Physical adsorption characterization of nanoporous materials: progress and challenges

Within the last two decades major progress has been achieved in understanding the adsorption and phase behavior of fluids in ordered nanoporous materials and in the development of advanced approaches based on statistical mechanics such as molecular simulation and density functional theory (DFT) of inhomogeneous fluids. This progress, coupled with the availability of high resolution experimental procedures for the adsorption of various subcritical fluids, has led to advances in the structural characterization by physical adsorption. It was demonstrated that the application of DFT based methods on high resolution experimental adsorption isotherms provides a much more accurate and comprehensive pore size analysis compared to classical, macroscopic methods. This article discusses important aspects of major underlying mechanisms associated with adsorption, pore condensation and hysteresis behavior in nanoporous solids. We discuss selected examples of state-of-the-art pore size characterization and also reflect briefly on the existing challenges in physical adsorption characterization.     

Selective Photoreceptor Gene Knock‐out Reveals a Regulatory Role for the Growth Behavior of Pseudomonas syringae

The plant pathogen Pseudomonas syringae (Ps) is a well‐established model organism for bacterial infection of plants. The genome sequences of two pathovars, pv. syringae and pv. tomato, revealed one gene encoding a blue and two genes encoding red/far red light‐sensing photoreceptors. Continuing former molecular characterization of the photoreceptor proteins, we here report selective photoreceptor gene disruption for pv. tomato aiming at identification of potentially regulatory functions of these photoreceptors. Transformation of Ps cells with linear DNA constructs yielded interposon mutations of the corresponding genes. Cell growth studies of the generated photoreceptor knock‐out mutants revealed their role in light‐dependent regulation of cell growth and motility. Disruption of the blue‐light (BL) receptor gene caused a growth deregulation, in line with an observed increased virulence of this mutant (Moriconi et al., Plant J., 2013, 76, 322). Bacterial phytochrome‐1 (BphP1) deletion mutant caused unaltered cell growth, but a stronger swarming capacity. Inactivation of its ortholog, BphP2, however, caused reduced growth and remarkably altered dendritic swarming behavior. Combined knock‐out of both bacteriophytochromes reproduced the swarming pattern observed for the BphP2 mutant alone. A triple knock‐out mutant showed a growth rate between that of the BL (deregulation) and the phytochrome‐2 mutant (growth reduction).     

Engineering Substrate Topography at the Micro‐ and Nanoscale to Control Cell Function

The interaction of mammalian cells with nanoscale topography has proven to be an important signaling modality in controlling cell function. Naturally occurring nanotopographic structures within the extracellular matrix present surrounding cells with mechanotransductive cues that influence local migration, cell polarization, and other functions. Synthetically nanofabricated topography can also influence cell morphology, alignment, adhesion, migration, proliferation, and cytoskeleton organization. We review the use of in vitro synthetic cell–nanotopography interactions to control cell behavior and influence complex cellular processes, including stem‐cell differentiation and tissue organization. Future challenges and opportunities in cell–nanotopography engineering are also discussed, including the elucidation of mechanisms and applications in tissue engineering.     

Inhibition of Swarming motility of Pseudomonas aeruginosa by Methanol extracts of Alpinia officinarum Hance. and Cinnamomum tamala T. Nees and Eberm

Bacterial drug resistance is a challenge in clinical settings, especially in countries like India. Hence, discovery of novel alternative therapeutics has become a necessity in the fight against drug resistance. Compounds that inhibit bacterial virulence properties form new therapeutic alternatives. Pseudomonas aeruginosa is an opportunistic, nosocomial pathogen that infects immune-compromised patients. Swarming motility is an important virulence property of Pseudomonas which aids it in reaching host cells under nutrient limiting conditions. Here, we report the screening of five plant extracts against swarming motility of P. aeruginosa and show that methanol extracts of Alpinia officinarum and Cinnamomum tamala inhibit swarming motility at 5 μg mL^?1 without inhibiting its growth. These extracts did not inhibit swimming and twitching motilities indicating a mode of action specific to swarming pathway. Preliminary experiments indicated that rhamnolipid production was not affected. This study reveals the potential of the two plants in anti-virulence drug discovery.     

A Chimeric Siderophore Halts Swarming Vibrio

Some bacteria swarm under some circumstances; they move rapidly and collectively over a surface. In an effort to understand the molecular signals controlling swarming, we isolated two bacterial strains from the same red seaweed, Vibrio alginolyticus B522, a vigorous swarmer, and Shewanella algae B516, which inhibits V. alginolyticus swarming in its vicinity. Plate assays combined with NMR, MS, and X‐ray diffraction analyses identified a small molecule, which was named avaroferrin, as a potent swarming inhibitor. Avaroferrin, a previously unreported cyclic dihydroxamate siderophore, is a chimera of two well‐known siderophores: putrebactin and bisucaberin. The sequenced genome of S. algae revealed avaroferrin’s biosynthetic gene cluster to be a mashup of putrebactin and bisucaberin biosynthetic genes. Avaroferrin blocks swarming through its ability to bind iron in a form that cannot be pirated by V. alginolyticus, thereby securing this essential resource for its producer.     

面向疾病应用的微纳米马达

微纳米马达是能将环境中的化学反应或外场(光、声、磁场、电场等)提供的能量转化为推进力,从而产生自主运动的微纳米级人造机器。由于具有集群效应、比表面积大、运动可控等多种特征,微纳米马达在环境修复、药物递送、微纳手术、抗感染、重金属清除等诸多领域受到关注。在一定条件下,微纳米马达能主动运动并聚集到病灶,将治疗或诊断药物递送到靶部位,有望在人体复杂环境中进行精细化的工作。因此,微纳米马达在疾病预防、诊断、治疗以及预后中具有巨大的发展空间。在此,本综述首先对微纳米马达进行简要介绍,包括其结构设计、驱动方式。其次,详细介绍微纳米马达在不同类型的疾病中的研究进展。最后,提出目前该技术面临的挑战与未来发展方向。     

A review of electrochemical reduction processes to treat oxidized contaminants in water

The purpose of this review is to provide a short overview of electrochemical reduction processes for oxidized contaminants in water. The major parameters affecting the electroreduction mechanisms and the impact of electrode choice are discussed with reference to both inorganic and organic pollutants that are either regulated or emerging (e.g., nonmetal oxyanions, perfluoroalkyl and polyfluoroalkyl substances). To conclude, a discussion is presented on the future directions and challenges that must be addressed to develop these electrochemical reduction processes at a larger, commercialized scale.     

Electrode materials and reaction mechanisms in solid oxide fuel cells: a brief review

This work is focused on the comparative analysis of electrochemical and transport properties in the major families of cathode and anode compositions for intermediate-temperature solid oxide fuel cells (SOFCs) and materials science-related factors affecting electrode performance. The first part presents a brief overview of the electrochemical and chemical reactions in SOFCs, specific rate-determining steps of the electrode processes, solid oxide electrolyte ceramics, and effects of partial oxygen ionic and electronic conductivities in the SOFC components. The aspects associated with materials compatibility, thermal expansion, stability, and electrocatalytic behavior are also briefly discussed. Primary attention is centered on the experimental data and approaches reported during the last 10–15 years, reflecting the main challenges in the field of materials development for the ceramic fuel cells.     

杂原子掺碳材料氧还原催化剂研究进展

开发替代Pt类高活性、低成本的非贵金属燃料电池阴极氧还原催化剂是实现燃料电池商业化的必由之路. 研发催化活性高,稳定性好,价格便宜的非贵金属催化剂是当务之急. 碳纳米材料,尤其杂原子掺杂的碳纳米材料有其独特的结构和催化性能而备受瞩目. 本文结合作者课题组的研究工作,综述了近年杂原子掺杂碳纳米材料催化剂燃料电池阴极氧电催化还原方面的研究进展.     

Exogenous agents that target transmembrane domains of proteins

Although membrane proteins account for approximately one third of all proteins encoded in the human genome, the functions and structures of their transmembrane domains are much less understood than the water-soluble regions. A major hurdle in studying these transmembrane domains is the lack of appropriate exogenous agents that can be used as specific probes. Despite the daunting challenges, major strides have recently been made in targeting the transmembrane domains of a variety of membrane proteins. High affinity and selectivity have been achieved in model biophysical systems, membranes of bacteria, and mammalian cells.     

Emergent Swarming States in Active Particles System with Opposite Anisotropic Interactions

From the organization of animal flocks to the emergence of swarming behaviors in bacterial suspension, populations of motile organisms at all scales display coherent collective motion. Recent studies showed that the anisotropic interaction between active particles plays a key role in the phase behaviors. Here we investigate the collective behaviors of based-active Janus particles that experience an anisotropic interaction of which the orientation is opposite to the direction of active force by using Langevin dynamics simulations in two dimensional space. Interestingly, the system shows emergence of collective swarming states upon increasing the total area fraction of particles, which is not observed in systems without anisotropic interaction or activity. The threshold for emergence of swarming states decreases as particle activity or interaction strength increases. We have also performed basic kinetic analysis to reproduce the essential features of the simulation results. Our results demonstrate that anisotropic interactions at the individual level are sufficient to set homogeneous active particles into stable directed motion.     

Increased stability of glycol-terminated self-assembled monolayers for long-term patterned cell culture

Self-assembled monolayers (SAMs) are widely used to confine proteins and cells to a pattern to study cellular processes and behavior. To fully explore some of these phenomena, it is necessary to control cell growth and confinement for several weeks. Here, we present a simple method by which protein and cellular confinement to a pattern can be maintained for more than 35 days. This represents a significant increase in pattern stability compared to previous monolayer systems and is achieved using an amide-linked glycol monomer on 50 ? titanium/100 ? gold-coated glass coverslips. In addition, this study provides insight into the method of SAM degradation and excludes interfacial mixing of the monomers and blooming of the adlayer as major mechanisms for SAM degradation.     

Macroscale Chemotaxis from a Swarm of Bacteria‐Mimicking Nanoswimmers

Inspired by the dynamics of bacterial swarming, we report a swarm of polymer‐brush‐grafted, glucose‐oxidase‐powered Janus gold nanoswimmers with a positive, macroscale chemotactic behavior. These nanoswimmers are prepared through the grafting of polymer brushes onto one side of gold nanoparticles, followed by functionalization with glucose oxidase on the other side. The resulting polymer‐brush‐functionalized Janus gold nanoswimmers exhibit efficient propulsion with a velocity of up to approximately 120 body lengths s^?1 in the presence of glucose. The comparative analysis of their kinematic behavior reveals that the grafted polymer brushes significantly improve the translational diffusion of Janus gold nanoswimmers. Particularly, these bacteria‐mimicking Janus gold nanoswimmers display a collectively chemotactic motion along the concentration gradient of a glucose resource, which could be observed at the macroscale.     

Forces,stresses and the (thermo?) dynamics of active matter

The statistical mechanics and microhydrodynamics of active matter systems have been studied intensively during the past several years, by various soft matter physicists, chemists, engineers, and biologists around the world. Recent attention has focused on the fascinating nonequilibrium behaviors of active matter that cannot be observed in equilibrium thermodynamic systems, such as spontaneous collective motion and swarming. Even minimal kinetic models of active Brownian particles exhibit self-assembly that resembles a gas–liquid phase separation from classical equilibrium systems. Self-propulsion allows active systems to generate internal stresses that enable them to control and direct their own behavior and that of their surroundings. In this review, we discuss the forces that govern the motion of active Brownian microswimmers, the stress (or pressure) they generate, and the implication of these concepts on their collective behavior. We focus on recent work involving the unique “swim pressure” exerted by active systems and discuss how this perspective may be the basic underlying physical mechanism responsible for self-assembly and pattern formation in all active matter. We discuss the utility of the swim pressure concept to quantify the forces, stresses, and the (thermo?) dynamics of active matter.     

碱性介质中氢氧化反应电催化剂的开发:从机理认识到材料设计

阴离子交换膜(AEM)燃料电池因具有使用非贵金属作为催化剂的优点而受到广泛关注.然而,在碱性体系中,AEM燃料电池中氢氧化反应(HOR)的反应动力学比在酸性介质中的慢两个数量级.针对HOR在碱中动力学缓慢的问题,有两种主要的理论来解释,(1)pH相关的氢结合能作为主要影响因素来控制HOR动力学的理论;(2)质子和氢氧根离子的吸附共同作为影响因子来控制HOR在碱性条件下的动力学的双功能理论.本文首先讨论了在碱性电解质中可能的HOR反应机理及其Tafel性能变化.除了传统的Tafel-Volmer和Heyrovsky-Volmer-HOR机理外,还讨论了最新提出的氢氧根离子吸附参与的HOR机理来说明在酸性和碱性介质中HOR机理的差异.然后,总结了具有代表性的碱性HOR催化剂(如贵金属、合金、金属间化合物、镍基合金、碳化物、氮化物等),简要介绍了它们相应的HOR反应机理,从而进一步理解在碱性介质中不同基元反应步骤给HOR性能带来的差异.最后,提出了一种未来设计HOR碱性催化剂的可行性方案,为今后碱性环境下的HOR催化剂设计提供参考.     

Unravelling the Anticancer Mechanisms of Traditional Herbal Medicines with Metabolomics

Metabolite profiling of cancer cells presents many opportunities for anticancer drug discovery. The Chinese, Indian, and African flora, in particular, offers a diverse source of anticancer therapeutics as documented in traditional folklores. In-depth scientific information relating to mechanisms of action, quality control, and safety profile will promote their extensive usage in cancer therapy. Metabolomics may be a more holistic strategy to gain valuable insights into the anticancer mechanisms of action of plants but this has remained largely unexplored. This review, therefore, presents the available metabolomics studies on the anticancer effects of herbal medicines commonly used in Africa and Asia. In addition, we present some scientifically understudied ‘candidate plants’ for cancer metabolomics studies and highlight the relevance of metabolomics in addressing other challenges facing the drug development of anticancer herbs. Finally, we discussed the challenges of using metabolomics to uncover the underlying mechanisms of potential anticancer herbs and the progress made in this regard.     

Progress in nuclear magnetic resonance studies of surfactant systems

Nuclear magnetic resonance (NMR), as a powerful technology, is widely used to characterize the physicochemical properties of surfactants in solution. As a sensitive technique to molecular environment, NMR is beyond the reach of other spectral methods in surfactant systems. Recent years, intensive investigations of surfactants by NMR were reported but not well summarized; therefore, we highlight these significant progresses, which may shed light on the challenges to understand their behavior and mechanisms in surfactant systems. The theory of various NMR methods was introduced, including chemical shifts, diffusion, relaxation, 2D nuclear Overhauser effect spectroscopy and rotating frame nuclear Overhauser effect spectroscopy. The behavior, interaction, and mechanisms among surfactants and other molecules from NMR technologies were discussed. Challenges to understand the behavior and mechanisms in surfactant systems and instrumentation limits are addressed as perspectives.     

Anticancer alpha-helical peptides and structure/function relationships underpinning their interactions with tumour cell membranes

Cancer is a major cause of premature death and there is an urgent need for new anticancer agents with novel mechanisms of action. Here we review recent studies on a group of peptides that show much promise in this regard, exemplified by arthropod cecropins and amphibian magainins and aureins. These molecules are alpha-helical defence peptides, which show potent anticancer activity (alpha-ACPs) in addition to their established roles as antimicrobial factors and modulators of innate immune systems. Generally, alpha-ACPs exhibit selectivity for cancer and microbial cells primarily due to their elevated levels of negative membrane surface charge as compared to non-cancerous eukaryotic cells. The anticancer activity of alpha-ACPs normally occurs at micromolar levels but is not accompanied by significant levels of haemolysis or toxicity to other mammalian cells. Structure/function studies have established that architectural features of alpha-ACPs such as amphiphilicty levels and hydrophobic arc size are of major importance to the ability of these peptides to invade cancer cell membranes. In the vast majority of cases the mechanisms underlying such killing involves disruption of mitochondrial membrane integrity and/or that of the plasma membrane of the target tumour cells. Moreover, these mechanisms do not appear to proceed via receptor-mediated routes but are thought to be effected in most cases by the carpet/toroidal pore model and variants. Usually, these membrane interactions lead to loss of membrane integrity and cell death utilising apoptic and necrotic pathways. It is concluded that that alpha-ACPs are major contenders in the search for new anticancer drugs, underlined by the fact that a number of these peptides have been patented in this capacity.