ABSTRACT
CpG methylation of DNA is common in mammalian cells. In sperm, the DNA has the highest level of CpG methylation and is condensed into toroidal structures. How CpG methylation affects DNA structures and interactions is important to understand its biological roles but is largely unknown. Using an RNA-DNA-RNA structure, we observed the equilibrium hopping dynamics between the condensed and extended states of DNA in the presence of polyamines or polylysine peptide as a reduced model of histone tails. Combing with the measured DNA elasticities, we report that CpG methylation of each cytosine nucleotide substantially increases DNA-DNA attraction by up to 0.2 kBT. For the DNA with 57% GC content, the relative increase caused by CpG methylation is up to 32% for the spermine-induced DNA-DNA attraction and up to 9% for the polylysine-induced DNA-DNA attraction. These findings help us to evaluate the energetic contributions of CpG methylation in sperm development and chromatin regulation.
Subject(s)
Chromatin/chemistry , Cytosine/chemistry , DNA Methylation , DNA/analysis , DNA/chemistry , Magnetic Phenomena , Nucleic Acid Conformation , CpG IslandsABSTRACT
In this study, the 2D porous graphitic carbon nitride (g-C3N4) nanosheets were successfully fabricated via a facile thermal decomposition polymerization method without any help of templates, and then novel porous g-C3N4/CdS complex catalysts of different mass fractions were is situ synthesized by a simple solvothermal process. The results of photocatalytic experiments demonstrate that the coupling g-C3N4/CdS cocatalysts exhibit significant enhanced visible-light-driven photocatalytic activity for the decolorization of methyl orange (MO) compared with individual porous g-C3N4 and CdS. In particular, an optimal porous g-C3N4 content in the hybridized composite has been determined to be 70 wt.%, corresponding to pseudo-first-order rate constant of 0.046 min-1, which is 7 and 11 times faster than that of pure porous g-C3N4 and CdS, respectively. Photoluminescence (PL) spectroscopy measurements clearly confirmed that the recombination of photoproduced electrons and holes in g-C3N4/CdS composites was efficiently inhibited due to the formation of heterojunctions. Furthermore, the possible mechanism of enhanced photocatalytic activity and photostability of prous g-C3N4/CdS are also tentatively proposed.
ABSTRACT
A new coordination polymer (CP), namely poly[(µ-4,4'-bipyridine)(µ3-3,4'-oxydibenzoato)cobalt(II)], [Co(C14H8O5)(C10H8N2)]n or [Co(3,4'-obb)(4,4'-bipy)]n (1), was prepared by the self-assembly of Co(NO3)2·6H2O with the rarely used 3,4'-oxydibenzoic acid (3,4'-obbH2) ligand and 4,4'-bipyridine (4,4'-bipy) under solvothermal conditions, and has been structurally characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography and powder X-ray diffraction (PXRD). Single-crystal X-ray diffraction reveals that each CoII ion is six-coordinated by four O atoms from three 3,4'-obb2- ligands, of which two function as monodentate ligands and the other as a bidentate ligand, and by two N atoms from bridging 4,4'-bipy ligands, thereby forming a distorted octahedral CoN2O4 coordination geometry. Adjacent crystallographically equivalent CoII ions are bridged by the O atoms of 3,4'-obb2- ligands, affording an eight-membered Co2O4C2 ring which is further extended into a two-dimensional [Co(3,4'-obb)]n sheet along the ab plane via 3,4'-obb2- functioning as a bidentate bridging ligand. The planes are interlinked into a three-dimensional [Co(3,4'-obb)(4,4'-bipy)]n network by 4,4'-bipy ligands acting as pillars along the c axis. Magnetic investigations on CP 1 disclose an antiferromagnetic coupling within the dimeric Co2 unit and a metamagnetic behaviour at low temperature resulting from intermolecular π-π interactions between the parallel 4,4'-bipy ligands.
ABSTRACT
Hierarchical SnO2 blooming nanoflowers were successfully fabricated via a simple yet facile hydrothermal method with the help of different surfactants. Here we focus on exploring the promotion effects of surfactants on the self-assembly of 2D SnO2 nanosheets into 3D SnO2 flower-like structures as well as their gas-sensing performances. The polyporous flower-like SnO2 sensor exhibits excellent gas-sensing performances to ethanol and H2S gas due to high porosity when polyvinyl pyrrolidone is added into the precursor solution as a surfactant. The response/recovery times were about 5 s/8 s for 100 ppm ethanol and 4 s/20 s for 100 ppm H2S, respectively. Especially, the maximum response value of H2S is estimated to be 368 at 180 °C, which is one or two orders of magnitude higher than that of other test gases in this study. That indicates that the sensor fabricated with the help of polyvinyl pyrrolidone has good selectivity to H2S.
