Showing papers on "Schiff base published in 1983"

Investigation of the Primary Photochemistry of Bacteriorhodopsin by Low‐Temperature Fourier‐Transform Infrared Spectroscopy

Abstract: The method of Fourrier-transform infrared difference spectroscopy was applied to investigate the transition at 77K of bacteriorhodopsin in its light-adapted form to K610, the first intermediate which is stable at low temperature. In addition to unmodified bacteriorhodopsin, bacteriorhodopsin in 2H2O and bacteriorhodopsin containing [15-2H]retinal was used. The results show that major rearrangements occur in the Schiff base in this transition. It is not possible to identify a C=N stretching vibration of the Schiff base in K610. The identification of an N-H bending vibration in K610 shows that the nitrogen of the previous Schiff base still has a proton attached. The fingerprint region exhibits very unusual features for K610 and bears no similarity to protonated retinylidene Schiff base model compounds of any isomeric composition. Therefore, no conclusions on the isomeric state of the retinal in K610 can be drawn. The spectra show that the terminal part of the retinal is predominantly reflected in the difference spectra. This indicates that the most polar part of the retinal is located near the Schiff base. We have evidence for protein molecular changes occurring in this transition at 77K.

Solid-state nitrogen-15 nuclear magnetic resonance study of the Schiff base in bacteriorhodopsin.

Abstract: Solid-state 15N NMR has been employed to examine protonation of the Schiff base linkage in epsilon-[15N]lysylbacteriorhodopsin, the single protein in purple membrane. It is shown with spectra of model compounds that protonation of a Schiff base results in an approximate 150-ppm change in the isotropic 15N chemical shift. Concurrently, the breadth of the shift anisotropy decreases by a factor of about two from 600 to 270 ppm. The isotropic shift of the Schiff base linkage observed in dark-adapted epsilon-[15N]lysylbacteriorhodopsin closely matches those observed for the protonated model compounds, particularly the more weakly hydrogen-bonded ones. It also seems to be affected slightly by isomerization of the retinal.

Reaction of glycolaldehyde with proteins: latent crosslinking potential of alpha-hydroxyaldehydes.

Abstract: The Schiff base adducts of glyceraldehyde with hemoglobin undergo Amadori rearrangement to form stable ketoamine structures; this reaction is similar to the nonenzymic glucosylation of proteins. In the present studies the analogous rearrangement of the Schiff base adducts of glycolaldehyde with proteins has been demonstrated. However, the Amadori rearrangement of the Schiff base adduct produces a new aldehyde function, an aldoamine, which is generated in situ and is capable of forming Schiff base linkages with another amino group, leading to covalent crosslinking of proteins. Sodium dodecyl sulfate gel electrophoresis of the glycoaldehyde-RNase A adduct showed the presence of dimers, trimers, and tetramers of RNase A, demonstrating the crosslinking potential of this alpha-hydroxyaldehyde. The crosslinked products exhibited an absorption band with a maximum around 325 nm and fluorescence around 400 nm when excited at 325 nm. The crosslinking reaction, the formation of a 325-nm absorption band, and the development of fluorescence were prevented when the incubation was carried out in the presence of sodium cyanoborohydride. This finding indicates that the Amadori rearrangement that generates a new carbonyl function is a crucial step in this covalent crosslinking. Glycolaldehyde could be a bifunctional reagent of unique utility because its crosslinking potential is latent, expressed only upon completion of the primary reaction.

Spectroscopic study of 1:1 copper(II) complexes with Schiff base ligands derived from salicylaldehyde and L-histidine and its analogs

Abstract: dro~ymethylene)camphor,~~~~~ or pyridoxal or pyridoxal ph~sphate,~J’~*~ ~~~-~~ usually with the aim of elucidating the mechanism of action of vitamin B6 containing enzyme^.^$-^^ Metal complexes with Schiff base ligands composed of salicylaldehyde and a primary amine have been studied for many Among these studies, a number have involved

Stereoselectivity in reactions of metal complexes VII. Asymmetric synthesis of amino acids by metal ion-promoted transamination

Abstract: Enantioselective synthesis of phenylalanine was performed by reacting phenylpyruvic acid with pyridoxamine followed by ketimine-aldimine isomerization of the Schiff base formed catalyzed by an optically active copper (II)-complex. By UV and CD measurements it was shown that the enantiomeric excess strongly depends on the reaction conditions and on the reaction time. In favorable cases it reached values up to 80%. The selectivity of the reaction is discussed on the basis of possible structures of the intermediate mixed ligand complex.

Exchange interaction in multinuclear transition-metal complexes. 4. Relative magnetic coupling in hydroxo- and methoxo-bridged dinuclear complexes of iron(III) with the heptadentate Schiff base trisalicylidenetriethylenetetramine

Abstract: Etude de la structure du complexe Fe 2 L(OH)Cl 2 •C 4 H 8 O et de son comportement magnetique de 4 a 200 K pour examiner l'effet d'un changement dans la densite electronique au niveau de l'atome pontant sur le couplage metal metal pour un systeme de fer(III) condense magnetiquement

Thin-layer spectroelectrochemical studies of copper and nickel unsymmetrical Schiff base complexes

Abstract: Resultats d'etudes voltammetriques et spectroelectrochimiques de l'oxydation et de la reduction dans du DMF, des complexes de Cu ou de Ni avec des bases de Schiff (slpsl, slesl, pyppy, etc., avec sl=salicylaldehyde, py=pyridinecarbaldehyde-2, e=ethylenediamine, p=propylenediamine)

Iron(III) complexes with semiquinone and hydroquinone ligands

Abstract: Resultats des reactions de 2p-quinones et 2o-quinones avec Fe II (salpren), Fe II (saloph), Fe II (salpren OH) et Fe II (saldien)

EPR Spectra of and exchange interactions in trinuclear complexes. II: Metal (II) adducts of tetradentate schiff base copper (II) complexes

Abstract: Spectres RPE de perchlorate de bis-[(N,N'-ethylene bis-salicylaldiminato)Cu(II)] Cu(II) trihydrate et de perchlorate de bis-[(N,N'-ethylene bis-(o-hydroxyacetophenone iminato)) Cu(II)] Cu(II) dihydrate. Interpretation des donnees obtenues en tenant compte d'un echange intermoleculaire

Compartmental ligands. Part 6. Transition-metal complexes of a non-symmetric, acyclic, Schiff base derived from heptane-2,4,6-trione,1-(o-hydroxyphenyl)butane-1,3-dione, and 1,2-diaminoethane

Abstract: The preparation and metal complexing properties of a non-symmetric, acyclic, Schiff base derived from heptane-2,4,6-trione, 1-(o-hydroxyphenyl)butane-1,3-dione, and 1,2-diaminoethane are described. The ligand has available dissimilar, adjacent, donor sets (N2O2 and O2O2). Both mononuclear positional isomers are found for nickel(II) and copper(II) complexes; oxovanadium(IV), dioxouranium(VI), and cobalt(II) gave only the O2O2 isomer.

Synthesis and Structural Features of S-Benzyl Dithiocarbazate Schiff Base Complexes of Si(IV)

Abstract: The present paper describes the synthesis and structural features of the silicon complexes with S-benzyldithiocarbazate Schiff bases. The resulting complexes of the type, Si(OAc)4–2Ln (where L is the dianion of the ligand and n = 1 or 2) have been characterized on the basis of elemental analyses, molecular weight determinations and conductivity measurements. The nature of bonding has been further discussed on the basis of IR and 1H NMR spectral data. The covalent bonding of oxygen and sulphur with silicon and a dative bond between silicon and nitrogen indicate trigonal bipyramidal and octahedral geometries for Si(OAc)2L and SiL2 type of derivatives, respectively. A few representative complexes have also been screened for their fungicidal as well as bactericidal activity and found to be quite active in this respect.

The Preparation and Characterization of Some Poly-Schiff Base Complexes

Abstract: A new series of four and six coordinate polychelates of 3d transition metal ions with a poly-Schiff base has been synthesized and characterized by elemental analysis, magnetic moment, visible and infrared spectroscopy Thermal and electrical measurements were carried out to study the thermal stability and semiconducting behaviour All the polychelates have 1:1 stoichiometry and are insoluble in all common organic solvents

Synthesis and X-ray structure of a bicopper(II) Schiff base macrocyclic complex having a single endogenous alkoxy bridge

Abstract: A bicopper(II) Schiff base macrocycle having an internal alkoxy bridge and strong antiferromagnetic coupling has been synthesised and its structure determined; the complex has similar co-ordination geometry and properties to those reported for oxy- and met-haemocyanin.

Studies on Ketene and Its Derivatives. CXII. Reaction of Ketene with Schiff Bases to give α-Unsubstituted β-Lactams

Abstract: The reaction of ketene with Schiff bases was investigated. Heating of ketene with Schiff bases (1a-l) without solvent gave α-unsubstituted β-lactams (2a-l). The reaction of ketene with ethyl N-furfurylideneglycinate (1k) to give the β-lactam 2k was carried out at various temperatures, and it was found that the yield of 2k was not much influenced by the reaction temperature. β-Lactams (2d, f, k, l) were treated with 10% aqueous sodium hydroxide in dioxane to give the corresponding carboxylic acids (4d, f, k, l) in good yields. Compounds 4d, f, l reacted with various amines in the presence of dicyclohexylcarbodiimide (DCC) to give the corresponding amides (5a-c, 8a-d).

Rhodium(I) complexes with pyridine-2-aldehyde and related Schiff-base ligands

Abstract: The synthesis of [Rh(TFB)(PyCH=NR)]ClO4 by reaction of the coordinated pyridine-2-aldehyde (PyCHO) moiety of [Rh(TFB)(PyCHO)]ClO4 with primary amines is described. They are active catalysts for the transfer of hydrogen from isopropanol to acetophenone. The catalytic activity depends upon the basicity of the parent amine. Reactions with carbon monoxide and triphenylphosphine give complexes [Rh(CO)2(PyCH=NR)]ClO4, [Rh(CO)(PPh3)2(PyCH=NR)]ClO4 and [Rh(CO)(PPh3)(PyCH=NR)]ClO4.