Synthesis of Ag@SiO2 yolk–shell nanoparticles for hydrogen peroxide detectionLiu, Chao; Li, Jiansheng; Wang, Jing; Qi, Junwen; Fan, Wenhong; Shen, Jinyou; Sun, Xiuyun; Han, Weiqing; Wang, Lianjun
doi: 10.1039/c4ra16061dpmid: N/A
Yolk–shell nanostructures are a potential platform for the application of sensors and detection. In this paper, Ag@SiO2 yolk–shell nanoparticles (YSNs) were synthesized by a facile “two solvents” impregnation–reduction approach. XRD, SEM, TEM and N2 adsorption characterization results revealed that the resultant Ag@SiO2 YSNs possess distinctive structures, such as movable cores, perpendicular mesoporous channels, protective shells and hollow cavities. A nonenzymatic H2O2 sensor was constructed using Ag@SiO2 YSNs as sensing interface. A three-electrode system was used for the measurement. Electrochemical results indicate that the Ag@SiO2 YSNs modified electrode exhibits outstanding performance toward the H2O2 reduction, with a faster amperometric response, a lower detection limit (3.5 μM) and a wider linear range (0.1–15 mM) than that based on Ag@SiO2 composites, which was synthesized by a direct impregnation method.
Investigation on the adsorption behavior of polyacrylamide on resin by dual polarization interferometryLi, Keyi; Duan, Ming; Wang, Hu; Zhang, Jian; Jing, Bo
doi: 10.1039/c5ra00291epmid: N/A
Polyacrylamide (PAM) is widely used in the petroleum industry to enhance oil recovery all over the world. However, introducing PAM into the liquid changes the property of the oil–water interface and, finally, makes the wastewater treatment more difficult. It is ambiguous whether PAM adsorbs onto the oil–water interface and influences the stability of the interface. In this study, resin, one of the most important components in crude oil, was immobilized onto the silicon oxynitride chip surface. The behavior of PAM on resin was investigated by dual polarization interferometry (DPI). DPI is a novel instrument to real-time monitor the adsorption behavior and structure changes of a polymer on resin. Different concentrations of PAM solutions were respectively injected onto the immobilized chips. The real-time mass, thickness and density changes of PAM on resin were accordingly recorded and calculated by DPI. In conclusion, when a low-concentration polymer solution was injected, polymer molecules were adsorbed on the resin in disorder; when a high-concentration polymer solution was injected, pre-adsorbed polymer molecules were rearranged to take in more molecules and an isotropic adsorption layer will be formed.
Vibrational and electronic peculiarities of NiTiO3 nanostructures inferred from first principle calculationsRuiz Preciado, M. A.; Kassiba, A.; Morales-Acevedo, A.; Makowska-Janusik, M.
doi: 10.1039/c4ra16400hpmid: N/A
Structural, electronic and vibrational properties of nanostructured (NiTiO3)n clusters were calculated by numerical models based on DFT and semi-empirical quantum chemistry codes. The clusters were built by using the initial atomic positions of crystalline ilmenite, which were relaxed to ensure stable and energetically favourable geometries. For the electronic properties, the semi-empirical PM6 parameterisation method was used to evaluate the HOMO–LUMO energy differences versus nanocrystal sizes. The quantum confinement effect was induced with cluster size reduction. Theoretical UV-Vis absorption and Raman spectroscopy showed the drastic influence of the surface characteristics on the electronic and the vibrational properties of the nanoclusters. Theoretically, it was proved that powder NiTiO3 exhibits a patchwork of the properties of the bulk ilmenite material, amorphous Ni–Ti–O structures and atoms located at the surface of the investigated cluster.
Ruthenium complexes as inhibitors of human islet amyloid polypeptide aggregation, an effect that prevents beta cell apoptosisMa, Lijuan; Fu, Yuanting; Yu, Lianling; Li, Xiaoling; Zheng, Wenjie; Chen, Tianfeng
doi: 10.1039/c4ra15152fpmid: N/A
Human islet amyloid polypeptide (hIAPP) aggregation is essential in the loss of insulin-producing pancreatic beta cells in type 2 diabetes mellitus (T2DM). Recent studies have identified hIAPP fibril as a therapeutic target of T2DM. Metal complexes could covalently bind to the intracellular peptides to regulate their biological functions. In the present study, ruthenium (Ru) complexes NAMI-A (1) [Ru(bpy)3](ClO4)2 (2) (bpy = 2,2′-dipyridyl), [Ru(pip)3](ClO4)2 (3) (pip = 2-phenylimidazo[4,5-f]-[1,10]phenanthroline) and [Ru(phtpy)(phen)Cl]ClO4 (4) (phtpy = 2,6-bis(2-pyridyl)-4-phenylpyridine, phen = 1,10-phenanthroline) were selected to investigate their influence on hIAPP fibrillation in vitro. The results of thioflavin T (ThT) fluorescence assay showed that Ru complexes effectively inhibited the formation of hIAPP fibril. AFM images and TEM images further validated that the hIAPP fibrillation was disaggregated by the Ru complexes and then formed nanoscale particles, which tends to be a time-dependent process. Moreover, Ru complexes demonstrated a protective effect towards hIAPP-caused cell damage by restraining ROS generation and blocking cell apoptosis. In addition, it has been found that Ru complexes can also disaggregate hIAPP fibrils effectively inside the cells, and that the effects were proportional to the lipophilicity of the Ru complexes. Taken together, this study provides a strategy for designing Ru complexes for treating T2DM by targeting hIAPP.
Unexpected thermal decomposition behavior of poly(N-vinylimidazole)-l-poly(tetrahydrofuran) amphiphilic conetworks, a class of chemically forced blendsFodor, Csaba; Bozi, János; Blazsó, Marianne; Iván, Béla
doi: 10.1039/c4ra16881jpmid: N/A
The underlying chemical processes of the unexpected thermal decomposition behavior of poly(N-vinylimidazole)-l-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) as chemically forced blends of the otherwise immiscible components in broad composition ranges were investigated by thermogravimetric analysis (TG) and thermogravimetry-mass spectrometry (TG-MS). Surprisingly, the thermal decomposition of these conetworks occurs not by an expected two-stage but an apparently single-stage process. The homolytic scission of the PTHF cross-linkers is preceded by a less significant volatile product evolving by a non-radical reaction, presumably related to the well-known cis-elimination of the methacrylate ester linkages. The temperatures of the highest weight loss rate (Td(max)) were found to fall between that of the pure PVIm and PTHF homopolymers, and a universal correlation exists between Td(max) and the composition of the conetworks. The main thermal decomposition reactions of the polymer components in the PVIm-l-PTHF APCNs remain the same as in the corresponding homopolymers. However, among the two main degradation reactions of PVIm, the free radical depolymerization is promoted by PTHF macroradicals of molecular vicinity via hydrogen abstraction, which results in PTHF chains with improved stability. In contrast to expectations, this leads to a single-stage decomposition process of the two chemically interacting polymers in the conetworks. These results are expected to contribute to designing a variety of bi- and multicomponent polymeric materials with predictable thermal behavior composed of chemically and physically interconnected polymer chains, ranging from polymer blends to networks, block copolymers, composites and hybrids of the nanoscale to macroscopic objects.
Uniformly dispersed silicon nanoparticle/carbon nanosphere composites as highly stable lithium-ion battery electrodesLee, Whon-hee; Kang, Da-Young; Kim, Jung Sub; Lee, Joong Kee; Moon, Jun Hyuk
doi: 10.1039/c4ra14823apmid: N/A
Engineered silicon and carbon composite materials have been demonstrated to be promising anode materials for lithium-ion batteries. In this paper, we demonstrate a facile approach to fabricating silicon/carbon composite electrodes via simple mixing of silicon nanoparticles (SNPs) and carbon nanospheres (CNSs). Size-monodisperse CNSs were obtained by the direct carbon conversion of polystyrene spheres. The mixture of SNPs with size-monodisperse CNSs allowed for a uniform dispersion with minimal SNP aggregation, which was evaluated through direct comparison of the SNP mixture with micrometer-sized carbon particles. This SNP/CNS composite electrode, containing 30 wt% SNPs, exhibited a reversible specific capacity of 1023 mA h g−1 at 100 mA g−1, which was more than three times higher than that of a bare CNS electrode. The capacity retention after 50 cycles was 73%, with a high Coulombic efficiency of 99%; in addition, the capacity retention was approximately 70% when the current density was increased tenfold. Specifically, the SNP/CNS electrode exhibited substantially less capacity fade than did SNPs dispersed in micrometer-sized carbon particles. Moreover, the SNP/CNS electrode exhibited improved capacity retention under high-current-density conditions compared to that of previously developed silicon/carbon composite anodes. We attributed this improved LIB performance to the uniform dispersion of SNPs in the CNS matrix, which resulted in stable SEI formation and effective accommodation of the volume change of silicon. We believe our CNS structures can be extended to other electrode-material systems that require a large volume change and good mass transport characteristics.
Two-photon absorption and two-photon circular dichroism of hexahelicene derivatives: a study of the effect of the nature of intramolecular charge transferDíaz, Carlos; Vesga, Yuly; Echevarria, Lorenzo; Stará, Irena G.; Starỳ, Ivo; Anger, Emmanuel; Shen, Chengshuo; El Sayed Moussa, Mehdi; Vanthuyne, Nicolas; Crassous, Jeanne; Rizzo, Antonio; Hernández, Florencio E.
doi: 10.1039/c4ra16732epmid: N/A
Herein we report on the theoretical–experimental analysis of the one- and two-photon absorption and circular dichroism spectra of two intrinsically chiral aromatic molecules – hexahelicene derivatives – with helical chirality and intramolecular charge transfer (ICT). The primary outcomes of our investigation demonstrate that the TPA cross-section and the amplitude of the TPCD signal of this type of helicenes are strongly affected by the strength of the ICT and the nature of the extension of the electronic delocalization, i.e. beyond (EXO-ICT) or within (ENDO-ICT) the helicene core. These results were corroborated through the comparative theoretical analysis of the corresponding contributions of the magnetic dipole transition moment and the electric quadrupole transition moment to the TPA rotatory strength on a series of five similar helicene derivatives with different molecular electron delocalization disposition. Two-photon absorption (TPA) and two-photon circular dichroism (TPCD) spectra were obtained using the double L-scan technique over a broad spectral range (400–900 nm) using 90 fs pulses at a low repetition rate (2–50 Hz) produced by an amplified femtosecond system. The theoretical simulations were performed using modern analytical response theory within the Time-Dependent Density Functional Theory (TD-DFT) approach using B3LYP and CAM-B3LYP, and the aug-cc-pVDZ and 6-311++G(d,p) basis sets.
Ultrafast chemical lithiation of single crystalline silicon nanowires: in situ characterization and first principles modelingSeo, Jong-Hyun; Chou, Chia-Yun; Tsai, Yu-Hao; Cho, Yigil; Seong, Tae-Yeon; Lee, Woo-Jung; Cho, Mann-Ho; Ahn, Jae-Pyoung; Hwang, Gyeong S.; Choi, In-Suk
doi: 10.1039/c4ra14953jpmid: N/A
Through a combined density functional theory and in situ scanning electron microscopy study, we provide evidence of the ultrafast chemical lithiation of a single crystalline Si nanowire which is brought into direct contact with Li metal in the absence of an applied external electric field. Unlike the previous in situ lithiation results, the ultra-fast lithiation process in this study is purely driven by the concentration gradient and is found to be limited by Li diffusion through the pristine/lithiated Si phase boundary. The experimental and calculated lithiation speeds are in excellent agreement at around 1 μm s−1, corresponding to a high Li diffusivity value of about 10−9 cm2 s−1. The improved understanding of lithiation kinetics may contribute to the design of higher-power Si-based anodes.