Perihan Gürkan

Synthesis and properties of some azo pyridone dyes and their Cu(II) complexes

Abstract A series of azo pyridone dyes derived by the coupling of 3-cyano-6-hydroxy-4-methyl 2 (IH) pyridone with diazotized para and meta substituted anilines, and the Cu(II) complex of the dyes, have been synthesized. The azo dyes and complexes have been characterized by elemental analysis, IR, 1H NMR and UV-visible spectra. The acid dissociation constants of the dyes and formation constants of the complexes have been determined spectrophotometrically. Substituent effects on these parameters have been discussed.

Synthesis, potentiometric and antimicrobial activity studies on DL-amino acids-Schiff bases and their complexes

A relationship between antimicrobial activities and the formation constants of amino acid-Schiff bases and their Cu(II) and Ni(II) complexes was studied. For this purpose, a series of Schiff bases were prepared from DL-amino acids (DL-glycine, DL-alanine) and halo aldehydes (5-chloro-2-hydroxybenzaldehyde, 5-bromo-2-hydroxybenzaldehyde). Schiff bases and their Cu(II) and Ni(II) complexes were characterized by the elemental analysis, spectral analysis, magnetic moment (at ca. 25°C), molar conductivity, and thermal analysis data. The complexes were found to have general compositions [ML(H2O)]. The protonation constants of the Schiff bases and stability constants of the complexes were determined potentiometrically in a dioxane-water (1: 1) solution at 25°C and 0.1 M KCl ionic strength. Antimicrobial activities of the Schiff bases and their complexes were estimated for six bacteria, such as Bacillus cereus RSKK 863, Staphylococcus aureus ATCC 259231, Micrococcus luteus NRLL B-4375, Escherichia coli ATCC 11230, Aeromonas hydrophila 106, Pseudomonas aeroginosa ATCC 29212, and the yeast Candida albicans ATCC 10239. The role of halogen substitution on the ligands, effect of the metal ion, and stabilities of the complexes are discussed on antimicrobial activities.

Synthesis, potentiometric and antimicrobial activity studies on 2-pyridinilidene-DL-amino acids and their complexes

To investigate the relationship between antimicrobial activities and the formation constants of CuII, NiII and CoII complexes with three Schiff bases, which were obtained by the condensation of 2-pyridinecarboxyaldehyde with DL-alanine, DL-valine and DL-phenylalanine, have been synthesized. Schiff bases and the complexes have been characterized on the basis of elemental analyses, magnetic moments (at ca. 25 °C), molar conductivity, thermal analyses and spectral (i.r., u.v., n.m.r.) studies. The i.r. spectra show that the ligands act in a monovalent bidentate fashion, depending on the metal salt used and the reaction pH = 9, 8 and 7 medium, for CuII, NiII and CoII, respectively. Square-planar, tetrahedral and octahedral structures are proposed for CuII, NiII and CoII, respectively. The protonation constants of the Schiff bases and stability constants of their ML-type complexes have been calculated potentiometrically in aqueous solution at 25 ± 0.1 °C and at 0.1 M KCl ionic strength. Antimicrobial activities of the Schiff bases and the complexes were evaluated for three bacteria (Bacillus subtillis, Staphylococcus aureus, and Escherichia coli) and a yeast (Candida albicans). The structure–activity correlation in Schiff bases and their metal(II) complexes are discussed, based on the effect of their stability contants.

Tetradentate asymmetric Schiff bases and their Ni(II) and Fe(III) complexes

Three asymmetric Schiff-base tetradentate diimines H2L1, H2L2, and H2L3 [(2-OH)C6H4N=CHC6H42-N=CHC6H3(2-OH)(5-X), X = H, CH3, Cl respectively] have been synthesized by a two step process. The reaction of 2-hydroxy aniline with 2-nitro-benzaldehyde in EtOH gave the starting Schiff base, 2-hydroxy-N-(2-nitrobenzylidene)aniline (SB-NO2), which was reduced into the amino derivative (SB-NH2) in solution. Reacting SB-NH2 with 2-hydroxybenzaldehyde, 2-hydroxy-5-methylbenzaldehyde and 2-hydroxy-5-chlorobenzaldehyde gave the three new ligands H2L1, H2L2, and H2L3 respectively. Their dimeric, binuclear metal complexes with Ni(II) and Fe(III) have also been synthesized. The ligands and their complexes were characterized by elemental analyses, LC–MS, IR, electronic, 1H and 13C-NMR spectra, TGA, conductivity and magnetic measurements. All of the spectroscopic, analytical and other data indicate octahedral geometry M2L2(H2O)X2 (M: Ni,Co;X: Cl or H2O), except for NiL2 which is monomeric. Antimicrobial activities of the ligands and the complexes were evaluated against five bacteria. While the ligands and the Ni complexes are inactive towards Pseudomonas aeruginosa and Staphylococcus aureus, Fe complexes are active; only Fe complexes are inactive against Escherichia coli. All of the compounds have antimicrobial activities against Bacillus subtilis, and Yersinia enterecolitica.

Yttrium(III), Cerium(III) and Lanthanum(III) Complexes of Salicylideneamino Acids. Synthesis, Characterization and Potentiometric Studies

Abstract New complexes of Y(III). Ce(III) and La(III) with Schiff bases derived from the condensation reaction of salicylaldehyde with DL-glycine, DL-alanine and DL-aline have been synthesized and characterized by elemental analyses, molar conductivities. magnetic moments. infrared. 1H NMR. electronic spectral data. and thermal analyses. The protonation constants of the Schiff bases and stability constants of their MI, -type complexes have been determined potentiometrically at 25±0.1 °C and μ = 0.1 M KCl in aqueous solutions.

Potentiometric determination of stability constants of Lanthanon(III) complexes with some Schiff bases and benzothiazolines

The protonation constants of five Schiff base and two benzothiazoline type ligands and stability constants of their complexes with six lanthanide ions were determined by potentiometrically in ethanol-water solution (1:1, v/v) at 25 +/- 0.1 degrees C. The Schiff base-type ligands were salicylidene 2-iminopyridine (SAPy), salicylidene-5-methyl-2-iminopyridine (SAPyMe), salicylidene-5-chloro-2-iminopyridine (SAPyCl), 2-(2-pyridylmethyleneamino) phenol (PyOH), 2-(2-quinolylmethyleneamino) phenol (QuOH) and the benzothiazoline-type ligands were pyridine-2-car-bozaldehydebenzothiazoline (PyS) and quinoline-2-carboxaldehydebenzothiazoline (QuS). The order of stability constants was found to be for metal ions La(III) < Pr(III) < Nd(III) < Eu(III) < Ho(III) < Yb(III), and for ligands SAPyCl < SAPy < QuS < QuOH < PyS < PyOH < SAPyMe. The FORTRAN programs PKAS and BEST were used for the calculation of protonation constants and stability constants, respectively.

Investigation of the solid-state conductivity and the potentiometric stability constant relationships of new amino acid-Schiff bases and their complexes

CuII, NiII and CoII complexes of new tridentate amino acid-Schiff bases derived from furfural and DL-alanine, DL-valine and DL-phenylalanine were prepared and characterized by analytical, spectroscopic, (i.r., u.v.–vis., 1H-n.m.r and 13C-n.m.r) techniques, molar conductivity, magnetic and thermal measurements. Protonation constants of the Schiff bases and stability constants of the complexes have been determined potentiometrically in water. Solid-state conductivities of the synthesized substances were measured using the four-probe technique on a compressed pellet at room temperature.

Synthesis of monosodium salts of N-(5-nitro-salicylidene)-D-amino acid Schiff bases and their iron(III) complexes: spectral and physical characterizations, antioxidant activities

Amino acid Schiff bases, [NaL]·nH2O (L = N-(2-hydroxy-5-nitrobenzylidene)alaninate, N-(2-hydroxy-5-nitrobenzylidene)valinate, and N-(2-hydroxy-5-nitrobenzylidene)phenylalaninate), were synthesized as monosodium salts (L1Na–L3Na). The structures of the monosodium salts were confirmed on the basis of elemental analysis, conductivity measurements, UV–vis, FT-IR, and 2D NMR (HMQC) spectroscopies. L1Na was also structurally determined by single-crystal X-ray diffraction. Hydrogen bond between the amino N(2)–H and phenolate O(1) of the salicylidene part of the molecule played important roles in stabilizing the zwitterion crystal structure. The ranges of the D–H…A angles and those of the H…A and D…A distances indicated the presence of short hydrogen bonds in the structure. In addition, the monosodium salts have been evaluated for in vitro antioxidant activity. Iron(III) complexes (L1Fe–L3Fe) have been obtained by reaction of the appropriate ligand with iron(III) chloride in a 2 : 1 M ratio. Fe(III) complexes were characterized by elemental and thermal analysis, conductivity and magnetic susceptibility measurements, UV–vis, FT-IR, and X-ray photoelectron spectroscopy methods. Graphical abstract

Some Novel Amino Acid-Schiff Bases and their Complexes Synthesis, Characterization, Solid State Conductivity Behaviors and Potentiometric Studies

Three new Schiff bases derived from the condensation reaction of thiophene-2-carbaldehyde and DL-alanine, DL-valine and DL-phenylalanine have been synthesized and their Co(II), Ni(II) and Cu(II) complexes have been prepared. The Schiff bases and the complexes have been characterized by their analytical and spectral data. The protonation constants of the Schiff bases and stability constants of the complexes have been determined potentiometrically in aqueous medium at 25 °C and 0.1 M KCl ionic strength. Solid state conductivities of the synthesized substances were using the four-probe technique on a compressed pellet at room temperature.

Titrations in non-aqueous media. Part VI. Effects of substituents on basicity or acidity of N-salicylidene-2-hydroxyaniline

Fifteen Schiff bases were synthesised from N-salicylidene-2-hydroxyaniline, which was chosen as the model base, by substituting methyl, hydroxy, chlorine, bromine and nitro groups for the hydrogen atoms, which are at the para positions with respect to the hydroxy groups that are already present on the model Schiff base. From each substituent, three derivatives of the model base were prepared stepwise. The effects of each substituent on the basicity or acidity of the model base, which is an amphoteric compound, were investigated; they were titrated potentiometrically either in nitrobenzene as the base or in pyridine as the acid. The following results were obtained. The increase in basicity due to the methyl group is approximately the same whether the latter is on the aldehyde or on the amine component of the model base. The sum of these effects is approximately equal to the separate effects of the methyl groups, when one is on the aldehyde and the other is on the amine component. Except for the basifying strength, the hydroxy group exerts the same effect on the basicity of the model as does the methyl group. A chlorine atom decreases the basicity of the model base more when it is on the aldehyde component than when it is on the amine component. However, the effect is again approximately equal to the sum of the effects of the two chlorine atoms when one is on the aldehyde and the other is on the amine component. Except for the basicity-decreasing strengths, the bromine and nitro functions show the same behaviour as the chlorine atom. Further, the bromine atom has a greater basicity-decreasing effect than the chlorine atom. The basicity-decreasing power decreases in the order NO2 > Br > Cl > H. In pyridine, the hydroxy group is acidifying when it is on either the aldehyde or amine component, but basifying when it is on both of the components. In pyridine, the chlorine, bromine and nitro functions are all acidifying when they are on the aldehyde or on the amine components or both. The acidifying effects of chlorine and bromine are approximately the same. Moreover, the effect of each substituent is additive.