A recent finding provides a good example to cover several different areas of IB chemistry.

One traditional foodstuff which contains antioxidants listed under Assessment statement F.3.11 in the Food Option is green tea. Green tea, unlike black tea, contains a substance called epigallocatechin gallate (EGCG) (right). This is an example both of a catechin and a flavanol and is a strong natural antioxidant due to the presence of many phenolic groups. From its structure you could ask students to identify functional groups (e.g. ester, phenol and ether). You could also ask them to predict whether it would be soluble in water, whether it could be optically active, and whether it would be expected to have acidic or basic properties. The teacher’s notes in F.3.11 state that natural oxidants such as EGCG have been linked to lowering levels of LDL (bad) cholesterol and blood sugar levels, reducing high blood pressure and preventing cancerous cell development.

Research in the past has shown that EGCG can be beneficial in treating several different types of cancer including prostate cancer where it is thought to bind selectively to a certain receptor in cancerous cells known as the 67-kDa laminin receptor (67LR). Current treatments for prostate cancer include chemotherapy which requires large doses and can result in toxic side effects and also injecting radioactive isotopes into the prostate but this again causes damage to surrounding cells and has not proved to be very effective against aggressive forms of the cancer. This week a team working at the University of Missouri-Columbia have reported in the National Academy of Sciences of the United States of America (PNAS) an interesting breakthrough which combines several areas of chemistry covered by the IB Chemistry programme. What they have done is insert radioactive gold nanoparticles into ECGC molecules. When the EGCG molecules then bind to the cancerous cells they effectively deliver the radiaoactivity directly to the target and destroy the cancerous cells without causing damage elsewhere in the body. Using mice as the subjects they showed that there was an 80% decrease in the volume of the cancerous cells after only 28 days using this method. This provides a good example for Assessment statement 2.17 “Discuss the use of radioisotopes” and Assessment statement C.7.4 “Discuss some of the implications of nanotechnology” as well as a good example for the use of natural antioxidants in Option F. The isotope used was ¹⁹⁸Au which decays by beta-emission to ¹⁹⁸Hg with a half-life of 2.7 days. The range of the beta-emission in the body is 11 mm which is long enough to penetrate the cancerous cells in the prostate but short enough not to cause damage to surrounding tissue. Interestingly enough chemists have adopted a new shorthand way of describing the nanoforms of radioactive isotopes by using NP (nanoparticle) so the isotope is known as ¹⁹⁸AuNP.