Spectroscopic and molecular modeling methods to investigate the interaction between psycho-stimulant modafinil and calf thymus DNA using ethidium bromide as a fluorescence probe.

Interaction type of modafinil with calf thymus DNA (ct-DNA) was examined systematically using ethidium bromide (EB) as a fluorescence probe by fluorescence spectroscopy, UV-Vis spectroscopy, viscosity and molecular docking method. The fluorescence quenching mechanism of ct-DNA-EB by modafinil can be combination of static and dynamic quenching. Results of UV-Vis absorption, competitive binding with Hoechst 33258, ionic strength effect studies, viscosity measurements were confirmed that the interaction type of modafinil with ct-DNA was intercalation. According to docking studies R-modafinil showed better interaction with ct-DNA which is consistent with known pharmacological properties of modafinil. The calculated thermodynamic parameters, enthalpy and entropy change, suggested that the driven forces are hydrogen bonding or van der Walls forces. Results of the docking studies were compatible with the experimental results and confirmed the hydrogen bond formation between modafinil and ct-DNA.

Multispectroscopic and Computational Investigation of ct-DNA Binding Properties with Hydroxybenzylidene Containing Tetrahydrocarbazole Derivative.

Mode of interaction of a new tetrahydrocarbazole derivative with ct-DNA has been investigated systematically using fluorescence spectroscopy, UV-Vis spectroscopy and circular dichroism spectroscopy. It is concluded that TAH could intercalate into the base pairs of ct-DNA, and the fluorescence quenching by ct-DNA was static quenching type. Beside the multispectroscopic results, computational studies were done. Molecular docking results revealed that the TAH-DNAs complexes might be classified as druggable molecule in drug design. Additionally, DNA binding studies exhibited that TAH complexes have different interaction and orientation abilities to each DNA isomer. Combination of experimental and computational data showed that reported TAH is promising structure and deserves further applications.

Investigation of binding properties of two ethidium derivatives with serum albumins: spectral and computational approach.

The interaction mechanisms of two ethidium derivatives, 3,8-dibenzoylamino-5-ethyl-6-phenylphenantridinium chloride (E2) and 3,8-diphenylacetylamino-5-ethyl-6-phenylphenantridinium chloride (E3) with serum albumins (BSA and HSA) have been investigated by a combined experimental and computational approach. Fluorescence quenching and UV-vis results revealed that the interaction of derivatives with albumins resulted in formation of ground-state complexes and the obtained Stern-Volmer quenching constants designate the presence of a static component in the quenching mechanisms. Thermodynamic parameters (ΔH and ΔS values) point out the ionic interactions play the major role in E2-BSA, E2-HSA and E3-HSA complexes. The van der Waals interactions are dominant forces in E3-BSA complex. Moreover, the obtained results in this study were supported with computational analyzes which have same tendency.

Metal-enhanced intrinsic fluorescence of nucleic acids using platinum nanostructured substrates.

We investigated the feasibility of using platinum nanostructures to accomplish the metal-enhanced fluorescence (MEF) in the UV spectral region. We examine the possibility for detection of the intrinsic fluorescence from nucleotides and G-quadruplex DNA on platinum nanoparticles. Guanosine monophosphate (GMP) showed significant increases (~20-fold) in fluorescence intensities in the presence of platinum nanostructures when compared to quartz controls. G-quadruplex DNA demonstrated ~5-fold increase in fluorescence intensity and higher photostability in the presence of Pt nanostructures. We performed finite element method simulations to explore how Pt nanoparticles interact with plane waves and conformed that the Pt nanostructures are promising for enhancing the fluorescence emission in the UV region.

Distance-Dependent Metal-Enhanced Intrinsic Fluorescence of Proteins Using Polyelectrolyte Layer-by-Layer Assembly and Aluminum Nanoparticles.

Previously reported studies indicate that aluminum nanostructured substrates can potentially find widespread use in metal-enhanced fluorescence (MEF) applications particularly in the UV or near-UV spectral region toward label-free detection of biomolecules. MEF largely depends on several factors, such as chemical nature, size, shape of the nanostructure and its distance from the fluorophore. A detailed understanding of the MEF and its distance-dependence are important for its potential application in biomedical sensing. Our goal is to utilize intrinsic protein fluorescence for label-free binding assays. This is made possible by the use of metallic nanostructures which provide localized excitation and enhanced fluorescence of UV fluorophores and will also provide a way to separate the surface-bound proteins from the bulk samples. We evaluated varied probe distances from plasmonic nanostructures by the well-established layer-by-layer (LbL) technique. The investigated proteins were adsorbed on different numbers of alternate layers of poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). Bovine serum albumin (BSA) was electrostatically attached to the positively charged PAH layer, and goat and rabbit IgG were attached to negatively charged PSS layer. We obtained a maximum of a ~ 9 fold increase in fluorescence intensity from BSA at a distance of ~9 nm from the Al nanostructured surface. Approximately 6- and 7- fold increases were observed from goat and rabbit IgG at a distance of ~8 nm, respectively. The minimum lifetimes were about 3-fold shorter than those on bare control quartz slides for all three proteins. The time-resolved intensity decays were analyzed with a lifetime distribution model to understand the distance effect on the metal-fluorophore interaction in detail. The present study indicates the distance dependence nature of metal-enhanced intrinsic fluorescence of proteins and potential of LbL assembly to control the metal-to-fluorophore distance in the UV wavelength region.

Distance-dependent intrinsic fluorescence of proteins on aluminum nanostructures.

In the past several years we have demonstrated the metal-enhanced fluorescence (MEF) and the significant changes in the photophysical properties of fluorophores in the presence of metallic nanostructures and nanoparticles using ensemble spectroscopic studies. In the represented study, we explored the distance effect on intrinsic fluorescence of proteins adsorbed on our layer-by-layer assembled metallic nanostructures. The study is expected to provide more information on the importance of positioning the proteins at a particular distance for enhanced fluorescence from metallic structures. For the present study, we considered using easy and inexpensive LbL technique to provide well-defined distance from metallic surface. The explored proteins were adsorbed on different numbers of alternate layers of poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). SA and BSA were electrostatically attached to the positively charged PAH layer. We obtained a maximum of ~11-fold and 9-fold increase in fluorescence intensity from SA and BSA, respectively. And also we observed ~3-fold decrease in BSA lifetime on metallic nanostructures than those on bare control quartz slides. This study reveals the distance dependence of protein fluorescence.

Plasmon-controlled fluorescence and single DNA strand sequenching.

During the past several years we have studied the effects of metallic surfaces and nanostructures with fluorophores. We have demonstrated the metal-enhanced fluorescence (MEF) and the significant changes in the photophysical properties of fluorophores in the presence of metallic nanostructures and nanoparticles using ensemble spectroscopic studies. These studies have shown dramatic increases in brightness and photostability, especially for low quantum yield fluorophores. Much of this work was performed using visible or NIR fluorophores. In the present study, we have extended our studies to UV wavelengths and have shown that aluminum and platinum particles can enhance the emission of UV fluorophores including intrinsic protein fluorescence from 300 to 420 nm. We used the finite-difference timedomain (FDTD) method to calculate the effects of aluminum nanoparticles on nearby fluorophores that emit in the UV. And also we performed experiments to investigate the effect of metallic nanoparticles on fluorescence intensity of DNA bases and DNA G-quadruplex. We observed increase in fluorescence intensities of DNA bases varied range changing from 20 to 3-fold in steady-state fluorescence emission measurements. We obtained ~5-fold increase in fluorescence intensity of DNA G-quadruplex on both Al and Pt metallic substrates when compared with control quartz substrates.

Fluorescence interaction and determination of calf thymus DNA with two ethidium derivatives.

In this paper, we reported the syntheses and investigation of the modes of binding to DNA of the two new ethidium derivatives containing benzoyl and phenylacetyl groups of both amines at 3-and 8- positions. The interactions between calf thymus DNA (ct-DNA) and the two derivatives, 3,8-dibenzoylamino-5-ethyl-6-phenylphenantridinium cloride (E2) and 3,8-diphenylacetylamino-5-ethyl-6-phenylphenantridinium chloride (E3), were investigated by fluorescence quenching spectra and UV-vis absorption spectra. The Stern-Volmer quenching constants, binding constants, binding sites and the corresponding thermodynamic parameters DeltaH, DeltaS and DeltaG were calculated at different temperatures. The results indicated the formation of E2 and E3-DNA complexes and van der Waals interactions as the predominant intermolecular forces in stabilizing for each complex. In addition, increasing nucleophilicity of the functional groups at 3- and 8- positions exhibited the respectable increment the DNA binding affinities of derivatives. The results of absorption, ionic strength and iodide ion quenching suggested that the interaction mode of E2 and E3 with ct-DNA was intercalative binding. The limit of detection (LOD) of ct-DNA were 7.49 x 10(-8) (n = 4) and 4.18 x 10(-8) mol/l (n = 7) in presence of E2 and E3, respectively.

Interaction of thyroxine with 7 hydroxycoumarin: a fluorescence quenching study.

The interaction between thyroxine hormone and 7 hydroxycoumarin (7HC) was investigated using fluorescence quenching method. The experimental results showed that thyroxine could quench the fluorescence of 7HC by forming the 7HC-thyroxine complex with static quenching. The apparent binding constants (K) between 7HC and thyroxine were determined to be 1.51 x 10(4) (297 K) and 9.06 x 10(3) (310 K). The binding sites (n) 0.98 +/- 0.1. The thermodynamic parameters showed that the interaction between 7HC and thyroxine was driven mainly by hydrogen bonding interactions and van der Waals force. Calibration for thyroxine, based on quenching titration data, was linear in the concentration range 2.0 x 10(-8) to 3.0 x 10(-7) mol/l. The relative standard deviation was 2.58% for 2.0 x 10(-7) mol/l thyroxine (n = 4) and the 3sigma limit of detection was 3.42 x 10(-8) mol/l in cationic surfactant CTAB medium.