3,3'-Diaminobenzidine
Chemical compound
From Wikipedia, the free encyclopedia
3,3′-Diaminobenzidine (DAB) is an organic compound with the formula (C6H3(NH2)2)2. This derivative of benzidine is a precursor to polybenzimidazole, which forms fibers that are renowned for their chemical and thermal stability.[2] As its water-soluble tetrahydrochloride, DAB has been used in immunohistochemical staining of nucleic acids and proteins.[3]
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| Names | |
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| Preferred IUPAC name
[1,1′-Biphenyl]-3,3′,4,4′-tetramine[1] | |
| Other names
3,3′,4,4′-Biphenyltetramine 3,3′,4,4′-Tetraamino-diphenyl | |
| Identifiers | |
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3D model (JSmol) |
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| 1212988 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.001.919 |
| EC Number |
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PubChem CID |
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| RTECS number |
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| UNII |
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| UN number | 2811 |
CompTox Dashboard (EPA) |
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| Properties | |
| C12H14N4 C12H18Cl4N4 (4HCl) | |
| Molar mass | 214.27 g/mol 360.11 g/mol (4HCl) |
| Melting point | 175 to 177 °C (347 to 351 °F; 448 to 450 K) (280 °C for 4HCl.2H2O) |
| Hazards | |
| GHS labelling: | |
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| Danger | |
| H341, H350 | |
| P201, P202, P281, P308+P313, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
mouse, oral Acute: 1834 mg/kg. |
| Safety data sheet (SDS) | External MSDS |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure
DAB is symmetric about the central carbon bond between both ring structures. In the crystal, the rings of each molecule are co-planar and the amine units connect molecules to form an intermolecular 3-dimensional hydrogen bond network.[4]
Preparation
Diaminobenzidine, which is commercially available, is prepared by treating 3,3′-dichlorobenzidine with ammonia with a copper catalyst at high temperature and pressure, followed by acidic workup.[5]
An alternate synthesis route involves the diacylation of benzidine with acetic anhydride under basic conditions:[2]
- (NH2)C6H4C6H4(NH2) + 2 (CH3CO)2O ⟶ (NHCOCH3)C6H4C6H4(NHCOCH3) + 2 CH3COOH
The diacetylated compound then undergoes nitration with nitric acid to produce an ortho-dinitro compound due to the ortho-directing acetyl substituents:[2]
- (NHCOCH3)C6H4C6H4(NHCOCH3) + 2HNO3 ⟶ (O2N)(NHCOCH3)C6H3C6H3(NHCOCH3)(NO2) + 2H2O
The acetyl groups are then removed through saponification:[2]
- (O2N)(NHCOCH3)C6H3C6H3(NHCOCH3)(NO2) + 2NaOH ⟶ (O2N)(NH2)C6H3C6H3(NH2)(NO2) + 2NaOCOCH3
The dinitrobenzidine compound is then reduced with hydrochloric acid and iron to produce 3,3′-diaminobenzidine:[2]
- (O2N)(NH2)C6H3C6H3(NH2)(NO2) + 12HCl + 6Fe0 ⟶ (NH2)2C6H3C6H3(NH2)2 + 6FeCl2 + 4H2O
The reduction of the dinitrobenzidine compound can also proceed with tin(II) chloride instead of iron powder or with sodium dithionite in methanol.[2]
Applications
In its main application, DAB is the precursor to polybenzimidazole.
Diaminobenzidine is oxidized by hydrogen peroxide in the presence of hemoglobin to give a dark-brown color. This color change is used to detect fingerprints in blood.[6] The solubility of DAB in water allows for adaptability compared to other detection solutions which use toxic solvents.[7] Improperly prepared tissue samples may give false positives.[8] In research, this reaction is used to stain cells that were prepared with hydrogen peroxidase enzyme, following common immunocytochemistry protocols. Relevant to Alzheimer's disease, Aβ protein amyloid plaques are targeted by a primary antibody, and subsequently by a secondary antibody, which is conjugated with a peroxidase enzyme. This will bind DAB as a substrate and oxidize it, producing an easily observable brown color. Plaques can then be quantified for further evaluation.[9] One other method uses complexes of injected biocytin with avidin or streptavidin, biotin, and then peroxidase.