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looking for explanation of experimental results

Koen Vercruysse writes "Dear Nanodot members,

I have some (small) experimental observations that, because I have little background in inorganic or physical chemistry, I am at a loss to explain.

I am studying the interaction between naturally-occurring anionic polysaccharides and multivalent cations. One of my test polysaccharides seems to bind strongly to various divalent or trivalent cations, but also seems to have an effect on the interaction with light of those cations. Mixing a solution of this one particular polysaccharide with a solution of copper(II)chloride results in a markedly enhanced blue coloring of the mixture (compared to the copper ions by themselves) and an enhanced (up to five-fold increase) absorption at 690 nm. Interestingly, years ago I observed a similar effect of the same polysaccharide interacting with terbium(III) or europium(III)chloride. The mixing of these cations with the polysaccharide resulted in a markedly enhanced (up to seven-fold) fluorescence emission of the cations, without affecting the excitation or emission spectrum. I am looking for a possible explanation of these effects and their potential significance (in other words, whether this is worth pursuing further). Somebody suggested to me that this could be due to the formation of nano-sized particles in the solution. Would that be a possibility?

I appreciate the time you might take in answering my questions.

Sincerely,"

2 Responses to “looking for explanation of experimental results”

  1. Anonymous Coward Says:

    This seems to be normal photochemistry

    How big is your polysaccharide? Are they big enough to fold? What's the siggested size of the "nano particles"? Yiou know, polysacharide alone could be defined as a nano-particle. You should get a book on photochemistry.

  2. tfowler Says:

    Complexation

    Well, I can try and explain the inorganic part of the situation.

    After doing a bit of research on your webpage, and on the structure of the polysaccharides you are using, I believe your observations are due to coordination compounds between the transition metal and the polysaccharides. The nitrogen (and some Oxygen atoms) in glycosaminoglycans have a lone pair, and through a lewis acid/base reaction, can form a complex with the unoccupied D orbitals of the metal cation. The complex will have significantly different spectral properties from the bare cation, and will also exhibit different reactive properties.

    You may want to go to the chemistry library and check out a book on inorganic chemistry. It will probably answer many of your questions.

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