Patrick Duffy and Polymorphism

The discovery and study of polymorphism in tristearin, a simple triglyceride, has been a fascinating and evolving area of research in lipid chemistry over the years. It started with Wilhelm Heintz's discovery of tristearin having two melting points in 1851, followed by Patrick Duffy's milestone papers on polymorphism in lipids in the 19th century. Duffy, a graduate student from University College London, made significant contributions to the field despite limited information available about him, and his work shed light on the confusion surrounding the nomenclature and composition of triglycerides at that time.

Marcellan Bertholot's synthesis of a triglyceride in 1854 further confirmed the hypothesis put forth by Chevreul that triglycerides consist of three moles of fatty acids and one mole of glycerol. Chevreul had made significant contributions to lipid chemistry, isolating various fatty acids and triglycerides from natural fats and proposing the concept of "stearins" as pure compounds. However, Heintz's work showed that some of the compounds identified by Chevreul were actually mixtures, and he also discovered the law of melting point depression and pointed out that triglycerides are composed of fatty acids divisible by four.

The mystery of multiple melting points in triglycerides persisted for about 80 years until Thomas Malkin's work using X-ray diffraction to examine fat crystals. Malkin identified four melting points for tristearin, including a non-crystalline glassy structure he named vitreous, as well as the alpha, beta prime, and beta forms. However, his work became controversial when American scientists entered the field and challenged his findings. Daubert, Lutton, and Bailey reported no evidence of the vitreous form and accused Malkin of misinterpreting X-ray patterns and using faulty sample preparations.

Despite the controversies, the polymorphism of tristearin has been extensively studied by other researchers over the years, and more recently, a fourth polymorph of tristearin was discovered by researchers at the University of Guelph. This discovery highlights that even after 200 years, the polymorphic nature of simple triglycerides continues to be revealed, and our understanding of lipid chemistry and triglyceride polymorphism is still evolving.

References

1. Duffy, P. (1853) Scheiding der glyceriden.  J. Chem. Soc. Lond. 5, 197.
2. Duffy, P. (1853) Constitutie en verzeeping van stearine.  J. Chem. Soc. Lond. 5, 303-316.
3. Heintz, W. Giant of the Past. List, G. and Kenar, J. A., Lipid Library, www.lipidlibrary.aocs.org.
4. Chevreul, M. E. (1823). Recherches chimiques sur les corps gras d'origine animale. Paris: F. G. Levrault.
5. Holman, R. T., Lundberg, W. O., & Malkin, T. (1954). Progress in the Chemistry of Fats and Lipids. vol, 2, 258.
6. Bailey, A. E. (1950). Melting and solidification of fats.
7. Lutton, E. S. (1945). The polymorphism of tristearin and some of its homologs. Journal of the American Chemical Society, 67(4), 524-527.
8. Dijkstra, A. J. (2009). How Chevreul (1786-1889) based his conclusions on his analytical results. Oléagineux, Corps gras, Lipides, 16(1), 8-13.
9. Daubert, B. F., Spiegl, C. J., & Longenecker, H. E. (1943). Unsaturated Synthetic Glycerides. II. Unsymmetrical Dioleo-monosaturated Triglycerides1. J. Am. Chem. Soc., 65(11), 2144-2145.
10. Daubert, B. F. (1944). Unsaturated Synthetic Glycerides. V. Unsymmetrical Monoelaidyl-Disaturated and Monosaturated-Dielaidyl Triglycerides1. J. Am. Chem. Soc., 66(2), 290-292.
11. Ghazani, S. M., & Marangoni, A. G. (2023). New Triclinic Polymorph of Tristearin. Crystal Growth & Design, 23(3), 1311-1317.