The fluorescence spectroscopic study on the interaction between imidazo[2,1-b]thiazole analogues and bovine serum albumin

Exploring antiviral and antiparasitic activity of gold N-heterocyclic carbenes with thiolate ligands

Gold(I) N-heterocyclic carbenes have been explored for their therapeutic potential against several diseases. Neglected tropical diseases, including leishmaniasis, Chagas disease, and viral infections, such as zika, mayaro, and chikungunya, urgently require new treatment options. The emergent SARS-CoV-2 also demands significant attention. Gold complexes have shown promise as alternative treatments for these conditions. Previously, gold(I)(1,3-bis(mesityl)imidazole-2-ylidene)Cl (AuIMesCl) demonstrated significant leishmanicidal and anti-Chikungunya virus activities. In this study, we synthesized and fully characterized a series of gold(I)(1,3-bis(mesityl)imidazole-2-ylidene)(SR) complexes, where SR includes thiolate donor species such as 1,3-thiazolidine-2-thione, 1,3-benzothiazole-2-thione, 2-mercaptopyrimidine, and 2-thiouracil. These compounds were stable in solution, and ligand exchange reactions with N-acetyl-L-cysteine indicated that complexes with SR ligands are more labile than those with chloride. Although the reactions are rapid, they reach equilibrium at varying molar ratios depending on the SR ligand. The increased lability of these compounds results in higher cytotoxicity to host cells, such as Vero E6 and bone marrow-differentiated macrophages, compared to AuIMesCl. Despite this, the compounds effectively inhibited viral replication, achieving 95.5% inhibition of Zika virus replication at 2 μM with 96% host cell viability. Although active at low concentrations (∼2 μM) against Leishmania (L.) amazonensis and Trypanosoma cruzi, their high cytotoxicity for macrophages confirmed AuIMesCl as a better candidate with a higher selectivity index. This work correlates the coordination chemistry of pyrimidines and thiazolidines with their in vitro biological activities against significant diseases.

Spectroscopic and molecular docking investigation on the interaction of a water-soluble Cu(II) complex containing diethanolamine and dipicolinic acid ligands with human serum albumin

Under physiological conditions, spectroscopic techniques as well as molecular docking simulation have been used to investigate the binding interaction mechanism between Cu(II) complex containing Pyridine-2,6-dicarboxylic acid (PDCA) and Diethanolamine (DEA) ligands, [Cu(DEA)(PDCA)] and human serum albumin (HSA). UV spectral changes of protein in the presence of the Cu(II) complex suggested the formation of a Protein-Cu(II) complex conjugate with specific new structure. The Cu(II) complex quenches the intrinsic fluorescence of the HSA via a static mechanism in which van der Waals interactions along with hydrogen bonds are fundamental binding forces. Displacement experiments performed by warfarin and ibuprofen site probes predict that the Cu(II) complex is located in subdomain IIA, Sudlow site 1 of HSA. Molecular docking results showed close resemblance with experimental data.Communicated by Ramaswamy H. Sarma.

Interactions of Amino Group Functionalized Tetraphenylvinyl and DNA: A Label-Free "On-Off-On" Fluorescent Aptamer Sensor toward Ampicillin

As a type of aggregation-induced emission (AIE) fluorescent probe, tetraphenylvinyl (TPE) or its derivatives are widely used in chemical imaging, biosensing and medical diagnosis. However, most studies have focused on molecular modification and functionalization of AIE to enhance the fluorescence emission intensity. There are few studies on the interaction between aggregation-induced emission luminogens (AIEgens) and nucleic acids, which was investigated in this paper. Experimental results showed the formation of a complex of AIE/DNA, leading to the quenching of the fluorescence of AIE molecules. Fluorescent test experiments with different temperatures proved that the quenching type was static quenching. The quenching constants, binding constants and thermodynamic parameters demonstrated that electrostatic and hydrophobic interactions promoted the binding process. Then, a label-free "on-off-on" fluorescent aptamer sensor for the detection of ampicillin (AMP) was constructed based on the interaction between the AIE probe and the aptamer of AMP. Linear range of the sensor is 0.2-10 nM with a limit of detection 0.06 nM. This fluorescent sensor was applied to detect AMP in real samples.

Fluorescent Imprinted Nanoparticles for Sensing of Chlorogenic Acid in Coffee Extracts

Green coffee beans are particularly rich in chlorogenic acids (CGAs), and their identification and quantification are usually performed by HPLC, coupled with mass spectrometry (LC-MS). Although there are a few examples of molecularly imprinted polymers (MIPs) for chlorogenic acid (5-CQA) recognition present in the literature, none of them are based on optical fluorescence, which is very interesting given its great sensitivity. In the present manuscript, fluorescent polymeric imprinted nanoparticles were synthetized following the non-covalent approach using hydrogenated 5-O-caffeoylquinic acid (H-5-CQA) as the template. The capability of the polymer to bind 5-CQA was evaluated by HPLC and fluorescence. A real sample of coffee extract was also analyzed to verify the selectivity of the polymer. Polymer fMIP01, containing 4-vinylpyridine and a naphtalimide derivative as monomers, showed a good response to the fluorescence quenching in the range 39 μM-80 mM. In the real sample, fMIP01 was able to selectively bind 5-CQA, while caffeine was not recognized. To demonstrate this, there is a promising system that can be exploited in the design of an optical sensor for 5-CQA detection. Polymer fMIP01 was immobilized by physical entrapment on a functionalized glass surface, showing a quenching of fluorescence with an increase of the CGA concentration between 156 μM and 40 mM.

Multi technique investigation on interaction between 5-(2-thiazolylazo)-2,4,6-triaminopyrimidine and HSA and BSA

In research laboratories and in various industries, azo compounds are among the most effective and commonly used organic dyes. The association between human (HSA) and bovine (BSA) serum albumins with 5-(2-thiazolylazo)-2,4,6-triaminopyrimidine (TTP) was investigated in this research using spectroscopy methods and molecular modeling study. The fluorescence quenching results showed that the quenching mechanisms were static and dynamic processes for HSA and BSA, respectively. From the thermodynamic observations, it is clear that the binding process is a spontaneous molecular interaction, in which van der Waals and hydrogen bonding interactions for HSA and hydrophobic interaction for BSA play the major roles. According to Förster energy transfer, non-radiative energy transferred from HSA and BSA to TTP, is provided by close distance (r₀) between TTP and Trp residues of HSA and BSA. The synchronous fluorescence spectroscopy, FT-IR findings and UV-Vis absorption data confirm that TTP can induce conformational and micro environmental changes in both the proteins. Furthermore, docking results predicted the probable binding site of TTP in subdomain IIA of HSA and BSA molecules where Trp residues are located. Types of amino acid residues surrounding the TTP molecule supported that van der Waals forces, hydrophobic forces and electrostatic forces play important roles in stabilization of drug-protein complexes formed.Communicated by Ramaswamy H. Sarma.

Triphenylphosphine gold(I) derivatives promote antiviral effects against the Chikungunya virus

Herein a systematic series of four [AuLL']n+ n = 0, +1 complexes, where L = 1,3-bis(mesityl)imidazole-2-ylidene (IMes), or triphenylphosphine (PPh3), and L' = chloride, or 4-dimethylaminopyridine (DMAP), had their in vitro antiviral activity assessed against Chikungunya virus (CHIKV). The PPh3 derivatives inhibited viral replication by 99%, whereas the IMes derivatives about 50%. The lipophilicity of the PPh3 derivatives is higher than the IMes-bearing compounds, which can be related to their more prominent antiviral activities. The dissociation of DMAP is faster than chloride in solution for both IMes and PPh3 derivatives; however, it does not significantly affect their in vitro activities, showing a higher dependence on the nature of L rather than L' towards their antiviral effects. All complexes bind to N-acetyl-L-cysteine, with the Ph3P-bearing complexes coordinating at a faster rate to this amino acid. The binding constants to bovine serum albumin (BSA) are in the order of 104, slightly higher for the DMAP complexes in both PPh3 and IMes derivatives. Mechanistic investigations of the PPh3 complexes showed a ubiquitous protective effect of the compounds in the pre-treatment, early stages, and post-entry assays. The most significant inhibition was observed in post-entry activity, in which the complexes blocked viral replication in 99%, followed by up to 95% inhibition of the early stages of infection. Pre-treatment assays showed a 92% and 80% replication decrease for the chloride and DMAP derivatives, respectively. dsRNA binding assays showed a significant interaction of the compounds with dsRNA, an essential biomolecule to viral replication.

Nitric oxide detection using catalytic properties of CuCo-PTC metal organic framework

As a vital gaseous signal molecule involved in various physiological and pathological processes, nitric oxide (NO) has attracted extensive attention in the last few decades. In this work, a copper and cobalt element-doped, biphenyl-(3, 4', 5)-tricarboxylic acid (H₃PTC)-synthesized metal organic framework (CuCo-PTC MOF) composite with catalytic ability was synthesized by solvothermal method. The material can catalyse the oxidation of o-phenylenediamine (OPD) groups by hydrogen peroxide (H₂O₂) to form fluorophores (OPDox) with yellow fluorescence emission and greatly improves its reaction rate. In the presence of NO, OPD will react with NO to produce N-(2-hydrazinophenyl) methylamine, and the group will not react with H₂O₂. Therefore, the concentration of NO can be measured indirectly by comparing the changes of fluorescence intensity in the presence and absence of NO. As the concentration of NO changes, the change of solution colour (from bright yellow to colourless) can also be observed under a 365-nm UV lamp. Furthermore, the method represents high selectivity for NO and shows a fast (within 5 min) and specific fluorescence response toward NO with a linear range from 0.25 to 2.0 μM; the strategy has a limit of detection (LOD) of  0.15 μM. More importantly, the probe was successfully used to detect NO in cell lysate. The recovery was between 98.5 and 103.6%, and the relative standard deviation was between 0.4 and 1.8%. The endogenous NO in cells was successfully detected under the stimulation of L-arginine, which proved the possibility of the probe in real-time and rapid sensing in actual samples and cells. The results indicate that this sensing strategy has the potential to detect NO in the internal environment. Schematic of fluorescence detection of NO.

A study of structure-activity relationship and anion-controlled quinolinyl Ag(I) complexes as antimicrobial and antioxidant agents as well as their interaction with macromolecules

In this communication, we feature the synthesis and in-depth characterization of a series of silver(I) complexes obtained from the complexation of quinolin-4-yl Schiff base ligands ((E)-2-((quinolin-4-ylmethylene)amino)phenol L_a, 2-(quinolin-4-yl)benzo[d]thiazole L_b, (E)-N-(2-fluorophenyl)-1-(quinolin-4-yl)methanimine L_c, (E)-N-(4-chlorophenyl)-1-(quinolin-4-yl)methanimine L_d, (E)-1-(quinolin-4-yl)-N-(p-tolyl)methanimine L_e, (E)-1-(quinolin-4-yl)-N-(thiophen-2-ylmethyl)methanimine L_f) and three different silver(I) anions (nitrate, perchlorate and triflate). Structurally, the complexes adopted different coordination geometries, which included distorted linear or distorted tetrahedral geometry. The complexes were evaluated in vitro for their potential antibacterial and antioxidant activities. In addition, their interactions with calf thymus-DNA (CT-DNA) and bovine serum albumin (BSA) were evaluated. All the complexes had a wide spectrum of effective antibacterial activity against gram-positive and gram-negative bacterial and good antioxidant properties. The interactions of the complexes with CT-DNA and BSA were observed to occur either through intercalation or through a minor groove binder, while the interaction of the complexes with BSA reveals that some of the complexes can strongly quench the fluorescence of BSA through the static mechanism. The molecular docking studies of the complexes were also done to further elucidate the modes of interaction with CT-DNA and BSA.

Investigation of the interactions between three flavonoids and human serum albumin by isothermal titration calorimetry, spectroscopy, and molecular docking

The interactions between three flavonoids (liquiritin, quercitrin, and taxifolin) and human serum albumin (HSA) are investigated by spectroscopic techniques, isothermal titration calorimetry (ITC), and molecular docking study. Results show that...

Preparation of β-lactoglobulin/gum arabic complex nanoparticles for encapsulation and controlled release of EGCG in simulated gastrointestinal digestion model

In this work, the β-lactoglobulin/gum arabic (β-Lg-GA) complexes were prepared to encapsulate epigallocatechin gallate (EGCG), forming β-Lg-GA-EGCG complex nanoparticles with an average particle size of 133 nm. The β-Lg-GA complexes exhibited excellent encapsulation efficiency (84.5%), and the antioxidant performance of EGCG in vitro was improved after encapsulation. It was recorded that 86% of EGCG could be released in simulated intestinal fluid after 3 h of digestion, much faster than that in simulated gastric fluid, indicating that the β-Lg-GA complexes were effective in enhancing EGCG stability, which was confirmed using SDS-PAGE and SEM. Further spectrum results demonstrated that various intramolecular interactions including electrostatic, hydrophobic and hydrogen bonding interactions contribute to the formation of β-Lg-GA-EGCG complex nanoparticles. Also, XRDexperiments indicated that EGCG was successfully encapsulated by β-Lg-GA complexes. Therefore, the β-Lg-GA complexes hold great potentials in the protective delivery of sensitive bioactives.

Study on the binding mechanism of thiamethoxam with three model proteins:spectroscopic studies and theoretical simulations

As a top-selling neonicotinoid insecticide widely used in the field, thiamethoxam is an environmental pollutant because of the accumulation in ecosystem and has also been reported that it has potential risks to the health of mammals even humans. In order to understand the binding mechanism of thiamethoxam with biological receptors, spectroscopic techniques and theoretical simulations was used to explore the specific interactions between thiamethoxam and proteins. Interestingly, the results indicated that hydrophobic interaction as the main driving force, thiamethoxam formed a single binding site complex with proteins spontaneously, resulting in a decrease in the esterase-like activity of human serum albumin. The results of computer simulation showed that there were hydrophobic, electrostatic and hydrogen bonding interactions between thiamethoxam and receptors. The results of experiment and computer simulation were mutually confirmed, so a model was established for the interaction between the two which uncovered the structural characteristics of the binding site. This research provided new insights for the structure optimization of thiamethoxam, as well as gave an effective reference for evaluating the risk of thiamethoxam systemically in the future.

Biophysical study of phloretin with human serum albumin in liposomes using spectroscopic methods

The ability of drugs to diffuse through the lipid bilayer of cell membranes is important for their metabolism, distribution, and efficacy. In this study, the interaction between phloretin and human serum albumin (HSA) in an L-egg lecithin phosphatidylcholine (PC) liposome suspension was investigated by fluorescence and absorbance spectroscopy. The spectroscopic and fluorescence quenching experiments show that phloretin molecules penetrated into the lumen of the liposome. The partition coefficient of phloretin in the PC liposome suspensions was calculated from fluorescence quenching measurements. The results show that phloretin efficiently quenches the intrinsic fluorescence of HSA through a combination of dynamic and static quenching. The values of Gibbs free energy, and the enthalpy and entropic change in the binding process of phloretin with HSA in the PC liposome suspensions were negative, suggesting that the binding process of phloretin and HSA was spontaneous. Hydrogen bonding and van der Waals force interactions play an important role in the interaction between the two molecules. In addition, binding of phloretin to HSA in liposome suspensions was investigated by synchronous fluorescence spectroscopy.

Insights into the binding interaction of substrate with catechol 2,3-dioxygenase from biophysics point of view

This study aims to clarify the interaction mechanism of substrate with catechol 2,3-dioxygenase (C23O) through multi-technique combination. A novel C23O (named C23O-2G) was cloned, heterogeneously expressed, and identified as a new member in subfamily I.2 of extradiol dioxygenases. Based on the simulations of molecular docking and dynamics, the exact binding sites of catechol on C23O-2G were identified, and the catalytic mechanism mediated by key residues was proposed. The roles of the predicted residues during catalysis were confirmed by site-directed mutagenesis, and the mutation of Thr254 could significantly increase catalytic efficiency and substrate specificity of C23O-2G. The binding and thermodynamic parameters obtained from fluorescence spectra suggested that catechol could effectively quench the intrinsic fluorescence of C23O-2G via static and dynamic quenching mechanisms and spontaneously formed C23O-2G/catechol complex by the binding forces of hydrogen bond and van der Waals force. The results of UV-vis spectra, synchronous fluorescence, and CD spectra revealed obvious changes in the microenvironment and conformation of C23O-2G, especially for the secondary structure. The atomic force microscope images further demonstrated the changes from an appearance point of view. This study could improve our mechanistic understanding of representative dioxygenases involved in aromatic compound degradation.

Understanding the structure and conformation of bovine hemoglobin in presence of the drug hydroxyurea: multi-spectroscopic studies supported by docking and molecular dynamics simulation

Binding interaction between the small antitumor drug Hydroxyurea (HU) and Bovine Hemoglobin (BHb) has been explored in details from multi-spectroscopic and computational studies. The formation of ground state complex between BHb and HU has been suggested from the electronic UV-Vis and steady-state fluorescence spectroscopic studies. The quenching in fluorescence of BHb in presence of HU at varied concentrations has been analyzed from the SV plots. Static type of quenching has been suggested from time-resolved fluorescence spectroscopic studies. Binding parameters associated with the BHb-HU complex have also been estimated from the temperature dependent fluorescence spectroscopic studies. Alterations in the micro-environment of the Tyr and Trp residues of BHb in presence of HU have been observed from the synchronous fluorescence measurement. The result obtained from CD spectroscopic measurements signify partial unfolding in the secondary structure of BHb due to binding with HU molecule. The experimental observations are supported by theoretical studies. Molecular docking and molecular dynamics simulations have been performed to investigate the structural stability and compactness of BHb in the binding interaction between BHb and HU. The interaction of BHb with HU is expected to provide fundamental insights towards understanding the therapeutic effectiveness of HU upon interaction with BHb used in chemo-, radio therpeutic procedures and also in the treatment of SCD.

Influence of pH on interaction of silver nanoparticles - protein: Analyses by spectroscopic and thermodynamic ideology

To investigate the interaction between bovine serum albumin (BSA) and silver nanoparticles (AgNPs) at five different pHs (below (3.0 and 4.0), above (7.4 and 9.2) and at the isoelectric point (4.7) of BSA) by spectroscopic (viz., UV-vis, fluorescence, circular dichroism (CD)), microscopic (viz., atomic force microscopy (AFM), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM)) and thermodynamic (viz., isothermal titration calorimetry (ITC)) methods. The fluorescence quenching spectra provided binding constants via Stern-Volmer plot, quenching constant (K_sv) and rate constant (K_q) were calculated. From the CD spectra, it is clear that the α-helix decreases by increasing the AgNP's concentration. However, at isoelectric point (pH = 4.7), BSA shows more helicity in the presence of AgNPs, which indicates that the structures of BSA become more ordered and stable, and aggregation occurs at strong acidic (3.0), and basic medium (9.2) Fluorescence spectra also indicate the aggregation of the protein at strong acidic (pH = 3.0) and basic medium (pH = 9.2). Furthermore, the morphological and topographical evolute ion upon the interaction was examined using TEM, FESEM, and AFM. The studies conclude the effect of the pH in the medium and behavior of AgNPs with BSA by using different spectroscopic and microscopic techniques.

Novel anticancer PdII complexes: The effect of the conjugation of transferrin binding peptide and the nature of halogen coordinated on antitumor activity

A series of Pd^II complexes with bis-(2-pyridylmethyl)glycine as a ligand of formula [PdX(bis-(2-pyridylmethyl)glycine)] where X = Cl, Br, I were prepared and the effect of the halogen nature in the antitumor activity of eight tumorigenic and one non-tumorigenic cell line was evaluated. The chloride derivative was further functionalized with a transferrin receptor binding peptide, generating the first Pd^II based metallopeptide. Its antitumor activity was also evaluated. However, among all the complexes, the chloride and iodine parent compounds showed the lowest GI₅₀ values in the panel evaluated, and lowest GI₅₀ than cisplatin in several cell lines. In contrast, the bromine derivative showed higher values of GI₅₀ than chloride and iodine (around 30 - 50 μM). The same trend was observed for the bovine serum albumin binding constant with higher values for iodine, chlorine, and bromine in this order. In aqueous solution, the chloride is exchanged by water while the bromine and iodine are not. DNA was evaluated as a target and showed no significative interaction for all the compounds. The results suggest sulfur-rich proteins and not DNA as a target. This report represents the first Pd^II metallopeptide reported, its evaluation in solution and antitumor activity. This work opens the possibilities for further functionalization of Pd^II complexes and the importance of the halogen coordination in the design of novel metallodrugs.

Determination of vertical ionization potential of nitroso-benzoimidazothiazole using charge transfer interaction with a series of acceptors

This is the first report of UV-Vis spectral investigations of electron donor-acceptor complexes of bio active 3-Nitroso-2-phenylbenzo[d]imidazo[2,1-b]thiazole (BIT1) with chloranils, nitrobenzenes and fullerenes in DMSO medium. Well defined charge transfer (CT) absorption bands in the visible region have been sited. Oscillator strengths, transition dipole and resonance energies of the CT complexes have been estimated. Utilizing Mulliken's equation vertical ionization potential of BIT1 has been determined. A possible mechanism for the interaction between electronic subsystems of chloranils, nitrobenzenes, [60]- and [70] fullerenes with this benzoimidazothiazole compound (BIT1) have been discussed in comparing the parameters like degree of charge transfer and binding constant in polar DMSO. ¹H NMR study helps to explain the mechanism well. Comparison of complexes is done with DFT/PW1PW91/6-31G* optimized gas phase geometries and FMO features of adducts.

Interactions between tetrahydroisoindoline-1,3-dione derivatives and human serum albumin via multiple spectroscopy techniques

Some tetrahydroisoindoline-1,3-dione derivatives (TDDs) possess potent herbicidal activity. To assess possible impacts of TDDs on humans, the interactions between TDDs and human serum albumin (HSA) were evaluated with steady-state and time-resolved fluorescence spectroscopy, synchronous fluorescence spectroscopy, Fourier transform-infrared spectroscopy, and circular dichroism spectroscopy. The thermodynamic data obtained at temperatures of 298, 307, and 316 K indicate that TDDs spontaneously bind to HSA and thus form a TDD-HSA complex. The conformation and secondary structure of HSA are changed, and the intrinsic fluorescence of HSA is statically quenched by TDDs. Moreover, the TDD-HSA complex is formed primarily through electrostatic interactions and has only one binding site on HSA. A competitive ligand-binding assay revealed that site II (subdomain IIIA) displays the greatest affinity for TDDs. In addition, an acute toxicity bioassay showed no zebrafish mortality upon exposure to 4000 μg L^-1 of TDDs. This work is helpful for understanding interactions between TDDs and HSA.

EPR studies of intermolecular interactions and competitive binding of drugs in a drug-BSA binding model

Understanding intermolecular interactions between drugs and proteins is very important in drug delivery studies. Here, we studied different binding interactions between salicylic acid and bovine serum albumin (BSA) using electron paramagnetic resonance (EPR) spectroscopy. Salicylic acid was labeled with a stable radical (spin label) in order to monitor its mobilized (free) or immobilized (bound to BSA) states. In addition to spin labeled salicylic acid (SL-salicylic acid), its derivatives including SL-benzoic acid, SL-phenol, SL-benzene, SL-cyclohexane and SL-hexane were synthesized to reveal the effects of various drug binding interactions. EPR results of these SL-molecules showed that hydrophobic interaction is the main driving force. Whereas each of the two functional groups (-COOH and -OH) on the benzene ring has a minute but detectable effect on the drug-protein complex formation. In order to investigate the effect of electrostatic interaction on drug binding, cationic BSA (cBSA) was synthesized, altering the negative net charge of BSA to positive. The salicylic acid loading capacity of cBSA is significantly higher compared to that of BSA, indicating the importance of electrostatic interaction in drug binding. Moreover, the competitive binding properties of salicylic acid, ibuprofen and aspirin to BSA were studied. The combined EPR results of SL-salicylic acid/ibuprofen and SL-ibuprofen/salicylic acid showed that ibuprofen is able to replace up to ∼83% of bound SL-salicylic acid, and salicylic acid can replace only ∼14% of the bound SL-ibuprofen. This indicates that ∼97% of all salicylic acid and ibuprofen binding sites are shared. On the other hand, aspirin replaces only ∼23% of bound SL-salicylic acid, and salicylic acid replaces ∼50% of bound SL-aspirin, indicating that ∼73% of all salicylic acid and aspirin binding sites are shared. These results show that EPR spectroscopy in combination with the spin labeling technique is a very powerful method to investigate drug binding dynamics in detail.

Evaluation by fluorescence, STD-NMR, docking and semi-empirical calculations of the o-NBA photo-acid interaction with BSA

Serum albumins present reversible pH dependent conformational transitions. A sudden laser induced pH-jump is a methodology that can provide new insights on localized protein (un)folding processes that occur within the nanosecond to microsecond time scale. To generate the fast pH jump needed to fast-trigger a protein conformational event, a photo-triggered acid generator as o-nitrobenzaldehyde (o-NBA) can be conveniently used. In order to detect potential specific or nonspecific interactions between o-NBA and BSA, we have performed ligand-binding studies using fluorescence spectroscopy, saturation transfer difference (STD) NMR, molecular docking and semi-empirical calculations. Fluorescence quenching indicates the formation of a non-fluorescent complex in the ground-state between the fluorophore and the quencher, but o-NBA does not bind much effectively to the protein (Ka~4.34×10(3)M(-1)) and thus can be considered a relatively weak binder. The corresponding thermodynamic parameters: ΔG°, ΔS° and ΔH° showed that the binding process is spontaneous and entropy driven. Results of (1)H STD-NMR confirm that the photo-acid and BSA interact, and the relative intensities of the signals in the STD spectra show that all o-NBA protons are equally involved in the binding process, which should correspond to a nonspecific interaction. Molecular docking and semi-empirical calculations suggest that the o-NBA binds preferentially to the Trp-212-containing site of BSA (FA7), interacting via hydrogen bonds with Arg-217 and Tyr-149 residues.

Spectroscopic studies and molecular docking on the interaction of organotin antitumor compound bis[2,4-difluoro-N-(hydroxy-⟨κ⟩O)benzamidato-⟨κ⟩O]diphenyltin(IV) with human cytochrome P450 3A4 protease

A novel organotin DFDPT was synthesized and characterized by elemental analysis, IR, (1)H, (13)C, (119)Sn, NMR techniques,etc. In order to investigate profoundly the relationship between DFDPT with human CYP3A4 proteaset and anticancer molecular mechanism of DFDPT, the intercalative mode of binding of DFDPT with CYP3A4 under physiological conditions were comprehensively evaluated using steady state, synchronous, three-dimensional fluorescence spectroscopy,circular dichroism and molecular docking. Fluorescence emission data showed that CYP3A4 fluorescence affected by DFDPT was a static quenching procedure, which implied that DFDPT-CYP3A4 complex had been formed. Apparent binding constants Kb of CYP3A4 with compound at 298 and 310K were 2.51×10(7) and 3.09×10(5), respectively. The binding sites number n was 1.64 and 1.22, respectively. The thermodynamic parameters ΔH and ΔS of the DFDPT-CYP3A4 complex were negative, which indicated that their interaction was driven mainly by hydrogen bonding and van der Waals force. The binding of DFDPT-CYP3A4 was spontaneous process in which ΔG was negative. The synchronous results showed DFDPT induced conformational changes of CYP3A4 protein. Three-dimensional fluorescence and circular dichroism spectra results also revealed conformation of CYP3A4 protein had been possible changed in the presence of DFDPT. Molecular docking was used to study the interaction orientation between DFDPT and CYP3A4 protease. The results indicated that DFDPT interacted with a panel of amino acids in the active sites of CYP3A4 protein mainly through formation of hydrogen bond. Furthermore, the predicted binding mode of DFDPT into CYP3A4 appeared to adopt an orientation with interactions among Arg105, Ser119 and Thr309.

Spectroscopic and molecular modeling methods to study the interaction between naphthalimide-polyamine conjugates and DNA

The effect of polyamine side chains on the interaction between naphthalimide-polyamine conjugates (1-7) and herring sperm DNA was studied by UV/vis absorption and fluorescent spectra under physiological conditions (pH=7.4). The diverse spectral data and further molecular docking simulation in silico indicated that the aromatic moiety of these compounds could intercalate into the DNA base pairs while the polyamine motif might simultaneously locate in the minor groove. The triamine compound 7 can interact more potently with DNA than the corresponding diamine compounds (1-6). The presence of the bulky terminal group in the diamine side chain reduced the binding strength of compound 1 with DNA, compared to other diamine compounds (2-6). In addition, the increasing methylene number in the diamine backbone generally results in the elevated binding constant of compounds-DNA complex. The fluorescent tests at different temperature revealed that the quenching mechanism was a static type. The binding constant and thermodynamic parameter showed that the binding strength and the type of interaction force, associated with the side chains, were mainly hydrogen bonding and hydrophobic force. And the calculated free binding energies of molecular docking are generally consistent with the stability of polyamine-DNA complexes. The circular dichroism assay about the impact of compounds 1-7 on DNA conformation testified the B to A-like conformational change.

Study on the interaction of antiviral drug 'Tenofovir' with human serum albumin by spectral and molecular modeling methods

This study was designed to examine the interaction of Tenofovir (Ten) with human serum albumin (HSA) under physiological conditions. The binding of drugs with human serum albumin is a crucial factor influencing the distribution and bioactivity of drugs in the body. To understand the action mechanisms between Ten and HSA, the binding of Ten with HSA was investigated by a combined experimental and computational approach. UV-vis results confirmed that Ten interacted with HSA to form a ground-state complex and values of the Stern-Volmer quenching constant indicate the presence of a static component in the quenching mechanism. As indicated by the thermodynamic parameters (positive ΔH and ΔS values), hydrophobic interaction plays a major role in the Ten-HSA complex. Through the site marker competitive experiment, Ten was confirmed to be located in site I of HSA. Furthermore, UV-vis absorption spectra, synchronous fluorescence spectrum and CD data were used to investigate the structural change of HSA molecules with addition of Ten, the results indicate that the secondary structure of HSA molecules was changed in the presence of Ten. The experimental results were in agreement with the results obtained via molecular docking study.

Investigation on interaction between Ligupurpuroside A and pepsin by spectroscopic and docking methods

Ligupurpuroside A is one of the major glycoside in Ku-Din-Cha, a type of Chinese functional tea. In order to better understand its digestion and metabolism in humans, the interaction between Ligupurpuroside A and pepsin has been investigated by fluorescence spectra, UV-vis absorption spectra and synchronous fluorescence spectra along with molecular docking method. The fluorescence experiments indicate that Ligupurpuroside A can effectively quench the intrinsic fluorescence of pepsin through a combined quenching way at the low concentration of Ligupurpuroside A, and a static quenching procedure at the high concentration. The binding constant, binding sites of Ligupurpuroside A with pepsin have been calculated. The thermodynamic analysis suggests that non-covalent reactions, including electrostatic force, hydrophobic interaction and hydrogen bond are the main forces stabilizing the complex. According to the Förster's non-radiation energy transfer theory, the binding distance between pepsin and Ligupurpuroside A was calculated to be 3.15 nm, which implies that energy transfer occurs between pepsin and Ligupurpuroside A. Conformation change of pepsin was observed from UV-vis absorption spectra and synchronous fluorescence spectra under experimental conditions. In addition, all these experimental results have been validated by the protein-ligand docking studies which show that Ligupurpuroside A is located in the cleft between the domains of pepsin.

Spectroscopic study on the interaction between naphthalimide-polyamine conjugates and DNA

The interaction of naphthalimide-polyamine conjugates with herring sperm DNA was studied by UV/vis absorption and fluorescent spectra under physiological conditions (pH=7.4). The observed spectral quenching of compounds by DNA and the displacement of EB from DNA-EB complex by compounds indicated that these naphthalimide-polyamine conjugates could intercalate into the DNA base pairs. The UV test also showed that these compounds caused the conformational alteration of DNA. Further caloric fluorescent tests revealed that the quenching mechanism was a static type, which Ksv of 1-DNA, 2-DNA and 1-DNA-EB, 2-DNA-EB 3-DNA-EB was 1.208×10(4), 7.792×10(3) and 1.712×10(4), 1.287×10(4), 2.874×10(4), respectively, at room temperature. The obtained quenching constant, binding constant and thermodynamic parameters suggested that binding strength was associated with substituted groups on naphthalene backbone, and the type of interaction force included mainly hydrogen bonding and weak van der Waals. The binding process was mainly driven by hydrogen bond and van der Waals. Additionally, the effect of NaCl on compounds-DNA interaction provided further evidence that their interaction modes were dependent on substituted groups.

Investigation on the interaction between endocrine disruptor triphenyltin with human serum albumin

The interaction between triphenyltin (TPT) and human serum albumin (HSA) in physiological buffer (pH=7.4) was investigated by the fluorescence quenching technique. The results of fluorescence titration revealed that TPT could strongly quench the intrinsic fluorescence of HSA through a static quenching procedure. The apparent binding constants K and number of binding sites n of TPT with HSA were 2.51×10(3) and 0.96 at 298 K which were obtained by the fluorescence quenching method. The thermodynamic parameters enthalpy change (ΔH), entropy change (ΔS) were positive, which indicated that the interaction of TPT with HSA was driven mainly by hydrophobic forces. The process of binding was a spontaneous process in which Gibbs free energy change was negative. The distance r between donor (HSA) and acceptor (TPT) was calculated to be 3.13 nm based on Forster's non-radiative energy transfer theory. The results of synchronous fluorescence, three-dimensional fluorescence and circular dichroism (CD) spectra showed that the triphenyltin induced conformational changes of HSA.

Studies on the interaction between triphenyltin and bovine serum albumin by fluorescence and CD spectroscopy

The interaction between triphenyltin (TPT) and bovine serum albumin (BSA) in physiological buffer (pH=7.4) was investigated by the fluorescence quenching technique. The results of fluorescence titration revealed that TPT could strongly quench the intrinsic fluorescence of BSA through a static quenching procedure. The apparent binding constants K and number of binding sites n of TPT with BSA were (7.04±0.0057)×10(2) and (0.77±0.016) which were obtained by the fluorescence quenching method. The thermodynamic parameters enthalpy change (ΔH), entropy change (ΔS) were positive, which indicated that the interaction of TPT with BSA was driven mainly by hydrophobic forces. The process of binding was a spontaneous process in which Gibbs free energy change was negative. The distance r between donor (BSA) and acceptor (TPT) was calculated to be 3.05nm based on Forster's non-radiative energy transfer theory. The results of synchronous fluorescence, three-dimensional fluorescence and Circular Dichroism (CD) spectra showed that the triphenyltin induced conformational changes of BSA.

Synthesis, luminescence properties of Eu(III) and Tb(III) complexes with a novel aromatic carboxylic acid and their interactions with bovine serum albumin

A novel aromatic carboxylic acid ligand (L) was synthesized and its corresponding Eu(III) and Tb(III) complexes, Na(3)EuLCl(3)·2H(2)O (EuL) and Na(3)TbLCl(3)·3H(2)O (TbL), were successfully prepared. L and its corresponding complexes were characterized by means of MS, elemental analysis, IR, (1)H NMR and TG. The luminescence spectra of Eu(III) and Tb(III) complexes were investigated and the results showed that L was an efficient sensitizer for Eu(III) and Tb(III) luminescence. The interactions of L, EuL and TbL with bovine serum albumin (BSA) have been investigated through fluorescence spectroscopy under physiological conditions. The Stern-Volmer analysis indicated that the fluorescence quenching of BSA by L, EuL and TbL was resulted from static mechanism, and the binding constants (K(a)) were 2.22×10(4), 1.33×10(5) and 4.27×10(5) at 300 K, respectively. The binding sites (n) and the corresponding thermodynamic parameters ΔH, ΔS, and ΔG were calculated at different temperatures. According to the theoretical and experimental results, van der Waals interactions and hydrogen bonds were found to play major roles in the binding reaction. Furthermore, UV-Vis absorption spectroscopy and synchronous fluorescence spectra indicated that the conformation of BSA was changed. The results obtained in the work can help understand the action mode between L and its corresponding Eu(III) and Tb(III) complexes with BSA, and they are also expected to provide important information of designs of new inspired drugs based on Eu and Tb.

Interaction of pyrrolizine derivatives with bovine serum albumin by fluorescence and UV-Vis spectroscopy

The interaction between pyrrolizine derivatives (PD) and bovine serum albumin (BSA) under imitated physiological conditions was analyzed by fluorescence and ultraviolet spectra. The experiments were conducted at three different temperatures (302, 306 and 310 K) and the results showed that PD caused the fluorescence quenching of BSA through a combined quenching procedure. The binding constant (K(a)), binding-site number (n) between PD and BSA at different temperatures were obtained. According to Förster non-radiation energy transfer theory, the binding distance (r) between BSA and PD was calculated. The corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) were also obtained. The comparison of binding potency of PD and BSA suggested that the substituent on the benzene ring could enhance the binding affinity of PD and BSA. Finally, we investigated the possible sub-domain on BSA where bind PD by displacement experiments.