Reactivity within a confined self-assembled nanospace

Confined nanospaces in which reactions can take place, have been created by various approaches such as molecular capsules, zeolites and micelles. In this tutorial review we focus on the application of self-assembled nanocapsules with well-defined cavities as nanoreactors for organic and metal catalysed transformations. The self-assembly of nanocapsules based on noncovalent bonds such as hydrogen bonds and metal-ligand interactions is discussed to introduce the properties of the building blocks and capsules thereof. We will elaborate on the encapsulation effects that can be expected when reactions are carried out in a capsule-protected environment. Subsequently, literature examples will be described in which self-assembled nanocapsules are applied as nanoreactors, for various types of organic and metal catalysed reactions.     

Importance of the number of acid molecules and the strength of the base for double-ion formation in (H2SO4)m x base x (H2O)6 clusters

Sulfuric acid and water clusters are important for new particle formation in the atmosphere. Recent experimental studies demonstrate that critical clusters in diverse atmospheric environments contain two acid molecules and may also include additional N-containing molecules (i.e., a base). We use first-principles molecular dynamics simulations to show that the presence of two sulfuric acid molecules in (H2SO4)m x base x (H2O)6 clusters is always sufficient to form a double ion, whereas a single acid molecule, even in the presence of a base, is not.     

Electronic structure of the water dimer cation

The spectroscopic signatures of proton transfer in the water dimer cation were investigated. The six lowest electronic states were characterized along the reaction coordinate using the equation-of-motion coupled-cluster with single and double substitutions method for ionized systems. The nature of the dimer states was explained in terms of the monomer states using a qualitative molecular orbital framework. We found that proton transfer induces significant changes in the electronic spectrum, thus suggesting that time-resolved electronic femtosecond spectroscopy is an effective strategy to monitor the dynamics following ionization. The electronic spectra at vertical and proton-transferred configurations include both local excitations (features similar to those of the monomers) and charge-transfer bands. Ab initio calculations were used to test the performance of a self-interaction correction for density functional theory (DFT). The corrected DFT/BLYP method is capable of quantitatively reproducing the proper energetic ordering of the (H2O)2(+) isomers and thus is a reasonable approach for calculations of larger systems.     

Cobalt-Catalyzed Enantioselective Hydrogenation of Trisubstituted Carbocyclic Olefins: An Access to Chiral Cyclic Amides

The enantioselective hydrogenation of cyclic enamides has been achieved using an earth-abundant cobalt-bisphosphine catalyst. Using CoCl₂/(S,S)-Ph-BPE, several trisubstituted carbocyclic enamides were reduced with high activity and excellent enantioselectivity (up to 99 %) to the corresponding saturated amides. The methodology can be extended to the synthesis of chiral amines by base hydrolysis of the hydrogenation products. Preliminary mechanistic investigations reveal the presence of a high spin cobalt (II) species in the catalytic cycle. We propose that the hydrogenation of the carbon-carbon double bond proceeds via a sigma-bond-metathesis pathway.     

On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18 %

The determination of molecular conformations of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of their resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F-Se and DIBP3F-S, which bridged two segments of Y6-derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O-shaped conformations other than S- or U-shaped counter-ones. Notably, this O-shaped conformation is likely governed by a distinctive “conformational lock” mechanism, arising from the intensified intramolecular π–π interactions among their two terminal groups within the dimers. PSCs based on DIBP3F-Se deliver a maximum efficiency of 18.09 %, outperforming DIBP3F-S-based cells (16.11 %) and ranking among the highest efficiencies for OA-based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high-performance PSCs.     

Pair Distribution Function from Liquid Jet Nanoparticle Suspension using Femtosecond X-ray Pulses

X-ray scattering data measured on femtosecond timescales at the SACLA X-ray Free Electron Laser (XFEL) facility on a suspension of HfO₂ nanoparticles in a liquid jet were used for pair distribution function (PDF) analysis. Despite a non-optimal experimental setup resulting in a modest Q_max of ~8 Å⁻¹, a promising PDF was obtained. The main features were reproduced when comparing the XFEL PDF to a PDF obtained from data measured at the PETRA III synchrotron light source. Refining structural parameters such as unit cell dimension and particle size from the XFEL PDF provided reliable values. Although the reachable Q_max limited the obtainable information, the present results indicate that good quality PDFs can be obtained on femtosecond timescales if the experimental conditions are further optimized. The study therefore encourages a new direction in ultrafast structural science where structural features of amorphous and disordered systems can be studied.     

A new ab initio ground-state dipole moment surface for the water molecule

A valence-only (V) dipole moment surface (DMS) has been computed for water at the internally contracted multireference configuration interaction level using the extended atom-centered correlation-consistent Gaussian basis set aug-cc-pV6Z. Small corrections to these dipole values, resulting from core correlation (C) and relativistic (R) effects, have also been computed and added to the V surface. The resulting DMS surface is hence called CVR. Interestingly, the C and R corrections cancel out each other almost completely over the whole grid of points investigated. The ground-state CVR dipole of H(2) (16)O is 1.8676 D. This value compares well with the best ab initio one determined in this study, 1.8539+/-0.0013 D, which in turn agrees well with the measured ground-state dipole moment of water, 1.8546(6) D. Line intensities computed with the help of the CVR DMS shows that the present DMS is highly similar to though slightly more accurate than the best previous DMS of water determined by Schwenke and Partridge [J. Chem. Phys. 113, 16 (2000)]. The influence of the precision of the rovibrational wave functions computed using different potential energy surfaces (PESs) has been investigated and proved to be small, due mostly to the small discrepancies between the best ab initio and empirical PESs of water. Several different measures to test the DMS of water are advanced. The seemingly most sensitive measure is the comparison between the ab initio line intensities and those measured by ultralong pathlength methods which are sensitive to very weak transitions.     

A Torsion Theory in the Category of Cocommutative Hopf Algebras

The purpose of this article is to prove that the category of cocommutative Hopf K-algebras, over a field K of characteristic zero, is a semi-abelian category. Moreover, we show that this category is action representable, and that it contains a torsion theory whose torsion-free and torsion parts are given by the category of groups and by the category of Lie K-algebras, respectively.     

Selective Co‐Encapsulation Inside an M6L4 Cage

There is broad interest in molecular encapsulation as such systems can be utilized to stabilize guests, facilitate reactions inside a cavity, or give rise to energy‐transfer processes in a confined space. Detailed understanding of encapsulation events is required to facilitate functional molecular encapsulation. In this contribution, it is demonstrated that Ir and Rh‐Cp‐type metal complexes can be encapsulated inside a self‐assembled M₆L₄ metallocage only in the presence of an aromatic compound as a second guest. The individual guests are not encapsulated, suggesting that only the pair of guests can fill the void of the cage. Hence, selective co‐encapsulation is observed. This principle is demonstrated by co‐encapsulation of a variety of combinations of metal complexes and aromatic guests, leading to several ternary complexes. These experiments demonstrate that the efficiency of formation of the ternary complexes depends on the individual components. Moreover, selective exchange of the components is possible, leading to formation of the most favorable complex. Besides the obvious size effect, a charge‐transfer interaction may also contribute to this effect. Charge‐transfer bands are clearly observed by UV/Vis spectrophotometry. A change in the oxidation potential of the encapsulated electron donor also leads to a shift in the charge‐transfer energy bands. As expected, metal complexes with a higher oxidation potential give rise to a higher charge‐transfer energy and a larger hypsochromic shift in the UV/Vis spectrum. These subtle energy differences may potentially be used to control the binding and reactivity of the complexes bound in a confined space.