p-Siletanylbenzylidene acetal: oxidizable protecting group for diols

[reactions: see text] Hydrogen peroxide oxidation of benzylidene acetals (and derivative benzyl ethers) that incorporate a siletane ring at the para position creates a deprotection pathway without affecting other important chemical properties of the benzylidene acetal, such as regioselective reductive ring opening.     

Stable Oxypyridinium Triflate (OPT) Salts for the Synthesis of Halobenzyl Ethers

A collection of new oxypyridinium triflate reagents (1a–d) for the synthesis of halobenzyl ethers from alcohols under “mix‐and‐heat” conditions is described. The reagents are stable organic salts that can be stored indefinitely and handled without special precautions, making them attractive for general use in organic synthesis. Halobenzylation of representative alcohols occurs in good to excellent yield.     

Effect of direct current dielectrophoresis on the trajectory of a non-conducting colloidal sphere in a bent pore

Dielectrophoresis has shown a wide range of applications in microfluidic devices. Force approximations utilizing the point-dipole method in dielectrophoresis have provided convenient predictions for particle motion by neglecting interactions between the particle and its surrounding electric and flow fields. The validity of this approach, however, is unclear when the particle size is comparable to the characteristic length of the channel and when the particle is in close proximity to the channel wall. To address this issue, we apply an accurate numerical approach based on the boundary-element method (BEM) to solve the coupled electric field, flow, and particle motion. This method can handle much closer particle-wall distances than the other numerical approaches such as the finite-element method. Using the BEM and integrating the Maxwell stress tensor, we simulate an electrokinetic, spherical particle moving within a bent cylindrical pore to investigate how the dielectrophoretic force affects the particle's trajectory. In the simulation, both the particle and the channel wall are non-conducting, and the electric double layers adjacent to the solid surfaces are assumed to be thin with respect to the particle radius and particle-wall gap. The results show that as the particle comes close to the wall, its finite size has an increasingly important effect on its own transient motion and the point-dipole approximation may lead to significant error.     

A Photoaffinity-Based Fragment-Screening Platform for Efficient Identification of Protein Ligands

Advances in genomic analyses enable the identification of new proteins that are associated with disease. To validate these targets, tool molecules are required to demonstrate that a ligand can have a disease-modifying effect. Currently, as tools are reported for only a fraction of the proteome, platforms for ligand discovery are essential to leverage insights from genomic analyses. Fragment screening offers an efficient approach to explore chemical space. Presented here is a fragment-screening platform, termed PhABits (PhotoAffinity Bits), which utilizes a library of photoreactive fragments to covalently capture fragment–protein interactions. Hits can be profiled to determine potency and the site of crosslinking, and subsequently developed as reporters in a competitive displacement assay to identify novel hit matter. The PhABit platform is envisioned to be widely applicable to novel protein targets, identifying starting points in the development of therapeutics.     

Diastereoselective reductive aldol reactions of Boc-protected electron deficient pyrroles

An anti-selective reductive aldol reaction of a Boc-protected, 2-substituted pyrrole is reported. Reduction with LiDBB generates an exocyclic lithium enolate, but optimal stereoselectivity is obtained by transmetallation to magnesium with MgBr₂·OEt₂. The corresponding syn-aldols can easily be obtained (protected as carbamates) by subsequent inversion.     

Application of low field NMR T2 measurements to clathrate hydrates

Low field (2 MHz) Nuclear Magnetic Resonance (NMR) proton spin–spin relaxation time (T₂) distribution measurements were employed to investigate tetrahydrofuran (THF)—deuterium oxide (D₂O) clathrate hydrate formation and dissociation processes. In particular, T₂ distributions were obtained at the point of hydrate phase transition as a function of the co-existing solid/liquid ratios. Because T₂ of the target molecules reflect the structural arrangements of the molecules surrounding them, T₂ changes of THF in D₂O during hydrate formation and dissociation should yield insights into the hydrate mechanisms on a molecular level. This work demonstrated that such T₂ measurements could easily distinguish THF in the solid hydrate phase from THF in the coexisting liquid phase. To our knowledge, this is the first time that T₂ of guest molecules in hydrate cages has been measured using this low frequency NMR T₂ distribution technique. At this low frequency, results also proved that the technique can accurately capture the percentages of THF molecules residing in the solid and liquid phases and quantify the hydrate conversion progress. Therefore, an extension of this technique can be applied to measure hydrate kinetics. It was found that T₂ of THF in the liquid phase changed as hydrate formation/dissociation progressed, implying that the presence of solid hydrate influenced the coexisting fluid structure. The rotational activation measured from the proton response of THF in the hydrate phase was 31 KJ/mole, which agreed with values reported in the literature.     

Kinetic analysis of the decomposition of piperidinium hexathiocyanoatochromate(III)

Summary The decomposition of piperidinium hexathiocyanatochromate(III), (pipH)₃[Cr(NCS)₆](s), into Cr(NCS)₃(s) and pipHSCN(g) has been studied isothermally and nonisothermally using t.g.a. Data from isothermal studies were analysed according to 17 different kinetic models and the (, T) data from nonisothermal experiments were analysed using 12 rate laws by the procedure of Reich and Stivala. It was found that while a first-order rate law gave the best fit to the data obtained from isothermal and nonisothermal experiments most frequently, considerable variation exists for both types of experiments. Using the first order model, the activation energy was found to be 77.2 ±4.4kJ mol^–1.