Synthesis, characterization and optical properties of silver and gold nanowires embedded in mesoporous MCM-41

Uniform nanowires of silver and gold inside the channels of MCM-41 were prepared by controlled reduction of their respective metal salts with sodium borohydride (NaBH₄). Presence of nanowires of silver and gold in MCM-41 were confirmed by high angle X-ray diffraction (XRD) data (peaks between 2ϑ = 30 − 60°) and transmission electron microscopy (TEM) confirmed the diameter of the nanowires. Diameter of nanowires is found to be ∼ 2.8 nm which is coincident with channel diameter of MCM-41. Optical properties of these heterostructured materials Ag-MCM-41 and Au-MCM-41 reveals the presence of surface plasmon absorption peaks of silver and gold respectively, and the shift in the absorption bands are associated to agglomeration of clusters inside the channels. Room temperature photoluminescence spectra exhibits interesting optical properties as observed for direct band gap semiconductors. Non-linear optical properties (NLO) corresponding to second harmonic generation (SHG) values were also recorded for self supported films of these heterostructured materials. Enhanced optical non-linearity was found to be arising from a corresponding increase of local field near the surface plasmon resonance. Further enhancement in SHG was found with poling due to an induction of orientation order.     

Hydroxyl radical mediated degradation of phenylarsonic acid

Phenyl-substituted arsonic acids have been widely used as feed additives in the poultry industry. While very few studies have been reported on the environmental impact of these compounds, they have been introduced into the environment through land application of poultry litter in large quantities (about 10(6) kg/year). Phenylarsonic acid (PA) was used as a model for problematic arsonic acids. Dilute aqueous solutions of PA were subjected to gamma radiolysis under hydroxyl radical generating conditions, which showed rapid degradation of PA. Product studies indicate addition of (.)OH to the phenyl ring forms the corresponding phenols as the primary products. Arsenite, H3As(III)O3, and arsenate, H3As(V)O4, were also identified as products. The optimized structures and relative calculated energies (using GAUSSIAN 98, the B3LYP/6-31G(d) method) of the various transient intermediates are consistent with the product studies. Pulse radiolysis was used to determine the rate constants of PA with (.)OH (k = 3.2 x 10(9) M(-1) s(-1)) and SO4(.-) (k = 1.0 x 10(9) M(-1) s(-1)). PA reacts slower toward O(.-) (k = 1.9 x 10(7) M(-1) s(-1)) and N3(.) (no detectable transient), due to the lower oxidation potential of these two radicals. Our results indicate advanced oxidative processes employing (.)OH and SO4(.-) can be effective for the remediation of phenyl-substituted arsonic acids.     

Synthesis of Polysubstituted Pyrazolo[3,4‐b]pyridine‐3‐Carbohydrazide and Pyrazolo[3,4‐d]pyridazine Derivatives

5‐Amino‐4‐formyl pyrazole carboxylate gave facile reactions with malononitrile, hydrazine, and ketones in the presence of piperidine furnished substituted pyrazolo[3,4‐b]pyridines and pyrazolo[3,4‐b]quinolones. The pyridazine sulfonamides were obtained by the reaction of 5‐chloro 4‐formyl pyrazole carboxylate with sulfonamide derivatives.     

A room temperature one-pot Knoevenagel-Chan-Evans-Lam coupling reaction for synthesis of N-aryl-2-Iminocoumarins in bio-mass-derived green solvent 2-methylTHF

An efficient approach for the synthesis of biologically interesting N-aryl-2-iminocoumarins by a copper-catalyzed one-pot procedure has been developed by the reaction of 2-hydroxybenzaldehydes, malononitrile and arylboronic acids using triethylamine as a base in a bio-mass-derived green solvent 2-MethylTHF at room temperature. This protocol allows access to several N-aryl-2-iminocoumarins in high yields in a relatively short period of time under mild reaction conditions. The procedure operates by a simple telescoped process wherein 2-imino-2H-chromene-3-carbonitriles are formed in situ by the reaction of 2-hydroxybenzaldehyde, malononitrile, and TEA. Further a subsequent one-pot reaction of imine with the arylboronic afforded the target compounds. To understand the reaction mechanism, MALDI-ESI studies were performed, which showed the in situ generated iminocoumarins to be in ligation cooper to form a copper-iminocoumarin complex thus facilitating the smooth formation of N-aryl-2-iminocoumarins in the reaction. Overall, this protocol is practically valuable, useful in organic synthesis, shows good functional group tolerance and provides access to a diverse array of N-aryl-2-iminocoumarins derivatives.     

Identification of a Critical Intermediate in Galvanic Exchange Reactions by Single‐Nanoparticle‐Resolved Kinetics

The realization of common materials transformations in nanocrystalline systems is fostering the development of novel nanostructures and allowing a deep look into the atomistic mechanisms involved. Galvanic corrosion is one such transformation. We studied galvanic replacement within individual metal nanoparticles by using a combination of plasmonic spectroscopy and scanning transmission electron microscopy. Single‐nanoparticle reaction trajectories showed that a Ag nanoparticle exposed to Au³⁺ makes an abrupt transition into a nanocage structure. The transition is limited by a critical structural event, which we identified by electron microscopy to comprise the formation of a nanosized void. Trajectories also revealed a surprisingly strong nonlinearity of the reaction kinetics, which we explain by a model involving the critical coalescence of vacancies into a growing void. The critical void size for galvanic exchange to spontaneously proceed was found to be 20 atomic vacancies.     

Determination of nitrite by simple diazotization method

A simple and rapid spectrophotometric method for the determination of nitrite is described. This is based upon simple diazotization reactions involving p-nitroaniline (PNA) and sulfanilamide (SA) with ethyl acetoacetate (EAA) as the coupling agent. The absorbance was measured at 507 and 356 nm, respectively. The method is optimized for acidity, amount of reagents required, amount of sodium hydroxide and the tolerance amount of other ions. The range of linearity for PNA-EAA couple was 0.05-6.0 μg ml⁻¹ of nitrite with molar absorptivity of 1.59×10⁴ l mol⁻¹ cm⁻¹; while that for SA-EAA couple was found to be 0.2-3.0 μg ml⁻¹ and 1.22×10⁴ l mol⁻¹ cm⁻¹, respectively. The method has been applied to various water and soil samples.     

Photo-neutron cross-section of 100Mo

The ¹⁰⁰Mo(γ, n) reaction cross-section was experimentally determined at end point bremsstrahlung energy of 10 and 12.5 MeV using off-line γ-ray spectrometric technique. It was also found that ¹⁰⁰Mo(γ, n) reaction cross-section increases sharply from the end point bremsstrahlung energy of 10 MeV to 12.5 MeV, which may be because of GDR around the energy region of 12–16 MeV. The ¹⁰⁰Mo(γ, n) reaction cross-section as a function of photon energy was calculated theoretically using TALYS 1.2 computer code. The flux-weighted average values of ¹⁰⁰Mo(γ, n) reaction cross-section for bremsstrahlung having end point energy of 10 and 12.5 MeV were also calculated using the experimental and theoretical data of mono-energetic photon. The present experimental ¹⁰⁰Mo(γ, n) reaction cross-sections were compared with the bremsstrahlung flux-weighted average values of experimental and theoretical data and found to be in the lower side for 10 MeV and in the higher side for 12.5 MeV.     

Traceless and site-specific ubiquitination of recombinant proteins

Protein ubiquitination is a post-translational modification that regulates almost all aspects of eukaryotic biology. Here we discover the first routes for the efficient site-specific incorporation of δ-thiol-L-lysine (7) and δ-hydroxy-L-lysine (8) into recombinant proteins, via evolution of a pyrrolysyl-tRNA synthetase/tRNA(CUA) pair. We combine the genetically directed incorporation of 7 with native chemical ligation and desulfurization to yield an entirely native isopeptide bond between substrate proteins and ubiquitin. We exemplify this approach by demonstrating the synthesis of a ubiquitin dimer and the first synthesis of ubiquitinated SUMO.     

插层FeSe高温超导体的高压研究进展

通过对FeSe进行化学插层可以将其超导转变温度（T_c）从约8 K提高到40 K以上,实现高温超导电性.最近,我们对两种插层FeSe高温超导材料（Li_0.84Fe_0.16）OHFe_0.98Se和Li_0.36（NH₃）_yFe₂Se₂开展了高压调控研究,发现压力会首先抑制高温超导相（称为SC-I相）,然后在临界压力P_c以上诱导出第二个高温超导相（称为SC-Ⅱ相）,呈现出双拱形T-P超导相图.这两个体系的P_c分别约为5和2 GPa,两个体系SC-Ⅱ相的最高T_c分别可以达到约52和55 K,比相应SC-I相的初始T_c提高了10 K.对（Li_0.84Fe_0.16）OHFe_0.98Se的正常态电输运性质分析表明,SC-I和SC-Ⅱ相的正常态分别具有费米液体和非费米液体行为,意味着这两个超导相可能存在显著差异.此外,还发现这两个体系的SC-Ⅱ相的T_c与霍尔系数倒数1/R_H（∝载流子浓度n_e）具有很好的线性依赖关系.对（Li_0.84Fe_0.16）OHFe_0.98Se的高压X射线衍射测量排除了其在10 GPa以内发生结构相变的可能,因此P_c以上SC-Ⅱ相的出现和载流子浓度的增加很可能起源于压力导致的费米面重构.     

Ultrafast vibrational dynamics of water at a charged interface revealed by two-dimensional heterodyne-detected vibrational sum frequency generation

Two-dimensional heterodyne-detected vibrational sum frequency generation (2D HD-VSFG) spectroscopy is performed for an aqueous interface for the first time. The 2D HD-VSFG spectra in the OH stretch region are obtained from a positively charged surfactant∕water interface with isotopically diluted water (HOD∕D(2)O) to reveal the femtosecond vibrational dynamics of water at the charged interface. The 2D HD-VSFG spectrum is diagonally elongated immediately after photoexcitation, clearly demonstrating inhomogeneity in the interfacial water. This elongation almost disappears at 300 fs owing to the spectral diffusion. Interestingly, the 2D HD-VSFG spectrum at the 0 fs shows an oppositely asymmetric shape to the corresponding 2D IR spectrum in bulk water: The bandwidth of the bleach signal gets narrower when the pump wavenumber becomes higher. This suggests that the dynamics and mechanism of the hydrogen bond rearrangement at the charged interface are significantly different from those in bulk water.