Biotin-functional oligo(p-phenylene vinylene)s synthesized using click chemistry

Using Cu(1)-catalyzed [3+2] Huisgen ‘click’ cycloaddition, a rigid rod - like oligo(p-phenylene vinylene) (OPV) was functionalized at both ends with biotin ligands, combining the valuable electro-optical properties of conjugated organic molecules with the biological recognition capability of biotin. Biotin can be placed at variable distances from the oligomer via appropriate length of a hydrophilic spacer, which also serves to regulate the binding capabilities of the two terminal biotin units. To demonstrate this binding potential, networks were formed with streptavidin-coated quantum dots. The synthetic conditions are presented, together with representative optimizations of the key reactions. The organic compounds were analyzed by means of ATR/FTIR, ¹H NMR (200 or 600 MHz), ¹³C NMR, 2D NMR (HMBC, HMQC experiments), MS (ESI or MALDI-TOF), and optical spectroscopy. Networks were imaged with TEM.     

Diastéréotopies dans la série du benchrotrène

¹H and ¹³C spectra of mono-and disubstituted (benzene)-tricarbonylchromium complexes have been analysed. The influence of the substituents is discussed and special attention is paid to the diastereotopy resulting from different types of chirality. The racemic pseudosymmetric isomer and the two meso pseudoasymmetric isomers of the glycols (OC)₃CrC₆H₄(CHOHCH₃)₂ are compared. The stereochemical requirements are also examined.     

Surface electrochemistry of CO as a probe molecule on carbon-supported Se-surface modified Ru nanoparticles via infrared reflection absorption spectroscopy

The carbon monoxide molecule is used to probe the electronic properties of Ru/C and Se surface-modified Ru/C nanocatalysts. Coordination of a Se to a Ru surface strongly affects the vibrational properties and reactivity of the CO adsorbed. Marked alteration of the CO stretching frequency; increase of the Stark tuning rate for C-O vibration; and a positive shift of the onset of CO oxidation are observed for Se-modified Ru particles and attributed to the electronic effect of Se.     

Existence’s Results for Parabolic Problems Related to Fully Non Linear Operators Degenerate or Singular

In this paper we prove some existence and regularity results concerning parabolic equations

$ u_t = F(x, \nabla u, D^2 u) + f(x,t) $

with some boundary conditions, on Ω×]0, T[, where Ω is some bounded domain which possesses the exterior cone property and F is some fully nonlinear elliptic operator, singular or degenerate.

     

Tetra(diethyl)amide-p-tert-butyl-thiacalix[4]arene in Cone Conformation: Synthesis and Binding Properties with Alkali,Alkaline Earth,Heavy and Transition Metal Ions

Tetra(diethyl)amide-p-tert-butylthiacalix[4]arene 1a in the cone conformation was synthesized and its binding properties towards a large variety of metal ions were established on the basis of liquid–liquid and solid–liquid extraction as well as complexation experiments. This compound is a less efficient and selective compound than the “classical” tetra(diethyl)amide-p-tert-butylcalix[4]arene 3 in the cone conformation for alkali and alkaline earth metal ions. However, Pb²⁺ is selectively extracted and complexed within heavy and transition metal ions.     

Magnetic properties and magnetic structures of synthetic natrochalcites, NaM(II)2(D3O2)(MoO4)2, M = Co or Ni

The magnetic properties and magnetic structures from neutron diffraction of two synthetic natrochalcites, NaM(II)2(H3O2)(MoO4)2, M = Co (1Co) or Ni (2Ni), are reported. They are isostructural (monoclinic C2/m) and consist of chains of edge-shared MO6 octahedra connected by mu-O from H3O2(-) and MoO4(2-). These chains form a three-dimensional network with O-H-O, O-Mo-O, and O-Na-O bridging 4, 3, and 4 metal ions, respectively. Both compounds behave as canted antiferromagnets but differ in their behaviors, 1Co showing a broad maximum (28 K) above the Neel transition (21 K) and the canting taking place at 13 K, some 8 K below T(N), while for 2Ni the canting takes place at T(N) (28 K). Analyses of the neutron powder diffraction data shed some light on the geometry of D3O2(-) and suggest antiferromagnetism with a propagation vector k = (0,0,0) with the moments within each chain being parallel but antiparallel to those in neighboring chains. The difference between 1Co and 2Ni is in the orientation of the moments; they are parallel to the chain axis (b-axis) for 1Co and perpendicular to it for 2Ni with a major component along the c-axis and a small one along the a-axis. The heat capacity data peak at 20.9(3) K (1Co) and 25.1(1) K (2Ni). The derived magnetic entropies, following correction of the lattice contribution using the measured data for the nonmagnetic Zn analogue, suggest S = 1/2 for 1Co but is lower than that expected for 2Ni (S = 1). In both cases, only ca. 60% of the entropy is found below the magnetic ordering temperature, suggesting considerable short-range correlations at higher temperatures. While the temperature at which the magnetic diffraction becomes observable coincides with that of at the peak in heat capacity, it is lower than T(N) observed by magnetization measurements in both cases, and there is evidence of short-range ordering in a narrow range of temperature (T(N) +/- 5 K).     

Can cluster structure affect kinetic method measurements? The curious case of glutamic acid’s gas-phase acidity

The gas-phase acidities of aspartic, glutamic, and 2-aminoadipic acid have been determined by the kinetic method in a triple-quadrupole instrument. Although aspartic acid behaves in the conventional way and gives a DeltaH(acid) value of 1340 kJ mol(-1), glutamic and 2-aminoadipic acids give kinetic method plots with two distinct slopes. This leads to DeltaH(acid) values of 1350 and 1366 kJ mol(-1) for glutamic acid, and 1355 and 1369 kJ mol(-1) for 2-aminoadipic acid. The value for aspartic acid and the low collision energy value for glutamic acid are consistent with recent measurements by Poutsma and co-workers in a quadrupole ion trap. The experiments are supported by calculations at the G3(MP2) and OLYP/aug-cc-pVTZ levels. Computational studies of model clusters of the amino acids with trifluoroacetate suggest there are distinct preferences. Glutamic and 2-aminoadipic acid prefer clusters where the amino acid adopts a zwitterion-like structure whereas aspartic acid prefers to adopt a conventional (canonic) structure in its clusters. This result along with the computed stabilities of zwitterion-like conformations of the deprotonated amino acids leads to the following explanation for the presence of two slopes in the kinetic method plots. At low collision energies, the deprotonated amino acid dissociates from the cluster, with rearrangement if necessary, to give its preferred conformation, but at high collision energies, the deprotonated amino acid directly dissociates in the conformation preferred in the cluster. For glutamic and 2-aminoadipic acids, this is a zwitterion-like structure that is about 20 kJ mol(-1) less stable than the global minimum.     

An Optimal Weight Method for CT Image Denoising

This paper proposes a novel exemplar- based method for reducing noise in computed tomography （CT） images. In the proposed method, denoising is performed on each block with the help of a given database of standard image blocks. For each noisy block, its denoised version is the best sparse positive linear combination of the blocks in the database. We formulate the problem as a constrained optimization problem such that the solution is the denoised block. Experimental results demonstrate the good performance of the proposed method over current state-of-the-art denoising methods, in terms of both objective and subjective evaluations.     

A new taxane from <Emphasis Type="Italic">Taxus canadensis</Emphasis> needles

A new 6/8/6-membered taxane was isolated from the needles of Taxus canadensis. The structure was characterized as 10β,13α-diacetoxy-5α,9α-dihydroxytaxa-4(20),11-diene (1) on the basis of 1D and 2D spectrascopic data.