Dormant states

Like some eukaryotic viruses (eg, herpes simplex, HIV), some bacterial viruses can either reside in a dormant state within the host chromosomes or can rephcate... 

In a normally growing culture of lysogenic bacteria, the majority of bacteria manage to keep their prophages in a dormant state. In a very small minority of cells, however, the prophage genes express themselves. This results in the multiplieation of the virus, lysis of the cells and liberation of infectious particles into the medium. 

Cytomegalovirus (CMV) Enveloped, icosahedral particles 150nm in diameter CMV is generally acquired in childhood as a subclinical infection. About 50% of adults carry the virus in a dormant state in white blood cells. The virus can cause severe disease (pneumonia, hepatitis, encephalitis) in immunocompromised patients. Primary infections during pregnancy can induce serious congenital abnormalities in the fetus... 

It has been known for some time that certain types of bacteria spend a certain amount of their lifespan in a dormant state. The bacteria are then known as en-dospores , or just spores . In this state, they appear not to undergo any metabolic processes and are important particularly because of their heat resistance. The formation of spores is a highly complex process of bacterial cell differentiation. 

In adverse conditions, some bacteria can enter a dormant state known as a spore. Spores can remain dormant for decades and can survive under extreme temperatures and other adverse environmental conditions. Unlike fungi (Chapter 20), formation of spores is not related to reproduction and is done strictly as a protective mechanism. Upon reactivation, each spore produces a single active bacteria. Spores are normally spherical or oval and are only a fraction of the size of the active (i.e., vegetative) cell. 

Inhibition of a catalytic reaction by impurities present may take place and sometimes this may have a temporary character. If it is permanent one cannot be mistaken in the kinetic measurements. Impurities that are more reactive than the substrates to be studied may block the catalyst if they react according to a scheme like that of Figure 3.7. Only after all inhibitor has been converted the conversion of the desired substrate can start. Another type of deactivation that may occur is the formation of dormant states, which is very similar to inhibition. Either the regular substrate or an impurity may lead to the formation of a stable intermediate metal complex that does not react further. There are examples where such intermediates can be rescued from this dormant state for instance by the addition of another reagent such as dihydrogen (Chapter 10, dormant states in propene polymerisation). 

More recently, Landis et al. studied the polymerisation kinetics of 1-hexene with (EBI)ZrMe( t-Me)B(C5F5)3 64 as catalyst in toluene [EBI = rac-C2H4(Ind)2]. Catalyst initiation was defined as the first insertion of monomer into the Zr-Me bond, 65 (Scheme 8.30). Deuterium quenching with MeOD was used to determine the number of catalytically active sites by NMR. The time dependence of the deuterium label in the polymer was taken as a measure of the rate of catalyst initiation. This method also provides information of the type of bonding of the growing polymer chain to zirconium, as n-or sec-alkyl, allyl etc. Hexene polymerisation is comparatively slow, with high regio- and stereoselectivity there was no accumulation of secondary zirconium alkyls as dormant states [96]. 

The nature of the dormant state was determined by H NMR end-group analysis. Two types of terminal unsaturations were found, vinylidene end groups indicative of (3-H elimination from 1,2-inserted polymeryl chains, and cis-butenyl end groups, arising from 2,1-misinsertions (Scheme 8.33) the latter were dominant (66%). 

NMR analysis of the polymer also detected low levels of stereo-errors due to enchained 2,1-misinsertions (cf Section 8.9), about 1 in 500. The data suggested that 2,1-insertion is slow but is responsible for the accumulation of dormant states carrying Zr-sec-alkyl chains. 

Very similar kinetics were observed with (SBI)ZrCl2/MAO although this catalyst is an order of magnitude less active, the concentration of active species turned out to be almost identical to the borate system kp/kp P = 0.08, with a similar accumulation of dormant states. Evidently the counteranion ([CN B(C6F5)3 2] vs. [Me-MAO] ) modulates the energetics of the chain growth cycle, i. e. the anion is intimately involved in the transition state, but does not influence the distribution between active and dormant states (Scheme 8.34) [97]. 

Further, a dynamic equilibrium is established at higher temperatures between so-called active (R and T ) and dormant states (R— T), as shown in Scheme 10.7. The equilibrium... 

Anderson, T.-H., and Domsch, K. H. (1985). Determination of ecophysical maintenance carbon requirements of soil microorganisms in a dormant state. Biol. Fertil. Soils 1, 81-89. 

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