Poly side-chain-labeled

Rhamnogalacturonan II. In rhamnogalacturonan II, the poly a-(l )-guluronan has four side-chains, labelled A-D, attached. Their relative location is not known with complete certainty, although a likely distribution is that in Figure 4.63. ... 

As Fig. 15b illustrates, the graphical relation appears to be linear for an interaction number of 3 to 4, if A 1. Alternatively, for A = 1, linearity is evident (Fig. 15c) when the interaction number is 5 to 6. Thus a large value of A is compatible with the smallest interaction number. Excimer formation occurs within the fluorescence lifetime, about 8 nsec. Within that time the pyrene-labeled amine side chains must approach within about 4 A of each other. For the 5.3% pyrenylpolyethylenimine derivative in ethanol, where no ground-state association occurs, the effective local concentration of pyrene on the polymer matrix is about 10-2 M, as calculated from excimer fluorescence. In aqueous solution, where clusters form within the polymer matrix, the effective local concentration of pyrene adduct must be even greater. The quantitative assessment of fluorescence intensities (Fig. 15) points to a minimum interaction number of 3 to 4 pyrenyl-labeled amine side chains, within the 8 nsec lifetime. Since A 1, it appears from (12) that kDM(A) kMD + kD. Thus excimer formation must be very rapid in the polymer environment. We can conclude, therefore, that the primary-amine side chains of poly-ethylenimine are very flexible and mobile. 

The effect of the side chain structure on the relaxational behavior of poly (itaconate)s was studied by Diaz Calleja and coworkers [238] in a family of poly(di-n-alkyl and diisoalkylitaconate)s. Specifically in poly(dimethyl itaconate) (PDMI), poly(diethylitaconate) (PDEI), poly(di-n-propyl itaconate) (PDPI), poly (di-n-butylitaconate) (PDIBI), poly(diisopropylitaconate) (PDIPI) and poly (diisobutylitaconate) (PDIBI). These systems show three dielectric relaxation processes, labelled as a, /3 and y. Nevertheless, in some polymers a poor resolution of... 

The peptide-based isocyanides 50a-e were successfully polymerized by Ni(II) catalysts under an inert atmosphere [63-66]. An alanine-derived isocyanide, whose isocyano group was labeled using 13C and 15N, was prepared and successfully polymerized for structure elucidation [67]. Several solvent systems were used in the polymerization of the peptide-based isocyanides, depending upon the solubility of the isocyanides. As mentioned earlier, the use of alcohols as a solvent or co-solvent can accelerate the polymerization. The protective groups on the ester, hydroxy, and imidazole groups were removed after polymerization by treatment with aqueous NaOH to yield poly(isocyanide)s bearing unprotected peptide side chains. 

Fig. 19. Top C-NMR spectra of the amorphous component of solid poly(p-hydroxyalkanoates) as a function of temperature. Spectra were obtained without MAS. Only the aliphatic region is shown, and the backbone and side-chain carbons are labeled bb and sd, respectively. The differential dynamics of the backbone and side chains is evident in the differential line widths. Bottom Schematic behavior of the line width, under conditions of decoupling, when the...

C and N NMR SS NMR experiments to distinguish between poly-morphs/solvatomorphs of Leu-enkephalin were published by Saito and coworkers [164,165]. The SS NMR spectra of various crystaUine forms of Leu-enkephalin revealed different amount of molecules and solvents in the asymmetric unit of crystal lattice and due to that the assignments of signals were ambiguous. On the basis of REDOR NMR experiment and relaxation studies, the differences in dynamics of the backbone and side chains for polymorphs have been shown. Based on that, authors also proved the less-restricted molecular motion of side residues in more hydrated sample. Dynamics of phenylalanine ring of enkephalin crystals have heen examined utihzing sohd-state NMR patterns (Fig. 2.28) and relaxation time (T ) measurements [166]. Results obtained for HsPhe-labelled samples were consistent with data from previous studies. 

Figure 19.3 Structure of fluorescence-labeled poly(methyl methacrylate)s, that are labeled at (a) the side chain, (b) the center segment, and (c) the chain end.

The MALDI spectrum of a polymer sample in which all chains possess the same backbone allows identification of the end-groups present at the chain ends. This type of analysis is referred to as end-group analysis. An example will be helpful. Figure 15.1 reports the MALDI spectrum of a poly(bisphenolA carbonate) (PC for short) sample [7], It displays a series of peaks from 2 up to 16 kDa, the most intense ones in the region from 5 up to 7 kDa. It also displays peak assignment and an expansion of the spectral region from 3.0 up to 3.7 kDa. Peaks at 3034, 3288, and 3542 are labeled as A and are due to PC chains terminated with phenolcarbonate on both sides. Peaks at 3168, 3422, and 3676 are labeled as B and are due to PC chains terminated with phenolcarbonate on one side and bisphenol-A on the other. Peaks at 3048, 3302, and... 

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