Re-initiation

Bjerketvedt, D., O. K. Sonju, and I. O. Moen. 1986. The influence of experimental condition on the re-initiation of detonation across an inert region. Progress in Astronautics and Aeroruiutics. 106 109-130. AIAA Inc., New York. 

The field of translation initiation has focused on the initial round ofribosomal subunit recruitment to an mRNA. Presumably, these events are mirrored in the subsequent rounds of initiation necessary for polyribosome formation. Importantly, because mRNAs are typically present in large polyribosomes (averaging 9-13 ribosomes per mRNA), the initiation events that govern ribosome recruitment to preexisting polyribosomes constitute the majority of translation initiation cycles occurring in an mRNA s lifetime. Whether or not these initiation events mimic the first round of initiation is not yet known. Since eukaryotic cells divide ribosomes between two subcellular compartments, the cytosol and ER membrane, it is also important to know if the mechanism of translation initiation on ER-bound ribosomes is similar to that occurring on soluble ribosomes and, importantly, whether ER-bound ribosomes can direcdy (re) initiate translation on bound polyribosmes. 

In each case the reaction is exothermic and the reaction enthalpy AHR known thereby the defining the adiabatic temperature rise which is always greater than ATadiab > 50 K. Below 60°C the reaction becomes dormant and an undesirable accumulation of reactants is to be expected. Major reaction energy releases are to be anticipated if the reaction re-initiates. 

As has been shown in Figure 4, the grafting rate decreased with the increase in the unsaturated groups contained in the polyethylenes. This result may indicate that the rate constants of the re-initiations (8-1)-(8-3) are considerably smaller than that of propagation (6). 

NMR analysis of the polyketone end groups and in situ NMR studies have shown that two transfer mechanisms in MeOH may occur simultaneously (a) methano-lysis of Pd-acyl and (b) protonolysis of Pd-alkyl (Scheme 7.15). The eventual presence of water in MeOH, even in trace amounts, gives rise to two similar terminations, yielding different end groups (-COOH) and metal re-initiator (Pd-OH) [5e-g, 13, 36]. Termination by P-H transfer (c) is typical for reactions performed in organic solvents. 

The chain transfer by alcoholysis involves the attack of ROH on a propagating Pd-acyl to give a free chain, bearing at least an ester-end group, and a Pd-hydride species, which re-initiates the chain growth by insertion of ethene (Scheme 7.15a). 

Re-calculate medians, re-initialize descriptor selection, and re-partition... 

To minimize the risk of induced arrhythmia, initiate or re-initiate therapy for > 3 days in a facility that can provide cardiac resuscitation and ECG monitoring. 

HuCNS-SC isolation and differentiation. Antibody-sorted cells expressing the stem-cell marker CD133 increased 1000-fold in population after five passages. CD133 cells retained their ability to re-initiate neurosphere formation when plated in differentiating media 437290... 

PBBs are no longer produced in the United States (SRI 2001). Re-initiation of manufacture requires approval from the EPA. Production of decaPBB in Great Britain was discontinued in 1977 and highly brominated PBBs were produced in Germany until mid-1985. Until the year 2000, the only PBB... 

An important advantage of the GRASSHopper device is the fact that after a complete MAH cycle of three orientations, the MAH device can be re-initialized by rotating backward to the initial orientation. For this reason, a number of flexible input and output lines to the sample chamber of the GRASSHopper device exist and allow a rotation of the fixed-bed reactor about an axis in the magic-angle while the system is gas-tight (Fig. 16). In the reported experiments 66), the 120° hop time... 

However a slow re-initiation of polymerisation, giving rise to a second slower stage, occurs on formation of a three membered cyclic sulphonium ion salt by intramolecular nucleophilic attack of the penultimate sulphur in the dormant polymer ... 

With these monomers polymerization again is complicated by the possibility of side reactions and termination reactions. In the butyl-lithium initiated polymerization of methylmethacrylate in tetrahydrofuran at —78°, monomer added repeatedly after quite long time intervals will polymerize rapidly (117). This is found to be true even if the solution is warmed to room temperature after each addition of monomer. The possibility remains that some termination occurs and that some reinitiation by lithium methoxide is also important. Similar experiments with fluorenyllithium under the same conditions (40) show that after 30 minutes a large percentage of the polymer chains is reactive towards tritiated acetic add. Addition of a second batch of monomer at —78° indicates that some chain termination occurs at this temperature but that no new chains are formed by re-initiation. Some other low molecular... 

Sodium naphthalenide in THF has also been shown to reduce Na-[M(CO)5] (M = Mn, Re). Initially it was believed that solutions of Na3-[M(CO)4] were obtained, but a more careful examination established that only very fine suspensions of insoluble and impure brown trisodium salts had formed. For example, treatment of Re2(CO)10 with 10 equivalents of NaC10H8 in THF provided a complete conversion to finely divided brown insoluble Na3[Re(CO)4] within an hour at room temperature (19). Although Na3[Re(CO)4] prepared with excess Na[C10H8] was impure, we discovered that these HMPA-free suspensions were useful in reactions in which removal of HMPA was very difficult. Attempts to find practical routes to relatively pure salts of [M(CO)4]3 , which do not involve the use of the toxic and high-boiling HMPA, have not been entirely successful to date. A summary of routes to insoluble (and impure) forms of A3[M(CO)4], where A = Na and K and M = Mn and Re, is shown in Eqs. (2) and (3). 

In the polymerization of allyl acetate, transfer to monomer produces an unreactive radical which fails to re-initiate growth of the polymer chain. Bartlett and Tate (31) compared the rates of polymerization for the unlabelled monomer and.the deuterated monomer CH2 CH-CD2 0-CO CH3. The deuterated monomer polymerized more rapidly giving a product of higher molecular weight. These observations suggest that the rate of polymerization and the molecular weight of the polymer are controlled by the reaction... 

If the rates at which monomer and an additive become incorporated in a polymer are compared by analyzing the polymer, it may be possible to calculate the transfer constant for the additive. In this connection, it is important to recognize that transfer is a two-stage process consisting of radical-displacement followed by re-initiation. In the simplest case, in which a hydrogen atom is abstracted by the polymer radical, the relevant reactions can be written as... 

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