Reda M. El-Shishtawy

Functional Dyes, and Some Hi-Tech Applications

An overview of the recent developments in functional dyes, which are useful for hi-tech applications for those based on optoelectronics, such as dye sensitized solar cells, photochromic dyes and biomedical applications, such as photodynamic therapy for the treatment of cancer and fluorescent sensors is presented.

Synthesis and spectroscopic studies of stable aqueous dispersion of silver nanoparticles.

A facile approach for the synthesis of stable aqueous dispersion of silver nanoparticles (AgNPs) using glucose as the reducing agent in water/micelles system, in which cetyltrimethylammonium bromide (CTAB) was used as capping agent (stabilizer) is described. The evolution of plasmon band of AgNPs was monitored under different conditions such as (a) concentration of sodium hydroxide, (b) concentration of glucose, (c) concentration of silver nitrate (d) concentration of CTAB, and (e) reaction time. AgNPs were characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), fluorescence spectroscopy and FT-IR spectroscopy. The results revealed an easy and viable strategy for obtaining stable aqueous dispersion of AgNPs with well controlled shape and size below 30 nm in diameter.

Synthesis and optophysical properties of dimeric aza-BODIPY dyes with a push–pull benzodipyrrolidone core

A series of benzodipyrrolidone-based dimeric aza-BODIPY dyes with a push-pull structure are synthesized. Single crystal X-ray diffraction demonstrates these extended aza-BODIPY dyes are planar. The resulting aza-BODIPY chromophores exhibit intense absorption in the 450-800 nm regions and possess lower-lying LUMO energy levels. Furthermore, the push-pull substituents on aza-BODIPYs core have a positive effect on their optophysical properties.

Horseradish peroxidase and chitosan: Activation, immobilization and comparative results

Recently, horseradish peroxidase (HRP) was immobilized on activated wool and we envisioned that the use of chitosan would be interesting instead of wool owing to its simple chemical structure, abundant nature and biodegradability. In this work, HRP was immobilized on chitosan crosslinked with cyanuric chloride. FT-IR spectroscopy and scanning electron microscopy were used to characterize immobilized HRP. The number of ten reuses of immobilized HRP has been detected. The pH was shifted from 5.5 for soluble HRP to 5.0 for immobilized enzyme. The soluble HRP had an optimum temperature of 30 °C, which was shifted to 35 °C for immobilized enzyme. The soluble HRP and immobilized HRP were thermal stable up to 35 and 45 °C, respectively. The apparent kinetic constant values (K(m)) of soluble HRP and chitosan-HRP were 35 mM and 40 mM for guaiacol and 2.73 mM and 5.7 mM for H2O2, respectively. Immobilization of HRP partially protected them from metal ions compared to soluble enzyme. The chitosan-HRP was remarkably more stable against urea, Triton X-100 and organic solvents. Chitosan-HRP exhibited large number of reuses and more resistance to harmful compounds compared with wool-HRP. On the basis of results obtained in the present study, chitosan-HRP could be employed in bioremediation application.

Synthesis of a new β-naphthothiazole monomethine cyanine dye for the detection of DNA in aqueous solution

Novel monomethine cyanine dye (MC) derived from beta-naphthothiazole and benzothiazole has been prepared and characterized by (1)H and (13)C NMR, FTIR, ESIMS, elemental analyses, absorption and fluorescence spectroscopy. The dye was conveniently synthesized by the condensation of two sulfate heterocyclic quaternary salts. The interaction between calf thymus DNA (ct-DNA) in tris(hydroxymethyl)aminomethane-HCl (Tris-HCl) aqueous buffer solution and MC has been studied with spectral fluorescence method. The binding constant value has been determined by fluorescence titration of MC with ct-DNA concentrations. The result obtained is consistent with an intercalative binding interaction between MC and ct-DNA. Compared with ethidium bromide (EB), MC showed a huge fluorescence enhancement upon mixing with ct-DNA.

Molecular design of donor-acceptor dyes for efficient dye-sensitized solar cells I: a DFT study

Dye-sensitized solar cells (DSSCs) have drawn great attention as low cost and high performance alternatives to conventional photovoltaic devices. The molecular design presented in this work is based on the use of pyran type dyes as donor based on frontier molecular orbitals (FMO) and theoretical UV-visible spectra in combination with squaraine type dyes as an acceptor. Density functional theory has been used to investigate several derivatives of pyran type dyes for a better dye design based on optimization of absorption, regeneration, and recombination processes in gas phase. The frontier molecular orbital (FMO) of the HOMO and LUMO energy levels plays an important role in the efficiency of DSSCs. These energies contribute to the generation of exciton, charge transfer, dissociation and exciton recombination. The computations of the geometries and electronic structures for the predicted dyes were performed using the B3LYP/6–31+G** level of theory. The FMO energies (EHOMO, ELUMO) of the studied dyes are calculated and analyzed in the terms of the UV- visible absorption spectra, which have been examined using time-dependent density functional theory (TD-DFT) techniques. This study examined absorption properties of pyran based on theoretical UV- visible absorption spectra, with comparisons between TD-DFT using B3LYP, PBE, and TPSSH functionals with 6–31+G (d) and 6–311++G** basis sets. The results provide a valuable guide for the design of donor-acceptor (D-A) dyes with high molar absorptivity and current conversion in DSSCs. The theoretical results indicated 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye (D2-Me) can be effectively used as a donor dye for DSSCs. This dye has a low energy gap by itself and a high energy gap with squaraine acceptor type dye, the design that reduces the recombination and improves the photocurrent generation in solar cell.

Immobilization of Trichoderma harzianum α-Amylase on Treated Wool: Optimization and Characterization

α-Amylase from Trichoderma harzianum was covalently immobilized on activated wool by cyanuric chloride. Immobilized α-amylase exhibited 75% of its initial activity after 10 runs. The soluble and immobilized α-amylases exhibited maximum activity at pH values 6.0 and 6.5, respectively. The immobilized enzyme was more thermally stable than the soluble one. Various substrates were hydrolyzed by immobilized α-amylase with high efficiencies compared to those of soluble α-amylase. The inhibition of the immobilized α-amylase by metal ions was low as compared with soluble enzyme. On the basis of the results obtained, immobilized α-amylase could be employed in the saccharification of starch processing.

Synthesis of nanocomposites of polypyrrole/carbon nanotubes/silver nano particles and their application in water disinfection

Contamination of drinking or irrigation water with pathogenic bacteria, such as Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), is a major global health problem. Nanomaterials have been of growing interest owing to their promising properties as antimicrobial agents. In this study, in situ oxidative polymerization of pyrrole with silver nitrate was employed to obtain nanocomposites materials containing different percentages of single wall carbon nanotubes (CNT0–60/PPy/AgNPs). The reaction proceeds smoothly at room temperature and the silver content was about 80 wt% of composite. The morphology of composites was determined by transmission electron microscope (TEM) to indicate the formation of core–shell structure in which AgNPs as core and PPy–CNT as shell with observed homogeneity in the nanocomposites. The samples were also characterized by ATR-FTIR, XRD, and TGA. CNT0–60/PPy/AgNPs materials were used for bacterial removal from water. The bacterial removal was evaluated using the column filter method. The results indicated that the removal percentage of E. coli ranged from 87.5% to 95% using CNT0–20/PPy/AgNPs. The data obtained in this study indicated that CNT60/PPy/AgNPs nanocomposite was found to be effective towards E. coli with 100% removal, whereas PPy/AgNPs obtained in this work was specific for the complete removal of S. aureus (100%).

Synthesis, linear and nonlinear optical properties of a new dimethine cyanine dye derived from phenothiazine

Dimethine cyanine dye (PTZIS) based on phenothiazine as the core donor and indolium salt as the acceptor has been synthesized and fully characterized. UV-Vis absorption and fluorescence properties of PTZIS were studied in different solvents. Absorption spectra revealed a large bathochromic shift of the intramolecular charge transfer (ICT) absorption band of PTZIS compared with those in the non-halogenated solvents. Also, the optical data of PTZIS showed a large Stokes shift compared with those in the non-halogenated solvents, indicating a great influence on the geometry of the emissive excited state. The nonlinear optical properties of PTZIS in ethanol solution at different concentrations and different laser powers have been studied using the Z-scan technique with a continuous wave (cw) argon ion laser at 514.5 nm. The closed aperture Z-scan data was used to estimate the nonlinear refractive index n2, while the open aperture scan provided the nonlinear absorption coefficient β. The values obtained are relatively very high and vary linearly with concentration.

Steric and Solvent Effect in Dye-Sensitized Solar Cells Utilizing Phenothiazine-Based Dyes

Three phenothiazine-based dyes have been prepared and utilized as dye-sensitized solar cells (DSSCs). The effects of dye-adsorption solvent on the performances of dye-sensitized solar cells based on phenothiazine dyes were investigated in this study. The highest conversion efficiency of 3.78% was obtained using ethanol (EtOH) and 2.53% for tetrahydrofuran (THF), respectively, as dye-adsorption solvents. Cell performance using EtOH as a dye-adsorption solvent showed relatively higher performance than that using THF. Electrochemical and photochemical tests of phenothiazine dyes in solution and adsorbed on the TiO2 surface showed less dye loading and coverage on the TiO2 surface during adsorption in the case of THF, which decreased the solar cell performance of the DSSC using THF as adsorption solvent compared with using EtOH as adsorption solvent. Meanwhile, the steric effect of phenothiazine-based (PT1–3) dyes was also investigated. Dye with longer and branched aliphatic chain in the order of PT1, PT2, and PT3 showed an increased resistance of the recombination reaction and electron lifetime, thereby increasing and enhancing the overall cell performance because of the sterically hindered conformation of the phenothiazines.