Links between primary and secondary

Pulrescine is an important link between primary and secondary metabolisms. It acts as a branch point for various biosynthetic pathways leading to a stmcturally diverse set of metabolites. Besides being an important intermediate in pytrohdine, pyrrolizidine, and tropane alkaloid biosynthesis, putrescine can be converted into spermidine (8) and spermine... 

There are basically two strategies for this. The first one is the attachment of whole and commercially available polyamines like spermine or their appropriate derivatives to solid phase. This mostly requires protection of the polyamine and at least one tedious chromatographic step before linking it to the solid support. All earlier examples in the literatme go back on this approach and they mostly adopt protection group strategies for tri- and tetra-aza-polyamines, which have already been established in solution phase. The differentiation between primary and secondary amines is a crucial factor. Depending on the type of resin (see Table 1) and the chosen substrate, the crosslinking reactions of symmetrical molecules must also be taken into account as these can decrease the overall yield and pmity of the final products. 

Cellulose is present in both primary and secondary cell-walls. However, differences in both the degree of polymerization and the control of chain length between the celluloses from these two sources suggest that the two types of cellulose are formed by different mechanisms.289-291 Whereas the mechanisms responsible for formation and orientation of cellulose fibrils are not yet known, some information is available concerning the enzymes capable of catalyzing the formation of celluloselike, 0-(l—>4)-linked D-glucans (see also, Ref. 217). 

For these systems, direct hydrogen abstraction by benzophenone triplets was observed in benzene whereas in a polar solvent electron transfer and hydrogen-atom abstraction were observed. Electron transfer followed by an intramolecular proton transfer was observed in these systems although such proton-transfer reactions are not observed in unlinked systems of primary and secondary amines. The observed differences between the linked and unlinked systems have been attributed to the dependence of electron transfer, proton transfer, and hydrogen transfer on mutual distance and orientation. In the unlinked systems, rotational and translational motion of two reacting molecules are usually much faster than those in linked systems. 

Gelation of aqueous solutions of animal glues upon cooling is an important characteristic. Gelation involves both intra- and intermolecular reorientation upon cooling of the solution. It is caused by the formation of random primary and secondary bonds. Intermolecular network formation is primarily the result of a cross-linking mechanism between molecular chains by hydrogen bonds [11]. 

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