Understanding Medicinal Plants: Their Chemistry and Therapeutic Action
Prof. Bryan Hanson
Instructor's Resource Page for Chapter 5
Chapter 5 is divided into three sections. The first discusses the use of solubility and acid-base behavior to help students understand how the polarity of a molecule can be used to extract it from a plant. This section then continues with a description of the process of chromatography as a means of separating an initial extract into increasingly pure fractions, guided by the use of appropriate bioassays. The second section considers how we know the structures of molecules. IR and 13C NMR are discussed as the most accessible techniques for determining the structure of an unknown that might be isolated from a plant (symmetry arguments and the use of a molecular formula are employed as well). For courses in which the audience might be willing to accept that there are methods to determine structure, without worrying about what they are, one could skip over this middle section without doing damage to students’ understanding of later topics. In my Medicinal Plants for Poets course, these first two sections are covered in the lab phase of the course.
The third section is a fairly detailed consideration of antioxidants, with an emphasis on lipid damage, the most well studied area. Antioxidants are molecules that appear in advertising and the news frequently as an important health issue, so students are likely to be a bit familiar and quite interested in this topic. The goal of this section, as with the rest of the book, is to show that antioxidants are not some kind of magic. Rather, there are specific processes occuring which degrade the molecules in our body, and there are specific defense mechanisms to at least partially counteract these processes.
- Understand the role of polarity & solubility in the process of extracting
useful compounds from a medicinal plant.
- Be able to compare structures and solvents and determine if a molecule
will dissolve in a given solvent.
- Understand how the acid-base behavior of amines and carboxylic acids
affects their polarity and therefore their solubility, and how this behavior
can be used in an extraction.
- Be able to describe the principles behind chromatography on a molecular
- Understand the process of chromatography and how it can be used to separate
molecules of medicinal interest.
- Be able to describe TLC and HPLC and their respective uses.
- Know why bioassays are useful, and what their limitations are.
- Be able to define the term spectroscopy.
- Understand what is occuring in IR spectroscopy on a molecular level.
- Be able to look at an IR spectrum and identify the functional groups
that may be present, with the aid of a correlation table.
- Know how to use the molecular formula of an unknown molecule and the
formula for the IHD to narrow the range of possible structures.
- Understand how 13C NMR can help determine the structure of an unknown,
using the number of lines in the spectrum, the concept of symmetry, and
the ppm range of different types of carbon atoms.
- Be able to use IR spectroscopy, 13C NMR, and the molecular formula together
to narrow down the structure of an unknown molecule.
- Know that mass spectrometry (MS) is primarily used to give the molecular
mass of an unknown molecule, and realize that this limits the possible
- Be able to describe how chromatographic techniques, combined with spectroscopic
measurements of the amounts of molecules, can be used to construct a calibration
curve to measure the amount of a molecule in a sample.
- Be able to define the following terms in the area of antioxidants: antioxidant,
reactive oxygen species, inflammation (both macroscopic and molecular levels),
primary ROS, in vivo, in vitro, and half-life.
- Be able to recognize a free radical molecule from its Lewis Structure.
- Understand that the reactivity of a molecule depends upon its reaction
partner and the reaction environment (temperature, solvent, concentration),
and that reactivity is primarily a measure of how fast a reaction occurs.
- Understand the relationship between reactivity and selectivity.
- Be able to compare the half-lives of several ROS and tell which one is
- Realize that energetically favorable reactions might not occur because
their rate of reaction is too slow.
- Know the two major and three minor sources of ROS in the human body.
- Be able to describe the fluid mosaic model of membranes and why a lipid
- Be able to describe several ways in which ROS cause damage to lipids
in membranes, which in turn causes the membrane to be less functional.
- Be able to describe how ROS can damage proteins and nucleic acids.
- Be able to describe the enzymatic and dietary defense systems which operate
in the human body to control ROS damage.
- Be able to describe the causes and process of atherosclerosis.
Teaching Ideas, Activities & Resources
Any number of published articles provide tables of the antioxidant characteristics of various materials which can be used to illustrate their value. Some specific sources you might consider include:
- Spice extracts: J. Agric. Food Chem. vol 53 no 20 (2005) Table 1 on pg 7751-7752
- Tea & common vegetables: J. Agric. Food Chem. vol 44 no 11 (1996) Table 1 on pg 3427
- Herbal extracts: J. Agric. Food Chem. vol 49 no 11 (2001) Table 1 on pg 5166
- Essential oils: J. Agric. Food Chem. vol 48 no 9 (2000) Table 2 on pg 3803
The background on this page is a 19th century woodcut of Phytolacca americana.
Last updated Thursday, September 1, 2011 . Contents & layout copyright 2011 Prof. Bryan Hanson