Iron(III) complexes of salicylidene amino acids

Several iron(III) complexes of tridentate dibasic salicylidene/substituted salicylidene amino acids (ONO donor set) have been prepared and characterized. All iron(III) compounds possess dimeric pseudo — octahedral structure established on the basis of elemental analysis, magnetic moment studies, superimposable infrared spectra of these complexes with those of nickel(II), cobalt(II), manganese(II), magnesium(II) and zinc(II) complexes, and thermogravimetric analysis.

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Zusammenfassung Mit dreizahnigen dibasichen substituierten und unsubstituierten Salizylidenaminosäuren (ONO Donorset) wurden einige Eisen(III)-komplexe hergestellt und diese beschrieben. Mittels Elementaranalyse, TG-Analyse, der Untersuchung des magnetischen Momentes und des Vergleiches von IR-Spektren mit denen von Nickel(II)-, Cobalt(II)-, Mangan(II)-, Magnesium(II)- und Zink(II)-komplexen konnte festgestellt werden, daß alle Eisen(III)-komplexe über eine pseudooktaedrische Dimerenstruktur verfügen.

     

Chromium(III) complexes of naturally occurring amino acids

Summary Amino acid complexes of CrCl₃Py₃ have been prepared and studied by elemental analysis, magnetic susceptibility, vibrational (i.r.), electronic and circular dichroism spectroscopy. Two peaks in the visible spectra are assigned to a d-d transition in pseudo octahedral symmetry. The spectrochemical parameters (Dq, B and ₃₅) for the complexes were calculated which confirm that pyridine nitrogen and/or chlorine are not removed. Prolonged heating or bubbling of air through the solution of CrCl₃-Py₃ containing l-(-)-histidine or l-(-)-threonine for several hours enhanced formation of chromium (VI).     

Mixed cobalt(III) complexes with aromatic amino acids and di­amines. III.

The title compound, [Co(C₉H₁₀NO₃)₂(C₂H₈N₂)]Cl·4H₂O, is one of six possible diastereomers of the (1,2‐di­amino­ethane)­bis(S‐tyrosinato)­cobalt(III) complex. The cobalt(III) ion has an octahedral coordination, with three five‐membered chelate rings which have deformed coordination angles and coordinated O atoms in trans positions. In comparison with the previously reported crystal structure of the Δ‐C₁‐cis(O) diastereomer [Miodragovi?et al. (2001). Enantiomer, 6 , 299–308], the compound presented in this paper has more planar five‐membered amino­carboxyl­ate rings. Complex cations, chloride anions and water mol­ecules of crystallization are linked together by a network of hydrogen bonds. The chloride anions lie approximately between two Co atoms and form hydrogen bonds with all coordinated NH₂ groups. In the crystal structure, there is a weak intermolecular π?π interaction between the phenyl rings.     

Rhenium(V) complexes with sulfur-containing amino acids

Rhenium(V) complexes with 2-amino-4-(methylthio)butanoic acid (methionine, Met) and 2-amino-3-sulfopropionic acid (cysteine, Cys) have been synthesized. Depending on the initial reagent ratio, the resulting complexes contain one or two ligand molecules. On heating the compounds with one amino acid molecule, two hydrogen halide molecules are removed at 128–132°C to form a molecular complex. The composition, structure, and thermal stability of the complexes have been studied by elemental analysis, conductometry, IR spectroscopy, NMR, and mass spectrometry.     

Characterization of an NH-pi interaction in Co(III) ternary complexes with aromatic amino acids

The NH-pi interaction has been detected in the crystal structures of Co(III) ternary complexes with N,N-bis(carboxymethyl)-(S)-phenylalanine (BCMPA) and aromatic amino acids including (S)-phenylalanine ((S)-Phe), (R)-phenylalanine ((R)-Phe), and (S)-tryptophan ((S)-Trp)). Additionally, this interaction has been studied in solution for Co(III) ternary complexes with BCMPA or NTA (NTA = nitrilotriacetic acid) and several amino acids (AA) by means of electronic absorption, circular dichroism (CD), and (1)H NMR spectroscopies. The CD intensities of the Co(III) complexes with aromatic amino acids measured in the d-d region ( approximately 20.5 x 10(3) cm(-)(1)) are significantly decreased in ethanol solutions relative to water. Analogous complexes with aliphatic amino acids do not exhibit this solvent effect. The (1)H NMR spectra of the Co(III) complexes with aromatic amino acids measured in DMSO-d(6) exhibit upfield shifts of the NH peaks compared with those with aliphatic amino acids, which suggest a shielding effect due to the aromaticity. The upshift values coincide with those experimentally evaluated from the crystal structures. The magnitude of the upfield shifts agrees well with Hammett's rule, indicating that the increase of pi-electron densities on the aromatic rings leads attractive NH-pi interaction that exerts a larger shielding effect for the NH protons. In ligand-substitution reactions of the carbonatocobalt(III) complexes with amino acids, the yields of those with aromatic amino acids are higher than the yields obtained for complexes with aliphatic amino acids. This observation is discussed in connection with the important contribution of the NH-pi interaction as one of the promotion factors in the reaction.     

Reactions and structural characterization of gold(III) complexes with amino acids, peptides and proteins

The present review article highlights recent findings in the field of gold(III) complexes with amino acids, peptides and proteins. The first section of this article provides an overview of the gold(III) reactions with amino acids, such as glycine, alanine, histidine, cysteine and methionine. The second part of the review is mainly focused on the results achieved in the mechanistic studies of the reactions between gold(III) and different peptides and structural characterization of gold(III)-peptide complexes as the final products in these reactions. The last section of this article deals with the reactions of gold(III) complexes with proteins as primary targets for cytotoxic gold compounds. Systematic summaries of these results contribute to the future development of gold(III) complexes as potential antitumor agents and also have importance in relation to the severe toxicity of gold-based drugs.     

Zinc(II) complexes of salicylidene amino acids

Several zinc(II) complexes of tridentate dibasic salicylidene amino acids have been prepared and characterized. All of them possess dimeric pseudo-octahedral structures, which were established on the basis of thermogravimetric analysis and superimposable infrared spectra of these complexes with those of manganese(II), cobalt(II), nickel(II), and magnesium(II) complexes.

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Zusammenfassung Einige Zink(II)-komplexe von dreizähligen, dibasischen Salizylidenaminosäuren wurden dargestellt und beschrieben. Alle diese Komplexe besitzen eine pseudooktaedrische Dimerstruktur. Dies wurde mittels thermogravimetrischer Analyse und auf Grund der deckungsgleichen IR-Spektren dieser Komplexe mit denen von Mangan(II)-, Kobalt(II)-, Nickel(II)- und Magnesium(II)-Komplexen festgestellt.

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The senior author (RKR) expresses his deep gratitude to Prof. R. L. Dutta, Department of Chemistry, Burdwan University, India, for valuable suggestions and discussions during the course of the work. He is also grateful to Dr. R. N. Banerjee of Jadavpur University and Dr. P. Banerjee of the Indian Association for the Cultivation of Science, Calcutta for laboratory and other facilities.     

Mixed-ligand platinum(IV) complexes with amino acids and cytosine

Complex formation in platinum(IV)-cytosine-amino acid (glycine, α-alanine, lysine, or histidine) systems is studied using pH titration. Stability constants for 1:1:1 stoichiometry of complexes are determined. The stability of the mixed-ligand complexes varies in the following order: Lys < Ala < Gly < His. Reactions of aqueous solutions yields the following complexes: Pt(Cyt)(Gly^?)Cl₃ · 3H₂O (I), pt(Cyt)(Ala^?)Cl₃ · 3H₂O (II), Pt(Cyt)(Hist)Cl₄ · 2H₂O (III), and Pt(Cyt)(Lys)Cl₄ · 2H₂O (IV). ¹³C NMR, IR, and XPS spectra show that glycine and alanine are complexed via amino and carboxy groups, lysine via its α-amino group exclusively, and histidine via its amino group and heterocyclic N3 atom. Cytosine in these complexes is bidentate (it is complexed via C=O oxygen and N3 heterocyclic atoms).     

Mixed-ligand platinum(IV) complexes with amino acids and adenine

Complexing in platinum(IV)-adenine-amino acid (α-alanine (Ala), lysine (Lys), or histidine (His)) systems was studied by pH titration. The stability constants of 1: 1: 1 complexes were determined. The stability of these mixed-ligand complexes changes in the following order: Lys < Ala < His. Reactions between aqueous solutions of H₂PtCl₆ and amino acids produced the following coordination compounds: Pt(C₃H₆NO₂)(C₅H₅N₅)Cl₃ · 2H₂O, or Pt(Ala^?)(Ade)Cl₃ · 2H₂O (I); Pt(C₅H₅N₅)(C₆H₁₄N₂O₂)Cl₄ · 2H₂O, or Pt(Ade)(Lys)Cl₄ · 2H₂O (II); and Pt(C₅H₅N₅)(C₆H₉N₃O₂)Cl₄ · 3H₂O or Pt(Ade)(Hist)Cl₄ · 3H₂O (III). These complexes were characterized by ¹³C NMR, IR, and X-ray photoelectron spectroscopy. Alanine is complexed via both amino and carboxy groups; lysine, via α-amino group exclusively; and histidine, via the amino group and the N3 heterocyclic atom. Adenine in these complexes is monodentate due to the N7 heterocyclic atom. The adenine amino group is apparently H-bonded to a water oxygen atom.     

Water-soluble heteroligand complexes of 2-methyl-4-oxo-4H-pyran-3-olatoneodymium(III) with amino acids

New water-soluble heteroligand complexes of 2-methyl-4-oxo-4H-pyran-3-olatoneodymium(III) with aliphatic amino acids (glycine, N-methylglycine, and alanine) have been prepared. Within the biological “transparency window” (700–900 nm) of their electronic absorption spectra, narrow bands of Nd³⁺ are found: ⁴F_7/2 ← ⁴I_9/2; ⁴F_5/2 ← ⁴I_9/2; ⁴F_3/2 ← ⁴I_9/2 (750, 810, and 880 nm). Such complexes can be used as markers for biological tissues visualization.     

π-Allylpalladium(II) complexes of amino acids

Novel π-allylpalladium(II) complexes with amino acid anions as bidentate chelating ligands were prerpared, characterized and investigated by means of IR, NMR and X-ra diffraction techniques. Single crystal X-ray analysis of (π-2-methylallyl)(glycinato) palladium(II) has been carried out: Cu-K₁ radiation, monoclinic, space group P2₁/c, a = 12.03(1), b = 12.85(1), c = 10.86(1)», β = 103° 50′(10′), Z = *, The only relevant difference between the two independent molecules in the unit cell was found in the conformation of the glycinato moiety which appears twisted in one molecule and essentially planar in the other.     

Hydration of copper(II) amino acids complexes

Hydration of the copper(II) bis‐complexes with glycine, serine, lysine, and aspartic acid was studied by DFT and MD simulation methods. The distances between copper(II) and water molecules in the 1st and 2nd coordination shells, the average number of water molecules and their mean residence times in the hydration shells were calculated. Good agreement was observed between the values obtained and those found by DFT and NMR relaxation methods. Influence of the functional groups of the ligands and the cis–trans isomerism of the complexes on the structural and dynamical parameters of the hydration shells was displayed and explained. Analysis of the MD trajectories reveals the competition for a copper(II) axial position between water molecules or water molecules and the functional chain groups of the ligands and confirms the suggestion on the pentacoordination of copper(II) in such complexes. MD simulations show that only one axial position of Cu(II) is basically occupied at each time step while in average the coordination number more than 5 is observed. © 2017 Wiley Periodicals, Inc.     

Thermal decomposition of potassium,rubidium and caesium fluoroantimonates(III)

The thermal decomposition of crystalline complexes of the types M₂[SbF₅], M[SbF₄], M[Sb₂F₇] and M[Sb₄F₁₃] (where M = K, Rb, Cs) was studied. Crystals were prepared by slight modifications of the methods described in the literature. On the basis of the results of thermal analyses the mechanisms of thermal decomposition were proposed. From thermogravimetric curves kinetic parameters were calculated using the methods of Coats and Redfern and Zsako. A comparison was made of the thermal stabilities in the light of available structural data.     

Ternary mixed-ligand copper(II) complexes with chiral aminophosphonic acids and amino acids

Ternary mixed-ligand complexes of divalent copper, where one ligand is an -aminoalkylphosphonic acid (APA) and the second ligand is L-phenylalanine, L-tyrosine, or L-dihydroxyphenylalanine, are studied by potentiometric titration in aqueous medium at 25°C and =0.1. A maximum in the formation of the ternary complexes is exhibited at pH 7–8. The log K_st for the complexes formed and the statistical parameters characterizing the ternary complexes logK and logX are determined. The effect of substituents on the -carbon atom of the -APA and of hydroxy groups on the phenyl substituent of the -amino acids on the nature of the distribution of the complexes formed is studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2482–2486, November 1989.The authors thank V. P. Solov'ev for helpful discussions.     

Luminescent properties of europium(III) and terbium(III) complexes with para- and ortho-ethoxybenzoic acids

The luminescent properties of europium(III) and terbium(III) complexes with para- and ortho-ethoxybenzoic acids are studied. The excitation energies of the triplet states of ligands are determined, a hypothesis is made about the efficient luminescence of europium(III) and terbium(III) complexes, the geometry of the coordination polyhedron of a europium complex is established, and the luminescence quantum yields of the complexes in solution are determined.     

New cyclopentadienylzirconium(IV) complexes of N-phthaloyl amino acids

Transition Metal Chemistry - Cyclopentadienylzirconium(IV) complexes of N-phthaloyl amino acids of general formulae Cp2Zr(L)nCl2?n (n = 1 or 2) and CpZrCl(L)2 (LH = N-phthaloyl derivatives of...     

Chromium(III) halide and nitrate complexes with amino derivatives of isoxazole

In the present work we have studied the complexes of the ligands 3-amino, 5-methylisoxazole (3-AMI) and 5-amino-3,4-dimethylisoxazole (5-ADI) with the metal salts CrX₃·nH₂O (where X = Cl, Br, I, NO₃; n = 9, 10). The compounds have been characterized on the basis of spectroscopic methods, magnetism and conductivity measurements. We have calculated the ligand field parameters. All the complexes are hexa-coordinate, with exception of Cr(3-AMI)I₃ which should have a distorted tetrahedral stereochemistry. The monomeric complexes are N_ring bonded while the polymeric compounds are bridging bidentate N_ring and O_ring bonded.     

The nonisothermal decomposition kinetics of copper(II) complexes with phthalanilic acids and amino acids

Fifteen new kinds of mixed ligand complexes Cu(x‐P)A [P = 2‐(COO)C₆H₄CONH‐C₆H₄; x = H, 2‐Cl, 2‐CH₃, 2‐OCH₃, 4‐OCH₂CH₃; A = dehydronium Met, Leu, Phen] were synthesized. The thermal decomposition behavior of each complex is studied by TG. Coats‐‐Redfern, MacCallum‐‐Tammer, and Zsako methods are adopted to estimate the values of the apparent activation energy E_a, the activation entropy δS^≠, the reaction order n, and the frequency factor A. The results showed that the reaction order is 2/3 for each of the complex. Studies on the mechanism of the thermal decomposition reactions suggested that these reactions all fit the kinetic equation 1 ? (1 ? α)^1/3 = © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 623–628, 2003     

Synthesis and characterization of uranium (IV) complexes with various amino acids

Complexes of uranium in its IV oxidation state, using cysteine, glycine, serine and aspartic acid as ligands, have been synthesized. Semi-microanalysis of the complexes indicate 1:1 metal to ligand ratio for all the synthesized complexes. Infrared spectra of solid complexes have been employed to establish the groups, coordinated to the metal ion. Effective magnetic moment of the complexes were also estimated.