Reactivity, accelerator

The 6-chloromethyl substituent (series 5 and 6) is required for the inactivation of a-chymotrypsin. Nevertheless, there is only a transient inactivation of HLE and thrombin through the formation of a stable acyl-enzyme in spite of the presence of this group as demonstrated by the spontaneous or hydroxylamine-accelerated reactivation of the treated enzymes (Scheme 11.3, pathway b).21 HLE is specifically inhibited when such an alkylating function is absent (series 7), always through the formation of a transient acyl-enzyme (Table 11.2). 

With few exceptions the high-energy chemist deals with materials that are in the solid state at normal room temperature. Solids mix very slowly with one another, and hence they tend to be quite sluggish in their reactivity. Rapid reactivity is usually associated with the formation, at higher temperatures, of liquids or gases. Species in these states can diffuse into one another more rapidly, leading to accelerated reactivity. 

Cowperthwaite, "Explicit Solutions for the Buildup of an Accelerating Reactive Shock to a Steady-State Detonation Wave , Ibid, 753-59 102) A.G. Istratov et al,... 

Mono-esterification of CRNl Accelerated reactivity caused Chen et al., 1996... 

An additional process which may occur on the phosphylated enzyme is a process termed ageing, which results in a covalently inhibited enzyme that is resistant to accelerated reactivation by therapeutic nucleophiles (see Section XII). Ageing results from PO—C bond cleavage in the alkoxy substituent as illustrated in equation 49 and occurs rapidly (within minutes) with phosphonofluoridates such as soman, whose highly branched alkoxy group produces a relatively stable secondary alkyl carbonium ion . The dealkylation is... 

A typical two-component system consists of a resin and a hardener, which are packaged separately. In a one-component system, the resin and hardener are packaged together. Other possible additives include accelerators, reactive diluents, plasticizers, resin modifiers, and fillers. 

A two-component epoxy system consists of a resin and a hardener, along with possible additives such as accelerators, reactive diluents, resin modifiers, plasticizers, and fillers. Typical hardeners include aliphatic polyamines, which cure at room temperature or at slightly elevated temperatures polyamides, which provide flexibility and are widely used aromatics, which are solid and anhydrides, which require elevated temperature cure and produce thermally stable but brittle adhesives. Low molecular weight epoxies are liquid and are usually cured by amines, carboxylic acid anhydrides, and Lewis acid and base catalyst. Higher molecular weight epoxies are cured through their hydroxyl groups. Cure of epoxies involves an exothermic reaction. 

Sometimes ligation proceeds slow and therefore give low yields. To accelerate reactivity, add catalytical amounts (0.1 equiv.) of sodium thiophenolate which forms more reactive thioesters in situ. To avoid rapid hydrolysis perform reaction at pH 7-8. Increase temperature while decreasing pH and vice versa. 

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