Transformation Of Small Molecules Research Articles

Influence of zinc oxide/expanded vermiculite composite on the rheological and anti-aging properties of bitumen

The bitumen modifier, zinc oxide (ZnO)/expanded vermiculite (EVMT) composite (ZnO/EVMT), was introduced into the bitumen with a dosage of 4%, 5%, and 6%. The surface morphology of EVMT and ZnO/EVMT was characterized by a field emission scanning microscope (FESEM). Further, the Superpave continuous grade of bitumen containing different amounts of ZnO/EVMT was determined by the dynamic shear rheometer (DSR) test and bending beam rheometer (BBR) test. The bitumen samples were aged by thin film oven test (TFOT), pressure aging vessel (PAV) aging test and ultraviolet (UV) aging test, and the influence of different amounts of ZnO/EVMT on both physical and rheological properties of the bitumen before and after aging were investigated. Moreover, the influence of ZnO/EVMT on the molecular distribution during aging was investigated by analyzing the change in the proportion of large molecular size (LMS) obtained from gel permeation chromatography (GPC). The FESEM result shows the ZnO particles are uniformly supported on the EVMT surface. Moreover, ZnO/EVMT slightly influences the high-temperature performance and improves the low-temperature cracking resistance of bitumen. In addition, no matter what aging method is adopted, ZnO/EVMT effectively increases the retained penetration and phase angle aging index, and decreases the viscosity aging index and complex modulus aging index of the bitumen, demonstrating the effectiveness of ZnO/EVMT in both resisting the thermo- and photo-oxidative aging of bitumen. Meanwhile, 6% and 4% ZnO/EVMT exhibit the best inhibitory effect on thermo- and photo-oxidative aging of bitumen, respectively. According to the GPC results, the composite inhibits the transformation of small molecules to large molecules during aging, resulting in a lower LMS increment and better anti-aging properties of the modified bitumen.

Construction of a low-valent thiolate-bridged dicobalt platform and its reactivity toward hydrogen activation and evolution

Low-valence transition metallic complexes have drawn longstanding attention due to their high reactivity toward catalytic transformation of various small molecules. Among these known complexes, the low-valence metal centres are commonly stabilized by neutral bulky ligands with strong electron-donating capacity. However, low-valence bimetallic complexes supported by anionic sulfur and cyclopentadienyl ligands are still difficult to obtain in high isolated yield. Herein, we report the synthesis and characterization of two scarce thiolate-bridged CoICoII and CoICoI complexes bearing sterically demanding ligands through two stepwise one-electron reduction processes. Interestingly, the CoICoII complex can facilely promote the homolytic cleavage of dihydrogen across the short Co−Co metallic bond to give a CoIICoIII dihydride bridged complex, which is capable of serving as a competent hydrogen atom transfer agent. Moreover, the anionic CoICoI complex can trigger a stepwise hydrogen generation cycle involving several isolated and structurally well-characterized intermediates.

Electrochemical Assembly for Synthesis of Middle-Sized Organic Molecules.

Electrochemical methods offer a powerful, reliable, and environmentally benign approach for the synthesis of small organic molecules, and such methods are useful not only for the transformation of small molecules, but also for the preparation of oligomers and polymers. Electrochemical assembly is a concept that allows structurally well-defined middle-sized organic molecules to be synthesized by applying electrochemical methods. The preparation of dendrimers, dendronized polymers, and oligosaccharides are introduced as examples of such an approach. Automated electrochemical assembly of oligosaccharides is also demonstrated using the electrochemical synthesizer developed by our group.

Insight into the Electronic Structure of Biomimetic Dinitrosyliron Complexes (DNICs): Toward the Syntheses of Amido-Bridging Dinuclear DNICs.

The ubiquitous function of nitric oxide (NO) guided the biological discovery of the natural dinitrosyliron unit (DNIU) [Fe(NO)2] as an intermediate/end product after Fe nitrosylation of nonheme cofactors. Because of the natural utilization of this cofactor for the biological storage and delivery of NO, a bioinorganic study of synthetic dinitrosyliron complexes (DNICs) has been extensively explored in the last 2 decades. The bioinorganic study of DNICs involved the development of synthetic methodology, spectroscopic discrimination, biological application of NO-delivery reactivity, and translational application to the (catalytic) transformation of small molecules. In this Forum Article, we aim to provide a systematic review of spectroscopic and computational insights into the bonding nature within the DNIU [Fe(NO)2] and the electronic structure of different types of DNICs, which highlights the synchronized advance in synthetic methodology and spectroscopic tools. With regard to the noninnocent nature of a NO ligand, spectroscopic and computational tools were utilized to provide qualitative/quantitative assignment of oxidation states of Fe and NO in DNICs with different redox levels and ligation modes as well as to probe the Fe-NO bonding interaction modulated by supporting ligands. Besides the strong antiferromagnetic coupling between high-spin Fe and paramagnetic NO ligands within the covalent DNIU [Fe(NO)2], in polynuclear DNICs, the effects of the Fe···Fe distance, nature of the bridging ligands, and type of bridging modes on the regulation of the magnetic coupling among paramagnetic DNIU [Fe(NO)2] are further reviewed. In the last part of this Forum Article, the sequential reaction of {Fe(NO)2}10 DNIC [(NO)2Fe(AMP)] (1-red) with NO(g), HBF4, and KC8 establishes a synthetic cycle, {Fe(NO)2}9-{Fe(NO)2}9 DNIC [(NO)2Fe(μ-dAMP)2Fe(NO)2] (1) → {Fe(NO)2}9 DNIC [(NO2)Fe(AMP)][BF4] (1-H) → {Fe(NO)2}10 DNIC 1-red → DNIC 1, for the transformation of NO into HNO/N2O. Of importance, the NO-induced transformation of {Fe(NO)2}10 DNIC 1-red and [(NO)2Fe(DTA)] (2-red; DTA = diethylenetriamine) unravels a synthetic strategy for preparation of the {Fe(NO)2}9-{Fe(NO)2}9 DNICs [(NO)2Fe(μ-NHR)2Fe(NO)2] containing amido-bridging ligands, which hold the potential to feature distinctive physical properties, chemical reactivities, and biological applications.

Electrochemistry of Ru(edta) complexes relevant to small molecule transformations: Catalytic implications and challenges

Electrochemistry of Ru(edta) complexes (edta4− = ethylenediaminetetraacetate) progressed over a period of several decades, with significant increase in understanding of the electro-catalytic processes involving the substrate coordinated to the metal center. While electrochemistry studies of many Ru(edta) complexes were published in several papers, no attempt has been made to provide a comprehensive and systematic overview of its electrochemical properties, evaluating its application to catalytic electrochemical transformation of small molecules. In this article, results of the electrochemical studies of both mononuclear and binuclear complexes of Ru(edta) are reviewed with regard to electron-transfer reaction mechanism and activity. Their potential to act as redox mediators or catalysts in electrochemical transformations of small molecules and enzymatic reactions, are highlighted. This review aims to contribute to the mechanistic understanding of Ru(edta) complexes in catalysis of such electrochemical transformations.

Oxidation-Induced "One-Pot" Click Chemistry.

Click chemistry has been established rapidly as one of the most valuable methods for the chemical transformation of complex molecules. Due to the rapid rates, clean conversions to the products, and compatibility of the reagents and reaction conditions even in complex settings, it has found applications in many molecule-oriented disciplines. From the vast landscape of click reactions, approaches have emerged in the past decade centered around oxidative processes to generate in situ highly reactive synthons from dormant functionalities. These approaches have led to some of the fastest click reactions know to date. Here, we review the various methods that can be used for such oxidation-induced “one-pot” click chemistry for the transformation of small molecules, materials, and biomolecules. A comprehensive overview is provided of oxidation conditions that induce a click reaction, and oxidation conditions are orthogonal to other click reactions so that sequential “click-oxidation-click” derivatization of molecules can be performed in one pot. Our review of the relevant literature shows that this strategy is emerging as a powerful approach for the preparation of high-performance materials and the generation of complex biomolecules. As such, we expect that oxidation-induced “one-pot” click chemistry will widen in scope substantially in the forthcoming years.

Isomerization and Selective Hydrogenation of Propyne: Screening of Metal-Organic Frameworks Modified by Atomic Layer Deposition.

Various metal oxide clusters upward of 8 atoms (Cu, Cd, Co, Fe, Ga, Mn, Mo, Ni, Sn, W, Zn, In, and Al) were incorporated into the pores of the metal-organic framework (MOF) NU-1000 via atomic layer deposition (ALD) and tested via high-throughput screening for catalytic isomerization and selective hydrogenation of propyne. Cu and Co were found to be the most active for propyne hydrogenation to propylene, and synergistic bimetallic combinations of Co and Zn, along with standalone Zn and Cd, were established as the most active for conversion to the isomerized product, propadiene. The combination of Co and Zn in NU-1000 diminished the propensity for full hydrogenation to propane as well as coking compared to its individual components. This study highlights the potential for high-throughput screening to survey monometallic and bimetallic cluster combinations that best affect the efficient transformation of small molecules, while discerning mechanistic differences in isomerization and hydrogenation by different metals.

Activation and Transformation of Small Molecules by Multimetallic Early Transition Metal Hydride Clusters

Activation and Transformation of Small Molecules by Multimetallic Early Transition Metal Hydride Clusters

Tunable solid-state photochromism based on proton and anion-controlled structural transformation of pyridinium-based organic small molecules

An organic molecular system with proton and anion-tunable photochromism properties based on a pyridinium derivative was developed. Through controlling the pH value and anion nature of the self-assembled systems, the novel three compounds displayed different photochromism behaviors. This work reveals that the introduction of additional groups into the molecule increases the diversity of the property of such complexes.

The Power of Hydrides

Qianru Wang is a graduate student pursuing her Ph.D. in physical chemistry at Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Her research focuses on hydride materials for catalytic ammonia synthesis. Jianping Guo is a professor at Dalian Institute of Chemical Physics, Chinese Academy of Sciences. His research focuses on exploring metal hydrides, imides, and amides in the activation and transformation of small molecules including N2, H2, and NH3. Ping Chen is a professor and division head of Hydrogen Energy and Advanced Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. The primary research interests of her group include materials development for hydrogen storage and catalysis.

Electrochemical and Photophysical Properties of Ruthenium(II) Complexes Equipped with Sulfurated Bipyridine Ligands.

The development of new solar-to-fuel scenarios is of great importance, but the construction of molecular systems that convert sunlight into chemical energy represents a challenge. One specific issue is that the molecular systems have to be able to accumulate redox equivalents to mediate the photodriven transformation of relevant small molecules, which mostly involves the orchestrated transfer of multiple electrons and protons. Disulfide/dithiol interconversions are prominent 2e-/2H+ couples and can play an important role for redox control and charge storage. With this background in mind, a new photosensitizer [Ru(S-Sbpy)(bpy)2]2+ (12+) equipped with a disulfide functionalized bpy ligand (S-Sbpy, bpy = 2,2'-bipyridine) was synthesized and has been comprehensively studied, including structural characterization by X-ray diffraction. In-depth electrochemical studies show that the S-Sbpy ligand in 12+ can be reduced twice at moderate potentials (around -1.1 V vs Fc+/0), and simulation of the cyclic voltammetry (CV) traces revealed potential inversion (E2 > E1) and allowed to derive kinetic parameters for the sequential electron-transfer processes. However, reduction at room temperature also triggers the ejection of one sulfur atom from 12+, leading to the formation of [Ru(Sbpy)(bpy)2]2+(22+). This chemical reaction can be suppressed by decreasing the temperature from 298 to 248 K. Compared to the archetypical photosensitizer [Ru(bpy)3]2+, 12+ features an additional low energy optical excitation in the MLCT region, originating from charge transfer from the metal center to the S-Sbpy ligand (aka MSCT) according to time-dependent density functional theory (TD-DFT) calculations. Analysis of the excited states of 12+ on the basis of ground-state Wigner sampling and using charge-transfer descriptors has shown that bpy modification with a peripheral disulfide moiety leads to an energy splitting between charge-transfer excitations to the S-Sbpy and the bpy ligands, offering the possibility of selective charge transfer from the metal to either type of ligands. Compound 12+ is photostable and shows an emission from a 3MLCT state in deoxygenated acetonitrile with a lifetime of 109 ns. This work demonstrates a rationally designed system that enables future studies of photoinduced multielectron, multiproton PCET chemistry.

Progress in chemical looping-based transformations of small molecules

Chemical looping is a process in which one reaction is split into two or more separate reactions that occur sequentially in one reactor or simultaneously in different reactors. The transport of matter and energy between reactants is achieved via a medium, and the valence of one element of the medium swings between two values. Compared to co-feed mode in conventional reaction technologies, alternative or separate feeding has the advantages of high exergy efficiency, excellent process safety, and flexible operation. It was ever commercialized to produce oxygen, hydrogen, and carbon dioxide before viable processes were developed. Since the 21st century, the application of chemical looping technology in transformations of small molecules like light hydrocarbons and nitrogen has attracted extensive attention all over the world. In this paper, the recent progress in the field is reviewed. The paper mainly focuses on solar CO2 and H2O splitting, methane reforming, selective hydrogen combustion coupled with dehydrogenation, and ammonia synthesis. The main challenges of the chemical looping-based transformations of small molecules are also briefly discussed.

Enhanced CO2 Separation Achieved by Fluorinated Membranes

Download : Download high-res image (299KB) Download : Download full-size image Dr. Zhenzhen Yang earned her PhD in 2013 from Nankai University under the advisement of Professor Liang-Nian He. Then she joined Professor Zhimin Liu’s group at the Institute of Chemistry of the Chinese Academy of Sciences, where she worked for 5 years. She currently works as a postdoctoral researcher at the University of Tennessee, Knoxville, in the lab of Professor Sheng Dai. Her research is mainly focused on the design of novel nanoporous materials for efficient adsorption, separation, activation, and transformation of small gas molecules.

Bioinspired metal complexes for energy-related photocatalytic small molecule transformation.

Bioinspired transformation of small-molecules to energy-related feedstocks is an attractive research area to overcome both the environmental issues and the depletion of fossil fuels. The highly effective metalloenzymes in nature provide blueprints for the utilization of bioinspired metal complexes for artificial photosynthesis. Through simpler structural and functional mimics, the representative herein is the pivotal development of several critical small molecule conversions catalyzed by metal complexes, e.g., water oxidation, proton and CO2 reduction and organic chemical transformation of small molecules. Of great achievement is the establishment of bioinspired metal complexes as catalysts with high stability, specific selectivity and satisfactory efficiency to drive the multiple-electron and multiple-proton processes related to small molecule transformation. Also, potential opportunities and challenges for future development in these appealing areas are highlighted.

Chemistry of Actinide Centers in Heterogeneous Catalytic Transformations of Small Molecules

The chemistry of actinide molecules and materials has shown remarkable conceptual advancements in the past decade illustrating their unique reactivity profiles, when compared with lanthanides and t...

Intracellular Catalysis with Selected Metal Complexes and Metallic Nanoparticles: Advances toward the Development of Catalytic Metallodrugs.

Platinum-containing drugs (e.g., cisplatin) are among the most frequently used chemotherapeutic agents. Their tremendous success has spurred research and development of other metal-based drugs, with notable achievements. Generally, the vast majority of metal-based drug candidates in clinical and developmental stages are stoichiometric agents, i.e., each metal complex reacts only once with their biological target. Additionally, many of these metal complexes are involved in side reactions, which not only reduce the effective amount of the drug but may also cause toxicity. On a separate note, transition metal complexes and nanoparticles have a well-established history of being potent catalysts for selective molecular transformations, with examples such as the Mo- and Ru-based catalysts for metathesis reactions (Nobel Prize in 2005) or palladium catalysts for C-C bond forming reactions such as Heck, Negishi, or Suzuki reactions (Nobel Prize in 2010). Also, notably, no direct biological equivalent of these transformations exists in a biological environment such as bacteria or mammalian cells. It is, therefore, only logical that recent interest has focused on developing transition-metal based catalytic systems that are capable of performing transformations inside cells, with the aim of inducing medicinally relevant cellular changes. Because unlike in stoichiometric reactions, a catalytically active compound may turn over many substrate molecules, only very small amounts of such a catalytic metallodrug are required to achieve a desired pharmacologic effect, and therefore, toxicity and side reactions are reduced. Furthermore, performing catalytic reactions in biological systems also opens the door for new methodologies to study the behavior of biomolecules in their natural state, e.g., via in situ labeling or by increasing/depleting their concentration at will. There is, of course, an art to the choice of catalysts and reactions which have to be compatible with biological conditions, namely an aqueous, oxygen-containing environment. In this review, we aim to describe new developments that bring together the far-distant worlds of transition-metal based catalysis and metal-based drugs, in what is termed "catalytic metallodrugs". Here we will focus on transformations that have been performed on small biomolecules (such as shifting equilibria like in the NAD+/NADH or GSH/GSSG couples), on non-natural molecules such as dyes for imaging purposes, or on biomacromolecules such as proteins. Neither reactions involving release (e.g., CO) or transformation of small molecules (e.g., 1O2 production), degradation of biomolecules such as proteins, RNA or DNA nor light-induced medicinal chemistry (e.g., photodynamic therapy) are covered, even if metal complexes are centrally involved in those. In each section, we describe the (inorganic) chemistry involved, as well as selected examples of biological applications in the hope that this snapshot of a new but quickly developing field will indeed inspire novel research and unprecedented interactions across disciplinary boundaries.

Visible light-driven organic photochemical synthesis in China

In recent years, visible light-driven organic photochemical synthesis has attracted wide research interest from academic and industrial communities due to its features of green and sustainable chemistry. In this flourishing area, Chinese chemists have devoted great efforts to different aspects of synthetic chemistry. This review will summarize their representative work according to the following categories: C–H functionalization, synthesis of aromatic aza-heterocycles, asymmetric organic photochemical synthesis, transformations of small molecules and biomolecule-compatible reactions.

Reductive Transformation of Layered-Double-Hydroxide Nanosheets to Fe-Based Heterostructures for Efficient Visible-Light Photocatalytic Hydrogenation of CO.

Conversion of syngas (CO, H2 ) to hydrocarbons, commonly known as the Fischer-Tropsch (FT) synthesis, represents a fundamental pillar in today's chemical industry and is typically carried out under technically demanding conditions (1-3 MPa, 300-400 °C). Photocatalysis using sunlight offers an alternative and potentially more sustainable approach for the transformation of small molecules (H2 O, CO, CO2 , N2 , etc.) to high-valuable products, including hydrocarbons. Herein, a novel series of Fe-based heterostructured photocatalysts (Fe-x) is successfully fabricated via H2 reduction of ZnFeAl-layered double hydroxide (LDH) nanosheets at temperatures (x) in the range 300-650 °C. At a reduction temperature of 500 °C, the heterostructured photocatalyst formed (Fe-500) consists of Fe0 and FeOx nanoparticles supported by ZnO and amorphous Al2 O3 . Fe-500 demonstrates remarkable CO hydrogenation performance with very high initial selectivities toward hydrocarbons (89%) and especially light olefins (42%), and a very low selectivity towards CO2 (11%). The intimate and abundant interfacial contacts between metallic Fe0 and FeOx in the Fe-500 photocatalyst underpins its outstanding photocatalytic performance. The photocatalytic production of high-value light olefins with suppressed CO2 selectivity from CO hydrogenation is demonstrated here.

Understanding Surface-Mediated Electrochemical Reactions: CO2 Reduction and Beyond

Understanding reaction pathways and mechanisms for electrocatalytic transformation of small molecules (e.g., H2O, CO2, and N2) to value-added chemicals is critical to enabling the rational design of high-performing catalytic systems. Tafel analysis is widely used to gain mechanistic insights, and in some cases, has been used to determine the reaction mechanism. In this Perspective, we discuss the mechanistic insights that can be gained from Tafel analysis and its limitations using the simplest two-electron CO2 reduction reaction to CO on Au and Ag surfaces as an example. By comparing and analyzing existing as well as additional kinetic data, we show that the Tafel slopes obtained on Au and Ag surfaces in the kinetically controlled region (low overpotential) are consistently ∼59 mV dec–1, regardless of whether catalysts are polycrystalline or nanostructured in nature, suggesting that the initial electron transfer (CO2 + e– → CO2–) is unlikely to be the rate-limiting step. In addition, we demonstrate how in...

Synthesis and applications of ordered and disordered mesoporous zeolites: Present and future prospective

Zeolites are microporous aluminosilicates that are used extensively for a wide variety of industrial applications. Applications of microporous zeolites are limited to transformations of small molecules due to the pore diffusion limitation imposed by the microporous network structure. In order to overcome this limitation, zeolites with inter-/intra-crystalline mesopores are generally preferred. This review article presents the details of various strategies for the preparation of mesoporous zeolites with inter-/intra-crystalline mesopores. A wide range of soft templates and additives is described in details for their use in the synthesis of mesoporous ZSM-5 and Beta zeolites. A brief report on the applications of mesoporous zeolites in various acid catalyzed reactions, involving large organic molecules, is provided in this article. Another important feature of this article is that it summarizes the applications of mesoporous zeolites in the electrochemical detection of various physiologically important biomolecules and organic/inorganic water pollutants. Further, the role of mesoporous zeolites based electrode materials for direct methanol fuel cell application is presented. Finally, the potential role of mesoporous zeolites in the field of biomedical engineering, particularly as a bone implant material, is summarized.