Interaction of different chloro-substituted phenylurea herbicides (diuron and chlortoluron) with bovine serum albumin: Insights from multispectral study

In this work, the interaction between different chloro-substituted phenylurea herbicides (diuron (DIU) and chlortoluron (CHL)) and BSA were investigated and compared at three different temperatures (283 K, 298 K and 310 K) adopting UV-vis, fluorescence, and circular dichroism spectra. The quenching mechanism of the interaction was also proposed. The energy transfer between BSA and DIU/CHL was investigated. The binding sites of DIU/CHL and BSA and the variations in the microenvironment of amino acid residues were studied. The changes of the secondary structure of BSA were analyzed. The results indicate that both DIU and CHL can significantly interact with BSA, and the degree of the interaction between DIU/CHL and BSA increases with the increase of the DIU/CHL concentration. The fluorescence quenching of BSA by DIU/CHL results from the combination of static and dynamic quenching. The DIU/CHL has a weak to moderate binding affinity for BSA, and the binding stoichiometry is 1:1. Their binding processes are spontaneous, and hydrophobic interaction, hydrogen bonds and van der Waals forces are the main interaction forces. DIU/CHL has higher affinity for subdomain IIA (Site I) of BSA than subdomain IIIA (Site II), and also interacts with tryptophan more than tyrosine residues. The energy transfer can occur from BSA to DIU/CHL. By comparison, the strength of the interaction of DIU-BSA is always greater than that of CHL-BSA, and DIU can destroy the secondary structure of BSA molecules greater than CHL and thus the potential toxicity of DIU is higher due to DIU with more chlorine substituents than CHL. It is expected that this study on the interaction can offer in-depth insights into the toxicity of phenylurea herbicides, as well as their impact on human and animal health at the molecular level.

Elucidation of binding mechanisms of bovine serum albumin and 1-alkylsulfonates with different hydrophobic chain lengths

In this article, the binding interactions between bovine serum albumin (BSA) and three 1-alkylsulfonates, namely sodium 1-dodecanesulfonate, sodium 1-decanesulfonate, and sodium 1-octanesulfonate, have been thoroughly investigated. The study employed various experimental techniques such as isothermal titration calorimetry (ITC), steady-state fluorescence spectroscopy (SF), circular dichroism spectroscopy (CD), and molecular dynamics-based simulations. The objective was to understand the influence of the alkyl chain length of the investigated ligands on several aspects, including the strength of the interaction, the stoichiometry of the resulting complexes, the number of BSA binding sites, and the underlying mechanisms of binding. Notably, the study also demonstrated that sodium dodecyl sulfate (S12S) can serve as an effective site marker for BSA when studying ligands with similar structural and topological features. These findings may have significant implications for enhancing our understanding of the interactions between small amphiphilic molecules and proteins.

Distinguishing the responsive mechanisms of fluorescent probes to hydrogen peroxide, proteins, and DNA/RNA

The responsive mechanisms of cationic quinolinium-vinyl-N,N-dimethylaniline boronate (QVD-B) derivative probes to hydrogen peroxide (H2O2), proteins and DNA/RNA are theoretically investigated in this study. The potential energy curves of QVD-B scanned on a dihedral angle (N+-C-CC) in the first singlet (S1) state exhibit large torsional energy barriers. Additionally, the energy of the lowest unoccupied molecular orbital (LUMO) of an acceptor moiety (-3.14 eV) is lower than that of a donor moiety (-1.13 eV) in QVD-B. This demonstrates that photoinduced electron transfer (PET) quenches the fluorescence of QVD-B, as opposed to the previous report of intramolecular single-bond rotation. After reacting with H2O2, the reaction product of quinoline-vinyl-N,N-dimethylaniline (QVD) turns off the PET pathway and turns on the fluorescence at 550 nm, which is consistent with the experimental results (580 nm). Among the possible configurations of QVD-B that forms with proteins and DNA, the calculated fluorescence values of corresponding twisted QVD-B-P (638 nm) and QVD-B-D (686 nm) are consistent with the experimental results (632 and 688 nm). The frontier molecular orbital and electron-hole analysis show that the charge transfer distance follows the order of QVD (1.88 Å) < QVD-B-P (4.49 Å) < QVD-B-D (6.39 Å), which induces the fluorescence red-shifts of QVD-B-P and QVD-B-D compared to that of QVD. The multi-detection mechanism of the fluorescent probe QVD-B is attributed to PET progress and different degrees of local charge transfer after photoexcitation.

Comprehending the intermolecular interaction of JAK inhibitor fedratinib with bovine serum albumin (BSA)/human alpha-1-acid glycoprotein (HAG): Multispectral methodologies and molecular simulation

The primary coverage of this paper is to investigate the molecular interaction of JAK2 inhibitor, fedratinib (FED) with BSA/HAG proteins through multispectral approaches and molecular docking as well as MD calculation. Arrival at a conclusion, the endogenous fluorescence of BSA/HAG protein was quenched separately in the form of static and mixed quenching. The FED-BSA and FED-HAG complexes with the stoichiometric ratio of 1:1 were formed in the interaction process. And, The Kb values of these complexes were of 104-105 M-1 and 105-106 M-1, respectively, representing that the FED-HAG complex exhibited a comparatively high affinity compared to the FED-BSA complex. It is confimed that FED inserted into the interface area between subdomain IIA and IIB of BSA (marked as site II') and the bucket-shaped hydrophobic cavity of HAG, respectively, resulting in the slight alteration in the secondary structure of BSA/HAG and the micro-environment round Tyr and Trp residues. The expetimental results also confirmed that van der Waals forces (VDW), hydrogen bonds and hydrophobic interaction played a dominant role in the formation of two stable complexes. The above experimental results were supplemented and verified through molecular docking and MD simulation. Meanwhile, the effects of common ions on affinity were explored. This study could shine a light on evaluating the pharmacological properties of the JAK inhibitor FED, understanding the distribution and operation of the drug in the body, and leading to the development of the creation of novel medication devise.

Comparative assessment of 9-bromo noscapine ionic liquid and noscapine: Synthesis, in-vitro studies plus computational & biophysical evaluation with human hemoglobin

Noscapine is a proficient anticancer drug active against wide variety of tumors including lung cancer. Over time, several noscapine analogues have been assessed to maximize the efficiency of the drug, amongst which 9-bromo noscapine remains one of the most potent analogues till date. In the present work, we have synthesized 9-bromo noscapine ionic liquid [9-Br-Nos]IBr2, an active pharmaceutical ingredient based ionic liquid (API-IL) to address the existing issues of solubility and targeted drug delivery in the parent alkaloid as well as the synthesized analogues. We have devised a novel two-step synthesis route (first-ever ionic to ionic bromination) to obtain the desired [9-Br-Nos]IBr2 which is advantageous to its organic analogue in terms of increased solubility, lesser reaction time and better yield. Furthermore, we have compared 9-bromo noscapine ionic liquid with noscapine based on its binding interaction with human hemoglobin (Hb) studied via computational along with spectroscopic studies, and bioactivity against non-small cell lung cancer. We inferred formation of a complex between [9-Br-Nos]IBr2 and Hb in the stoichiometric ratio of 1:1, similar to noscapine. At 298 K, [9-Br-Nos]IBr2-Hb binding was found to exhibit Kb and ∆G of 36,307 M-1 and -11.5 KJmol-1, respectively, as compared to 159 M-1 and -12.5 KJmol-1 during Noscapine-Hb binding. This indicates a more stronger and viable interaction between [9-Br-Nos]IBr2 and Hb than the parent compound. From computational studies, the observed higher stability of [9-Br-Nos]I and better binding affinity with Hb with a binding energy of -91.75 kcalmol-1 supported the experimental observations. In the same light, novel [9-Br-Nos]IBr2 was found to exhibit an IC50 = 95.02 ± 6.32 μM compared to IC50 = 128.82 ± 2.87 μM for noscapine on A549 (non-small lung cancer) cell line at 48 h. Also, the desired ionic liquid proved to be more cytotoxic inducing a mortality rate of 87 % relative to 66 % evoked by noscapine at concentrations of 200 μM after 72 h.

Molecular recognition of two bioactive coumarin derivatives 7-hydroxycoumarin and 4-methyl-7-hydroxycoumarin by hen egg white lysozyme: Exploring the binding mechanism, thermodynamic parameters and structural changes using multispectroscopic and computational approaches

Multispectroscopic and computational methods of exploring the interaction between a carrier protein and therapeutic compounds provide a preliminary investigation into establishing the efficacy of such compounds. Here, two coumarin derivatives, 7-hydroxycoumarin (7-HC) and 4-methyl-7-hydroxycoumarin (4-Me-7-HC), were selected to carry out numerous biophysical interaction studies with a model carrier protein, hen egg white lysozyme (HEWL). Fluorescence spectroscopy studies conducted between HEWL and 7-HC/4-Me-7-HC revealed the binding constants (K_b) were in the range of 10⁴ M^-1, indicating a moderate nature of binding. The quenching mechanism observed during complexation process was an unusual static quenching due to the effect of temperature on the rate constant. Thermodynamic parameters revealed a positive ΔH and ΔS for HEWL-7-HC/4-Me-7-HC, indicating hydrophobic forces played a dominant role in the interaction process. FRET studies suggested a possible non-radiative energy transfer from the donor (HEWL) to the acceptor (coumarins). Molecular docking studies revealed the interaction of 7-HC/4-Me-7-HC with intrinsic fluorophores, Trp63 and Trp108, Trp108 being an essential residue for binding as proven by molecular dynamic (MD) simulation. MD simulation studies also indicated conformational stability gained by HEWL upon interaction with 7-HC and 4-Me-7-HC. The microenvironment surrounding the Trp residues showed a significant Stoke's shift on carrying out 3-D fluorescence. CD studies revealed a decrease in the alpha helical content of HEWL upon interacting with the ligands. Enzymatic assay conducted for HEWL in the presence of 7-HC/4-Me-7-HC saw an increase in the activity of HEWL, suggesting a change in structural conformation and stability of the protein, altering its activity.Communicated by Ramaswamy H. Sarma.

Half-Sandwich Cyclometalated RhIII Complexes Bearing Thiolate Ligands: Biomolecular Interactions and In Vitro and In Vivo Evaluations

A class of cyclometalated Rh^III complexes [Cp*Rh(ppy)(SR)] bearing thiolate ligands, Cp* = pentamethylcyclopentadienyl, ppy = 2-phenylpyridinate, and R = pyridyl (Spy, 2), pyrimidyl (SpyN, 3), benzimidazolyl (Sbi, 4), and benzothiazolyl (Sbt, 5), were produced and identified by means of spectroscopic methods. The in vitro cytotoxicity of the Rh^III compounds in three different human mortal cancerous cell lines (ovarian, SKOV3; breast, MCF-7; lung, A549) and a normal lung (MRC-5) cell line were evaluated, indicating the selectivity of these cyclometalated Rh^III complexes to cancer cells. Complex 5, selected for in vivo experiment, has shown an effective inhibition of tumor growth in SKOV3 xenograft mouse model relative to control (p-values < 0.05 and < 0.01). Importantly, the outcomes of H&E (hematoxylin and eosin) staining and hematological analysis revealed negligible toxicity of 5 compared to cisplatin on a functioning of the main organs of mouse. Molecular docking, UV-vis, and emission spectroscopies (fluorescence, 3D fluorescence, synchronous) techniques were carried out on 1-5 to peruse the mechanism of the anticancer activities of these complexes. The obtained data help to manifest the binding affinity between the rhodium compounds and calf thymus DNA (CT-DNA) through the interaction by DNA minor groove and moderate binding affinity with bovine serum albumin (BSA), particularly with the cavity in the subdomain IIA. It can be concluded that the Rh-thiolate complexes are highly promising leads for the development of novel effective DNA-targeted anticancer drugs.

Tracking the concentration of Al3+ in the aqueous system up to nanomolar range using modified biopolymer chitosan based fluorophore

The paper reports the development of biopolymer chitosan based fluorophore for selective detection of Al3+ in aqueous streams. Fluorescence sensing based on the change in the photophysical properties of the...

Multi-Targeted Anticancer Activity of Imidazolate Phosphane Gold(I) Compounds by Inhibition of DHFR and TrxR in Breast Cancer Cells

A class of phosphane gold(I) compounds, made of azoles and phosphane ligands, was evaluated for a screening on the regards of Breast Cancer cell panels (BC). The compounds possess N-Au-P or Cl-Au-P bonds around the central metal, and they differ for the presence of aprotic or protic polar groups in the azoles and/or the phosphane moieties to tune their hydrophilicity. Among the six candidates, only the compounds having the P-Au-N environment and not displaying neither the hydroxyl nor carboxyl groups in the ligands were found active. The compounds were screened by MTT tests in SKBR3, A17, and MDA-MB231 cancer cells, and two compounds (namely the 4,5-dicyano-imidazolate-1yl-gold(I)-(triphenylphosphane, 5, and 4,5-dichloro-imidazolate-1yl-gold(I)-triphenylphosphane, 6) were found very cytotoxic, with the most active with an IC₅₀ value of 3.46 μM in MDA-MB231 cells. By performing enzymatic assays in the treated cells lysates, the residual enzymatic activity of dihydrofolate reductase (DHFR) has been measured after cell treatment for 4 or 12 h in comparison with control cells. Upon 12 h of treatment, the activity of DHFR was significantly reduced in both SKBR3 and A17 cells by compounds 5 and 6, but not in human MDA-MB231 cells; interestingly, it was found remarkably high after 4 h of treatment, revealing a time dependence for the DHFR enzymatic assays. The DHFR inhibition data have been compared to those for the thioredoxin reductase (TrxR), the most recognized molecular target for gold compounds. For this latter, similar residual activities (i.e., 37 and 49% for the match of SKBR3 cells and compound 5 or 6, respectively) were found. Binding studies on the regards of ct-DNA (calf-thymus-DNA) and of plasma transporters proteins, such as BSA (bovine serum albumin) and ATF (apo transferrin), were performed. As expected for gold compounds, the data support strong binding to proteins (K_sv values range: 1.51 ÷ 2.46 × 10⁴ M⁻¹) and a weaker interaction with ct-DNA's minor groove (K_sv values range: 1.55 ÷ 6.12 × 10³ M⁻¹).

Targeting the heme protein hemoglobin by (−)-epigallocatechin gallate and the study of polyphenol–protein association using multi-spectroscopic and computational methods

(−)-Epigallocatechin gallate binds to BHb and exhibits anti-glycating as well as antioxidant behaviors towards glycation and photo-oxidation of BHb.

Combination mode of antimalarial drug mefloquine and human serum albumin: Insights from spectroscopic and docking approaches

The interaction between mefloquine (MEF), the antimalarial drug, and human serum albumin (HSA), the main carrier protein in blood circulation, was explored using fluorescence, absorption, and circular dichroism spectroscopic techniques. Quenching of HSA fluorescence with MEF was characterized as static quenching and thus confirmed the complex formation between MEF and HSA. Association constant values for MEF-HSA interaction were found to fall within the range of 3.79-5.73 × 10⁴  M^-1 at various temperatures (288, 298, and 308 K), which revealed moderate binding affinity. Hydrogen bonds and hydrophobic interactions were predicted to connect MEF and HSA together in the MEF-HSA complex, as deduced from the thermodynamic data (ΔS = +133.52 J mol^-1 K^-1 and ΔH = +13.09 kJ mol^-1 ) of the binding reaction and molecular docking analysis. Three-dimensional fluorescence spectral analysis pointed out alterations in the microenvironment around aromatic amino acid (tryptophan and tyrosine) residues of HSA consequent to the addition of MEF. Circular dichroic spectra of HSA in the wavelength ranges of 200-250 and 250-300 nm hinted smaller changes in the protein's secondary and tertiary structures, respectively, induced by MEF binding. Noncovalent conjugation of MEF to HSA bettered protein thermostability. Site marker competitive drug displacement results suggested HSA Sudlow's site I as the MEF binding site, which was also supported by molecular docking analysis.

Unraveling Binding Mechanism of Alzheimer's Drug Rivastigmine Tartrate with Human Transferrin: Molecular Docking and Multi-Spectroscopic Approach towards Neurodegenerative Diseases

Studying drug–protein interactions has gained significant attention lately, and this is because the majority of drugs interact with proteins, thereby altering their structure and, moreover, their functionality. Rivastigmine tartrate (RT) is a drug that is in use for mild to moderate Alzheimer therapy. This study was targeted to characterize the interaction between human transferrin (hTf) and RT by employing spectroscopy, isothermal titration calorimetry (ITC), and molecular docking studies. Experimental results of fluorescence quenching of hTf induced by RT implied the formation of a static complex between hTf and RT. Further elucidation of the observed fluorescence data retorting Stern–Volmer and modified Stern–Volmer resulted in binding constants for hTf–RT complex of the order 10⁴ M⁻¹ over the studied temperatures. Thermodynamic parameters of hTf–RT interaction were elucidated further by employing these obtained binding constant values. It was quite evident from obtained thermodynamic attributes that RT spontaneously binds to hTf with a postulated existence of hydrogen bonding or Van der Waals forces. Further, Circular dichroism spectroscopy (CD) also confirmed RT–hTf complex formation owing to upward movement of CD spectra in the presence of RT. ITC profiles advocated the existence of reaction to be spontaneous. Moreover, molecular docking further revealed that the important residues play a pivotal role in RT–hTf interaction. The findings of this study can be of a significant benefit to the drug-designing industry in this disease-prone era.

Studies on the interaction between HSA and new halogenated metformin derivatives: influence of lipophilic groups in the binding ability

In the type II diabetes mellitus, Metformin hydrochloride is recommended as a common FAD approved drug. Synthesis of novel metformin series has been widely explored, mainly due to its biological importance and to improve their pharmacokinetic profile. Generally, human serum albumin (HSA) is the main protein used to study drug viability in vitro analysis. Thus, the present study reports the synthesis of three new halogenated metformin derivatives (MFCl, MFBr and MFCF₃) and its interaction toward HSA by multiple spectroscopic techniques (UV-Vis, circular dichroism, steady-state, time-resolved and synchronous fluorescence), combined to computational methods (molecular docking and quantum chemical calculation). The interaction between each halogenated metformin derivative and HSA is spontaneous (ΔG°<0), entropically driven (ΔS°>0), moderate (K_a and K_b ≈ 10⁴ M^-1) and occurs preferentially in the subdomain IIA (close to Trp-214 residue). Molecular docking results suggested hydrogen bonding, van der Waals and hydrophobic interactions as the main binding forces. Quantum chemical calculations suggested imino groups as the most intense electrostatic negative potentials, while the positive electrostatic potential is located at the hydrogen atoms on N,N-dimethyl and the phenyl systems which can help the hydrophobic interactions. [Formula: see text]Communicated by Ramaswamy H. Sarma.

Synthesis of (E)-Ethyl-4-(2-(furan-2-ylmethylene)hydrazinyl)benzoate, crystal structure, and studies of its interactions with human serum albumin by spectroscopic fluorescence and molecular docking methods

A novel hydrazone, (E)-Ethyl-4-(2-(furan-2-ylmethylene)hydrazinyl)benzoate (EFHB), has been synthesized and characterized by FT-IR, NMR and Mass spectroscopy, and X-ray diffraction; compound crystallized as translucent light yellow thin plates. EFHB was studied for their binding to human serum albumin (HSA) using the fluorescence quench titration method. Molecular docking was also performed to get a more detailed insight into their interaction with HSA at the binding site. Addition of this hydrazone to HSA produced significant fluorescence quenching and splitting of emission spectra of HSA through static quenching mechanism with binding constants of about 10⁴ M^-1 at 292.15, 298.15, 304.15 and 310.15 K. According to the synchronous fluorescence, tryptophan and tyrosine residues of the protein are most perturbed by the binding process. Thermodynamic parameters ΔG, ΔH, and ΔS were got and the main sort of acting force between EFHB and HSA was studied. Results of molecular docking have shown that EFHB binds to subdomain IIA of HSA mainly by hydrophobic interaction, energy binding are in good agreement with those obtained by fluorescence study (ΔG_the = -7.32 ± 0.09 kcal mol^-1 and ΔG_exp = -6.76 ± 0.03 kcal mol^-1).

Lysozyme-luteolin binding: molecular insights into the complexation process and the inhibitory effects of luteolin towards protein modification

In the proposed work, the complexation of bioactive flavonoid luteolin with hen egg white lysozyme (HEWL) along with its inhibitory influence on HEWL modification has been explored with the help of multi-spectroscopic and computational methods. The binding affinity has been observed to be moderate in nature (in the order of 10⁴ M^-1) and the static quenching mechanism was found to be involved in the fluorescence quenching process. The binding constant (K_b) shows a progressive increase with the increase in temperature from (4.075 ± 0.046 × 10⁴ M^-1) at 293 K to (6.962 ± 0.024 × 10⁴ M^-1) at 313 K under experimental conditions. Spectroscopic measurements along with molecular docking calculations suggest that Trp62 is involved in the binding site of luteolin within the geometry of HEWL. The positive changes in enthalpy (ΔH = +19.99 ± 0.65 kJ mol^-1) as well as entropy (ΔS = +156.28 ± 2.00 J K^-1 mol^-1) are indicative of the presence of hydrophobic forces that stabilize the HEWL-luteolin complex. The micro-environment around the Trp residues showed an increase in hydrophobicity as indicated by synchronous fluorescence (SFS), three dimensional fluorescence (3D) and red edge excitation (REES) studies. The % α-helix of HEWL showed a marked reduction upon binding with luteolin as indicated by circular dichroism (CD) and Fourier-transform infrared spectroscopy (FTIR) studies. Moreover, luteolin is situated at a distance of 4.275 ± 0.004 nm from the binding site as indicated by FRET theory, and the rate of energy transfer k_ET (0.063 ± 0.004 ns^-1) has been observed to be faster than the donor decay rate (1/τ_D = 0.606 ns^-1), which is indicative of the non-radiative energy transfer during complexation. Leaving aside the binding study, luteolin showed promising inhibitory effects towards the d-ribose mediated glycation of HEWL as well as towards HEWL fibrillation as studied by fluorescence emission and imaging studies. Excellent correlation with the experimental observations as well as precise location and dynamics of luteolin within the binding site has been obtained from molecular docking and molecular dynamics simulation studies.

Proton transfer in fluorescent secondary amines: synthesis, photophysics, theoretical calculation and preparation of photoactive phosphatidylcholine-based liposomes

New proton-transfer lipophilic based benzazoles.

In vitro and in vivo antiproliferative activity of organo-nickel SCS-pincer complexes on estrogen responsive MCF7 and MC4L2 breast cancer cells. Effects of amine fragment substitutions on BSA binding and cytotoxicity

A family of organonickel complexes has been prepared, fully characterized, and tested for their antiproliferative activity against estrogen-responsive human breast cancer cells (MCF7). The three SCS-type pincer ligands HL1, HL2, and HL3 and their corresponding Ni(ii) complexes NiL1, NiL2, and NiL3 have been synthesized and fully characterized, including by single crystal diffraction studies for the complexes. The complexes possess square planar geometry with two symmetrical 5-membered nickellacycles. Fluorescence spectroscopy, circular dichroism measurements, molecular modeling, colorimetric based assay and tumor transplantation studies were used to evaluate the protein binding and antiproliferative activities of these organometallic complexes both in vitro and in vivo. Fluorescence quenching was used to investigate bovine serum albumin (BSA) interaction at different temperatures (293, 303 and 313 K), and the results were analyzed using the classical Stern-Volmer equation, allowing us to propose a dynamic quenching mechanism. Studies in vitro on the antiproliferative activity of the three organonickel complexes against estrogen-responsive human breast cancer cells (MCF7) showed promising antitumor activity for NiL1 containing pyrrolidine fragments. In vivo administration of this compound significantly inhibits tumor growth in estrogen-dependent MC4L2 cancer cells in female BALB/c mice.

Nonionic but water soluble, [Glycine-Pd-Alanine] and [Glycine-Pd-Valine] complexes. Their synthesis, characterization, antitumor activities and rich DNA/HSA interaction studies

Two novel, neutral and water soluble Pd(II) complexes of formula [Pd(Gly)(Ala)] (1) and [Pd(Gly)(Val)] (2) (Gly, Ala, and Val are anionic forms of glycine, alanine, and valine amino acids, respectively) have been synthesized and characterized by FT-IR, UV-Vis, ¹H-NMR, elemental analysis, and molar conductivity measurement. The data revealed that each amino acid binds to Pd(II) through the nitrogen of -NH₂ and the oxygen of -COO^- groups and acts as a bidentate chelate. These complexes have been assayed against leukemia cells (K₅₆₂) using MTT method. The results indicated that both of the complexes display more cytotoxicity than the well-known anticancer drug, cisplatin. The interaction of the compounds with calf thymus DNA (CT-DNA) and human serum albumin (HSA) were assayed by a series of experimental techniques including electronic absorption, fluorescence, viscometry, gel electrophoresis, and FT-IR. The results indicated that the two complexes have interesting binding propensities toward CT-DNA as well as HSA and the binding affinity of (1) is more than (2). The fluorescence data indicated that both complexes strongly quench the fluorescence of ethidium bromide-DNA system as well as the intrinsic fluorescence of HSA via static quenching procedures. The thermodynamic parameters (ΔH°, ΔS°, and ΔG°) calculated from the fluorescence studies showed that hydrogen bonds and van der Waals interactions play a major role in the binding of the complexes to DNA and HSA. We suggest that both of the Pd(II) complexes exhibit the groove binding mode with CT-DNA and interact with the main binding pocket of HSA. Communicated by Ramaswamy H. Sarma.

Binding studies of triclocarban with bovine serum albumin: Insights from multi-spectroscopy and molecular modeling methods

The antimicrobial triclocarban (TCC) is frequently found in various personal care products (PCPs), and recent studies have demonstrated that it shows a high unintended biological activity on humans and wildlife. To evaluate the toxicity of TCC at the protein level, the effect of TCC on bovine serum albumin (BSA) has been investigated using various spectroscopic methods in combination with molecular modeling. Analysis of fluorescence quenching data of BSA revealed the formation of a ground state BSA-TCC complex with a binding constant of 2.58 × 10⁴ M^-1 at 298 K. The values of the thermodynamic parameters suggested that the binding of TCC to BSA was driven mainly by hydrophobic interaction and hydrogen bond. Site marker competitive experiments coupled with molecular docking studies confirmed that site I was the main binding site for TCC on BSA. Furthermore, TCC binding to BSA led to conformational and structural alterations of BSA as revealed by multi-spectroscopic studies. In addition, the stability of BSA and BSA-TCC complex were well analyzed by the molecular dynamics studies. In short, this work indicated that TCC could interact with BSA and impact the conformation of BSA, which could provide valuable information to understand the toxicity mechanism of TCC.

Influence of substituents on DNA and protein binding of cyclometalated Ir(iii) complexes and anticancer activity

Synthesis of terpyridyl based ligands 3-([2,2':6',2''-terpyridin]-4'-yl)-7-methoxy-2-(methylthio)-quinolone, (L1); 3-([2,2':6',2''-terpyridin]-4'-yl)-6-methoxyquinolin-2(1H)-one, (L2); 3-([2,2'-:6',2''-terpyridin]-4'-yl)-6-methylquinolin-2(1H)-one (L3) and cyclometalated iridium(iii) complexes [[Ir(ppy)₂L1]⁺PF₆^- (1), [Ir(ppy)₂L2]⁺PF₆^- (2), [Ir(ppy)₂L3]⁺PF₆^- (3) (2-phenylpyridine = Hppy)] involving these ligands has been described. The ligands L1-L3 and complexes 1-3 have been thoroughly characterized by elemental analyses, spectral studies (IR, ¹H, ¹³C NMR, UV/vis and fluorescence) ESI-MS, and the structure of 3 has been unambiguously authenticated by single crystal X-ray analyses. UV/vis, fluorescence and circular dichroism spectroscopic studies showed rather efficient binding of 1 with CT-DNA (calf thymus DNA) and BSA (bovine serum albumin) relative to 2 and 3. Molecular docking studies unveiled binding of 1-3 with minor groove of CT-DNA via van der Waal's forces and electrostatically with the hydrophobic moiety of HSA (human serum albumin). The ligands and complexes exhibited moderate cytotoxicity towards MDA-MB-231 (breast cancer cell line) and significant influence on HeLa (cervical cancer cell line) cells. Cytotoxicity, morphological changes, and apoptosis have been followed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide) assay, Hoechst 33342/PI (PI = propidium iodide) staining, cell cycle analysis by FACS (fluorescence activated cell sorting), and ROS (reactive oxygen species) generation by DCFH-DA (dichlorodihydrofluorescein diacetate) dye. Confocal microscopy images revealed that the drug efficiently initiates apoptosis in the cell cytosol. The IC₅₀ values showed superior cytotoxicity of 1-3 against the HeLa cell line relative to cisplatin, and their ability to induce apoptosis is in the order 1 > 2 > 3.

Molecular interactions of thymol with bovine serum albumin: Spectroscopic and molecular docking studies

Thymol is the main monoterpene phenol present in the essential oils which is used in the food industry as flavoring and preservative agent. In this study, the interaction of thymol with the concentration range of 1 to 6 μM and bovine serum albumin (BSA) at fixed concentration of 1 μM was investigated by fluorescence, UV-vis, and molecular docking methods under physiological-like condition. Fluorescence experiments were performed at 5 different temperatures, and the results showed that the fluorescence quenching of BSA by thymol was because of a static quenching mechanism. The obtained binding parameters, K, were in the order of 10⁴  M^-1 , and the binding number, n, was approximately equal to unity indicating that there is 1 binding site for thymol on BSA. Calculated thermodynamic parameters for enthalpy (ΔH), entropy (ΔS), and Gibb's free energy (ΔG) showed that the reaction was spontaneous and hydrophobic interactions were the main forces in the binding of thymol to BSA. The results of UV-vis spectroscopy and Arrhenius' theory showed the complex formation in the interaction of thymol and BSA. Negligible conformational changes in BSA by thymol were observed in fluorescence experiments, and the same results were also obtained from UV-vis studies. Results of molecular docking indicated that the subdomain IA of BSA was the binding site for thymol.

An azine based sensor for selective detection of Cu2+ ions and its copper complex for sensing of phosphate ions in physiological conditions and in living cells

A simple and cost effective unsymmetrical azine based Schiff base, 5-diethylamino-2-[(2-hydroxy-benzylidene)hydrazonomethyl]-phenol (1) was synthesized which selectively detect Cu²⁺ ions in the presence of other competitive ions through "naked eye" in physiological conditions (EtOH-buffer (1:1, v/v, HEPES 10mM, pH=7.4)). The presence of Cu²⁺ induce color change from light yellow green to yellow with the appearance of a new band at 450nm in UV-Vis spectra of Schiff base 1. The fluorescence of Schiff base 1 (10μM) was quenched completely in the presence of 2.7 equiv. of Cu²⁺ ions. Sub-micromolar limit of detection (LOD=3.4×10^-7M), efficient Stern-Volmer quenching constant (K_SV=1.8×10⁵Lmol^-1) and strong binding constant (log K_b=5.92) has been determined with the help of fluorescence titration profile. Further, 1-Cu²⁺ complex was employed for the detection of phosphate ions (PO₄^3-, HPO₄^2- and H₂PO₄^-) at micromolar concentrations in EtOH-buffer of pH7.4 based on fluorescence recovery due to the binding of Cu²⁺ with phosphate ions. Solubility at low concentration in aqueous medium, longer excitation (406nm) and emission wavelength (537nm), and biocompatibility of Schiff base 1 formulates its use in live cell imaging.

Characterization of the binding of strychnine with bovine β-lactoglobulin and human lysozyme using spectroscopic, kinetic and molecular docking analysis

The binding interaction of a well known alkaloid strychnine (STN) with the mammalian milk protein β-lactoglobulin and human lysozyme has been explored by using several spectroscopic techniques along with computational studies.

Ni(II) Complexes with Schiff Base Ligands: Preparation, Characterization, DNA/Protein Interaction and Cytotoxicity Studies

In this study, two Ni(II) complexes, namely [Ni(HL1)₂(OAc)₂] (1) and [Ni(L2)₂] (2) (where HL1 and HL2 are (E)-1-((1-(2-hydroxyethyl)-1H-pyrazol-5-ylimino)methyl)-naphthalen-2-ol) and (E)-ethyl-5-((2-hydroxynaphthalen-1-yl)methyleneamino)-1-methyl-1H-pyrazole-4-carboxylate, respectively), were synthesized and characterized by X-ray crystallography, Electrospray Ionization Mass Spectrometry (ESI-MS), elemental analysis, and IR. Their uptake in biological macromolecules and cancer cells were preliminarily investigated through electronic absorption (UV-Vis), circular dichroism (CD) and fluorescence quenching measurements. Bovine serum albumin (BSA) interaction experiments were investigated by spectroscopy which showed that the complexes and ligands could quench the intrinsic fluorescence of BSA through an obvious static quenching process. The spectroscopic studies indicated that these complexes could bind to DNA via groove, non-covalent, and electrostatic interactions. Furthermore, in vitro methyl thiazolyl tetrazolium (MTT) assays and Annexin V/PI flow cytometry experiments were performed to assess the antitumor capacity of the complexes against eight cell lines. The results show that both of the complexes possess reasonable cytotoxicities.

Glandular hair constituents of Mallotus philippinensis Muell. fruit act as tyrosinase inhibitors: Insights from enzyme kinetics and simulation study

The glandular hair extracts from the fruit rind of Mallotus philippinensis Muell. is employed to treat various skin infections, however the anti-tyrosinase activity remains unknown. Hence the present study inspected on the anti-melanogenic activity of M. philippinensis constituents. Lineweaver Burk plot revealed mixed inhibition for Rottlerin; non-competitive type of inhibition for mallotophilippen A and B respectively. Thermodynamic studies resulted in static quenching forming ground state complex with higher binding constant temperature dependently. Fluorescence and circular dichroism study implicated conformational change in secondary and tertiary structure of tyrosinase. Molecular docking suggests rottlerin has high binding affinity to the active site pocket of tyrosinase. Simulation study further proved that the compactness of inhibitor with tyrosinase by hydrogen bonding influenced the stability of the enzyme. Depigmentation efficacy is further proved in Aspergillus niger spores. Thus our findings delineate that rottlerin could be utilized as a depigmentation agent in food pharmaceutical and agricultural industries.

Micro-solvation of tyrosine-kinase inhibitor AG1478 explored with fluorescence spectroscopy and computational chemistry

Fluorescence quenching of the anticancer AG1478, by at least three explicit water molecules, can be exploited to probe drug–protein binding interactions.

Interaction of anticancer drug clofarabine with human serum albumin and human α-1 acid glycoprotein. Spectroscopic and molecular docking approach

The binding interaction between clofarabine, an important anticancer drug and two important carrier proteins found abundantly in human plasma, Human Serum Albumin (HSA) and α-1 acid glycoprotein (AAG) was investigated by spectroscopic and molecular modeling methods. The results obtained from fluorescence quenching experiments demonstrated that the fluorescence intensity of HSA and AAG is quenched by clofarabine and the static mode of fluorescence quenching is operative. UV-vis spectroscopy deciphered the formation of ground state complex between anticancer drug and the two studied proteins. Clofarabine was found to bind at 298K with both AAG and HSA with the binding constant of 8.128×10³ and 4.120×10³ for AAG and HSA, respectively. There is stronger interaction of clofarabine with AAG as compared to HSA. The Gibbs free energy change was found to be negative for the interaction of clofarabine with AAG and HSA indicating that the binding process is spontaneous. Binding of clofarabine with HSA and AAG induced ordered structures in both proteins and lead to molecular compaction. Clofarabine binds to HSA near to drug site II. Hydrogen bonding and hydrophobic interactions were the main bonding forces between HSA-clofarabine and AAG-clofarabine as revealed by docking results. This study suggests the importance of binding of anticancer drug to AAG spatially in the diseases like cancers where the plasma concentration of AAG increases many folds. Design of drug dosage can be adjusted accordingly to achieve optimal treatment outcome.

Binding affinities of Schiff base Fe(II) complex with BSA and calf-thymus DNA: Spectroscopic investigations and molecular docking analysis

The binding interaction of a synthesized Schiff base Fe(II) complex with biological macromolecules viz., bovine serum albumin (BSA) and calf thymus(ct)-DNA have been investigated using different spectroscopic techniques coupled with viscosity measurements at physiological pH and 298K. Regular amendments in emission intensities of BSA upon the action of the complex indicate significant interaction between them, and the binding interaction have been characterized by Stern Volmer plots and thermodynamic binding parameters. On the basis of this quenching technique one binding site with binding constant (Kb=(7.6±0.21)×10(5)) between complex and protein have been obtained at 298K. Time-resolved fluorescence studies have also been encountered to understand the mechanism of quenching induced by the complex. Binding affinities of the complex to the fluorophores of BSA namely tryptophan (Trp) and tyrosine (Tyr) have been judged by synchronous fluorescence studies. Secondary structural changes of BSA rooted by the complex has been revealed by CD spectra. On the other hand, hypochromicity of absorption spectra of the complex with the addition of ct-DNA and the gradual reduction in emission intensities of ethidium bromide bound ct-DNA in presence of the complex indicate noticeable interaction between ct-DNA and the complex with the binding constant (4.2±0.11)×10(6)M(-1). Life-time measurements have been studied to determine the relative amplitude of binding of the complex to ct-DNA base pairs. Mode of binding interaction of the complex with ct-DNA has been deciphered by viscosity measurements. CD spectra have also been used to understand the changes in ct-DNA structure upon binding with the metal complex. Density functional theory (DFT) and molecular docking analysis have been employed in highlighting the interactive phenomenon and binding location of the complex with the macromolecules.

Exploring the interaction of l-cysteine capped CuS nanoparticles with bovine serum albumin (BSA): a spectroscopic study

l-Cysteine capped copper sulfide nanoparticles with an average particle size of 6 nm were synthesized using a chemical co-precipitation method and their interactions with bovine serum albumin were explored using various spectroscopic techniques.

Heteroleptic arene Ru(ii) dipyrrinato complexes: DNA, protein binding and anti-cancer activity against the ACHN cancer cell line

The in vitro cytotoxicities of heteroleptic Ru(ii) complexes were studied in ACHN cell lines by MTT assay, DNA cleavage, (AO/EtBr) and FACS analysis.