Raafat M. Issa

Unusual Cu(III)—Schiff's base complexes

A new series of CU(III) complexes of the type [Cu(SB)]ClO4, where SB is a dibasic tetradentate Schiffs base, were synthesized and characterized by elemental analysis, IR and electronic spectra. The prepared complexes are compared with Cu(II) complexes of the same ligands. The room temperature magnetic susceptibility and the x-band EPR spectra of the two types of complexes showed different behaviour. Cu(II) complexes were non conducting whereas Cu(III) complexes gave a conductance corresponding to 1:1 electrolyte. In fact this is the first report on the Cu(III) complexes with the tetradentate Schiff base ligands.

Controlled release of herbicides bound to poly[oligo(oxyethylene) methacrylate] hydrogels

A series of polymeric hydrogels containing different oxyethylene oligomers has been prepared by radical polymerization of oligo(oxyethylene) methacrylate monomers in the presence of different amounts of N,N′-methylenebisacrylamide as crosslinking agent or acrylamide as hydrophilic comonomer. Systemic herbicides, such as 2,4-dichlorophenoxyacetic acid and 4-chloro-2-methylphenoxyacetic acid, were covalently supported on the polymeric hydrogels by esterification of the side chain hydroxyl groups. In the investigated samples, swelling in water depends mainly on the length of the oligo(oxyethylene) side chains, the content of hydrophilic comonomer and, to a minor extent, on the degree of crosslinking. Herbicide loading produces a substantial drop in the water uptake by the polymer. The release of herbicides, investigated at room temperature in water at different pH values, is very much affected by alkalinity and to a lesser extent by the polymer structure.

High-valent manganese complexes of tetradentate schiff base ligands. ESR-active and ESR-silent dimeric species

Abstract Two new complexes of type [Mn(SB)(Me2CO)] Y (SB is a dianion of a tetradentate Schiff base ligand, Y = NO3 or ClO4) have been synthesised and characterised. The complexes are probably dimeric via bridging acetone ligands. Base hydrolysis of these complexes in chloroform yielded new dimeric species tentatively assigned as [Mn2(SB)2(O)(OH)]·H2O and [Mn(SB)(O)]2·H2O. Elemental analyses, infrared, electronic and ESR spectra, as well as conductivity and room temperature magnetic susceptibility measurements are reported.

Synthesis, characterization, thermal, and antimicrobial studies of binuclear metal complexes of sulfa-guanidine Schiff bases

A series of metal complexes of Schiff bases derived from condensation of sulfa-guanidine with 1-benzoylacetone (H2L1), 2-hydroxybenzophenol (H2L2), dibenzoylmethane (H2L3), 5-methylisatine (H2L4), and 1-methylisatine (H2L5) have been synthesized. The complexes are characterized by elemental analysis, molar conductance, magnetic moment measurements, IR, UV–Vis, 1H NMR, and ESR spectra, as well as thermogravimetric analysis. The low molar conductance values indicate the complexes are nonelectrolytes. IR and 1H NMR spectra show that H2L1–H2L5 are coordinated to metal ions by two bidentate centers. Mn(II), Co(II), Ni(II), and Cu(II) complexes display paramagnetic behavior, whereas the Zn(II)-complex was diamagnetic. All studies confirm the formation of an octahedral geometry for [Cu2L1(AcO)2(H2O)6] · 3H2O (1), [Mn2L4(AcO)2(H2O)6] · 2H2O (6), [Ni2L4(AcO)2(H2O)6] · 2H2O (8), a tetrahedral geometry for [Cu2L2(AcO)2(H2O)2] (2), [Cu2(L4)2] (4), [Co2(L4)2] · 2H2O (7) and [ZnHL4(AcO)(H2O)] · 2H2O (9) and a trigonal bipyramid geometry for [Cu2L3(AcO)2(H2O)4] (3) and [Cu2HL5(AcO)3(H2O)3] · H2O (5). H2L4 was most effective on Gram negative, Gram positive bacteria, and fungi (diameters inhibition zone ranged between 10.5–27.5 mm) after 24 and 48 h, respectively. Complex 8 showed moderate antimicrobial activity. Its minimum inhibitory concentration (MIC) against Escherichia coli, Bacillus subtilis, Candida albicans and Aspargllus flavas was 20 mg L–1. The compound proved to be of moderate toxicity and its LD50 was 20 mg L–1.

Spectral and photophysical studies of inclusion complexes of 2-amino-4,6-dimethyl pyrimidine with β-cyclodextrin

The interaction of 2-amino-4,6-dimethyl pyrimidine (ADMP) with beta-cyclodextrin (beta-CD) has been studied by means of UV absorption, steady state and time resolved fluorescence techniques. Spectral characteristics, bandwidths and photophysical parameters indicating that ADMP experience two different environments in aqueous solutions: bulk water and 1:1 (ADMP:beta-CD) inclusion complexation. The size restriction of the upper rim of beta-CD partially include ADMP and prevent the possibility of formation of 1:2 complex. The effective polarity of the cyclodextrin cavity experienced by the induced ADMP is equivalent with the polarity of an 80:20 methanol-water mixture.

Polymer complexes XXXIV. Potentiometric and thermodynamic studies of monomeric and polymeric complexes containing 2-acrylamidosulphadiazine

Abstract 2-Acrylamidosulphadiazine (ASD) was synthesized and characterized by elemental analyses, IR and 1 H NMR spectra. Proton–monomeric ligand dissociation and metal–monomeric ligand stability constants of ASD with some metal ions were determined potentiometrically in 0.1 M KCl and 40% (v/v) ethanol–water mixture. In the presence of 2,2′-azobisisobutyronitrile as initiator, the dissociation and stability constants of ASD were determined in polymeric form (PASD). The influence of temperature on the dissociation of ASD and the stability constants of their complexes in monomeric and polymeric forms were critically studied. The pK2H value of PASD was found to be higher than ASD, this means that the vinyl group in the monomeric form decreases the electron density and hence reduces the N–H bond strength. The stability constants of the metal complexes in polymeric form are higher than those of the monomeric form. This is quite reasonable because the ligand in a polymeric form is considered as a better complexing agent.

Controlled Release of Herbicides Supported on Polysaccharide Based Hydrogels

Polymeric hydrogels based on polysaccharides, hydroxyethylcellu lose and dextran, were attained by cross-linking with epichlorohydrin. The cross-linked polymer beads were loaded with 2,4-dichlorophenoxyacetic acid by direct esterification in the presence of carbonyldiimidazole. Loads ranging be tween 0.5 and 2.2 mol of 2,4-dichlorophenoxyacetyloyl groups per glucose unit were obtained. The release of 2,4-D herbicide was investigated in buffered aqueous solution at different pH values (4, 7 and 9) and evaluated with respect to different structural parameters, such as nature of the polymer matrices, cross-linking extent and herbicide loading. A fairly slow release, ranging from 10 to 25% after four months, was recorded under neutral and acid conditions, whereas at pH 9 an initial burst in the release profile, reaching almost 90% release of 2,4-D loading, was observed. In the majority of the cases, the release kinetics are reproduced by the combination of two exponential decay processes, that differ by about three orders of magnitude in their absolute rates.

A rapid, selective and sensitive spectrophotometric method for the determination of Ce(III) using some bisazophenyl-β-diketone derivatives

A rapid, simple, selective and sensitive spectrophotometric method for the determination of cerium(III) using the title azo dyes [1,3-phenylenediamine bisazoacetylacetone (I(a));1,3-phenylenediamine bisazobenzoylacetone (I(b));1,4-phenylenediamine bisazoacetylacetone (I(c)); and 1,4-phenylenediamine bisazobenzoylacetone (I(d))] has been developed in neutral and slightly alkaline (pH 7.00, 7.50, 8.00 and 7.00) media. The 1:1 and 2:1 (M:L) complexes formed exhibit their highest absorbances in 30% (v/v) dioxane solutions, having formation constants (log K) of 4.44, 4.95. 5.63 and 5.22 and 8.51, 8.76, 9.73 and 9.37 respectively. Beers law is obeyed over the concentration ranges 0.10-2.50, 0.05-3.00, 0.05-3.75 and 0.10-3.50 mug ml(-1) of cerium(III). More accurately, Ringbom optimum concentration ranges are 0.2-2.25, 0.2-2.6, 0.2-3.5 and 0.2-3.3 mug ml(-1) for the complexes of reagents I(a),I(b),I(c) and I(d) respectively. The molar absorptivities, Sandell sensitivities and relative standard deviations were also calculated. The interferences of 50 foreign ions on the determination of cerium(III) were studied. The method allows the determination of cerium(IV) after prior reduction to the trivalent state. The proposed method was used for cerium determination in two different monazite samples and the results were compared with certified values obtained using atomic absorption spectrometry, indicating that the procedure provided accurate and precise results.

Herbicide containing methacrylates: synthesis, polymerization and release investigation

Abstract The preparation is reported of two series of oligo(oxyethylene) methacrylates containing residues of 2,4-D and CMPA herbicides covalently bound via an ester bond to oligoether side groups having different degree of oligomerization (DPn = 2, 4, 8). The two series of monomers, when submitted to free radical polymerization gave the corresponding homopolymers, that exhibited a water uptake generally lower than 50%. A series of linear and crosslinked polymeric herbicides was also prepared by copoly-merization of the CMPA-containing tetraoxyethylene methacrylate with different comonomers, such as dioxyethylene and octaoxyethylene monomethacrylate, acrylamide, methylene bisacrylamide and 4-vinylpyridine. All the synthesized polymeric herbicides were tested for their release properties in aqueous solution buffered at pH 4, 7 and 9. The herbicide release profiles have been discussed in relation to the polymer inherent structural features and compared with the corresponding polymers obtained by 2,4-D and CMPA binding to preformed poly [oligo(oxyethylene) methacrylate]s. In any case the release kinetics do not fit a simple diffusional scheme and they can be reproduced by the contemporary occurrence of two exponential decay processes, differing by three orders of magnitude in their absolute rates

Ionogenic polymer pro-herbicides based on partially quaternized poly[oligo(oxyethylene) methacrylate]s. synthesis and herbicide release

Abstract The preparation and structural characterization of polymeric proherbicides consisting of 4-chloro-2-methylphenoxyacetic acid (CMPA) ionically bound to linear and crosslinked polymer matrices based on oligo(oxyethylene) monomethacrylates (DPn oligooxyethylene: 2, 4 and 8), containing quaternary onium groups (%-mol: 8–60) are described. CMPA loading was carried out by an ion-exchange procedure and CMPA contents in the range 0.15–0.45 mmol/g of dry polymer were attained. The loaded polymer samples displayed typical moderate to strong hydrogel character. The herbicide release, performed in water medium at controlled pH (4, 7 and 9) and saline content, reached, after three months, a 55% value at best. No definite correlation between structural parameters and release behaviour can be drawn, whereas alkaline conditions seem to favourably affect the herbicide release. The release profiles can be reproduced by a best fit analysis based on the occurrence of two exponential decay processes differing by three orders of magnitude in their absolute rates.