Showing papers on "Schiff base published in 1985"

Copper(II) and nickel(II) complexes of unsymmetrical tetradentate Schiff base ligands

Abstract: Preparation de bases de Schiff tetradentees a partir de chloro-5 hydroxy-2 benzophenone, diamino-1,2 benzene et salicylaldehydes substitues. Synthese des complexes de Cu et Ni. Structures cristallines

Synthesis and molecular structure of oxochromium(V) cations. Coordination with donor ligands

Abstract: Preparation d'une serie de complexes et etude structurale du triflate de N,N'-ethylenebis(salicylidene aminato) oxochrome et du compose d'addition forme avec l'oxyde de pyridine

Rare examples of structurally characterized five–coordinate organocobalt complexes. Novel dynamic NMR evidence for synergistic enhancement of cis and trans effects in B12 models

Abstract: Determination des structures cristallines des 3 complexes Co (saloph)-i-C 3 H 7 •1,5H 2 O, Co (saloph) CH 3 •0,5H 2 O et pyCo (saloph) CH 2 CF 3 avec saloph-dianion du disalicylidene-o-phenylenediamine. Spectres RMN

Water photolysis. Part 1. The photolysis of co-ordinated water in [{MnL(H2O)}2][ClO4]2(L = dianion of tetradentate O2N2-donor Schiff bases). A model for the manganese site in photosystem II of green plant photosynthesis

Abstract: A number of manganese(III) complexes of the type [{MnL(H2O)}2]2+(L = dianion of O2N2 tetradentate Schiff base), in aqueous solution, have been shown to liberate dioxygen and reduce p-benzoquinone to hydroquinone when irradiated with visible light. The photoactivity is critically dependent on the structure of the ligand, the complex [{Mn(salpd)(H2O)}2][ClO4]2[salpd = propane-1,3-diylbis(salicylideneiminate)] being the most active. All the active complexes exhibit a band at 590 nm in the electronic spectrum, which is absent for the inactive complexes. Amongst the parameters of the photolysis which have been studied are: wavelength of light, temperature, complex and quinone concentrations, ligand structure, pH, and solvent nature. The rate of dioxygen evolution is dependent on the manganese(III) complex (first order) and quinone concentrations (order, 0.5) and the pH of the reaction medium, but is independent of solvent. The water which is photolysed is that bound to the manganese (suggesting that a model for the manganese site of photosystem II of the green plant is represented by these complexes). The energy of activation for O2 evolution in [{Mn(salpd)(H2O)}2][ClO4]2 is ca. 80 kJ mol–1, and the evidence points to homolytic, rather than heterolytic, fission of water. The manganese complex is converted to [{Mn(salpd)}2O] in the photolysis, i.e. no oxidation state change of manganese is involved. In addition to p-benzoquinone, methylene blue has been shown to be a hydrogen acceptor in this system.

Reactions of Cyclopalladated Benzylidene‐aniline Schiff's Base Complexes. Selective Synthesis of 2′‐Substituted Schiff's Base Derivatives and the X‐Ray Crystal Structure of the Dimer [Pd(μ‐OAc)(5′‐OCH3C6H3CHNC6H4‐4‐CH3)]2

Abstract: The 2′-cyclopalladated imine complex , reacts with CO in MeOH to afford the 2′-substituted aryl imine 2′-CO2CH3-5′-OCH3C6H3CHNTol (Tol = C6H4-4-CH3). The product of this reaction can be altered by changing the bridging ligand from AcO to Cl, in which case only the 5-membered ring heterocyclic compound is obtained. [Pd(μ-OAc)(1a)]2 with 2 equiv. of Ph3P and CO (1 atm) gives the heterocyclic which arises from two CO insertion reactions, whereas [PdX(1a)]2 (X = AcO, Cl) with 4 equiv. of CNBut and 4 equiv. of Ph2PCH2CH2PPh2 affords the heterocyclic ketenimine [PdCl(1a)]2 reacts with CH2CHCO2CH2CH3 to afford 2′(CHCHCO2CH2CH3)-5′-OCH3C6H3CHO, and [Pd(μ-OAc)(1a)]2 with I2 to give 2′-I-5′-OCH3C6H3CHO. Excess CH3O2CCCCO2CH3 reacts with various substituted cyclopalladated Schiff's bases in MeOH to afford which we formulate as possessing two PdC bonds, and one coordinated ester O atom. The X-ray crystal structure of [Pd(μ-OAc)(1a)]2 has been determined; relevant bond lengths [A] and bond angles [°] are: PdO(1), 2.139(6), PdO(2), 2.026(6), PdN, 2.039(6), PdC(2′), 1.951(8), PdPd, 3.113(1), NPdC(2′), 80.9(3), NPdO(1), 97.5(2), C(2′)PdO(2), 91.7(3), O(1)PdO(2), 89.2(2).

Magnetic exchange interactions in binuclear transition-metal complexes of a binucleating clathrochelate ligand

Abstract: Determination de la structure du complexe [LCoFc]BF 4 . Mesures de susceptibilite magnetique des complexes [LM a II M b II ]BF 4

Formation of a specific co-ordination cavity for a chiral amino acid by template synthesis of a polymer Schiff base cobalt(III) complex

Abstract: A template polymer complex, which incorporates N-benzyl-D-valine with almost 100% stereospecificity, was synthesised by copolymerization of Δ-β2-[CO{(R,R)-N,N′-bis[4-(p-vinylbenzyloxy)salicylidene]-1,2-diaminocyclohexane}(N-benzyl-D-valine)](3), styrene, and divinylbenzene, followed by dissociation of the co-ordinated amino acid.

Studies on spin-equilibrium iron(III) complexes. Part 1. Syntheses and magnetic properties of a new family of spin cross-over iron(III) complexes with a unidentate ligand over a wide range of the spectrochemical series and a quinquedentate ligand derived from salicylaldehyde and di(3-aminopropyl)amine. X-Ray crystal structure of [4-azaheptamethylene-1,7-bis(salicylideneiminato)](4-methylpyridine)iron(III) tetraphenylboratet

Abstract: Iron(III) complexes of general formula [Fe(X)L]n+(n= 0 or 1) have been prepared and characterized, where X is a unidentate ligand such as Cl–, N3–, NCO–, CN–, pyridine (py), 3-methylpyridine (3Me-py), 4-methylpyridine (4Me-py), 4-aminopyridine (apy), 3,4- dimethylpyridine (3,4Me,-py), imidazole (Him), N-methylimidazole (mim), or 2- methylimidazole (2Me-im), and L denotes a quinquedentate Schiff base derived from salicylaldehyde and di(3-aminopropyl)amine. On the basis of the cryomagnetic data, these complexes can be classified into three groups: high spin (S=5//2) for X = Cl, N3, Him, mim; low spin (S=5//2) for X = CN; spin cross-over (S =½⇌S=5//2) for X = py, 3Me-py, 4Me-py, 3,4Me2-py, 2Me-im. This indicates that the spin state for the series of complexes depends predominantly on the order in the spectrochemical series of the ligand X. The magnetic moments for the spin cross-over complexes increased gradually with increase of the temperature and showed no thermal hysteresis, indicating that the present complexes are of continuous spin-transition type. The spin cross-over complexes showed a thermochromism both in the solids and solutions, changing colour from dark violet to blue green, with decreasing temperature, and the thermochromism was studied by the temperature dependence of the electronic spectra in dichloromethane solution. The temperature dependence of the Mossbauer spectra for [Fe(2Me-im)L]BPh4 and [Fe(4Me-py)L]BPh4 has also provided evidence that the spin transition between the high- and low-spin states takes place and that the rate of spin interexchange is as fast as the inverse of the lifetime (1 × 10–7 s) of the Mossbauer nucleus. One of the complexes, [Fe(4Me-py)L] BPh4, was also subjected to a single-crystal X-ray analysis. The result verified the detailed structure in which the iron(III) atom assumes a pseudo-octahedral co-ordination geometry with a trans geometry for the two salicylideneiminate moieties, and the two axial positions are occupied by the secondary amine nitrogen of the di(3-aminopropyI)amine moiety of L and the nitrogen atom of the 4-methylpyridine ligand.

Synthesis and characterization of copper(II) and nickel(II) complexes of the Schiff base derived from 2-(2-aminophenyl)benzimidazole and salicylaldehyde

Abstract: Copper(II) and nickel(II) complexes with the Schiff base derived from 2-(2-aminophenyl)benzimidazole and salicylaldehyde, L, have been prepared. They are of the general types ML2X2 (M = Ni or Cu and X = Cl, Br, NO3 or ClO4) and NiL(NCS)2.

Modification of pK values caused by change in H-bond geometry

Abstract: The competition between various groups for a proton is studied by ab initio molecular orbital methods. It is found that reorientations of the two groups involved in a H-bond can reverse the equilibrium position of the proton shared between them. Specifically, the carbonyl and hydroxyl groups were modeled by H2CO and HOH. In the H-bond between these two groups, association of the proton with the carbonyl (H2COH...OH2)+ is favored over the hydroxyl (H2CO...HOH2)+ when the latter group is situated along a lone pair of the carbonyl oxygen. However, displacement of the water to the C = O axis between the two carbonyl lone pairs reverses the situation and (H2CO...HOH2)+ is more stable. A similar reversal of stability is observed in the H-bond involving a Schiff base (modeled by CH2NH) and amine (NH3). In one arrangement where the lone pairs of the two groups point toward one another, the proton prefers the Schiff base to the amine--i.e., (H2CHNH...NH3)+ is more stable than (H2CHN...HNH3)+. On the other hand, rotation of the lone pair of the amine away from the Schiff base nitrogen results in proton transfer across to the amine. These shifts in stability correspond to reversal of relative pK of the groups involved. A fundamental principle emerging from the calculations is that ion-dipole electrostatic interactions favor transfer of a proton to the group that is positioned as closely as possible to the negative end of the dipole moment vector of the other. The ideas developed here suggest a number of means by which conformational changes may be utilized to shift protons from residue to residue within a protein molecule such as an enzyme or bacteriorhodopsin.

Preparation and spectral, magnetic, and electrochemical characterization of a flexible phenoxo-bridged binuclear copper(II) complex

Abstract: Preparation du coordinat pentadente: bis-((salicylideneamino) methyl)-2,6methyl-4phenol et des complexes de Cu(II) avec le pyrazolate pontant. Reduction electrochimique de Cu 2 L

Structural and electronic properties of six-coordinate mixed aquo(imidazole)iron(III) Schiff-base complexes. Crystal structure of [Fe(3-MeO-salen)(5-Ph-imd)(H2O)]BPh4

Abstract: Le compose du titre cristallise dans le systeme triclinique, groupe P1. Formation de dimeres par l'interaction de liaisons hydrogene entre les complexes cationiques. Mesure de susceptibilite magnetique, effet Mossbauer et spectres RPE

Nature of fluorescent compounds generated by exposure of protein to oxidizing lipids

Abstract: Exposure of protein to oxidizing lipid induces fluorescence with excitation wavelengths of 350–360 nm and emission wavelength of 420–430 nm. This fluorescence was studied in freeze-dried emulsions of methyl linoleate with chicken egg lysozyme and other proteins, and in solution with amino acids and several aldehydes. Generation of this fluorescence was found to depend on the reaction of amines with 2, 4-decadienal or one of its breakdown products. Evidence was found suggesting that Schiff base formation of protein lysyl amines with conjugated dicarbonyls other than malonaldehyde is responsible for the fluorescence generated in the lysozymemethyl linoleate system.

Kinetics and mechanism of ligand substitution in four-coordinate nickel(II) chelate complexes: study on the reactivities of planar and tetrahedral configurational isomers and octahedral adducts

Abstract: Cinetique de substitution des complexes NiA 2 (A=alkylsalicylaldimine, dialkyl amino-2 tropone imine, alkylbenzoylacetone imine) par acetylacetone et N,N'-disalicylideneethylenediamine. Constantes d'equilibre et parametres d'activation

Enantioselectivity of nickel(II) and copper(II) complexes of Schiff bases derived from amino acids and (S)-o-[(N-benzylprolyl)amino]-acetophenone or (S)-o-[(N-benzylprolyl)amino]benzaldehyde. Crystal and molecular structures of [Ni{(S)-bap-(S)-Val}] and [Cu{(S)-bap-(S)-Val}]

Abstract: Copper(II) and nickel(II) complexes of Schiff bases derived from (S)-o-[(N-benzylprolyl)amino]-acetophenone [(S)-bap] and the amino acids (aa) : glycine, (R)- and (S)- and (S)-valine (val), (R)- and (S)-adamant-1-ylalanine, and (R)- and (S)-adamant-1-ylglycine have been synthesized. The structure of the complexes has been determined by physical and chemical methods; in addition the structures of [Cu{(S)-bap-(S)-Val}] and [Ni{(S)-bap-(S)-Val}] have been determined by X-ray crystallographic analysis. The kinetic CH-acidity and deuterium exchange of the hydrogen of an amino acid moiety under the action of bases has been studied. The deuterium exchange is accompained with epimerization which results in 80% excess of the (S)-2-[2H]amino acid. The stereoselectivity in the nickel complexes has been found to be higher than in the copper ones. The epimerization rate constant lies within the range 5 × 10–4–1.2 × 10–1 dm3 mol–1 s–1. The observed stereoselective effects are interpreted on the basis of X-ray analysis, circular dichroism, and 1H n.m.r. spectroscopic data. It is suggested that the [Ni{(S)-bap-aa}] complexes can be used for determining the absolute configuration of the amino acids.

A convenient synthetic method for schiff bases. the trimethylsilyl trifluoromethanesulfonate-catalyzed reaction of n,n-bis(trimethylsilyl)amines with aldehydes and ketones

Abstract: N,N-Bis (trimethylsilyl)amines react with aldehydes or ketones in the presence of trimethylsilyl trifluoromethanesulfonate to give Schiff bases in high yields. In situ utilization of the reaction solution as the Schiff base is also demonstrated.

EXPERIMENTAL and THEORETICAL STUDIES OF SCHIFF BASE CHLOROPHYLLS

Abstract: — A protonated Schiff base of Ni (II)-pyrochlorophyll a has been synthesized which exhibits a reversible bathochromic shift of 504 cm-1 relative to Ni (II)-pyrochlorophyll a. The magnitude of this shift lies between those observed for P700 and P680, the photoactive pigments of photosystems I and II in plants. Cyclic voltammetric measurements show that the protonated Schiff base is about 0.2 V more difficult to oxidize than its unprotonated form. These results suggest that a protonated Schiff base may be a better model for P680 than, as was originally assumed, for P700. In addition, the results of solvent and counterion effect studies show that microenvironmental perturbations in the neighborhood of the protonated Schiff base moiety are unlikely to induce further spectral shifts. Ab initio quantum mechanical calculations show a small hypsochromic shift rather than the observed bathochromic one, and the reasons for this discrepancy are discussed.