Laila M. Al-Harbi

Anion induced azo-hydrazone tautomerism for the selective colorimetric sensing of fluoride ion

The design, synthesis, characterization and their anion sensing properties of two receptors capable of exhibiting azo-hydrazone tautomerism are reported. The anion sensing properties have been investigated using electronic, fluorescence and nuclear magnetic spectral studies in addition to electrochemical and visual detection experiments. Both the receptors selectively bind fluoride ion with >100 nm red-shift in the electronic spectrum and the color changes from yellow to red. The results of the spectral studies revealed that the sensing mechanism involves fluoride ion induced change of chromophore from C=N (hydrazone form) to N=N (azo form) in these receptors leading to the visible color change. Density Functional Theory calculations were conducted to rationalize the optical response of the receptors.

Design, synthesis and characterization of indole based anion sensing receptors

The design and synthesis of six new receptors (R1–R6) and their anion sensing properties through multiple channels are reported. These receptors are constructed in such a way that they possess indole groups as the binding sites and different acceptors units of varying electron acceptor strengths. Receptors R1, R3 and R5 could recognize fluoride ions visually and spectroscopically with high selectivity over other anions in DMF, which was demonstrated by a visual detection experiment and UV-Vis, fluorescence and 1H NMR spectral studies. The remaining three receptors (R2, R4 and R6) exhibited colour changes with both fluoride and cyanide ions. The binding constants for fluoride binding by these receptors were determined to be in the order of 104 to 106 M−1 and found to depend on the electron accepting property of the acceptor unit in the intra molecular charge transfer (ICT) transition existing with the indole donor units. 1H NMR titration experiments not only provide evidence for the existence of H-bonding interactions between the indolic N–H groups of these receptors and F−, but also offer key insight into the strengths of the receptor–anion complexes of stoichiometry 1:2. The higher fluoride binding ability of the receptor containing the naphthoquinone signalling unit has been interpreted in terms of the greater electron deficiency of the acceptor unit (quinone) and enhanced H-bond donating character of the indole N–H group. The results of the electrochemical and DFT computation studies corroborate well with the spectroscopic studies.

Computational studies of molecular charge transfer complexes of heterocyclic 4-methylepyridine-2-azomethine-p-benzene derivatives with picric acid and m-dinitrobenzene

Charge transfer complexes of substituted aryl Schiff bases as donors with picric acid and m-dinitrobenzene as acceptors were investigated by using computational analysis calculated by Configuration Interaction Singles Hartree-Fock (CIS-HF) at standard 6-31G∗ basis set and Time-Dependent Density-Functional Theory (TD-DFT) levels of theory at standard 6-31G∗∗ basis set, infrared spectra, visible and nuclear magnetic resonance spectra are investigated. The optimized geometries and vibrational frequencies were evaluated. The energy and oscillator strength were calculated by Configuration Interaction Singles Hartree-Fock method (CIS-HF) and the Time-Dependent Density-Functional Theory (TD-DFT) results. Electronic properties, such as HOMO and LUMO energies and band gaps of CTCs set, were studied by the Time-Dependent density functional theory with Becke-Lee-Young-Parr (B3LYP) composite exchange correlation functional and by Configuration Interaction Singles Hartree-Fock method (CIS-HF). The ionization potential Ip and electron affinity EA were calculated by PM3, HF and DFT methods. The columbic force was calculated theoretically by using (CIS-HF and TD-DFT) methods. This study confirms that the theoretical calculation of vibrational frequencies for (aryl Schiff bases--(m-dinitrobenzene and picric acid)) complexes are quite useful for the vibrational assignment and for predicting new vibrational frequencies.

Anhydrates and/or hydrates in nitrate, sulphate and phosphate salts of 4-aminopyridine, (4-AP) and 3,4-diaminopyridine (3,4-DAP): the role of the water molecules in the hydrates

Several salt forms of 4-aminopyridine and 3,4-diaminopyridine with nitric, sulfuric, and phosphoric acids, comprising anhydrates and some hydrates, have been prepared and structurally characterized, and the role of water assessed in the latter cases. Our study has confirmed that anhydrates can be obtained even when water is present in the crystallizing solution. Protonation of the aminopyridines is consistent with ΔpKa differences. 4-Aminopyridine uniquely forms a mono cation only, with protonation at the pyridine nitrogen, whilst 3,4-diaminopyridine forms both a mono cation, again with protonation at the pyridine nitrogen, and a dication, with the second protonation at the 3-amino position. Thus, 4-aminopyridine forms a 1 : 1 nitrate anhydrate, a 1 : 1 bisulphate anhydrate, a 2 : 1 sulfate hydrate and a 1 : 1 dihydrogen phosphate hydrate. 3,4-Diaminopyridine forms a 1 : 1 nitrate anhydrate and 1 : 2 nitrate anhydrate and hydrate, 2 : 1 and 1 : 1 sulfate hydrates and a 1 : 1 dihydrogen phosphate anhydrate. Analysis of the structures found suggests that the H-bonding capability of the water O–H donors and O acceptor components have similar tendencies to N–H donors and other O acceptors. At the same time, we recognise that, whilst water molecules may occasionally be structure forming, they also act as spacers or fillers in the development of the primary H-bonded assemblies. These will mainly be controlled by the stoichiometries and H-bonding possibilities of the anion/cation components. It is also possible that, in some circumstances, the inclusion or otherwise of water in structures may be competitive with supplementary weak interactions such as C–H⋯O hydrogen bonding.

Adsorption of Polyvinylpyrrolidone over the Silica Surface: As Affected by Pretreatment of Adsorbent and Molar Mass of Polymer Adsorbate

The adsorption of polyvinylpyrrolidone over the surface of silica has been investigated. The impact of molar mass of the polymer, pH, and pretreatment temperature of silica particles have been evaluated by means of FTIR spectroscopy and electrophoretic measurements. The silica particles used have narrow particle size distribution. The zeta potential of the aqueous silica suspension was decreased with the increase in pH. The amount of polymer adsorbed was increased with the increase in pretreatment temperature, time, concentration, pH, zeta potential, and molar mass of the polymer. The addition of polymer to the system increased the zeta potential due to adsorption of polymer on the surface of the particles. However, the impact increased with the increase in molecular mass of the polymer. The IR spectra obtained before and after adsorption of polymer concluded that, mostly, hydrogen bonding is responsible for the adsorption phenomena; however, hydrophobic interactions also play a significant role. The mechanism has been investigated and established through FTIR spectroscopy.

Anisotropy in the mechanical properties of organic crystals: temperature dependence

The nanoindentation technique has recently been utilized for quantitative evaluation of the mechanical properties of molecular materials successfully, including their temperature (T) dependence. In this paper, we examine how the mechanical anisotropy varies with T in saccharin and L-alanine single crystals. Our results show that elastic modulus (E) decreases linearly in all the cases examined, with the T-dependence of E being anisotropic. Correspondence between directional dependence of the slopes of the E vs. T plots and the linear thermal expansion coefficients was found. The T-dependence of hardness (H), on the other hand, was found to be nonlinear and significant when (100) of saccharin and (001) of L-alanine are indented. While the anisotropies in E and H of saccharin and E of L-alanine enhance with T, the anisotropy in H of L-alanine was found to reduce with T. Possible mechanistic origins of these variations are discussed.

Inspired Preparation of Zinc Oxide Nanocatalyst and the Photocatalytic Activity in the Treatment of Methyl Orange Dye and Paraquat Herbicide

As the need to use green chemistry routes increases, environmentally friendly catalytic processes are a demand. One of the most important and abundant naturally occurring catalysts is chlorophyll. Chlorophyll is the first recognized catalyst; it is a reducing agent due to its electron-rich structure. The effects of spinach on the preparation of zinc oxide nanoparticles and the photocatalytic degradation of methyl orange and paraquat in sunlight and under a UV lamp and photocatalytic degradation in sunlight were studied. Different parameters of the catalytic preparation process and photocatalytic degradation process were studied. Characterization of differently prepared samples was carried out using different analytical techniques such as XRD, SEM, and EDX and finally the photocatalytic activity towards decomposition of methyl orange and paraquat.

The photocatalytic activity of TiO 2 -zeolite composite for degradation of dye using synthetic UV and jeddah sunlight

In this research different composites of impregnated TiO2 with LTA or FAU zeolites were used as different weight% ratio for photodegradation of organic dye. Normal laboratory UV-lamps were used as a source of UV irradiation. In addition a setup of system of mirrors was used to collect real Jeddah sunlight. A comparison of UV and real sunlight photodegradation activity showed that the real sunlight enhances new centers of active sites exhibiting higher catalytic activity than that of UV irradiated samples.

Impact of Block Length and Temperature over Self-Assembling Behavior of Block Copolymers

Self-assembling behavior of block copolymers having water-soluble portion as one of the blocks plays key role in the properties and applications of the copolymers. Therefore, we have synthesized block copolymers of different block length and investigated their self-assembling behavior with reference to concentration and temperature using surface tension and conductance measurement techniques. The results obtained through both techniques concluded that critical micelles concentration (CMC) was decreased from 0.100 to 0.078 g/dL with the increase in length of water insoluble block and 0.100 to 0.068 g/dL for the increased temperature. was also decreased with the increase in temperature of the system, concluding that the micellization process was encouraged with the increase in temperature and block length. However, values were highest for short block length copolymer. The surface excess concentration obtained from surface tension data concluded that it was highest for short block length and vice versa and was increased with the increase in temperature of the system. However, the minimum area per molecule was largest for highest molecular weight copolymers or having longest water insoluble block and decreases with the increase in temperature.

Controlled Preparation of Thermally Stable Fe-Poly(dimethylsiloxane) Composite by Magnetic Induction Heating

The most challenging task in the preparation of poly(dimethylsiloxane) composites is to control the curing time as well as to enhance their thermal and swelling behavior. Curing rate can be modified and controlled by a range of iron powder contents to achieve a desired working time, where iron is used as self-heating particles. Iron under alternative current magnetic field (ACMF) is able to generate thermal energy, providing a benefit in accelerating the curing of composites. Three types of iron-Poly(dimethylsiloxane) (Fe-PDMS) composites were prepared under ACMF with iron content 5, 10, and 15 wt %. The curing process was investigated by FTIR, while the morphology and the thermal stability were examined by SEM, DMA, and TGA. The heating’s profile was studied as functions of iron content and induction time. It was found that the time required to complete curing was reduced and the curing temperature was controlled by varying the iron content and induction time. In addition, the thermal stability and the swelling behavior of the prepared composites were enhanced in comparison with the conventional PDMS and thus offer a promising route to obtain thermally stable composites.