Performance of 4,5-diphenyl-1H-imidazole derived highly selective 'Turn-Off' fluorescent chemosensor for iron(III) ions detection and biological applications

Two fluorescent chemosensors, denoted as chemosensor 1 and chemosensor 2, were synthesized and subjected to comprehensive characterization using various techniques. The characterization techniques employed were Fourier-transform infrared (FTIR), proton (1 H)- and carbon-13 (13 C)-nuclear magnetic resonance (NMR) spectroscopy, electrospray ionization (ESI) mass spectrometry, and single crystal X-ray diffraction analysis. Chemosensor 1 is composed of a 1H-imidazole core with specific substituents, including a 4-(2-(4,5-c-2-yl)naphthalene-3-yloxy)butoxy)naphthalene-1-yl moiety. However, chemosensor 2 features a 1H-imidazole core with distinct substituents, such as 4-methyl-2-(4,5-diphenyl-1H-imidazole-2-yl)phenoxy)butoxy)-5-methylphenyl. Chemosensor 1 crystallizes in the monoclinic space group C2/c. Both chemosensors 1 and 2 exhibit a discernible fluorescence quenching response selectively toward iron(III) ion (Fe3+ ) at 435 and 390 nm, respectively, in dimethylformamide (DMF) solutions, distinguishing them from other tested cations. This fluorescence quenching is attributed to the established mechanism of chelation quenched fluorescence (CHQF). The binding constants for the formation of the 1 + Fe3+ and 2 + Fe3+ complexes were determined using the modified Benesi-Hildebrand equation, yielding values of approximately 2.2 × 103 and 1.3 × 104  M-1 , respectively. The calculated average fluorescence lifetimes for 1 and 1 + Fe3+ were 2.51 and 1.17 ns, respectively, while for 2 and 2 + Fe3+ , the lifetimes were 1.13 and 0.63 ns, respectively. Additionally, the applicability of chemosensors 1 and 2 in detecting Fe3+ in live cells was demonstrated, with negligible observed cell toxicity.

Caffeic Acid Phenethyl Ester Encapsulated in Self-Assemble Rice Peptides Nanoparticles: Storage Stability, In Vitro Release, and Their Interaction Mechanisms

Caffeic acid phenethyl ester (CAPE) is an important active component of propolis with many bioactivities. However, its efficiency and practical application are restricted due to its poor aqueous solubility and storage stability. In this study, a nanocarrier was fabricated to encapsulate CAPE using self-assembled rice peptides obtained by controllable enzymolysis. The physicochemical properties, encapsulation efficiency, and loading capacity of rice peptides nanoparticles (RPNs) were characterized. The storage stability, in vitro release, and interaction mechanisms between CAPE and RPNs were investigated. The results showed that RPNs, mainly assembled by disulfide bonds and hydrogen bonds, possessed an effective diameter of around 210 nm and a high encapsulation efficiency (77.77%) and loading capacity (3.89%). Importantly, the water solubility of CAPE was increased by 45 times after RPNs encapsulation. Moreover, RPNs encapsulation also significantly increased CAPE stability, about 1.4-fold higher than that of unencapsulated CAPE after 18-day storage. An in vitro release study demonstrated that RPNs could delay the release of CAPE, implying a better CAPE protection against extreme environments during digestion. Hydrogen bond and van der Waals force are the predominant interaction forces between RPNs and CAPE. Therefore, the newly developed nanoparticle is a potential delivery system that could effectively improve the aqueous solubility and stability of CAPE.

Host-Guest Mechanism via Induced Fit Fullerene Complexation in Porphin Receptor to Probe Salivary Alpha-Amylase in Dental Caries for Clinical Applications

Salivary α-amylase is the most abundant protein of human saliva that potentially binds to streptococcus and other bacteria via specific surface-exposed α-amylase-binding proteins and plays a significant role in caries development. The detection of α-amylase in saliva can be used as a bioindicator of caries development. Herein, a facile strategy has been applied, tailoring the photochemical properties of 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphine (TPPOH) and the fullerene C60 complex. The fluorescence emission of TPPOH is quenched by starch-coated fullerene C60 via charge-transfer effects, as determined by UV absorption and fluorescence spectroscopic studies. The starch-coated C60 has been thoroughly characterized via Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), optical microscopy, thermal gravimetric analysis (TGA), static water contact angle measurements, and zeta potential measurements. The analytical response of the assay showed a linear fluorescent response in α-amylase concentrations ranging from 0.001-0.1 Units/mL, with an LOD of 0.001 Units/mL. The applicability of the method was tested using artificial saliva with quantitative recoveries in the range 95-100%. The practicability of the procedure was verified by inspecting saliva samples of real clinical samples covering all age groups. We believe that the proposed method can serve as an alternative analytical method for caries detection and risk assessment that would also minimize the cost of professional preventive measures and treatments.

Deciphering the binding mechanism of gingerol molecules with plasma proteins: implications for drug delivery and therapeutic potential

Ginger is a highly valued herb, renowned globally for its rich content of phenolic compounds. It has been traditionally used to treat various health conditions such as cardiovascular diseases, digestive issues, migraines, Alzheimer's disease, tumor reduction and chronic inflammation. Despite its potential medicinal applications, the therapeutic effectiveness of ginger is hindered by its limited availability and low plasma concentration levels. In this study, we explored the interaction of ginger's primary phenolic compounds, specifically 6-gingerol (6 G), 8-gingerol (8 G) and 10-gingerol (10 G), with plasma proteins which are human serum albumin (HSA) and α-1-acid glycoprotein (AGP). These two plasma proteins significantly influence drug distribution and disposition as they are key binding sites for most drugs. Fluorescence emission spectra indicated strong binding of 6, 8 and 10 G with HSA, with binding constants of 2.03 ± 0.01 × 104 M-1, 4.20 ± 0.01 × 104 M-1 and 6.03 ± 0.01 × 106 M-1, respectively. However, the binding of gingerols with AGP was found to be negligible. Molecular displacement by site-specific probes and molecular docking analyses revealed that gingerols bind at the IIA domain, with stability provided by hydrogen bonds, van der Waals forces, conventional hydrogen bonds, carbon-hydrogen bonds, alkyl and Pi-alkyl interactions. Further, the partial unfolding of the protein was observed upon binding the gingerol compound with HSA. In addition, molecular dynamic simulations demonstrated that gingerols remained stable in the subdomain IIA over 100 ns. This stability, coupled with Molecular Mechanics Generalized Born Surface Area indicating free energies of -43.765, -57.504 and -66.69 kcal/mol for 6, 8 and 10 G, respectively, reinforces the robust binding potential of these compounds. Circular dichroism studies suggested that the interaction of gingerols leads to the minimal transformation of HSA secondary structure, with the pattern being 10 G > 8 G > 6 G, a finding further substantiated by root mean square deviation and root mean square fluctuation fluctuations. These results propose that HSA has a stronger affinity to gingerols than AGP, which could have significant implications on the therapeutic circulating levels of gingerols.Communicated by Ramaswamy H. Sarma.

PAS domain of flagellar histidine kinase FlrB has a unique architecture and binds heme as a sensory ligand in an unconventional fashion

Phosphorylation of the σ54-dependent transcription activator FlrC by the sensor histidine kinase FlrB is essential for flagellar synthesis of Vibrio cholerae. Despite that, the structure, sensory signal, and mechanistic basis of function of FlrB were elusive. Here, we report the crystal structure of the sensory PAS domain of FlrB in its functional dimeric state that exhibits a unique architecture. Series of biochemical/biophysical experiments on different constructs and mutants established that heme binds hydrophobically as sensory ligand in the shallow ligand-binding cleft of FlrB-PAS without axial coordination. Intriguingly, ATP binding to the C-terminal ATP-binding (CA) domain assists PAS domain to bind heme, vis-à-vis, heme binding to the PAS facilitates ATP binding to the CA domain. We hypothesize that synergistic binding of heme and ATP triggers conformational signaling in FlrB, leading to downstream flagellar gene transcription. Enhanced swimming motility of V. cholerae with increased heme uptake supports this proposition.

Binding mechanism, photo-induced cleavage and computational studies of interaction cefepime drug with Human serum albumin

The binding interaction of cefepime to human serum albumin (HSA) in aqueous solution was investigated by molecular spectroscopy (UV spectra, fluorescence spectra and CD spectra), photo-cleavage and modeling studies under simulative physiological conditions. Spectrophotometric results are rationalized in terms of a static quenching process and binding constant (Kb) and the number of binding sites (n ≈ 1) were calculated using fluorescence quenching approaches at three temperature settings. Thermodynamic data of ΔG, ΔH and ΔS at different temperatures were evaluated. The results showed that the electrostatic and hydrogen bonding interactions play a major role in the binding of cefepime to HSA. The value of 3.4 nm for the distance r between the donor (HSA) and acceptor (cefepime) was derived from the fluorescence resonance energy transfer (FRET). FTIR and CD measurements has been reaffirmed HSA-cefepime association and demonstrated reduction in α-helical content of HSA. Furthermore, the study of molecular modeling also indicated that cefepime could strongly bind to the site I (subdomain IIA) of HSA. Additionally, cefepime shows efficient photo- cleavage of HSA cleavage. Our results may provide valuable information to understand the pharmacological profile of cefepime drug delivery in blood stream.Communicated by Ramaswamy H. Sarma.

Synergistic interaction of Cu(II) with caffeic acid and chlorogenic acid in α-glucosidase inhibition

BACKGROUND

Phenolic acids are widespread in foods and are beneficial to human health. However, the role of metal ions in influencing the binding of proteins with phenolic acids that contain the same parent nucleus structure remains unclear. This study investigated the inhibitory effect of caffeic acid (CA) and chlorogenic acid (CHA) on α-glucosidase and the biological effect of copper on this process.

RESULTS

It was found that the esterification of CA with quinic acid could increase the fluorescence quenching, conformational change, and inhibitory effect of CHA on α-glucosidase. Copper ions reduced their fluorescence quenching and conformation-changing ability by binding to the neighboring phenolic hydroxyl group but also increased their ability to alter secondary structure and to inhibit α-glucosidase and in vitro anti-glycation.

CONCLUSION

Overall, this study shows that the binding of copper ions to the phenolic hydroxyl group adjacent to CA and CHA synergistically inhibited α-glucosidase. The findings will offer a theoretical basis for investigating the properties of metal ions and phenolic acid in food chemistry and their potential applications in the prevention and treatment of diabetes mellitus. © 2023 Society of Chemical Industry.

Recognition of human telomeric G-quadruplex DNA by 1,5-disubstituted diethyl-amido anthraquinone derivative in different ion environments causing thermal stabilization and apoptosis

Ligand binding to G-quadruplex (G4) structures at human telomeric DNA ends promotes thermal stabilization, disrupting the interaction of the telomerase enzyme, which is found active in 80-85% of cancers and serves as a molecular marker. Anthraquinone compounds are well-known G-quadruplex (G4) binders that inhibit telomerase and induce apoptosis in cancer cells. Our current investigation is based on 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione, a derivative of anthraquinone and its binding characterization with two different human telomeric DNA structures, wHTel26 and HTel22, in the effect of K+ and Na+ by using an array of biophysical, calorimetry, molecular docking and cell viability assay techniques. Binding constants (Kb) in the range of ∼105-107 M-1 and stoichiometries of 1:1, 2:1 & 4:1 were obtained from the absorbance, fluorescence, and circular dichroism study. Remarkable hypochromism (55, 97%) and ∼17 nm shift in absorbance, fluorescence quenching (95, 97%), the unaltered value of fluorescence lifetime, restoration of Circular Dichroism bands, absence of ICD band, indicated the external groove binding/binding somewhere at loops. This is also evident in molecular docking results, the ligand binds to groove forming base (G4, G5, G24, T25) and in the vicinity to TTA loop (G14, G15, T17) bases of wHTel26 and HTel22, respectively. Thermal stabilization induced by ligand was found greater in Na+ ion (27.5 °C) than (19.1 °C) in K+ ion. Ligand caused cell toxicity in MCF-7 cancer cell lines with an IC50 value of ∼8.4 µM. The above findings suggest the ligand, 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione could be a potent anticancer drug candidate and has great therapeutic implications.Binding of disubstituted amido anthraquinone derivative, 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione to human telomere HTel22 antiparallel conformation induced thermal stabilization.Communicated by Ramaswamy H. Sarma.

Elucidation of binding mechanism of rhodanine derivative P4OC on bovine serum albumin

Rhodanine is an important scaffold in medicinal chemistry and it act as potent anticancer agent and other pharmacological effects. In pharmacokinetics and pharmacodynamics studies of the drug, the drug binding properties on serum protein is crucial for producing better drug. This study was designed to explore the binding interactions between the Rhodanine derivative (P4OC) on Bovine Serum Albumin (BSA). The interactions between P4OC and BSA were investigated using biophysical approach and molecular docking. The quenching mechanism and binding constants of P4OC on BSA were determined by biophysical approach through fluorescence spectroscopic experiments. Circular dichroism (CD) spectroscopy was used to study the secondary structural changes of BSA upon P4OC binding. The fluorescence experiments of P4OC binding on BSA show good drug binding with static quenching constants using stern Volmer plot and found the quenching constant value KP4OC = 1.12762 × 1013 M-1 with corresponding binding free energy (ΔG) -2.303 kcal/mol. The molecular displacement fluorescence emission on BSA-P4OC complex by site specific markers shows that P4OC binds at I A sub-domain of BSA further confirmed peak shift by synchronous fluorescence of P4OC on BSA with tyrosine, tryptophan and phenylalanine amino acids. Increasing concentration of P4OC on BSA found secondary structural changes, the percentage of α-helix was decreased as well increase percentage of β-sheet and random coil. The binding of P4OC to BSA was computationally studied by molecular docking methods. Thus, results obtained are in excellent agreement with experimental and theoretical results with respect to the binding mechanism and binding constant of P4OC on BSA. We concluded that, the rhodanine derivative P4OC possesses good drug binding properties on BSA. Further P4OC may be evaluated its potential pharmacological activities on clinical trial.Communicated by Ramaswamy H. Sarma.

Simultaneous Detection and Decontamination of Dichromate Ions: The Fluorescence Response and Photocatalysis of Thiadiazole-Modified Zr-Metal-Organic Frameworks

The simultaneous analysis and removal of highly toxic hexavalent chromium (Cr (VI)) in contaminated water via an easy method remain a serious task. Based on the guidance of bibliometric analysis, a thiadiazole ligand-modified zirconium metal-organic framework (Zr-MOF) heralds a new and simple approach to Cr (VI) treatment. The concentration can be determined by fluorescence quenching with a low detection limit of 1.4 μM and a high quenching constant of 6.88 × 103 M-1. For the sensing mechanism, the fluorescence intensity of the Zr-MOF decreased rapidly due to the competition of Cr (VI) with the Zr-MOF for absorption excitation energy and the induction of Zr-MOF aggregation. The analysis system also displayed satisfactory stability and applicability. Apart from sensing application, Zr-MOF can convert Cr (VI) to Cr (III), and the reduction rate constant was 0.004 min-1 under irradiation. Therefore, the bifunctional Zr-MOF provided a potential application method for controlling the pollution caused by Cr (VI) in wastewater.

Perylene Diimide Based Fluorescent Sensors for Drug Simulant Detection: The Effect of Alkyl-Chain Branching on Film Morphology, Exciton Diffusion, Vapor Diffusion, and Sensing Response

Luminescence-based sensing has been demonstrated to be a powerful method for rapid trace detection of chemical vapors (analytes). Analyte diffusion has been shown to be the critical factor for real-time luminescence-based detection of explosive analytes via photoinduced electron transfer in amorphous films of conjugated polymers and dendrimers. However, similar studies to determine the critical factors for sensing have not been performed on materials that employ photoinduced hole transfer (PHT) to detect low electron affinity analytes such as illicit drugs. Nor have such studies been performed on semicrystalline sensing films. We have developed a family of perylene diimide-based sensing materials capable of undergoing PHT with amine-group containing analytes. It was found that the choice of branched alkyl chain [1-hexylheptyl (PHH), 2-hexyloctyl (PHO), or 2,2-dihexyloctyl (PDHO)] attached to the nitrogen atoms of the imide moiety strongly affected the solution-processed film morphology. PHH and PHO were found to contain crystalline phases, whereas PDHO was essentially amorphous. The degree of crystallinity strongly influenced exciton diffusion, with PHH and PHO exhibiting exciton diffusion coefficients that were 20× and 10× greater than the value of the amorphous PDHO. The degree of film crystallinity was also found to be critical when the films were applied to detect N-methylphenethylamine (MPEA), a simulant of methamphetamine. While PHH had the largest exciton diffusion coefficient [(1.0 ± 0.2) × 10-2 cm2 s-1] and analyte uptake (12.3 ± 1.8 ng) it showed the smallest quenching efficiency (2.6% ng-1). In contrast, PHO, which sorbed the least analyte (6.1 ± 0.4 ng) of the three compounds, had the largest quenching efficiency (7.1% ng-1) due to its molecular packing and hence exciton diffusion coefficient [(4.5 ± 1.4) × 10-3 cm2 s-1] not being affected by sorption of the analyte. These results show that when applying fluorescent films in practical detection scenarios there is a potential trade-off between a high exciton diffusion constant and analyte diffusion for semicrystalline sensing materials and that a high exciton diffusion coefficient in an as-cast film does not necessarily translate into a more efficient fluorescent quenching. The results also show that sensing materials that form semicrystalline films, whose packing is not disrupted by analyte diffusion, provide a route for overcoming these effects and achieving high sensitivity.

Low molecular weight chitosan oligosaccharides form stable complexes with human lactoferrin

Proteins in tears, including human lactoferrin (HLF), can be deposited and denatured on contact lenses, increasing the risk of microbial cell attachment to the lens and ocular complications. The surfactants currently used in commercial contact lens care solutions have low clearance ability for tear proteins. Chitosan oligosaccharide (COS) binds to a variety of proteins and has potential for use in protein removal, especially in contact lens care solutions. Here, we analyzed the interaction mechanism of COSs hydrolyzed from chitosan from different resources with HLF. The molecular weights (MWs) and concentrations of COSs were key factors for the formation of COS-HLF complexes. Lower MWs of COSs could form more stable COS-HLF complexes. COS from Aspergillus ochraceus had a superior effect on HLF compared with COS from shrimp and crab shell with the same MWs. In conclusion, COSs could bind to and cause a conformational change in HLF. Therefore, COSs, especially those with low MWs, have potential as deproteinizing agents in contact lens care solution.

Molecular insights into α-glucosidase inhibition and antiglycation properties affected by the galloyl moiety in (-)-epigallocatechin-3-gallate

BACKGROUND

Diabetes mellitus poses a substantial threat to public health due to rising morbidity and mortality. α-Glucosidase is one of the key enzymes affecting diabetes. Herein, (-)-epigallocatechin-3-gallate (EGCG) and (-)-epigallocatechin (EGC) were applied to clarify the role of the galloyl moiety of tea polyphenols in the inhibition of glycation and α-glucosidase activity. The structure-activity relationship of the galloyl moiety in EGCG on α-glucosidase was investigated in terms of inhibition kinetics, spectroscopy, atomic force microscopy and molecular docking. A bovine serum protein-fructose model was employed to determine the effect of the galloyl moiety on glycation.

RESULTS

The results indicated that the introduction of a galloyl moiety enhanced the capacity of EGCG to inhibit glycation and α-glucosidase activity. The IC50 value of EGC is approximately 2400 times higher than that of EGCG. Furthermore, the galloyl moiety in EGCG altered the microenvironment and secondary structure of α-glucosidase, resulting in a high binding affinity of EGCG to α-glucosidase. The binding constant of EGCG to α-glucosidase at 298 K is approximately 28 times higher than that of EGC.

CONCLUSION

Overall, the galloyl moiety of EGCG plays a crucial role in inhibiting glycation and α-glucosidase activity, which helps to enhance the molecular understanding of the structure and function of the polyphenol galloyl moiety in the science of food and agriculture. © 2023 Society of Chemical Industry.

Utility of the food colorant erythrosine B as an effective green probe for quantitation of the anticancer sunitinib. Application to pharmaceutical formulations and human plasma

Sunitinib is a tyrosine kinase inhibitor used for the treatment of renal cell carcinoma and gastrointestinal stromal tumors. In this study, two spectroscopic methods, spectrofluorometric and spectrophotometric, were utilized to quantify sunitinib in different matrices. In method I, the native fluorescence of erythrosine B was quenched by forming ion-pair complex with increasing quantities of sunitinib. This approach was utilized for measuring sunitinib in its dosage forms and spiked plasma. After excitation at 528 nm, the quenching of fluorescence is linearly related to the concentration across the range of 0.05-0.5 μg mL-1 at 550 nm in Britton-Robinson buffer (pH 4.0), with a correlation value of 0.9999 and a high level of sensitivity with detection limit down to 10 ng mL-1 . Method II relies on spectrophotometric measurements of the produced complex at 550 nm across a range of 0.5-10.0 μg mL-1 , with good correlation value of 0.9999. This method has a detection limit down to 0.16 μg mL-1 . The proposed methodologies were validated according to International Conference on Harmonization (ICH) guidelines with satisfactory results. The stoichiometry of the reaction was determined through the application of Job's method, while the mechanism of quenching was investigated by employing the Stern-Volmer plot. The designated methods were used to estimate sunitinib in its capsules and in spiked human plasma. Additionally, the statistical analysis of the data revealed no substantial differences when compared to previous reported spectroscopic method. Green assessment tools provide further details about the eco-friendly nature of the methods.

Effects of Graphene Oxide (GO) and Reduced Graphene Oxide (rGO) on Green-Emitting Conjugated Copolymer's Optical and Laser Properties Using Simulation and Experimental Studies

The properties of a conjugated copolymer (CP), poly[(9,9-Dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene) (PDVF-co-MEH-PV), were investigated in the presence of graphene oxide (GO) and reduced graphene oxide (rGO) using absorption, fluorescence, laser, and time-resolved spectroscopy. CPs are usually dissolved in low-polar solvents. Although GO does not dissolve well, rGO and PDVF-co-MEH-PV dissolve in chloroform due to their oxygen acceptor sites. Hence, we studied rGO/PDVF-co-MEH-PV (CP/rGO), performing all experiments and simulations in chloroform. We performed simulations on PDVF-co-MEH-PV, approximate GO, and rGO using time-dependent density-functional theory calculations to comprehend the molecular dynamics and interactions at the molecular level. The simulation polymer used a tail-truncated oligomer model with up to three monomer units. The simulation and experimental results were in agreement. Further, the PDVF-co-MEH-PV exhibited fluorescence, laser quenching, rGO-mediated laser blinking, and spectral broadening effects when GO and rGO concentrations increased. The experimental and simulation results were compared to provide a plausible mechanism of interaction between PDVF-co-MEH-PV and rGO. We observed that for lower concentrations of rGO, the interaction did not considerably decrease the amplified spontaneous emissions of PDVF-co-MEH-PV. However, the fluorescence of PDVF-co-MEH-PV was considerably quenched at higher concentrations of rGO. These results could be helpful for future applications, such as in sensors, solar cells, and optoelectronic device design. To demonstrate the sensor capability of these composites, a paper-based sensor was designed to detect ethanol and nitrotoluene. An instrumentation setup was proposed that is cheap, reusable, and multifunctional.

[Characteristics of Microplastic-derived Dissolved Organic Matter(MPDOM) and the Complexation Between MPDOM and Sulfadiazine/Cu2]

Microplastic-derived dissolved organic matter(MPDOM) during the aging process could be complexed with organic pollutants, heavy metals, and other contaminants and thus affect their migration and transformation. In this study, two types of microplastics, polyethylene terephthalate(PET) and polystyrene(PS), were selected to investigate the spectral properties of MPDOM and their effect on the complexation between MPDOM and sulfadiazine(SDZ)/copper ion(Cu2+) using the fluorescence quenching method, various spectroscopic analysis techniques, and the Ryan-Weber quenching model. The results of UV-vis absorption spectroscopy analysis showed that the molecular weight of the two MPDOMs decreased; the aromaticity and humification increased; and the carboxyl, carbonyl, hydroxyl, and ester substituents on aromatic rings increased after aging. The fluorescence quenching process between MPDOM and SDZ/Cu2+ was static quenching. After quenching, the aromaticity and humification of the two MPDOMs were similar, and the molecular weights were comparable. Combined with three-dimensional fluorescence spectra and parallel factor analysis, two humic-like components and one protein-like component were identified. In addition, the protein-like components of MPDOM reacted preferentially with SDZ and were more sensitive to Cu2+. The results of the Ryan-Weber quenching model revealed that the binding ability of humic-like components to PET-DOM was higher in both SDZ and Cu2+ quenching systems, but the binding ability of MPDOM in the SDZ quenching system was generally stronger than that in the Cu2+ system.

Development of a Screening Method for Fluoroquinolones in Meat Samples Using Molecularly Imprinted Carbon Dots

An accurate and simple screening method has been developed for the determination of fluoroquinolone antibiotics. Carbon dots were synthesized by simple hydrothermal treatment as highly fluorescent nano-sensors. They were subsequently used in the synthesis of organic-based molecularly imprinted polymers to develop fluorescence-based polymeric composites using enoxacin as a representative dummy template molecule of fluoroquinolones. The method was optimized concerning the pH of the medium and composite concentration. The normalized fluorescence intensity showed efficient quenching under optimized conditions upon successive addition of the template, with an excellent correlation coefficient. The proposed method was applied to eight other fluoroquinolones, exhibiting, in all cases, good correlation coefficients (0.65-0.992) within the same linearity range (0.03-2.60 mg mL-1). Excellent detection and quantification limits were been obtained for the target analytes down to 0.062 and 0.186 mg L-1, respectively. All studied analytes showed no interference with enrofloxacin, the most commonly used veterinary fluoroquinolone, with a percentage of cross-reactivity varying from 89.00 to 540.00%. This method was applied successfully for the determination of enrofloxacin in three different types of meat samples: beef, pork, and chicken, with good recoveries varying from 70 to 100% at three levels. This new procedure is an easy analytical method that can be useful as a screening method for monitoring the environmental hazard of fluoroquinolones in quality control laboratories.

SDS-capped 1-pyrenecarboxaldehyde nanoprobe for selective detection of Cu2+ ion from water samples: Spectroscopic approach

Sodium dodecyl sulfate (SDS)-capped 1-pyrenecarboxaldehyde nanoparticles (PyalNPs) were prepared using a reprecipitation method in an aqueous medium and exhibited red-shifted aggregation-induced enhanced emission (AIEE). The dynamic light scattering (DLS) examination showed narrower particle size distribution with an average particle size of 41 nm, whereas -34.5 mV zeta potential value indicate the negative surface charge and good stability of nanoparticles (NPs) in an aqueous medium. The AIEE was seen at λmax  = 473 nm in a fluorescence spectrum of a PyalNP suspension. In the presence of Cu2+ ions, the fluorescence of PyalNPs quenches very significantly, even in the presence of other metal ions like Ba2+ , Ca2+ , Cd2+ , Co2+ , Al3+ , Fe2+ , Hg2+ , Ni2+ and Mg2+ . The changes in the fluorescence lifetime of PyalNPs in the presence of Cu2+ ions suggested that the type of quenching was dynamic. The fluorescence quenching data for the NPs suspension fitted well into a typical Stern-Volmer relationship in the concentration range 1.0-25 μg/ml of Cu2+ ions. The estimated value of the correlation coefficient R2  = 0.9877 was close to 1 and showed the linear relationship between quenching data and Cu2+ ion concentration. The limit of detection (LOD) was found to be 0.94 ng/ml and is far below the tolerable intake limit value of 1.3 μg/ml accepted by the World Health Organization for Cu2+ ions in drinking water. The fluorescence quenching approach for a SDS-capped Pyal nanosuspension for copper ion quantification is of high specificity and coexisting ions were found to interfere very negligibly. The developed method was successfully applied for the estimation of copper ions in river water samples.

One-dimensional coordinated polymers of tetraphenylethene pyridine and copper-iodide for fluorescence detection of nitroaromatic explosives

The spatial arrangement of molecules plays a crucial role in determining the macroscopic properties of functional materials. Coordinated polymers (CPs) formed by self-assembly of organic isomeric ligands and metals offer unique performance characteristics. In this study, we present the investigation of a one-dimensional CP, named CIT-E, composed of tetraphenylethene pyridine derivative (TPE-2by-2-E) ligands and copper iodide. The resulting CP exhibits a one-dimensional bead chain structure with exceptional thermal and chemical stability. By leveraging the competitive absorption between CIT-E and the explosive analog 2,4-dinitroaniline, we achieve detection of the explosive through changes in the absorption intensity of the excitation light source and subsequent fluorescence response. The CP demonstrates high selectivity and anti-interference ability in detecting 2,4-dinitroaniline in aqueous solution, with a detection linear range of 0.1 to 300 μM and a detection limit of 0.05 μM, surpassing the national third-level emission standard. These findings highlight the potential of CP CIT-E as a promising material for the detection of explosive nitroaromatic compounds.

Interactions between gold nanoparticles with different morphologies and human serum albumin

Introduction: Three different shapes of gold nanoparticles were synthesized in this experiment. At the same time, studies compared their effects with human serum albumin (HSA). Methods: Gold nanoparticles (AuNPs) with three different morphologies, such as, nanospheres (AuNSs), nanorods (AuNRs), and nanoflowers (AuNFs) were synthesized via a seeding method and their characteristic absorption peaks were detected using ultraviolet-visible (UV-vis) absorption spectroscopy, Telectron microscopy (TEM), Dynamic Light Scattering (DLS) and Zeta potential measurements, circular dichroism (CD), and Fourier transform infrared spectroscopy (FTIR) to study the interactions between them and HSA. By comparing the thermodynamic parameters and quenching mechanism of the three materials, similarities and differences were determined in their interactions with HSA. Results: The results showed that with an increase in the concentration of the AuNPs with the three different morphologies, the UV-vis absorption peak intensity of the mixed solution increased, but its fluorescence intensity was quenched. This indicates that the three types of AuNPs interact with HSA, and that the interactions between them represent a static quenching process, which is consistent with the conclusions derived from three-dimensional fluorescence experiments. Through variable-temperature fluorescence experiments, the binding constants, number of binding sites, and thermodynamic parameters of the interactions between the three types of AuNPs and HSA were determined. The Gibbs free energy changes were <0, indicating that the reactions of the three types of AuNPs with HSA are spontaneous, resulting in associated matter. Binding constant measurements indicated that the strongest binding took place between the AuNFs and HSA. In addition, the results of fluorescence, CD spectroscopy, and FTIR showed that three different shapes of AuNPs can induce conformational changes in HSA and reduce the α-helix content. Among them, AuNFs have the smallest ability to induce conformational changes. Discussion: According to studies, AuNFs interact more favorably with HSA. This can be used as a reference for the administration of drugs containing AuNPs.

Carbon dots derived from citric acid and urea as fluorometric probe for determining melamine contamination in infant formula sample

Melamine has been intentionally added into food products to increase the protein count at less cost, especially in dairy products for infant resulting in serious adverse effects on health of consumers. Therefore, this study aimed to develop a method to quantify melamine in dairy products based on the change of fluorescent properties of carbon dots (CDs) as sensing probe. CDs with green-fluorescent emission were synthesized from citric acid and urea under microwave irradiation. The synthesized CDs emitted fluorescence at the maximum wavelength of 538 nm with excitation wavelength of 410 nm. Thus, they provided high sensitivity and selectivity on melamine detection by which fluorescent emission of the CDs was increasingly quenched upon increasing melamine concentrations. Optimal conditions for melamine determination using the CDs was under pH 6, volume ratio between CDs and sample of 2:8 and reaction time of 15 min. The developed method provided high precision of melamine determination with less than 5% of %RSD (n = 5), wide detection range from 1.0 to 200.0 ppm, and high sensitivity with limit of detection (LOD) of 0.47 ppm and limit of quantification (LOQ) of 1.56 ppm, which is within the regulated level by the Food and Drug Administration of the United States for melamine in dairy products. Several analytical characterization techniques were conducted to elucidate the reaction mechanism between CDs and melamine, and the hydrogen bonding interaction was proposed.

Studies on the interaction of 2,4-dibromophenol with human hemoglobin using multi-spectroscopic, molecular docking and molecular dynamics techniques

2,4-Dibromophenol (DBP) has several industrial applications, including as a wood preservative and flame retardant. This study investigated the interaction between DBP and human hemoglobin (Hb) using spectroscopic, molecular docking and molecular dynamic techniques. The UV-visible spectra showed ground-state complex formation between DBP and Hb. Fluorescence studies revealed that DBP binding caused significant quenching of Hb fluorescence by the static quenching mechanism. The binding of DBP to Hb is a spontaneous process that involves van der Waals forces and hydrogen bonds. There is one DBP binding site on each Hb molecule that is located at the α1β2 interface of Hb. DBP binding did not alter the microenvironment of tyrosine and tryptophan residues in Hb. Circular dichroism studies revealed that DBP increased the α-helical content of Hb. The intrinsic esterase activity of Hb was inhibited by DBP in a concentration-dependent manner. Molecular docking showed that DBP binds to Hb via hydrogen bonds, hydrophobic, van der Waals and π - π interactions. Molecular dynamics simulation confirmed that the Hb-DBP complex is stable. Overall, the results of this study clearly show that DBP induces structural changes and interferes with the function of Hb. This can have important implications for human health.Communicated by Ramaswamy H. Sarma.

[Screening of quality markers and activity verification of Glycyrrhizae Radix et Rhizoma based on small molecule compound-protein interaction]

In order to solve the problem of weak correlation between quality control components and efficacy of Glycyrrhizae Radix et Rhizoma, this study detected the interaction between small molecular chemical components of Glycyrrhizae Radix et Rhizoma and total proteins of various organs of mice by fluorescence quenching method to screen potential active components. The 27 chemical components in Glycyrrhizae Radix et Rhizoma were detected by HPLC and their deletion rates in 34 batches of Glycyrrhizae Radix et Rhizoma were calculated. Combined with the principle of component effectiveness and measurability, the potential quality markers(Q-markers) of Glycyrrhizae Radix et Rhizoma were screened. RAW264.7 macrophage injury model was induced by microplastics. The cell viability and nitric oxide content were detected by CCK-8 and Griess methods. The levels of inflammatory factors(TNF-α, IL-1β, IL-6, CRP) and oxidative stress markers(SOD, MDA, GSH) were detected by the ELISA method to verify the activity of Q-markers. It was found that the interaction strength between different chemical components and organ proteins in Glycyrrhizae Radix et Rhizoma was different, reflecting different organ selectivity and 18 active components were screened out. Combined with the signal-to-noise ratio of the HPLC chromatographic peaks and between-run stability of the components, seven chemical components such as liquiritin apioside, liquiritin, isoliquiritin apioside, isoliquiritin, liquiritigenin, isoliquiritigenin and ammonium glycyrrhizinate were finally screened as potential Q-markers of Glycyrrhizae Radix et Rhizoma. In vitro experiments showed that Q-markers of Glycyrrhizae Radix et Rhizoma could dose-dependently alleviate RAW264.7 cell damage induced by microplastics, inhibit the secretion of inflammatory factors, and reduce oxidative stress. Under the same total dose, the combination of various chemical components could synergistically enhance anti-inflammatory and antioxidant effects compared with the single use. This study identified Q-markers related to the anti-inflammatory and antioxidant effects of Glycyrrhizae Radix et Rhizoma, which can provide a reference for improving the quality control standards of Glycyrrhizae Radix et Rhizoma.

Environmentally friendly protocol for the determination of sitagliptin phosphate in pharmaceutical preparations and biological fluids using l-tyrosine as a fluorescence probe

A responsive spectrofluorometric method was developed for the determination of sitagliptin phosphate using l-tyrosine as a fluorescence probe. The fluorescence intensity of l-tyrosine was quenched with sitagliptin phosphate. The fluorescence intensity was recorded at 307 nm using a 272 nm excitation wavelength. The calibration plot between fluorescence intensity and the concentration of drug was linear in the range of 0.1 to 2.0 mM with a good correlation value of 0.997. The limit of detection and quantification were established to be 3.7 × 10-4 and 1.23 × 10-3  mM, respectively. Commonly used excipients did not interfere with sitagliptin phosphate measurement. The proposed method was used to measure the sitagliptin phosphate in its standard type, dosage form, and biological samples. The percent recovery ranged from 97.41-103.36%. The static quenching was shown to be responsible for quenching as indicated by the Stern-Volmer plot. The method was validated using ICH guidelines and profitably applied for the content uniformity test, resulting in a high percent recovery and small relative standard deviation. The proposed approach is effortless, susceptible, selective, economic, and provides a high precision and accuracy, and can be used to determine sitagliptin phosphate in the pharmaceutical industry.

In vitro and in silico binding studies of phytochemical isochroman with calf thymus DNA using multi-spectroscopic and computational modelling techniques

A wide range of therapeutic molecules uses deoxyribonucleic acid (DNA) as an intracellular target. The interaction of small molecules to DNA is a key feature in pharmacology and plays a vital role in the development of novel and more efficient drugs with increased selective activity and enhanced therapeutic effectiveness. Isochroman (IC) is a constituent of Olea europea plant, which has been shown to exhibit several beneficial pharmacological activities. At present, its interaction studies using calf thymus DNA (ct-DNA) have not been explained. A set of multi-spectroscopic techniques has been performed to determine the interaction mechanism of isochroman with ct-DNA. Absorption spectra and quenching in fluorescence studies show that isochroman and ct-DNA form a complex. The static mode of quenching was determined by the Stern-Volmer plot. The value of binding constant, Kb = 4.0 × 103 M-1 revealed moderate type of binding. Effects of single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) and ionic strength were studied to examine the isochroman binding to ct-DNA. Potassium iodide (KI) quenching effects and competitive binding studies clearly showed that isochroman binds in the minor groove of ct-DNA. Circular dichroic and DNA melting experiments also confirmed these results. The experimental outputs were further corroborated via in silico computational modelling studies. Lipinski's rule of 5 and SwissADME showed drug-likeness and oral bioavailability scores. Protox ІІ online software predicts oral and organ toxicity.Communicated by Ramaswamy H. Sarma.