Figure demonstrates that the simple DEAC450 modification of ATP 6 did not bestow tissue penetration properties on the nucleotide compared to the negative control. In contrast, zebrafish treated with (G2-NH2-) 21 after 24 h incubation showed much more intense fluorescence in the skin, nasal placode (Figure , e) and brain (Figure , f), compared to the zebrafish control groups (Figure , a-b). This demonstrates that a significant amount of (G2-NH2-) 21 penetrated through the skin of zebrafish and entered the nasal placode and brain. Therefore, (G2-NH2-) 21 is able to penetrate tissue of zebrafish embryos efficiently. Likewise, zebrafish embryos incubated with (G2-guanidine-) 22 showed a fluorescence signal in the oral cavity, pharynx, nasal placode, but not in the brain (Figure , g-h). The fluorescence signal was much less intense as compared to (G2-NH2-) 21. The only difference between the two molecules is the amine versus guanidine exchange in the dendron structure. It is interesting to see such large differences in uptake efficiency.