In this study, thermally reversible polyurethanes (PUs) with shape memory effect were developed by using hydrogen bonding to enhance physical interactions. Two different types of PUs were synthesized: (1) a linear PU whose hard segment consists of methylene di-para-phenyl isocyanate (MDI) and di(ethylene glycol) (DEG); its soft segment is made of Tone 0260 polyol, a polyester polyol; (2) a side-chain dendritic PU which replaces DEG with different generations of dendritic chain extenders. By incorporation of the dendritic structure with peripheral long alkyl chains (strong van der Waals forces), the miscibility between hard and soft segments can be significantly improved. Consequently, the hydrogen bonding reinforced hard segments (malonamide linkages) of side chain dendritic PUs result in greatly enhanced mechanical properties and shape memory effect. During cyclic shape memory tests, one of the series can effortlessly achieve complete recovery in less than 10 second without any deficiency
This study synthesized a facile and high sensitive fluorescent probe based on sulfur-doped carbon dots (S-CDs) using a one-step microwave irradiation method. The probe exhibited a strong blue emission and a high quantum yield (QY) of 36.40%. In the detection, the presence of trivalent chromium (Cr(III)) strongly quenched the PL intensity of S-CDs by the inner filter effect (IFE) quenching mechanism of Cr(III) on the S-CDs. The S-CDs exhibited good sensitivity to turn-off Cr(III) detection with a linear range concentration of 0–45 μM and a detection limit of 0.17 μM. Furthermore, the proposed method has been successfully applied for Cr(III) detection in natural water samples with the 93.68–106.20% recoveries.
We report here a biophysical and biochemical approach to determine the differences in interactions of NiCR and NiCR-2H with DNA. Our goal is to determine whether such interactions are responsible for the recently observed differences in their cytotoxicity toward MCF-7 cancer cells. Viscosity measurement and fluorescence displacement titration indicated that both NiCR and NiCR-2H bind weakly to duplex DNA in the grooves. The coordination of NiCR-2H with the N-7 of 2′-deoxyguanosine 5′-monophosphate (5′-dGMP) is stronger than that of NiCR as determined by 1H NMR. NiCR-2H, like NiCR, can selectively oxidize guanines present in distinctive DNA structures (e.g., bulges), and notably, NiCR-2H oxidizes guanines more efficiently than NiCR. In addition, UV and 1H NMR studies revealed that NiCR is oxidized into NiCR-2H in the presence of KHSO5 at low molar ratios with respect to NiCR (≤4).
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