Showing papers on "Schiff base published in 1977"
TL;DR: The individual resonance Raman spectra of the PM568 and M412 forms of light-adapted purple membrane from Halobacterium halobium have been measured and indicate that the retinal chromophore is linked to the purple membrane protein via a protonated and unprotonated Schiff base.
Abstract: The individual resonance Raman spectra of the PM568 and M412 forms of light-adapted purple membrane from Halobacterium halobium have been measured using the newly developed flow technique. For comparison purposes, the Raman spectra of the model chromophores, all-trans- and 13-cis retinal n-butylamine, both as protonated and unprotonated Schiff bases, have also been obtained. In agreement with previous work, the Raman data indicate that the retinal chromophore is linked to the purple membrane protein via a protonated. Schiff base in the case of the PM568 and an unprotonated Schiff base for the M412 form. The basic mechanism for color regulation in both forms appears to be electron delocalization. The spectral features of the two forms are different from each other and different from the model compound spectra.
271 citations
TL;DR: Tris-and bis-ligand complexes of nickel with S-benzyldithiocarbazate (SBDTC) have been synthesized and characterized by electronic and IR spectroscopy and magnetic measurements as discussed by the authors.
205 citations
TL;DR: In this paper, the 2-methoxybenzaldehyde Schiff base (MeONSH) was derived from S-benzyldithiocarbazate and a spin-paired octahedral structure was proposed for the complex.
128 citations
104 citations
TL;DR: Reductive alkylation procedure is applicable to most proteins, except those containing readily reducible components or prosthetic groups, such as pyridoxal phosphate and rhodopsin, or those which are not stable at the required alkaline pH values.
Abstract: Publisher Summary Many simple aldehydes and ketones react rapidly and reversibly with amino groups of proteins. Neither the initial adduct or the Schiff base formed upon dehydration is very stable in dilute aqueous solution, but extensive modification of protein amino groups can be obtained by the reduction of the Schiff base to a stable secondary amine. Reductive alkylation of protein amino groups can, thus, be accomplished with many different aldehydes and ketones under very mild conditions by using sodium borohydride as the reductant. Under the conditions described in the chapter, both α- and ɛ-amino groups are readily modified, but other common protein groups are not affected. Because the modified groups experience only a small change in basicity and, at neutral pH, retain their normal cationic charges, the overall charge and the relative distribution of charged groups in most proteins are not greatly changed by reductive alkylation. By using a large variety of readily available aldehydes and ketones, the size, shape, and hydrophobicity of added substituents can be easily varied. Reductive alkylation procedure is applicable to most proteins, except those containing readily reducible components or prosthetic groups, such as pyridoxal phosphate and rhodopsin, or those which are not stable at the required alkaline pH values.
96 citations
73 citations
70 citations
TL;DR: Rat growth assays showed that the synthetic e-N-deoxyketosyl-L-lysine was not utilized as a source of lysine and that the true Schiff’s bases resulting from the reaction of l Lysine with aromatic aldehydes were 100% utilized indicating that the Schiff”s base ⇄ aldosylamine are also 100% utilization.
Abstract: During the heat-treatment of milk, the Maillard reaction which takes place between the epsilon-amino group of lysine and lactose leads to the formation of two well-defined chemical types : the Schiff’s base in equilibrium with its aldosylamine form and the deoxyketose (Amadori product). Rat growth assays showed that the synthetic e-N-deoxyketosyl-L-lysine was not utilized as a source of lysine and that the true Schiff’s bases resulting from the reaction of lysine with aromatic aldehydes were 100% utilized indicating that the Schiff’s base ⇄ aldosylamine are also 100% utilized.
63 citations
47 citations
TL;DR: In this paper, the magnetic susceptibilities of new iron(III) complexes containing quadridentate Schiff bases, [Fe(L)AB]n+, were analyzed and classified into four types: (1) high-spin (S=5⁄2), (2) low-spin, (3) intermediate spin, and (4) crossover complexes, the last of which have a ligand-field strength near the crossover point of high spin and low spin types.
Abstract: New iron(III) complexes containing quadridentate Schiff bases, [Fe(L)AB]n+, were prepared, where H2L represents a quadridentate Schiff base, and A and B, unidentate ligands, such as imidazole, pyridine derivatives, and cyanide ions. The magnetic moments of the complexes are in the range of 1.9–6.0 B.M. at room temperature. Based on the magnetic susceptibilities at various temperatures (90–295 K), these compleses were classified into four types: (1) high-spin (S=5⁄2), (2) low-spin (S=1⁄2), (3) intermediate spin (S=3⁄2), and (4) cross-over complexes, the last of which have a ligand-field strength near the cross-over point of high-spin and low-spin types. From the ESR spectra obtained, the existence of a spin-equilibrium was established for the cross-over complexes.
47 citations
TL;DR: In this article, 18 new volatile N-substituted salicylideneiminatotrialkyltin derivatives have been synthesized by the reactions of trialkyl-ltin chlorides or alkoxides with the corresponding Schiff bases.
TL;DR: In this paper, the infrared spectra of a series of nickel(II) complexes of Schiff bases formed by the condensation of 5-chloro-2-hydroxybenzophenone and some alkanediamines, H2N(CH2)nNH2 (n = 2−12), has been investigated.
TL;DR: The nuclear magnetic resonance spectra of aqueous suspensions of bovine rhodopsin which contain the chromophore enriched with 13C at specific positions in the retinylidene carbon chain clearly support an unprotonated retylidene Schiff base as the visual Chromophore in contrast to the earlier chemical and physical evidence which supports a protonated form.
Abstract: THE chromophore of visual pigments is generally assumed to be a protonated Schiff base of the 11-cis retinylidene (rhodopsins) or the 11-cis 3-dehydroretinylidene (porphyropsins) groups linked through a lysine amino group to a specific glycoli-poprotein moiety (opsin)1. This protonated Schiff base hypothesis has been supported by plausible though not unequivocal chemical evidence2,3. Recent studies using the physical technique of resonance Raman spectroscopy have also seemed to support this view4–7. In an attempt to confirm this assignment and to explore further the structure and microenvironment of the chomophore, we have studied the nuclear magnetic resonance (NMR) spectra of aqueous suspensions of bovine rhodopsin which contain the chromophore enriched with 13C at specific positions in the retinylidene carbon chain. We report here our findings which clearly support an unprotonated retinylidene Schiff base as the visual chromophore in contrast to the earlier chemical and physical evidence which supports a protonated form.
TL;DR: Computer simulations of this model reproduced all the observed features of the enzyme behavior and showed that the free pyridoxal phosphate‐dependent activity can be abolished when either all substrate or all cofactor are in the form of Schiff base.
Abstract: — The kinetic behavior of glutamate decarboxylase from mouse brain was analyzed in a wide range of glutamate and pyridoxal 5′-phosphate concentrations, approaching three limit conditions: (I) in the absence of glutamate-pyridoxal phosphate Schiff base; (II) when all glutamate is trapped in the form of Schiff base; (III) when all pyridoxal phosphate is trapped in the form of Schiff base. The experimental results in limit condition (I) are consistent with the existence of two different enzyme activities, one dependent and the other independent of free pyridoxal phosphate. The results obtained in limit conditions (II) and (III) give further support to this postulation. These data show that the free pyridoxal phosphate-dependent activity can be abolished when either all substrate or all cofactor are in the form of Schiff base. The free pyridoxal phosphate-independent activity is also abolished when all substrate is trapped as Schiff base, but it is not affected by the conversion of free pyridoxal phosphate into the Schiff base. A kinetic and mechanistic model for brain glutamate decarboxylase activity, which accounts for these observations as well as for the results of previous dead end-inhibition studies, is postulated. Computer simulations of this model, using the experimentally obtained kinetic constants, reproduced all the observed features of the enzyme behavior. The possible implications of the kinetic model for the regulation of the enzyme activity are discussed.
TL;DR: The Schiff base (I) from glycine tert-butyl ester and benzaldehyde was treated with lithium diisopropylamide to give the corresponding α-carbanion as discussed by the authors.
Abstract: The Schiff base (I) from glycine tert-butyl ester and benzaldehyde was treated with lithium diisopropylamide to give the corresponding α-carbanion Alkylation of the α-carbanion with benzyl or butyl halide followed by removal of benzylidene group yielded phenylalanine or norleucine tert-butyl ester (IIa or IIb), accompanied by dialkylated product (IIIa or IIIb) The Schiff base (IV) from alanine tert-butyl ester and (-)-men-thone (VI) was also treated as above to furnish α-methylphenylalanine or α-methyl-β-(3, 4-dimethoxyphenyl) alanine tert-butyl ester (Va or Vb) in 21 or 24% asymmetric yield
TL;DR: In this paper, a series of dioxouranium(VI) complexes were synthesised with the tetradentate Schiff base ligands (N 2 O 2 donor set) obtained by the condensation of ethylenediamine with salicyladehyde(H 2 salen), acetylacetone (H 2 aaen) or benzoyl acetone (h 2 baen) and ter-dentate bases derived by condensing of Salicylaldehyde with glycine(glysal), o -aminophenol(APhSal) or 2
TL;DR: The synthesis and properties of some oxovanadium(IV) complexes, [VOL2], containing N-substituted salicylal-dimines (L) are reported in this article.
Abstract: The synthesis and properties of some oxovanadium(IV) complexes, [VOL2], containing N-substituted salicylal-dimines (L) are reported. An unusually low VO stretching frequency (<900 cm–1) has been observed when R = C6H4Cl-4 and C6H4NO2-4. This reduction in frequency has previously been attributed to polymerisation of the VO unit, however the present crystal-structure analysis shows that bis[N-(4-chlorophenyl)salicylideneiminato]oxovanadium(IV) is monomeric in the solid state. The co-ordination polyhedron, which in the crystal has C2 symmetry, is based on a distorted trigonal bipyramid. The three oxygen and vanadium atoms are in the equatorial plane and the two nitrogen donors occupy axial positions. The vanadium–oxygen bond length (1.615 A) is among the largest found in oxovanadium complexes.
TL;DR: Calculations of the spectra of protonated Schiff bases under a variety of conditions have been considered in conjunction with the spectral data to provide a model for the nature of the chromophore interactions with its environment.
Abstract: — Retinylidine Schiff base spectra have been investigated in a variety of solvents that were chosen primarily to mimic possible environments of the chromophore in visual pigments. These studies have identified particular amino acid side chains which can have important influences on visual pigment spectra. Most amino acid side chain analogues or solvents which mimic the peptide bond environment have little effect on retinylidine Schiff base spectra. Tyrosine, tryptophan, and cysteine analogues and ionized aspartic and glutamic acid analogues produce pronounced red shifts in the spectra. As is explained in more detail in the following paper the presence of these amino acids in the chromophore “pocket” of the protein is sufficient to account for the spectra of many visual pigments. Calculations of the spectra of protonated Schiff bases under a variety of conditions have been considered in conjunction with the spectral data to provide a model for the nature of the chromophore interactions with its environment.
In solution and in rhodopsin the protonated Schiff base linkage is likely to be associated with an anion. The presence of certain amino acid side chains along the remainder of the retinal chain in the protein can modify the spectrum by altering the polarizability and polarity of the environment. The polarity in the region of the ionone ring appears to be particularly important for shifting the spectrum. In solution the nucleophilicity of the solvent also has an important influence on the anion-protonated Schiff base region of the chromophore.
TL;DR: In this article, the ESR spectra of several low-spin six-coordinated iron(III) complexes with the general formula, [FeLAB]n+ were measured, where H2L represents a quadridentate Schiff base and A and B, various unidentate ligands, such as imidazole, pyridine derivatives and cyanide ion.
TL;DR: Two homologous series of liquid crystalline Schif base esters of the following structural formula are synthesized by condensing p)p′ -n-alkoxybenzoyloxy)benzaldehydes with p-anisidine and p-toluidine as mentioned in this paper.
Abstract: Two homologous series of liquid crystalline Schif base esters of the following structural formula are synthesized by condensing p)p′ -n-alkoxybenzoyloxy)benzaldehydes with p-anisidine and p-toluidine.
TL;DR: Adducts of sodium perchlorate, sodium thiocyanate, and lithium perchlorates with NN′-ethylenebis(salicylideneiminato)- and NN´-ethylenesbis(acetylacetoneimini-inato-nickel(II) are reported in this paper.
Abstract: Adducts of sodium perchlorate, sodium thiocyanate, and lithium perchlorate with NN′-ethylenebis(salicylideneiminato)- and NN′-ethylenebis(acetylacetoneiminato)-nickel(II) are reported. All have alkali-metal ion: nickel complex ratios of 1 : 2. The title complex crystallizes in the space group C2/c with a= 19.728(4), b= 10.832(2), c= 15.012(3)A, β= 112.85(8)°, and Z= 4. The X-ray structure determination (heavy-atom method, 2 549 unique reflections measured by a four-circle diffractometer, R 0.04) has shown that the Na+ ion lies on a crystallographic two-fold axis with an irregular six-fold co-ordination sphere defined by oxygen atoms from two nickel complexes and a disordered perchlorate anion.
TL;DR: In this paper, the synthesis and characterization of cobalt(II) complexes with two macrocyclic Schiff base ligands, 5,7, 7,12, 14, 14 and 14,14, hexamethyl and 4,11-diene, was reported.
Abstract: We report the synthesis and characterization of cobalt(II) complexes with two macrocyclic Schiff base ligands, 5,7,7,12,14,14-hexamethyl-1,4,8,11,-tetraazacyclotetradeca-4,11-diene(Me6 [14]4,11-die...
TL;DR: Evidence is presented that the myo-inositol-1-P synthases studied are neither Class I nor Class II aldolases, and simply use base catalysis in the cyclization step.
TL;DR: In this paper, three new volatile trialkyltin derivatives of sulphur containing Schiff bases have been synthesized by the reactions of trimethyltin hydroxide with 2,2-disubstituted benzothiazolines.
TL;DR: In this article, the reaction between dioxygen and some cobalt(II) Schiff-base complexes, [CoL], has been studied in dimethyl-formamide and pyridine, and equilibrium constants for the oxygenation reaction in both solvents have been obtained through manometric and spectrophotometric measurements.
Abstract: The reaction between dioxygen and some cobalt(II) Schiff-base complexes, [CoL], has been studied in dimethyl-formamide and pyridine [L = ethylene-, 1,2-diphenylethylene-, butane-2,3-diyl-, and 1,2-cyclohexylene-bis-(salicylideneiminato)]. Equilibrium constants for the oxygenation reaction in both solvents have been obtained through manometric and spectrophotometric measurements. Steric effects of conformational origin are indicated and are discussed on the basis of the possible stereochemistry and conformation of the complexes in solution.
TL;DR: A third polymorph of the title compound has been grown by careful choice of solvent and an X-ray analysis has allowed comparison with the structure of the two forms already known as discussed by the authors.