Interaction between olanzapine and human serum albumin and effect of metal ions, caffeine and flavonoids on the binding: A spectroscopic study

The interaction of isoquinoline alkaloid crebanine with immunoglobulin G and cytotoxic effects toward MCF-7 breast cancer cell line

In this study, the interaction of crebanine, an isoquinoline alkaloid, with immunoglobulin G (IgG) was evaluated. Subsequently, the anticancer effects of crebanine in MCF-7 breast cancer cells were assessed. The results demonstrate that static quenching plays a key role in the fluorescence quenching of the IgG by crebanine, and some embedded hydrophobic patches of the IgG are exposed upon interaction with crebanine, while the characteristic β-sheet conformation of the IgG was almost preserved. Theoretical studies also show that several hydrophilic and hydrophobic residues play a crucial role in the formation of hydrogen bonds between crebanine and IgG, along with the stability of the complex. Cellular studies indicate that crebanine induces selective anticancer effects in MCF-7 cells (IC50: 36.76 μM) compared to human embryonic kidney cells (HEK-293, IC50: 723.77 μM) through the inhibition of colony formation, induction of oxidative stress and lipid peroxidation, upregulation of the Bax/Bcl-2 ratio, and cytochrome c release, which are indicative of the intrinsic apoptosis pathway. In conclusion, this study provides valuable information regarding the protein binding affinity and anticancer activity of crebanine, which are essential factors for determining the pharmacological activity of small molecules as drug candidates.

Molecular interaction study of flavonols with human serum albumin by theoretical simulations

The human serum albumin (HSA)-drug binding characteristic is directly related to the pharmacokinetic, pharmacodynamic profile and side effect properties of drug. Though much is known about the protein binding characteristics of flavonol, the influence of molecular structure of flavonol and dynamic behaviour of protein conformations have received little attention. Here, we studied the interactions of HSA with flavonols by using molecular docking, molecular dynamics simulations coupled with molecular mechanics- Poisson Boltzmann/generalized Born surface area (MM-PB/GBSA) method. The results demonstrated the probable flavonol-binding position of HSA exist near the large hydrophobic cavity of Sudlow's site 1; and the predicted binding free energies of HSA-flavonol complexes were consistent with the trend of the experimental data that the binding affinity increased with the growth in number of hydroxyl groups on B-ring, and the van der Waals contribution is the dominated component for the binding; and Quercetin and Myricetin with one or two adjacent hydroxyl groups can exist stably in the binding pocket by strong hydrophobic interactions and extensive hydrogen bond interactions. The present work provides further information on the dynamical behaviors of binding pocket and reasonable binding models for HSA to five flavonols, and the adjacent hydroxyl groups introduced to B-ring might be beneficial to HSA-binding.

Reactivity of Olanzapine and Tricyclic Antidepressants on the Protective Effects of Trolox on Lipid Peroxidation Evaluated Using Fluorescence Anisotropy, Electron Paramagnetic Resonance Spectrometry, and Thermal Analysis

Multiacting receptor-targeting antipsychotics and tricyclic antidepressants stimulate various neurotransmitter receptors despite the different targets of postsynaptic receptors and presynaptic reuptake transporters. Their auxiliary and adverse effects may be caused by multiple targets or the modification of the neuronal membrane. To evaluate the membrane responses to olanzapine, imipramine, desipramine, amitriptyline, lidocaine, and dibucaine, we examined the inhibition of lipid peroxidation in egg yolk phosphatidylcholine liposomes. By contrast, their effects on membrane fluidity were measured as the suppressive contributions of the inhibitory activity of Trolox on lipid oxidation. These drugs inhibit lipid peroxidation and exclude harmful reactive oxygen species and the protective effect of Trolox. The fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene in saturated phospholipid liposome-containing drugs suggested that olanzapine, imipramine, and dibucaine enhanced membrane fluidity. The radical scavenging activity of 2,2-diphenylpicrylhidrazyl and galvinoxyl radicals was determined using electron paramagnetic resonance experiments, and their molecular flexibility was determined using thermograms for differential scanning calorimetry. Multiple regression analyses of the linear free energy relationship approach and comparative investigations revealed that the membranous fluidity of the liposomes, independent of the radical scavenging activity of the drugs, induced the inhibitory activity on lipid peroxidation. We discussed how these drugs act on nervous membranes and aimed to identify the relationship between uncertified functions and membranous fluidity.

Aggregation and cytotoxicity of food additive dye (Azorubine)-albumin adducts: a multi-spectroscopic, microscopic and computational analysis

Protein and peptide misfolding is a central factor in the formation of pathological aggregates and fibrils linked to disorders like Alzheimer's and Parkinson's diseases. Therefore, it's essential to understand how food additives, particularly Azorubine, affect protein structures and their ability to induce aggregation. In this study, human serum albumin (HSA) was used as a model protein to investigate the binding and conformational changes caused by azorubine, a common food and drink colorant. The research revealed that azorubine destabilized the conformation of HSA at both physiological (pH 7.4) and acidic (pH 3.5) conditions. The loss of tryptophan fluorescence in HSA suggested significant structural alterations, particularly around aromatic residues. Far UV-CD analysis demonstrated disruptions in HSA's secondary structure, with a notable reduction in α-helical structures at pH 7.4. At pH 3.5, Azorubine induced even more extensive perturbations, resulting in a random coil conformation at higher azorubine concentrations. The study also investigated aggregation phenomena through turbidity measurements, RLS analysis, and TEM imaging. At pH 3.5, larger insoluble aggregates formed, while at pH 7.4, only conformational changes occurred without aggregate formation. Cytotoxicity assessments on neuroblastoma (SH-SY5Y) cells highlighted the concentration-dependent toxicity of albumin aggregates. Molecular dynamics simulations reaffirmed the stable interaction between azorubine and HSA. This research provides valuable insights into the mechanisms by which azorubine influences protein conformations. To further advance our understanding and contribute to the broader knowledge in this area, several future directions can be considered such as exploring other proteins, studying dose-response relationship, gaining mechanistic insights, biological relevance, toxicity assessment, identifying alternative food colorants, and mitigation strategies to prevent adverse effects of azorubine on serum proteins.Communicated by Ramaswamy H. Sarma.

Photophysical Properties, Fluorescence Quenching of Metformin Hydrochloride by Caffeine, and its Docking with the AMP-activated protein kinase receptor

In this research, the photophysical properties of metformin hydrochloride (MF-HCl) were studied using spectroscopic and molecular docking techniques. The interaction between metformin hydrochloride and caffeine is essential for understanding the pharmacokinetics of metformin, particularly in populations with high caffeine consumption. Metformin is a first-line medication for managing type 2 diabetes, while caffeine is a widely consumed dietary stimulant. Knowing how caffeine may affect the action of metformin is crucial for effective diabetes management. The spectroscopic techniques results showed that the photophysical properties (fluorescence quantum yields, lifetime, radiative, and non-radiative decay) of the drug are influenced by solvent polarity and drug concentration. The binding mechanism of metformin hydrochloride-caffeine (MF-HCl-CAF) was identified through the fluorescence quenching method. The quenching of drugs induced by caffeine is due to ground state complex formation. The binding occurs due to hydrogen bonds and Van der Waals forces in the reaction. The förster resonance energy transfer (FRET) between metformin hydrochloride and caffeine was also calculated using flourtools.com software. The threshold distance (R0), for 50% energy transfer from metformin hydrochloride to caffeine is 1.81 nm and the binding distance (r), between caffeine and the amino acid residue in metformin hydrochloride is 1.55 nm. Dynamic light scattering (DLS), Zeta potential, and Fourier transform infrared (FTIR) spectroscopy confirm the conformational change of the drugs, as the caffeine molecule binds to metformin hydrochloride molecules. The molecular docking of metformin hydrochloride with the amp-activated protein kinase receptor (PDB Id: 1z0n) is analyzed. Again the docking of both metformin hydrochloride and caffeine (two ligands) with the protein receptor (PDB Id: 1z0n) was also analyzed and the results agreed with the fluorescence quenching techniques.

Green Tea Polyphenol Epigallocatechin Gallate Interactions with Copper-Serum Albumin

Epigallocatechin gallate (EGCg), an abundant phytochemical in green tea, is an antioxidant that also binds proteins and complex metals. After gastrointestinal absorption, EGCg binds to serum albumin in the hydrophobic pocket between domains IIA and IIIA and overlaps with the Sudlow I site. Serum albumin also has two metal binding sites, a high-affinity N-terminal site (NTS) site that selectively binds Cu(II), and a low-affinity, less selective multi-metal binding site (MBS). We proposed to determine whether EGCg binds or reacts with Cu(II)-serum albumin using fluorescence, UV-Visible and electron paramagnetic resonance (EPR) spectroscopy. Our results suggest that when serum albumin is loaded with Cu(II) in both sites, EGCg binds to the MBS-Cu(II) and reduces the copper to Cu(I). EGCg does not bind to or react with Cu(II) in the high-affinity NTS site. Potential consequences include changes in copper homeostasis and damage from pro-oxidative Fenton reactions.

Eco-Friendly Analytical Approach for Sensitive Spectrofluorimetric Determination of the Flavonoid Chrysin in Capsules and Human Plasma

Chrysin is a plant flavonoid that has different therapeutic effects as anti-inflammatory, anti-cancer, anti-oxidant, and immune booster. Spectrofluorimetry has received a lot of interest lately because of its ecological greenness and analytical performance. This approach employed the native fluorescence of chrysin at 339 nm following excitation at 231 nm in distilled water. Modern advances in analytical chemistry have been used to lessen occupational and environmental concerns by employing distilled water as a dilution solvent through method development and application. The approach was found to be excellent green supported by eco-scale score of 97 and 0.94 AGREE rating, in addition to an overall whiteness score of 88.80. The design aimed to analyze chrysin in raw materials, Chrysin® capsules and human plasma. The method was linear over 0.5-7.0 ng mL⁻1 chrysin, with LOD of 0.06 ng mL⁻1 and LOQ of 0.20 ng mL⁻1. The offered method was effectively applied for determination of chrysin in the commercial capsules Chrysin® and spiked human plasma samples with average recoveries of 99.76% and 99.98%, respectively for capsules and spiked human plasma. Up to date, no spectrofluorimetric method has been described for chrysin analysis, then, this presented an opportunity to develop a sensitive, quick, reliable, environmentally friendly, and valid fluorescence-based method.

Copper(II) and Zinc(II) Complexes with Bacterial Prodigiosin Are Targeting Site III of Bovine Serum Albumin and Acting as DNA Minor Groove Binders

The negative environmental and social impacts of food waste accumulation can be mitigated by utilizing bio-refineries' approach where food waste is revalorized into high-value products, such as prodigiosin (PG), using microbial bioprocesses. The diverse biological activities of PG position it as a promising compound, but its high production cost and promiscuous bioactivity hinder its wide application. Metal ions can modulate the electronic properties of organic molecules, leading to novel mechanisms of action and increased target potency, while metal complex formation can improve the stability, solubility and bioavailability of the parent compound. The objectives of this study were optimizing PG production through bacterial fermentation using food waste, allowing good quantities of the pure natural product for further synthesizing and evaluating copper(II) and zinc(II) complexes with it. Their antimicrobial and anticancer activities were assessed, and their binding affinity toward biologically important molecules, bovine serum albumin (BSA) and DNA was investigated by fluorescence emission spectroscopy and molecular docking. The yield of 83.1 mg/L of pure PG was obtained when processed meat waste at 18 g/L was utilized as the sole fermentation substrate. The obtained complexes CuPG and ZnPG showed high binding affinity towards target site III of BSA, and molecular docking simulations highlighted the affinity of the compounds for DNA minor grooves.

Unraveling the binding interactions between two Pt(II) complexes of aliphatic glycine derivatives with human serum albumin: A comprehensive computational and multi-spectral investigation

This article delves into the interaction between HSA protein and synthesized platinum complexes, with formula: [Pt(Propyl-NH2)2(Propylglycine)]NO3 and [Pt(Tertpentyl-NH2)2(Tertpentylglycine)]NO3, through a range of methods, including spectroscopic (UV-visible, fluorescence, synchronous fluorescence and CD) analysis and computational modeling (molecular docking and MD simulation). The binding constants, the number of binding sites, and thermodynamic parameters were obtained at 25 to 37 °C. The study found that both complexes could bind with HSA (moderate affinity for Tertpentyl and strong affinity for Propyl derivatives) and occupied one binding site in HSA (validated with, Stern-Volmer, Job-plots, and molecular docking investigations) located in subdomain IIA. The binding mechanisms of both mentioned Pt(II) agents were different, with the Propyl derivative predominantly using van der Waals forces and hydrogen bond interactions with a static quenching mechanism and the Tertpentyl derivative mainly utilizing hydrophobic force with a dynamic quenching mechanism. However, the two ligands affected protein differently; the Tertpentyl complex did not significantly alter the protein structure upon binding, as evidenced by synchronous fluorescence spectroscopy (SFS), CD spectroscopy, and MD analysis. The outcome helps in understanding the binding mechanisms and structural modifications induced by the ligands, which could aid in the innovation of more effective and stable Pt(II)-based drugs.

Bio-study: Modeling of natural nanomolecules as a nanocarrier surface for antioxidant and glucose biosensor

The nature of nano molecules as a self-assembled nanocomposite surface depends on the nanoparticles of sodium butyrate, cellulose, and pycnogenol; the synthesis is achieved via precipitation and grinding methods. The excellent functionalized surface of nanocomposite (NCP) enables the loading of the selected drugs, where the efficiency of the NCP surface arrived at 92.2 %. The electrochemical behavior emphasized the success of a functionalized NCP surface for incorporation with drugs for the drug delivery system, the results of cytotoxicity detect the effect of NCP on the mouse normal liver (BNL) cells, where the high and low concentrations on the BNL cells have a safe dose. Cell viability with BNL cells was reported at 101.8 % with10 μL and 100.12 % with 100 μL, the interaction between the NCP and the human serum albumin (HSA) at room temperature. The low interaction rate with the glutamate and increased binding with the oxidized glutathione disulfide (GSSG) and reduced glutathione (SGH) reflect the antioxidant activity of NCP. The strong binding of NCP with biomolecules such as glucose is referred to as the biosensor property. The results recommend that NCP is an excellent nanocarrier for drug delivery and glucose biosensors for diabetes.

Analysis of the binding mechanism for a water-soluble Pd(II) complex containing β-amino alcohols with HSA applying experimental and computational methods

In the study ahead, the binding interactions of the [Pd (HEAC) Cl2] complex with human serum albumin (HSA) protein have been assayed in vitro (pH= 7.40) utilizing computational and experimental procedures. The mentioned complex was synthesized as a water-soluble complex from {2-((2-((2-hydroxyethyl)amino)ethyl)amino) cyclohexanol} ligand = HEAC. The results of electronic absorption and circular dichroism investigations illustrated that the hydrophobicity of the Tryptophan microenvironment in HSA undergoes the changes by binding to the Pd(II) complex without substantial perturbations on the protein secondary structure. The fluorescence emission spectroscopy analysis revealed that with rising temperature, the quenching constant (Ksv) in the Stern-Volmer's relation decreases; so, it can be said that the interaction process is along with a static quenching mechanism. The values of 2.88 × 105 M-1, and 1.26 represent the binding constant (Kb) and the number of the binding sites (n), respectively. The Job graph showed the maximum point at χ = 0.5, which means organizing a new set with 1:1 stoichiometry. Thermodynamic profile (ΔH < 0, ΔS < 0, and ΔG < 0) has affirmed that van der Waals forces and hydrogen bonds have a basic function in the Pd(II) complex-albumin bindings. The ligand-competitive displacement studies utilizing warfarin and ibuprofen have represented that Pd(II) complex interacts with albumin by site II (subdomain IIIA). The computational molecular docking theory approved the results of the site-competitive tests; also, it indicated the existence of hydrogen bonds and van der Waals forces in Pd(II) complex-albumin interactions.Communicated by Ramaswamy H. Sarma.

Investigation of the interaction between S-isoalkyl derivatives of the thiosalicylic acid and human serum albumin

S-isoalkyl derivatives of thiosalicylic acid (isopropyl-(L1), isobutyl-(L2) and isoamyl-(L3)) were selected in order to investigate the binding interaction with the human serum albumin (HSA) using different spectroscopic methods and molecular docking simulation. Association constants and number of binding sites were used to analyze the quenching mechanism. The experimental results showed that the fluorescence quenching of HSA by L1, L2 and L3 occurs because of static quenching and that binding processes were spontaneous, with the leading forces in bonding by hydrogen bonding, hydrophobic interactions, and electrostatic interactions. Fluorescence spectroscopy, UV-Vis spectroscopy and synchronous fluorescence spectroscopy showed that ligands (L1, L2 and L3) can bind to HSA and that the binding of ligands induced some microenvironmental and conformational changes in HSA. The calculated distance between the donor and the acceptor according to fiFörster's theory confirms the energy transfer efficiency between the acceptor and HSA. Results of site marker competitive experiments showed that the tested compounds bind to HSA in domain IIA (Site I). Molecular dynamics and docking calculations demonstrated that L3 binds to the Sudlow site I of HSA with lower values of binding energies compared to L1 and L2, indicating the formation of the most stable ligand-HSA complex. Understanding the binding mechanisms of S-isoalkyl derivatives of the thiosalicylic acid to HSA may provide valuable data for the future studies of their biological activity and application as potential antitumor drugs.Communicated by Ramaswamy H. Sarma.

Digital Database of Absorption Spectra of Diverse Flavonoids Enables Structural Comparisons and Quantitative Evaluations

Flavonoids play diverse roles in plants, comprise a non-negligible fraction of net primary photosynthetic production, and impart beneficial effects in human health from a plant-based diet. Absorption spectroscopy is an essential tool for quantitation of flavonoids isolated from complex plant extracts. The absorption spectra of flavonoids typically consist of two major bands, band I (300-380 nm) and band II (240-295 nm), where the former engenders a yellow color; in some flavonoids the absorption tails to 400-450 nm. The absorption spectra of 177 flavonoids and analogues of natural or synthetic origin have been assembled, including molar absorption coefficients (109 from the literature, 68 measured here). The spectral data are in digital form and can be viewed and accessed at http://www.photochemcad.com. The database enables comparison of the absorption spectral features of 12 distinct types of flavonoids including flavan-3-ols (e.g., catechin, epigallocatechin), flavanones (e.g., hesperidin, naringin), 3-hydroxyflavanones (e.g., taxifolin, silybin), isoflavones (e.g., daidzein, genistein), flavones (e.g., diosmin, luteolin), and flavonols (e.g., fisetin, myricetin). The structural features that give rise to shifts in wavelength and intensity are delineated. The availability of digital absorption spectra for diverse flavonoids facilitates analysis and quantitation of these valuable plant secondary metabolites. Four examples are provided of calculations─multicomponent analysis, solar ultraviolet photoprotection, sun protection factor (SPF), and Förster resonance energy transfer (FRET)─for which the spectra and accompanying molar absorption coefficients are sine qua non.

Elucidation of binding dynamics of tyrosine kinase inhibitor tepotinib, to human serum albumin, using spectroscopic and computational approach

Tepotinib (TPT), an anticancer drug, is a fibroblast growth factor receptor inhibitor approved by the FDA for the chemotherapy of urothelial carcinoma. The binding of anticancer medicines to HSA can affect their pharmacokinetics and pharmacodynamics. The absorption, fluorescence emission, circular dichroism, molecular docking, and simulation studies were used to evaluate the binding relationship between TPT and HSA. The absorption spectra exhibited a hyperchromic effect upon the interaction of TPT with HSA. The Stern-Volmer and binding constant of the HSA-TPT complex demonstrates that fluorescence quenching is triggered by a static rather than a dynamic process. Further, the displacement assays and molecular docking results revealed that TPT preferred binding to site III of HSA. Circular dichroism spectroscopy confirmed that TPT binding to HSA induces conformational changes and reduces α-helical content. The thermal CD spectra reveal that tepotinib enhances protein's stability in the temperature range of 20 to 90 °C. The findings of MDS studies provide further evidence for the stability of the HSA-TPT complex. Consequently, the findings of the present investigation provide a clear picture of the impacts of TPT on HSA interaction. These interactions are thought to make the microenvironment around HSA more hydrophobic than in its native state.

Unveiling interaction mechanisms between myricitrin and human serum albumin: Insights from multi-spectroscopic, molecular docking and molecular dynamic simulation analyses

Myricitrin is a natural polyhydroxy flavonoid and is mainly derived from the bark and leaves of the Chinese Bayberry tree (Myrica rubra). It has different pharmacological activities, including antioxidative, anti-inflammatory, hypoglycemic, antiviral, liver protection and cholagogue properties, and may be added to foods, pharmaceuticals, and cosmetic products for antioxidant purposes. In this study, the interaction mechanism between myricitrin and human serum albumin (HSA) was investigated using spectroscopic methods, molecular docking techniques, and molecular dynamic simulations. We showed that the HSA/myricitrin interaction exhibited a static fluorescence quenching mechanism, and that binding processes were spontaneous in nature, with the main forces exemplified by hydrogen bonding, hydrophobic interactions, and electrostatic interactions. Fluorescence spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, synchronous fluorescence spectroscopy, three-dimensional (3D) fluorescence spectroscopy, micro-Fourier transform infrared spectroscopy (micro-FTIR), and circular dichroism (CD) spectroscopy showed that myricitrin binding altered the HSA conformation to some extent. Competitive binding and molecular docking studies showed that the preferred binding of myricitrin on HSA was in the sub-structural domain IIA (Site I); molecular dynamic simulations revealed that myricitrin interacted with HSA to produce a well stabilized complex, and it also generated a conformational change in HSA. The antioxidant capacity of the HSA-myricitrin complex was reduced when compared with free myricitrin. The identification of HSA-myricitrin binding mechanisms provides valuable insights for the application of myricitrin to the food and pharmaceutical industries.

Synthesis and characterization of the new ligand, 1,2,4-triazino[5,6-b]indol-3-ylimino methyl naphthalene-2-ol and its Ni(II) and Cu(II) complexes: comparative studies of their in vitro DNA and HSA Binding

A new ligand 1,2,4-triazino[5,6-b]indol-3-ylimino methyl naphthalene-2-ol (HL) was derived from 5H-[1,2,4]triazino[5,6-b]indol-3-amine and 2-hydroxy-1-naphthaldehyde. The metal complexes of the type [Ni(L)(Bipy)]1/2SO₄ (1), [Cu(L)(Bipy)(H₂O)₂]1/2SO₄ (2), [Ni(L)(Phen)]1/2SO₄ (3) and [Cu(L)(Phen)(H₂O)₂]1/2SO₄ (4) were synthesized. The ligand (HL) and complexes 1-4 were thoroughly characterized by elemental analysis and spectroscopic methods (FT-IR, ToF-MS, ¹H NMR, ¹³C NMR), molar conductance and magnetic moment determination. The Ni(II) complexes 1 and 3 adopt the square planar geometry and Cu(II) complexes 2 and 4 acquire distorted octahedral arrangement. In vitro DNA binding behavior of ligand (HL) and metal complexes 1-4 was explored by fluorescence spectral and ethidium bromide studies. The outcomes reveal that the complexes interact with DNA via non-covalent groove binding and electrostatic interactions. The higher binding constant (K) values of 4.35 × 10⁴ and 9.12 × 10⁴ M^-1 for complexes 2 and 4 indicate stronger binding ability with DNA. Moreover, in vitro human serum albumin (HSA) binding experiment with HL and complexes 1-4 reveals conformational modulations in the Trp-214 microenvironments in the subdomain IIA pocket.

Biological activity of bis-(morpholineacetato)palladium(II) complex: Preparation, structural elucidation, cytotoxicity, DNA-/serum albumin-interaction, density functional theory, in-silico prediction and molecular modeling

In an effort to discover a novel potential bioactive compound, a mono-nuclear Pd(II) complex with an amino acid derivative as ligand was synthesized and characterized through experimental and computational methodologies. A square-planar configuration was suggested for palladium(II) complex utilizing density functional theory. MEP map and Mulliken atomic charge were detected electrophilic and nucleophilic regions of the compound for reactions. The lipophilicity and cytotoxic activity of the complex was more effective than cisplatin. Also, OSIRIS DataWarrior revealed proper oral bioavailability and good drug-likeness for the compound. In-vitro binding behavior of the Pd(II) complex with DNA and serum albumin (BSA) were fully determined via variety of procedures including fluorescence, UV-Vis, CD, viscosity, gel electrophoresis experiments and molecular simulation. The negative signs of ΔH° and ΔS° for Pd(II) complex-CT-DNA/-BSA systems indicated the existence of hydrogen bonding/van der Waals interactions for both binding systems. Additionally, docking simulation illustrated the interaction of Pd(II) complex with the minor groove of DNA and the hydrophobic cavity of the BSA (drug binding site I).

Spectroscopic investigation on the binding interactions between graphene quantum dots and carbonic anhydrase

As a new member of the nanomaterials family, ultrasmall graphene quantum dots (GQDs) have shown broad application prospects in the field of biomedicine, but the analysis of their biological effects at the molecular level is yet limited. Herein, carbonic anhydrase (CA) was selected as a model protein to assess the interactions between GQDs and biomacromolecules. A range of spectroscopic techniques were employed to systematically investigate the binding interactions between GQDs and CA and the catalytic function of CA in the presence of GQDs was evaluated. Experimental results showed that GQDs could quench the intrinsic fluorescence of CA and the concentration dependent quenching efficiency exhibited an obvious deviation from the linear plot, indicating a static binding mode. Further investigation suggested that van der Waal interactions and hydrogen bonding were the main driving forces. Additionally, circular dichroism measurement showed that the binding of GQDs induced slight conformational changes of CA. The catalytic capability assessment proved that these binding interactions resulted in the reduction of the biological functions of CA. This comprehensive study provided important insight into the interaction of GQDs with biomacromolecules, which would be crucial for the further applications of GQDs and other nanomaterials in the biomedical field.

Synthesis of 4-dimethylaminobenzyl chrysin ester-Zn fluorescent chemical sensor for the determination of Cr(VI) in water

Cr(VI) is a type of dangerous effluent that has caused great harm to human health and the environment. Recognition and perception of Cr(VI) by artificial receptors has attracted extensive attention. A novel fluorescent chemical sensor based on the 5,7-dihydroxyflavone skeleton was designed and synthesized for the selective recognition of Cr(VI). As confirmed by fluorescence technology, the fluorescent probe 4-dimethylaminobenzyl chrysin ester-Zn (DBC-Zn) showed high sensitivity and selectivity for dichromate and a fast response (less than 30 sec) recognition. The fluorescence intensity of DBC-Zn varies linearly with the concentration of Cr(VI) in the range 0.1-1 μM. The detection limit of Cr₂ O₇ ^2- by DBC-Zn is 2.3 nM, which is far lower than the national safe drinking water standard stipulated by the US Environmental Protection Agency (1.9 μM). The quenching mechanism of the probe can be attributed to the interaction of the dynamic quenching effect and the fluorescence internal filtration effect. In addition, the probe has good stability in both neutral and alkaline environments, and the accuracy of quantitative analysis of Cr₂ O₇ ^2- in lake water or tap water is more than 80%. The test paper based on DBC-Zn can effectively detect Cr₂ O₇ ^2- at the concentration of 100 ppb. This shows that the probe has a certain practical application value.

Interaction of 4'-methylflavonoids with biological membranes, liposomes, and human albumin

The aim of the study was to compare the impact of three synthesized chemical compounds from a group of methylated flavonoids, i.e. 2'-hydroxy-4-methylchalcone (3), 4'-methylflavanone (4), and 4'-methylflavone (5), on a red blood cell membranes (RBCMs), phosphatidylcholine model membranes (PC), and human serum albumin (HSA) in order to investigate their structure-activity relationships. In the first stage of the study, it was proved that all of the compounds tested do not cause hemolysis of red blood cells and, therefore, do not have a toxic effect. In biophysical studies, it was shown that flavonoids have an impact on the hydrophilic and hydrophobic regions of membranes (both RBCMs and PC) causing an increase in packing order of lipid heads and a decrease in fluidity, respectively. Whereas, on the one hand, the magnitude of these changes depends on the type of the compound tested, on the other hand, it also depends on the type of membrane. 4'-Methylflavanone and 4'-methylflavone are located mainly in the hydrophilic part of lipid membranes, while 2'-hydroxy-4-methylchalcone has a greater impact on the hydrophobic area. A fluorescence quenching study proved that compounds (3), (4) and (5) bind with HSA in a process of static quenching. The binding process is spontaneous whereas hydrogen bonding interactions and van der Waals forces play a major role in the interaction between the compounds and HSA.

Profiling the interaction of a novel toxic pyruvate dehydrogenase kinase inhibitor with human serum albumin

To discover novel pyruvate dehydrogenase kinase (PDK) inhibitors, a new compound 2,2-dichloro-1-(4-((4-isopropylphenyl)amino)-3-nitrophenyl)ethan-1-one, namely XB-1 was identified, which inhibited PDK activity with a half maximal inhibitory concentration (IC₅₀) value of 337.0 nM, and reduced A549 cell proliferation with a half maximal effective concentration (EC₅₀) value of 330.0 nM. However, the compound appears to exhibit a negligible selectivity between cancer cell and normal one, indicating a potential toxicity existed for the compound. Herein, the interaction of the toxic XB-1 to human serum albumin (HSA) was firstly explored by spectroscopic approaches with the aim to reduce/avoid the toxicity of PDK inhibitors in the next hit-to-lead campaign. In detail, it was found that the XB-1 could effectively bind to HSA mainly via hydrogen bond interaction in PBS buffer (pH = 7.4, 10.0 mM), resulting in the formation of HSA-XB-1 complex. The negative value of ΔG showed that the binding of XB-1 to HSA is a spontaneous process. The result from site-selective binding assay suggested that the XB-1 bound to the site I of HSA by competing with warfarin, which was perfect in agreement with the molecular docking method. The results of this paper may offer a valuable theoretical basis to study the toxicity of biofunctional molecules and may offer thoughts about how to avoid/reduce toxicity for a small molecule.

Investigation on the binding of cyanobacterial metabolite calothrixin A with human serum albumin for evaluating its potential toxicology

Calothrixin A (CLA), as a carbazole-1,4-quinone alkaloid with unique indolo [3,2-j] phenanthridine framework, is a natural metabolite from the Calothrix cyanobacteria. Since the interaction to the functional serum albumins may play an important role in estimating its potential physiological or toxicological effects in vivo, we here explored the binding information of CLA with human serum albumin (HSA) by multi-spectroscopic experiments and computational approaches. The molecular docking results showed that there was one binding site of CLA to the site I (subdomain IIA) of HSA, causing the spontaneous formation of the ground state complex of CLA-HSA through the integration of hydrogen bond, hydrophobic interaction, and electrostatic interaction. Moreover, CLA could effectively trigger the change of HSA's secondary structure because of an obvious decrease of α-helical content in HSA. Taking into consideration of the crucial role of HSA to transport extraneous functional small molecules in vivo, this study may provide a worthy theoretical basis to evaluate the in vivo toxicity of CLA, aiming to reduce/avoid the potential toxic side effects of CLA in the next hit-to-lead campaign.