Narrow Results

We investigate formal properties, mainly issues connected with propositional logic, of reaction systems introduced by Ehrenfeucht and Rozenberg. We are concerned only with the most simple variant of the systems. Basic properties of propositional formulas are expressed in terms of reaction systems. This leads to NP-completeness (resp. co-NP-completeness) of many problems concerning reaction systems. Among such problems are: (i) deciding whether the function defined by the system is total, (ii) determining the inverse of the function, (iii) deciding whether state sequences always end with a loop. Propositional formulas with monotonic truth-functions yield a particularly simple representation in terms of reaction systems.

We study the discrete Gierer–Meinhardt model of reaction–diffusion on three different types of networks: regular, random and scale-free. The model dynamics lead to the formation of stationary Turing patterns in the steady state in certain parameter regions. Some general features of the patterns are studied through numerical simulation. The results for the random and scale-free networks show a marked difference from those in the case of the regular network. The difference may be ascribed to the small world character of the first two types of networks.

The corrosion behavior of the austenitic chromium–nickel steel in different concentrations (0.001, 0.002, 0.005, and 0.01 M) of dimethyl 2-(2–hydroxy phenyl amino)-3-(triphenyl phosphoranilidin) butane dioate (L–OH) in 0.5 M H₂SO₄ was investigated by potentiostatic polarization measurements. The effect of concentration and temperature on inhibition properties was determined. It was found that the presence of L–OH reduces markedly the corrosion rate of steel in the acid solution. The inhibition efficiency increases as the L–OH concentration is increased. Maximum inhibition efficiency (95%) was obtained for alloy in acid solution containing 0.01 M of L–OH. Thermodynamic parameters for adsorption of L–OH are calculated. It was found that the inhibitor is adsorbed on the steel surface and the experimental results are in agreement with Timken's isotherm. Negative values of the free energy of adsorption were obtained indicating the spontaneity of adsorption process. Scanning electron microscopy was done from the surface of exposed sample indicating uniform film on the surface of the alloy.

Hybrid organic–inorganic coatings are deposited on 304 stainless steel substrates by the sol–gel technique to improve the corrosion resistance. A titania-based nanostructured hybrid sol–gel coating is impregnated with three different microencapsulated healing agents (inhibitors) including cerium, Benzotriazole (BTA), and 8-Hydroxyquinoline (8H). Field-emission scanning electron microscopy (FE-SEM) and electrochemical impedance spectroscopy (EIS) are performed to investigate the barrier performance properties. The optimum conditions to achieve corrosion protective coatings for 304 stainless steel were determined. The Nyquist plots demonstrate that the activation time of the coating containing 8H as an organic healing agent shows improved behavior when compared to other coatings including cerium and BTA. Cerium as an inorganic healing agent is second and BTA is third and minimum. An increase in the impedance parameters such as resistance and capacitance as a function of immersion time is achieved in a 3.5wt.% NaCl solution by using healing agents such as BTA. Actually, over the course of immersion, the barrier performance behavior of the coatings changes and reduction of the impedance observed from the coatings containing Ce and 8H discloses deterioration of the protection system after immersion for 96h of immersion in the 3.5% NaCl solution. However, after 96h of immersion time, the concentration of chloride ions is high and causes increase in defects, micro cracks, hole on the surface of hybrid titania nanostructured coating containing Ce and 8H by destruction of coating, and also hybrid titania nanostructured coating containing BTA; BTA is released from coating to improve the resistance of passive film, which is created on the surface.

The corrosion inhibition effect of synthesized 1,3-benzothiazole at very low concentrations on 410 martensitic stainless steel in 3MH₂SO₄ solution was studied through potentiodynamic polarization and weight loss measurements. The observation showed that the organic compound performed effectively with average inhibition efficiencies of 94% and 98% at the concentrations studied from both electrochemical methods due to the inhibition action of protonated inhibitor molecules in the acid solution. The amine and aromatics functional groups of the molecules active in the corrosion inhibition reaction were exposed from Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) spectroscopic analysis. Thermodynamic calculations showed cationic adsorption to be chemisorption adsorption, obeying the Langmuir adsorption isotherm. Images from optical microscopy showed an improved morphology in comparison to images from corroded stainless steel. Severe surface deterioration and macro-pits were observed in the uninhibited samples.

The inhibition effects of garlic extract on copper corrosion under a thin electrolyte layer (TEL) were investigated using weight-loss measurements, electrochemical methods and surface analysis. Results showed that the volatile organosulfur compounds of garlic extract, such as diallyl trisulfide and di-2-propenyl disulfide, among others, could adsorb on the surface of copper and have a significant inhibitory effect on copper corrosion. Garlic extract acted as a mixed-type inhibitor for copper under TEL. Surface analyses, such as scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), were conducted to illustrate the inhibitive mechanisms of this plant extract under a TEL.

The inhibition effect of synthesized corrosion inhibitor namely 5,5^′-(1,4-phenylene)bis($N$-phenyl-1,3,4-thiadiazol-2-amine) (PBPA) on the corrosion of mild steel in 1-M hydrochloric acid environment are examined by gravimetric techniques at various temperature (303–343 K). The synthesized inhibitor concentrations are 0.1–0.5mM. The inhibition efficiency increased with the increase of the inhibitor concentration. The inhibition efficiency reached 94% at the highest studied concentration of 0.5mM for 5h of immersion time and 303K. Moreover, the inhibition efficiency decreased with the temperature increase. The adsorption of tested inhibitor molecules on the surface of mild steel follows the Langmuir adsorption isotherm. The studied inhibitor molecules showed excellent inhibition since PBPA molecules have nitrogen and sulfur atoms in addition to phenyl and thiadiazol rings which were linked together in conjugation system.

Corrosion suppression effect of the combination of citrus paradise and cymbopogon oil distillates on mild steel (MS) in 0.5M H₂SO₄ and HCl solution was studied by potentiodynamic polarization, open circuit potential measurement, optical microscopy characterization, and ATF-FTIR spectroscopy. The distillates performed adequately in both acids at all concentrations considered with average inhibition efficiency above 90%. Corrosion rate of the non-inhibited steel at 7.690 and 2.819mm/y from both acids were substantially reduced to values between 0.465 and 0.466mm/y in H₂SO₄ while the values in HCl are 0.081 and 0.034mm/y. The distillates exhibit mixed type inhibition performance in both acids. However, polarization plots displayed cathodic passivation effect at higher distillate concentration in H₂SO₄ while cathodic-anodic passivation plots were observed at all distillate concentrations in HCl solution. Corrosion potential plots from open circuit measurement at specific distillate concentrations were significantly electropositive compared to the non-inhibited steel which was electronegative. Inhibition effect of the distillates occurred through chemisorption adsorption mechanism with Gibbs free energy values greater than $-$40KJ/Mol, in agreement with Langmuir isotherm model. Optical images of the non-inhibited steel displayed a severely degraded exterior which significantly contrast the protected exterior of the inhibited steel.

In this work, we have tested a new inhibitor formulation that is effective, economically efficient and in accordance with environmental legislation. The inhibitor tested is the crude extract of the oat plant (denoted as OE) obtained by the reflux method in the water. This extract is then used as a corrosion inhibitor of mild steel in 3% NaCl. This study was carried out by using electrochemical polarizations, Electrochemical Impedance Spectroscopy and gravimetric techniques. The results obtained showed that this extract satisfactorily inhibits the dissolution rate of mild steel. The inhibition efficiency increases with inhibitor concentration and reaches 72% at 5g$\cdot$L${}^{-1}$ of oat extract. Polarization data indicate that the extract acted as mixed type. The adsorption of the inhibitor on the mild steel surface in 3% NaCl follows the Langmuir adsorption isotherm. SEM analysis of the electrode surface condition confirms the results obtained.

Corrosion resistance of A36 carbon steel was assessed in 0.5M H₂SO₄ and HCl media in the presence of specific concentrations of Commiphoramyrrha (CM), Cymbopogon (CP) essential oil extracts and their combined admixture (CMCP). Values from potentiodynamic polarization showed CM extract reacted poorly in both acids at low concentration, but effectively at higher concentrations with optimal performance of 89.76% and 92.83%. CP extract generally performed effectively with inhibition values above 90%. CMCP performed very poorly in H₂SO₄ compared to its performance in HCl which was generally above 80% inhibition efficiency. The oil extracts exhibited mixed-type inhibition effect coupled with dominant anodic shift in corrosion potential and similar anodic slope configuration at all extract concentrations. ATR-FTIR spectra plots showed that most of the identified functional groups within the extract molecules generally adsorbed unto the A36 steel surface. Curves from open circuit potential analysis showed CM extract in H₂SO₄, and CP extract in H₂SO₄ and HCl solution significantly decreased the thermodynamic tendency of A36 steel to degrade. The curves of other extracts displayed significant time and extract concentration dependent active–passive transition behavior. Optical images of the unprotected steel exhibited severe general and localized surface deterioration compared to the inhibited steel with significantly protected morphology. Weight-loss analysis showed the effective protection effect of CP extract in both acids and CMCP in H₂SO₄ is independent of time and concentration from the onset of exposure compared to their remaining counterparts whose performance significantly varies over time and is concentration dependent. X-ray phase identification diagrams and identified patterns list revealed the presence of FeO(OH) on the steel surface without oil extracts while the phase compounds identified in the presence of the extracts are FeNi and Fe₃C.

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The extracellular signal-regulated protein kinase 2 (ERK2) is a pivotal member involving in Ras/Raf/MEK/ERK signal transduction pathway, acting as a central point where multiple signaling pathways coalesce to drive transcription. The pyrazolylpyrrole compounds as ATP competitive inhibitors of ERK2 can bind target with a special binding mode and have higher inhibitory potency than other ERK2-inhibitors. We investigated the interaction mode of ERK2-inhibitor using molecular dynamics simulation. The molecular mechanics Poisson–Boltzmann surface area approach is used to calculate the binding free energy of ERK2 with pyrazolylpyrrole inhibitors to analyze the factors of improving the affinity. The results indicated that the electrostatic interactions play the most important role in keeping the stabilization of ERK2-inhibitor. The structural analyses showed that the protein motions can be controlled by changing the structures of inhibitors; furthermore, the full use of available space in the binding site by improving the flexibilities of inhibitors and introducing hydrophobic groups can increase the inhibitory effect.

Quantitative structure-activity relationship (QSAR) has been a technique to study the relationship between chemical structures and properties, and variable selection is an important problem for finding the informative variables and building reliable models. A variable selection method based on variable stability is proposed and used for selecting the informative descriptors in the QSAR model of inhibitors. In the method, a series of models are built by leave-one-out cross validation (LOOCV), and variable stability is defined as the ratio of the absolute mean value and standard deviation of the regression coefficients in the models for a descriptor. Therefore, the descriptors with larger stabilities are more informative to the model. To further enhance the difference among the descriptors, an exponential parameter is used to modify the standard deviation. The results show that 13 descriptors are selected as informative ones from 1217 descriptors for the QSAR model of inhibitors. An effective prediction model can be constructed by them.

Over the past decades, many existing drugs and clinical/preclinical compounds have been repositioned as new therapeutic indication from which they were originally intended and to treat off-target diseases by targeting their noncognate protein receptors, such as Sildenafil and Paxlovid, termed drug repurposing (DRP). Despite its significant attraction in the current medicinal community, the DRP is usually considered as a matter of accidents that cannot be fulfilled reliably by traditional drug discovery protocol. In this study, we proposed an integrated computational/experimental (iC/E) strategy to facilitate the DRP within a framework of rational drug design, which was practiced on the identification of new neuronal nitric oxide synthase (nNOS) inhibitors from a structurally diverse, functionally distinct drug pool. We demonstrated that the iC/E strategy is very efficient and readily feasible, which confirmed that the phosphodiesterase inhibitor DB06237 showed a high inhibitory potency against nNOS synthase domain, while other two general drugs, i.e. DB02302 and DB08258, can also inhibit the synthase at nanomolar level. Structural bioinformatics analysis revealed diverse noncovalent interactions such as hydrogen bonds, hydrophobic forces and van der Waals contacts across the complex interface of nNOS active site with these identified drugs, conferring both stability and specificity for the complex recognition and association.

A series of tetrapyrrolic macrocycles such as porphyrins, phthalocyanines and corroles were found to have inhibitory abilities toward acetylcholinesterase (AChE). Their structure-activity relationship was studied. Several compounds were found to have good inhibitory abilities, which could be developed as potential candidates of acetylcholinesterase (AchE) inhibitors.