[opsomath]

Hi folks, I have a little bit of a puzzling issue in the lab. I have been working with a carboxymethyl dextran polymer (which gives great results in my experiments) that we get from a supplier who has stopped selling it. (Cue "FFFFUUUUUUUU..!!!!")



This polymer has a DS (degree of substitution) of 41%, which should be slightly more than one carboxymethyl group per glucose repeat unit. (Right? Since there are three free -OH groups on each repeat unit, a fully substituted polymer would have three COOH groups per repeat unit, and have DS = 100%)

I bought a high-quality CMD from a new supplier to see if it would work in place of the stuff I was using. (Dun dun DUNNNN...) It doesn't. The bottle on the new stuff doesn't list a degree of substitution, though, it just gives "0.1 mmol COOH/gram."

The thing is, if I'm calculating correctly that is a TERRIBLE degree of substitution. A DS = 33.3% polymer should have a repeat unit weight of 220 g/mol and a 1:1 stoichiometry of repeat units to COOH groups, meaning that it has 1g/220g = 4.54 mmol COOH/gram. Interpolating, that means that the stuff with only 0.1 mmol/gram has a DS of less than 1%. Furthermore, every other supplier I've been able to find sells similarly low-substitution stuff.

Am I making a really dumb mistake here, or is it just that no one sells the good stuff any more? I'm in the process of trying to make some high-substitution stuff by reacting dextran with a large excess of bromoacetic acid in NaOH, but it would be nice to be able to just buy a starting material.

[Mitch]

Who else in your field uses carboxymethyl dextran polymer? You guys can probably put your heads together to get some. Synthesizing polymers if you haven't done it before does not seem like the most efficient way to go.

[opsomath]

So what did you get for the DS substitution for the 0.1 mmol/g stuff?