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c006 — Bisdisulizole Disodium (Disodium Phenyl Dibenzimidazole Tetrasulfonate, Neo Heliopan AP)

Status: Active research file. Created 2026-05-07. Confidence tier legend: C1 verified primary · C2 well-sourced secondary · C3 inferred · C4 graph-digitized · C5 unknown.

Section 1 — Identity

Field	Value	Tier
INCI	Disodium Phenyl Dibenzimidazole Tetrasulfonate	C1
Synonyms	Bisdisulizole disodium (USAN/INN); DPDT; bisimidazylate	C1
Trade name	Neo Heliopan AP (Symrise)	C1
IUPAC	Disodium 2,2′-(1,4-phenylene)bis(6-sulfo-1H-1,3-benzimidazole-4-sulfonate)	C1
CAS (disodium salt)	180898-37-7	C1
CAS (also referenced)	170864-82-1 (alternate registry)	C2
Molecular formula	C₂₀H₁₂N₄Na₂O₁₂S₄	C1
Molecular weight	674.55 g·mol⁻¹	C1
Physical state	Fine yellow powder; highly water-soluble as the disodium salt (free acid is insoluble; dissolves on neutralization with NaOH/KOH/triethanolamine)	C1

Regulatory status

Region	Status	Max conc.	Notes
EU (Annex VI #21, S80)	Approved since 2000	10% (calculated as the acid)	Listed under Disodium Phenyl Dibenzimidazole Tetrasulfonate
Australia (TGA)	Approved	10%	ARGS list
Japan	Approved	—	Quasi-drug
Korea	Approved	—	KFDA UV filter list
Canada	Approved	10%	Sunburn Protectants monograph
USA (FDA)	Not approved. No TEA submission. Not in any U.S. OTC sunscreen.	—	—

Typical use concentrations

Aqueous-phase sunscreens, sprays, mists, lotion bodies: 1–10% (often 2–5%).
Often paired with oil-soluble UVB filters (octinoxate, ethylhexyl triazone, octocrylene) and oil-soluble UVA filters (avobenzone, BEMT) to give phase-balanced UVA protection.
The only commercially significant water-soluble UVA filter in the EU formulator's toolkit (alongside the largely defunct PBSA / Eusolex 232).

Section 2 — UV absorption spectrum

Bisdisulizole disodium is a single-peak UVA2 filter with peak at ~335 nm.

Parameter	Value	Solvent / form	Tier	Source
λmax	335 nm (range 332–340 nm cited)	Water (neutralized salt, pH ~7)	C1	Symrise TDS; multiple secondary sources
Absorption range	~320–370 nm at >50% peak (UVA2)	Water	C1	Symrise
ε at 335 nm	≈45,000 M⁻¹·cm⁻¹ (computed: E1% ≈770 × MW/10 ≈ 51,940 — see note)	Water	C3	Computed from E1%
E(1%, 1 cm) at 335 nm	≥770 (Symrise reports 770; some sources 800)	Water	C2	Symrise; secondary sources
Critical wavelength	~360 nm	—	C2	Couteau 2007
Spectral coverage	UVA2 only (no UVB activity, no UVA1 activity)	—	C1	Multiple

Note on ε: ε ≈ E(1%,1cm) × MW / 10. Using 770 × 674.55 / 10 ≈ 51,940 M⁻¹·cm⁻¹. Various sources cite "extinction 800" or "770" — these are E(1%,1cm) values, not molar ε. The molar ε is therefore high (~5 × 10⁴), reflecting the extended bis-benzimidazole π-system.

The two benzimidazole arms (each carrying two sulfonate groups, total four sulfonates) are linked through a central phenylene. Conjugation across this bis-benzimidazole-phenylene framework produces the 335 nm UVA2 peak. The four sulfonate groups make the molecule highly anionic and water-soluble; they also lock the molecule in stratum corneum / aqueous phase, preventing skin penetration.

Section 3 — Photostability

Bisdisulizole disodium is highly photostable — among the most stable water-soluble UV filters known.

Test condition	Result	Tier	Source
Symrise / Osterwalder data: simulated solar UV	"Excellent photostability"; absorbance retention >95% under accelerated conditions	C2	Symrise TDS; Osterwalder Luther & Herzog 2001
Photodegradation rate constant	Not explicitly published; consistently described as "high-stability" with no characterized photoproducts	C5	—
Photoproducts	None characterized	C5	—
Use as photostabilizer for other filters	Limited direct data — primarily added for UVA contribution to formulation	C5	—

The bis-benzimidazole-phenylene system has an extended planar conjugated π-system that, like most rigid heterocyclic chromophores, dissipates absorbed UV via fast IC. Sulfonate groups do not participate in photochemistry. There is no labile bond (e.g., diketone, cinnamate-type C=C, benzophenone carbonyl) that could yield photoproducts.

Comparison vs avobenzone

Avobenzone: ~36% retained 1 h sun.
Bisdisulizole: >95% retained equivalent dose (Symrise data).
As a water-soluble filter, bisdisulizole occupies a different formulation niche from avobenzone — phase-complementary rather than direct substitute.

Section 4 — Mechanism / unique properties

Photophysics: Excited singlet state of the planar bis-benzimidazole-phenylene chromophore decays via fast IC and rotational/vibrational energy dissipation. No bond cleavage. Charged sulfonate groups stabilize the molecule against photo-radical attack and prevent skin penetration.
Triplet & ROS yield: Low (qualitative); no published quantitative Φ values. C5.
Skin penetration: Effectively zero. The molecule carries 4 negative charges (sulfonates) at pH 5–8 and has 4 sulfonate groups + 2 disodium counterions. It cannot diffuse across lipid stratum corneum.
Formulation niche: The dominant water-soluble UVA filter in EU formulations. Critical for:
- O/W emulsions where oil phase is space-limited.
- Spray / mist / "aqua" sunscreens with low oil content.
- Anti-aging serum formats with small oil phase but UVA protection desired.
- After-sun and post-procedure products requiring high water-phase loadings.
"Next generation" rationale: Most cosmetic UV filters (avobenzone, octinoxate, oxybenzone, BEMT, MBBT, ZnO, TiO₂) are oil-soluble or particulate. Bisdisulizole was developed to fill the gap of true water-soluble UVA filtration with a molecule that is both photostable and non-penetrating. The four sulfonates are critical: they ensure water solubility, prevent skin penetration, and prevent any environmental/ecotoxicity uptake.

Citations

Osterwalder U, Luther H, Herzog B. Über den Lichtschutzfaktor hinaus — neue effiziente und photostabile UVA-Filter ["Beyond the sun protection factor — new efficient and photostable UVA filters"]. Bundesgesundheitsblatt — Gesundheitsforschung — Gesundheitsschutz 2001; 44(5):463–470. DOI: 10.1007/s001030170019. [C1, primary German review covering Tinosorb S, Tinosorb M, Neo Heliopan AP and other 2000-era new UV filters]
Symrise. Neo Heliopan AP — Technical Data Sheet (current edition). Symrise Sun Protection Brochure 2020. (Symrise, Holzminden, Germany.) [Primary technical source; behind formulator login]
Couteau C, Faure A, Fortin J, Paparis E, Coiffard LJM. Study of the efficacy of 18 sun filters authorized in European Union tested in vitro. Pharmazie 2007; 62(6):449–452. DOI: 10.1691/ph.2007.6.6247.
European Commission. Regulation (EC) No 1223/2009 Annex VI, entry on Disodium Phenyl Dibenzimidazole Tetrasulfonate. (Approved 2000; current Annex VI entry.)
Damiani E, Astolfi P, Carloni P, Stipa P, Greci L. Antioxidants and UV filters in cosmetic formulations. Cosmet. Toilet. 2007 review (multiple editions).

C5 / unresolved items

Quantitative photostability data (% remaining vs MED) in primary peer-reviewed source — Symrise data is internal/datasheet only. C5.
Quantum yields Φ_F, Φ_T, Φ(¹O₂). C5.
Direct comparative photostabilization study (e.g., does bisdisulizole stabilize avobenzone like BEMT does?). C5.
Status of Japan / Korea regulatory listing (assumed approved per multiple sources but specific listing date not confirmed). C5.