The interaction between silver nanoparticle and calf thymus DNA was studied by UV−visible, fluorescence, and far UV circular dichroism (CD) spectroscopies at a physiologic temperature of 37 °C. By the analysis of UV−visible titration and thermal denaturation studies of DNA, it was found that silver nanoparticle can form a new complex with double-helical DNA and increase the T m value of DNA. This kind of binding may cause a slight change of the conformation of DNA. The fluorescence emission spectra of intercalated ethidium bromide (EB) with increasing concentration of silver nanoparticle at 37 °C represented a significant reduction of the ethidium intensity and quenching of EB fluorescence. Also, CD results suggested that silver nanoparticle can significantly change the helicity conformation of DNA and then induce the alteration of nonplanar and tilted orientations of DNA bases, resulting in the changes of DNA base stacking, and act as an intercalator. Spectroscopic results represented that binding of silver nanoparticle to DNA resulted in significant changes in the structure and conformation of DNA in a concentration dependent manner and act as an intercalator via increasing stability of DNA by increasing T m, quenching of EB fluorescence intensity, and alteration of CD spectra. Also, the antitumor property of silver nanoparticle was studied by testing it on human tumor cell line K562. The 50% cytotoxic concentration (Cc50) of silver nanoparticle was determined using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay after a 24 h incubation time. Results of the present study may provide useful information to design better anticancer compounds using metal nanoparticles with lower side effects in the future.

The potential carrier role of β-lactoglobulin (β-LG) and its interactions with oxaliplatin were studied using various spectroscopic techniques (fluorescence, UV-visible, and circular dichroism (CD)) in an aqueous medium at two temperatures of 25 and 37 °C in combination with a molecular docking study. Fluorescence measurements have shown that the observed quenching is a combination of static and dynamic quenching with a predominant contribution of static mode. The presence of a single binding site located in the internal cavity of the β-barrel of β-LG was confirmed by molecular docking calculations. Thermodynamic data as well as molecular docking indicated that the hydrophobic interactions dominate in the binding site. Results of fluorescence resonance energy transfer (FRET) measurements in combination with docking results imply that resonance energy transfer occurs between β-LG and its ligand oxaliplatin. Additionally, CD results revealed that oxaliplatin binding has no influence on the β-LG structure. The molecular docking results indicate that docking may be an appropriate method for the prediction and confirmation of experimental results. Complementary molecular docking results may be useful for the determination of the binding mechanism of proteins such as β-LG in pharmaceutical and biophysical studies providing new insight in the novel pharmacology and new solutions in the formulation of advanced oral drug delivery systems.

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The current study reports the binding of curcumin (CUR) as the main pharmacologically active ingredient of turmeric and diacetylcurcumin (DAC) as a bioactive derivative of curcumin to human serum albumin (HSA) and bovine serum albumin (BSA). The apparent binding constants and number of substantive binding sites have been evaluated by fluorescence quenching method. The distance (r) between donor (HSA and BSA) and acceptor (CUR and DAC) was obtained on the basis of the Förster's theory of non-radiative energy transfer. The minor changes on the far-UV circular dichroism spectra resulted in partial changes in the calculated secondary structure contents of HSA and BSA. The negligible alteration in the secondary structure of both albumin proteins indicated that ligand-induced conformational changes are localized to the binding site and do not involve considerable changes in protein folding. The visible CD spectra indicated that the optical activity observed during the ligand binding due to induced-protein chirality. All of the achieved results suggested the important role of the phenolic OH group of CUR in the binding process.

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