Influence of the Grain Size Distribution of the Limestone Additives on the Color Properties and Phase Composition of Sintered Ceramic Materials Based on Cream-Firing Clays.

The study focused on determining color changes in materials made of cream-firing clays from the Opoczno region (Poland) due to the addition of calcium carbonate in the form of limestone. Moreover, the influence of the grain size distribution of this additive on the color properties of the materials and their phase composition was determined. Test samples were prepared using theplastic method and fired at four different temperatures: 1120, 1140, 1160 and 1180 °C.

Influence of Firing Temperature on Phase Composition and Color Properties of Ceramic Tile Bodies.

This study is focused on the behavior of the cream-firing clays from Opoczno region (Poland). The ceramic masses on which tests were carried out consisted of cream-firingBorkowice clay and dolomite in two different grain sizes as an additive that changes the color of ceramic materials. Test samples were prepared by plastic method and fired at range of 1100-1240 °C.

Products of Cu(II)-catalyzed oxidation of the N-terminal fragments of alpha-synuclein in the presence of hydrogen peroxide.

Reactive oxygen species (ROS) may provide the covalent modifications of amino acid residues in proteins, formation of protein-protein cross-linkages, and oxidation of the protein backbone resulting in protein fragmentation. In an attempt to elucidate the products of the copper(II)-catalyzed oxidation of the (1-17), (1-28), (1-39) and (1-39)(A30P) fragments of alpha-synuclein, the high performance liquid chromatography (HPLC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) methods and Cu(II) /hydrogen peroxide as a model oxidizing system were employed. Peptide solution (0.

Coordination abilities of N-terminal fragments of alpha-synuclein towards copper(II) ions: a combined potentiometric and spectroscopic study.

Copper(II) complexes of the 1-17 (MDVFMKGLSKAKEGVVA-NH(2)), 1-28 (MDVFMKGLSKAKEGVVAAAEKTKQGVAE-NH(2)), 1-39 (MDVFMKGLSKAKEGVVAAAEKTKQGVAEAPGKTKEGVLY-NH(2)) and 1-39 (A30P) fragments of alpha-synuclein were studied by potentiometric, UV-Vis (UV-visible), CD (circular dichroism) and EPR (electron paramagnetic resonance) spectroscopic methods to determine the stoichiometry, stability constants and coordination modes of the complexes formed. The beta-carboxylate group of Asp residue in second position of the peptide chain coordinates strongly to Cu(II) ion over the pH range 4-9.5 to give unusually stable 2N complex with {NH(2), N(-), beta-COO(-), H(2)O} coordination mode.

Prediction of high-performance liquid chromatography retention of peptides with the use of quantitative structure-retention relationships.

Quantitative structure retention relationships (QSRR) were derived allowing prediction of reversed-phase high-performance liquid chromatography (HPLC) retention of peptides. To quantitatively characterize the structure of a peptide, and then to predict its gradient retention time under given HPLC conditions, the following descriptors are employed: logarithm of the sum of retention times of the amino acids composing the peptide, log Sum(AA), logarithm of Van der Waals volume of the peptide, log VDW(Vol), and logarithm of its calculated n-octanol-water partition coefficient, clog P. The first descriptor is based on a set of empirical data for 20 natural amino acids.

Behavior of peptides and computer-assisted optimization of peptides separations in a normal-phase thin-layer chromatography system with and without the addition of ionic liquid in the eluent.

The addition of an ionic liquid into the mobile phase appeared to be useful in optimization of chromatographic separation of peptides. Different behavior of peptides in thin-layer chromatography (TLC) was observed after addition of 1-ethyl-3-methylimidazolium tetra fluoroborate to the eluent in comparison to the system without the ionic liquid. Nonlinear dependence of the retention coefficient, R(M), of peptides on the volume percentage of acetonitrile in the eluent was found in normal-phase TLC with and without immidazolium tetra fluoroborate in the mobile phase.

Identification of a novel high affinity copper binding site in the APP(145-155) fragment of amyloid precursor protein.

The copper(II) binding features of the APP(145-155) and APP(145-157) fragments of the amyloid precursor protein, Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-NH2 and Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-Glu-Thr-NH2 were studied by NMR spectroscopy and NMR findings were supported by UV-vis, CD and EPR spectra. Potentiometric measurements were performed only for the more soluble Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-Glu-Thr-NH2 peptide fragment. The following was shown: (i) the imidazole rings of all the three His residues are involved in metal coordination; (ii) metal binding induces ionisation of Leu-148 and His-149 amide nitrogens that complete the donor set to copper(II) in the species dominant at neutral pH; (iii) the unusual coordination scheme of the His-Xxx-His-Xxx-His consensus sequence justifies the high specificity for Cu(II) when compared to SOD-like or albumin-like peptides or even in amyloid Abeta fragments.

Products of Cu(II)-catalyzed oxidation in the presence of hydrogen peroxide of the 1-10, 1-16 fragments of human and mouse beta-amyloid peptide.

The interactions of proteins with reactive oxygen species (ROS) may result in covalent modifications of amino acid residues in proteins, formation of protein-protein cross-linkages, and oxidation of the protein backbone resulting in protein fragmentation. In an attempt to elucidate the products of the metal-catalyzed oxidation of the human (H) and mouse (M) (1-10H), (1-10M), (1-16H) and (1-16M) fragments of beta-amyloid peptide, the high performance liquid chromatography (HPLC) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) methods and Cu(II)/H(2)O(2) as a model oxidizing system were employed. Peptide solution (0.

Coordination abilities of the 1-16 and 1-28 fragments of beta-amyloid peptide towards copper(II) ions: a combined potentiometric and spectroscopic study.

Stoichiometry, stability constants and solution structures of the copper(II) complexes of the (1-16H), (1-28H), (1-16M), (1-28M), (Ac-1-16H) and (Ac-1-16M) fragments of human (H) and mouse (M) beta-amyloid peptide were determined in aqueous solution in the pH range 2.5-10.5.

Possible involvement of copper(II) in Alzheimer disease.

The beta-amyloid (Abeta) peptide is a principal component of insoluble amyloid plaques that are characteristic neuropathological features of Alzheimer disease (AD). The amyloid peptide also exists as a normal soluble protein that undergoes a pathogenic transition to an aggregated, fibrous form. This transition can be affected by extraneous proteinaceous elements and nonproteinaceous elements such as copper ions, which may promote aggregation and/or stabilization of the fibrils.

Coordination of copper(II) ions by the 11-20 and 11-28 fragments of human and mouse beta-amyloid peptide.

A potentiometric and spectroscopic (UV-vis, CD and EPR) study of Cu(II) binding to the (11-20), (11-28), (Ac-11-20H) and (Ac-11-28) fragments of human (H) and mouse (M) beta-amyloid peptide was carried out. The values of the protonation constants of the two lysine side chain amino groups for the (11-28) and (Ac-11-28) fragments of beta-amyloid peptide differ noticeably suggesting considerable interactions between the two residues. The N-terminal amino acid sequence Xaa-Yaa-His for the (11-20H) and (11-28H) fragments determines the coordination ability of the fragments studied to copper(II) ions.