Offline combination of pressurized fluid extraction and electron paramagnetic resonance spectroscopy for antioxidant activity of grape skin extracts assessment

A comprehensive characterization of grape skin methanolic and ethanolic extracts prepared by pressurized fluid extraction (PFE) at various temperatures within 40 to 120 °C from two wine grape varieties, St. Laurent and Alibernet was performed. For the first time, an offline combination of PFE and electron paramagnetic resonance (EPR) spectroscopy together with other experimental methods was employed to assess the effect of extraction conditions on numerous extract characteristics including antioxidant or radical-scavenging ability, HPLC profile of anthocyanins, total phenolic compounds content (TPC), tristimulus color values (CIE Lab), and pH values. The properties of extracts depend on the solvent used, the mass of grape skins as well as on the extraction conditions among which the temperature plays a crucial role. In spite of wide interval of extraction temperatures, all extracts still retain their antioxidant and/or radical-scavenging properties, indicating that the extracts prepared by PFE can serve as potential source of functional food supplements or color enhancers.     

Iminodiacetic acid-modified magnetic poly(2-hydroxyethyl methacrylate)-based microspheres for phosphopeptide enrichment

Magnetic non-porous hydrophilic poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate) microspheres prepared by the dispersion polymerization and modified with iminodiacetic acid (IDA) were employed for the IMAC separation of phosphopeptides. Fe³⁺ and Ga³⁺ ions immobilized on IDA-modified magnetic microspheres were used for the enrichment of phosphopeptides from the proteolytic digests of two model proteins differing in their physico-chemical properties and phosphate group content: porcine pepsin A and bovine α-casein. The optimum conditions for phosphopeptide adsorption and desorption in both cases were investigated and compared. The phosphopeptides separated from the proteolytic digests were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The ability of the prepared Fe³⁺- and Ga³⁺-IDA-modified magnetic microspheres to capture phosphopeptides from complex mixtures was shown on an example of bovine milk proteolytic digest.     

Decavanadates with complex cations: synthesis and structure of (NH4)2[M(H2O)5(NH3CH2CH2COO)]2V10O28·nH2O (M?=?ZnII, n?=?4; M?=?MnII, n?=?2)

Decavanadates with complex cations, (NH₄)₂[Zn(H₂O)₅(NH₃CH₂CH₂COO)]₂V₁₀O₂₈·4H₂O (4) and (NH₄)₂[Mn(H₂O)₅(NH₃CH₂CH₂COO)]₂V₁₀O₂₈·2H₂O (5), have been prepared and characterized by elemental analysis, i.r., Raman, UV–vis. and ⁵¹V-n.m.r. spectroscopies and by thermal analysis. The X-ray structure determination revealed, both in 4 and 5, the presence of complex cations with hexacoordinated central atoms and monodentate β-alanine ligands, and decavanadate V₁₀O₂₈ ⁶⁻ anions. The differences in the structural arrangement in 4 and 5 are probably a consequence of the different ionic radii of Zn²⁺ and Mn²⁺ (high spin).     

Estimation of acidity constants,ionic mobilities and charges of antimicrobial peptides by capillary electrophoresis

Capillary electrophoresis (CE) was employed for the determination of thermodynamic acidity constants (pK_a) and actual ionic mobilities of polycationic antimicrobial peptides (AMPs). The effective electrophoretic mobilities of AMPs were measured by CE in a series of the background electrolytes within a wide pH range (2.00–12.25), at constant ionic strength (25 mM) and ambient temperature, using polybrene coated fused silica capillaries to suppress sorption of cationic AMPs to the capillary wall. Eventually, Haarhoff–Van der Linde peak fitting function was used for the determination of correct migration times of some AMPs peaks that were distorted by electromigration dispersion. The measured effective mobilities were corrected to 25°C. Mixed acidity constants, , and actual ionic mobilities, m_i, of AMPs were determined by the nonlinear regression analysis of pH dependence of their effective mobilities. The values were recalculated to thermodynamic pK_as using the Debye–Hückel theory. Thermodynamic pK_a of imidazolium group of histidine residues was found to be in the range 3.72–4.98, pK_a of α‐NH₃⁺ group was in the range 6.14–6.93, and pK_a of ε‐NH₃⁺ group of lysine spanned the interval 7.26–9.84, depending on the particular amino acid sequence of the AMPs. Actual ionic mobilities of AMPs with positive charges from one to six elementary units achieved values (9.8 – 36.5) × 10^?9 m²V^?1s^?1.     

Study on the interactions of sulfonylurea antidiabetic drugs with normal and glycated human serum albumin by capillary electrophoresis‐frontal analysis

Diabetes is one of the most widespread diseases characterized by a deficiency in the production of insulin or its ineffectiveness. As a result, the increased concentrations of glucose in the blood lead not only to damage to many of the body's systems but also cause the nonenzymatic glycation of plasma proteins affecting their drug binding. Since the binding ability influences its pharmacokinetics and pharmacodynamics, this is a very important issue in the development of new drugs and personalized medicine. In this study, capillary electrophoresis‐frontal analysis was used to evaluate the affinities between human serum albumin or its glycated form and the first generation of sulfonylurea antidiabetics, since their inadequate concentration may induce hypoglycaemia or on the contrary hyperglycaemia. The binding constants decrease in the sequence acetohexamide > tolbutamide > chlorpropamide > carbutamide both for normal and glycated human serum albumins, with glycated giving lower values. These results provide a more quantitative picture of how these drugs bind with normal and modified human serum albumin and indicate capillary electrophoresis‐frontal analysis to be another tool for examining the changes arising from modifications of albumin, or any other protein, with all its benefits like short analysis time, small sample requirement, and automation.     

Sensitive voltammetric method for the fast analysis of the antioxidant pyrogallol using a boron-doped diamond electrode in biofuels

A sensitive voltammetric method for the determination of pyrogallol (PY) was developed employing a boron-doped diamond electrode (BDDE). The composition of the supporting electrolyte was investigated during the development of the methodology. Linear sweep voltammetry (LSV) under the optimized experimental conditions was applied for PY determination with a limit of detection and limit of quantification of 0.85 and 2.82 μmol L^?1, respectively. These values are satisfactory for application to real samples. The usability of this method for the quantification of pyrogallol was in range from 2.82 to 296.00 μmol L^?1. Finally, the developed method was successfully used for the analysis of real samples of biodiesel produced from rapeseed oil and its blend with diesel fuel. Samples of biodiesel and biodiesel blends were analyzed directly in an electrochemical cell, while samples with very low concentrations of PY in biodiesel were extracted with water using the proposed simple and fast process.     

Polyaniline/montmorillonite nanocomposite thin layers deposited on different substrates

Preparation method of polyaniline/montmorillonite (PANI/MMT) nanocomposite in the form of thin layer deposited on various substrates is optimized in this work to obtain high electrical conductivity. Simple method (i.e. polymerization of anilinium sulfate in the presence of MMT) has been used for the preparation and following four conditions were varied: preparation temperature (T = 10 or 20 °C), preparation time (t = 4 or 6 h), size fraction of MMT (p < 1 or 5 µm), and type of substrate (microscope glass slides, silica glass slides, polyester foils). Therefore, 24 samples were prepared, characterized and their electrical conductivity was compared. Raman spectroscopy and scanning electron microscopy were used for the characterization of the structure of samples. Thickness of layers was measured using atomic force microscopy. Based on the comparison of samples and with respect to the aim of obtaining high electrical conductivity, it was found that the most suitable substrate is polyester foil and preparation conditions are T = 20 °C, t = 6 h, p < 5 µm. To obtain highly conductive layers on glass substrates (although less conductive than layers on foil), preparation time have to be shortened to 4 h.