Fluorescence and circular dichroism studies on binding and conformational aspects of an anti-leukemic drug with DNA.

In the present study, we have explored the mode of binding of an anti-leukemic drug, imatinib (IMT) mesylate with DNA and resulting conformational changes in DNA double helix. UV-Vis absorption, fluorescence and circular dichroism spectroscopic techniques were employed to study these interactions. Spectroscopic results revealed that the intercalation was the primary mode of interaction between IMT and DNA. The binding constant value of 6.62 × 10(3 )M(-1) indicated the moderate interaction between IMT and DNA. Melting temperature of DNA increased from 75 to 80 °C upon interaction with IMT.

Elucidation of binding mechanism and identification of binding site for an anti HIV drug, stavudine on human blood proteins.

The binding of stavudine (STV) to two human blood proteins [human hemoglobin (HHb) and human serum albumin (HSA)] was studied in vitro under simulated physiological conditions by spectroscopic methods viz., fluorescence, UV absorption, resonance light scattering, synchronous fluorescence, circular dichroism (CD) and three-dimensional fluorescence. The binding parameters of STV-blood protein were determined from fluorescence quenching studies. Stern-Volmer plots indicated the presence of static quenching mechanism in the interaction of STV with blood proteins. The values of n close to unity indicated that one molecule of STV bound to one molecule of blood protein. The binding process was found to be spontaneous. Analysis of thermodynamic parameters revealed the presence of hydrogen bond and van der Waals forces between protein and STV. Displacement experiments indicated the binding of STV to Sudlow's site I on HSA. Secondary structures of blood proteins have undergone changes upon interaction with STV as evident from the reduction of α-helices (from 46.11% in free HHb to 38.34% in STV-HHb, and from 66.44% in free HSA to 52.26% in STV-HSA). Further, the alterations in secondary structures of proteins in the presence of STV were confirmed by synchronous and 3D-fluorescence spectral data. The distance between the blood protein (donor) and acceptor (STV) was found to be 5.211 and 5.402 nm for STV-HHb and STV-HSA, respectively based on Föster's non-radiative energy transfer theory. Effect of some metal ions was also investigated. The fraction of STV bound to HSA was found to be 87.8%.

Interactions of polyphenols with plasma proteins: insights from analytical techniques.

Phenolic compounds are commonly found in natural sources like plant-based foods and beverages. These compounds have received much attention due to their unique biological properties. Polyphenols possess a significant binding affinity for serum albumins which are known to be principal extracellular proteins with a high concentration in blood plasma. They act as carriers of several drugs to different molecular targets. This review summarizes the salient features of the reported work on polyphenol-protein interactions by analytical methods viz., chromatography, circular dichroism, fluorescence spectroscopy (steady state and time resolved), light scattering, equilibrium dialysis, differential scanning calorimetry, UV-vis spectroscopy, isothermal calorimetry, MALDI-TOF mass spectrometry, size exclusion chromatography, capillary electrophoresis, electrospray ionization mass spectrometry, FT-IR, molecular modelling, HPLC, NMR, cyclic voltammetry etc. Polyphenol-serum albumin interaction studies assume significance from the view point of pharmacokinetics and pharmacodynamics.

Investigations to reveal the nature of interactions of human hemoglobin with curcumin using optical techniques.

Curcumin (CUR) is an important bioactive compound present in the rhizome of Curcuma longa. Herein, we report the interaction of CUR with human hemoglobin (Hb) using various biophysical methods viz., fluorescence, UV absorption, resonance light scattering spectra (RLS), synchronous fluorescence, fluorescence anisotropy, circular dichroism (CD) and three-dimensional fluorescence. There was a considerable quenching of the intrinsic fluorescence of Hb upon binding to CUR through dynamic quenching mechanism. The distance (r) between the donor and acceptor was obtained from the Forster's theory of fluorescence resonance energy transfer (FRET) and found to be 1.55 nm. Alterations in the conformation of Hb due to its interaction with CUR were confirmed by UV absorption and CD spectroscopic methods. The α-helicity of Hb was found to decrease upon binding with CUR.

Interaction of antioxidant flavonoids with calf thymus DNA analyzed by spectroscopic and electrochemical methods.

Mechanism of interaction of bioactive flavonoids, hesperitin (HES) and naringenin (NAR) with calf thymus deoxyribonucleic acid (DNA) was studied employing UV absorption, fluorescence, circular dichroism, melting temperature, fluorescence anisotropy and differential pulse voltammetric methods. The observed fluorescence quenching of DNA-ethidium bromide system by the flavonoid indicated the intercalative mode of binding between the flavonoid and DNA. Stern-Volmer plots have revealed the presence of static quenching mechanism. Binding and thermodynamic characteristics of interaction were evaluated. Melting temperature of DNA was found to be increased up to 5 °C in the presence of the flavonoid indicating the stabilization of DNA double helix upon binding. CD and fluorescence anisotropic results have revealed the conformational changes in DNA upon binding to the flavonoid. The observed positive shift in peak potential and decreased peak current of the flavonoid in the presence of DNA further supported the intercalative mode of binding.

Optical, structural and thermodynamic studies of the association of an anti-leucamic drug imatinib mesylate with transport protein.

The interaction of an anti-leukemic drug, imatinib mesylate (IMT) with human serum albumin (HSA) was investigated by fluorescence, synchronous fluorescence, three-dimensional fluorescence, circular dichroism and UV-vis absorption techniques under physiological condition. The process of binding of IMT on HSA was observed to be through a spontaneous molecular interaction procedure. IMT effectively quenched the intrinsic fluorescence of HSA via static quenching. The values of binding constant, number of molecules that interact simultaneously with the binding site and thermodynamic parameters were evaluated by carrying out the interactions at three different temperatures. Based on thermodynamic parameters and displacement studies with site probes, it was proposed that the drug bound at Sudlow's site I of subdomain IIA. The change in the conformation of HSA was evident from synchronous, three-dimensional fluorescence and circular dichroism studies. The distance between the donor (protein) and acceptor (drug) was calculated based on the Foster's theory of resonance energy stransfer and it was found to be 1.30 nm. The effect of different metal ions on the binding of the drug to protein was also investigated.

Exploring the binding mechanism of ondansetron hydrochloride to serum albumins: spectroscopic approach.

The mechanism of interaction of ondansetron hydrochloride (OND) to serum albumins [bovine serum albumin (BSA) and human serum albumin (HSA)] was studied for the first time employing fluorimetric, circular dichroism, FTIR and UV-vis absorption techniques under the simulated physiological conditions. Fluorimetric results were utilized to investigate the binding and conformational characteristics of protein upon interaction with varying concentrations of the drug. Higher binding constant values revealed the strong interaction between the drug and protein while the number of binding sites close to unity indicated single class of binding site for OND in protein. Thermodynamic results revealed that both hydrogen bond and hydrophobic interactions played a major role in stabilizing drug-protein complex. Site marker competitive experiments indicated that the OND bound to albumins at subdomin II A (Sudlow's site I). Further, the binding distance between OND and serum albumin was calculated based on the Förster's theory of non-radioactive energy transfer and found to be 2.30 and 3.41 nm, respectively for OND-BSA and OND-HSA. The circular dichroism data revealed that the presence of OND decreased the α-helix content of serum albumins. 3D-fluorescence results also indicated the conformational changes in protein upon interaction with OND. Further, the effects of some cations have been investigated in the interaction of drug to protein.

Interaction of triprolidine hydrochloride with serum albumins: thermodynamic and binding characteristics, and influence of site probes.

The interaction between triprolidine hydrochloride (TRP) to serum albumins viz. bovine serum albumin (BSA) and human serum albumin (HSA) has been studied by spectroscopic methods. The experimental results revealed the static quenching mechanism in the interaction of TRP with protein. The number of binding sites close to unity for both TRP-BSA and TRP-HSA indicated the presence of single class of binding site for the drug in protein. The binding constant values of TRP-BSA and TRP-HSA were observed to be 4.75 ± 0.018 × 10(3) and 2.42 ± 0.024 × 10(4)M(-1) at 294 K, respectively. Thermodynamic parameters indicated that the hydrogen bond and van der Waals forces played the major role in the binding of TRP to proteins. The distance of separation between the serum albumin and TRP was obtained from the Förster's theory of non-radioactive energy transfer. The metal ions viz., K(+), Ca(2+), Co(2+), Cu(2+), Ni(2+), Mn(2+) and Zn(2+) were found to influence the binding of the drug to protein. Displacement experiments indicated the binding of TRP to Sudlow's site I on both BSA and HSA. The CD, 3D fluorescence spectra and FT-IR spectral results revealed the changes in the secondary structure of protein upon interaction with TRP.

Evaluation of binding and thermodynamic characteristics of interactions between a citrus flavonoid hesperitin with protein and effects of metal ions on binding.

The mechanism of interaction of a non-glycosidic citrus flavonoid, hesperitin (HES) with bovine serum albumin (BSA) was studied by UV-vis absorption, fluorescence, FT-IR, circular dichroism, fluorescence anisotropy and synchronous fluorescence spectroscopy in phosphate buffer of pH 7.4. Fluorescence data revealed that the fluorescence quenching of BSA by HES was the result of the formed complex of HES-BSA. The binding constants and thermodynamic parameters at four different temperatures, the location of binding, and the nature of binding force were determined. The hydrogen bonds interactions were found to be the predominant intermolecular forces to stabilize the complex. The conformation of BSA was discussed by synchronous fluorescence and CD methods. The alterations of protein secondary structure upon complexation with HES were evident from the gradual decrease in α-helicity. The distance between the donor (BSA) and acceptor (flavonoid) was calculated from the fluorescence resonance energy transfer and found to be 1.978 nm. Common ions viz., Zn(2+), K(+), Cu(2+), Ni(2+), Mn(2+) and Co(2+) were found to influence the binding of flavonoid to protein.

Binding of an anti-inflammatory drug lornoxicam with blood proteins: insights from spectroscopic investigations.

The interaction between an anti-inflammatory drug, lornoxicam (LXM) and protein (human serum albumin and bovine serum albumin) was studied by spectroscopic techniques (Fluorescence, synchronous, FT-IR, UV-vis absorption and circular dichroism). The quenching mechanism of fluorescence of the protein by the drug was discussed. Based on the interaction studies carried out at different temperatures by spectrofluorometry, the binding constant and the number of binding sites for drug on protein have been evaluated. The nature of binding force operating between the drug and protein was proposed to be electrostatic and hydrophobic based on thermodynamic parameters. The distance r between the donor (protein) and acceptor (drug) was determined based on the Förster's theory of non-radiation energy transfer and found to be 2.38 nm and 2.56 nm for LXM-BSA and LXM-HSA respectively. Displacement studies with different site probes revealed that the drug bound to the hydrophobic pocket located in sub domain IIA; that is to say, Trp-214 was near or within the binding site. Circular dichroism data of protein in the presence of drug revealed the decreased α-helicity and hence changes in secondary structure of protein. The effects of some common ions were also investigated.