The Inverted Philosopher’s Stone: how to turn silver to a base metal

Metals often are classified as “noble” or “base”—characterizing their reduction potential as one of the most important chemical properties. We show that metals are only as noble as allowed by their environment, i.e. this is a relative term, and the “frame of reference” simply is the solvent in which the redox system is present. We prove that silver is a prime example for a noble metal that forfeits its noble character in the simple ionic liquid HMIM Br (1-hexyl-3-methylimidazolium bromide) as an example for such a solvent.

Graphical Abstract

     

Motion and recombination of charge carriers in a polydiacetylene single crystal

From photocurrent transients excited by a ruby laser γ/μ = (6.3±1.5) × 10^–6 V cm is derived for the ratio of carrier recombination coefficient to mobility in polydiacetylene-bis (toluenesulfonate) single crystals. The sum of electron and hole mobility in chain direction is 2.8 cm²/V s with a uncertainly of a factor of 2 in both directions.     

Proton NMR investigation of a hydrogen-bonded liquid crystal gel

Proton NMR is employed to determine director distributions in a hydrogen-bonded liquid crystal gel in the presence of a magnetic field. The samples consist of the mesogen 8CB mixed with small percentages of gelator, which forms a hydrogen-bonded network when the sample is cooled below the gelation point in the isotropic liquid. Since the gelation occurs above the clearing point, a non-oriented random director configuration is frozen in. The configuration of the hydrogen-bonded network is found to be isotropic. It fixes a preferential random local orientation of the nematic director, even in the presence of an external magnetic field of a few Tesla. The NMR spectra of the samples give information on orientation and order in such systems. A simple model for the director field is provided.     

Proton NMR investigation of a hydrogen-bonded liquid crystal gel

Proton NMR is employed to determine director distributions in a hydrogen-bonded liquid crystal gel in the presence of a magnetic field. The samples consist of the mesogen 8CB mixed with small percentages of gelator, which forms a hydrogen-bonded network when the sample is cooled below the gelation point in the isotropic liquid. Since the gelation occurs above the clearing point, a non-oriented random director configuration is frozen in. The configuration of the hydrogen-bonded network is found to be isotropic. It fixes a preferential random local orientation of the nematic director, even in the presence of an external magnetic field of a few Tesla. The NMR spectra of the samples give information on orientation and order in such systems. A simple model for the director field is provided.     

Structure and aggregation number of a lyotropic liquid crystal: a fluorescence quenching and molecular dynamics study

The structure and aggregation number of a discotic lyotropic liquid crystal, prepared from tetradecyltrimethylammonium chloride (TDTMACl)/decanol (DeOH)/NaCl/H2O, have been examined using fluorescence quenching of pyrene by hexadecylpyridinium chloride and molecular dynamics (MD). The fluorescence method gives an aggregation number of 258 +/- 25 units (DeOH + TDTMACl). From the MD simulation, a lower limit for the aggregate dimension of 130 units of DeOH + TDTMACl is predicted. A stable oblate aggregate of 240 units was studied in detail. A strong polarization between the ammonium headgroups and chloride ions is observed from the calculated trajectory. DeOH headgroups are located, on average, 0.3 nm more to the interior of the aggregate than the TDTMACl headgroup and contribute to widening the interface by forming H-bonds with water. The radial distribution function of the ammonium headgroup shows that there are 16 water molecules in the first solvation sphere. The diagonal elements of the order parameter tensor of the tail atoms of both surfactants indicate that the interior of the micelle preserves about the same degree of order as at the interface, up to the last three atoms of the aliphatic chain, where the order starts to decrease.     

Correlated electron dynamics: how aromaticity can be controlled

In this Article, we show that the aromaticity of a molecule can be turned off by controlling the electron dynamics. We present a controlled switching from the aromatic ground state of benzene to two different nonaromatic states, using a laser pulse. The propagation of the molecular wave function is carried out with the time-dependent configuration interaction method. The laser pulse for switching between the ground and excited states is optimized using optimal control theory. Bond orders and Mulliken charges serve as an aromaticity criterion. The nonaromatic target states exhibit localized bonds and partial charges on the carbon atoms; these localized electrons circulate on an attosecond time scale in the ring system.     

Simultaneous chirality transfer and structured aggregation of a cyclopeptide in a liquid crystal

We report the finding that a chiral cyclopeptide dissolved in a nematic liquid crystal (LC) host could aggregate in a manner that is controlled by the texture (LC director configuration) of a cholesteric phase that is induced by the cyclopeptide itself. On one hand, with the fingerprint texture, where the helical axis formed by rotating LC molecules, that lies in the substrate plane, the cyclopeptide can use the LC texture as a template to aggregate and form long-range-ordered ribbons that mimic the helical configuration of the LC director. On the other hand, with the planar texture, where the helical axis is normal to the substrate plane, the cyclopeptide can migrate into the "oily-streak" defect regions of the cholesteric phase and stabilize a network of defects that dictates the electrooptical response of the LC. This is the first example of a molecular species exhibiting such a structured aggregation and defect stabilization effect in a cholesteric LC, but similar phenomena were previously reported for platinum nanoparticles and silica colloidal particles, respectively, dispersed in a cholesteric LC host. This study provides more evidence for the potential interest of exploring LCs as an anisotropic medium for mediating the aggregation and assembly of cyclopeptides.     

Effect of charge inhomogeneity and mobility on colloid aggregation

The aggregation of inhomogeneously charged colloids with the same average charge is analyzed using Monte Carlo simulations. We find aggregation of colloids for sizes in the range 10-200 nm, which is similar to the range in which aggregation is observed in several experiments. The attraction arises from the strongly correlated electrostatic interactions associated with the increase in the counterion density in the region between the particles; this effect is enhanced by the discreteness and mobility of the surface charges. Larger colloids attract more strongly when their surface charges are discrete. We study the aggregation as functions of the surface charge density, counterion valence, and volume fraction.     

Two ammonium tetrachloridoaluminate salts: how a twinned orthorhombic structure emulates a trigonal crystal system

We have determined the crystal structures of two tetrachloridoaluminate salts. Tetrabutylammonium tetrachloridoaluminate benzene hemisolvate, (C₁₆H₃₆N)[AlCl₄]·0.5C₆H₆, (I), crystallizes with discrete cations, anions and solvent molecules. The benzene molecule is located on a centre of inversion. The structure of the benzene‐free polymorph has been determined previously. Tetraethylammonium tetrachloridoaluminate, (C₈H₂₀N)[AlCl₄], (II), also crystallizes with discrete cations and anions, and forms crystals which appear trigonal but are actually orthorhombic. With the additional reflections of the second and third domains of this nonmerohedral twin, a trigonal lattice is emulated, although the correct crystal system is orthorhombic.     

Utilising tetraphenylethene as a dual activator for intramolecular charge transfer and aggregation induced emission

We report a simple design and synthesis of a donor-acceptor tetraphenylethene-naphthalimide (TPE-NI) dyad, in which TPE acts both as an electron-donor for intramolecular charge transfer (ICT) and activator for aggregation induced emission (AIE). Strong solvent-dependent photoluminescence covering almost the whole visible spectrum and AIE in its nanoparticle state compared to its solution state are demonstrated.     

Assembly of a polyoxometalate into an anisotropic gel

The self-assembly of the polyoxomolybdate [MnMo6O18[(OCH2)3CNHCO(4-C5H4N)]2]3- and [PdCl2(PhCN)2] yields a transparent and birefringent gel.     

Evidence of aggregation induced emission enhancement and keto-enol-tautomerism in a gallic acid derived salicylideneaniline gel

A novel salicylideneaniline type fluorescent organogelator based on a 3,4,5-(tri-dodecyloxy)benzoyl group immobilizes aromatic solvents. The resulting gels show enhancement in emission and thermochromic/non-photochromic behaviour during sol-to-gel transition.     

Scaling of the kinetics of slow aggregation and gel formation for a fluorinated polymer colloid

The aggregation and gelation kinetics in moderately concentrated (0.004 相似文献   

Control over charge separation in phthalocyanine-anthraquinone conjugates as a function of the aggregation status

We have prepared three isomeric donor-acceptor systems, in which two phthalocyanine (Pc) units have been attached to the 1-,5- (1a), 1-,8- (1b), or 2-,6- (1c) positions of a central anthraquinone (AQ) moiety, leading to packed (1b) or extended (1a and 1c) topologies. The electronic interactions between the donor and the acceptor in the ground state or in the excited states have been studied by different electrochemical and photophysical techniques. Due to the markedly different topologies, we have been able to modify these interactions at the intramolecular level and, by a proper choice of the solvent environment, at the intermolecular level within aggregates. In triad 1b, the ZnPc units are forced to pi-stack cofacially and out of the plane of the AQ ring. Consequently, this molecule shows strong inter-Pc interactions that give rise to intramolecular excitonic coupling but a relatively small electronic communication with the AQ acceptor through the vinyl spacers. On the contrary, the 1-,5- or 2-,6-connections of triads 1a and 1c allow for an efficient pi-conjugation between the active units that extends over the entire planar system. These two molecules tend to aggregate in aromatic solvents by pi-pi stacking, giving rise to J-type oligomers. Photoexcitation of the Pc units of 1a-c results in the formation of the Pc.+-AQ.- charge transfer state. We have demonstrated that the kinetics of these electron transfer reactions is greatly dependent on the aggregation status of the triads.     

Modeling the Electrostatics and Size Effect within a Crowded Bioenvironment

Biological fluids typically contain a large number of macromolecules occupying up to 40% of the total volume. Current understanding of the effect of high concentration, or ‘macromolecular crowding’, on cellular processes is primarily based on the excluded-volume considerations in which all intermolecular interactions beyond the short-ranged repulsion are neglected. In this work, a density functional theory (DFT) accompanied by Monte Carlo simulations is employed to investigate the structural and thermodynamic properties of a crowded cellular environment within the primitive model where biomacromolecules are represented by neutral and charged hard spheres and the solvent by a continuous dielectric medium. The performance of the DFT has been tested with extensive results from Monte Carlo (MC) simulations for the pair correlation functions (PCFs), excess internal energies, and osmotic coefficients under a variety of solution conditions.     

Pyroelectric investigations of a hydrogen bonded ferroelectric liquid crystal gel by LIMM

The laser intensity modulation method (LIMM) is employed to determine spatially resolved polarization distributions in sandwich cells containing a hydrogen‐bonded ferroelectric liquid crystal (FLC) gel. At no external electric fields, contributions to the distributions at the surface of the FLC layer are dominating in all the samples with different concentration of gel former. These are attributed to non‐vanishing polarization due to surface interaction. In this case, the effect of hydrogen‐bonded network on the polarization distribution is not visible. In external electric fields, additional contribution to the resulting distribution caused by the induced polarization due to unwinding the FLC helix has been observed. Furthermore, the influence of hydrogen‐bonded network on the polarization distribution is also detected when the gel former content is increased up to 5.0 wt%. Therein the shape of the measured pyrospectra is completely different to other FLC gel samples with lower gel former concentration, where their maximum distributions still locate at the surface of FLC layer which is comparable to the initial field‐free state. These result indicate that the helical structure and orientation director of FLC are able to be stabilized effectively by the gel network even under strong external electric field. Copyright © 2004 John Wiley & Sons, Ltd.