Hydrogel‐based three‐dimensional cell culture for organ‐on‐a‐chip applications

Recent studies have reported that three‐dimensionally cultured cells have more physiologically relevant functions than two‐dimensionally cultured cells. Cells are three‐dimensionally surrounded by the extracellular matrix (ECM) in complex in vivo microenvironments and interact with the ECM and neighboring cells. Therefore, replicating the ECM environment is key to the successful cell culture models. Various natural and synthetic hydrogels have been used to mimic ECM environments based on their physical, chemical, and biological characteristics, such as biocompatibility, biodegradability, and biochemical functional groups. Because of these characteristics, hydrogels have been combined with microtechnologies and used in organ‐on‐a‐chip applications to more closely recapitulate the in vivo microenvironment. Therefore, appropriate hydrogels should be selected depending on the cell types and applications. The porosity of the selected hydrogel should be controlled to facilitate the movement of nutrients and oxygen. In this review, we describe various types of hydrogels, external stimulation‐based gelation of hydrogels, and control of their porosity. Then, we introduce applications of hydrogels for organ‐on‐a‐chip. Last, we also discuss the challenges of hydrogel‐based three‐dimensional cell culture techniques and propose future directions. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:580–589, 2017     

Two‐Dimensional Materials for Beyond‐Lithium‐Ion Batteries

Lithium‐ion batteries (LIBs) have dominated the portable electronics industry and solid‐state electrochemical research and development for the past two decades. In light of possible concerns over the cost and future availability of lithium, sodium‐ion batteries (SIBs) and other new technologies have emerged as candidates for large‐scale stationary energy storage. Research in these technologies has increased dramatically with a focus on the development of new materials for both the positive and negative electrodes that can enhance the cycling stability, rate capability, and energy density. Two‐dimensional (2D) materials are showing promise for many energy‐related applications and particularly for energy storage, because of the efficient ion transport between the layers and the large surface areas available for improved ion adsorption and faster surface redox reactions. Recent research highlights on the use of 2D materials in these future ‘beyond‐lithium‐ion’ battery systems are reviewed, and strategies to address challenges are discussed as well as their prospects.     

Glass‐Ceramic‐Like Vanadate Cathodes for High‐Rate Lithium‐Ion Batteries

Nanostructured electrode materials are good candidates in batteries especially for high‐rate applications, yet they often suffer from extensive side reactions due to anomalously large surface areas. While micrometer‐size materials provide better stability, the lattice diffusivity is often too slow for lithium ion intercalation over the same length scale in a short time. Herein, a simple method to synthesize glass‐ceramic‐like vanadate cathodes for lithium‐ion batteries with abundant internal boundaries that allow fast lithium ion diffusion while maintaining a small surface area that thus minimize the contact and side reactions with organic electrolyte, is reported. Such samples heat‐treated under optimized conditions can deliver an impressive high‐rate capacity of 103 mAh g^?1 at 4000 mA g^?1 over 500 cycles, which has better kinetics and cycling stability than similar vanadate‐based materials. A striking grain‐size refinement effect accompanied by a low‐temperature growth‐controlled phase transition, can be achieved by fine tuning the heat‐treatment process. It is believed that the findings are general for other transition metal oxides for energy applications.     

Efficient racemization of N‐phenylacetyl‐D‐glufosinate for L‐glufosinate production

Most amino acids contain chiral centres and exist as both D‐enantiomer and L‐enantiomer. The optically pure enantiomer is often more valuable than the racemate. Enzymatic resolution provides an effective strategy to obtain optically pure amino acids but often results in large amounts of unwanted isomer. In this study, optically pure L‐glufosinate (L‐PPT) was obtained by coupling amidase‐mediated hydrolysis of N‐phenylacetyl‐D,L‐glufosinate with racemization of N‐phenylacetyl‐D‐glufosinate (NPDG), which exclusively exhibits effective herbicidal properties compared with its D‐enantiomer. To improve the yield of L‐PPT, the racemization reaction conditions were optimized, and through single‐factor experiments, the optimal reaction temperature, reaction time, and mole ratio of phenylacetic acid to NPDG were determined to be 150°C, 30 minutes, and 1.5, respectively. The response surface methodology was applied to further optimize the racemization conditions, and the final yield of L‐PPT reached 96.13% with optimum reaction temperature of 154°C, reaction time of 23 minutes, and phenylacetic acid/NPDG mole ratio of 1.7, respectively. Moreover, adding a small amount of acetic anhydride further raised the yield of L‐PPT to 97.02%.     

Synthesis of enantiomers of exo‐2‐norbornyl‐N‐n‐butylcarbamate and endo‐2‐norbornyl‐N‐n‐butylcarbamate for stereoselective inhibition of acetylcholinesterase

The acetylcholinesterase inhibition by enantiomers of exo‐ and endo‐2‐norbornyl‐N‐n‐butylcarbamates shows high stereoselelectivity. For the acetylcholinesterase inhibitions by (R)‐(+)‐ and (S)‐(?)‐exo‐2‐norbornyl‐N‐n‐butylcarbamates, the R‐enantiomer is more potent than the S‐enantiomer. But, for the acetylcholinesterase inhibitions by (R)‐(+)‐ and (S)‐(?)‐endo‐2‐norbornyl‐N‐n‐butylcarbamates, the S‐enantiomer is more potent than the R‐enantiomer. Optically pure (R)‐(+)‐exo‐, (S)‐(?)‐exo‐, (R)‐(+)‐endo‐, and (S)‐(?)‐endo‐2‐norbornyl‐N‐n‐butylcarbamates are synthesized from condensations of optically pure (R)‐(+)‐exo‐, (S)‐(?)‐exo‐, (R)‐(+)‐endo‐, and (S)‐(?)‐endo‐2‐norborneols with n‐butyl isocyanate, respectively. Optically pure norborneols are obtained from kinetic resolutions of their racemic esters by lipase catalysis in organic solvent. Chirality 2010. © 2009 Wiley‐Liss, Inc.     

High‐Voltage Oxygen‐Redox‐Based Cathode for Rechargeable Sodium‐Ion Batteries

Recently, anionic‐redox‐based materials have shown promising electrochemical performance as cathode materials for sodium‐ion batteries. However, one of the limiting factors in the development of oxygen‐redox‐based electrodes is their low operating voltage. In this study, the operating voltage of oxygen‐redox‐based electrodes is raised by incorporating nickel into P2‐type Na_2/3[Zn_0.3Mn_0.7]O₂ in such a way that the zinc is partially substituted by nickel. As designed, the resulting P2‐type Na_2/3[(Ni_0.5Zn_0.5)_0.3Mn_0.7]O₂ electrode exhibits an average operating voltage of 3.5 V and retains 95% of its initial capacity after 200 cycles in the voltage range of 2.3–4.6 V at 0.1C (26 mA g^?1). Operando X‐ray diffraction analysis reveals the reversible phase transition: P2 to OP4 phase on charge and recovery to the P2 phase on discharge. Moreover, ex situ X‐ray absorption near edge structure and X‐ray photoelectron spectroscopy studies reveal that the capacity is generated by the combination of Ni²⁺/Ni⁴⁺ and O^2?/O^1? redox pairs, which is supported by first‐principles calculations. It is thought that this kind of high voltage redox species combined with oxygen redox could be an interesting approach to further increase energy density of cathode materials for not only sodium‐based rechargeable batteries, but other alkali‐ion battery systems.     

All‐Surface‐Atomic‐Metal Chalcogenide Sheets for High‐Efficiency Visible‐Light Photoelectrochemical Water Splitting

Artificial all‐surface‐atomic 2D sheets can trigger breakthroughs in tailoring the physical and chemical properties of advanced functional materials. Here, the conceptually new all‐surface‐atomic semiconductors of SnS and SnSe freestanding sheets are realized using a scalable strategy. As an example, all‐surface‐atomic SnS sheets undergo surface atomic elongation and structural disordering, which is revealed by X‐ray absorption fine structure spectroscopy and first‐principles calculations, endowing them with high structural stability and an increased density of states at the valence band edge. These exotic atomic and electronic structures make the all‐surface‐atomic SnS sheet‐based photoelectrode exhibit an incident photon‐to‐current conversion efficiency of 67.1% at 490 nm, much higher than the efficiencies of other visible‐light‐driven water splitting. A photocurrent density of 5.27 mA cm^‐2, which is two orders of magnitude higher than that of the bulk counterpart, is also achieved for the all‐surface‐atomic SnS sheets‐based photoelectrode. This will allow the manipulation of the basic properties of advanced materials on the atomic scale, thus paving the way for innovative applications.     

Solid‐State Prelithiation Enables High‐Performance Li‐Al‐H Anode for Solid‐State Batteries

Lithium alanates exhibit high theoretical specific capacities and appropriate lithiation/delithiation potentials, but suffer from poor reversibility, cycling stability, and rate capability due to their sluggish kinetics and extensive side reactions. Herein, a novel and facile solid‐state prelithiation approach is proposed to in situ prepare a Li₃AlH₆‐Al nanocomposite from a short‐circuited electrochemical reaction between LiAlH₄ and Li with the help of fast electron and Li‐ion conductors (C and P6₃mc LiBH₄). This nanocomposite consists of dispersive Al nanograins and an amorphous Li₃AlH₆ matrix, which enables superior electrochemical performance in solid‐state cells, as much higher specific capacity (2266 mAh g^?1), Coulombic efficiency (88%), cycling stability (71% retention in the 100th cycle), and rate capability (1429 mAh g^?1 at 1 A g^?1) are achieved. In addition, this nanocomposite works well in the solid‐state full cell with LiCoO₂ cathode, demonstrating its promising application prospects. Mechanism analysis reveals that the dispersive Al nanograins and amorphous Li₃AlH₆ matrix can dramatically enhance the lithiation and delithiation kinetics without side reactions, which is mainly responsible for the excellent overall performance. Moreover, this solid‐state prelithiation approach is general and can also be applied to other Li‐poor electrode materials for further modification of their electrochemical behavior.     

High‐throughput SNPs for all: genotyping‐in‐thousands

Understanding the genetic structure of species is essential for conservation. It is only with this information that managers, academics, user groups and land‐use planners can understand the spatial scale of migration and local adaptation, source‐sink dynamics and effective population size. Such information is essential for a multitude of applications including delineating management units, balancing management priorities, discovering cryptic species and implementing captive breeding programmes. Species can range from locally adapted by hundreds of metres (Pavey et al. 2010 ) to complete species panmixia (Côté et al. 2013 ). Even more remarkable is that this essential information can be obtained without fully sequenced or annotated genomes, but from mere (putatively) nonfunctional variants. First with allozymes, then microsatellites and now SNPs, this neutral genetic variation carries a wealth of information about migration and drift. For many of us, it may be somewhat difficult to remember our understanding of species conservation before the widespread usage of these useful tools. However most species on earth have yet to give us that ‘peek under the curtain’. With the current diversity on earth estimated to be nearly 9 million species (Mora et al. 2011 ), we have a long way to go for a comprehensive meta‐phylogeographic understanding. A method presented in this issue by Campbell and colleagues (Campbell et al. 2015 ) is a tool that will accelerate the pace in this area. Genotyping‐in‐thousands (GT‐seq) leverages recent advancements in sequencing technology to save many hours and dollars over previous methods to generate this important neutral genetic information.     

Structural determinants in bacterial 2‐keto‐3‐deoxy‐D‐gluconate dehydrogenase KduD for dual‐coenzyme specificity

Short‐chain dehydrogenase/reductase (SDR) is distributed in many organisms, from bacteria to humans, and has significant roles in metabolism of carbohydrates, lipids, amino acids, and other biomolecules. An important intermediate in acidic polysaccharide metabolism is 2‐keto‐3‐deoxy‐d ‐gluconate (KDG). Recently, two short and long loops in Sphingomonas KDG‐producing SDR enzymes (NADPH‐dependent A1‐R and NADH‐dependent A1‐R′) involved in alginate metabolism were shown to be crucial for NADPH or NADH coenzyme specificity. Two SDR family enzymes—KduD from Pectobacterium carotovorum (PcaKduD) and DhuD from Streptococcus pyogenes (SpyDhuD)—prefer NADH as coenzyme, although only PcaKduD can utilize both NADPH and NADH. Both enzymes reduce 2,5‐diketo‐3‐deoxy‐d ‐gluconate to produce KDG. Tertiary and quaternary structures of SpyDhuD and PcaKduD and its complex with NADH were determined at high resolution (approximately 1.6 Å) by X‐ray crystallography. Both PcaKduD and SpyDhuD consist of a three‐layered structure, α/β/α, with a coenzyme‐binding site in the Rossmann fold; similar to enzymes A1‐R and A1‐R′, both arrange the two short and long loops close to the coenzyme‐binding site. The primary structures of the two loops in PcaKduD and SpyDhuD were similar to those in A1‐R′ but not A1‐R. Charge neutrality and moderate space at the binding site of the nucleoside ribose 2′ coenzyme region were determined to be structurally crucial for dual‐coenzyme specificity in PcaKduD by structural comparison of the NADH‐ and NADPH‐specific SDR enzymes. The corresponding site in SpyDhuD was negatively charged and spatially shallow. This is the first reported study on structural determinants in SDR family KduD related to dual‐coenzyme specificity. Proteins 2016; 84:934–947. © 2016 Wiley Periodicals, Inc.     

Efficient approximate k‐fold and leave‐one‐out cross‐validation for ridge regression

In model building and model evaluation, cross‐validation is a frequently used resampling method. Unfortunately, this method can be quite time consuming. In this article, we discuss an approximation method that is much faster and can be used in generalized linear models and Cox’ proportional hazards model with a ridge penalty term. Our approximation method is based on a Taylor expansion around the estimate of the full model. In this way, all cross‐validated estimates are approximated without refitting the model. The tuning parameter can now be chosen based on these approximations and can be optimized in less time. The method is most accurate when approximating leave‐one‐out cross‐validation results for large data sets which is originally the most computationally demanding situation. In order to demonstrate the method's performance, it will be applied to several microarray data sets. An R package penalized, which implements the method, is available on CRAN.     

Nanostructured p‐n Junctions for Kinetic‐to‐Electrical Energy Conversion

Piezoelectric ZnO nanorods grown on a flexible substrate are combined with the p‐type semiconducting polymer PEDOT:PSS to produce a p‐n junction device that successfully demonstrates kinetic‐to‐electrical energy conversion. Both the voltage and current output of the devices are measured to be in the range of 10 mV and 10 μA cm^?2. Combining these figures for the best device gives a maximum possible power density of 0.4 mW cm^?3. Systematic testing of the devices is performed showing that the voltage output increases linearly with applied stress, and is reduced significantly by illumination with super‐band gap light. This provides strong evidence that the voltage output results from piezoelectric effects in the ZnO. The behavior of the devices is explained by considering the time‐dependent changes in band structure resulting from the straining of a piezoelectric material within a p‐n junction. It is shown that the rate of screening of the depolarisation field determines the power output of a piezoelectric energy harvesting device. This model is consistent with the behavior of a number of previous devices utilising the piezoelectric effect in ZnO.     

Iron‐Oxide‐Based Advanced Anode Materials for Lithium‐Ion Batteries

Iron oxides, such as Fe₂O₃ and Fe₃O₄, have recently received increased attention as very promising anode materials for rechargeable lithium‐ion batteries (LIBs) because of their high theoretical capacity, non‐toxicity, low cost, and improved safety. Nanostructure engineering has been demonstrated as an effective approach to improve the electrochemical performance of electrode materials. Here, recent research progress in the rational design and synthesis of diverse iron oxide‐based nanomaterials and their lithium storage performance for LIBs, including 1D nanowires/rods, 2D nanosheets/flakes, 3D porous/hierarchical architectures, various hollow structures, and hybrid nanostructures of iron oxides and carbon (including amorphous carbon, carbon nanotubes, and graphene). By focusing on synthesis strategies for various iron‐oxide‐based nanostructures and the impacts of nanostructuring on their electrochemical performance, novel approaches to the construction of iron‐oxide‐based nanostructures are highlighted and the importance of proper structural and compositional engineering that leads to improved physical/chemical properties of iron oxides for efficient electrochemical energy storage is stressed. Iron‐oxide‐based nanomaterials stand a good chance as negative electrodes for next generation LIBs.     

Application of NMR spectroscopy for assignment of the absolute configuration of 8‐tert‐butyl‐2‐hydroxy‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]dec‐6‐en‐10‐one

In order to assign the absolute configurations of 8‐tert‐butyl‐2‐hydroxy‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]dec‐6‐en‐10‐one ( 2a , 2b ), their esters ( 5a , 5b , 5c , 5d ) with (R)‐ or (S)‐2‐methoxyphenylacetic acid ( 4a , 4b ) have been synthesized. The absolute configurations of these compounds have been determined on the basis of NOESY correlations between the protons of the tert‐butyl group and the cyclopentane fragment of the molecules. The crucial part of this analysis was assignment of the absolute configuration at C‐5. Additionally, by calculation of the chemical shift anisotropy, δ^RS, for the relevant protons, it was also possible to confirm the absolute configurations at the C‐2 centres of compounds 2a , 2b and 5a , 5b , 5c , 5d . Chirality, 25:422–426, 2013.© 2013 Wiley Periodicals, Inc.     

Heteroatom‐Doped and Oxygen‐Functionalized Nanocarbons for High‐Performance Supercapacitors

Electrochemical capacitors (best known as supercapacitors) are high‐performance energy storage devices featuring higher capacity than conventional capacitors and higher power densities than batteries, and are among the key enabling technologies of the clean energy future. This review focuses on performance enhancement of carbon‐based supercapacitors by doping other elements (heteroatoms) into the nanostructured carbon electrodes. The nanocarbon materials currently exist in all dimensionalities (from 0D quantum dots to 3D bulk materials) and show good stability and other properties in diverse electrode architectures. However, relatively low energy density and high manufacturing cost impede widespread commercial applications of nanocarbon‐based supercapacitors. Heteroatom doping into the carbon matrix is one of the most promising and versatile ways to enhance the device performance, yet the mechanisms of the doping effects still remain poorly understood. Here the effects of heteroatom doping by boron, nitrogen, sulfur, phosphorus, fluorine, chlorine, silicon, and functionalizing with oxygen on the elemental composition, structure, property, and performance relationships of nanocarbon electrodes are critically examined. The limitations of doping approaches are further discussed and guidelines for reporting the performance of heteroatom doped nanocarbon electrode‐based electrochemical capacitors are proposed. The current challenges and promising future directions for clean energy applications are discussed as well.     

Slow‐growth high‐mortality: A meta‐analysis for insects

The slow growth‐high mortality hypothesis (SG‐HG) predicts that slower growing herbivores suffer greater mortality due to a prolonged window of vulnerability. Given diverse plant–herbivore–natural enemy systems resulting from different feeding ecologies of herbivores and natural enemies, this hypothesis might not always be applicable to all systems. This is evidenced by mixed support from empirical data. In this study, a meta‐analysis of the SG‐HM hypothesis for insects was conducted, aiming to find conditions that favor or reject SG‐HM. The analysis revealed significant within‐ and between‐group heterogeneity for almost all explanatory variables and overall did not support SG‐HM. In this analysis, SG‐HM was supported when any of the following 5 conditions was met: (1) host food consisted of artificial diet; (2) herbivore growth was measured as larval mass; (3) herbivores were generalists; (4) no or multiple species of natural enemies were involved in the study; and (5) parasitoids (i.e., parasitic insects) involved in the study were gregarious. SG‐HM was rejected when any of the following 5 conditions was met: (1) herbivores were from the order Hymentoptera; (2) parasitoids from more than 1 order caused herbivore mortality; (2) parasitoids were specialists; (3) parasitoids were solitary; (4) parasitoids were idiobionts or koinobionts; and (5) single species of natural enemy caused mortality of specialist herbivores. All known studies investigated herbivore mortality for a short period of their life cycle. Researchers are encouraged to monitor herbivore mortality during the entire window of susceptibility or life cycle using life tables. Studies involving multiple mortality factors (i.e., both biotic and abiotic) or multiple natural enemy species are also encouraged since herbivores in nature face a multitude of risks during the entire life cycle. More comprehensive studies may increase our understanding of factors influencing the relationships between herbivore growth and mortality.