Oxidised dextran

The most versatile method for the introduction of bioactive molecules with terminal NH2 functions such as proteins and enzymes is the coupling via formation of a Schiff base (Fig. 47). It is necessary to oxidise the dextran backbone in the first step to obtain reactive aldehyde moieties. The Schiff base formed between the amine group of the bioactive molecule and the oxidised dextran is usually reduced in a separate step to obtain a stable conjugate. 

Dextran-spermine-based conjugates have been prepared via reductive amination between oxidised dextran and spermine [11]. Spermine, a naturally occurring linear polyamine, is involved in cellular metabolism and is a polycation at physiological pH. Dextran was initially oxidised with potassium periodate and the obtained dialdehyde derivative was then reacted under basic conditions with spermine. Dextran-spermine displayed particularly high transfection efficiency, which was attributed to the unique complexation properties between DNA and the grafted spermine moieties. Dextran-spermine and their derivatives have shown high transfection of p-DNA both in vitro and in vivo [12]. 

Polymers can also be cross-hnked if the enzyme generates reactive functionalities in the polymer chain (Fig. 6.14). Tyramine, for example, can be incorporated into the polymer (e.g., hyaluronic acid, dextran or alginate) and used to cross-link the material through oxidation of the phenol by HRP in the presence of H2O2 (Jin et al., 2007 Kurisawa et al., 2005 Sakai and Kawakami, 2007). In polypeptides, tyrosinase has also been used to oxidise tyrosine to quinone moieties that are able to react further with the functional groups in the side chains of a number of other amino acids (Chen et al., 2002). 

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