[STM]

Hello everyone,

I intend to use Triphenylphosphine (TPP) to confirm the presence or absence of lipid hydroperoxides in water medium. However, TPP is insoluble in water but soluble in methanol which is miscible with water.

My worry is that if I dissolve TPP in methanol and then introduce it into water, will the TPP not precipitate out upon getting into water and therefore will not participate in the reaction which may lead to wrong conclusion.

I have considered other lipid peroxide reducing agents like sodium dithionite or sodium borohydride (both are water soluble). However, their reactive nature to water or special conditions of reaction may not be beneficial to my study. TPP will proceed to react with  lipid hydroperoxide even at room temperature. Hence, TPP is my first choice.

Kindly advice me on how I can incorporate TPP into this study in water medium. Otherwise, I also welcome suggestions on how I can safely and effectively handle sodium dithionite or sodium borohydride in the water medium for my study.

Thank you for your response.

[Corribus]

Is there a reason you don't want to use iodometry, which is a common way to quantify peroxides? A quick Google search shows that there are methods for lipid hydroperoxides.

E.g., http://www.jlr.org/content/4/2/212.full.pdf

[STM]

Dear Corribus,

Thank you for your response. I don't want to use Iodometric titration because it will change the system matrix too much and it is not sensitive enough at the level of my application (few nM concentration). Secondly, my purpose is not necessarily to quantify lipid hydroperoxide. I am working on using a selective probe which is more sensitive to lipid hydroperoxides at this few nM concentration. My aim of seeking to use TPP is to confirm that my probe is reacting with lipid hydroperoxide in the sample matrix and not other components of the sample. Hence, the TPP or other reducing agents I am considering is to differentiate the proportion of the sample matrix that contains lipid hydroperoxides amongst other potential interference.

Basically, the TPP or other reducing agents I am considering is to ''Scavenge" and thereby differentiate the presence of lipid hydroperoxide in my sample matrix thereby authenticating the reaction of my probe with lipid hydroperoxide.

Thank you

[Corribus]

Just curious. I'm afraid I don't have much advice on the triphenylphosphine issue. The best thing to do may be just to try it, and then validate at high concentrations it against a method you know should work (like iodometry). If you are having trouble with solubility of TPP in water, my thought was maybe you could use a version with appropriately functionalized phenyl groups, but I don't know how easy that will be. Other than that, you might get some more insight if this thread were moved to the organic chemistry forum.

[billnotgatez]

This post has been moved from Analytical Chemistry Forum to Organic Chemistry Forum in the hope that there might be more participation by members.

[phth]

borohydride will change its from in water. Can you draw the mechanism? 
Are you trying to do this in the presence of oxygen? In addition, TPP will react with oxygen to form the OPPh3.  The common way to use phosphines int he prescense of water is to use an alkyl phosphine (alkyl phosphines are more reactive than TPP) with carboxylic acids attached to the end of the chains. http://www.sciencedirect.com/science/article/pii/S1044030510000486 this is a common way to reduce disulphides in biological samples.  Have you considered acetonitrile?

[STM]

Dear phth,

Thank you for your suggestions and particularly informing me about Tris (2-carboxylethyl) phosphine via the link you shared. It might even serve me better than the TPP or other reducing agents I mentioned.

The fact that it is soluble in water, more stable to air oxidation and can reduce lipid hydroperoxides makes it promising for my research which is related to authenticating lipid hydroperoxides in some water samples.

Regarding TPP, I was thinking preparing it in methanol and adding a little quantity of it at 10 or 100-fold dilution into my water sample might work.

Thank you