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Organic radicals consisting of light elements exhibit a low spin-orbit coupling and weak hyperfine interactions with a long spin coherence length, which are crucial for future applications in molecular spintronics. However, the synthesis and characterization of these organic radicals have been a formidable challenge due to their chemical instability arising from unpaired electrons. Here, we report a direct imaging of the surface chemical transformation of an organic monoradical synthesized via the monodehydrogenation of a chemically designed precursor. Bond-resolved scanning tunneling microscopy unambiguously resolves various products formed through a complex structural dissociation and rearrangement of organic monoradicals. Density functional theory calculations reveal detailed reaction pathways from the monoradical to different cyclized products. Our study provides unprecedented insights into complex surface reaction mechanisms of organic radical reactions at the single molecule level, which may guide the design of stable organic radicals for future quantum technology applications.

Constructing hierarchical superstructures to achieve comparable complexity and functions to proteins with four-level hierarchy is challenging, which relies on the elaboration of novel building blocks with complex structures. We present a series of catenated cages with unique structural complexity and tailorability. The rational design was realized as such: A catenane of two symmetric cages (CSC), CSC-1, with all rigid imine panels was converted to a catenane of two dissymmetric cages (CDC), CDC-1, with two exterior flexible amine panels, and CDC-5 was tailored from CDC-1 by introducing an additional methyl group on each blade to increase lateral hindrance. CDC-1s with the most irregular and flexible configuration formed supramolecular dimers, which self-organized into 3D continuous wavelike plank with a three-level hierarchy, previously undiscovered by conventional building blocks. A drastically different 3D triclinic crystalline phase with a four-level hierarchy and trigonal phase with a three-level hierarchy were constructed of distorted CSC-1s and the most symmetric CDC-5s, respectively. The wavelike plank exhibited the lowest order, and the triclinic phase had a lower order than the trigonal phase which had the highest order. It correlates with the configuration of the primary structures, namely, the most disordered shape of CDC-1, the low-order configuration of CSC-1, and the most ordered geometry of CDC-5. The catenated cages with subtle structural differences therefore provide a promising platform for the search of emerging hierarchical superstructures that might be applied to proton conductivity, ferroelectricity, and catalysis.

The combination of distinct peptide ligation techniques to facilitate chemical protein synthesis represents one of the long-standing goals in the field. A new combination ligation method of N-to-C sequential native chemical ligation and Ser/Thr ligation (NCL-STL) is described for the first time. This method relies on the peptide salicylaldehyde S,S-propanedithioacetal (SALPDT)-ester prepared by a new 1,3-propanedithiol-mediated reaction. The peptide SALPDT-ester, which is compatible with NCL, can be fully activated by N-chlorosuccinimide (NCS)/AgNO3 in aqueous solution to afford peptide SAL-ester for use in the subsequent STL. The practicality of the combined NCL-STL method is illustrated by the synthesis of S-palmitoylated matrix-2 (S-palm M2) ion channel from Influenza A virus and S-palmitoylated interferon-induced transmembrane protein 3 (S-palm IFITM3). This approach expands the multiple-segments peptide ligation toolkit for producing important and complex custom-made protein samples by chemical protein synthesis.

Pd-catalyzed cross-coupling reactions have achieved tremendous accomplishments in the past decades. However, C(sp3)-hybridized nucleophiles generally remain as challenging coupling partners due to their sluggish transmetalation compared to the C(sp2)-hybridized counterparts. While a single-electron-transfer-based strategy using C(sp3)-hybridized nucleophiles had made significant progress recently, fewer breakthroughs have been made concerning the traditional two-electron mechanism involving C(sp3)-hybridized nucleophiles. In this report, we present a series of unique alkyl carbagermatranes that were proven to be highly reactive in cross-coupling reactions with our newly developed electron-deficient phosphine ligands. Generally, secondary alkyl carbagermatranes show slightly lower, yet comparable activity to its Sn analogue. Meanwhile, primary alkyl carbagermatranes exhibit high activity, and they were also proved stable enough to be compatible with various reactions. Chiral secondary benzyl carbagermatran...

The combination of distinct peptide ligation techniques to facilitate chemical protein synthesis represents one of the long-standing goals in the field. A new combination ligation method of N-to-C sequential native chemical ligation and Ser/Thr ligation (NCL-STL) is described for the first time. This method relies on the peptide salicylaldehyde

The low solubility of gases in aqueous solution is the major kinetic limitation of reactions that involve gases. To address this challenge, we report a nanochannel reactor with joint gas–solid–liquid interfaces and controlled wettability. As a proof of concept, a porous anodic alumina (PAA) nanochannel membrane with different wettability is used for glucose oxidase (GOx) immobilization, which contacts with glucose aqueous solution on one side, while the other side gets in touch with the gas phase directly. Interestingly, it is observed that the O2 could participate in the enzymatic reaction directly from gas phase through the proposed nanochannels, and a hydrophobic interface is more favorable for the enzymatic reaction due to the rearrangement of GOx structure as well as the high gas adhesion. As a result, the catalytic efficiency of GOx in the proposed interface is increased up to 80-fold compared with that of the free state in traditional aqueous air-saturated electrolyte. This triphase interface with ...

Copper electrocatalysts can reduce CO2 to hydrocarbons at high overpotentials. However, a mechanistic understanding of CO2 reduction on nanostructured Cu catalysts has been lacking. Herein we show that the structurally precise ligand-protected Cu-hydride nanoclusters, such as Cu32H20L12 (L is a dithiophosphate ligand), offer unique selectivity for electrocatalytic CO2 reduction at low overpotentials. Our density functional theory (DFT) calculations predict that the presence of the negatively charged hydrides in the copper cluster plays a critical role in determining the selectivity of the reduction product, yielding HCOOH over CO with a lower overpotential. The HCOOH formation proceeds via the lattice-hydride mechanism: first, surface hydrides reduce CO2 to HCOOH product, and then the hydride vacancies are readily regenerated by the electrochemical proton reduction. DFT calculations further predict that hydrogen evolution is less competitive than HCOOH formation at the low overpotential. Confirming the pr...

Pd-catalyzed cross-coupling reactions have achieved tremendous accomplishments in the past decades. However, C(sp

Graphite-phase polymeric carbon nitride (GPPCN) has emerged as a promising metal-free material toward optoelectronics and (photo)catalysis. However, the insolubility of GPPCN remains one of the biggest impediments toward its potential applications. Herein, we report that GPPCN could be dissolved in concentrated sulfuric acid, the first feasible solvent so far, due to the synergistic protonation and intercalation. The concentration was up to 300 mg/mL, thousands of time higher than previous reported dispersions. As a result, the first successful liquid-state NMR spectra of GPPCN were obtained, which provides a more feasible method to reveal the finer structure of GPPCN. Moreover, at high concentration, a liquid crystal phase for the carbon nitride family was first observed. The successful dissolution of GPPCN and the formation of highly anisotropic mesophases would greatly pave the potential applications such as GPPCN-based nanocomposites or assembly of marcroscopic, ordered materials.

Copper electrocatalysts can reduce CO

Chemical processes driven by nonthermal energy (e.g., visible light) are attractive for future approaches to energy conversion, synthesis, photocatalysis, and so forth. The growth of anisotropic metal nanostructures mediated by excitation of a localized surface plasmon resonance (LSPR) is a prototype example of such a reaction. Important aspects, notably the growth mechanism and a possible role of plasmonic “hot spots” within the metal nanostructures, remain poorly understood. Here, we use in situ electron microscopy to stimulate and image the plasmon-mediated growth of triangular Ag nanoprisms in solution. The quantification of the time-dependent evolution of the lateral size and thickness of the nanoprisms, enabled by nanometer-scale real-time microscopy in solution, shows a transition from an early stage of uniform Ag0 incorporation exclusively in the prism side facets to a size regime with accelerated growth in thickness. Differences in attachment rate at this advanced stage correlate with local plasm...

Successful single-cell isolation is a primary step for subsequent chemical and biological analyses of single cells. Conventional single-cell isolation methods often encounter operational complexity, limited efficiency, deterioration of cell viability, incompetence in the isolation of a single-cell into nanoliter liquid, and/or inability to select single adherent cells with specific phenotypes. Here, we develop a hand-held single-cell pipet (hSCP) that is rapid, operationally simple, highly efficient, and inexpensive for unbiased isolation of single viable suspended cells directly from submicroliter cell suspensions into nanoliter droplets without the assistance of any additional equipment. An integrated SCP (iSCP) has also been developed for selective isolation of single suspended and adherent cells according to the fluorescence imaging and morphological features. The isolated single cells can be conveniently transferred into standard 96-/384-well plates, Petri dishes, or vials for cloning, PCR, and other single-cell biochemical assays.

A new kind of cationic superatom compounds (M-F)(+) (M = OLi4, NLi5, CLi6, BLi7, and Al14) with low vertical electron affinities (VEA) has been designed based on the distinctive electronic structure of superalkaline-earth atom. The stability of the studied superatom architectures is guaranteed by strong M-fluorine interactions, considerable HOMO-LUMO gaps, as well as large dissociation energies. What is extraordinary is that fluorination plays an important role in lowering the VEA value of M(+) and enables the resulting (M-F)(+) fluorides to join the superalkali family. However, the same strategy does not work as well for the alkaline-earth atoms whose valence electrons are more tightly bound. The comparative study on (OLi4-X)(+) (X = F, Cl, Br) reveals that fluorination is more effective than chlorination and bromination to reduce the VEA value of the OLi4(+) cation. As for the (Al14-X)(+) species, there is no obvious dependence of VEA values on halogen atomic number.

The new N,C-chelate boron compounds B(2-phenylazolyl)Mes2 [Mes = mesityl; azolyl = benzothiazolyl (1a), 4-methylthiazolyl (2a), benzoxazolyl (3a), benzimidazolyl (4a)] undergo an unprecedented multistructural transformation upon light irradiation or heating, sequentially producing isomers b, c, d, and e. The dark isomers b generated by photoisomerization of a undergo a rare thermal intramolecular H-atom transfer (HAT), reducing the azole ring and generating new isomers c, which are further transformed into isomers d. Remarkably, isomers d can be converted to their diastereomers e quantitatively by heating, and e can be converted back to d by irradiation at 300 nm. The structures of isomers 1d and 1e were established by X-ray diffraction. The unusual HAT reactivity can be attributed to the geometry of the highly energetic isomers b and the relatively low aromaticity of the azole rings. The boryl unit plays a key role in the reversible interconversion of d and e, as shown by mechanistic pathways established through DFT and TD-DFT calculations.

Inverse-micelle-encapsulated water formed in the two-phase Brust-Schiffrin method (BSM) synthesis of Au nanoparticles (NPs) is identified as essential for dialkyl diselenide/disulfide to react with the Au(III) complex in which the Se-Se/S-S bond is broken, leading to formation of higher-quality Au NPs.

A self-healing dielectric elastomer is achieved by the incorporation of metal-ligand coordination as cross-linking sites in nonpolar polydimethylsiloxane (PDMS) polymers. The ligand is 2,2'-bipyridine-5,5'-dicarboxylic amide, while the metal salts investigated here are Fe(2+) and Zn(2+) with various counteranions. The kinetically labile coordination between Zn(2+) and bipyridine endows the polymer fast self-healing ability at ambient condition. When integrated into organic field-effect transistors (OFETs) as gate dielectrics, transistors with FeCl2 and ZnCl2 salts cross-linked PDMS exhibited increased dielectric constants compared to PDMS and demonstrated hysteresis-free transfer characteristics, owing to the low ion conductivity in PDMS and the strong columbic interaction between metal cations and the small Cl(-) anions which can prevent mobile anions drifting under gate bias. Fully stretchable transistors with FeCl2-PDMS dielectrics were fabricated and exhibited ideal transfer characteristics. The gate leakage current remained low even after 1000 cycles at 100% strain. The mechanical robustness and stable electrical performance proved its suitability for applications in stretchable electronics. On the other hand, transistors with gate dielectrics containing large-sized anions (BF4(-), ClO4(-), CF3SO3(-)) displayed prominent hysteresis due to mobile anions drifting under gate bias voltage. This work provides insights on future design of self-healing stretchable dielectric materials based on metal-ligand cross-linked polymers.

C,C-chelate dimesitylboron (BMes(2)) compounds containing an N-heterocyclic carbene (NHC) donor have been obtained. Single-crystal X-ray diffraction analyses established that the boron atom in these compounds is bound by four carbon atoms in a distorted tetrahedral geometry. Compared to previously reported N,C-chelate dimesitylboron compounds, the new C,C-chelate boron compounds have a much larger HOMO-LUMO energy gap (3.60 eV). They do, however, respond to UV irradiation (300 nm) in the same manner as N,C-chelate BMes(2) compounds do, undergoing photoisomerization and converting to an intensely colored (yellow or orange) isomer A quantitatively, with a high quantum efficiency (0.60-0.75). NMR and single-crystal X-ray diffraction analyses established that the structure of A is similar to the dark isomers obtained from N,C-chelate BMes(2) compounds. However, unlike the N,C-chelate dark isomers that have the tendency to thermally reverse back to the light colored isomers, the isomers A of the C,C-chelate BMes(2) are thermally stable and no reverse isomerization was observed even when heated to 80 °C (or 110 °C) for hours. The most unusual finding is that isomers A undergo further photoisomerization when irradiated at 350 nm, forming a new colorless species B nearly quantitatively. NMR and single-crystal X-ray diffraction analyses established the structure of isomer B, which may be considered as an intramolecular C-H insertion product via a borylene intermediate. Mechanistic aspects of this unusual two-step photoisomerization process have been examined by DFT computational studies.

To control proton delivery across biological membranes, we synthesized a photoresponsive molecular switch and incorporated it in a lipid layer. This proton gate was reversibly activated with 390 nm light (Z-isomer) and then deactivated by 360 nm irradiation (E-isomer). In a lipid layer this stimuli responsive proton gate allowed the regulation of proton flux with irradiation to a lipid-buried O2 reduction electrocatalyst. Thus, the catalyst was turned on and off with the E-to-Z interconversion. This light-induced membrane proton delivery system may be useful in developing any functional device that performs proton-coupled electron-transfer reactions.

A new compound with electride characteristics, Li@calix[4]pyrrole, is designed in theory. The Li atom in Li@calix[4]pyrrole is ionized to form a cation and an excess electron anion. Its structure with C(4v) symmetry resembles a cup-like shape. It may be a stable organic electride at room temperature. The first hyperpolarizability of the cup-like electride molecule is first investigated by the DFT (B3LYP) method. The result shows that this electride molecule has a considerably large first hyperpolarizability with beta(0) = 7326 au (63.3 x 10(-30) esu), while the beta(0) value of the related calix[4]pyrrole system is only 390 au. Obviously, the Li atom doped in calix[4]pyrrole brings a dramatic change to the electronic structure, so that the first hyperpolarizability of Li@calix[4]pyrrole is almost 20 times larger than that of calix[4]pyrrole. We find that the excess electron from the Li atom plays an important role in the large first hyperpolarizability of Li@calix[4]pyrrole. The present investigation reveals a new idea and different means for designing and synthesizing high-performance NLO materials.

Surface diffusion of a water monomer is not as simple as previously imagined. Using state-of-the-art density functional theory, we have obtained important molecular insights relating to the elementary steps of atop-to-atop diffusion of a water monomer. We provide theoretical evidence for an anisotropic effect of rotation-jump coupling on Pd{100}; the preference of H-down tumbling motion along the nearest-neighbor direction of the square lattice was identified. The tumbling motion is attributed to quantum-tunneling-assisted diffusion, while the next-neighbor motion on the square lattice as well as the nearest-neighbor motion on Pd{111} favors molecular- axis-guided classical hopping motion whenever possible. The physical origin of the classical diffusions is discussed in the framework of the electronic structure. Our study gives useful direction for further studies on molecular couplings in the elementary steps.

Qinghaosu and derivatives were easily reduced by ferrous sulfate in aqueous acetonitrile to give results different from those reported for other reducing systems. The unstable epoxide 7, a compound that was postulated earlier as a species responsible for the antimalarial activity, now has been isolated and characterized. The earlier speculative secondary C-4 radical has also been trapped with 2-methyl-2-nitrosopropane and thus provides the very first direct evidence for the involvement of radicals in the in vitro cleavage of QHS-type compounds. A unified mechanism featuring interchangeable radical anions and reversible intramolecular radical reactions is proposed for the ferrous ion induced cleavage of the 1,2,4-trioxanes (i.e., QHS and the like). On the basis of this framework, together with consideration of counterion and solvent effects, a large body of divergent experimental outcomes can be satisfactorily rationalized, not only the formation of the main products but also the product ratios as well as ...

Ivorenolide A (1), a novel 18-membered macrolide featuring conjugated acetylenic bonds and five chiral centers, was isolated from Khaya ivorensis. The structure of 1 was fully determined by spectroscopic analysis, single-crystal X-ray diffraction, and bioinspired total synthesis. Both compound 1 and its synthetic enantiomer 2 showed potent and selective immunosuppressive activity.

Here we report the first unambiguous identification of the chemical structures of the precursor species involving metal (Au and Ag) ions and Te-containing ligands in the Brust–Schiffrin syntheses of the respective metal nanoparticles, through which the different reaction pathways involved are delineated.

A redox-responsive quadruple hydrogen-bonding module (eDAN) has been developed. The strong binding between the reduced form and its partner (DeUG) can be significantly decreased upon oxidation but restored upon subsequent reduction. This on–off switch was successfully applied to provide reversible control of macroscopic supramolecular polymer networks.

A diboron compound with both 3-coordinate boron and 4-coordinate boron centers, (5-BMes2-2-ph-py)BMes2 (1) and its monoboron analogue, (2-ph-py)BMes2 (2) have been synthesized. Both compounds are luminescent but have a high sensitivity toward light. UV and ambient light cause both compounds to isomerize to 1a and 2a, respectively, via the formation of a C-C bond between a mesityl and the phenyl group, accompanied by a drastic color change from yellow or colorless to dark olive green or dark blue. The structures of 1a and 2a were established by 2D NMR experiments and geometry optimization by DFT calculations. Both 1a and 2a can thermally reverse back to 1 and 2 via the breaking of a C-C bond, with the activation barrier being 107 and 110 kJ/mol, respectively. The N,C-chelate ligands in 1 and 2 were found to play a key role in promoting this unusual and reversible photo-thermal isomerization process on a tetrahedral boron center. Reactions with oxygen molecules convert 1a and 2a to 5-BMes2-2-[(2-Mes)-ph]-pyridine (1b) and 2-(2-Mes)-ph-pyridine (2b), respectively.

A highly efficient diastereoselective synthesis of cyclohexadiene epoxide derivatives with a multi-stereocenter has been developed via a tandem ylide Michael addition/epoxidation. By employing a chiral sulfonium ylide, up to 96% ee can be achieved in good yields.

A new type of alkalide compound, Li+(calix[4]pyrrole)M- (M = Li, Na, and K), is presented in theory, which may be stable at room temperature. It has been shown by our calculations that the first hyperpolarizability (beta) is considerably large by means of the density functional theory method. The beta values are determined at the B3LYP/6-311++G level (for the alkali atoms the 6-311++G(3df) basis set is employed) as 8.9 x 103, 1.0 x 104, and 2.4 x 104 au for M = Li, Na, and K, respectively. These beta values are much larger than that of electride Li+(calix[4]pyrrole)e- (beta = 7.3 x 103 au) by a factor of 1.2 to 3.4. Comparing to the cryptand calix[4]pyrrole, the beta values of Li+(calix[4]pyrrole)M- are enhanced by 20-60 times. It is revealed, for the first time, that the beta value of alkalide compounds depends on the atomic number of the alkali anion, and it can be enhanced by choosing the akali anions with larger atomic numbers. The alkali anion in the alkalide compound decreases the transition energy and also increases the oscillator strength of the main transition, consequently the beta value is enhanced. This study proposes such a novel way to synthesize and design new NLO materials by using the alkali atom with a larger atomic number to create an anion in alkalide compounds.

A block copolymer with diselenide bonds in the polymer backbone was reported. This block copolymer was capable of forming micellar aggregates that were responsive to redox stimuli. Compared with other redox responsive aggregates, this type of diselenide-containing block copolymer aggregates could be responsive to both oxidants and reductants even in a solution with a very low concentration under mild conditions.

In the presence of Ph3P and catalytic Fe(TCP)Cl, ketenes could react with EDA to give allenes in high yields under neutral conditions for the first time. By employing chiral phosphine instead of PPh3, allenes could be synthesized with high enantioselectivity (93−98% ee) in good yields.

A new type of alkalide compound, Li+(calix[4]pyrrole)M- (M = Li, Na, and K), is presented in theory, which may be stable at room temperature. It has been shown by our calculations that the first hyperpolarizability (beta) is considerably large by means of the density functional theory method. The beta values are determined at the B3LYP/6-311++G level (for the alkali atoms the 6-311++G(3df) basis set is employed) as 8.9 x 103, 1.0 x 104, and 2.4 x 104 au for M = Li, Na, and K, respectively. These beta values are much larger than that of electride Li+(calix[4]pyrrole)e- (beta = 7.3 x 103 au) by a factor of 1.2 to 3.4. Comparing to the cryptand calix[4]pyrrole, the beta values of Li+(calix[4]pyrrole)M- are enhanced by 20-60 times. It is revealed, for the first time, that the beta value of alkalide compounds depends on the atomic number of the alkali anion, and it can be enhanced by choosing the akali anions with larger atomic numbers. The alkali anion in the alkalide compound decreases the transition energy and also increases the oscillator strength of the main transition, consequently the beta value is enhanced. This study proposes such a novel way to synthesize and design new NLO materials by using the alkali atom with a larger atomic number to create an anion in alkalide compounds.

New insights into the formation chemistry of chalcogenate-protected metal nanoparticles (NPs) synthesized via the well-known Brust-Schiffrin two-phase method are presented here. On the basis of Raman, NMR, and surface plasmon resonance characterizations, it is concluded that, before the formation of any metal-chalcogen bonds, metal nucleation centers/NPs are first formed inside the inverse micelles of the tetrabutylammonium bromide in the organic solvent, where the metal ions are reduced by NaBH(4). The ensuing formation of the metal-chalcogen bonds between the naked metal NPs inside the micelles and the organo-chalcogen ligands in the organic solvent is the mechanism by which the further growth of the metal core can be controlled. This proposed mechanism is further examined in the formation of Ag and Cu NPs.