Showing papers on "Schiff base published in 1970"

Complexes of binucleating ligands. II. Geometrical models for potential nitrogen fixing systems

Abstract: The synthesis and some properties of a series of complexes, LCu2(X), are discussed where L is the binucleating trianion derived from d-methylisophthal-aldehyde di-2'-hydroxyanil [2-hydroxy-5-methyl-1,3-xylene-?,?'-diylidenebis(2-hydroxyphenylamine)] and X- is OH-, OR- ; pyrazolate anion; binuclear structures are assigned to these compounds on the basis of spectral and magnetic evidence. In the compound formulated as (L,H2O)Cu2(OCH3) it is suggested that the water molecule is added across one Schiff base link in L. The possible relevance of the results to a long-term project concerned with the synthesis of potential nitrogen-fixing systems is briefly discussed.

7 Schiff Base Intermediates in Enzyme Catalysis

Abstract: Publisher Summary This chapter discusses some properties of Schiff bases. The Schiff base may be defined as the imine (III) arising from the condensation of an amine and a carbonyl-containing compound. The versatility of the imine bond in promoting an extraordinary variety of apparently different reactions is of biochemical importance. Imines of many carbonyl compounds promote such reactions, even in the absence of specific enzyme proteins, and their effectiveness is especially pronounced when the imine is conjugated with an electron sink—for example, that provided by pyridoxal 5’-phosphate. Such nonenzymic reactions constitute useful models for the enzymic systems. The protein portion of the enzyme, however, by supplying a specific affinity for the substrate and a variety of additional appropriately placed catalytic functional groups enhances the rates of the nonenzymic reactions by factors as high as 10 7 or more and imparts reaction specificity to the system.

Asymmetric syntheses of optically active α-amino acids by hydrocyanic acid addition to the optically active Schiff base

Abstract: The syntheses of L(+) and D(−) enantiomers of α-amino acids, norvaline, norleucine, and leucine, as their hydrochloride salts have been achieved in almost 100% optical purity and 40–60% overall yield.

Some organometallic and ‘simple’ Schiff-base chelates of tin(IV)

Abstract: Organotin(IV) chelates with a quadridentate Schiff base of the type R2Sn(salen)(R = Me or Ph) have been synthesised by use of the recently reported Tl2(salen) complex. The n.m.r. spectra of the chelates suggest that the R groups are cis to each other with the salen ligand in the unusual twisted configuration. A number of tin(IV) Schiff-base complexes of the types SnCl4,2(salH-N-p-MeC6H4); SnCl4,(salenH2); Sn(salen)Cl2 and SnCl3-(salH-N-(2-OC6H4), Et3N are also described. I.r., 1H n.m.r., and mass spectra and conductance measurements have been used where possible to suggest possible structures for the complexes.

Complexes of transition metals with Schiff bases and the factors influencing their redox properties. Part I. Nickel and copper complexes of some diketone bisthiosemicarbazones

Abstract: A series of nickel complexes, containing a planar NiN2S2 co-ordination unit, where the ligand is a tricyclic tetradentate Schiff base derived from R1CO·COR2(R1= R2= H or Me; R1= H, R2= Me), cyclohexane-1,2-dione, camphorquinone, hexane-2,5-dione, hexene-2,5-dione and phthaladehyde and either thiosemicarbazide or 4-methylthiosemicarbazide {NH2·NH·C(:S)·NHMe}, have been prepared and characterised. Diacetylbis-(thiosemicarbazonato) copper(II), and its 3-ethoxybutane-1,2-dione bis-(4-methylthiosemicarbazonato) analogue, have also been prepared. A polarographic and cyclic voltammetric examination of these complexes has revealed that they undergo an ill defined, irreversible oxidation process, at ca.+1·0 V, but that they may be reduced in two, reversible, one-electron steps. The half-wave potentials for the reduction waves depend on the substituents attached to the periphery of the tricyclic ligand framework, on the central metal atom, and on the extent of the conjugation around the ligand. A macrocyclic complex, obtained by treatment of hexane-2,5-dione bis-(4-methylthiosemicarbazonato) nickel with αα′-o-dibromoxylene, has been prepared, and is believed to contain octahedrally co-ordinated nickel(II)(axial Br).

S-Sulphinates of cobalt(III) planar chelates and sulphur dioxide insertion into a cobalt(III)-carbon bond

Abstract: The reactivity of the cobalt-carbon bond towards sulphur dioxide has been investigated in the compounds Rco111(L)B where L = N,N'-ethylenebis(salicyl-aldiminato), N,N'-phenylenebis(salicylaldiminato), or bis(dimethylg1yoximato);B = water or pyridine. In the Schiff base complexes, for R = alkyl, insertion into the cobalt-carbon bond proceeds smoothly to give the corresponding sulphinato derivatives. Reaction also occurs with methylcobaloxime and a pentafluorobenzene- cobalt-Schiff base compound, but the products are not so well defined. There is no reaction with cobalt-aryl bonds for any of the chelates. The alkane- and arene- sulphinato complexes can be synthesized by an alternative oxidative-addition reaction NaCOL+RSO2Cl or a replacement reaction XCoL+AgSO2R or NaSO2R (X = Cl,I). The infrared spectra of the complexes show that the sulphinato group is bonded in the manner shown: (See diagram in article) The p.m.r. spectra of the complexes are discussed in some detail. Reactions of the sulphinato derivatives with donor molecules and the halogens are briefly described.

Etude par fluorescence de bases de schiff du pyridoxal, comparaison avec la l aspartate‐aminotransferase

Abstract: — –Absorption and emission spectra of Schiff bases of pyridoxal-HCI or pyridoxal-5-phosphate with L-valine, n-butylamine or N-α-acetyl-L-lysine-N-methylamide have been studied as a function of pH We can write the complete ionization diagram and equilibria The results of Martell[6] are confirmed: the forms analogous to the coenzyme in aspartate aminotransferase, which absorb at 410 nm and 360 nm (or 340 nm for the Schiff base with n-butyl-amine) have the phenol OH ionized; the imine nitrogen is protonated for species absorbing at 410nm (in the enzyme: inactive form and complex with aminoacid) and unprotonated for species absorbing at 360 nm (in the enzyme, active form) Their fluorescence wavelengths are respectively 500 nm and 430 nm Protonation of the pyridine nitrogen of these forms does not shift the absorption band; the fluorescence intensity is 20-fold greater for the N-protonated forms The real pK of the imine nitrogen is 85 ±08 for species with pyridine N-protonated or 104 for the non-protonated forms The observed pK 63 in the enzyme can be explained if the imine nitrogen is hydrogen bonded to an amino-acid side chain of the protein: lysine, tyrosine, serine, sulfhydryl The quantum yield of the coenzyme fluorescence in the enzyme has been compared to that of the analogous Schiff base (absorbing at the same wavelength) According to the results, we cannot deduce whether the pyridine nitrogen is protonated in pyridoxal form of the enzyme If it is protonated, as in the pyridoxamine form, the coenzyme environment is not the same in the two forms If the pyridine nitrogen is unprotonated in the pyridoxal form and protonated in the pyridoxamine form, the environment of the coenzyme is the same in these two forms of the enzyme

Magnetic behaviour of bivalent copper complexes of some tridentate Schiff bases

Abstract: The magnetic susceptibilities in the temperature range 90-400oK are reported for copper(11) complexes of the general formula CuL, where L is a tridentate Schiff base. The magnetic behaviour of some of the complexes is interpreted in terms of pairwise antiferromagnetic interaction and of others in terms of linear antiferromagnetism involving infinite chains of copper atoms.

Thallium(I) Schiff base compounds

Abstract: Complexes of thallium(1) and N-substituted salicylaldimines have been prepared of general formulae Tl(sal-NR), Tl2(salen), Tl2(salophen), and Tl2(sa1-N-(2-OC6H4)). The infrared, ultraviolet, p.m.r., and mass spectra of the complexes are discussed in the light of their probable structures. It is shown that these thallium(1) complexes provide a facile and efficient route to the preparation of other metal and organometallic Schiff base chelates.

Schiff Base: An Overview of its Medicinal Chemistry Potential for New Drug Molecules

Abstract: Schiff base denotes a reaction product of a primary amine and a carbonyl compound. Schiff bases possess a wide variety of biological activity specially antibacterial and antifungal properties. Metal complexes of Schiff base have been studied for their biological activities. This review articles provide a summary of medicinal chemistry features of Schiff base and various reports published on biological activities of Schiff base and its metal complexes.

The colour isomerism and structure of copper co-ordination compounds. Part XX. Crystal structure of di-µ-NN′-m-phenylene-tetrakis(salicylideneiminato)dicopper(II)

Abstract: A three dimensional X-ray analysis of the copper complex of the Schiff base prepared from salicylaldehyde and m-phenylenediamine has revealed a dimeric, centrosymmetric, molecular structure in which two bis(salicylidene-iminato)copper(II) residues are bridged by two m-phenylene groups. The co-ordination geometry at each copper atom is almost midway between cis-planar and tetrahedral. Two chloroform molecules are associated with each dimer in a manner suggesting a very weak bifurcated hydrogen-bonding interaction with donor oxygen atoms.

The Stability of Fused Rings in Metal Chelates. VII. Copper(II) Complexes of Schiff Bases Derived from 2-Acetylpyridine or Pyridine-2-aldehyde and Dipeptides Containing Glycine, β-Alanine and/or α-Aminoisobutyric Acid

Abstract: Eight new copper(II) complexes of SchifF bases derived from 2-acetylpyridine or pyridine-2-aldehyde and dipeptides containing glycine, β-alanine and/or α-aminoisobutyric acid have been prepared, and their relative stability was discussed on the basis of numerical data obtained by spectrophotometric, polarographic and other measurements. As a result, it was found that the stability of fused-ring systems decreases in the order 5-5-6-\simeq5-6-5->5-5-5->5-6-6-system (the first number represents the number of ring members containing pyridine derivatives and the second and third numbers represent those of ring members containing dipeptide moieties). The conclusion proposed previously that SchifF base chelates of aldehydes are generally less stable than those of corresponding ketones, has been proved to be valid also for the copper(II) chelates. It was found that transamination reactions take place in the copper(II) chelates of Schiff bases with pyridine-2-aldehyde and glycylglycine or glycyl-β-alanine.

Reactions of some copper(II) complexes of the Schiff bases of amino-acid esters

Abstract: Bis[ethyl N-(o-hydroxybenzylidene)valinato]copper(II)[Cu(salvalEt)2] and bis[ethyl N-(o-hydroxybenzylidene)-leucinato]copper(II)[Cu(salleuEt)2] have been prepared for the first time. Bis(o-hydroxybenzylideneamine)-copper(II)[Cu(salNH)2] is isolated in small yield from the oxidation by molecular oxygen at room temperature of these two complexes in absolute ethanol solution. The general formation of Cu(salα),xH2O by hydrolysis of Cu(salαR)2 in aqueous ethanol is observed. Cu(salval) and Cu(salleu), are assigned dimeric structures on the basis of their analyses and subnormal magnetic moments. The complex Cu(salphe),xH2O is formulated as a carbinolamine species rather than a Schiff base. The copper(II) complex of the Schiff base of methyl anthranilate has been prepared for the first time and is converted into the corresponding ethyl ester complex upon being heated in ethanol. Evidence was also found for the hydrolysis of this complex, and of the copper(II) complex of the tetradentate double Schiff-base formed between lysine ethyl ester and salicylaldehyde (1 : 2). The rapid racemisation of the complexes Cu(sal[graphic omitted]R)2 is shown to be a general reaction. The complexes Cu(sal[graphic omitted]),xH2O are optically stable in neutral solution, but racemise quickly under alkaline conditions. A general mechanism of catalysis in the complexes Cu(salαR)2 is proposed involving the addition of water or alcohols to the azomethine links. The reverse reaction, the reformation of the Schiff base, provides a nucleophile in a favourable position to effect the various reactions found in this system. It is suggested that a similar carbinolamine mechanism may be involved in the catalysis of amino-acid reactions by pyridoxal in model systems and enzymes.

Eight-co-ordinated zirconium(IV) Schiff-base compounds: an X-ray study

Abstract: The crystal structure of tetrakis-(N-ethylsalicylaldiminato)zirconium(IV) contains eight-co-ordinated (dodecahedral) tetrachelated zirconium in the unusual S4 configuration with remarkably long Zr–N bond lengths; n.m.r. evidence suggests that the N-isopropyl derivative is also eight-co-ordinate whereas the N-t-butyl derivative involves a lower co-ordination of the zirconium.

Titanium(IV) Complexes of Bifunctional Tridentate or Tetradentate Schiff Bases

Abstract: Reactions of titanium isopropoxide with bifunctional tridentate Schiff bases, such as salicylidene-o-aminophenol, acetylacetone-o-aminophenol and benzoylacetone-o-aminophenol and bifunctional tetradentate Schiff bases, such as bis-acetylacetone ethylenediimine, bis-benzoylacetone ethylenediimine, bis-salicylaldehyde ethylenediamine and glyoxal-o-aminohpenol have been investigated in different stoichiometrc ratios. The resulting products Ti (OPrⁱ) ₂ (SB), Ti (SB) ₂, Ti (OPrⁱ) ₂ (S′B′), Ti (OPrⁱ) ₂ (S″B″) and Ti (OPrⁱ) (S″B″) (S″B″H) (where SBH₂ = bifunctional tridentate Schiff base, S′B′H₂ = bis-acetylacetone or bis-benzoylacetone ethylenediimine and S″B″H₂ = bis-salicylaldehyde ethylenediamine or glyoxal-o-aminophenol) have been isolated in almost quantitative yields. The molecular weights of the products soluble in benzene have been determined ebullioscopically and plausible structure indicated. The thermogravimetric analysis of the salicylidine-o-aminophenol derivatives has also been carried out.

The Crystal and Molecular Structure of Bis(2-hydroxyethylimino-salicylaldehydato)copper(II)

Abstract: The crystal structure of bis(2-hydroxyethyliminosalicylaldehydato)copper(II) has been determined by means of an X-ray diffraction study of a single-crystal specimen. Four formula units are contained in the monoclinic unit cell, the P21⁄c space group, with lattice parameters of: a=18.41 A, b=4.82 A, c=19.86 A, and β=99.1° (Dm=1.50 g·cm−3; Dx=1.50 g·cm−3). The structure has been refined, by means of three-dimensional difference syntheses and the least-squares method, to R=0.095. It has been confirmed that copper(II) links to the 2-hydroxyethyliminopyruvate anion through the phenolic oxygen and the nitrogen of the Schiff base linkage, while the alcoholic oxygen in the ethanol-amine moiety is free from coordination. The two Schiff-base ligands are coordinated around copper(II) in the trans-configuration. All the bond distances and angles in the complex are within the range of normal values. The N-Cu-O angles (91.3 and 91.8°) in the chelate rings are close to a right angle, showing that there is less strain in...

The crystal and molecular structure of a binuclear cobalt(III) complex with bis-(3-methoxysalicylaldehyde)ethylenedi-imine. Evidence for the bridging ability of some quadridentate Schiff bases

Abstract: Cobalt(III) complexes of general formula Co2(chel)3[chel =NN′-ethylenebis(salicylidene- and 3-methoxysalicylidene-iminato)] have been isolated, in which the Schiff base acts both as quadridentate ligand, in a non-planar conformation, and as chelate ligand bridging the two cobalt atoms.

The crystal and molecular structure of a five-covalent copper(II) complex

Abstract: The crystal and molecular structure of a five-co-ordinated copper(II) complex has been determined by X-ray diffraction methods. The complex has the formula [Cu(bpe,MeOH)Br]ClO4 where bpe represents the Schiff base formed by the condensation of two moles of pyridine-2-carbaldehyde with one of ethane-1,2-diamine. The unit cell is monoclinic with dimensions a= 9·28 ± 0·03, b= 13·22 ± 0·04, c= 16·05 ± 0·05 A, β= 98·3 ± 0·3°, space group P21/c, with Z= 4. The structure was determined from three-dimensional Patterson, Fourier, and difference syntheses and refined by least squares. The crystal is built up of copper(II) complex cations and perchlorate anions, the copper atom being surrounded by four nitrogen atoms of the methanol–Schiff-base quadridentate ligand and a bromine atom in an arrangement intermediate between a square pyramid and a trigonal bipyramid. All five atoms are at normal covalent distances from the copper atom. The methanol molecule is added across one of the imine groups of the Schiff base, resulting in a less strained arrangement of the quadridentate ligand about the copper.