Self-assembly of semifluorinated dendrons attached to electron-donor groups mediates their pi-stacking via a helical pyramidal column

Semifluorinated first-generation self-assembling dendrons attached via a flexible spacer to electron-donor molecules induce pi-stacking of the donors in the center of a supramolecular helical pyramidal column. These helical pyramidal columns self-organize in various columnar liquid crystal phases that mediate self-processing of large single crystal liquid crystal domains of columns and self-repair their intracolumnar structural defects. In addition, all supramolecular columns exhibit a columnar phase at lower temperatures that maintains the helical pyramidal columnar supramolecular structure and displays higher intracolumnar order than that in the liquid crystals phases. The results described here demonstrate the universality of this concept, the power of the fluorous phase or the fluorophobic effect in self-assembly and the unexpected generality of pyramidal liquid crystals.     

Robust entanglement through macroscopic quantum jumps

We propose an entanglement generation scheme that requires neither the coherent evolution of a quantum system nor the detection of single photons. Instead, the desired state is heralded by a macroscopic quantum jump. Macroscopic quantum jumps manifest themselves as a random telegraph signal with long intervals of intense fluorescence (light periods) interrupted by the complete absence of photons (dark periods). Here we show that a system of two atoms trapped inside an optical cavity can be designed such that a dark period prepares the atoms in a maximally entangled ground state. Achieving fidelities above 0.9 is possible even when the single-atom cooperativity parameter is as low as 10 and when using a photon detector with an efficiency as low as eta=0.2.     

A new structure type of RE4B4O11F2: High-pressure synthesis and crystal structure of La4B4O11F2

The first lanthanum fluoride borate La₄B₄O₁₁F₂ was obtained in a Walker-type multianvil apparatus at 6 GPa and 1300 °C. La₄B₄O₁₁F₂ crystallizes in the monoclinic space group P2₁/c with the lattice parameters a=778.1(2) pm, b=3573.3(7) pm, c=765.7(2) pm, β=113.92(3)° (Z=8), and represents a new structure type in the class of compounds with the composition RE₄B₄O₁₁F₂. The crystal structure contains BO₄-tetrahedra interconnected with two BO₃-groups via common vertices, B₂O₅-pyroborate units, and isolated BO₃-groups. The structure shows a wave-like modulation along the b-axis. The crystal structure and properties of La₄B₄O₁₁F₂ are discussed and compared to Gd₄B₄O₁₁F₂.     

Structure alterations in microporous (Mg,Fe)2Al4Si5O18 crystals induced by energetic heavy-ion irradiation

The microporous framework structure of (Mg_1−xFe_x)₂Al₄Si₅O₁₈ (=cordierite) has been subject to a comparative study on the effect of structural alterations originating from exposure to high-energy heavy ions. Oriented samples (with x=0.061, 0.122, and 0.170) were irradiated with swift ¹²⁴Xe, ¹⁹⁷Au and ⁹⁶Ru ions with 11.1 MeV per nucleon energy and fluences of 1×10¹² and 1×10¹³ ions/cm². Irradiated and non-irradiated samples were investigated by means of X-ray diffraction, Mössbauer spectroscopy and optical absorption spectroscopy. Structural investigations reveal an essentially unchanged Al,Si ordering, which appears to be unaffected by irradiation. The most remarkable macroscopic change is the ion-beam induced colouration, which could be assigned to electronic charge transfer transitions involving the Fe cations. Mössbauer spectra indicate an increased amount of ^[4]Fe³⁺ for the irradiated sample. The most noticeable structural alteration concerns irradiation-induced dehydration of extra-framework H₂O, which is accompanied by a reduction in the molar volume by ∼0.2 vol%.     

Structure formation of surfactants in concentrated sulphuric acid: a light scattering study

A common cationic surfactant,n-hexadecylammonium hydrogensulphate, dissolved in concentrated sulphuric acid, has been studied by static and dynamic light scattering. Micelle formation has been observed even in this unusual solvent. An apparent molar mass of 45 500±4.5% was found for the aggregates. A translational diffusion coefficientD ₀=5.5×10^–9 cm²/s was measured which gave a hydrodynamically effective radius ofR _h=17.7 nm. The geometric radius of gyration wasR _g=76.2 nm. The ratioR _g/R _h=4.33 is indicative for rodlike structures. Assuming a polydispersity ofL _w/L _n=2 this corresponds to a cylinder ofL _w=152 nm. An axial ratiop _w=(L _w/d)=60.4 nm was estimated which leads to a cylinder diameter of 2.53 nm. At surfactant concentrations higher than 5% (w/vol) the rod-like micelles aggregate to form more globular structures. The time correlation function, recorded by dynamic light scattering, exhibited a two-step decay which indicates a bimodal distribution of particle sizes. The fast motion coincides with that of the micelles at low concentrations while the other is slower than the fast one by three orders of magnitude and corresponds to the translational motion of large clusters.     

Influence of terpyridine as pi-acceptor ligand on the kinetics and mechanism of the reaction of NO with ruthenium(III) complexes

The kinetics of the unusually fast reaction of cis- and trans-[Ru(terpy)(NH3)2Cl]2+ (with respect to NH3; terpy=2,2':6',2"-terpyridine) with NO was studied in acidic aqueous solution. The multistep reaction pathway observed for both isomers includes a rapid and reversible formation of an intermediate Ru(III)-NO complex in the first reaction step, for which the rate and activation parameters are in good agreement with an associative substitution behavior of the Ru(III) center (cis isomer, k1=618 +/- 2 M(-1) s(-1), DeltaH(++) = 38 +/- 3 kJ mol(-1), DeltaS(++) = -63 +/- 8 J K(-1) mol(-1), DeltaV(++) = -17.5 +/- 0.8 cm3 mol(-1); k -1 = 0.097 +/- 0.001 s(-1), DeltaH(++) = 27 +/- 8 kJ mol(-1), DeltaS(++) = -173 +/- 28 J K(-1) mol(-1), DeltaV(++) = -17.6 +/- 0.5 cm3 mol(-1); trans isomer, k1 = 1637 +/- 11 M(-1) s(-1), DeltaH(++) = 34 +/- 3 kJ mol(-1), DeltaS(++) = -69 +/-11 J K(-1) mol(-1), DeltaV(++) = -20 +/- 2 cm3 mol(-1); k(-1)=0.47 +/- 0.08 s(-1), DeltaH(++)=39 +/- 5 kJ mol(-1), DeltaS(++) = -121 +/-18 J K(-1) mol(-1), DeltaV(++) = -18.5 +/- 0.4 cm3 mol(-1) at 25 degrees C). The subsequent electron transfer step to form Ru(II)-NO+ occurs spontaneously for the trans isomer, followed by a slow nitrosyl to nitrite conversion, whereas for the cis isomer the reduction of the Ru(III) center is induced by the coordination of an additional NO molecule (cis isomer, k2=51.3 +/- 0.3 M(-1) s(-1), DeltaH(++) = 46 +/- 2 kJ mol(-1), DeltaS(++) = -69 +/- 5 J K(-1) mol(-1), DeltaV(++) = -22.6 +/- 0.2 cm3 mol(-1) at 45 degrees C). The final reaction step involves a slow aquation process for both isomers, which is interpreted in terms of a dissociative substitution mechanism (cis isomer, DeltaV(++) = +23.5 +/- 1.2 cm3 mol(-1); trans isomer, DeltaV(++) = +20.9 +/- 0.4 cm3 mol(-1) at 55 degrees C) that produces two different reaction products, viz. [Ru(terpy)(NH3)(H2O)NO]3+ (product of the cis isomer) and trans-[Ru(terpy)(NH3)2(H2O)]2+. The pi-acceptor properties of the tridentate N-donor chelate (terpy) predominantly control the overall reaction pattern.     

Anhydride curing of epoxy resins via chain reaction

In contrast to common curing reactions, the anhydride curing of epoxies follows a living anionic chain growth. The resulting consequences of this mechanism, i.e. (1) DP_n = a[M_o]/[I_o], (2) first-order kinetics and (3) Poisson chain-length distribution were tested with the phenyl glycidyl ether/phthalic acid anhydride system, using l-methyl imidazole. Overall agreement was found and the observed deviations could be explained with a modified Poisson process. Conformational properties of the resins were measured by static and dynamic light scattering and by viscometry. These were compared with the quantities of a corresponding branched system prepared with a mixture of phenyl glycidyl ether and bisphenol-A diglycidyl ether. Typical deviations to smaller dimensions were observed at high molar masses as a result of increasing branching.