Local pH Changes Research Articles

Hydrological cycle amplification imposes spatial patterns on the climate change response of ocean pH and carbonate chemistry

Abstract. ​​​​​​​Ocean CO2 uptake and acidification in response to human activities are driven primarily by the rise in atmospheric CO2 but are also modulated by climate change. Existing work suggests that this “climate effect” influences the uptake and storage of anthropogenic carbon and acidification via the global increase in ocean temperature, although some regional responses have been attributed to changes in circulation or biological activity. Here, we investigate spatial patterns in the climate effect on surface ocean acidification (and the closely related carbonate chemistry) in an Earth system model under a rapid CO2-increase scenario and identify a different driving process. We show that the amplification of the hydrological cycle, a robustly simulated feature of climate change, is largely responsible for the spatial patterns in this climate effect at the sea surface. This “hydrological effect” can be understood as a subset of the total climate effect, which includes warming, hydrological cycle amplification, circulation, and biological changes. We demonstrate that it acts through two primary mechanisms: (i) directly diluting or concentrating dissolved ions by adding or removing freshwater and (ii) altering the sea surface temperature, which influences the solubility of dissolved inorganic carbon (DIC) and acidity of seawater. The hydrological effect opposes acidification in salinifying regions, most notably the subtropical Atlantic, and enhances acidification in freshening regions such as the western Pacific. Its single strongest effect is to dilute the negative ions that buffer the dissolution of CO2, quantified as alkalinity. The local changes in alkalinity, DIC, and pH linked to the pattern of hydrological cycle amplification are as strong as the (largely uniform) changes due to warming, explaining the weak increase in pH and DIC seen in the climate effect in the subtropical Atlantic Ocean.

Finite Element Analysis of Local pH Variations in Electrolysis with Porous Electrodes, Considering Water Self-Ionization.

A finite element model was developed to simulate ion fluxes and local pH changes within and around porous electrodes during the H2 evolution reaction (HER) in acidic electrolytes. This model is particularly characterized by its ability to simulate scenarios in which the local pH inside and near the cathode exceeds 7, even under bulk acidic conditions (e.g., pH = 1), by considering the self-ionization of water. Steady-state calculations using meshes with an appropriate spatial distribution inside and near the cathode revealed that the relationship between the local pH and the double-layer potential at the interface between the porous catalyst layer and the electrolyte domains changed notably when the local pH exceeded the threshold of 7. By comparing the fluxes of H+ and OH- ions at the interface and using the thickness of the catalyst layer as a variable, we determined that the presence of H+ ions within the pores or the supply of OH- ions from the pores to the interface was responsible for the characteristic change in the local pH observed for the porous electrode. The porous electrode model constructed in this study can potentially serve as a basis that can be extended to a wide range of electrolysis systems, including not only the HER, but also the reduction of CO2, H2O2, and O2, and even oxidation reactions such as the O2 evolution reaction.

Benchmarking Local pH of Electrocatalysts for Water Electrolysis Using the Rotating Ring-Disk Electrode Technique

Water electrolysis is an important route for production of green hydrogen and remains a field of active research in pursuit of improved electrocatalytic activity and durability. Operating with a near-neutral feed is critical for this technology to be more widely adapted, because it allows the direct use of various water sources and imposes less stringent requirements on the components of the electrochemical cell.During water electrolysis, the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) involving protons and hydroxides can experience a significant change in local pH at the surface of the catalyst, especially in near-neutral bulk conditions. This change in local pH is usually dictated by the reaction conditions such as electrolyte composition and mass transport within the system. Notably, there has been an increase in development of catalysts for water electrolysis with the ability to modulate their local pH in recent years. 1–6 However, comparing and quantifying the local pH modulation effects of these catalysts is challenging due to varying experimental techniques and protocols. The rotating ring-disk electrode (RRDE) with a potentiometric pH sensing ring has been presented as a promising and facile tool for in-situ local pH detection. 3,4,7,8 The local pH at the disk is estimated from the ring pH through solving the convective-diffusion equation under the well-defined mass transport conditions of an RRDE system. 8 In this study, we have investigated the local pH of iridium oxide during OER in both unbuffered and buffered electrolytes under near-neutral to alkaline bulk conditions using the RRDE technique. Our results provide benchmarks for future studies on the local pH modulation effects of catalysts and insights into the impact of electrolyte composition on local pH. In combination with mass transport modelling, we further examined the limitations of this technique and provide suggestions for best practices. References X. Liu et al., Appl. Catal. B Environ., 331, 122715 (2023).Z. Li et al., Angew. Chemie Int. Ed., 62, e202217815 (2023).J. Guo et al., Nat. Energy, 8, 264–272 (2023).X. Zheng et al., Nat. Commun. 2023 141, 14, 1–13 (2023).X. Wang, C. Xu, M. Jaroniec, Y. Zheng, and S. Z. Qiao, Nat. Commun. 2019 101, 10, 1–8 (2019).H. Tan et al., Nat. Commun. 2022 131, 13, 1–9 (2022).Y. Yokoyama et al., Chem. Lett., 49, 195–198 (2020).W. J. Albery and E. J. Calvo, J. Chem. SOC., Faraday Trans. 1, 79, 2583–2596 (1983). Figure 1

(Invited) Graphene Oxide As an Additive for Ni-Fe Electrodeposition

In contrast to graphene, graphene oxide (GO) is readily disperse in aqueous electrolytes and can be reduced along with nickel and iron metal ions. While others had incorporated graphene in Ni-Fe deposits, no previous studies have addressed the role of GO particles on metal deposition. Ni-Fe is characterized by the anomalous codeposition behavior where there is a tendency of more Fe to be deposited than Ni even though there is an excess of Ni ions in the electrolyte. This behavior has been modeled assuming adsorbed intermediates. Here, the influence of GO on the deposit composition, structure and anomalous codeposition effect is investigated. The deposits were galvanostatically electrodeposited from a boric acid-sulfamate electrolyte at pH 2 containing commercial graphene oxide platelets. Two different cell configurations were examined:1) a rotating cylinder electrode (RCE) and 2) a copper mesh. The rotating cylinder as a working electrode was used in order to investigate mass transport. The copper mesh working electrode was placed in close contact to a flat bottom pH probe in order to examine the local pH change. The addition of GO to the electrolyte had an effect on the deposit composition and the local pH change (Fig 1). The deposit composition had either more Ni or remained the same compared to an electrolyte without GO on the RCE electrode at electrode rotation rates of 372 and 1000 rpm (Fig 1 (a) and (b)). The larger Ni content in the deposit was due to an enhanced Ni partial current density in the presence of GO. The local pH during the deposition on the mesh electrode with vigorous electrolyte stirring increased the local pH (Fig 1(c)). The composition behavior is similar to the results from the RCEs, with higher Ni content in the presence of GO. The local pH increase when GO was present is considered a factor that drives the enhanced Ni content, that may be a consequence of changes in adsorbed hydrogen. GO was not incorporated into the deposit; however, it had a dramatic effect on the morphology. There was less micro-cracks when GO was present in the electrolyte suggesting less adsorbed hydrogen. Thus, GO influenced the adsorbed intermediates making the electrodeposition less anomalous and having less cracks. Acknowledgement: This work was supported in part by the AESF Foundation. Figure 1. The influence of GO in the electrolyte during Ni-Fe electrodeposition (a) composition on a RCE, rotating rate (a) 372, (b)1000 rpm and (c) local pH measurements on a mesh electrode under vigorous stirring, 30 mA/cm2. Figure 1

Triple-function carbon-based Ca2+ ion-selective pH ring microelectrode to study real-time bacteria-mediated hydroxyapatite corrosion

BackgroundThe local pH change mediated by the pathogenic bacterial species Streptococcus mutans plays a significant role in the corrosion of hydroxyapatite (HA) present in the tooth in the dynamic oral cavity. The acid produced by the bacteria decreases the local pH and releases Ca2+ ions from the HA. We studied the bacteria-mediated demineralization of HA by scanning electrochemical microscopy (SECM) after growing S. mutans biofilm on HA for 7 days. ResultsWe notably developed a triple-function SECM-compatible tip that could be positioned above the biofilm. It can also measure the pH and [Ca2+] change simultaneously above the biofilm-HA substrate. The triple-function SECM tip is a combination of a potentiometric pH sensor deposited with iridium oxide and a dual-function carbon-based Ca2+ ion-selective membrane electrode with a slope of 67 mV/pH and 34.3 mV/log [Ca2+], respectively. The distance-controlled triple-function SECM tip monitored real-time pH and [Ca2+] changes 30 μm above the S. mutans biofilm. The high temporal resolution pH data demonstrated that after approximately 20 min of sucrose addition, S. mutans started to produce acid to titrate the solution buffer, causing a pH change from 7.2 to 6.5 for HA and from 7.2 to 5 for the glass substrate. We observed that, after 30 min of acid production, ∼300 μM of Ca2+ ions were increased at pH 6.5 above the biofilm surface as a result of the pH change in the local microenvironment. After the release of Ca2+ from HA, the pH environment again shifted toward the neutral side, from 6.5 to 7.2. Therefore, precipitation of Ca2+ happens at the top of the biofilm, thus corroding the HA from underneath. For a glass substrate, in contrast, no Ca2+ ions were released, and the pH did not change back to 7.2. We were able to observe the dynamics of the HA demineralization–remineralization process simultaneously with our newly developed triple-function SECM tip or microprobe. SignificanceThis technique could notably advance the study of similar complex processes, such as bacteria-mediated corrosion in biomedical and environmental contexts.

Mussels Put Their Best “pH”oot Forward: Importance of pH in Formation of Biological and Bio‐Inspired Materials

AbstractMussel byssus offers bio‐inspired designs for advanced adhesives, coatings, and supramolecular hydrogels. Solidification of secreted proteins into mechanically robust fibers is triggered by a pH jump from acidic fluid condensates to basic seawater conditions driving protein crosslinking by metal coordination with 3,4‐dihydroxyphenylalanine (DOPA). Knowledge of the dynamic and localized pH changes during secretion is currently lacking. Yet, this information is crucial for controlling the gelation and properties of mussel‐inspired DOPA‐modified materials. Here, an iridium oxide‐based pH microsensor combining high mechanical stability and spatial resolution is used to measure the acidic pH during byssus secretion and to map mussel‐inspired hydrogels revealing compositional heterogeneity resulting in mechanically distinct regions. Within the hydrogel, high pH values >12 are measured which are detrimental to DOPA due to its strong propensity for oxidation, which adversely alters gel properties. This demonstrates the need to improve preparation methods of mussel‐inspired adhesive materials to more closely mimic native processes.

Interrogation of Oxidative Pulsed Methods for the Stabilization of Copper Electrodes for CO2 Electrolysis.

Using copper (Cu) as an electrocatalyst uniquely produces multicarbon products (C2+-products) during the CO2 reduction reaction (CO2RR). However, the CO2RR stability of Cu is presently 3 orders of magnitude shorter than required for commercial operation. One means of substantially increasing Cu catalyst lifetimes is through periodic oxidative processes, such as cathodic-anodic pulsing. Despite 100-fold improvements, these oxidative methods only delay, but do not circumvent, degradation. Here, we provide an interrogation of chemical and electrochemical Cu oxidative processes to identify the mechanistic processes leading to stable CO2RR through electrochemical and in situ Raman spectroscopy measurements. We first examine chemical oxidation using an open-circuit potential (OCP), identifying that copper oxidation is regulated by the transient behavior of the OCP curve and limited by the rate of the oxygen reduction reaction (ORR). Increasing O2 flux to the cathode subsequently increased ORR rates, both extending lifetimes and reducing "off" times by 3-fold. In a separate approach, the formation of Cu2O is achieved through electrochemical oxidation. Here, we establish the minimum electrode potentials required for fast Cu oxidation (-0.28 V vs Ag/AgCl, 1 M KHCO3) by accounting for transient local pH changes and tracking oxidation charge transfer. Lastly, we performed a stability test resulting in a 20-fold increase in stable ethylene production versus the continuous case, finding that spatial copper migration is slowed but not mitigated by oxidative pulsing approaches alone.

Real-Time pH Sensor in Bacterial Microenvironments Using Liquid Crystal Core-Shell Microspheres.

It is well-known that the bacterial microenvironment imposes restrictions on the growth and behavior of bacteria. The localized monitoring of microenvironmental factors is appreciated when consulting bacterial adaptation and behavior in the presence of chemical or mechanical stimuli. Herein, we developed a novel liquid crystal (LC) biosensor in a microsphere configuration for real-time 3D monitoring of the bacteria microenvironment, which was implemented by a microfluidic chip. As a proof of concept, a LC gel (LC-Gel) microsphere biosensor was prepared and employed in the localized pH changes of bacteria by observing the configuration change of LC under polarized optical microscopy. Briefly, the microsphere biosensor was constructed in core-shell configuration, wherein the core contained LCE7 (a nematic LC) doped with 4-pentylbiphenyl-4'-carboxylic acid (PBA), and the shell encapsulated the bacteria. The protonation of carboxyl functional groups of the PBA induced a change in charge density on the surface of LCE7 and the orientation of E7 molecules, resulting in the transitions of the LC nucleus from axial to bipolar. The developed LC-Gel microspheres pH sensor exhibited its dominant performance on localized pH real-time sensing with a resolution of 0.1. An intriguing observation from the prepared pH biosensor was that the diverse bacteria impelled distinct acidifying or alkalizing effects. Overall, the facile LC-Gel microsphere biosensor not only provides a versatile tool for label-free, localized pH monitoring but also opens avenues for investigating the effects of chemical and mechanical stimuli on cellular metabolism within bacterial microenvironments.

Urea Biosensing through Integration of Urease to the PEDOT-Polyamine Conducting Channels of Organic Electrochemical Transistors: pH-Change-Based Mechanism and Urine Sensing

We present the construction of an organic electrochemical transistor (OECT) based on poly(3,4-ethylendioxythiophene, PEDOT) and polyallylamine (PAH) and its evaluation as a bioelectronic platform for urease integration and urea sensing. The OECT channel was fabricated in a one-step procedure using chemical polymerization. Then, urease was immobilized on the surface by electrostatic interaction of the negatively charged enzyme at neutral pH with the positively charged surface of PEDOH-PAH channels. The real-time monitoring of the urease adsorption process was achieved by registering the changes on the drain–source current of the OECT upon continuous scan of the gate potential during enzyme deposition with high sensitivity. On the other hand, integrating urease enabled urea sensing through the transistor response changes resulting from local pH variation as a consequence of enzymatic catalysis. The response of direct enzyme adsorption is compared with layer-by-layer integration using polyethylenimine. Integrating a polyelectrolyte over the adsorbed enzyme resulted in a more stable response, allowing for the sensing of urine even from diluted urine samples. These results demonstrate the potential of integrating enzymes into the active channels of OECTs for the development of biosensors based on local pH changes.

Spectral Characteristics of Water-Soluble Rhodamine Derivatives for Laser-Induced Fluorescence.

We present a comprehensive fluorescence characterization of seven water-soluble rhodamine derivatives for applications in laser-induced fluorescence (LIF)techniques. Absorption and emission spectra for these dyes are presented over the visible spectrum of wavelengths (400 to 700nm). Their fluorescence properties were also investigated as a function of temperature for LIF thermometry applications. Rhodamine 110 depicted the least fluorescence emission sensitivity to temperature at -0.11%/°C, while rhodamine B depicted the most with a -1.55%/°C. We found that the absorption spectra of these molecules are independent of temperature, supporting the notion that the temperature sensitivity of their emission only comes from changes in quantum yield with temperature. Conversely, these rhodamine fluorophores showed no change in emission intensities with pH variations and are, therefore, not suitable tracers for pH measurements. Similarly, fluorescent lifetime, which is also a property sensitive to local environmental changes in temperature, pH, and ion concentration, measurements were conducted for these fluorophores. It was found that rhodamine B and kiton red 620 have shorter fluorescence timescales compared to those of the other five rhodamine dyes, making them least suitable for applications where temporal changes in emission are monitored. Lastly, we conducted experiments to assess the physicochemical absorption characteristics of these dyes' molecules into polydimethylsiloxane (PDMS), the most common material for microfluidic devices. Rhodamine B showed the highest diffusion into PDMS substrates as compared to the other derivative dyes.

Dynamic Release from Acetalated Dextran Nanoparticles for Precision Therapy of Inflammation.

Polymer-based nanoparticles (NPs) that react to altered physiological characteristics have the potential to enhance the delivery of therapeutics to a specific area. These materials can utilize biochemical triggers, such as low pH, which is prone to happen locally in an inflammatory microenvironment due to increased cellular activity. This reduced pH is neutralized when inflammation subsides. For precise delivery of therapeutics to match this dynamic reaction, drug delivery systems (DDS) need to not only release the drug (ON) but also stop the release (OFF) autonomously. In this study, we use a systematic approach to optimize the composition of acetalated dextran (AcDex) NPs to start (ON) and stop (OFF) releasing model cargo, depending on local pH changes. By mixing ratios of AcDex polymers (mixed NPs), we achieved a highly sensitive material that was able to rapidly release cargo when going from pH 7.4 to pH 6.0. At the same time, the mix also offered a stable composition that enabled a rapid ON/OFF/ON/OFF switching within this narrow pH range in only 90 min. These mixed NPs were also sensitive to biological pH changes, with increased release in the presence of inflammatory cells compared to healthy cells. Such precise and controllable characteristics of a DDS position mixed NPs as a potential treatment platform to inhibit disease flare-ups, reducing both systemic and local side effects to offer a superior treatment option for inflammation compared to conventional systems.

Time-Separated Pulse Release-Activation of an Enzyme from Alginate-Polyethylenimine Hydrogels Using Electrochemically Generated Local pH Changes.

β-Glucosidase (EC 3.2.1.21) from sweet almond was encapsulated into pH-responsive alginate-polyethylenimine (alginate-PEI) hydrogel. Then, electrochemically controlled cyclic local pH changes resulting from ascorbate oxidation (acidification) and oxygen reduction (basification) were used for the pulsatile release of the enzyme from the composite hydrogel. Activation of the enzyme was controlled by the very same pH changes used for β-glucosidase release, separating these two processes in time. Importantly, the activity of the enzyme, which had not been released yet, was inhibited due to the buffering effect of PEI present in the gel. Thus, only a portion of the released enzyme was activated. Both enzymatic activity and release were monitored by confocal fluorescence microscopy and regular fluorescent spectroscopy. Namely, commercially available very little or nonfluorescent substrate 4-methylumbelliferyl-β-d-glucopyranoside was hydrolyzed by β-glucosidase to produce a highly fluorescent product 4-methylumbelliferone during the activation phase. At the same time, labeling of the enzyme with rhodamine B isothiocyanate was used for release observation. The proposed work represents an interesting smart release-activation system with potential applications in biomedical field.

Folding Kinetics and Volume Variation of the β-Hairpin Peptide Chignolin upon Ultrafast pH-Jumps.

In-depth characterization of fundamental folding steps of small model peptides is crucial for a better understanding of the folding mechanisms of more complex biomacromolecules. We have previously reported on the folding/unfolding kinetics of a model α-helix. Here, we study folding transitions in chignolin (GYDPETGTWG), a short β-hairpin peptide previously used as a model to study conformational changes in β-sheet proteins. Although previously suggested, until now, the role of the Tyr2-Trp9 interaction in the folding mechanism of chignolin was not clear. In the present work, pH-dependent conformational changes of chignolin were characterized by circular dichroism (CD), nuclear magnetic resonance (NMR), ultrafast pH-jump coupled with time-resolved photoacoustic calorimetry (TR-PAC), and molecular dynamics (MD) simulations. Taken together, our results present a comprehensive view of chignolin's folding kinetics upon local pH changes and the role of the Tyr2-Trp9 interaction in the folding process. CD data show that chignolin's β-hairpin formation displays a pH-dependent skew bell-shaped curve, with a maximum close to pH 6, and a large decrease in β-sheet content at alkaline pH. The β-hairpin structure is mainly stabilized by aromatic interactions between Tyr2 and Trp9 and CH-π interactions between Tyr2 and Pro4. Unfolding of chignolin at high pH demonstrates that protonation of Tyr2 is essential for the stability of the β-hairpin. Refolding studies were triggered by laser-induced pH-jumps and detected by TR-PAC. The refolding of chignolin from high pH, mainly due to the protonation of Tyr2, is characterized by a volume expansion (10.4 mL mol-1), independent of peptide concentration, in the microsecond time range (lifetime of 1.15 μs). At high pH, the presence of the deprotonated hydroxyl (tyrosinate) hinders the formation of the aromatic interaction between Tyr2 and Trp9 resulting in a more disorganized and dynamic tridimensional structure of the peptide. This was also confirmed by comparing MD simulations of chignolin under conditions mimicking neutral and high pH.

Multi-Gene Single Nucleotide Polymorphism Detection in Gastric Cancer Based on Ion Semiconductor Sequencing Platform.

Gastric cancer is a common heterogeneous tumor. Most patients have advanced gastric cancer at the time of diagnosis and often need chemotherapy. Although 5-fluorouracil (5-FU) is widely used for treatment, its therapeutic sensitivity and drug tolerance still need to be determined, which emphasizes the importance of individualized administration. Pharmacogenetics can guide the clinical implementation of individualized treatment. Single nucleotide polymorphisms (SNPs), as a genetic marker, contribute to the selection of appropriate chemotherapy regimens and dosages. Some SNPs are associated with folate metabolism, the therapeutic target of 5-FU. Methylenetetrahydrofolate reductase (MTHFR) rs1801131 and rs1801133, dihydrofolate reductase (DHFR) rs1650697 and rs442767, methionine synthase (MTR) rs1805087, gamma-glutamyl hydrolase (GGH) rs11545078 and solute carrier family 19 member 1 (SLC19A1) rs1051298 have been investigated in different kinds of cancers and antifolate antitumor drugs, which have potential forecasting and guiding significance for application of 5-FU. The ion torrent next-generation semiconductor sequencing technology can rapidly detect gastric cancer-related SNPs. Each time a base is extended in a DNA chain, an H+ will be released, causing local pH changes. The ionic sensor detects pH changes and converts chemical signals into digital signals, achieving sequencing by synthesis. This technique has low sample requirement, simple operation, low cost, and fast sequencing speed, which is beneficial for guiding individualized chemotherapy by SNPs.

Customizing oxygen electrocatalytic microenvironment with S, N codoped carbon nanofibers confining carbon nanocapsules and Co9S8 nanoparticles for rechargeable Zn-air batteries

Rational design and modulation of oxygen electrocatalytic microenvironment are crucial for achieving high performance in rechargeable Zn-air batteries (RZABs). We report a high-efficiency bifunctional electrocatalyst based on S, N codoped carbon fibers confining carbon nanocapsules attached with Co9S8 nanoparticles to customize the oxygen electrocatalytic microenvironment. The inner carbon nanocapsules function as a “gas buffer”, while the outer fiber skeleton acts as a self-supporting structure, which jointly refine the oxygen electrocatalytic microenvironment and improve accessibility of the active sites. Such a unique nanostructure proves advantageous for O2 adsorption/diffusion and mitigation of local pH changes during oxygen reduction reaction, and favors the release of generated O2 and the transfer of interfacial electron during the oxygen evolution reaction as well. The constructed liquid RZABs deliver a large peak power density (280 mW cm−2) and robust cyclability (1200 h at 10 mA cm−2), and the assembled quasi-solid state flexible RZABs further indicate long-term durability.

Probing Local pH Change during Electrode Oxidation of TEMPO Derivative: Implication of Redox-Induced Acidity Alternation by Imidazolium-Linker Functional Groups.

The chemical degradation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-based aqueous energy storage and catalytic systems is pH sensitive. Herein, we voltammetrically monitor the local pH (pHlocal) at a Pt ultramicroelectrode (UME) upon electro-oxidation of imidazolium-linker functionalized TEMPO and show that its decrease is associated with the greater acidity of the cationic (oxidized) rather than radical (reduced) form of TEMPO. The protons that drive the decrease in pH arise from hydrolysis of the conjugated imidazolium-linker functional group of 4-[2-(N-methylimidazolium)acetoxy]-2,2,6,6-tetramethylpiperidine-1-oxyl chloride (MIMAcO-T), which was studied in comparison with 4-hydroxyl-TEMPO (4-OH-T). Voltammetric hysteresis is observed during the electrode oxidation of 4-OH-T and MIMAcO-T at a Pt UME in an unbuffered aqueous solution. The hysteresis arises from the pH-dependent formation and dissolution of Pt oxides, which interact with pHlocal in the vicinity of the UME. We find that electrogenerated MIMAcO-T+ significantly influences pHlocal, whereas 4-OH-T+ does not. Finite element analysis reveals that the thermodynamic and kinetic acid-base properties of MIMAcO-T+ are much more favorable than those of its reduced counterpart. Imidazolium-linker functionalized TEMPO molecules comprising different linking groups were also investigated. Reduced TEMPO molecules with carbonyl linkers behave as weak acids, whereas those with alkyl ether linkers do not. However, oxidized TEMPO+ molecules with alkyl ether linkers exhibit more facile acid-base kinetics than those with carbonyl ones. Density functional theory calculations confirm that OH- adduct formation on the imidazolium-linker functional group of TEMPO is responsible for the difference in the acid-base properties of the reduced and oxidized forms.

Few- and single-molecule reservoir computing experimentally demonstrated with surface-enhanced Raman scattering and ion gating.

Molecule-based reservoir computing (RC) is promising for achieving low power consumption neuromorphic computing, although the information-processing capability of small numbers of molecules is not clear. Here, we report a few- and single-molecule RC that uses the molecular vibration dynamics in the para-mercaptobenzoic acid (pMBA) detected by surface-enhanced Raman scattering (SERS) with tungsten oxide nanorod/silver nanoparticles. The Raman signals of the pMBA molecules, adsorbed at the SERS active site of the nanorod, were reversibly perturbated by the application of voltage-induced local pH changes near the molecules, and then used to perform time-series analysis tasks. Despite the small number of molecules used, our system achieved good performance, including >95% accuracy in various nonlinear waveform transformations, 94.3% accuracy in solving a second-order nonlinear dynamic system, and a prediction error of 25.0 milligrams per deciliter in a 15-minute-ahead blood glucose level prediction. Our work provides a concept of few-molecular computing with practical computation capabilities.

Observation on Microenvironment Changes of Dynamic Catalysts in Acidic CO2 Reduction.

Electrochemical CO2 reduction reaction (CO2RR) in acid can solve alkalinity issues while highly corrosive and reductive acidic electrolytes usually cause catalyst degradation. Inhibiting catalyst degradation is crucial for the stability of acidic CO2RR. Here, we reveal the microenvironment changes of dynamic Bi-based catalysts and develop a pulse chronoamperometry (CA) strategy to improve the stability of acidic CO2RR. In situ fluorescence mappings show that the local pH changes from neutral to acid, and the in situ Raman spectra reveal the dynamic evolution of interfacial water structures in the microenvironment. We propose that the surface charge properties of dynamic catalysts affect the competitive adsorption of K+ and protons, thereby causing the differences in local pH and CO2RR intermediate adsorption. We also develop a pulse CA strategy to reactivate catalysts, and the stability of acidic CO2RR is improved by 2 orders of magnitude for 100 h operation, which is higher than most reports on the stability of acidic CO2RR. This work gives insights on how microenvironment changes affecting the stability of acidic CO2RR, and provides guidance for designing stable catalysts in acidic electrolytes.

Durable Attenuation of Tumor pH-Platelet Linkage Reinstates Bioorthogonal Targeting of Residual Tumors Post-Debulking.

There are circumstances where tumors can only be partially resected. Therefore, multimodality therapy targeting post-operative residuals is important. Here, we show that bioorthogonal click chemistry enables targeted delivery to heterogeneous tumors, but its utility against tumor post-debulking is ineffective due to platelet cloaks that shield tumor cells from bioorthogonal pairing. We further discover tumor-infiltrating platelet levels respond to local pH changes. Elucidating this pH-platelet linkage, we design an injectable hydrogel for resection cavity implantation that simultaneously azido-tags tumor cells and inhibit their catalysis to acidify surrounding milieu. Unlike transient buffering, tumor acidification blockade sustains pH normalization, leading to durable platelet reduction. This reinstates bioorthogonal targeting of dibenzyl cyclooctyne-modified nanoparticles, thereby enhancing photodynamic ablation of residuals while amplifying systemic antitumor immunity. Concurrently, platelet/pH normalization interrupts metastasis cascade from invasion to circulation to colonization. Overall, attenuating tumor pH-platelet linkage unlocks bioorthogonal chemistry as a potential option for adjuvant therapy after tumor debulking.

Bioelectrochemically triggered apoferritin-based bionanoreactors: synthesis of CdSe nanoparticles and monitoring with leaky waveguides.

Herein, we describe a novel method for producing cadmium-selenide nanoparticles (CdSe NPs) with controlled size using apoferritin as a bionanoreactor triggered by local pH change at the electrode/solution interface. Apoferritin is known for its reversible self-assembly at alkaline pH. The pH change is induced electrochemically by reducing O2 through the application of sufficiently negative voltages and bioelectrochemically through O2 reduction catalyzed by laccase, co-immobilized with apoferritin on the electrode surface. Specifically, a Ti electrode is modified with (3-aminopropyl)triethoxysilane, followed by glutaraldehyde cross-linking (1.5% v/v in H2O) of apoferritin (as the bionanoreactor) and laccase (as the local pH change triggering system). This proposed platform offers a universal approach for controlling the synthesis of semiconductor NPs within a bionanoreactor solely driven by (bio)electrochemical inputs. The CdSe NPs obtained through different synthetic approaches, namely electrochemical and bioelectrochemical, were characterized spectroscopically (UV-Vis, Raman, XRD) and morphologically (TEM). Finally, we conducted online monitoring of CdSe NPs formation within the apoferritin core by integrating the electrochemical system with LWs. The quantity of CdSe NPs produced through bioelectrochemical means was determined to be 2.08 ± 0.12 mg after 90 minutes of voltage application in the presence of O2. TEM measurements revealed that the bioelectrochemically synthesized CdSe NPs have a diameter of 4 ± 1 nm, accounting for 85% of the size distribution, a result corroborated by XRD data. Further research is needed to explore the synthesis of nanoparticles using different biological nanoreactors, as the process can be challenging due to the elevated buffer capacitance of biological media.