Glucose is ubiquitous in nature. It's a monosaccharide, meaning single sugar unit, that's found not only as a component of table sugar but also as the building block for the larger molecules starch and cellulose, or fiber. Several scientists were involved in the discovery and characterization of the glucose molecule, which took place in the 18th and 19th centuries.
History
The glucose molecule was first isolated, meaning separated from a mixture of many chemical compounds, by Andreas Marggraf in 1747, according to the Imperial College in the United Kingdom. Marggraf worked with raisins, which contain a mixture of many molecules--including many sugars. He isolated and purified a white powder, which later became known as glucose, through a series of chemical extraction techniques. Upon examination, Marggraf determined that he had isolated a compound with a sweetness somewhat less than that of table sugar.
Identification
Over many years, scientists continued to work with extractions of glucose from raisins and other sources in an attempt to determine whether the new substance was pure or was a mixture of other substances. As explained by Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry," researchers use melting point to determine whether a compound is pure. Pure compounds have discreet melting points, while mixtures melt over ranges. Through verifying that the glucose powder had a melting point of around 302 degrees Fahrenheit, Marggraf was able to show that it was a pure substance.
Characterization
In science, it's not sufficient to discover the existence of a molecule--complete discovery also involves a characterization of the molecule and determination of its chemical structure and properties. Emil Fischer worked with glucose in the late 19th century and determined that it was made up of 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen. He also determined how those atoms were connected to one another, putting together a structure of glucose, notes Imperial College.
Properties
Fischer went on to discover that glucose actually exists in two forms, one of which is naturally occurring and one of which is not. The naturally occurring form rotates plane-polarized light to the right, Fischer discovered. This interesting property led him to add the prefix "D" to the name of the molecule, to indicate that the molecule showed dextrorotatory properties, explain Drs. Garrett and Grisham. The non-naturally occurring form rotates plane-polarized light to the left.
Expert Insight
Fischer went on to work more with the glucose molecule and found that D-glucose can be found in nature as a straight chain or as one of two possible ring forms. The ring forms of the molecule are called alpha-D-glucopyranose and beta-D-glucopyranose, note Drs. Mary Campbell and Shawn Farrell in their book, "Biochemistry." Fischer then used what he'd learned about glucose to characterize other sugars, eventually earning a Nobel Prize for his work in advancing the field of biochemistry.
References
- Imperial College: Glucose Discovery
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
