Synthesis, computational, spectroscopic, thermal and antimicrobial activity studies on some metal-urate complexes

New sixteen uric acid metal complexes of different stoichiometry, stereo-chemistries and modes of interactions were synthesized using different metals Cr, Mn, Fe, Co, Ni, Cu, Cd, UO(2), Na and K. The synthesized complexes were characterized by elemental analysis, spectral (IR, UV-Vis and ESR) methods, thermal analysis (TG, DTA and DSC) and magnetic susceptibility studies. Molecular modeling calculations were used to characterize the ligation sites of the free ligand. Furthermore, quantum chemical parameters of uric acid such as the energies of highest occupied molecular orbital (E(HOMO)), energies of lowest unoccupied molecular orbital (E(LUMO)), the separation energy (ΔE=E(LUMO)-E(HOMO)), the absolute electronegativity, χ, the chemical potential, P(i), the absolute hardness, η and the softness (σ) were obtained for uric acid. Eight different microbial categories were used to study the antimicrobial activity of the free ligand and ten of its complexes. The results indicate that the ligand and its metal complexes possess antimicrobial properties. The stoichiometry of iron-uric acid complex was studied by using different spectrophotometric methods.

Phosphate Positioning and Availability in the Starch Granule Matrix as Studied by EPR

Cu(2+) was introduced as an EPR probe into the starch granules isolated from different starch crop genotypes including transgenically modified potatoes generated for extreme amylose and starch phosphate monoester concentrations. Several discrete copper adducts bound to the starch matrix with different strength was revealed. It was found that phosphate has a significant influence on the type of these species, their number, location in the structure, and strength of binding. Well dispersed Cu(2+) complexes with axial symmetry are formed in the semicrystalline part of the starch linked through O-P- bonds in the phosphorylated starches. In the amorphous part of the starch, freely rotating hexaaqua complexes of Cu(2+) and complexes coupled antiferromagnetically are formed. The amount of the former increases with content of phosphate indicating enhanced binding of water in the granules. The results complement previous experimental data and molecular models for the starch granule with respect to the location and effects of phosphate and crystalline matter.

Electron paramagnetic resonance study of water distribution in starch granules

An electron paramagnetic resonance (EPR) study was performed for potato and wheat starch containing Cu2+ ions as a paramagnetic probe. Distribution of water in the starch granules as well as the interactions between the copper and starch matrix of different crystalline structures were determined. EPR spectra of the native starches consisted of two different centers of Cu2+. One of them, giving at 293 and 77 K an EPR signal of axial symmetry with a well-resolved hyperfine structure (HFS), was assigned to the Cu2+ -starch complex in which Cu2+ ions strongly interacted with oxygen atoms of the starch matrix. Another Cu2+ species, exhibiting an isotropic signal at 293 K and an axial signal with resolved HFS at 77 K, was attributed to a [Cu(H2O)6]2+ complex freely rotating at room temperature and immobilized at low temperatures. Interaction of Cu2+ with the starch matrix and the relative number of the particular copper species depended on the crystallographic type of starch. Dehydration at 393 K resulted in elimination of the rotating complex signal and decrease of the total intensity of the EPR spectrum caused by clustering of the Cu2+ ions. Freezing at 77 K and thawing led to restoring of the spectrum intensity and reappearing of the signal of the [Cu(H2O)6]2+ complex. This effect, related to liberation of water molecules from the granule semicrystalline growth rings on freezing/thawing, was especially visible for wheat starch, indicating differences in the water retention ability of starch granules of different crystallographic structure.