Hemoglobin and the Heme Group:
Metal Complexes in the Blood for Oxygen Transport

Authors: Rachel Casiday, Richard Krathen, and Regina Frey

Key Concepts: Metal complexes; protein structure and conformational changes; spectroscopy.

Blood is part of the body's circulatory system, and thus is continually being pumped through our bodies as long as we are alive. The blood distributes oxygen and nutrients to the many different cells in the body, carries CO2 generated by the cells to the lungs for exhalation, and carries other waste products to the kidneys and liver for processing and elimination. Many finely tuned chemical processes occur in the blood to allow the blood to carry out all of these functions and provide for the needs of the body. One of the most important functions of blood is to carry O2 to all parts of the body via the hemoglobin protein. This oxygen transport is accomplished by the heme group (a component of the hemoglobin protein), which is a metal complex with iron as the central metal atom, that can bind or release molecular oxygen. Heme groups are embedded in the hemoglobin protein, so the tutorial gives a view of hemoglobin and its major structural features. The tutorial also describes gas exchange in the blood (CO2 exchanged for O2 in the lungs, and O2 exchanged for CO2 in the muscles), and how both the hemoglobin protein and the heme group undergo conformational changes upon oxygenation and deoxygenation. In addition to showing a molecular view of the changes that occur when hemoglobin is oxygenated or deoxygenated, the tutorial describes the color changes that occur when blood is oxygenated or deoxygenated, and shows how spectroscopy can be used to determine the oxidation of hemogloin. This tutorial is one of four blood-chemistry tutorials available for General Chemistry from Washington University in St. Louis.

At Washington University in St. Louis, this tutorial accompanies a first-semester experiment in which students learn about metal complexes by synthesizing [Co(NH3)6]Cl3 and Cu(NH3)4SO4•H2O in lab. In laab, the students explore ligand-exchange reactions of the Co complex and analyze the results spectrophotometrically. This tutorial explains coordinate-covalent bonding in metal complexes in more detail, and explores how the body uses metal complexes in the protein hemoglobin to transport and release the oxygen ligand. Hence, the tutorial illustrates a biological application of the course material, and lays a foundation for future exploration of these concepts in general chemistry and biology courses.

Click here to view the tutorial.