Showing papers on "Schiff base published in 1974"

Topics in the methodology of substitution reactions with agarose.

Abstract: Publisher Summary Agarose beads have been one of the most useful solid supports in affinity chromatography This chapter describes various alternative methods that can be used to activate agarose for the covalent attachment of small ligands and proteins In addition, some general problems encountered in the use of such derivatives are presented and possible solutions are suggested Nearly all methods for coupling ligands or proteins to agarose depend on the initial modification of the gel with CNBr An alternative method that is rapid, simple, and safe and which promises to result in chemically stable ligand-agarose bonds has been developed The method depends on the oxidation of cis-vicinal hydroxyl groups of agarose by sodium metaperiodate (NalO 4 ) to generate aldehyde functions These aldehydic functions react at pH 4–6 with primary amines to form Schiff bases; these are reduced with sodium borohydride (NaBH 4 ) to form stable secondary amines The reductive stabilization of the intermediate Schiff base is best achieved with sodium cyanoborohydride (NaBH 3 CN) because this reagent, at a pH between 6 and 65, preferentially reduces Schiff bases without reducing the aldehyde functions of the agarose Because sodium cyanoborohydride selectively reduces only the Schiff bases, it shifts the equilibrium of the reaction to the right and thereby drives the overall reaction to completion

SCHIFF BASE COMPLEXES OF OXOCATIONS Part II Oxovanadium(IV) complexes with tetradentate optically active Schiff bases

Abstract: The synthesis and properties of oxovanadium(IV) complexes with tetradentate Schiff bases obtained by condensation of two moles of acetylacetone, trifluoroacetylacetone, salicylaldehyde and its 5-chloro and 5-nitro derivatives, with optically active 1,2-diamines, namely (+) propylenediamine, (+) and meso butanediamine, (+) and meso cyclohexanediamine, (-) and meso stilbenediamine, are described. The infrared, circular dichroism and electronic spectra are reported and discussed. The factors influencing the formation of hexacoordinate adducts with donor bases are also discussed.

Terdentate NNN Donor Ligands Derived from 2,6-Diacetylpyridine

Abstract: The Schiff base condensation of 2,6-diacetylpyridine with aniline, p-methoxyaniline and benzylamine gives high yields of 2,6-diacetylpyridine-bis (arylimines). Complexation of 2,6-diacetylpyridinebis (anil) with nickel (II) and zinc (II) to form five- and six-coordinate complexes of the types MCl2·L and [ML2] (C104)2 illustrates the versatility of these new terdentate NNN donor ligands.

ESR Studies of the Triplet State Dimers of the Salicylaldehyde Schiff Base Complexes of Copper(II) in Toluene and in Chloroform

Abstract: The ESR spectra of triplet-state dimers have been obtained for various bidentate and quadridentate salicylaldehyde Schiff base complexes of copper(II) in frozen solutions. The spectra have been analysed on the basis of the previously-obtained results concerning the non-coaxial g and fine-structure tensors. The results indicate that the angles between the g|| axis and the copper-copper axis of the dimers for the quadridentate Schiff base complexes are considerably smaller than those for the bidentate ones. Each of the actually-measured ESR spectra, however, consisted of two mutually-overlapping spectra; one is due to dimers (M2), and the other, to monomers (M). The equilibrium constant for 2M\ightleftharpoonsM2 has been estimated by comparing the ESR spectral intensities of the two species. The factors which govern the dimer formations have been discussed in some detail.

Synthesis and characterization of titanium(iv) schiff base complexes. i. titanium(iv) complexes of salicylaldehyde-2-mercaptoanil

Abstract: The synthesis of new Schiff base complexes of titanium(IV) of the type TiX2(SSP), where X =SSP/2, OEt, OPri, OBut, and (h5–C5H5)C1/2, and SSP is the dianion of the tridentate ONS donor ligand salicylaldehyde-2-mercaptoanil, is reported. Electronic, infrared, nmr, and mass spectral data indicate that the colorless ligand exists in the heterocyclic benzthiazoline form but rearranges to the chelating Schiff base from in the titanium complexes. The titanium(IV) atom is six-coordinate in the monomeric Ti(SSP)2 and dimeric Ti(OR)2 (SSP) (R =Et, Pr1) complexes and five-coordinate in the monomeric Ti(OBut)2 (SSP) and (h5-C5H5)TiCl(SSP) compounds.

Kinetics of reactions of Schiff base complexes of iron(II). V. Reactions of the complex of the hexadentate ligand NN‴-bis-[α-(2-pyridyl)benzylidene]triethylenetetramine in acid solution and with hydroxide, cyanide, and peroxodisulphate

Abstract: The preparation and characterization of the iron(II) complex of the hexadentate Schiff base ligand NN‴-bis-[α-(2-pyridyl)benzylidene]triethylenetetramine are reported. Kinetic patterns and rate constants for aquation of this complex, and for its reactions with hydroxide, cyanide, and peroxodisulphate have been determined. Activation parameters for the reaction with cyanide, in aqueous solution, are ΔH‡ = 24.3 kcal/mole and ΔS‡ = +1 cal/deg-mole.

Schiff Base Derivatives of Lanthanides - Synthesis of La(III), Pr(III) and Nd(III) Complexes of Alkylimines and Arylimines Derived from 2-Hydroxy-1-Naphthaldehyde

Abstract: Methods of synthesis of lanthanide derivatives of the type, In(0-i-C3H7)2(2-OC10H6CH:NR) and In(0-i-C3H7) (2-OC10H6CH:NR)2 in high yields and in high purity have been described. These have been synthesized by the 1:1 and 1:2 molar reactions of the isopropoxides of lanthanides with monofunctional bidentate Schiff bases, 2-HOC10H6CH:N-n-C4H9 and 2-HOC10H6CH:NC6H5. Their exchange reactions with an excess of t-butyl alcohol have yielded the corresponding t-butyl derivatives. The resulting compounds have been characterized by elemental analyses and molecular weight determinations. Their infrared spectra have also been recorded and tentative assignments were made.

Gallium(III) complexes of monofunctional bidentate Schiff bases

Abstract: Reactions of gallium isopropoxide with monofunctional bidentate Schiff bases, O-HOC 6 H 4 C(HC 3 ):NR and 2-HOC 10 H 6 CH:NR' (R = n -C 4 H 9 or C 6 H 5 , R′ = C 2 H 5 or C 6 H 5 ), containing the donor system N-OH, have been investigated and found to yield complexes of the type, Ga(Opr i ) 2 (SB), Ga(OPr i (SB) 2 and Ga(SB) 3 (SB − = the anion of the Schiff base SBH). The resulting complexes have been obtained in high yield and in a state of sufficient purity. The presence of tetra-, penta- and hexacoordinated gallium atoms in the diisopropoxy mono-Schiff base, monoisopropoxy bis-Schiff base and tris-Schiff base derivatives, respectively, is probably indicated by their monomeric nature. The ν (Ga-O) frequencies are observed in the region 675-620 cm −1 , whereas ν (C = N) frequencies remain almost unchanged on complex formation.

High-spin iron(II) chelate complexes with β-diketonate and Schiff base ligands: Mössbauer and electronic spectra

Abstract: A number of high-spin iron(II) chelate complexes with some bidentate monoanionic ligands (β-diketonates, salicylaldehydate, and N-alkylsalicylideneiminates) and the quadridentate dianion NN′-ethylenebis(salicylideneiminate), and its analogues, has been studied by means of Mossbauer and electronic spectroscopy. In all the complexes the iron atom is probably six-co-ordinate because of intermolecular interactions, even in complexes of the quadridentate ligands. The isomer shifts mainly depend on the nature of the ligand atoms bound directly to the iron. For a series of closely related complexes, a linear relation has been observed between isomer shifts and quadrupole splittings. From an analysis of the temperature dependence of the quadrupole splitting, it may be inferred that the complexes studied undergo large axial distortion. This conclusion also rationalizes the relatively narrow range (2·0–2·9 mm s–1) of quadrupole splittings observed.

Factors Contributing to the Absorption and Fluorescence Characteristics of Pyridoxal Phosphate in Glycogen Phosphorylase b

Abstract: The Schiff base formed between salicylaldehyde and n-hexylamine has absorption bands peaked at 255 and 317 nm in non-polar solvents. In a polar solvent (ethanol) an additional band appears at 405 nm and a shoulder is resolved at 275 nm. The fluorescence band has a peak at 535 nm in non-polar solvents (with the exception of CCl4) which is blue shifted to 505 nm in ethanol. These spectral data are similar to those of Schiff bases formed between pyridoxal phosphate and aliphatic amines. On the other hand, the spectral properties of the Schiff base of o-methoxybenzaldehyde with n-hexylamine are very different. It may thus be concluded that the nitrogen atom of the aromatic ring does not have to be invoked in explaining the spectral properties of pyridoxal phosphate Schiff bases and of pyridoxal phosphate in glycogen phosphorylase. The hydroxyl group seems however to play an important role in determining the spectral properties of Schiff bases of o-hydroxyaldehydes. The optical rotatory power of the pyridoxal phosphate in phosphorylase is of comparable magnitude for the chromophore in the ground state or the electronically excited state, indicating similarity of mode of binding of the chromophore to the protein in the two electronic states. Measurements of circular dichroism indicate that the “deformer” imidazole citrate affects the interaction of the pyridoxal phosphate with the protein when the cofactor Schiff base is in the ketoenamine form but not when in the enolimine form.