Olga A. Zaporozhets

“Reported, but Still Unknown.” A Closer Look into 3,4-Bis- and 3,4,5-Tris(trifluoromethyl)pyrazoles

Straightforward practical synthetic approaches to 3,4-bis- and 3,4,5-tris(trifluoromethyl)pyrazoles have been developed. The key step of the both syntheses is a transformation of the carboxylic group in a pyrazole core into the trifluoromethyl group by sulfur tetrafluoride. The elaborated synthetic protocols allow gram-scale preparation of the target products. The obtained compounds are comprehensively characterized by means of crystallographic analysis, determination of pK(a) values and fluorescence measurements.

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 2Aps 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.

Tautomers of a Fluorescent G Surrogate and Their Distinct Photophysics Provide Additional Information Channels

Thienoguanosine ((th) G) is an isomorphic nucleoside analogue acting as a faithful fluorescent substitute of G, with respectable quantum yield in oligonucleotides. Photophysical analysis of (th) G reveals the existence of two ground-state tautomers with significantly shifted absorption and emission wavelengths, and high quantum yield in buffer. Using (TD)-DFT calculations, the tautomers were identified as the H1 and H3 keto-amino tautomers. When incorporated into the loop of (-)PBS, the (-)DNA copy of the HIV-1 primer binding site, both tautomers are observed and show differential sensitivity to protein binding. The red-shifted H1 tautomer is strongly favored in matched (-)/(+)PBS duplexes, while the relative emission of the H3 tautomer can be used to detect single nucleotide polymorphisms. These tautomers and their distinct environmental sensitivity provide unprecedented information channels for analyzing G residues in oligonucleotides and their complexes.

Molecular modelling and synthesis of a polymer for the extraction of amiloride and triamterene from human urine

A new solid-phase extraction resin with high affinity towards amiloride and triamterene was developed with the assistance of computational modelling. Itaconic acid was selected as the best functional monomer capable of forming strong complexes with amiloride and triamterene. Conditions for selective solid-phase extraction of the diuretics from human urine and for their separation using a custom-designed adsorbent were optimised. It was shown that this adsorbent provided a high level of purification of the diuretics from human urine, which made their quantification using spectrophotometry possible.

Solid-phase spectrophotometric and test determination of silicate in natural water

Quaternary ammonium salts (QAS) of aliphatic (tetradecylammonium nitrate) and heterocyclic (lucigenine) nature immobilized onto silica surface have been proposed as effective anion-exchangers for the adsorptional extraction of silicate in the form of the reduced molybdo-silicic heteropoly anion for the successive determination in the solid phase by using spectrophotometric and visual test techniques. The interface interaction has been investigated. On the basis of the results obtained the new solid-phase spectrophotometric and visual test techniques for the direct silicon determination in the rage of its concentrations 14-400 μg L(-1) have been proposed. The tolerance limits of the major components in natural waters and other ions capable of producing heteropoly anions in the silicate determination have been reported. The techniques have been successfully applied for the silicate determination in natural waters.

One-Pot Parallel Synthesis of Alkyl Sulfides, Sulfoxides, and Sulfones

A simple and cost-effective one-pot parallel synthesis approach to sulfides, sulfoxides, and sulfones from thiourea was elaborated. The method combines two procedures optimized to the parallel synthesis conditions: alkylation of thiourea with alkyl chlorides and mono or full oxidation of in situ generated sulfides with H2O2 or H2O2-(NH4)2MoO4. The experimental set up required commonly used lab equipment: conventional oven and ultrasonic bath; the work up includes filtration or extraction with chloroform. The method was evaluated on an 81 member library of drug-like sulfides, sulfoxides, and sulfones yielding the compounds on a 30-300 mg scale. A small-scale synthesis of 2-(benzhydrylsulfinyl)acetamide (modafinil) utilizing our approach resulted in similar efficiency to the published procedures.

Spectrophotometric determination of oxyhalides with N,N-diethylaniline

We have developed procedures for the spectrophotometric determination of ClO−, BrO3−, and IO3− in waters of different origin. The procedures are based on the oxidation of N,N-diethylaniline in acidic media and their detection limits (by 3s criterion) are 0.04, 0.18, and 0.53 μg/mL, respectively. The calibration curves are linear in the concentration ranges 0.1–2.0, 0.4–12.5, and 1.6–40 μg/mL, respectively. The procedures provide simple and rapid determination of these analytes.

2,2,2-Trifluoroethyl Chlorooxoacetate--Universal Reagent for One-Pot Parallel Synthesis of N(1)-Aryl-N(2)-alkyl-Substituted Oxamides.

A one-pot parallel synthesis of N(1)-aryl-N(2)-alkyl-substituted oxamides with 2,2,2-trifluoroethyl chlorooxoacetate was developed. The synthesis of a library of 45 oxamides revealed higher efficiency of this reagent over the known ethyl chlorooxoacetate. The reagent was successfully used to prepare the known oxamide-containing HIV entry inhibitors.

Silica-Coated Magnetite Nanoparticles Modified with 3-Aminopropyl Groups for Solid-Phase Extraction of Pd(II) Ions from Aqueous Solutions

Here we report a simple two-step synthesis of magnetite nanoparticles (NPs) coated with silica shell functionalized with 3-aminopropyl groups. The content of surface amino groups within the range of 0.7–2.8 mmol g−1 was established by elemental analysis and acid–base titration. The materials obtained are hydrolytically stable in acidic medium and are rapidly separated from the solution using an external magnetic field. It was shown that the prepared NPs efficiently extract palladium(II) ions in the form of [PdCl4]2– from the solution. The kinetics of adsorption was well described by the second-order model with the rate constant of approximately 0.76 g mmol−1 minute−1. The isotherm of adsorption is fitted by the Langmuir model with the maximum [PdCl4]2– adsorption capacity of 0.158 mmol g−1.

Chemiluminescence determination of dissolved copper(II) in natural waters

AbstractsThe catalytic effect of copper(II) on the chemiluminescence reaction of luminol oxidation in the presence of some modeling organic substances of natural waters, i.e., EDTA and citric and glutamic acids, is studied. A comparison of the data obtained with the calculated profiles of copper distribution among the dissolved forms in model solutions revealed that the binding of copper to citrate does not affects and its binding with the other organic reagents reduces the catalytic effect of copper(II) in the chemiluminescence reaction. Free ions and monohydroxo complexes of copper(II) demonstrate the highest activity in the CL reaction. The chemiluminescence method is applicable to the direct (with no preliminary separation) determination of labile copper species in natural surface waters.