Molecular recognition of malachite green by hemoglobin and their specific interactions: insights from in silico docking and molecular spectroscopy

Interaction of plant phenol vanillin with human hemoglobin: A spectroscopic and molecular docking study

Vanillin is a phenolic aldehyde widely used as a flavouring agent in the food industry. Vanillin has many health benefits and has gained attention in pharmacological industries also, due to its antioxidant properties and non-toxic nature. The interaction of vanillin with human hemoglobin (hHb), an abundant tetrameric heme protein, was investigated by several spectroscopic techniques and molecular modeling methods. UV-visible spectra showed that the binding of vanillin to hHb induces structural changes due to alterations in the micro-environment of hHb. Vanillin quenches the intrinsic fluorescence of hHb by the dynamic mechanism, which was confirmed by both temperature dependent and time resolved fluorescence studies. Vanillin binds spontaneously to hHb at a single site and the binding is stabilized by hydrogen bonds and hydrophobic interactions. The circular dichroism spectra showed that the binding of vanillin altered the secondary structure of hHb due to change in its alpha-helical content. Molecular docking identified the amino acids of hHb involved in binding to vanillin and also that the free energy change of the binding reaction is -5.5 kcal/mol. Thus, our results indicate that vanillin binds spontaneously to hHb at a single site and alters its secondary structure. This will help in understanding the potential use of vanillin and related antioxidants as therapeutic agents in various hematological disorders.

Interaction between polydopamine-based IONPs and human serum albumin (HSA): a spectroscopic analysis with cytotoxicity impact

Iron oxide nanoparticles (IONPs) have been extensively explored in biomedicine, bio-sensing, hyperthermia, and drug/gene delivery, attributed to their versatile and tunable properties. However, owing to its numerous applications, the functionalization of IONPs with appropriate materials is in demand. To achieve optimal functionalization of IONPs, polydopamine (PDA) was utilized due to its ability to provide a superior functionalized surface, near-infrared light absorption, and adhesive nature to customize desired functionalized IONPs. This notion of involving PDA led to the successful synthesis of magnetite-PDA nanoparticles, where PDA is surface-coated on magnetite (Fe3O4@PDA). The Fe3O4@PDA nanoparticles were characterized using techniques like TEM, FESEM, PXRD, XPS, VSM, and FTIR, suggesting PDA's successful attachment with magnetite crystal structure retention. Human serum albumin (HSA), the predominant protein in blood plasma, interacts with the delivered nanoparticles. Therefore, we have employed various spectroscopic techniques, along with cytotoxicity, to inspect the effect of Fe3O4@PDA NPs on the stability and structure of HSA. The structural alterations were examined using circular dichroism (CD) and synchronous fluorescence spectroscopy (SFS). It has been observed that there are no structural perturbations in the secondary structure of the HSA protein after interaction with Fe3O4@PDA. Studies using steady-state fluorescence revealed that the inherent fluorescence intensities of HSA were suppressed after interaction with Fe3O4@PDA. In addition, temperature-dependent fluorescence measurements suggested that the type of quenching consists of both static and dynamic quenching simultaneously. A cytotoxicity study in Drosophila melanogaster larvae revealed no cytotoxic effects but did show a minor genotoxic effect only at higher concentrations.

Exploring the Structural Importance of the C3=C4 Double Bond in Plant Alkaloids Harmine and Harmaline on Their Binding Interactions with Hemoglobin

Harmine and harmaline are two structurally similar heterocyclic β-carboline plant alkaloids with various therapeutic properties, having a slight structural difference in the C3=C4 double bond. In the present study, we have reported the nature of the interaction between hemoglobin (Hb) with harmine and harmaline by employing several multispectroscopic, calorimetric, and molecular docking approaches. Fluorescence spectroscopic studies have shown stronger interaction of harmine with Hb compared to that of almost structurally similar harmaline. Steady-state anisotropy experiments further show that the motional restriction of harmine in the presence of Hb is substantially higher than that of the harmaline-Hb complex. Circular dichroism (CD) study demonstrates no conformational change of Hb in the presence of both alkaloids, but CD study in 1-cm cuvette path length also demonstrates stronger affinity of harmine toward Hb compared to harmaline. From the thermal melting study, it has been found that both harmine and harmaline slightly affect the stability of Hb. From isothermal titration calorimetry (ITC), we have found that the binding process is exothermic and enthalpy driven. Molecular docking studies indicated that both harmine and harmaline prefer identical binding sites in Hb. This study helps us to understand that slight structural differences in harmine and harmaline can alter the interaction properties significantly, and this key information may help in the drug discovery processes.

Perception of the interaction behavior between pepsin and the antimicrobial drug secnidazole with combined experimental spectroscopy and computer-aided techniques

Drug-pepsin interaction possibly affects pepsin activity, leads to undesirable shift of its functionality, and likely induces adverse effects in the gastrointestinal tract. The present study aims at exploring the interaction of pepsin with the antiprotozoal/antibacterial drug secnidazole adopting a combination of experimental spectroscopy and computational techniques. For this purpose, different spectroscopic methods including fluorescence, synchronous fluorescence, UV-Visible absorption, and infrared spectroscopy were adopted and coordinated with in silico analysis via molecular docking. The employed synchronized approaches evidenced that; pepsin interacted with secnidazole via static mechanism at stomach pH inferring some consequent conformational changes in the structure of pepsin. Thermodynamic study of drug-pepsin interaction demonstrated that the interaction is spontaneous via van der Waals and hydrogen bonding interaction and the orientation of ligand within pepsin cavity was illustrated by molecular docking. The synchronous fluorescence study proved that tyrosine amino acid residues were involved in the interaction more than tryptophan amino acid residues. Eventually, the combined experimental and molecular docking approaches suggest that secnidazole interacts with pepsin and alter its structure, that finding correlates to gastrointestinal side effects related to secnidazole oral administration.

Study on the Interaction Mechanism of Theaflavin with Whey Protein: Multi-Spectroscopy Analysis and Molecular Docking

The interaction mechanism of whey proteins with theaflavin (TF1) in black tea was analyzed using multi-spectroscopy analysis and molecular docking simulations. The influence of TF1 on the structure of bovine serum albumin (BSA), β-lactoglobulin (β-Lg), and α-lactoalbumin (α-La) was examined in this work using the interaction of TF1 with these proteins. Fluorescence and ultraviolet-visible (UV-vis) absorption spectroscopy revealed that TF1 could interact with BSA, β-Lg and α-La through a static quenching mechanism. Furthermore, circular dichroism (CD) experiments revealed that TF1 altered the secondary structure of BSA, β-Lg and α-La. Molecular docking demonstrated that the interaction of TF1 with BSA/β-Lg/α-La was dominated by hydrogen bonding and hydrophobic interaction. The binding energies were -10.1 kcal mol^-1, -8.4 kcal mol^-1 and -10.4 kcal mol^-1, respectively. The results provide a theoretical basis for investigating the mechanism of interaction between tea pigments and protein. Moreover, the findings offered technical support for the future development of functional foods that combine tea active ingredients with milk protein. Future research will focus on the effects of food processing methods and different food systems on the interaction between TF1 and whey protein, as well as the physicochemical stability, functional characteristics, and bioavailability of the complexes in vitro or in vivo.

Insights into the Photodynamics of Fluorescence Emission and Singlet Oxygen Generation of Fluorogen Activating Protein-Malachite Green Systems

The self-assembled fluorogen activating protein (FAP)-malachite green (MG) complex is a well-established protein-ligand system, which can realize binding-caused fluorescence turn-on of MG and singlet oxygen (¹ O₂ ) generation by MG iodination. To clarify the mechanism of fluorescence activation and ¹ O₂ generation, the photodynamics of different halogen-substituted MG derivatives and their corresponding FAP-MG complexes were studied by femtosecond transient absorption spectroscopy and theoretical computations. The results show that the rotation of MG is restricted by FAP binding, which prevents a rapid internal conversion to allow a longer lifetime for the excited MG to undergo fluorescence emission and intersystem crossing. Moreover, these FAP-MG complexes exhibit notably varied fluorescence quantum yields (Φ_FL ) and ¹ O₂ yields. The study on the decay pathways indicates that such an anti-heavy atom effect predominately stems from the lifetimes of the excited-state species. The photodynamic mechanism study here will lead to more advanced FAP-MG systems with high spatiotemporal resolution.

Triphenylmethane dye (C52H54N4O12) is potentially a hazardous substance in edible freshwater fish at trace level: toxicity, hematology, biochemistry, antioxidants, and molecular docking evaluation study

Malachite green (C₅₂H₅₄N₄O₁₂) is a synthetic dye that is used in textile industries as a colorant and in aquaculture sectors to contain microbial damage. Aquatic contamination of malachite green (MG) has been reported globally. Fish is the highest trophic organism among aquatic inhabitants, highly sensitive to waterborne contaminants (metals, coloring agents, etc.). Toxicity of waterborne chemicals on nontarget organisms can be determined by assessing biomarkers. Assessing blood parameters and tissue antioxidants (enzymatic and nonenzymatic) is useful to evaluate MG toxicity. To initiate the MG toxicity data for freshwater fish (Cyprinus carpio), the median lethal toxicity was primarily evaluated. Then, hematological, blood biochemical (glucose, protein, and cholesterol) and tissue biochemical (amino acids, lipids), and vital tissue (gills, liver, and kidney) antioxidant capacity (CAT, LPO, GST, GR, POxy, vitamin C, and GSH) of C. carpio were analyzed under acute (LC_50-96 h) and sublethal (Treatment I-1/10^th and Treatment II-1/5^th LC_50-96 h) exposure periods (28 days). Molecular docking for MG with hemoglobin was also obtained. Biomarkers examined were affected in the MG-treated groups with respect to the control group. Significant changes (p < 0.05) were observed in hematology (Hb, RBCs, and WBCs), glucose, proteins, lipids and tissue CAT, LPO, and GST activities under acute MG exposure. In sublethal treatment groups, biomarkers studied were significant (p < 0.05) throughout the study period. The potential for MG binding to hemoglobin was tested in this study. MG is potentially a multiorgan toxicant. Literally a chemical that is harmful to the aquatic environment if safety is concerned.

Biochemical aspects of hemoglobin-xenobiotic interactions and their implications in drug discovery

Hemoglobin, a homodimeric globular protein, is found predominantly in red blood cells and in a small amount in blood plasma. Along with binding to certain native molecules, it also interacts with various xenobiotics. The present review aims at studying these interactions and the resultant tangible impact on the structure and function of the protein if any. The review also encompasses various analytical and computational approaches which are routinely used to study these interactions. A detailed discussion on types of interaction exhibited by individual xenobiotics has been included herein. Additionally, the effects of xenobiotic binding on the oxygen carrying capacity of hemoglobin have been reviewed. These insights would be of great value in drug design and discovery. Envisaging probable interactions of designed ligands with hemoglobin would help improvise the process of drug development. This would also open up new avenues for studying hemoglobin-mediated drug delivery.

Water-soluble polymeric particle embedded cryogels: Synthesis, characterisation and adsorption of haemoglobin

Making cryogels, which are among today’s accepted adsorbents, more functional with different methods, has been one of the subjects spent overtime. In this study, water-soluble poly(maleic anhydride-alt-acrylic acid) polymer embedded in poly(2-hydroxyethyl methacrylate) cryogels. Copper ions were then immobilised to this structure, and this polymer was used for adsorption of haemoglobin from aqueous systems. Adsorption interaction was carried out on an electrostatic basis, and approximately 448.62 mg haemoglobin/g polymer adsorption capacity value was obtained. It was found that the same material has managed to maintain its adsorption ability by 90.3% even after the use of it five times in the adsorption/desorption cycle. The adsorption interaction was determined to be appropriate for the Langmuir model by isotherm studies. The change in Gibbs free energy value was calculated as −2.168 kJ/mol.

Effect of local anesthetic drug procaine hydrochloride on the conformational stability of bovine hemoglobin: Multi-spectroscopic and computational approaches

The interaction between bovine hemoglobin (BHb) and local anesthetic drug procaine hydrochloride (PCH) was examined by spectroscopic and computational studies. Intrinsic fluorescence analysis explored the ground-state complex formation in the binding of PCH with BHb through static quenching mechanism. The binding constants (K_b) are 29.38 × 10³, 22.54 × 10³ and 17.99 × 10³ M^-1 at 288, 298 and 308 K, respectively, and the ratio of BHb:PCH was 1:1 in the interaction mechanism of PCH and BHb. The acquired thermodynamic parameters (ΔH⁰, ΔG⁰ and ΔS⁰) demonstrated that interaction mechanism is spontaneous and enthalpy driven. The van der Waals forces and hydrogen bonding have been played a predominant role in the binding mechanism. The UV-vis spectroscopy validates the ground-state complexation between PCH and BHb and the binding constant (K_b) has been evaluated utilizing Benesi-Hildebrand equation. Fluorescence resonance energy transfer (FRET) results have demonstrated that the distance between donor (BHb) and acceptor (PCH) is very short (2.34 nm) suggesting a significant probability to energy transfer from BHb to PCH. Synchronous fluorescence results revealed that the alteration in the micro-environment of Tyrosine (Tyr) is more than tryptophan (Trp) residues suggesting that PCH molecule is close to Tyr residue. The secondary structure alterations were confirmed by CD, 3-D fluorescence and FT-IR spectroscopic measurements. Moreover, computational analyses further corroborated that PCH molecules are closer to Tyr residues as compared to Trp residues of BHb during the interaction process. The BHb-PCH complexes may contribute to a deeper understanding of the metabolism of drug, blood circulation process and may help to illustrate the relationship between functions and structure of BHb.Communicated by Ramaswamy H. Sarma.

An insight into the interaction between malachite green oxalate with human serum albumin: Molecular dynamic simulation and spectroscopic approaches

Cationic triarylmethane dyes such as malachite green are aromatic xenobiotic compounds causing environmental pollution. The affinity between hazardous materials and biomolecules makes it important to understand the properties of such compounds. Accordingly, in this study, the possible molecular interaction between this pollutant and the human serum albumin (HSA) was investigated using a combination of molecular docking, molecular dynamic simulation and multi-spectroscopic approaches. The docking results illustrated that malachite green oxalate (MGO) could bind to some of the HSA amino acids with the estimated free energy = -32.93 kJ/mol. Further, the results of the dynamic simulation revealed that MGO had a steady interaction with the protein though increasing flexibility and decreasing the HSA compactness. These results were, therefore, in agreement with those obtained by spectroscopic techniques. The MGO concentration of 0.0005 mM could quench the HSA's intrinsic fluorescence by %16.88. The protein structural changes also revealed that the binding interaction of MGO-HSA was accompanied by an increase in the α-helix and a decrease in the β-sheet of the protein. Overall, this study indicated the suitable molecular modeling interaction of MGO and HSA.

Esterase activity and interaction of human hemoglobin with diclofenac sodium: A spectroscopic and molecular docking study

To get an idea about the pharmacokinetics and pharmacodynamics, it is important to study the drug-protein interaction. Therefore, herein, we studied the interaction of diclofenac sodium (DIC) with human hemoglobin. The binding study of nonsteroidal antiinflammatory drug, DIC with human hemoglobin (HHB) was done by utilizing fluorescence, UV-visible, time-resolved fluorescence and far-UV circular dichroism spectroscopy (CD). Various thermodynamic parameters such as enthalpy change (ΔH), entropy change (ΔS), and Gibbs free energy change (ΔG) were also calculated. CD results showed that DIC induces secondary structure change in HHB. Fluorescence resonance energy transfer was also performed. Additionally, it was also observed that DIC inhibits the esterase-like enzymatic activity of HHB via competitive inhibition.

Structural alteration of myoglobin with two homologous cationic surfactants and effect of β-cyclodextrin: multifaceted insight and molecular docking study

Structural alteration and regeneration of myoglobin.

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.

Conformational and solution dynamics of hemoglobin (Hb) in presence of a cleavable gemini surfactant: Insights from spectroscopy, atomic force microscopy, molecular docking and density functional theory

Herein, we have explored the conformational alterations of hemoglobin (Hb) in presence of a cleavable gemini surfactant (C16-C4O2-C16). The concerned surfactant was found to induce significant structural perturbations in Hb. UV-vis spectroscopy, steady-state/time-resolved fluorescence, and other utilized techniques have authenticated the complexation of Hb with the gemini surfactant. CD has demonstrated the alterations in secondary structural elements (α-helicity, β-sheet, β-turn, and random coil) of Hb upon C16-C4O2-C16 addition. Atomic force microscopy (AFM) has revealed the existence of unique star-shaped gemini surfactant microstructures aligned to Hb in a necklace pattern. The ¹H NMR peak broadening and lower delta values hint at the binding of the concerned gemini surfactant to Hb. Molecular docking and DFT calculations have further substantiated the Hb-gemini complex formation and the involvement of electrostatic/hydrophobic forces therein. In future, these results might pave-the-way to construct self-assembled, sustainable, and green surfactant-protein mixtures for their end-use in industrial, engineering, biomedical, drug delivery, gene transfection, and other relevant excipient formulations.

Para-tertiary butyl catechol induces eryptosis in vitro via oxidative stress and hemoglobin leakage in human erythrocytes

Exposure of human population to industrial chemicals is believed as a significant contributing factor to the outgrowth of occupational diseases especially in developing countries due to improper safety measures and sanitary conditions. Para-tertiary butylcatechol (PTBC) widely employed in petrochemical, thermofax and phototypesetting industries, induces melanocytotoxicity and contact dermatitis leading to occupational leukoderma/vitiligo. Few vitiligo patients were reported for oxidative stress-induced hemolytic anemia and thrombocytopenia, however its impact on blood components is still not clear. Erythrocytes are the major cell population in circulation and play a prominent role in various diseases. In this work, the effect of PTBC on human erythrocytes is evaluated in vitro. PTBC induces oxidative stress-mediated eryptosis (erythrocyte death) causing detrimental changes such as depleted antioxidant levels, altered surface morphology, hemoglobin denaturation and heinz body formation. These findings validate that PTBC could induce toxic effects on human erythrocytes. Exposure of humans to toxic chemicals constitutes an important issue in various industries; one such issue is the exposure of PTBC at work place resulting in a spectrum of dermal complications. Therefore, it is imperative to appraise the long-term toxicities in order to further delineate the mechanisms of resultant disorders associated with PTBC and to establish the therapeutic interventions.

Interaction of promethazine and adiphenine to human hemoglobin: A comparative spectroscopic and computational analysis

The binding nature of amphiphilic drugs viz. promethazine hydrochloride (PMT) and adiphenine hydrochloride (ADP), with human hemoglobin (Hb) was unraveled by fluorescence, absorbance, time resolved fluorescence, fluorescence resonance energy transfer (FRET) and circular dichroism (CD) spectral techniques in combination with molecular docking and molecular dynamic simulation methods. The steady state fluorescence spectra indicated that both PMT and ADP quenches the fluorescence of Hb through static quenching mechanism which was further confirmed by time resolved fluorescence spectra. The UV-Vis spectroscopy suggested ground state complex formation. The activation energy (E_a) was observed more in the case of Hb-ADP than Hb-PMT interaction system. The FRET result indicates the high probability of energy transfer from β Trp37 residue of Hb to the PMT (r=2.02nm) and ADP (r=2.33nm). The thermodynamic data reveal that binding of PMT with Hb are exothermic in nature involving hydrogen bonding and van der Waal interaction whereas in the case of ADP hydrophobic forces play the major role and binding process is endothermic in nature. The CD results show that both PMT and ADP, induced secondary structural changes of Hb and unfold the protein by losing a large helical content while the effect is more pronounced with ADP. Additionally, we also utilized computational approaches for deep insight into the binding of these drugs with Hb and the results are well matched with our experimental results.

Multispectroscopic and bioimaging approach for the interaction of rhodamine 6G capped gold nanoparticles with bovine serum albumin

Binding interaction of Bovine Serum Albumin (BSA) with newly prepared rhodamine 6G-capped gold nanoparticles (Rh6G-Au NPs) under physiological conditions (pH 7.2) was investigated by a wide range of photophysical techniques. Rh6G-Au NPs caused the static quenching of the intrinsic fluorescence of BSA that resulted from the formation of ground-state complex between BSA and Rh6G-Au NPs. The binding constant from fluorescence quenching method (K_a = 1.04 × 10⁴ L mol^-1; LoD = 14.0 μM) is in accordance with apparent association constant (K_app = 1.14 × 10¹ M^-1), which is obtained from absorption spectral studies. Förster resonance energy transfer (FRET) efficiency between the tryptophan (Trp) residue of BSA and fluorophore of Rh6G-Au NPs during the interaction was calculated to be 90%. The free energy change (ΔG = -23.07 kJ/mol) of BSA-Rh6G-Au NPs complex was calculated based on modified Stern-Volmer Plot. The time-resolved fluorescence analysis confirmed that quenching of BSA follows static mechanism through the formation of ground state complex. Furthermore, synchronous and three-dimensional fluorescence measurement, Raman spectral analysis and Circular Dichroism spectrum results corroborate the strong binding between Rh6G-Au NPs and BSA, which causes the conformational changes on BSA molecule. In addition, fluorescence imaging experiments of BSA in living human breast cancer (HeLa) cells was successfully demonstrated, which articulated the value of Rh6G-Au NPs practical applications in biological systems.

Deciphering the role of the head group of cationic surfactants in their binding interactions with heme protein and their release by β-cyclodextrin

We decipher the mode of binding of surfactants with hemoglobin and their release by β-cyclodextrin.

Size Dependent Uptake and Hemolytic Effect of Zinc Oxide Nanoparticles on Erythrocytes and Biomedical Potential of ZnO-Ferulic acid Conjugates

Despite zinc oxide nanoparticles (ZnONPs) being increasingly used as carriers in biomedical fields due to their multifaceted properties and therapeutic importance, better understanding of the mechanisms and cellular consequences resulting from their interaction with cells and cellular components has been warranted. In the present study, we investigate the size-dependent interaction of ZnONPs on RBCs, and its impact on cell viability, DNA damage, ROS generation and morphological changes, employing cellular and analytical methods. Size, charge, stability and solubility were confirmed by DLS, zeta potential, ICP-AES and TEM analysis. Further ICP-AES, TEM, spectroscopic observations and cell based assays showed that ZnONPs exhibited a size dependent impact on RBCs and haemoglobin (Hb), particularly size <50 nm. Conversely, ferulic acid (FA) conjugates and serum albumin significantly reduced the adverse effects exhibited by ZnONPs. The extent of DNA damage and ROS generation is comparatively low in ZnONPs-FA than in ZnONPs alone treated cells. Thus our study documents a novel conceptualization delineating the influence of size on the material properties and therapeutic potential of nanoparticle.

Unraveling the interaction of hemoglobin with a biocompatible and cleavable oxy-diester-functionalized gemini surfactant

Surfactant-protein mixtures have attracted considerable research interest in recent years at the interface of chemical biology and medicinal chemistry. Herein, the interaction between a green gemini surfactant (C₁₆-E2O-C₁₆) and a redox protein hemoglobin was examined through a series of in vitro experimental techniques with an attempt to provide a comprehensive knowledge of the surfactant-protein binding interactions. Quantitative appraisal of the fluorescence/CV data showed that the binding of C₁₆-E2O-C₁₆ to Hb leads to the formation of thermodynamically favorable non-covalent adduct with 1:1 stoichiometry. UV-vis spectra demonstrated that the effect of C₁₆-E2O-C₁₆ on Hb is highly concentration dependent. Far-UV and near-UV CD spectra together elucidated the formation of molten globule state of Hb upon C₁₆-E2O-C₁₆ addition. Temperature dependent CD explicated the effect of C₁₆-E2O-C₁₆ on the thermal stability of Hb. Furthermore, the structural investigation of Hb via pyrene/synchronous/three-dimensional fluorescence and FT-IR spectroscopy provided the complementary information related to its microenvironmental and conformational changes. Computational studies delineated that C₁₆-E2O-C₁₆ binds in the vicinity of β-37 Trp at the α₁β₂ interface of Hb. Overall, this study is expected to clarify the binding mechanism between Hb/other congeners and surfactant at the molecular level that are known to have immense potential in biomedical and industrial areas.

Multispectroscopic and calorimetric studies on the binding of the food colorant tartrazine with human hemoglobin

Interaction of the food colorant tartrazine with human hemoglobin was studied using multispectroscopic and microcalorimetric techniques to gain insights into the binding mechanism and thereby the toxicity aspects. Hemoglobin spectrum showed hypochromic changes in the presence of tartrazine. Quenching of the fluorescence of hemoglobin occurred and the quenching mechanism was through a static mode as revealed from temperature dependent and time-resolved fluorescence studies. According to the FRET theory the distance between β-Trp37 of hemoglobin and bound tartrazine was evaluated to be 3.44nm. Synchronous fluorescence studies showed that tartrazine binding led to alteration of the microenvironment around the tryptophans more in comparison to tyrosines. 3D fluorescence and FTIR data provided evidence for conformational changes in the protein on binding. Circular dichroism studies revealed that the binding led to significant loss in the helicity of hemoglobin. The esterase activity assay further complemented the circular dichroism data. Microcalorimetric study using isothermal titration calorimetry revealed the binding to be exothermic and driven largely by positive entropic contribution. Dissection of the Gibbs energy change proposed the protein-dye complexation to be dominated by non-polyelectrolytic forces. Negative heat capacity change also corroborated the involvement of hydrophobic forces in the binding process.

A comparative spectroscopic and calorimetric investigation of the interaction of amsacrine with heme proteins, hemoglobin and myoglobin

The binding of the anilido aminoacridine derivative amsacrine with the heme proteins, hemoglobin, and myoglobin, was characterized by various spectroscopic and calorimetric methods. The binding affinity to hemoglobin was (1.21 ± .05) × 10⁵ M^-1, while that to myoglobin was three times higher (3.59 ± .15) × 10⁵ M^-1. The temperature-dependent fluorescence study confirmed the formation of ground-state complexes with both the proteins. The stronger binding to myoglobin was confirmed from both spectroscopic and calorimetric studies. The binding was exothermic in both cases at the three temperatures studied, and was favored by both enthalpy and entropy changes. Circular dichroism results, three-dimensional (3D) and synchronous fluorescence studies confirmed that the binding of amsacrine significantly changed the secondary structure of hemoglobin, while the change in the secondary structure of myoglobin was much less. New insights, in terms of structural and energetic aspects of the interaction of amsacrine with the heme proteins, presented here may help in understanding the structure-activity relationship, therapeutic efficacy, and drug design aspects of acridines.

Binding of fluorescent acridine dyes acridine orange and 9-aminoacridine to hemoglobin: Elucidation of their molecular recognition by spectroscopy, calorimetry and molecular modeling techniques

The molecular interaction between hemoglobin (HHb), the major human heme protein, and the acridine dyes acridine orange (AO) and 9-aminoacridine (9AA) was studied by various spectroscopic, calorimetric and molecular modeling techniques. The dyes formed stable ground state complex with HHb as revealed from spectroscopic data. Temperature dependent fluorescence data showed the strength of the dye-protein complexation to be inversely proportional to temperature and the fluorescence quenching was static in nature. The binding-induced conformational change in the protein was investigated using circular dichroism, synchronous fluorescence, 3D fluorescence and FTIR spectroscopy results. Circular dichroism data also quantified the α-helicity change in hemoglobin due to the binding of acridine dyes. Calorimetric studies revealed the binding to be endothermic in nature for both AO and 9AA, though the latter had higher affinity, and this was also observed from spectroscopic data. The binding of both dyes was entropy driven. pH dependent fluorescence studies revealed the existence of electrostatic interaction between the protein and dye molecules. Molecular modeling studies specified the binding site and the non-covalent interactions involved in the association. Overall, the results revealed that a small change in the acridine chromophore leads to remarkable alteration in the structural and thermodynamic aspects of binding to HHb.

Interaction of toxic azo dyes with heme protein: biophysical insights into the binding aspect of the food additive amaranth with human hemoglobin

A biophysical study on the interaction of the food colorant amaranth with hemoglobin was undertaken. Spectrophotometric and spectrofluorimetric studies proposed for an intimate binding interaction between the dye and the protein. The dye quenched the fluorescence of the protein remarkably and the mechanism of quenching was found to be static in nature. Synchronous fluorescence studies suggested that the polarity around the tryptophan residues was altered in the presence of amaranth whereas the polarity around tyrosine residues remained largely unaltered. 3D fluorescence, FTIR and circular dichroism results suggested that the binding reaction caused conformational changes in hemoglobin. The negative far-UV CD bands exhibited a significantly large decrease in magnitude in the presence of amaranth. From calorimetry studies it was established that the binding was driven by a large positive entropic contribution and a small but favorable enthalpy change.

Malachite green interacts with the membrane skeletal protein, spectrin

Energy minimized complex of MG with the self association domain of spectrin.

Unraveling the binding interaction of Toluidine blue O with bovine hemoglobin – a multi spectroscopic and molecular modeling approach

Toluidine blue O (TBO) is a cationic photosensitizer that belongs to the class of phenothiazinium dyes.

Hydrogen bonding plays a significant role in the binding of coomassie brilliant blue-R to hemoglobin: FT-IR, fluorescence and molecular dynamics studies

Coomassie brilliant blue-R (CBB-R) specifically binds to bovine hemoglobin with a stoichiometric ratio of 1 : 1.

Targeting the heme proteins hemoglobin and myoglobin by janus green blue and study of the dye–protein association by spectroscopy and calorimetry

The binding of the phenazinium dye janus green blue (JGB) to two heme proteins, hemoglobin (Hb) and myoglobin (Mb), was studied by biophysical and microcalorimetry techniques.

Interaction of the dietary pigment curcumin with hemoglobin: energetics of the complexation

The energetics of the interaction of a dietary pigment, curcumin, with hemoglobin have been elucidated using microcalorimetric techniques.