Rafael Moreno-Esparza

Synthesis and characterization of mixed ligand complexes of copper with nalidixic acid and (NN) donors. Crystal structure of [Cu(Phen)(Nal)-(H2O)]NO3·3H2O

Abstract The synthesis of two new mixed ligand complexes of Cu(II), [Cu(Phen)(Nal)]+ and [Cu(Bipy)-(Nal)]+, is presented (Nal= nalidixate). The results obtained confirm those suggested in a previous paper: the nalidixic acid (I) binds to metal ions by the 3-carboxylate and 4-oxo groups in the solid state. The complex [Cu(Phen)(Nal)(H2O)]NO3·3H2O is triclinic with a = 16.654(3), b = 11.130(2), c = 7.918(2) A, α = 98.53(2), β = 112.12(2), γ = 89.94(2)°, V = 1342.2(8) A3, P I - , Dx = 1.551 g cm−3, Z = 2, F(000) = 650, λ(Mo Kα) = 0.71069 A, μ(Mo Kα) = 9.20 cm−1, 288 K.

Some mixed-ligand complexes of copper(II) with drugs of the quinolone family and (NN) donors. Crystal structure of [Cu(phen)(Cnx)(H2O)]NO3 · H2O

Abstract The synthesis of eight new mixed-ligand complexes of Cu(II) of the type [Cu(NN)(Antb)]X is reported, where NN is 1,10-phenanthroline (phen) or 2,2′-bipyridine (bipy), Antb is the anion of cinoxacin (Cnx) or oxolinic acid (Oxo), both drugs of the quinolone family. The crystal structure of [Cu(phen)(Cnx)(H 2 O)NO 3 · H 2 O is presented and discussed. The results here reported together with those previously reported for the complex [Cu(phen)(Nal)(H 2 O)]NO 3 · 3H 2 O and preliminary crystal data for the complex [Cu(bipy)(Oxo)]NO 3 · H 2 O, suggest that all the quinolone type drugs behave in a similar way as ligands under equivalent conditions.

The influence of coffee with milk and tea with milk on the bioavailability of tetracycline

The effect of milk added to coffee or black tea on the bioavailability of tetracycline was evaluated in 12 healthy volunteers according to a crossover design. Results showed that even a small volume of milk containing extremely small amounts of calcium severely impair the absorption of the drug, so that the presence of this metal ion should be carefully controlled in order to avoid decreasing the available tetracycline.

CU-O STRETCHING FREQUENCY CORRELATION WITH PHENANTHROLINE PKA VALUES IN MIXED COPPER COMPLEXES

Abstract A study of Cu–O vibration frequencies in 32 isostructural mixed copper complexes containing eight differently substituted phenanthrolines and four different oxygen donor bidentate ligands, is presented. In all cases linear correlation was found between phenanthroline p K a values and the studied vibration frequencies, suggesting that an increase in phenanthroline basicity weakens Cu–O bonds in this type of compound.

Stability constants of copper(II) mixed complexes with some 4-quinolone antibiotics and (N-N) donors

Studies of complexation equilibria of the antibiotic anions nalidixate and cinoxacinate with [Cu(phen)]2+ and [Cu(bipy)]2+ are reported. These studies indicate that the stability of this type of complex is strongly related to the metal environment. A correlation between the stability constants, determined here, with the sigma donation character of the ligand is proposed. This study shows that the stability constant for the reaction between the quinolones and the moiety [Cu(N-N)]2+ is dependent on the coordinate diamine to the metal ion. This is in agreement with previous studies where other physical properties as their electronic absorption spectra in the visible region, display similar behavior. These results suggest that inside the living cells, a possible interaction with some metal ion will be strongly controlled by the type of ligand bound to the cation.

Spin Crossover Behavior in a Series of Iron(III) Alkoxide Complexes

The synthesis, crystal structures, magnetic behavior, and electron paramagnetic resonance studies of five new Fe(III) spin crossover (SCO) complexes are reported. The [Fe(III)N5O] coordination core is constituted of the pentadentate ligand bztpen (N5) and a series of alkoxide anions (ethoxide, propoxide, n-butoxide, isobutoxide, and ethylene glycoxide). The methoxide derivative previously reported by us is also reinvestigated. The six complexes crystallize in the orthorhombic Pbca space group and show similar molecular structures and crystal packing. The coordination octahedron is strongly distorted in both the high- and low-temperature structures. The structural changes upon spin conversion are consistent with those previously observed for [Fe(III)N4O2] SCO complexes of the Schiff base type, except for the Fe-O(alkoxide) bond distance, which shortens significantly in the high-spin state. Application of the Slichter-Drickamer thermodynamic model to the experimental SCO curves afforded reasonably good simulations with typical enthalpy and entropy variations ranging in the intervals ΔH = 6-13 kJ mol(-1) and ΔS = 40-50 J mol(-1) K(-1), respectively. The estimated values of the cooperativity parameter Γ, found in the interval 0-2.2 kJ mol(-1), were consistent with the nature of the SCO. Electron paramagnetic resonance spectroscopy confirmed the transformation between the high-spin and low-spin states, characterized by signals at g ≈ 4.47 and 2.10, respectively. Electrochemical analysis demonstrated the instability of the Fe(II) alkoxide derivatives in solution.

Mercaptoethanesulfonic acid studies with nickel(II) complexes of tetra- and hexadentate ligands containing pyridyl groups: synthesis, structure, spectra and redox behavior

Abstract Nickel(II)complexes of N,N,N′N′-tetrakis(2-pyridylmethyl)ethylenediamine (L1), N,N,N′N′-tetrakis(2-pyridylmethyl)-1,2-diaminopropane (L2), N,N,N′N′-tetrakis(2-pyridylmethyl)-1,3-diaminopropane (L3), N,N′-bis(2-pyridylmethyl)ethylenediamine (L4), N,N′-bis(2-pyridylmethyl)-1,2-diaminopropane (L5) and N,N′-bis(2-pyridylmethyl)-1,3-diaminopropane (L6) were prepared and their spectroscopic and redox behaviors studied. The distorted octahedral geometry was determined for [NiL2](ClO4)2 by using X-ray crystallography. The electronic spectral bands (3A2g→3T2g and 3A2g→1Eg transitions) of NiN6 and NiN4O2 were analyzed; it shows that the former complexes possess well-resolved bands compared to the latter compounds. In addition, the ligand field parameter Dq found for NiN4O2 complexes was much lower than that of NiN6 compounds; thereby, a more positive redox potential was detected for NiN4O2 complexes in electrochemistry over the NiN6 compounds. Further, the coordination studies of 2-mercaptoethanesulfonic acid as a simulator of coenzyme M reductase (CoM) with NiN4 or NiN6 chromophores were discussed.

Revisiting 23-iodospirostanes. New facts and full characterization.

In addition to a previous report, the reaction of tigogenin acetate with ICl in refluxing CHCl(3) produced the hitherto unknown 23R-iodotigogenin acetate, bearing an axial iodine atom at C-23 and its already reported 23S-epimer. The same treatment of sarsasapogenin acetate led to a single diasteromer characterized as 23S-iodosarsasapogenin acetate. A full characterization of the obtained compound including (1)H, (13)C NMR, MS and X-ray diffraction is provided.

Stability of ternary copper and nickel complexes with 1,10-phenanthroline

Abstract This work presents a comparative analysis of the behavior of copper(II) and nickel (II) towards the formation of mixed-ligand complexes with 1,10-phenanthroline as primary ligand. Secondary ligands were acetylacetonate, salicylaldehydate (OO donors), glycinate, or tyrosinate (ON donors). The formation of hexacoordinate complexes was observed in the case of nickel. Stability enhancement compared to statistical expectations is found for complexes where the secondary ligand is an OO donor and for tyrosinate. These observations are explained in terms of a hardness increase in the species M(phen)2+, as compared to M2+, due to the well-known π-acceptor behavior of aromatic imines, which makes the first species more attractive to harder ligands as oxygen donors. In the case of tyrosinate, increase in stability is attributed to a hydrophobic interaction between the phenolic group and 1,10-phenanthroline.

Template reaction of [Ni(ben)3](ClO4)2 with acetone. Crystal structure of 1,11-bis-benzyl-5,7,7-trimethyl-1,4,8,11-tetra-aza-undeca-4-ene nickel(II) perchlorate

Abstract The template synthesis of a new open-chain tetra-aza ligand derived from N-benzylethylenediamine is reported. X-ray structural analysis of the title compound has been determined. 13C CP-MAS NMR for the [Ni(benacet)](ClO4)2 complex was made and assignment of the signals was carried out by the use of the open gate decoupling technique and by comparison with the Ni(II) and Zn(II) complexes of the trans-[14]diene ligand as well as with the perchlorate salt of the free macrocycle. Based on the type of isolated compound, a hypothesis of the possible mechanism of reaction that explains the formation of the mesityl moiety during the template reaction is discussed. This hypothesis could also be used to explain how in the original reaction made by Curtis, a mixture of cis- and trans-isomers are formed.