Hasil untuk "physics.atom-ph"

Qian Chen, Liangzhu Feng, Jingjing Liu et al.

Jie Zheng, Wenchao Sheng, Z. Zhuang et al.

A universal correlation is established between HOR/HER activity and hydrogen binding energy on platinum-group metals. Understanding how pH affects the activity of hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is key to developing active, stable, and affordable HOR/HER catalysts for hydroxide exchange membrane fuel cells and electrolyzers. A common linear correlation between hydrogen binding energy (HBE) and pH is observed for four supported platinum-group metal catalysts (Pt/C, Ir/C, Pd/C, and Rh/C) over a broad pH range (0 to 13), suggesting that the pH dependence of HBE is metal-independent. A universal correlation between exchange current density and HBE is also observed on the four metals, indicating that they may share the same elementary steps and rate-determining steps and that the HBE is the dominant descriptor for HOR/HER activities. The onset potential of CO stripping on the four metals decreases with pH, indicating a stronger OH adsorption, which provides evidence against the promoting effect of adsorbed OH on HOR/HER.

H. Nyein, W. Gao, Ziba Shahpar et al.

A. Yadollahi, N. Shamsaei, S. Thompson et al.

Jin Qu, Xin Zhao, P. Ma et al.

Shanshan Jiang, Junzhou Ding, J. Andrade et al.

Christoph Ratzke, J. Gore

Microbes usually exist in communities consisting of myriad different but interacting species. These interactions are typically mediated through environmental modifications; microbes change the environment by taking up resources and excreting metabolites, which affects the growth of both themselves and also other microbes. We show here that the way microbes modify their environment and react to it sets the interactions within single-species populations and also between different species. A very common environmental modification is a change of the environmental pH. We find experimentally that these pH changes create feedback loops that can determine the fate of bacterial populations; they can either facilitate or inhibit growth, and in extreme cases will cause extinction of the bacterial population. Understanding how single species change the pH and react to these changes allowed us to estimate their pairwise interaction outcomes. Those interactions lead to a set of generic interaction motifs—bistability, successive growth, extended suicide, and stabilization—that may be independent of which environmental parameter is modified and thus may reoccur in different microbial systems.

Erez Persi, Miquel Duran-Frigola, Mehdi Damaghi et al.

A reverse pH gradient is a hallmark of cancer metabolism, manifested by extracellular acidosis and intracellular alkalization. While consequences of extracellular acidosis are known, the roles of intracellular alkalization are incompletely understood. By reconstructing and integrating enzymatic pH-dependent activity profiles into cell-specific genome-scale metabolic models, we develop a computational methodology that explores how intracellular pH (pHi) can modulate metabolism. We show that in silico, alkaline pHi maximizes cancer cell proliferation coupled to increased glycolysis and adaptation to hypoxia (i.e., the Warburg effect), whereas acidic pHi disables these adaptations and compromises tumor cell growth. We then systematically identify metabolic targets (GAPDH and GPI) with predicted amplified anti-cancer effects at acidic pHi, forming a novel therapeutic strategy. Experimental testing of this strategy in breast cancer cells reveals that it is particularly effective against aggressive phenotypes. Hence, this study suggests essential roles of pHi in cancer metabolism and provides a conceptual and computational framework for exploring pHi roles in other biomedical domains. Tumors often exhibit a pH gradient, with an acidic extracellular space and alkaline cytoplasm. Here the authors develop a computational model to show how alkaline pHi supports changes inherent to cancer cell metabolism and acidification disables these adaptations, and demonstrate the effect of acidic pHi on breast cancer cell survival.

Zilong Han, Peng Wang, G. Mao et al.

As one of the most promising drug delivery carriers, hydrogels have received considerable attention in recent years. Many previous efforts focused on diffusion-controlled release which allows hydrogels to load and release drugs in vitro and/or in vivo. However, it hardly applies to lipophilic drug delivery due to their poor compatibility with hydrogels. Herein, we propose a novel method for lipophilic drug release based on a dual pH-responsive hydrogel actuator. Specifically, the drug is encapsulated and can be released by a dual pH-controlled capsule switch. Inspired by the deformation mechanism of Drosera leaves, we fabricate the capsule switch with a double-layer structure that is made of two kinds of pH-responsive hydrogel. Two layers are covalently bonded together through silane coupling agents. They can bend collaboratively in basic or acidic environment to achieve "turn on" motion of capsule switch. By incorporating an array of parallel elastomer-stripes on one side of the hydrogel bilayer, various motions (e.g., bending, twisting, and rolling) of the hydrogel bilayer actuator were achieved. We conducted in vitro lipophilic drug release test. The feasibility of this new drug release method is verified. We believe this dual pH-responsive actuator-controlled drug release method may enlighten the possibilities for various drug delivery systems.

P. Lund, D. De Biase, Oded Liran et al.

Microbes from the three domains of life, Bacteria, Archaea, and Eukarya, share the need to sense and respond to changes in the external and internal concentrations of protons. When the proton concentration is high, acidic conditions prevail and cells must respond appropriately to ensure that macromolecules and metabolic processes are sufficiently protected to sustain life. While, we have learned much in recent decades about the mechanisms that microbes use to cope with acid, including the unique challenges presented by organic acids, there is still much to be gained from developing a deeper understanding of the effects and responses to acid in microbes. In this perspective article, we survey the key molecular mechanisms known to be important for microbial survival during acid stress and discuss how this knowledge might be relevant to microbe-based applications and processes that are consequential for humans. We discuss the research approaches that have been taken to investigate the problem and highlight promising new avenues. We discuss the influence of acid on pathogens during the course of infections and highlight the potential of using organic acids in treatments for some types of infection. We explore the influence of acid stress on photosynthetic microbes, and on biotechnological and industrial processes, including those needed to produce organic acids. We highlight the importance of understanding acid stress in controlling spoilage and pathogenic microbes in the food chain. Finally, we invite colleagues with an interest in microbial responses to low pH to participate in the EU-funded COST Action network called EuroMicropH and contribute to a comprehensive database of literature on this topic that we are making publicly available.

I. Fernando, Yan Zhou

Widespread usage of silver nanoparticles (AgNPs) in consumer products has resulted in their presence in the aquatic environment. The evolution of the properties of AgNPs with changes in pH and time in terms of colloidal stability, dissolution and aggregation were investigated in a series of short and long-term experiments using freshly synthesized uncoated AgNPs. The solution pH modifies the surface charge and the oxidative dissolution of AgNPs. As a result, the particle behavior varied in acidic and alkaline conditions. The particle size decreased with the increasing pH at a given time frame resulting in lower aggregation in the higher pH regime and increased particle stability. These results have been further proved with the direct evidence obtained using time resolved in situ imaging acquired through Liquid cell transmission electron microscopy (LCTEM). Furthermore, the magnitude of the impact of the pH on the particle properties is higher than the impact of the dissolved oxygen concentration. The derived empirical formulae reflect that the AgNP oxidation depends on both dissolved oxygen and protons while the AgNP dissolution increasing with the increase of either of these. Overall, our results highlight the impact of the solution pH on the evolution of the properties of AgNPs over the time and provide an insight to confidently extend the results to predict the environmental transformation of AgNPs from ideal systems to the real.

M. Ghoneim, A. Nguyen, N. Dereje et al.

pH-sensing materials and configurations are rapidly evolving toward exciting new applications, especially those in biomedical applications. In this review, we highlight rapid progress in electrochemical pH sensors over the past decade (2008-2018) with an emphasis on key considerations, such as materials selection, system configurations, and testing protocols. In addition to recent progress in optical pH sensors, our main focus in this review is on electromechanical pH sensors due to their significant advances, especially in biomedical applications. We summarize developments of electrochemical pH sensors that by virtue of their optimized material chemistries (from metal oxides to polymers) and geometrical features (from thin films to quantum dots) enable their adoption in biomedical applications. We further present an overview of necessary sensing standards and protocols. Standards ensure the establishment of consistent protocols, facilitating collective understanding of results and building on the current state. Furthermore, they enable objective benchmarking of various pH-sensing reports, materials, and systems, which is critical for the overall progression and development of the field. Additionally, we list critical issues in recent literary reporting and suggest various methods for objective benchmarking. pH regulation in the human body and state-of-the-art pH sensors (from ex vivo to in vivo) are compared for suitability in biomedical applications. We conclude our review by (i) identifying challenges that need to be overcome in electrochemical pH sensing and (ii) providing an outlook on future research along with insights, in which the integration of various pH sensors with advanced electronics can provide a new platform for the development of novel technologies for disease diagnostics and prevention.

Weijie Chen, Xiaoxie Ma, Huijuan Chen et al.

Abstract The homeostasis of acid/base and alkali metal played critical roles in life process. To get insight into their functional mechanism, a large amount of detectors, especially based on organic fluorescent probes have been largely developed and used to monitor the dynamic changes of pH and alkali metal ions. Importantly, fluorescent probes provide a portable means to carry out a real-time determination and even a clinical diagnosis for abnormal pathological states. Over the past decades, numerous fluorescent probes for the pH and alkali metals analytes have been extensively developed and applied in living systems. In this review, we outlined the recent advances on fluorescent probes for pH and alkali metal ions containing their sensing mechanism, binding modes and application.

Shijie Zhuo, Feng Zhang, Junyu Yu et al.

The development of precise and personalized medicine requires novel formulation strategies to deliver the therapeutic payloads to the pathological tissues, producing enhanced therapeutic outcome and reduced side effects. As many diseased tissues are feathered with acidic characteristics microenvironment, pH-sensitive biomaterials for drug delivery present great promise for the purpose, which could protect the therapeutic payloads from metabolism and degradation during in vivo circulation and exhibit responsive release of the therapeutics triggered by the acidic pathological tissues, especially for cancer treatment. In the past decades, many methodologies, such as acidic cleavage linkage, have been applied for fabrication of pH-responsive materials for both in vitro and in vivo applications. In this review, we will summarize some pH-sensitive drug delivery system for medical application, mainly focusing on the pH-sensitive linkage bonds and pH-sensitive biomaterials.

J. Michl, K. Park, P. Swietach

A fundamental variable in culture medium is its pH, which must be controlled by an appropriately formulated buffering regime, since biological processes are exquisitely sensitive to acid–base chemistry. Although awareness of the importance of pH is fostered early in the training of researchers, there are no consensus guidelines for best practice in managing pH in cell cultures, and reporting standards relating to pH are typically inadequate. Furthermore, many laboratories adopt bespoke approaches to controlling pH, some of which inadvertently produce artefacts that increase noise, compromise reproducibility or lead to the misinterpretation of data. Here, we use real-time measurements of medium pH and intracellular pH under live-cell culture conditions to describe the effects of various buffering regimes, including physiological CO2/HCO3− and non-volatile buffers (e.g. HEPES). We highlight those cases that result in poor control, non-intuitive outcomes and erroneous inferences. To improve data reproducibility, we propose guidelines for controlling pH in culture systems. Johanna Michl et al. use real-time pH measurements of cell culture media and intracellular pH data from live-cell culture conditions to explore the effects of commonly-used buffers. Based on these data, they propose guidelines for controlling pH in cell culture systems and improving reproducibility.

Hannah Banks, John Carlton, Benjamin Elder et al.

Screened scalars are ubiquitous in many dark-sector models. They give rise to non-trivial fifth forces whilst evading experimental constraints through density-dependent screening mechanisms. We propose equipping a 10\,m-scale long-baseline atom interferometer with an annular planar source mass inside the vacuum chamber to search for such screened fifth forces. Two key challenges arise: distinguishing the static fifth force from backgrounds, and isolating it from the plate's Newtonian gravity. We introduce the `$Q$-flip protocol', which alternates between interferometry sequences to induce controllable time-dependence, aiding signal extraction and de-trending of transient noise. We further develop an \emph{in situ} calibration procedure to characterise the plate's Newtonian gravity and reach shot-noise-limited sensitivity. We show that our proposal could test theoretically motivated parameter space, advancing existing bounds in chameleon and symmetron screened scalar models by $1$ to $1.5$ orders of magnitude. Our proposal is directly applicable to forthcoming experiments, such as AION-10 or VLBAI, and is readily extensible to broader theoretical models and longer baselines.

Wenting Qian, Bin Ma, Xiyao Li et al.

Partial-denitrification (nitrate to nitrite) can supply nitrite for anammox which can reduce organic matter consumption in wastewater treatment plants (WWTPs). In order to achieve stable partial-denitrification, the effect of pH on denitrification were investigated for 420 days in three reactors with influent pH of 5.0, 7.0 and 9.0. The results indicate that the nitrite accumulation rate (NAR) increased with pH, with average effluent NARs being 21%, 38% and 57% in the above reactors, respectively. The sludge cultivated at a high pH of 9.0 was resistant to pH shock, with a high NAR being maintained at 83% when it was exposed to a low pH of 5.0. Metagenomic analysis showed that the higher NAR at pH 9.0 was correlated with an enrichment of Thauera, which harbored more nitrate reductase (8098 hits) than nitrite reductase (2950 hits). Based on these findings, a novel process was proposed for achieving partial-denitrification/anammox in mainstream WWTPs.

Shu-Hua Kuo, C. Shen, Ching-Fen Shen et al.

As a highly influential physiological factor, pH may be leveraged as a tool to diagnose physiological state. It may be especially suitable for diagnosing and assessing skin structure and wound status. Multiple innovative and elegant smart wound dressings combined with either pH sensors or drug control-released carriers have been extensively studied. Increasing our understanding of the role of pH value in clinically relevant diagnostics should assist clinicians and improve personal health management in the home. In this review, we summarized a number of articles and discussed the role of pH on the skin surface as well as the factors that influence skin pH and pH-relevant skin diseases, but also the relationship of skin pH to the wound healing process, including its influence on the activity of proteases, bacterial enterotoxin, and some antibacterial agents. A great number of papers discussing physiological pH value have been published in recent decades, far too many to be included in this review. Here, we have focused on the impact of pH on wounds and skin with an emphasis on clinically relevant diagnosis toward effective treatment. We have also summarized the differences in skin structure and wound care between adults and infants, noting that infants have fragile skin and poor skin barriers, which makes them more vulnerable to skin damage and compels particular care, especially for wounds.

J. Carstensen, C. Duarte

A synthesis of long-term changes in pH of coastal ecosystems shows that, in contrast to the uniform trends of open-ocean acidification (-0.0004 to -0.0026 pH units yr-1) driven by increased atmospheric CO2, coastal ecosystems display a much broader range of trends (-0.023 to 0.023 pH units yr-1) and are as likely to show long-term increase as decline in pH. The majority of the 83 investigated coastal ecosystems displayed nonlinear trends, with seasonal and interannual variations exceeding 1 pH unit for some sites. The high pH variability of coastal ecosystems is primarily driven by inputs from land. These include freshwater inputs that typically dilute the alkalinity of seawater thereby resulting in reduced buffering, nutrients enhancing productivity and pH, as well as organic matter supporting excess respiration driving acidification. For some coastal ecosystems, upwelling of nutrient-rich and corrosive water may also contribute to variability in pH. Metabolic control of pH was the main factor governing variability for the majority of coastal sites, displaying larger variations in coastal ecosystems with low alkalinity buffering. pH variability was particularly pronounced in coastal ecosystems with strong decoupling of production and respiration processes, seasonally or through stratification. Our analysis demonstrate that coastal pH can be managed by controlling inputs of nutrients, organic matter, and alkalinity. In well-mixed coastal waters, increasing productivity can improve resistance to ocean acidification, whereas increasing productivity enhances acidification in bottom waters of stratified coastal ecosystems. Environmental management should consider the balance between the negative consequences of eutrophication versus those of acidification, to maintain biodiversity and ecosystem services of our coastal ecosystems.

Mariana C. O. Monteiro, M. Koper

Abstract Localized pH measurements are important in various areas of electrochemistry, from corrosion to bio-electrochemistry and electrocatalysis. Different techniques are available to perform these measurements and offer numerous possibilities in terms of spatial and temporal resolution, sensitivity, and precision. In this brief review we present the recent progress made and summarize the main techniques available for localized pH measurements in electrochemistry such as scanning probe techniques (SECM, SICM, SIET), laser (confocal) fluorescence microscopy, rotating ring-disc electrode (RRDE) voltammetry, and infra-red spectroscopy, among others.