Showing papers on "Schiff base published in 1986"
TL;DR: The first homodinuclear macrocyclic lanthanide complexes were obtained as compounds of the 2:2 Schiff base formed by condensing 2,6-diformyl-p-cresol and triethylenetetramine (L7) by a template procedure using lanthanides nitrates and perchlorates.
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TL;DR: In this paper, the asymmetric oxidation of sulfides into the corresponding sulfoxides was achieved with organic hydroperoxides in the presence of a catalytic amount of optically active Schiff base-oxovanadium(IV) complexes.
Abstract: The asymmetric oxidation of sulfides into the corresponding sulfoxides was achieved with organic hydroperoxides in the presence of a catalytic amount of optically active Schiff base-oxovanadium(IV) complexes; in most cases the optical yields (e.e.) ranged between 20 and 40%.
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TL;DR: In this paper, the effects of CF3 substituent on the spectra, photocycles, and Schiff base pKa values of the pigments were analyzed, and the results lead to unambiguous characterization of the (direct) titration of the Schiff base in bacteriorhodopsin and to the conclusion that the deprotonation rate during the photocycle (i.e., the generation of the M412 intermediate) is determined by a structural change in the protein.
Abstract: Artificial bacteriorhodopsin pigments based on synthetic retinal analogues carrying an electron-withdrawing CF3 substituent group were prepared. The effects of CF3 on the spectra, photocycles, and Schiff base pKa values of the pigments were analyzed. A reduction of 5 units in the pKa of the Schiff base is observed when the CF3 substituent is located at the C-13 polyene position, in the vicinity of the protonated Schiff base nitrogen. The results lead to the unambiguous characterization of the (direct) titration of the Schiff base in bacteriorhodopsin and to the conclusion that the deprotonation rate of the Schiff base during the photocycle (i.e., the generation of the M412 intermediate) is determined by a structural change in the protein.
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TL;DR: Asymmetric carbon-carbon bond formation was obtained in optical yields up to 57 % in allylic alkylations using benzophenone imine of glycine methyl ester 1 as a prochiral nucleophile.
TL;DR: The transposition hexene-5yl→cyclopentylmethyl is a transposition moleculaire d'une serie de complexes hexene -5yl-Co(III) avec diverses bases de Schiff a lieu par un processus radicalaire en chaine inhabituel.
Abstract: La transposition moleculaire d'une serie de complexes hexene-5yl-Co(III) avec diverses bases de Schiff a lieu par un processus radicalaire en chaine inhabituel. Influence de traces d'impuretes sur la facilite de la transposition hexene-5yl→cyclopentylmethyl
TL;DR: In this paper, the reactions de substitution par des coordinats monoanioniques are studied. But they do not consider the effects of substitution in the context of nomenclature of nombreux complexes.
Abstract: Syntheses de [(THF)V(acaceu)Cl] qui est precurseur de nombreux complexes. Etude des reactions de substitution par des coordinats monoanioniques. Etude RX
TL;DR: In this paper, two new complexes of type [Mn(SB)(Me2CO)] Y (SB is a dianion of a tetradentate Schiff base ligand, Y = NO3 or ClO4) have been synthesised and characterised.
TL;DR: In this paper, a mechanism for the photocycle of halorhodopsin is presented, which, in close analogy to an earlier proposed mechanism for BR, involves the sequence of all-trans → 13-cis, 14s-Cis → 13cis → alltrans isomerizations of the chromophore, a Schiff base of retinal.
Abstract: The chromophore in halorhodopsin (HR) which acts as a light-driven chloride pump in halobacteria shares many properties with its counterpart in bacteriorhodopsin (BR): (i) a similar retinal protein interaction, (ii) trans to cis isomerization and (iii) similar intermediates of its photocycle. One major difference between the two chromoproteins is that the HR chromophore does not become deprotonated during its photocycle. A mechanism for the photocycle of HR is presented, which, in close analogy to an earlier proposed mechanism for BR, involves the sequence of all-trans → 13-cis, 14s-cis → 13-cis → all-trans isomerizations of the chromophore, a Schiff base of retinal. In contrast to the situation in BR the 13-cis, 14s-cis→13-cis isomerization is induced not by deprotonation of the retinal Schiff base chromophore but rather by the movement of an anion (Cl-) towards the protonated nitrogen of the Schiff's base. The suggested mechanism involves the Schiff base directly in the chloride translocation in halorhodopsin.
TL;DR: In this article, a tridentate ligand for salicylaldehyde-4-aminoantipyrine (SAAP) complexes with the general formula [Ln(AAP)2]-NO3)3 (where Ln = Pr, Nd, Sm, Gd, Dy or Y) was proposed.
TL;DR: In this article, a stable and flexible chelator capable to coordinate both Cu(I) and Cu(II) and which would be catalytically active to accelerate superoxide dismutation was devised.
TL;DR: In this article, a new proposal is made which implies Schiff base to counter-ion proton translocation with concomitant isomerization and reprotonation of the chromophore.
Abstract: The photochemical step in the functioning of visual and bacterial rhodopsins entails cis–trans or trans–cis isomerization and changes in the state of protonation of the retinylidene Schiff base chromophore. In this review our present knowledge on these two events is discussed as well as the role of interactions between the chromophore and the surrounding protein, opsin. The relation between protonation and hydrogen bonding at the Schiff base nitrogen, the problems of stabilization of the proton bridge and charge separation are also discussed. A new proposal is made which implies Schiff base to counter-ion proton translocation with concomitant isomerization and reprotonation of the chromophore.
TL;DR: In this article, the authors developed two routes for the preparation of the title compound 6 and showed that the yield of unsymmetrical ligand is evidently influenced by the acidic properties of the hydrogen atom (of atoms) of the ring substituent in the ortho position to the carbonyl group.
TL;DR: In this article, the photochemical and thermal isomerization of Schiff bases derived from o-hydroxybenzaldehydes and aromatic or aliphatic diamines was investigated.
TL;DR: Depending on the substituent patterns, the activities of the complexes in the present study range from inactive to highly active, and the best ED50-values approach the ED50 of cisplatin.
TL;DR: The results suggest that during the photocycle of bacteriorhodopsin the chromophore, a retinal Schiff base, is deprotonated via a Schiff base - asp hydrogen bond, and a hypothesis is developed with regard to the molecular mechanism of thedeprotonation of the Schiff base of BR.
TL;DR: In this paper, a Schiff base bis(crown ether) ligand containing recognition sites for alkali and transition metal guest cations has been presented, and its stoicheiometry is dependent upon the stereochemical requirements of co-bound silver(I) or copper(II) guest cation.
Abstract: A novel Schiff base bis(crown ether) ligand containing recognition sites for alkali and transition metal guest cations has been prepared; preliminary complexation studies reveal that the stoicheiometry of Schiff base bis(crown ether) ligand to potassium guest cations is dependent upon the stereochemical requirements of co-bound silver(I) or copper(II) guest cations.
TL;DR: While the all-trans pigment loses its Schiff base proton very rapidly at its pKa, there is a kinetic barrier to this deprotonation in the 13-cis photointermediate that can be partially overcome by the reversible protonation of an extrinsic anionic base, which shuttles protons between the interior of the protein and the aqueous medium.
Abstract: It has been shown earlier that the deprotonation of the Schiff base of illuminated halorhodopsin proceeds with a much lower pK/sub a/ than that of the unilluminated pigment and the reversible protonation change is catalyzed by azide and cyanate. The authors have studied the kinetics of the proton-transfer events with flash spectroscopy and compared a variety of anionic bases with different pK/sub a/ with regard to the apparent binding constants and the catalytic activities. The results suggest a general base catalysis mechanism in which the anionic bases bind with apparently low affinity to halorhodopsin, although with some degree of size- and/or shape-dependent specificity. The locus of the catalysis is accessible from the cytoplasmic side of the membrane and is not at site I, where various anions bind and shift the pK/sub a/ of the deprotonation. Neither is it at site II, where a few specific anions (like chloride) bind to the all-trans pigment. It may be concluded that while the all-trans pigment loses its Schiff base proton very rapidly at its pK/sub a/, there is a kinetic barrier to this deprotonation in the 13-cis photointermediate that can be partially overcome by the reversible protonation of an extrinsic anionic base, whichmore » shuttles protons between the interior of the protein and the aqueous medium. The need for an extrinsic proton acceptor for efficient deprotonation of the Schiff base of halorhodopsin is one of the main differences between this pigment and the analogous retinal protein, bacteriorhodopsin.« less
TL;DR: Several substitution products of organotin(IV) chloride with biologically active schiff bases derived by the condensation of furfuraldehyde, thiophene-2-aldehyde, indol-3-carboxyaldehyde and cinnamaldehyde with thiosemicarbazide have been synthesized as discussed by the authors.
Abstract: Several substitution products of organotin(IV) chloride with biologically active schiff bases derived by the condensation of furfuraldehyde, thiophene-2-aldehyde, indol-3-carboxyaldehyde and cinnamaldehyde with thiosemicarbazide and having the general formulae R2SnCl (TSCZ) and R2 Sn (TSCZ)2 (where R = CH3 and TSCZ = anion of Schiff base) have been synthesised. These have been characterized by elemental analyses, molecular weight determinations and conductivity measurements. The mode of bonding has been deduced on the basis of IR and 1H NMR spectral studies.
TL;DR: The first MnIV Schiff base complex to be structurally characterized by X-ray crystallography, MnIV(saladhp)2(1) as mentioned in this paper, has been synthesized and its physical properties reported (EPC= −460 mV vs. Ag/AgCl and a small axial zero field splitting parameter); the reported data are of potential importance to the understanding of manganoenzymes.
Abstract: The first MnIV Schiff base complex to be structurally characterized by X-ray crystallography, MnIV(saladhp)2(1)(saladhp = 2-salicylideniminato-1,3-dihydroxy-2-methylpropane) has been synthesized and its physical properties reported (EPC=–460 mV vs. Ag/AgCl and a small axial zero field splitting parameter); the reported data are of potential importance to the understanding of manganoenzymes.
TL;DR: In this article, binuclear copper(II) complexes derived from 2,6-diacetyl-4-methylphenol are reported, which are antiferromagnetically coupled with the singlet-triplet separation 2J = 0.0605, for 3 074 reflections.
Abstract: The syntheses of binuclear copper(II) complexes derived from 2,6-diacetyl-4-methylphenol are reported. Magnetic susceptibility measurements in the temperature range 6–300 K establish that the two Cu2+ in bis(2,6-diacetyl-4-methylphenolato)dicopper(II) diperchlorate (3) and µ-[2,6-bis(5′-amino-1′-methyl-2′-azapent-1′-enyl)-4-methylphenolato]-µ-hydroxo-diperchloratodi-copper(II)(4) are antiferromagnetically coupled with the singlet–triplet separation 2J=–460 and –493 cm–1, respectively. In bis[4-methyl-2,6-bis(1′-oxido-3′-oxobut-1′-enyl)phenol]dicopper(II)(5), on the other hand, the two Cu2+ are magnetically independent. Electrochemical studies of the three compounds in dimethyl sulphoxide solutions reveal highly irreversible behaviours due to chemical and/or stereochemical changes subsequent to electron transfer. Upon reduction, (3) and (4) give stable copper(I) species, but (5) is reduced directly to copper metal. The crystal structure of complex (4) is triclinic, R= 0.0605, for 3 074 reflections. The molecule comprises a binuclear copper(II) cation in which the metals are separated by 2.9571(15)A and asymmetrically bridged by an endogenous phenoxy-bridge and an exogenous hydroxy-bridge.