“Click” Chemistry Mildly Stabilizes Bifunctional Gold Nanoparticles for Sensing and Catalysis

A large family of bifunctional 1,2,3‐triazole derivatives that contain both a polyethylene glycol (PEG) chain and another functional fragment (e.g., a polymer, dendron, alcohol, carboxylic acid, allyl, fluorescence dye, redox‐robust metal complex, or a β‐cyclodextrin unit) has been synthesized by facile “click” chemistry and mildly coordinated to nanogold particles, thus providing stable water‐soluble gold nanoparticles (AuNPs) in the size range 3.0–11.2 nm with various properties and applications. In particular, the sensing properties of these AuNPs are illustrated through the detection of an analogue of a warfare agent (i.e., sulfur mustard) by means of a fluorescence “turn‐on” assay, and the catalytic activity of the smallest triazole–AuNPs (core of 3.0 nm) is excellent for the reduction of 4‐nitrophenol in water.     

Chemistry with ADF

We present the theoretical and technical foundations of the Amsterdam Density Functional (ADF) program with a survey of the characteristics of the code (numerical integration, density fitting for the Coulomb potential, and STO basis functions). Recent developments enhance the efficiency of ADF (e.g., parallelization, near order‐N scaling, QM/MM) and its functionality (e.g., NMR chemical shifts, COSMO solvent effects, ZORA relativistic method, excitation energies, frequency‐dependent (hyper)polarizabilities, atomic VDD charges). In the Applications section we discuss the physical model of the electronic structure and the chemical bond, i.e., the Kohn–Sham molecular orbital (MO) theory, and illustrate the power of the Kohn–Sham MO model in conjunction with the ADF‐typical fragment approach to quantitatively understand and predict chemical phenomena. We review the “Activation‐strain TS interaction” (ATS) model of chemical reactivity as a conceptual framework for understanding how activation barriers of various types of (competing) reaction mechanisms arise and how they may be controlled, for example, in organic chemistry or homogeneous catalysis. Finally, we include a brief discussion of exemplary applications in the field of biochemistry (structure and bonding of DNA) and of time‐dependent density functional theory (TDDFT) to indicate how this development further reinforces the ADF tools for the analysis of chemical phenomena. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 931–967, 2001     

Reversible Thermal Switching of Aqueous Dispersibility of Multiwalled Carbon Nanotubes

Easily reversible aqueous dispersion/precipitation of multiwalled carbon nanotubes (MWNTs) has been demonstrated using small‐molecule non‐ionic pyrene‐based surfactants, which exhibit lower critical solution temperature (LCST) phase behaviour. The MWNTs are dispersed by means of non‐covalent interactions. The dispersibility can be switched “off” (i.e., MWNTs precipitated) upon heating and switched “on” (i.e., MWNTs re‐dispersed) upon cooling and merely swirling the sample at room temperature, that is, under very mild conditions. This effect is also observed under high ionic strength conditions with NaCl in the aqueous phase.     

Mean‐field theoretical analysis of brush‐coated nanoparticle dispersion in polymer matrices

The equilibrium dispersion of nanoparticles with grafted polymer chains into polymer matrices, of the same chemical structure as the brush, is studied through the device of mean‐field theory. Our results show that the disperion of brush‐coated nanoparticles into a matrix polymer is improved with (i) decreasing particle radius and (ii) increasing brush chain length. Both of these aspects can be understood based on the fact that, unlike the case of planar surfaces, homopolymer chains end‐grafted to spherical nanoparticle surfaces tangentially spread away from the surface thus alleviating the packing frustration that is created by the relatively high grafting densities. This permits significant brush/matrix overlap, even at high grafting densities, a regime that has only recently become experimentally available due to advances in polymer synthesis (i.e., the “grafting‐to” methods). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 351–358, 2008     

Renewable benzoxazine monomer from Vanillin: Synthesis,characterization, and studies on curing behavior

A novel renewable based benzoxazine, 3‐(furan‐2‐ylmethyl)?8‐methoxy‐3,4‐dihydro‐2H‐1,3‐benzoxazine‐6‐formyl (Va‐Bz), has been synthesized from a lignin derived chemical “vanillin” without solvents. Poly (Va‐Bz) has high Tg and excellent thermal and adhesive properties. A mechanism of cross‐linking, due to electrophilic substitution at furan and decarboxylation of carboxylic group of benzene ring, is suggested. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 7–11     

Bonding Nature of Local Structural Motifs in Amorphous GeTe

Despite its simple chemical constitution and unparalleled technological importance, the phase‐change material germanium telluride (GeTe) still poses fundamental questions. In particular, the bonding mechanisms in amorphous GeTe have remained elusive to date, owing to the lack of suitable bond‐analysis tools. Herein, we introduce a bonding indicator for amorphous structures, dubbed “bond‐weighted distribution function” (BWDF), and we apply this method to amorphous GeTe. The results underline a peculiar role of homopolar Ge? Ge bonds, which locally stabilize tetrahedral fragments but not the global network. This atom‐resolved (i.e., chemical) perspective has implications for the stability of amorphous “zero bits” and thus for the technologically relevant resistance‐drift phenomenon.     

Controlled polymer synthesis in homogeneous and heterogeneous processes

Research in polymer synthesis can be oriented toward method or structure. This review is intended to document both approaches. Recent examples from our own work as well as future prospectives will be presented. A general concern is to work out the impact from organic and supramolecular chemistry. Examples of method oriented work are (i) a unique polycondensation via carbon sulfur‐bond formation providing hybrid structures of, e.g., polyphenylenesulfide and polyaniline; (ii) a triazoline additive establishing a novel self‐regulation process in controlled radical polymerization; (iii) a metallocene catalyzed polyolefin synthesis which is performed by using “smart”, reversibly cross‐linked polymer resins as support; and (iv) hydrogen‐bonded aggregates suggesting new emulsifiers for emulsion polymerization thus leading to functional nanoparticles. Examples of structure oriented work are (i) rod‐coil block copolymers (1D case) as a “covalently bound combination” of rigid and flexible segments whereby a key synthetic concern is the chemical modification and quantitative end‐functionalization of polyphenylene chains; (ii) discs (2D case) as molecularly defined graphite subunits which are obtained via a remarkably mild intramolecular cyclodehydrogenation; and (iii) dendrimers (3D case) as shape‐persistent nanoparticles whose high degree of structural precision results from a new cycloaddition‐deprotection protocol.     

Metal‐Catalyzed “On‐Demand” Production of Carbonyl Sulfide from Carbon Monoxide and Elemental Sulfur

The group 6 molybdenum(II) cyclopentadienyl amidinate (CPAM) bis(carbonyl) complex [Cp*Mo{N(iPr)C(Ph)N(iPr)}(CO)₂] (Cp*=η⁵‐C₅Me₅) serves as a precatalyst for the high‐yielding photocatalytic production of COS from CO and S₈ under near‐ambient conditions (e.g., 10 psi, 25 °C). Further documented is the isolation and structural characterization of several key transition‐metal intermediates which collectively support a novel molybdenum(IV)‐based catalytic cycle as being operative. Finally, in the presence of an excess amount of a primary amine, it is demonstrated that this catalytic system can be successfully used for the “on‐demand” generation and utilization of COS as a chemical reagent for the synthesis of ureas.     

Mesogeneous Catalysts: A New Concept in Nanotechnology

Summary: A novel type of catalysis, neither homogeneous nor heterogeneous, is presented. This new “mesogeneous catalysis” combines the high efficiency characteristic of the homogeneous process with the advantages of the heterogeneous one (i.e., the possibility of removing and reusing the catalyst and obtaining catalyst‐free products). The reactions are performed on the surface of nano‐particles, where catalytic‐active sites have been previously chemically anchored by a short dangling organic chain, thus forming a nanohybrid system.

Methanol produced by the different catalysts, after 60 min.     

Combining renewable gum rosin and lignin: Towards hydrophobic polymer composites by controlled polymerization

Rosin polymer–grafted lignin composites were prepared via “grafting from” atom transfer radical polymerization (ATRP) with the aid of 2‐bromoisobutyryl ester‐modified lignin as macroinitiators. Three different monomers derived from dehydroabietic acid (DA) were used for execution of grafting from ATRP, while DA was separately attached onto lignin by a simple esterification reaction. Kinetic studies indicated controlled and “living” characteristics of all monomer polymerizations. Thermal studies indicated that rosin polymer–grafted lignin composites exhibited glass transition temperatures in a broad temperature range from ～20 to 100°C. The grafting of both DA and rosin polymers significantly enhanced hydrophobicity of lignin. Static contact angle measurement of water droplets showed ～90° for all these rosin modified lignin composites. X‐ray photoelectron spectroscopy demonstrated that the surface of rosin–lignin composites was dominated with chemical compositions originating from the hydrocarbon rich rosin moiety. The impartation of hydrophobicity of rosin into lignin provided excellent water resistance of this class of renewable polymers, as all rosin‐modified lignin composites showed water uptake below 1.0 wt %. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A Density Functional Theory (DFT) Quantum‐Chemical Approach to the Real Structure of Poly(methylaluminoxane)

DFT quantum chemical calculations have been performed in order to optimize the geometric and electronic cage structure of poly(methylaluminoxane) (MAO) with oligomerization degree n = 9–15, and to find such structures that fit most closely the existing experimental data on the MAO composition and structure. The following peculiarities of the MAO structure were found: i) In “classic” MAO (n = 9, 12, 15; Al : CH₃ : O = 1 : 1 : 1), which has a triple‐layer cage structure, the inner layer contains highly reactive Al‐O bonds. ii) The reaction between “classic MAO” and trimethylaluminium (TMA) proceeds by the concerted mechanism, with the insertion of Al‐CH₃ groups into these Al‐O bonds producing “true” MAO (Al : CH₃ : O = 1 : 1.5 : 0.75). The calculated geometric and electronic structures of “true” MAO with n = 6, 9, 12 are presented. iii) “True” MAO and “classic” MAO exist in equilibrium. The driving force for the formation of “true” MAO is the decrease in enthalpy, and of “classic” MAO the increase in entropy, in the equilibrium reaction between “classic” MAO and TMA.     

Growth and morphology of single crystals of linear aliphatic polyesters

In order to elucidate the relations between morphological habits and chemical structure of polymers, poly(ethylene sebacate), poly(hexamethylene sebacate) and poly(decamethylene 1,16-hexadecanedicarboxylate) were crystallized from dilute solutions in n-hexanol, isoamyl acetate etc., and were studied with the electron microscopy and x-ray diffraction. The crystal structure of these polyesters are tentatively determined. Morphological “regularity” and “simplicity” of the single crystals are correlated with the chemical structure of the polymers. The crystallization conditions under which “regular” and “simple” single crystals are obtained are relaxed with increase of methylene sequence length in chemical repeat unit. The Bragg extinction bands in the single crystals of poly(hexamethylene sebacate) and poly(decamethylene 1,16-hexadecanedicarboxylate) suggest nonplanar nature of these crystals. The molecular chains in the poly(ethylene sebacate) single crystals are inclined from the normal of the basal plane; the fold surface corresponds to the (001) plane.     

Photobiocatalysis: Activating Redox Enzymes by Direct or Indirect Transfer of Photoinduced Electrons

Biocatalytic transformation has received increasing attention in the green synthesis of chemicals because of the diversity of enzymes, their high catalytic activities and specificities, and mild reaction conditions. The idea of solar energy utilization in chemical synthesis through the combination of photocatalysis and biocatalysis provides an opportunity to make the “green” process greener. Oxidoreductases catalyze redox transformation of substrates by exchanging electrons at the enzyme′s active site, often with the aid of electron mediator(s) as a counterpart. Recent progress indicates that photoinduced electron transfer using organic (or inorganic) photosensitizers can activate a wide spectrum of redox enzymes to catalyze fuel‐forming reactions (e.g., H₂ evolution, CO₂ reduction) and synthetically useful reductions (e.g., asymmetric reduction, oxygenation, hydroxylation, epoxidation, Baeyer–Villiger oxidation). This Review provides an overview of recent advances in light‐driven activation of redox enzymes through direct or indirect transfer of photoinduced electrons.     

Structural Studies of a Copper(II) Complex with Inequivalent 2‐Acetylpyridine 3‐Piperidylthiosemicarbazonato Ligands and a Nickel(II) Complex with Different Modes of Coordination by the Two Thiosemicarbazonato Moieties of 1‐Phenylglyoxal Bis{N(4)‐diethylthiosemicarbazone}

The crystal structure of a copper(II) complex of 2‐acetylpyridine 3‐piperidylthiosemicarbazone, [Cu(Acpip)₂], indicates a tridentate, monoanionic ligand (i. e., pyridine nitrogen, imine nitrogen and thiolato sulfur atoms) and a bidentate, monanionic ligand (i. e., imine nitrogen and thiolato sulfur atoms). The stereochemistry approaches square pyramidal with the bidentate ligand occupying an apical (imine nitrogen atom) and basal (thiolato sulfur atom) position. The structure of a nickel(II) complex of 1‐phenylglyoxal N(4)‐diethylthiosemicarbazone, [Ni(Pg4DE)], has a 4‐6‐5 trichelate system rather than the 5‐5‐5 system common to bis(thiosemicarbazones). Coordination of the hydrazinic nitrogen atom of the “phenyl arm” along with the thiolato sulfur atom provides the 4‐membered chelate ring.     

Nanocatalosomes as Plasmonic Bilayer Shells with Interlayer Catalytic Nanospaces for Solar‐Light‐Induced Reactions

Interest and challenges remain in designing and synthesizing catalysts with nature‐like complexity at few‐nm scale to harness unprecedented functionalities by using sustainable solar light. We introduce “nanocatalosomes”—a bio‐inspired bilayer‐vesicular design of nanoreactor with metallic bilayer shell‐in‐shell structure, having numerous controllable confined cavities within few‐nm interlayer space, customizable with different noble metals. The intershell‐confined plasmonically coupled hot‐nanospaces within the few‐nm cavities play a pivotal role in harnessing catalytic effects for various organic transformations, as demonstrated by “acceptorless dehydrogenation”, “Suzuki–Miyaura cross‐coupling” and “alkynyl annulation” affording clean conversions and turnover frequencies (TOFs) at least one order of magnitude higher than state‐of‐the‐art Au‐nanorod‐based plasmonic catalysts. This work paves the way towards next‐generation nanoreactors for chemical transformations with solar energy.     

“Metal‐Free” Catalytic Oxygen Reduction Reaction on Heteroatom‐Doped Graphene is Caused by Trace Metal Impurities

The oxygen reduction reaction (ORR) is of high industrial importance. There is a large body of literature showing that metal‐based catalytic nanoparticles (e.g. Co, Mn, Fe or hybrid Mn/Co‐based nanoparticles) supported on graphene act as efficient catalysts for the ORR. A significant research effort is also directed to the so‐called “metal‐free” oxygen reduction reaction on heteroatom‐doped graphene surfaces. While such studies of the ORR on nonmetallic heteroatom‐doped graphene are advertised as “metal‐free” there is typically no sufficient effort to characterize the doped materials to verify that they are indeed free of any trace metal. Here we argue that the claimed “metal‐free” electrocatalysis of the oxygen reduction reaction on heteroatom‐doped graphene is caused by metallic impurities present within the graphene materials.     

高中生“芳香烃”心智模型的测评及其教学启示*

采用二阶式纸笔测验以及半结构化访谈法对高中生持有的“芳香烃”心智模型进行测评,并重点分析了学生建构的与“芳香烃和苯的同系物的概念”“芳香烃的结构”“苯及其同系物的化学性质”等概念群相关的缺陷模型。研究发现学生建构的有关“芳香烃”缺陷模型包括3大类共计11种;学生对有机物空间结构的想象力和建构能力较为薄弱;学生对“有机化合物结构内基团之间相互作用对其化学性质的影响”认识不足,“性质结构”模型不完善;学生建构的有机化学的心智模型尚不具备整体性。     

Studies on polymers and composites from lignin and fiber derived from sugar cane

Sugarcane fiber (i.e. bagasse) lignin has a larger fraction of aromatics unsubstitution in the ortho position than hardwood or softwood lignin and hence has the greater ability to be derivatized. Furthermore, organosolv lignin has a higher purity than sulfonated and kraft lignins. This work examines the purification of organosolv lignin derived from bagasse and the physico‐chemical properties of the lignin and lignin‐phenol formaldehyde (PF) resin coatings, and composites. The wetability tests have shown that lignin and lignin‐PF resin films are effective water barrier coatings, though the contact angles of lignin‐PF resin films were considerably less than the wax films. The overall mechanical properties (i.e. peak stress, peak strain and modulus) of the bagasse fiber composites were lower than the values obtained with the composites without the inclusion of bagasse fiber. Copyright © 2007 John Wiley & Sons, Ltd.     

Vital significance of addition of “shape similarity” between solutes to shape complementarity for more precise molecular recognition in aqueous binary solvents

Precise and specific molecular recognition is vital to living systems. Discrimination has mainly been studied by using particular host molecules (e.g., crown ethers, cyclodextrin and urea derivatives). Several studies in various fields have pointed out that the famous “lock‐and‐key theory” (the concept of shape complementarity) is, at present, insufficient for understanding precise discrimination. This seems to come from the fact that various types of intermolecular interactions are decisive in such discrimination. This Review intends to describe the novel concept that “shape similarity” between interacting solutes should be added to “shape complementarity” for more precise discrimination to be achieved. Further, the role of shape similarity between solvent and solute molecules is also described. In relation to precise molecular recognition, weak interactions, which depend on the three‐dimensional shape of substituents (shape‐specific weak interactions), are described. Possibility of alterations in solvent structures is discussed in aqueous binary solvents. DOI 10.1002/tcr.201100001     

Square‐wave Voltammetry of Two‐step Surface Electrode Mechanisms Coupled with Chemical Reactions – A Theoretical Overview

Square‐wave voltammetry (SWV) of so‐called “surface redox reactions” is seen as a simple and efficient tool to quantify large number of drugs, physiologically active substances and other important chemicals. It also provides elegant methods to get access to relevant kinetic and thermodynamic parameters related to many lipophilic compounds. Moreover, with this technique we can study activity of various enzymes by exploring the “protein‐film voltammetry” set up. In this work, we focus on theoretical SWV features of four complex surface electrode mechanisms, in which the electron exchange between the working electrode and the studied redox substrate takes place in two successive steps. While we present large number of calculated square‐wave voltammograms, we give hints to recognize particular two‐step surface mechanism, but also to distinguish it from other similar mechanisms. We present plenty of relevant aspects of surface two‐step surface EE, two‐step surface ECE and surface catalytic EEC’ mechanisms. Moreover, we present for the first time a series of theoretical results related to two‐step surface EECrev mechanism (i. e. two‐step surface reaction coupled to follow‐up reversible chemical step). The simulated voltammetric patterns presented in this work can bring relevant aspects to resolve some experimental situations met in voltammetry of many redox enzymes and other important substances whose electrochemical transformation occurs in two‐steps.