Lipids, Chloroform, and Their Intertwined Histories
From Firenze University Press Journal: Substantia
Carlos Ramírez, Department of Chemical Engineering, University of Puerto Rico
Modern-day students and young researchers sometimes fail to identify events in one discipline that can help explain similar phenomena in another. They also have difficulty envisioning how materials with different physico-chemical properties can lead to common applications. It is precisely this latter problem that serves as the goal of the present article. Lipids and chloroform have long, separate histories. They have also shared scientific pathways for many decades, a fact likely unknown to most readers.As the initial step of an experimental research project involving a specific class of lipids and chloroform, their individual histories were scrutinized. Their isolation, characterization, and synthesis were thoroughly studied, in many cases going back to the original published sources in the 19th Century.
It is our goal to summarize the historical scientific high-lights of lipids (fatty acids in particular) and chloroform, leading to their combined usage to this day. Their individual histories will be addressed separately, while their intertwined pathways will be covered in the last section. The best example of the synergistic use of lipids and chloroform is that their physical and chemical properties served to determine the structure and function of new families of mammalian brain tissue components.
Biochemistry is the science dealing with the chemistry of life, as well as the title of a timeless textbook written by Professor Albert L. Lehninger of The Johns Hopkins University School of Medicine, Baltimore, MD, USA. A chapter of this venerable reference is entitled “Lipids, Lipoproteins, and Membranes”, a subject matter relevant to this work. Lipids are natural substances pre-sent in animal and plant tissues. They are mostly insoluble in water, but soluble in many organic solvents. Lipids are actually families of compounds, with similar physical and chemical characteristics, and can be conveniently grouped according to their backbone structure. For example, acylglycerols (triglycerides) are the most abundant lipids in nature. The reader must have heard of them when, during a routine medical checkup, the doctor pulled his/her ear for having a high blood triglyceride level. Solid triglycerides are known as “fats” and their liquid counterparts as “oils”. They all have a glycerol (triol) backbone joined through ester linkages to fatty acids. The latter consist of a hydrocarbon (aliphatic) chain of varying length and degree of saturation, indicating the presence or absence of double bonds, with a carboxylic acid terminus. The following discussion will focus on fatty acids, since they are the building blocks of many lipid groups, as well as being part of our current research interests. In a later section, we will return to the broader lipid family as we explore its historical relationship with chloroform.Fatty acids were first isolated in 1813 from ani-mal fats (“corps gras”) by the French scientist Michel-Eugène Chevreul (1786–1889), Professor of Chemistry at the Lycée Charlemagne, Paris. They have been the subject of extensive academic and industrial research ever since. Within the body, fatty acids are found in their esterified form since they are practically insoluble in water. To illustrate with a numerical example, the saturated 6-carbon hexanoic acid has an approximate solubility of 1 g fatty acid per 100 g water at room temperature. This translates to a very small fatty acid mole fraction of order 10–3, with this quantity being relevant in mass transfer processes such as those found typically in the field of chemical engineering. The water solubility decreases considerably as the number of aliphatic carbons in the chain increases. Fatty acids are transported in blood bound to serum albumin, a globular protein with an approximate molecular mass of 68000. They can also cross cell membranes, of which they are key constituents, by diffusion (proportional to a concentration gradient) and protein-facilitated mechanisms.
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