Natural rubber is a kind of indispensable biopolymers with great use and strategic importance in human society. However, its production relies almost exclusively on rubber-producing plants
, which ...have high requirements for growth conditions, and the mechanism of natural rubber biosynthesis remains largely unknown. In the past two decades, details of the rubber chain polymerization and proteins involved in natural rubber biosynthesis have been investigated intensively. Meanwhile, omics and other advanced biotechnologies bring new insight into rubber production and development of new rubber-producing plants. This review summarizes the achievements of the past two decades in understanding the biosynthesis of natural rubber, especially the massive information obtained from the omics analyses. Possibilities of natural rubber biosynthesis in vitro or in genetically engineered microorganisms are also discussed.
•Global plastic waste trade networks (GPWTNs) from 1988 to 2017 are established.•The spatiotemporal evolution of the GPWTNs is analyzed.•The direct and indirect impacts of China’s import ban on the ...GPWTNs are evaluated.•Practical implications are given according to analysis of the GPWTNs.
Millions of tonnes (teragrams) of plastic waste are traded around the world every year, which plays an important role in partially substituting virgin plastics as a source of raw materials in plastic product manufacturing. In this paper, global plastic waste trade networks (GPWTNs) from 1988 to 2017 are established using the UN-Comtrade database. The spatiotemporal evolution of the GPWTNs is analyzed. Attention is given to the country ranks, inter- and intra-continental trade flows, and geo-visual communities in the GPWTNs. We also evaluate the direct and indirect impacts of China’s plastic waste import ban on the GPWTNs. The results show that the GPWTNs have small-world and scale-free properties and a core-periphery structure. The geography of the plastic waste trade is structured by Asia as the dominant importer and North America and Europe as the largest sources of plastic waste. China is the unrivaled colossus in the global plastic waste trade. After China’s import ban, the plastic waste trade flows have been largely redirected to Southeast Asian countries. Compared with import countries, export countries are more important for the robustness of GPWTNs. Clearly, developed countries will not announce bans on plastic waste exports; these countries have strong motivation to continue to shift plastic waste to poorer countries. However, the import bans from developing countries will compel developed countries to build new disposal facilities and deal with their plastic waste domestically.
Owing to their distinctive 1,3‐dipolar structure, the catalytic asymmetric hydrogenation of nitrones to hydroxylamines has been a formidable and longstanding challenge, characterized by intricate ...enantiocontrol and susceptibility to N−O bond cleavage. In this study, the asymmetric hydrogenation and transfer hydrogenation of nitrones were accomplished with a tethered TsDPEN‐derived cyclopentadienyl rhodium(III) catalyst (TsDPEN: p‐toluenesulfonyl‐1,2‐diphenylethylene‐1,2‐diamine), the reaction proceeds via a novel 7‐membered cyclic transition state, producing chiral hydroxylamines with up to 99 % yield and >99 % ee. The practical viability of this methodology was underscored by gram‐scale catalytic reactions and subsequent transformations. Furthermore, mechanistic investigations and DFT calculations were also conducted to elucidate the origin of enantioselectivity.
The enantioselective reduction of 1,3‐dipolar nitrones to hydroxylamines was achieved by Rh(III)‐catalyzed asymmetric hydrogenation and transfer hydrogenation. A wide range of chiral N,N‐disubstituted hydroxylamines were synthesized with up to 99 % yield and >99 % ee. Mechanistic investigations and DFT calculations were conducted to elucidate the origin of reactivity and enantioselectivity.
A robust and highly active homogeneous chiral nickel–phosphine complex for the asymmetric hydrogenation of aliphatic γ‐ and δ‐ketoacids has been discovered. The hydrogenation could proceed smoothly ...in the presence of 0.0133 mol% catalyst loading (S/C=7500). The coordination chemistry and catalytic behavior of Ni(OTf)2 with (S,S)‐Ph‐BPE were explored by 1H NMR and HRMS. The mechanistic studies revealed that a proton promoted the activation of the substrate C=O bond and controlled the stereoselectivity through hydrogen bonds. A series of chiral γ‐ and δ‐alkyl substituted lactones were obtained in high yields with excellent enantioselectivities (up to 98 % yield and 99 % ee). In addition, this catalytic system also demonstrated that levulinic acid produced from a biomass feedstock was converted into chiral γ‐valerolactone without loss of ee value.
A robust and efficient nickel–phosphine complex has been discovered for the asymmetric hydrogenation of aliphatic ketoacids. A proton promoted the activation of C=O bonds and controlled the stereoselectivity through hydrogen bonds to obtain the corresponding products in high yields with excellent enantioselectivities.
Double‐network (DN) hydrogel has intrinsic tough mechanical properties due to its unique two contrasting network structures. The research on DN hydrogel is a fast growing field, mainly focusing on ...network structures, formation, and interactions at the molecular level. In this trend article, we take a critical review at the important and latest research findings, current research challenges, and future research directions in the DN hydrogel field. We discuss some issues on the discovery of fundamentally new phenomena versus performance benchmarking for different types of the DN hydrogels. Finally we offer our personal opinions to several unique aspects for future DN gel research.
Double network hydrogels (DN gels), consisting of two asymmetric, interpenetrating polymer networks, are considered as the toughest hydrogels. This Trend article summarizes the latest important findings of DN gels, covering new gel structures, functionalities, applications, and future perspectives.
Multiple stretchability has never been demonstrated as supercapacitors because the hydrogel used cannot fully recover after being heavily deformed. Now, a highly reversibly stretchable all‐polymer ...supercapacitor was fabricated using a developed double network hydrogel (DN hydrogel) as electrolyte and pure polypyrrole (PPy) as electrode. The DN hydrogel provides excellent mechanical properties, which can be stretched up to 500 % many times and then restore almost 100 % of the original length. To fabricate the fully recoverable stretchable supercapacitor, we annealed a free‐standing pure conducting polymer film as electrode so that the electrodes induced retardance is minimized. The as‐fabricated DN hydrogel/pure conducting polymer supercapacitors can be perfectly recovered from 100 % strain with almost no residual deformation left and the electrochemical performance can be maintained even after 1000 stretches (but not bending).
Elastic supercaps: An agar/hydrophobically associated polyacrylamide (HPAAm) double network (DN) hydrogel and pure polypyrrole (PPy) film based all‐polymer supercapacitor was fabricated. It is highly elastic and reversibly stretchable. This supercapacitor can be stretched and recovered for 1000 times with no obvious performance degradation and strain residue, exhibiting excellent elasticity at the device level.
Abstract
Asymmetric hydrogenation of α,β-unsaturated acids catalyzed by noble metals has been well established, whereas, the asymmetric hydrogenation with earth-abundant-metal was rarely reported. ...Here, we describe a cobalt-catalyzed asymmetric hydrogenation of α,β-unsaturated carboxylic acids. By using chiral cobalt catalyst bearing electron-donating diphosphine ligand, high activity (up to 1860 TON) and excellent enantioselectivity (up to >99% ee) are observed. Furthermore, the cobalt-catalyzed asymmetric hydrogenation is successfully applied to a broad spectrum of α,β-unsaturated carboxylic acids, such as various α-aryl and α-alkyl cinnamic acid derivatives, α-oxy-functionalized α,β-unsaturated acids, α-substituted acrylic acids and heterocyclic α,β-unsaturated acids (30 examples). The synthetic utility of the protocol is highlighted by the synthesis of key intermediates for chiral drugs (6 cases). Preliminary mechanistic studies reveal that the carboxy group may be involved in the control of the reactivity and enantioselectivity through an interaction with the metal centre.
Rapid urbanization generates substantial demand, use, and demolition waste of construction materials. However, the existing top‐down or bottom‐up frameworks combining material flow analysis (MFA) and ...geographic information system (GIS) tend to underestimate both input and output of construction material flows due to insufficient descriptions of key processes in building construction and demolition. To address this limitation, this study identifies four important and complementary processes—construction, demolition, replacement, and maintenance, and integrates them into an improved framework to capture all material flows. We take Xiamen, a rapidly urbanizing city, as a case study to verify this framework. The results show that ∼40% of material inputs and ∼65% of outputs are underestimated by previous frameworks because they fail to capture material inputs in building maintenance and outputs in construction. These findings indicate a better estimation of such key flows in the modeling framework helps to accurately characterize building material metabolism. Based on systematic counting of material stocks and flows, the improved framework can help design effective policies for urban resource management by explicitly recognizing the spatiotemporal patterns and processes of material metabolism.
In-use stock of a product is the amount of the product in active use. In-use product stocks provide various functions or services on which we rely in our daily work and lives, and the concept of ...in-use product stock for industrial ecologists is similar to the concept of net manufactured capital stock for economists. This study estimates historical physical in-use stocks of 91 products and 9 product groups and uses monetary data on net capital stocks of 56 products to either approximate or compare with in-use stocks of the corresponding products in the United States. Findings include the following: ( i ) The development of new products and the buildup of their in-use stocks result in the increase in variety of in-use product stocks and of manufactured capital; ( ii ) substitution among products providing similar or identical functions reflects the improvement in quality of in-use product stocks and of manufactured capital; and ( iii ) the historical evolution of stocks of the 156 products or product groups in absolute, per capita, or per-household terms shows that stocks of most products have reached or are approaching an upper limit. Because the buildup, renewal, renovation, maintenance, and operation of in-use product stocks drive the anthropogenic cycles of materials that are used to produce products and that originate from natural capital, the determination of in-use product stocks together with modeling of anthropogenic material cycles provides an analytic perspective on the material linkage between manufactured capital and natural capital.
Significance The determination of long-term in-use stocks of manufactured products can complement existing monetary approaches to measuring manufactured capital and helps to explore the linkage between manufactured capital and natural capital in terms of materials transfer. The development of new products, substitution among products, and the historical evolution of in-use product stocks in the United States reveal the increase in variety, improvement in quality, and growth in quantity of US manufactured capital. Because products are produced from materials, and products developed more recently tend to use a greater diversity of materials, this study also reveals that US modern manufactured capital relies on the use of more diverse materials and on the increasing use of materials that originate from natural capital.
Graphene nanoribbons (GNRs) are quasi-one-dimensional subunits of graphene and have open bandgaps in contrast to the zero-bandgap graphene. The high potential of GNRs as a new family of carbon-based ...semiconductors,
e.g.
for nanoelectronic and optoelectronic applications, has boosted the research attempts towards fabrication of GNRs. The predominant top-down methods such as lithographical patterning of graphene and unzipping of carbon nanotubes cannot prevent defect formation. In contrast, bottom-up chemical synthesis, starting from tailor-made molecular precursors, can achieve atomically precise GNRs. In this account, we summarize our recent research progress in the bottom-up synthesis of GNRs through three different methods, namely (1) in solution, (2) on-surface under ultrahigh vacuum (UHV) conditions, and (3) on-surface through chemical vapour deposition (CVD). The solution synthesis allows fabrication of long (>600 nm) and liquid-phase-processable GNRs that can also be functionalized at the edges. On the other hand, the on-surface synthesis under UHV enables formation of zigzag GNRs and
in situ
visualization of their chemical structures by atomic-resolution scanning probe microscopy. While the on-surface synthesis under UHV is typically costly and has limited scalability, the industrially viable CVD method can allow lower-cost production of large GNR films. We compare the three methods in terms of the affordable GNR structures and the resulting control of their electronic and optical properties together with post-processing for device integration. Further, we provide our views on future perspectives in the field of bottom-up GNRs.
Graphene nanoribbons (GNRs) with various structures and properties can be synthesized in solution or on surface.
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