The Effect of Backbone Stereochemistry on the Folding of Acyclic β2, 3‐Aminoxy Peptides

As a new type of foldamer, β‐aminoxy peptides have the ability to adopt novel β N? O turns or β N? O helices in solution. Herein, we describe a new subclass of β‐aminoxy peptide, that is, peptides of acyclic β^{2, 3}‐aminoxy acids (NH₂OCHR₁CHR₂COOH), in which the presence of two chiral centers provides insight into the effect of backbone stereochemistry on the folding of β‐aminoxy peptides. Acyclic β^{2, 3}‐aminoxy peptides with syn and anti configurations have been synthesized and their conformations investigated by NMR, IR, and circular dichroism (CD) spectroscopic, and X‐ray crystallographic analysis. The β N? O turns or β N? O helices, which feature nine‐membered rings with intramolecular hydrogen bonds and have been identified previously in peptides of β³‐ and β^{2, 2}‐aminoxy acids, are also predominantly present in the acyclic β^{2, 3}‐aminoxy peptides with a syn configuration and N? O bonds gauche to the C_α? C_β bonds in both solution and the solid state. In the acyclic β^{2, 3}‐aminoxy peptides with an anti configuration, an extended strand (i.e., non‐hydrogen‐bonded state) is found in the solid state, and several conformations including non‐hydrogen‐bonded and intramolecular hydrogen‐bonded states are present simultaneously in nonpolar solvents. These results suggest that the backbone stereochemistry does affect the folding of the acyclic β^{2, 3}‐aminoxy peptides. Theoretical calculations on the conformations of model acyclic β^{2, 3}‐aminoxy peptides with different backbone stereochemistry were also conducted to elucidate structural characteristics. Our present work may provide useful guidelines for the design and construction of new foldamers with predicable structures.     

Self‐Assembly of Discrete Homochiral,Helical, Hydrogen‐Bonded Nanocages: From Vesicles to Microspheres and Tubules Capable of Gelating Solvents

The chiral tris‐monodentate imidazolinyl ligands 1 a – c exhibit a strong tendency to form the discrete, helical [2+3] nanocages 3 ([ 1 ₂ ?2 ₃]) with tartaric acids 2 . Circular dichroism (CD) spectra and theoretical calculations reveal that supramolecular handedness of capsulelike architectures is determined only by the chirality of the imidazolinyl ligands rather than tartaric acids. The chirality of imidazolinyl ligands is transferred to the helicity of the complexes through the directed hydrogen bonds between the N3 atom of imidazoline rings and the carboxyl of tartaric acids. These hydrogen‐bonded nanocages can spontaneously self‐assemble into spherical vesicles, during which the hydrogen bonding that arises from the hydroxyl groups of tartaric acids plays a crucial issue. The vesicles formed by [{(S,S,S)‐ 1 a }₂( 2 ^L)₃] ( 3 a ) may further evolve into microspheres that gelate organic solvents after being aged at ?20 °C for 24 h, and can also be unprecedentedly transformed to tubular assemblies capable of rigidifying the solvents when subjected to ultrasound irradiation.     

Chemical Synthesis,Structure Characterization,and Optical Properties of Hollow PbSx–Solid Au Heterodimer Nanostructures

Heterodimer nanostructures have attracted extensive attention, owing to an increasing degree of complexity, functionality, and then importance. So far, all the reported ones are built from solid nanoparticles. Herein, nearly monodisperse heterodimer nanostructures are constructed by hollow PbS_x and solid Au domains simultaneously through a mild reaction between PbS nanocrystals and the gold species in the presence of dodecylamine. Control experiments clearly reveal the underlying formation mechanism of the hollow PbS_x–solid Au heterodimers. The Au^III species in the solution, lead to the etching of PbS nanocrystals and the Au^I species facilitate the control of the number of gold domains per nanoparticle. Dodecylamine molecules not only work as a stabilizer in the reaction, but also act as a reducing agent that could greatly affect the morphology of the product. The optical properties of the heterodimers are investigated based on UV/Vis absorption spectroscopy and Raman spectroscopy. This novel heterodimer nanostructure pushes the development of complex nanocrystal‐based architectures forward, and also provides many opportunities for potential applications.     

Amminelithium Amidoborane Li(NH3)NH2BH3: A New Coordination Compound with Favorable Dehydrogenation Characteristics

The monoammoniate of lithium amidoborane, Li(NH₃)NH₂BH₃, was synthesized by treatment of LiNH₂BH₃ with ammonia at room temperature. This compound exists in the amorphous state at room temperature, but at ?20 °C crystallizes in the orthorhombic space group Pbca with lattice parameters of a=9.711(4), b=8.7027(5), c=7.1999(1) Å, and V=608.51 ų. The thermal decomposition behavior of this compound under argon and under ammonia was investigated. Through a series of experiments we have demonstrated that Li(NH₃)NH₂BH₃ is able to absorb/desorb ammonia reversibly at room temperature. In the temperature range of 40–70 °C, this compound showed favorable dehydrogenation characteristics. Specifically, under ammonia this material was able to release 3.0 equiv hydrogen (11.18 wt %) rapidly at 60 °C, which represents a significant advantage over LiNH₂BH₃. It has been found that the formation of the coordination bond between ammonia and Li⁺ in LiNH₂BH₃ plays a crucial role in promoting the combination of hydridic B? H bonds and protic N? H bonds, leading to dehydrogenation at low temperature.     

Preparation,characterization and luminescent properties of spherical CaTiO3:Pr3+ phosphors by spray pyrolysis

In this paper, spherical Pr³⁺-doped CaTiO₃ phosphor particles were fabricated through a two-step spray pyrolysis process, using citric acid and polyethylene glycol (PEG) as additives. X-ray diffraction (XRD), scanning electron microscopy (SEM), High-resolution transmission electron microscopy (HRTEM), thermogravimetric and differential thermal analysis (TG–DTA), X-ray photoelectron spectra (XPS), photoluminescence (PL), cathodoluminescence (CL) spectroscopy, and lifetime measurements were employed to characterize these samples. The results reveal that the as-prepared CaTiO₃:Pr³⁺ phosphors are spherical with submicron particle size. The particles show a strong red emission corresponding to ¹D₂–³H₄ (612 nm) of Pr³⁺ under the ultraviolet excitation (325 nm) and low voltage electron beams (1–5 kV). Furthermore, the morphology, PL and CL intensities of the CaTiO₃:Pr³⁺ phosphors can be tuned by altering the concentration of PEG, annealing temperature, and acceleration voltage. These phosphors show potential applications in the field of field emission displays (FEDs).     

Hydrothermal synthesis and characterization of a new organically templated three-dimensional open-framework gallium phosphate–phosphite (C6N2H18)2(C6N2H17)Ga15(OH)8(PO4)2(HPO4)12(HPO3)6·2H2O

Using H₃PO₃ as a phosphorus source and oxalic acid as a reducing agent, the first three-dimensional open-framework gallium phosphate–phosphite formula as (C₆N₂H₁₈)₂(C₆N₂H₁₇)Ga₁₅(OH)₈(PO₄)₂(HPO₄)₁₂(HPO₃)₆·2H₂O (1), has been hydrothermally synthesized in the presence of N,N,N′,N′-tetramethylenediamine (TMEDA) as a structure-directing agent. Compound 1 crystallizes in trigonal system with space group P ? 3, a = b = 19.046(3) Å, c = 8.3306(17) Å, γ = 120°, V = 2617.1(7) Å³, and Z = 1. Its 3-D network is based on alternated Ga-centered (GaO₄ tetrahedra, GaO₅ trigonal bipyramids, and GaO₆ octahedra) and P-centered (PO₄^3?, HPO₄^2?, and HPO₃^2?) units. Protonated organic amines and water molecules are located in the 12-membered ring channels.     

Understanding the nature of vanadium species supported on activated carbon and its catalytic properties in the aerobic oxidation of aromatic alcohols

Vanadium oxide catalysts supported on activated carbon (V/AC) with V loadings ranging from 1 to 20 wt.% were prepared by a wet-impregnation method. Various physicochemical characterization techniques, including nitrogen physisorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray absorption (XANES and EXAFS), X-ray photoelectron spectroscopy (XPS), and electron spin resonance (ESR), were employed to understand the nature of vanadium species on activated carbon. The results revealed that vanadium oxide mainly existed in a highly dispersed state for 10 wt.% or less vanadium loadings; a large amount of vanadium resulted in aggregated microcrystalline phase. Vanadium species on activated carbon surface showed a similar local coordination structure to that of NH₄VO₃ with a distorted tetrahedral symmetry at low vanadium loadings, whereas octahedral coordination was dominant at high vanadium loadings (>10 wt.%). All V/AC samples showed V⁵⁺ as the major oxidation state. Nevertheless, V⁴⁺ centered in a distorted tetrahedral symmetry could be detected at a vanadium loading greater than 4 wt.%. The catalytic activity for the benzyl alcohol oxidation largely depended on the dispersion, oxidation state, and local coordination of vanadium oxides on activated carbon. Highly dispersed vanadium (5+) species with a distorted tetrahedral coordination were postulated to account for the excellent catalytic performances of V/AC catalysts (TOF = 39.1 h^?1).     

A label-free electrochemical RNA aptamer for selective detection of theophylline

In this work, we report a novel electrochemical RNA aptamer for the selective detection of theophylline. Firstly, gold nanoparticles were electrodeposited on the surface of glassy carbon (GC) electrode to form a gold nanoparticles modified electrode. Secondly, the designed single-stranded RNA (ssRNA) was immobilized on gold nanoparticles through a thiol linker as a probe RNA. Then, the complement stranded RNA, which can combine with the probe ssRNA to form a double-stranded RNA (dsRNA) with a recognition unit of theophylline, was linked on the probe RNA through a hybrid reaction in the presence of theophylline. Doxorubicin was selected as an electrochemical indicator. The proposed RNA aptamer presents an excellent selectivity for the detection of theophylline. The detectable concentration range of theophylline is from 2.0 to 50.0 μM with a limit of detection of 1.2 μM.