I'm working on starch, for instance. It has got linear and branched units. In order to estimate the number of OH groups, and the possibilities of making H bonds, I need to know the number of repeating units of the polymer. is there any way to do that?
That's pretty simple for many polymers, just determine the molecular weight using viscometry, light scattering or chromatography. However starch is probably much more challenging.
Thanks Peter Farrington . That's the trouble. It's really confused me. Should look into it to see if I can find out something that might work. I literally have no clue, yet.
You may see the attached papers.
http://www.aaccnet.org/publications/plexus/cfwplexus/pub/2012/CFW-55-3-0139.pdf
Article Molecular weight, chain profile of rice amylopectin and star...
First you have to deal with a fundamental difficulty. Starch is a mixture of two biopolymers, linear amylose (MW ca 10E6) and branched amylopectin (MW ca 10E8). So starch has a bimodal molar mass distribution which is very broad. Because for most starches, amylopectin is the dominant fraction (typically 70-80 %) and because the preferred experimental method is size exclusion chromatography with light scattering detection, which is more sensitive to the high molar mass species, the molar mass of amylopectin is a rather good approximation for that of whole starch, except for the amylose-rich starches.
In doing molar mass determinations one has to ensure that the starch has been molecularly dissolved in a way that no molecular degradation has occurred. This is not a simple task. Fortunately, suitable methods have been developed and literature values for most common starches are available. The authors of the paper provided by Md. Abdur Rahman are real experts in the field but their paper does not provide numerical values. Data for various starches were presented in a paper by Yoo and Jane (Carbohydr. Polym. 49 (2002) 307-314) which you find in the attachment.
Dear Peter A. M. Steeneken
That was an amazing explanation I have ever heard. You really saved my life. I was wondering how on earth can I determine the MW of these two units for maize starch as the same time. You saved my life by the assumption of taking the amylopectin as a suitable approximate.
Thank you so much for very clear explanation. I'll try to find out their papers as well. But as you said, Yoo and Jane have provided the numerical value, which I reckon, I should be fine if I use this in my further analysis.
Thanks so much again for your help, which is much appreciated.
Regards,
Saeid
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