Dopamine
Properties
| State | Solid (white to slightly yellowish crystalline powder) |
| Color | White (darkens on exposure to air) |
| Solubility | Freely soluble in water; soluble in dilute acids; oxidizes readily in air |
| Melting Point | 128°C |
| Boiling Point | Decomposes before boiling |
About Dopamine
Dopamine is the catechol-amine that sits at the branch point of the entire catecholamine biosynthesis pathway: tyrosine gets hydroxylated to L-DOPA by tyrosine hydroxylase (the rate-limiting step, and the reason L-DOPA bypasses it therapeutically), then aromatic amino acid decarboxylase strips the carboxyl to give dopamine. Downstream, dopamine β-hydroxylase converts it to norepinephrine, and PNMT methylates that to epinephrine — so dopamine isn't just a neurotransmitter, it's the synthetic precursor for the whole sympathetic catecholamine family. The catechol diol is what makes dopamine chemically interesting and pharmacologically problematic: the 3,4-dihydroxy aromatic ring is exquisitely easy to oxidize. Air alone turns it brown via dopaminequinone, and inside neurons that same chemistry is what generates neuromelanin (the dark pigment in the substantia nigra) and is part of why dopaminergic neurons are selectively vulnerable in Parkinson's disease. Functionally, the mesolimbic projection from VTA to nucleus accumbens encodes reward prediction error — Schultz's monkey experiments in the 1990s showed dopamine neurons fire not for reward itself but for unexpected reward, which is the entire mechanistic basis for how cocaine, amphetamine, nicotine, and opioids hijack motivation. The nigrostriatal projection handles motor initiation, and losing 60-80% of those neurons gives you the Parkinsonian triad.
Where you'll encounter it
If you've ever weighed out dopamine HCl from a bottle, you've noticed it's stored under argon in amber glass for a reason — the catechol oxidizes within hours of air exposure, and a brown-tinged powder is already partly dopaminequinone. In a clinical setting, dopamine shows up as an IV pressor for cardiogenic shock and septic hypotension (dosed in µg/kg/min, with renal-dose, inotropic, and vasopressor effects at increasing infusion rates). In a research lab, you encounter it constantly in HPLC with electrochemical detection — the catechol oxidizes cleanly at +0.7 V vs. Ag/AgCl, which is how microdialysis quantifies extracellular dopamine in striatum down to nanomolar levels.
Common Uses
- IV vasopressor and inotrope for cardiogenic shock and septic hypotension
- HPLC-ECD analytical standard for catecholamine quantification in microdialysis
- Reference compound for D1/D2/D3 receptor binding and pharmacology screens
- Substrate for studying MAO-A and MAO-B kinetics in mitochondrial preparations
- Catechol monomer for mussel-inspired polydopamine surface coatings on biomaterials
- Precursor in semi-synthesis of apomorphine and related dopamine agonists
- Calibration standard for fast-scan cyclic voltammetry in behavioral neuroscience
- Substrate for tyrosinase activity assays in melanin biosynthesis research
Safety Information
IV dopamine has a narrow therapeutic window — extravasation causes severe local vasoconstriction and tissue necrosis (treated with phentolamine infiltration). Tachyarrhythmias and ventricular ectopy are dose-dependent above ~10 µg/kg/min. As a powder, the main lab hazard is air oxidation: handle under inert atmosphere, store at -20 °C protected from light, and discard once the solid darkens. Solutions in saline degrade within 24 hours and are typically stabilized with sodium metabisulfite at clinical pharmacies. No OSHA PEL, but treat as a moderate skin and eye irritant.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.