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Dihydroxyacetone: structure, properties, production, uses

Unlike other sugars, DHA lacks asymmetric carbons, so it does not have a D or L configuration and does not have optical activity; that is, it cannot deflect polarized light. What it does share in common with sugars, being a ketosis, is a characteristic sweet taste and great solubility in water.

Structural Formula of Dihydroxyacetone

In the upper image we have the structural formula of dihydroxyacetone. The central C = O group is the reason why DHA is a ketosis.

Structure

In the upper image we have the structure of a DHA molecule represented with a spheres and bars model. As can be seen, the red spheres correspond to the oxygen atoms. Its geometry is almost flat, since the OH and H groups protrude slightly from the plane formed by the three carbon atoms and the carbonyl oxygen atom.

Molecular structure of dihydroxyacetone. Source: Jynto / CC0

The DHA molecule is quite polar. The C = O and C-OH groups leave a side with a high electron density , while its carbon skeleton is deficient in electrons.

Their intermolecular interactions are therefore based on dipole-dipole forces, especially those of the hydrogen bond type. All of this contributes to DHA existing as a crystalline solid under normal conditions.

Properties of dihydroxyacetone

Physical appearance

Colorless crystalline solid, with a characteristic sweet odor and taste. It is highly hygroscopic, so it absorbs moisture from the environment.

Molar mass

90.078 g / mol

Melting point

89 to 91 ° C. This imprecise value is due to the fact that not all DHA molecules are in the explained state, but the vast majority of them form dimers.

Indeterminate, as it decomposes.

Solubility

It is very soluble in water, having an approximate solubility of 930 kg / L at 25 ºC. This is due to its highly polar character, and to the ability of water to hydrate it by forming hydrogen bonds with any of the three oxygen atoms in its molecule. However, it slowly dissolves in a 1:15 water-ethanol mixture.

Hydrolysis and dissolution

In the solid state, DHA tends to exist as a dimer, which when in contact with water undergoes a hydrolysis reaction that ends up giving rise to the individual molecules or monomers of DHA. The transformation would be the one shown below:

Conversion of the DHA dimer to its monomer when it dissolves in water. Source: Steffen 962 at German Wikipedia / Public domain

Since DHA in its monomeric form is very hygroscopic, as it dries quickly and absorbs moisture, it returns to establish the dimer with its dioxane ring.

Collection and synthesis

Naturally DHA can be obtained by extracting it from sugar canes or sugar beets.

On the other hand, when it comes to synthesizing or producing it, there are several alternatives, all based on the oxidation reaction of glycerin. One of them is to oxidize glycerin or glycerol with hydrogen peroxide using ferrous salts as catalysts. In another reaction, the glycerin is oxidized with air, oxygen or benzoquinone but using special palladium catalysts.

We also have the commercial method of production of DHA, in which glycerin is oxidized using acetic acid bacteria in a fermentation process .

During the synthesis of DHA, glyceraldehyde, its structural isomer, is also produced.

Risks

The risks around DHA are not entirely clear. In its phosphate form, dihydroxyacetone phosphate, is a product of glycolysis and an intermediate in the metabolism of fructose, since the enzyme triosaphosphate isomerase transforms it into D-glyceraldehyde 3-phosphate. However, an excessive dose of DHA, according to medical studies, can negatively alter this entire mechanism, even causing cell death.

That is why DHA is considered dangerous if it is ingested or if, especially, it is inhaled. In addition to this, there are studies that confirm that its topical applications increase the concentration of reactive oxygen species (ROS), which attack skin cells causing aging and the appearance of wrinkles.

This collateral reaction is even more pronounced when the skin impregnated with DHA is exposed to the UV rays of the sun, therefore the risks of damage to the skin increase.

Experts therefore recommend not using DHA outdoors immediately after applying tanning lotions to the skin.

To reduce this risk, lotions contain additives such as vegetable oils and antioxidants, as well as microcapsules that gradually release DHA.

Dihydroxyacetone Uses

Tanning lotions that contain DHA are a safer option when it comes to tanning the skin without the need to be exposed to the sun’s rays

Dihydroxyacetone is synonymous with cosmetics, as it is the active ingredient in many tanning products, be they creams, sprays, masks, lotions, etc. When applying these bronzers on the skin, the Maillard reaction occurs, responsible for making it acquire a more orange color, without the need to visit the beach or expose yourself to long hours in the morning sun.

At first, around 1960, tans were exaggeratedly orange, to such an extent that for decades the general public rejected this type of bronzer. However, since then the formulations have been improving, so that the tans look more natural, radiant and pleasing to the eye, while guaranteeing lower risks after use.

Various brands, including Coco Channel, reduced DHA concentrations to a maximum of 20%, also incorporating erythrulose, another sugar that also reacts with skin proteins, and components that neutralize the effects of UV rays. They also sought to prolong the durability of the tan after its application.

Nowadays, new tanning products are coming onto the market, which will continue to grow until medical studies certify that tanning is not worth the possible risks of the topical application of DHA, which is believed to be able to be absorbed in the deeper layers of the skin.

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