SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Ionic bond

166

Until now, few sp carbon materials simultaneously exhibit superior performance for specific surface area (SSA) and electrical conductivity at bulk state. Thus, it is extremely important to make such materials at bulk scale with those two outstanding properties combined together. Here, we present a simple and green but very efficient approach using two standard and simple industry steps to make such three-dimensional graphene-based porous materials at the bulk scale, with ultrahigh SSA (3523 m/g) and excellent bulk conductivity. We conclude that these materials consist of mainly defected/wrinkled single layer graphene sheets in the dimensional size of a few nanometers, with at least some covalent bond between each other. The outstanding properties of these materials are demonstrated by their superior supercapacitor performance in ionic liquid with specific capacitance and energy density of 231 F/g and 98 Wh/kg, respectively, so far the best reported capacitance performance for all bulk carbon materials.

Concepts: Fundamental physics concepts, Density, Water, Chemical bond, Physical quantities, Ionic bond, Specific surface area, Porous media

35

In vivo tumor imaging with nanoprobes suffers from poor tumor specificity. Here, we introduce a nanosystem, which allows selective background quenching to gain exceptionally tumor-specific signals. The system uses near-infrared quantum dots and a membrane-impermeable etchant, which serves as a cation donor. The etchant rapidly quenches the quantum dots through cation exchange (ionic etching), and facilitates renal clearance of metal ions released from the quantum dots. The quantum dots are intravenously delivered into orthotopic breast and pancreas tumors in mice by using the tumor-penetrating iRGD peptide. Subsequent etching quenches excess quantum dots, leaving a highly tumor-specific signal provided by the intact quantum dots remaining in the extravascular tumor cells and fibroblasts. No toxicity is noted. The system also facilitates the detection of peritoneal tumors with high specificity upon intraperitoneal tumor targeting and selective etching of excess untargeted quantum dots. In vivo cation exchange may be a promising strategy to enhance specificity of tumor imaging.The imaging of tumors in vivo using nanoprobes has been challenging due to the lack of sufficient tumor specificity. Here, the authors develop a tumor-specific quantum dot system that permits in vivo cation exchange to achieve selective background quenching and high tumor-specific imaging.

Concepts: Cancer, Tumor, Ionic bond

30

The rational design of improved electrode-electrolyte interfaces (EEI) for energy storage is critically dependent on a molecular-level understanding of ionic interactions and nanoscale phenomena. The presence of non-redox active species at EEI has been shown to strongly influence Faradaic efficiency and long-term operational stability during energy storage processes. Herein, we achieve substantially higher performance and long-term stability of EEI prepared with highly dispersed discrete redox-active cluster anions (50 ng of pure ∼0.75 nm size molybdenum polyoxometalate (POM) anions on 25 μg (∼0.2 wt%) carbon nanotube (CNT) electrodes) by complete elimination of strongly coordinating non-redox species through ion soft landing (SL). Electron microscopy provides atomically resolved images of a uniform distribution of individual POM species soft landed directly on complex technologically relevant CNT electrodes. In this context, SL is established as a versatile approach for the controlled design of novel surfaces for both fundamental and applied research in energy storage.

Concepts: Electron, Quantum mechanics, Molecule, Atom, Chemical bond, Ion, Carbon nanotube, Ionic bond

29

The degradation of some organophosphorus pesticides (OPPs) in the presence of metal ions was studied by (31)P-NMR spectroscopy. Both (31)P-NMR and gas chromatography/mass spectroscopy results were used in order to determine the nature of metabolites formed after degradation. The degraded organophosphorus pesticide were investigated for chlorpyrifos and phoxim in the presence of several metal ions including Hg(2+), Cu(2+), Cd(2+), Ni(2+), Pb(2+), and Ag(+). (31)P-NMR results indicated Ag(+) and Hg(2+) ion promoted degradation of OPPs and other metal ions formed complex with OPPs and cannot degrade OPPs. We found that the degradation of chlorpyrifos and phoxim with Ag(+) or Hg(2+) led to the formation of O,O-diethyl-O-methyl phosphorothionate, (C(2)H(5)O)(2)(CH(3)O)PS, at metal ion/pesticide mole ratios ≤1.0 and completely decomposed at a higher mole ratio of 10. Finally, the method was successfully applied to the degradation study of a number of technical and formulated pesticides in the presence of Ag(+) ion at a metal ion/pesticide mole ratio of 10.

Concepts: Iron, Hydrogen, Metal, Solid, Potassium, Silver, Ionic bond, Nickel

28

Pyramidane is one of the elusive and highly desirable targets for synthetic chemists that has attracted a great deal of attention because of its nonclassical structure and unusual bonding features. Although well studied on theoretical grounds, neither parent pyramidane nor its derivatives have ever been isolated and characterized. In this contribution, we report on the synthesis and structural elucidation of the first stable representatives of this class of highly strained polyhedral compounds: germa- and stannapyramidanes Ge[C4(SiMe3)4] and Sn[C4(SiMe3)4]. The peculiar structural and bonding features of these compounds are verified by combined experimental and computational analyses, showing these derivatives to be nonclassical neutral compounds with a very large contribution of ionic character.

Concepts: Scientific method, Structure, Science, Philosophy of science, Logic, Ionic bond, Polyhedron, Polyhedral compound

28

The time-of-flight secondary ion mass spectrometry (TOF-SIMS) has emerged as a powerful tool for the unswerving detection of biomolecules, in particular, proteins and peptides. To date, there is very little information available on the direct determination of trimethyl/triethyl amines using TOF-SIMS. One major hurdle in this regard is an ultrahigh vacuum system, usually needed in TOF-SIMS, which hampers its usability to trimethyl/triethyl amines owing to their high evaporation rate. We designed an efficient and sensitive protocol for rapid identification and sensitive determination of tertiaryalkyl amines using TOF-SIMS. The amines were derivatized by reaction with 1,4-butane sultone and sulphuric acid sequentially to afford the corresponding sulphonic acidic ionic liquids (ILs). The TOF-SIMS analysis of these task-specific ILs (TSILs) was carried out in both positive and negative polarity. The positive ion mass spectra of TSILs showed sharp fragmented peaks for tertiaryalkyl amines at typical level and up to 10ppm. The possible mechanism for different fragmentation pathways in positive polarity was discussed.

Concepts: Amino acid, Acid, Ammonia, Mass spectrometry, Hydrogen, Ion source, Ionic bond, Polarity item

27

Ion conduction and transport in solids are both interesting and useful and are found in widely distinct materials, from those in battery-related technologies to those in biological systems. Scientists have approached the synthesis of ion-conductive compounds in a variety of ways, in the areas of organic and inorganic chemistry. Recently, based on their ion-conducting behavior, porous coordination polymers (PCPs) and metal-organic frameworks (MOFs) have been recognized for their easy design and the dynamic behavior of the ionic components in the structures. These PCP/MOFs consist of metal ions (or clusters) and organic ligands structured via coordination bonds. They could have highly concentrated mobile ions with dynamic behavior, and their characteristics have inspired the design of a new class of ion conductors and transporters. In this Account, we describe the state-of-the-art of studies of ion conductivity by PCP/MOFs and nonporous coordination polymers (CPs) and offer future perspectives. PCP/MOF structures tend to have high hydrophilicity and guest-accessible voids, and scientists have reported many water-mediated proton (H(+)) conductivities. Chemical modification of organic ligands can change the hydrated H(+) conductivity over a wide range. On the other hand, the designable structures also permit water-free (anhydrous) H(+) conductivity. The incorporation of protic guests such as imidazole and 1,2,4-triazole into the microchannels of PCP/MOFs promotes the dynamic motion of guest molecules, resulting in high H(+) conduction without water. Not only the host-guest systems, but the embedding of protic organic groups on CPs also results in inherent H(+) conductivity. We have observed high H(+) conductivities under anhydrous conditions and in the intermediate temperature region of organic and inorganic conductors. The keys to successful construction are highly mobile ionic species and appropriate intervals of ion-hopping sites in the structures. Lithium (Li(+)) and other ions can also be transported. If we can optimize the crystal structures, this could offer further improvements in terms of both conductivity and the working temperature range. Another useful characteristic of PCP/MOFs is their wide application to materials fabrication. We can easily prepare heterodomain crystal systems, such as core-shell or solid solution. Other anisotropic morphologies (thin film, nanocrystal, nanorod, etc.,) are also possible, with retention of the ion conductivity. The flexible nature also lets us design morphology-dependent ion-conduction behaviors that we cannot observe in the bulk state. We propose (1) multivalent ion and anion conductions with the aid of redox activity and defects in structures, (2) control of ion transport behavior by applying external stimuli, (3) anomalous conductivity at the hetero-solid-solid interface, and (4) unidirectional ion transport as in the ion channels in membrane proteins. In the future, scientists may use coordination polymers not only to achieve higher conductivity but also to control ion behavior, which will open new avenues in solid-state ionics.

Concepts: Ammonia, Hydrogen, Chemistry, Ion, Solid, Sodium, Inorganic chemistry, Ionic bond

27

Chitosan grafted with polymethyl methacrylate (PMMA-g-CS) was prepared via a free-radicals polymerization technique as a carrier for enzyme immobilization. α-Chymotrypsin (CT), as an enzyme model in this study, was immobilized onto the prepared PMMA-g-CS via covalent bonding. Calcium alginate (CA) beads were developed for encapsulating PMMA-g-CS-CT to produce PMMA-g-CS-CT/CA composite beads. Morphology and size of PMMA-g-CS particles were investigated by TEM and found to be in the nanoscale. The structure and surface morphology of the beads before and after immobilization process were characterized by FT-IR and SEM, respectively. Both the bound CT content and relative activity of immobilized enzyme were measured. A higher retained activity (about 97.7%) obtained for the immobilized CT at pH 9 for 24h. The results indicated that immobilized CT maintained excellent performance even after 25 reuses and retained 75% from its original activity after 60 days of storage at 25°C.

Concepts: Electron, Enzyme, Atom, PH, Covalent bond, Ionic bond, Immobilized enzyme, Calcium alginate

26

Metal isotope coded profiling (MICP) introduces a universal discovery platform for metal chelating natural products that act as metallophores, ion buffers or sequestering agents. The detection of cation and oxoanion complexing ligands is facilitated by the identification of unique isotopic signatures created by the application of isotopically pure metals.

Concepts: Hydrogen, Ligand, Metal, Solid, Potassium, Silver, Ionic bond, Chelation

26

The dissolution of NaCl has been systematically investigated by employing ab initio molecular dynamics (AIMD) on different NaCl nanocrystals as well as on a surface system immersed in water. We discovered a complex dissolution process simultaneously involving multiple ions initiated at the corner sites of the crystal. Our simulations indicated a difference in the dissolution rates of sodium and chlorine. While sodiums readily became partially solvated, chlorines more frequently transitioned into the fully solvated state leading to an overall greater dissolution rate for Cl. We determined that this difference arises due to faster water mediated elongations of individual ionic bonds to Na, but a significantly slower process for the last bond in comparison to Cl. In an attempt to investigate this phenomenon further, we performed metadynamics based free energy simulations on a surface slab presenting corner sites similar to those in cubic crystals, aiming to extract the dissolution free energy profile of corner ions. In qualitative agreement with the nanocrystal simulations, this revealed a shallower first free energy minimum for Na, but no statistically significant difference in the corresponding barriers and inconclusive results for the latter stage. Finally, simulations of smaller NaCl crystals illustrated how dissolution proceeds beyond the point of crystal lattice collapse, highlighting the strength of solvated ion interactions.

Concepts: Chemistry, Atom, Chemical bond, Sodium chloride, Ion, Sodium, Chlorine, Ionic bond