Magnetohydrodynamic pressure drop in ducted two-phase flows

Two models are presented for predicting magnetohydrodynamic pressure drop in two phase gas—liquid flows of conducting fluids for large values of Hartmann number. The first of these models treats the gas—liquid mixture as a single homogeneous pseudofluid with averaged mixture properties. The second model assumes that the flow pattern is one where the liquid is displaced to the duct walls as a liquid film and the gas flows in the central core. It is shown that the two models do not differ significantly in their predictions of overall pressure drop for vaporising two-phase flow of potassium. There is little experimental data available for testing the models but very satisfactory agreement is found between measurements of magnetic pressure drop of NaK—nitrogen mixtures at low quality and the predictions of both models.     

Metal-organic framework from an anthracene derivative containing nanoscopic cages exhibiting high methane uptake

A microporous metal-organic framework, PCN-14, based on an anthracene derivative, 5,5'-(9,10-anthracenediyl)di-isophthalate (H4adip), was synthesized under solvothermal reaction conditions. X-ray single crystal analysis revealed that PCN-14 consists of nanoscopic cages suitable for gas storage. N2-adsorption studies of PCN-14 at 77 K reveal a Langmuir surface area of 2176 m2/g and a pore volume of 0.87 cm3/g. Methane adsorption studies at 290 K and 35 bar show that PCN-14 exhibits an absolute methane-adsorption capacity of 230 v/v, 28% higher than the DOE target (180 v/v) for methane storage.     

A fast synthetic route to GDP-sugars modified at the nucleobase

The direct structural modification of GDP-mannose via the bromination and Suzuki-Miyaura cross-coupling of the unprotected sugar-nucleotide, to produce 8-substituted fluorescent analogues of GDP-mannose.     

Metal-organic framework based on a trinickel secondary building unit exhibiting gas-sorption hysteresis

An interpenetrating microporous metal-organic framework based on a mu3-oxotrinickel basic carboxylate secondary building unit has been synthesized and structurally characterized. It exhibits pronounced gas-sorption hysteresis and selective adsorption of carbon dioxide over methane.     

Ab initio studies of push–pull systems

Twelve push–pull ethylene derivatives, NH₂CH=CHX, NH₂C≡CCH=CHX, and ⁻OCHX=CHX (with X=BH₂, C≡N, NO₂, and CH₂ ⁺) have been studied by ab initio calculations. The rotational barrier around the central double bond was chosen as a probe for push–pull effects, as push–pull effects would remove electron density from the central double bond. The amount of reduction of double bond character will increase with the contribution of the zwitterionic resonance hybrid structure. Complete geometry optimizations and calculations of vibrational frequencies were performed for all minima and transition state structures of these 12 systems. The calculations were carried out with the B3LYP and MP2 methods using the 6-311+G(d,p) and the 6-311++G(d,p) basis sets. All the systems investigated exhibited properties consistent with push–pull effects such as elongated C=C double bonds, dipolar electronic structures, and reduced barriers to internal rotation.     

Ortho‐Stabilized 18F‐Azido Click Agents and their Application in PET Imaging with Single‐Stranded DNA Aptamers

Azido ¹⁸F‐arenes are important and versatile building blocks for the radiolabeling of biomolecules via Huisgen cycloaddition (“click chemistry”) for positron emission tomography (PET). However, routine access to such clickable agents is challenged by inefficient and/or poorly defined multistep radiochemical approaches. A high‐yielding direct radiofluorination for azido ¹⁸F‐arenes was achieved through the development of an ortho‐oxygen‐stabilized iodonium derivative (OID). This OID strategy addresses an unmet need for a reliable azido ¹⁸F‐arene clickable agent for bioconjugation reactions. A ssDNA aptamer was radiolabeled with this agent and visualized in a xenograft mouse model of human colon cancer by PET, which demonstrates that this OID approach is a convenient and highly efficient way of labeling and tracking biomolecules.