Investigation on the Interaction of Norgestrel with Human Serum Albumin Using Spectroscopy and Molecular‐Docking Method

The interaction of norgestrel with human serum albumin (HSA) was investigated by spectroscopy and molecular‐docking methods. Results of spectroscopy methods suggested that the quenching mechanism of norgestrel on HSA was static quenching and that the quenching process was spontaneous. Negative values of thermodynamic parameters (ΔG, ΔH, and ΔS) indicated that hydrogen bonding and van der Waals forces dominated the binding between norgestrel and HSA. Three‐dimensional fluorescence spectrum and circular dichroism spectrum showed that the HSA structure was slightly changed by norgestrel. Norgestrel mainly bound with Sudlow site I based on a probe study, as confirmed by molecular‐docking results. Competition among similar structures indicated that ethisterone and norethisterone affected the binding of norgestrel with HSA. CH₃ in R₁ had little effect on norgestrel binding with HSA. The surface hydrophobicity properties of HSA, investigated using 8‐anilino‐1‐naphthalenesulfonic acid, was changed with norgestrel addition.     

Interaction of a tyrosine kinase inhibitor,vandetanib with human serum albumin as studied by fluorescence quenching and molecular docking

Interaction of a tyrosine kinase inhibitor, vandetanib (VDB), with the major transport protein in the human blood circulation, human serum albumin (HSA), was investigated using fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and molecular docking analysis. The binding constant of the VDB–HSA system, as determined by fluorescence quenching titration method was found in the range, 8.92–6.89?×?10^3?M^?1 at three different temperatures, suggesting moderate binding affinity. Furthermore, decrease in the binding constant with increasing temperature revealed involvement of static quenching mechanism, thus affirming the formation of the VDB–HSA complex. Thermodynamic analysis of the binding reaction between VDB and HSA yielded positive ΔS (52.76 J?mol^?1 K^?1) and negative ΔH (?6.57?kJ?mol^?1) values, which suggested involvement of hydrophobic interactions and hydrogen bonding in stabilizing the VDB–HSA complex. Far-UV and near-UV CD spectral results suggested alterations in both secondary and tertiary structures of HSA upon VDB-binding. Three-dimensional fluorescence spectral results also showed significant microenvironmental changes around the Trp residue of HSA consequent to the complex formation. Use of site-specific marker ligands, such as phenylbutazone (site I marker) and diazepam (site II marker) in competitive ligand displacement experiments indicated location of the VDB binding site on HSA as Sudlow’s site I (subdomain IIA), which was further established by molecular docking results. Presence of some common metal ions, such as Ca²⁺, Zn²⁺, Cu²⁺, Ba²⁺, Mg²⁺, and Mn²⁺ in the reaction mixture produced smaller but significant alterations in the binding affinity of VDB to HSA.     

Multi-spectroscopic,thermodynamic and molecular docking studies to investigate the interaction of eplerenone with human serum albumin

The binding of small molecular drugs with human serum albumin (HSA) has a crucial influence on their pharmacokinetics. The binding interaction between the antihypertensive eplerenone (EPL) and HSA was investigated using multi-spectroscopic techniques for the first time. These techniques include ultraviolet-visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR), native fluorescence spectroscopy, synchronous fluorescence spectroscopy and molecular docking approach. The fluorescence spectroscopic study showed that EPL quenched HSA inherent fluorescence. The mechanism for quenching of HSA by EPL has been determined to be static in nature and confirmed by UV absorption and fluorescence spectroscopy. The modified Stern–Volmer equation was used to estimate the binding constant (K_b) as well as the number of bindings (n). The results indicated that the binding occurs at a single site (K_b = 2.238 × 10³ L mol⁻¹at 298 K). The enthalpy and entropy changes (∆H and ∆S) were 58.061 and 0.258 K J mol⁻¹, respectively, illustrating that the principal intermolecular interactions stabilizing the EPL–HSA system are hydrophobic forces. Synchronous fluorescence spectroscopy revealed that EPL binding to HSA occurred around the tyrosine (Tyr) residue and this agreed with the molecular docking study. The Förster resonance energy transfer (FRET) analysis confirmed the static quenching mechanism. The esterase enzyme activity of HSA was also evaluated showing its decrease in the presence of EPL. Furthermore, docking analysis and site-specific markers experiment revealed that EPL binds with HSA at subdomain IB (site III).     

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).     

Insights into the binding of paclitaxel to human serum albumin: multispectroscopic studies

The interaction of paclitaxel with human serum albumin (HSA) was studied using fluorescence, resonance light scattering, ultraviolet‐visible, circular dichroism and Fourier transform infrared spectroscopy at pH 7.4. Fluorescence data revealed that the fluorescence quenching of HSA by paclitaxel was a static quenching procedure. Time‐resolved fluorescence data also confirmed the quenching mode, which present a constant decay time of about 5 ns. The binding sites were approximately 1 and the binding constant suggested a weak association (324/M at 298 K), which is helpful for the release of the drug to targeted organs. The thermodynamic parameters, ΔG^○, ΔH° and ΔS° were calculated as – 1.06 × 10⁴ J/mol, 361 J/mol per K and 9.7 × 10⁴ J/mol respectively at 298 K, suggesting that binding was spontaneous and was driven mainly by hydrophobic interactions. The binding distance between HSA and paclitaxel was determined to be 2.23 nm based on the Förster theory. Analysis of circular dichroism, ultraviolet‐visible, three‐dimensional fluorescence, Fourier transform infrared and resonance light scattering spectra demonstrated that HSA conformation was slightly altered in the presence of paclitaxel and dimension of the individual HSA molecules were larger after interacting with paclitaxel. These results were confirmed by a molecular docking study. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Characterizing the interaction between pyrogallol and human serum albumin by spectroscopic and molecular docking methods

In the present study, the interaction of Pyrogallol (PG) with human serum albumin (HSA) was investigated by UV, fluorescence, Circular dichroism (CD), and molecular docking methods. The results of fluorescence experiments showed that the quenching of intrinsic fluorescence of HSA by PG was due to a static quenching. The calculated binding constants (K) for PG-HSA at different temperatures were in the order of 10⁴?M ^?1, and the corresponding numbers of binding sites, n were approximately equal to unity. The thermodynamic parameters, ΔH and ΔS were calculated to be negative, which indicated that the interaction of PG with HSA was driven mainly by van der Waals forces and hydrogen bonds. The negative value was obtained for ΔG showed that the reaction was spontaneous. In addition, the effect of PG on the secondary structure of HSA was analyzed by performing UV–vis, synchronous fluorescence, and CD experiments. The results indicated that PG induced conformational changes in the structure of HSA. According to Förster no-radiation energy transfer theory, the binding distance of HSA to PG was calculated to be 1.93?nm. The results of molecular docking calculations clarified the binding mode and the binding sites which were in good agreement with the results of experiments.

Communicated by Ramaswamy H. Sarma     

Interaction of cyproheptadine hydrochloride with human serum albumin using spectroscopy and molecular modeling methods

The interaction between cyproheptadine hydrochloride (CYP) and human serum albumin (HSA) was investigated by fluorescence spectroscopy, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy (FT‐IR) and molecular modeling at a physiological pH (7.40). Fluorescence of HSA was quenched remarkably by CYP and the quenching mechanism was considered as static quenching since it formed a complex. The association constants K_a and number of binding sites n were calculated at different temperatures. According to Förster's theory of non‐radiation energy transfer, the distance r between donor (human serum albumin) and acceptor (cyproheptadine hydrochloride) was obtained. The effect of common ions on the binding constant was also investigated. The effect of CYP on the conformation of HSA was analyzed using FT‐IR, synchronous fluorescence spectroscopy and 3D fluorescence spectra. The thermodynamic parameters ΔH and ΔS were calculated to be ?14.37 kJ mol^?1 and 38.03 J mol^?1 K^?1, respectively, which suggested that hydrophobic forces played a major role in stabilizing the HSA‐CYP complex. In addition, examination of molecular modeling indicated that CYP could bind to site I of HSA and that hydrophobic interaction was the major acting force, which was in agreement with binding mode studies. Copyright © 2012 John Wiley & Sons, Ltd.     

Exploration of interaction of canthaxanthin with human serum albumin by spectroscopic and molecular simulation methods

The interaction between the food colorant canthaxanthin (CA) and human serum albumin (HSA) in aqueous solution was explored by using fluorescence spectroscopy, three‐dimensional fluorescence spectra, synchronous fluorescence spectra, UV–vis absorbance spectroscopy, circular dichroism (CD) spectra and molecular docking methods. The thermodynamic parameters calculated from fluorescence spectra data showed that CA could result in the HSA fluorescence quenching. From the K_SV change with the temperature dependence, it was concluded that HSA fluorescence quenching triggered by CA is the static quenching and the number of binding sites is one. Furthermore, the secondary structure of HSA was changed with the addition of CA based on the results of synchronous fluorescence, three‐dimensional fluorescence and CD spectra. Hydrogen bonds and van der Waals forces played key roles in the binding process of CA with HSA, which can be obtained from negative standard enthalpy (ΔH) and negative standard entropy (ΔS). Furthermore, the conclusions were certified by molecular docking studies and the binding mode was further analyzed with Discovery Studio. These conclusions can highlight the potential of the interaction mechanism of food additives and HSA.     

Interaction of coumarin triazole analogs to serum albumins: Spectroscopic analysis and molecular docking studies

The interaction of triazole substituted 4‐methyl‐7‐hydroxycoumarin derivatives (CUM1‐4) with serum albumin (bovine serum albumin [BSA] and human serum albumin [HSA]) have been studied employing ultraviolet‐visible (UV‐Vis), fluorescence, circular dichroism (CD) spectroscopy, and molecular docking methods at physiological pH 7.4. The fluorescence quenching occurred with increasing concentration of CUMs, and the binding constant of CUM derivatives with BSA and HSA obtained from fluorescence quenching experiment was found to be ~ 10⁴ L mol^?1. CD study showed conformational changes in the secondary structure of serum albumin upon titration of CUMs. The observed experimental results were further validated by theoretical studies involving density functional theory (DFT) and molecular docking.     

Combined spectroscopies and molecular docking approach to characterizing the binding interaction between lisinopril and bovine serum albumin

To further understand the mode of action and pharmacokinetics of lisinopril, the binding interaction of lisinopril with bovine serum albumin (BSA) under imitated physiological conditions (pH 7.4) was investigated using fluorescence emission spectroscopy, synchronous fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD) and molecular docking methods. The results showed that the fluorescence quenching of BSA near 338 nm resulted from the formation of a lisinopril–BSA complex. The number of binding sites (n) for lisinopril binding on subdomain IIIA (site II) of BSA and the binding constant were ~ 1 and 2.04 × 10⁴ M^–1, respectively, at 310 K. The binding of lisinopril to BSA induced a slight change in the conformation of BSA, which retained its α‐helical structure. However, the binding of lisinopril with BSA was spontaneous and the main interaction forces involved were van der Waal's force and hydrogen bonding interaction as shown by the negative values of ΔG⁰, ΔH⁰ and ΔS⁰ for the binding of lisinopril with BSA. It was concluded from the molecular docking results that the flexibility of lisinopril also played an important role in increasing the stability of the lisinopril–BSA complex. Copyright © 2015 John Wiley & Sons, Ltd.     

Binding of fluphenazine with human serum albumin in the presence of rutin and quercetin: An evaluation of food‐drug interaction by spectroscopic techniques

The interactions between human serum albumin (HSA) and fluphenazine (FPZ) in the presence or absence of rutin or quercetin were studied by fluorescence, absorption and circular dichroism (CD) spectroscopy and molecular modeling. The results showed that the fluorescence quenching mechanism was static quenching by the formation of an HSA–FPZ complex. Entropy change (ΔS ⁰) and enthalpy change (ΔH ⁰) values were 68.42 J/(mol? K) and ?4.637 kJ/mol, respectively, which indicated that hydrophobic interactions and hydrogen bonds played major roles in the acting forces. The interaction process was spontaneous because the Gibbs free energy change (ΔG ⁰) values were negative. The results of competitive experiments demonstrated that FPZ was mainly located within HSA site I (sub‐domain IIA). Molecular docking results were in agreement with the experimental conclusions of the thermodynamic parameters and competition experiments. Competitive binding to HSA between flavonoids and FPZ decreased the association constants and increased the binding distances of FPZ binding to HSA. The results of absorption, synchronous fluorescence, three‐dimensional fluorescence, and CD spectra showed that the binding of FPZ to HSA caused conformational changes in HSA and simultaneous effects of FPZ and flavonoids induced further HSA conformational changes.     

Study of the Enantioselective Interaction of Diclofop and Human Serum Albumin by Spectroscopic and Molecular Modeling Approaches In Vitro

In this contribution, the enantioselective interactions between diclofop (DC) and human serum albumin (HSA) were explored by steady‐state and 3D fluorescence, ultraviolet‐visible spectroscopy (UV‐vis), and molecular modeling. The binding constants between R‐DC and HSA were 0.9213 × 10⁵, 0.9118 × 10⁵, and 0.9009 × 10⁵ L · mol^‐1 at 293, 303, 313 K, respectively. Moreover, the binding constants of S‐DC for HSA were 1.4766 × 10⁵, 1.2899 × 10⁵, and 1.0882 × 10⁵ L · mol^‐1 at 293, 303, and 313 K individually. Such consequences markedly implied the binding between DC enantiomers and HSA were enantioselective with higher affinity for S‐DC. Steady‐state fluorescence study evidenced the formation of DC‐HSA complex and there was a single class of binding site on HSA. The thermodynamic parameters (ΔH, ΔS, ΔG) of the reaction clearly indicated that hydrophobic effects and H‐bonds contribute to the formation of DC‐HSA complex, which was in excellent agreement with molecular simulations. In addition, both site‐competitive replacement and molecular modeling suggested that DC enantiomers were located within the binding pocket of Sudlow's site II. Furthermore, the alterations of HSA secondary structure in the presence of DC enantiomers were verified by UV‐vis absorption and 3D fluorescence spectroscopy. This study can provide important insight into the enantioselective interaction of physiological protein HSA with chiral aryloxyphenoxy propionate herbicides and gives support to the use of HSA for chiral pesticides ecotoxicology and environmental risk assessment. Chirality 25:719–725, 2013. © 2013 Wiley Periodicals, Inc.     

Micronomicin/tobramycin binding with DNA: fluorescence studies using of ethidium bromide as a probe and molecular docking analysis

Two aminoglycosides, micronomicin (MN), and tobramycin (TB), binding with DNA were studied using various spectroscopic techniques including fluorescence, UV–Vis, FT-IR, and CD spectroscopy coupled with relative viscosity and molecular docking. Studies of fluorescence quenching and time-resolved fluorescence spectroscopy all revealed that MN/TB quenching the fluorescence of DNA–EB belonged to static quenching. The binding constants and binding sites were obtained. The values of ΔH, ΔS, and ΔG suggested that van der Waals force or hydrogen bond might be the main binding force. FT-IR and CD spectroscopy revealed that the binding of MN/TB with DNA had an effect on the secondary structure of DNA. Binding mode of MN/TB with DNA was groove binding which was ascertained by viscosity measurements, CD spectroscopy, ionic strength, melting temperature (T_m), contrast experiments with single stranded (ssDNA), and double stranded DNA (dsDNA). Molecular docking analysis further confirmed that the groove binding was more acceptable result.     

Spectroscopic and molecular modeling approaches to investigate the binding of proton pump inhibitors to human serum albumin

The interaction between two proton pump inhibitors viz., omeprazole (OME) and esomeprazole (EPZ) with human serum albumin (HSA) was studied by fluorescence, absorption, circular dichroism (CD), Fourier transform infrared spectroscopy (FT-IR), voltammetry, and molecular modeling approaches. The Stern–Volmer quenching constants (K_sv) for OME-HSA and EPZ-HSA systems obtained at different temperatures revealed that both OME and EPZ quenched the intensity of HSA through dynamic mode of quenching mechanism. The binding constants of OME-HSA and EPZ-HSA increased with temperature, indicating the increased stability of these systems at higher temperatures. Thermodynamic parameters viz., ?H^°, ?S^°, and ?G^° were determined for both systems. These values revealed that both systems were stabilized by hydrophobic forces. The competitive displacement and molecular docking studies suggested that OME/EPZ was bound to Sudlow’s site I in subdomain IIA in HSA. The extent of energy transfer from HSA to OME/EPZ and the distance of separation in tryptophan (Trp214) Trp214-OME and Trp214-EPZ was determined based on the theory of fluorescence resonance energy transfer. UV absorption, 3D fluorescence, and CD studies indicated that the binding of OME/EPZ to HSA has induced micro environmental changes around the protein which resulted changes in its secondary structure.     

Study on the interactions of mapenterol with serum albumins using multi‐spectroscopy and molecular docking

The interactions of mapenterol with bovine serum albumin (BSA) and human serum albumin (HSA) have been investigated systematically using fluorescence spectroscopy, absorption spectroscopy, circular dichroism (CD) and molecular docking techniques. Mapenterol has a strong ability to quench the intrinsic fluorescence of BSA and HSA through static quenching procedures. At 291 K, the binding constants, K_a, were 1.93 × 10³ and 2.73 × 10³ L/mol for mapenterol–BSA and mapenterol–HAS, respectively. Electrostatic forces and hydrophobic interactions played important roles in stabilizing the mapenterol–BSA/has complex. Using site marker competitive studies, mapenterol was found to bind at Sudlow site I on BSA/HSA. There was little effect of K⁺, Ca²⁺, Cu²⁺, Zn²⁺ and Fe³⁺ on the binding. The conformation of BSA/HSA was changed by mapenterol, as seen from the synchronous fluorescence spectra. The CD spectra showed that the binding of mapenterol to BSA/HSA changed the secondary structure of BSA/HSA. Molecular docking further confirmed that mapenterol could bind to Sudlow site I of BSA/HSA. According to Förster non‐radiative energy transfer theory (FRET), the distances r₀ between the donor and acceptor were calculated as 3.18 and 2.75 nm for mapenterol–BSA and mapenterol–HAS, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Investigations on the interactions of DiAmsar with serum albumins: Insights from spectroscopic and molecular docking techniques

Diamine‐sarcophagine (DiAmsar) binding to human serum albumin (HSA) and bovine serum albumin (BSA) was investigated under simulative physiological conditions. Fluorescence spectra in combination with Fourier transform infrared (FT‐IR), UV‐visible (UV–vis) spectroscopy, cyclic voltammetry (CV), and molecular docking method were used in the present work. Experimental results revealed that DiAmsar had an ability to quench the HSA and BSA intrinsic fluorescence through a static quenching mechanism. The Stern–Volmer quenching rate constant (K_sv) was calculated as 0.372 × 10³ M^‐1 and 0.640 × 10³ M^‐1 for HSA and BSA, respectively. Moreover, binding constants (K_a), number of binding sites (n) at different temperatures, binding distance (r), and thermodynamic parameters (?H°, ?S°, and ?G°) between DiAmsar and HSA (or BSA) were calculated. DiAmsar exhibited good binding propensity to HSA and BSA with relatively high binding constant values. The positive ?H° and ?S° values indicated that the hydrophobic interaction is main force in the binding of the DiAmsar to HSA (or BSA). Furthermore, molecular docking results revealed the possible binding site and the microenvironment around the bond. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

Binding of methacycline to human serum albumin at subdomain IIA using multispectroscopic and molecular modeling methods

This study was designed to examine the interaction of methacyline (METC) with human serum albumin (HSA) by multispectroscopy and a molecular modeling method under simulative physiological conditions. The quenching mechanism was suggested to be static quenching based on fluorescence and ultraviolet–visible (UV–Vis) spectroscopy. According to the Vant' Hoff equation, the values of enthalpy (?H) and entropy change (?S) were calculated to be ?95.29 kJ/mol and ?218.13 J/mol/K, indicating that the main driving force of the interaction between HSA and METC were hydrogen bonds and van der Waals's forces. By performing displacement measurements, the specific binding of METC in the vicinity of Sudlow's site I of HSA was clarified. An apparent distance of 3.05 nm between Trp214 and METC was obtained via the fluorescence resonance energy transfer (FRET) method. Furthermore, the binding details between METC and HSA were further confirmed by molecular docking studies, which revealed that METC was bound at subdomain IIA through multiple interactions, such as hydrophobic effect, polar forces, hydrogen bonding, etc. The results of three‐dimensional fluorescence and Fourier transform infrared (FTIR) spectroscopy showed that METC caused conformational and some microenvironmental changes in HSA and reduced the α‐helix significantly in the range of 52.3?40.4% in HSA secondary structure. Moreover, the coexistence of metal ions such as Ca²⁺, Al³⁺, Fe³⁺, Zn²⁺, Cu²⁺, Cr³⁺ and Cd²⁺ can decrease the binding constants of METC–HSA. Copyright © 2012 John Wiley & Sons, Ltd.     

Spectroscopic investigation and in vitro cytotoxic activity toward HepG2 cells of a copper compound complexed with human serum albumin

The human serum albumin (HSA) interaction of a mixed‐ligand copper compound (1) with an imidazole and taurine Schiff base derived from salicylaldehyde and taurine was investigated using fluorescence spectroscopy, UV–vis spectroscopy, time‐resolved fluorescence spectroscopy, circular dichroism (CD) spectroscopy, Fourier transform infrared (FT‐IR) spectroscopy and a molecular docking technique. The results of fluorescence and time‐resolved fluorescence spectroscopy indicated that 1 can effectively quench the HSA fluorescence by a static mechanism. Binding constants (K) and the number of binding sites (n ≈ 1) were calculated using modified Stern–Volmer equations. The thermodynamic parameters were calculated. UV–vis, CD and FT‐IR spectroscopy measurements confirm the alterations in the HSA secondary structure induced by 1. The site marker competitive experiment confirms that 1 is located in subdomain IB of HSA. The combination of molecular docking results and fluorescence experimental results reveal that hydrophobic interaction and hydrogen bonds are the predominant intermolecular forces stabilizing the 1–HSA complex. The 1–HSA complex increases approximately three times its cytotoxicity in cancer cells but has no effect on normal cells in vitro. Compared with unbound 1, the 1–HSA complex promotes HepG2 cells apoptosis and also has a stronger capacity for cell cycle arrest at the S phase of HepG2 cells.