Subject sequence length

Equations (7.40) and (7.41) suggest a second method, in addition to the copolymer composition equation, for the experimental determination of reactivity ratios. If the average sequence length can be determined for a feedstock of known composition, then rj and r2 can be evaluated. We shall return to this possibility in the next section. In anticipation of applying this idea, let us review the assumptions and limitation to which Eqs. (7.40) and (7.41) are subject ... 

A study of the difference in monomer sequence length distribution and hence of the possibility of strain-induced crystallization and other structural parameters,including long-chain branching, of samples prepared with the above-mentioned various catalyst systems is under way and constitutes the subject of a subsequent paper. 

The copolymerization equation is valid if all propagation steps are irreversible. If reversibility occurs, a more complex equation can be derived. If the equilibrium constants depend on the length of the monomer sequence (penultimate effect), further changes must be introduced into the equations. Where the polymerization is subjected to an equilibrium, a-methylstyrene was chosen as monomer. The polymerization was carried out by radical initiation. With methyl methacrylate as comonomer the equilibrium constants are found to be independent of the sequence length. Between 100° and 150°C the reversibilities of the homopolymerization step of methyl methacrylate and of the alternating steps are taken into account. With acrylonitrile as comonomer the dependence of equilibrium constants on the length of sequence must be considered. 

The type of error (I or II) in stereosequence propagation in the most highly isotactic polypropylenes has been subject of considerable attention. This is because error type has implications not only for the determination of mean isotactic sequence length, but also for the mechanism of stereosequence polymerization. 

To answer the question whether the ds-transisomerization of the bridged polypeptides with a Ala-Gly-Pro sequence represents the rate-determining step, the following experiment was carried out The polypeptide with a chain length n = 8 was denaturated in a rapid reaction with a temperature jump from 9.2 to 30 °C and subjected to renatura-tion at 9.2 °C after an incubation time of 25 s. In a second and a third experiment, the incubation in the coiled state was prolonged respectively to 75 and 125 s. It could be observed that the amplitude of the rapid phase depends on the time that lapses between the denaturation and renaturation (Fig. 32). 

Fig. 4.2a (Felinger et al., 1990) reports the effect of superimposing several ordered sequences S, of retention points the individual ordered patterns are lost and the overall SC sequence is seen as random. This property appears evident when three windows of equal length are separately considered (see Fig. 4.2a) they contain six, three or five points, respectively, which are clearly randomly varying numbers. We also understand that when the number of sequences, imax, increases, the randomness degree will be greater and greater, but our subjective feeling proves unable to precisely define the nature and the degree of such an increasing randomness.

The salient features of A. faecalis pseudoazurin are that (1) it has a Cu-Met bond length shorter than that of either plastocyanin or azurin (see Table III) (2) it has only one NH - S bond, as does plastocyanin and (3) its overall architecture resembles plastocyanin (see Fig. 4), with an extended carboxy terminus folded into two a helices [a preliminary sequence comparison suggested that the folding would resemble plastocyanin (Adman, 1985)]. It retains the exposed hydrophobic face found in azurin and plastocyanin. Just how it interacts with nitrite reductase is still a subject of investigation. It is intriguing that the carboxy-terminal portion folds up onto the face of the molecule where the unique portions of other blue proteins are the flap in azurin, and, as we see below in the multi-copper oxidase, entire domains. 

The 1 1 mixtures of strands 19 and 20 (0.5 mM each) were prepared in CH2CI2, methanol, and water. The samples were subjected to redox conditions (I2) for various lengths of time and then examined by matrix assisted laser desorption ionization (MALDI). As expected, 19 and 20 sequence specifically associated with each other in CH2CI2, leading to the disulfide cross-linked 19-20 as the major product. With an increasing ratio of methanol in CH2CI2, the cross-linked 19-20 stUl appeared as the dominant product. The same phenomenon was observed in pure methanol and even in water (Fig. 9.14b). The sequence dependence of the cross-linking of 19 and... 

Since the equilibrium constants for the addition of monomer onto the sequence of length 1 or to longer sequences are so different, the following situation must be considered. The living sequences with two monomer units cannot split off a monomer unit, but higher sequences are subject to polymerization-depolymerization equilibria with an equilibrium constant which no longer depends on chain length. We consider the special case in which the equilibrium constant K2 and the constants... 

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