What molecule am I?
Tartrazine came into being in the late 19th century. Swiss dye chemist Johann Heinrich Ziegler at Bindschedler'sche Fabrik für Chemische Industrie (Basel) developed the yellow azo dye in 1884 and published his results in 1887. By the 1890s, the process was being used for fabric dye and food coloring. Today, tartrazine is known by several names throughout the world (e.g., FD&C Yellow 5, E102, Acid Yellow 23); it is used in foods, cosmetics, and paints.
Tartrazine’s chemical properties, however, make it much more significant than a safe, readily available dye. It has sharp absorption resonances in the near-UV spectrum (300–400 nm) and the blue region of the visible spectrum (400–500 nm).
Biology researchers want to develop deep-tissue optical imaging methods that can penetrate opaque tissue and are suitable for living animals. Last year, in a counterintuitive hypothesis, Mark L. Brongersma, Guosong Hong, and a large team of co-workers at Stanford University (CA) suggested that strongly absorbing molecules, such as those in dyes, can achieve optical transparency in live biological tissues. After testing 21 dyes, they found that tartrazine’s absorption range meets that requirement.
The team first applied tartrazine to slices of chicken breast and “watched them turn into what looked like a see-through jelly”. They then moved on to tests on mice. By massaging the dye into a mouse’s scalp, they were able to see the cerebral blood vessels; an application on a mouse’s abdomen allowed them to watch it digest its latest meal. The transparent effect lasted 10–20 minutes; the dye is easily washed off.
The medical possibilities for noninvasive in vivo testing are far-ranging. The path to use on humans, however, will not be easy; human skin presents myriad variations to challenge researchers.
For more information about tartrazine, see the ScienceDirect topics page.
Tartrazine hazard information*
| Hazard class** | GHS code and hazard statement | |
|---|---|---|
| Acute toxicity, oral, category 4 | H302—Harmful if swallowed |  |
| Skin corrosion/irritation, category 3 | H316—Causes mild skin irritation | |
| Skin sensitization, category 1 | H317—May cause an allergic skin reaction | |
| Serious eye damage/eye irritation, category 2B | H320—Causes eye irritation | |
| Acute toxicity, inhalation, category 5 | H333—May be harmful if inhaled | |
| Respiratory sensitization, category 1 | H334—May cause allergy or asthma symptoms or breathing difficulties if inhaled |  |
*Compilation of multiple safety data sheets, in which hazard statements vary considerably. Others state, “not a hazardous substance or mixture”.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.
Molecules from the Journals
Thiophene sulfone1 (aka thiophene S,S-dioxide) is formally an oxidation product of thiophene2, but the direct oxidation of thiophene leads mostly to other products. In 1953, William J. Bailey and Earl W. Cummins at Wayne University and the University of Maryland (both in College Park, MD) were the first to synthesize it in a complex six-step procedure beginning from butadiene sulfone3 (better known as sulfolene).
In recent decades, thiophene sulfone and its derivatives have been studied for their applications in electronics and optics. In 1998, for example, Giovanna Barbarella at Area Ricerca C.N.R. (Bologna Italy), Olga Pudova at the Latvian Institute of Organic Synthesis (Riga), and collaborators at other institutions reported that oligothiophene S,S-dioxides had high electron affinities, increased electron delocalization, and decreased HOMO–LUMO energy gaps compared with their non-oxide counterparts.
Last month, Panče Naumov, Jialiang Xu, and colleagues, principally at New York University Abu Dhabi and Nankai University (Tianjin, China), described single-crystal thiophene sulfone as a “thermally responsive molecular crystal that exhibits both structural and optical reversibility”. They stated that the crystal is “a favorable choice for prototypical low-power precision applications such as microactuators, soft robotics, and wearable devices”.
Gypsum4 (calcium sulfate dihydrate, CaSO4•2H2O) is a common mineral and a major byproduct of phosphoric acid manufacture. It is widely used in agriculture as a calcium and sulfur nutrient and for improving soil structure. It is also used in construction, especially for manufacturing drywall. It was first mentioned in the literature in 1903 by German chemist Paul Rohland in an article about the conversions among gypsum, its half-hydrate (CaSO4•½H2O, plaster of Paris), and anhydrite (CaSO4).
Last month, Merve Yeşilbaş and colleagues at the SETI Institute (Mountain View, CA), Umeå University (Sweden), Caltech (Pasadena, CA), and Université Grenoble Alpes (France) reported that geochemical transformations of gypsum in various environments on Earth may have implications for calcium sulfate detection and potential water flow on Mars. Their experiments demonstrated two ways that gypsum could dehydrate under Martian conditions: loss of water from gypsum at ≈110 ºC (below the Martian surface) and the interaction of gypsum and chloride salts to displace water.
1. CAS Reg. No. 27092-46-2.
2. CAS Reg. No. 110-02-1.
3. CAS Reg. No. 77-79-2.
4. CAS Reg. No. 10101-41-4.
Molecules from the Journals
MOTW briefly describes noteworthy molecules that appeared in recent ACS journal articles. See this week's edition.
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Tartrazine fast facts
| CAS Reg. No. | 1934-21-0 |
| SciFindern name | 1H-Pyrazole-3- carboxylic acid, 4,5- dihydro-5-oxo-1-(4- sulfophenyl)-4-[2-(4- sulfophenyl)diazenyl]-, sodium salt (1:3) |
| Empirical formula | C16H9N4Na3O9S2 |
| Molar mass | 534.36 g/mol |
| Appearance | Bright orange-yellow powder |
| Melting point | >300 ºC (dec.) |
| Water solubility | 200 g/L (25 ºC) |
Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.
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