Multi spectroscopic and molecular simulation studies of propyl acridone binding to calf thymus DNA in the presence of electromagnetic force.

Introduction: Here, the interaction behavior between propyl acridones (PA) and calf thymus DNA (ct-DNA) has been investigated to attain the features of the binding behavior of PA with ct-DNA, which includes specific binding sites, modes, and constants. Furthermore, the effects of PA on the conformation of ct-DNA seem to be quite significant for comprehending the medicine's mechanism of action and pharmacokinetics. Methods: The project was accomplished through means of absorbance studies, fluorescence spectroscopy, circular dichroism, viscosity measurement, thermal melting, and molecular modeling techniques. Results: The intercalation of PA has been suggested by fluorescence quenching and viscosity measurements results while the thermal melting and circular dichroism studies have confirmed the thermal stabilization and conformational changes that seem to be associated with the binding. The binding constants of ct-DNA-PA complex, in the absence and presence of EMF, have been evaluated to be 6.19 × 104 M-1 and 2.95 × 104 M-1 at 298 K, respectively. In the absence of EMF, the ∆H0 and ∆S0 values that occur in the interaction process of PA with ct-DNA have been measured to be -11.81 kJ.mol-1 and 51.01 J.mol-1K-1, while in the presence of EMF they were observed to be -23.34 kJ.mol-1 and 7.49 J.mol-1K-1, respectively. These numbers indicate the involvement of multiple non-covalent interactions in the binding procedure. In a parallel study, DNA-PA interactions have been monitored by molecular dynamics simulations; their results have demonstrated DNA stability with increasing concentrations of PA, as well as calculated bindings of theoretical ΔG0. Conclusion: The complex formation between PA and ct-DNA has been investigated in the presence and absence of EMF through the multi spectroscopic techniques and MD simulation. These findings have been observed to be parallel to the results of KI and NaCl quenching studies, as well as the competitive displacement with EB and AO. According to thermodynamic parameters, electrostatic interactions stand as the main energy that binds PA to ct-DNA. Regarding the cases that involve the Tm of ct-DNA, EMF has proved to increase the stability of binding between PA and ct-DNA.

Determining the Interaction Behavior of Calf Thymus DNA with Anastrozole in the Presence of Histone H1: Spectroscopies and Cell Viability of MCF-7 Cell Line Investigations.

The interaction of calf thymus DNA (ct DNA) with anastrozole, which is acknowledged as an antineoplastic drug, has been enquired into in the absence and presence of histone H1, through the means of absorbance, fluorescence, circular dichroism spectroscopy, viscosity, thermal melting, and molecular modeling techniques. In addition, the effects of anastrozole on MCF 7 cell line have been thoroughly investigated. Fluorescence spectroscopy results have indicated that quenching mechanism of ct DNA-anastrozole are known as static quenching procedures, since the Stern-Volmer quenching constant (KSV) seems to face a decrease as the temperature is enhanced; this is a significant evidence for intercalative binding mode of anastrozole with ct DNA. Regarding the ternary system in the presence of H1, the constant of Stern-Volmer quenching was increased as the temperature was heightened. The thermodynamic parameters suggested that the binding could be characterized as exothermic by negative and positive enthalpy and entropy changes in both binary and ternary systems, respectively. It is vital to mention that hydrogen bonds and hydrophobic contributions play significant roles in anastrozole association to ct DNA in the absence and presence of H1. In accordance to the absorption spectroscopy and melting temperature curve outcomes, the binding mode of anastrozole with ct DNA in absence and presence of H1 was indicative of intercalative and nonintercalative bindings, respectively. The viscosity results as binary and ternary systems, which have been elucidated from a sensitive viscometer, have confirmed the fluorescence spectroscopy determinations. The intercalation of anastrozole to ct DNA seemed to be significantly related to an induced reduction in MCF-7 cell proliferation. The molecular modeling results have suggested that anastrozole could bind to H1 in ct DNA-H1 complex in ternary systems, which supports the conclusions that have been obtained from experimental data.

Oil-in-water nanoemulsions comprising Berberine in olive oil: biological activities, binding mechanisms to human serum albumin or holo-transferrin and QMMD simulations.

Berberine is widely used in traditional Iranian medicine to treat diabetes and inflammatory conditions. This study was aimed at developing a method for the preparation of Berberine nanoparticles (Nano-Ber) in order to improve its aqueous-phase solubility and its complex formation with human serum albumin (HSA) and holo-transferrin (HTF) from the viewpoint of interaction behavior. Nano-Ber was prepared with olive oil as the oil phase, Tween 80 as the surfactant and Span 60 as the co-surfactant. Nano-Ber was obtained with a spherical shape and a mean particle size of 43.7 ± 3.6 nm, with an optimal oil:surfactant:co-surfactant ratio of 1:2:2, w/w/w. The antioxidant activity of Nano-Ber in comparison with Berberine was tested using DPPH and it was found that Nano-Ber had a large antioxidant activity. The cytotoxicity effects of Nano-Ber and Berberine on HepG2 were compared by MTT assay and detected in the treated HepG2 cells at concentrations up to 0.1 mM. The binding constants of HSA-Nano-Ber and HTF-Nano-Ber complexes formation were (2.93 ± 0.02) × 104 and (9.62 ± 0.03) × 103 M -1, respectively. Hydrogen bonds and van der Waals interactions were the predominant forces in the HSA-Nano-Ber and HTF-Nano-Ber complexes, and the process of Nano-Ber binding HSA and HTF was driven by ΔH 0 = -122.76 kJ mol-1, ΔS 0 = -325.49 J mol-1K-1 for HSA and ΔH 0 = -125.09 kJ mol-1, ΔS 0 = -43.37 J mol-1K-1 for HTF. The results of the simulation demonstrated that the Nano-Ber molecules were stabilized on the surface of final aggregates through both hydrophilic and hydrophobic interactions. Communicated by Ramaswamy Sarma.

Isothermal titration calorimetry and stopped flow circular dichroism investigations of the interaction between lomefloxacin and human serum albumin in the presence of amino acids.

The present study was designed to investigate the influence of two indispensable and two dispensable amino acids, including methionine, histidine, cysteine and proline, on the binding interaction between human serum albumin (HSA) and an antibiotic agent lomefloxacin (LMF). The fluorescence quenching experiments showed that the intrinsic emission of HSA was considerably quenched following binding to LMF in all the systems. Furthermore, in all the interactions the maximum wavelength of HSA was slightly decreased. The spectral changes observed in the binding systems we e all attributed to the alteration of the micro-environment around the tryptophan and tyrosine residues of HSA. The Kb values o HSA-LMF complex in the absence and presence of histidine, methionine, cysteine and proline have been obtained 6.02 × 105, 4.83 × 105, 5.05 × 105, 4.94 × 105 and 6.20 × 105 M-1 respectively. The various kind of Kb values showed the different interaction behavior between HSA and LMF in the absence and presence of amino acids mentioned. The data gathered by isothermal titration calorimetry (ITC) studies revealed that although all the binding interactions were exothermic, the amount of the heat exchanged during the HSA-LMF interaction increased in the presence of the amino acids especially cysteine. In the present study, the binding kinetics and affinity of LMF to HSA in the absence and presence of the amino acids were studies using stopped-flow circular dichroism and ITC techniques respectively. The results of these two techniques revealed that the bindig affinity and binding rate of the LMF-HSA interaction decreased in the presence of histidine, methionine and cysteine. In the presence of proline, the binding process of LMF-HSA was sped up and the affinity of LMF to HSA slightly increased. All the experimental results were then supported by the data collected from molecular modeling studies using density functional theory. Communicated by Ramaswamy H. Sarma.

Determining the binding site and binding affinity of estradiol to human serum albumin and holo-transferrin: fluorescence spectroscopic, isothermal titration calorimetry and molecular modeling approaches.

The interactions between estradiol and two carrier proteins, i.e. human serum albumin (HSA) and holo-transferrin (HTF) in aqueous solution at pH = 7.4 were studied by three-dimensional fluorescence emission spectroscopy, isothermal titration calorimetry (ITC), zeta-potential, resonance light-scattering and molecular modeling. Extensive fluorescence quenching was observed throughout the interaction between the drug and both proteins. Moreover, conformational changes were determined by observing the rearrangement of Trp residues during binding of estradiol with HSA and HTF at different concentrations. ITC experiments revealed that, in the presence of estradiol, both van der Waals forces and hydrogen bonding became predominant. In addition, other binding parameters such as enthalpy and entropy changes were determined by the zeta potential method. Molecular modeling suggested that estradiol was situated within sub-domain IB sited in the hydrophobic cluster in Site I, whereas the drug was located in the N-terminal of HTF where it was hydrogen bonded with Ala 670.

Study on effect of lomefloxacin on human holo-transferrin in the presence of essential and nonessential amino acids: Spectroscopic and molecular modeling approaches.

The purpose of this study was to determine how lomefloxacin (LMF) interacts with human holo-transferrin (HTF) in the presence of two kinds of essential and nonessential amino acids. The investigations were carried out by fluorescence spectroscopy, zeta potential and molecular modeling techniques under imitated physiological conditions. We were able to determine the number of binding sites, the drug binding affinity to HTF in the presence of essential and nonessential amino acids and the quenching source of HTF. The interaction between HTF with LMF suggested that the microenvironment of the Trp residues was altered causing a strong static fluorescence quenching in the binary and ternary systems. The results pointed at the formation of a complex in the binary and ternary systems which caused an enhancement of the RLS intensity that was analyzed using synchronous fluorescence spectroscopy. The density functional theory (DFT) was employed to determine the amino acid residues on HTF that interacted with LMF. Also, Steric and van der Waals forces as well as the contribution of small amounts of hydrogen bonds were stronger or Tyr 71 in chain (b) than for 128 Trp in chain (a) of HTF.