Showing papers on "Schiff base published in 1993"
TL;DR: Tetracoordinated metal-chelate complexes with six-membered metallocycles as discussed by the authors have been shown to be stable in the presence of tautomeric forms of the ligands.
545 citations
TL;DR: In this article, the chemical structure of chiral Schiff-base-titanium alkoxide complexes is discussed based on their 13 C NMR spectra, field desorption (FD) mass spectra and molecular weights.
Abstract: A variety of aldehydes (aromatic, heteroaromatic, α,β-unsaturated, and nonconjugate aliphatic aldehydes) has been trimethylsilylcyanated in highly enantiomeric excess (ee) with a catalyst prepared in situ from titanium tetraisopropoxide [Ti(O-i-Pr) 4 ] and chiral Schiff bases. A remarkable rate enhancement was brought about by the addition of the Schiff base into the titanium alkoxide mediated silylcyanation of aldehydes. The chemical structure of chiral Schiff-base-titanium alkoxide complexes is discussed based on their 13 C NMR spectra, field desorption (FD) mass spectra, and molecular weights
184 citations
TL;DR: By using factor analysis and decomposition, bacteriorhodopsin's intramolecular reactions have been assigned to photocycle intermediates and their pure spectra have been separated in contrast to other approaches at which unphysiological conditions or mutants have been used or specific Photocycle models have been assumed.
167 citations
TL;DR: It is shown here, however, that proton uptake, as indicated by bromocresol purple, and Schiff base deprotonation (380-nm absorption change) show different kinetics when the protein is solubilized in suitable detergents.
Abstract: Rhodopsin is a retinal protein and a G-protein-coupled receptor; it shares with both of these families the seven helix structure. To generate the G-interacting helix-loop conformation, generally identified with the 380-nm absorbing metarhodopsin II (MII) photoproduct, the retinal Schiff base bond to the apoprotein must be deprotonated. This occurs as a key event also in the related retinal proteins, sensory rhodopsins, and the proton pump bacteriorhodopsin. In MII, proton uptake from the aqueous phase must be involved as well, since its formation increases the pH of the aqueous medium and is accelerated under acidic conditions. In the native membrane, the pH effect matches MII formation kinetically, suggesting that intramolecular and aqueous protonation changes contribute in concert to the protein transformation. We show here, however, that proton uptake, as indicated by bromocresol purple, and Schiff base deprotonation (380-nm absorption change) show different kinetics when the protein is solubilized in suitable detergents. Our data are consistent with a two-step reaction:
144 citations
TL;DR: The V IV complexes VO(H 2 O)L (H 2 L) as mentioned in this paper are a Schiff base derived from o-hydroxynaphthalenecarbaldehyde and the amino acids glycine or phenylalanine.
Abstract: The V IV complexes VO(H 2 O)L (H 2 L is a Schiff base derived from o-hydroxynaphthalenecarbaldehyde and the amino acids glycine or phenylalanine) react with amines under aerobic conditions to V V complexes of the general composition VO(OH)L(amine) (amine=imidazole, methylimidazole, pyrrole, pyridine, histidine, and histidine derivatives).
111 citations
TL;DR: A wide range of asymmetric Schiff base ligands containing primary amine functions can be prepared in one step and in high yield by the reaction of VO(OEt) 3 with salicylaldehyde and the appropriate diamine.
Abstract: A wide range of asymmetric Schiff base ligands containing primary amine functions can be prepared in one step and in high yield by the reaction of VO(OEt) 3 with salicylaldehyde and the appropriate diamine. The resulting VO 2 L complexes contain tridentate ligands with phenolate, imine, and amine coordination to the dioxovanadium(V) complex ion. An X-ray structure of one compound ([VO 2 (1,2-pnSAL), 5A, where 1,2-pnSAL=1(N-salicylideneamina)-2-aminopropane) demonstrates that it is a dimer in the solid state with a V 2 O 4 score
105 citations
TL;DR: The anomalous changes in charge density reflected in the rhodopsin NMR chemical shifts can be qualitatively modeled by placing a single negative charge above C12, and the calculated fit improves when a carboxylate counterion is used to model the retinal binding site.
101 citations
TL;DR: The pK(a) values of D85 in the wild-type and R82Q, as well as R82A recombinant bacteriorhodopsins, and the Schiff base in the D85N, D85T, and D85n/R82Q proteins, have been determined by spectroscopic titrations in the dark to estimate the coulombic interaction energies.
97 citations
TL;DR: In this paper, a general interpretation of hyperporphyrin spectra in terms of charge-transfer excited states, involving charge movement either into or out of the porphyrin ring, was presented.
Abstract: Successive protonation by trifluoroacetic acid of meso-tetraphenylporphyrin derivatives bearing one, two, or four p-dimethylamino groups gives rise to new types of spectra. With one free amino group, the spectrum of the centrally protonated porphyrin shows a strong far-red band, a broad, flat absorption in the visible, and a less intense Soret band. With two or more free amino groups, the Soret band of the centrally protonated porphyrin is further split into two components. Complete protonation, including the peripheral amino groups, in all cases restores the spectral structure of the unsubstituted tetraphenylporphyrin dication. The spectra of the dianions of tetraanilino- and tetraphenylporphyrins are also similar. These results, and the related behavior of p-oxyphenylporphyrins and protonated Schiff base porphyrins, lead to a general interpretation of hyperporphyrin spectra in terms of charge-transfer excited states, involving charge movement either into or out of the porphyrin ring. 26 refs., 4 figs., 2 tabs.
97 citations
TL;DR: The combination of [SalenMn(III)][sup +] and a terminal oxidant affords efficient and specific cleavage of right-handed double-helical DNA in regions rich in A:T base pairs as discussed by the authors.
Abstract: The combination of [SalenMn(III)][sup +] and a terminal oxidant affords efficient and specific cleavage of right-handed double-helical DNA in regions rich in A:T base pairs. Metal complexes of the tetradentate chelating ligands Salen (Salen = N,N[prime]-ethylenebis(salicylideneaminato)) have been part of the inorganic chemistry literature for several decades. The cationic manganese(III) complex [SalenMn(III)][sup +] (1) is an efficient catalyst for the epoxidation of olefins with terminal oxidants such as iodosylbenzene. 1 also catalyzes oxidative C-H bond activation. The flat, crescent shape of 1, its aromatic and cationic nature, and its ability to catalyze hydrocarbon oxidation are features shared in whole or in part by metal complexes which bind to DNA and cleave it via oxidative processes. These similarities prompted the authors to evaluate the DNA-cleaving properties of 1, and they now report that 1 mediates specific cleavage of right-handed double-helical DNA in a reaction requiring a terminal oxidant. 20 refs., 3 figs., 1 tab.
89 citations
TL;DR: In this article, the chiral NiII complex 1 of a Schiff's base derived from (S)-o-[N-(benzylprolyl)amino] benzophenone (BPB) and glycine was treated with fluoro-substituted aldehydes (aliphatic and aromatic) in MeOH or CHCl3.
Abstract: The chiral NiII complex 1 of a Schiff's base derived from (S)-o-[N-(N-benzylprolyl)amino] benzophenone (BPB) and glycine was treated with fluoro-substituted aldehydes (aliphatic and aromatic)in MeOH or CHCl3. The addition proceeds with high diastereoselectivity to give, if catalysed by MeONa in MeOH, the corresponding complexes of syn-(2R)-3-fluorophenylserines (84–100% d.e.) and syn-(2S)-fluoroalkylserines (90% d.e.), and, if catalysed by NEt3 or DABCO (MeOH or CHCl3), the corresponding complexes of syn-(2S)-, and anti-(2S)-3-fluorophenylserines and fluoroalkylserines. The second-order asymmetric transformation may be successfully employed to obtain diastereoisomerically pure complexes of anti-(2R)-3-fluorophenylserines. Condensation of trifluoroacetone with complex 1, catalysed by MeONa, gave predominantly (at least >95% d.e.) the diastereoisomeric complex, containing (2S,3S)-β-(trifluoromethyl)threonine, as shown by an X-ray diffraction structural study. Diastereoisomerically and enantiomerically pure fluorine-containing 3-phenyl- and 3-alkyl-serines were obtained from the corresponding diastereoisomerically pure complexes, separated by chromatography or crystallization. The initial chiral auxiliary BPS was recovered (80–98%). The influence of the reaction's conditions and the nature of the corresponding fluoro-substituted aldehydes on the diastereoselectivity of the reactions is discussed.
TL;DR: In this paper, a number of ruthenium(II) complexes, [Ru(PPh3)2L2] (L = monoanions of Schiff bases formed from 2,3-dihydroxybenzaldehyde, 3,5-dibromosalicylaldehyde with aniline or its p-substituents), have been prepared.
TL;DR: It is suggested that the proton transfer from D96 to the Schiff base in the wild-type photocycle is driven also by such a decrease in the pKa of D96.
Abstract: In the bacteriorhodopsin photocycle the transported proton crosses the major part of the hydrophobic barrier during the M to N reaction; in this step the Schiff base near the middle of the protein is reprotonated from D96 located near the cytoplasmic surface. In the recombinant D212N protein at pH > 6, the Schiff base remains protonated throughout the photocycle [Needleman, Chang, Ni, Varo, Fornes, White, & Lanyi (1991) J. Biol. Chem. 266, 11478-11484]. Time-resolved difference spectra in the visible and infrared are described by the kinetic scheme BR-->K L N (-->N')-->BR. As evidenced by the large negative 1742-cm-1 band of the COOH group of the carboxylic acid, deprotonation of D96 in the N state takes place in spite of the absence of the unprotonated Schiff base acceptor group of the M intermediate. Instead of internal proton transfer to the Schiff base, the proton is released to the bulk, and can be detected with the indicator dye pyranine during the accumulation of N'. The D212N/D96N protein has a similar photocycle, but no proton is released. As in wild-type, deprotonation of D96 in the N state is accompanied by a protein backbone conformational change indicated by characteristic amide I and II bands. In D212N the residue D96 can thus deprotonate independent of the Schiff base, but perhaps dependent on the detected protein conformational change. This could occur through increased charge interaction between D96 and R227 and/or increased hydration near D96. We suggest that the proton transfer from D96 to the Schiff base in the wild-type photocycle is driven also by such a decrease in the pKa of D96.
TL;DR: The data suggest that the apparent pKa of the protonated Schiff base is above 16.5, and the alternative possibility that the retinal Schiff base linkage in bovine rhodopsin is not accessible for titration from the aqueous bulk medium cannot be definitely ruled out.
TL;DR: In this article, femtosecond time-resolved fluorescence spectroscopy was used to study the excited-state dynamics of a protonated Schiff base of all-trans retinal in methanol, which is known to be the chromophore of the retinal proteins.
TL;DR: In this article, the Schiff base N,N-ethylenebis((ferrocenylmethylidene)amine), (η 5 -C 5 H 5 )Fe[( η 5 C 5 H 4 ),Fe 2 L, and the complex [Cu(Fc 2 L) 2 (NO 3 ) 2 ].2CH 3 OH are reported.
Abstract: The synthesis of the Schiff base N,N-ethylenebis((ferrocenylmethylidene)amine), (η 5 -C 5 H 5 )Fe[(η 5 -C 5 H 4 )CH=N-(CH 2 ) 2 N=CH(η 5 -C 5 H 4 )]Fe(η 5 -C 5 H 5 ) , its Parent amine (η 5 -C 5 H 4 )Fe[(η 5 -C 5 H 4 )CH 2 NH(CH 2 ) 2 NHCH 2 (η 5 -C 5 H 4 )]Fe(η 5 -C 5 H 5 ),Fe 2 L , and the complex [Cu(Fc 2 L) 2 (NO 3 ) 2 ].2CH 3 OH are reported.
TL;DR: Anaerobic, single-wavelength stopped-flow spectroscopy data provide approximate rate constants for each of the kinetic processes corresponding to enzyme-substrate Schiff base formation, to enzyme reduction, and to the formation and decay of the quinonoid intermediate.
Abstract: Anaerobic, rapid-scanning stopped-flow spectroscopy has been used to investigate the UV-visible absorbance changes (300-540 nm) that occur in the spectrum of bovine serum amine oxidase during reduction by benzylamine, p-hydroxybenzylamine, and p-methoxybenzylamine. The reaction of enzyme with benzylamine generates detectable relaxations at 310, 340, and 480 nm, which are attributed to the production of reduced cofactor (310 and 480 nm) and to an enzyme-substrate Schiff base complex (340 nm). Additional transients have been observed at 440, 425, and 460 nm with p-hydroxybenzylamine, p-methoxybenzylamine, and p-(N,N-dimethylamino)benzylamine, respectively. These relaxations are ascribed to quinonoid species, formed reversibly from Schiff base complexes between oxidized product and reduced cofactor. With the spectral detection of enzyme-product Schiff base complexes, evidence now exists for each of the postulated chemical intermediates along the reaction path of bovine serum amine oxidase [cf. Hartmann, C., & Klinman, J. P. (1991) Biochemistry 30, 4605]. Anaerobic, single-wavelength stopped-flow data, collected in conjunction with rapid-scanning studies for benzylamine and p-hydroxy-benzylamine, provide approximate rate constants for each of the kinetic processes corresponding to enzyme-substrate Schiff base formation, to enzyme reduction, and to the formation and decay of the quinonoid intermediate.
TL;DR: Acyclic compartmental Schiff bases (H4L) have been synthesized by condensation of 2, 3-dihydroxybenzaldehyde with the diamines NH2-RNH2 (R- (CH2)2, H4LA; C(CH3)2, C(CH2-2, CH2-3), H4LB, C6H4, C4LD; as discussed by the authors.
TL;DR: The results show that the presence of a protonated Schiff base in the ground state is not necessarily required for efficient photoactivation of visual pigments, and support the hypothesis that the key role of the protonations in visible-absorbing pigments is to stabilize the groundstate and to allow absorbance at wavelengths above about 420 nm.
Abstract: The photoactivation pathway of an ultraviolet-absorbing rhodopsin mutant was studied. The mutant pigment, in which the retinylidene Schiff base counterion, Glu113, was replaced by glutamine (E113Q), was known to exist in a pH-dependent equilibrium between spectral forms absorbing at about 380 and 490 nm. The 380-nm form contains an unprotonated Schiff base chromophore linkage, whereas the 490-nm form contains a protonated Schiff base chromophore linkage. The role of the Schiff base proton in photoactivation was investigated by measuring transducin activation as a function of photoactivation wavelength. The transducin activation action spectra of rhodopsin and of mutant E113Q were found to be very similar to their UV-visible absorption spectra. Thus, the 380-nm UV form of the mutant E113Q could be activated directly by UV light to catalyze nucleotide exchange by transducin. The quantum efficiency of photoactivation of the UV-absorbing form of E113Q was similar to that of its visible-absorbing form. These results show that the presence of a protonated Schiff base in the ground state is not necessarily required for efficient photoactivation of visual pigments. They support the hypothesis that the key role of the protonated Schiff base in visible-absorbing pigments is to stabilize the ground state and to allow absorbance at wavelengths above about 420 nm. The findings are also consistent with transducin activation studies of mutant apoproteins regenerated with all-trans-retinal, or of mutant apoproteins alone, suggesting that the active state of rhodopsin can be formed via a number of pathways.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: In this paper, the synthesis and characterization of an N 4 O 3 amine phenol (tris(((2-hydroxy-3-methoxybenzyl)amino)ethyl)amine, H 3 L 4) and its lanthanide complexes [Ln(H 3 L4)(NO 3 ) 3 ] (Ln=Pr, Nd) and [ln(L 4 L4 2 ](NO 3 ),
Abstract: The synthesis and characterization of an N 4 O 3 amine phenol (tris(((2-hydroxy-3-methoxybenzyl)amino)ethyl)amine, H 3 L4) and its lanthanide complexes [Ln(H 3 L4)(NO 3 ) 3 ] (Ln=Pr, Nd) and [Ln(H 3 L4) 2 ](NO 3 ) (Ln=Pr, Nd, Gd, Yb), are reported. The N 4 O 3 amine phenol ligand is the KBH 4 reduction product of the Schiff base derived from the reaction of tris(2-aminoethyl)amine (tren) and 3 equiv of o-vanillin.
TL;DR: In this article, the reaction of Ru(PPh 3 ) 3 X 2 (X Cl, Br) with the Schiff base condensate of 4-substituted benzaldehyde (RC 6 H 4 CHO) and 2-aminophenol under aerobic conditions affords the complexes Ru III (RL)(PPH 3 ) 2 X in which RL is the Schiffbase ligand bound to the metal centre at the phenolic oxygen (deprotonated azomethine nitrogen and an ortho carbon atom (deprobated) of the benzaldehyde fragment
TL;DR: In this paper, methods have been developed for the preparation of insoluble polysiloxane ligands containing pendant -N(CH 2 CH 2 NH 2 ) 2 groups and their salicylaldimine Schiff base and cyclised derivatives.
Journal Article•
TL;DR: In this paper, the X-ray results of a series of [Cu(phen) 2 (CH 3 CO 2 )]Y and [cu(bipyam) 2(ONO)]Y cation-distortion isomers and of monomeric cobalt-dioxygen Schiff base complexes with identical equatorial ligands and different nitrogenous axial bases are presented.
Abstract: The X-ray results of a series of [Cu(phen) 2 (CH 3 CO 2 )]Y and [Cu(bipyam) 2 (ONO)]Y cation-distortion isomers and of a series of monomeric cobalt-dioxygen Schiff base complexes with identical equatorial ligands and different nitrogenous axial bases are presented. The distortional behavior of the Cu(II) pseudo-Jahn-Teller complexes is explicable in terms of the warped Mexican hat energy surface distorted by tetragonal and orthorhombic strain originating from chemical differences between ligands and crystal-packing forces. The Cu-O static bond lengths allow an estimation of the amount of tetragonal strain, whereas the application of Boltzmann statistics to the temperature variation of the Cu-O bond lengths allows an estimation of the amount of orthorhombic strain
TL;DR: In this article, it was shown that the two octahedral tin sites in the structure of SnMe2Cl2·2[Ni(3MeO-salphen)·H2O appear to result from two isomeric forms of the adduct coexisting in a lattice as a result of hydrogen-bonding interactions.
Abstract: 1:1 Addition complexes of [NiIIL]·H2O [H2L =N,N′-bis(3-methoxysalicylidene)ethylenediamine (3MeO-H2salen), N,N′-bis(3-methoxysalicylidene)propane-1,2-diamine (3MeO-H2salpn) or N,N′-bis(3-methoxysalicylidene)-o-phenylenediamine (3O-H2salphen)] with SnR2Cl2(R = Me or Ph), SnBunCl3, or SnCl4 have been found to be generally monoaqua adducts of the tin Lewis acids with the water engaged in hydrogen bonding with the methoxy and phenolic oxygen atoms of the Schiffbase ligand. Both water and methoxy oxygen atoms are involved in donor-bond formation to tin in the polymeric structures 2SnMe2Cl2·[Ni(3MeO-salen)]·H2O and SnMe2Cl2·[Ni(3MeO-salphen)]·H2O, each of which has two very different tin environments. The two octahedral tin sites in the structure of SnMe2Cl2·2[Ni(3MeO-salphen)·H2O] appear to result from two isomeric forms of the adduct co-existing in a lattice as a result of hydrogen-bonding interactions. Crystal-structure determinations revealed that the monoaqua adducts of dimethyltin dichloride which exist in the structures SnMe2Cl2·[Ni(3MeO-salen)]·H2O and SnMe2Cl2·[Ni(3MeO-salon)]·H2O differ in that, in the former tin is in a trigonal-bipyramidal environment, whereas in the latter it is in an octahedral environment as a result of an intermolecular Sn ⋯ Cl contact of 3.615 A.
TL;DR: The results show that the ligand is coordinated to the central metal ion via amide nitrogen, imino nitrogen, phenolic oxygen and carboxyl oxygen to form a quadridentate complexes.
Abstract: Two new Schiff bases, N-4-hydroxysalicylidene-glycylglycine (K·GGRS·H2O), N-O-vanillal-glycylglycine (K· GGVS·3H2O) and their manganese(II), cobalt(II), nickel(II) and copper(II) complexes have been synthesized and characterized by elemental analysis, t.g.a., molar conductance, i.r. and u.v. spectral studies. The 13Cn.m.r. spectrum of one of the Schiff base ligands has been recorded. The results show that the ligand is coordinated to the central metal ion via amide nitrogen, imino nitrogen, phenolic oxygen and carboxyl oxygen to form a quadridentate complexes. Some of the complexes exhibit strong inhibitory action towards Candida albicans and Cryptococcus neoformans.
TL;DR: The Schiff base complexes (X-SALPRN)Mn II [X=H, 5-Cl, 5 CH 3 O; SALPRN=1,3-bis(salicylideneamino)propane] were reacted with dioxygen in CH 3 CN and CH 2 Cl 2.
Abstract: The Schiff-base complexes (X-SALPRN)Mn II [X=H, 5-Cl, 5-CH 3 O; SALPRN=1,3-bis(salicylideneamino)propane] were reacted with dioxygen in CH 3 CN and CH 2 Cl 2 . Mn(IV), Mn(IV) bis(μ-oxo) dimers [(X-SALPRN)-Mn IV (μ-O)] 2 [X=H (1), 5-Cl (2), 5-CH 3 O (3)] were isolated in high yields and as the sole products from oxygenation in CH 3 CN, but two products were isolated when the oxygenation was performed in CH 2 Cl 2 .
TL;DR: The Schiff base counterion in rhodopsin can be repositioned to form a pigment with an apparently unperturbed Schiff base pKa and a specific amino acid residue that acts as a Schiff base proton acceptor is not strictly required for photoconversion of r Rhodopsin to its active MII form.
TL;DR: New tridentate pyrimidine-derived NNO and NNS donor Schiff base ligands and their nickel(II), copper( II) and zinc(II) chelates have been synthesized and characterized on the basis of elemental analysis, 1H-NMR, IR and electronic spectral data and conductance and magnetic measurements.
Abstract: New tridentate pyrimidine-derived NNO and NNS donor Schiff base ligands and their nickel(II), copper(II) and zinc(II) chelates have been synthesized and characterized on the basis of elemental analysis, 1H-NMR, IR and electronic spectral data and conductance and magnetic measurements. The synthesized ligands and their metal chelates have been screened and compared for their antibacterial action against bacterial species Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae.
TL;DR: Nickel(II) complexes with N 2 O 2 Schiff base ligands based on 2-hydroxy-1-naphthaldehyde and three different diamines have been prepared and their electrochemical behaviour in (CH 3 ) 2 SO studied by cyclic voltammetry as discussed by the authors.