M.P. Sánchez-Sánchez

Transition metal complexes with monodeprotonated isoorotic and 2-thioisoorotic acids: Crystal structure, spectral and magnetic study, and antimicrobial activity

Abstract The reaction, in ethanol or water medium, of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), and Pt(II) ions with isoorotic and 2-thioisoorotic acids (H 3 L) has allowed the isolation of complexes with the general formula M II (H 2 L) 2 ·2H 2 O. These were characterized by means of elemental analysis, spectral techniques (UV-Vis-NIR, IR, EPR, 13 C and 1 H NMR), magnetic moments, and conductivity measurements. The molar conductivities in dimethylsulphoxide indicate the non-ionic nature of isolated compounds. The most common coordination mode of uracil monoanions seems to be a O4-OCO bidentate scheme which leads to a six-membered chelate ring. Complexes of first row transition ions display an octahedral structure, whereas for Pd(II) and Pt(II) compounds a square-planar structure is suggested. The MO 6 octahedral structure has been corroborated from the single crystal x-ray study of bis-isoorotato-diaquazinc(II). This compound is monoclinic, space group P2 1 /c, with a = 5.067(5) A, b = 15.072(4) A, c = 11.239(8) A, β = 125.80(9)°, V = 696(1) A 3 , and Z = 2. The structure was solved by means of the heavy atom method from the zinc special position. Full matrix refinements based on F o were performed to R = 0.060 for 1884 data. The structure consists of discrete [Zn(H 2 CU) 2 (H 2 O) 2 ] units in which the Zn(II) ion is octahedrally MO 6 coordinated by two bidentate O4-OCO isoorotato ligands (MO, 2.033 and 2.039 A) and two water molecules occupying the axial positions (MO w , 2.170 A). Likewise, a previous study of biological activity of these complexes against several bacteria and yeasts was carried out. In general, complexes with the 2-thioisoorotato ligand possess greater antimicrobial activity than those with the isoorotate ligand, specially in the case of cobalt(II) complexes.

Thermal studies on purine complexes. III. Palladium complexes of xanthine and some xanthine derivatives

Abstract Some complexes |PdL 2 Cl 2 | (where L = xanthine, theophylline, theobromine, 3,8-dimethylxanthine, caffeine and 1,3,8-trimethylxanthine) have been prepared in acid medium. Their structure has been established from IR and 1 H-NMR data. The thermal behaviour of these complexes has been studied by TG, DTG and DSC techniques. Heats of dehalogenation have been calculated from the DSC curves.

Stability and thermodynamic parameters of thiopyrimidines, 2-thioxanthine and their complexes with Zn(II) and Cd(II)

Abstract The thermodynamic protonation constants of 4-amino-1,6-dihydro-2-methylthio-5-nitroso-6-oxo-pyrimidine (MTH), 4-amino-5-nitroso-6-oxo-1,2,3,6,-tetrahydro-2-thiopyrimidine (TANH) and 2-thioxanthine (TXH) in aqueous media at 25, 30, 40 and 50 ± 0.1°C, have been determined potentiometrically by Bjerrum and Robinsons methods. The ionic strength was maintained constant by using 0.1 M NaNO3 as the supporting electrolyte. The stability constants and thermodynamic functions for Zn(II) and Cd(II) complexes of MTH and TXH, at different ionic strengths and temperatures, have been calculated.

Effect of ionic strength and temperature on ionization constants and stability constants of 4-amino-1,6-dihydro-2-methylthio-5-nitroso-6-oxo-pyrimidine and its complexes with Fe(II), Co(II), Ni(II) and Cu(II)

Abstract The influence of ionic strength and temperature on the ionization constants of 4-amino-1,6-dihydro-2-methylthio-5-nitroso-6-oxo-pyrimidine (MTH) has been determined. Stability constants for Fe(II), Co(II), Ni(II) and Cu(II) complexes of MTH at different ionic strengths and temperatures have also been calculated.

Synthesis, characterization, and crystal structure of 1,3,7,9-tetramethylpyrido-[2,3-d∶6,5-d′]-dipyrimidine-2,4,6,8-tetrone

A new and easy method for the preparation of 1,3,7,9-tetramethylpyrido-[2,3-d∶6,5-d′]-dipyrimidine-2,4,6,8-tetrone is described. The structure of this compound has been solved by means of X-ray diffraction methods. The chemical characterization by spectral (mass, ultraviolet, infrared, and proton nuclear magnetic resonance) and thermal (thermogravimetry and differential scanning calorimetry) method is also reported. The compound is monoclinic, space groupP21/c,a=12.720(5),b=13.688(7),c=8.079(2) Å, β=107.06(4)°,Z=4. The structure consists of discrete tricyclic molecules, stacking playing an important role in crystal packing.

Thermal analysis applied to the study of metal complexes: thermal behaviour of 6-amino-2-thiouracil and its complexes with several transition metal ions

Abstract The thermal decomposition processes of 6-amino-2-thiouracil and its Co(II), Ni(II), Cu(I), Ag(I), Zn(II), Cd(II) and Hg(II) complexes have been studied by TG and DSC techniques. Heats of dehydration have been calculated from the DSC curves. Infrared spectroscopy applied to some of these complexes heated in air has elucidated the decomposition steps and the nature of the intermediate products. The pyrolysis of these compounds ends between 600 and 800°C with different products as final residues.

Thermal studies on purine complexes: XVI. Thermal behaviour of some metal complexes of 6-thioguanine

Some metal-6-thioguanine complexes have been prepared and studied in aqueous solution by potentiometric methods. In addition to this, eight new solid metal complexes of 6-thioguanine have been prepared and characterized on the basis of elemental analysis and IR spectroscopy. The thermal behaviour of these compounds has been studied using TG and DSC techniques.

Thermal studies on purine complexes. II. Thermal behaviour of some metal complexes of theophylline

Abstract The thermal behaviour of the complexes of theophylline with Co(II), Cu(II), Ag(I), Zn(II) and Cd(II) was studied by thermogravimetry (TG), differential scanning calorimetry (DSC) and IR spectroscopy. The complexes decompose in three steps, dehydration, deammination and decomposition of the anhydrous complexes to metal or metal oxide.

Thermal behaviour of metal-xanthosine complexes

Abstract Several complexes of xanthosine, 9-β-D-ribofuranosylxanthine (Xao) with 3d metal ions have been prepared. The new complexes appear to be generally monomeric, involving terminal N3-bonded Xao ligands. The thermal behaviour of these complexes has been studied by TG, DTG and DSC techniques.

Thermal studies on purine complexes: XI. Thermal behaviour of 2-thioxanthine, its chlorohydrate and some thioxanthine complexes of Ag(I), Cd(II), Hg(II) and Hg(I)

Abstract The chlorohydrate of 2-thioxanthine has been prepared in an acid medium, as well as some Ag(I), Cd(II), Hg(II) and Hg(I) 2-thioxanthine complexes. These compounds have been characterized by spectroscopic techniques and thermal analysis. The thermal behaviour of 2-thioxanthine (TXH), its chlorohydrate (TXH 2 Cl) and the above complexes has been studied by TG, DTG and DSC techniques. Dehalogenation enthalpies have been calculated.