Guanine
Properties
| State | Solid (white to yellowish amorphous powder) |
| Color | White to yellowish |
| Solubility | Very slightly soluble in water (0.004 g/L at 25°C); soluble in dilute acids and bases |
| Melting Point | 360°C (decomposes) |
| Boiling Point | Decomposes before boiling |
About Guanine
Guanine is a purine nucleobase — a fused bicyclic ring system (six-membered pyrimidine fused to five-membered imidazole) with an amino group at C2, a carbonyl at C6, and the keto-amino tautomer dominating at physiological pH. Molar mass 151.127 g/mol. In a DNA double helix, guanine pairs with cytosine through three hydrogen bonds (N1-H to N3, C6=O to C4-NH2, C2-NH2 to C2=O) — one more than the two bonds in an A-T pair, which is why GC-rich DNA has a higher melting temperature (Tm rises about 0.41 °C per percent GC content). PCR primer designers exploit this constantly: aim for 40-60% GC content to balance specific binding against ease of dissociation. Guanine itself is wretchedly insoluble in water at neutral pH (about 4 mg/L at 25 °C) because the planar molecules stack via pi-pi interactions and the amide-like N1-H makes a strong hydrogen-bond network in the solid; you can dissolve it in dilute HCl (which protonates N7) or dilute NaOH (which deprotonates N1). The name comes from guano — Unverdorben isolated it from accumulated seabird droppings in 1846, where it crystallizes as a metabolic waste product. Modern fish and reptile skin still uses dense guanine crystals as a structural color: the iridescent silvery-white reflectance of trout scales, the green eyeshine of cats, and the metallic blue of some chameleons all come from guanine crystals arranged as multilayer photonic mirrors. The cosmetics industry harvests guanine crystals from fish-scale washing for use as the pearlescent additive in nail polish, eye shadow, and lipstick. Beyond structural color, guanine carries information: as part of GTP it powers ribosomal translation and the GDP-GTP cycle of every G-protein in every cell, and as cyclic GMP it's the second messenger that nitric oxide uses to relax vascular smooth muscle — the mechanism behind Viagra (which inhibits the cGMP-degrading enzyme PDE5).
Where you'll encounter it
If you've ever applied pearlescent nail polish, watched a fish flash silver as it turned in sunlight, or taken a PCR class where the instructor stressed designing primers around 50% GC content, you've worked with guanine — the photonic crystals in fish scales are pure guanine, and Tm calculations for every PCR primer in every molecular biology lab depend on counting Gs and Cs. In a molecular-biology workflow designing a 20-mer PCR primer, the standard nearest-neighbor Tm calculation adds about 4 °C per G or C and 2 °C per A or T, then anneals at 5 °C below that — a calculation IDT's online tools have automated to the point that nobody does it by hand anymore. In a cosmetics formulation plant, guanine crystals harvested from herring scale-washing solutions are dispersed in nitrocellulose lacquer at 0.5–2% to give the pearlescent finish on a nail polish bottle.
Common Uses
- Nucleobase paired with cytosine in DNA and RNA
- Pearlescent crystals in cosmetics (nail polish, eyeshadow, lipstick) from fish-scale recovery
- GTP component powering ribosomal translation and G-protein signaling
- Cyclic GMP signaling molecule for vascular smooth muscle relaxation
- Substrate for IMP dehydrogenase studies and immunosuppressant drug design
- Standard reference for purine HPLC quantification in nucleotide analysis
- Component of GpC and CpG dinucleotide Toll-like receptor 9 ligands
Safety Information
Non-toxic at relevant exposure levels; oral LD50 in rodents is greater than 5 g/kg. No GHS hazard classification for research use. The clinically relevant concern is downstream metabolism: high purine intake (organ meats, anchovies, beer) drives uric acid production via xanthine oxidase, and urate crystals precipitating in joints and kidneys cause gout and uric acid nephrolithiasis. Patients on allopurinol or febuxostat (xanthine oxidase inhibitors) are managing this exact pathway. Guanine itself is essentially inert in the GI tract — it's barely absorbed and most dietary purines hit the gut microbiota first. Standard lab PPE (gloves, dust mask if weighing dry powder) is sufficient. Guanine dust at high concentrations can cause minor respiratory irritation but isn't a recognized occupational hazard.
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.