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

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

Synergistic Antifungal Interactions between Antibiotic Amphotericin B and Selected 1,3,4-thiadiazole Derivatives, Determined by Microbiological, Cytochemical, and Molecular Spectroscopic Studies.

In recent years, drug-resistant and multidrug-resistant fungal strains have been more frequently isolated in clinical practice. This phenomenon is responsible for difficulties in the treatment of infections. Therefore, the development of new antifungal drugs is an extremely important challenge. Combinations of selected 1,3,4-thiadiazole derivatives with amphotericin B showing strong synergic antifungal interactions are promising candidates for such formulas. In the study, microbiological, cytochemical, and molecular spectroscopy methods were used to investigate the antifungal synergy mechanisms associated with the aforementioned combinations. The present results indicate that two derivatives, i.e., C1 and NTBD, demonstrate strong synergistic interactions with AmB against some Candida species. The ATR-FTIR analysis showed that yeasts treated with the C1 + AmB and NTBD + AmB compositions, compared with those treated with single compounds, exhibited more pronounced abnormalities in the biomolecular content, suggesting that the main mechanism of the synergistic antifungal activity of the compounds is related to a disturbance in cell wall integrity. The analysis of the electron absorption and fluorescence spectra revealed that the biophysical mechanism underlying the observed synergy is associated with disaggregation of AmB molecules induced by the 1,3,4-thiadiazole derivatives. Such observations suggest the possibility of the successful application of thiadiazole derivatives combined with AmB in the therapy of fungal infections.

Micronized Powder of Raspberry Pomace as a Source of Bioactive Compounds.

Red raspberries, which contain a variety of nutrients and phytochemicals that are beneficial for human health, can be utilized as a raw material in the creation of several supplements. This research suggests micronized powder of raspberry pomace production. The molecular characteristics (FTIR), sugar, and biological potential (phenolic compounds and antioxidant activity) of micronized raspberry powders were investigated. FTIR spectroscopy results revealed spectral changes in the ranges with maxima at ~1720, 1635, and 1326, as well as intensity changes in practically the entire spectral range analyzed. The discrepancies clearly indicate that the micronization of the raspberry byproduct samples cleaved the intramolecular hydrogen bonds in the polysaccharides present in the samples, thus increasing the respective content of simple saccharides. In comparison to the control powders, more glucose and fructose were recovered from the micronized samples of the raspberry powders. The study's micronized powders were found to contain nine different types of phenolic compounds, including rutin, elagic acid derivatives, cyanidin-3-sophoroside, cyanidin-3-(2-glucosylrutinoside), cyanidin-3-rutinoside, pelargonidin-3-rutinoside, and elagic acid derivatives. Significantly higher concentrations of ellagic acid and ellagic acid derivatives and rutin were found in the micronized samples than in the control sample. The antioxidant potential assessed by ABTS and FRAP significantly increased following the micronization procedure.

Evaluation of the Quality of Selected White and Red Wines Produced from Moravia Region of Czech Republic Using Physicochemical Analysis, FTIR Infrared Spectroscopy and Chemometric Techniques.

The FTIR-ATR method coupled with the multivariate analysis of specific spectral areas of samples was developed to characterize two white grape varieties (Sauvignon Blanc and Hibernal) and two blue grape varieties (André and Cabernet Moravia) of wine planted and harvested in the Moravia region, Czech Republic. Principal component analysis and hierarchical cluster analysis were performed using fingerprint regions of FTIR spectra for all wines. The results obtained by principal component analysis in combination with linear discriminant analysis (PCA-LDA) scores yielded clear separation between the four classes of samples and showed very good discrimination between the wine samples, with a 91.7% overall classification rate for the samples. The conducted FTIR spectroscopy studies coupled with chemometrics allowed for the swift analysis of multiple wine components with minimal sample preparation. These methods can be used in research to improve specific properties of these wines, which will undoubtedly enhance the quality of the final wine samples obtained.

Design, Spectroscopy, and Assessment of Cholinesterase Inhibition and Antimicrobial Activities of Novel Coumarin-Thiadiazole Hybrids.

A novel series of coumarin-thiadiazole hybrids, derived from substituted coumarin-3-carboxylic acids was isolated and fully characterized with the use of a number of spectroscopic techniques and XRD crystallography. Several of the novel compounds showed intensive fluorescence in the visible region, comparable to that of known coumarin-based fluorescence standards. Moreover, the new compounds were tested as potential antineurodegenerative agents via their ability to act as acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitors. Compared to the commercial standards, only a few compounds demonstrated moderate AChE and BuChE activities. Moreover, the novel derivatives were tested for their antimicrobial activity against a panel of pathogenic bacterial and fungal species. Their lack of activity and toxicity across a broad range of biochemical assays, together with the exceptional emission of some hybrid molecules, highlights the possible use of a number of the novel hybrids as potential fluorescence standards or fluorescence imaging agents.

Effect of Antibiotic Amphotericin B Combinations with Selected 1,3,4-Thiadiazole Derivatives on RPTECs in an In Vitro Model.

4-(5-methyl-1,3,4-thiadiazole-2-yl) benzene-1,3-diol (C1) and 4-[5-(naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl] benzene1,3-diol (NTBD) are representative derivatives of the thiadiazole group, with a high antimycotic potential and minimal toxicity against normal human fibroblast cells. The present study has proved its ability to synergize with the antifungal activity of AmB. The aim of this work was to evaluate the cytotoxic effects of C1 or NTBD, alone or in combination with AmB, on human renal proximal tubule epithelial cells (RPTECs) in vitro. Cell viability was assessed with the MTT assay. Flow cytometry and spectrofluorimetric techniques were used to assess the type of cell death and production of reactive oxygen species (ROS), respectively. The ELISA assay was performed to measure the caspase-2, -3, and -9 activity. ATR-FTIR spectroscopy was used to evaluate biomolecular changes in RPTECs induced by the tested formulas. The combinations of C1/NTBD and AmB did not exert a strong inhibitory effect on the viability/growth of kidney cells, as evidenced by the negligible changes in the apoptotic/necrotic rate and caspase activity, compared to the control cells. Both NTBD and C1 displayed stronger anti-oxidant activity when combined with AmB. The relatively low nephrotoxicity of the thiadiazole derivative combinations and the protective activity against AmB-induced oxidative stress may indicate their potential use in the therapy of fungal infections.

Low-Carbohydrate, High-Protein, and Gluten-Free Bread Supplemented with Poppy Seed Flour: Physicochemical, Sensory, and Spectroscopic Properties.

BACKGROUND: This study aimed to determine the effect of poppy seed flour (PF) on the physicochemical and spectroscopic properties of low-carbohydrate, high-protein, and gluten-free bread. METHODS: The changes at the molecular level were assessed in bread using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Bread prepared with buckwheat, flaxseed, and pea protein was enriched with PF at a concentration of 5-15%. RESULTS: The results showed that the pasting parameters of dough supplemented with PF were significantly decreased compared to the control sample. The obtained bread samples were characterized by good quality and had 14.6% of carbohydrate, 16.3% of protein, 10.2% of fiber, and 4.0% of fat, with a caloric value of 177 kcal/100 g. The addition of PF had little influence on crumb mechanical properties. The ATR-FTIR analyses revealed spectral changes in the region related to protein and carbohydrate structures, as well as changes in band intensity characteristic of α-1,4-glycoside and α-1,6-glycoside bonds. The analyses showed that the main starch skeleton remained clearly visible. CONCLUSIONS: PF up to 10% can be potentially applied as a functional ingredient in the production of bread based on buckwheat and linseed flour. Such low-carbohydrate bread can be particularly useful to diabetics.

Classification of Honey Powder Composition by FTIR Spectroscopy Coupled with Chemometric Analysis.

Fourier transform infrared spectroscopy (FTIR) in connection with chemometric analysis were used as a fast and direct approach to classify spray dried honey powder compositions in terms of honey content, the type of diluent (water or skim milk), and carrier (maltodextrin or skim milk powder) used for the preparation of feed solutions before spray drying. Eleven variants of honey powders containing different amounts of honey, the type of carrier, and the diluent were investigated and compared to pure honey and carrier materials. Chemometric discrimination of samples was achieved by principal component analysis (PCA), hierarchical clustering analysis (HCA), linear discriminant analysis (LDA), and partial least squares-discriminant analysis (PLS-DA) modelling procedures performed on the FTIR preprocessed spectral data for the fingerprint region (1800-750 cm-1) and the extended region (3600-750 cm-1). As a result, it was noticed that the type of carrier is a significant factor during the classification of different samples of powdered multifloral honey. PCA divided the samples based on the type of carrier, and additionally among maltodextrin-honey powders it was possible to distinguish the type of diluent. The result obtained by PCA-LDA and PLS-DA scores yielded a clear separation between four classes of samples and showed a very good discrimination between the different honey powder with a 100.0% correct overall classification rate of the samples.

Insight into dual fluorescence effects induced by molecular aggregation occurring in membrane model systems containing 1,3,4-thiadiazole derivatives.

This work reports on biophysical insights into the excited state intramolecular proton transfer (ESIPT) processes taking place in three 1,3,4-thiadiazole derivatives that served as model compounds, on which electronic absorption, fluorescence, Fourier-transform infrared spectroscopy (FTIR), surface plasmon resonance (SPR) and electrochemical impedance spectroscopy (EIS) studies were performed. The fluorescence spectra recorded in various solvents revealed an interesting dual fluorescence effect. In molecules in their monomeric form, the effect is associated with the ESIPT phenomenon, and may be further enhanced by aggregation-related effects, such as aggregation-induced emissions. Other spectroscopic studies on the selected molecules in a liposomal medium as a model revealed that, in a biomimetic environment, they can exist in both monomeric and aggregated forms. In both cases, however, the effects observed are closely related to the lipid's main phase transition temperature and the structure of the molecule. Introduction of specific substituents to the phenyl moiety either allows or prevents proton transfer from occurring in the excited state. The hydrophobicity changes in a lipid environment may result in an emergence of specific molecular forms and therefore either facilitate or hinder ESIPT processes. SPR and EIS confirmed the significant hydrophobicity changes in the model lipid systems, while FTIR measurements revealed a notable influence of 1,3,4-thiadiazoles on the fluidity of liposomal membranes. The results obtained clearly show that the thiadiazole derivatives are very good model molecules for studying hydrophobic-hydrophilic environments, and particularly with polymers or liposomes used as drug delivery systems.

Biodirected Synthesis of Silver Nanoparticles Using Aqueous Honey Solutions and Evaluation of Their Antifungal Activity against Pathogenic Candida Spp.

Silver nanoparticles (AgNPs) were synthesized using aqueous honey solutions with a concentration of 2%, 10%, and 20%-AgNPs-H2, AgNPs-H10, and AgNPs-H20. The reaction was conducted at 35 °C and 70 °C. Additionally, nanoparticles obtained with the citrate method (AgNPs-C), while amphotericin B (AmB) and fluconazole were used as controls. The presence and physicochemical properties of AgNPs was affirmed by analyzing the sample with ultraviolet-visible (UV-Vis) and fluorescence spectroscopy, scanning electron microscopy (SEM), and dynamic light scattering (DLS). The 20% honey solution caused an inhibition of the synthesis of nanoparticles at 35 °C. The antifungal activity of the AgNPs was evaluated using opportunistic human fungal pathogens Candida albicans and Candida parapsilosis. The antifungal effect was determined by the minimum inhibitory concentration (MIC) and disc diffusion assay. The highest activity in the MIC tests was observed in the AgNPs-H2 variant. AgNPs-H10 and AgNPs-H20 showed no activity or even stimulated fungal growth. The results of the Kirby-Bauer disc diffusion susceptibility test for C. parapsilosis strains indicated stronger antifungal activity of AgNPs-H than fluconazole. The study demonstrated that the antifungal activity of AgNPs is closely related to the concentration of honey used for the synthesis thereof.

Novel Coumarin-Thiadiazole Hybrids and Their Cu(II) and Zn(II) Complexes as Potential Antimicrobial Agents and Acetylcholinesterase Inhibitors.

A series of coumarin-thiadiazole hybrids and their corresponding Cu(II) and Zn(II) complexes were synthesized and characterized with the use of spectroscopic techniques. The results obtained indicate that all the coumarin-thiadiazole hybrids act as bidentate chelators of Cu(II) and Zn(II) ions. The complexes isolated differ in their ligand:metal ratio depending on the central metal. In most cases, the Zn(II) complexes are characteristic of a 1:1 ligand:metal ratio, while in the Cu(II) complexes the ligand:metal ratio is 2:1. All compounds were tested as potential antibacterial agents against Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacterial strains demonstrating activities notably lower than commercially available antibiotics. The more promising results were obtained from the assessment of antineurodegenerative potency as all compounds showed moderate acetylcholinesterase (AChE) inhibition activity.

Structural Features of 1,3,4-Thiadiazole-Derived Ligands and Their Zn(II) and Cu(II) Complexes Which Demonstrate Synergistic Antibacterial Effects with Kanamycin.

Classical synthetic protocols were applied for the isolation of three novel 1,3,4-thiadiazole derivatives which were then complexed with the biologically important Cu(II) and Zn(II) ions. All free ligands and their corresponding complexes were characterized using a number of spectroscopic techniques including Ultraviolet-visible (UV-vis), Fluorescence, Infrared (FT-IR), tandem liquid chromatography-mass (LC-MS), X-ray diffraction (XRD), and Nuclear Magnetic Resonance (NMR) spectroscopy (1H, 13C, HSQC, HMBC). The results obtained are consistent with the formation of dihydrate complexes, in which the chelation of the metal ion occurs via one of the thiadiazole nitrogen atoms and the deprotonated hydroxyl group of the neighboring resorcynyl moiety. The Zn(II) complexes utilize a 1:1 ligand-metal ratio, while in the Cu(II) complexes the ligand-metal ratio is 2:1. Although the antibacterial testing identified moderate activity of the compounds against the tested bacterial strains and additionally modest antioxidant activity, a strong synergistic antibacterial effect against Staphylococcus aureus, using concomitant treatment of thiadiazole derivatives with the commercial antibiotic kanamycin, was observed. The most active thiadiazole derivative demonstrated a minimal inhibitory concentration (MIC) of 500 µg/mL while it was 125 µg/mL in the presence of kanamycin. Moreover, in the presence of few thiadiazole derivatives the MIC value of kanamycin decreased from 0.39 µg/mL to 0.5 µg/mL. The antioxidant activity (IC50) of the most active thiadiazole derivative was determined as 0.13 mM which was nearly three-fold lower compared to that of TROLOX (0.5 mM).

Opuntia Fruits as Food Enriching Ingredient, the First Step towards New Functional Food Products.

Prickly pear (Opuntia ficus indica (L.) Mill.) is a rich source of vitamins C, B1, B2, A, and E, minerals such as calcium, potassium, magnesium, iron, and phosphorus, as well as bioactive substances, i.e., carotenoids, betalains, and phenolic compounds. Of these, the phenolic acids, betalains, and flavonoids are notable in that they are largely responsible for the health-promoting properties of this plant. The purpose of the presented research was to first determine the antioxidant properties and the content of polyphenolic compounds (including individual phenolic acids) in prickly pear fruit, then to produce an innovative gluten-free pasta from rice-field bean flour enriched with various amounts of pear prickly fruit. The content of free phenolic acids, the sum of polyphenols and antioxidant properties of pasta were subsequently determined in the supplemented pasta. Chromatographic analysis (HPLC-ESI-MS/MS) showed a wide variety of phenolic acids. In the fruit sample, 14 acids were detected, whereas in the pasta sample without additives, 9. The dominant acid was isoferulic. The total content of free phenolic acids and the sum of polyphenols increased with increasing content of the functional additive. Moreover, the content of individual acids generally increased as the Opuntia fruit was added. The antioxidant activity was also positively correlated with the addition of fruit, with the content of free phenolic acids and the sum of polyphenols. Our research has shown that our innovative pasta with the addition of prickly fruit can become a source of the free phenolic acids indispensable for human health.

ESIPT-Related Origin of Dual Fluorescence in the Selected Model 1,3,4-Thiadiazole Derivatives.

In our previous work, we discussed the emergence of the dual fluorescence phenomenon in selected compounds from the group of 1,3,4-thiadiazoles. The results obtained in a number of experimental studies, supported by [TD]DFT calculations, clearly indicated that the phenomenon of dual fluorescence stemmed from an overlap of several factors, including the correct conformation of the analyzed molecule and, very significantly in this context, aggregation effects. Where those two conditions were met, we could observe the phenomenon of intermolecular charge transfer (CT) and the emergence of electronic states responsible for long wave emissions. However, in light of the new studies presented in this paper, we were able, for the first time, to provide a specific theory for the effect of dual fluorescence observed in the analyzed group of 1,3,4-thiadiazoles. We present the results of spectroscopic measurements conducted for two selected analogues from the 1,3,4-thiadiazole group, both in polar and non-polar solvents, which clearly evidence (as we have already suspected in the past, albeit have not shown in publications to date) the possibility of processes related to emission from the tautomer formed in the process of excited state intramolecular proton transfer, which is responsible for the long-wavelength emissions observed in the selected analogues. The presented results obtained with the use of UV-Vis, fluorescence (stationary and time-resolved), FTIR, and Raman spectroscopy, as well as from calculations of dipole moment changes between the ground and excited state with the use of two derivatives with different structures of the resorcylic system, corroborated our standing hypothesis. At the same time, they excluded the presence of ground state keto forms of the analyzed analogues unless necessitated by the structure of the molecule itself. In this case, aggregation factors enhance the observed effects related to the dual fluorescence of the analyzed compounds (by way of AIE-aggregated induced emissions).

Fluorescence Quenching-Based Mechanism for Determination of Hypochlorite by Coumarin-Derived Sensors.

A fluorescence quenching-based mechanism for the determination of hypochlorite was proposed based on spectroscopic and chromatographic studies on the hypochlorite-sensing potency of three structurally similar and highly fluorescent coumarins. The mode of action was found to rely upon a chlorination of the coumarin-based probes resulting from their reaction with sodium hypochlorite. Importantly, the formation of chlorinated derivatives was accompanied by a linear decrease in the fluorescence intensities of the probes tested. The results obtained suggest the applicability of a coumarin-dependent hypochlorite recognition mechanism for the detection of, as well as for quantitative determination of, hypochlorite species in vitro.

Non-Typical Fluorescence Effects and Biological Activity in Selected 1,3,4-thiadiazole Derivatives: Spectroscopic and Theoretical Studies on Substituent, Molecular Aggregation, and pH Effects.

The below article presents the results of spectroscopic research, theoretical (time-dependent density functional theory (TD-DFT)), microbiological, and antioxidative calculations for three compounds from the group of 1,3,4-thiadiazoles: 2-amino-5-phenyl-1,3,4-thiadiazole (TB), 2-amino-5-(2-hydroxyphenyl)-1,3,4-thiadiazole (TS), 2-amino-5-(2-hydroxy-5-sulfobenzoyl)-1,3,4-thiadiazole (TSF). In the fluorescence emission spectra (TS) of solutions with varying concentrations of hydrogen ions, a particularly interesting effect of dual fluorescence was observed. The aforementioned effect was observed even more clearly in the environment of butan-1-ol, relative to the compound's concentration. Depending on the modification of the resorcylic substituent (TS and TSF), we observed the emergence of two separate, partially overlapping, fluorescence emission spectra or a single emission spectrum. Interpretation of the obtained spectra using stationary and time-resolved spectroscopy allowed the correlation of the effect's emergence with the phenomenon of molecular aggregation (of a particular type) as well as, above all, the structure of the substituent system. The overlap of said effects most likely induces the processes related to the phenomenon of charge transfer (in TS) and is responsible for the observed fluorescence effects. Also, the position of the -OH group (in the resorcylic ring) is significant and can facilitate the charge transfer (CT). The determinations of the changes in the dipole moment and TD-DFT calculations further corroborate the above assumption. The following paper presents the analysis (the first for this particular group of analogues) of the fluorescence effects relative to the changes in the structure of the resorcylic group combined with pH effects. The results of biological studies also indicate the highest pharmacological potential of the analogue in the case where the effects of dual fluorescence emission are observed, which predisposes this particular group of fluorophores as effective fluorescence probes or potential pharmaceuticals with antimycotic properties.

Anti-Hypochlorite and Catalytic Activity of Commercially Available Moringa oleifera Diet Supplement.

Aiming at the assessment of the pro-health, and especially anti-hypochlorite properties of Moringa oleifera species a representative, commercially available Moringa oleifera dietary supplement was used as a substrate for the preparation of aqueous Moringa extract. The anti-hypochlorite activity of the extract was assessed using the hypochlorite-specific coumarin-based fluorescence turn-off sensor, namely 7-diethylamino-coumarin-3-carboxylic acid (7-DCCA). This compound was synthesized via the Knoevenagel condensation of 4-diethylamino-2-hydroxybenzaldehyde with Meldrum's acid and the Moringa extract was employed as a medium and catalyst. Moreover, the total phenolic content (TPC) as well as the reactive oxygen species (ROS)-scavenging ability of the aqueous Moringa extract were determined. The results obtained demonstrated the applicability of Moringa extract as an anti-hypochlorite agent. Additionally, the satisfactory yield of the 7-DCCA obtained suggests the usefulness of the extract as a catalyst and the reaction medium. The antioxidative potential of the extract was notably lower than that of the standard (TROLOX). Determination of TPC in 100 g of the dry weight (DW) of studied material revealed a high number of polyphones present.

Content of Phenolic Compounds and Antioxidant Activity of New Gluten-Free Pasta with the Addition of Chestnut Flour.

Chestnut fruit abounds in carbohydrates, proteins, unsaturated fatty acids, fiber, polyphenolic compounds, as well as vitamins and micronutrients, that are behind the health-promoting properties of this plant. The purpose of the discussed research was to obtain innovative gluten-free pasta from rice and field bean flour enriched with a various addition of chestnut flour. Regarding the studied pasta, the following were determined: the content of free phenolic acids, total polyphenols, and antioxidant properties. Chromatographic analysis (HPLC-ESI-MS/MS (high-performance liquid chromatography-electrospray ionization tandem mass spectrometry)) revealed a wide variety of phenolic acids. In a sample with 20% and higher content of chestnut flour, as many as 13 acids were detected. Isoferulic acid prevailed. The total content of free phenolic acids and total polyphenols increased along with the increasing chestnut content. Moreover, in most cases, the content of individual acids increased with the addition of chestnut flour. Besides, the antioxidant activity was positively correlated with the addition of chestnut fruit flour, the content of free phenolic acids, and total polyphenols. Our research has demonstrated that our innovative gluten-free pasta, with the addition of chestnut flour, has a potential to be a source of polyphenolic compounds, including free phenolic acids, that are valuable for human health.

Spectroscopic and Theoretical Studies of Fluorescence Effects in 2-Methylamino-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole Induced by Molecular Aggregation.

The article presents the results of fluorescence analyses of 2-methylamino-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole (MDFT) in an aqueous environment. MDFT dissolved in aqueous solutions with a pH value in the range from 1 to 4.5 yielded an interesting effect of two clearly separated fluorescence emissions. In turn, a single fluorescence was observed in MDFT dissolved in water solutions with a pH value from 4.5 to 12. As it was suggested in the previous investigations of other 1,3,4-thiadiazole compounds, these effects may be associated with conformational changes in the structure of the analysed molecule accompanied by aggregation effects. Crystallographic data showed that the effect of the two separated fluorescence emissions occurred in a conformation with the -OH group in the resorcyl ring bound on the side of the sulphur atom from the 1,3,4-thiadiazole ring. The hypothesis of aggregation as the mechanism involved in the change in the spectral properties at low pH is supported by the results of (Time-Dependent) Density Functional Theory calculations. The possibility of rapid analysis of conformational changes with the fluorescence spectroscopy technique may be rather important outcome obtained from the spectroscopic studies presented in this article. Additionally, the presented results seem to be highly important as they can be easily observed in solutions and biologically important samples.

Spectroscopic Studies of Dual Fluorescence in 2-(4-Fluorophenylamino)-5-(2,4-dihydroxybenzeno)-1,3,4-thiadiazole: Effect of Molecular Aggregation in a Micellar System.

The article presents the results of spectroscopic studies focused on a selected compound from the 1,3,4-thiadiazole group-2-(4-fluorophenylamino)-5-(2,4-dihydroxybenzeno)-1,3,4-thia-diazole (FABT)-in a micellar system formed by Triton X-100, a non-ionic detergent. Fluorescence measurements revealed the phenomenon of dual fluorescence whose emergence is related to the particular molecular organisation of the compound, which depends both on the concentration of the detergent and, most of all, the concentration of the compound itself. Dual fluorescence of FABT in a micellar system was observed for the compound dissolved in a methanol aqueous system, i.e., an environment wherein the dual fluorescence of the compound had never been reported before. Based on the interpretation of UV-Vis electronic absorption, resonance light scattering (RLS), emission and excitation fluorescence spectra, as well as measurements of dynamic light scattering (DLS) and Principal Component Analysis (PCA), we were able to relate the occurrence of this effect to the process of molecular aggregation taking place between FABT molecules in the micellar system in question. Results of fluorescence spectra measurements and time-correlated single photon counting (TCSPC) indicate that dual fluorescence occurs at detergent concentrations necessary to form micellar systems, which in turn facilitate the process of aggregation of FABT molecules. The correlation between the observed fluorescence effects and the previous measurements performed for analogues from this group suggests the possibility of charge transfer (CT) within the range of detergent concentrations wherein the aforementioned fluorescence effects are observed. It ought to be emphasised that this type of fluorescence effects are relatively easy to induce, which predisposes this groups of fluorophores as ideal fluorescence probes in the context of biological samples.