Destruction Of Secondary Structure Research Articles

SURFACE MODIFICATION OF MACHINE PARTS AND MECHANISMS IN THE CONDITIONS OF FRICTION AND WEAR

The issues of surface modification of machine parts and mechanisms in conditions of friction and wear with and without oil further develops that work. The dependence of antifriction and friction on the special state of only the surface layers of friction parts is considered. It is revealed that the structural changes that occur in the surface microlayer of conjugate materials, the formation and destruction of secondary structures are responsible for the nature of the friction node. The authors propose to create on the friction surface such protective coatings that have properties and mechanism of action corresponding to secondary structures in order to be able to control the phenomena of antifriction and fractionality in the friction zone of conjugate parts. The aim of the study is achieved by processing iron-carbon alloys in the environment of superheated steam of aqueous solutions of salts. The optimal parameters of the technological process of forming coatings during vapor oxidation are selected. Laboratory tests of different chemical composition of the formed coating on the tribotechnical properties of friction steam were carried out. During the study, the authors concluded that by establishing a qualitative and quantitative relationship between the composition of oxide coatings and their tribotechnical properties, it is possible to change the conditions of the friction unit from antifriction to friction, using the same structural materials - ferrocarbon alloys. Thus, complex oxides, which differ in chemical composition and structure, which are coatings on ferrocarbon alloys, can significantly affect the thermomechanophysical processes that occur during operation and allow their renovation in the presence of lubricant and without it. Coatings formed on the surface of ferrocarbon alloys in accordance with the operating conditions can have both friction and antifriction properties.

Corrosive and tribocorrosive behavior of plasma powder coatings

Purpose. To investigate corrosion and tribocorrosion characteristics of plasma-powder coatings on the basis of iron, nickel and Fe-Ni system in the envyronments containing chlorides, hydrogen sulfide and ammonia. Metodology: corrosive-electrochemical, tribological, metallographic methods have been used.Results It was established that as the pH of the solution increases, the corrosion resistance of the coatings increases. The highest corrosion resistance has a surfaced layer based on nickel 06Х17Н80С3Р3, however, under tribocorrosion conditions, fragile component of coatings form an abrasive in the friction zone that intensifies the destruction. Compared to others, the coating 06Х17Н80С3Р3 has the lowest resistance to corrosion-mechanical destruction.The fragile component is absent in layers, deposited from powders 01H17N8S6G and 08Х17Н35С3Р. The solid phases are uniformly distributed in a plastic matrix corresponding to the Sharpi-Bochvar rule. In this coatings, the contact interaction occurs in the absence of abrasive wear, which explains the high resistance to tribocorrosion.It is possible to qualitatively evaluate the processes of formation and destruction of secondary structures in the friction zone of tribocorrosion by comparing of the corrosion potentials, tribocorrosion potentials and passivation potentials. Additional information may be provided by the level of local oscillations of the tribopotential, which characterizes the repassivation rate.Practical result. A new composition 08Х17Н35С3Р3 for plasma-powder coatings has been proposed to increase the wear and corrosion resistance of steel surface.

Five individual polyphenols as tyrosinase inhibitors: Inhibitory activity, synergistic effect, action mechanism, and molecular docking

Polyphenols can inhibit the enzymatic browning in food, but their indistinct synergistic effect and conformational change have limited their applications. In this paper, the mixture of quercetin, cinnamic acid and ferulic acid (Group 11, KI = 0.239 mM) possessed a higher inhibition ability than quercetin (KI = 0.361 mM), which could promote the spontaneous binding process. The final Group 11-tyrosinase complex is more stable, and the hydrophobic effect is the major driving force during the binding process. Moreover, there is not a direct relationship between the destruction of secondary structures and catalytic activity of tyrosinase. The interaction between ferulic acid and tyrosinase could destroy the secondary structures of enzyme but it had little impact on the tyrosinase activity. Molecular docking suggested that three polyphenols from Group 11 have synergistic effect on tyrosinase. This study provides new perspectives about the development of tyrosinase inhibitors in food products.

The Role of E27-K31 and E56-K10 Salt-Bridge Pairs in the Unfolding Mechanism of the B1 Domain of Protein G

Molecular dynamics simulations of the B1 fragment of protein G (56 residues) have been performed at 325, 350, 375, 400, 450 and 500 K for 10 ns. An analysis of its structural and energetic parameters has indicated that the unfolding process of the GB1 protein begins at 900 ps of a 500-K simulation. The unfolding process is initiated when hydrogen bonds in the hydrophobic core region are broken; it continues with the α-helix transformation into coils and turns and ends with the destruction of the β-hairpins. These unfolding events are consistent with the hybrid model of the protein folding/unfolding mechanism, which is a compromise between the hydrophobic core collapse model and the zipper model. Salt-bridge pairs were found to play an important role in the unfolding process by maintaining the integrity of the tertiary structure of the protein. The breaking (or disappearance) of the salt-bridge pairs E27–K31 (in the α-helix) and E56–K10 (connecting β4 and β1) has resulted in the destruction of secondary structures and indicates the beginning of the unfolding process. Our results also suggest that the unfolding process in this simulation was not a complete denaturation of the protein because some β-hairpins remained

Structural analysis of the DNA-binding domain of alternatively spliced steroid receptors.

We have generated 24 DNA-binding domain structure models of alternatively spliced or mutated steroid receptor variants by homology-based modeling. Members of the steroid receptor family dispose of a DNA-binding domain which is built from two zinc fingers with a preserved sequence homology of about 90%. Data from crystallographic analysis of the glucocorticoid receptor DNA-binding domain are therefore appropriate to serve as a template structure. We inserted or deleted amino acid residues in order to study the structural details of the glucocorticoid, mineralocorticoid, and androgen receptor splice variants. The receptor variants are created by QUANTA- and MODELLER-based modeling. Subsequently, the resulting energy-minimized models were compared with each other and with the wild-type receptor respectively. A prediction for the receptor function based mainly on the preservation or destruction of secondary structures has been carried out. The simulations showed that amino acid insertions of one, four or nine additional residues of existing steroid receptor splice variants were tolerated without destruction of the secondary structure. In contrast, a deletion of four amino acids at the splice site junction leads to modifications in the secondary structure of the DNA-recognition helix which apparently disturb the receptor-DNA interaction. Furthermore, an insertion of 23 amino acid residues between the zinc finger of the androgen receptor leads to a large loop with an additional alpha-helical structure which seems to disconnect a specific contact from its hormone response element. Thereafter, the prediction of receptor function based on the molecular models was compared with the available experimental results from the in vitro function tests. We obtained a close correspondence between the molecular modeling-based predictions and the conclusions of receptor function drawn from in vitro studies.

Removal of attenuator region of thr operon increases the production of threonine in Escherichia coli

Expression of the threonine (thr) operon of Escherichia coli is regulated by an attenuation mechanism. The regulatory portion of the thr operon contains a region coding for leader peptide that includes both consecutive threonine and isoleucine codons. Translation of the leader peptide controls the frequency of transcription termination at the attenuator site. The effect of attenuator region on the production of threonine by using the threonine overproducing strain E. coli HS528 was examined. The plasmids which caused an increase in the productivity were due to the destruction of secondary structure of mRNA around the attenuator located in the leader sequence. Among them, plasmids pEd9, pEd64, and pEd69 increased threonine production that was caused by disruption of the transcription terminator. E. coli HS528 cells harboring the plasmids gave 2–3 times more threonine than the host. These results indicated that the change in the secondary structure of mRNA in the leader sequence of the thr operon have an effect on the productivity of threonine in E. coli.

Adsorption of polypeptides on the solid surface. II. Effect of secondary chain structure and helix–coil transition

AbstractThe theory of adsorption of semistiff chains on a planar surface developed by the authors previously has been used to consider the helix–coil transition in single‐stranded macromolecule interacting with an adsorbent plane. The cases of nonselective interaction when the adsorption energy is independent of the unit conformation (a) and selective interaction with only helical (b) or coiled (c) sequences active in adsorption were investigated. In case (b) the existence of secondary structure favors chain bonding to the surface. This leads to the increase in the stability of the helical state and complete polypeptide chain spiralization. The profile of the conformational helix–coil transition acquires an asymmetrical shape inherent to the second‐order phase transition.In case (c) the bonding of a partially helical chain to the surface is similar to the adsorption of Gaussian coils and is accompanied by the destruction of secondary structure, this destruction being appreciable even if the helical state in space was favorable.

Studies on chitin, 2. Effect of deacetylation on solubility

AbstractA reproducible method for obtaining water‐soluble chitin and a relationship between solubility and degree of deacetylation of chitin were studied. It was found that the regenerated chitin isolated at low temperature from an alkali chitin solution left at 25°C for 48 to 77h showed very good solubility in water at 0°C. The degree of deacetylation of an alkaline treated chitin was determined by titration with hydrochloric acid. It increased rapidly to about 75% as the alkaline treatment time increased and began to level off to about 90% and only the regenerated chitin samples with around 50% of deacetylation were found to be soluble in water. The X‐ray diffraction diagrams showed that these were amorphous, although both chitin with lower degree of deacetylation and chitosan had crystallinity. The improved solubility of chitin with about 50% of deacetylation would be attributed to the partial deacetylation which probably brought about the destruction of secondary structure and also the increase of the hydrophilic property on account of the increased number of amino groups.