Aminopropyl group-modified SBA-15 covalent attachment Mn(salen) complexes as catalysts for styrene epoxidation

<p>A series of aminopropyl group-modified ordered mesoporous silica materials impregnated with Mn(salen) were prepared using successive grafting procedures. The prepared composite catalysts were well characterized by inductively coupled plasma atomic emission spectroscopy, Fourier transform-infrared, UV–Vis diffuse reflectance spectroscopy, X-ray diffraction analysis, and transmission electron microscopy in order to confirm the structure integrities of the Mn(salen) units after the incorporation, to evidence the formation of a covalent bond between the starting Mn(salen) units and the aminopropyl group-modified SBA-15 matrix in the presence of NaOH by abstraction of an HCl molecule. These heterogeneous catalysts exhibited comparable catalytic activity and selectivity to those of the homogeneous counterpart in the epoxidation of styrene by using NaClO as oxidant. In addition, the effects of key reaction parameters, including the loadings of the neat Mn(salen), molar ratios of NaClO to styrene, and PPNO amount on the reactivity and selectivity, were also studied. Finally, the reusability of the prepared heterogeneous catalyst was evaluated.</p

Table_1_A Novel Iron Transporter SPD_1590 in Streptococcus pneumoniae Contributing to Bacterial Virulence Properties.DOCX

<p>Streptococcus pneumoniae, a Gram-positive human pathogen, has evolved three main transporters for iron acquisition from the host: PiaABC, PiuABC, and PitABC. Our previous study had shown that the mRNA and protein levels of SPD_1590 are significantly upregulated in the ΔpiuA/ΔpiaA/ΔpitA triple mutant, suggesting that SPD_1590 might be a novel iron transporter in S. pneumoniae. In the present study, using spd1590-knockout, -complemented, and -overexpressing strains and the purified SPD_1590 protein, we show that SPD_1590 can bind hemin, probably supplementing the function of PiuABC, to provide the iron necessary for the bacterium. Furthermore, the results of iTRAQ quantitative proteomics and cell-infection studies demonstrate that, similarly to other metal-ion uptake proteins, SPD_1590 is important for bacterial virulence properties. Overall, these results provide a better understanding of the biology of this clinically important bacterium.</p

Molecular Turnstiles Regulated by Metal Ions

A family of novel molecular turnstiles <b>1</b>–<b>3</b> composed of two stators with pyridyl binding sites and a different-sized triptycene rotor was synthesized. The molecular turnstiles behave in an open state at room temperature in the absence of metal ions but display significantly different closed states in the presence of Ag⁺ and Pd²⁺. The Ag⁺-mediated turnstiles <b>1</b>–<b>3Ag</b> exhibited closed states but unreadable bistability at ambient temperature because the Ag⁺-mediated macrocyclic framework is not able to restrict the rotations of the rotors; while temperature was decreased, the macrocyclic frameworks became stable enough to halt the rotations of the rotors, eventually leading to the readable closed states for <b>1</b>–<b>3Ag</b>. In contrast, Pd²⁺-mediated macrocyclic frameworks are stable, giving rise to a detectable closed state of turnstiles <b>1</b>–<b>3Pd</b> in a wide range of temperatures. These findings have also been supported by DFT calculations

Molecular Turnstiles Regulated by Metal Ions

A family of novel molecular turnstiles <b>1</b>–<b>3</b> composed of two stators with pyridyl binding sites and a different-sized triptycene rotor was synthesized. The molecular turnstiles behave in an open state at room temperature in the absence of metal ions but display significantly different closed states in the presence of Ag⁺ and Pd²⁺. The Ag⁺-mediated turnstiles <b>1</b>–<b>3Ag</b> exhibited closed states but unreadable bistability at ambient temperature because the Ag⁺-mediated macrocyclic framework is not able to restrict the rotations of the rotors; while temperature was decreased, the macrocyclic frameworks became stable enough to halt the rotations of the rotors, eventually leading to the readable closed states for <b>1</b>–<b>3Ag</b>. In contrast, Pd²⁺-mediated macrocyclic frameworks are stable, giving rise to a detectable closed state of turnstiles <b>1</b>–<b>3Pd</b> in a wide range of temperatures. These findings have also been supported by DFT calculations

Flexible, Linear Chains Act as Baffles To Inhibit the Intramolecular Rotation of Molecular Turnstiles

In artificial molecular devices, flexible, linear chains typically exhibit very weak capability in inhibiting molecular motion. Herein, we describe the dynamic properties of a series of molecular turnstiles consisting of a rigid frame and a phenyl rotator flanked with linear alkoxy­methyl substituents. The long, flexible substituents act as elastic baffles to inhibit the rotations of the rotator at medium to fast speeds on the NMR time scale. When the rotator moves slowly, the substituents become more relaxed, thus obtaining an opportunity to completely thread through the cavity of the turnstiles. These findings reveal a basic but missing correlation between steric hindrance and speed of motion for flexible, linear chains in dynamic molecular devices, thus opening up a new direction toward molecular machines with more elaborate dynamic functions

Flexible, Linear Chains Act as Baffles To Inhibit the Intramolecular Rotation of Molecular Turnstiles

In artificial molecular devices, flexible, linear chains typically exhibit very weak capability in inhibiting molecular motion. Herein, we describe the dynamic properties of a series of molecular turnstiles consisting of a rigid frame and a phenyl rotator flanked with linear alkoxy­methyl substituents. The long, flexible substituents act as elastic baffles to inhibit the rotations of the rotator at medium to fast speeds on the NMR time scale. When the rotator moves slowly, the substituents become more relaxed, thus obtaining an opportunity to completely thread through the cavity of the turnstiles. These findings reveal a basic but missing correlation between steric hindrance and speed of motion for flexible, linear chains in dynamic molecular devices, thus opening up a new direction toward molecular machines with more elaborate dynamic functions

Highly Sensitive Surface-Enhanced Raman Spectroscopy (SERS) Platforms Based on Silver Nanostructures Fabricated on Polyaniline Membrane Surfaces

Here, we demonstrate a facile synthesis of homogeneous Ag nanostructures fully covering the polyaniline (PANI) membrane surface simply by introducing organic acid in the AgNO₃ reaction solution, as an improved technique to fabricate well-defined Ag nanostructures on PANI substrates through a direct chemical deposition method [<i>Langmuir</i> <b>2010</b>, <i>26</i>, 8882]. It is found that the chemical nature of the acid is crucial to create a homogeneous nucleation environment for Ag growth, where, in this case, homogeneous Ag nanostructures that are assembled by Ag nanosheets are produced with the assistance of succinic acid and lactic acid, but only scattered Ag particles with camphorsulfonic acid. Improved surface wettability of PANI membranes after acid doping may also account for the higher surface coverage of Ag nanostructures. The Ag nanostructures fully covering the PANI surface are extremely sensitive in the detection of a target analyte, 4-mercaptobenzoic acid (4-MBA), using surface-enhanced Raman spectroscopy (SERS), with a detection limit of 10^–12 M. We believe the facilely fabricated SERS-active substrates based on conducting polymer-mediated growth of Ag nanostructures can be promising in the trace detection of chemical and biological molecules