Experimental versus theoretical evidence for the rate-limiting steps in uncatalyzed and H+ - and HO− -catalyzed hydrolysis of the amide bond

Recycling and Degradation of Polyamides

As one of the five major engineering plastics, polyamide brings many benefits to humans in the fields of transportation, clothing, entertainment, health, and more. However, as the production of polyamide increases year by year, the pollution problems it causes are becoming increasingly severe. This article reviews the current recycling and treatment processes of polyamide, such as chemical, mechanical, and energy recovery, and degradation methods such as thermal oxidation, photooxidation, enzyme degradation, etc. Starting from the synthesis mechanism of polyamide, it discusses the advantages and disadvantages of different treatment methods of polyamide to obtain more environmentally friendly and economical treatment schemes. Finding enzymes that can degrade high-molecular-weight polyamides, exploring the recovery of polyamides under mild conditions, synthesizing environmentally degradable polyamides through copolymerization or molecular design, and finally preparing degradable bio-based polyamides may be the destination of polyamide.

The source, activity influencing factors and biological activities for future development of chitin deacetylase

Chitin deacetylase (CDA), a prominent member of the carbohydrate esterase enzyme family 4 (CE4), is found ubiquitously in bacteria, fungi, insects, and crustaceans. This metalloenzyme plays a pivotal role in recognizing and selectively removing acetyl groups from chitin, thus offering an environmentally friendly and biologically-driven preparation method for chitosan with immense industrial potential. Due to its diverse origins, CDAs sourced from different organisms exhibit unique functions, optimal pH ranges, and temperature preferences. Furthermore, certain organic reagents can induce structural changes in CDAs, influencing their catalytic activity. Leveraging CDA's capabilities extends beyond chitosan biocatalysis, as it demonstrates promising application value in agricultural pest control. In this paper, the source, reaction mechanism, influencing factors, the fermentation methods and applications of CDA are reviewed, which provides theoretical help for the research and application of CDA.

Mechanism of Heterogeneous Alkaline Deacetylation of Chitin: A Review

This review provides an analysis of experimental results on the study of alkaline heterogeneous deacetylation of chitin obtained by the authors and also published in the literature. A detailed analysis of the reaction kinetics was carried out considering the influence of numerous factors: reaction reversibility, crystallinity and porosity of chitin, changes in chitin morphology during washing, alkali concentration, diffusion of hydroxide ions, and hydration of reacting particles. A mechanism for the chitin deacetylation reaction is proposed, taking into account its kinetic features in which the decisive role is assigned to the effects of hydration. It has been shown that the rate of chitin deacetylation increases with a decrease in the degree of hydration of hydroxide ions in a concentrated alkali solution. When the alkali concentration is less than the limit of complete hydration, the reaction practically does not occur. Hypotheses have been put forward to explain the decrease in the rate of the reaction in the second flat portion of the kinetic curve. The first hypothesis is the formation of “free” water, leading to the hydration of chitin molecules and a decrease in the reaction rate. The second hypothesis postulates the formation of a stable amide anion of chitosan, which prevents the nucleophilic attack of the chitin macromolecule by hydroxide ions.

Can a Typical Protein Assist the Rate of its Own Aqueous Cleavage?

A recent finding of a large rate enhancement in the intramolecular secondary amide group-assisted cleavage of an adjacent tertiary amide bond predicts the possibility of the cleavage of the peptide bond of a protein through a similar reaction mechanism. Based upon enzymatic partial model reactions, the usual proton-switch mechanism has been suggested for the acylation step of the chymotrypsin–catalysed cleavage of the peptide bond which does not favour a His57-shift mechanism - an essential component of the classical charge relay mechanism. Also, the proton-switch mechanism does not necessarily require the two proton-transfer of the classical charge relay mechanism. The unique structural feature of the imidazole moiety of His57 is concluded to be essential in decreasing the rate of collapse of the proposed reactive tetrahedral intermediate back to the reactants. The proposed intramolecular intimate ion-pair formation between anionic Asp102 and cationic His57 is attributed to the energetically preferred location of the proton at Nδ1 of the imidazole moiety of His57. Thus, the analysis described in this review does not favour the necessary requirements of a two proton-transfer and His57-shift as proposed in the classical charge relay mechanism as well as the relatively recently proposed His57-flip mechanism.