High Charge Mobility of a Perylene Bisimide Dye with Hydrogen-bond Formation Group

Charge carrier mobility is one of the most important parameters concerning the performance of organic electronic devices1.High mobility usually leads to high calculation speed in computer and high short-circuit current in organic solar cells.Unfortunately,the intrinsic charge mobilities for organic semiconductors are of orders of magnitude lower than amorphous silicon.As a promising n-type organic semiconductor,N,N′-n-alkyl-perylene bisimides have shown their electron mobility to be up to10-…     

Two‐Dimensional Polymers: Just a Dream of Synthetic Chemists?

In light of the considerable impact synthetic 2D polymers are expected to have on many fundamental and applied aspects of the natural and engineering sciences, it is surprising that little research has been carried out on these intriguing macromolecules. Although numerous approaches have been reported over the last several decades, the synthesis of a one monomer unit thick, covalently bonded molecular sheet with a long‐range ordered (periodic) internal structure has yet to be achieved. This Review provides an overview of these approaches and an analysis of how to synthesize 2D polymers. This analysis compares polymerizations in (initially) a homogeneous phase with those at interfaces and considers structural aspects of monomers as well as possibly preferred connection modes. It also addresses issues such as shrinkage as well as domain and crack formation, and briefly touches upon how the chances for a successful structural analysis of the final product can possibly be increased.     

Modulating Mobility: a Paradigm for Protein Engineering?

Proteins are highly mobile structures. In addition to gross conformational changes occurring on, for example, ligand binding, they are also subject to constant thermal motion. The mobility of a protein varies through its structure and can be modulated by ligand binding and other events. It is becoming increasingly clear that this mobility plays an important role in key functions of proteins including catalysis, allostery, cooperativity, and regulation. Thus, in addition to an optimum structure, proteins most likely also require an optimal dynamic state. Alteration of this dynamic state through protein engineering will affect protein function. A dramatic example of this is seen in some inherited metabolic diseases where alternation of residues distant from the active site affects the mobility of the protein and impairs function. We postulate that using molecular dynamics simulations, experimental data or a combination of the two, it should be possible to engineer the mobility of active sites. This may be useful in, for example, increasing the promiscuity of enzymes. Thus, a paradigm for protein engineering is suggested in which the mobility of the active site is rationally modified. This might be combined with more “traditional” approaches such as altering functional groups in the active site.     

Visible‐Light Photocatalysis: Does It Make a Difference in Organic Synthesis?

Visible‐light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. Photocatalytic variants have been reported for many important transformations, such as cross‐coupling reactions, α‐amino functionalizations, cycloadditions, ATRA reactions, or fluorinations. To help chemists select photocatalytic methods for their synthesis, we compare in this Review classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed under milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, such as air, oxygen, or amines. Does visible‐light photocatalysis make a difference in organic synthesis? The prospect of shuttling electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible‐light‐absorbing photocatalyst holds the promise to improve current procedures in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown, especially by merging photocatalysis with organo‐ or metal catalysis.     

Proton conduction in 1H‐1,2,3‐triazole polymers: Imidazole‐like or pyrazole‐like?

Proton transport (PT) plays an important role in many biological processes as well as in materials for renewable energy devices. Gaining insights into functional group requirements for PT would aid the design of new materials that provide enhanced proton conduction. In this report, we outline our efforts to understand the most probable proton conduction pathway in 1H‐1,2,3‐triazole systems. In triazole‐based systems, both imidazole‐ and pyrazole‐like pathways are possible. By systematically comparing structurally analogous polymers based on N‐heterocycles and benz‐N‐heterocycles, we find that the imidazole‐like pathway makes a significant contribution to the proton transfer in 1H‐1,2,3‐triazole systems, while the contribution from pyrazole‐like pathway is negligible. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1851–1858, 2010     

Photoinduced Charge‐Carrier Generation in Epitaxial MOF Thin Films: High Efficiency as a Result of an Indirect Electronic Band Gap?

For inorganic semiconductors crystalline order leads to a band structure which gives rise to drastic differences to the disordered material. An example is the presence of an indirect band gap. For organic semiconductors such effects are typically not considered, since the bands are normally flat, and the band‐gap therefore is direct. Herein we show results from electronic structure calculations demonstrating that ordered arrays of porphyrins reveal a small dispersion of occupied and unoccupied bands leading to the formation of a small indirect band gap. We demonstrate herein that such ordered structures can be fabricated by liquid‐phase epitaxy and that the corresponding crystalline organic semiconductors exhibit superior photophysical properties, including large charge‐carrier mobility and an unusually large charge‐carrier generation efficiency. We have fabricated a prototype organic photovoltaic device based on this novel material exhibiting a remarkable efficiency.     

Targeting RNA G‐Quadruplex in SARS‐CoV‐2: A Promising Therapeutic Target for COVID‐19?

The COVID‐19 pandemic caused by SARS‐CoV‐2 has become a global threat. Understanding the underlying mechanisms and developing innovative treatments are extremely urgent. G‐quadruplexes (G4s) are important noncanonical nucleic acid structures with distinct biofunctions. Four putative G4‐forming sequences (PQSs) in the SARS‐CoV‐2 genome were studied. One of them (RG‐1), which locates in the coding sequence region of SARS‐CoV‐2 nucleocapsid phosphoprotein (N), has been verified to form a stable RNA G4 structure in live cells. G4‐specific compounds, such as PDP (pyridostatin derivative), can stabilize RG‐1 G4 and significantly reduce the protein levels of SARS‐CoV‐2 N by inhibiting its translation both in vitro and in vivo. This result is the first evidence that PQSs in SARS‐CoV‐2 can form G4 structures in live cells, and that their biofunctions can be regulated by a G4‐specific stabilizer. This finding will provide new insights into developing novel antiviral drugs against COVID‐19.     

l‐Cysteinium semioxalate: a new monoclinic polymorph or a hydrate?

The title compound, C₃H₈NO₂S⁺·C₂HO₄⁻, (I), crystallizes in the monoclinic C2 space group and is a new form (possibly a hydrate) of l ‐cysteinium semioxalate with a stoichiometric cation–anion ratio of 1:1. In contrast to the previously known orthorhombic form of l ‐cysteinium semioxalate, (I) has a layered structure resembling those of monoclinic l ‐cysteine, as well as of dl ‐cysteine and its oxalates. The conformations of the cysteinium cation and the oxalate anion in (I) differ substantially from those in the orthorhombic form. The structure of (I) has voids with a size sufficient to incorporate water molecules. The residual density, however, suggests that if water is in fact present in the voids, it is strongly disordered and its amount does not exceed 0.3 molecules per void. The difference in conformation of the cysteinium cations in (I) and in the orthorhombic form is similar to that in dl ‐cysteine under ambient conditions and in dl ‐cysteine under high pressure or at low temperature.