Small-angle X-ray scattering studies on nucleation formation of dextran precipitation in the presence of boron

In the present study, the nucleation formation process of dextran precipita tion in the presence of boron was investigated by small-angle X-ray scatter ing (SAXS) techniques. The formation mechanism of aggregates or nuclei is v ery important in the initial step of crystallization. SAXS measurement is a n excellent technique for observing these processes. The results of SAXS me asurement suggest that boron, as a trace impurity, induces the aggregating of dextran molecules intermolecularly as a process in the nucleation format ion of dextran precipitate nuclei and causes precipitation of dextran throu gh an elongation process. These reactions occur readily at low boron Concen trations. In fact, boron, which was detected at low levels in dextran solut ions, was concentrated in the precipitates. Therefore, an aqueous solution of boron-free dextran should be resistant to precipitation. (C) 2000 Academ ic Press.