Reactive chemical groups

Chemical instability of medicinal agents may take many forms, because the drugs in use today are of such diverse chemical constitution. Chemically, drug substances are alcohols, phenols, aldehydes, ketones, esters, ethers, acids, salts, alkaloids, glycosides, and others, each with reactive chemical groups having different stability characteristics. Chemically, the most frequently encountered destructive processes involve hydrolysis and oxidation. 

Reagents with multiple reactive chemical groups should be avoided in library enumeration because their presence most likely requires specific protections of certain functional groups which complicates chemical reactions and makes library production unpractical. 

To identify groups that are part of or very near to the active site of a protein, reagents can be designed that carry a reactive chemical group into the active site.291 The related photoaffinity labeling292 293 is also widely used (see also Chapter 23). 

Chemical bonds are formed by electrons, and formation or breakage of bonds requires the migration of electrons. In broad terms, reactive chemical groups function either as electrophiles or as nucleophiles. Electrophiles are electron-deficient substances that react with electron-rich substances nucleophiles are electron-rich substances that react with electron-deficient substances. The task of a catalyst often is to make a potentially reactive group more reactive by increasing its electrophilic or nucleophilic character. In many cases the simplest way to do this is to add or remove a proton. 

Although present in several approved drugs, protein reactive chemical groups are known to produce screening artefacts and are undesirable starting points for F2L optimization.1461 We eliminated potentially protein reactive chemical groups, such as aldehydes, phosphon-ate esters and activated ketones, in order to avoid identification of covalent, irreversible fragment binders. Furthermore, we also removed potential toxicophores. 

Whenever any organic solvent or any constituent of an organic solvent may be classified from its chemical structure into more than one of the above groups of organic compounds, it shall be considered as a member of the most reactive chemical group, that is, that group having the least allowable percent of the total volume of solvents. 

Pigments. An obvious prerequisite for the selection of pigments in urethane coating formulations is their non-reactivity toward Isocyanates. Many pigments exhibit an affinity for moisture, and the presence of some reactive chemical groups limits the use of some pigments in urethane formulations. 

Another key step is the proper development of surface chemistry to attach addressable probes onto different membrane sensors. This can be achieved by patterning UV-curable acrylic-based polymers inside the microfluidic channel doped with different monomers containing charged or functional groups. Such polymers are ion-selective and provide reactive chemical groups on their surfaces for the attachment of DNA/RNA probes. The functionality of aU the devices proposed here relies on the ion-selectivity of the polymeric material, which is less dependent on... 

The characteristics of PF resins and the reactive chemical groups they present render them particularly suitable for the preparation of binders by coreaction with other resins. This is still a relatively young field, and the most interesting and relevant co-resins that are being used or explored in this respect are the aminoplastic resins, in particular urea-formaldehyde (UF) and melamine-formaldehyde (MF) (the copolymerization with the latter being a somewhat older use), and the diisocyanates. 

If the reaction mixture contains chemical groups such as aromatic nitro, nitrate ester or nitramine, it is possible that it will detonate. A fuller, but not exhaustive, list of dangerously reactive chemical groups is ... 

Covalent chemical bonds can form across the interface and are Ukely to occur in cross-Unked adhesives and thermoset coatings. This type of bond is usually the strongest and most durable. However, they require that mutually reactive chemical groups should exist. Some surfaces, such as previously coated surfaces, wood, composites, and some plastics, contain various functional groups that under appropriate conditions can produce chemical bonds with the adhesive material. There are ways to intentionally generate these conditions, such as by surface treatment of plastics with techniques like corona or flame treatment. 

Step polymerization, also known as condensation polymerization, should be contrasted with Chain polymerization. In step polymerization, monomers react with one another because they contain mutually reactive chemical groups, of which there are at least two per monomer molecule. Some common groups and their reactions are given below. In many, but not all, cases, a small molecnle such as water is released. 

Isocyanate-alcohol reaction n. Reaction involving a very reactive chemical group, -N=C=0 with an alcohol to form a highly cross-linked polymer, importance in polyurethane formation. Odian GC (2004) Principles of polymerization. John Wiley and Sons Inc., New York. 

A reactive chemical grouping of a nitrogen atom bonded to a carbon atom bonded to an oxygen atom -N = C = O. A chemical compound, usually organic, containing one or more isocyanate groups. 

Chemical bonding is expected to be the most durable and the strongest, and it is often possible to form covalent bonds across the interface of the substrate and coating. However, a requirement for this type of bonding is the presence of mutually reactive chemical groups bounded firmly to the coating and the substrate surface. 

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