gallic acid

Proteases are a major virulence factor in pathogenic fungi and can serve as a potential therapeutic target. The interaction of gallic acid (GA) with Aspartic fungal protease (PepA) was investigated using biophysical and in silico approaches. UV–Vis and fluorescence spectroscopy showed complex formation and static quenching of PepA by GA with Ka of 7.4 × 105 M−1 and stoichiometric binding site (n) of 1.67. CD-spectroscopy showed marked changes in helical content and synchronous fluorescence spectra measurements indicated significant changes in the microenvironment around tryptophan residues in the GA-PepA complex. Outcomes of Isothermal Titration Calorimetry (ITC) measurement and molecular modelling studies validated the spectroscopic results. The binding of GA to Human Serum albumin (HSA) was moderate (Ka = 1.9 × 103 M−1) and did not cause structural disruption of HSA. To conclude, gallic acid is strongly bound to fungal protease leading to structural disruption and inhibition whereas HSA structure was largely conserved. Gallic acid thus appears to be a potential therapeutic agent against fungal proteases.

Reflection-enhanced laser-induced fluorescence spectroscopy to improve the analytical sensitivity in liquids

The current work demonstrates a novel approach to enhancing the analytical sensitivity of the laser-induced fluorescence (LIF) technique in liquids. An increase in the fluorescence spectral band intensity of about sixfold compared to the conventional LIF has been achieved. Such betterment has been accomplished by having the fluorophore liquid in a cuvette having a reflecting mirror-like side facing the exciting incident laser beam. The silvered or aluminized reflecting side of the cuvette was tested. The pilot test of the proposed cuvette was performed using an excitation laser light of 405 nm wavelength and five mW average power on chlorophyll-a (Chl-a) samples of different concentrations. As a result, a pronounced improvement in the Chl-a fluorescence spectral band intensity is achieved. Such a novel approach, the reflection-enhanced laser-induced fluorescence (RELIF), has been used to analyze six Egyptian brands of extra virgin olive oil (EVOO). Compared to the LIF measurement results on the same EVOO, the RELIF was superior in terms of the fluorescence-spectrum intensity enhancement factor. Both Ag and Al coatings of the cuvette revealed similar results. Statistical analysis of the measured fluorescence spectra via the partial least square regression (PLSR) method for LIF and RELIF revealed a higher coefficient of determination R2 for both RELIF measurements (with silver and aluminum coating) than for LIF. The proposed novel RELIF approach can be utilized for other fluorophore liquids at higher analytical sensitivity than conventional LIF. On the other hand, the RELIF technique is straightforward, cost-effective, and does not complicate the traditional LIF setup.

Study of fluorescence spectroscopy and molecular mechanisms for the interaction of Hg2+ ions and R-phycoerythrin from marine algae (Porphyra yezoensis).

Heavy metal is a worldwide hazardous material, and many efforts were made to detect them sensitively and selectively. R-phycoerythrin (R-PE), a marine fluorescent protein, is abundant in red algae and participates in photosynthesis. In this work, the fluorescence spectroscopy and molecular mechanism of Hg2+ ions and R-PE were further explored through fluorescence spectrum measurements, time-resolved fluorescence lifetimes, peak fitting of Fourier transform infrared spectroscopy, and molecular docking simulation in this study. It was proved by fluorescent spectrum measurements that Hg2+ ions could lead to static fluorescence quenching. Besides, the interaction was a spontaneous and exothermic process driven by hydrogen bond and Van der Waals (VDW) force. Importantly, Hg2+ ions bound to 78LYS and 82CYS on the α chain and 73CYS and 82CYS on the β chain, which resulted in the structural changes of the peptide chain and affected the secondary structure contents of R-PE. This study further explained the effect of Hg2+ ions on marine fluorescent protein R-PE.

Excited-state dynamics of all-trans protonated retinal Schiff base in CRABPII-based rhodopsin mimics

The rhodopsin mimic is a chemically synthetized complex with retinyl Schiff base (RSB) formed between protein and the retinal chromophore that can mimic the natural rhodopsin-like protein. The artificial rhodopsin mimic is more stable and designable than the natural protein and hence has wider uses in photon detection devices. The mimic structure RSB, like the case in the actual rhodopsin-like protein, undergoes isomerization and protonation throughout the photoreaction process. As a result, understanding the dynamics of the RSB in the photoreaction process is critical. In this study, the ultrafast transient absorption spectra of three mutants of the cellular retinoic acid-binding protein II-based rhodopsin mimic at acidic environment were recorded, from which the related excited-state dynamics of the all-trans protonated RSB (AT-PRSB) were investigated. The transient fluorescence spectra measurements are used to validate some of the dynamic features. We find that the excited-state dynamics of AT-PRSB in three mutants share a similar pattern that differs significantly from the dynamics of 15-cis PRSB of the rhodopsin mimic in neutral solution. By comparing the dynamics across the three mutants, we discovered that the aromatic residues near the β-ionone ring structure of the retinal may help stabilize the AT-PRSB and hence slow down its isomerization rate. The experimental results provide implications on designing a rhodopsin-like protein with significant infrared fluorescence, which can be particularly useful in the applications in biosensing or bioimaging in deeper tissues.

Monitoring of natural water pollution by fluorescence spectroscopy

Introduction. Environmental monitoring of the state of water bodies is an important component of environmental protection. A promising direction for assessing the quality of water bodies is to determine their generalized indicators. Fluorescence spectroscopy can serve as a source of important information about the state of water bodies and sources of their pollution. Purpose of the study - to assess the water pollution of the Moskva River and its tributaries using the fluorescence spectroscopy method. To reveal the influence of oil products on the fluorescence spectra of river water. Materials and methods. The object of the study was water from the Moskva River and its tributaries: Pakhra, Kotlovka, Setun. Water samples from the Moskva River were taken in different parts of the city, which are characterized by varying degrees of pollution. Water fluorescence spectra were measured with SM2203 spectrofluorimeter (ZAO Solar, Belarus), total organic and inorganic carbon, on a TOC-VCHP total carbon analyzer (Shimadzu, Japan). Results. The nature of the fluorescence spectra of the Moskva River and its tributaries in the absence of significant anthropogenic pollution are characterized by relative constancy. Bacterial pollution and pollution with aromatic compounds of anthropogenic origin, including oil products, leads to an increase in the fluorescence intensity in the short-wavelength part of the spectrum. The correlation coefficient between the optical density at a wavelength of 254 nm and the content of dissolved organic carbon (DOC) for the studied samples was 0.66, and between the fluorescence intensity at a wavelength of 400 nm and DOC was 0.74. Limitations. The method cannot be used for the quantitative determination of individual substances; it is intended for a semi-quantitative assessment of water pollution. Conclusion. Measurement of fluorescence spectra and total organic carbon makes it possible to give a general assessment of the contamination of a water body (which is especially important for a sample of unknown composition) and to choose the optimal scheme for its targeted analysis. High dissolved organic carbon (DOC) values and high fluorescence intensity at 320 nm are highly likely to indicate chemical contamination of water, while DOC values characteristic of a water body and high fluorescence intensity at 320 nm indicate bacterial contamination.