Photoprotection of TiO2 Using Propenoic Acid Esters

Aug 21, 2014 | Contact Author | By: Robert S. Hu, Jean Zhang, Gary A. Neudahl and Craig A. Bonda, The HallStar Company
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Title: Photoprotection of TiO2 Using Propenoic Acid Esters
titanium dioxidex metal oxidesx photostabilityx UVx photoprotectionx propenoic estersx
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Keywords: titanium dioxide | metal oxides | photostability | UV | photoprotection | propenoic esters

Abstract: Titanium dioxide (TiO2) is known to be photocatalytically active. Even with surface modifications, it catalyzes the decomposition of organic materials and promotes the formation of reactive oxygen species. However, a particular propenoic acid ester is shown here to protect TiO2 from inducing such reactions, making it a more effective and safer UV filter.

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RS Hu, J Zhang, GA Neudahl and CA Bonda, Photoprotection of TiO2 Using Propenoic Acid Esters, Cosm & Toil 129(9) 54 (2014)

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Metal oxides with a wide band gap absorb and reflect UV energy from the sun. Such metal oxides include the broadly-utilized TiO2 and zinc oxide (ZnO). These metal oxides are often used as UV filters in the cosmetics industry, and as pigments and fillers in applications such as polymer processing, coatings and adhesives. Their photocatalytic capabilities also are used in photovoltaic, antibacterial, water treatment, air purification and self-cleaning applications.

Photocatalytic reactions derived from these metal oxides normally lead to the decomposition of the organic materials with which they come into contact. This photoactive reactivity results in the generation of singlet oxygen1 and other reactive oxygen species (ROS).2-4 Such consequences are not desired in personal care or industrial applications, so to alleviate these unwanted reactions, surface modifications are made to the metal oxides. However, currently available treatments do not completely eliminate the photoreactivity of these metal oxides; some of these surface treatments are provided in the product literature of major metal oxide suppliers for the personal care industry.5, 6

TiO2 and ZnO therefore need improved protection to eliminate their adverse effects in personal care and industrial applications, in turn making them safer and more effective UV filters. In relation, propenoic acid derivatives are known to form interacting complexes with Lewis acid species such as TiO2.7-10 In this study, the authors evaluate a member of the propenoic acid ester family—a 2-ethylhexyl ester of 2-cyano-3-(4-methoxyphenyl)-3-phenyl-2-propenoic acid (EHCMPPPa)—for its potential to safeguard TiO2 in cosmetic applications.

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Table 1. Formulas for Compositions Tested

Table 1. Formulas for Compositions Tested

The test vehicles for this study were BMDBM-containing, o/w emulsion-based lotions, evaluated with and without TiO2, and with and without EHCMPPP.

Table 2. Pump Program

Table 2. Pump Program

The eluted material was mixed well and passed through a polytetrafluoroethylene (PTFE) filter before being subjected to HPLC analysisf-j.

Figure 1. Molecular structures of BMDBM and EHCMPPP

Figure 1. Molecular structures of BMDBM and EHCMPPP

EHCMPPP is a specially designed ester based on the propenoic unsaturated structure.

Figure 2. HPLC chromatograms of photoproducts

Figure 2. HPLC chromatograms of photoproducts from BMDBM in EHCMPPP-free test lotions following irradiation in the absence (A) and presence (B) of TiO<sub>2</sub>

Following irradiation, the EHCMPPP-free test lotions containing 1% BMDBM, without (A) and with (B) TiO2, exhibited significant differences in the photodecomposition products, as assessed by HPLC.

Figure 3. BMDBM remaining in EHCMPPP-free test lotions

Figure 3. BMDBM remaining in EHCMPPP-free test lotions after 10 MED irradiation, as determined by HPLC

After 10 MED irradiation, as determined by HPLC, shown here is the BMDBM remaining in EHCMPPP-free test lotions. In addition to impacting the reaction patterns of BMDBM photodecomposition (see Figure 2), the presence of TiO2 greatly increased the rate of decomposition of BMDBM.

Figure 4. BMDBM remaining in test lotions containing 3% EHCMPPP

Figure 4. BMDBM remaining in test lotions containing 3% EHCMPPP after 10 MED irradiation, as determined by HPLC

To the 3% BMDBM test lotion base, 3% EHCMPPP was added and the decomposition of BMDBM under the same irradiation conditions (10 MED) was assessed by HPLC in the presence and absence of TiO2.

Footnotes (CT1409 Hu)

a SolaStay S1 (INCI: Ethylhexyl Methoxycrylene), The HallStar Company
b TTO-80(A) (INCI: Titanium Dioxide (and) Aluminum Hydroxide), Kobo Products Inc.
c Neo Heliopan 357 (INCI: Butyl Methoxydibenzoylmethane), Symrise AG
d GE 124, Technical Glass Products Inc.
e Q-SUN Xe-1 with Daylight-BB Optical Filter, Q-Lab Corp.
f-h (Hewlett Packard) Series 1100 HPLC System; g ChemStation for LC 3D; and h Dynamic Absorbance Detector (DAD); Agilent Technologies Inc.
j Luna 5 μm C18(2) 100Ǻ, Phenomenex Inc.

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