Remarkable effects of terminal groups and solvents on helical folding of o-phenylene oligomers

Although o-phenylene oligomers (OP(n)R) made of dimethoxyphenylene units are thought to be intrinsically dynamic due to π-electronic repulsion, we show that they fold into a regular helical geometry in CH(3)CN when they carry terminal groups such as CH(3), CH(2)OH, Br, CO(2)Bn, and NO(2). We evaluated their helical inversion kinetics via optical resolution of long-chain oligomers (e.g. 16- and 24-mers) by chiral HPLC. OP(24)Br at 298 K shows a half-life for the optical activity of 5.5 h in CH(3)OH/water (7/3 v/v) and requires 34 h for complete racemization. The perfectly folded helical conformers of OP(n)R, unlike their imperfectly folded ones, are devoid of extended π-conjugation and show a cyclic voltammogram featuring reversible multistep oxidation waves.     

Synthesis and Characterization of the Crystal Structure and Magnetic Properties of the New Fluorophosphate LiNaCo[PO(4)]F

The new compound LiNaCo[PO(4)]F was synthesized by a solid state reaction route, and its crystal structure was determined by single-crystal X-ray diffraction measurements. The magnetic properties of LiNaCo[PO(4)]F were characterized by magnetic susceptibility, specific heat, and neutron powder diffraction measurements and also by density functional calculations. LiNaCo[PO(4)]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9334(6), b = 6.2934(11), c = 11.3556(10) ?, and Z = 8. The structure consists of edge-sharing CoO(4)F(2) octahedra forming CoFO(3) chains running along the b axis. These chains are interlinked by PO(4) tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The magnetic susceptibility follows the Curie-Weiss behavior above 60 K with θ = -21 K. The specific heat and magnetization measurements show that LiNaCo[PO(4)]F undergoes a three-dimensional magnetic ordering at T(mag) = 10.2(5) K. The neutron powder diffraction measurements at 3 K show that the spins in each CoFO(3) chain along the b-direction are ferromagnetically coupled, while these FM chains are antiferromagnetically coupled along the a-direction but have a noncollinear arrangement along the c-direction. The noncollinear spin arrangement implies the presence of spin conflict along the c-direction. The observed magnetic structures are well explained by the spin exchange constants determined from density functional calculations.     

New insight into mesoporous silica for nano metal-organic framework

In this paper the particle volume fraction and temperature dependence of the dynamic viscosity of highly concentrated transformer oil based magnetic nanofluids was investigated in the absence of an external magnetic field. The solid particle volume fraction dependence of the relative viscosity was found to be very well fitted by the Krieger-Dougherty formula, whence the mean ellipticity of the colloidal particles and the effective surfactant layer thickness were obtained. Using the information on the particles' size and shape statistics obtained from TEM, DLS and magnetogranulometry investigations, it was concluded that the magnetite nanoparticles agglomerate in small clusters of about 1.3 particles/cluster, due to the van der Waals interactions. The effective thickness of the oleic acid surfactant layer was estimated as about 1.4 nm, in very good agreement with the value resulted from previous SANS investigations.     

N-(2-Alkoxyphenyl)-substituted double rhodanine indoline dyes for zinc oxide dye-sensitized solar cell

The effect of N-(2-alkoxyphenyl) group in double rhodanine indoline dye on the performance of zinc oxide dye-sensitized solar cell was examined. Both J_sc and V_oc were improved by introducing long alkoxy group due to prevention of H-aggregates formation and inhibition of electron recombination from zinc oxide surface to electrolyte.     

Energy and electron transfer from fluorescent mesostructured organosilica framework to guest dyes

Energy and electron transfer from frameworks of nanoporous or mesostructured materials to guest species in the nanochannels have been attracting much attention because of their increasing availability for the design and construction of solid photofunctional systems, such as luminescent materials, photovoltaic devices, and photocatalysts. In the present study, energy and electron-transfer behavior of dye-doped periodic mesostructured organosilica films with different host-guest arrangements were systematically examined. Fluorescent tetraphenylpyrene (TPPy)-silica mesostructured films were used as a host donor. The location of guest perylene bisimide (PBI) dye molecules, acting as an acceptor, could be controlled on the basis of the molecular design of the PBI substituent groups. PBI dyes with bulky substituents and polar anchoring groups were located at the pore surface with low self-aggregation, which induced efficient energy or electron transfer because of the close host-guest arrangement. However, PBI dye with bulky and hydrophobic substituents was located in the center of template surfactant micelles; the fluorescence emission from the host TPPy groups was hardly quenched when the host-guest distance was longer than the critical F?rster radius (ca. 4.5 nm). The relationship between the energy or electron-transfer efficiency and the location of guest species in the channels of mesostructured organosilica was first revealed by molecular design of the PBI substituents.     

Adaptive basis expansion via \ell _1 trend filtering

We propose a new approach for nonlinear regression modeling by employing basis expansion for the case where the underlying regression function has inhomogeneous smoothness. In this case, conventional nonlinear regression models tend to be over- or underfitting, where the function is more or less smoother, respectively. First, the underlying regression function is roughly approximated with a locally linear function using an \(\ell _1\) penalized method, where this procedure is executed by extending an algorithm for the fused lasso signal approximator. We then extend the fused lasso signal approximator and develop an algorithm. Next, the residuals between the locally linear function and the data are used to adaptively prepare the basis functions. Finally, we construct a nonlinear regression model with these basis functions along with the technique of a regularization method. To select the optimal values of the tuning parameters for the regularization method, we provide an explicit form of the generalized information criterion. The validity of our proposed method is then demonstrated through several numerical examples.     

A 2.75-approximation algorithm for the unconstrained traveling tournament problem

A 2.75-approximation algorithm is proposed for the unconstrained traveling tournament problem, which is a variant of the traveling tournament problem. For the unconstrained traveling tournament problem, this is the first proposal of an approximation algorithm with a constant approximation ratio. In addition, the proposed algorithm yields a solution that meets both the no-repeater and mirrored constraints. Computational experiments show that the algorithm generates solutions of good quality.     

Stereoselective synthesis of N,N-acetals by cyclization of an N-acyliminium ion through interaction with an N-sulfonyl group

A new method for the stereoselective synthesis of five- and six-membered bicyclic N,N-acetals with trans configuration was developed using N-acyliminium ion cyclization. The N-sulfonyl substituted compounds were effectively cyclized to give the corresponding acetals in high yields and stereoselectivities, suggesting that the intramolecular interaction between the iminium and the sulfonyl group plays a key role in the cyclization.     

Asymmetric synthesis of 2-alkyl-4-hydroxycyclohex-2-en-1-ones by scandium(III) triflate-catalyzed fragmentation of 2-alkyl-3-iodo-1-oxocyclohexan-2,4-carbolactones

Fragmentation of (2S,3S,4S)-2-allyl-3-iodo-1-oxocyclohexan-2,4-carbolactone to (4S)-2-allyl-4-hydroxycyclohex-2-en-1-one, a chiral building block of (−)-platensimycin, proceeded efficiently by using scandium(III) triflate in DMF-H₂O (1:3) at 100 °C.     

Ultra low level deep water <Superscript>137</Superscript>Cs activity in the South Pacific Ocean

We determined ¹³⁷Cs concentrations in deep water samples of the subtropical gyre in the South Pacific collected during the BEAGLE2003 cruise. This was done at an underground facility to achieve extremely low background γ-spectrometry, and we, therefore, obtained reliable values of ¹³⁷Cs activity in the deeper layers. ¹³⁷Cs activity in the layers between 2000 and 4500 m ranged from 7 ± 4 mBq m⁻³ to 25 ± 11 mBq m⁻³. The inventory of ¹³⁷Cs in the water column from 2000 m to the sea bottom was estimated to be 20 ± 8 Bq m⁻² to 94 ± 41 Bq m⁻² in this region.