Kinetic inhibitors delay

A kinetic inhibitor is a polymeric chemical that, when added to a production stream, will not change the hydrate formation temperature but will delay the growth of hydrate crystals. These chemicals are polymeric... 

The usual practice for avoiding the plugging of production facilities by hydrates is to add thermodynamic inhibitors, such as methanol or glycol. A newer concept is the injection of low-dosage additives either kinetic inhibitors, which delay nucleation or prevent the growth of hydrate crystals, or hydrate dispersants, which prevent the agglomeration of hydrate particles and allow them to be transported within the flow [880,1387]. Hydrate control is discussed extensively in Chapter 13. Classes of hydrate control agents are shown in Table 11-9, and additives are shown in Table 11-10. 

The advantage of micelles is that diffusion into them is so rapid that initiator and inhibitors can be injected into the bulk aqueous phase and they equilibrate into the linoleic micelle layer too fast for any delay to be observed in our kinetic traces. (See Figure 1 and Reference Q2.)... 

Flavonoids are well known as inhibitors of hyaluronidase. Li 1950 Rodney et al, reported the effect of several flavonoids on hyaluronidase using in vitro and in vivo methods [79], Knppusamy et al. investigated the structure-activity relationship of die flavonoids as inhibitors of testicular hyaluronidase [80] and hyaluronidase from snake, scorpion, and bee venom [81]. They showed that flavones. flavanols. and chalcones possess the general ability to inhibit hyaluronidase Kinetic investigations showed that these compounds acted as competitive inhibitors [80]. Several hyaluronidase inhibitors were shown to be able to delay the action of snake venom when injected into mice [8ll One caimnt rule out the possible interaction of the flavonoids with other components of the venom, as the inhibitory effects of flavonoids are not specific to hyaluronidase... 

Over the last decade or so, many research efforts have been focused on developing what are termed low-dosage hydrate inhibitors , or LDHIs, that potentially can kinetically inhibit hydrate formation/ LDHIs operate via a much different mechanism than thermodynamic inhibitors such as methanol. They are often effective at concentrations as low as 0.5 wt% and act by delaying the onset of hydrate formation, while thermodynamic inhibitors are effective only at much higher concentrations and act by changing the conditions of hydrate thermodynamic stability, thus shifting the phase diagram. 

This does not mean that they have a common site of action. For instance, the inorganic inhibitors - Mn +, Ni +and Co2+ - act at the outer surface of the cell membrane, where they compete with Ca + for binding sites (34,54). By contrast the organic inhibitors - eg. verapamil, D-600 appear to act at the cytosolic surface (55,56). Even the organic inhibitors differ in their precise mode of action. For example, nifedipine (46) reduces the number of channels that are operational at a given time without altering the kinetics of channel activation or inactivation, whereas verapamil (17) alters the kinetics of channel reactivation so that recovery is delayed after a prior period of activity. Possibly this effect of verapamil is associated with its ability to displace Ca2+ from superficially located binding sites (47). 

In vitro studies with human term placental microsomes showed that PED displayed the typical properties of a mechanism-based inhibitor of cytochrome P450, namely (a) NADPH-dependent inhibition (b) time-dependent loss of enzymatic activity, followed by pseudo-first-order kinetics and (c) natural substrates delayed the irreversible inhibition. The irreversibility of inhibition was further substantiated by dialysis experiments ... 

Figure 2. Examples of the kinetics of effects of different herbicides. I. A rapidly phytotoxic compound II, an inhibitor which has a delayed action (e.g. it affects growth after one division or after depletion of a critical metabolite) III, a phytotoxic compound with a transitory effect,( the cells recover).

A special case of delaying the polymerization process is its inhibition. The radical B originating f from the inhibitive substance, that is from the inhibitor, is completely unreactive and causes a gradual termination (ending) of the kinetic chain growth reaction. The time needed to wear the total amount of inhibitor is ealled the period of inhibition. 

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