Ahmed M. Ramadan

Physicochemical characterization of novel Schiff bases derived from developed bacterial cellulose 2,3-dialdehyde

The synthesis of two novel Schiffs bases (cellulose-2,3-bis-[(4-methylene-amino)-benzene-sulfonamide] (5) & cellulose-2,3-bis-[(4-methylene-amino)-N-(thiazol-2-yl)-benzenesulfonamide] (6) via condensation reactions of periodate oxidized developed bacterial cellulose ODBC (2) with sulfa drugs [sulfanilamide (3) & sulfathiazole (4)] was reported. The physicochemical characterization of the condensation products was performed using FTIR, (1)H NMR, (13)C NMR spectral analyses, X-ray diffraction and DTA. The ODBC exhibited the highest degree of oxidation based on the aldehyde group number percentage (82.9%), which confirms the highest reactivity of developed bacterial cellulose [DBC (1)]. The X-ray diffractograms indicated an increase in the interplanar distance of the cellulose Schiff base (6) compared to ODBC (2) due to sulfathiazole (4) inclusion between ODBC (2) sheets corresponding to the 1 1 0 plane. In addition, the aldehyde content of Schiff base (6) was (20.8%) much lower than that of Schiff base (5) (41.5%). These results confirmed the high affinity of sulfathiazole (4) to the ODBC (2) chain, and the substantial changes in the original properties of ODBC were due to these chemical modifications rather than the sulfanilamide (3).

Stability constants and complex formation equilibria between iron, calcium, and zinc metal ions with vitamin B9 and glycine

The complexation equilibria of folic acid (FA) and glycine (Gly) were studied in aqueous solutions at room temperature (ca. 298.15 K) and in fixed ionic strength (0.15 mol.dm−3 NaNO3), by means of potentiometry technique. The ferric (Fe3+), ferrous (Fe2+), calcium (Ca2+), and zinc (Zn2+) complex-forming capacities of FA and Gly, and their overall stability constants in aqueous solutions were obtained by applying the potentiometric data in Hyperquad 2008 computer program. From the determined stability constants of the metal complex species, the concentration distribution of the various metal ion complex species involving FA and Gly in solutions was estimated using HySS 2009 software. The complex species distribution diagrams were explained and discussed. Supplementary, the Gibbs free energies and the molecular structures of the formed complexes were evaluated and predicted using Gaussian 09 software molecular modeling and calculations. GRAPHICAL ABSTRACT

Nitrosophenol complexes of transition metal salts

Complexes derived from 4-substituted-2-nitrosophenols, 3-Me-2-nitrosophenol, nitrosophyrogallol, nitrososalicylic acid and nitrosogallic acid with cobalt(II), nickel(II) and copper(II) have been prepared and characterized by elemental analysis, electronic and vibrational spectra, together with magnetic susceptibility measurements. The e.s.r. spectra of the copper(II) complexes were investigated, and detailed thermal properties of selected complexes are discussed.

Peculiar behavior of starch 2,3-dialdehyde towards sulfanilamide and sulfathiazole.

In this study, starch (1) was oxidized to starch-2,3-dialdehyde (DAS; 2) using potassium periodate. In addition, two novel Schiffs bases (5 &6) were synthesized via a condensation reaction between DAS (2) and sulfa drugs (sulfanilamide; 3 & sulfathiazole; 4). The synthesized Schiffs bases (5 &6) were characterized by FT-IR spectroscopy, X-ray diffraction and DSC analysis. DAS can easily be oxidized owing to its high aldehyde content (91.0%). However, it has low reactivity towards sulfanilamide (3) and sulfathiazole (4). According to the diffraction functional theory, this peculiar behavior is caused by the absence of V-shape in α-glucan linkage in DAS molecules, making the carbonyl group least electropositive. This reduces the nucleophilic attacks of the amino group in sulfa drugs towards the carbonyl group in DAS.

Solvatochromic responses and pH effects on the electronic spectra of some azo derivatives of 1-amino-2-hydroxy-4-naphthalenesulfonic acid

Synthesis and characterization of five arylazo derivatives of 1-amino-2-hydroxy-4-naphthalenesulfonic acid (H2L1) are reported. The UV/Vis absorption spectra of the parent compound (H2L1) and its arylazo derivatives (H2L2–H4L6) have been measured at room temperature in seven solvents of different polarities and with variable parameters. The electronic transitions were analyzed using SPSS program, linear regression technique and Kamlet–Taft’s equation to permit a good understanding of solvent-induced spectral shifts. The electronic absorption spectra of the prepared compounds containing different substituents were studied in aqueous solutions at different pH values. The pK values of the investigated compounds were evaluated spectrophotometrically. The prevailing acid species present at any pH range are judged from the constructed distribution diagrams.

An unexpected reactivity during periodate oxidation of chitosan and the affinity of its 2, 3-di-aldehyde toward sulfa drugs

In an attempt to determine the reactivity during the periodate oxidation of the vicinal amino sugar, chitosan was oxidized by KIO4 in a neutral medium. The reactivity was unexpectedly found to be low. The formation of di-aldehyde chitosan (DACT) might cause the low reactivity of chitosan oxidation. Therefore, density functional theory (DFT) calculations were carried out, which revealed that the greater stability of the cyclic amino iodate intermediate might retard the ring opening to form DACT. Furthermore, the affinity of the formation of two novel Schiff bases from the interaction of delivered DACT with two sulfa drugs [sulfanilamide and sulfathiazole] was also investigated using aldehyde content estimation. DACT and Schiffs bases were characterized by FT-IR spectroscopy, X-ray diffraction, and DTA analysis. The X-ray diffraction plane (110) of DACT at the high angle side was expanded more by sulfathiazole than sulfanilamide, indicating that sulfathiazole reacted effectively with DACT. The lowest interaction of DACT with sulfa drugs could be ascribed to the lowest aldehyde content and the intramolecular hemiacetal formation that hinders the Schiffs base condensation.