Simulation studies of dipole correlation in the isotropic liquid phase

The Kirkwood correlation factor g₁ determines the preference for local parallel or antiparallel dipole association in the isotropic phase. Calamitic mesogens with longitudinal dipole moments and Kirkwood factors greater than 1 have an enhanced effective dipole moment along the molecular long axis. This leads to higher values of Δ? in the nematic phase. This paper describes state-of-the-art molecular dynamics simulations of two calamitic mesogens 4-(trans-4-n-pentylcyclohexyl)benzonitrile (PCH5) and 4-(trans-4-n-pentylcyclohexyl)chlorobenzene (PCH5-Cl) in the isotropic liquid phase using an all-atom force field and taking long range electrostatics into account using an Ewald summation. Using this methodology, PCH5 is seen to prefer antiparallel dipole alignment with a negative g₁ and PCH5-Cl is seen to prefer parallel dipole alignment with a positive g₁; this is in accordance with experimental dielectric measurements. Analysis of the molecular dynamics trajectories allows an assessment of why these molecules behave differently.     

Irigermanone,a Noriridal with Unprecedented Methylketone Function,from Iris germanica

A new iridal, irigermanone ( 1 ) and nine known congeners, 2 – 10 , respectively, have been isolated from the dried rhizomes of German iris (Iris germanica). The structure of 1 was established by spectroscopic methods including HR‐ESI‐MS, 1D‐ and 2D‐NMR, and electronic circular dichroism (ECD) spectroscopy. Compound 1 is a structurally unique noriridal, and it possesses an unprecedented methylcarbonyl group instead of the α,β‐unsaturated aldehyde function typical for this group of triterpenes.     

Selective Zinc-Catalyzed 1,2-hydroboration of N-heteroaromatics via a Non-Hydride Mechanism

A novel bidentate amine-imine ligand precursor LH has been synthesized. This compound was reacted with ZnMe₂ to generate the zinc methyl complex, LZnMe ( 4 ). The latter compound was fully characterized by NMR spectroscopy and single crystal X-ray diffraction. Compound 4 is a catalyst for the hydroboration and hydrosilylation of N-heterocycles, but with moderate catalytic activity. A more active catalyst, the zinc hydride complex LZnH ( 5 ) was synthesized by reacting the lithium salt LLi with ZnCl₂ followed by sequential reaction with tBuOK and PhMeSiH₂. Compound 5 catalyzes the selective 1,2-hydroboration of nitrogen heteroaromatics with decreased catalyst load and under mild conditions. Deuterium-labeling experiments and kinetic studies provided insight into the possible reaction mechanism. It is proposed that hydride transfer to the substrate proceeds directly from the reductant (borane) via a six-membered transition state facilitated by the catalyst, in which it plays an ambiphilic role, activating the substrate via coordination to the Lewis acidic zinc and enhancing the hydricity of the borane through coordination to the zinc hydride.     

A lithography-free pathway for chemical microstructuring of macromolecules from aqueous solution based on wrinkling

We report on a novel lithography-free method for obtaining chemical submicron patterns of macromolecules on flat substrates. The approach is an advancement of the well-known microcontact printing scheme: While for classical microcontact printing lithographically produced masters are needed, we show that controlled wrinkling can serve as an alternative pathway to producing such masters. These can even show submicron periodicities. We expect upscaling to larger areas to be considerably simpler than that for existing techniques, as wrinkling results in a macroscopic deformation process that is not limited in terms of substrate size. Using this approach, we demonstrate successful printing of aqueous solutions of polyelectrolytes and proteins. We study the effectiveness of the stamping process and its limits in terms of periodicities and heights of the stamps' topographical features. We find that critical wavelengths are well below 355 nm and critical amplitudes are below 40 nm and clarify the failure mechanism in this regime. This will permit further optimization of the approach in the future.     

Realisation of truly microporous pillared clays

When pillaring a well crystalline synthetic hectorite using molecular pillars, we obtained a truly microporous material for the first time that displays long range order of the pillars and consequently a narrow pore size distribution.     

Exploring similarities in reactivity of superatom species: a combined theoretical and experimental investigation

The replacement of group 10-based materials by superatoms has gained great attention due to studies presenting similarities in electronic character and reactive nature between pairs. The current study extends the concept to systems of larger and varied composition as the pairs PdO(+) and ZrO(2)(+) as well as NiO(+) and TiO(2)(+) are interacted with C(2)H(4) and CO through DFT calculations and guided-ion-beam mass spectrometry. It is determined that the pairs readily oxidize C(2)H(4) while oxygen transfer is limited towards CO. Interestingly, within the reaction profiles for oxidation of C(2)H(4) by PdO(+) and NiO(+), a spin crossover is observed which greatly increases the exothermicity of the process. This investigation presents a major step in identifying replacements for expensive group 10 metals in catalytic materials.     

Breaking the mode degeneracy of surface plasmon resonances in a triangular system

In this paper, we present a systematic investigation of symmetry-breaking in the plasmonic modes of triangular gold nanoprisms. Their geometrical C(3v) symmetry is one of the simplest possible that allows degeneracy in the particle's mode spectrum. It is reduced to the nondegenerate symmetries C(v) or E by positioning additional, smaller gold nanoprisms in close proximity, either in a lateral or a vertical configuration. Corresponding to the lower symmetry of the system, its eigenmodes also feature lower symmetries (C(v)), or preserve only the identity (E) as symmetry. We discuss how breaking the symmetry of the plasmonic system not only breaks the degeneracy of some lower order modes, but also how it alters the damping and eigenenergies of the observed Fano-type resonances.