Chiral assemblies of plasmonic nanoparticles are known for strong circular dichroism but not for high optical asymmetry, which is limited by the unfavorable combination of electrical and magnetic field components compounded by strong scattering. Here we show that these limitations can be overcome by long-range organization of nanoparticles similar to liquid crystals found in helical assemblies of gold nanorods with human islet amyloid polypeptide. Strong polarization-dependent spectral shift and reduced scattering of energy states with antiparallel orientation of dipoles activated in assembled helices increase optical asymmetry g-factors by more than 4600 times. The liquid crystal-like color variations and nanorods-accelerated fibrillation enable drug screening in complex biological media. Improvement of long-range order also provides structural guidance for the design of materials with high optical asymmetry.

No abstract

Phosphorothioate (PS) modified oligonucleotides (S-DNA) naturally exist in bacteria and archaea genome and are widely used as an antisense strategy in gene therapy. However, the introduction of PS as a redox active site may trigger distinct UV photoreactions. Herein, by time-resolved spectroscopy, we observe that 266 nm excitation of S-DNA d(A ps ) 20 and d(A ps A) 10 leads to direct photoionization on the PS moiety to form hemi-bonded -P-S∴S-P-radicals, in addition to A base ionization to produce A +• /A(-H) • . Fluorescence spectroscopy and global analysis indicate that an unusual charge transfer state (CT) between the A and PS moiety might populate in competition with the common CT state among bases as key intermediate states responsible for S-DNA photoionization. Significantly, the photoionization bifurcating to PS and A moieties of S-DNA is discovered, suggesting that the PS moiety could capture the oxidized site and protect the remaining base against ionization lesion, shedding light on the understanding of its existence in living organisms.

Triplex DNA structure has potential therapeutic application in inhibiting the expression of genes involved in cancer and other diseases. As a DNA-targeting antitumor and antibiotic drug, coralyne shows a remarkable binding propensity to triplex than canonical duplex and thus can modulate the stability of triplex structure, providing a prospective gene targeting strategy. Much less is known, however, about coralyne binding interactions with triplex. By combining multiple steady-state spectroscopy with ultrafast fluorescence spectroscopy, we have investigated the binding behaviors of coralyne with typical triplexes. Upon binding with G-containing triplex, the fluorescence of coralyne is markedly quenched owing to photoinduced electron transfer (PET) of coralyne with G base. Systematic studies show that the PET rates are sensitive to the binding configuration and local microenvironment, from which coexisting binding modes of monomeric (full and partial) intercalation and aggregate stacking along sugar-phosphate backbone are distinguished and their respective contributions are determined. It shows that coralyne has preferences for monomeric intercalation within CGG triplex and pure TAT triplex, whereas CGC+ triplex adopts mainly backbone binding of coralyne aggregates due to charge repulsion, revealing the sequence-specific binding selectivity. The triplex-DNA-induced aggregation of coralyne could be used as a probe for recognizing the water content in local DNA structures. The strong π-π stacking of intercalated coralyne monomer with base-triplets plays important roles in stabilizing the triplex structure. These results provide mechanistic insights for understanding the remarkable propensity of coralyne in selective binding to triplex DNA and shed light on the prospective applications of coralyne-triplex targeted anti-gene therapeutics.

Cyclobutane pyrimidine dimer (CPD) is the most abundant DNA photolesion, and it can be repaired by photolyases based on electron-transfer mechanisms. However, photolyase is absent in the human body and lacks stability for applications. Can one develop natural enzyme mimetics utilizing nanoparticles (termed nanozymes) to mimic photolyase in repairing DNA damage? Herein, we observe the successful reversal of thymine dimer T<>T to normal T base by TiO2 under UVA irradiation. Time-resolved spectroscopy provides direct evidence that the photogenerated electron of TiO2 transfers to T<>T, causing structural instability and initiating the repair process. T–T – would then undergo bond cleavage to form T and T – , and T – returns an electron to TiO2, finishing the photocatalytic cycle. For the first time, TiO2 is discovered to exhibit photocatalytic properties similar to those of natural enzymes, pointing to its extraordinary application potential as a nanozyme to mimic photolyase in repairing DNA damage.