Xanthophylls

Plant pigments are an important source of non-toxic compounds for use as food or cosmetic colouring agents. The coloured xanthophylls in capsicum are important sources of pigments that can replace carcinogenic synthetic dyes.


Xanthopylls are very similar to carotenes but often contain hydroxyl groups.
Cryptoxanthin, shown to the right, is an example of a xanthophyll.

β-carotene, shown on the left, is an example of a carotene.

Until now, the common method for extracting red pigments from dried fruit of Capsicum has used hexane as the extraction solvent. Current extraction processes are limiting in that the red pigment can only be recovered from American paprika varieties or other mild cultivars.

A study from the New Mexico State University presents a process for the efficient extraction of these pigments using a "green chemistry" method that generates an oleoresin from dried capsicum fruit with virtually the same xanthophyll composition as the hexane extraction method.

Reference
Richard D. Richins, Laura Hernandez, Barry Dungan, Shane Hambly, F. Omar Holguin, and Mary A. O'Connell. A 'Green' Extraction Protocol to Recover Red Pigments from Hot Capsicum Fruit. HortScience, 2010; 45: 1084-1087

Further Reading
Functional Groups
Empirical and Molecular Formula
Molecular Mass (Formula Weight)
Percentage Composition
Oxidation of Alcohols
Intermolecular Forces

Study Questions

1. Circle the hydroxyl group in cryptoxanthin.
2. Write the molecular formula for cryptoxanthin.
3. What is the empirical formula for cryptoxanthin?
4. What percentage by mass of carbon is present in cryptoxanthin?
5. Write the molecular formula for β-carotene.
6. What is the empirical formula for β-carotene?
7. What percentage by mass of hydrogen is present in β-carotene?
8. Which molecule, β-carotene or cryptoxanthin, would be the most polar? Explain your answer.
9. If you were given a solution that contained either cryptoxanthin or β-carotene, how might you be able to decide which of the compounds is present in the solution? Explain your answer.
10. If cryptoxanthin were to react with a strong oxidizing agent, what product(s) might you expect from the reaction? Explain your answer.
    

Crystal Violet Lactone

Crystal violet lactone (CVL) is known as a leuco dye.
In a basic environment, the central carbon atom of crystal violet lactone (CVL) forms 4 covalent bonds and the molecule is colourless. In an acidic environment, the lactone ring is broken and the central carbon atom gains a positive charge through the loss of a valence electron, this is the coloured form of the molecule.
These reactions are shown below:

CVL was the first dye used in carbonless copy papers.
Carbonless paper consists of sheets of paper coated with a microencapsulated dye or a reactive clay.
The back of the first sheet is coated with the dye, the top of the lowest sheet is coated with a clay that quickly reacts with the dye to form a permanent mark. When you write on the sheets, the pressure of the pen tip breaks open the micor-capsules of dye, the dye reacts with the clay, and a permanent copy is made of the document.
Chemists in Poland have also discovered that CVL molecules emit white light with continuous spectrum covering almost the entire visible range. This is an important discovery because it is known that white light from artificial sources such as fluorescent lights is devoid of many colour components and that this is responsible for causing tired eyes. Making a better artificial white light could result in improved productivity in humans.

Reference:
Jerzy Karpiuk, Ewelina Karolak, Jacek Nowacki. Tuneable white fluorescence from intramolecular exciplexes. Physical Chemistry Chemical Physics, 2010; 12 (31): 8804 DOI: 10.1039/B927232A

Further Reading
http://www.ausetute.com.au/fungroup.html
http://www.ausetute.com.au/acidbase.html

Study Questions

1. Identify the various functional groups in each of the molecules shown above.
2. Name each of these functional groups.
3. Carefully read the introductory paragraph in the story above, and study the reaction diagram. Can you circle a lactone ring?
4. Imagine you could obtain pure samples of each of the two molecules shown. In what ways would the samples be similar? In what ways would they be different?
5. Describe two tests that you could used to distinguish between each of the pure samples above.
   

Fluorescence and Counterfieting

Fluorescence is an emission of electromagnetic radiation. Certain organic dyes are fluorescent, when hit within a certain wavelength range they emit light at a greater wavelength. The wavelength and intensity of this light depends on the physical and chemical properties of the materials to which the dye was applied.

To make a product counterfeit-proof, multiple dyes can be added to the material in very minute quantities, such as just a few parts per billion, to create a marker. At such low concentrations, the marker is virtually impossible to decode, and the counterfeit protection cannot be removed since it permeates the whole material. Fluorescent dye markers produce precise characteristics so it is easy to recognize if the material is original or if it is a copy.

Reference:
Fraunhofer-Gesellschaft (2010, June 15). Brilliant counterfeit protection. ScienceDaily. Retrieved June 18, 2010, from http://www.sciencedaily.com­ /releases/2010/06/100614093627.htm

Study Questions

1. What is meant by the term electromagnetic radiation?
2. Fluorescein is an example of a fluorescent dye that has been used as a marker for airplanes downed at sea. Find the structural formula for fluorescein.
3. Some fluorescent compounds are used as fabric whiteners in washing powders and are referred to as optical bleaches. Find an example of an optical bleach and describe how it works.
   
4. A number of naturally occurring minerals are fluorescent. Can you list examples of these?
5. Phosphorescence is similar to fluorescence. What is the difference between phosphorescence and fluorescence?
6. If an aqueous solution of fluorescein has a concentration of 175ppb, what is its equivalent concentration in,

• ppm
• parts per hundred
• g/mL
• μg/mL
• mol/L