The Aggregation Pattern of Aβ1–40 is Altered by the Presence of N-Truncated Aβ4–40 and/or CuII in a Similar Way through Ionic Interactions

Alzheimer's disease (AD) is one of the most common of the multifactorial diseases and is characterized by a range of abnormal molecular processes, such as the accumulation of extracellular plaques containing the amyloid-β (Aβ) peptides and dyshomeostasis of copper in the brain. In this study, we have investigated the effect of Cu^II on the aggregation of Aβ_1–40 and Aβ_4–40, representing the two most prevalent families of Aβ peptides, that is, the full length and N-truncated peptides. Both families are similarly abundant in healthy and AD brains. For either of the studied peptides, substoichiometric Cu^II concentrations accelerated aggregation, whereas superstoichiometric Cu^II inhibited fibril formation, likely by stabilizing the oligomers. The addition of either Aβ_4–40 or substoichiometric Cu^II affected the aggregation profile of Aβ_1–40, by yielding shorter and thicker fibrils; amorphous aggregates were formed in the presence of a molar excess of Cu^II. The similarity of these two effects can be attributed to the increase in the positive charge on the Aβ N terminus, caused both by Cu^II complexation and N truncation at position 4. Our findings provide a better understanding of the biological Aβ aggregation process as these two Aβ species and Cu^II coexist and interact under physiological conditions.     

Chemical Stability of the Fertilizer Chelates Fe-EDDHA and Fe-EDDHSA over Time

In application conditions, the influence of environmental parameters on used fertilizer chelates and their distribution over time is important. For this purpose, the changes in the content of micronutrient ions and Fe-EDDHA and Fe-EDDHSA chelates in an aqueous medium at different pH values were studied. In the assumed time, changes in the ions content were analyzed using the voltammetry method at pH 3, 5 and 7. The content of isomers and chelate forms was analyzed by ion pair chromatography at pH 3, 5 and 7. These studies allowed us to determine the effect of pH on the stability of iron chelates over time.     

Highly enantioselective Henry reaction catalyzed by chiral tridentate heteroorganic ligands

New tridentate enantiomerically pure heteroatom catalysts, containing hydroxyl, sulfinyl and amino groups, proved to be highly efficient in the enantioselective nitroaldol (Henry) reaction to give the desired adducts in very high yields (up to 90%) and with ees up to 98%. The influence of the stereogenic centres located on the sulfinyl sulfur atom and in the amine moiety is also discussed.     

New highly efficient aziridine-functionalized tridentate sulfinyl catalysts for enantioselective diethylzinc addition to carbonyl compounds

New tridentate enantiomerically pure heteroorganic catalysts, containing hydroxyl, sulfinyl, and aziridine moieties, have proven to be highly efficient in the enantioselective diethylzinc addition to aryl and alkyl aldehydes to give the desired products in very high yields (up to 99%) and with ee’s up to 97%. The influence of the stereogenic centers located on the sulfinyl sulfur atom and in the aziridine moiety on the stereochemical course of the reaction are discussed.     

The structure and thermal behaviour of sodium and potassium multinuclear compounds with hexamethylenetetramine

Sodium and potassium thiocyanate complex compounds of formulae [Na(hmta)(H₂O)₄]₂²⁺·2SCN⁻ (1) and [K₂(hmta)(SCN)₂] _n (2) have been synthesized and characterised by IR spectroscopy, thermogravimetry coupled with differential thermal analysis, elemental analysis and X-ray crystallography. Each sodium and potassium cation is six co-ordinated, the sodium by one monofunctional hmta molecule, three terminal water molecules and two bridging water molecules, and the potassium by two bridging tetrafunctional hmta molecules and four bridging tetrafunctional thiocyanate ions. The coordination polyhedra of the central atoms can be described as distorted tetragonal bipyramids. The complex cations and anions of (1) are interconnected by multiple intramolecular O(water)—H···N(hmta/NCS) and O(water)—H···S hydrogen bonds to the three dimensional net. In each complex cation the intramolecular O–H···O hydrogen bonds link two terminal water molecules bonded to two metal cations. The compound (2) forms the three dimensional hybrid network in which the classical two-dimensional coordination polymers are linked by inorganic SCN⁻ spacers to the third-dimension. Thermal analyses show that the compounds decompose gradually in three (for 1) and two (for 2) steps with formation of Na₂SO₄ and K₂S as the final products, respectively, for 1 and 2.     

Revisiting Thin-Layer Chromatography as a Lipophilicity Determination Tool. Part II — Is Silica Gel a Reliable Adsorbent for Lipophilicity Estimation?

JPC – Journal of Planar Chromatography – Modern TLC - Lipophilicity is often estimated by thin-layer chromatography (TLC) as a fundamental property related to biological and...     

Evaluation of Two Techniques for Extraction of Cortisol from Human Saliva

The aim of the study was to compare two kinds of extraction of cortisol from human saliva. The first was made with dichloromethane and the second by solid-phase extraction. Saliva was sampled in the evening into plastic tubes then cortisol was extracted and analyzed by LC with detection at 240 nm. The limit of detection was 1 ng mL^?1 for extraction with dichloromethane and 3 ng mL^?1 for SPE extraction. Both methods of extraction were applied to the analysis of saliva samples without any interference peaks.     

Zeta potential determination as a new way of stationary phases characterization for liquid chromatography

A set of seven homemade octadecyl silica‐based bonded phases was investigated. Their zeta potential data in methanol and ACN as well as in methanol–water and ACN–water solution were obtained using Zetasizer. The influence of both the coverage density of bonded ligands and the end‐capping of the modified surface on these data was investigated. Presented results may give useful information about the accessibility of the residual silanols in different mobile phases during the chromatographic analysis. Those measurements may be useful to choose chemically bonded stationary phases for CEC. The results also confirm the phenomena of anion exclusion from the pores of stationary‐bonded phase.     

Capillary electrophoresis of microbial aggregates

Uncontrolled aggregation of bacterial cells is a significant disadvantage of electrophoretic separations. Various aspects of the electrophoretic behavior of different strains of Gram‐positive Bacillus cereus, Bacillus subtilis, Sarcina lutea, Staphylococcus aureus(1), and Micrococcus luteus bacteria and Gram‐negative Escherichia coli bacteria were investigated in this study. Our findings indicate that bacteria can be rapidly analyzed by CZE with surface charge modification by calcium ions (Ca²⁺). Bound Ca²⁺ ions increase zeta potential to more than 2.0 mV and significantly reduce repulsive forces. Under the above conditions, bacterial cells create compact aggregates, and fewer high‐intensity signals are observed in electropherograms. The above can be attributed to the bridging effect of Ca²⁺ between bacterial cells. CE was performed to analyze bacterial aggregates in an isotachophoretic mode. A single peak was observed in the electropherogram.     

Differentiation of Diastereoisomers of Protected 1,2-Diaminoalkylphosphonic Acids by EI Mass Spectrometry and Density Functional Theory

Electron ionization mass spectrometry and density functional theory (DFT) calculations have been used to study the fragmentation of diastereoisomers of protected 1,2-diaminoalkylphosphonic acids. The loss of a diethoxyphosphoryl group and the elimination of diethyl phosphonate were found to be competitive fragmentation processes, which can be used to differentiate both stereoisomers. Selective deuterated analogs and product- and precursor-ion mass spectra allowed the elucidation of the fragmentation mechanisms. The structures of the transition states and product ions were optimized using the density functional theory (DFT), and free energy calculations confirmed the observed differences in the formation and relative intensities of specific fragment ions.