Enantioselective Synthesis of Polycyclic Carbocycles via an Alkynylation-Allylation-Cyclization Strategy

A new general three-stage strategy to access polycyclic ring systems bearing all-carbon quaternary centers with high enantioselectivity is reported. The required starting materials were readily accessed in racemic form through the alpha-alkynylation of ketoesters with EBX (EthynylBenziodoXolone) hypervalent iodine reagents. A Pd-catalyzed asymmetric decarboxylation allylation was then achieved in high yields and enantioselectivities with Trosts biphosphine ligands. Finally, transition-metal catalyzed cyclization of the obtained chiral enynes gave access to fused and spiro polycyclic ring systems constituting the core of many bioactive natural products

Method for nmr spectrometry or mri measurement using dissolution dynamic nuclear polarization (dnp) with scavenging of free radicals

PROBLEM TO BE SOLVED: To provide a method for extending longitudinal relaxation time and transverse relaxation time in nuclear magnetic resonance (NMR), while removing free radicals from hyperpolarized solution. SOLUTION: A method for preparing samples for magnetic resonance measurement by using dissolution dynamic nuclear polarization-based hyperpolarization, includes the step (1.1) to prepare frozen beads of a first kind containing paramagnetic substances in addition to a solute under examination; the step (2.1) to insert the frozen beads into a polarization magnet; the step (3.1) to create a higher polarization state of the nuclei in a magnetic field; the step (4.1) to heat the sample up to room temperature, the step (5.1) to transfer samples into MR magnet; and the step (6.1) to perform MR measurement. Further, additional steps are included, the step (1.2) to prepare frozen beads of a second kind containing a reduction agent, and the step (2.2) to insert the frozen beads of a second kind together with the frozen beads of the first kind into the polarization magnet. ;COPYRIGHT: (C)2011,JPO&INPI

Full House: Microbial and Nonmicrobial Volatile Organic Compounds Competing for “Residency” in Indoor Environments at Cycling Relative Humidity

Office of the VP for Researc

Photochromic Torsional Switch (PTS): a Light-Driven Actuator for the Dynamic Tuning of π-Conjugation Extension

Here we present a molecular architecture that can reversibly change the geometric conformation of its π-system backbone via irradiation with two different wavelengths. The proposed ‘molecular actuator’ consists of a photoswitchable azobenzene orthogonally connected to a π-conjugated bithiophene by both direct and aliphatic linker-assisted bonding. Upon exposure to 350 nm light, the trans azobenzene moiety isomerizes to its cis form, causing the bithiophene to assume a semiplanar anti conformation (extended π-conjugation). Exposure to 254 nm light promotes the isomerization of the azobenzene unit back to its initial extended trans conformation, thus forcing the bithiophene fragment to twist out of coplanarity (restricted π-conjugation). The molecular conformation of the bithiophene was characterized using steady-state UV-Vis and nuclear magnetic resonance spectroscopy, as well as ab initio computations. The proposed molecular design could be envisaged as a π-conjugation modulator, which has potential to be incorporated into extended linear π-systems, i.e. via the terminal alfa-thiophene positions, and used to tune their optical and electronic properties

Dynamic nuclear polarization of quadrupolar nuclei using cross polarization from protons: surface-enhanced aluminium-27 NMR

The surface of gamma-alumina nanoparticles can be characterized by dynamic nuclear polarization (DNP) surface-enhanced NMR of Al-27. DNP is combined with cross-polarization and MQ-MAS to determine local symmetries of Al-27 sites at the surface

Using Predefined M₃(μ₃‑O) Clusters as Building Blocks for an Isostructural Series of Metal–Organic Frameworks

Metal–organic frameworks (MOFs) have attracted much attention in the past decade owing to their unprecedented internal surface areas, tunable topologies, designable surfaces, and various potential applications. One bottleneck in the field regarding MOF synthesis is controlling the metal-containing secondary building unit (SBU) incorporated into the structure. In this work we report the synthesis and characterization of five trimeric [M₃(μ₃-O)­(CH₃CO₂)₆]^<i>x</i> clusters (where M = Fe³⁺, Cr³⁺, Fe³⁺/Cr³⁺, Fe³⁺/Co²⁺, or Fe³⁺/Ni²⁺ and <i>x</i> = +1 or 0). The monocarboxylate capping ligand, acetate in this case, readily undergoes exchange with several difunctional counterparts, including 1,4-benzene­dicarboxylic acid (H₂-BDC) and biphenyl-4,4′-dicarboxylic acid (H₂-BPDC), for the formation of an isostructural series of MOFs, several of which are newly reported (for M = Fe³⁺/Cr³⁺, Fe³⁺/Co²⁺, and Fe³⁺/Ni²⁺) and show excellent CO₂ adsorption properties. In this report, a host of techniques including NMR, ICP, and ESI-MS are used to probe the ligand exchange process and composition of the SBUs, and XAS is used to monitor the Fe³⁺ and Cr³⁺ environment throughout the reactions, giving strong evidence that the clusters stay intact throughout the MOF synthesis. This work reveals that predefined SBUs is an effective means to create metal-substituted analogues of known frameworks. Further, CO adsorption and in situ IR are used to probe accessibility of the metals after solvent removal. We show for the first time that the incorporation of the neutral clusters, containing weaker Lewis acids like Ni²⁺ and Co²⁺, can promote the formation of open metal sites in the MOF frameworks, structural features known to enhance the binding energy of small guest molecules like CO₂

Limit of detection: Phantom with TFA.

<p>(A) Concentration in M of TFA per well. (B) Equivalent number of ¹⁹F atoms per well. (C) Axial view of the tubes. Upper panels: ¹⁹F images acquired; lower panels: ¹⁹F and ¹H overlaid images. Voxel volume: 0.63mm³. (D) Coronal view of the tubes, ¹H images. (E) Mean SNR in the region of interest (ROI) with respect to ¹⁹F atoms/voxel. Each line corresponds to the acquisition of a slice as shown in panel D.</p