Evaluation of the Binding Properties of A New Phenylurea Appended Carbazole Compound to Pepsin/Trypsin by Computational and Multi-Spectral Analysis.

A novel carbazole compound, named 1-(9-ethyl-9H-carbazol-3-yl)-3-phenylurea (Cpu) was synthesized and its binding properties with protease enzymes (pepsin and trypsin) has been examined by steady-state fluorescence measurements, UV/vis absorption, infrared (FT-IR) and circular dicroism (CD) spectroscopies and also computational methods. The fluorescence experimental results indicated that the quenching mechanism of enzyme by Cpu is static process. The thermodynamic parameters (both negative ΔH/ΔS) and molecular docking results suggested that the binding of Cpu to pepsin/trypsin were driven by hydrogen bonds and van der Waals forces. Based on Förster's theory, the binding distance (r) between pepsin/trypsin and Cpu was calculated to be 3.072/2.784 nm, which implies that non-radiative energy transfer occurs from enzyme to Cpu. Furthermore, absorption, CD, and FT-IR spectral analysis provided an evidence that the presence of Cpu induced notable changes in the secondary structures and microenvironmental of both pepsin and trypsin, supporting its significant influence on these enzymes.

A Study on the Luminescent Terbium(III) and Pyridine 2,6 Dicarboxylate Complexes by Experimental and TD-DFT Approaches.

Tb3+ luminescence is enhanced by complex formation in aqueous phases as its pyridine 2,6 dicarboxylate (dpa2-) complexes by using experimental spectroscopic techniques and theoretical time-dependent density functional theory (TD-DFT) calculations. The fluorimetric titration of Tb3+ ion with dpa2- ion is followed at λext/λems = 310/490 nm and 310/545 nm, the emission intensities of which are graphed against the mol ratios of the ligand to metal ion [moles of dpa2-/mol of Tb3+]. Experimental results denote that the tris complex; [Tb(dpa)3]3- is the most stable form at pH > 5.3. Molecular absorption spectra of tris complex shows a batho-chromic shift of 222 nm of dpa2- band to 232 nm accompanied by the hyper-chromic effect at 272 nm band. The luminescence intensities at 490, 545, 592 and 620 nm are enhanced over 100 times in tris complex. The coordination of complexes calculated by thermodynamic cycles and with supporting the experimental result, the most stable form was found to be nine coordinated tris complex; [Tb(dpa)]3-. The theoretical TD-DFT calculations perfectly matched the experimental absorption and emission bands of tris-complex. The novelty of this study is to present the first theoretical calculation of the phosphorescence results and energy transfer process for emission path of Tb3+ and pda2- aqua complexes.

A Novel Fluorescent Probe for the Detection of Cyanide Ions in Solutions and Studies on Its Biophysical Interactions with ctDNA and Proteases.

A new cationic indolium based styryl dye (Ci) as a fluorescent probe was synthesized and its anions selectivity/sensitivity properties/molecular interactions with protease enzymes (pepsin/trypsin) and ctDNA has been studied by spectroscopic and computational methods. The fluorescence measurements at different temperatures indicated that quenching mechanism of enzymes by Ci was static. ΔH and ΔS data pointed out electrostatic/hydrophobic interactions with pepsin, and also hydrogen bonds/van der Waals forces with trypsin of Ci. According to Förster's non-radiative energy transfer, binding distances (r) were calculated as 3.53/3.27 nm for pepsin/trypsin. It was also investigated that groove binding is effective in interaction with ctDNA. The results were supported with molecular docking analyzes which have same tendency. Ci has been demonstrated hypsochromic effect with a decrease in polarity of solvents and it showed highly selective colorimetric and fluorometric sensing behavior for cyanide in organic solvent and in aqueous solution. 1H NMR titration was performed to examine the interaction mechanism between Ci and cyanide. The LOD values of cyanide ion were reported as 4.87 × 10-9 M and 9.70 × 10-7 M in DMSO and DMSO/H2O binary mixture, respectively. In addition, sensitivity of Ci as a chemosensor to cyanide was investigated in bitter almond samples.

Synthesis of new morpholine containing 3-amido-9-ethylcarbazole derivative and studies on its biophysical interactions with calf thymus DNA/HSA.

In this work, we presented the synthesis and investigation of binding properties of the new morpholine containing 3-amido-9-ethylcarbazole derivative (CMR) to calf thymus DNA (ctDNA) and human serum albumin (HSA) by fluorescence spectroscopy, UV absorption spectroscopy and molecular docking method. A decrease in Stern-Volmer constants was obtained with increase in temperature; it shows that static quenching mechanism leads to formation of new CMR-DNA/HSA complexes, which have hydrophobic interaction as the predominant role in the binding modes. Also, binding properties of DNA were investigated with competition assays on two probes (EB and H33258) by absorption, ionic strength and iodide ion quenching methods. The results suggested that CMR entered into the minor groove binding on the A-T region of DNA. The spectral data further confirmed by molecular docking which elicited that CMR complexes have similar interaction and conformation trends to each target, DNA and HSA. The experimental and computational results show that CMR has been classified as a promising molecule in drug designing of other carbazole derivatives.Communicated by Ramaswamy H. Sarma.

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.

Investigation of binding properties of dicationic styrylimidazo[1,2-a]pyridinium dyes to human serum albumin by spectroscopic techniques.

The binding interaction between two dicationic styrylimidazo[1,2-a]pyridinium dyes and human serum albumin (HSA) was investigated at physiological conditions using fluorescence, UV-vis absorption, and circular dichroism (CD) spectroscopies. Analysis of the fluorescence titration data at different temperatures suggested that the fluorescence quenching mechanism of HSA by these dyes was static. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) indicated that hydrogen bonding and van der Waals forces played a major role in the formation of the dye-HSA complex. Binding distances (r) between dyes and HSA were calculated according to Förster's non-radiative energy transfer theory. Studies of conformational changes of HSA using CD measurements indicate that the α-helical content of the protein decreased upon binding of the dyes. Copyright © 2016 John Wiley & Sons, Ltd.

Study of Binding Properties Between Two New Ibuprofen and Naproxen Based Acyl Hydrazone Derivatives and Trypsin.

Two acyl hydrazone derivatives, AHI and AHN,made from ibuprofen and naproxen-derived hydrazides, were prepared and studied of binding properties with serine protease trypsin by UV-vis absorption and fluorescence quenching at pH 7.4. The results suggest that both hydrazones can interact strongly with trypsin and there are the formation of trypsin-hydrazone complexes. The Stern-Volmer constants, binding constants,binding sites and the corresponding thermodynamic parameters ΔH°, ΔS° and ΔG° were calculated at different temperatures.The effect of common metal ions on the constants was also discussed. The binding modes can be explained on the basis of hydrogen bonds and van der Waals forces. The binding distance(r) ~3 nm between the donor (trypsin) and acceptors (AHI and AHN) was obtained according to Förster's non-radiative energy transfer theory. Moreover, LOD and LOQ of hydrazones were calculated in the presence of trypsin.

Fluorescence interaction and determination of sulfathiazole with trypsin.

The mechanism of interaction of trypsin with the sulfathiazole was studied through using fluorescence quenching and UV-visible absorption spectra at pH 7.4. The Stern-Volmer quenching constants, binding constants, number of binding sites and the corresponding thermodynamic parameters ΔH(o), ΔS(o) and ΔG(o) were calculated at different temperatures. The effect of common metal ions on the constants was also discussed. The results suggest that sulfathiazole can interact strongly trypsin and that there is the formation of trypsin-sulfathiazole complex and the interaction can be explained on the basis of hydrogen bonds and van der Waals forces. The binding distance (r) between the donor (trypsin) and acceptor (sulfathiazole) was 3.52 nm based on the Förster's non-radiative energy transfer theory. The detection and quantification limits of sulfathiazole were calculated as 2.52 and 8.40 µM in the presence of trypsin, respectively. The relative standard deviation (RSD) was 4.086% for determinations (n = 7) of a sulfathiazole solution with the concentration of 7.54 µM.

Studies on the interactions of 3,6-diaminoacridine derivatives with human serum albumin by fluorescence spectroscopy.

This study reports the preparation and investigation of the modes of binding of the two symmetric 3,6-diaminoacridine derivatives obtained from proflavine, which are 3,6-diphenoxycarbonyl aminoacridine and 3,6-diethoxycarbonyl aminoacridine to human serum albumin (HSA). The interaction of HSA with the derivatives was investigated using fluorescence quenching and ultraviolet-visible absorption spectra at pH 7.2 and different temperatures. The results suggest that the derivatives used can interact strongly with HSA and are the formation of HSA-derivative complexes and hydrophobic interactions as the predominant intermolecular forces in stabilizing for each complex. The Stern-Volmer quenching constants, binding constants, binding sites and corresponding thermodynamic parameters ΔH, ΔS and ΔG were calculated at different temperatures. The binding distance (r) ~ 3 nm between the donor (HSA) and acceptors (3,6-diethoxycarbonyl aminoacridine, 3,6-diphenoxycarbonyl aminoacridine and proflavine) was obtained according to Förster's non-radiative energy transfer theory. Moreover, the limit of detection and limit of quantification of derivatives were calculated in the presence of albumin.