What molecules are we?
This year鈥檚聽National Chemistry Week聽has the theme "Picture Perfect Chemistry"鈥攖he 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,听1聽in the images], more correctly called ammonium ferric citrate, and potassium ferricyanide (K3[Fe(CN)6], image聽2), aka potassium hexacyanoferrate.
In the basic blueprint process, paper is impregnated with a solution of compound聽1聽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聽1聽to iron(II). Next, the paper is treated with a solution of compound聽2, which reacts with the exposed reduced iron to form the insoluble pigment聽Prussian blue1, Fe4[Fe(CN)6]3. Finally, excess compounds听1听补苍诲听2聽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 Blueprinting has been replaced by xerography and computer-aided design; but it has an indelible (pardon the pun) place in imaging history.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鈥檚聽Molecule of the Future聽below for a different blueprint connection.
1. CAS Reg. No. 14038-43-8.
Ferric ammonium citrate聽hazard information*
| Hazard class** | GHS code and hazard statement | |
|---|---|---|
| Skin corrosion/irritation, category 2 | H315鈥擟auses skin irritation |  |
| Serious eye damage/eye irritation, category 2A | H319鈥擟auses serious eye irritation | |
| Specific target organ toxicity, single exposure, respiratory system, category 3 | H335鈥擬ay cause respiratory irritation | |
*Some 聽safety data sheets state not a hazardous substance or mixture.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. .
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鈥搇ike kinase 2 (ALK2) protein.聽
BLU-782 was first described in World Patent 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 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
Once a month we bring you a newly discovered or developed molecule that has important implications for the future of chemistry or society in general. Look for it the third week of each month.聽Learn more about this month's Molecule of the Future.
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Ferric ammonium citrate fast facts
| CAS Reg. No. | 1185-57-5 |
| SciFindern name | 1,2,3-Propanetricarboxylic acid, 2-hydroxy-, ammonium iron(3+) salt |
| Empirical formula | C12H28FeN5O14a |
| Molar mass | 528.27 g/mola |
| Appearance | Yellowish brown to red solid |
| Melting point | 120鈥�130 掳C (dec.)b |
| Water solubility | 100 g/L |
a. Not all sources give the formula or molar mass shown.
b. Some references report 1539 潞C, but this seems unlikely.
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