Binding of the bioactive component jatrorrhizine to human serum albumin

The interaction between Jatrorrhizine with human serum albumin (HSA) were studied by fluorescence quenching technique, circular dichroism (CD) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. Fluorescence data revealed the presence of a single class of binding site on HSA and its binding constants (K) are 7.278 x 10(4), 6.526 x 10(4), and 5.965 x 10(4) L.mol(-1) at 296, 303, and 310 K, respectively. The CD spectra and FT-IR spectra have proved that the protein secondary structure changed in the presence of Jatrorrhizine in aqueous solution. The effect of common ions on the binding constants was also investigated. In addition, the thermodynamic functions standard enthalpy (DeltaH(0)) and standard entropy (DeltaS(0)) for the reaction were calculated to be -10.891 kJ.mol(-1) and 56.267 J.mol(-1) K(-1), according to the van't Hoff equation. These data indicated that hydrophobic and electrostatic interactions played a major role in the binding of Jatrorrhizine to HSA. Furthermore, the displacement experiments indicated that Jatrorrhizine could bind to the site I of HSA, which was also in agreement with the result of the molecular modeling study.     

Specific interaction of chalcone-protein: cardamonin binding site II on the human serum albumin molecule

Cardamonin (2',4'-dihydroxy-6'-methoxychalcone), one of the main constituents from the seeds of Alpinia katsumadai Hayata, belongs to chalcone with its antibacterial, antiinflammatory and other important therapeutic activities of significant potency and low systemic toxicity. In this article, the interaction of cardamonin to human serum albumin (HSA) has been studied for the first time by spectroscopic methods including Fourier transform infrared (FTIR) spectroscopy, circular dichroism (CD), and UV-absorption spectroscopy in combination with fluorescence quenching under physiological conditions with drug concentrations of 0.67-4.0 microM. The results of the spectroscopic measurements and the thermodynamic parameters obtained (the enthalpy change DeltaH(0) and the entropy change DeltaS(0) were calculated to be -25.312 and 7.040 J.mol(-1).K(-1) according to the van't Hoff equation) suggest that hydrophobic interaction is the predominant intermolecular forces stabilizing the complex, which is also in good agreement with the results of the molecule modeling study. The alterations of protein secondary structure in the presence of cardamonin in aqueous solution were quantitatively calculated by the evidence from CD and FTIR spectroscopes with reductions of alpha-helices of about 20%, decreases of beta-sheet structures of about 14%, and increases of beta-turn structures of about 15%. The quenching mechanism and the number of binding sites (n approximately 1) were obtained by fluorescence titration data. Fluorescent displacement measurements confirmed that cardamonin binds HSA on site II. In addition, the effects of common ions on the constants of the cardamonin-HSA complex were also discussed.     

Interaction of rhein with human serum albumin investigation by optical spectroscopic technique and modeling studies

The binding of rhein with human serum albumin (HSA) has been studied in detail by spectroscopic method including circular dichroism (CD), Fourier transformation infrared spectra (FT-IR), fluorescence spectra. The binding parameters for the reaction have been calculated according to Scatchard equation at different temperatures. The plots indicated that the binding of HSA to rhein at 303, 310 and 318 K is characterized by one binding site with the affinity constant K at (4.93+/-0.16)x10(5), (4.02+/-0.16)x10(5) and (2.69+/-0.16)x10(5) M-1, respectively. The secondary structure compositions of free HSA and its rhein complexes were estimated by the FT-IR spectra. FT-IR and curve-fitted results of amide I band are in good agreement with the analyses of CD spectra. Molecular Modeling method was used to calculate the interaction modes between the drug and HSA.     

Interaction of isofraxidin with human serum albumin

This study was designed to examine the interaction of isofraxidin with human serum albumin (HSA) under physiological conditions with drug concentrations in the range of 3.3 x 10(-6) mol L(-1)-3.0x10(-5) mol L(-1) and HSA concentration at 1.5 x 10(-6) mol L(-1). Fluorescence quenching methods in combination with Fourier transform infrared (FT-IR) spectroscopy and circular dichroism (CD) spectroscopy were used to determine the drug-binding mode, the binding constant and the protein structure changes in the presence of isofraxidin in aqueous solution. Spectroscopic evidence showed that the interaction results in one type of isofraxidin-HSA complex with binding constants of 4.1266 x 10(5) L mol(-1), 3.8612 x 10(5) L mol(-1), 3.5063 x 10(5) L mol(-1), 3.1241 x 10(5) L mol(-1) at 296 K, 303 K, 310 K, 318 K, respectively. The thermodynamic parameters, enthalpy change (DeltaH) and entropy change (DeltaS) were calculated to be -10.08 kJ mol(-1) and 73.57 J mol(-1) K(-1) according to van't Hoff equation, which indicated that hydrophobic interaction played a main role in the binding of isofraxidin to HSA. The experiment results are nearly in accordance with the calculation results obtained by Silicon Graphics Ocatane2 workstation.     

Probing the binding of scutellarin to human serum albumin by circular dichroism, fluorescence spectroscopy, FTIR, and molecular modeling method

The binding of scutellarin with human serum albumin (HSA) was investigated at four temperatures, 296, 303, 310, and 318 K, by fluorescence, circular dichroism (CD), Fourier transform infrared spectroscopy (FT-IR), and molecular modeling study at pH 7.40. The binding parameters were determined by Scatchard's procedure, which are approximately consistent with the results of Stern-Volmer equation. The thermodynamic parameters were calculated according to the dependence of enthalpy change on the temperature as follows: DeltaH degrees is a small negative value (-8.55 kJ/mol), whereas DeltaS degrees is a positive value (65.15 J/mol K). Quenching of the fluorescence HSA in the presence of scutellarin was observed. Data obtained by fluorescence spectroscopy and CD experiment, FT-IR experiment, and molecular modeling method suggested that scutellarin can strongly bind to the HSA and the primary binding site of scutellarin is located in site I of HSA. It is considered that scutellarin binds to site I (subdomain II) mainly by a hydrophobic interaction and there are hydrogen bond interactions between the scutellarin and the residues Arg222 and Arg257.     

Spectroscopic investigations on the binding of Pyronin Y to human serum albumin

The interaction of Pyronin Y with human serum albumin (HSA) has been investigated systematically by fluorescence, absorption, fluorescence decay lifetime measurements, FTIR, synchronous fluorescence spectroscopy, and molecular modeling method. The spectroscopic and fluorescence quenching experiments show that Pyronin Y may show a static quenching mechanism with HSA. The specific binding distance of 1.96 nm between HSA and Pyronin Y was obtained via Förster non-radiation energy transfer method. The thermodynamic parameters indicate that the electrostatic interactions play a significant role during the binding process. In addition, synchronous fluorescence and FT-IR spectra indicated that the conformation and microenvironment of HSA were not influenced with the addition of Pyronin Y. The obtained results can be of biological significance in photodynamic therapy.     

Molecular interaction of manganese based carbon monoxide releasing molecule (MnCORM) with human serum albumin (HSA)

In the present study, the interaction between the HSA and MnCORM in vitro under physiological conditions, was investigated through ultraviolet-visible (UV-vis) absorption, fluorescence, time-resolved fluorescence, circular dichroism (CD), Fourier transform infrared (FT-IR) spectroscopic techniques and in silico molecular docking methods. Binding parameters such as the binding constant, number of binding sites and binding force were obtained from the fluorescence data. Thermodynamic interaction revealed that the reaction was spontaneous (ΔG < 0) and hydrogen bond and van der Waals interaction were primarily involved in the binding. The changes induced in the secondary structure conformation due to the MnCORM interaction were monitored using CD and FT-IR spectroscopic techniques. The results showed reduction in α-helix conformation and corresponding increase in β-sheet and unordered structures due to slight unfolding. The time-resolved fluorescence decay confirmed the static quenching mechanism of the MnCORM. The molecular docking studies revealed that the MnCORM interacted at Sudlow’s site II of domain IIIA through hydrogen bond and van der Waals interactions. In order to understand the drug distribution and elimination, studies on the drug molecule interaction with HSA are vital. Therefore, it is evident that MnCORM interacts with HSA through ground state complex formation and thus suitable for in vivo delivery.     

Comparison of binding interactions of lomefloxacin to serum albumin and serum transferrin by resonance light scattering and fluorescence quenching methods

The interaction between lomefloxacin (LMF) and two drug carrier proteins, human serum albumin (HSA) and serum transferrin (TF), were studied and compared by fluorescence quenching, resonance light scattering (RLS), and circular dichroism (CD) spectroscopic along with molecular modeling. Fluorescence data show that LMF has a stronger quenching effect on HSA than on TF. The binding constant and the number of binding sites were calculated as 6.00 x 10(5) M(-1) and 0.77 for HSA, and 4.66 x 10(5) M(-1) and 1.02, for TF, respectively. Also, these binding parameters were calculated by RLS data, as a novel approach and were compared to that obtained from fluorescence. The micro-environment changes of Trp residues were evident in both proteins. The quantitative analysis of the secondary structure in both proteins further confirmed the drug-induced conformational changes. The distance (r) between donors (HSA and TF) and acceptor (LMF) were obtained by fluorescence resonance energy transfer (FRET) theory and found to be 1.83 nm and 1.71 nm for HSA and TF respectively. Moreover, molecular modeling studies suggested the sub-domain IB in HSA and N-lobe in TF as the candidate place for the formation of the binding site of LMF on these proteins.     

Comparison of the characterization on binding of alpinetin and cardamonin to lysozyme by spectroscopic methods

Studies on the binding affinity of protein to the active components of herbs are novel in biochemistry and are valuable for the information about speciation of drugs and exchange in biological systems. Alpinetin and cardamonin, two of the main constituents from the seeds of Alpinia katsumadai Hayata, have been used in traditional herbs as antibacterial, anti-inflammatory, and other important therapeutic activities of significant potency and low systemic toxicity. The interactions between two flavonoids analogs and lysozyme have been studied for the first time by spectroscopic method including Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) and UV-absorption spectroscopy in combination with Fluorescence quenching study. Both molecules showed high affinities to lysozyme under the experimental condition with drug concentrations from 3.33 × 10⁻⁶ to 2.67 × 10⁻⁵ mol L⁻¹ for alpinetin and 1.67 × 10⁻⁶ to 13.33 × 10⁻⁶ mol L⁻¹ for cardamonin. The alterations of protein secondary structure in the presence of drugs in aqueous solution were quantitatively estimated by the evidences from CD and FT-IR spectroscopy. The thermodynamic parameters obtained and the results of spectroscopic measurements suggest that hydrophobic and electrostatic interactions are the predominant intermolecular forces stabilizing two coordination compounds. The quenching mechanism and the number of binding site (n ≈ 1) were obtained by fluorescence titration data. The efficiency of energy transfer provided the binding distances of 4.04 and 5.90 nm for alpinetin-LYSO and cardamonin-LYSO systems, respectively.     

Binding of the bioactive compound 5,7,4'-trihydroxy-6,3',5'-trimethoxyflavone to human serum albumin

5,7,4'-trihydroxy-6,3',5'-trimethoxyflavone is one of the bioactive components isolated from Artemisia plants possessing antitumor therapeutic activities. In this paper, its binding properties and binding sites located on human serum albumin (HSA) have been studied using UV absorption spectroscopy, fluorescence spectroscopy and Fourier transform infrared (FT-IR) spectra. The results of fluorescence titration revealed that 5,7,4'-trihydroxy-6,3',5'-trimethoxyflavone could strongly quench the intrinsic fluorescence of HSA by static quenching and there was only one class of binding sites on HSA for this drug. The binding constants at four different temperatures (289, 298, 310, and 318 K) were 1.93, 1.56, 1.22, and 0.93x10(5) L mol-1, respectively. The FT-IR spectra evidence showed that the protein secondary structure changed with reduction of alpha-helices about 27.6% at the drug to protein molar ratio of 3. The thermodynamic functions standard enthalpy change (DeltaH0) and standard entropy change (DeltaS0) for the reaction were calculated to be -18.70 kJ mol-1 and 36.62 J mol-1 K-1 according to the van't Hoff equation. These results and the molecular modeling study suggested that hydrophobic interaction was the predominant intermolecular force stabilizing the complex, and 5,7,4'-trihydroxy-6,3',5'-trimethoxyflavone could bind to the site I of HSA (the Warfarin Binding site).     

Characterization of the interaction between nitrofurazone and human serum albumin by spectroscopic and molecular modeling methods

The interaction of nitrofurazone (NF) and human serum albumin (HSA) has been studied by fluorescence spectroscopy, FT-IR spectroscopy and molecular modeling methods. The results showed that the fluorescence of HSA was quenched by NF in a static quenching mechanism. Thermodynamic parameters revealed that hydrogen bonds and van der Waals force played the major role during the interaction. The calculated binding distance (r) indicated that the non-radioactive energy transfer came into being in the interaction between NF and HSA. HSA had a single class of binding site at Sudlow' site I in subdomain IIA for NF, which was verified by the displacement experiment. The molecular modeling study further confirmed the specific binding sites of NF on HSA, such as the interaction between N11 and N14 of NF with Lue 283 and Ser 287 predominately through hydrogen bonds. Three-dimensional fluorescence spectra indicated that the polarity around the tryptophan residues decreased and the conformation of HSA changed after adding NF. FT-IR spectra showed that NF could induce the polypeptides of HSA unfolding because it changed α-helix and β-sheet into β-turn and random structure of HSA.     

Interactions of human serum albumin with chlorogenic acid and ferulic acid

The interactions of chlorogenic acid and ferulic acid with human serum albumin (HSA) have been investigated by fluorescence and Fourier transformed infrared (FT-IR) spectrometry. Fluorescence results showed that one molecule of protein combined with one molecule of drugs at the molar ratio of drug to HSA ranging from 1 to 10, and their binding affinities (KA) are 4.37 x 10(4) M(-1) and 2.23 x 10(4) M(-1) for chlorogenic acid and ferulic acid, respectively. The primary binding site for chlorogenic acid is most likely located on IIA and that for ferulic acid in IIIA. The main mechanism of protein fluorescence quenching was static quenching process. Combining the curve-fitting results of infrared amide I and amide III bands, the alterations of protein secondary structure after drug complexation were estimated. With increasing the drug concentration, the protein alpha-helix structure decreased gradually and the reduction of protein alpha-helix structure reached about 7% and 5% for protein binding with chlorogenic acid and ferulic acid individually at the drug to protein molar ratio of 30. This indicated a partial unfolding of HSA in the presence of the two acids. From the fluorescence and FT-IR results, the binding mode was discussed.     

Human serum albumin interaction with formononetin studied using fluorescence anisotropy, FT-IR spectroscopy, and molecular modeling methods

Interaction of formononetin with a model transport protein, human serum albumin (HSA), has been studied using fluorescence anisotropy, FT-IR spectroscopy, and molecular modeling methods. Upon binding with HSA, the fluorescence spectrum of formononetin exhibits appreciable hypsochromic shift along with an enhancement in the fluorescence intensity. Gradual addition of HSA led to a marked increase in fluorescence anisotropy (r). From the value of fluorescence anisotropy, it is argued that the drug is located in a restricted environment of protein. The binding constant (K approximately 1.6 x 10(5) M(-1)) and the standard free energy change (DeltaG(0) approximately -29.9 kJ/mol) of formononetin-HSA interaction have been calculated according to the relevant fluorescence data. Fourier transform infrared measurements have shown that the secondary structures of the protein have been changed by the interaction of formononetin with HSA. Computational mapping of the possible binding sites of formononetin revealed the molecule to be bound in the large hydrophobic cavity of subdomain IIA.     

Probing the mechanism of interaction of metoprolol succinate with human serum albumin by spectroscopic and molecular docking analysis

In the present work, the mechanism of the interaction between a β1 receptor blocker, metoprolol succinate (MS) and human serum albumin (HSA) under physiological conditions was investigated by spectroscopic techniques, namely fluorescence, Fourier transform infra‐red spectroscopy (FT‐IR), fluorescence lifetime decay and circular dichroism (CD) as well as molecular docking and cyclic voltammetric methods. The fluorescence and lifetime decay results indicated that MS quenched the intrinsic intensity of HSA through a static quenching mechanism. The Stern–Volmer quenching constants and binding constants for the MS–HSA system at 293, 298 and 303 K were obtained from the Stern–Volmer plot. Thermodynamic parameters for the interaction of MS with HSA were evaluated; negative values of entropy change (ΔG°) indicated the spontaneity of the MS and HSA interaction. Thermodynamic parameters such as negative ΔH° and positive ΔS° values revealed that hydrogen bonding and hydrophobic forces played a major role in MS–HSA interaction and stabilized the complex. The binding site for MS in HSA was identified by competitive site probe experiments and molecular docking studies. These results indicated that MS was bound to HSA at Sudlow's site I. The efficiency of energy transfer and the distance between the donor (HSA) and acceptor (MS) was calculated based on the theory of Fosters' resonance energy transfer (FRET). Three‐dimensional fluorescence spectra and CD results revealed that the binding of MS to HSA resulted in an obvious change in the conformation of HSA. Cyclic voltammograms of the MS–HSA system also confirmed the interaction between MS and HSA. Furthermore, the effects of metal ions on the binding of MS to HSA were also studied.     

Analysis of binding interaction between the natural apocarotenoid bixin and human serum albumin by circular dichroism and fluorescence spectroscopy

Bixin is an important, pharmacologically active dietary cis-carotenoid, but its interaction with potential macromolecular targets is completely unexplored. This work was aimed to study the binding of bixin to human serum albumin (HSA), the most abundant protein in blood plasma. Circular dichroism (CD) spectroscopy in combination with UV/VIS absorption spectroscopy and fluorescence quenching techniques were applied. Appearance of induced CD bands in the UV- and VIS-absorption spectral regions indicated the formation of non-covalent carotenoid-albumin complexes. Shape and spectral position of the extrinsic Cotton effects suggested the binding of a single bixin molecule to HSA in chiral conformation. Scatchard and non-linear regression analyses of CD titration data resulted in similar values for the association constant (Ka = 6.6 and 4.6x10(5) M(-1), resp.) and for the number of binding sites (n = 1). The binding interaction was independently confirmed by fluorescence-quenching experiment from which the binding parameters were also calculated. CD Displacement measurements performed with marker ligands established that the main drug binding sites of HSA are not involved in binding of bixin. Palmitic acid decreased the amplitude of the induced CD bands suggesting a common albumin binding site for bixin and long-chain fatty acids. The above data indicate that HSA plays a significant role in the plasma transportation of bixin and related dietary carboxylic acid carotenoids.     

Interaction of bovine (BSA) and human (HSA) serum albumins with ionic surfactants: spectroscopy and modelling

The binding of several different categories of small molecules to bovine (BSA) and human (HSA) serum albumins has been studied for many years through different spectroscopic techniques to elucidate details of the protein structure and binding mechanism. In this work we present the results of the study of the interactions of BSA and HSA with the anionic sodium dodecyl sulfate (SDS), cationic cethyltrimethylammonium chloride (CTAC) and zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonium-1-propanesulfonate (HPS) monitored by fluorescence spectroscopy of the intrinsic tryptophans at pH 5.0. Similarly to pH 7.0 and 9.0, at low concentrations, the interaction of BSA with these surfactants shows a quenching of fluorescence with Stern-Volmer quenching constants of (1.1+/-0.1)x10(4) M(-1), (3.2+/-0.1)x10(3) M(-1) and (2.1+/-0.1)x10(3) M(-1) for SDS, HPS and CTAC, respectively, which are associated to the 'effective' association constants to the protein. On the interaction of these surfactants with HSA, an opposite effect was observed as compared to BSA, i.e., an enhancement of fluorescence takes place. For both proteins, at low surfactant concentrations, a positive cooperativity was observed and the Hill plot model was used to estimate the number of surfactant binding sites, as well as the association constants of the surfactants to the proteins. It is worthy of notice that the binding constants for the surfactants at pH 5.0 are lower as compared to pH 7.0 and 9.0. This is probably due to fact that the protein at this acid pH is quite compact reducing the accessibility of the surfactants to the hydrophobic cavities in the binding sites. The interaction of myristic acid with both proteins shows a similar fluorescence behaviour, suggesting that the mechanism of the interaction is the same. Recently published crystallographic studies of HSA-myristate complex were used to perform a modelling study with the aim to explain the fluorescence results. The crystallographic structure reveals that a total of five myristic acid molecules are asymmetrically bound in the macromolecule. Three of these sites correspond to higher affinity ones and correlate with high association constants described in the literature. Our models for BSA and HSA with bound SDS suggest that the surfactant could be bound at the same sites as those reported in the crystal structure for the fatty acid. The differences in tryptophan vicinity upon surfactant binding are explored in the models in order to explain the observed spectroscopic changes. For BSA the quenching is due to a direct contact of a surfactant molecule with the indole of W131 residue. It is clear that the binding site in BSA which is very close, in contact with tryptophan W131, corresponds to a lower affinity site, explaining the lower binding constants obtained from fluorescence studies. In the case of HSA the enhancement of fluorescence is due to the removal of static quenching of W214 residue in the intact protein caused by nearby residues in the vicinity of this tryptophan.     

Studies on the interaction between vincamine and human serum albumin: a spectroscopic approach

The interaction between vincamine (VCM) and human serum albumin (HSA) has been studied using a fluorescence quenching technique in combination with UV/vis absorption spectroscopy, Fourier transform infrared (FT–IR) spectroscopy, circular dichroism (CD) spectroscopy and molecular modeling under conditions similar to human physiological conditions. VCM effectively quenched the intrinsic fluorescence of HSA via static quenching. The binding constants were calculated from the fluorescence data. Thermodynamic analysis by Van't Hoff equation revealed enthalpy change (ΔH) and entropy change (ΔS) were ?4.57 kJ/mol and 76.26 J/mol/K, respectively, which indicated that the binding process was spontaneous and the hydrophobic interaction was the predominant force. The distance r between the donor (HSA) and acceptor (VCM) was obtained according to the Förster's theory of non‐radiative energy transfer and found to be 4.41 nm. Metal ions, viz., Na⁺, K⁺, Li⁺, Ni²⁺, Ca²⁺, Zn²⁺ and Al³⁺ were found to influence binding of the drug to protein. The 3D fluorescence, FT–IR and CD spectral results revealed changes in the secondary structure of the protein upon interaction with VCM. Furthermore, molecular modeling indicated that VCM could bind to the subdomain IIA (site I) of HSA. Copyright © 2013 John Wiley & Sons, Ltd.     

Saffron carotenoids (crocin and crocetin) binding to human serum albumin as investigated by different spectroscopic methods and molecular docking

Therapeutic effects of saffron ingredients were studied in some diseases. The pharmacokinetics and pharmacodynamics of these ingredients were also studied, but their transport mechanism is not clearly known. Serum albumin has been known as the most important transporter of many drugs in the body that affects their disposition, transportation, and bioavailability. Here, we investigated the interaction of crocin (Cro) with HSA, for the first time, and compared with the crocetin (Crt)–HSA interaction. UV and fluorescence spectroscopy, circular dichroism (CD), and molecular docking was applied to investigate the possibility and mechanism of binding of HSA with these natural carotenoids. The gradually addition of Cro increased HSA absorbency at 278 nm, while Crt decreased it. Both of these changes induced HSA unfolding that was confirmed by the decreased α-helix content, as determined by the CD. Both carotenoids quenched HSA fluorescence emission, but with different mechanisms. The Stern–Volmer plots indicated a dynamic quenching of intrinsic emission of HSA due to Cro addition, while Crt quenching followed both static and dynamic quenching mechanisms. Docking results indicated binding of Cro/Crt in sub-domain IIA, Sudlow site I of HSA, which accompanied with the hydrogen bonding of Cro/Crt with Tyr138. The interaction of these ligands (Cro/Crt) caused HSA unfolding and affects the hydrophobic environment of Trp241, which result in the quenching of Trp fluorescence. The UV spectroscopy and fluorescence quenching data indicated the differences in the mechanisms of interaction of Cro/Crt with HSA, which is due to the differences in the structure and hydrophobicity of these ligands.     

Investigation of the interaction of aurantio‐obtusin with human serum albumin by spectroscopic and molecular docking methods

The interaction between human serum albumin (HSA) and aurantio‐obtusin was investigated by spectroscopic techniques combined with molecular docking. The Stern–Volmer quenching constants (K_SV) decreased from 8.56 × 10⁵ M^?1 to 5.13 × 10⁵ M^?1 with a rise in temperatures from 289 to 310 K, indicating that aurantio‐obtusin produced a static quenching of the intrinsic fluorescence of HSA. Time‐resolved fluorescence studies proved again that the static quenching mechanism was involved in the interaction. The sign and magnitude of the enthalpy change as well as the entropy change suggested involvement of hydrogen bonding and hydrophobic interaction in aurantio‐obtusin–HSA complex formation. Aurantio‐obtusin binding to HSA produced significant alterations in secondary structures of HSA, as revealed from the time‐resolved fluorescence, Fourier transform infrared (FT‐IR) spectroscopy, three‐dimensional (3D) fluorescence and circular dichroism (CD) spectral results. Molecular docking study and site marker competitive experiment confirmed aurantio‐obtusin bound to HSA at site I (subdomain IIA).     

Interaction and photo-induced cleavage studies of a copper based chemotherapeutic drug with human serum albumin: spectroscopic and molecular docking study

The interaction of new dinuclear copper(ii) complex 1; [Cu(2)(glygly)(2)(ppz)(H(2)O)(4)]·2H(2)O, derived from dipeptide (glycyl glycine) and piperazine as a metallopeptide drug with human serum albumin (HSA) was examined by means of fluorescence spectroscopy which revealed that complex 1 has a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The alterations of HSA secondary structure in the presence of complex 1 were confirmed by UV-visible, FT-IR, CD and 3D fluorescence spectroscopy. The binding constants (K), and binding site number (n), corresponding thermodynamic parameters ΔG, ΔH and ΔS at different temperatures were calculated. The molecular docking technique was utilized to ascertain the mechanism and mode of action towards the molecular target HSA indicating that complex 1 was located at the entrance of site I by electrostatic and hydrophobic forces, consistent with the corresponding experimental results. Complex 1 shows efficient photo-induced HSA cleavage activity, indicating the involvement of hydroxyl radicals as the reactive species. Furthermore, the cytotoxicity of 1 was examined on a panel of human tumor cell lines of different histological origins showing significant GI(50) values specifically towards MIAPACA2, A498 and A549 tumor cell lines. These results complement previous biological studies of new specific target metallopeptides, providing additional information about possibilities of their transport and disposition in blood plasma.