Difference Between Alpha and Beta Glucose

Glucose is a simple carbohydrate with the molecular formula C6H12O6. It forms a part of the monosaccharides. It is mainly produced by plants and algae during the process of photosynthesis. It is sweet to taste. 

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The atoms or molecules in the structure of glucose can be arranged in different ways according to the Fischer Projection, Chair Conformation and Haworth Projection. The most appropriate way of structuring glucose is Chair Conformation.

The major isomers, namely, alpha glucose and beta glucose are a result of this conformation. 

Alpha and beta glucose are simple sugars. Both having the same molecular formula with four -OH groups with the spatial arrangement. Both alpha and beta glucose are optically active due to the presence of chiral carbon atoms. However, they differ in the three-dimensional structure.

Alpha vs Beta Glucose

The difference between Alpha and Beta Glucose is that in alpha glucose, the -OH group on the first carbon is present on the same side as that of the CH2OH group, it has a complex structure but is less stable. The beta glucose, the -OH group on the first carbon atom is placed on the opposite side of the CH2OH group, it is comparatively more stable and therefore it is difficult to take out molecules from it.

Alpha vs Beta Glucose

Comparison Table

Parameter of ComparisonAlpha Glucose Beta Glucose
What it refers to?Alpha glucose is an isomer of glucose that has -OH group present on the first carbon atom is on the same side as that of the CH2OH molecule group. Beta glucose is also an isomer of D-glucose in which the -OH group placed on the first carbon atom is placed on the opposite side of the CH2OH group.
Crystallization propertyAlpha glucose has the property to crystallize as alpha-glycopyranose in the aqueous solution of it.Beta glucose has the ability to crystalize either as beta glycopyranose or as beta glycopyranose hydrate from its aqueous solution. 
Stability and melting pointAlpha glucose has a compact structure but its molecules can be separated from it, therefore, it is comparatively less stable. The melting point of it is 146 degree Celsius.Beta glucose is more stable and therefore molecules can not be taken it easily. The melting point of beta glucose is 150 degree Celsius.
Bonding and Inter conversionThe glycosidic or 1-4 bond between two alpha glucose molecules results in the formation of disaccharides which is termed as Maltase. Alpha glucose can be easily converted to beta glucose.The glycosidic bond between two beta glucose leads to the formation of cellobiose. Beta glucose is easily convertible into alpha glucose. 
Other propertiesThe specific rotation of alpha D-glucose is 112.2 degrees. Starch is a polymer of alpha glucose which can be broken down easily by enzymes. The beta glucose has a specific rotation of 18.7 degrees. Cellulose is a polymer of beta glucose and can not be broken down by enzymes.

What is Alpha Glucose? 

Alpha glucose is an isomer of D-glucose in which the -OH group present on the first carbon atom is on the same side of the CH2OH group. As per the chair conformation, alpha glucose has a cyclic structure with four -OH groups attached to the carbon chain.

The structural cycle is formed by an oxygen bridge which means that the two carbon atoms of the terminals of the carbon chain are joined through an oxygen bond. The ring structure of alpha glucose is a three-dimensional structure and to avoid confusion, it is known as glucopyranose.

The alpha glucose is comparatively less stable. The melting point of alpha glucose is 146 degree Celsius and a specific rotation of it is 112.2 degrees. Alpha glucose can be easily transformed into beta glucose.

The glycosidic bond of two glucose molecules results in the formation of a disaccharide called Maltase. The polymer of alpha glucose is known as starch which can be easily broken down by enzymes.

alpha glucose

What is Beta Glucose?

Beta glucose is an isomer of D-glucose in which the -OH group present on the first carbon atom is on the opposite side of the CH2OH group. It has the -OH group attached to the main carbon chain. The cyclic structure of beta glucose is the same as that of alpha glucose.

Beta glucose is more stable. The melting point of beta glucose is 150 degree Celsius and a specific rotation of it is 18.7 degrees. Beta glucose can also be easily transformed into alpha glucose.

The glycosidic bond of two beta glucose molecules results in the formation of cellobiose. The polymer of beta glucose is known as cellulose which can not be easily broken down by enzymes.

beta glucose

Main Differences Between Alpha and Beta Glucose 

  1. Alpha and beta glucose are the isomers of D-glucose.
  2. In alpha glucose, the -OH group present on the first carbon atom of the molecule is on the same side as that of the CH2OH group while in beta glucose, the -OH group of the first carbon is on the opposite side of the CH2OH group. 
  3. Alpha glucose crystallizes into alpha glycopyranose in the aqueous solution whereas beta glucose crystallize either into beta glycopyranose or beta glycopyranose hydrate in the aqueous solution. 
  4. Alpha glucose has a complex structure but is less stable and Hereford molecules can be easily taken away from it, on the other hand, beta glucose is more stable and therefore it is not easy to break it.
  5. The melting point of the alpha glucose is 146 degree Celsius whereas the melting point of beta glucose is 150 degree Celsius. 
  6. The specific rotation in alpha glucose is 112.2 degrees whereas in beta glucose it is 18.7 degrees.
  7. Alpha and beta glucose are interconvertible into one another.
  8. Starch is a polymer of alpha glucose and cellulose is a polymer of beta glucose.

References

  1. https://pubs.acs.org/doi/pdf/10.1021/j150276a006
  2. https://www.cabdirect.org/cabdirect/abstract/19491404323
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