Bell-shaped Dependence Research Articles

Tuning the Stability and Kinetics of Dioxazaborocanes.

We investigated the equilibrium reaction of boronic acid (BA), diethanolamines (DEA), and 1,3,6,2-dioxazaborocanes (DOAB) in aqueous solutions, both theoretically and experimentally. Our findings show that the association constant can be adjusted by substituting BA and DEA derivatives, ranging from 100 to 103 M-1, exhibiting a bell-shaped pH dependency. The highest stability was achieved when the pKa values of DEA and BA were closely matched. This approach enabled the preparation of a highly stable DOAB under physiological conditions. Furthermore, the hydrolysis kinetics of DOABs were controllable over a range of five orders of magnitude based on the substituent's steric effect. In the slowest case, this resulted in quasi-static stability with only 1 % cleavage in the first hour, followed by a week-long cleavage period to reach equilibrium. These insights could establish a unique chemistry platform for designing scheduled cleavability on a day-to-week timescale, relevant to protein engineering, immunotherapy, and other smart drug delivery applications.

Albumin incorporation into recognising layer of HER2-specific magnetic nanoparticles as a tool for optimal targeting of the acidic tumor microenvironment

Cancer is unquestionably a global healthcare challenge, spurring the exporation of novel treatment approaches. In recent years, nanomaterials have garnered significant interest with the greatest hopes for targeted nanoformulations due to their cell-specific delivery, improved therapeutic efficacy, and reduced systemic toxicity for the organism. The problem of successful clinical translation of nanoparticles may be related to the fact that most in vitro tests are performed at pH values of normal cells and tissues, ranging from 7.2 to 7.4. The extracellular pH values of tumors are characterized by a shift to a more acidic region in the range of 5.6–7.0 and represent a crucial target for enhancing nanoparticle delivery to cancer cells. Here we show the method of non-active protein incorporation into the surface of HER2-targeted nanoparticles to achieve optimal cellular uptake within the pH range of the tumor microenvironment. The method efficacy was confirmed in vitro and in vivo showing the maximum binding of nanoparticles to cells at a pH value 6.4. Namely, fluorescent magnetic nanoparticles, modified with HER2-recognising affibody ZHER2:342, with proven specificity in terms of HER2 recognition (with 62-fold higher cellular uptake compared to control nanoparticles) were designed for targeting cancer cells at slightly acidic pH values. The stabilizing protein, namely, bovine serum albumin, one of the major blood components with widespread availability and biocompatibility, was used for the decoration of the nanoparticle surface to alter the pH response of the targeting magnetic conjugates. The optimally designed nanoparticles showed a bell-shaped dependency of interaction with cancer cells in the pH range of 5.6–8.0 with maximum cellular uptake at pH value 6.4 close to that of the tumor microenvironment. In vivo experiments revealed that after i.v. administration, BSA-decorated nanoparticles exhibited 2 times higher accumulation in tumors compared to magnetic nanoparticles modified with affibody only. Thus, we demonstrated a valid method for enhancing the specificity of targeted nanoparticle delivery to cancer cells without changing the functional components of nanoparticles.

Налоговая нагрузка НДФЛ и страховых взносов в Российской Федерации

Introduction: the period between 2000 to 2020 was marked by serious changes in taxation in the Russian Federation. The consequences of these changes for both the budget system and residents of Russia are still poorly studied, in particular, with reference to the impact of changes in social contribution rates and the introduction of various tax benefits on reducing income inequality. Such studies are necessary for both determining the degree of distortion in various incentives by tax policy measures and evaluating the effectiveness of these measures. Objectives: to assess the tax burden on individuals and households in order to determine the degree to which tax reforms comply with the originally stated goals, primarily, in terms of fairness criteria. Methods: analysis of distribution curves, regression analysis. Results: the tax wedge assessments based on the survey data revealed the differences between the actual level of the tax burden and the formal tax burden as well as tax evasion typical for low-income groups of the population. At the same time, there were no significant differences found in the tax burden distribution in individuals and households. Conclusions: the taxation system for individuals in Russia is regressive. The results obtained turned out to be robust to the choice of specifications of the estimated equations. It is important to note that there is a relatively high degree of regressiveness of the taxation scale in terms of insurance premiums and, at the same time, a bell-shaped dependence of the tax burden on the size of the payroll.

Photocatalytic efficiency of TiO2 films immobilized by annealing on glassy support as a function of material mass loading

The impact on the structure and photocatalytic behavior of annealed TiO2 films at 450°C on glassy support prepared by the doctor blade method with different amounts of material loadings was evaluated. Raman, SEM-EDS, and X-ray analyses indicated that higher material loading only increased the thickness of the annealed TiO2 films, but not their surface roughness, which remained almost constant at 290 ± 13 nm. Quantum yields for photocatalytic generation of ROS (HO• or O2•−) and degradation of model organic pollutants such as rhodamine B and methylene blue were also determined under different illumination configurations up to three photodegradation cycles without loss of photocatalytic activity. A marked bell-shaped dependence with mass loading was observed, with the film with approximately 0.1 mg TiO2.cm−2 and 1 μm thickness providing the highest efficiency. Under these conditions, increased light penetration through the film occurs through various internal reflections, which enhances the excitation of the TiO2 particles on the surface of the material in contact with the aqueous solution. Therefore, the results highlight the intricate interplay between material loading and film thickness with excitation light to achieve optimal photocatalytic activity of immobilized TiO2, a factor that can be considered in the rational design of efficient photoreactors.

A Critical Study on DNA Probes Attached to Microplate for CRISPR/Cas12 Trans-Cleavage Activity.

CRISPR/Cas12-based biosensors are emerging tools for diagnostics. However, their application of heterogeneous formats needs the efficient detection of Cas12 activity. We investigated DNA probes attached to the microplate surface and cleaved by Cas12a. Single-stranded (ss) DNA probes (19 variants) and combined probes with double-stranded (ds) and ssDNA parts (eight variants) were compared. The cleavage efficiency of dsDNA-probes demonstrated a bell-shaped dependence on their length, with a cleavage maximum of 50%. On the other hand, the cleavage efficiency of ssDNA probes increased monotonously, reaching 70%. The most effective ssDNA probes were integrated with fluorescein, antibodies, and peroxidase conjugates as reporters for fluorescent, lateral flow, and chemiluminescent detection. Long ssDNA probes (120-145 nt) proved the best for detecting Cas12a trans-activity for all of the tested variants. We proposed a test system for the detection of the nucleocapsid (N) gene of SARS-CoV-2 based on Cas12 and the ssDNA-probe attached to the microplate surface; its fluorescent limit of detection was 0.86 nM. Being united with pre-amplification using recombinase polymerase, the system reached a detection limit of 0.01 fM, thus confirming the effectiveness of the chosen ssDNA probe for Cas12-based biosensors.

The Formation of Small Amounts of Cyclopropane during Pulsed Pyrolysis of C4–C5 Acyclic Alkanes in the Adiabatic Compression Reactor

During high-temperature pulse pyrolysis of acyclic butanes and pentanes under adiabatic compression conditions, cyclopropane, a stressed cyclic hydrocarbon, was found among the reaction products in small quantities for the first time. The analysis of the reaction products was performed by gas chromatography using three capillary columns of different polarity, selectivity and sufficient efficiency. The identification of reaction products, including cyclopropane, was performed using retention times of individual substances and model mixtures, as well as comparing chromatograms with reference chromatograms from the literature and the ScanView Application Database. It was shown that the chromatographic peak attributed to cyclopropane could not be a ghost peak. Additional confirmation of this conclusion was obtained in a series of experiments on the pyrolysis of n-butane at a reduced initial temperature of the adiabatic compression reactor (from 120 °C to 50 °C) and a modified mode of GC analysis. Cyclopropane yields as a function of maximum temperature have a bell-shaped asymmetric dependence. The maximum value of the yield of cyclopropane increases with the transition from normal alkanes to isoalkanes, and from pentanes to butanes; for n-pentane, 0.009 wt. %, and for isobutene, ≈0.017 wt. %. During the pulse pyrolysis of isobutane, n-butane, isopentane and n-pentane, cyclopropane is not a primary product. Further theoretical and experimental studies are needed to establish the mechanism of cyclopropane formation during pyrolysis of C4–C5 acyclic alkanes.

Two different types of kinetics, where the initial rate increases faster or slower than the reactant concentration, can coexist on bell-shaped kinetic dependencies

Two different types of kinetics, where the initial rate increases faster or slower than the reactant concentration, can coexist on bell-shaped kinetic dependencies

Multi-Electron Transfer at H-Terminated p-Si Electrolyte Interfaces: Large Photovoltages under Inversion Conditions.

Photovoltages for hydrogen-terminated p-Si(111) in an acetonitrile electrolyte were quantified with methyl viologen [1,1'-(CH3)2-4,4'-bipyridinium](PF6)2, abbreviated MV2+, and [Ru(bpy)3](PF6)2, where bpy is 2,2'-bipyridine, that respectively undergo two and three one-electron transfer reductions. The reduction potentials, E°, of the two MV2+ reductions occurred at energies within the forbidden bandgap, while the three [Ru(bpy)3]2+ reductions occurred within the continuum of conduction band states. Bandgap illumination resulted in reduction that was more positive than that measured with a degenerately doped n+-Si demonstrative of a photovoltage, Vph, that increased in the order MV2+/+ (260 mV) < MV+/0 (400 mV) < Ru2+/+ (530 mV) ∼ Ru+/0 (540 mV) ∼ Ru0/- (550 mV). Pulsed 532 nm excitation generated electron-hole pairs whose dynamics were nearly constant under depletion conditions and increased markedly as the potential was raised or lowered. A long wavelength absorption feature assigned to conduction band electrons provided additional evidence for the presence of an inversion layer. Collectively, the data reveal that the most optimal photovoltage, as well as the longest electron-hole pair lifetime and the highest surface electron concentration, occurs when E° lies energetically within the unfilled conduction band states where an inversion layer is present. The bell-shaped dependence for electron-hole pair recombination with the surface potential was predicted by the time-honored SRH model, providing a clear indication that this interface provides access to all four bias conditions, i.e., accumulation, flat band, depletion, and inversion. The implications of these findings for photocatalysis applications and solar energy conversion are discussed.

Nonisothermal Crystallization Kinetics by DSC: Practical Overview

Providing a minimum of theory, this review focuses on practical aspects of analyzing the kinetics of nonisothermal crystallization as measured with differential scanning calorimetry (DSC). It is noted that kinetic analysis is dominated by approaches based on the Avrami and Arrhenius equations. Crystallization kinetics should not be considered synonymous with the Avrami model, whose nonisothermal applications are subject to very restrictive assumptions. The Arrhenius equation can serve only as a narrow temperature range approximation of the actual bell-shaped temperature dependence of the crystallization rate. Tests of the applicability of both equations are discussed. Most traditional kinetic methods tend to offer very unsophisticated treatments, limited only to either glass or melt crystallization. Differential or flexible integral isoconversional methods are applicable to both glass and melt crystallization because they can accurately approximate the temperature dependence of the crystallization rate with a series of the Arrhenius equations, each of which corresponds to its own narrow temperature interval. The resulting temperature dependence of the isoconversional activation energy can be parameterized in terms of the Turnbull–Fisher or Hoffman–Lauritzen theories, and the parameters obtained can be meaningfully interpreted and used for kinetic simulations.

Voltammetric oxidation behavior of single-stranded DNA on carbon screen printed electrodes: From short oligonucleotides to ultralong amplification products

To deeper understand the electrochemical behavior of nucleic acids, the synthetic DNA oligonucleotides of general formula (ACTG)n, where n = 1–12, as well as 16-mer DNA oligonucleotides varying in the number of guanine (dG; G-n, n = 0–7) or adenine (dA; A-n, n = 0–8) residues, and single-stranded DNA (ssDNA) amplification products were employed to systematically investigate their oxidation in the ‘dissolved’ and ‘adsorbed’ forms on carbon screen printed electrodes by square wave and cycling voltammetry in the potential range of 0.5–1.5 V (vs. Ag/AgCl). Two signals at 0.9–1.0 V and 1.1–1.2 V, attributed to the oxidation of dG and dA, respectively, were registered for the most of oligonucleotides. The oxidation process of ‘dissolved’ (ACTG)n with n = 1–2 via dG was found diffusion-controlled, while (ACTG)3 has demonstrated a mixed mechanism of oxidation reaction. At the same time, ‘adsorbed’ oligonucleotides demonstrated adsorption-limited responses, except for (ACTG)1 showing a mixed reaction mechanism. At a constant nucleotide or oligonucleotide molar concentration, the registered signals for (ACTG)n exponentially decreased with the molecule length. The signals of all studied oligonucleotides after pre-adsorption on electrode surface were up to 10-fold higher than those in the soluble form, except for (ACTG)1. The dG oxidation signal for G-n oligonucleotides, registered at about 0.9 V, was practically insensitive to the position of a single dG (at the end or in the middle of polynucleotide chain), while demonstrating a bell-shaped dependence on the dG amount with a maximum at n = 3–4. The dG oxidation signal for A-n oligonucleotides with a constant portion of dG also increased with the number of dA residues in the bell-shaped fashion with a maximum at n = 5. The folding of oligonucleotides into hairpins with a stem formed via dG/dC pairing resulted in a shift of the peak potential for dG oxidation to higher values. Finally, ultralong ssDNA products generated by rolling circle amplification (RCA) were found to produce strong non-Faradaic current masking the dG and dA oxidation signals. The electrochemical detection of RCA products via dG and dA oxidation was found possible if ultralong ssDNA is fragmented by carrying out RCA in the presence of an appropriate restrictase.

High-field 1/f noise in hBN-encapsulated graphene transistors

$1/f$ electronic noise is a conductance fluctuation, expressed in terms of a mobility ``$\ensuremath{\alpha}$-noise'' by Hooge and Kleinpenning. Understanding this noise in graphene is key for high-performance electronics. Early investigations pointed out a deviation from the standard Hooge formula, with the free-carrier density substituted by a constant density ${n}_{\mathrm{\ensuremath{\Delta}}}\ensuremath{\sim}{10}^{12}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. Here we investigate hBN-encapsulated graphene transistors where high mobility gives access to the velocity-saturation regime. We show that $\ensuremath{\alpha}$-noise is still accounted for by the Hooge formula on substituting conductance by differential conductance $G$, resulting in a bell-shaped dependence of flicker noise with bias voltage. The same analysis holds in the Zener regime at even larger bias, with two main differences. The first one is a strong enhancement of the Hooge parameter reflecting the hundred-times larger coupling of interband excitations to the hyperbolic phonon-polariton (HPhP) modes of the midinfrared Reststrahlen (RS) bands of hBN, which is supported by microwave noise thermometry measurements. The second is an exponential suppression of this coupling at large fields, which we attribute to decoherence effects. The phenomenology of $1/f$ noise in graphene supports a quantum-coherent bremsstrahlung interpretation of $\ensuremath{\alpha}$-noise.

Photocatalytic Hydrogen Evolution by a De Novo Designed Metalloprotein that Undergoes Ni-Mediated Oligomerization Shift.

De novo metalloprotein design involves the construction of proteins guided by specific repeat patterns of polar and apolar residues, which, upon self-assembly, provide a suitable environment to bind metals and produce artificial metalloenzymes. While a wide range of functionalities have been realized in de novo designed metalloproteins, the functional repertoire of such constructs towards alternative energy-relevant catalysis is currently limited. Here we show the application of de novo approach to design a functional H2 evolving protein. The design involved the assembly of an amphiphilic peptide featuring cysteines at tandem a/d sites of each helix. Intriguingly, upon NiII addition, the oligomers shift from a major trimeric assembly to a mix of dimers and trimers. The metalloprotein produced H2 photocatalytically with a bell-shape pH dependence, having a maximum activity at pH 5.5. Transient absorption spectroscopy is used to determine the timescales of electron transfer as a function of pH. Selective outer sphere mutations are made to probe how the local environment tunes activity. A preferential enhancement of activity is observed via steric modulation above the NiII site, towards the N-termini, compared to below the NiII site towards the C-termini.

Model Membranes and Antimicrobial Activities of pH-Sensitive Copolymers

Polymers are options as antimicrobials for skin protection, antifouling surfaces, and fabrics. Here we analyzed the interaction of polymers based on poly(methacrylate) (PMMA) and poly((dimethylamino ethyl) methacrylate) (PDMAEMA) with model membranes and bacteria. We used the homopolymers PMMA, PDMAEMA, and the diblock copolymer(s) prepared with different PMMAm:PDMAEMAn ratios (m/n). The interactions of PDMAEMA and PMMAm-b-PDMAEMAn with large unilamellar vesicles (LUVs) prepared with phosphatidylcholine and phosphatidylglycerol at different pHs, were analyzed by nuclear magnetic resonance (NMR), dynamic light scattering, and zeta potential. These polymers promoted LUVs leakage of a fluorescent probe (5,6-carboxyfluorescein) localized exclusively in the internal aqueous compartment. Interestingly, all copolymers exhibit a bell-shaped pH dependence for the polymer-induced LUVs leakage. The interaction of the positively charged polymers and the pH effect was also demonstrated using giant unilamellar vesicles. These copolymers inhibited bacterial growth in the micromolar range and can be used to prevent bacterial growth on surfaces.

Relationship between red blood cell aggregation and dextran molecular mass

The aim of this study was to investigate the aggregation of red blood cells (RBCs) suspended in dextran solution at various levels of molecular mass. Dextran solutions at molecular mass 40, 70, 100 and 500 kDa at concentration from 2 to 5 g/dL were used to suspend the RBCs. The radius and velocity of sedimenting RBC aggregates were investigated using image analysis. The radius and sedimentation velocity of aggregates increased initially, then decreased after achieving maxima. The maximal velocity of RBC aggregates showed a bell-shaped dependence on dextran molecular mass and concentration, whereas maximal radius showed monotonic increase with both factors. Difference between aggregate and solution density was estimated using aggregate radius and sedimentation velocity and dextran solution viscosity, and was consistent across most molecular mass and concentration levels. This allowed to calculate the porosity of aggregates and to show that it monotonically decreased with the increase in the solution density, caused by the increase in the dextran concentration. The results provide insight into the RBC aggregation process in solutions of proteins of different size, reflecting various pathological conditions. The currently reported data can be potentially applied to specific pathophysiological conditions giving an interpretation that is not yet fully discussed in the literature.

Magnetic-Field Dependence of LC-Photo-CIDNP in the Presence of Target Molecules Carrying a Quasi-Isolated Spin Pair.

NMR spectroscopy is well known for its superb resolution, especially at high applied magnetic field. However, the sensitivity of this technique is very low. Liquid-state low-concentration photo-chemically-induced dynamic nuclear polarization (LC-photo-CIDNP) is a promising emerging methodology capable of enhancing NMR sensitivity in solution. LC-photo-CIDNP works well on solvent-exposed Trp and Tyr residues, either in isolation or within proteins. This study explores the magnetic-field dependence of the LC-photo-CIDNP experienced by two tryptophan isotopologs in solution upon in situ LED-mediated optical irradiation. Out of the two uniformly 13C,15N-labeled Trp (Trp-U-13C,15N) and Trp-α-13C-β,β,2,4,5,6,7-d7 species employed here, only the latter bears a quasi-isolated 1Hα-13Cα spin pair. Computer simulations of the predicted polarization due to geminate recombination of both species display a roughly bell-shaped field dependence. However, while Trp-U-13C,15N is predicted to show a maximum at ca. 500 MHz (11.7 T) and a fairly weak field dependence, Trp-α-13C-β,β,2,4,5,6,7-d7 is expected to display a much sharper field dependence accompanied by a dramatic polarization increase at lower field (ca. 200 MHz, 4.7 T). Experimental LC-photo-CIDNP studies on both Trp isotopologs at 1μM concentration, performed at selected fields, are consistent with the theoretical predictions. In summary, this study highlights the prominent field-dependence of LC-photo-CIDNP enhancements () experienced by Trp isotopologs bearing a quasi-isolated spin pair.

Anomalous Chiral Transfer: Supramolecular Polymerization in a Chiral Medium of a Mesogenic Molecule.

Here, we report a medium-to-polymer anomalous chiral transfer in the supramolecular polymerization of a tetraphenylporphyrin-based achiral hydrogen-bonding monomer (TPP) in a chiral medium of 5-cyanobiphenyl CB*. A mixture of TPP in (R)-CB* ([TPP]=7.7 mol %) at 40 °C gave a columnar oblique LC mesophase, where the individual columns were composed of an optically active helical supramolecular polymer of TPP as a consequence of a successful medium-to-polymer chiral transfer. Meanwhile, upon dilution of CB* with achiral 5-cyanobiphenyl CB, the optical activity of the system showed an anomalous bell-shaped dependency on the composition of CB*/CB, where the gabs value of 0.049 at CB*/CB=50/50 was 6.0 times larger than the gabs value of CB* alone. Such anomalous chiroptical amplification in CD is most likely due to a change in the stacking geometry of TPP in the oblique columnar LC upon lateral compression.

Cryo-EM structure and electrophysiological characterization of ALMT from Glycine max reveal a previously uncharacterized class of anion channels.

Aluminum-activated malate transporters (ALMTs) form an anion channel family that plays essential roles in diverse functions in plants. Arabidopsis ALMT12, also named QUAC1 (quick anion channel 1), regulates stomatal closure in response to environmental stimuli. However, the molecular basis of ALMT12/QUAC1 activity remains elusive. Here, we describe the cryo-EM structure of ALMT12/QUAC1 from Glycine max at 3.5-Å resolution. GmALMT12/QUAC1 is a symmetrical dimer, forming a single electropositive T-shaped pore across the membrane. The transmembrane and cytoplasmic domains are assembled into a twisted two-layer architecture, with their associated dimeric interfaces nearly perpendicular. GmALMT12/QUAC1-mediated currents display rapid kinetics of activation/deactivation and a bell-shaped voltage dependency, reminiscent of the rapid (R)–type anion currents. Our structural and functional analyses reveal a domain-twisting mechanism for malate-mediated activation. Together, our study uncovers the molecular basis for a previously uncharacterized class of anion channels and provides insights into the gating and modulation of the ALMT12/QUAC1 anion channel.

The regulation of mitochondrial NO synthase activity under nitroglycerine application in rat heart and liver mitochondria

Nitroglycerine (NG) affords cardioprotection via NO formation, but the impact of NG application on reactive nitrogen species (RNS) metabolism remains little studied yet. Mitochondrial NO synthase (mtNOS) is an important endogenous source of RNS. Our aim was to study the effect of NG application on mtNOS activity and RNS production in rat heart and liver mitochondria. Different regulation of mtNOS activity in the heart and liver under NG treatment was found. While in heart mitochondria it increased dose-dependently, in liver mitochondria only moderate elevation and bell-shaped dose dependence of mtNOS activity on NG was observed. Nitrite and nitrate, which are the end products of L-arginine transformation by NOS, showed similar dose dependence on NG. To find an explanation for the observed dependences, we studied the effects of NG administration on the activity of arginase which competes with NOS for physiological substrate, Larginine. A strong reciprocal dependence between mtNOS and arginase activities was found. As we observed, the arginase activity increased under NG application. However, while in heart mitochondria high mtNOS activity agreed with moderate arginase activation, in liver mitochondria high arginase activity coincided with suppression of mtNOS activity at high doses of NG. Low arginase and high mtNOS activities observed in heart mitochondria were consistent with high NO2 − and NO3 − production and low hydroperoxide (H2O2) formation, whereas high arginase activity in liver mitochondria was accompanied by the reduction of NO2− /NO3− formation and simultaneous elevation of H2O2 production. A linear correlation between the arginase activity and hydroperoxide formation was found. We came to the conclusion that under NG administration arginase activation resulted in reciprocal regulation of RNS and ROS production in mitochondria, dependent on the proportion of mtNOS to arginase activity. Suppression of RNS metabolism could be the cause of ROS overproduction caused by high arginase and low mtNOS activity.

Анализ влияния предела текучести на коррозионное растрескивание под напряжением мартенситных и ферритных сталей в кислых средах

To evaluate the effect of yield stress on hydrogen embrittlement (HE) of martensitic and ferritic steels, the effect of hydrogen (H) capture by structural inhomogeneities (hydrogen traps) and the effect of plastic deformation and stress on the mechanism of stress corrosion cracking (SCC) are considered. In the presence of hydrogen, the brittle fracture of high-strength martensitic steels consists of flat areas of intergranular fracture at the initial austenitic grain boundaries and quasi-brittle cracks at the boundaries of martensite blocks. In low-strength steels, brittle fracture manifests itself in the form of transgranular fracture of ferrite grains. The decrease in the characteristics of martensitic steels with an increase in the yield strength occurs due to an increase in the hydrogen concentration at the stage of anodic dissolution (AD) due to the growth of the carbide/matrix interface. The reason for the growth hydrogen concentration in ferritic steels is a large mechanical overstress, an increase in the number of active dissolution centers, the formation of an electrochemical pearlite-ferrite pair, and an increase in surface roughness with increasing deformation. It is concluded that the bell-shaped dependences of the critical stress of the transition from AD to SCC and other characteristics of mechanical tests on magnitude are due to different mechanisms of hydrogen accumulation in martensitic and ferritic steels.

Analysis of the effect of yield stress on stress corrosion cracking of martensitic and ferritic steels in acidic environments

To evaluate the effect of yield stress on hydrogen embrittlement (HE) of martensitic and ferritic steels, the effect of hydrogen (H) capture by structural inhomogeneities (hydrogen traps) and the effect of plastic deformation and stress on the mechanism of stress corrosion cracking (SCC) are considered. In the presence of hydrogen, the brittle fracture of high-strength martensitic steels consists of flat areas of intergranular fracture at the initial austenitic grain boundaries and quasi-brittle cracks at the boundaries of martensite blocks. In low-strength steels, brittle fracture manifests itself in the form of transgranular fracture of ferrite grains. The decrease in the characteristics of martensitic steels with an increase in the yield strength occurs due to an increase in the hydrogen concentration at the stage of anodic dissolution (AD) due to the growth of the carbide/matrix interface. The reason for the growth hydrogen concentration in ferritic steels is a large mechanical overstress, an increase in the number of active dissolution centers, the formation of an electrochemical pearlite-ferrite pair, and an increase in surface roughness with increasing deformation. It is concluded that the bell-shaped dependences of the critical stress of the transition from AD to SCC and other characteristics of mechanical tests on magnitude of the yield stress are due to different mechanisms of hydrogen accumulation in martensitic and ferritic steels. Keywords: hydrogen embrittlement, high-angle boundaries, interfaces, traps, hydrogen binding energy, structural inhomogeneities, fracture.