Oxidative Cleavage Research Articles

An air- and moisture-stable ruthenium precatalyst for diverse reactivity

Versatile, efficient and robust (pre)catalysts are pivotal in accelerating the discovery and optimization of chemical reactions, shaping diverse synthetic fields such as cross-coupling, C–H functionalization and polymer chemistry. Yet, their scarcity in certain domains has hindered the advancement and adoption of new applications. Here we present a highly reactive air- and moisture-stable ruthenium precatalyst [(tBuCN)5Ru(H2O)](BF4)2, featuring a key exchangeable water ligand. This versatile precatalyst drives an array of transformations, including late-stage C(sp2)–H arylation, primary/secondary alkylation, methylation, hydrogen/deuterium exchange, C(sp3)–H oxidation, alkene isomerization and oxidative cleavage, consistently outperforming conventionally used ruthenium (pre)catalysts. The generality and applicability of this precatalyst is exemplified through the potential for rapid screening and optimization of photocatalytic reactions with a suite of in situ generated ruthenium photocatalysts containing hitherto unknown complexes, and through the rapid discovery of reactivities previously unreported for ruthenium. The diverse applicability observed is suggestive of a generic platform for reaction simplification and accelerated synthetic discovery that will enable broader applicability and accessibility to state-of-the-art ruthenium catalysis.

Groundwater‐surface water interaction, dissolved organic carbon oxidation and dissolution in carbonate aquifers

AbstractThe high primary porosity and permeability of eogenetic karst aquifers permit water recharged through secondary dissolution features to be temporarily stored in aquifer matrix porosity. The recharged water contains elevated dissolved organic carbon (DOC) concentrations that, when oxidized, enhance limestone dissolution and impact carbon cycling. We evaluate the relationship between DOC oxidation and limestone dissolution using observations at a stream sink‐rise system and reversing spring in the Floridan aquifer, north‐central Florida, USA, where subsurface residence times of recharged water are days and months, respectively. We estimate water chemical compositions during surface water‐groundwater interactions at these two systems with mixing models of surface water and groundwater compositions and compare them with measured DOC, dissolved inorganic carbon (DIC), Ca2+ and dissolved organic nitrogen (DON) concentrations. Differences between measured and modelled concentrations represent net changes that can be attributed to calcite dissolution and redox reactions, including DOC oxidation. DOC losses and Ca2+ gains exhibit significant (p < 0.01) inverse linear correlations at both the reversing spring (slope = −0.9, r2 = 0.99) and the sink‐rise system (slope = −0.4, r2 = 0.72). DOC oxidation in both systems was associated with decreases in the molar C:N ratio (DOC:DON). Significant (p < 0.01) positive linear correlations between increases in Ca2+ and DIC concentrations after correcting for DIC derived from calcite dissolution occurred at both the reversing spring (slope = 1.3, r2 = 0.99) and the sink‐rise system (slope = 1.61, r2 = 0.75). Greater deviations from the expected slope of −1 or +1 at the sink‐rise system than at the reversing spring indicate DOC oxidation contributes less dissolution at the sink‐rise system than at the reversing spring, likely from shorter storage in the subsurface. A portion of the deviation from expected slope values can be explained by the dissolution of Mg‐rich carbonate or dolomite rather than pure calcite dissolution. Despite this, slope values reflect kinetic effects controlling incomplete consumption of carbonic acid during dissolution reactions.

Oxidation of organics in water by active chlorine performed in microfluidic electrochemical reactors: a new way to improve the performances of the process

Wastewater polluted by organics can be treated by using electro-generated active chlorine, even if this promising route presents some important drawbacks such as the production of chlorinated by-products. Here, for the first time, this process was studied in a microfluidic electrochemical reactor with a very small inter-electrode distance (145 μm) using a water solution of NaCl and phenol and a BDD anode. The potential production of chloroacetic acids, chlorophenols, carboxylic acids, chlorate and perchlorate was carefully evaluated. It was shown, for the first time, up to our knowledge, that the use of the microfluidic device allows to perform the treatment under a continuous mode and to achieve higher current efficiencies and a lower generation of some important by-products such as chlorate and perchlorate. As an example, the use of the microfluidic apparatus equipped with an Ag cathode allowed to achieve a high removal of total organic carbon (about 76%) coupled with a current efficiency of 17% and the production of a small amount of chlorate (about 30 ppm) and no perchlorate. The effect of many parameters (namely, flow rate, current density and nature of cathode) was also investigated.

Synthesis of 2-aryl quinoxaline derivatives and their in silico investigation for breast cancer medication

The main objective of the present work is to synthesize and identify the potential breast cancer medication of 2-aryl quinoxaline ­derivatives via in silico investigations. Synthesis of 2-aryl quinoxaline derivatives have been achieved via the reaction of 3-aroylmethylene-2H-indol-2-ones 1 with various 1,2-diamines. Good yields were obtained at 60 °C in methanol by using graphene oxide (GO) as catalyst, however, the regio selectivity in case of unsymmetrically substituted diamines were low to moderated. This is the first report of the oxidative cleavage of C = C bond during the course of the reaction. Molecular docking study of these synthesized compounds were employed to calculate the binding affinity with human epidermal growth factor receptor 2 (HER2). 6-Bromo-3-phenylpyrido[2,3-b]pyrazine 3k showed highest binding energy of −7.70 kcal/mol depicting the potential inhibitor of HER2 receptor protein. However, this study needs to be supported by in vitro and in vivo studies.

Oligomerization mechanism of epigallocatechin-3-O-gallate during autoxidation

The autoxidation of tea catechins by dissolved oxygen proceeds in pH-neutral aqueous solutions, and the major products are oligomers. However, the reaction mechanisms have not been clarified. In this study, the autoxidation of (−)-epigallocatechin-3-O-gallate (1) was examined. The autoxidation with β-cyclodextrin, which includes the A-ring of 1, significantly suppressed oligomer production and increased the formation of products generated by the oxidative cleavage of the B-ring, indicating the participation of the A-ring in the oligomerization. Further, the autoxidation of 1 in the presence of phloroglucinol, a mimic of the catechin A-ring, yielded products via the nucleophilic addition of phloroglucinol to the B-ring quinone of 1. These results indicated that the oxidative A–B ring couplings accounted for the major oligomerization mechanism.

Oxidative pyrolysis of poplar sawdust: Probing the influence of oxidation reactions on property of biochar

Partial oxidation of some organics is desirable in some scenarios for compensation of the heat required for pyrolysis, which, however, impacts not only composition of bio-oil but also possibly property of biochar. This was investigated herein by oxidative pyrolysis of poplar sawdust from 300 to 600 °C and further analysis of the pyrolytic products, especially biochar. The results showed that O2 could oxidize some organics on surface of biochar, forming more volatiles below 400 °C. Above this temperature the excessive oxidation of the light and heavy organics with π-conjugated structures in bio-oil dominated, producing more gases. Weight loss of biochar from oxidation of organics on its surface was only remarkable at 300 °C, while some weight gain was observed from introduction of additional oxygen-containing functionalities from the oxidation. The removal of aromatic structures on biochar at 500 or 600 °C via oxidation was rather difficult. However, the oxidation reactions did make the biochar oxygen-rich but hydrogen-deficient, which, in overall, improved thermal stability and comprehensive combustion performance of the biochar. Additionally, oxygen presence enhanced aromatic degree of biochar by increasing regularity of (100) facet of carbon crystals while narrowing interplanar spacing of (002) facets. The oxygen-rich nature also made the biochar from the oxidative pyrolysis more hydrophilic while the removal of some organics via oxidation promoted development of the pore structures.

Pliocene CO2 rise due to sea-level fall as a mechanism for the delayed ice age

Global sea level fell progressively during the Pliocene in response to the growth of ice sheets at high northern latitudes. However, not until ∼2.7 Ma did the climate system actually generate and maintain major ice sheets in the Northern Hemisphere. A decline in atmospheric CO2 levels (pCO2) is thought to be responsible for the Pleistocene ice ages. However, the link between pCO2 and Pliocene glaciations, or their delay, is not well understood, mainly because the magnitude of pCO2 remains uncertain beyond the maximum age of ice cores (∼0.8 Ma). Here, we develop a carbonate clumped isotope (∆47) geothermometer specifically for pedogenic carbonate in Chinese loess, which we use to reconstruct temperatures in northern China, and pCO2, for the past 7.24 Ma. The palaeotemperature results show an oscillatory cooling trend over time in the East Asian monsoon region, in good agreement with coeval tropical sea surface temperature records. The pCO2 reconstruction using the pedogenic carbonate palaeobarometer reveals low values (150–325 ppmv) during the intervals of 7.24–4.3 Ma and 2.6–0 Ma. In contrast, there is a three-step rise in pCO2 up to 535 ppmv from 4.3 to 2.6 Ma, coincident with an oscillatory decrease in sea level and in benthic δ13C. We suggest that the Pliocene CO2 rise was causally related to the sea-level fall and associated organic carbon oxidation on exposed continental shelves, thereby delaying the onset of the ice age. This implies a negative feedback mechanism induced by long-term cooling since the Late Miocene, which may have delayed the onset of the ice age but did not prevent it.

Leakage of old carbon dioxide from a major river system in the Canadian Arctic.

The Canadian Arctic is warming at an unprecedented rate. Warming-induced permafrost thaw can lead to mobilization of aged carbon from stores in soils and rocks. Tracking the carbon pools supplied to surrounding river networks provides insight on pathways and processes of greenhouse gas release. Here, we investigated the dual-carbon isotopic characteristics of the dissolved inorganic carbon (DIC) pool in the main stem and tributaries of the Mackenzie River system. The radiocarbon (14C) activity of DIC shows export of "old" carbon (2,380 ± 1,040 14C years BP on average) occurred during summer in sampling years. The stable isotope composition of river DIC implicates degassing of aged carbon as CO2 from riverine tributaries during transport to the delta; however, information on potential drivers and fluxes are still lacking. Accounting for stable isotope fractionation during CO2 loss, we show that a large proportion of this aged carbon (60 ± 10%) may have been sourced from biospheric organic carbon oxidation, with other inputs from carbonate weathering pathways and atmospheric exchange. The findings highlight hydrologically connected waters as viable pathways for mobilization of aged carbon pools from Arctic permafrost soils.

Electrochemical hydrogenation and oxidation of organic species involving water.

Fossil fuel-driven thermochemical hydrogenation and oxidation using high-pressure H2 and O2 are still popular but energy-intensive CO2-emitting processes. At present, developing renewable energy-powered electrochemical technologies, especially those using clean, safe and easy-to-handle reducing agents and oxidants for organic hydrogenation and oxidation reactions, is urgently needed. Water is an ideal carrier of hydrogen and oxygen. Electrochemistry provides a powerful route to drive water splitting under ambient conditions. Thus, electrochemical hydrogenation and oxidation transformations involving water as the hydrogen source and oxidant, respectively, have been developed to be mild and efficient tools to synthesize organic hydrogenated and oxidized products. In this Review, we highlight the advances in water-participating electrochemical hydrogenation and oxidation reactions of representative organic molecules. Typical electrode materials, performance metrics and key characterization techniques are firstly introduced. General electrocatalyst design principles and controlling the microenvironment for promoting hydrogenation and oxygenation reactionsinvolving waterare summarized. Furthermore, paired hydrogenation and oxidation reactions are briefly introduced before finally discussing the challenges and future opportunities of this research field.

Enhanced solar light-induced performance of a step-scheme heterojunction nanostructure (C3N4/ZrO2) for mixed dye degradation and methanol oxidation

This study focuses on the high demand for innovative nanostructured materials with boosted photocatalytic performance for the degradation of organic pollutants and oxidation of organic compounds. A nanostructure consisting of graphitic carbon nitride (C3N4) and zirconium oxide (ZrO2) denoted as C3N4/ZrO was synthesized via direct thermal pyrolysis. A comprehensive array of characterization techniques (XRD, FESEM, HRTEM and UV-DRs analysis) was utilized for a detailed analysis of the prepared photocatalysts. The photoactivity of the C3N4/ZrO nanostructure was explored by the photocatalytic degradation of a mixture of dyes (Rh B + CV), and methanol oxidation reaction and compared with those of pristine C3N4 and ZrO2. The photoactivity of C3N4/ZrO for degrading the mixed dye under simulated solar light was 97% higher than those of pristine C3N4 (88%) and ZrO2 (31%). The C3N4/ZrO nanostructure, functioning as a step-scheme heterojunction, demonstrated superior photocatalytic performance due to enhanced charge transport facilitated by robust interfacial contact between C3N4 and ZrO2. This enhanced photodegradation efficiency, reaching 97%, establishes a foundation for the development of heterojunction catalysts with exceptional photocatalytic activities. Furthermore, the methanol oxidation activity of the C3N4/ZrO nanostructure was exceptionally high, yielding a 138.25 mA/cm2 current density at a 2 M methanol. The proposed material has a high application potential for mitigating pollution and energy issues.

Cation-mediated acid-base pairs for mild oxidative cleavage of lignocellulosic β-1,4-glycosidic bonds

Solar-driven lignocellulosic biomass photoreforming holds significant promise for the production of value-added chemicals and fuels. The cleavage of the β-1,4-glycosidic bond is crucial for the effective conversion of lignocellulosic biomass. Polymeric carbon nitride (PCN) with acid-base pairs (M-C sites) is developed through heteroatomic carbon incorporation and cation insertion. It can be used for the gentle oxidation of cellobiose to monosaccharides, bypassing the formation of organic acids such as gluconic acid and glucaric acid. A series of different alkaline/alkaline-earth cation for regulation of acid-base pairs exhibited a negative correlation between β-1,4-glycosidic bond cleavage and cation radii. In particular, the introduction of short-radius cations (such as Li) into PCN enabled the formation of acid-base (M-C) pairs characterized by strong acidity. It also enhanced electron delocalization around M-C sites, potentially promoting the generation of reactive radicals in the reaction. Electron paramagnetic resonance analysis confirmed the presence of •OH radicals. The mild oxidative species, are the primary reactive radicals responsible for β-1,4-glycosidic bond cleavage in cellobiose. This study provides insightful evidence for the rational regulation of acid-base sites in facilitating β-1,4-glycosidic bond cleavage. It sheds light on the oxidative cleavage mechanisms integral to lignocellulosic biomass photoreforming, offering insights for advancing sustainable biomass conversion technologies.

Fluorenone‐Based Covalent Triazine Frameworks/Twinned Zn0.5Cd0.5S S‐scheme Heterojunction for Efficient Photocatalytic H2 Evolution

AbstractPhotocatalytic hydrogen evolution reaction (HER) is a very promising and sustainable technology, yet precisely exploring effective HER photocatalysts remains a critical challenge due to the rapid charge recombination. In this work, a brand‐new S‐scheme heterojunction is successfully designed and constructed by in situ growth of twinned Zn0.5Cd0.5S Solid Solution (CZS) on a novel fluorenone‐based covalent triazine framework (FOCTF). The S‐scheme heterojunctions is identified via in situ irradiation XPS, and electron spin resonance, which can greatly improve the photocatalytic HER rate and stability. Under illumination, the highest photocatalytic HER rate of well‐designed CZS‐FOCTF is 247.62 mmolg−1h−1, 3.83 times as high as that of pure CZS. Experimental and theoretical investigations corroborate that the new FOCTF has a well‐matched staggered band alignment and work function difference with CZS. The as‐fabricated CZS‐FOCTF S‐scheme heterojunction can establish a favorable internal electric field, which accelerates the directional S‐scheme charge migration, thereby enhancing the separation and utilization efficiency of carriers. This finding precisely achieves the spatially oriented powerful electron transport and separation at the interfaces of inorganic–organic hybrid heterojunctions. It is thus desirable that this work can furnish an alternative strategy to rationally design new CZS‐based S‐scheme heterojunction photocatalysts based on novel organic oxidation semiconductors for diversified photocatalytic reactions.

Photocatalytic, Oxidative Cleavage of C-C Bond in Lignin Models and Native Lignin.

It is challenging to realize the selective C-C bond cleavage of lignin β-O-4 linkages for production of high-value aromatic chemicals due to its intrinsic inertness and complex structure. Here we report a light-driven, chlorine-radical-based protocol to realize the oxidative C-C bond cleavage in various lignin model compounds catalyzed by commercially available TPT and CaCl2, achieving high conversion and good to high product yields at room temperature. Mechanistic studies reveal that the preferential activation of Cβ-H bond facilitates the oxidation and C-C bond cleavage of lignin β-O-4 model via chlorine radical. Furthermore, this method is also applicable to the depolymerization of natural lignin extracts, furnishing the aromatic oxygenates from the cleavage of Cα-Cβ bonds. This study provides experimental foundations to the depolymerization and valorization of lignin into high value-added aromatic compounds.

ZnIn2S4/MOF S-scheme photocatalyst for H2 production and its femtosecond transient absorption mechanism

Photocatalytic water splitting is a popular pathway for H2 evolution, but the slow water oxidation greatly hampers the overall activity. To harness photogenerated holes in an efficient and lucrative way, the water oxidation reaction is replaced by selective oxidation of organic compounds to achieve simultaneous production of H2 and value-added chemicals. Herein, an alternative tactic is reported where an organic compound (benzylamine, BA) not only serves as the precursor for N-benzylidene-benzylamine (NBBA) production but also provides hydrogen sources for H2 evolution, achieving the goal under anhydrous conditions. This process is realized using an S-scheme photocatalyst composed of ZnIn2S4 and the UiO-66-NH2 (U6N) metal-organic framework (MOF). The S-scheme carrier transfer mechanism was validated by in-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) and femtosecond transient absorption (fs-TA) spectroscopy. With increased carrier efficiency and reinforced redox power endowed by the S-scheme heterojunction, the composite performed better than ZnIn2S4 and MOF. The performance was further ameliorated by Pt-cocatalyst modification, achieving an H2 production rate of 5275 μmol h−1 g−1 as well as BA conversion of 94.3% with 99.3% NBBA selectivity. Mechanistic studies reveal that BA is initially oxidized to carbon-centered radicals and further to imines along with the release of protons. The imine reacts with another BA molecule to form NBBA, while the protons are reduced to H2. This work provides new insights into concurrent photocatalytic H2 production and selective organic oxidation from organic amines using S-scheme photocatalysts.

Toward a Sustainable Photocatalytic Oxidative Cleavage of Olefins Mediated by Nitrate Radicals: The Influence of the Physicochemical Features of the Photocatalyst

Toward a Sustainable Photocatalytic Oxidative Cleavage of Olefins Mediated by Nitrate Radicals: The Influence of the Physicochemical Features of the Photocatalyst

Frontiers in Photoelectrochemical Catalysis: A Focus on Valuable Product Synthesis.

Photoelectrochemical (PEC) catalysis provides the most promising avenue for producing value-added chemicals and consumables from renewable precursors. Over the last decades, PEC catalysis, including reduction of renewable feedstock, oxidation of organics, and activation and functionalization of C─C and C─H bonds, are extensively investigated, opening new opportunities for employing the technology in upgrading readily available resources. However, several challenges still remain unsolved, hindering the commercialization of the process. This review offers an overview of PEC catalysis targeted at the synthesis of high-value chemicals from sustainable precursors. First, the fundamentals of evaluating PEC reactions in the context of value-added product synthesis at both anode and cathode are recalled. Then, the common photoelectrode fabrication methods that have been employed to produce thin-film photoelectrodes are highlighted. Next, the advancements are systematically reviewed and discussed in the PEC conversion of various feedstocks to produce highly valued chemicals. Finally, the challenges and prospects in the field are presented. This review aims at facilitating further development of PEC technology for upgrading several renewable precursors to value-added products and other pharmaceuticals.

Long‐Emission‐Wavelength Humic‐Like Component (L‐HULIS) as a Secondary Source Tracer of Brown Carbon in the Atmosphere

AbstractThe optical properties of secondary brown carbon (BrC) aerosols are poorly understood, hampering quantitative assessments of their impact. We propose a new method for estimating secondary source of BrC using excitation‐emission matrix (EEM) fluorescence spectroscopy, combined with parallel factor analysis (PARAFAC) and partial least squares regression (PLSR). Experiments were conducted on a collection of PM2.5 samples from urban areas in five Chinese cities during winter and summer. The humic‐like component with long‐emission wavelengths (L‐HULIS) was identified as a secondary source tracer of BrC. This was confirmed by correlating PARAFAC components with secondary organic aerosol tracers and molecular oxidation indices obtained from Fourier transform ion cyclotron resonance mass spectrometry analysis. Using L‐HULIS as a secondary tracer of BrC, it was determined that the contribution of secondary sources to water‐soluble BrC (WS‐BrC) in source emission samples is significantly smaller than in PM2.5 from five Chinese cities, supporting our method. In the five cities, secondary source derived via L‐HULIS contributes a dominant potion (80% ± 3.5%) of WS‐BrC at 365 nm during the summer, which is approximately twice as high as during the winter (45% ± 4.9%). Radiocarbon isotope (14C) analysis provides additional constraints to the sources of L‐HULIS‐derived secondary WS‐BrC in urban PM2.5, suggesting that aged biomass burning is the dominant contributor to secondary WS‐BrC in winter, and biogenic emission is dominant during summer. This study is the first report on identification of secondary sources of BrC using the fluorescence technique. It demonstrates the potential of this method in characterizing non‐fossil source secondary BrC in the atmosphere.

Hydrologic and Landscape Controls on Rock Weathering Along a Glacial Gradient in South Central Alaska, USA

AbstractRock weathering impacts atmospheric CO2 levels with silicate rock dissolution removing CO2, and carbonate dissolution, pyrite oxidation, and organic rock carbon oxidation producing CO2. Glacierization impacts the hydrology and geomorphology of catchments and glacier retreat due to warming can increase runoff and initiate landscape succession. To investigate the impact of these changes on catchment scale weathering CO2 balances, we report monthly samples of solute chemistry and continuous discharge records for a sequence of glacierized watersheds draining into Kachemak Bay, Alaska. We partition solute and acid sources and estimate inorganic weathering CO2 balances using an inverse geochemical mixing model. Furthermore, we investigated how solutes vary with discharge conditions utilizing a concentration‐runoff framework. We develop an analogous fraction‐runoff framework which allows us to investigate changes in weathering contributions at different flows. Fraction‐runoff relationships suggest kinetic limitations on all reactions in glacierized catchments, and only silicate weathering in less glacierized catchments. Using forest cover as a proxy for landscape age and stability, multiple linear regression shows that faster reactions (pyrite oxidation) contribute less to the solute load with increasing forest cover, whereas silicate weathering (slow reaction kinetics) contributes more. Overall, in glacierized catchments, we find elevated weathering fluxes at high runoff despite significant dilution effects. This makes flux estimates that account for dilution more important in glacierized catchments. Our findings quantify how glaciers modify the inorganic weathering CO2 balance of catchments through hydrologic and geomorphic forcings, and support the previous hypothesis that deglaciation will be accompanied by a shift in inorganic weathering CO2 balances.

Electrochemical synthesis in company with hydrogen production via renewable energy: Opportunities and challenges

Organic electromechanical synthesis is an eco-friendly and efficient method for material synthesis, effectively addressing the high energy consumption and pollution problems in the traditional chemical industry. By combining hydrogen production from water electrolysis with organic electromechanical synthesis, the reactive oxygen/hydrogen from water hydrolysis can be utilized to oxidize/reduce organic compounds, reducing energy consumption and producing valuable organic products. However, this strategy still faces challenges when implemented in the industry. This paper addresses major technical challenges in the field, providing new insights for future advancements. Firstly, when selecting anode reactions for hydrogen production, it is important to consider the value and market demand of the oxidation product to match the production scale. Secondly, the development of efficient electrocatalysts and electrodes is required to enhance the oxidation kinetics and mass transfer of organics at the current density levels of industrial hydrogen production (500–2000 mA cm−2). Thirdly, it is essential to improve the selectivity and Faraday efficiency of the anode target product to lower the cost of subsequent separation and purification. Fourthly, existing anion and oxygen ion exchange membranes lack corrosion resistance to organic matter, and new separator materials with high ion conductivity and stability are crucial for the electrolytic coupling system. Finally, when combining organic oxidation and water electrolysis, the complexity of product separation increases, and it is recommended to integrate distillation, extraction, membrane separation, and electrochemical reactions to improve process efficiency.

POTENTIAL THREATS TO THE ECOLOGICAL STATE OF WATER IN THE SEVASTOPOL BAY

The purpose of the work is to discuss the main environmental problems of the state of waters in the Sevastopol Bay and to identify the causes affecting their quality. Four seasonal surveys of the Sevastopol Bay water area in 2022 confirmed the prime impact of the Black River runoff, a main source of nutrients, on the hydrochemical composition of the bay waters.At the same time, it is noted that the hydrochemical parameters of the South Bay waters are predominantly affected by freshwater runoff in the estuarine part of the area rather than by the Black River water. It is assumed that the runoff is permanent, and not emergency, as previously thought. With the winds of the southern directions, the spread of the South Bay water to the central part of the Sevastopol Bay is possible, thus affecting the state of its ecosystem.In summer an additional source of ammonium ions was recorded in the estuarine part of the Artillery Bay, next to which the Crystal city beach is located, with concentrations 80 times higher than the background. Since ammonium is a product of organic matter oxidation, its appearance may indicate the predominance of destructive processes, which affect living conditions of biological organisms and, in general, the ecological state of waters. In the warm season a constant deficiency of oxygen was observed in the bottom waters of an artificial depression under the floating dock, which in some cases leads to the formation of hydrogen sulfide. All detected threats affect the ecological state of entire ecosystem of the bay, the living conditions of biological organisms and the recreational potential of the bay