Norbert Buzás

Unusual coordination behavior of D-fructose towards dimethyltin(IV): metal-promoted deprotonation of alcoholic OH groups in aqueous solutions of low pH

Abstract To study the effect of the conformation of sugar hydroxy groups on metal complexation processes, complex formation of eight saccharides (D-fructose, L-sorbose, L-arabinose, D-arabinose, D-glucose, D-sorbitol, 2-deoxy-D-glucose and D-saccharose) with dimethyltin(IV) cations was investigated in aqueous solution by potentiometric equilibrium measurements, 13 C NMR, polarimetric and Mossbauer spectroscopic methods. The experimental results proved that deprotonation of D-fructose and L-sorbose is caused by the coordination of dimethyltin(IV) in the unusual low pH interval 4–6 in contrast to the other saccharides deprotonated in analogous way at pH > 8. Increasing the pH of the solution resulted in the formation of further complexes. Stability and composition of the species was determined by potentiometric studies. 13 C NMR measurements led to the assignment of the sugar OH groups participating in the processes. Mossbauer investigations in the quick-frozen solutions permitted the determination of the stereochemistry of tin(IV) in the complexes.

Equilibrium and spectroscopic studies of diethyltin(IV) complexes formed with carbohydrate derivatives of thiazolidine-4-carboxylic acid

Abstract Coordination of six 2-substituted thiazolidine-4-carboxylic acid derivatives by the diethyltin(IV) cation was studied in aqueous solutions. The formation constants of the complexes MLH, ML and MLOH and of the hydrolysis products of diethyltin(IV) ion were determined by potentiometric equilibrium measurements. The ligands are effective complexing agents with amino acid type coordination in the pH> 5 range, where the mixed hydroxo species MLOH predominates. The polyhydroxyalkyl substituents on the ligand do not show direct coordination to tin(IV), they exert only sterical effects on the process. The solid compounds with composition MLOH show, according to Mossbauer investigations based on the partial quadrupole splitting concept and according to IR spectroscopic studies, trigonal bipyramidal arrangement of the donor atoms around the tin(IV) ion with hydroxide, carboxylate and amine coordination.

COORDINATION PROPERTIES OF L-CYSTEINE AND ITS DERIVATIVES TOWARDS DIETETHYLTIN(IV) IN AQUEOUS SOLUTION

Complex formation equilibria of L-cysteine (LH3), S-methyl-L-cysteine (LH2) and N-acetyl-Lcysteine (LH2) with diethyltin(IV) were studied in aqueous solution (I = 0.1 Μ NaC104). The formation constants of the complexes were determined by Potentiometrie equilibrium measurements. Besides the carboxil-oxygen, thiol-sulphur of L-cysteine and of its N-acetyl derivative were shown to be deprotonated and coordinated to the metal in the acidic region. Due to the stabilizing effect of additional thioether coordination in case of S-methyl-L-cysteine the formation of an MLH complex was detected. In case of Lcysteine and its S-methyl derivative, amino nitrogen served as third donor atom at higher pH. N-acetyl-Lcysteine participated in the complex formation only by two donor atoms in the whole pH range studied (211). For the system containing L-cysteine as ligand, Mössbauer investigations in quick-frozen solutions based on the partial quadrupole splitting concept reflected the geometry of the species formed.

Slurry nebulization ICP-AES spectrometry method for the determination of tin in organotin(IV) complexes

This paper proposes a quick, novel method for tin determination in organotin chemicals by slurry nebulization inductively coupled plasma atomic emission (ICP-AES) spectrometry. The method was tested by the measurement of five organotin carboxylate complexes of known composition for obtaining simple stoichiometric data. The slurries were prepared by first dissolving the organotins in an adequate solvent (methanol, pyridine or acetone) well miscible with water and then adding this solution drop-by-drop to a 0.005% TX-100 tenzide solution while maintaining intensive mixing. Dynamic laser light scattering experiments showed that the average equivalent particle size in the resulting slurry was approximately 0.3 mum for all samples and solvents. Under suitable ICP-AES measuring conditions, the signal recoveries were found to be between 101.8 and 106.6%, which allowed direct nebulization and calibration against aqueous solutions. Typically, 70 mug l(-1) detection limit and 1-5% relative S.D. on five replicates can be achieved by the described method.

Nuclear techniques in structural chemistry

The discovery of radioactivity started the nuclear research. The nuclear techniques are very powerful tools in structural chemistry, as well. We would like to support this statement by two examples in this paper. We present a series of Mössbauer measurements which give information about the coordination structure of some dibutyltin (IV) complexes of carbohydrate derivates. The other example will demonstrate how the positron lifetime spectra can reflect the temperature dependence of water structure.

Structural investigation of dibenzyltin(IV) complexes of carbohydrates

Dibenzyltin(IV) complexes of carbohydrate derivatives were prepared and studied by Mössbauer and FTIR spectroscopy and by thermogravimetry. The Mössbauer studies indicated that the reaction between dibenzyltin(IV)-dichloride and sugar-type ligands led to reaction products containing tin(IV)-oxide. beside the dibenzyltin(IV) sugar complex. These two type of species were shown to be in weak interaction. Comparison of the experimental quadrupole splitting values with those calculated on the basis of the partial quadrupole splitting concept revealed the steric arrangements of the coordination sphere of tin(IV) in the sugar complexes.

Silver and phosphate functionalized reactive TiO 2/polymer composite films for destructions of resistent bacteria using visible light

Abstract Phosphate and silver co-functionalized TiO2 catalysts were prepared by varying amount of silver (0-1 wt.%) with constant phosphate content (0.25 wt.%). Two methods, the well-know photodeposition and a new simple method, i.e. heterocoagulation, are presented for preparing Ag-TiO2 and the optical, photochemical and photobiological properties of the different samples have been compared. Due to the silver modification, the photocatalysts showed a new Plasmon resonance peak at λmax= 455 nm. The photocatalytic efficiencies of the new photo catalysts were studied under UV-A/visible (λ > 360 nm) irradiation. Mechanically stable hydrophilic poly(EA-co-MMA) and hydrophobic poly(Bi.A-co-Ech.) based composite films were prepared by spray coating technique. The photocatalytic efficiencies decreased only by ~ 15% on the hydrophilic and ~ 63% on the hydrophobic polymer compared to the reference pure photocatalyst films. The antibacterial activity of the films was also studied under visible light (λ > 400 nm) irradiation. Methicillin resistant Staphylococcus aureus (MRSA) was used as test bacterium. The best antibacterial activity (90% of bacteria destruction in 15 minutes) could be observed on the Ag- TiO2/p(EA-co-MMA) film.

Spherical LDH-Ag°-montmorillonite heterocoagulated system with a pH-dependent sol-gel structure for controlled accessibility of AgNPs immobilized on the clay lamellae.

Aqueous suspensions of spherical ZnMgAl-layered double hydroxides [LDH(sph)] and antibacterial silver nanoparticles (AgNPs) deposited on the lamellae of montmorillonite were used for the synthesis of composites, which behave like coherent gels at low pH (≲4.5) and incoherent sols at higher pH (≳4.5). The composition of the composite was chosen as LDH(sph)/Ag°-montm. = 25:75 wt % in order to ensure a sol-gel transition that can also be characterized by viscometry. This pH-sensitive heterocoagulated system consisting of oppositely charged colloid particles was suitable for the release of antimicrobial AgNPs immobilized on the clay lamellae via a pH-controlled gel-sol transition. The heterocoagulation process was also characterized by surface charge titration measurements. Spherical LDH/Ag°-montmorillonite composite samples were identified by X-ray diffraction (XRD) measurements. The morphological properties of the composites were studied, and the presence of the heterocoagulated structure was confirmed by scanning electron microscopy (SEM). The nanoscale structure of the LDH(sph)-Ag°-montmorillonite composite obtained was also verified by small-angle X-ray scattering (SAXS), and the rheological characteristics were studied at various pH values. The viscosity and yield value of the composite decreased by an order of magnitude upon increasing the pH from 3.0 to 5.5. The sol-gel transition of the composite suspension was reversible in the previously mentioned pH range.

Co-ordination number, symmetry of the co-ordination sphere of tin(IV) and oligomerization in carbohydrate complexes of dibutyltin(IV)

Dibutyltin(IV) complexes with 19 different carbohydrates were prepared and studied by Mossbauer spectroscopy. Comparison of the experimental quadrupole splitting values with those calculated on the basis of the partial quadrupole splitting concept revealed that the complexes are of four types: with the central tin(IV) atoms surrounded by donor atoms in a trigonal-bipyramidal, octahedral, both a trigonal-bipyramidal and octahedral or a tetrahedral arrangement. This procedure also distinguished between the different structural isomers of both trigonal-bipyramidal and octahedral complexes. Conclusions could therefore be drawn as to the factors determining which of the isomers is formed in the systems. The changes in the room-temperature Debye–Waller factors and the integral intensities of the Mossbauer doublets assigned to the tin(IV) in different surroundings reflected the oligomerization in the systems. The Mossbauer spectra revealed a temperature-dependent Goldanski–Karyagin effect.

Manganese(II) and nickel(II) complexes of some 2-(polyhydroxyalkyl) thiazolidine-4-carboxylic acid derivatives

Abstract The manganese(II) and nickel(II) ion coordination equilibria of some 2-(polyhydroxyalkyl) thiazolidine-4-carboxylic acid (PHTAC) derivatives were studied by potentiometric titration in the pH range 2–11. Nickel(II) parent complexes with (1, 1, 0) and (1, 2, 0) compositions and manganese(II) complexes with (1, 1, 0) composition were formed. In both systems, mixed-ligand complexes involving hydroxide ion coordination and/or further deprotonation of the alcoholic hydroxy groups of the sugar moieties were observed at pH > 6. EPR measurements indicated that in alkaline solution all the manganese(II)-PHTAC complexes are dimeric. The magnitudes of the complex-formation constants were shown to depend on the conformation of the hydroxy groups on the first carbon atoms of the polyol chains.