Subtle pH Changes Research Articles

Ultra-low threshold pH sensor based on a whispering gallery mode microbubble resonator

Laser sensing has a wide range of applications. In this paper, we propose a pH sensing laser with an ultra-low threshold and low sample consumption based on a whispering-gallery-mode microbubble resonator. Rhodamine 6G aqueous solutions with different pH values are injected through microfluidic channels as the lasing gain media and interact with a high-quality factor microbubble cavity with a sample consumption of only 550 pL to achieve lasing. Subtle pH changes of the aqueous solution lead to changes in lasing intensity in real time, and the threshold reaches a minimum of 0.091 μ J/mm2. The low pump energy density effectively avoids the self-aggregation and photobleaching effects of dye molecules present in high-concentration rhodamine 6G solutions. The lasing characteristics under different pH conditions were determined experimentally and theoretically, and the results are in good agreement. Due to the deprotonation of amino groups in highly alkaline environments, the lasing threshold is highly dependent on the pH of rhodamine 6G aqueous solutions. In the pH range of 10.16–13.14, the lasing intensity changes considerably with the increasing pH. The proposed pH-sensing laser exhibits a fast response time, low toxicity, and a high signal-to-noise ratio, making it promising for highly sensitive alkaline detection in biological applications.

Membrane-disruptive homo-polymethacrylate with both hydrophobicity and pH-sensitive protonation for selective cancer therapy.

The membrane-disruptive strategy, which involves host defense peptides and their mimetics, is a revolutionary cancer treatment based on broad-spectrum anticancer activities. However, clinical application is limited by low selectivity towards tumors. In this context, we have established a highly selective anticancer polymer, i.e. poly(ethylene glycol)-poly(2-azepane ethyl methacrylate) (PEG-PAEMA), that can mediate the membrane-disruptive activity via a subtle pH change between physiological pH and tumor acidity for selective cancer treatment. Specifically, the resulting PEG-PAEMA can assemble into neutral nanoparticles and silence the membrane-disruptive activity at physiological pH and disassemble into cationic free-chains or smaller nanoparticles with potent membrane-disruptive activity after the protonation of the PAEMA block due to tumor acidity, resulting in high selectivity towards tumors. Dramatically, PEG-PAEMA exhibited a >200-fold amplification in hemolysis and <5% in IC50 against Hepa1-6, SKOV3 and CT-26 cells at pH 6.7 as compared to those at pH 7.4, thanks to the selective membrane-disruptive mechanism. Moreover, mid- and high-dose PEG-PAEMA demonstrated higher anticancer efficacy than an optimal clinical prescription (bevacizumab plus PD-1) and, significantly, had few side effects on major organs in the tumor-bearing mice model, agreeing with the highly selective membrane-disruptive activity in vivo. Collectively, this work showcases the latent anticancer pharmacological activity of the PAEMA block, and also brings new hope for selective cancer therapy.

Novel Sterically Crowded and Conformationally Constrained α-Aminophosphonates with a Near-Neutral pKa as Highly Accurate 31P NMR pH Probes. Application to Subtle pH Gradients Determination in Dictyostelium discoideum Cells.

In order to discover new 31P NMR markers for probing subtle pH changes (<0.2 pH unit) in biological environments, fifteen new conformationally constrained or sterically hindered α-aminophosphonates derived from diethyl(2-methylpyrrolidin-2-yl)phosphonate were synthesized and tested for their pH reporting and cytotoxic properties in vitro. All compounds showed near-neutral pKas (ranging 6.28–6.97), chemical shifts not overlapping those of phosphorus metabolites, and spectroscopic sensitivities (i.e., chemical shifts variation Δδab between the acidic and basic forms) ranging from 9.2–10.7 ppm, being fourfold larger than conventional endogenous markers such as inorganic phosphate. X-ray crystallographic studies combined with predictive empirical relationships and ab initio calculations addressed the inductive and stereochemical effects of substituents linked to the protonated amine function. Satisfactory correlations were established between pKas and both the 2D structure and pyramidalization at phosphorus, showing that steric crowding around the phosphorus is crucial for modulating Δδab. Finally, the hit 31P NMR pH probe 1b bearing an unsubstituted 1,3,2-dioxaphosphorinane ring, which is moderately lipophilic, nontoxic on A549 and NHLF cells, and showing pKa = 6.45 with Δδab = 10.64 ppm, allowed the first clear-cut evidence of trans-sarcolemmal pH gradients in normoxic Dictyostelium discoideum cells with an accuracy of <0.05 pH units.

Subtle changes in pH affect the packing and robustness of fatty acid bilayers.

Connecting molecular interactions to emergent properties is a goal of physical chemistry, self-assembly, and soft matter science. We show that for fatty acid bilayers, vesicle rupture tension, and permeability to water and ions are coupled to pH via alterations to lipid packing. A change in pH of one, for example, can halve the rupture tension of oleic acid membranes, an effect that is comparable to increasing lipid unsaturation in phospholipid systems. We use both experiments and molecular dynamics simulations to reveal that a subtle increase in pH can lead to increased water penetration, ion permeability, pore formation rates, and membrane disorder. For changes in membrane water content, oleic acid membranes appear to be more than a million times more sensitive to protons than to sodium ions. The work has implications for systems in which fatty acids are likely to be found, for example in the primitive cells on early Earth, biological membranes especially during digestion, and other biomaterials.

Evaluation of renewable pH-responsive starch-based flocculant on treating and recycling of highly saline textile effluents

Herein, we report a novel renewable pH-responsive starch-based flocculant (CIAT-ST) via etherifying 2-chloro-4,6-isopropylamino-[1,3,5]-triazine (CIAT) onto the starch backbones for decontamination and reuse of highly saline effluents. The obtained CIAT-ST shows a unique pH-sensibility and reversibility in response to a subtle pH change due to a pH-controllable surface charge density of polymer chains. The level of residual CIAT-ST in the solution can be facilely monitored by using UV–vis detection. The dye flocculation performance of CIAT-ST was evaluated by using a batch experiment. The results exhibited that the dye removal was highly dependent on the solution pH (optimal pH was 2), the flocculation equilibrium can be achieved within 5 min, and the maximum flocculation capacity of CIAT-ST for K–2BP and KN–B5 were calculated to be 2452.6 ± 23.9 and 792.7 ± 14.1 mg/g, respectively. The multiple flocculation mechanisms, including charge neutralization, bridging and charge patching, may participate in the flocculation process. Adjustment in pH-mediated hydrophilicity-hydrophobicity switch of flocculant facilitates readily recovery and then sequentially reused three times while retaining satisfying flocculation efficiency. A significant contribution was also confirmed that the highly saline effluents after flocculation and sedimentation were reused in three successive dyeing processes without sacrificing fabric quality (ΔE* < 1) due to relatively low polymer residuals, and the efficiency of salt reuse for consecutive regeneration processes could be achieved above 85%. The present work could provide alternative thoughts for the reutilization of spent flocculant and clarified saline wastewater, which is also an efficient and sustainable strategy for textile wastewater management.

An FRET-ICT-based ratiometric fluorescent and colorimetric probe for pH monitoring in lysosomes and water

A novel FRET-ICT-based ratiometric fluorescent and colorimetric pH probe (BDMNP) was developed. BDMNP exhibited 96% energy transfer efficiency and good linear response in the pH ranges of 5.4–6.8 (pKa = 6.10) with high selectivity and sensitivity. BDMNP has been successfully applied to monitor lysosomal pH changes in living cells. Meanwhile, BDMNP can also be used to detect the subtle pH changes of a variety of environmental water samples.

Ionic strength effect on the formation of organonitrate compounds through photochemical degradation of vanillin in liquid water of aerosols

The ionic strength can affect the photochemical reactions occurring in the liquid core of the aerosol deliquescent particles. Yet, the investigations related to ionic strength effect on aqueous-phase reactions are limited. Here we assess the photochemical degradation of a typical lignin-derived compound, vanillin (VL), upon addition of either sodium nitrate (NaNO3) or sodium sulfate (Na2SO4). The UV-VIS absorption spectra of VL exhibits a hyperchromic effect and a bathochromic shift of the n→π* absorption band, in going from λmax = 310 nm in the dilute aqueous phase to λmax = 346 nm at I = 0.3 M adjusted by Na2SO4. A hypsochromic shift of the n→π* absorption band of VL, in going from λmax = 310 nm in the dilute liquid water to λmax = 303 nm at Ieff = 0.124 M is observed when the ionic strength was adjusted with NaNO3.At fixed pH ≈ 4, representing both the cloud droplets and the liquid core of the aerosol particles, the pseudo-first-order rate constant, k1st (Ieff.→0) = (1.5 ± 0.2) x 10−5 s−1, in dilute aqueous solution (Ieff = 0 M, NaNO3), linearly decreases to (k1st = (3.7 ± 0.2) x 10−6 s−1), at Ieff = 0.124 M (NaNO3) with kinetic salting coefficient b = -(4.8 ± 0.2) L mol−1. The very subtle pH change of the absorption spectra of irradiated VL is observed due to the formation of carboxylic acids, hydroxylated compounds and oligomers which presence was confirmed by FT-ICR MS analysis. Most likely aliphatic like CHO compounds are formed upon photodegradation of VL in dilute aqueous phase while the condensed aromatic CHO and CHON compounds are produced in presence of nitrate ions (Ieff = 0.124 M). These results suggest that inorganic ions present in the liquid water of aerosols alters the kinetics and the product formation of photochemical degradation of organic compounds which in turn can affect the light absorption properties of aerosols.

Dynamics of Microbial Community Structure and Ecological Functions in Estuarine Intertidal Sediments

Microbial communities are important indicators of aquatic ecosystem health, responsible for functional roles sustaining the ecosystem such as nutrient cycling, as well as environmental problems. Urbanized estuaries are vulnerable intersections between terrestrial and marine ecosystems and are susceptible to pressure and perturbation from both natural processes and human activities over time. The response by microbial communities towards changes in the environment should be closely monitored and studied. In this study, microbial communities in brackish intertidal sediments, sampled seasonally over a year along the coast of Yangtze River estuary, were analyzed using 16S rRNA gene sequencing. Potential compositional and functional changes in microbial communities resulting from temporal variation and associated physiochemical gradients in the environment were studied and notable patterns were observed over time. Summer season was recorded with the lowest microbial community α-diversity. For β-diversity, spatiotemporal differentiation in community structures was recorded with seasonal clustering. Proteobacteria was recorded as the most dominant phylum among all sampling sites throughout the year but its relative abundance showed no temporal changes. Instead, relative abundances of phyla Actinobacteria, Chloroflexi, and Verrucumicrobia were found to differ significantly over time, generally favoring the wet Spring and Summer. In contrast, temporal variation was observed for the class Deltaproteobacteria and some of the corresponding sulfate/sulfur-reducing bacterial genera, favoring the dry Autumn and Winter. However, there were no major temporal changes in ecological functions contributed by microbial communities throughout the study period. While results from redundancy analysis showed that the subtle changes in pH in the environment had the greatest impact on microbial community composition, the variation it explained remained relatively low. Alternatively, precipitation, distinguishing the dry and wet seasons of the subtropical monsoon climate zone, was suggested to be another potential key factor influencing microbial community composition and their relative abundances. The present study provides new data and insights on the impact of temporal variation on microbial community composition and ecological function in an urbanized estuarine ecosystem.

A ratiometric near-infrared fluorescence strategy based on spiropyran in situ switching for tracking dynamic changes of live-cell lysosomal pH

Abnormal lysosomal pH values have been associated with cellular dysfunctions and many diseases. However, tools to monitor dynamic changes of pH values in live-cell lysosomes are limited. Herein, biocompatible near-infrared (NIR) fluorescent dyes HAN1-4 for lysosome-targeting staining were rationally designed and synthesized with the aid of a spiropyran in situ switching (SIS) strategy. The novel SIS-based dyes share the following special characteristics: 1) pH-dependent ratiometric fluorescent patterns matched nicely with pH windows of lysosomes, 2) light-independent real-time spiropyran in situ switching behavior in lysosomes and 3) pH-sensitive fluorescence in the NIR region, thereby ensuring their applications in obtaining highly specific images of live-cell lysosomes with a weak background signal. Among them, the HAN2 probe was found to induce the best ratiometric response toward pH in the range corresponding to lysosomal pH window, thus being further applied for the real-time tracking of lysosomal subtle pH changes in stressed cells undergoing drug and heat stimulations. Live-cell super-resolution and confocal fluorescent imaging indicate that our SIS-based NIR probes are robust and can be applied for the accurate detection of lysosomal pH in complex biosystems.

Microcapsules Containing pH-Responsive, Fluorescent Polymer-Integrated MoS2: An Effective Platform for in Situ pH Sensing and Photothermal Heating

We report the design of a novel microcapsule platform for in situ pH sensing and photothermal heating, which involves the encapsulation of pH-responsive polymer-coated molybdenum disulfide (MoS2) nanosheets (NSs) in microcapsules with an aqueous core and a semipermeable polymeric shell. The MoS2 NSs were functionalized with pH-responsive polymers having fluorescent groups at the distal end to provide pH-sensitive Förster resonance energy transfer (FRET) effect. The pH-responsive polymers were carefully designed to produce a dramatic change in the polymer conformation, which translated to a change in the FRET efficiency near pH 7.0 in response to subtle pH changes, enabling the detection of cancer cells. The pH-sensitive MoS2 NSs were microfluidically encapsulated within semipermeable membranes to yield microcapsules with a uniform size and composition. The microcapsules retained the MoS2 NSs without leakage while allowing the diffusion of small ions and water through the membrane. At the same time, the membranes excluded adhesive proteins and lipids in the surrounding media, protecting the encapsulated MoS2 NSs from deactivation and enabling in situ pH monitoring. Moreover, the encapsulated MoS2 NSs showed high-performance photothermal heating, rendering the dual-functional microcapsules highly suitable for cancer diagnosis and treatment.

Imaging Lysosomal pH Alteration in Stressed Cells with a Sensitive Ratiometric Fluorescence Sensor.

The organelle-specific pH is crucial for cell homeostasis. Aberrant pH of lysosomes has been manifested in myriad diseases. To probe lysosome responses to cell stress, we herein report the detection of lysosomal pH changes with a dual colored probe (CM-ROX), featuring a coumarin domain with "always-on" blue fluorescence and a rhodamine-lactam domain activatable to lysosomal acidity to give red fluorescence. With sensitive ratiometric signals upon subtle pH changes, CM-ROX enables discernment of lysosomal pH changes in cells undergoing autophagy, cell death, and viral infection.

Transition from disordered aggregates to ordered lattices: kinetic control of the assembly of a computationally designed peptide.

Natural biomolecular self-assembly typically occurs under a narrow range of solution conditions, and the design of sequences that can form prescribed structures under a range of such conditions would be valuable in the bottom-up assembly of predetermined nanostructures. We present a computationally designed peptide that robustly self-assembles into regular arrays under a wide range of solution pH and temperature conditions. Controling the solution conditions provides the opportunity to exploit a simple and reproducible approach for altering the pathway of peptide solution self-assembly. The computationally designed peptide forms a homotetrameric coiled-coil bundle that further self-assembles into 2-D plate structures with well-defined inter-bundle symmetry. Herein, we present how modulation of solution conditions, such as pH and temperature, can be used to control the kinetics of the inter-bundle assembly and manipulate the final morphology. Changes in solution pH primarily influence the inter-bundle assembly by affecting the charged state of ionizable residues on the bundle exterior while leaving the homotetrameric coiled-coil structure intact. At low pH, repulsive interactions prevent 2-D lattice nanostructure formation. Near the estimated isoelectric point of the peptide, bundle aggregation is rapid and yields disordered products, which subsequently transform into ordered nanostructures over days to weeks. At elevated temperatures (T = 40 °C or 50 °C), the formation of disordered, kinetically-trapped products largely can be eliminated, allowing the system to quickly assemble into plate-like nanostructured lattices. Moreover, subtle changes in pH and in the peptide charge state have a significant influence on the thickness of formed plates and on the hierarchical manner in which plates fuse into larger material structures with observable grain boundaries. These findings confirm the ability to finely tune the peptide assembly process to achieve a range of engineered structures with one simple 29-residue peptide building block.

Pb-Sr isotopic and geochemical constraints on sources and processes of lead contamination in well waters and soil from former fruit orchards, Pennsylvania, USA: A legacy of anthropogenic activities

Isotopic discrimination can be an effective tool in establishing a direct link between sources of Pb contamination and the presence of anomalously high concentrations of Pb in waters, soils, and organisms. Residential wells supplying water containing up to 1600ppb Pb to houses built on the former Mohr orchards commercial site, near Allentown, PA, were evaluated to discern anthropogenic from geogenic sources. Pb (n=144) and Sr (n=40) isotopic data and REE (n=29) data were determined for waters from residential wells, test wells (drilled for this study), and surface waters from pond and creeks. Local soils, sediments, bedrock, Zn-Pb mineralization and coal were also analyzed (n=94), together with locally used Pb-As pesticide (n=5). Waters from residential and test wells show overlapping values of 206Pb/207Pb, 208Pb/207Pb and 87Sr/86Sr. Larger negative Ce anomalies (Ce/Ce*) distinguish residential wells from test wells. Results show that residential and test well waters, sediments from residential water filters in water tanks, and surface waters display broad linear trends in Pb isotope plots. Pb isotope data for soils, bedrock, and pesticides have contrasting ranges and overlapping trends. Contributions of Pb from soils to residential well waters are limited and implicated primarily in wells having shallow water-bearing zones and carrying high sediment contents. Pb isotope data for residential wells, test wells, and surface waters show substantial overlap with Pb data reflecting anthropogenic actions (e.g., burning fossil fuels, industrial and urban processing activities). Limited contributions of Pb from bedrock, soils, and pesticides are evident. High Pb concentrations in the residential waters are likely related to sediment build up in residential water tanks. Redox reactions, triggered by influx of groundwater via wells into the residential water systems and leading to subtle changes in pH, are implicated in precipitation of Fe oxyhydroxides, oxidative scavenging of Ce(IV), and desorption and release of Pb into the residential water systems. The Pb isotope features in the residences and the region are best interpreted as reflecting a legacy of industrial Pb present in underlying aquifers that currently supply the drinking water wells.

Crystal structures of influenza A virus matrix protein M1: variations on a theme.

Matrix protein 1 (M1) of the influenza A virus plays multiple roles in virion assembly and infection. Interest in the pH dependence of M1's multiple functions led us to study the effect of subtle pH changes on M1 structure, resulting in the elucidation of a unique low-pH crystal structure of the N1-165-domain of A/WSN/33 (H1N1) M1 that has never been reported. Although the 2.2 Å crystal structure of M1 N-terminus shows a dimer with the two monomers interacting in a face-to-face fashion at low pH as observed earlier, a 44° rotation of the second monomer has led to a significantly different dimer interface that possibly affects dimer stability. More importantly, while one of the monomers is fully defined, the N-terminal half of the second monomer shows considerable disorder that appears inherent in the protein and is potentially physiologically relevant. Such disorder has not been observed in any other previously reported structure at either low or high pH conditions, despite similar crystallization pH conditions. By comparing our novel N1-165-domain structure with other low-pH or neutral-pH M1 structures, it appears that M1 can energetically access different monomer and dimer conformations, as well as oligomeric states, with varying degree of similarities. The study reported here provides further insights into M1 oligomerization that may be essential for viral propagation and infectivity.

PH-controlled multiple chiral inversion that induces molecular dimerization in a gold(I)-cobalt(III) coordination system with L-cysteinate.

Herein, a unique coordination system that exhibits multiple chiral inversions and molecular dimerization in response to a subtle pH change is reported. Treatment of (Δ)2-H3[Au3Co2(L-cys)6] (H3[1 a]) with [Co3(aet)6](NO3)3 (aet=2-aminoethanethiolate) in water at pH 7 gave a 1:1 complex salt of [Co3(aet)6](3+) and [1 a](3-), retaining the Au(I)3Co(III)2 structure and chiral configurations of [1 a](3-). Similar treatment at pH 9 led to not only the inversion of all of the chiral Co(III) and S centers but also the dimerization of [1 a](3-), giving a 2:1 complex salt of [Co3(aet)6](3+) and (Λ)4(R)12-[Au6Co4(L-cys)12](6-) ([2](6-)). When dissociated from [Co3(aet)6](3+) in solution, [2](6-) was converted to (Λ)2(R)6-[Au3Co2(L-cys)6](3-) ([1 b](3-)) with retention of the chiral configurations.

Self-assembled peptide nanoparticles as tumor microenvironment activatable probes for tumor targeting and imaging

Design of specific and sensitive imaging probes for targeting tumor microenvironment holds great promise to achieve precise detection and rapid responsiveness to neoplastic tissues. Dysregulated pH, one of the most remarkable hallmarks of tumor microenvironment, can be considered as a good specific trigger for the design of broad-spectrum and local-environment responsive imaging probes. However, the current existing design strategies for pH-responsive systems are insufficient to meet the needs for a rapid and tumor-specific diagnosis. Here we reported a novel biomimetic nanostructure based on oligopeptide self-assembly that can quickly switch into dissociated stage with active fluorescence property from self-assembled stage with quenched fluorescence activity when encountering a subtle pH-change in tumor microenvironment (pH6.8 vs. 7.4). This oligopeptide-assembly is examined as tumor microenvironment activatable probes for both intratumoral and intravenous in vivo tumor imaging. Through the distinct fluorescent intensities, it is validated that the acidic tumor microenvironment can activate stronger fluorescence signals. The tailor-made self-assembled oligopeptide nanomaterials have the potential for efficient and specific in situ diagnosis of various solid tumors with a weakly acidic microenvironment, which is expected to be of crucial importance for clinical tumor diagnostics.

A near-infrared-emitting fluorescent probe for monitoring mitochondrial pH.

We demonstrate a new small molecule fluorescent probe, possessing near-infrared (NIR) emission and an unusually large Stokes shift. It can be readily taken up by live cells and mitochondria, and track subtle pH changes with effectively reduced biological background fluorescence and improved measurement accuracy.

Resveratrol‐induced apoptosis is enhanced in low pH environments associated with cancer

Many critical factors such as hypoxia, nutrient deficiency, activation of glycolytic pathway/Warburg effect contribute to the observed low pH in tumors compared to normal tissue. Studies suggest that such tumor specific acidic environment can be exploited for the development of therapeutic strategies against cancer. Independent observations show reduction in pH of mammalian cells undergoing internucleosomal DNA fragmentation and apoptosis. As such, our group has extensively demonstrated that anticancer mechanisms of different plant polyphenols involve mobilization of endogenous copper and consequent internucleosomal DNA breakage. Copper is redox active metal, an essential component of chromatin and is sensitive to subtle pH changes in its microenvironment. Here we explored whether, acidic pH promotes growth inhibition, apoptosis, and DNA damaging capacity of chemopreventive agent resveratrol. Our results reveal that growth inhibition and internucleosomal DNA fragmentation induced apoptosis in Capan-2 and Panc-28 pancreatic cancer cell lines (and not in normal HPDE cells) by resveratrol is enhanced at lower pH. Using comet assay, we further demonstrate that DNA breakage by resveratrol is enhanced with acidification. Membrane permeable copper specific chelator neocuproine (and not iron chelator orthophenanthroline) abrogated growth inhibition and apoptosis by resveratrol. Western blot results show enhanced activation of DNA laddering marker H2.aX by resveratrol at acidic pH that was reversed by neocuproine and not by orthophenanthroline. Our findings provide irrevocable proof that low pH environment can be turned into tumor weakness and assist in eradication of cancer cells by resveratrol.

Helicobacter pylori Exhibits a Fur-Dependent Acid Tolerance Response

Helicobacter pylori colonizes the acid environment of the gastric mucosa. Like other enteric bacterial pathogens, including Salmonella enterica, which must survive a brief exposure to that environment, H. pylori displays a rapid response to subtle changes in pH, which confers an increased ability to survive at more extreme acidic pH. This two-step acid tolerance response (ATR) requires de novo protein synthesis and is dependent on the function of the global regulatory protein Fur. We have explored the physiological bases of the ATR in H. pylori. Proteomic analysis of phenotypes of H. pylori and fur mutant strains show that subtle pH changes elicit significant changes in the pattern of proteins synthesized. A loss-of-function mutation in the fur gene, obtained by insertion of an antibiotic resistance cassette, indicated that Fur regulates the expression of a fraction of H. pylori proteins. A subset of proteins is involved in the ATR and confer a negative ATR phenotype.

Redox‐Mediated Self‐Organization of Metallosupramolecular Architectures Composed of D‐Penicillaminato CuI8CuII6 Clusters: Drastic Structural Change by Subtle pH Changes

Redox‐Mediated Self‐Organization of Metallosupramolecular Architectures Composed of <scp>D</scp>‐Penicillaminato Cu^I₈Cu^II₆ Clusters: Drastic Structural Change by Subtle pH Changes