On the Stability of the Schiff Bases of Pyridoxal 5′-Phosphate with Polypeptides Containing L-Lysine

We determined the apparent equilibrium constant of formation, K_pH, of the Schiff bases of pyridoxal 5′-phosphate (PLP) and poly- and copolymers containing L -lysine, as a function of pH at 25° and a constant ionic strength of 0.1 M . The K_pH values obtained at acidic and neutral pH were larger that those reported for Schiff bases of PLP and hexylamine. We determined calorimetrically ΔH of formation of Schiff bases of PLP and poly(L -lysine) (?4.5′kcal/mol), and PLP and hexylamine (?3.4 kcal/mol) at pH 7.00. Semi-empirical theoretical calculations (INDO and AMI methods) of a model compound of Schiff base of PLP and polypeptide containing L -lysine show the capability of specific interactions between groups of PLP and the peptide skeleton.     

Determination of the Rates of Formation and Hydrolysis of the Schiff Bases Formed by Pyridoxal 5′-Phosphate with Copolypeptides Containing L-Lysine and Aromatic L-Amino Acids

The apparent rate constants of formation (k₁) and hydrolysis (k₂) of the Schiff bases formed between pyridoxal 5′-phosphate and the poly(L -Lys,L -Trp)4 : 1 copolymer at different pH values, a temperature of 25 °C and an ionic strength of 0.1 M were determined. The individual rate constants of formation and hydrolysis of the Schiff bases of pyridoxal 5′-phosphate with poly(L -Lys,L -Trp)4 : 1, poly(L -Lys,L -Tyr)4 : 1, and poly(L -Lys,L -Phe)1 : 1 corresponding to the different chemical species present in the medium as a function of its acidity were also determined, as were the pK values for the Schiff bases. The significance of the interactions between the pyridine ring in pyridoxal 5′-phosphate and the aromatic ring in the L -phenylalanine, L -tyrosine, and L -tryptophan side chains is demonstrated.     

Kinetic Study on Stability of Schiff Base of Pyridoxal 5′-Phosphate and Leucine in Water Media with Cationic Surfactants

We studied the stability of the Schiff bases formed between pyridoxal 5′-phosphate (PLP) and leucine in the presence of (hexadecyl)trimethylammonium bromide (CTAB) over a wide pH range by determining the kinetic constants of formation and hydrolysis of these compounds. The results show that the stability of the Schiff bases is increased by the presence of CTAB as a result of increased rates of formation and decreased hydrolysis rate constants. The ionic head groups of CTAB favour the formation of the bases, while its hydrophobic rests protect the imine double bond from hydrolysis. This model system permits one to obtain partially hydrophobic media with no need for any non-aqueous solvents.     

Determination of the rates of formation and hydrolysis of the Schiff bases formed by pyridoxal 5′-phosphate and copolypeptides containing l-lysine

We determined the apparent rate constants of formation (k₁) and hydrolysis (k₂) of the Schiff bases formed between pyridoxal 5′-phosphate (PLP) and l-lysine and l-alanine copolymers of different compositions, as well as those formed between PLP and l-lysine and l-glutamic acid copolymers, at various pH values, a temperature of 25 °C and an ionic strength of 0.1 M. The k₁ values obtained in neutral and acidic media were independent of the copolymer composition. The efficiency of the intramolecular acid catalysis for the formation of the Schiff bases was found to be somewhat higher than that of PLP—primary amine systems (the slope of the Brøwted plot was α=0.77). The most stable of the Schiff bases studied was that with a protonated imine nitrogen and phosphate group and a unprotonated pyridine nitrogen.     

Unusual Acid-Catalyzed Rearrangement of Two α,α′-Diimino-oximes

2-[2-(Alkylimino)-2-phenylethylidene]pyrrolidines (vinamidines, 3 – 6 ) were obtained either via activation of the corresponding vinologous amide 1 with Meerwein salt and subsequent treatment of the intermediate 2 with an amine, or more directly by acid-catalyzed condensation of the Schiff bases derived from acetophenone with 2-ethoxy-1-pyrroline. Nitrosation of these vinamidines led to α,α′-diimino-oximes. In two cases ( 10 , 11 ), these oximes underwent acid-catalyzed rearrangement with formation of a 5,6,7,8-tetrahydroimidazo[1,2-a]pyridine ring system ( 12 , 13 ). X-Ray analysis of one of these products ( 13 ) and also of one of the vinamidine salts ( 6 ) are presented.     

Chemoselectivity of 6-bromo-2-methyl-3,1-benzoxazin-4-one towards amines,Schiff bases,and azines

Summary 6-Bromo-2-methyl-3,1-benzoxazin-4-one (1) undergoes an unusual cleavage at position 4 when it is allowed to react witho-phenylenediamine or anthranilic acid in dry benzene to give the corresponding compounds2–5, respectively. The reaction of1 withSchiffbases and azines results in the formation of the compounds6a–d and8a,b, respectively. The reaction involves a cleavage of theSchiff base or the azine into its amine and arylidene moieties which are smoothly incorporated into1 via nucleophilic attack of the amine at position 4 and condensation of the aldehyde with a reactive methyl group, at position 2 respectively. No displacement of the arylidene segment was observed.

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Zur Chemoselektivität von 6-Brom-2-methyl-3,1-benzoxazin-4-on gegenüber Aminen,Schiffschen Basen und Azinen

Zusammenfassung 6-Brom-2-methyl-3,1-benzoxazin-4-on reagiert mito-Phenylendiamin oder Anthranilsäure in trockenem Benzol unter einer ungewöhnlichen Bindungstrennung zu den Verbindungen2–5. Die Reaktion von1 mitSchiffschen Basen und Azinen führt zu den Verbindungen6a–d und8a,b. Die Reaktion verläuft über eine Spaltung derSchiffschen Base oder des Azins in ihre Amin- und Arylidenreste, die über einen nucleophilen Angriff des Amins an Position 4 und Kondensation des Aldehyds mit der reaktiven Methylgruppe in Position 2 glatt in1 übergeführt werden. Es wurde kein Arylidenaustausch beobachtet.

     

Indium(III) complexes with some salicylidene aromaticSchiff bases

In(III) complexes with salicylidene aromaticSchiff bases have been prepared. The nature of the complexes has been studied by microanalysis of the solid complexes, conductometric titration, uv and ir spectrophotometric measurements. The complexes are of the type 11 and 21 [Ligand: In(III)] depending upon theSchiff base. The tendency of the salicylideneSchiff base molecule towards complex formation with In(III) is found to depend largely on the strength of the intramolecular hydrogen bond established between the aldehydic OH group and C=N. Furthermore, it is concluded that theseSchiff bases cordinate to In(III) as tri- or bidentate ligands depending upon the molecular structure of theSchiff base (not as monodentate ligand as previously described). The high molar absorbance of the 12 In(III) complex with salicylidene-o-hydroxyaniline I (17,800 mol^–1 cm²) can be applied for the micro determination of small amounts of Indium as low as 0.57 g/ml solution.

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Indium(III)-Komplexe mit aromatischen Schiff-Basen

Zusammenfassung Es wurden einige In(III)-Komplexe mit (von Salicylaldehyd hergeleiteten)Schiff-Basen hergestellt. Elementaranalyse, konduktometrische Titration und UV- sowie IR-Spektroskopie wurden zur Aufklärung der Komplexe herangezogen. Es werden je nach verwendeterSchiff-Base 11-oder 21-Komplexe gebildet. Die Bildungstendenz der Komplexe mit denSchiff-Basen als drei- oder zweizähnige Liganden hängt weitgehend von Stärke und Ausbildungsmöglichkeit von H-Brückenbindungen ab. Einer der beschriebenen Komplexe ist zur photometrischen Mikrobestimmung von In(III) geeignet.

     

Anil-Synthese. 24. Mitteilung. über die Herstellung von Styryl- und Stilbenyl-Derivaten des 1H-Benzotriazols

Preparation of Styryl and Stilbenyl Derivatives of 1H-Benzotriazoles 1-(p-Tolyl)-substituted 1H-benzotriazoles react with anils of aromatic aldehydes in the presence of dimethylformamide and potassium hydroxide to yield the corresponding 1-(styr-4′-yl)-1H-benzotriazoles and 1-(stilben-4′-yl)-1H-benzotriazoles, respectively (‘anil synthesis’). Further, under the same reaction conditions, the Schiff's bases derived from p-chloroaniline and 4-(1′H-benzotriazol-1′-yl)benzaldehydes give, with p-tolyl-substituted heterocycles, the corresponding heterocyclic substituted stilbenyl derivatives.     

Solute-Solvent Interaction Effects on Protonation Equilibrium of Substituted N-Benzylidene-2-hydroxyanilines in Aqueous Ethanol: The Application of Factor Analysis to Solvatochromic Parameters and Protonation Equilibria

Summary. In this study, the stoichiometric protonation constants, logK_OH and logK_NH, of sixteen substituted N-benzylidene-2-hydroxyanilines have been determined potentiometrically in ethanol-water mixtures of varying composition (10–80% ethanol by volume) at 25.0±0.1°C. The values of the constants, logK, were submitted to factor analysis in order to obtain the number of factors which affect the variation of the whole data sets of protonation constants and, afterwards, to target factor analysis to identify these factors. The influence of solvatochromic parameters in the interactions between Schiff bases derivatives and the solvent studied was identified and quantified. Kamlet and Taft general equations allow calculation of the logK values of Schiff bases studied in any ethanol-water mixtures up to 80% (v/v) and thus provide the knowledge of the acid-base behaviour in these solvent media. Further, the quasi-lattice quasi-chemical (QLQC) theory of preferential solvation has been applied to quantify the preferential solvation by water of electrolytes in ethanol-water mixtures.     

Solute-Solvent Interaction Effects on Protonation Equilibrium of Substituted N-Benzylidene-2-hydroxyanilines in Aqueous Ethanol: The Application of Factor Analysis to Solvatochromic Parameters and Protonation Equilibria

In this study, the stoichiometric protonation constants, logK_OH and logK_NH, of sixteen substituted N-benzylidene-2-hydroxyanilines have been determined potentiometrically in ethanol-water mixtures of varying composition (10–80% ethanol by volume) at 25.0±0.1°C. The values of the constants, logK, were submitted to factor analysis in order to obtain the number of factors which affect the variation of the whole data sets of protonation constants and, afterwards, to target factor analysis to identify these factors. The influence of solvatochromic parameters in the interactions between Schiff bases derivatives and the solvent studied was identified and quantified. Kamlet and Taft general equations allow calculation of the logK values of Schiff bases studied in any ethanol-water mixtures up to 80% (v/v) and thus provide the knowledge of the acid-base behaviour in these solvent media. Further, the quasi-lattice quasi-chemical (QLQC) theory of preferential solvation has been applied to quantify the preferential solvation by water of electrolytes in ethanol-water mixtures.     

Synthesis and Characterization of Dendrimeric Bridged Salen/Saloph Complexes and Investigation of Their Magnetic and Thermal Behaviors

Eight new multinuclear Fe^III and Cr^III complexes involving the tetradentate Schiff bases N,N′‐bis(salicylidene)ethylenediamine (salenH₂) or N,N′‐bis(salicylidene)benzene‐1,2‐diamine (salophH₂) and the two new ligands 4,4′,4″,4′′′,4′′′′,4′′′″‐[1,3,5‐triazine‐2,4,6‐triyltris(nitrilomethylidyne‐4,1‐phenyleneoxy‐1,3,5‐triazine‐6,2,4‐triyldiimino)]hexakis[benzoic acid] ( 4 ) or 5,5′,5″,5′′′,5′′′′,5′′′″‐[1,3,5‐triazine‐2,4,6‐triyltris(nitrilomethylidyne‐4,1‐phenyleneoxy‐1,3,5‐triazine‐6,2,4‐triyldiimino)]hexakis[benzene‐1,3‐dicarboxylic acid] ( 5 ) were synthesized (Schemes 1 and 2) and characterized by means of ¹H‐NMR and FT‐IR spectroscopy, elemental analysis, LC/MS analysis, AAS (atomic‐absorption spectrum) analysis, thermal analyses, and magnetic‐susceptibility measurements. The complexes can also be characterized as low‐spin distorted‐octahedral Fe^III and Cr^III complexes bridged by carboxylato moieties.     

Anil-Synthese. 23. Mitteilung. Über die Herstellung von Styryl- und Stilbenyl-Derivaten des Pyrimidins

Preparation of Styryl and Stilbenyl Derivatives of Pyrimidines 2- and 4-(p-Tolyl)-substituted pyrimidines react with anils of hetero-aromatic aldehydes in the presence of dimethylformamide and potassium hydroxide or potassium t-butoxide to yield the corresponding 2- and 4-[4″-(heteroaryl)stilben-4′-yl]pyrimidines or the 2- and 4-[a-(heteroaryl)-4′-styryl]pyrimidines respectively (‘Anil synthesis’). Furthermore, the Schiff′s bases derived from p-chloroaniline and 4-(pyrimidine-2-yl and 4-yl)benzaldehydes give, with methyl- and with p-tolyl-substituted heterocycles, the corresponding heterocyclic substituted styryl and stilbenyl derivatives. Alkyl-, alkoxy- or phenyl-substituted pyrimidines undergo also the ‘Anil synthesis’.     

Thiosemicarbazone Scaffold as a Multidentate Ligand for Transition‐Metal Ions: Synthesis,Characterization, In Vitro Antimicrobial,Anthelmintic, DNA Cleavage,and Cytotoxic Studies

New series of Schiff bases derived from o‐substituted thiosemicarbazides and 8‐formyl‐7‐hydroxy‐4‐methylcoumarin have been synthesized and their coordination tendency toward Co(II), Ni(II), and Cu(II) metal ions is studied. Analytical, spectral (IR, UV‐Vis, ESR, and FAB‐mass), magnetic, and thermal studies suggests octahedral geometry of the type ML₂ for all the Co(II), Ni(II), and Cu(II) complexes. The complexes are soluble in DMF/DMSO and are non‐electrolytes. The Schiff bases and their metal complexes have been screened for antibacterial (Escherichia coli, Staphylococcus aureus, Salmonella typhi, and Pseudomonas aeruginosa) and antifungal activities (Aspergillus flavus, Aspergillus niger, and Cladosporium) by minimum inhibitory concentration method. DNA cleavage is studied by agarose gel electrophoresis method. Metal (II) complexes show good anthelmintic activity when compared to Schiff bases.     

Antimony(III) complexes of bifunctional tridentateSchiff bases

Several newSchiff base derivatives of antimony(III) have been synthesized by the reaction of antimony(III) isopropoxide with theSchiff bases having the donor system, O–N–O. The reactions in 1:1 and 2:3 molar ratios [Sb(O-i-C₃H₇)₃: :Schiff base] have yielded Sb(O-i-C₃H₇) (SB) and Sb₂ (SB)₃ type of derivatives (whereSB represents the anion of theSchiff base andSBH₂=o-hydroxyacetophenone-2-hydroxy-1-propylimine, o-hydroxycetophenone-3-hydroxy-1-propylimine, salicylidene-2-hydroxyethylamine, salicylidene-2-hydroxy-1-propylamine and 2-hydroxy-1-naphthylidene-2-hydroxyethylamine) resp. In the resultingSchiff base derivatives, the central antimony atom appears to be tetracoordinated as indicated by their monomeric state determined ebullioscopically. The infrared spectra of the resulting complexes have been recorded and tentative structures indicated. The thermogravimetric analysis of antimony-monoisopropoxysalicylidene-2-hydroxy-1-propylamine has also been carried out.With 1 Figure     

Thorium[IV], Uranium[VI] and Ce[III] complexes with bidentate and tridentateSchiff bases

Thorium(IV), Uranium(VI) and Cerium(III) complexes with some bidentate and tridentateSchiff bases-derived from salicyladehyde-have been prepared. The effect of the molecular structure of theSchiff base molecule on its tendency towards complex formation has been studied. The structures of the complexes have been investigated by elemental analysis, molar ratio and continuous variation spectrophotometric methods, infrared spectra and conductometric titrations; the apparent formation constants have been determined as well.

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Thorium(IV)-, Uran(VI)- und Cer(III)-Komplexe mit zwei- und dreizähnigen Schiff-Basen

Zusammenfassung Es wurden Thorium(IV)-, Uran(VI)- und Cer(III)-Komplexe einiger zwei-und dreizähnigerSchiff-Basen (hergeleitet vom Salicylaldehyd) dargestellt, um den Einfluß der Molekülstruktur derSchiff-Base auf das Komplexierungsvermögen zu studieren. Die Struktur der Komplexe wurde mittels Elementaranalyse, elektronenspektrometrischer Methoden, IR-Spektrometrie und Leitfähigkeitsmessungen untersucht. Die Komplexbildungskonstanten wurden gleich-falls bestimmt.

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Deceased December 1977.     

Zirconium(IV) complexes ofSchiff bases

Zirconium(IV)Schiff base derivatives have been synthesised by reacting zirconium isopropoxide with monofunctional bidentateSchiff bases in different stoichiometric ratios. The resulting derivatives of the type Zr(O-Isopr)₃(SB) and Zr(O-Isopr)₂(SB)₂, whereSB ^– is the anion of the correspondingSchiff baseSBH, have been isolated in almost quantitative yields. Their molecular weights have been determined ebullioscopically and their ir spectra recorded.

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Zirkonium(IV)-Komplexe von Schiff-Basen

Zusammenfassung Es wurden Zirkonium(IV)-Schiff-Basen-Derivate in verschiedenen stöchiometrischen Zusammensetzungen über die Reaktion von Zirkoniumisopropoxid mit monofunktionellen zweizähnigenSchiff-Basen synthetisiert. Die Komplexe vom Typ Zr(O-Isopr)₃(SB) und Zr(O-Isopr)₂(SB)₂ [SB ^– als Anion derSchiff-BaseSBH] wurden in fast quantitativer Ausbeute erhalten. Es werden Strukturen vorgeschlagen, die auf ebullioskopisch bestimmten Molekulargewichten und den IR-Spektren basieren.

     

Aluminium(III)-derivate zweiwertiger,dreizähnigerSchiffscher Basen

Several newSchiff base derivatives of aluminium have been synthesized by the reaction of aluminium isopropoxide with theSchiff bases having the donor system, O–N–O. The reactions in 11 and 23 molar ratios [Al(OPr ⁱ)₃:Schiff base] have yielded Al(OPr ⁱ)(SB) and Al₂(SB)₃ types of products [where SB^–- represents the anion of theSchiff base andSBH₂= (2-hydroxy-1-naphthylidene)-2-hydroxyethylamine, (2-hydroxy-1-naphthylidene)-3-hydroxy-1-propylamine, (2-hydroxy-1-naphthylidene)-1-hydroxy-sec.-butylamine and (o-hydroxyacetophenone)-3-hydroxy-1-propylimine, resp. In these resulting monoisopropoxy aluminiumSchiff base and dialuminium tris-Schiff base derivatives, the central aluminium atom appears to be penta-and tetracoordinated, resp., as indicated by their dimeric and monomeric states determined ebullioscopically. The infrared spectra of the resulting derivatives have also been recorded and tentative assignments have been made.     

Crystal Structure and Spectral Characterization of a Rare Example of a Salen-Type Zinc Complex with Neutral Monodentate Oxygen Donor Ligands Coordination

Summary. The new zinc complex of the N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine ligand as a product of the [2 + 1] Schiff base condensation process was synthesized in the one-step metal-promoted reaction between salicylaldehyde and 4-methyl-1,3-phenylenediamine in ethanol in the presence of zinc chloride. The two potentially tetradentate N₂O₂ Schiff bases function as neutral monodentate ligands involving only one oxygen atom in coordination. This rare coordination pattern of a mononuclear salen-type zinc complex was revealed by X-ray crystallography and correlated with spectroscopic characterization.     

Crystal Structure and Spectral Characterization of a Rare Example of a Salen-Type Zinc Complex with Neutral Monodentate Oxygen Donor Ligands Coordination

The new zinc complex of the N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine ligand as a product of the [2 + 1] Schiff base condensation process was synthesized in the one-step metal-promoted reaction between salicylaldehyde and 4-methyl-1,3-phenylenediamine in ethanol in the presence of zinc chloride. The two potentially tetradentate N₂O₂ Schiff bases function as neutral monodentate ligands involving only one oxygen atom in coordination. This rare coordination pattern of a mononuclear salen-type zinc complex was revealed by X-ray crystallography and correlated with spectroscopic characterization.     

Fluoroimines from the reaction of fluoro amino acids or fluoroketo acids with the aldehyde or amine form of vitamin B6: 2—Stereochemical aspects of their formation from β-fluoroaspartates or β-fluorooxaloacetate,using 19F NMR

The fluorine NMR spectra of systems initially containing 0.05–0.1 M of pyridoxal 5′-phosphate and erythro-β-fluoroaspartate (or threo-β-fluoroaspartate) in D₂O solution were examined over the pD range 1–12. The formation of the aldimine Schiff base gave only one stereoisomer, whcih was trapped with sodium borohydride. Reactions of pyriodoxamine 5′-phosphate and fluorooxaloacetate were examined under the same conditions. A mixture of two products was given, identified as two ketimine Schiff bases (E and Z isomers) with well characterized fluorine chemical shifts and ²J(DF) values. This mixture, trapped with sodium borohydride, gives the two reduced erythro and threo aldimines. The configurations and conformations of all reaction products were determined using the ³J(HF) values and their correlation with the fluorine chemical shift. The role of the 3-phenolate oxygen of the pyridine ring, of the conjugate acid of the iminium nitrogen and of the carboxylate oxygen in ionic or hydrogen bond interactions in the determination of the stereochemistry is discussed.