Showing papers on "Schiff base published in 1987"
TL;DR: Etude de l'epoxydation catalytique des olefines par une large variete de complexes du nickel II, derivant de differents macrocycles tetraaza, bases de Schiff, porphyrines et phosphines bidentes as discussed by the authors.
Abstract: Etude de l'epoxydation catalytique des olefines par une large variete de complexes du nickel II, derivant de differents macrocycles tetraaza, bases de Schiff, porphyrines et phosphines bidentes
148 citations
TL;DR: Weak hydrogen bonding between the Schiff base linkage in bacteriorhodopsin (bR) and its counteranion or poor solvation of the positively charged Schiff base nitrogen can account for the C = N stretching frequency and the deuterium isotope effect observed in this pigment.
Abstract: Factors affecting the C=N stretching frequency of protonated retinal Schiff base (RSBH/sup +/) were studied with a series of synthetic chromophores and measured under different conditions. Interaction of RSBH/sup +/ with nonconjugated positive charges in the vicinity of the ring moiety or a planar polyene conformation (in contrast to the twisted retinal conformation in solution) shifted the absorption maxima but did not affect the C=N stretching frequency. The latter, however, was affected by environmental perturbations in the vicinity of the Schiff base linkage. Diminished ion pairing achieved either by substituting a more bulky counteranion or by designing models with a homoconjugation effect lowered the C=N stretch energy. Decreasing solvation of the positively charged nitrogen leads to a similar trend. These effects in the vicinity of the Schiff base linkage also perturb the deuterium isotope effect observed upon deuteriation of the Schiff base. The results are interpreted by considering the mixing of the C=N stretching and C=N-H bending vibration. The C=N mode is shifted due to electrostatic interaction with nonconjugated positive charges in the vicinity of the Schiff base linkage, an interaction that does not influence the isotope effect. Weak hydrogen bonding between the Schiff base linkage in bacteriorhodopsin (bR) andmore » its counteranion or, alternatively, poor solvation of the positively charged Schiff base nitrogen can account for the C=N stretching frequency of 1640 cm/sup -1/ and the deuterium isotope effect of 17 cm/sup -1/ observed in this pigment. Conversion of bR to the photochemically induced intermediate K/sub 610/ involves environmental perturbation in the vicinity of the C=N linkage, lowering the C=N stretch energy.« less
122 citations
TL;DR: Mn(SALADHP) 2 •2DMF cristallise dans le systeme monoclinique, groupe d'espace P2 1 /a and sa structure est affinee jusqu'a R=0,076 as mentioned in this paper.
Abstract: Mn(SALADHP) 2 •2DMF cristallise dans le systeme monoclinique, groupe d'espace P2 1 /a et sa structure est affinee jusqu'a R=0,076
110 citations
TL;DR: Etude de l'acidification aerobie par HCl du complexe du titre donnant V IV Cl 2 (SALEN). Voltammetrie cyclique.
Abstract: Etude de l'acidification aerobie par HCl du complexe du titre donnant V IV Cl 2 (SALEN). Voltammetrie cyclique. Structure cristalline de V V O(SALEN)ClO 4
108 citations
TL;DR: Mn(SALPS)CH 3 CN cristallisent dans le systeme triclinique, groupe d'espace P1 et leur structure est affinee respectivement jusqu'a R=0,029 and R= 0,040 as discussed by the authors.
Abstract: Mn(SALPS)CH 3 OH•CH 3 OH et [Mn(SALPS)] 2 •2CH 3 CN cristallisent dans le systeme triclinique, groupe d'espace P1 et leur structure est affinee respectivement jusqu'a R=0,029 et R=0,040
95 citations
TL;DR: Le complexe de Pt cristallise dans le systeme triclinique, groupe d'espace P1 et sa structure is affinee jusqu'a R=0.037 as discussed by the authors.
Abstract: Le complexe de Pt cristallise dans le systeme triclinique, groupe d'espace P1 et sa structure est affinee jusqu'a R=0,037. Le complexe de Pd cristallise dans le systeme monoclinique, groupe d'espace Ce R=0,028
81 citations
TL;DR: In this paper, the composes du titre sont isomorphes et cristallisent dans le systeme monoclinique avec le groupe d'espace P2 1.
Abstract: Les composes du titre sont isomorphes et cristallisent dans le systeme monoclinique avec le groupe d'espace P2 1 . Affinement des structures jusqu'a 0,048 et 0,039 respectivement. Les Cu 2+ sont pontes par l'atome O phenolique par le coordinat exogene
79 citations
TL;DR: In this article, the crystal structure of [Tb(H2Lc)(NO3)2]NO3 was determined by X-ray crystallography and the structure was refined to R = 0.078.
73 citations
TL;DR: In this paper, L'etude RX montre que l'uree est coordinee au cation uranyle par une paire d'electrons de l'oxygene du CO
Abstract: Preparation d'un tel complexe. L'etude RX montre que l'uree est coordinee au cation uranyle par une paire d'electrons de l'oxygene du CO
70 citations
TL;DR: A series of complexes of formula (C6H5)3SnX·L (X = Cl, NCS) for a range of ligands were synthesised by the reactions of triphenyltin chloride or isothiocyanate with N-aryl-salicylideneimines and N- Daryl-2-hydroxynaphthylidenesimines as discussed by the authors.
60 citations
TL;DR: C 22 H 24 N 2 O 6 Ni cristallise dans le systeme triclinique, groupe d'espace P1 et sa structure est affinee jusqu'a R=0,0435 as discussed by the authors.
Abstract: C 22 H 24 N 2 O 6 Ni cristallise dans le systeme triclinique, groupe d'espace P1 et sa structure est affinee jusqu'a R=0,0435. C 30 H 20 N 2 O 6 Ni cristallise dans le systeme monoclinique, groupe d'espace P2 1 /c avec R=0,0423. < 30 H 20 N 2 O 6 Ni cristallise dans P2 1 /n avec R=0,048 s
TL;DR: In this paper, the synthesis and dioxygen affinities of six cobalt(II) Schiff base complexes in diglyme solution in the presence of excess aromatic bases are reported.
Abstract: The synthesis and dioxygen affinities of six cobalt(II) Schiff base complexes in diglyme solution in the presence of excess aromatic bases are reported. The cobalt(II) chelates investigated are bis-salicylaldehydetetramethylethylenediiminocobalt(II) (CoSALTMEN), bis-salicylaldehyde-o-phenylenediiminocobalt(II) (CoSALOPHEN), bis-(2-hydroxyacetophenone)-ethylenediiminocobalt(II) (Co CH3SALEN), bis-(3,5-dichlorosalicylaldehyde)-o-phenylenediiminocobalt(II) (Co35ClSALOPHEN), bis-(3-methoxysalicylaldehyde)-o-phenylenedi iminocobalt(II) (Co3Me0SAL0PHEN), and the parent compound, bis-salicylaldehydeethylenediiminocobalt(II) (SALCOMINE). Axial bases employed are pyridine, 4-methylpyridine, 4-dimethylaminopyridine, and 4-cyanopyridine. In the solvent medium employed the Schiff base chelates combine with only one axial base; no 2:1 adducts were observed. Electronwithdrawing substituents on the Schiff bases were found to decrease the affinity of the cobalt Schiff base for dioxygen. Equilibrium dioxygen uptake measurements over a range of temperatures provide values of ΔH° and ΔS° of oxygenation which fall in the range -6 to -13 kcal mole-1 for ΔH° and -30 to -52 cal degree-1 mole-1 for AS°, and are in line with values reported for analogous dioxygen complexes in the literature.
TL;DR: Two tetranuclear manganese(II) complexes have been obtained by Schiff-base condensation of 1,3-diamino-2-hydroxypropane and 2,6-diacetylpyridine in the presence of Ba2+, followed by transmetallation using Mn2+. as mentioned in this paper.
Abstract: Two tetranuclear manganese(II) complexes (2) and (3) have been obtained by Schiff-base condensation of 1,3-diamino-2-hydroxypropane and 2,6-diacetylpyridine in the presence of Ba2+, followed by transmetallation using Mn2+. The complexes have been characterised by analytical, spectroscopic, 252Cf plasma desorption mass spectroscopic, and single-crystal X-ray diffraction methods. Complex (2) contains a 40-membered macrocycle formed by a (4 + 4) Schiff-base condensation of four molecules of 1,3-diamino-2-hydroxypropane with four molecules of 2,6-diacetylpyridine. The macrocycle is wrapped around a cubane-like Mn4(alkoxide)4 core. Complex (3) is dimeric. The asymmetric unit contains two binuclear, 20-membered macrocycles each formed by a (2 + 2) Schiff-base condensation reaction. This complex contains five geometrically distinct thiocyanate groups. Routes for the formation of (3) are discussed and the possible significance of the compounds as models for the photosynthetic water-splitting system is noted.
TL;DR: In this article, the Fourier transform infrared spectra was used to estimate the degree of protonation required for Schiff base in chloroform solution with pK/sub a/ values between 0.66 and 4.87.
Abstract: trans-Retinylidene-tert-butylamine was put into contact with a series of acids (HCl, HBr, and HI and six carboxylic acids, trichloro-, dichloro-, monochloro-, and monobromoacetic acids, and 3-chloropropionic and propionic acids) whose pK/sub a/ values vary from 0.66 to 4.87. It can be inferred from the Fourier-transform infrared spectra that in order to obtain complete protonation of the Schiff base in chloroform solution an acid having a pK/sub a/ value of at least 2 is needed. With a pK/sub a/ value of about 4, similar to that of aspartic or glutamic acid, the estimated degree of protonation is about 65%. This shows that a mechanism is required to bring about 100% or nearly 100% protonation in rhodopsins. The intensification of the C double bond C bands upon protonation shows that the positive charge is delocalized along the conjugated chain. The N/sup +/H stretching region of the spectrum could be studied to advantage but the N/sup +/H in-plane bending bands could not be identified.
TL;DR: Barium and lead(II) complexes of tetraimine Schiff base macrocycles derived from the condensation of heterocyclic dicarbonyls (2,6-diacetylpyridine and furan-2,5-dicarbaldehyde) are reported in this paper.
Abstract: Barium and lead(II) complexes of tetraimine Schiff base macrocycles derived from the (2 + 2) condensation of heterocyclic dicarbonyls (2,6-diacetylpyridine and furan-2,5-dicarbaldehyde) and 1,n-diamino-n′-hydroxyalkanes (1,3-diamino-2-hydroxypropane, 1,4-diamino-2-hydroxybutane, and 1,5-diamino-3-hydroxypentane) are reported. The crystal structures of four complexes have been determined.
TL;DR: Two new quadridentate Schiff base ligands formed from 2,5-hexanedione and S-alkyldithiocarbazic acids and their nickel, zinc, and cadmium(II) complexes having the general formula [M(SNNS) 2− is the dinegatively charged ligands) have been synthesized and characterized by elemental analysis and magnetic and spectroscopic methods.
TL;DR: In this article, a trinuclear mixed-valence complex of the type [CoII(µ-SO3)2( µ-L)2CoIII2(H2O)n(ROH)2−n]·2PrnOH showed the presence of bridging phenolic oxygens and sulphite ions.
Abstract: Mixed-valence complexes of the type [CoII(µ-SO3)2(µ-L)2CoIII2(H2O)n(ROH)2–n](n= 0, 1, or 2; R = Me or Prn) have been prepared and characterized, where the deprotonated Schiff-base ligands L2– are either symmetrical, such as N,N′-ethylenebis(salicylideneiminate)(salen), N,N′-ethylenebis(α-methylsalicylideneiminate)(α,α′-Me2-salen), propane-1,3-diylbis(salicylideneiminate)(salpd), and propane-1,3-diylbis(α-methylsalicylideneiminate)(α,α′-Me2-salpd), or unsymmetrical such as propane-1,3-diyl(α-methylsalicylideneiminate)(salicylideneiminate)(α-Me-salpd). An X-ray structure determination of [COII(µ-SO3)2(µ-α,α′Me2-salpd)2CoIII2(PrnOH)2]·2PrnOH showed the presence of bridging phenolic oxygens and sulphite ions. The mixed-valence state CoIII(S= 0)–CoII(S=)–CoIII(S= 0) in these trinuclear complexes has been demonstrated by cryomagnetic measurements because the effective magnetic moments (4.40–5.00) at room temperature correspond to the monomeric complex of a cobalt(II) ion in a high-spin state. Down to 77 K, no spin-exchange interaction was observed between the cobalt(III) and cobalt(II) ions. I.r. spectra and thermal gravimetric-differential thermal analysis data have been obtained and discussed with regard to the co-ordination modes of the solvent molecules water, methanol, ethanol, and propan-1-ol.
TL;DR: In this article, the crystal structures of three iron(III) complexes, [Fe(acen)(Him)2]BPh4(1), [Fe[salen]-Him2]ClO4·H2O (2), and [Fe
Abstract: The crystal structures of three iron(III) complexes, [Fe(acen)(Him)2]BPh4(1), [Fe(salen)(Him)2]ClO4·H2O (2), and [Fe(salphen)(Him)2]BPh4(3), were determined by the X-ray diffraction method [H2acen =NN′-ethylenebis(acetylacetonylideneimine), H2salen =NN′-ethylenebis(salicylideneimine), H2salphen =o-phenylenebis(salicylideneimine), and Him = imidazole. The low-spin complex (1) crystallizes in monoclinic space group P21/n with a= 32.939(7), b= 12.705(2), c= 8.991(1)A, β= 93.63(2)°, and Z= 4. The high-spin complex (2) crystallizes in monoclinic space group P21/a with a= 16.146(8), b= 15.205(3), c= 10.042(3)A, β= 92.73(3)°, and Z= 4. The high-spin complex (3) crystallizes in orthorhombic space group Pna21 with a= 26.966(8), b= 16.969(7), c= 8.977(3)A, and Z= 4. The complex cation contains a quadridentate Schiff base in the equatorial plane and two imidazole molecules at the axial positions. The mean Fe–N (Schiff base), Fe–O, and Fe–N (imidazole) bond distances are 1.899, 1.920, and 1.990 A for (1), respectively, 2.108, 1.917, and 2.143 A for (2), and 2.125, 1.896, and 2.165 A for (3), indicating that the metal to imine nitrogen bond distances are sensitive to the spin state of iron, whereas the changes in the Fe–O bond distances are very little affected. The cause of this trend, which was also found for other iron(III) complexes, is discussed in terms of the feasibility of π bonding. No relation between the relative orientation of axial imidazole rings and spin state was detected.
TL;DR: Le (N,N'-disolicylideneethylenediamine) cobalt II forme un complexe de coordination avec le copolymere methacrylate d'octyle (I)/vinyl-4 pyridine ou (I/vinyl)-1 imidazole as mentioned in this paper.
Abstract: Le (N,N'-disolicylideneethylenediamine) cobalt II forme un complexe de coordination avec le copolymere methacrylate d'octyle (I)/vinyl-4 pyridine ou (I/vinyl-1 imidazole
TL;DR: In this article, a chiral glycine Schiff base derived from (S)-2-hydroxy-3-pinanone to vinyl phosphorus compound was used to obtain (R)-(−)-Phosphinothricin.
Abstract: (S)-(+)-Phosphinothricin was prepared in good optical yield by the Michael addition of chiral glycine Schiff base derived from (S)-2-hydroxy-3-pinanone to vinyl phosphorus compound. (R)-(−)-Phosphinothricin, an enantiomeric isomer, can also be prepared from the same chiral glycine Schiff base by choosing suitable reaction temperature.
TL;DR: A force field is developed that accurately fits the observed ethylenic and protonated Schiff base stretching frequencies of rhodopsin and labeled derivatives and suggests that models for the efficient conversion of light to chemical energy in the r Rhodopsin to bathorhodopin photoconversion based solely on salt bridge separation of the protonate Schiff base and its counterion are probably incorrect.
Abstract: The authors have obtained the resonance Raman spectra of bovine rhodopsin, bathorhodopsin, and isorhodopsin for a series of isotopically labeled retinal chromophores. The specific substitutions are at retinal's protonated Schiff base moiety and include -HC=NH/sup +/-, -HC=ND/sup +/-. -H/sup 13/C=NH/sup +/-, and -H/sup 13/C=ND/sup +/-. Apart from the doubly labeled retinal, they find that the protonated Schiff base frequency is the same, within experimental error, for both rhodopsin and bathorhodopsin for all the substitutions measured here and elsewhere. They develop a force field that accurately fits the observed ethylenic (C=C) and protonated Schiff base stretching frequencies of rhodopsin and labeled derivatives. Using MINDO/3 quantum mechanical procedures, they investigate the response of this force field, and the ethylenic and Schiff base stretching frequencies, to the placement of charges close to retinal's Schiff base moiety. Specifically, they find that the Schiff base frequency should be measurably affected by a 3.0-4.5-A movement of a negatively charged counterion from the positively charged protonated Schiff base moiety. That there is no experimentally discernible difference in the Schiff base frequency between rhodopsin and bathorhodopsin suggests that models for the efficient conversion of light to chemical energy in the rhodopsin to bathorhodopsin photoconversion based solely on saltmore » bridge separation of the protonated Schiff base and its counterion are probably incorrect. They discuss various alternative models and the role of electrostatics in the rhodopsin to bathorhodopsin primary process.« less
TL;DR: In this paper, transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol.
Abstract: The solvatochromic behaviour of several complexes [Fe(LL)2(CN)2] with LL=Schiff base diimine has been established in a series of non-aqueous solvents, as has that of two analogues containing diazabutadiene ligands. Transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol, and for [Fe(bipy)2(CN)2] into several binary aqueous solvent series. The usefulness of solvatochromic shifts and transfer chemical potentials as indicators of selective solvation is discussed. Kinetics of oxidation of catechol and of 4-t-butyl catechol by [Fe(bipy)(CN)4]− in aqueous solution are described.
TL;DR: In this article, twelve mixed-ligand complexes of Fe(III), Ni(II), Cu(II) and Zn(II)-with Schiff bases of N,N -diethylamino-dithiocarbamate and thiocyanate as ligands, have been synthesized and characterized on the basis of elemental analysis, infrared and electronic spectral studies, as well as magnetic measurements.
TL;DR: Time-resolved resonance Raman spectra of the hRL intermediate of halorhodopsin have been obtained and it is shown that hRL contains a 13-cis chromophore and that an all-trans----13- cis isomerization occurs in the halor Rhodopsin photocycle.
Abstract: Time-resolved resonance Raman spectra of the hR/sub L/ intermediate of halorhodopsin have been obtained. The structurally sensitive fingerprint region of the hR/sub L/ spectrum is very similar to that of bacteriorhodospin's L/sub 550/ intermediate, which is known to have a 13-cis configuration. This indicates that hR/sub L/ contains a 13-cis chromophore and that an all-trans ..-->.. 13-cis isomerization occurs in the halorhodopsin photocycle.hR/sub L/ exhibits a Schiff base stretching mode at 1644 cm/sup -1/, which shifts to 1620 cm/sup -1/ in D/sub 2/O. This demonstrates that the Schiff base linkage to the protein is protonated. The insensitivity of the C-C stretching mode frequencies to N-deuteriation suggests that the Schiff base configuration is anti. The 24 cm/sup -1/ shift of the Schiff base mode in D/sub 2/O indicates that the Schiff base proton in hR/sub L/ has a stronger hydrogen-bonding interaction with the protein than does hR/sub 578/.
TL;DR: In this article, the coordination chemistry of Schiff bases with acyclic and macrocyclic ligands has been investigated and reviewed over the last few years, and the formation of metal complexes with binucleating ligands is provided to study the intramolecular binding and possible activation of small molecules between the metal centres, along with magnetic exchange interactions and multielectron redox reactions.
TL;DR: In this article, the effect of counterion location on the level ordering of retinyl Schiff bases and Schiff base salts was analyzed using molecular orbital theory and two-dimensional /sup 1/H NMR.
Abstract: The ..pi pi..* excited singlet state manifolds of the visual chromophores, all-trans-retinylpyrrolidiniminium perchlorate (ATRSBS) and all-trans-N-retinylidene-n-butylimine:HCl (ATRPSB) are studied by using one-photon and two-photon laser spectroscopy. The goal is a better understanding of how protonation and counterion location affect level ordering in retinyl Schiff bases. Ambient temperature two-photon thermal lensing spectra indicate that ATRSBS has a lowest lying /sup 1/A/sub g/*/sup -/-like state as was observed previously for all-trans-retinal and the Schiff base of all-trans-retinal. In contrast, two-photon spectra of ATRPSB indicate that the protonated Schiff base has a lowest lying /sup 1/B/sub u/*/sup +/-like state. The origin of this level ordering reversal is analyzed by using molecular orbital theory as well as /sup 13/C and two-dimensional /sup 1/H NMR. They conclude that the relative level ordering of the low-lying covalent and ionic ..pi pi..* excited states of protonated Schiff bases and Schiff base salts is highly sensitive to counterion location (diffuseness). INDO-PSDCI molecular orbital theory is shown to be a reliable theoretical method of predicting the effect of counterion location on the one-photon and two-photon properties of retinyl protonated Schiff bases and Schiff base salts. This study provides further experimental support for the conclusions of a previous two-photon investigationmore » of the rhodopsin binding site which demonstrated that the protein bound 11-cis-retinyl chromophore is protonated and occupies a neutral binding site.« less
TL;DR: In this paper, a non-symmetrical tetradentate Schiff base complexes with N3O donor sites have been obtained using the half-unit 7-amino-4-methyl-5-aza-hept-3-ene-2-one (AEH).