Poly , temperature dependence spectra

The distribution of conformers in the unordered conformation depends on the amino acid sequence and on the solvent and temperature. However, there is a substantial body of evidence 151 that poly(Pro)II-like conformers are present at significant levels in unordered peptides at room temperature, and become increasingly important as the temperature decreases. This was first pointed out by Tiffany and Krimm/152 who noted the striking similarity of the CD spectra of ionized poly(Lys) and poly(Glu) to that of poly(Pro)II. The spectra are indeed very similar, if one allows for a red shift of -10 nm in the poly(Pro)II spectrum, attributable to the difference between tertiary and secondary amides. The case for poly(Pro)-Il-like conformers in unordered peptides is greatly strengthened by observations that the vibrational CD spectrum of unordered peptides is qualitatively like that of poly(Pro)Il 153 154 ... 

The contribution of the poly(Pro)II conformation to the ensemble of unordered peptides has been considered.1158 The temperature dependence of [0]222 for the peptide Ac-YEAAAKEAPAKEAAAKA-NH2 in 8 M guanidinium chloride and of poly(Lys) in water and in ethylene glycol/water (2 1) mixtures 156 was fitted to a two-state equation for a poly(Pro)II-unordered equilibrium with a temperature-independent AH and temperature-independent molar ellipticities for the two components. The peptide with a Pro at the central position is an unordered peptide, the spectrum of which has pronounced poly(Pro)II-like features at low temperatures. This fit yielded [0]222=- -9580 deg-cm2dmol 1 for the poly (Pro)II component and —5560 deg-cm2-dmol 1 for the unordered component. These values provide a method for roughly estimating the poly(Pro)II content, /Pn, of an unordered peptide from [0]222 ... 

Roovers and Bywater 76 examined the temperature dependents of the electronic spectrum of poly(isoprenyi)iithium and were able to calculate an equilibrium constant for the dissociation event. On the basis that the process involved was tetramers dimers, the dissociation enthalpy was determined to be 12.3 kcal/mole in n-octane while a value of 9.0 kcal/mole was found in benzene solution. The latter value was thought to be due to weak solvations of the active centers by benzene. The approach used by Roovers and Bywater 76) is predicated on the assumption that the 272 and 320 nm absorptions represent species differing in their association state. 

Figure 14.42 (page 281) shows the temperature-dependent H spectrum of a 1 1 mixture of adenosine and Poly U. At 30°C, the spectrum is identical to that... 

Fig. 23. Temperature dependence of ESR spectrum of poly(2,6-dimethylphenyl-eneoxide) in xylene. Irradiation at a 60° C, b 100° C and c 150° C...

Figure 3. Temperature dependence of the NMR spectrum at 109.3 MHz of 145 bp poly(dAdT) hairpins in 10 mM tris-Cl (pH 8.0, 0.1 M NaCl, and 1 mM. EDTA). (Reproduced, with permission, from Ref. 5. Copyright 1979, American Society of Biological Chemists.)...

In a study on the radical polymerization of various methacrylates in 2-methyltetra-hydrofuran (MTHF) rigid glass, Kamachi et al. observed even at room temperature the ESR spectrum of the poly(triphenylmethyl methacrylate) (polyTPMA) radical, which has a bulky side group. They investigated the temperature dependence of the... 

In this way, Kamachi et al. succeeded in explaining the temperature dependence of the ESR spectrum of the poly(TPMA) radical on the basis of two conformations their calculated results are summarized in Table 2. Later, they substantiated the simulated spectra by ESR measurements on the radical polymerization several methacrylates at room temperature. The details will be described in Section 5.4. 

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