Hasil untuk "physics.comp-ph"

D. Neina

In the natural environment, soil pH has an enormous influence on soil biogeochemical processes. Soil pH is, therefore, described as the “master soil variable” that influences myriads of soil biological, chemical, and physical properties and processes that affect plant growth and biomass yield. This paper discusses how soil pH affects processes that are interlinked with the biological, geological, and chemical aspects of the soil environment as well as how these processes, through anthropogenic interventions, induce changes in soil pH. Unlike traditional discussions on the various causes of soil pH, particularly soil acidification, this paper focuses on relationships and effects as far as soil biogeochemistry is concerned. Firstly, the effects of soil pH on substance availability, mobility, and soil biological processes are discussed followed by the biogenic regulation of soil pH. It is concluded that soil pH can broadly be applied in two broad areas, i.e., nutrient cycling and plant nutrition and soil remediation (bioremediation and physicochemical remediation).

C. Penn, J. Camberato

Occasionally, the classic understanding of the effect of pH on P uptake from soils is questioned through the claim that maximum P uptake occurs at a pH much lower than 6.5–7. The purpose of this paper was to thoroughly examine that claim and provide a critical review on soil processes that control how soil pH affects P solubility and availability. We discuss how individual P retention mechanisms are affected by pH in isolation and when combined in soils, and how both real and apparent exceptions to the classic view can occasionally occur due to dynamics between mechanisms, experimental techniques (equilibration time, method of soluble P extraction, and pH adjustment), and plant species that thrive under acidic conditions. While real exceptions to the rule of thumb of maximum P availability at near neutral pH can occur, we conclude that the classic textbook recommendation is generally sound.

Haitao Ding, Ping Tan, Shiqin Fu et al.

Microenvironment-responsive drug delivery systems (DDSs) can achieve targeted drug delivery, reduce drug side effects and improve drug efficacies. Among them, pH-responsive DDSs have gained popularity since the pH in the diseased tissues such as cancer, bacterial infection and inflammation differs from a physiological pH of 7.4 and this difference could be harnessed for DDSs to release encapsulated drugs specifically to these diseased tissues. A variety of synthetic approaches have been developed to prepare pH-sensitive DDSs, including introduction of a variety of pH-sensitive chemical bonds or protonated/deprotonated chemical groups. A myriad of nano DDSs have been explored to be pH-responsive, including liposomes, micelles, hydrogels, dendritic macromolecules and organic-inorganic hybrid nanoparticles, and micron level microspheres. The prodrugs from drug-loaded pH-sensitive nano DDSs have been applied in research on anticancer therapy and diagnosis of cancer, inflammation, antibacterial infection, and neurological diseases. We have systematically summarized synthesis strategies of pH-stimulating DDSs, illustrated commonly used and recently developed nanocarriers for these DDSs and covered their potential in different biomedical applications, which may spark new ideas for the development and application of pH-sensitive nano DDSs.

Junjun Zhang, Xiaobo Zou, Xiaodong Zhai et al.

This study aims to develop an intelligent indicating film based on biodegradable polymers incorporated with roselle anthocyanins to monitor pork freshness. Three different films were prepared by using two substances of starch, polyvinyl alcohol and chitosan. The UV-vis spectra and color of anthocyanins changed at pH 2-12. SEM photographs showed that the compatibility of films was improved with the addition of anthocyanins. Furthermore, the polyvinyl alcohol/chitosan/roselle anthocyanins film had the highest tensile strength (98.28 MPa). The starch/polyvinyl alcohol/roselle anthocyanins film had the highest antioxidant activity (524.07%) and the best color stability. The starch/polyvinyl alcohol/roselle anthocyanins film showed visible changes from red to green when employed to monitor the freshness of pork stored at 25 °C, before the TVB-N value of the pork gradually increased to the rejection limit (15 mg/100 g) at 36 h. Therefore, the indicator film can be used to monitor pork freshness for intelligent packaging.

Andreas Steinegger, O. Wolfbeis, S. Borisov

This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and pKa values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

Swarup Roy, J. Rhim

Abstract Recently, interest in smart packaging, which can show the color change of the packaging film according to the state of the food and evaluate the quality or freshness of the packaged food in real-time, is increasing. As a color indicator, a natural colorant, anthocyanin, drew a lot of attention due to their various colors as well as useful functions properties such as antioxidant activity and anti-carcinogenic and anti-inflammatory effects, prevention of cardiovascular disease, obesity, and diabetes. In particular, the pH-responsive color-changing function of anthocyanins is useful for making color indicator smart packaging films. This review addressed the latest information on the use of natural pigment anthocyanins for intelligent and active food packaging applications. Recent studies on eco-friendly biodegradable polymer-based color indicator films incorporated with anthocyanins have been addressed. Also, studies on the use of smart packaging films to monitor the freshness of foods such as milk, meat, and fish were reviewed. This review highlights the potential and challenges for the use of anthocyanins as pH-responsive color-changing films for intelligent food packaging applications, which may be beneficial for further development of smart color indicator films for practical use.

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.

Misbah Naz, Z. Dai, Sajid T. Hussain et al.

Soil microbial community is the main indicator having a crucial role in the remediation of polluted soils. These microbes can alter soil pH, organic matter in soils (SOM), soil physic-chemical properties, and potential soil respiration rate via their enzymatic activities. Similarly, heavy metals also have a crucial role in soil enzymatic activities. For this purpose, a number of methods are studied to evaluate the impact of soil pH (a key factor in the formation of biogeographic microbial patterns in bacteria) on bacterial diversity. The effects of pH on microbial activity are glamorous but still unclear. Whereas, some studies also indicate that soil pH alone is not the single key player in the diversity of soil bacteria. Ecological stability is achieved in a pollution-free environment and pH value. The pH factor has a significant impact on the dynamics of microbes' communities. Here, we try to discuss factors that directly or indirectly affect soil pH and the impact of pH on microbial activity. It is also discussed the environmental factors that contribute to establishing a specific bacterial community structure that must be determined. From this, it can be concluded that the environmental impact on soil pH, reducing soil pH and interaction with this factor, and reducing the effect of soil pH on soil microbial community.

N. Barrow, A. Hartemink

The effects of pH on nutrient availability are not solely caused by to the effects on reaction with soils but are an interaction between these effects and the effects on rate of uptake by plants. Some effects are specific to particular ions, but an important aspect is that plant roots and soil particles both have variable charge surfaces. This influences availability, but in opposite directions. Sulfate is an example of this interplay. Its sorption by soil decreases markedly with increasing pH and thus “soil availability” increases. However, plant uptake also decreases with increasing pH thus “plant availability” decreases. For phosphate, the plant effect is stronger than the soil effect and uptake decreases with increasing pH. In contrast, effects of increasing pH on molybdate adsorption are so large that they dominate the overall effect. Sorption of cations, such as zinc or copper, increases with increasing pH but uptake rate also increases. The net effect is a small decrease in availability with increasing pH. Boron is an exception; there are small effects of pH on sorption; and it is the uncharged boric acid molecules that are taken up by plant roots. Their uptake is not affected by charge and uptake is proportional to the concentration of uncharged boric acid molecules. We argue that emphasis on the effects of pH on reactions with soil has led to a distorted picture of the effects of pH on nutrient availability.

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.

Chaoqun Wang, Y. Kuzyakov

Priming of soil organic matter (SOM) decomposition by microorganisms is a key phenomenon of global carbon (C) cycling. Soil pH is a main factor defining priming effects (PEs) because it (i) controls microbial community composition and activities, including enzyme activities, (ii) defines SOM stabilization and destabilization mechanisms, and (iii) regulates intensities of many biogeochemical processes. In this critical review, we focus on prerequisites and mechanisms of PE depending on pH and assess the global change consequences for PE. The highest PEs were common in soils with pH between 5.5 and 7.5, whereas low molecular weight organic compounds triggered PE mainly in slightly acidic soils. Positive PEs up to 20 times of SOM decomposition before C input were common at pH around 6.5. Negative PEs were common at soil pH below 4.5 or above 7 reflecting a suboptimal environment for microorganisms and specific SOM stabilization mechanisms at low and high pH. Short‐term soil acidification (in rhizosphere, after fertilizer application) affects PE by: mineral‐SOM complexation, SOM oxidation by iron reduction, enzymatic depolymerization, and pH‐dependent changes in nutrient availability. Biological processes of microbial metabolism shift over the short‐term, whereas long‐term microbial community adaptations to slow acidification are common. The nitrogen fertilization induced soil acidification and land use intensification strongly decrease pH and thus boost the PE. Concluding, soil pH is one of the strongest but up to now disregarded factors of PE, defining SOM decomposition through short‐term metabolic adaptation of microbial groups and long‐term shift of microbial communities.

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 (

Alicja Kicińska, R. Pomykała, M. Izquierdo

In the present paper, the authors attempt to explain the importance of pH in soil environment studies and show what mistakes to avoid when measuring pH and interpreting the results obtained. The tests conducted (i.e., extraction in aqua regia, buffer capacity determination, and the impact of acidification on the amount of heavy metals extracted from soils) demonstrated how soil pollution and buffer capacity affect the pace of extracting cadmium (Cd), lead (Pb) and zinc (Zn) cations from heavily polluted and unpolluted soils following gradual acidification. It was shown that soil acidification caused a significant increase in metal mobility in the following order Cd > Zn > Pb and that the highest decrease in pH was observed after adding the first portion of acid. Further addition of acid caused a gradually lower decrease in pH. Soils from the polluted area presented a high buffer capacity. The control samples displayed a distinctly poorer resistance to pH changes in the soil environment. Special focus was placed on cadmium due to its high mobility in soils, even with neutral and slightly alkaline pH. The analyses revealed that in areas heavily polluted by long‐term industrial activity (Igeo > 5 for Zn, Pb and Cd), it is very important to conduct extensive geochemical studies related to the presence and circulation of particularly toxic elements. This is because every environmental factor, especially pH, may significantly affect their mobility, causing metal ions to become more or less active or increasing or decreasing environmental risk related to their presence.

J. Singh, P. Nayak

Polymer science has applications in biomedical engineering, prosthetics, surgical implants, and prospective pharmaceutical excipients for drug delivery. “Intelligent or Smart Polymers” are created for drug targeting either by derivatization of natural polymers or controlled radical polymerization of electrolytes. Their mode of action is governed by the environmental stimuli viz. temperature, pH, ionic concentration, magnetism, and so on. pH‐responsive polymers, because of their self‐assembling behavior, alter their solubility, conformation, surface activity, and hydrophilicity when exposed to a specific pH. The physiological pH varies from acidic nuclei to alkaline cytoplasm and highly acidic gastric juice to slightly alkaline plasma; thus, various polymers are under study for delivering small molecules, genes, peptides, enzymes, growth factors, and antibodies. The non‐invasive drug delivery routes like oral, ocular, nasal, pulmonary, transdermal, and rectal routes can be explored for targeting recombinant proteins, monoclonal antibodies, and small molecules with particular emphasis on the individual's physiological and pathological state. Further, these polymers can be designed into various architectures like dendrimers, liposomes, micelles, and metallic nanoparticles that can serve as drug reservoirs for sustaining drug release. The challenges in this field are the selection of biocompatible polymers with ease of synthesis and scale‐up, ensuring effective drug‐loading, and stability aspects, producing robust pharmacological data, and timely regulatory approvals. This review exclusively explores the physicochemical characteristics of pH‐responsive polymers, their categorization, various architectural entities, recent studies and patents, and their emerging applications concerning specific diseases.

Tingting Cui, Jiafei Yu, Cai‐Feng Wang et al.

The pH value in the wound milieu plays a key role in cellular processes and cell cycle processes involved in the process of wound healing. Here, a microfluidic assembly technique is employed to fabricate micro‐gel ensembles that can precisely tune the pH value of wound surface and accelerate wound healing. The micro‐gel ensembles consist of poly (hydroxypropyl acrylate‐co‐acrylic acid)‐magnesium ions (poly‐(HPA‐co‐AA)‐Mg2+) gel and carboxymethyl chitosan (CMCS) gel, which can release and absorb hydrogen ion (H+) separately at different stages of healing in response to the evolution of wound microenvironment. By regulating the wound pH to affect the proliferation and migration of cell on the wound and the activity of various biological factors in the wound, the physiological processes are greatly facilitated which results in much accelerated healing of chronic wound. This work presents an effective strategy in designing wound healing materials with vast potentials for chronic wound management.

Shunli Chu, Xiaolu Shi, Ye Tian et al.

The complexity of the tumor microenvironment presents significant challenges to cancer therapy, while providing opportunities for targeted drug delivery. Using characteristic signals of the tumor microenvironment, various stimuli-responsive drug delivery systems can be constructed for targeted drug delivery to tumor sites. Among these, the pH is frequently utilized, owing to the pH of the tumor microenvironment being lower than that of blood and healthy tissues. pH-responsive polymer carriers can improve the efficiency of drug delivery in vivo, allow targeted drug delivery, and reduce adverse drug reactions, enabling multifunctional and personalized treatment. pH-responsive polymers have gained increasing interest due to their advantageous properties and potential for applicability in tumor therapy. In this review, recent advances in, and common applications of, pH-responsive polymer nanomaterials for drug delivery in cancer therapy are summarized, with a focus on the different types of pH-responsive polymers. Moreover, the challenges and future applications in this field are prospected.

A. Hartemink, N. Barrow

Nour Alsawaftah, Nahid S Awad, W. Pitt et al.

A number of promising nano-sized particles (nanoparticles) have been developed to conquer the limitations of conventional chemotherapy. One of the most promising methods is stimuli-responsive nanoparticles because they enable the safe delivery of the drugs while controlling their release at the tumor sites. Different intrinsic and extrinsic stimuli can be used to trigger drug release such as temperature, redox, ultrasound, magnetic field, and pH. The intracellular pH of solid tumors is maintained below the extracellular pH. Thus, pH-sensitive nanoparticles are highly efficient in delivering drugs to tumors compared to conventional nanoparticles. This review provides a survey of the different strategies used to develop pH-sensitive nanoparticles used in cancer therapy.

Yuki Nakagaki, Eiji Yamamoto

The PI3K/AKT signaling pathway is triggered by recruitment of AKT to cellular membranes. Although AKT is a multidomain serine/threonine kinase composed of an N-terminal pleckstrin homology (PH) domain and a C-terminal kinase domain, how these domains cooperate to regulate AKT activation on membranes remains unclear at the molecular level. Here, using molecular dynamics simulations of full-length AKT on PIP$_3$-containing lipid bilayers, we identify four distinct membrane-binding modes that differ in the orientations and membrane contacts of the PH and kinase domains. In addition to PIP$_3$ binding to the PH domain, we observe specific PIP$_3$ interactions with basic residues in the kinase domain. In the most stable mode, PIP$_3$ interacts with both the canonical and a secondary binding site in the PH domain, while the kinase domain adopts an orientation in which the activation-loop phosphorylation site is exposed to the solvent. Interestingly, the populations of these binding modes depend on the PIP$_3$ concentration in the membrane, leading to changes in the preferred orientation of AKT. These findings shed light on how lipid recognition by the PH domain and the kinase domain of AKT cooperatively shape its membrane-bound conformations.

Susi Lehtola, Martin Head-Gordon

The pairing hierarchy of perfect pairing (PP), perfect quadruples (PQ) and perfect hextuples (PH) are sparsified coupled cluster models that are exact in a pairing active space for 2, 4, and 6 electron clusters, respectively. We describe and implement three extensions for radicals. First is the trivial generalization that does not correlate radical orbitals. The second model (PQr, PHr) includes terms that entangle pair indices and radical indices such that their maximum total number is 2 for PQ and 3 for PH (like their closed-shell versions). The third family of extended radical models (PPxr, PQxr, and PHxr) include cluster amplitudes that entangle up to 1, 2, and 3 pair indices with up to 1, 2, and 3 radical indices. Notably, PPxr and PQxr are exact for (3e,3o) and (5e,5o), respectively, while still having only $O(N)$ and $O(N^{2}$) amplitudes like their parent models (for $N$ paired electrons). Orbital optimization is considered for PPxr. A series of large-scale numerical tests of these models are presented for spin gaps, and ionization energies of polyenes and polyenyl radicals, ranging in size from ethene and allyl radical up to C$_{22}$H$_{24}$ in full-valence active spaces up to (122e,122o). The xR models perform best.