X-Ray Studies On Crystalline Complexes Involving Amino-Acids And Peptides .11. Peptide Aggregation And Water-Structure In The Crystals Of A Hydrated 1-1 Complex Between L-Histidyl-L-Serine And Glycyl-L-Glutamic Acid

The hexahydrate of a 1:1 complex between L-histidyl-L-serine and glycyl-L-glutamic acid crystallizes in space group P1 with a = 4.706(1), b= 8.578(2), c= 16.521(3) ÅA; α= 85.9(1), β= 89.7(1)°, = 77.4(1). The crystal structure, solved by direct methods, has been refined to an R value of 0.046 for 2150 observed reflections. The two peptide molecules in the structure have somewhat extended conformations. The unlike molecules aggregate into separate alternating layers. Each layer is stabilized by hydrogen bonded head-to-tail sequences as well as sequences of hydrogen bonds involving peptide groups. The arrangement of molecules in each layer is similar to one of the plausible idealized arrangements of L-alanyl-L-alanine worked out from simple geometrical considerations. Adjacent layers in the structure are held together by interactions involving side chains as well as water molecules. The water structure observed in the complex provides a good model, at atomic resolution, for that in protein crystals. An interesting feature of the crystal structure is the existence of two water channels in the interfaces between adjacent peptide layers.

Iron(II, III) complexes with N, N'-DI(2-)Pyridyl Thiourea. Moumlssbauer and other spectroscopic studies

Several iron(II, III) complexes of N, N'-di(2-)pyridyl thiourea have been synthesized. The preparation of the complexes from iron(III) salts proceeds through a reduction of iron(III) to iron(II) followed by a subsequent reoxidation. The Moumlssbauer, electronic and infrared spectra of these complexes have been measured. The results are concordant with the coordination of pyridine nitrogens and thiocarbonyl sulfur yielding polymeric complexes. A variable temperature NMR study of the free ligand shows that two conformation are accessible for it in solution at subambient temperatures.

Infrared spectral assignments of methyl and ethyl xanthato complexes of nickel(II)

Assignments of the infrared frequencies of methyl and ethyl xanthato complexes of nickel(II) have been made with the aid of normal coordinate analyses. The assignments are discussed in relation to those in related molecules.

Synthesis and Characterisation of Metal Hydrazine Nitrate, Azide and Perchlorate Complexes

Metal hydrazine nitrate complexes of the type M(N2H4)Nn (NO3)2 where M = Mg, n = 2; M = Mn, Fe, Co, Ni, Zn and Cd and n = 3; metal dihydrazine azide complexes of the type M(N2H4)2 (N3)2 where M = Mg, Co, Ni and Zn; and Mg(N2H4)2 (C1O4)2 have been prepared by dissolving the respective metal powders in the solution of corresponding ammonium salts (NO3, N3 and C1O4) in hydrazine hydrate. These hydrazine complexes were also prepared by the conventional method involving the addition of alcoholic hydrazine hydrate to the aqueous solution of metal salts. The hydrazine complexes have been characterised by chemical analysis, infrared spectra and differential thermal analysis (DTA). Impact sensitivities of hydrazine complexes were determined by the drop weight method. The reactivity of these hydrazine complexes does not change with the method of preparation.

X-ray studies on crystalline complexes involving amino acids. IV. The structure of L-arginine L-ascorbate

L-Arginine ascorbate, C6HIsN40+.C6H706, a 1"1 crystalline complex between the amino acid arginineand the vitamin ascorbic acid, crystallizes in the monoclinic space group P21 with two formula units in a cell of dimensions a = 5.060 (8), b = 9.977 (9), c = 15.330 (13) A, fl = 97.5 (2) °. The structure was solved by the symbolic addition procedure and refined to an R of 0.067 for 1501 photographically observed reflec- tions. The conformation of the arginine molecule in the structure is different from any observed so far. The present structure provides the first description of the ascorbate anion unaffected by the geometrical constraints and disturbances imposed by the requirements of metal coordination. The lactone group and the deprotonated enediol group in the anion are planar and the side chain assumes a conformation which appears to be sterically the most favourable. In the crystals, the arginine molecules and the ascorbate anions aggregate separately into alternating layers. The molecules in the arginine layer are held together by interactions involving a-amino and ~t-carboxylate groups, a situation analogous to that found in proteins. The two layers of unlike molecules are interconnected primarily through the interactions of the side-chain guanidyl group of arginine with the ascorbate ion. These involve a specific ion-pair interaction accompanied by two convergent hydrogen bonds and another pair of nearly parallel hydrogen bonds.

Studies on crystalline complexes involving amino acids. V. The structure of L-serine-L-ascorbic acid

L-Serine-L-ascorbic acid, C3HTNOa. C6HsO6, a 1:1 complex between the amino acid serine and the vitamin ascorbic acid, crystallizes in the orthorhombic space group P2~2~2~ with four formula units in a cell of dimensions a = 5.335(3), b = 8.769(2), c = 25.782 (5) A. The structure was solved by direct methods and refined by full-matrix least squares to an R of 0.036 for 951 observed reflections. Both molecules are neutral in the structure. The conformation of the serine molecule is different from that observed in the crystal structures of L-serine, DL-serine and L-serine monohydrate. The enediol group in the ascorbic acid molecule is planar, whereas significant departures from planarity are observed in the lactone group. The conformation of this molecule is similar to that observed in arginine ascorbate. The unlike molecules aggregate into separate columns in the crystal structure. The columns are held together by hydrogen bonds. Among these, a pair of hydrogen bonds between the enediol group of ascorbic acid and the carboxylate group of serine provides a possible model for a specific interaction between ascorbic acid and a carboxylate ion.

Complexes of rare earth perchlorates with di-2-pyridyl ketone

Abstract is not availabe.

Mechanism of vapour phase oxidation of anthracene over cobalt molybdate catalyst

Vapour phase oxidation of anthracene over cobalt molybdate catalyst was investigated in an isothermal flow reactor in the temperature range of 280—340°C. Fifteen different models based on redox, Langmuir—Hinshelwood and Rideal mechanisms were tested in order to elucidate the mechanism of the above reaction. These models were compared on the basis of three criteria and were finally discriminated employing the non-intrinsic parameter method. Two-stage redox mechanism was found to explain the data satisfactorily.

Polymer supported metal complexes as catalysts for oxidation of thiosalts by molecular oxygen IV. Quaternised poly(4-vinyl pyridine) complexes with Cu2+ as template

Copper(II) complexes of quaternised poly(4-vinylpyridine) (PVP) of different degrees of quaternisation and copper content have been prepared by crosslinking the polymer with 1,2-dibromoethane in the presence of Cu2+ ion as template. The stability constant of the PVP---Cu(II) complexes is found to increase with the degree of crosslinking quaternisation of the resin, but the rate at which Cu2+ is adsorbed by the resin decreases. An optimum combination of both stability and rate can be achieved with a moderate degree (31%) of crosslinking. A kinetic study reveals that quaternisation increases significantly the catalytic activity of the complex for the oxidation of S2O2−3 by O2 compared with PVP----Cu(II) without quaternisation, but it deactivates the complex for the oxidation of both S3O2−6 and S4O2−6. The batch reactor oxidation kinetics at pH 2.16, where the rate is observed to be maximum, is well explained by the Langmuir—Hinshelwood model assuming the coordination of both O2 and thioanion to Cu(II) as a precursor to the oxidation reaction.

Mechanism of vapour phase oxidation of anthracene over cobalt molybdate catalyst

Vapour phase oxidation of anthracene over cobalt molybdate catalyst was investigated in an isothermal flow reactor in the temperature range of 280—340°C. Fifteen different models based on redox, Langmuir—Hinshelwood and Rideal mechanisms were tested in order to elucidate the mechanism of the above reaction. These models were compared on the basis of three criteria and were finally discriminated employing the non-intrinsic parameter method. Two-stage redox mechanism was found to explain the data satisfactorily.

Mononitrosalted and phenylamido substituted chelate linkage isomers of quadridentate Schiff base copper(II) complexes

The nitrosation of monophenylamido substututed quadridentate Schiff base complexes of copper(II) are observed to adopt N-bonded isonitroso coordination whereas the phenylisocyanation of the corresponding mononitrosated quadridentate complexes are found to prefer O-bonded isonitroso coordination.

Lanthanide perchiorate complexes of 4-cyano puridine N-oxide, 4-chloro 2-picoline-B-Oxide and 4_dimethyl amino-2-Picoline N Oxide

Complexes of lanthanide perchlorates with 4-cyano pyridine-1-oxide, 4-chloro 2-picoline-1-oxide and 4-dimethyl amino 2-picoline-1-oxide have been isolated for the first time and characterized by analysis, conductance, infrared, NMR and electronic spectra.

2-Thioacetamido thiazole as an ambidentate ligand. Complexes of Zn(II), Cd(II), Hg(II) and Cu(I)

Metal complexes of thiazoles have been studied in recent years[I-3] because of their biochemical importance[4,5]. However, data on metal complexes of thiazole derivatives containing another coordinating function are limited[2]. We have synthesized and examined the donor characteristics of a new ligand, 2-thioacetamide thiazole (TATZ)(I) towards chlorides and bromides of Zn(II), Cd(II), Hg(II) and Cu(I). The presence of four potential donor atoms and extensive charge delocalization should render TATZ a versatile ligand.

Metal complexes of thiophene 2-thiocarboxamide. Proton and 13C NMR, IR and electronic spectral studies

The complexes of thiophene 2-thiocarboxamide (TTCA) with some metal chlorides and bromides [M = Ni(II), Zn(II), Cd(II), Hg(II) and Cu(I)] are described. Elemental analyses, magnetic susceptibilities and conductance studies, electronic, IR, proton and 13C magnetic resonance spectra are reported. The results suggest exclusive coordination of TTCA through the thiocarbonyl sulfur. The influence of the thiophene ring on the donor properties of the thioamide are discussed.

1-D hydrogen-bonded organization of hexanuclear {3d-4f-5d} complexes: evidence for slow relaxation of the magnetization for [{LMe2Ni(H2O)Ln(H2O)4.5}2{W(CN)8}2] with Ln = Tb and Dy

Heterometallic {3d-4f-5d} aggregates with formula [{LMe2Ni(H2O)Ln(H2O)4.5}2{W(CN)8}2]·15H2O, (LMe2 stands for N,N-2,2-dimethylpropylenedi(3-methoxysalicylideneiminato) Schiff-base ligand) with Ln = Gd, Tb, Dy, have been obtained by reacting bimetallic [LMe2Ni(H2O)2Ln(NO3)3] and Cs3{W(CN)8} in H2O. The hexanuclear complexes are organized in 1-D arrays by means of hydrogen bonds established between the solvent molecules coordinated to Ln and the CN ligands of an octacyanometallate moiety. The X-ray structure was solved for the Tb derivative. Magnetic behavior indicates ferromagnetic {W–Ni} and {Ni–Ln} interactions (JNiW = 18.5 cm-1, JNiGd = 1.85 cm-1) as well as ferromagnetic intermolecular interactions mediated by the H-bonds. Dynamic magnetic susceptibility studies reveal slow magnetic relaxation processes for the Tb and Dy derivatives, suggesting SMM type behavior for these compounds.