An anomalous heavy atom effect in phenazine and its halogeno derivatives

The Remarkable Effect of Halogen Substitution on the Membrane Transport of Fluorescent Molecules in Living Cells

“…As substitution of heavier halogen may lead to higher toxicity,t he cell viability was determined by using the standard MTT assay.I nterestingly,t he toxicity of the bromo and iodo compounds (7)(8)(9)(10)(11)(12)(13)(14)(15)was found to be almost identical to that of the unsubstituted compounds 1-3 ( Figure 3C), indicating that the introduction of heavier halogen atoms does not alter the toxicity of the compounds.W hile the compounds did not exhibit any cytotoxicity up to 10 mm concentration, they were found to be toxic to the cells at concentrations of 25 mm and above.R ecently,Y ang and coworkers reported ab iocompatible halogen-containing fluorescent probe (HKOH-1r) based on fluorescein for the detection of endogenous hydroxyl radicals in living cells. [4c] In this work, the authors demonstrated that the diiodophenol acts as aq uencher of fluorescein or 2',7'-dichlorofluorescein, and the steric hindrance of the two iodine atoms blocks the oxidation by strong oxidants such as HOCl or peroxynitrite.…”

“…Forexample,t he cellular entry of compounds 6, 9, 12,a nd 15,i sh igher than that of the unsubstituted compound 3,a nd the uptake follows the order I > Br > Cl. Fort he iodo compounds 10-15,t he internalization of the diiodo compounds 13-15 is found to be higher than that of the corresponding monoiodo compounds (10)(11)(12). It is known that halogen atoms form halogen bonds with electron donors and their halogen bonding ability increases from chlorine to bromine to iodine.…”

“…Thef luorescent properties of compounds 1-15 were studied in phosphate-buffered saline (PBS) at room temperature.Asthese compounds have low solubility in an aqueous medium, the compounds were dissolved in DMSO and diluted with PBS buffer by 1:100. [12] To understand the lipophilicity of compounds 1-15,the partition coefficient (P)i nt he octanol-water biphasic system was determined by using HPLC and compared the experimental log P values with the corresponding theoretical values obtained using the ALOGPS program ( Figure 2E). Af urther increase in the fluorescence intensity was observed when an À NMe 2 group was introduced at the 4-position of the naphthalimide moiety (compound 3).…”

“…As imilar trend was observed when halogen atoms were introduced to the phenolic ring at 2,6-positions.H owever, agradual decrease in the fluorescence intensity was observed upon introduction of chlorine,b romine,a nd iodine atoms ( Figure 2D), which is in agreement with the heavy-atom effect observed for other related fluorescent systems. [12] To understand the lipophilicity of compounds 1-15,the partition coefficient (P)i nt he octanol-water biphasic system was determined by using HPLC and compared the experimental log P values with the corresponding theoretical values obtained using the ALOGPS program ( Figure 2E). [13] These results indicate that there is no major change in the lipophilicity upon introduction of heavier halogen atoms.…”

Synthesis, characterization, and photoluminescence properties of difluoroboron complexes with bis-β-diketone ligands

“…Nevertheless, the complex 3b containing high electronegative 4-fluoro group in benzene ring displayed much more intense photoluminescence and quantum yields than complex 4b, which attributed to the heavy atom effect of the chlorine atom for complex 4b [23]. Additionally, the complex 5b exhibited the strongest photoluminescence and highest quantum yield (U u = 0.93) in these difluoroboron complexes, which due to the larger donor character of two methoxyphenyl moieties.…”