Synthesis,Spectroscopic and EPR Results and Crystal Structure of Copper(II) Formato Derivatives with Pyrazine and Dimethylpyrazines

The complexes of copper formato with pyrazine and dimethylpyrazines: Cu(HCOO)₂(pyrz) ( 1 ), Cu₂(HCOO)₄(pyrz) ( 2 ), Cu₂(HCOO)₄(2,3‐Me₂pyrz) ( 3 ), Cu₂(HCOO)₄(2,5‐Me₂pyrz) ( 4 ), and Cu₂(HCOO)₄(2,6‐Me₂pyrz)₂ ( 5 ) have been synthesized and characterized by chemical analysis and IR and electronic spectro scopies. The three‐dimensional structure of compound 1 consists of –Cu–pyrz–Cu–pyrz– chains joined by bridging formate groups coordinated, in configuration syn‐anti, to two copper atoms. The coordination around the copper atom is orthorhombic with two Cu–O distances of 2.374(1) Å, two Cu–O of 1.952 Å and two Cu–N of 2.080 Å. Compound 5 is formed by molecular dimers with the [Cu₂(μ‐HCOO)₄] unit, two copper atoms and four syn‐syn fomate groups, and two ligands coordinated to the copper atoms in the axial positions. In compounds 2 and 3 chains of [Cu₂(μ‐HCOO)₄] dimers with pyrz or 2,3‐Me₂pyrz as bridging ligands are formed. The EPR signal of 1 is orthorhombic (g = 2.23, 2.20 and 2.06). In the EPR spectra of 2 – 5 compounds the triplet (S = 1) signals are observed. The g_?, g_∥ and D values are been calculated.     

Determination of oxytetracycline in urine and human serum by differential pulse polarography

Summary A differential pulse polarographic method for the determination of oxytetracycline in urine and human serum in acid media (HClO₄ of pH 2) is proposed. The effects of the amount of sample taken and the concentration of HClO₄ present were investigated. The detection limit was 5.5×10^–6 mol/l. The standard deviation of the determination of 5.5×10^–5 mol/l of oxytetracycline in 2 ml of urine was 1.7×10^–6 mol/l and that of the determination of 5.5×10^–5 mol/l of oxytetracycline in 2 ml of human serum was 1.9×10^–6 mol/l.

---

Bestimmung von Oxytetracyclin in Urin und Humanserum durch Differential-Pulspolarography

     

Determination of Clobazam, Clorazepate, Flurazepam and Flunitrazepam in pharmaceutical preparations

The separation of four benzodiazepines (Flurazepam, Flunitrazepam, Clobazam and Clorazepate) in pharmaceutical products by micellar electrokinetic chromatography (MEKC) is described. It was carried out at 25 degrees C and 25 kV by using a 57 cm (50 cm to the detector)x75 mum i.d. fused silica capillary and a 15 mM borate buffer (pH 9.2), 35 mM sodium dodecylsulfate (SDS) and 35 mM sodium deoxycholate water solution. Under these conditions, the analysis was performed in 8 min with acceptable limits of quantification (between 3 and 5 mg l(-1)). The method has been applied for quantifying these benzodiazepines in serum and different commercial formulations with recoveries near 100%.     

Molecular recognition of biotin, barbital and tolbutamide with new synthetic receptors

We have measured, by means of NMR titrations, the binding constants for the complexes between hosts N,N′-bis(6-methylpyridin-2-yl)-1,3-benzenedicarboxamide (7) and 4-chloro-N,N′-bis(6-methylpyridin-2-yl)-2,6-pyridinedicarboxamide (8, hydrated) with biotin methyl ester (1), N,N′-dimethylurea (2), 2-imidazolidone (3), N,N′-trimethylenurea (4), barbital (5) and tolbutamide (6) as guests. Molecular Mechanics calculations (Monte Carlo Conformational Search, AMBER and OPLS force fields, MacroModel v.8.1) on the complexes formed between the foregoing guests and hosts 7 and 8, comparatively with 4-oxo-N,N′-bis(6-methylpyridin-2-yl)-1,4-dihydro-2,6-pyridinedicarboxamide (9a) have been carried out in order to determine the correlation between experimental and theoretical results and to understand the behaviour of the designed new hosts. Finally we have performed single point DFT [B3LYP/6-31G(d,p)] calculations on the optimised Molecular Mechanics geometries for the complexes between hosts 7-9 and water.     

Monocarbonyl cationic rhodium(I) complexes

Summary The preparations and characterisation of cationic complexes of the type [Rh(CO)(MeCN)(PR₃)₂]ClO₄, [Rh(CO)L(PR₃)₂]ClO₄ (L=py or 2-MeOpy), [Rh(CO)(L-L)(PR₃)₂]ClO₄ (L-L = bipy or phen) and [Rh(CO)(PR₃)₃]ClO₄ with PR₃ = P(p-YC₆H₄)₃ (Y=Cl, F, Me or MeO) are described.     

The Counterion Effect on the Assembly of Coordination Networks of Cationic (η3‐Allyl)palladium Complexes Containing 3,5‐Dimethyl‐4‐nitro‐1H‐pyrazole

Two new (η³‐allyl)palladium complexes containing the ligand 3,5‐dimethyl‐4‐nitro‐1H‐pyrazole (Hdmnpz) were synthesized and characterized as [Pd(η³‐C₃H₅)(Hdmnpz)₂]BF₄ ( 1 ) and [Pd(η³‐C₃H₅)(Hdmnpz)₂]NO₃ ( 2 ). The structures of these compounds were determined by single‐crystal X‐ray diffraction to evaluate the intermolecular assembly. Each complex exhibits similar coordination behavior consistent with cationic entities comprised of two pyrazole ligands coordinated with the [Pd(η³‐C₃H₅)]⁺ fragment in an almost square‐planar coordination geometry. In 1 , the cationic entities are propagated through strong intermolecular H‐bonds formed between the pyrazole NH groups and BF ions in one‐dimensional polymer chains along the a axis. These chains are extended into two‐dimensional sheet networks via bifurcated H‐bonds. New intermolecular interactions established between NO₂ and Me substituents at the pyrazole ligand of neighboring sheets give rise to a three‐dimensional network. By contrast, compound 2 presents molecular cyclic dimers formed through N? H???O H‐bonds between two NO counterions and the pyrazole NH groups of two cationic entities. The dimers are also connected to each other through C? H???O H‐bonds between the remaining O‐atom of each NO ion and the allyl CH₂ H‐atom. Those interactions expand in a layer which lies parallel to the face (101).     

The Structure of a Non-Symmetric Disordered Tetramer: A Crystallographic and Solid State Multinuclear NMR Study of the Properties of 3(5)-Ethyl-5(3)-Phenyl-1H-Pyrazole

The X-ray structure and the solid-state NMR measurements, mainly ¹⁵N CPMAS of the labelled compound, allow to determine the static and dynamic properties of 3(5)-ethyl-5(3)-phenyl-1H-pyrazole. The compound is a tetramer formed by three 5-ethyl-3-phenyl-1H-pyrazole and one 3-ethyl-5-phenyl-1H-pyrazole tautomers in dynamic equilibrium with the complementary situation.     

Lipid-Based Nanostructures for the Delivery of Natural Antimicrobials

Encapsulation can be a suitable strategy to protect natural antimicrobial substances against some harsh conditions of processing and storage and to provide efficient formulations for antimicrobial delivery. Lipid-based nanostructures, including liposomes, solid lipid nanoparticles (SLNs), and nanostructured lipid nanocarriers (NLCs), are valuable systems for the delivery and controlled release of natural antimicrobial substances. These nanostructures have been used as carriers for bacteriocins and other antimicrobial peptides, antimicrobial enzymes, essential oils, and antimicrobial phytochemicals. Most studies are conducted with liposomes, although the potential of SLNs and NLCs as antimicrobial nanocarriers is not yet fully established. Some studies reveal that lipid-based formulations can be used for co-encapsulation of natural antimicrobials, improving their potential to control microbial pathogens.     

Imaging the Magnetic Reversal of Isolated and Organized Molecular‐Based Nanoparticles using Magnetic Force Microscopy

In the race towards miniaturization in nanoelectronics, magnetic nanoparticles (MNPs) have emerged as potential candidates for their integration in ultrahigh‐density recording media. Molecular‐based materials open the possibility to design new tailor‐made MNPs with variable composition and sizes, which benefit from the intrinsic properties of these materials. Before their implementation in real devices is reached, a precise organization on surfaces and a reliable characterization and manipulation of their individual magnetic behavior are required. In this paper, it is demonstrated how molecular‐based MNPs are accurately organized on surfaces and how the magnetic properties of the individual MNPs are detected and tuned by means of low‐temperature magnetic force microscopy (LT‐MFM) with variable magnetic field. The magnetization reversal on isolated and organized MNPs is investigated; in addition, the temperature dependence of their magnetic response is evaluated.     

Determination of trace amounts of cobalt in water by solid-phase spectrophotometry after preconcentration on a nitroso R salt chelating resin

A sensitive method for the determination of microamounts of cobalt by ion-exchanger spectrophotometry has been developed. The chromogenic agent, Nitroso-R-Salt (NRS), was loaded on an anionic-exchange resin (Amberlite CG-400). The absorbance of the NRS-cobalt complex on the chelating resin was measured at 508 nm. The best conditions for the preconcentration of cobalt on the resin before the spectrophotometric determination were a pH value of 6, temperature of 80 °C, and heating times of 45 or 90 min for 50 and 400 ml of sample, respectively. The detection limits were 27 ng/ml (50-ml samples) and 1.8 ng/ml (400-ml samples). Interference by other metals was investigated. The method is useful for determination of cobalt in natural waters.