Difference Between Alpha and Beta Glucose

Main Difference – Alpha vs Beta Glucose

Glucose is a simple carbohydrate. It is a sugar that has a sweet taste. The molecular formula of glucose is C₆H₁₂O₆. The structure of glucose can be given in different ways such as the Fischer projection, Haworth projection or Chair conformation. The most accurate way of the representing glucose is the chair confirmation, which is typically the most stable structure of most of the cyclic molecules. The major isomers of glucose include D-glucose and L-glucose. According to the chair confirmation, there are two isomers of D-glucose that can be found in nature. Those are alpha glucose and beta glucose. The main difference between alpha and beta glucose is that the –OH group attached to the first carbon atom in alpha glucose is located on the same side as the –CH₂OH group whereas the –OH group attached to the first carbon atom of in beta glucose is located on the opposite side from the –CH₂OH group.

Key Areas Covered

1. What is Alpha Glucose
      – Definition, Structure, Properties
2. What is Beta Glucose
      – Definition, Structure, Properties
3. Similarities Between Alpha and Beta Glucose
      – Outline of Common Features
4. What is the Difference Between Alpha and Beta Glucose
      – Comparison of Key Differences

Key Terms: α-Glycopyranose, β-Glycopyranose, Alpha Glucose, Beta Glucose, Chair Confirmation, Glucopyranose, Glucose, Oxygen Bridge

What is Alpha Glucose

Alpha Glucose is an isomer of D-glucose whose –OH group of the first carbon atom is located on the same side as the –CH₂OH group. Alpha glucose is a sugar. When considering the chair confirmation structure, alpha glucose is a cyclic structure having four –OH groups attached to the main carbon chain. The cycle is formed through an “Oxygen bridge”. That means, two carbon atoms of the terminal of the main carbon chain are attached through an oxygen atom.

Difference Between Alpha and Beta Glucose

Figure 1: Alpha D-Glucose

The ring structure is not planar and is a 3D structure. In order to avoid any confusion, the chair confirmation of glucose is called glucopyranose. Therefore, alpha glucose is also known as α-glycopyranose. The melting point of alpha glucose is about 146⁰c.

Alpha glucose can easily be crystallized from its aqueous solution. The solid crystals appear as white crystals. The chair confirmation of alpha glucose shows four chiral carbon atoms. (C₂, C₃, C₄ and C₅). Therefore, alpha glucose is highly optical active. Alpha glucose act as the building block of starch.

What is Beta Glucose

Beta glucose is an isomer of D-glucose whose –OH group of the first carbon atom is located on the opposite side from the –CH₂OH group. Beta Glucose is also a sugar. It has four –OH groups attached to the main carbon chain. Beta glucose is also called β-glycopyranose. It is a cyclic structure and has four chiral carbon atoms, same as in alpha glucose. Therefore, beta glucose is also optically active.

Figure 2: Beta D-Glucose

The melting point of beta glucose is about 150⁰C. It can be crystallized from its aqueous solution as white crystals of β-glycopyranose or β-glycopyranose hydrate form. The polymerization of beta glucose results in cellulose.

Similarities Between Alpha and Beta Glucose

Alpha and beta glucose are simple sugars.
Both have four –OH groups in their chemical structure.
The spatial arrangement of –OH groups (except for the –OH group at first carbon) is the same.
Both can be crystallized from their aqueous solutions.
Both sugars are optically active due to the presence of chiral carbons.

Definition

Alpha Glucose: Alpha glucose is an isomer of D-glucose that has the –OH group of the first carbon atom positioned on the same side as the –CH₂OH group.

Beta Glucose: Beta Glucose is an isomer of D-Glucose that has the –OH group of the first carbon atom positioned on the opposite side from the –CH₂OH group.

Melting Point

Alpha Glucose: The melting point of alpha glucose is 146⁰C.

Beta Glucose: The melting point of beta glucose is 150⁰C.

Crystallization

Alpha Glucose: Alpha Glucose can be crystallized as α-glycopyranose from its aqueous solution.

Beta Glucose: Beta Glucose can be crystallized as either β-glycopyranose or as β-glycopyranose hydrate from its aqueous solution.

Conclusion

D-glucose is the most stable and abundant isomer among various isomers of glucose. When considering the chair confirmation of D-glucose, there are two different forms of d-glucose as alpha glucose and beta glucose. The main difference between alpha and beta glucose is the position of the -OH group attached to their first carbon atom.

References:

1.Wasserman, Robin. “What Is Alpha Glucose?” LIVESTRONG.COM. Leaf Group, 17 Nov. 2015. Web. Available here. 07 July 2017.
2.Hunt, Dr Ian R. “What do the α- and β- forms look like?” Ch25: alpha and beta forms. N.p., n.d. Web. Available here. 07 July 2017.

Image Courtesy:

1.”Alpha-D-Glucose” By Yikrazuul – Own work (Public Domain) via Commons Wikimedia
2. “Beta-D-Glucose” By Yikrazuul – Own work (Public Domain) via Commons Wikimedia