Agar and agrose gels:

Agar or agar-agar, as it was called earlier, is acquired from several species of sea- weeds. It is a combination of linear polysaccharides comprising mainly of D-galactose and 3, 6-anhydro-L-galactose residues. A partial structure of agrose is shown in Figure.

Figure:  A schematic representation of partial structure of agrose

These gels are unique combining fractionation ranges at extremely high molecular masses with good mechanical stability. They are a good supplement to the dextran gels and polyacrylamide gels. The agar gels along with the lowest fractionation ranges correspond approximately in their fractionation properties to the dextran and polyacrylamide gels with the highest fractionation ranges. These gels could fractionate in the range intermediate among molecules and particles.

Agrose gel for chromatographic work are available from Pharmacia Fine Chemicals (trade name Sepharose) and Bio-Rad (trade name Bio-Gel A). Sepharose is available within three normal kinds and three corresponding type's crosslinked along with 2, 3- dibromopropanol. The normal types are Sepharose 2B, 4B and 6B and crosslinked types being Sepharose CL2B, CL4B and CL6B.  The numbers denotes the percentage of dry gel in the particles. Bio-Gel A is available in six kinds.

Unlike the gels discussed previously, the macromolecules of gel matrix are not bound through covalent bonds. They are supposed to be held together through hydrogen bonds. The polysaccharide chains seem to aggregate in bundles. Among the bundles, there are very large openings in the gel matrix. The structure is extremely open and at the similar time mechanically stable.