Experiment chain cleavage

Fig. 6. ES MS" spectra of the pentaglycosylated saponin 4 from the fruit methanolic extract of P. dodecandra (Phytotaccaceae). Sample (1 mg/ml) injected by a syringe pump (5pl/min) (infusion experiment). For LC/MS conditions, see experimental. This experiment allowed a sequential fragmentation of the saponin sugar chain (cleavage of only one sugar at each MS/MS step), clarifying the structural determination.

An unsettling feature of the system is the instability of its characteristics other than cytokinin-dependency. For example, the time taken following transfer to cytokinin-free medium (at a fixed cell density) before mitotic arrest is liable to shift between experiments. A simple explanation for the shifts might be the spontaneous occurrence in the culture of variant types with altered cytokinin metabolism. The spontaneous occurrence of an unstable line with enhanced activity of zeatin side chain cleavage has been described [32]. It seems that the renowned phenotypic instability of callus tissue [33] is accentuated by suspension culture, in which each small clump of cells is a separate entity with its own selective advantages in the fierce competition to contribute cells to the inoculum for the next batch. 

From her experiments Kim concludes that in the initial phase of degradation in ozone-free oxygen stress or strain have no effect on the rate of chain cleavage. 

Low-molecular weight chains do not experience enough shear force to induce scission. Watson et al." demonstrated (by the intrinsic viscosity characterization of masticated NR) that the limiting molecular weight for the shear-induced degradation is in the order of 0.7-1.0 X 10 Frenkel independently speculated that shear-induced cleavage occurs near the midpoint of the polymer chain. 

This discussion of the structures of diene polymers would be incomplete without reference to the important contributions which have accrued from applications of the ozone degradation method. An important feature of the structure which lies beyond the province of spectral measurements, namely, the orientation of successive units in the chain, is amenable to elucidation by identification of the products of ozone cleavage. The early experiments of Harries on the determination of the structures of natural rubber, gutta-percha, and synthetic diene polymers through the use of this method are classics in polymer structure determination. On hydrolysis of the ozonide of natural rubber, perferably in the presence of hydrogen peroxide, carbon atoms which were doubly bonded prior to formation of the ozonide... 

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