Hasil untuk "physics.geo-ph"

Grzegorz Boczkaj, A. Fernandes

M. Kanamala, W. Wilson, Mimi Yang et al.

A. Malik, J. Puissant, Kate M. Buckeridge et al.

Soil microorganisms act as gatekeepers for soil–atmosphere carbon exchange by balancing the accumulation and release of soil organic matter. However, poor understanding of the mechanisms responsible hinders the development of effective land management strategies to enhance soil carbon storage. Here we empirically test the link between microbial ecophysiological traits and topsoil carbon content across geographically distributed soils and land use contrasts. We discovered distinct pH controls on microbial mechanisms of carbon accumulation. Land use intensification in low-pH soils that increased the pH above a threshold (~6.2) leads to carbon loss through increased decomposition, following alleviation of acid retardation of microbial growth. However, loss of carbon with intensification in near-neutral pH soils was linked to decreased microbial biomass and reduced growth efficiency that was, in turn, related to trade-offs with stress alleviation and resource acquisition. Thus, less-intensive management practices in near-neutral pH soils have more potential for carbon storage through increased microbial growth efficiency, whereas in acidic soils, microbial growth is a bigger constraint on decomposition rates. Land use intensification could modify microbial activity and thus ecosystem function. Here, Malik et al. sample microbes and carbon-related functions across a land use gradient, demonstrating that microbial biomass and carbon use efficiency are reduced in human-impacted near-neutral pH soils.

Gökhan Koçak, C. Tuncer, V. Bütün

M. Rizwan, R. Yahya, A. Hassan et al.

Improving the safety efficacy ratio of existing drugs is a current challenge to be addressed rather than the development of novel drugs which involve much expense and time. The efficacy of drugs is affected by a number of factors such as their low aqueous solubility, unequal absorption along the gastrointestinal (GI) tract, risk of degradation in the acidic milieu of the stomach, low permeation of the drugs in the upper GI tract, systematic side effects, etc. This review aims to enlighten readers on the role of pH sensitive hydrogels in drug delivery, their mechanism of action, swelling, and drug release as a function of pH change along the GI tract. The basis for the selection of materials, their structural features, physical and chemical properties, the presence of ionic pendant groups, and the influence of their pKa and pKb values on the ionization, consequent swelling, and targeted drug release are also highlighted.

Laura Clarizia, D. Russo, I. D. Somma et al.

M. Kharat, Zheyuan Du, Guodong Zhang et al.

E. Proksch

The pH plays an important physiological role in nature and humans. pH varies from 1 to 8 in human organs with tight regulation in blood and epithelia of barrier organs. The physiological pH of the stratum corneum is 4.1–5.8 and several mechanisms contribute to its formation: filaggrin degradation, fatty acid content, sodium‐hydrogen exchanger (NHE1) activation and melanosome release. First, the acidic pH of the stratum corneum was considered to present an antimicrobial barrier preventing colonization (e.g. by Staphylococcus aureus and Malassezia). Later on, it was found that the pH influences skin barrier function, lipid synthesis and aggregation, epidermal differentiation and desquamation. Enzymes of ceramide metabolism (e.g. β‐glucocerebrosidase or acid sphingomyelinase) as well as proteases (e.g. chymotryptic enzyme or cathepsin D linked to epidermal differentiation and desquamation) are regulated by the pH. Experimental disruption of the physical barrier leads to an increase of pH, returning to normal levels only after many hours. Inflammatory skin diseases and diseases with an involvement of the epidermis exhibit a disturbed skin barrier and an increased pH. This is known for atopic dermatitis, irritant contact dermatitis, ichthyosis, rosacea and acne, but also for aged and dry skin. Normalizing the pH by acidification through topical treatment helps to establish a physiological microbiota, to repair skin barrier, to induce epidermal differentiation and to reduce inflammation.

I. Choi, J. Lee, M. Lacroix et al.

Xinyan Liu, P. Schlexer, Jianping Xiao et al.

We present a microkinetic model for CO(2) reduction (CO(2)R) on Cu(211) towards C2 products, based on energetics estimated from an explicit solvent model. We show that the differences in both Tafel slopes and pH dependence for C1 vs C2 activity arise from differences in their multi-step mechanisms. We find the depletion in C2 products observed at high overpotential and high pH to arise from the 2nd order dependence of C-C coupling on CO coverage, which decreases due to competition from the C1 pathway. We further demonstrate that CO(2) reduction at a fixed pH yield similar activities, due to the facile kinetics for CO2 reduction to CO on Cu, which suggests C2 products to be favored for CO2R under alkaline conditions. The mechanistic insights of this work elucidate how reaction conditions can lead to significant enhancements in selectivity and activity towards higher value C2 products. CO2 conversion to reduced products provides a use for greenhouse gases, but reaction complexity stymies mechanistic studies. Here, authors present a microkinetic model for CO2 and CO reduction on copper, based on ab initio simulations, to elucidate pH’s impact on competitive reaction pathways.

Yingnan Zhu, Jiamin Zhang, Jiayin Song et al.

Diabetic ulcer is the most common kind of chronic wound worldwide. Though great efforts have been devoted, diabetic ulcer still remains as a challenge that requires constant monitoring and management. In this work, a multifunctional zwitterionic hydrogel is developed to simultaneously detect two fluctuant wound parameters, pH and glucose level, to monitor the diabetic wound status. A pH indicator dye (phenol red) and two glucose sensing enzymes, glucose oxidase (GOx) and horseradish peroxidase (HRP), are encapsulated in the anti‐biofouling and biocompatible zwitterionic poly‐carboxybetaine (PCB) hydrogel matrix. The visible images are collected by a smartphone and transformed into RGB signals to quantify the wound parameters. Results show that the activity and stability of both two enzymes are improved within PCB hydrogel, and the Kcat/Km value of PCB‐HRP is ≈5.5 fold of free HRP in artificial wound exudate. This novel wound dressing can successfully monitor the pH range of 4–8 and glucose level of 0.1–10 × 10−3 m. Meanwhile, it also provides a moist healing environment that can promote diabetic wound healing. This multifunctional wound dressing may open vistas in chronic wound management and guide the diabetes treatment in clinical applications.

P. Ezati, J. Rhim

Abstract A chitosan-based pH-responsive functional film was prepared by the incorporation of alizarin and its properties were tested for active and intelligent food packaging applications. SEM and FTIR results showed that alizarin was uniformly distributed in the chitosan matrix to form a homogeneous film. The alizarin-added chitosan film showed high UV-blocking property with increased elongation at break, surface hydrophobicity, and thermal stability of the film. The release rate of alizarin from the film was dependent on the solution showing a higher release rate in a 50% ethanol solution than that in water, 10% and 95% ethanol solutions. The synergistic effect of antibacterial activity by the addition of alizarin was negligible against E. coli but slightly increased against L. monocytogenes. However, the antioxidant activity of the chitosan film was significantly increased by the addition of alizarin. The color of the composite film changed vividly from slightly yellow to purple in response to a pH change in the range of 4–10, and the composite film was very sensitive to ammonia vapor. The composite coating could indicate the onset of fish spoilage by showing color change from khaki to light brown as the pH of the packaged fish changed.

Libu Manjakkal, D. Szwagierczak, R. Dahiya

Abstract Electrochemical pH sensors are on high demand in numerous applications such as food processing, health monitoring, agriculture and nuclear sectors, and water quality monitoring etc., owing to their fast response (

A. Król, K. Mizerna, M. Bożym

The paper presents the results obtained in pHstat leaching test and assesses the influence of pH changes and occurring processes on the release of heavy metals (Cd, Ni, Crtotal, Pb, Cu and Zn) from metallurgical slag in a zinc smelter. Additionally, the analysis of the potential maximum amount of element available for leaching and releasing in the batch leaching test was carried out. All the results of the leaching tests were compared with the total content of heavy metals in the material. In order to evaluate the chemical forms of elements, a sequential extraction study was also carried out. On the basis of test results obtained in pHstat test, a strong dependence of heavy metals leaching on the pH was found. The highest concentrations of the analysed elements were observed in acidic environment. For most metals, except for lead, an increase in the pH of the solution caused a decrease in their concentration. Lead showed an upward trend of release under alkaline conditions. A sharp increase of copper leaching at pH 10.5 was also observed. Based on the results of the study, cadmium can be considered the most mobile element from metallurgical slag. Chromium indicated the lowest degree of release.

R. Johnston, L. J. Su, J. Pinckney et al.

Li‐Qing Jiang, B. Carter, R. Feely et al.

The ocean’s chemistry is changing due to the uptake of anthropogenic carbon dioxide (CO2). This phenomenon, commonly referred to as “Ocean Acidification”, is endangering coral reefs and the broader marine ecosystems. In this study, we combine a recent observational seawater CO2 data product, i.e., the 6th version of the Surface Ocean CO2 Atlas (1991–2018, ~23 million observations), with temporal trends at individual locations of the global ocean from a robust Earth System Model to provide a high-resolution regionally varying view of global surface ocean pH and the Revelle Factor. The climatology extends from the pre-Industrial era (1750 C.E.) to the end of this century under historical atmospheric CO2 concentrations (pre-2005) and the Representative Concentrations Pathways (post-2005) of the Intergovernmental Panel on Climate Change (IPCC)’s 5th Assessment Report. By linking the modeled pH trends to the observed modern pH distribution, the climatology benefits from recent improvements in both model design and observational data coverage, and is likely to provide improved regional OA trajectories than the model output could alone, therefore, will help guide the regional OA adaptation strategies. We show that air-sea CO2 disequilibrium is the dominant mode of spatial variability for surface pH, and discuss why pH and calcium carbonate mineral saturation states, two important metrics for OA, show contrasting spatial variability.

P. Ezati, J. Rhim

pH-responsive pectin-based functional films have been prepared by incorporating curcumin and sulfur nanoparticles (SNP). FTIR and SEM results indicated that curcumin and SNP were uniformly dispersed in the pectin to form a well-developed composite film. Addition of curcumin and SNP significantly influenced the surface color and UV-blocking properties of the composite films. The composite films showed a higher water contact angle and thermal stability compared with the neat pectin film, however, the mechanical and water vapor barrier properties did not change significantly. The composite film exhibited antibacterial activity against E. coli and L. monocytogenes, and strong antioxidant activity. When applied to shrimp packaging, the film showed a pH-responsive highly distinctive color change from yellow to orange as the quality of the shrimp changed.

L. Palanikumar, Sumaya Al-Hosani, M. Kalmouni et al.

The practical application of nanoparticles (NPs) as chemotherapeutic drug delivery systems is often hampered by issues such as poor circulation stability and targeting inefficiency. Here, we have utilized a simple approach to prepare biocompatible and biodegradable pH-responsive hybrid NPs that overcome these issues. The NPs consist of a drug-loaded polylactic-co-glycolic acid (PLGA) core covalently ‘wrapped’ with a crosslinked bovine serum albumin (BSA) shell designed to minimize interactions with serum proteins and macrophages that inhibit target recognition. The shell is functionalized with the acidity-triggered rational membrane (ATRAM) peptide to facilitate internalization specifically into cancer cells within the acidic tumor microenvironment. Following uptake, the unique intracellular conditions of cancer cells degrade the NPs, thereby releasing the chemotherapeutic cargo. The drug-loaded NPs showed potent anticancer activity in vitro and in vivo while exhibiting no toxicity to healthy tissue. Our results demonstrate that the ATRAM-BSA-PLGA NPs are a promising targeted cancer drug delivery platform. Palanikumar et al. prepare pH-responsive nanoparticles with drug-loaded PLGA core, cross-linked BSA corona to avoid opsonisation, and functionalised with ATRAM peptide that binds the cell membrane at low pH such as tumour microenvironment. The nanoparticles display both in vitro and in vivo efficacy while evading recognition by macrophages.

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.

Nitish Govindarajan, Ao Xu, Karen Chan

Description Three mechanisms underlie the impact of pH on the activity of electrochemical reactions A promising approach to the sustainable and fossil-free production of fuels and chemicals is the electrochemical conversion of atmospherically available gases such as H2O, CO2, O2, and N2 to fuels and chemicals with renewable electricity (1). Electrocatalysts are essential for practical processes because they increase the reaction rate, efficiency, and selectivity toward desired products. Unfortunately, state-of-the-art electrocatalysts have drawbacks such as the use of precious metals that limit widespread adoption and large overpotentials that lead to very low efficiency. The outstanding challenge is to design and discover active and selective electrocatalysts that are based on earth-abundant materials. It has been understood for decades that the electrolyte pH affects the activity of electrochemical processes. However, the origins of this effect are still under debate.