Interaction of Lysozyme with Rhodamine B: A combined analysis of spectroscopic & molecular docking

Evaluation of the structure and stability of myoglobin after interaction with ribose: spectroscopic and molecular simulation approach

Osmolytes, as small organic molecules, possess a remarkable ability to exert protective effects on biomacromolecules, including proteins, while preserving their inherent functionality. Myoglobin, a globular protein comprising a sequence of 153 amino acids, fulfills a crucial biological role by exhibiting reversible oxygen binding capabilities and facilitating its efficient transfer to the muscular tissues. In this study, the effects of ribose on myoglobin protein in sodium phosphate buffer were studied by UV-Vis's spectrophotometry and spectrofluorimetric investigations at pH 7.4. Also, the interaction was theoretically studied through molecular dynamics simulation and molecular docking techniques. The results showed that the ribose stabilizes the protein structure by increasing the melting temperature (Tm) of myoglobin. The fluorescence intensity of myoglobin decreased with a static quenching mechanism at different temperatures. The thermodynamic data obtained from the experimental results also predicted that the intermolecular forces affecting the formation of a myoglobin-ribose complex are mainly the van der Waals interactions and hydrogen bindings. Theoretical molecular docking analyses unveiled the favored binding site of ribose within the structure of myoglobin. Subsequent molecular dynamics simulations validated the stability of the complex formed between ribose and myoglobin. Our findings are fundamental for understanding the molecular-level details of myoglobin-ligand interactions, opening avenues for innovative approaches to prevent or alleviate myoglobin dysfunction in various disease conditions.

A spectroscopic, molecular docking and molecular dynamic simulation study on the interaction of human hemoglobin with 2,4-dichlorophenoxyacetic acid

2,4-Dichlorophenoxyacetic acid (2,4-D) is a systemic herbicide widely used to control dicotyledonous weeds. The general population is routinely exposed to 2,4-D due to consumption of contaminated food and water. 2,4-D is known to damage cellular components in human erythrocytes. This study investigated in detail the interaction of 2,4-D with human hemoglobin (Hb), the major protein in erythrocytes (>95%), and characterized the binding properties utilizing multi-spectrometric and in silico techniques. The UV-visible spectra suggested that 2,4-D interacts with Hb. The fluorescence quenching studies at three different temperatures further showed the binding of 2,4-D to Hb and the formation of a ground-state complex. The results indicated that 2,4-D binds spontaneously to a single moderate-affinity binding site on Hb. Furthermore, the binding process involved van der Waals forces and hydrogen bonding. Circular dichroism and synchronous fluorescence spectra showed that the binding of 2,4-D altered the conformation of Hb and decreased the polarity around its tryptophan residues. 2,4-D binding inhibited the inherent esterase activity of Hb. Computational analysis demonstrated that the Hb-2,4-D complex was stable and identified the amino acid residues at the binding site. Thus, 2,4-D interacts with Hb, modifies the protein conformation and consequently impairs its functions.

Discovery of sugar-based natural framework as phytopathogenic virus capsid protein inhibitors using a state-of-the-art multiple screening strategy

The prompt and efficient identification of targeted inhibitors against unscrupulous pathogenic viruses holds promise for preventing epidemic disease outbreaks. Herein, a comprehensive multichannel screening method (multiple docking cross-validation, molecular dynamics simulation, and density functional theory calculation) integrated with bioactivity identification is rationally established using sugar-based natural ligand libraries to target tobacco mosaic virus (TMV) capsid proteins. Encouragingly, compounds A0 (Kd = 0.14 μM) and A4 (Kd = 1.43 μM) were evaluated to have excellent binding capacities to TMV capsid protein, evidently exceeding that of viricide Ningnanmycin (Kd = 3.47 μM) by 24.8 and 2.4-folds. Moreover, A0 and A4 significantly down-regulated the expression of capsid proteins at the transcriptional level, effectively blocking the biosynthesis and assembly of TMV in tobacco. Additionally, bioactivity evaluation illustrated that the anti-TMV curative effects of A0 (EC50 = 310.9 μg/mL) and A4 (EC50 = 371.2 μg/mL) were comparable to Ningnanmycin (EC50 = 343.8 μg/mL). Considering the availability, cost and synthesis difficulty of precursors, the more affordable A4 is reckoned to be a promising candidate for capsid protein inhibitors and warrants further exploration in follow-up studies. Current findings highlight that this state-of-the-art virtual strategy, integrated with bioactivity validation, facilitates the discovery of targeted candidates to combat pathogenic viruses.

Mechanisms underlying the improvement in foaming properties of ovalbumin via non-covalent binding to polymeric proanthocyanidins from Averrhoa carambola fruits

The strong binding capacity of proanthocyanidins towards proteins provides a potential for natural modification of ovalbumin (OVA) and eventually altering its functionalities. In this study, polymeric proanthocyanidins from the fruit of Averrhoa carambola (APAs) were prepared and structurally characterized, and then the possibility and underlying mechanisms of enhancing OVA foaming properties via non-covalent binding to APAs were evaluated. Procyanidins consisting predominately of epicatechin units connected by both A- and B-type interflavan bonds were identified as APAs principal components. UV-vis absorption, fluorescence, CD, FT-IR spectroscopy and molecular docking results revealed that APAs could bind to OVA to form the ground-state complexes and statically quench the intrinsic fluorescence of OVA. The conformation of OVA was changed by its interaction with APAs, and the main binding forces between them were hydrogen bonding and hydrophobic interactions. Moreover, the surface hydrophobicity, contact angle and surface tension of OVA were declined after complexation with APAs, while the free sulfhydryl content, apparent viscosity and interfacial protein content were increased. The addition of APAs significantly promoted the foaming performance of OVA with an improvement of 15 % in foaming capacity and 7 % in foam stability. These results suggested that APAs might be applied as foaming additives in food industry.

Assessing the molecular interaction between a COVID-19 drug, nirmatrelvir, and human serum albumin: calorimetric, spectroscopic, and microscopic investigations

The research examined the molecular interaction between nirmatrelvir (NIR), a drug used to treat COVID-19, and human serum albumin (HSA) using various techniques, viz., isothermal titration calorimetry (ITC), absorption, fluorescence, CD spectroscopy, and atomic force microscopy (AFM). ITC analysis showed that the NIR-HSA system possessed a moderate binding affinity, with a K a value of 6.53 ± 0.23 × 104 M-1 at a temperature of 300 K. The thermodynamic values demonstrated that the NIR-HSA complex was stabilized by hydrophobic contacts, hydrogen bonds, and van der Waals forces. The research also discovered modifications in the UV-Vis absorption spectrum of the protein as well as swelling of the HSA molecule when exposed to NIR, based on AFM results. The three-dimensional fluorescence spectral data indicated changes in the microenvironment around HSA's Trp and Tyr residues. Alterations in the protein structure (both secondary and tertiary structures) of HSA after NIR binding were verified using CD spectral studies in the far-UV and near-UV regions. The identification of the NIR binding site in subdomain IB (Site III) of HSA was predicted through competitive displacement experiments.

Green synthesis of zinc ferrite nanoparticles from Nyctanthes arbor-tristis: unveiling larvicidal potential, protein binding affinity and photocatalytic activities

Environmental pollution, being a major concern worldwide, needs a unique and ecofriendly solution. To answer this, researchers are aiming in utilizing plant extracts for the synthesis of nanoparticles. These NPs synthesized using plant extracts provide a potential, environmentally benign technique for biological and photocatalytic applications. Especially, plant leaf extracts have been safe, inexpensive, and eco-friendly materials for the production of nanoparticles in a greener way. In this work, zinc ferrite nanoparticles (ZnFe2O4 NPs) were prepared using Nyctanthes arbor-tristis leaf extract by hydrothermal method, and its biological and photocatalytic properties were assessed. The synthesized ZnFe2O4 NPs were characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FT-IR). X-ray diffraction confirmed the arrangement of the fcc crystal structure of the nanoparticles and that some organic substances were encapsulated within the zinc ferrite. According to the SEM analysis, the resulting nanoparticles got agglomerated and spherical in shape. The ZnFe2O4 nanoparticles are in their pure form, and all of their elemental compositions were shown by the energy-dispersive X-ray analysis (EDAX) spectrum. The FTIR results revealed that the produced nanoparticles contained distinctive functional groups. Fluorescence spectroscopy was used to examine the binding affinities between bovine serum albumin (BSA) and ZnFe2O4 nanoparticles in terms of protein binding, stability, and conformation. The interaction between BSA and ZnFe2O4 NPs was examined using steady-state and time-resolved fluorescence measurements, and it was evident that static quenching occurred. The ability of ZnFe2O4 nanoparticles to kill Culex quinquefasciatus (C. quinquefasciatus) larvae was evaluated. The synthesized NPs demonstrated a noteworthy toxic effect against the fourth instar larvae of C. quinquefasciatus with LC50 values of 43.529 µg/mL and LC90 values of 276.867 µg/mL. This study revealed the toxicity of green synthesized ZnFe2O4 NPs on mosquito larvae, proving that these NPs are good and effective larvicides. Furthermore, the ZnFe2O4 NPs were utilized for dye degradation of methylene blue under visible light treatment and achieved 99.5% degradation.

Novel evidence on iodoacetic acid-induced immune protein functional and conformational changes: Focusing on cellular and molecular aspects

Elevated levels of iodide occur in raw water in certain regions, where iodination disinfection byproducts are formed during chloramine-assisted disinfection of naturally iodide-containing water. Iodoacetic acid (IAA) is one of the typical harmful products. The mechanisms underlying IAA-induced immunotoxicity and its direct effects on biomolecules remained unclear in the past. Cellular, biochemical, and molecular methods were used to investigate the mechanism of IAA-induced immunotoxicity and its binding to lysozyme. In the presence of IAA, the cell viability of coelomocytes was significantly reduced to 70.8 %, as was the intracellular lysozyme activity. Upon binding to IAA, lysozyme underwent structural and conformational changes, causing elongation and unfolding of the protein due to loosening of the backbone and polypeptide chains. IAA effectively quenched the fluorescence of lysozyme and induced a reduction in particle sizes. Molecular docking revealed that the catalytic residue, Glu 35, which is crucial for lysozyme activity, resided within the docking range, suggesting the preferential binding of IAA to the active site of lysozyme. Moreover, electrostatic interaction emerged as the primary driving force behind the interaction between IAA and lysozyme. In conclusion, the structural and conformational changes induced by IAA in lysozyme resulted in impaired immune protein function in coelomocytes, leading to cellular dysfunction.

Unravelling the molecular interactions of phenyl isothiocyanate and benzoyl isothiocyanate with human lysozyme: Biophysical and computational analyses

Phenyl isothiocyanate and benzoyl isothiocyanate are the phytochemicals present in the Brassicaceae family. They have antibacterial, antiapoptotic and antifungal properties. Protein-small molecule interaction studies are done to assess the changes in structure, dynamics, and functions of protein and to decipher the binding mechanism. This study is based on the comparative binding of PT and BT with human lysozyme using in vitro and computational techniques. UV, fluorescence emission, and FRET spectra gave insight into the complex formation, quenching mechanism, and binding parameters. Both PT and BT quenched the intrinsic fluorescence of Lyz by a static quenching mechanism. Synchronous, 3D fluorescence and CD spectroscopy substantiated conformational and microenvironmental alterations in the Lyz. The metal ions and β-cyclodextrin had a pronounced effect on the binding strength of Lyz-PT and Lyz-BT complexes. Accessible surface area analysis was determined to characterise the amino acid residue packing. Molecular docking further validated the wet lab experimental results.

Orange G is a potential inhibitor of human insulin amyloid fibrillation and can be used as a probe to study mechanism of amyloid fibrillation and its inhibition

The extracellular insoluble deposits of highly ordered cross-β-structure-containing amyloid fibrils form the pathological basis for protein misfolding diseases. As amyloid fibrils are cytotoxic, inhibition of the process is a therapeutic strategy. Several small molecules have been identified and used as fibrillation inhibitors in the recent past. In this work, we investigate the effect of Orange G on insulin amyloid formation using fluorescence-based assays and negative-stain electron microscopy (EM). We show that Orange G effectively attenuates nucleation, thereby inhibiting amyloid fibrillation in a dose-dependent manner. Fluorescence quenching titrations of Orange G showed a reasonably strong binding affinity to native insulin. Binding isotherm measurements revealed the binding of Orange G to pre-formed insulin fibrils too, indicating that Orange G likely binds and stabilizes the mature fibrils and prevents the release of toxic oligomers which could be potential nuclei or templates for further fibrillation. Molecular docking of Orange G with native insulin and amyloid-like peptide structures were also carried out to analyse the contributing interactions and binding free energy. The findings of our study emphasize the use of Orange G as a molecular probe to identify and design inhibitors of amyloid fibrillation and to investigate the structural and toxic mechanisms underlying amyloid formation.

Probing the Role of Cu(II) Ions on Protein Aggregation Using Two Model Proteins

Copper is an essential trace element for human biology where its metal dyshomeostasis accounts for an increased level of serum copper, which accelerates protein aggregation. Protein aggregation is a notable feature for many neurodegenerative disorders. Herein, we report an experimental study using two model proteins, bovine serum albumin (BSA) and human serum albumin (HSA), to elucidate the mechanistic pathway by which serum albumins get converted from a fully folded globular protein to a fibril and an amorphous aggregate upon interaction with copper. Steady-state fluorescence, time-resolved fluorescence studies, and Raman spectroscopy were used to monitor the unfolding of serum albumin with increasing copper concentrations. Steady-state fluorescence studies have revealed that the fluorescence quenching of BSA/HSA by Cu(II) has occurred through a static quenching mechanism, and we have evaluated both the quenching constants individually. The binding constants of BSA-Cu(II) and HSA-Cu(II) were found to be 2.42 × 104 and 0.05 × 104 M-1, respectively. Further nanoscale morphological changes of BSA mediated by oligomers to fibril and HSA to amorphous aggregate formation were studied using atomic force microscopy. This aggregation process correlates with the Stern-Volmer plots in the absence of discernible lag phase. Raman spectroscopy results obtained are in good agreement with the increase in antiparallel β-sheet structures formed during the aggregation of BSA in the presence of Cu(II) ions. However, an increase in α-helical fractions is observed for the amorphous aggregate formed from HSA.

Water-Soluble Dioxidovanadium(V) Complexes of Aroylhydrazones: DNA/BSA Interactions, Hydrophobicity, and Cell-Selective Anticancer Potential

Five new anionic aqueous dioxidovanadium(V) complexes, [{VO₂L^1,2}A(H₂O)_n]_α (1-5), with the aroylhydrazone ligands pyridine-4-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)hydrazide (H₂L¹) and furan-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)hydrazide (H₂L²) incorporating different alkali metals (A = Na⁺, K⁺, Cs⁺) as countercation were synthesized and characterized by various physicochemical techniques. The solution-phase stabilities of 1-5 were determined by time-dependent NMR and UV-vis, and also the octanol/water partition coefficients were obtained by spectroscopic techniques. X-ray crystallography of 2-4 confirmed the presence of vanadium(V) centers coordinated by two cis-oxido-O atoms and the O, N, and O atoms of a dianionic tridentate ligand. To evaluate the biological behavior, all complexes were screened for their DNA/protein binding propensity through spectroscopic experiments. Finally, a cytotoxicity study of 1-5 was performed against colon (HT-29), breast (MCF-7), and cervical (HeLa) cancer cell lines and a noncancerous NIH-3T3 cell line. The cytotoxicity was cell-selective, being more active against HT-29 than against other cells. In addition, the role of hydrophobicity in the cytotoxicity was explained in that an optimal hydrophobicity is essential for high cytotoxicity. Moreover, the results of wound-healing assays indicated antimigration in case of HT-29 cells. Remarkably, 1 with an IC₅₀ value of 5.42 ± 0.15 μM showed greater activity in comparison to cisplatin against the HT-29 cell line.

Self-Assembled Biophotonic Lasing Network Driven by Amyloid Fibrils in Microcavities

Self-assembled biological structures have played a significant role in many living systems for its functionality and distinctiveness. Here, we experimentally demonstrate that the random dynamic behavior of strong light-matter interactions in complex biological structures can provide hidden information on optical coupling in a network. The concept of biophotonic lasing network is therefore introduced, where a self-assembled human amyloid fibril network was confined in a Fabry-Perot optical cavity. Distinctive lasing patterns were discovered from self-assembled amyloids with different structural dimensions (0D, 1D, 2D, and 3D) confined in a microcavity. Network laser emission exhibiting evidence of light coupling at different wavelengths and locations was spectrally resolved. Dynamic changes of lasing patterns can therefore be interpreted into a graph to reveal the optical correlation in biophotonic networks. Our findings indicate that each graph represents the highly unclonable features of a self-assembled network which can sensitively respond to environmental stimulus. This study offers the potential for studying dynamic biological networks through amplified interactions, shedding light on the development of biologically controlled photonic devices, biosensing, and information encryption.

Investigation on the binding interaction of rhodamine B with human serum albumin: effect of metal ions

The binding of rhodamine B (RB) to human serum albumin (HSA) in the absence and presence of Cu²⁺ or Fe³⁺ under simulated physiological conditions was studied by using various biophysical methods for the first time. The results showed that the interaction between HSA and RB could spontaneously result in the formation of HSA-RB complex (namely, static quenching mechanism) through hydrophobic interactions and hydrogen bonds irrespective of the absence or presence of metal ions. The presence of metal ions led to the reduction of binding affinity of RB to HSA compared with no metal ions, which might result from the conformational change of HSA caused by the binding of metal ions. Furthermore, the analysis of UV-vis absorption, circular dichroism, synchronous fluorescence and three-dimensional fluorescence experiments demonstrated that the addition of RB induced conformational and microenvironmental changes of HSA without and with metal ions. In short, this work will be helpful to in-depth understand the transport mechanism and biological effect of RB and the effect of metal ions on the interaction of HSA-RB in vivo.

Exploring the binding interactions of janus green blue with serum albumins from spectroscopic and calorimetric studies aided by in silico calculations

Binding interactions of the phenazinium dye Janus green blue (JGB) with human and bovine serum albumins (BSA - and BSA) have been explored for the first time from multi-spectroscopic and calorimetric measurements aided by in silico calculations. The formation of ground state complexes between JGB and the respective serum albumins have been suggested from the UV-Vis and steady-state fluorescence spectroscopic studies. The nonlinear Stern Volmer (SV) plots at higher concentrations of JGB primarily indicate the formation of more than one ground state complexes in BSA -/BSA-JGB systems. Modified SV plots and isothermal titration calorimetry (ITC) studies however signify the possibilities of one type of binding complexes between HSA/BSA - JGB systems. Binding constants and the thermodynamic parameters associated with the HSA/BSA-JGB complexes have also been estimated from the ITC studies. Förster distances (R₀) for HSA-JGB and BSA-JGB complexes are estimated from Förster resonance energy transfer (FRET) results. Variations in the micro-environment of the Tyr and Trp residues of the serum proteins in presence of JGB have been observed from the synchronous fluorescence measurements. The conformational changes in the protein structures induced by the dye JGB have been revealed from 3 D fluorescence and circular dichroism (CD) studies. The experimental observations are supported by in silico calculations. This in depth investigation on the interactions of serum albumins with JGB may provide the fundamental information toward exploring the therapeutic efficacy of JGB as a potent drug molecule. Communicated by Ramaswamy H. Sarma.

Synthesis, structure and characterization of new dithiocarbazate-based mixed ligand oxidovanadium(iv) complexes: DNA/HSA interaction, cytotoxic activity and DFT studies

The synthesis, structure and characterization of mixed ligand oxidovanadium(iv) complexes [V^IVOL^1–2(L^N–N)] (1–3) are reported. With a view to evaluating their biological activity, their DNA/HSA interaction and cytotoxicity activity have been explored.

Effect of curcumin derivatives on hen egg white lysozyme amyloid fibrillation and their interaction study by spectroscopic methods

Two novel Boc-L-isoleucine-functionalized curcumin derivatives have been synthesized and characterized, which exhibited enhanced solubility in water compared with the natural curcumin. The solubility could reach 2.12mg/mL for the monosubstituted compound and 3.05mg/mL for the disubstituted compound, respectively. Their anti-amyloidogenic capacity on the model protein, hen egg white lysozyme (HEWL), was examined in aqueous solution. ThT fluorescence assay showed that the operation concentration was only 0.5mM when the inhibition ratio was above 70%. Meanwhile, the inhibitory capacity of monosubstituted curcumin derivative on the formation of HEWL amyloid fibrils was found to be superior to that of disubstituted derivative, suggesting that the phenolic hydroxyl group might contribute to the anti-amyloidogenic activity. Interaction study showed that both curcumin derivatives could bind with HEWL near tryptophan residues and form new ground-state complex before HEWL self-assemblies into amyloid fibrils and thus inhibits the formation of amyloid fibrils. Both of the two cucumin derivatives have displayed low cytotoxicity with HeLa cell.

Multiple covalent fluorescence labeling of eukaryotic mRNA at the poly(A) tail enhances translation and can be performed in living cells

Post-transcriptional regulation of gene expression occurs by multiple mechanisms, including subcellular localization of mRNA and alteration of the poly(A) tail length. These mechanisms play crucial roles in the dynamics of cell polarization and embryonic development. Furthermore, mRNAs are emerging therapeutics and chemical alterations to increase their translational efficiency are highly sought after. We show that yeast poly(A) polymerase can be used to install multiple azido-modified adenosine nucleotides to luciferase and eGFP-mRNAs. These mRNAs can be efficiently reacted in a bioorthogonal click reaction with fluorescent reporters without degradation and without sequence alterations in their coding or untranslated regions. Importantly, the modifications in the poly(A) tail impact positively on the translational efficiency of reporter-mRNAs in vitro and in cells. Therefore, covalent fluorescent labeling at the poly(A) tail presents a new way to increase the amount of reporter protein from exogenous mRNA and to label genetically unaltered and translationally active mRNAs.

DNA/Lysozyme-binding affinity study of novel peptides from TAT (47-57) and BRCA1 (782-786) in vitro by spectroscopic analysis

SISLL-TAT and TAT-SISLL were synthesized by modifying the N- or C-termini of cell-penetrating peptides as transacting activator of transcription TAT (47-57) by attaching BRCA1 (782-786) (SISLL). The novel peptides were synthesized through Fmoc solid-phase synthesis procedures and characterized by LCQ Fleet MS, ¹H NMR and ¹³C NMR. SISLL-TAT and TAT-SISLL displayed forceful antibacterial activities against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Salmonella typhimurium with low hemolysis. SISLL-TAT showed better antibacterial activity than TAT-SISLL, with the minimum inhibitory concentration (MIC) values of 10-33 μg·mL^-1. The results of the DNA-binding activities showed that both SISLL-TAT and TAT-SISLL could interact with DNA via the minor groove mode, and the binding constants were 4.97 × 10⁵ L·mol^-1 and 4.42 × 10⁵ L·mol^-1 at 310 K, respectively. Circular dichroism analysis showed slight transformation of the lysozyme secondary structure caused by SISLL-TAT and TAT-SISLL. We also found that the novel peptides SISLL-TAT and TAT-SISLL targeted bacterial DNA resulting in cell death. This explains the antibacterial mechanism of SISLL-TAT and TAT-SISLL, and is a solid theoretical basis for further designing novel and highly effective antibiotics for clinical application.

Binding and inhibitory effect of the food colorants Sunset Yellow and Ponceau 4R on amyloid fibrillation of lysozyme

Amyloid fibrillogenesis of proteins is known to be the root cause of a large number of diseases like Parkinson's, Alzheimer's, and Huntington's disease, spongiform encephalopathy, amyloid polyneuropathy, type-II diabetes, etc.

Study on the interactions between toxic nitroanilines and lysozyme by spectroscopic approaches and molecular modeling

Being exogenous environmental pollutants, nitroanilines (NAs) are highly toxic and have mutagenic and carcinogenic activity. Being lack of studies on interactions between NAs and lysozyme at molecular level, the binding interactions of lysozyme with o-nitroaniline (oNA), m-nitroaniline (mNA) and p-nitroaniline (pNA) were investigated by means of steady-state fluorescence, synchronous fluorescence, UV-vis absorption spectroscopy, as well as molecular modeling. The experimental results revealed that the fluorescence of lysozyme is quenched by oNA and mNA through a static quenching, while the fluorescence quenching triggered by pNA is a combined dynamic and static quenching. The number of binding sites (n) and the binding constant (K_b) corresponding thermodynamic parameters ΔH^⊖, ΔS^⊖, ΔG^⊖ at different temperatures were calculated. The reactions between NAs and lysozyme were spontaneous and entropy driven and the binding of NAs to lysozyme induced conformation changes of lysozyme. The difference of the position of -NO₂ group affected the binding and the binding constants K_b decreased in the following pattern: K_b (pNA) >K_b (mNA) >K_b (oNA). Molecular docking studies were performed to reveal the most favorable binding sites of NAs on lysozyme. Our recently results could offer mechanistic insights into the nature of the binding interactions between NAs and lysozyme and provide information about the toxicity risk of NAs to human health.

Selective non-enzymatic total bilirubin detection in serum using europium complexes with different β-diketone-derived ligands as luminescence probes

Three europium(III) complexes, Eu(ectfd)₃ (Hectfd = 1-(9-ethyl-9H-carbazol-7-yl)-4,4,4-trifluorobutane-1,3-dione), Eu(tta)₃ (Htta = 4,4,4-trifluoro-1-(thiophen-2-yl)-butane-1,3-dione), and Eu(dbt)₃ (Hdbt = 2-(4',4',4'-trifluoro-1',3'-dioxobutyl)dibenzothiophene), were synthesized and employed to detect total bilirubin (BR) in blood-serum samples. UV-visible absorption and fluorescence (FL) spectroscopies were used to evaluate the selectivity of each europium (III) fluorescence probe to BR, which was shown to remarkably reduce the luminescence intensities of the europium(III) complexes at a wavelength of 612 nm. The luminescence intensity of each complex is linearly related to BR concentration. Eu(tta)₃ was shown to be the more-appropriate fluorescence probe for the sensitive and reliable detection of total BR in blood serum samples than either Eu(ectfd)₃ or Eu(dbt)₃. This observation can be ascribed to special σ-hole bonding between Htta and BR. In addition, the optimal pH test conditions for the detection of BR in human serum by the Eu(tta)₃ probe were determined. Sensitivity was shown to be dramatically affected by the pH of the medium. The experimental results reveal that pH 7.5 is optimal for this probe, which coincides with the pH of human serum. Furthermore, BR detection using the Eu(tta)₃ luminescence probe is simple, practical, and relatively free of interference from coexisting substances; it has a minimum detection limit (DL) of 68 nM and is a potential candidate for the routine assessment of total BR in serum samples. Graphical Abstract ᅟ.