Recovered fluorescence of the Cd-nanocluster-Hg(II) system based on experimental results and computational methods.

Human Serum Albumin, a plasma protein existing in abundance, was selected as a template and reducing agent for the formation of CdNCs due to two factors: its stability and low cost. In the presence of human serum albumin (HSA), a selective and sensitive, low-cost, environmental friendly, and label-free off-on fluorescent sensor was synthesized and characterized for a bioaccumulating and toxic heavy metal, Hg2+ and biothiols. HSA - CdNCs can specifically recognize Hg2+ through aggregating NCs and causing fluorescence quenching. Subsequently, with increase in the concentration of biothiols, Hg2+ was eliminated from the surface of NC, while the fluorescence was restored. The calculated limits of detection (LOD) were 55 pM for Hg(II) and 14 nM for GSH, respectively. The assay was capable of detecting Hg2+ ions and GHS at different concentrations in the range of 0.008 to 8530 nM and 7.5-5157 nM, respectively. Furthermore, the appropriate molecular mechanics (MM) as well as quantum mechanical (QM) methods were performed to optimize and the theoretical investigation of the discussed HSA-profile structures and its interactions with the Cd-NCs (one atom of Cd), Hg2+ and glutathione (G).

Molecular docking and spectroscopic studies on the interaction of new fifth-generation antibacterial drug ceftobiprole with calf thymus DNA.

The interaction of the cefobiprole drug with calf thymus DNA (ct-DNA) at physiological pH was investigated by UV-visible spectrophotometry, fluorescence measurement, dynamic viscosity measurements, circular dichroism spectroscopy and molecular modeling. The binding constant obtained of UV-visible was 4 × 104 L mol-1. Moreover, the results of circular dichroism (CD) and viscosity measurements displayed that the binding of the cefobiprole to ct-DNA can change the conformation of ct-DNA. Furthermore, thermodynamic parameters indicated that hydrogen bond and van der waals play main roles in the binding of cefobiprole to ct-DNA. Optimal results of docking, it can be concluded that ceftobiprole-DNA docked model is in approximate correlation with our experimental results.

Nontoxic silver nanocluster-induced folding, fibrillation, and aggregation of blood plasma proteins.

In recent years, concerns have been raised considering the potential risks of nanocluster (NC) for the environment and human health. Since the blood circulation system is probably the first entry route of NC into the human body, adsorption of blood proteins on NC may change cellular responses, including cellular uptake efficiency, bio distribution patterns, and nanotoxicity profiles, besides other biological effects. Therefore, the interaction of NCs with proteins and the cellular implications can be therapeutically of great importance. Adsorption of human blood proteins on NCs has been methodically investigated. In the present study, the first analysis of fibrillation was conducted between MBI-AgNCs and human serum (a complex biofluid). AgNCs were prepared by coating with 2-mercaptobenzimidazole. Then, interactions with human blood proteins, such as immunoglobulin, albumin, and insulin were investigated using various experimental approaches. Upon protein association, the fluorescence of proteins significantly decreased, accompanied by a blue shift in the AgNCs-human serum albumin (HSA) system and a red shift in the AgNCs-insulin/γ-globulin. Concomitantly, circular dichroism spectroscopy and atomic force microscopy were employed to investigate the effects of protein binding to NCs. We found that AgNCs induced γ-globulin aggregation. HSA at the AgNC surface was partially unfolded and could promote protein self-assembly into amyloid fibrils, while the surface morphology remained unchanged after insulin incubation. The atomic force microscopy (AFM) data and the ThT and CR analysis of the proteins, as well as circular dichroism (CD) and fluorescence findings, support the use of AgNCs as an indicator for monitoring the progress of HSA fibrillogenesis. Additionally, cytotoxicity assays were used to ensure the biocompatibility of nanoparticles within the applicable limits.

DNA-binding study of anticancer drug cytarabine by spectroscopic and molecular docking techniques.

The interaction of anticancer drug cytarabine with calf thymus DNA (CT-DNA) was investigated in vitro under simulated physiological conditions by multispectroscopic techniques and molecular modeling study. The fluorescence spectroscopy and UV absorption spectroscopy indicated drug interacted with CT-DNA in a groove-binding mode, while the binding constant of UV-vis and the number of binding sites were 4.0 ± 0.2 × 104 L mol-1 and 1.39, respectively. The fluorimetric studies showed that the reaction between the drugs with CT-DNA is exothermic. Circular dichroism spectroscopy was employed to measure the conformational change of DNA in the presence of cytarabine. Furthermore, the drug induces detectable changes in its viscosity for DNA interaction. The molecular modeling results illustrated that cytarabine strongly binds to groove of DNA by relative binding energy of docked structure -20.61 KJ mol-1. This combination of multiple spectroscopic techniques and molecular modeling methods can be widely used in the investigation on the interaction of small molecular pollutants and drugs with biomacromolecules for clarifying the molecular mechanism of toxicity or side effect in vivo.

A fluorescent sensor based on methyldopa drug modified γ-Fe2O3 nanoparticles for ultrasensitive detection of calf thymus DNA.

We reported the study of calf thymus DNA (ct-DNA) adsorption by the polymer of methyldopa (2-amino-3-(3,4-dihydroxyphenyl)-2-methyl acid, propanoic) (PMDP), magnetofluorescent PMDP-γ-Fe2O3 nanocrystal. The method is based on the extraordinarily high quenching efficiency of ct-DNA and the specific interaction between ct-DNA and PMDP-γ-Fe2O3 via guanine base and metal coordination, probably. It was found that the designed magnetic nanoparticles can adsorb ct-DNA in nM levels in the presence of NaCl and KCl. In acetate and phosphate buffers DNA were adsorbed completely. Also, we found that pH plays an important role in DNA adsorption onto PMDP-γ-Fe2O3 nanocrystal. PMDP-γ-Fe2O3 nanocrystal is highly hydrophilic and DNA desorption wasn't observed. We believe this study will further stimulate the application of PMDP-γ-Fe2O3 nanocrystal in bioanalytical chemistry and nanotechnology. PMDP-γ-Fe2O3 nanocrystal possesses the ability to interact with ct-DNA via a partial intercalative binding mechanism, as demonstrated by fluorescence displacement experiments and a significant red shift (ca, 10nm) in UV-vis spectra.

Application of a fluorescent biosensor based-on magneto-γ-Fe2 O3 -methyldopa nanoparticles for adsorption of human serum albumin.

Understanding and controlling the interaction between the polymer methyldopa (2-amino-3-(3,4-dihydroxyphenyl)-2-methyl-propanoic acid) (PMDP)-γ-Fe2 O3 nanoparticles and biological fluids is important if the potential of nanoparticles (NPs) in biomedicine is to be realized. Physicochemical studies on the interactions between proteins and NPs are influenced by the surface properties of the NPs. To identify the effects of the NP surface, interactions between human serum albumin (HSA) and PMDP-γ-Fe2 O3 NPs were investigated. Here, the adsorption of HSA onto small (10-30 nm diameter) PMDP-γ-Fe2 O3 NPs was quantitatively analyzed using spectroscopic methods. The fluorescence quenching data were checked for the inner-filter effect, the main confounding factor in the observed quenching. The binding constants, Ka , were calculated at different temperatures, using a nonlinear fit to the experimental data, and the thermodynamic parameters ∆H, ∆S and ∆G were given. The obtained thermodynamic signature suggests that hydrophobic interactions at least are present. This result indicates that the structure of the protein turns from a structureless denatured state at pH 3 into an ordered biologically active native state on addition of PMDP-γ-Fe2 O3 NPs. Copyright © 2015 John Wiley & Sons, Ltd.

Design of green magneto-fluorescent γ-Fe2O3-methyldopa conjugate nanocrystal as a targeted probe for monitoring of esterase activity.

One of the most important aspects of the biological systems is the retention of HSA activity. It is known that serum albumin, in addition to ligand binding capabilities, possesses some enzymatic properties such as esterase activity with p-nitrophenyl acetate substrate. The aim of this study was to synthesize and characterize the mono-dispersed magneto-fluorescent methyldopa coated (MNPs-MDP) which provides a unique opportunity to control and monitor the biological interactions by using magnetic force. An Organic fluorophore methyldopa (2-amino-3-(3,4-dihydroxyphenyl)-2-methyl acid, propanoic) (MDP) was introduced into γ-Fe2O3 particles and made the fluorescent and stable colloidal nanocrystals. As a biological host, human serum albumin (HSA) was chosen which is a major constituent of soluble human blood plasma proteins and is therefore considered as a suitable target for nanoparticle-protein interaction studies. MDP-γ-Fe2O3 nanocrystals showed inherent properties including excellent water solubility, and longtime stability against aggregation, biocompatibility and multifunctional surface rich in carboxyl groups. In addition, we tried to assess the influence of PMDP-γ-Fe2O3 binding on the activity of HSA. Such MDP-γ-Fe2O3 showed an increase in esterase activity in comparison with the free HSA. This method therefore provides a unique platform for preserving the protein structure and conformation.

Multi-spectroscopic and molecular modeling studies on the interaction of antihypertensive drug; methyldopa with calf thymus DNA.

The interaction of methyldopa [(S)-2-amino-3-(3,4-dihydroxyphenyl)-2-methyl propanoic acid] (MDP), antihypertensive drug, with calf thymus DNA (ct-DNA) was investigated by spectroscopic and viscometric techniques. According to the results arising from the fluorescence spectra, viscosity measurements and molecular modeling studies; we concluded that MDP is a minor groove binder of ct-DNA and preferentially binds to AT rich regions. Ethidium bromide (EB) displacement studies revealed that MDP did not have any effect on EB bound DNA which is indicative of groove binding. This was substantiated by displacement studies with Hoechst 33258, a known minor groove binder. In addition, the thermodynamic and docking parameters showed that hydrophobic interaction via drug aromatic rings inside the DNA minor groove plays a major role in this binding.

Study on the interaction of food colourant quinoline yellow with bovine serum albumin by spectroscopic techniques.

The interaction of a food colourant, quinoline yellow (Qy), and bovine serum albumin (BSA) was investigated by spectrophotometry, spectrofluorometry, FT-IR and circular dichroism (CD) techniques. The experimental results indicated that the quenching mechanism of BSA by the dye was a static procedure. Various binding parameters were evaluated. The negative value of ΔH, negative value of ΔS and the negative value of ΔG indicated that van der Waals force and hydrogen bonding play major roles in the binding of Qy and BSA. Based on Forster's theory of non-radiation energy transfer, the binding distance, r, between the donor (BSA) and acceptor (Qy) was evaluated. The results of CD and UV-vis spectroscopy showed that this dye could bind to BSA and the conformation of BSA changed.

Study on the interaction of silver(I) complex with bovine serum albumin by spectroscopic techniques.

The interaction of silver(I) complex, [Ag (2,9-dimethyl-1,10-phenanthroline)(2)](NO(3))·H(2)O, and bovine serum albumin (BSA) was investigated by spectrophotometry, spectrofluorimetry and circular dichroism (CD) techniques. The experimental results indicated that the quenching mechanism of BSA by the complex was a static procedure. Various binding parameters were evaluated. The negative value of ΔH, negative value of ΔS and the negative value of ΔG indicated that van der Waals force and hydrogen bonding play major roles in the binding of the complex and BSA. Based on Forster's theory of non-radiation energy transfer, the binding distance, r, between the donor (BSA) and acceptor (Ag(I) complex) was evaluated. The results of CD and UV-vis spectroscopy showed that the binding of this complex could bind to BSA and be effectively transported and eliminated in the body.

Interaction of calf thymus DNA with the antiviral drug Lamivudine.

One approach to accelerate the availability of new cancer drugs is to test drugs approved for other conditions as anticancer agents. In recent years, some researchers have shown that antiviral drugs, such as ritonavir, saquinavir, and nelfinavir, inhibit the growth of over 60 cancer cell lines derived from nine different tumor types. This article studied the anticancer potential of an antiviral drug, lamivudine (LA). The interaction of LA and calf thymus DNA (CT-DNA) was studied using emission, absorption, circular dichroism (CD), and viscosity techniques. The binding constants evaluated from fluorescence data at different temperatures revealed that fluorescence enhancement is a static process that involves complex-DNA formation in the ground state. Further, the enthalpy and entropy of the reaction between the drug and CT-DNA showed ΔH<0 (-126.38±0.61 kJ mol(-1)) and ΔS<0 (-352.17±2.1 J mol(-1) K(-1)); therefore, van der Waals interactions or hydrogen bonds are the main forces in the binding of LA to CT-DNA. The values of K(f) clearly underscore the high affinity of LA to DNA. In addition, detectable changes in the CD spectrum of CT-DNA in the presence of LA indicated conformational changes. All these results showed that groove binding is the binding mode of this drug and CT-DNA.

DNA binding and gel electrophoresis studies of a copper (II) complex containing mixed aliphatic and aromatic dinitrogen ligands.

The interaction of a novel mixed ligand copper (II) complex, [Cu(N-N)(L)(EtOH)](NO(3))(2) . 2H(2)O, in which N-N indicates 2,9-dimethyl-1,10-phenanthroline and L indicates N,N-dimethyltrimethylenediamine with calf thymus DNA was investigated by absorption, circular dichroism, voltammetric, and viscosimetric techniques. The absorption spectra of the complex with calf thymus DNA showed a marked hypochromism in the pi --> pi* and metal to ligand charge transfer (MLCT) transitions, with no obvious red shift attributed to a partial intercalation. The intrinsic binding constant (K(b)) was determined as 2 x 10(5) M(-1). There was slight to appreciable changes in the relative viscosity of DNA, which is consistent with enhanced hydrophobic interaction of the methyl-substituted phen ring and partial intercalation mode of binding. Electrochemical studies showed a decrease in the peak current, which is ascribed to the strong binding between Cu (II) complex and DNA. The fluorescence spectral characteristics showed that the Cu (II) complex is able to displace the methylene blue bound to DNA, but not as complete as intercalative molecules. It is remarkable that this mixed ligand complex, in contrast to [Cu(2,9-dmp)(2)](+) (2,9-dmp = 2,9-dimethyl-1,10-phenanthroline), which fails to cleave DNA, has ability to cleave the supercoiled plasmid DNA.