Molecular Recognition in Self‐Assembled Integrated Circuits: Getting Smaller while under Control

Available in small print : Block copolymer lithography has great potential for reducing the size and fabrication time of integrated circuits. Hydrogen‐bonding‐mediated molecular recognition in self‐assembly processes can be used to produce highly ordered square arrays of block copolymers on the surface of a silicon substrate (see picture).

     

Understanding the Supramolecular Self‐Assembly of the Fullerene Derivative PCBM on Gold Surfaces

We report a DFT study on the self‐assembly of the fullerene derivative PCBM on the Au(111) surface. Recent STM experiments (Angew. Chem. 2007 , 119, 8020–8023^[1]) show a coverage‐dependent transition of the adsorption and self‐assembly of PCBM on this surface. To understand the origin of this observation, we compute the geometries and relative energies of ten PCBM dimers and four tetramers. The calculations show that the self‐assembly of PCBM at high coverage is mainly controlled by hydrogen bonding between the PCBM tails. Due to the large size of the fullerene cage, the hydrogen bonds are formed far away from the surface; hence they are very similar to those found in the gas phase. This picture successfully explains the observed site‐insensitive adsorption at high coverage and the 2D arrangement of PCBM on the surface.     

Complexation and Fluorescence of Tricyclic Basic Dyes Encapsulated in Cucurbiturils

Tricyclic basic dyes (proflavine, acridine orange, pyronine, pyronine Y, oxonine, thionine and methylene blue) often form one‐to‐one or two‐to‐one complexes with CB[7] and CB[8], respectively. In the case of pyronine Y, the complexes with CB[7] and CB[8] have a one‐to‐one and three‐to‐one stoichiometry, respectively. The binding constants for CB[7] complexes range from 3.07×10⁶ to 1.70×10⁷ m ^?1. In the case of CB[8], the association constant varies between 3.24×10¹³ and 2.50×10¹⁶ m ^?2. Overall, these binding constants are four orders of magnitude higher than those reported for the same dyes in β and γ‐cyclodextrins. Formation of the host–guest complexes leads to an increase in the fluorescence quantum yields in the case of CB[7], while the dimeric or trimeric dye encapsulated in CB[8] are remarkably less fluorescent than the same dye in diluted solutions.     

Synthesis and Structure of Monomeric,Trimeric, and Mixed Phenylcyanamides

In a new synthetic approach phenylcyanamide (Hpca) was synthesized by methylation of phenylthiourea followed by a basic work‐up. All products along the synthetic route have been fully characterized by means of NMR, IR, and X‐ray studies. The first structural report of neutral mixed crystals of phenylcyanamide containing monomeric and trimeric Hpca is presented. Examination of these intriguing mixed crystals revealed the formation of distinct layers of monomeric and trimeric Hpca. These layers are interconnected by weak hydrogen bonds. The trimer represents triphenylisomelamine, which readily isomerizes to the triphenylmelamine in the melt, in accord with computations at the B3LYP level, indicating an exothermic process (ΔH=?49.4 kcal mol^?1). Pure trimeric Hpca (triphenylisomelamine) was obtained either by recrystallization of the mixed crystals from boiling water or by trimerization of monomeric Hpca in isopropanol for 12 h under reflux conditions. For comparison tritylcyanamide (Htca) and potassium phenylcyanamide as an [18]crown‐6 complex [K([18]crown‐6)pca] have been synthesized, and the solid‐state structures were determined using X‐ray diffraction techniques. The thermal behavior was studied by thermo‐analytical experiments. In agreement with the experimental results, computations predict an exothermic cyclotrimerization process for Hpca (ΔH=?41.3 kcal mol^?1).     

A Heterogeneous‐Catalyst‐Based,Microwave‐Assisted Protocol for the Synthesis of 2,2′‐Bipyridines

A new method of preparing 2,2′‐bipyridines with short reaction times by using microwave assistance and heterogeneous catalysts has been developed. With a Negishi‐like protocol, it was found that Ni/Al₂O₃–SiO₂ afforded 2,2′‐bipyridine products in up to 86 % yield in 1 h. Palladium supported on alumina also provided yields of 2,2′‐bipyridines comparable to those seen for homogeneous PEPPSI^TM (1,3‐diisopropylimidazol‐2‐ylidene)(3‐chloropyridyl)palladium(II)dichloride) and tetrakis(triphenylphosphanyl)palladium complexes.     

On the Validity of Stokes–Einstein and Stokes–Einstein–Debye Relations in Ionic Liquids and Ionic‐Liquid Mixtures

Stokes–Einstein (SE) and Stokes–Einstein–Debye (SED) relations in the neat ionic liquid (IL) [C₂mim][NTf₂] and IL/chloroform mixtures are studied by means of molecular dynamics (MD) simulations. For this purpose, we simulate the translational diffusion coefficients of the cations and anions, the rotational correlation times of the C(2)? H bond in the cation C₂mim⁺, and the viscosities of the whole system. We find that the SE and SED relations are not valid for the pure ionic liquid, nor for IL/chloroform mixtures down to the miscibility gap (at 50 wt % IL). The deviations from both relations could be related to dynamical heterogeneities described by the non‐Gaussian parameter α(t). If α(t) is close to zero, at a concentration of 1 wt % IL in chloroform, both relations become valid. Then, the effective radii and volumes calculated from the SE and SED equations can be related to the structures found in the MD simulations, such as aggregates of ion pairs. Overall, similarities are observed between the dynamical properties of supercooled water and those of ionic liquids.     

Experimental and Theoretical Study of Helium Broadening and Shift of HCO+ Rotational Lines

An experimental and theoretical study of pressure broadening and pressure shift of HCO⁺ rotational lines perturbed by collisions with He is presented. Results are reported from measurements at 88 K for the lines j=4←3, 5←4 and 6←5 with frequencies ranging from 0.35 to 0.54 THz. Using a new CCSD(T)/aug‐cc‐pVQZ potential energy surface for the He–HCO⁺ interaction, the collisional line shape parameters are studied from fully quantum and semiclassical calculations. Results from the quantum treatment are in satisfactory agreement with experiments whereas the semiclassical approach can lead to appreciable differences. A study of the dependence of line width Γ and shift s as a function of the translational energy shows the presence of quantum oscillations. Calculations on a previous Hartree–Fock‐based potential energy surface lead to quite similar results for the collisional line shape parameters. Using a simplified version of the potential morphing method it is found that the line width Γ is particularly sensitive to the long‐range part of the potential energy surface. This also explains the success of the first line‐broadening calculations which date back to the 1950s.     

Freezing and Melting of Water Confined in Silica Nanopores

In nanosized pores, liquid water can be thermodynamically stable down to temperatures well below the limit of homogeneous nucleation of bulk water (～235 K). Studies of water in such pores therefore offer an opportunity to reveal the anomalous behavior of deeply supercooled water. Herein we focus on recent studies of the limits of freezing and melting of water in the cylindrical pores of ordered mesoporous silicas with pore diameters in the range of 2–10 nm, based on vapor sorption measurements, calorimetric studies, NMR spectroscopy and cryoporometry, and neutron diffraction studies.     

Recent Advances in Asymmetric Catalysis Using p-Block Elements

The development of new methods for enantioselective reactions that generate stereogenic centres within molecules are a cornerstone of organic synthesis. Typically, metal catalysts bearing chiral ligands as well as chiral organocatalysts have been employed for the enantioselective synthesis of organic compounds. In this review, we highlight the recent advances in main group catalysis for enantioselective reactions using the p-block elements (boron, aluminium, phosphorus, bismuth) as a complementary and sustainable approach to generate chiral molecules. Several of these catalysts benefit in terms of high abundance, low toxicity, high selectivity, and excellent reactivity. This minireview summarises the utilisation of chiral p-block element catalysts for asymmetric reactions to generate value-added compounds.     

Revealing the CO2 Conversion at Electrode/Electrolyte Interfaces in Li–CO2 Batteries via Nanoscale Visualization Methods

Lithium–carbon dioxide (Li–CO₂) battery technology presents a promising opportunity for carbon capture and energy storage. Despite tremendous efforts in Li–CO₂ batteries, the complex electrode/electrolyte/CO₂ triple-phase interfacial processes remain poorly understood, in particular at the nanoscale. Here, using in situ atomic force microscopy and laser confocal microscopy-differential interference contrast microscopy, we directly observed the CO₂ conversion processes in Li–CO₂ batteries at the nanoscale, and further revealed a laser-tuned reaction pathway based on the real-time observations. During discharge, a bi-component composite, Li₂CO₃/C, deposits as micron-sized clusters through a 3D progressive growth model, followed by a 3D decomposition pathway during the subsequent recharge. When the cell operates under laser (λ=405 nm) irradiation, densely packed Li₂CO₃/C flakes deposit rapidly during discharge. Upon the recharge, they predominantly decompose at the interfaces of the flake and electrode, detaching themselves from the electrode and causing irreversible capacity degradation. In situ Raman shows that the laser promotes the formation of poorly soluble intermediates, Li₂C₂O₄, which in turn affects growth/decomposition pathways of Li₂CO₃/C and the cell performance. Our findings provide mechanistic insights into interfacial evolution in Li–CO₂ batteries and the laser-tuned CO₂ conversion reactions, which can inspire strategies of monitoring and controlling the multistep and multiphase interfacial reactions in advanced electrochemical devices.