University of Otago, New Zealand

Chemistry

Te Tari Hua-Ruanuku

Hands-On Science 2007

Friday 30 November 2007

Chemistry: Natural Products Chemistry

This year for our Hands On Science Chemistry project we investigated Natural Products Chemistry. Natural Products Chemistry is mainly about identifying interesting naturally occurring molecules and their structures, then proceeding to extract and eventually synthesise those products. Many medicines are natural products and so this area of chemistry is very important. This week, the molecule we investigated was the stimulant caffeine.

On Monday, we started our investigation by extracting and isolating caffeine from various everyday sources such as energy drinks, coffee and tea. We dissolved our drink in dichloromethane, then filtered the solution and evaporated off the solvent to extract the caffeine crystals. After extracting and weighing the caffeine crystals we compared our results to the values given by the manufacturers. For the most part our results agreed. Predictably coffee had the highest caffeine content with Mountain Dew having a similar result to Red Bull.

On Tuesday we synthesised caffeine using one of either theobromine or theophylline. We weighed out 125 mg into a culture tube, which is a little test tube with a small cap on it, and put a stir bar inside. Next we added NaOH solution and some dimethyl sulphate. Then we stirred it for 30 minutes. And then we added chloroform and this formed a layer below the water layer, in which was our caffeine. Then we separated the layers using a separating funnel, which is kind of like a burette. We ran off the lower chloroform layer and added magnesium sulphate to remove any remaining water. Next we evaporated the solution using a rotary evaporator and what was left was a white solid which was caffeine.


On Wednesday we used a 500 MHz Nuclear Magnetic Resonance Spectrometer to identify the structure of the caffeine which we had synthesised on the previous day. The magnet in the NMR has a field strength of about 200 000 times that of earth’s magnetic field. The samples tested were solutions consisting of the synthesised caffeine and deuterated chloroform, CDCl3. Deuterated chloroform was used because unlike normal chloroform, CHCl3, it does not contain hydrogen which is what the NMR detects and therefore did not impair the results. After using the NMR we had a go at an alternative means of identifying the structure of caffeine. This was the Infra-red Spectrometer and required us to mix the caffeine with a long chain oil and place the mixture between two NaCl slides. This technique tells us what sorts of chemical bonds are in the molecule.

On Thursday, we had a seminar from Dr John van Klink, who told us about the work that he does as part of the Plant Extracts Research Unit (PERU). They are involved in studying natural products from native New Zealand plants like manuka. Following the seminar we were introduced to the nucleus of the university; the glass blower. We entered his office and before us lay a room with enough glassware to sink a ship and Bunsen burners more spectacular than dragons could ever be. Amidst the chaos sat John Wells, glass engineer extraordinaire. This is the room where dreams are shattered and remade and luckily for us Jamie did not break anything although it was not for lack of trying. Then on Thursday afternoon, we had a chance to blow some things up, make some slime and check out a coke-and-mentos fountain on the roof of the chemistry building.

The Chemistry group were: Tracey Bag, Kalib Bell, Cam Berry, Hadleigh Bodle, Adam Bryce, Andy Chen, Natalia Krasnova, Jamie Lee, Grace Li, Julia Raynes, Thomas van der Merwe and Seamus Woods.

The Project leaders were: Br David McMorran, Lisa Bucke, Karen Rowley, Ian Billinghurst, Natasha Munro, John Wells and Dr John van Klink.

You may also like to look at the Hands-On Science Home Page