Magnitude Of Binding Constant Research Articles

Supramolecular interaction of PCBM with porphyrins in solution: Photophysical insights

This work reports the self-assembly between [6,6]-phenyl C71 butyric acid methyl ester (PCBM) and 2,3,7,8,12,13,17,18-octaethyl-21H,23H porphyrin (1)(and/2,3,7,8,12,13,17,18-octaethyl-21H,23H porphyrin Zn(II) (2) in toluene. Ground state intermolecular interaction is evidenced from absorption spectrophotometric measurements. New absorption bands are observed in the visible region which may be identified due to charge transfer (CT). Several important physicochemical factors are enumerated for PCBM-1 and PCBM-2 systems. Fluorescence investigations elicit complex formation of PCBM with porphyrins (with both 1 and 2) and reveal considerable magnitude of binding constant (K) for PCBM-2 system, i.e., KPCBM-2 = 80,435 dm3⋅mol−1 compared to PCBM-1 system, i.e., KPCM-1 = 12,600 dm3·mol-1 as well as highly ratio of selectivity in binding (KPCBM-2/KPCBM-1 ∼ 6.4). Time resolved fluorescence experiments reveal that photoexcited decay from the excited singlet state of porphyrins (i.e., 1* and 2*) by PCBM is statically controlled compared to dynamic path. Magnitude of solvent reorganization energy indicates possibility of faster charge recombination in case of PCBM-2 system. Both 1H and 13C NMR measurements provide substantial support behind complexation of PCBM with porphyrins (both 1 and 2) in solution. Ab initio calculations in vacuo support the trend in K for PCBM-1 and PCBM-2 systems and establish the proper orientation of PCBM towards 1 (and/ 2) during complexation. Transient absorption measurements establish two different mode of energy transfer pathway from porphyrin to PCBM in toluene.

Intercalation of anticancer drug Palbociclib with calf-thymus DNA: new insights from molecular spectroscopic, molecular dynamic simulations and cleavage studies

The interaction between the anti-cancer drug Palbociclib (PAL) and calf-thymus DNA (CT-DNA) was investigated using various biophysical techniques in a physiological buffer (pH 7.4). It was found that PAL intercalated into the base pairs of CT-DNA as evidenced from the results of UV-Vis, fluorescence, circular dichroism (CD), competitive binding assay with ethidium bromide (EB) and Hoechst 33258, KI quenching study, the effect of denaturing agent and viscosity measurements. The magnitude of binding constants (106 M−1) at different temperatures suggested strong binding between PAL and CT-DNA during complexation. The observed ΔHo > 0 and ΔSo > 0 indicated that the binding process is primarily driven by hydrophobic interactions. Molecular docking studies indicated partial intercalation of pyridopyrimidine ring between the base pairs of DNA. Free energy surface (FES) analysis derived from metadynamics simulation studies revealed the PAL-induced cleavage of DNA, which was confirmed by gel electrophoresis experiments. Communicated by Ramaswamy H. Sarma

Quercetin-induced inactivation and conformational alterations of alpha-2-macroglobulin: multi-spectroscopic and calorimetric study

Quercetin is a widely used bioflavonoid found in onions, grapes, berries and citrus fruits. Under certain conditions, quercetin acts as a pro-oxidant thereby generating reactive oxygen species and promoting the oxidation of molecules. Our study investigates the effect of quercetin on the structure and function of alpha-2-macroglobulin (α2M) by employing various biophysical techniques and trypsin inhibitory assay. α2M is the major antiproteinase present in the plasma of vertebrates. Results of activity assay indicated that α2M loses its 56% of inhibitory activity on treatment with quercetin in the presence of light. UV spectroscopy reveals hyper chromaticity in absorption spectra of protein on interaction with quercetin suggesting structural change. The intrinsic fluorescence studies showed quenching of α2M spectra in the presence of quercetin, and the mode of quenching was found to be static in nature. Synchronous fluorescence indicated the alteration in the microenvironment of tryptophan residues. CD and FTIR spectroscopy confirms concentration-dependent alterations in secondary structure of α2M instigated by quercetin. The magnitude of binding constant, enthalpy change, entropy change and free energy change during the interaction process was determined by isothermal titration calorimetry. Hydrogen bonding and hydrophobic interaction were the main intermolecular forces involved during the process. This study identifies and signifies the damage induced by quercetin to α2M due to its pro-oxidant action. Communicated by Ramaswamy H. Sarma

Binding studies of trans-resveratrol with superoxide dismutase (SOD1): Docking assessment and Thermoanalysis

The binding pursuits of trans-resveratrol (t-RSV), an amazing health supplement are investigated with an antioxidant enzyme, superoxide dismutase (SOD1). The aim of the study is to dock t-RSV on the adrenaline binding site on SOD1 in order to explore its potential to act as a safety net against amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder that affects motor neurons. In silico GLIDE docking methodology and in vitro microcalorimetry technique is utilized for the investigation of binding parameters of t-RSV with SOD1. The study provides useful and distinct information about the amino acids involved in the interactions at molecular level along with the nature of forces involved in binding of t-RSV with SOD1. The docking analysis using the scoring functions of Schrodinger's Glide package depicts that GLU100, PRO28, LYS23, TRP32 residues of the peptide backbone on SOD 1 interact with phenolic groups of t-RSV. The information on thermodynamic parameters, i.e. binding constant (Kb), free energy (ΔG) and enthalpy (ΔH) generated through calorimetric titrations suggests that the reaction between t-RSV and SOD 1 is spontaneous and exothermic. Both the studies are found to be in close agreement with each other based as far as the magnitude of binding constant (Kb =9.9 x10 4) is concerned.

Binding interaction of harpagoside and bovine serum albumin: spectroscopic methodologies and molecular docking

Scrophularia ningpoensis has exhibited a variety of biological activities and been used as a pharmaceutical product for the treatment of inflammatory ailment, rheumatoid arthritis, osteoarthritis and so on. Harpagoside (HAR) is considerer as a main bioactive compound in this plant. Serum albumin has important physiological roles in transportation, distribution and metabolism of many endogenous and exogenous substances in body. It is of great significance to study the interaction mechanism between HAR and bovine serum albumin (BSA). The mechanism of interaction between HAR and BSA was investigated using 2D and 3D fluorescence, synchronous florescence, ultraviolet spectroscopy and molecular docking. According to the analysis of fluorescence spectra, HAR could strongly quench the fluorescence of BSA, and the static quenching process indicated that the decrease in the quenching constant was observed with the increase in temperature. The magnitude of binding constants (KA) was more than 1×10⁵ L·mol⁻¹, and the number of binding sites(n) was approximate to 1. The thermodynamic parameters were calculated through analysis of fluorescence data with Stern-Volmer and Van't Hoff equation. The calculated enthalpy change (ΔH) and entropy change (ΔS) implied that the main interaction forces of HAR with BSA were the bonding interaction between van der Waals forces and hydrogen. The negative values of energy (ΔG) demonstrated that the binding of HAR with BSA was a spontaneous and exothermic process. The binding distance(r) between HAR and BSA was calculated to be about 2.80 nm based on the theory of Frster's non-radiation energy transfer, which indicated that energy is likely to be transfer from BSA to HAR. Both synchronous and 3D florescence spectroscopy clearly revealed that the microenvironment and conformation of BSA changed during the binding interaction between HAR and BSA. The molecular docking analysis revealed HAR is more inclined to BSA and human serum albumin (HSA) in subdomain ⅡA (Sudlow's site I). This study will provide valuable information for understanding the action mechanism of HAR.

Investigation on the interaction of glipizide with bovine hemoglobin by spectroscopy and molecular docking

ABSTRACTThis study aims to investigate the interaction between glipizide and bovine hemoglobin using fluorescence quenching, circular dichroism spectroscopy in various temperatures (293, 303, and 310 K) and molecular docking methods. The results demonstrated that glipizide could cause strong fluorescence quenching of bovine hemoglobin by a dynamic quenching mechanism, during which the hydrophobic interaction played a dominant role in this system. The order of magnitude of binding constant is 104, and the number of binding site in the system was close to 1. It also showed that tyrosine residues and tryptophan residues were both involved in the binding of glipizide with bovine hemoglobin, and was closer to the later. Circular dichroism spectra revealed that the conformation of bovine hemoglobin was changed during the binding reaction. The interaction of the system was studied by both spectroscopic method and molecular docking simulation, and the conclusions are consistent.

Interaction of transferrin with cefuroxime sodium

ABSTRACTThe interaction between cefuroxime sodium and transferrin in physiological buffer (pH 7.4) was investigated by spectroscopy at 298, 310, and 318 K. The analysis of data indicated that quenching mechanism of the transferrin–cefuroxime sodium system was probably static. The electrostatic force played an important role in the conjugation reaction between transferrin and cefuroxime sodium. The order of magnitude of binding constants (Ka) was 104, and the number of binding site (n) in the binary system was approximately equal to 1. Besides, the values of Hill’s coefficients were lager than 1, which indicated very weakly positive cooperativity in the transferrin–cefuroxime sodium system. The synchronous fluorescence spectra and circular dichroism spectra revealed that the microenvironment and the conformation of transferrin were changed during the binding reaction.

New photophysical insights on effect of gold nanoparticles on the interaction between phthalocyanine and PC70BM in solution

Photoinduced processes in phthalocyanine/functionalized gold nanoparticles (Pc/AuNps) have been investigated by spectroscopic measurements. It is observed while AuNps reduce the magnitude of binding constant for the non-covalent complexation between [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) and H2-Pc by 15.8 times in comparison to PC70BM/ZnPc system in toluene, fluorescence of ZnPc is strongly quenched in presence of AuNp. Fluorescence lifetime determined by time-correlated single photon counting is also strongly reduced for ZnPc in presence of AuNp compared to H2-Pc. Symbolic enhancement in quantum yield of charge-separation associated with well-defined electrostatic interaction has been confirmed for PC70BM/ZnPc supramolecule in presence of AuNp. Transient absorption measurements establish that energy transfer mechanism is operative for both PC70BM/H2-Pc and PC70BM/ZnPc supramolecules in absence and presence of AuNp in toluene.

Comparative Studies on the Interaction of Aspirin with Bovine Serum Albumin by Fluorescence Quenching Spectroscopy and Synchronous Fluorescence Spectroscopy

ABSTRACT The interaction of aspirin with bovine serum albumin was studied at different temperatures using fluorescence quenching and synchronous fluorescence methods. The results indicated that aspirin could quench the intrinsic fluorescence of bovine serum albumin through a static quenching process; the electrostatic interaction contributes to the binding reaction between aspirin and bovine serum albumin. The order of magnitude of binding constants was 103, and the primary binding site for aspirin was found to be sub-hydrophobic domain IIA of bovine serum albumin. The results obtained by the two methods were consistent, which indicated synchronous fluorescence spectrometry was a new method of studying the binding mechanism between drug and protein, and it was a useful supplement to the conventional method.

Fluorescence resonance energy transfer between ZnSe ZnS quantum dots and bovine serum albumin in bioaffinity assays of anticancer drugs

In the current work, using ZnSe ZnS quantum dots (QDs) as representative nanoparticles, the affinities of seven anticancer drugs for bovine serum albumin (BSA) were studied using fluorescence resonance energy transfer (FRET). The FRET efficiency of BSA–QD conjugates can reach as high as 24.87% by electrostatic interaction. The higher binding constant (3.63×107Lmol−1) and number of binding sites (1.75) between ZnSe ZnS QDs and BSA demonstrated that the QDs could easily associate to plasma proteins and enhance the transport efficacy of drugs. The magnitude of binding constants (103–106Lmol−1), in the presence of QDs, was between drugs–BSA and drugs–QDs in agreement with common affinities of drugs for serum albumins (104–106Lmol−1) in vivo. ZnSe ZnS QDs significantly increased the affinities for BSA of Vorinostat (SAHA), Docetaxel (DOC), Carmustine (BCNU), Doxorubicin (Dox) and 10-Hydroxycamptothecin (HCPT). However, they slightly reduced the affinities of Vincristine (VCR) and Methotrexate (MTX) for BSA. The recent work will not only provide useful information for appropriately understanding the binding affinity and binding mechanism at the molecular level, but also illustrate the ZnSe ZnS QDs are perfect candidates for nanoscal drug delivery system (DDS).

ZnO-ZnS QDs interfacial heterostructure for drug and food delivery application: enhancement of the binding affinities of flavonoid aglycones to bovine serum albumin

Zero-dimensional nanostructures are green nanomaterials that have recently attracted increasing attention. However, very little information is available on whether or not these heterostructures affect drug transport in blood. In current work, flavonoid aglycones were studied for their affinities for bovine serum albumin (BSA) in the presence and absence of zinc oxide-zinc sulfide quantum dots (ZnO-ZnS QDs) in vitro. The fluorescence intensity of BSA decreased remarkably with increasing concentration of ZnO-ZnS QDs, resulting in an obvious red-shift of the maximum emission of BSA from 340 to 348 nm. The magnitudes of binding constants in the presence of QDs ranged from 104 to 106 L/mol, and the number of binding sites per BSA molecule (n) was determined as 1.12 ± 0.17. Although ZnO-ZnS QDs significantly increased the affinities for BSA of myricetin, luteolin, gallocatechin gallate, tectorigenin, and formononetin, they barely affected the binding affinities of flavone, (-)-epicatechin gallate, and quercetin. From the Clinical EditorSerum albumins are major transport proteins in blood that reversibly bind fatty acids, amino acids, drugs, and inorganic ions, which interactions have important effects on the distribution, free concentration, and metabolism of drugs in blood. In this research nine flavonoid aglycones were studied for their affinities for bovine serum albumin (BSA). Interestingly it was found that presence of ZnO-ZnS QDs significantly increased the affinities of BSA for several of these aglycones.

Interaction of dietary flavonoids with gamma-globulin: molecular property-binding affinity relationship aspect

The molecular property-affinity relationship of dietary flavonoids for bovine gamma-globulin (γ-globulin) was investigated by fluorescence titration analysis. The quenching effects of flavonoids on γ-globulin fluorescence depended on the structures of flavonoids. The magnitudes of binding constants between flavonoids and γ-globulin were within the range of 10(3)-10(5) L mol(-1). These data were much smaller than the affinities between flavonoids and purified bovine and human serum albumins. The affinities of flavonoids for γ-globulin were strongly influenced by the structural differences of the compounds under study. The affinities for γ-globulin decreased with increasing partition coefficients and increased with increasing hydrogen bond acceptor numbers of flavonoids, which suggested that the binding interaction was mainly caused by hydrogen bond forces.

Molecular property–binding affinity relationship of flavonoids for common rat plasma proteins in vitro

The structural difference of flavonoids strongly affects the binding process with plasma proteins. This work in here mainly concerns about the molecular property–binding affinity relationship of dietary flavonoids for common rat plasma proteins (CRPP). The magnitudes of binding constants between flavonoids and CRPP were within the range of 10 4–10 5 L/mol and the number of binding sites ( n) was determined as 1.02 ± 0.19. These data were much smaller than the affinities between flavonoids and purified bovine and human serum albumins. The hydroxylation on rings A, B and C of flavonoids significantly affected the binding affinity. The glycosylation of dietary flavonoids decreased the binding affinity and the C2 C3 double bond hardly affected it. The galloylated catechins have higher binding affinities for CRPP than non-galloylated catechins. Flavonoids played as a hydrogen bond acceptor when bound to CRPP. The flavonoids with high topological polar surface areas (TPSA) are bound tightly while those with low TPSA are not.

Metal ion-directed DNA recognition by chelating DNA ligands.

Novel DNA ligand bearing oxine and pyridinium group has been synthesized. The DNA binding of this ligand was regulated by coexisting Cu2+ over the range of more than three orders in magnitude of binding constant. This should be due to the metal-mediated dimerization of the ligand and concomitant emergence of cationic charges. There were definite two DNA binding modes for the ligand dimer depending on the P/L ratio.

Evidence for an androgen receptor in the human placenta

A steroid-binding protein was examined in human placental cytosol and nuclei which had several characteristics of an androgen receptor. It binds R 1881 (methyltrienolone), a steroid specific for androgen receptors, with high affinity (dissociation constant = 1.3 to 50 nM) and low capacity (n = 1.2 to 21 fmoles/mg of protein). The steroid-binding protein is found in the nuclei as well as the cytosol of the placenta but is not found in either the cytosol or the nuclei of fetal membranes; thus, it is tissue-specific. Among the natural steroids, 5α-dihydrotestosterone competes most efficiently with R 1881 for binding to the protein. Testosterone is the next best competitor. When the ranges of dissociation constants and concentrations of binding sites for placentas of various gestational periods are compared, no significant differences are observed between period of gestation and magnitude of binding constants.