Solvents and skin: Solid state NMR of fluid molecules

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  • Published: Feb 1, 2017
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Solvents and skin: Solid state NMR of fluid molecules

Soft skin

Swedish scientists have used solid state nuclear magnetic resonance (NMR) spectroscopy to investigate how individual organic solvent molecules used in skin creams, medicated ointments and cleaning products interact with the biochemistry of human skin and whether or not they can enter the skin. Photo by David Bradley

Swedish scientists have used solid state nuclear magnetic resonance (NMR) spectroscopy to investigate how individual organic solvent molecules used in skin creams, medicated ointments and cleaning products interact with the biochemistry of human skin and whether or not they can enter the skin.

Quoc Dat Phama, Daniel Topgaarda, and Emma Sparr of the Division of Physical Chemistry at Lund University explain in the US journal Proceedings of the National Academy of Sciences that our skin is endlessly exposed to a range of compounds from the solvents present in cosmetics, washing and sanitary agents, to drug formulations and over-the-counter creams and emollients. They point out that the uptake of solvent molecules into the skin could cause changes to the properties and health of the skin. For instance, the flexibility and the softness of the skin and even its protective nature might be compromised by repeated exposure to particular compounds.

The team has examined a range of solvents pertinent to readily available skin products and sanitary products by exposing samples of intact stratum corneum, the outer layer of the skin to those solvents. It was possible to track the path of solvent molecules through and within the stratum corneum. Moreover, the solid state, polarization transfer carbon-13 NMR spectra allowed them to reveal any changes in the fluid skin molecules, such as skin lipids and proteins, when they interact with the molecules of different solvents. Only a small proportion of the molecules in the skin is in a fluid state, however the mobile molecules are critical elasticity and the skin's barrier function. Ultimately, the changes seen depend on solvent identity and concentration and on the degree of hydration of the stratum corneum.

Stratum corneum

"These types of measurements have not been done before," Sparr says. "Our results complement previous studies that have measured how molecules penetrate the skin under different conditions. Our contribution is that we have now increased our understanding of how molecules - both added components and skin molecules - are affected by each other," she adds. The team reports that, "All solvents investigated cause an increased fluidity of stratum corneum lipids, with the most prominent effects shown for the apolar hydrocarbon solvents and 2-propanol." The researchers add that no solvent other than water was able to fluidize the amino acids in the skin's keratin filaments. Conversely, "The solvent molecules themselves show reduced molecular mobility when incorporated in the stratum corneum matrix," they report.

Skin applications

The research might now be applied to various fields that involve products that come in contact with the skin, such as hygiene products, cosmetics and pharmaceuticals. The team points out that while it might be desirable for a medicated ointment to carry active ingredients through the barrier of the skin, and a "moisturizing" skin cream may have the purpose of softening and smoothing the skin, there is pressing need to ensure that disinfectants, for example, do not affect skin detrimentally.

"Deepened understanding of molecular effects of foreign compounds in stratum corneum fluidity can therefore have strong impact on the development of skin products in pharmaceutical, cosmetic, and sanitary applications," the team reports. "Through an increased understanding of molecular mechanisms we are able to more efficiently influence and regulate skin properties," adds Sparr.

Related Links

Proc Natl Acad Sci (USA) 2017, 114, E112-E121: "Tracking solvents in the skin through atomically resolved measurements of molecular mobility in intact stratum corneum"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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