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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: an12345 on July 17, 2012, 09:38:59 AM

Title: Polyethylene glycol dissolved in Phosphate buffer turns yellow?
Post by: an12345 on July 17, 2012, 09:38:59 AM

I have been working with 4 arm PEG-thiol, dissolved in phosphate buffer at 20%. I have been told the solution should be clear and colorless, however my solution turned yellowish-green. I checked the pH of both the buffer and the buffer with PEG at they are both about 7.4 (which was my desired pH). I checked the solution under a fluorescent microscope (in case the PEG was attached to fluorescin or something like it) but it was not fluorescent.

Does anyone know why this would happen?

Title: Re: Polyethylene glycol dissolved in Phosphate buffer turns yellow?
Post by: Babcock_Hall on July 17, 2012, 02:23:09 PM

Would you explain a bit more about what the compound is, or provide a link to a structure?

Title: Re: Polyethylene glycol dissolved in Phosphate buffer turns yellow?
Post by: Yggdrasil on July 17, 2012, 03:18:37 PM

How long and under what conditions have you been storing the PEG?  Is it possible that something is growing in the PEG (is it cloudy)?

Title: Re: Polyethylene glycol dissolved in Phosphate buffer turns yellow?
Post by: Babcock_Hall on July 17, 2012, 05:31:36 PM

PEGs and PEG-based detergents are sometimes contaminated with aldehydes or peroxides which have to be removed.  I am not sure whether the contaminants are relevant to your question or not.  This reference may help:  Ray WJ and Puvathingal JR, Analytical Biochemistry, 1985, 146, pp. 307-312, http://www.ncbi.nlm.nih.gov/pubmed/4025798

Title: Re: Polyethylene glycol dissolved in Phosphate buffer turns yellow?
Post by: an12345 on July 19, 2012, 11:32:12 AM

Hello,
Sorry for the delayed response.
This is a link to the structure of the compound http://laysanbio.com/clientuploads/directory/products/4arm-PEG-SH.JPG


The PEG was purchased 2 weeks ago and stored in the freezer, in a desiccator, in a light protected vial. The vial came with a protective seal which was opened only 1 minute prior to dissolving. The PEG was vortexed in the phosphate buffer (a mixture of monobasic and dibasic sodium phosphate at a pH 7.4) for about 30 seconds and it immediately turned greenish.
I should also mention that the product is not a fine powder like I was expecting it to be. It has larger size particles, clumped together.

Title: Re: Polyethylene glycol dissolved in Phosphate buffer turns yellow?
Post by: Babcock_Hall on July 19, 2012, 03:09:31 PM

It is conceivable that a contaminant in the PEG-based reagent is reacting with a contaminant in the buffer salts.  I don't have any specific hypothesis, however.