Poly relaxation activity

DNA topoisomerases have been found to be subject to covalent modifications that modulate their DNA-relaxing activities. An example of this is the ADP-ribosylation of calf thymus topoisomerase I by poly(ADP-ribose) synthetase (Ferro et al., 1983 Jongstra-Bilen et al., 1983 Ferro and Olivera, 1984). The modified enzyme is less active in DNA relaxation. The possibility that topoisomerase I and poly(ADP-ribose) synthetase are associated in vivo was suggested by the observation that they copurify (Ferro et al., 1983 Jongstra-Bilen et al., 1983). 

The predominant sub-Tg process in poly(aIkyl methacrylates) is the 8 relaxation (activation energy of 80-121 kJmoP ) appearing around 285-336 K and nearly independent of the length of the alkyl group (e.g., methyl, ethyl, propyl, and butyl) while Tg decreases with increasing side chain length (i.e., internal plasticization) [33]. In the... 

The only previous report of activation energies for poly (methyl o chloroacrylates) is for the "conventional" free radical polymer which can be assumed to be reasonably syndiotactic (16). The values quoted are 130 kcal/mole for the a relaxation and 26 kcal/mole for the 3 relaxation. The present results (Table II) are in qualitative agreement with these values. In general the activation energies for the relaxations decrease with increasing ester side chain length or bulkiness and the isotactic isomers have a relaxation activation energies about 35-50 kcal/mole lower than the comparable syndiotactic isomers. This effect, as already discussed, is a consequence of the Tg difference between the i somers. 

A number of examples have been studied in recent years, including liquid sulfur [1-3,8] and selenium [4], poly(o -methylstyrene) [5-7], polymer-like micelles [9,11], and protein filaments [12]. Besides their importance for applications, EP pose a number of basic questions concerning phase transformations, conformational and relaxational properties, dynamics, etc. which distinguish them from conventional dead polymers in which the reaction of polymerization has been terminated. EP motivate intensive research activity in this field at present. 

The dissociation of 7 (Scheme 5) from poly[(G-C)] showed three relaxation times and the amplitude corresponded to the total signal, while the dissociation of 7 from poly[(A-T)] was faster and only two relaxation times, corresponding to 70% of the total signal were observed in the stopped-flow experiment. The biological activity of this class of molecules was correlated to the presence of four relaxation times when the dissociation process is measured with DNA, in particular the presence of the long-lived component of hundreds of milliseconds.86,104 105,132 143 The difference in the dissociation kinetics observed with the two polydeoxynucleotides indicates that intercalation into G-C sites is responsible for the biological activity. The dissociation of 7 from ct-DNA led to four relaxation times, a result that is in line with the relaxation times observed with poly[(G-C)] and poly[(A-T)]. 

Table 18. Values of correlation parameter g, relaxation time tJ.p and activation energy EJ p of a relaxation process of dipole polarization for some comb-like poly(methacrylates) in toluene solutions...

A typical loss maximum of this type was observed for poly(methyl methacrylate) containing caprolactam or derivatives of cyclohexane12,13. It is noteworthy70 that in the latter case the relaxation induced by the cyclohexyl group present in the incorporated plasticizer and the secondary relaxation of poly(cyclohexyl methacrylate) or poly(cyclohexyl acrylate) are characterized by an identical temperature position, 190 K (1 Hz), and activation energy, 47.9 kJ/mol (AU = 47.7 kJ/mol is reported for the chair-chair transition of cydohexanol). Hence, it can be seen that the cyclohexyl ring inversion, which represents a specific molecular motion, is remarkably insensitive to the surrounding molecules. 

Dynamic mechanical response spectra of elastin145 (insoluble protein of vessels and ligaments), poly(ethylene terephthalate)141 and polycarbonate based on Bisphenol A (4,4 -dihydroxydiphenylmethane)141 show that incorporated water brings about enlargement of the existing secondary loss peak and its displacement toward lower temperatures. In conformity with the latter result, the activation energy of the relaxation process of elastin decreases. So far, no detailed data on this type of relaxation have been collected so that the copartidpation of water in the molecular motion cannot be specified more accurately. 

Both polymers show a strong relaxation at about 120°C and 100°C for as can be seen in Figs. 2.15 and 2.16, for (P2tBCHM) and, (P4tBCHM) as Dfaz Calleja et al. [32] have reported. Moreover P2tBCHM show a complex secondary relaxation at about -80° and a remainder of the mechanical activity at about -20°C and 30°C respectively [32] poly(4-tert butylcycloheyl methacrylate) (P4tBCHM) respectively. 

At high temperatures and low frequencies conductivity contribution are important since the loss permittivity tends to increase continuously. Figure 2.41 show the Arrhenius plot for the determination of the activation energy for the 5 relaxation which is about 28 kJ mol-1. This is a value very close to those reported for similar structurally poly(methacrylate)s [28,29], Increasing the temperature, a y relaxation is observed. 

The evolution of the frequency of the maxima show a linear dependency with the inverse temperature according to the expectations as shown in Fig. 2.41. The activation energies calculated from the Arrhenius plot for each process are 68.2 0.6kJ mol-1 for p relaxation and48.0 0.3 kJ mol-1 for y relaxation. These values are very close to those found for structurally related to P4THPMA such a PCHM [29,30], PMCHMA [59], poly(2-chlorocyclohexyl methacrylate) [33] and PDMA [104] (70-82 and 41-50 kJ mor1 [38],... 

The variation of fanS with temperature at 1 kHz for the six poly(thiocarbonate)s is represented in Fig. 2.86. In all cases a prominent relaxation associated to the glass transition temperature labelled as a -relaxation is observed in Figure PT-1. A secondary relaxation which covers a range of about hundred degrees and which by comparison with the results reported for PCs is labeled as y relaxation. Between 80°C and 100°C a slightly dielectric activity is observed (f) zone) and at — 120°C another relaxation labelled as 5 relaxation for polymers 4,5 and 6. 

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