Visual-test and Sorption-spectrophotometric Determination of Melamine in Biological Objects

Melamine may have toxic effects on humans and animals. It is well known that melamine accumulates in the body and causes reproductive damages, forms bladder or kidney stones, which can lead to bladder cancer. Trace amounts of melamine at ppm levels may occur in certain food commodities due to its migration from melamine-containing disposable tableware plastics. It was intentionally adulterated to milk products to show a false increase in protein concentration. Considering these facts there is a need for establishing sensitive and reliable methods of melamine determination. As uncostly, rapid and selective melamine detection methods are highly required, the hyphenated sorption-spectrophotometric and visual test methods seem to be perspective candidates.In the present work the optimal conditions of sorption concentration of melamine from aqueous solutions ontо the silica gel surface were studied. The calibration graph for the sorption-spectrophotometric method is linear in 0.02 – 9.8 μmol.L-1 mg L-1 melamine concentration range. Proposed method allows naked-eye monitoring of biological samples.

Вісник Харківського національного університету

The adsorption of reduced forms of molybdo-phosphoric, molybdo-antimono-phosphoric and molybdosilicic heteropoly acids with few anion-exchanger on the base of tetradecylammonium nitrate absorbed onto amorphous silica was investigated. The interaction of heteropoly acids with immobilized quaternary ammonium salts was investigated via UV/VIS and solid-phase spectrophotometric methods. The significant influence of the surface groups on the chromophorous system of adsorbed heteropoly anions was shown. Unexpected strong fixing of HPA on the surface was found to be a result of formation of ion associates between heteropoly acids and immobilized tetradecylammonium nitrate and HPA interaction with active groups of the nonmodified silica surface

Platinum surface complexes as precursors for H–O recombination catalysts

In this work, the adsorption of platinum (II, IV) chloride complexes from acidic solutions on silica gel modified with quaternary ammonium salts (QAS) was studied. The uptake of the platinum chloride complexes is caused by the formation of ionic (QAS + ) 2 [PtCl x ] 2− ( x  = 4, 6) associates on the surface of silica gel. The isotherms of adsorption are fitted by the Langmuir model. The maximum capacity for [PtCl 4 ] 2− and [PtCl 6 ] 2− is 0.99 and 1.13 mmol/g, correspondingly. The respective adsorption constants K L  = 6.8 and 10 × 10 5  l/mol prove the high affinity of the adsorbates to the QAS-modified surface. Platinum metal nanoparticles supported on the surface of the silica gel were prepared by reducing the adsorbed platinum (II, IV) complexes. Such nanoparticles functioning at the moderate temperature regime have demonstrated a reasonable catalytic activity for the hydrogen and oxygen recombination, and an excellent stability over 35 cycles of the reaction

Interaction of Molybdo-Phosphoric and Molybdo-Antimono-Phosphoric Heteropoly Acids with Silica Gels Modified with Aliphatic and Heterocyclic Quaternary Ammonium Salts

The interaction of molybdo-phosphoric and molybdo-antimonophosphoric heteropoly acids with aliphatic (tetradecylammonium nitrate and trinonyloctadecylammonium iodide) and heterocyclic (lucigenine and safranine) quaternary ammonium salts immobilized onto silica has been studied using adsorption and spectroscopic methods. It has been shown that the formation of ionassociates between the quaternary ammonium cations and the heteropoly anions is accompanied by their interaction with surface silica groups which accounts for the tight binding of heteropoly acids to the surface. Such interfacial reactions can successfully be applied to the development of spectroscopic and semi-quantitative visual test techniques for detecting trace amounts of phosphorus and antimony

Difluoro-Substituted bicyclo[1.1.1]pentanes as Novel Motifs for Medicinal Chemistry: Design, Synthesis and Characterization

Herein we developed a practical synthetic approach to the previously unknown difluoro-substituted bicyclo[1.1.1]pentanes. The key step was an addition of difluorocarbene to electron-rich bicyclo[1.1.0]butanes by CF3TMS/NaI system. The obtained difluoro-bicyclo[1.1.1]pentanes are a new generation of saturated bioisosteres of the benzene ring for drug discovery projects

Conquering 2‑Aminopurine’s Deficiencies: Highly Emissive Isomorphic Guanosine Surrogate Faithfully Monitors Guanosine Conformation and Dynamics in DNA

The archetypical fluorescent nucleoside analog, 2-aminopurine (2Ap), has been used in countless assays, though it suffers from very low quantum yield, especially when included in double strands, and from the fact that its residual emission frequently does not represent biologically relevant conformations. To conquer 2Ap's deficiencies, deoxythienoguanosine (d(th)G) was recently developed. Here, steady-state and time-resolved fluorescence spectroscopy was used to compare the ability of 2Ap and d(th)G, to substitute and provide relevant structural and dynamical information on a key G residue in the (-) DNA copy of the HIV-1 primer binding site, (-)PBS, both in its stem loop conformation and in the corresponding (-)/(+)PBS duplex. In contrast to 2Ap, this fluorescent nucleoside when included in (-)PBS or (-)/(+)PBS duplex fully preserves their stability and exhibits a respectable quantum yield and a simple fluorescence decay, with marginal amounts of dark species. In further contrast to 2Ap, the fluorescently detected d(th)G species reflect the predominantly populated G conformers, which allows exploring their relevant dynamics. Being able to perfectly substitute G residues, d(th)G will transform nucleic acid biophysics by allowing, for the first time, to selectively and faithfully monitor the conformations and dynamics of a given G residue in a DNA sequence

Novel Cyclic Peptides for Targeting EGFR and EGRvIII Mutation for Drug Delivery

The epidermal growth factor–epidermal growth factor receptor (EGF-EGFR) pathway has become the main focus of selective chemotherapeutic intervention. As a result, two classes of EGFR inhibitors have been clinically approved, namely monoclonal antibodies and small molecule kinase inhibitors. Despite an initial good response rate to these drugs, most patients develop drug resistance. Therefore, new treatment approaches are needed. In this work, we aimed to find a new EGFR-specific, short cyclic peptide, which could be used for targeted drug delivery. Phage display peptide technology and biopanning were applied to three EGFR expressing cells, including cells expressing the EGFRvIII mutation. DNA from the internalized phage was extracted and the peptide inserts were sequenced using next-generation sequencing (NGS). Eleven peptides were selected for further investigation using binding, internalization, and competition assays, and the results were confirmed by confocal microscopy and peptide docking. Among these eleven peptides, seven showed specific and selective binding and internalization into EGFR positive (EGFR+ve) cells, with two of them—P6 and P9—also demonstrating high specificity for non-small cell lung cancer (NSCLC) and glioblastoma cells, respectively. These peptides were chemically conjugated to camptothecin (CPT). The conjugates were more cytotoxic to EGFR+ve cells than free CPT. Our results describe a novel cyclic peptide, which can be used for targeted drug delivery to cells overexpressing the EGFR and EGFRvIII mutation

Solid phase extractive preconcentration of silver from aqueous samples and antimicrobial properties of the clinoptilolite–Ag composite

Sorptive properties of the Transcarpathian clinoptilolite compared to Ag(I) were studied in a dynamic way. The sorptive capacity value of clinoptilolite under the optimal conditions is 11.7 mg of Ag per 1 g of zeolite. The solid-phase extraction procedure with natural clinoptilolite thermally activated at 550℃ was used to preconcentrate trace amounts of silver ions in aqueous solutions to be finally determined by the atomic absorption method. It was established that the Ag–clinoptilolite composite has a powerful antimicrobial effect against gram-negative bacteria and yeasts as well as affects significantly vital activity of Staphylococcus aureus