Molecular Quantum Dot Cellular Automata Based on Diboryl Monoradical Anions

Field-effect transistor (FET)-based microelectronics is approaching its size limit due to unacceptable power dissipation and short-channel effects. Molecular quantum dot cellular automata (MQCA) is a promising transistorless paradigm that encodes binary information with bistable charge configurations instead of currents and voltages. However, it still remains a challenge to find appropriate candidate molecules for MQCA operation. Inspired by recent progress in boron radical chemistry, we theoretically predicted a series of new MQCA candidates built from diboryl monoradical anions. The unpaired electron resides mainly on one boron center and can be shifted to the other by an electrostatic stimulus, forming bistable charge configurations required by MQCA. By investigating various bridge units with different substitutions (ortho-, meta-, and para-), we suggested several candidate molecules that have potential MQCA applications

Surface molecular tailoring using pH-switchable supramolecular dendron-ligand assemblies

[Image: see text] The rational design of materials with tailored properties is of paramount importance for a wide variety of biological, medical, electronic and optical applications. Here we report molecular level control over the spatial distribution of functional groups on surfaces utilizing self-assembled monolayers (SAMs) of pH-switchable surface-appended pseudorotaxanes. The supramolecular systems were constructed from a poly(aryl ether) dendron-containing a dibenzo[24]crown-8 (DB24C8) macrocycle and a thiol ligand-containing a dibenzylammonium recognition site and a fluorine end group. The dendron establishes the space (dendritic effect) that each pseudorotaxane occupies on the SAM. Following SAM formation, the dendron is released from the surface by switching off the noncovalent interactions upon pH stimulation, generating surface materials with tailored physical and chemical properties

On-demand electrical switching of antibody-antigen binding on surfaces

The development of stimuli-responsive interfaces between synthetic materials and biological systems is providing the unprecedented ability to modulate biomolecular interactions for a diverse range of biotechnological and biomedical applications. Antibody–antigen binding interactions are at the heart of many biosensing platforms, but no attempts have been made yet to control antibody–antigen binding in an on-demand fashion. Herein, a molecular surface was designed and developed that utilizes an electric potential to drive a conformational change in surface bound peptide moiety, to give on-demand control over antigen–antibody interactions on sensor chips. The molecularly engineered surfaces allow for propagation of conformational changes from the molecular switching unit to a distal progesterone antigen, resulting in promotion (ON state) or inhibition (OFF state) of progesterone antibody binding. The approach presented here can be generally applicable to other antigen–antibody systems and meets the technological needs for in situ long-term assessment of biological processes and disease monitoring on-demand

Whole-genome sequencing of the snub-nosed monkey provides insights into folivory and evolutionary history

Colobines are a unique group of Old World monkeys that principally eat leaves and seeds rather than fruits and insects. We report the sequencing at 146× coverage, de novo assembly and analyses of the genome of a male golden snub-nosed monkey (Rhinopithecus roxellana) and resequencing at 30× coverage of three related species (Rhinopithecus bieti, Rhinopithecus brelichi and Rhinopithecus strykeri). Comparative analyses showed that Asian colobines have an enhanced ability to derive energy from fatty acids and to degrade xenobiotics. We found evidence for functional evolution in the colobine RNASE1 gene, encoding a key secretory RNase that digests the high concentrations of bacterial RNA derived from symbiotic microflora. Demographic reconstructions indicated that the profile of ancient effective population sizes for R. roxellana more closely resembles that of giant panda rather than its congeners. These findings offer new insights into the dietary adaptations and evolutionary history of colobine primates

Electron switch in the double-cage fluorinated fullerene anions, e \u3csup\u3e-\u3c/sup\u3e@C\u3csub\u3e20\u3c/sub\u3eF\u3csub\u3e18\u3c/sub\u3e(XH)\u3csub\u3e2\u3c/sub\u3eC\u3csub\u3e20\u3c/sub\u3eF\u3csub\u3e18\u3c/sub\u3e (X = N, B): new candidates for molecular quantum-dot cellular automata

A new type of molecular quantum-dot cellular automata (MQCA) candidates is suggested using the double-cage fluorinated fullerene molecules, e -@C20F18(XH)2C20F 18 (X = N, B), which have bistable charge configurations that could be used to encode binary information. The electron switch between the two cages leads to the QCA function

Polarizable force fields based on physical models and quantum chemical calculations

Nonpolarizable force fields cannot guarantee the accurate calculation of optical dielectric constants. The parameterization of polarizable FFs is not trivial, but electrostatics approaches, like the FQ model, Drude model, and the ID model, as well as fragment-based low-scaling QM methods show great potential in the hands of the community of developers.This perspective gives a brief overview of recent developments of the polarizable force fields (FFs)-a kind of specific FF method that includes polarization effect into conventional molecular mechanics. The commonly adopted polarizable models, that is, the fluctuating charge model, Drude model, and the inducible dipole model are expatiated. Taking advantage of the recent development of computational techniques and fragment-based low-scaling quantum mechanics (QM) methods, QM-based polarizable FFs appeared and particularly aroused great interest in biological systems. Current applications and limitations of several models are discussed. Opportunities and challenges for future development are also addressed

Electrically responsive surfaces: experimental and theoretical investigations

Stimuli-responsive surfaces have sparked considerable interest in recent years, especially in view of their biomimetic nature and widespread biomedical applications. Significant efforts are continuously being directed at developing functional surfaces exhibiting specific property changes triggered by variations in electrical potential, temperature, pH and concentration, irradiation with light, or exposure to a magnetic field. In this respect, electrical stimulus offers several attractive features, including a high level of spatial and temporal controllability, rapid and reverse inducement, and noninvasiveness. In this Account, we discuss how surfaces can be designed and methodologies developed to produce electrically switchable systems, based on research by our groups. We aim to provide fundamental mechanistic and structural features of these dynamic systems, while highlighting their capabilities and potential applications. We begin by briefly describing the current state-of-the-art in integrating electroactive species on surfaces to control the immobilization of diverse biological entities. This premise leads us to portray our electrically switchable surfaces, capable of controlling nonspecific and specific biological interactions by exploiting molecular motions of surface-bound electroswitchable molecules. We demonstrate that our self-assembled monolayer-based electrically switchable surfaces can modulate the interactions of surfaces with proteins, mammalian and bacterial cells. We emphasize how these systems are ubiquitous in both switching biomolecular interactions in highly complex biological conditions while still offering antifouling properties. We also introduce how novel characterization techniques, such as surface sensitive vibrational sum-frequency generation (SFG) spectroscopy, can be used for probing the electrically switchable molecular surfaces in situ. SFG spectroscopy is a technique that not only allowed determining the structural orientation of the surface-tethered molecules under electroinduced switching, but also provided an in-depth characterization of the system reversibility. Furthermore, the unique support from molecular dynamics (MD) simulations is highlighted. MD simulations with polarizable force fields (FFs), which could give proper description of the charge polarization caused by electrical stimulus, have helped not only back many of the experimental observations, but also to rationalize the mechanism of switching behavior. More importantly, this polarizable FF-based approach can efficiently be extended to light or pH stimulated surfaces when integrated with reactive FF methods. The interplay between experimental and theoretical studies has led to a higher level of understanding of the switchable surfaces, and to a more precise interpretation and rationalization of the observed data. The perspectives on the challenges and opportunities for future progress on stimuli-responsive surfaces are also presented

A density-functional-theory study of biradicals from benzene to hexacene

The singlet-triplet energy gap of biradicals created in benzene and polyacenes is investigated by density-functional-theory calculations. For the biradicals in benzene, naphthalene, anthracene, tetracene, pentacene, and hexacene, we find that the singlet state is energetically favored over the triplet state by 189, 191, 184, 199, 218, and 244 meV, respectively. The monotonous increase of the singlet-triplet energy gap from anthracene to hexacene is attributed to the enhanced stability of the singlet state for longer polyacenes. Our analysis shows that the spin density of the singlet state is delocalized over all benzene rings, but such a spin delocalization is not present for the triplet state

Electrocatalytically inactive SnS2 promotes water adsorption/dissociation on molybdenum dichalcogenides for accelerated alkaline hydrogen evolution

Molybdenum dichalcogenides, in particular, MoS2 and MoSe2, are very promising nonprecious metal-based electrocatalysts for hydrogen evolution reaction (HER) in acidic media. They exhibit inferior alkaline HER activity, however, due to the sluggish water dissociation process. Here, we design and synthesize new molybdenum dichalcogenide-based heterostructures with the basal planes decorated with SnS2 quantum dots towards enhanced alkaline HER activity. The electrochemical results reveal that the alkaline hydrogen evolution kinetics of molybdenum dichalcogenides is substantially accelerated after incorporation of SnS2 quantum dots. The optimal MoSe2/SnS2 heterostructure delivers a much lower overpotential of 285 mV than MoSe2 (367 mV) to reach a current density of 10 mA cm−2 in 1 M KOH. The improved catalytic activity is predominantly owing to the enhanced water dissociation kinetics of the heterostructures with well-defined interfaces. Density functional theory (DFT) calculations reveal that the presence of SnS2 significantly promotes the water adsorption capability of MoSe2 nanosheets, which consequently facilitates the subsequent water dissociation process. These results open up a new avenue for the rational design of well-defined heterostructures with enhanced water adsorption/dissociation capability for the development of high-performance alkaline HER electrocatalysts

Heteroatom-doped MoSe2 Nanosheets with Enhanced Hydrogen Evolution Kinetics for Alkaline Water Splitting

Electrochemical water splitting for hydrogen generation is a vital part for the prospect of future energy systems, however, the practical utilization relies on the development of highly active and earth-abundant catalysts to boost the energy conversion efficiency as well as reduce the cost. Molybdenum diselenide (MoSe2) is a promising nonprecious metal-based electrocatalyst for hydrogen evolution reaction (HER) in acidic media, but it exhibits inferior alkaline HER kinetics in great part due to the sluggish water adsorption/dissociation process. Herein, the alkaline HER kinetics of MoSe2 is substantially accelerated by heteroatom doping with transition metal ions. Specifically, the Ni-doped MoSe2 nanosheets exhibit the most impressive catalytic activity in terms of lower overpotential and larger exchange current density. The density functional theory (DFT) calculation results reveal that Ni/Co doping plays a key role in facilitating water adsorption as well as optimizing hydrogen adsorption. The present work paves a new way to the development of low-cost and efficient electrocatalysts towards alkaline HER