Mechanical destruction, irreversible

Both effects resulting from solvent cointercalation, the mechanical destruction and the higher irreversible specific charge losses, seriously complicate the operation... 

A very drastic and common deactivation phenomenon with automotive emission control catalysts is the irreversible mechanical destruction of the support during road use by breakage in the case of ceramic monoliths, by telescoping of the matrix or breakage of the foil in the case of some metallic substrates and, formerly, by attrition in the case of bead catalysts. With ceramic monoliths, sudden temperature changes can cause thermal stresses and consequent breakage. 

Mechanism-based irreversible inhibition occurs when a reactive metabolic intermediate is formed in situ that can (1) bind covalently with the prosthetic heme through N-alkyllary-lation (e.g., secobarbital), f"2 alkylate the apo-cytochrome (e.g., chloramphenicol or 2-ethy-nylnaphthalene), or (5) cause destruction of the prosthetic heme to products that irreversibly bind to the apocytochrome (e.g. CCI4) (158). These mechanism-based inactivators have primarily been designed and used for the selective inhibition of specific CYP enzymes and elucidating the mechanism of P450 reactions. Some drugs (e.g., aromatase inhibitors)... 

Ironically, while water is critical in maintaining molecular shape, the aqueous state is not one in which proteins are long resistant to denaturation. A variety of environmental changes such as temperature, pH, salts and solvents can cause protein inactivation in the aqueous state, and the mechanisms of irreversible protein inactivation often follow conunon pathways. These include cystein destruction, thiol-catalyzed disulfide interchange, oxidation of cystein residues, deamidation of asparagine and glutamine residues and hydrolysis of peptide bonds at aspartic acid residues. 

The current efficiency is mainly dependent on membrane performance. On the cathode side the membrane is in contact with a concentrated NaOH solution, while the anode side has a pH of approximately 2-4. This leads to a pH gradient across the membrane cross section. The solubility of impurities, which are always present in the pure brine, depends on the pH. Therefore, depending on the type of impurities and on the pH, precipitation inside the membrane can take place. This leads to mechanical destruction of the membrane, which has a irreversible effect on current efficiency. In addition, the cell voltage rises due to the crystals formed inside the membrane. 

The gelling temperature is an important factor for the characterization and application of pectins. The pectin consumer wants a pectin fulfilling his special requirements, this can mean either working with or without pregelation. Pregelation, the weakening of gel structure, occurs when pectin preparations are stressed below their gelation temperature so that the mechanical treatment leads to an irreversible destruction of the three-dimensional network. 

One of the most potent and physiologically irreversible mechanisms of antibiotic resistance is via chemical destruction of the antibiotic warhead or scaffold. This destruction can occur through several mechanisms, but hydrolytic approaches predominate (Fig. 4). Resistance to the highly important fS-lactam antibiotics by fi-lactamases is the archetype of this class. The fS-lactams include the natural product penicifhn and cephalos... 

Mechanism-based inactivation of CYP450 (or suicide inhibition) occurs when a non-toxic drug is metabolised by CYP450 to generate a metabolite that can bind irreversibly with the enzyme. The mechanism of inhibition usually involves free-radical alkylation or acylation of the active site and results in destruction of enzyme activity. Examples of drugs that act in this way include the antibiotic chloramphenicol and the anticancer agent cyclophosphamide. 

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