The distribution and speciation features of gold in ores and minerals of the Natalkinskoe gold deposit (North-East Russia) are studied using light microscopy (LM), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX), X-ray electron probe microanalysis (EPMA), "phase" chemical analysis with atomic absorption spectrometry (PCA-AAS) and atomic absorption spectrometry with analytical data selections for single crystals (AAS-ADSSC). The vein and streaky-vein ores are high-grade ores, whereas veinlet-disseminated ores are less rich and disseminated ores are poor in gold. Up to 85 % of the gold in the ores is in a free native state, associated with quartz and sulfide minerals. LM, SEM-EDX and EPMA reveal that the predominant gold grains are 0.01 to 2.00 mm in size and at a fineness of 720 to 900 ‰. The finely dispersed and submicron elemental gold particles (Au0) amounted to 20 % and are mainly enclosed into arsenopyrite and pyrite. According to PCA-AAS data, the highest Au concentrations (up to 1383 ppm) are recorded in arsenopyrite; lower contents are typical of pyrite (up to 158.2 ppm). In these sulfides, two non-mineral species of "invisible" Au are the structurally bound and surface-bound species recognized by AAS-ADSSC. The structural Au is included in the mineral structure. The surface-bounded Au prevails and is confined to nano-sized, non-autonomous phases (NAPs) on the sulfide surface. In common with "invisible" Au, the micro-sized particles of native gold are often observed on the surface and within the surface layers of sulfide crystals. This is consistent with the model of post-growth transformations of nano-sized NAPs, resulting in the formation of nano and micro-sized Au0 particles. It is expected that the major part of gold contained in arsenopyrite and pyrite as finely dispersed and submicron particles, as well as the surface-bound gold in NAPs, can be won with modified current schemes of gold concentration, which enhances the value of the gold ore mining.

Dihydroquercetin (DHQ) is a bioflavonoid with high antioxidant, capillary-protective, and anti-inflammatory activity. DHQ has previously been used for treating Middle East respiratory syndrome coronavirus (MERS-CoV) infection and is currently considered a potential regulator of oxidative stress as part of COVID-19 multipurpose therapy. DHQ has a high safety profile but low bioavailability that limits its use. Innovative techniques (liposomization, crystal engineering, etc.) can be used to increase its bioavailability.

The main aspects of the antiviral, anti-inflammatory, antioxidant and hepatoprotective properties of dihydroquercetin (DHQ), which may affect the course of COVID-19, are considered. Given the low toxicity and a wide range of biological activity, aimed not only at suppressing enzymatic reactions with the participation of coronavirus, but also at eliminating the lesions caused by it in all the main target organs, dihydroquercetin can be recommended for inclusion in the complex therapy of the disease and during the recovery period of COVID-19.

Дигидрокверцетин (ДГК) — биофлавоноид, обладающий высокой антиоксидантной, капилляропротекторной и противовоспалительной активностью. Ранее ДГК применялся при инфекции, вызванной коронавирусом ближневосточного респираторного синдрома (MERS-CoV). В настоящее время ДГК рассматривается в качестве потенциального регулятора окислительного стресса в составе комплексной терапии COVID-19. ДГК характеризуется высоким профилем безопасности, но низкой биодоступностью, ограничива-ющей его применение. Для повышения биодоступности ДГК могут быть использованы инновационные технологии (липосомирование, инженерия кристаллов и др.).

As the world continues to fight COVID-19, along with the search for effective treatments, attention is focused on food ingredients that can help strengthen the immune system. This review outlines the potential role of vitamins and minerals as immunonutrients in supporting the body's nonspecific defenses against COVID-19.

The results of the two- and three-dimensional modeling of X-ray excitation during electron-probe microanalysis by the Monte Carlo method are compared. The study is based on a description of the X-ray distribution in pure elements such as Cu, Ag, and Au, which are of interest in the exploration of minerals at gold ore deposits. The absorption corrections calculated using the Monte Carlo models for 2D and 3D x-ray distribution over the sample depth are compared. For electrons with an energy of about 3 keV and more, calculations of the absorption factor for 2D modeling are in satisfactory agreement with those for 3D modeling. The functions of the radial and lateral x-ray distribution in the sample, which characterize the spatial resolution of electron-probe microanalysis, are constructed. The obtained approximations make it possible to estimate the resolution for elements which are generally determined by analytical lines of the K series and for some elements which are determined by L-series lines.

The composition, structure and formation features of the exogenous anomalous geochemical fields (AGFs) identified by lithochemical stream sediments (LSSs) are considered using the examples of the Dukat gold–silver ore-forming system and the deposit with the same name. The research was carried out in the Balygychan–Sugoy trough (Magadan region, north–east of Russia). Areal geochemical surveys on the 1:200,000 and 1:50,000 scales were conducted. Exogenous AGFs of basic element indicators of all known mineralization types were studied. It is shown that the surveys on the 1:200,000 scale are characterized by simplicity, relative depth and the possibility to obtain information operatively about the metallogeny of the area as a whole. At the same time, the anomalies were revealed as a result of surveys often making a relatively poor component composition and low contrast compared with ores. The violation of quantitative and sometimes qualitative relationships can be seen between elements, especially those related to gold–silver mineralization. In this situation, the most informative are surveys of LSSs on the 1:50,000 scale. The AGFs were revealed as a result of their performance to have a richer component composition and high contrast, conforming to different ore types. It is shown that, while prospecting for gold–silver mineralization with LSSs in cryolithogenesis zone conditions, the binding forms study of mineralization element indicators is effective. In watercourse heads, where alluvium is practically absent, mosses are proposed for sampling, as they hold the sandy silt material firmly. The obtained results are recommended for use at all stages of prospecting, not only in the north–east of Russia but also in other similar climatic regions.

A method for estimating the native gold composition in micron‐ and submicron‐sized inclusions in the matrix of a sulfide mineral with electron probe X‐ray microanalysis is proposed. Such inclusion sizes are comparable with or less than the X‐ray generation volume, and therefore, the analytical signal is a mixture of signals from the matrix elements and the inclusion elements, which significantly complicates the quantification. The proposed procedure is based upon the extrapolation of the trend of the dependence of the measured elemental contents in the inclusions, for example, Au or Ag, versus the content of matrix elements, namely, S, Fe, and As. To define the influence of the inclusion size on the intensity of the excited X‐rays, the trajectories of the electrons in a sample were simulated by the Monte Carlo method. It was found that the trends in the behavior calculated by the Monte Carlo method are consistent with the data measurements of an artificial pyrite sample with a sprayed pure gold layer (approximately 1 μm thick) arranged perpendicular to the sample surface. The measurements were performed on a Superprobe JXA‐8200 microanalyzer. The proposed method was demonstrated by analyzing natural, finely dispersed gold inclusions in arsenopyrite. This approach made it possible to evaluate the Au and Ag contents in the approximately 1 μm inclusions and assess the uncertainty of the measurement.

A special procedure was proposed to evaluate the gold content in gold-bearing particles found within the sulfide minerals. These particles' dimensions were comparable or less than the x-ray radiation area during the electron probe microanalysis (EPMA). The procedure was based on the extrapolation of the linear trend dependence of the inclusion element content (or intensity of X-ray) from the content (or intensity) of the surrounding matrix elements in the sulfide mineral. It was justified with the attracting experimental data and computed dependences of x-ray radiation intensity obtained by the modeling of trajectories of electrons in the substance using the Monte-Carlo method. A simple 2-D version of the Monte-Carlo modeling was employed to evaluate the dependence of intensity of x-ray radiation excited by the electrons from the particle size in a homogenous matrix. The model was grounded upon the formula for the law of the Bethe electron stopping power and the Rutherford formula for the angle of elastic scattering of electron in colliding with the atom. The impact parameter in the Rutherford formula was calibrated to ensure the agreement of computed backscattering factor of electrons with the referenced literature data by Duncumb and Reed. The model was tested by comparing the computed data for the adsorption factor the calculations by known Philibert's formula for some pure elements, composite sulfide minerals and some sulfides. The proposed procedure was tested with a synthetic sample of sulfide mineral of pyrite with plated pure gold. The measurements were performed by the electron probe microanalyzer JXA 8200 (JEOL, Japan). With the described above procedure it was feasible to evaluate the contents of gold and silver in the particles of gold-bearing inclusions with the dimensions less than 1 µm in arsenopyrite of the gold ore deposit. Keywords : X-ray electron probe microanalysis, gold inclusions, sulphide minerals, Monte Carlo simulation of electron track DOI: http://dx.doi.org/10.15826/analitika.2017.21.3.006 V.V. Tatarinov 1, 2 , А.L. Finkelshtein 1, 2 , R.G. Kravtsova 1 , L.А. Pavlova 1 1 Vinogradov Institute of Geochemistry SB RAS, 1A, Favorsky St, Irkutsk 664033, Russian Federation 2 Irkutsk State University, 1, Karl Marx St, Irkutsk, 664033, Russian Federation

X-ray fluorescence ( XRF ) techniques have been developed for the determination of major rock forming elements in small mass 50 and 110 mg of rock samples. In order to remove the influence of particle size and mineralogical composition on the results of the analysis, the samples fusion with lithium tetraborate and lithium metaborate was used. The metrological parameters of the different procedures of the sample preparation with different fluxes and dilution rates were comparable with the parameters of the routine procedure of sample preparation using 500 mg sample mass. The repeatability of the XRF analysis for the certified reference samples of ultramafic, mafic, intermediate and felsic rocks doesn’t exceed the allowable standard deviation for the wide range of contents for all preparation procedures. Certified reference materials of rocks (SDU-1, ST-2, SGD-1, SA-1, GBPg-1, SNS-2, SSn-1, SSV-1, SG-1, SG-2, SG-3, MGL-OShBO and SI-2) were used to obtain the calibration curves. Relative standard deviation for the obtained calibration curves doesn’t exceed the allowed values. The accuracy of the technique was estimated by the comparison of XRF determination results of 10 major rock forming elements with the certified values in CRM MGL-GAS, SGD-2, SKD-1 and SG-4. The relative standard deviation of XRF analysis was 0.4-8.9 % on average, depending on the element, the level of content and the procedure of the sample preparation. It was shown that the developed technique allows us to use the obtained glass beads for further determination of rare earth elements by inductively coupled plasma mass spectrometry analysis. Keywords : X-ray fluorescence analysis, rocks, major rock forming elements (Russian) DOI: http://dx.doi.org/10.15826/analitika.2015.19.2.009 A.A. Amosova 1 , S.V. Panteeva 2 , V.V. Tatarinov 3 , V.M. Chubarov 1 , A.L. Finkelshtein 1 1 Vinogradov Institute of Geochemistry SB RAS, Irkutsk, Russian Federation 2 Institute of the Earth’s crust SB RAS, Irkutsk, Russian Federation 3 Irkutsk National Research Technical University, Irkutsk, Russian Federation

X-ray fluorescence ( XRF ) techniques have been developed for the determination of major rock forming elements in small mass 50 and 110 mg of rock samples. In order to remove the influence of particle size and mineralogical composition on the results of the analysis, the samples fusion with lithium tetraborate and lithium metaborate was used. The metrological parameters of the different procedures of the sample preparation with different fluxes and dilution rates were comparable with the parameters of the routine procedure of sample preparation using 500 mg sample mass. The repeatability of the XRF analysis for the certified reference samples of ultramafic, mafic, intermediate and felsic rocks doesn’t exceed the allowable standard deviation for the wide range of contents for all preparation procedures. Certified reference materials of rocks (SDU-1, ST-2, SGD-1, SA-1, GBPg-1, SNS-2, SSn-1, SSV-1, SG-1, SG-2, SG-3, MGL-OShBO and SI-2) were used to obtain the calibration curves. Relative standard deviation for the obtained calibration curves doesn’t exceed the allowed values. The accuracy of the technique was estimated by the comparison of XRF determination results of 10 major rock forming elements with the certified values in CRM MGL-GAS, SGD-2, SKD-1 and SG-4. The relative standard deviation of XRF analysis was 0.4-8.9 % on average, depending on the element, the level of content and the procedure of the sample preparation. It was shown that the developed technique allows us to use the obtained glass beads for further determination of rare earth elements by inductively coupled plasma mass spectrometry analysis. Keywords : X-ray fluorescence analysis, rocks, major rock forming elements (Russian) DOI: http://dx.doi.org/10.15826/analitika.2015.19.2.009 A.A. Amosova 1 , S.V. Panteeva 2 , V.V. Tatarinov 3 , V.M. Chubarov 1 , A.L. Finkelshtein 1 1 Vinogradov Institute of Geochemistry SB RAS, Irkutsk, Russian Federation 2 Institute of the Earth’s crust SB RAS, Irkutsk, Russian Federation 3 Irkutsk National Research Technical University, Irkutsk, Russian Federation

Interaction of methyl esters of acylpyruvic acids with 3-aminophenolum afforded to 2-aroilmethylen-6-hydroxy-2,3-dihydroindol-3-ones. The proposed structures of synthesized compounds were confirmed by IR and NMR spectroscopy. Antibacterial activity of some obtained compounds was studied.

The interaction of methyl esters of aroylpyruvic acids with 2-aminophenol was used to form 2-aroylmethylene-6-hydroxy-2,3-dihydroindol-3-ones. The structures of these compounds were verified by IR and 1H NMR spectroscopy; the antimicrobial activity of the compounds synthesized here was studied.