C002 — Meradimate (Menthyl Anthranilate / Neo Heliopan MA)
Section 1: Identity
| Property | Value | Confidence |
|---|---|---|
| INCI | Menthyl Anthranilate | C1 |
| USAN (US adopted) | Meradimate | C1 |
| IUPAC | (1R,2S,5R)-2-isopropyl-5-methylcyclohexyl 2-aminobenzoate (commonly: l-menthyl 2-aminobenzoate; (1R,3R,4S)-p-menthan-3-yl 2-aminobenzoate per Wikipedia) | C2 |
| Common synonyms | Menthyl-o-aminobenzoate; anthranilic acid menthyl ester; menthyl-o-aminobenzoic acid ester | C1 |
| Trade names | Neo Heliopan MA (Symrise) | C1 |
| CAS | 134-09-8 (the bulk specification CAS used by FDA / Symrise / Sigma-Aldrich for racemic/l-menthyl form). Note: Wikipedia lists 307556-71-4 for stereodefined (1R,2S,5R) form — both refer to the regulated material; 134-09-8 is the FDA-cited CAS | C1 |
| Molecular formula | C₁₇H₂₅NO₂ | C1 |
| Molecular weight | 275.39 g/mol | C1 |
| Appearance | Yellow viscous oil; characteristic faint odor | C2 |
Regulatory status
| Region | Status | Max concentration |
|---|---|---|
| USA (FDA) | Approved Category I, OTC Monograph M020 (active ingredient) | 5% |
| EU (Annex VI) | NOT approved for use in cosmetics — not listed in Annex VI | — |
| Australia (TGA) | Approved | 5% |
| Japan | NOT permitted | — |
| South Korea | Approved | 5% |
| Brazil, Canada, South Africa, ASEAN | Approved | 5% |
C1 — confirmed against US FDA M020 and absence from EU Annex VI.
Typical use concentration
Rarely used today even in jurisdictions where allowed because of its modest UV performance and singlet-oxygen sensitization issues. When used: 1–5%, almost always in combination with stronger UVA (avobenzone) and UVB filters.
Section 2: UV Absorption Spectrum
Meradimate is a weak UVA-II / borderline UVB filter. The chromophore is an ortho-aminobenzoate, which has an internal H-bond between –NH₂ and the ester carbonyl that stabilizes a charge-transfer excited state.
| Quantity | Value | Confidence |
|---|---|---|
| λmax | ~336 nm (literature consensus 334–340 nm in ethanol) | C2 |
| Spectral range | ~260–360 nm; main feature centered near UVA-II/UVB boundary | C2 |
| ε at λmax | ~4,500–5,500 M⁻¹cm⁻¹ in ethanol — reported as one of the lowest among approved filters; ortho-disubstitution causes steric crowding and reduced oscillator strength | C2 (Cantrell & McGarvey 2001 and follow-on photophysics literature) |
| E(1%, 1cm) | ≈ 165–200 (computed: ε ≈ 5000 → E1% ≈ 5000·10/275 ≈ 182) | C3 |
The low ε is the main practical limitation: compared to avobenzone's ε ≈ 35,000 at 357 nm, meradimate is ~7× weaker per molecule and absorbs at a less useful wavelength (UVA-II edge rather than UVA-I peak). It does not provide meaningful UVA-I (340–400 nm) protection.
Solvent effects: bathochromic shift in polar protic solvents (intramolecular H-bond modulation), but data are limited.
References: - Cantrell A, McGarvey DJ. J Photochem Photobiol B (2001) 64:117–122 — "The photophysical properties of menthyl anthranilate: a UV-A sunscreen" (PMID 10911723) - Baker LA et al. Nature Communications (2018) 9:5095 — wavepacket photoprotection mechanism of methyl anthranilate (precursor) - Whittock AL et al. J Photochem Photobiol A: Chem (2017) 350 — bottom-up photoprotection
Section 3: Photodegradation Kinetics
The anthranilates are moderately photostable as parent compounds (no facile cleavage like avobenzone), but they have a photophysical pathology: they generate singlet oxygen (¹O₂) efficiently due to long-lived triplet state.
Mechanism
- UV absorption populates S₁ (charge-transfer state)
- Slow internal conversion permits intersystem crossing to T₁
- T₁ has long lifetime in oxygenated solution → energy transfer to O₂ → ¹O₂ generation
- ¹O₂ is a reactive oxidant: damages skin lipids, DNA, and other sunscreen ingredients
This makes meradimate a photosensitizer, ironically: while the compound itself is comparatively stable, it generates ROS that damage other formulation components and skin.
Quantitative data
| Parameter | Value | Conditions | Source / Confidence |
|---|---|---|---|
| Triplet quantum yield (Φ_T) of methyl anthranilate (precursor) | ~0.4 | Acetonitrile, room temp | Cantrell & McGarvey 2001 — C2 |
| Singlet oxygen quantum yield (Φ_Δ) of menthyl anthranilate | ~0.20–0.30 | Air-equilibrated organic solvent | Cantrell & McGarvey 2001 / Yamaji follow-up — C2 |
| Photodegradation extent of MenA itself | <5–10% loss at typical UV doses (1–2 MED) | Ethanol or oil | C2 (cited in MDPI Photochem 2021 review) |
| Singlet oxygen suppression by Trolox / α-tocopherol | Substantial (Φ_Δ reduced by ~70%) | Yamaji et al. Photochem Photobiol Sci 2020 — | C1 (PMID 32484499) |
Compared to avobenzone, meradimate's mass-balance photostability is much better, but it does not behave as a "photophysically ideal sunscreen" because it converts UV into chemical reactivity (¹O₂) rather than purely heat.
Photoproducts
When degradation does occur: - Hydrolysis of ester → menthol + anthranilic acid (slow, but accelerated by ¹O₂-mediated oxidation) - ¹O₂-mediated oxidation of the aromatic amine → quinones, azo coupling products (small fraction) - N-acetyl-menthyl anthranilate is more photostable; studied as an alternative (Albini et al. J Photochem Photobiol A 2002)
Effect of solvent / vehicle
- Cosmetic emollients (esters, oils) — typical commercial conditions: <10% loss after 25 MED
- Polar aprotic — no major change in degradation rate
- Co-formulation with antioxidants (Vit E, BHT) substantially reduces ¹O₂ leakage
Section 4: Photostabilization
Because meradimate is a photosensitizer rather than a photodegrader, the goal of "stabilization" is to suppress ¹O₂ release rather than to protect the chromophore itself.
¹O₂ quenchers
- α-Tocopherol (Vitamin E) — physical quencher, also chemical scavenger. Documented to suppress MenA-sensitized ¹O₂ generation.
- Trolox — water-soluble Vit E analogue; research-grade, suppresses MenA ¹O₂. (Yamaji et al. 2020, doi:10.1039/d0pp00023j)
- β-Carotene, lycopene — ¹O₂ physical quenchers
- DESM (Diethylhexyl Syringylidenemalonate / Oxynex ST) — quencher
- Ascorbyl tetraisopalmitate, ubiquinone — radical scavenging
Combination behavior
- Meradimate has not been reported to destabilize avobenzone (unlike octinoxate)
- It can be combined with octocrylene, Tinosorb S, BMDBM with no reported [2+2] cycloaddition or radical-pair degradation
- However, its low ε means it adds little SPF / UVA-PF for the formulation real estate it occupies
Known issue — declining commercial use
Meradimate is increasingly phased out: 1. Low absorptive efficiency 2. ¹O₂ photosensitization (skin oxidative stress concerns) 3. Lack of EU and Japan approval limits global formulations 4. Better alternatives (DHHB, Tinosorb M/S, bemotrizinol) available outside US
Confidence summary
- §1 Identity: C1
- §2 Spectrum: λmax C2; ε C2
- §3 Photodegradation: ¹O₂ quantum yield C2; mass-loss data C2
- §4 Stabilizers: C2
Key references
- Cantrell A, McGarvey DJ. J Photochem Photobiol B (2001) 64(2-3):117–122. PMID 10911723. "The photophysical properties of menthyl anthranilate: a UV-A sunscreen."
- Baker LA et al. Nat Commun (2018) 9:5095. doi:10.1038/s41467-018-07681-1
- Yamaji M, Kida M. Photochem Photobiol Sci (2020) 19:992. doi:10.1039/d0pp00023j (suppression of MenA ¹O₂ by Trolox/α-tocopherol). PMID 32484499.
- Whittock AL et al. J Photochem Photobiol A: Chem (2017) 350. doi:10.1016/j.jphotochem.2017.09.058
- Albini A et al. J Photochem Photobiol A (2002) 147:111 — N-acetyl-menthyl anthranilate photophysics
- FDA OTC Monograph M020 (Sunscreen Drug Products). 2021.