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Ionic liquids (ILs) are a special category of molten salts solely composed of ions with varied molecular symmetry and charge delocalization. The versatility in combining varied cation-anion moieties and in functionalizing ions with different atoms and molecular groups contributes to their peculiar interactions ranging from weak isotropic associations to strong, specific, and anisotropic forces. A delicate interplay among intra- and intermolecular interactions facilitates the formation of heterogeneous microstructures and liquid morphologies, which further contributes to their striking dynamical properties. Microstructural and dynamical heterogeneities of ILs lead to their multifaceted properties described by an inherent designer feature, which makes ILs important candidates for novel solvents, electrolytes, and functional materials in academia and industrial applications. Due to a massive number of combinations of ion pairs with ion species having distinct molecular structures and IL mixtures containing varied molecular solvents, a comprehensive understanding of their hierarchical structural and dynamical quantities is of great significance for a rational selection of ILs with appropriate properties and thereafter advancing their macroscopic functionalities in applications. In this review, we comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions. [ABSTRACT FROM AUTHOR]

Metallopeptidases cleave polypeptides bound in the active-site cleft of catalytic domains through a general base/acid mechanism. This involves a solvent molecule bound to a catalytic zinc and general regulation of the mechanism through zymogen-based latency. Sixty reported structures from 11 metallopeptidase families reveal that prosegments, mostly N-terminal of the catalytic domain, block the cleft regardless of their size. Prosegments may be peptides (5-14 residues), which are only structured within the zymogens, or large moieties (<227 residues) of one or two folded domains. While some prosegments globally shield the catalytic domain through a few contacts, others specifically run across the cleft in the same or opposite direction as a substrate, making numerous interactions. Some prosegments block the zinc by replacing the solvent with particular side chains, while others use terminal α-amino or carboxylate groups. Overall, metallopeptidase zymogens employ disparate mechanisms that diverge even within families, which supports that latency is less conserved than catalysis. [ABSTRACT FROM AUTHOR]

Two hybrid dyes possessing tetraphenylethylene moieties weakly conjugated with a pyrrolo[3,2-b]pyrrole core have been synthesized. Both dyes display a weak emission in solution, however, in the solid state a ∼100-fold increase in the fluorescence quantum yield is observed. The position of the molecular rotors about the core greatly influences the photophysical characteristics. The variances in emission properties were assigned to entirely different changes in dihedral angles upon excitation, which in turn have substantial effects on radiative rate constants, allowed transitions, and HOMO/LUMO distribution. [ABSTRACT FROM AUTHOR]

We have investigated dimethyl disulfide as the basic moiety for understanding the photochemistry of disulfide bonds, which are central to a broad range of biochemical processes. Picosecond time-resolved X-ray absorption spectroscopy at the sulfur K-edge provides unique element-specific insight into the photochemistry of the disulfide bond initiated by 267 nm femtosecond pulses. We observe a broad but distinct transient induced absorption spectrum which recovers on at least two time scales in the nanosecond range. We employed RASSCF electronic structure calculations to simulate the sulfur-1s transitions of multiple possible chemical species, and identified the methylthiyl and methylperthiyl radicals as the primary reaction products. In addition, we identify disulfur and the CH2S thione as the secondary reaction products of the perthiyl radical that are most likely to explain the observed spectral and kinetic signatures of our experiment. Our study underscores the importance of elemental specificity and the potential of time-resolved X-ray spectroscopy to identify short-lived reaction products in complex reaction schemes that underlie the rich photochemistry of disulfide systems. [ABSTRACT FROM AUTHOR]

We manufactured a hybrid adhesive film capable of curable deoxidization by combining thermoplastics and thermosets. The generated acidic moieties on this hybrid adhesive film completely removed the oxide layer of various Sn-based metal solders and Cu, leading to electrical interconnection. The chemical structure, reaction rate, and glass transition temperature (Tg) of the films were examined via Fourier transform infrared spectroscopy and differential scanning calorimetry. The initial reaction rate of the hybrid deoxidizing adhesive films increased with increasing concentration of anhydride and phenoxy resin. Meanwhile, the reaction rate at the end for curing completion decreased as a function of anhydride and phenoxy resin. Tg of the films decreased with the increase in anhydride and phenoxy resin concentrations. The fabricated film resulted in complete wetting of the solder/Cu for electrical interconnection between semiconductor chips as a promising electronic application. This hybrid film can be useful for various applications requiring deoxidization and adhesion [ABSTRACT FROM AUTHOR]

Upon light-induced isomerization, diarylethenes (DAEs) equipped with reactive aldehyde moieties rearrange selectively in the presence of amines, accompanied by decoloration. In a comprehensive study, the probe structure was optimized with regard to its inherent reactivity in the nucleophile-triggered rearrangement reaction. Detailed structure-reactivity relationships could be derived, in particular with regard to the type of integrated (het)aryl moieties as well as the location of the formyl residue, and the probes' intrinsic reactivity with primary and secondary amines was optimized. Utilizing an ancillary base, the initially formed rearrangement product can engage in a subsequent catalytic cycle, leading to an amplified decoloration process. This additional catalytic pathway allows us to enhance the sensitivity of our method and successfully discriminate between amines and thiols. Moreover, probes that exhibit strong analyte-induced fluorescence modulation have been designed to further decrease the detection limit by using a more sensitive read-out. The optimized DAE probes are promising molecular components for future programmable sensing materials and devices. [ABSTRACT FROM AUTHOR]

The noncovalent functionalization of surfaces has gained widespread interest in the scientific community, and it is progressively becoming an extremely productive research field offering brand new directions for both supramolecular and materials chemistry. As the end-groups often play a dominant role in the surface properties obtained, creating loops with end-groups only at the surface will lead to unexpected architectures and hence properties. Here we report the self-assembly of discrete block molecules--structures in-between block copolymers and liquid crystals--featuring oligodimethylsiloxanes (ODMS) end-capped with naphthalenediimides (NDIs) at the 1-phenyloctane/highly oriented pyrolytic graphite (1-PO/HOPG) interface. These structures produce unprecedented vertically nanophase-separated monolayers featuring NDI moieties that regularly arrange on the HOPG surface, while the highly dynamic ODMS segments form loops above them. Such arrangement is preserved upon drying and generates hydrophobic HOPG substrates in which the ODMS block length tunes the hydrophobicity. Thus, the exact structural fidelity of the discrete macromolecules allows for the correlation of nanoscopic organization with macroscopic properties of the self-assembled materials. We present a general strategy for tunable hydrophobic coatings on graphite based on molecularly combining crystalline aromatic moieties and immiscible oligodimethylsiloxanes. [ABSTRACT FROM AUTHOR]

The stable redox properties of ferrocene/ferrocenium have been used to investigate ferrocene-based functional materials. Herein, the steric effects of an exterior cage on the redox properties of interior metallocenes have been investigated using cyclic voltammetry measurements of ferrocene-diyl bridged macrocages and their noncage isomers. As the half-wave potential (E1/2) depends on ferrocenium stabilization through solvation, positive shifts in the E1/2 were observed in the macrocages. As peak separation between potentials of the anodic and cathodic peaks depends on the rate of electron transfer, marked broadening from the ideal value was observed in the macrocages due to the insulating effect of the outer cage. These steric effects of the cage on the redox properties of ferrocenes could aid the molecular design of metallocene-based functional molecules. [ABSTRACT FROM AUTHOR]

This report describes the C-O, C-N, and C-halogen functionalization of the NiIII-Ar moiety stabilized within a pincer framework that serves as a model system for studying C-heteroatom coupling reactions promoted by high-valent Ni compounds. Treating van Koten's pincer complex (NCN)NIIIIBr2 under a nitrogen atmosphere with water, 1° or 2° alcohols, 1° amines, HCl, or HBr results in heterofunctionalization at the ipso-C of the pincer ligand's aryl moiety. The yields of these heterofunctionalizations are generally <50%, which has been attributed to the occurrence of a comproportionation reaction between the trivalent precursor and a NiI species arising from the reductive elimination step in the functionalization process. Other side-reactions include a C-OH coupling with residual water and C-H coupling (net protonation) that is prevalent with mineral acids, some alcohols, and aqueous NH3. Kinetic measurements have established that the reaction with MeOH is first-order with respect to [(NCN)NiIIIIBr2], and a kinetic isotope effect of 0.47 has been obtained for functionalization with CH3OH/CD3OD. These and other observations have allowed us to propose two different mechanistic postulates for the involvement of trivalent intermediates in the functionalization reactions under discussion. Tetravalent species such as [(NCN)NiIVBr2]+ can be generated in situ under strongly oxidative conditions and they do promote C-Br coupling, but such species play no role in the C-heteroatom coupling reactions under nonoxidative conditions. [ABSTRACT FROM AUTHOR]

Klebsazolicin (KLB) is a recently discovered Klebsiella pneumonia peptide antibiotic targeting the exit tunnel of bacterial ribosome. KLB contains an N-terminal amidine ring and four azole heterocycles installed into a ribosomally synthesized precursor by dedicated maturation machinery. Using an in vitro system for KLB production, we show that the YcaO-domain KlpD maturation enzyme is a bifunctional cyclodehydratase required for the formation of both the core heterocycles and the N-terminal amidine ring. We further demonstrate that the amidine ring is formed concomitantly with proteolytic cleavage of azole-containing pro-KLB by a cellular protease TldD/E. Members of the YcaO family are diverse enzymes known to activate peptide carbonyls during natural product biosynthesis leading to the formation of azoline, macroamidine, and thioamide moieties. The ability of KlpD to simultaneously perform two distinct types of modifications is unprecedented for known YcaO proteins. The versatility of KlpD opens up possibilities for rational introduction of modifications into various peptide backbones. [ABSTRACT FROM AUTHOR]

Heterocyclic polymers have gained enormous attention for their unique functionalities and wide applications. In contrast with the well-studied polymer systems with five-or six-membered heterocycles, functional polymers with readily openable smallring heterocycles have rarely been explored due to their large synthetic difficulty. Herein, a facile one-pot multicomponent polymerization to such polymers is developed. A series of functional polymers with multisubstituted and heteroatom-rich azetidine frameworks are efficiently generated at room temperature in high atom economy from handy monomers. The four-membered azetidine rings in the polymer skeletons can be easily transformed into amide and amidine moieties via a fast and efficient acid-mediated ring-opening reaction, producing brand-new polymeric materials with distinctive properties. All the as-prepared azetidine-containing polymers exhibit intrinsic visible luminescence in the solid state under long-wavelength UV irradiation even without conventionally conjugated structures. Such unconventional luminescence is attributed to the clusteroluminogens formed by through-space electronic interactions of heteroatoms and phenyl rings. All the obtained polymers show excellent optical transparency, high and tunable refractive indices, low optical dispersions and good photopatternability, which make them promising materials in various advanced electronic and optoelectronic devices. The ring-opened polymers can also function as a lysosome-specific fluorescent probe in biological imaging. [ABSTRACT FROM AUTHOR]

The critical roles of solvent, enthalpic, and entropic contributions in complexes between different hyaluronic acid derivatives bearing monomeric β-cyclodextrin and adamantene moieties are assessed combining our previously designed free energy oriented method and a recently proposed density-based noncovalent interaction analysis. This establishes the relevant thermodynamics signatures and identifies the stabilizing/destabilizing noncovalent interactions within the complexes used as models for the junction points. It is observed that structural variations promote major changes in the thermodynamic variables. The presence of the amphiphilic chains emphasizes inclusion and drastically increases the binding constant (to ca. 1028). A comprehensive thermodynamic scheme is thus provided, in which host-guest interactions, host conformation, and solvation play the leading roles. These results have direct implications for the rational design of supramolecular materials with specific properties based on these host-guest systems. [ABSTRACT FROM AUTHOR]

Foams from poly(phthalazinone ether sulfone ketone) containing biphenyl moieties (PPBESK) are prepared by a two-stage batch process using CO2 as foaming agent. Closed microcellular and bicontinuous nanoporous cell morphologies are observed. The effects of saturation pressure, the concentration of CO2 dissolved in PPBESK, and foaming temperature on the porous structure were studied. The results indicate that the key factor for the structure transformation is the concentration of CO2 dissolved in PPBESK. When the CO2 concentration is above the critical value (2.80 g CO2/100 g polymer), the closed microcellular structure changes to bicontinuous nanoporous. So controllable preparation of closed microcellular and bicontinuous nanoporous foams from PPBESK can be achieved by controlling the concentration of CO2 which dissolved in the polymer. Moreover, the tensile properties of the foams were investigated. It is found that the tensile strength of the foams is closely related to its cell structure especially the cell type. [ABSTRACT FROM AUTHOR]

The macrocycle 1 containing four photoresponsive fluorenylidene moieties was designed. The EZEZ form of 1, 1EZEZ, was selectively produced. Reversible photochemical isomerization between 1EZEZ and 1ZZZZ was achieved, the extent of which was dependent on the light source used. Furthermore, the intermediate 1EZZZ was selectively isomerized to 1ZZZZ thermally and photochemically. [ABSTRACT FROM AUTHOR]

Vitrimers are covalently cross-linked polymeric materials that can be thermally processed in a liquid state without losing their network integrity. In this work, novel vitrimers based on the dynamic amine exchange reaction of vinylogous urea moieties are introduced. Following a systematic exploration of different vinylogous acyl compounds (urethanes, amides, and urea), vinylogous urea clearly emerges as showing the fastest intrinsic exchange kinetics. The combination of these networks with a simple acid catalyst (0.5 mol % pTsOH) resulted in materials with good mechanical properties (Tg ~ 110 °C, E ~ 2.2 GPa) and remarkably short relaxation times above Tg, in the order of a few seconds when heated. This attractive combination of properties made it possible to prepare vinylogous urea based composites as enduring prepregs. We demonstrate that the dynamic material properties give fully cured composites that still allow an efficient thermal fusion of multiple layers as well as thermoforming. Finally, we also demonstrate fiber recycling by a simple chemical treatment. [ABSTRACT FROM AUTHOR]

Block copolymer electrolytes have been shown to increase the cycle life of rechargeable batteries that utilize high capacity lithium anodes. Most block copolymer electrolyte studies have been centered on polystyrene-b-poly(ethylene oxide) (SEO) mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and are limited to salt concentrations in the vicinity of r ≡ [Li]/[EO] = 0.1, where [Li] and [EO] are the concentration of lithium and ethylene oxide moieties, respectively, as the conductivity of poly(ethylene oxide) (PEO) homopolymer electrolytes is maximized at this concentration. In this work, we study the morphology and conductivity of electrolytes derived from a high molecular weight SEO block copolymer over the wide LiTFSI concentration range of 0 ≤ r ≤ 0.550. For electrolytes with r ≥ 0.125, the crystallization of PEO--LiTFSI complexes with stoichiometric ratios of 6:1, 3:1, or 2:1 (EO:Li) is shown to correlate with morphology as determined by small-angle X-ray scattering (SAXS) and scanning transmission electron microscopy (STEM): some samples that are semicrystalline at room temperature exhibit regions of periodic lamellar ordering, whereas those that do not crystallize have aperiodic packed-ellipsoid morphologies. SAXS profiles below and above the melting temperatures of the crystals are identical, indicating that the crystals are confined within the block copolymer domains. The conductivities of SEO/LiTFSI mixtures with r = 0.275, r = 0.300, and r = 0.350 are within experimental error of PEO/LiTFSI at the same salt concentrations, in spite of the presence of insulating polystyrene (PS) domains in the SEO/LiTFSI samples. We attribute this to enhanced segmental dynamics of the PEO chains in the SEO electrolytes, based on differential scanning calorimetry (DSC) measurements of glass transition temperatures. The dependence of ionic conductivity on salt concentration in the SEO/LiTFSI electrolytes at temperatures above the melting temperature of the crystalline complexes shows three local maxima that correlate with the formation of crystalline complexes when r ≥ 0.125. These maxima arise due to a combination of the enhanced segmental dynamics and changes in morphology observed by SAXS and STEM. [ABSTRACT FROM AUTHOR]

By reaction of AlEt3 with less than 3 equiv of HORF (RF = C(CF3)3) the ethylaluminum sesquialkoxide (Et)2Al(μ-ORF)2Al(Et)(ORF) (1a; NMR, XRD) can be obtained. As a univalent electronegative residue, the perfluorinated alkoxy moieties can be seen as pseudohalides. In this respect, 1a represents the closest approximation to the hitherto unknown crystal structure of the alkylaluminum sesquihalide Al2R3X3. By further reaction of 1a with HORF, the Lewis superacid Al(ORF)3 is formed, which reacts with Me3SiCl to give Me3Si-Cl-Al(ORF)3 (2a; NMR, XRD, IR, Raman). 2a can be used for further reactions as prepared but slowly decomposes at ca. 0 °C to give the known Me3Si-F-Al(ORF)3 (2b) and several byproducts. The observed decomposition products, combined with quantum chemical calculations, provide evidence for an even higher silylating potential of 2a over that of 2b. [ABSTRACT FROM AUTHOR]

The versatile reactivity of disilenides, heavier analogues of vinyl anions, opened the door to novel heavier group 14 structure motifs with residual functionalities in the periphery around the Si≡Si moiety. The corresponding germanium analogue, digermenide Tip2Ge≡Ge(Tip)Li•dme2 (Tip = 2,4,6-triisopropylphenyl, dme = 1,2-dimethoxyethane), has now been obtained from the reduction of Tip2GeCl2 with 3.3 equiv of Li powder and a catalytic amount of naphthalene in dme at -70 °C. The lithium digermenide was characterized by NMR spectroscopy, UV/vis spectroscopy, X-ray diffraction, and DFT calculations. As proof of principle for its suitability for the nucleophilic transfer of the Ge≡Ge motif, the reaction with chlorosilanes leads to the unsymmetrically substituted digermenes Tip2Ge≡Ge(Tip)SiR3. [ABSTRACT FROM AUTHOR]

Gut microbiota plays important roles in the host health. The host and symbiotic gut microbiota coproduce a large number of metabolites during the metabolism of food and xenobiotics. The analysis of fecal metabolites can provide a noninvasive manner to study the outcome of the host-gut microbiota interaction. Herein, we reported the comprehensive profiling of fecal metabolome of mice by an integrated chemical isotope labeling combined with liquid chromatography-mass spectrometry (CIL-LC-MS) analysis. The metabolites are categorized into several submetabolomes based on the functional moieties (i.e., carboxyl, carbonyl, amine, and thiol) and then analysis of the individual submetabolome was performed. The combined data from the submetabolome form the metabolome with relatively high coverage. To this end, we synthesized stable isotope labeling reagents to label metabolites with different groups, including carboxyl, carbonyl, amine, and thiol groups. We detected 2302 potential metabolites, among which, 1388 could be positively or putatively identified in feces of mice. We then further confirmed 308 metabolites based on our established library of chemically labeled standards and tandem mass spectrometry analysis. With the identified metabolites in feces of mice, we established mice fecal metabolome database, which can be used to readily identify metabolites from feces of mice. Furthermore, we discovered 211 fecal metabolites exhibited significant difference between Alzheimer's disease (AD) model mice and wild type (WT) mice, which suggests the close correlation between the fecal metabolites and AD pathology and provides new potential biomarkers for the diagnosis of AD. [ABSTRACT FROM AUTHOR]

Ligand-to-surface interactions are critical factors in surface and interface chemistry to control the mechanisms governing nanostructured colloidal suspensions. In particular, molecules containing carboxylate moieties (such as citrate anions) have been extensively investigated to stabilize metal, metal oxide, and metal fluoride nanoparticles. Using YF3 nanoparticles as a model system, we show here the self-assembly of citrate-stabilized nanostructures (supraparticles) with a size tunable by temperature. Results from several experimental techniques and molecular dynamics simulations show that the self-assembly of nanoparticles into supraparticles is due to ionic bridges between different nanoparticles. These interactions were caused by cations (e.g., ammonium) strongly adsorbed onto the nanoparticle surface that also interact strongly with nonbonded citrate anions, creating ionic bridges in solution between nanoparticles. Experimentally, we observe self-assembly of nanoparticles into supraparticles at 25 and 100 °C. Interestingly, at high temperatures (100 °C), this citrate-bridge self-assembly mechanism is more efficient, giving rise to larger supraparticles. At low temperatures (5 °C), this mechanism is not observed, and nanoparticles remain stable. Molecular dynamics simulations show that the free energy of a single citrate bridge between nanoparticles in solution is much larger than the thermal energy and in fact is much larger than typical adsorption free energies of ions on colloids. Summarizing our experiments and simulations, we identify as key aspects of the self-assembly mechanism the requirement of NPs with a surface able to adsorb anions and cations and the presence of multidentate ions in solution. This indicates that this new ion-mediated self-assembly mechanism is not specific of YF3 and citrate anions, as supported by preliminary experimental results in other systems. [ABSTRACT FROM AUTHOR]

The synthesis of well-defined graft copolymers with designed intervals between branches was achieved using cyclic acetal moieties as two-stage latent initiating sites. A cyclic acetal was shown to initiate the living cationic polymerization of vinyl ethers (VEs), yielding a polymer with a hydroxy group at the α-end derived from the cyclic acetal. The newly generated hydroxy group was able to efficiently induce the subsequent ring-opening anionic polymerization of l-lactide (LLA), and a diblock copolymer with a narrow molecular weight distribution (MWD) was obtained. For the synthesis of a graft copolymer, a five-membered cyclic acetal moiety was introduced at the ω-chain ends of poly(VE)s, which was employed as the initiating site for the living cationic polymerization of VEs. Repeated polymerization and acetalization generated a macroinitiator with several hydroxy groups on the side chain of a poly(VE) backbone. Graft copolymers possessing branches with narrow MWDs and regular spaces between the branches were synthesized by the ring-opening polymerization of LLA using this macroinitiator. [ABSTRACT FROM AUTHOR]

X-shaped 1,4-phenyleneethynylenes containing a combination of two main group element moieties of B, Si, or P as part of the side chain have been synthesized. The halogen-lithium exchange of 2-bromo-5-dimethylphenylsilyl-1,4-bis(phenylethynyl)benzene followed by addition of fluorodimesitylborane or chlorodiphenylphosphine gave the "X-shaped" B/Si and Si/P, respectively. The P-containing molecule was oxidized to afford a P(═O) derivative. The B/PO moieties were introduced to the 1,4-phenyleneethynylene unit by 3 steps, i.e., the halogen-lithium exchange of 2,5-dibromo-1,4-bis(trimethylsilylethynyl)benzene followed by sequential addition of fluorodimesitylborane and chlorodiphenylphosphine oxide, desilylation, and the Sonogashira coupling with aryl iodides. Then, the reduction of the B/PO gave "X-shaped" B/P derivative. The absorption and fluorescence spectra of the "X-shaped" molecules showed the molecules have two-dimensional conjugation systems, i.e., the π-conjugation of the original π-conjugation backbone and p(B)π-π* conjugation of B, σ*-π* conjugation of Si, and n-π and σ*-π* conjugation of P, extended from the π-core. The highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy levels are significantly altered because of a lowering of the LUMO level due to p-π* conjugation for B and σ*-π* conjugation for Si and P compared with the parent phenyleneethynylene, which are also supported by density functional theory calculations. [ABSTRACT FROM AUTHOR]

Oxo-metal-halide moieties have often been implicated as C-H bond activating oxidants with the terminal oxo-metal entity identified as the electrophilic oxidant. The electrophilic reactivity of metal-halide species has not been investigated. We have prepared a high-valent nickel-halide complex [NiIII(Cl)(L)] (2, L = N,N'-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamide) by one-electron oxidation of a [NiII(Cl)(L)]- precursor. 2 was characterized using electronic absorption, electron paramagnetic resonance, and X-ray absorption spectroscopies and mass spectrometry. 2 reacted readily with substrates containing either phenolic O-H or hydrocarbon C-H bonds. Analysis of the Hammett, Evans-Polanyi, and Marcus relationships between the determined rate constants and substrate pKa, X-H bond dissociation energy, and oxidation potential, respectively, was performed. Through this analysis, we found that 2 reacted by a hydrogen atom transfer (HAT) mechanism. Our findings shine light on enzymatic high-valent oxo-metal-halide oxidants and open new avenues for oxidative halogenation catalyst design. [ABSTRACT FROM AUTHOR]

In situ formation of N-benzylideneaniline (NBA) side groups achieved photoinduced cooperative reorientation of photoinactive copolymers with phenylaldehyde (PA) and benzoic acid (BA) side groups doped with 4-methoxyaniline (AN) molecules. Thermally stimulated molecular reorientation of the side groups was generated due to the axis-selective photoreaction of the NBA moieties. Selective coating with AN on the copolymer film formed NBA moieties in the desired region, resulting in a photoinduced birefringent pattern. Additionally, postannealing at an elevated temperature for a long time attained photoinactivation of the reoriented film, and recoating with AN to form NBA achieved the multiple birefringent patterns and repatterning of the reoriented structures. The slow thermal hydrolysis of NBA, which was 50 times slower than the thermally stimulated self-organization of the side groups due to the presence of BA side groups, contributed to the photodurability of the reoriented film and multiple birefringent patterns. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) with their porous structures that are accommodative of Li salts are considered to be potential candidates for solid-state fast Li+ conductors. However, Li salts simply infiltrated in the pores of solid-state COFs tend to be present in closely associate ion pairs, resulting in slow ionic diffusion dynamics. Here we incorporate cationic skeleton into the COF structure to split the Li salt ion pair through stronger dielectric screening. It is observed that the concentration of free Li+ ions in the resulting material is drastically increased, leading to a significantly improved Li+ conductivity in the absence of any solvent (up to 2.09 × 10-4 S cm-1 at 70 °C). [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) have shown great promise in catalysis, mainly due to their high content of active centers, large internal surface areas, tunable pore size, and versatile chemical functionalities. However, it is a challenge to rationally design and construct MOFs that can serve as highly stable and reusable heterogeneous catalysts. Here two new robust 3D porous metal-cyclam-based zirconium MOFs, denoted VPI-100 (Cu) and VPI-100 (Ni), have been prepared by a modulated synthetic strategy. The frameworks are assembled by eight-connected Zr6 clusters and metallocyclams as organic linkers. Importantly, the cyclam core has accessible axial coordination sites for guest interactions and maintains the electronic properties exhibited by the parent cyclam ring. The VPI-100 MOFs exhibit excellent chemical stability in various organic and aqueous solvents over a wide pH range and show high CO2 uptake capacity (up to ∼9.83 wt% adsorption at 273 K under 1 atm). Moreover, VPI-100 MOFs demonstrate some of the highest reported catalytic activity values (turnover frequency and conversion efficiency) among Zrbased MOFs for the chemical fixation of CO2 with epoxides, including sterically hindered epoxides. The MOFs, which bear dual catalytic sites (Zr and Cu/Ni), enable chemistry not possible with the cyclam ligand under the same conditions and can be used as recoverable stable heterogeneous catalysts without losing performance. [ABSTRACT FROM AUTHOR]

Glassy carbon electrodes were functionalized with redox-active moieties by condensation of o-phenylenediamine derivatives with o-quinone sites native to graphitic carbon surfaces. Electrochemical and spectroscopic investigations establish that these graphite-conjugated catalysts (GCCs) exhibit strong electronic coupling to the electrode, leading to electron transfer (ET) behavior that diverges fundamentally from that of solution-phase or surface-tethered analogues. We find that (1) ET is not observed between the electrode and a redox-active GCC moiety regardless of applied potential. (2) ET is observed at GCCs only if the interfacial reaction is ioncoupled. (3) Even when ET is observed, the oxidation state of a transition metal GCC site remains unchanged. From these observations, we construct a mechanistic model for GCC sites in which ET behavior is identical to that of catalytically active metal surfaces rather than to that of molecules in solution. These results suggest that GCCs provide a versatile platform for bridging molecular and heterogeneous electrocatalysis. [ABSTRACT FROM AUTHOR]

In semicrystalline polymers, the segments around the crystallites typically relax significantly slower than in the purely amorphous phase. This results in an, on average, slower dynamics. Here we present a contrary effect in a star-shaped polymer based on a polyhedral oligomeric silesquioxane (POSS) molecule as center and isotactic polystyrene arms. Measurements by means of broadband dielectric spectroscopy reveal a reduction of the mean relaxation time by up to 1 decade. Analyzing the relaxation time distribution unravels three moieties of different dynamics beyond the crystalline fraction. These are assumed to form respective domains: a rigid amorphous fraction around crystallites, a mobile amorphous fraction, and a confined amorphous fraction of enhanced dynamics presumably located around the POSS centers. Probably, the crystallites in combination with the starlike architecture stabilize the average volume which balances the higher density of the growing crystallites by an increase in free volume in the amorphous domains. [ABSTRACT FROM AUTHOR]

A facile and efficient synthetic grafting-through strategy for preparing well-defined bottlebrush block copolymers (BBCPs) was developed through a combination of living anionic polymerization (LAP) and ring-opening metathesis polymerization (ROMP). ω-End-norbornyl polystyrene (NPSt) and poly(4-tert-butoxystyrene) (NPtBOS) were synthesized by LAP using terminator of chlorine moiety containing silane-protecting amine and coupled with a subsequent amidation using norbornyl activated ester. Bottlebrush homopolymers of NPSt were obtained by ROMP with ultrahigh molecular weights (MWs, Mw = 2928 kDa) and narrow molecular weight distributions (MWDs, Đ = 1.07) at high degree of polymerizations (DPw = 1084). Well-defined BBCPs with ultrahigh MWs (Mw ~ 3055 kDa) and narrow MWDs (Đ ~ 1.13) were synthesized through sequential ROMP of NPSt with NPtBOS. The effect of ultrahigh MWs was investigated by self-assembly of the BBCPs in which the phase-separated BBCPs presented periodic lamellar structures and exhibited structural colors from blue to pink. [ABSTRACT FROM AUTHOR]

Dynamic-covalent chemistry has enabled the facile synthesis of a new generation of degradable materials, but controlling the rate at which these materials degrade remains elusive. Using segmented hyperbranched polymers (SHPs) as model branched architectures, we demonstrate that SHPs containing imine cross-links degrade under acidic conditions into well-defined linear chains at rates controllable via modification of the imine N-substituent. Imine-cross-linked SHPs were synthesized in a one-pot protocol by reversible addition-fragmentation chain transfer (RAFT) copolymerization of novel divinyl compounds containing dynamic-covalent oxime, semicarbazone, and acyl hydrazone moieties. The extent of SHP branching could be controlled through the relative stoichiometric ratios of cross-linker and chain transfer agent (CTA), and studies of the polymerization kinetics confirmed the growth of polydisperse branched species at high monomer conversions. When subjected to aqueous acidic conditions, the polydisperse branched architecture degraded into well-defined polymers, a process that was accelerated under more strongly acidic conditions and by incorporating less hydrolytically stable imine cross-links. Finally, we found that the rate of SHP degradation could be tuned with an unprecedented level of control by cross-linking the polymers with different proportions of multiple imines. [ABSTRACT FROM AUTHOR]

The driving force for the electron transfer (ET) step in the catalytic cycle of cytochrome P450BM3 is investigated using three sets of 1μs molecular dynamic simulations for the resting state of P450 in complex with the flavin (FMN) in the reductase domain. These sets involve the following: (i) substrate-free (SF), (ii) substrate (N-palmitoyl glycine, i.e., NPG)-bound (SB), and (iii) SB with the semiquinone radical anion (SQ-) of FMN. Starting from the X-ray structure of the SF heme domain, we observe that the α1-helix (of the reductase) and the C-helix (of the heme) undergo reorientation to a parallel orientation, which is the thermochemically stable form. The reorientation of the helices pushes away the FMN to a distance of 18.4 Å from the heme's center. When the substrate binds it causes the I-helix of the heme domain to kink and push the C-helix toward the α1-helix, thereby locking the latter two into a stabilized perpendicular conformation, wherein the FMN -- heme distance is 12 Å. The distance drops further in the SQ- form, and upon QM/MM geometry optimization the two moieties approach 8.8 Å, which enhances the ET rate (by 104-106 fold) to the heme's Fe[sup 3+] ion. These motions are driven by hydrogen bond strengthening between the C- and the α1-helices. Finally, substrate binding leads to formation of an organized water chain connecting the FMN and heme moieties. The water channel assists the ET and couples it to the proton transfer steps that should activate O2 and create the oxo -- iron active species. [ABSTRACT FROM AUTHOR]

Over the past two decades, metal-organic frameworks (MOFs) have matured from interesting academic peculiarities toward a continuously expanding class of hybrid, nanoporous materials tuned for targeted technological applications such as gas storage and heterogeneous catalysis. These oft-times crystalline materials, composed of inorganic moieties interconnected by organic ligands, can be endowed with desired structural and chemical features by judiciously functionalizing or substituting these building blocks. As a result of this reticular synthesis, MOF research is situated at the intriguing intersection between chemistry and physics, and the building block approach could pave the way toward the construction of an almost infinite number of possible crystalline structures, provided that they exhibit stability under the desired operational conditions. However, this enormous potential is largely untapped to date, as MOFs have not yet found a major breakthrough in technological applications. One of the remaining challenges for this scale-up is the densification of MOF powders, which is generally achieved by subjecting the material to a pressurization step. However, application of an external pressure may substantially alter the chemical and physical properties of the material. A reliable theoretical guidance that can presynthetically identify the most stable materials could help overcome this technological challenge. In this Account, we describe the recent research the progress on computational characterization of the mechanical stability of MOFs. So far, three complementary approaches have been proposed, focusing on different aspects of mechanical stability: (i) the Born stability criteria, (ii) the anisotropy in mechanical moduli such as the Young and shear moduli, and (iii) the pressure-versus-volume equations of state. As these three methods are grounded in distinct computational approaches, it is expected that their accuracy and efficiency will vary. To date, however, it is unclear which set of properties are suited and reliable for a given application, as a comprehensive comparison for a broad variety of MOFs is absent, impeding the widespread use of these theoretical frameworks. Herein, we fill this gap by critically assessing the performance of the three computational models on a broad set of MOFs that are representative for current applications. These materials encompass the mechanically rigid UiO-66(Zr) and MOF-5(Zn) as well as the flexible MIL-47(V) and MIL-53(Al), which undergo pressure-induced phase transitions. It is observed that the Born stability criteria and pressure-versus-volume equations of state give complementary insight into the macroscopic and microscopic origins of instability, respectively. However, interpretation of the Born stability criteria becomes increasingly difficult when less symmetric materials are considered. Moreover, pressure fluctuations during the simulations hamper their accuracy for flexible materials. In contrast, the pressure-versus-volume equations of state are determined in a thermodynamic ensemble specifically targeted to mitigate the effects of these instantaneous fluctuations, yielding more accurate results. The critical Account presented here paves the way toward a solid computational framework for an extensive presynthetic screening of MOFs to select those that are mechanically stable and can be postsynthetically densified before their use in targeted applications. [ABSTRACT FROM AUTHOR]

Large aromatic carbon nanostructures are cornerstone materials due to their increasingly active role in functional devices, but their synthesis in solution encounters size and shape limitations. New on-surface strategies facilitate the synthesis of large and insoluble planar systems with atomic-scale precision. While dehydrogenation is usually the chemical zipping reaction building up large aromatic carbon structures, mostly benzenoid structures are being produced. Here, we report on a new cyclodehydrogenation reaction transforming a sterically stressed precursor with conjoined cove regions into a planar carbon platform by incorporating azulene moieties in their interior. Submolecular resolution STM is used to characterize this exotic large polycyclic aromatic compound on Au(111) yielding unprecedented insight into a dehydrogenative intramolecular aryl-aryl coupling reaction. The resulting polycyclic aromatic carbon structure shows a [18]annulene core hosting peculiar pore states confined at the carbon cavity. [ABSTRACT FROM AUTHOR]

Some polyzwitterionic brushes exhibit a strong "anti-polyelectrolyte effect" and ionic specificity that make them versatile platforms to build smart surfaces for many applications. However, the structure-property relationship of zwitterionic polymer brushes still remains to be elucidated. Herein, we aim to study the structure-dependent relationship between different zwitterionic polymers and the anti-polyelectrolyte effect. To this end, a series of polyzwitterionic brushes with different cationic moieties (e.g., imidazolium, ammonium, and pyridinium) in their monomeric units and with different carbon spacer lengths (e.g., CSL = 1, 3, and 4) between the cation and anion were designed and synthesized to form polymer brushes via the surface-initiated atom transfer radical polymerization. All zwitterionic brushes were carefully characterized for their surface morphologies, compositions, wettability, and film thicknesses by atomic force microscopy, contact angle measurement, and ellipsometry, respectively. The salt-responsiveness of all zwitterionic brushes to surface hydration and friction was further examined and compared both in water and in salt solutions with different salt concentrations and counterion types. The collective data showed that zwitterionic brushes with different cationic moieties and shorter CSLs in salt solution induced higher surface friction and lower surface hydration than those in water, exhibiting strong anti-polyelectrolyte effect salt-responsive behaviors. By tuning the CSLs, cationic moieties, and salt concentrations and types, the surface wettability can be changed from a highly hydrophobic surface (~60°) to a highly hydrophilic surface (~9°), while interfacial friction can be changed from ultrahigh friction (μ ≈ 4.5) to superior lubrication (μ ≈ 10-3). This work provides important structural insights into how subtle structural changes in zwitterionic polymers can yield great changes in the salt-responsive properties at the interface, which could be used for the development of smart surfaces for different applications. [ABSTRACT FROM AUTHOR]

A series of monomers comprising units bearing both imidazolium bromide ionic liquid (IL) and zwitterionic imidazolium alkyl carboxylate moieties with different alkyl spacer groups are designed and synthesized. RAFT polymerization of these monomers produces a new class of ionic homopolymers, named poly(zwitterionic ionic liquid)s (PZILs), which behave like poly(ionic liquid)s as well as poly(zwitterion)s depending on the solution pH. Such PZILs exhibit an isoelectric point (pI) at pH 5.7, where they exist in their zwitterionic form, making them dual responsive to both pH and temperature. Above pH 5, the aqueous transparent solution of PZIL transforms into turbid suspension due to the formation of insoluble hierarchical nanoaggregates (NAs) of various morphologies such as small spheres, large spheres, flower-like, dendrite-shaped, and dendritic fibril-like depending upon the solution pH and PZILs' structures. The dissolution of aggregates upon heating and reaggregation upon cooling suggests existence of reversible upper critical solution temperature (UCST)-type phase transition above pH 5. Below pH 5, owing to the presence of cationic IL moieties, aqueous PZIL solution exhibits transparent-to-turbid transition due to the formation of anion-induced NAs of various dendritic morphologies upon addition of various chaotropic anions within the Hofmeister series. Upon heating, this colloidal turbid suspension becomes transparent, showing a distinct UCST-type phase transition, and the process is reversible. It is easily possible to fine-tune the cloud point and morphologies of the NAs by changing various parameters such as molecular weight, concentrations, structure of PZILs, nature and concentration of anions, and solution pH. [ABSTRACT FROM AUTHOR]

The syndioselective copolymerization of styrene with ethylene (in bulk or in aliphatic hydrocarbon solutions, (nBu)2Mg as scavenger, Tpolym = 60-140 °C) was achieved in the presence of a series of ansa-lanthanidocenes of the type {R2C(C5H4)(R'R'Flu)}Ln(1,3-C3H3(SiMe3)2)(THF)x (1-Nd-K-allyl, 2-7-Nd, and 2-Sc,La,Sm,Pr). While precursors based on small ionic radius metals (2-Sc) or bearing bulky substituents in 3,6-positions of the fluorenyl moieties (3-Nd and 5-Nd) were poorly or not active under standard polymerization conditions (60 °C), 2-La,Pr,Nd,Sm which bear 2,7-tBu2 substituents on the Flu ligand produced efficiently sPSE materials (productivity 300-400+ kg mol(Ln)-1 h-1, [r]5 = 71%; controlled amount of ethylene inserted in the range 1-15 mol %). Under harsher conditions (Tpolym = 100-140 °C, [St]0/[Nd]0 = 40 000-147 000 equiv), 2-Nd produced similar sPSE materials with a productivity increased by 1 order of magnitude (up to 5430 kg mol(Nd)-1 h-1). Theoretical DFT investigations including the solvent model, performed on the first three insertion steps for the benchmark catalysts {(Me2C(C5H4)(Flu)}Nd(C3H5)(THF) (I), the putative 1-Nd, and the most effective 2-Nd, allowed to corroborate the nature of the obtained copolymers, with ethylene units randomly distributed within long sPS sequences. These studies established also that the presence of bulky substituents on the fluorenyl ligands is crucial in the activity, but the nature of the substituents on the allyl group has no effect on the chemistry and the nature of the resulting styrene-ethylene copolymer but only influences the initiation step in which the first ethylene insertion will be more or less favored with respect to the styrene insertion. [ABSTRACT FROM AUTHOR]

Solid-state organic photoswitches with reversible luminescence modulation property are highly attractive because of their wide prospects in advanced photonic applications, such as optical data storage, anticounterfeiting and bioimaging. Yet, developing such materials has long been a significant challenge. In this work, we construct an efficient solid-state photoswitch based on a spiropyran-functionalized distyrylanthracene derivative (DSA-2SP) that exhibits exceptional reversible absorption/luminescence modulation ability. Efficient photoswitching between DSA-2SP and its photoisomer DSA-2MC are facilitated by large free volumes induced by nonplanar molecular structures of DSA moieties, as well as the intramolecular hydrogen bonds between the DSA and MC moieties. Consequently, the excellent solid-state photochromic property of DSA-2SP is highly applicable as both anticounterfeiting inks and super-resolution imaging agents. [ABSTRACT FROM AUTHOR]

Peptides are among the most efficient classes of crystal growth modifiers for a wide range of natural and synthetic systems owing to their unmatched design space that affords the opportunity to construct highly specific sequences to tailor crystal growth. In the case of zeolite crystallization, the high pH and temperature of common synthesis conditions renders peptides ineffective for such applications. Here, we introduce peptoids as a biomimetic platform for the rational design of zeolite growth modifiers. The chemical robustness of peptoids coupled with their facile and efficient synthesis on solid support, which enables the generation of versatile sequences with diverse chemical functionality, make these materials ideal for the relatively harsh conditions of zeolite crystallization. A library of peptoids incorporating combinations of alcohol, amine, ether, and aromatic functional moieties were synthesized and tested in growth solutions of zeolite L (LTL type), a common commercial material. Our findings reveal that peptoids are potent modifiers of zeolite L crystallization. Syntheses with 1 wt % are often sufficient to suppress nucleation, indicating a strong interaction between peptoids and the amorphous precursors formed during the early stages of zeolite L synthesis. Chemical analysis reveals that a significant fraction of peptoid remains intact at pH 13 and 160 °C, though peptoid degradation occurs with prolonged hydrothermal treatment. Time-resolved analysis of products removed from zeolite L growth mixtures reveals that amines interact more favorably than alcohols with precursors/crystals. Our studies also confirm that peptoids can be tailored to either increase or decrease the length-to-width aspect ratio of cylindrical zeolite L crystals through the insertion of hydrophilic or hydrophobic groups, respectively. The mechanisms of peptoid action are discussed within the context of complex nonclassical pathways of zeolite crystallization. Moreover, this study provides the first testing and validation of peptoids as zeolite growth modifiers, thus opening new avenues in the future to extend this general platform to other zeolite framework types and related materials grown under conditions that are too severe for biomolecules. [ABSTRACT FROM AUTHOR]

O-Methyloscillatoxin D and its analogues were concisely synthesized by a bioinspired intramolecular Mukaiyama aldol reaction as a key step, which involves the construction of a novel spiro-ether moiety. [ABSTRACT FROM AUTHOR]

Three new compounds, designated scopranones A-C, were isolated from the culture broth of a soil isolate, Streptomyces sp. BYK-11038, and shown to be inhibitors of bone morphogenetic protein (BMP) induced alkaline phosphatase activity in a BMP receptor mutant cell line. The structures were elucidated using NMR and other spectral data. The scopranones have an unusual structure with two atypical scooplike moieties linked at the tails to form part of a unique 3-furanone ring. [ABSTRACT FROM AUTHOR]

Manginoids A-G (1-7), seven monoterpene-shikimate-conjugated meroterpenoids with a spiro ring system, were isolated from Guignardia mangiferae. Compounds 1-4 are four isomers with epimeric and double-bond isomeric features possessing a 6-oxaspiro[bicyclo[3.2.1]octane-3,5'-indene] ring, which represent the first examples of spiro meroterpenoids bearing a bridged spirocyclohexanedione moiety. Compounds 5 and 6 possess an unexpected 2,4-dioxatricyclo[3.3.1.03,7]nonane motif, which fuses with a 6-oxabicyclo[3.2.1]octane moiety. Compound 1 exhibits inhibitory activities against 11β-hydroxysteroid dehydrogenase type 1 with an IC50 value of 0.84 μM. [ABSTRACT FROM AUTHOR]

Two prenyltransferases from Aspergillus ruber control the echinulin biosynthesis via exceptional sequential prenylations. EchPT1 catalyzes the first prenylation step, leading to preechinulin. The unique EchPT2 attaches, in a consecutive prenylation cascade, up to three dimethylallyl moieties to preechinulin and its dehydro forms neoechinulins A and B, resulting in the formation of at least 23 2- to 4-fold prenylated derivatives. Confirming these products in fungal extracts unravels the unprecedented catalytic relevance of EchPT2 for structural diversity. [ABSTRACT FROM AUTHOR]

The microdynamic volume phase transition mechanism of poly[di(ethylene glycol)ethyl ether acrylate] (PDEGA)-based microgels with newly developed thermoresponsive polyionic liquid (PIL) (poly(tetrabutylphosphonium styrenesulfonate) P[P4,4,4,4][SS]) moieties was studied by applying temperature-variable Fourier transform infrared (FTIR) spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and the perturbation correlation moving window (PCMW) technique. It can be found that the content of hydrophilic PIL moieties plays a significant role in the thermally induced phase transition behavior of microgel systems; namely, the microgels containing fewer PIL moieties present a sharp transition behavior and a gel-like state (10%, w/v) in water whereas the microgels with more PIL moieties undergo a slightly broad phase transition process and a flowable solution state. Herein, the C=O… D2O-PIL hydrogen bonds as the interaction between PDEGA and P[P4,4,4,4][SS] moieties result in a complete dehydration process for the microgels with fewer PIL moieties and the dehydrated behavior of SO3 - groups acts as the driving force during the phase transition. As for the microgels with more PIL moieties, the whole transition process is dominated by the hydrophobic interaction of C-H groups. Even though the intermolecular hydrogen bonds (C=O… D2O-PIL) appear as well, the more remarkable effect of the Coulombic repulsive force of PIL restrains the water molecules from breaking away, thus causing a gradual and incomplete dehydration process during heating. [ABSTRACT FROM AUTHOR]

Quenching of the excited singlet states of a water-soluble, sterically congested tetraarylpyrene, 1,3,6,8-tetrakis(2,6-dimethyl-4-(a-carboxy)methoxyphenyl)pyrene (Py4C), by a series of iodide salts has been investigated by steady-state and time-resolved fluorescence measurements. Access to the pyrenyl group of Py4C is restricted sterically as a result of the four flanking (2,6-dimethylphenoxy)acetic acid groups and the energy costs associated with their rotation. Deprotonation of the carboxylic acid groups of Py4C permits examination of ion-ion electrostatic interactions on the rates of quenching by iodide salts in which different steric and electrostatic factors are introduced by varying the cationic portions. At the same concentrations and with the same cations, chloride anions are ineffective quenchers. The quenching rate constants of Py4C by iodide are found to correlate linearly with the ionic radii of the cations and their enthalpies of hydration. These correlations are discussed in terms of the Hofmeister series. Furthermore, the results indicate that the cations that flank Py4C decrease the quenching efficiency of iodide through polarization and shielding effects (i.e., lowering the effective charge), which isolate to varying degrees the p-system. The effects of the different cations on quenching the fluorescence of a simpler and sterically unencumbered pyrenyl derivative, 1-pyrenylbutyric acid (PyBu), by iodide are much smaller. Overall, the results with Py4C indicate that the fluorescence quenching efficiency by iodide is influenced by direct interactions with the cations associated with the carboxylate groups of Py4C and not the solvation of water molecules. This observation is germane to a topic of current debate: Are the effects of the cations more closely related to bulk water properties or to direct ion-ion interactions? The conclusions obtained from these studies are applicable clearly to a wide variety of other systems in which ion pairing influences cooperative or inhibitory interactions. [ABSTRACT FROM AUTHOR]

We present a strategy for robustly cross-linking self-assembled lamellar mesophases made from plant-derived materials to generate polymer nanosheets decorated with a high density of functional groups. We formulate a supramoleclar complex by hydrogen-bonding conjugated linoleic acid moieties to a structure-directing tribasic aromatic core. The resulting constructs self-assemble into a thermotropic lamellar mesophase. Photo-cross-linking the mesophase with the aid of an acrylate cross-linker yields a polymeric material with high-fidelity retention of the lamellar mesophase structure. Transmission electron microscopy images demonstrate the preservation of the large area, highly ordered layered nanostructures in the polymer. Subsequent extraction of the tribasic core and neutralization of the carboxyl groups by NaOH result in exfoliation of polymer nanosheets with a uniform thickness of ~3 nm. The nanosheets have a large specific area of ~800 m²/g, are decorated by negatively charged carboxylate groups at a density of 4 nm-2, and exhibit the ability to readily adsorb positively charged colloidal particles. The strategy as presented combines supramolecular self-assembly with the use of renewable or sustainably derived materials in a scalable manner. The resulting nanosheets have potential for use as adsorbents and, with further development, rheology modifiers. [ABSTRACT FROM AUTHOR]

Macrophorins are representative examples of isoprenoid epoxycyclohexenones containing cyclized drimane moieties. We located and characterized the biosynthetic gene cluster of macrophorin from Penicillium terrestris. MacJ encoded by this cluster was characterized to be the first example of a membrane-bound type-II terpene cyclase catalyzing the cyclization of meroterpenoids via direct protonation of the terminal olefinic bond in acyclic yanuthones. The late-stage functionalization and substrate promiscuity of MacJ make it a potential biocatalyst for the synthesis of macrophorin analogues. [ABSTRACT FROM AUTHOR]

An unprecedented Dy8 cluster, [Dy8(µ4-O)(µ3-OH)8(vht)4(NO3)2(H2O)8](NO3)4, composed of two fused and distorted [Dy4(µ3-OH)4]8+ cubane units is reported. The bridging of the two cubanes occurs through a planar µ4-O (oxide) moiety, and leads to the largest reported distortion of the Dy-O-Dy angles within a [Dy4(OH)4] cubane core. In turn, this leads to clear zero-field slow relaxation of the magnetization, characteristic of single-molecule magnets (SMMs). Further magnetic analyses suggest that the relaxation may be largely dictated by quantum tunneling of the magnetization and Raman processes. [ABSTRACT FROM AUTHOR]

Electrospinning provides a facile and versatile method for generating nanofibers from a large variety of starting materials, including polymers, ceramic, composites, and micro-/nanocolloids. In particular, incorporating functional nanoparticles (NPs) with polymeric materials endows the electrospun fibers/sheets with novel or better performance. This work evaluates the spinnability of polyacrylamide (PAAm) solution containing thermoresponsive poly(N-isopropylacrylamide-co-tert-butyl acrylate) microgel nanospheres (PNTs) prepared by colloid electrospinning. In the presence of a suitable weight ratio (1:4) of PAAm and PNTs, the in-fiber arrangements of PNTs-electrospun fibers will evolve into chain-like arrays and beads-on-string structures by confining of PAAm nanofibers, and then the free amide groups of PAAm can bind amide moieties on the surfaces of PNTs, resulting in the assembling of PNTs in the cores of PAAm fibers. The present work serves as a reference in the fabrication of novel thermoresponsive hybrid fibers involving functional nanospheres via electrospun packing. The prepared nanofibers with chain-like and thermoresponsive colloid arrays in the cores are expected to have potential application in various fields. [ABSTRACT FROM AUTHOR]

We report the formation of macroscopic wires up to centimeters in length from a series of structurally flexible, covalently tethered small-molecular fluorophore-quencher dyads (FQDs, average MW = 425 Da), comprised of carbazole, melatonin, and cyanobenzoate moieties. These FQDs are nonemissive in organic solutions but become moderately to highly luminescent (ΦF = 0.037-0.39) upon formation of wires with emission maxima in the blue region (446-483 nm). The blue photoluminescence (PL) is ascribed to a combination of singlet charge transfer, localized triplet state, and possibly delayed fluorescence emissions with intrinsic luminescence lifetimes ranging from 0.228 to 21333 μs, based on luminescence, transient absorption measurements, X-ray diffraction, and calculations. [ABSTRACT FROM AUTHOR]

Despite its commercial success, isotactic polypropylene (PP) is not suitable for the applications that require long-term exposure to high-energy conditions, such as elevated temperatures, UV radiation, or high electric fields, due to the combination of polymer chain oxidative degradation, incompatibility with polar additives (antioxidants, stabilizers, etc.), and low material softening temperature. This paper presents a new solution that can simultaneously address both chemical and physical limitations. The idea is to develop a new PP-HP copolymer that contains some specific hindered phenol (HP) groups, homogeneously distributed along the polymer chain. These PP-bound HP pendant groups can not only effectively protect PP chains from the oxidative degradation but also engage in a facile cross-linking reaction to form a 3-D network structure during the oxidation reaction. One accelerated oxidation test in air at 190-210 °C shows this distinctive advantage. While a commercial PP polymer (containing common antioxidants and stabilizers) degrades within 1 h, a PP-HP copolymer with about 1 mol % (9 wt %) HP groups shows almost no detectable weight loss after 1000 min. In an ASTM endurance test under a targeted application temperature (140 °C in air), the commercial PP shows 1% weight loss within about 10 days. On the other hand, this new PP-HP lasts for 105 days (4 order increase) under the same condition. In the strain-stress curve measurement, the PP-HP film also shows no detectable change in tensile strength and modulus after constant heating the polymer film at 140 °C in air for 1 week. Overall, the experiment results present the potential of expanding PP applications into a much higher temperature range (>140 °C) under oxygen oxidative environments. [ABSTRACT FROM AUTHOR]