Hoechst 33258

Hoechst stains are part of a family of blue fluorescent dyes used to stain DNA. These Bis-benzimides were originally developed by Hoechst AG, which numbered all their compounds so that the dye Hoechst 33342 is the 33342nd compound made by the company. There are three related Hoechst stains: Hoechst 33258, Hoechst 33342, and Hoechst 34580. The dyes Hoechst 33258 and Hoechst 33342 are the ones most commonly used and they have similar excitation/emission spectra.

Both dyes are excited by ultraviolet light at around 350 nm, and both emit blue-cyan fluorescent light around an emission spectrum maximum at 461 nm. Unbound dye has its maximum fluorescence emission in the 510–540 nm range. Hoechst stains can be excited with a xenon- or mercury-arc lamp or with an ultraviolet laser. There is a considerable Stokes shift between the excitation and emission spectra that makes Hoechst dyes useful in experiments in which multiple fluorophores are used. The fluorescence intensity of Hoechst dyes also increases with the pH of the solvent.

Hoechst dyes are soluble in water and in organic solvents such as dimethyl formamide or dimethyl sulfoxide. Concentrations can be achieved of up to 10 mg/mL. Aqueous solutions are stable at 2–6 °C for at least six months when protected from light. For long-term storage the solutions are instead frozen at ≤-20 °C.

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