A bis‐triarylborane tetracation (4‐Ar2B‐3,5‐Me2C6H2)‐C≡C−C≡C‐(3,5‐Me2C6H2‐4‐BAr2 [Ar=(2,6‐Me2‐4‐NMe3‐C6H2)+] (24+) shows distinctly different behaviour in its fluorimetric response than that of our recently published bis‐triarylborane 5‐(4‐Ar2B‐3,5‐Me2C6H2)‐2,2′‐(C4H2S)2–5′‐(3,5‐Me2C6H2‐4‐BAr2) (34+). Single‐crystal X‐ray diffraction data on the neutral bis‐triarylborane precursor 2 N confirm its rod‐like dumbbell structure, which is shown to be important for DNA/RNA targeting and also for BSA protein binding. Fluorimetric titrations with DNA/RNA/BSA revealed the very strong affinity of 24+ and indicated the importance of the properties of the linker connecting the two triarylboranes. Using the butadiyne rather than a bithiophene linker resulted in an opposite emission effect (quenching vs. enhancement), and 24+ bound to BSA 100 times stronger than 34+. Moreover, 24+ interacted strongly with ss‐RNA, and circular dichroism (CD) results suggest ss‐RNA chain‐wrapping around the rod‐like bis‐triarylborane dumbbell structure like a thread around a spindle, a very unusual mode of binding of ss‐RNA with small molecules. Furthermore, 24+ yielded strong Raman/SERS signals, allowing DNA or protein detection at ca. 10 nm concentrations. The above observations, combined with low cytotoxicity, efficient human cell uptake and organelle‐selective accumulation make such compounds intriguing novel lead structures for bio‐oriented, dual fluorescence/Raman‐based applications.
A strong impact of fluorophores’ charge and length on the binding mode, intracellular distribution and antiproliferative activity; intriguing theragnostic potential.
Recently, various bio‐medical applications of nanoporous silicon (np‐Si) have been suggested. This work investigates the biocompatibility of np‐Si particles taking into account hazardous residua confined in the pores after preparation. The emphasis is on the potential application of such particles as oxygen photosensitizer for photodynamic therapy of cancer, which requires both negligible toxicity of np‐Si particles in darkness and a high photo‐cyto‐toxic effect due to generation of singlet oxygen under illumination. Considerable amounts of water soluble toxic impurities are found to be present in the nanoporous shell of micrometer‐sized np‐Si particles immediately after their preparation by chemical etching of bulk silicon powder. The effects of several ordinary cleaning treatments are investigated by using thermal effusion mass‐spectroscopy and FTIR spectroscopy. A particular purification procedure is developed, capable to reduce the concentration of residual impurities to levels acceptable for bio‐medical applications while preserving the required photo‐activity of the np‐Si particles.
To explore in greater detail the recently reported rare kinetic differentiation between homo-polymeric and alternating AT-DNA sequences by using sterically restricted phosphonium dyes that form dimers within the DNA minor groove, new analogues were prepared in which the quinolone phosphonium moiety was kept constant, while the size and hydrogen bonding properties of the rest of the molecule were varied. Structure-activity relationship studies revealed that a slight increase in length by an additional methylene unit results in loss of kinetic AT selectivity, but yielded an AT-selective fluorescence response. These DNA/RNA-groove-bound dyes combine very low cytotoxicity with efficient cellular uptake and intriguingly specific fluorescent marking of mitochondria. In contrast to longer analogues, a decrease in length (by methylene unit removal) and rearrangement of positive charge resulted in dyes that had switched to the intercalative binding mode to GC DNA/dsRNA but that still form dimers in the minor groove of AT sequences, consequently yielding a significantly different chiro-optical response. The latter dyes also revealed strongly selective antiproliferative activity toward HeLa cancer cells.
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