Marwa N. El-Nahass

Molecular aggregation, solvato- and acidochromic properties of symmetrical ketocyanines

AbstractThe absorption and fluorescence spectral characteristics of some symmetrical ketocyanine dyes have been investigated in different solvents of various polarities using steady-state absorption and emission spectroscopic techniques. The absorption spectral features are less sensitive to the solvent characteristics than the corresponding fluorescence spectra. A large excited state dipole moment parallel to the smaller ground state dipole moment was calculated. The large dipole moment change with the strongly solvatofluorochromic behaviour, as the solvent polarity increases, demonstrates the formation of an intramolecular charge-transfer (ICT) excited state, which is confirmed by theoretical calculation using semiempirical PM3 method. Also, the effect of dye concentration on the electronic absorption spectra for the investigated dyes has been studied in ethanol. In addition, the acidochromic behaviour of these dyes has been studied using sulphuric acid at different Ho values. A progressive red-shift in the absorption and emission spectra has been observed upon increasing the concentration of sulphuric acid with dramatic changes in colour. This suggests the design of potential optical sensors for probing acidity of the medium or water content in sulphuric acid. The calculated excited state protonation constants

Fluorescence Characteristics and Inclusion of ICT Fluorescent Probe in Organized Assemblies

\left( {\mbox{p}K_{\rm a}^\ast } \right)

The Effect of Ring Size on the Optical Behavior of Novel Photochromic Push-Pull Dyes

are lower than p

Immobilization of horseradish peroxidase into cubic mesoporous silicate, SBA-16 with high activity and enhanced stability

K_{\rm a\thinspace}

Diarylethylene guest anchored into a cyclodextrin molecular host: optical, quantum chemical studies and biological activity

values calculated for the ground state, indicating that the investigated ketocyanines become more basic in the first excited singlet state. Graphical AbstractSignificant changes in the spectral characteristics of the investigated ketocyanines suggest that they can serve as good reporters of solvent polarity, hydrogen-bond donating ability and the acidity of the medium. The colour change upon increasing sulfuric acid concentrations may lead to design of potential optical sensors for probing acidity of the medium.

Photo-Induced Intermolecular Electron Transfer from Donating Amines to Accepting Diarylethylenes in Different Solvents

The inclusion behavior of an intramolecular charge transfer (ICT) fluorescent probe namely; 2-[3-(4-dimethylamino-phenyl)-allylidene]-tetralone (DMAPT) in organized assemblies of aqueous micellar, α- and β-cyclodextrins (CDs) and bovine serum albumin (BSA) pockets have been studied using steady-state absorption and fluorescence spectroscopy. The fluorescence characteristics (energy and intensity) of DMAPT are highly sensitive to the properties of the medium. The ICT maximum is strongly blue-shifted with a great enhancement of the fluorescence intensity upon addition of different surfactants, confirming the solubilization of DMAPT in the hydrophobic micellar assembly. In addition, the fluorescence of DMAPT is more sensitive to the nature and concentration of the added CDs. In α- or β-CD solutions, the fluorescence intensity increases strongly (by 6 and 23 orders of magnitude, respectively). Upon encapsulation in the CD cavity, the molecular flexibility decreases due to the geometrical restrictions of the CD nanocavity which decreases the non radiative transition via the free rotation around the single and/or double bonds of the butadiene bridge. This was supported by finding that the fluorescence quantum yield of DMAPT increases with increasing the viscosity of the medium. The binding constants of DMAPT with micelles, α- and β-CD solutions have been calculated and were found to be highly dependent on the nature of the used surfactants or CDs. The thermodynamic parameters have been also determined and the difference in magnitude between the formed α- and β-CD-DMAPT inclusion complexes is discussed on the basis of the cavity size. Finally, the binding constant of DMAPT with bovine serum albumin was calculated, indicating the relative stability of the DMAPT–BSA complex. The energy transfer distance between BSA as a donor and DMAPT as an acceptor was obtained following the fluorescence quenching of BSA by DMAPT, via resonance mechanism as a quencher.

Selective “on–off–on” switchable chemosensor for metal ions detection and its complexes

The photophysical behaviors of newly synthesized photochromic dyes have been investigated in different solvents of various polarities using steady-state absorption and emission techniques. It was found that, the absorption and emission spectra of these dyes depend on the ring size and the solvent polarity. The higher values of the dipole moments of the investigated dyes in the excited state than those in the ground state suggest that these dyes can serve as good candidate components of nonlinear optical materials. Additionally, the photoisomerization parameters (percentage of composition of cis isomers and quantum yields of photoisomerization) depend on the polarity and the viscosity of the used solvents as well as the ring size. The molecular motion that occurs in the isomerization process has facilitated the development of molecular devices. Finally, the halochromic behaviors of the investigated dyes promise them to act as acid–base indicators.

Intramolecular charge transfer emission of a new ketocyanine dye: Effects of hydrogen bonding and electrolyte

Mesoporous silicate, SBA-16 is one of the most promising supports for horseradish peroxidase. In this study, SBA-16 was synthesized, and the anchored HRP enzyme in the organized porous networks, SBA-16. The mesoporous material, SBA-16 and the anchored HRP enzyme were characterized by Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption isotherms, low-angle XRD and thermogravimetric analysis. The percentage of immobilized HRP was 57%. The enzyme affinity constant, Km values of soluble and immobilized enzyme were 5.27 and 3.9 mM for hydrogen peroxide and 12 and 10.4 mM for guiacol, respectively, indicating that the immobilized enzyme had more affinity to the substrate than free HRP. Also, the free and immobilized enzyme had pH and temperature optima at 5.6, and 40 °C, respectively. The free enzyme was stable at 40 °C but that for the immobilized enzyme was detected up to 60 °C. Reusability of immobilized enzyme was found to be 10 cycles; the immobilized enzyme can only retain 50% of its activity after 5 cycles. The results indicate the higher efficiency, stability, and reusability of the immobilized enzyme than free enzyme. The HRP immobilized to SBA-16 due to the large surface area, and narrow pore size distribution of SBA-16.

Chalcones isothiocyanate anchored into mesoporous silicate: Synthesis, characterization and metal ions sensing response

Abstract The host–guest complexation between a novel guest namely; 2-(4-pyridinylbenzothiazolyl) ethane, PBE and β-cyclodextrin was studied using steady-state absorption and emission techniques. The fluorescence maximum is strongly blue-shifted with a great enhancement in the fluorescence intensity upon addition of β-CD, confirming the formation of inclusion complexes. The solid inclusion complex between PBE and β-CD has been prepared, characterised using FT-IR, X-ray diffraction and scanning electron microscope techniques. PBE is encapsulated with β-CD nanocavity and 1:1 PBE–β-CD host–guest interaction is identified. This is confirmed using semi-empirical quantum chemical calculations. PBE guest entered into the less polar cavity through the benzothiazole moiety. The negative values of enthalpy and free energy changes suggest that the encapsulation process is thermodynamically favourable. Additionally, the fluorescence is more sensitive to the micellar medium, whether it was cationic, anionic or neutral as well as metal ions like, Li+, Cu2+ and Fe3+. Finally, the antimicrobial activities of PBE guest and its inclusion complex with β-CD host are studied.

Chalcone isothiocyanate-mesoporous silicates: Selective anchoring and toxic metal ions detection

The fluorescence quenching of newly synthesized diarylethylenes by some aliphatic and aromatic amines has been carried out at room temperature in solvents of various polarities and viscosities including acetonitrile, methanol, ethanol, and cyclohexane using steady-state measurements. Additionally, the cyclic voltammetric behavior of the investigated diarylethylenes has been studied, in order to determine their reduction potentials, which are necessary for calculation the Gibbs energy change for the photoinduced, electron transfer (ET) reactions in diarylethylene–amine systems. No change in the shape of the fluorescence spectra was observed, except for diarylethylenes–N,N-dimethyl aniline pairs in cyclohexane at which an exciplex was observed. The quenching mechanism is due to the ET from the ground state amines to the excited diarylethylenes. Both linear and non-linear Stern–Volmer behaviors have been encountered. The observed kq values for different diarylethylenes–amine pairs do not correlate with the basicity (pKb) of the amines but decrease with increasing the oxidation potentials of the amines. The bimolecular quenching rate constants have been correlated with ∆G° values for the ET reactions according to the Marcus outer-sphere ET theory.