Binding Constants Of Complexes Research Articles

Oxadiazole based Os(IV) compounds as potential DNA intercalator and cytotoxic agents

Os(IV) compounds and ligands have been synthesized and well characterized. DNA cleavage tendency of compounds has been evaluated using gel electrophoresis and binding behavior has been evaluated by viscosity measurements, absorption titration, fluorescence, and docking studies. All the compounds show the intercalation mode of binding. The binding constant of complexes falls at about 1.8–7.6 × 104 M−1. Bacteriostatic activity of compounds has been evaluated on a series of gram+ve and gram−ve bacteria in terms of their MIC values. Also, the compounds have been screened for in vivo and in vitro cytotoxicity assays on S. Pombe cell’s DNA and HCT-116 cell line. LC50 of ligands and Os(IV) complexes are in the range of 7.92–19.91 and 4.00–11.74 μg/mL respectively.

Quantifying Non‐Covalent Binding Interactions between Tobacco Alkaloids and Cyclodextrin Using Mass Spectrometry and the Application in Cigarette Smoke

Quantifying Non‐Covalent Binding Interactions between Tobacco Alkaloids and Cyclodextrin Using Mass Spectrometry and the Application in Cigarette Smoke

Tetrazolo[1,5-a]quinoline moiety-based Os(IV) complexes: DNA binding/cleavage, bacteriostatic and photocytotoxicity assay

Biological applications of platinum group metal-based complexes have been widely explored in synthetic and inorganic chemistry. The compounds have been subjected to DNA binding, DNA cleavage, In-vivo and In-vitro photocytotoxicity (HCT-116 cell line) and bacteriostatic activities. Binding constant of complexes are 1.42–5.62 × 104 M −1, whereas that of ligands are 1.12–4.72 × 104 M −1. K sv of complexes are about 1.32–5.21 × 103 M −1, whereas K f is about 1.24–6.83 × 103 M −1. IC50 of compounds screened using HCT-116 cell line in dark are found to be 121–342 μg/mL. Whereas photocytotoxicity is found in the range of 48–316 μg/mL. Docking energy of molecules have been evaluated to evaluate efficacy of binding. Molecular docking energy of complexes are in the range of −286.00 to −303.11 kJ/mol. Whereas that of ligands are −254.03 to −282.96 kJ/mol. MIC of complexes are 47 ± 2.5 to 77.50 ± 7.5 μM. LC50 values of ligands fall in the range of 4.05–19.72 μg/mL and that of Os(IV) complexes fall in the range of 3.99–15.99 μg/mL. The Os(IV) complexes dominate in proving its potentiality compared to N, N-donor ligands in biological activities. Communicated by Ramaswamy H. Sarma

Interaction of zearalenone-14-sulfate with cyclodextrins and the removal of the modified mycotoxin from aqueous solution by beta-cyclodextrin bead polymer

The xenoestrogenic mycotoxin zearalenone is a common food contaminant produced by Fusarium strains. The modified mycotoxin zearalenone-14-sulfate (Z14S) is formed in both fungi and mammals during the biotransformation of zearalenone. Cyclodextrins (CD) are cyclic oligosaccharides which can form host-guest type complexes with some mycotoxins, including zearalenone, zearalenols, and zearalenone-14-glucoside. As a result of the complex formation, the fluorescence signal of these mycotoxins strongly increases. Furthermore, CD polymers seem to be suitable for the extraction of some mycotoxins from aqueous solutions and beverages. In this study, the interaction of Z14S with CDs and soluble CD polymers was examined with fluorescence spectroscopy and molecular modeling. Furthermore, the removal of Z14S from aqueous solution by β-CD bead polymer (BBP) was also tested. Our results demonstrate the formation of stable Z14S-CD complexes (K = 0.1 to 5.0 × 104 L/mol). Dimethyl-β-CD (DIMEB) produced the most stable complexes with Z14S at pH 5.0 and 7.4. At pH 10.0, the binding constant of Z14S-DIMEB complex decreased and quaternary ammonium-β-CD showed similar affinity toward the mycotoxin than DIMEB. In addition, Z14S was successfully removed from aqueous solutions by BBP. Considering the above-listed observations, besides the parent mycotoxins, some of their modified/masked derivatives can also interact with CDs.

Formation mechanism and photo physical behaviors of Pyrene-Methyl-beta-cyclodextrin complex at excited state

Structural characterization of the Pyrene-Methyl-beta-cyclodextrin (Py-Me-β-CD) complex, obtained in aqueous medium, was carried out through Fourier Transform Infrared spectroscopy (FTIR), X-ray diffractometry (XRD), 1H NMR and two-dimensional correlated spectroscopy (2D COSY). Thermal characterization of the Py-Me-β-CD complex was performed with differential scanning calorimetry (DSC) and thermogravimetry (TG). Gibbs free energy and excited singlet state energy values of the complex were calculated. The stoichiometry of the complex was determined to be 1:2 by the Benesi-Hildebrand method. The complex binding constant (Kb), which was 1.5 × 1011 M−1, indicated a strong inclusion complex. Both thermal and XRD analyzes showed that the crystallinity of the pyrene decreased and its thermal stability increased as a result of complex formation. The most obvious quenching effect in the transition metals (cobalt, iron, zinc, copper, manganese and nickel) was obtained with iron. Calculated Stern-Volmer constant (Ksv) and the quenching activation energy (Ea) values showed that iron interacted with the complex differently. The lifetime (τ) and bimolecular quenching rate constant (kq) calculations pointed to diffusion controlled dynamic quenching for the metals, other than iron. In addition, with the energy band calculations made, it was shown by means of Tauc plots, that electron transfer was made to iron and manganese metals from the complex fluorophore group, as part of the quenching mechanism. The value of the activation energy for iron indicated a weakly bound encounter complex formation.

Dirhenium(III) complex with beta-alanine ligand: anticancer, antioxidant and DNA-binding properties

Earlier we have shown that dirhenium(III) dicarboxylate complex with γ-aminobutyric acid possessed higher antitumor activity, than those of the previously investigated alkylcarboxylates, also may act as a modulator of cisplatin mechanism of action and as a stabilizer of red blood cells in tumor-bearing organisms. Thus, the task of the work was to investigate anticancer activity of the complex cis-[Re2(β-Ala)2Cl6] (I) in the model of tumor growth in vivo and to realize if the amino acid residue influences the DNA-binding activity of the amino acid derivatives of the cluster rhenium(III) compounds. Antitumor properties of the complex I were studied in the model of tumor growth with the use of Wistar rats inoculated by tumor carcinoma Guerink cells. The introduction of the compound alone in free and liposomal forms inhibited the tumor growth by 36 % and 45 % correspondingly, that is more than for dirhenium(III) clusters with alkyl ligands. The combined introduction of I and cisplatin had a significant impact on the tumor growth and showed the disappearance of the tumors in most of the animals. No considerable differences were found between introduction of liposomal and free form of I. The electronic absorption spectra of Calf Thymus DNA (CT-DNA) exhibit hyperchromism in the presence of increasing amounts of I. The DNA band at ~ 260 nm arises from the π-π* transitions of the nucleic acid bases and changes in the intensity and slight wavelength shifts of this characteristic band reflect the corresponding structural modifications of the DNA, which include changes in stacking, disruption of the hydrogen bonds between complementary strands, covalent binding of the DNA bases, intercalation of aromatic rings and others. The binding constant Kb(I) = 2.43 × 103 M-1 to CT-DNA was obtained that was lower than the values reported for the classical DNA intercalators and compares well with the magnitude of the binding constants for other complexes of dirhenium(III); titration of СT-DNA with cisPt and hydrogen peroxide also leads to a hypochromic effect, weak at low concentrations and more significant at high concentrations of I; the DNA binding constants increased in several times when using H2O2 or cisplatin that confirms a mechanism for redox activation of interaction of I with DNA in a cancer cell. The obtained results demonstrate the possibility of application of the amino acid derivatives of dirhenium(III) clusters in antitumor therapy.

Determination of binding constants of multiple charged cyclodextrin complexes by ACE using uncorrected and ionic strength corrected actual mobilities of the species involved.

In this study, the apparent binding constants and limiting mobilities of the multiply charged complexes of the Δ- and Λ-enantiomers of Ru(II)- and Fe(II)-polypyridyl associates ([Ru(2,2'-bipyridine)3 ]2+ , [Ru(1,10-phenanthroline)3 ]2+ , and [Fe(1,10-phenanthroline)3 ]2+ ) with single-isomer 2,3-diacetylated-6-sulfated-cyclodextrins (CDs) (12Ac-6S-α-CD, 14Ac-7S-β-CD, and 16Ac-8S-γ-CD) were determined by ACE using uncorrected and ionic strength corrected actual mobilities of the species involved. Two limiting models were tested for the ionic strength correction of the actual mobilities based on an empirical relation for the ionic strength correction of multivalent ionic species. In model 1, the nominal values of the charge numbers (zS,nom ) and analytical concentrations (cS,nom ) of the above CD selectors in the BGEs were applied for calculation of the BGE ionic strength, as usual. In model 2, the CD selectors were considered as singly charged species (zS =-1) with |zS,nom |-times higher concentrations in the BGE than their analytical concentrations (cS =|zS,nom |×cS,nom ) in the calculation of the BGE ionic strength. In all three cases-with uncorrected actual mobilities as well as with actual mobilities corrected according to the two limiting models-the measured effective mobilities of the above enantiomers fit well the theoretical curves of their mobility dependences on the CD selectors concentrations in the BGE, with high average coefficients of determination (R2 =0.9890-0.9995). Nevertheless, the best physico-chemically meaningful values of the apparent binding constants and the limiting mobilities of the enantiomer-CDs complexes with low RSDs were obtained using the actual mobilities of the species involved corrected according to model 2.

Molecular interaction of sulfonamides and ovalbumin, an allergenic egg protein, exploring biophysical, theoretical and biological studies.

Biophysical, theoretical and biological in vitro studies were carried out to evaluate the interaction of the main allergen protein of egg white (ovalbumin, OVA) with sulphonamides (SA): sulphathiazole (S1), sulfaquinoxaline (S2), sulfadimethoxine (S3) and sulfamethazine (S4). The binding constants for the OVA-SA supramolecular complexes ranged from 1.20 to 30.66 × 105 M-1, observing the following order of affinity: S1 > S2 > S4 > S3. The preferential forces in the stabilization of the OVA complexes with S2 and S3 were hydrogen bonds and Van der Waals forces, whereas for OVA-S1 and OVAS4, were electrostatic interactions. Interaction process led to a change in the native structure of the protein, which may potentiate its natural allergenicity. Cations Ca(II), Mg(II) and Fe(III) favor the interaction of OVA with S1 and S2. The theoretical studies performed were consistent with the spectroscopic data. Finally, it was found that the interaction process for sulfonamides evaluated with OVA change the inhibition activity profile these antibiotics against strains of Escherichia coli ATCC 25922 and Bacillus megaterium APFSG3isox, but not the minimal inhibitory concentration values.

Synthesis of Two Mononuclear Schiff Base Metal (M = Fe, Cu) Complexes: MOF Structure, Dye Degradation, H2O2 Sensing, and DNA Binding Property.

O-Vanillin and ethylenediamine were used for the synthesis of N,N′-bis(O-vanillinidene)ethylenediamine (O-VEDH2) Schiff base ligand, which was characterized by UV–visible and 1H NMR spectroscopy. The Schiff base ligand O-VEDH2 has been employed to synthesize novel [C18H22FeN2O6]NO3 (1) and C18H16CuN2O5 (2) complexes by the simple slow evaporation method. The single crystals were characterized by X-ray crystallography, as well as Fourier-transform infrared and UV–visible spectroscopy techniques. Complexes 1 and 2 crystallize in monoclinic and orthorhombic space groups with P121/n1 (14) and Pnma (62) point groups, respectively, and both show metal–organic frameworks like structures. Complexes 1 and 2 have optical band gaps of 4.1 and 2.9 eV, respectively, indicating their semiconducting properties. The dye degradation activity and H2O2 sensing of the complexes 1 and 2 were determined in different conditions. The photocatalytic test was performed in the presence of sunlight, methylene blue (MB), and complexes 1 and 2. An interesting result was obtained that complex 2 has degradation ability against MB and the rate constant (K) is 5.46 × 10–5 s–1, whereas complex 1 has H2O2 sensing properties. Both complexes are bound to Calf-thymus DNA by intercalation binding mode, and binding constants (Kb) of complexes 1 and 2 are 3.77 × 103 and 1.49 × 104 M–1, respectively.

Influence of alcohols/electrolytes on the interaction of reactive red dye with surfactant and removal of dye from solutions

Interactions of anionic textile dye -reactive red (RR) with cetyltrimethylammonium bromide (CTAB), a cationic surfactant in the absence as well as the presence of different electrolytes and alcohols of different concentrations have been studied with the help of UV–vis spectroscopy and molecular dynamics simulation. The dye-surfactant binding was observed to be taken place at a concentration of the surfactant far below cmc (generally cmc varies from 0.9 mM to 1.2 mM). The binding of dye and surfactant was reflected by a significant change in λmax with the appearance of splitting of the band in the spectrum of the dye. The binding constant (Kb) of complexation was executed by means of the Benesi-Hildebrand plot. The binding constant (Kb) of RR-CTAB complexes increased with increasing concentration of dye, concentration of electrolytes added, dielectric constant and pH of the medium. The values of binding constant for RR-CTAB system dwindled with the enhancement of the temperature. TheΔG0 values of the complexes were found to be negative which indicate that complex formation was thermodynamically spontaneous. The negative values of ΔH0 indicate that the complexation process is exothermic and positive values of ΔS0 indicate that RR-CTAB complexation is both an enthalpy & entropy governed phenomena. The dye can be effectively removed from the waste water by the interaction of dye with surfactant in presence of salt of higher concentration and 30% ethanol. Moreover, MD simulations provided a detailed analysis of the mechanism of interaction between the dye and surfactant molecules.

Complexation of chitosan with gum Arabic, sodium alginate and κ-carrageenan: Effects of pH, polymer ratio and salt concentration

The effects of pH, ionic strength and polymer ratio in the complexation of chitosan (CHI) with different anionic polysaccharides, namely gum Arabic (GA), sodium alginate (ALG) and κ-carrageenan (CRG), were investigated. This was made using titration techniques, which allowed the determination of stoichiometry and binding constant of complexes. The sulfated polysaccharide interacted more strongly with CHI than carboxylated polysaccharides. The increase of ionic strength (0–100 mM NaCl) in the polysaccharides complexation resulted in a significant reduction in the binding constant of GA:CHI and CRG:CHI, but did not influence the complexation of ALG with CHI. The pH and polymer ratio affected the formation and solubility of complexes GA:CHI, while for ALG:CHI and CRG:CHI, insoluble complexes were observed in all pH and polymer ratio evaluated. A phase transition of coacervate to gel was proposed to ALG:CHI and CRG:CHI, which can be related to the self-association of anionic polymers, when these are in excess.

Host-guest interaction studies of polycyclic aromatic hydrocarbons (PAHs) in alkoxy bridged binuclear rhenium (I) complexes.

The interaction of two neutral alkoxy bridged binuclear rhenium(I) complexes, 1 and 2 [{Re(CO)3(1,4-NVP)}2(μ2-OR)2] (1, R = C4H9; 2, R = C10H21; 1,4-NVP = 4-(1-naphthylvinyl)pyridine] with polycyclic aromatic hydrocarbons (PAH) is investigated. UV-vis absorption, emission, 1H NMR spectral titrations, TCSPC lifetime studies and DFT theoretical calculations were carried out to examine the binding responses of complexes 1 and 2 with various PAHs such as pyrene, naphthalene, anthracene and phenanthrene. The UV-Vis absorption spectra showed an increase in absorbance of the metal-to ligand charge-transfer (MLCT) and ligand centered (LC) bands upon addition of various PAH molecules to 1 and 2, whereas the emission behavior was found to show emission quenching, which might occur through energy transfer pathway. The binding constants (K) of complexes 1 and 2 for various PAHs are found to be in the order of 104 M-1 with a 1:1 binding mode, as determined from UV-vis absorption and emission spectral titration studies. 1H NMR spectral studies show that the chemical shifts of pyrene guest and the 1,4-NVP moiety of 2 are shifted up-field, whilst the alkoxy protons do not show any appreciable change in their chemical shifts. It is believed that the open cavities present in the Re(I) complexes may lead to the recognition of PAHs via CH···π interaction.

Thermodynamic parameters for the complexation of water-insoluble betulin derivatives with (2-hydroxypropyl)-γ-cyclodextrin determined by phase-solubility technique combined with capillary zone electrophoresis.

The complexation of betulinic and betulonic acids (BIA and BOA) (pentacyclic lupane triterpenoids) with (2-hydroxypropyl)-γ-cyclodextrin (HP-γ-CD) was studied at different temperatures using the method combining phase-solubility technique and CZE. In contrast to mobility shift ACE utilizing the electrophoretic mobility, in this approach, the peak areas are used. The apparent binding (stability, formation) constants are obtained by the Higuchi and Connors method from the linear segment of compound solubility diagrams in CD solutions. It was found that the apparent binding constants of the HP-γ-CD complexes of BIA and BOA decrease with increasing temperature. The binding constants of BOA complexes are slightly higher than those of BIA complexes; this can be explained by difference in the hydration degrees of carbonyl and hydroxyl groups. On the basis of the binding constants obtained and their temperature dependences (van't Hoff plot), the enthalpy as well as entropy changes and Gibbs free energies were calculated. It was found that the complexation was characterized by negative changes of enthalpy and entropy, that is, it was controlled by enthalpy changes. The results obtained can be used for the optimization of microcapsulation processes of BOA and BIA with the HP-γ-CD application in order to increase solubility and bioavailability of these compounds.

A comparative spectroscopic, surface plasmon resonance, atomic force microscopy and molecular docking studies on the interaction of plant derived conferone with serum albumins

Abstract The binding mechanism of conferone, a natural sesquiterpene-coumarin, on human and bovine serum albumins (HSA/BSA), was studied using circular dichroism (CD), fluorescence and FT-IR spectroscopy as well as atomic force microscopy (AFM), surface plasmon resonance (SPR) and molecular docking methods. For real time monitoring the interaction between albumins and conferone, after immobilization of HSA/BSA on carboxymethyl dextran hydrogel Au chip (CMD) and activation of carboxylic groups on chip surface, the refractive index of metal sensor chip variations upon interaction of albumins with conferone were analyzed by SPR method, separately. The affinity values (KA) about 1.9 × 106 for HSA-conferone and 1.35 × 106 for BSA-conferone complex demonstrated moderate affinity for conferone interaction. Further, the intrinsic fluorescences of HSA/BSA were quenched by addition of conferone through the formation of a ground state complex and static quenching mechanism. The number of binding sites (≈1 for both systems), and overall binding constants (K) for HSA-conferone and BSA-conferone complexes were calculated about 104 and 102, respectively. Analysis of the thermodynamic parameters indicated that hydrogen bonding and van der Waals interaction were major intermolecular forces between conferone and HSA/BSA. Probing the secondary structure of the albumins by FTIR, AFM and circular dichroism spectroscopy and molecular docking simulation demonstrated that, binding of conferone induces alterations in the secondary structure of albumins and suggested the subdomain IB of HSA and subdomain IA of BSA as specific binding sites for conferone interaction.

Interaction of cobalt(II) and copper(II) hydroxamates with polyriboadenylic acid: An insight into RNA based drug designing

The polyadenylic acid [poly(A)] tail of mRNA plays a noteworthy role in the initiation of the translation, maturation, and stability of mRNA. It also significantly contributes to the production of alternate proteins in eukaryotic cells. Hence, it has recently been recognized as a prospective drug target. Binding affinity of bis(N-p-tolylbenzohydroxamato)Cobalt(II), [N-p-TBHA-Co(II)] (1) and bis(N-p-naphthylbenzohydroxamato)Copper(II), [N-p-NBHA-Cu(II)] (2) complexes with poly(A) have been investigated by biophysical techniques namely, absorption spectroscopy, fluorescence spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, circular dichroism spectroscopy, viscometric measurements and through molecular docking studies. The intrinsic binding constants (Kb) of complexes were determined following the order of N-p-TBHA-Co(II)] > N-p-NBHA-Cu(II), along with hyperchromism and a bathochromic shift for both complexes. The fluorescence quenching method revealed an interaction between poly(A)-N-p-TBHA-Co(II)/poly(A)-N-p-NBHA-Cu(II). The mode of binding was also determined via the fluorescence ferrocyanide quenching method. The increase in the viscosity of poly(A) that occurred from increasing the concentration of the N-p-TBHA-Co(II)/N-p-NBHA-Cu(II) complex was scrutinized. The characteristics of the interaction site of poly(A) with N-p-TBHA-Co(II)/N-p-NBHA-Cu(II) were adenine and phosphate groups, as revealed by DRS-FTIR spectroscopy. Based on these observations, a partial intercalative mode of the binding of poly(A) has been proposed for both complexes. Circular dichroism confirmed the interaction of both the complexes with poly(A). The molecular docking results illustrated that complexes strongly interact with poly(A) via the relative binding energies of the docked structure as −259.39eV and −226.30eV for N-p-TBHA-Co(II) and N-p-NBHA-Cu(II) respectively. Moreover, the binding affinity of N-p-TBHA-Co(II) is higher in all aspects than N-p-NBHA-Cu(II) for poly(A).

In vitro cytotoxicity studies of parent and nanoencapsulated Holmium-2,9-dimethyl-1,10-phenanthroline complex toward fish-salmon DNA-binding properties and antibacterial activity

In this study, the interaction of Holmium (Ho) complex including 2, 9-dimethyl-1,10-phenanthroline, also called Neocuproine (Neo), [Ho(Neo)2Cl3.H2O], as fluorescence probe with fish-salmon DNA (FS-DNA) is studied during experimental investigations. Multi-spectroscopic methods are utilized to determine the affinity binding constants (Kb) of complex–FS-DNA. It is found that fluorescence of Ho complex is strongly quenched by the FS-DNA through a static quenching procedure. Under optimal conditions in Tris(trishydroxymethyl-aminomethane)–HCl buffer at 25 °C with pH ≈ 7.2, intrinsic binding constant Kb of Ho complex is 6.12 ± 0.04 × 105 M−1. Also, the binding site number and Stern–Volmer quenching constant are calculated. There are different approaches, including iodide quenching assay, salt effect and thermodynamical assessment to determine the features of the binding mode between Ho complex and FS-DNA. Also, the parent and starch and lipid nanoencapsulated Ho complex, as potent antitumor candidates, were synthesized. The main structure of Ho complex is maintained after encapsulation using starch and lipid nanoparticles. 3-[4,5-Dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) method was used to assess the anticancer properties of Ho complex and its encapsulated forms on human cancer cell lines of human lung carcinoma cell line and breast cancer cell line. In conclusion, these compounds could be considered as new antitumor candidates.Communicated by Ramaswamy H. Sarma

Fluorescein derived Schiff base as fluorimetric zinc (II) sensor via ‘turn on’ response and its application in live cell imaging

A novel Schiff base L composed of fluorescein hydrazine and a phenol functionalized moiety has been designed and prepared via cost-effective condensation reaction. The L is utilized for selective sensing of Zn2+ over other environmental and biological relevant metal ions in aqueous alcoholic solution under physiological pH range. The binding of Zn2+ to the receptor L is found to causes ~23 fold fluorescence enhancement of L. The 1:1 binding mode of the metal complex is established by combined UV-Vis, fluorescence, and HRMS (high-resolution mass spectroscopy) spectroscopic methods. The binding constant (Ka) for complexation and the limit of detection (LOD) of Zn2+ is calculated to be 2.86 × 104 M-1 and 1.59 μM, respectively. Further photophysical investigations including steady-state, time-resolved fluorescence analysis and spectral investigations including NMR (nuclear magnetic resonance), IR (infrared spectroscopy) suggest introduction of CHEF (chelation enhance fluorescence) with the suppression of CN isomerization and PET (photo-induced electron transfer) mechanism for the strong fluorescent response towards Zn2+. Finally, the sensor L is successfully employed to monitor a real-time detection of Zn2+ by means of TLC (thin layer chromatography) based paper strip. The L is used in the cell imaging study using African green monkey kidney cells (Vero cells) for the determination of exogenous Zn2+ by Immunofluorescence Assay (IFA) process.

Multi-spectroscopic approaches and molecular simulation research of the intermolecular interaction between the angiotensin-converting enzyme inhibitor (ACE inhibitor) benazepril and bovine serum albumin (BSA).

Benazepril, a common ACE inhibitor, widely used in the treatment of arterial hypertension and congestive heart failure. In this study, We evaluated the characteristics of the interaction between benazepril and BSA under the simulated physiological condition (pH7.4) through various spectroscopic and molecular docking methods. Fluorescence and absorption spectroscopy results showed benazepril quenched the intrinsic fluorescence of BSA through a combined dynamic and static quenching mechanism. The number of binding sites (n) and the binding constant (Kb) of benazepril-BSA complex were circa 1 and 6.81×103M-1 at 298K, respectively, indicating that the binding affinity between benazepril and BSA was moderate. The displacement experiments confirmed that benazepril binding to the site I of BSA, which was quite in accordance with molecular docking. The values of the Gibbs free energy (ΔG0), enthalpic change (ΔH0) and entropic change (ΔS0) were negative, verifying that van der Waals force and hydrogen bonding interaction played a predominant roles in the process of spontaneous bonding. Furthermore, a slight change of the conformation in BSA upon benazepril interaction was proved through SF, 3-DF and FTIR spectroscopy results.

Determination of the binding constants of propeller-like metal complexes of picolinaldehyde-2-pyridylhydrazone

Herein, we determined the binding constants for transition metal complexes of Cu2+, Co2+, Fe2+, Ni2+, and Zn2+ ions formed with the ligand picolinaldehyde-2-pyridylhydrazone (PapyH) using the Benesi-Hildebrand method. Stoichiometry 2:1 (ligand: metal) was previously determined by the Job’s method and confirmed by single-crystal X-ray diffraction finding a propeller-like structure of the [Fe(Papy)2] compound. PapyH and the metal complexes were characterized by 1H NMR and UV-Vis spectroscopy, respectively. The Cu2+ complex exhibited the highest stability constant, which was confirmed by competitive reaction of different metal ions with the ligand PapyH.

Comparative Studies on DNA Binding, Photocleavage, and Photophysical Properties of Ru(II) Complexes Containing TIP {TIP = 2-(Thiophen-2-yl)-1H-imidazo[4,5-f][1,10]-phenanthroline} Ligand

A thiophene contained imidazo phenanthroline ligand TIP {TIP = 2-(thiophen-2-yl)-1H-imidazo-[4,5-f][1,10]phenanthroline{ and its mononuclear Ru(II) polypyridyl complexes [Ru(phen)2TIP]2+ (1) (phen = 1,10-phenanthrolene) and [Ru(bpy)2TIP]2+ (2) (bpy = 2,2'-bipyridyl), are synthesized and characterized by UVVis, IR, 1H and 13C NMR, and ESI-MS spectra. Interaction of these complexes with CT-DNA is studied using UV-Vis and florescence spectra, viscosity measurements and molecular docking studies. The latter supports binding ability of complexes with stability constants deduced from UV-Vis and florescence spectra. The studies reveal that both Ru(II) polypyridyl complexes bind to DNA predominantly by intercalation, and the binding constant of complex 1 is greater than that of complex 2. Complexes 1 and 2 cleave the pBR 322 DNA under UV light.