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. The color properties of the surface of ceramic materials were determined in CIE-Lab color space using a colorimeter. Quantitative phase analysis was performed using the Rietveld method. The research showed that the addition of calcium carbonate causes an increase in the yellow color factor and a decrease in the red color factor and the brightness of the material. Moreover, it was proven that the grain size distribution of the additive used significantly influences the phase composition of the materials, thus determining the values of physical properties and the color of the materials.

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. Phase composition of theinvestigated materials was characterized by XRD method with quantitive analysis of the amorphous phase determined by the Retvield technique. Color properties of the surface of the obtained ceramic materials were determined in CIE-Lab color space. The phase composition of the obtained ceramics depends on the firing temperature. The color of the surface of the ceramic materials also depends on the firing temperature. There was a tendency to decrease the brightness, decrease the blue shade, and increase the yellow shade of the surface of materials with increasing the temperature. The conducted tests allowed to conclude that the color of ceramic materials depends on their phase composition. The most important role in the formation of color correspond to the amorphous phase, formed during the process. The lower content of the amorphous phase in the material allows to obtain brighter products with a lower proportion of yellow, and therefore closer to white. Moreover, following tests were carried out: total water absorption, total open porosity, linear shrinkage, and flexural strength. With increasing the temperature, total water absorption and total open porosity decrease, and total linear shrinkage increases due to the progressive sintering process. Flexural strength increases with the increase of the firing temperature for materials consisting of Borkowice clay. The addition of dolomite introduced new pores into the material, which resulted in an increase in flexural strength at lower firing temperatures and a decrease in flexural strength at higher firing temperatures.

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 (0.50 mM) was incubated at 37 degrees C for 24 h with metal:peptide:hydrogen peroxide molar ratio 1:1:4 in phosphate buffer, pH 7.4. Oxidation targets for all peptide studied are the methionine residues (M(1), M(5)). Incubation 24 h of the (1-28), (1-39) and (1-39)(A30P) fragments in aerobic conditions lead to the oxidation of one methionine residue to methionine sulfoxide. Reaction of hydrogen peroxide with all fragments of alpha-synuclein resulted in oxidation of two methionine residues (M(1), M(5)) to methionine sulfoxides. For the Cu(II):peptide:hydrogen peroxide 1:1:4 molar ratio systems the further oxidation of methionine residues to sulfone was observed. The cleavage of the peptide bond M(1)-D(2) for all peptides studied was observed as metal binding residues. For the (1-39) and (1-39)(A30P) fragments of alpha-synuclein the molecular ions with lower molecular masses (A(11)-Y(39), E(13)-Y(39)) were also detected.

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. At pH above 7 the results suggest the formation of 2N, 3N, 4N complexes (in equatorial plane) and the involvement of the lateral NH(2) group of Lys residue in the axial coordination of Cu(II) ion. In CD spectra sigma (epsilon-NH(2)-Lys)-->Cu(II) charge transfer transition is observed. Addition of the 18-28 and 18-39 fragments to the 1-17 peptide does not change the coordination mode and the 1-39 fragment forms the Cu(II) complexes with higher stabilities compared to those of the 1-17, 1-28 and 1-39(A30P) fragments of alpha-synuclein.

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. Copper has been found in abnormally high concentrations in amyloid plaques and AD-affected neuropil, and copper-selective chelators have been shown to dissolve Abeta peptide from postmortem brain specimens. Although Cu(2+) is an essential element for life and the function of numerous enzymes is basic to neurobiology, free or incorrectly bound Cu(2+) can also catalyze generation of the most damaging radicals, such as hydroxyl radical, giving a chemical modification of the protein, alternations in protein structure and solubility, and oxidative damage to surrounding tissue.

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. The potentiometric and spectroscopic data (UV-Vis, CD, EPR) show that acetylation of the amino terminal group induces significant changes in the coordination properties of the (Ac-1-16H) and (Ac-1-16M) peptides compared to the (1-16H) and (1-16M) fragments, respectively. The (Ac-1-16H) peptide forms the 3N [N(Im)(6), N(Im)(13), N(Im)(14)] complex in a wide pH range (5-8), while for the (Ac-1-16M) fragment the 2N [N(Im)(6), N(Im)(14)] complex in the pH range 5-7 is suggested. At higher pH values sequential amide nitrogens are deprotonated and coordinated to copper(II) ions. The N-terminal amino group of the (1-16) and (1-28) fragments of human and mouse beta-amyloid peptide takes part in the coordination of the metal ion, although, at pH above 9 the complexes with the 4N [N(Im), 3N(-)] coordination mode are formed. The phenolate -OH group of the Tyr(10) residue of the human fragments does not coordinate to the metal ion.

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 (0.50 mM) was incubated at 37 degrees C for 24 h with metal:peptide:H(2)O(2) molar ratio 1:1:1 for the (1-16H), (1-16M) fragments, and 1:1:2 for the (1-10H), (1-10M) peptides in phosphate buffer, pH 7.4. Oxidation targets for all peptide studied are the histidine residues coordinated to the metal ions. For the (1-16H) peptide are likely His(13) and/or His(14), and for the (1-16M) fragment His(6) and/or His(14), which are converted to 2-oxo-His. Metal-binding residue, the aspartic acid (D(1)) undergoes the oxidative decarboxylation and deamination to pyruvate. The cleavages of the peptide bonds by either the diamide or alpha-amidation pathways were also observed.

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. Addition of the (17-20) and (17-28) sequences to the (11-16) fragment of human and mouse beta-amyloid peptide does not change the coordination mode, and the stabilities of the complexes formed are comparable to those of the (11-16) peptide, although 1N complexes of the (11-28) fragments are stabilized by about one order of magnitude compared to those of the (11-16) peptides. The (Ac-11-28) peptides form complexes with the same coordination mode as those for the (Ac-11-16) fragments. The stability of the complexes for the (Ac-11-28H) fragment is one or two orders of magnitude higher compared to those of the (Ac-11-16H) fragment. This stabilization may result from structural organization of a peptide in copper(II) complexes.

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. The next two descriptors are easily calculated from a structural formula. The predicted gradient retention times are in excellent agreement with the experimental data, determined for a structurally diversified series of 101 peptides. The QSRR equation obtained predicts in a convenient and reliable manner the retention times for any peptide in a once characterized HPLC system.

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. In general, R(M) increased with increasing concentration of acetonitrile. In TLC systems without the ionic liquid, R(M) can be described well with a quadratic function. On the other hand, in a TLC system with an ionic liquid as the additive to the mobile phase, the retention behavior is better described with a third-degree polynomial function. The potential usefulness of ionic liquids for optimization of separation of peptides was demonstrated. Optimization of the separation conditions was supported by a commercially available computer program.

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. The present findings may represent the key for interpreting the observed requirement of His residues conservation for the redox cycling between Cu(II) and Cu(I) by soluble APP.