The following questions refer to changes of chlorophyll B molecules following tr

Question

The following questions refer to changes of chlorophyll B molecules following treatment with the Dowex 50W X8 strong cation exchange column. i) Provide the correct name for the molecule exiting the column, ii) describe the change in colour that was observed when the molecule passed through the column, iii) describe the likely spectroscopic properties (absorbance properties in the visible range spectrum) of the molecules after they passed through the ion exchange colume and iv) name the structural feature of the molecule that facilitates the absorption of visible light. (1.5 marks)

Explanation / Answer

Dowex 50W X8 is a strong ion exchange cationic binding resin acts as stationary phase.

This contains acidic functional groups like sulphonic acid

SO3H attached to inert polymer. This adsorbs Mg+2 ions of chlorophyll B and exchanges H+ ionion. This produces pheophytin B.

This shows that magnesium (Mg+2) is the molecule that excites the column for ion exchange.

This makes the change in colour from green to olive green/dark green.

Usually cholorophyll B absorbs blue and red light but reflects green light.

This is due to the presence of magnesium ion that influence the wavelength of light absorbed by the chlorophyll B.

This shows that more green light is absorbed without magnesium ions.

So Magnesium ions prevent the chlorophyll B to absorb more green light in order to make the structure rigid.

Due to removal of magnesium ions from chlorophyll B forms pheophytin B that facilitates the absorption of visible light.

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