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.

Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties.

Herein we report the synthesis and characterization of a new series of styryl-based push-pull dyes containing a free amino group and their Schiff base derivatives. The dyes include the dicyanomethylene group as an acceptor and different para-substituted alkylamines as donors. Morever as a proton-sensitive group a pyridin-2-yl substituent was attached to the para-position of the phenyl moiety in both series of compounds. The photophysical properties of the dyes were examined in various solvents with different polarities and showed absorption in the visible region and green-red emission with low quantum yields. The absorption and the emission maxima were shifted bathocromically by increasing the solvent's polarity. However, there was no correlation with the polarity parameters of the solvents. The pH-sensitive properties of all prepared Schiff bases were examined against TBAOH in DMSO, via deprotonation of the OH group in the salicylidene moiety and their reverse protonation was also investigated using TFA. The Schiff bases exhibited a bathochromic shift upon the addition of TBAOH to their solutions in DMSO. Therefore, they showed potential to be utilized as colorimetric and luminescence pH sensors. The second-order nonlinear optical (NLO) responses of the dyes were measured by the electric field-induced second harmonic (EFISH) generation method. The highest µß values were obtained for the dyes bearing the julolidine donor as 1430 × 10-48 esu (for free amino derivative) and 1950 × 10-48 esu (for Schiff base derivative), respectively. The structural and electronic properties of the dyes as well as their NLO properties were further studied using DFT calculations. The thermal stabilities of all dyes were evaluated by thermogravimetric analysis (TGA). The TGA data showed that all dyes were thermally stable up to 250 °C.

Switching off the charge transfer and closing the S1-T1 ISC channel in excited states of quinolizinium derivatives: a theoretical study.

Excited states of benzo[b]quinolizinium (BQ) derivatives that show efficient pH-responsive fluorescence switching properties were studied quantum-chemically by employing the CASSCF/CASPT2 and TD-DFT methods. Protonation of aminophenyl-BQ at the electron-donor amine moiety converts the nitrogen lone pair into a σ bond and the HOMO into a lower-lying orbital that is no longer involved in the excitation, thereby rationalizing the suppression of the charge transfer. An S1-T1 seam between the vertically excited Franck-Condon (FC) point and the S1 equilibrium geometry favors intersystem crossing (ISC). The T1 state of the protonated form remains well below S1 (1.5 eV) because of favorable exchange interactions, whereas the T1 state of the unprotonated form does not experience any analogous stabilization because of the difference in the spatial domains of the singly occupied orbitals in the S1 and T1 states. The S1 surface from the FC point until the equilibrium geometry for the protonated species is energetically downhill. Calculations on models and available experimental data suggest design principles for similarly functioning pH-responsive species, namely, an amine lone pair as the electron donor and a cationic ring of moderate size as the electron acceptor that are structurally separated by virtue of a spacer.

The syntheses, photophysical properties and pH-sensitive studies of heterocyclic azo dyes bearing coumarin-thiophene-thiazole.

This study reports the synthesis of two novel thiazolylazo dyes (4 and 5) bearing coumarin-thiophene moiety. UV-Vis spectroscopy was used to investigate the photophysical properties of 4 and 5 in different solvents. The dyes displayed good potential for hydroxide sensing in different mediums. The reversibility was also studied, and it was found that 4 and 5 could be reverted to their original state by adding acid. Furthermore, the acidochromic properties were studied in protic and aprotic media. Both dyes displayed a good acidochromic response in DCM. Moreover, 4 and 5 were investigated for pH sensing, and it was found that both compounds displayed changes in absorption spectra in a basic media. The theoretical calculations were carried out to investigate the deprotonation and protonation mechanisms using density functional theory (DFT). The thermal properties of the dyes were investigated using thermogravimetric analysis (TGA). The results showed good thermal stability up to around 200 °C.

Synthesis, characterization, molecular docking and in vitro screening of new metal complexes with coumarin Schiff base as anticholine esterase and antipancreatic cholesterol esterase agents.

In this work, Combining coumarin and thiazole with 3-tertiary butyl salicylaldehyde into in a single molecule, new Schiff base (CTS), and its metal complexes with palladium and platinum were synthesized and characterized by using well-known spectroscopic techniques such as 1H-NMR, 13C-NMR, FT-IR and LC-MS. And also, the formation of these complexes were confirmed by magnetic moment and conductivity measurements. The photophysical properties of CTS were studied and it was observed that the Schiff base has a sensitivity to CN-, F-, and AcO- anions. The quantum chemical calculations based on density functional theory (DFT) were done for explaining some experimental, structural, and spectroscopic data of the dyes. Also, to evaluate the binding interactions between the ligand (CTS) and its metal complexes and enzymes, molecular docking studies were performed and all the compounds tested to determine its inhibition potential against the cholinesterase (AChE and BChE) and pancreatic cholesterol esterase (CEase) enzymes. Both in vitro and in silico the results showed that all of the compounds could act as potent inhibitors of AChE, BChE, and CEase. The Pt (II) complex showed the most potent inhibitory property against all of the enzymes with IC50 values of 12 µM for AChE, 23 µM for BChE, and 21 µM for CEase.Communicated by Ramaswamy H. Sarma.

Amino-substituted-1,1-dicyano-2,4-diaryl-1,3-butadiene chromophores: Synthesis and photophysical properties.

A series of D-π-A chromophores based on allylidenemalononitrile electron-withdrawing group was designed. The influence of the amino-electron-donating group on the photophysical properties was studied. These compounds, highly thermally stable, exhibit orange-red emission in solution and in solid state. The experimental results have been rationalized by theoretical DFT calculations. The second order nonlinear optical properties were also studied using the electric field induced second harmonic generation (EFISH) method.

New platinum (II) and palladium (II) complexes of coumarin-thiazole Schiff base with a fluorescent chemosensor properties: Synthesis, spectroscopic characterization, X-ray structure determination, in vitro anticancer activity on various human carcinoma cell lines and computational studies.

A new coumarin-thiazole based Schiff base (Ligand, L) and its Pd(II), Pt(II) complexes; ([Pd(L)2] and [Pt(L)2]), were synthesized and characterized using spectrophotometric techniques (NMR, IR, UV-vis, LC-MS), magnetic moment, and conductivity measurements. A single crystal X-ray analysis for only L was done. The crystals of L have monoclinic crystal system and P21/c space group. To gain insight into the structure of L and its complexes, we used density functional theory (DFT) method to optimize the molecules. The photophysical properties changes were observed after deprotonation of L with CN- via intermolecular charge transfer (ICT). Additionally, as the sensor is a colorimetric and fluorimetric cyanide probe containing active sites such as coumarin-thiazole and imine (CH=N), it showed fast color change from yellow to deep red in the visible region, and yellow fluorescence after CN- addition to the imine bond, in DMSO. The reaction mechanisms of L with CN-, F- and AcO- ions were evaluated using 1H NMR shifts. The results showed that, the reaction of L with CN- ion was due to the deprotonation and addition mechanisms at the same time. The anti-cancer activity of L and its Pd(II) and Pt(II) complexes were evaluated in vitro using MTT assay on the human cancer lines MCF-7 (human breast adenocarcinoma), LS174T (human colon carcinoma), and LNCAP (human prostate adenocarcinoma). The anti-cancer effects of L and its complexes, on human cells, were determined by comparing the half maximal inhibitory concentration (IC50) values. The activity results showed that, the Pd(II) complex of L has higher anti-tumor effect than L and its Pt(II) complex against the tested human breast adenocarcinoma (MCF-7), human prostate adenocarcinoma (LNCAP), and human colon carcinoma (LS174T) cell lines.

Phenylazoindole dyes--part I: the syntheses, characterizations, crystal structures, quantum chemical calculations and antimicrobial properties.

In this study, the synthesis of four new phenylazo indole dyes (dye 1-4) were carried out by diazotization of 4-aminoacetophenone and coupling with various 2- and 1,2-disubstituted indole derivatives. The dyes were characterized by UV-vis, FT-IR, (1)H NMR, HRMS and X-ray single crystal diffraction methods. Azo-hydrazone tautomeric bahavior of the dyes in different solvents (DMSO, methanol, acetic acid and chloroform) was investigated by using (1)H NMR and UV-vis results. The experimental results were compared with the corresponding calculated values. The results of experimental data and theoretical calculations showed that the azo tautomer is more stable than hydrazone tautomer. In addition to this, the antimicrobial activity of the dyes was also evaluated.