(+)-Blebbistatin is the inactive enantiomer of (–)-blebbistatin , which is a selective inhibitor of non-muscle myosin II ATPases. Prolonged exposure to blue light (450-490 nm) results in degradation of blebbistatin to an inactive product via cytotoxic intermediates, which may be problematic for its use in fluorescent live cell imaging applications. (R)-nitro-Blebbistatin is a more stable form of (+)-blebbistatin. The addition of a nitro group stabilizes the molecule to circumvent its degradation by prolonged blue light exposure. (R)-nitro-Blebbistatin has the same stereochemistry as the inactive (+)-blebbistatin enantiomer.