Graphene quantum dots (GQDs) are great promising in various applications owing to the quantum confinement and edge effects in addition to their intrinsic properties of graphene, but the preparation of the GQDs in bulk scale is challenging. We demonstrated in this work that the micrometer sized graphene oxide (GO) sheets could react with Fenton reagent (Fe(2+)/Fe(3+)/H(2)O(2)) efficiently under an UV irradiation, and, as a result, the GQDs with periphery carboxylic groups could be generated with mass scale production. Through a variety of techniques including atomic force microscopy, X-ray photoelectron spectroscopy, gas chromatography, ultraperformance liquid chromatography-mass spectrometry, and total organic carbon measurement, the mechanism of the photo-Fenton reaction of GO was elucidated. The photo-Fenton reaction of GO was initiated at the carbon atoms connected with the oxygen containing groups, and C-C bonds were broken subsequently, therefore, the reaction rate depends strongly on the oxidization extent of the GO. Given the simple and efficient nature of the photo-Fenton reaction of GO, this method should provide a new strategy to prepare GQDs in mass scale. As a proof-of-concept experiment, the novel DNA cleavage system using as-generated GQDs was constructed.

Composition, morphology, and surface characteristics of solid substrates play critical roles in regulating immobilized enzyme activity. Grapheme oxide (GO), a novel nanostructured material, has been illustrated as an ideal enzyme immobilization substrate due to its unique chemical and structural properties. Physical properties and catalytic activity of GO immobilized horseradish peroxidase (HRP) and its application in phenolic compound removal are described in the present study. HRP loading on GO was found to be much higher than that on reported substrates. The GO immobilized HRP showed improved thermal stability and a wide active pH range, attractive for practical applications. The removal of phenolic compounds from aqueous solution using the GO immobilized HRP was explored with seven phenolic compounds as model substrates. The GO immobilized HRP exhibited overall a high removal efficiency to several phenolic compounds in comparison to soluble HRP, especially for 2,4-dimetheoxyphenol and 2-chlorphenol, the latter a major component of industrial wastewater.

DNA sequences with guanine repeats can form G-quartets that adopt G-quadruplex structures in the presence of specific metal ions. Using circular dichroism (CD) and ultraviolet-visible (UV–Vis) spectroscopy, we determined the spectral characteristics and the overall conformation of a G-quadruplex of PS2.M with an oligonucleotide sequence, d(GTG3TAG3CG3TTG2). UV-melting curves demonstrate that the Pb2+-induced G-quadruplex formed unimolecularly and the highest melting temperature (Tm) is 72°C. The analysis of the UV titration results reveals that the binding stoichiometry of Pb2+ ions to PS2.M is two, suggesting that the Pb2+ ions coordinate between adjacent G-quartets. Binding of ions to G-rich DNA is a complex multiple-pathway process, which is strongly affected by the type of the cations. Kinetic studies suggest that the Pb2+-induced folding of PS2.M to G-quadruplex probably proceeds through a three-step pathway involving two intermediates. Structural transition occurs after adding Pb(NO3)2 to the Na+- or K+-induced G-quadruplexes, which may be attributed to the replacement of Na+ or K+ by Pb2+ ions and the generation of a more compact Pb2+–PS2.M structure. Comparison of the relaxation times shows that the Na+→Pb2+ exchange is more facile than the K+→Pb2+ exchange process, and the mechanisms for these processes are proposed.

No abstract

Fluorescent polymers without conventional fluorescent units are attracting extensive interest because of their excellent biocompatibility. Succinimides are generally known as common fluorescence quenchers of proteins due to some degree of electron transfer between the excited state and the quencher. In this work, we observed unexpected fluorescence from succinimide-containing polymers. We synthesized a series of succinimides and found that 2,3-dithio-succinimide and 2-amino-succinimide were fluorescent, presenting solvent-dependent emission. This study is the first to report that nonfluorescent succinimides become fluorescent only by thiol and amine group substitutions, without employing any fluorescent units. The unusual fluorescence of dithio/amino-succinimides resulted from the spatial separation of HOMO and LUMO based on density functional theory calculations. Compared with monomers, polymers containing 2-amino-succinimide exhibited substantial fluorescence enhancement (maximum of ∼200fold) because of the isolation effect, in which nonradiative decay among succinimide fluorophores was significantly suppressed.

It has been shown that guanine-rich DNA can fold into a G-quadruplex with certain metal cations. The spectral characteristics, thermostability, and kinetics for the formation of a Pb(2+)-driven G-quadruplex of thrombin-binding aptamer (TBA) were measured in the current work using a combination of ultraviolet (UV) and circular dichroism (CD) spectroscopy along with stopped-flow technique. CD spectra demonstrated that TBA could fold into a unique G-quadruplex with a strong positive peak at 312 nm. Analysis of the titration data reveals that the binding stoichiometry is 1:1 for the titration of TBA with Pb(NO(3))(2), which is in accordance with the localization of the Pb(2+) ion between the adjacent G-quartets. Thermal denaturation profiles indicate that the Pb(2+)-induced intramolecular G-quadruplex is more stable than those driven by Na(+) or K(+) ions. Kinetic studies suggest that the Pb(2+)-induced folding G-quadruplex of TBA probably proceeds through the rapid formation of an intermediate Pb(2+)-TBA complex, which then isomerizes to the fully folded structure. Conformational changes transpire after the addition of Pb(NO(3))(2) to the Na(+)- or K(+)-induced G-quadruplexes, which may be attributed to the replacement of Na(+) or K(+) ions by Pb(2+) ions and the generation of a more compact structure of the Pb(2+)-TBA structure. The relaxation time, τ, of folding the G-quadruplex is reduced from 1.05 s in the presence of Pb(2+) ions alone to 0.34 s under the cooperation of initially added Na(+) ions, while τ is increased to 8.33 s under the competition of initially added K(+) ions.

Metal-free carbon monoxide-releasing polymers (CORPs) are synthesized via a direct polymerization approach, exhibiting not only improved stability but also accelerated wound healing performance as compared to CORM-3.

No abstract