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 water‐soluble tetracationic quadrupolar bis‐triarylborane chromophore showed strong binding to ds‐DNA, ds‐RNA, ss‐RNA, as well as to the naturally most abundant protein, BSA. The novel dye can distinguish between DNA/RNA and BSA by fluorescence emission separated by Δtrueν˜
=3600 cm−1, allowing for the simultaneous quantification of DNA/RNA and protein (BSA) in a mixture. The applicability of such fluorimetric differentiation in vitro was demonstrated, strongly supporting a protein‐like target as a dominant binding site of 1 in cells. Moreover, our dye also bound strongly to ss‐RNA, with the unusual rod‐like structure of the dye, decorated by four positive charges at its termini and having a hydrophobic core, acting as a spindle for wrapping A, C and U ss‐RNAs, but not poly G, the latter preserving its secondary structure. To the best of our knowledge, such unmatched, multifaceted binding activity of a small molecule toward DNA, RNA, and proteins and the selectivity of its fluorimetric and chirooptic response makes the quadrupolar bis‐triarylborane a novel chromophore/fluorophore moiety for biochemical applications.
A strong impact of fluorophores’ charge and length on the binding mode, intracellular distribution and antiproliferative activity; intriguing theragnostic potential.
We report four new luminescent tetracationic bis‐triarylborane DNA and RNA sensors that show high binding affinities, in several cases even in the nanomolar range. Three of the compounds contain substituted, highly emissive and structurally flexible bis(2,6‐dimethylphenyl‐4‐ethynyl)arene linkers (3: arene=5,5′‐2,2′‐bithiophene; 4: arene=1,4‐benzene; 5: arene=9,10‐anthracene) between the two boryl moieties and serve as efficient dual Raman and fluorescence chromophores. The shorter analogue 6 employs 9,10‐anthracene as the linker and demonstrates the importance of an adequate linker length with a certain level of flexibility by exhibiting generally lower binding affinities than 3–5. Pronounced aggregation–deaggregation processes are observed in fluorimetric titration experiments with DNA for compounds 3 and 5. Molecular modelling of complexes of 5 with AT‐DNA, suggest the minor groove as the dominant binding site for monomeric 5, but demonstrate that dimers of 5 can also be accommodated. Strong SERS responses for 3–5 versus a very weak response for 6, particularly the strong signals from anthracene itself observed for 5 but not for 6, demonstrate the importance of triple bonds for strong Raman activity in molecules of this compound class. The energy of the characteristic stretching vibration of the C≡C bonds is significantly dependent on the aromatic moiety between the triple bonds. The insertion of aromatic moieties between two C≡C bonds thus offers an alternative design for dual Raman and fluorescence chromophores, applicable in multiplex biological Raman imaging.
Magnetic susceptibilities of a series of ternary intermetallic compounds of the general composition ThM2X2(M = Cr, Mn, Fe, Co, Ni and Cu; X = Si and Ge) were determined by means of FARADAY method in the temperature interval 100–570°K. The results confirm the previously proposed magnetic behaviour of these compounds, based on the observation of the basic crystallographic parameters as a function of the atomic number of the transition metal element. The compounds were found to be alternatively ferromagnetics and antiferromagnetics depending on the atomic number of the transition metal atom.
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