Theoretical insight into stereoselective reaction mechanisms of 2,4-pentanediol-tethered ketene-olefin [2 + 2] cycloaddition

We report ab initio molecular dynamics calculations based on density functional theory performed on an intramolecular [2 + 2] cycloaddition between ketene and olefin linked with a 2,4-pentanediol (PD) tether. We find that the encounter of the ketene and olefin moieties could be prearranged in the thermal equilibrated state before the cycloaddition. The reaction mechanism is found to be stepwise, similar to that of intermolecular ketene [2 + 2] cycloadditions with ordinary alkenes. A distinct feature of the reaction pathway for a major diastereoisomer is a differential activation free energy of about 1.5 kcal/mol, including 2.8 kcal/mol as the differential activation entropy, with a transition state consisting of a flexible nine-membered ring in the olefin-PD-ketene moiety. This theoretical study provides a reasonable explanation for the strict stereocontrollability of the PD-tethered ketene-olefin cycloaddition, irrespective of reaction types or conditions.     

Label‐Free Amperometric Detection of Albumin with an Oil/Water‐type Flow Cell for Urine Protein Analysis

The 1,2‐dichloroethane (DCE)/water interface, with an anionic surfactant, dinonylnaphthalenesulfonate (DNNS^?), being present in DCE, was utilized for label‐free detection of albumin. An oil/water‐type flow cell was prepared using a porous PTFE tube and dipping the tube in the DCE solution containing DNNS^?. This flow cell provided a well‐defined current response linear to the albumin concentration up to 10 µM with a detection limit of 1.2 µM. The current response is due to the interfacial adsorption of albumin molecules depending on the Galvani potential difference. Possible interference from creatinine in the urine could be avoided by a conventional dialysis treatment.     

Iron-catalyzed alkyl-alkyl suzuki-miyaura coupling

Chemoselective Suzuki-Miyaura coupling of primary and secondary alkyl halides is realized by using an iron/Xantphos catalyst. Primary and secondary alkyl bromides undergo the reaction to give the coupling products in good yields. Application to the synthesis of long-chain fatty acid derivatives is also described.     

Hyperstoichiometric interaction between silver and mercury at the nanoscale

Breaking through the stoichiometry barrier: as the diameter of silver particles is decreased below a critical size of 32 nm, the molar ratio of aqueous Hg(II) to Ag(0) drastically increases beyond the conventional Hg/Ag ratio of 0.5:1, leading to hyperstoichiometry with a maximum ratio of 1.125:1. Therein, around 99% of the initial silver is retained to rapidly form a solid amalgam with reduced mercury.     

Goeritz invariants of pretzel links

The Goeritz matrix of a connected link diagram is diagonalized to a normal form by the elementary divisor theory. The integer sequence given by the diagonal entries of this form is a link invariant called the Georitz invariant. In this paper, we study the Goeritz invariants of pretzel links.     

Experimental investigation of flame spreading over pure methane hydrate in a laminar boundary layer

Flame spreading over pure methane hydrate in a laminar boundary layer is investigated experimentally. The free stream velocity (U_∞) was set constant at 0.4 m/s and the surface temperature of the hydrate at the ignition (T_s) was varied between ?10 and ?80 °C. Hydrate particle sizes were smaller than 0.5 mm. Two types of flame spreading were observed; “low speed flame spreading” and “high speed flame spreading”. The low speed flame spreading was observed at low temperature conditions (T_s = ?80 to ?60 °C) and temperatures in which anomalous self-preservation took place (T_s = ?30 to ?10 °C). In this case, the heat transfer from the leading flame edge to the hydrate surface plays a key role for flame spreading. The high speed flame spreading was observed when T_s = ?50 and ?40 °C. At these temperatures, the dissociation of hydrate took place and the methane gas was released from the hydrate to form a thin mixed layer of methane and air with a high concentration gradient over the hydrate. The leading flame edge spread in this premixed gas at a spread speed much higher than laminar burning velocity, mainly due to the effect of burnt gas expansion.     

Production Spectra of the ΣNN Quasibound States in 3He(K −, π ∓) Reactions

We theoretically demonstrate the inclusive and semiexclusive spectra in the ³He (K ^?, π ^?) reactions at 600 MeV/c (4°) within a distorted-wave impulse approximation, using a coupled (2N ? Λ) + (2N ? Σ) model with a spreading potential. It is shown that a signal of a ${^3_\Sigma{\rm He}}$ quasibound state is clearly observed near the Σ threshold in the π ^? spectrum, whereas a peak of a ${^3_\Sigma{\rm n}}$ quasibound state is relatively reduced in the π ⁺ spectrum. The mechanism of Σ production for these spectra is discussed.     

Immobilizing single lipid and channel molecules in artificial lipid bilayers with annexin A5

The effects of annexin A5 on the lateral diffusion of single-molecule lipids and single-molecule proteins were studied in an artificial lipid bilayer membrane. Annexin A5 is a member of the annexin superfamily, which binds preferentially to anionic phospholipids in a Ca2+-dependent manner. In this report, we were able to directly monitor single BODIPY 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DHPE) and ryanodine receptor type 2 (RyR2) labeled with Cy5 molecules in lipid bilayers containing phosphatidylserine (PS) by using fluorescence microscopy. The diffusion coefficients were calculated at various annexin A5 concentrations. The diffusion coefficients of BODIPY-DHPE and Cy5-RyR2 in the absence of annexin A5 were 4.81 x 10(-8) cm(2)/s and 2.13 x 10(-8) cm(2)/s, respectively. In the presence of 1 microM annexin A5, the diffusion coefficients of BODIPY-DHPE and Cy5-RyR2 were 2.2 x 10(-10) cm(2)/s and 9.5 x 10(-11) cm(2)/s, respectively. Overall, 1 microM of annexin A5 was sufficient to induce a 200-fold decrease in the lateral diffusion coefficient. Additionally, we performed electrophysiological examinations and determined that annexin A5 has little effect on the function of RyR2. This means that annexin A5 can be used to immobilize RyR2 in a lipid bilayer when imaging and analyzing RyR2.     

Influence of dissolved-air concentration on spatial distribution of bubbles for sonochemistry

The pulsation of ultrasonic cavitation bubbles at various dissolved-air concentration in a sonochemical reaction field of standing-wave type is investigated experimentally by laser-light scattering. When a thin light sheet, finer than half the wavelength of sound, is introduced into the cavitation bubbles at an antinode of sound pressure, the scattered light intensity oscillates. The peak-to-trough light intensity is correlated with the number of bubbles that contribute to the sonochemical reaction. It is shown that as the dissolved air concentration becomes higher, the weighted center of the spatial distribution of the peak-to-trough intensity tends to shift towards the liquid surface. At higher concentration of the dissolved air, a great deal of bubbles with size distribution generated due to coalescence between bubbles disturbs sound propagation to change the sound phase easily. A standing wave to trap tiny oscillating bubbles is established only at the side which is nearer to the liquid surface. Also at higher concentration, liquid flow induced by drag motion of bubbles by the action of radiation force becomes apparent and position-unstable region of bubble is enlarged from the side of sound source towards the liquid surface. Therefore, the position of oscillating bubbles active for sonochemical reaction is limited at the side which is nearer to the liquid surface at higher concentration of the dissolved air.