What molecules are we?
This year’s National Chemistry Week has the theme "Picture Perfect Chemistry"—the chemistry of photography and images. Instead of covering a topic on the leading edge of imaging technology, MOTW is going old-school: the chemistry of blueprints.
Blueprinting was once the preeminent technique for reproducing technical and engineering drawings. Also known as the cyanotype process, it was invented in 1842 by eminent English scientist John Herschel, who also was a pioneer in the development of photography.
The creation of blueprints involves two iron(III) complex salts: ferric ammonium citrate [(NH4)5Fe(C6H4O7)2, 1 in the images], more correctly called ammonium ferric citrate, and potassium ferricyanide (K3[Fe(CN)6], image 2), aka potassium hexacyanoferrate.
In the basic blueprint process, paper is impregnated with a solution of compound 1 and dried. A tracing paper drawing of the desired image is then placed over the impregnated paper and irradiated with visible light to reduce the iron(III) in photosensitive 1 to iron(II). Next, the paper is treated with a solution of compound 2, which reacts with the exposed reduced iron to form the insoluble pigment Prussian blue1, Fe4[Fe(CN)6]3. Finally, excess compounds 1 and 2 are washed off; and the paper is dried again. The image appears in white on the familiar blue background.
The advantages of blueprinting are that the image is stable; it does not require an advanced lighting system; the image is on the same scale as the original; and the blue background makes the image difficult to change. Blueprinting has been replaced by xerography and computer-aided design; but it has an indelible (pardon the pun) place in imaging history.
See this month’s Molecule of the Future below for a different blueprint connection.
1. CAS Reg. No. 14038-43-8.
Potassium ferricyanide hazard information*
| Hazard class** | GHS code and hazard statement | |
|---|---|---|
| Serious eye damage/eye irritation, category 2A | H319—Causes serious eye irritation |  |
| Short-term (acute) aquatic hazard, category 2 | H401—Toxic to aquatic life |  |
| Long-term (chronic) aquatic hazard, category 2 | H411—Toxic to aquatic life with long-lasting effects | |
*Some safety data sheets state not a hazardous substance or mixture.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.
BLU-7821 is a medication developed by Blueprint Medicines (Cambridge, MA) to treat fibrodysplasia ossificans progressiva (FOP), a rare disease that causes excess bone formation and leads to early death. Affected people suffer from heterotopic ossification (HO), in which bone replaces skeletal muscle and connective tissue, resulting in the inability to move the neck, shoulders, and elbows. FOP is caused by gain-of-function variants in the gene that encodes the activin receptor–like kinase 2 (ALK2) protein.
BLU-782 was first described in World Patent WO2017181117 to Natasja Brooijmans and co-inventors at Blueprint Medicines. This past May, Timothy P. LaBranche at Blueprint and 21 colleagues there and at other Boston-area companies reported that BLU-782 inhibited ALK2 and prevented HO in a mouse model that expresses the most common disease-causing variant of ALK2 in humans. Prophylactic treatment with the compound blocked HO formation in mice in which the conditions for ossification was later induced.
1. CAS Reg. No. 2141955-96-4; SciFindern name: 1-piperazinecarboxylic acid, 4-(6-{5-[4-ethoxy-1-(1-methylethyl)-4-piperidinyl]-2-pyridinyl}pyrrolo[1,2-b]pyridazin-4-yl)-, (3R)-tetrahydro-3-furanyl ester.
Molecule of the Future
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Potassium ferricyanide
fast facts
| CAS Reg. No. | 13746-66-2 |
| SciFindern name | Ferrate(3–), hexakis(cyano-κC)-, potassium |
| Empirical formula | C6FeK3N6 |
| Molar mass | 329.24 g/mol |
| Appearance | Bright red crystals or powder |
| Melting point | 300 °C (dec.) |
| Water solubility | 385 g/L |
Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.
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