Low Chloride Concentrations Research Articles

Influencing Factors on the Wet Impregnation of Additive‐Manufactured Catalyst Support Structures

AbstractThe wet impregnation of additive manufactured aluminum oxide cylinders with platinum is investigated. The influence of five parameters on the penetration depth and the platinum loading is evaluated. A smaller penetration depth is obtained by increasing pH, sodium chloride concentration in the impregnation solution, decreasing impregnation solution volume, heating rate during subsequent calcination, and no vacuum during prewetting before the impregnation. A pH range of 2 to 4, a low chloride concentration, a small liquid volume, and no vacuum drawing lead to high platinum uptake. This investigation is crucial in understanding and optimizing the wet impregnation process, providing practical guidance for future research with more complex structures.

Investigation of Scaling and Materials’ Performance in Simulated Geothermal Brine

Geothermal energy generation faces challenges in efficiency, partly due to restrictions on reinjection temperatures caused by scaling issues. Therefore, developing strategies to prevent scaling is critical. This study aims to simulate the scaling tendencies and corrosion effects of geothermal fluids on various construction materials used in scaling reactor/retention tank systems. A range of materials, including carbon steel, austenitic stainless steel, duplex stainless steel, two proprietary two-part epoxy coatings, and thermally sprayed aluminium (TSA), were tested in a simulated geothermal brine. Experiments were conducted in a laboratory vessel designed to replicate the wall shear stress conditions expected in a scaling reactor. The tests revealed varying scaling tendencies among the materials, with minimal corrosion observed. The dominant scale formed was calcium carbonate, consistent with geochemical modelling. The findings suggest that despite the high operating temperatures, the risk of corrosion remains low due to the brine’s low chloride content, while the wettability of materials after immersion may serve as a useful indicator for selecting those that promote scaling.

The combined leaching of copper, gold and uranium in chloride solutions. II. Concentrate leach tests

This study of the simultaneous leaching of copper, gold and uranium from a flotation concentrate is aimed at establishing the conditions that could be applied in a possible heap leach process that would recover all three metals (plus silver, if present) in a single step. The results obtained in this study confirm the results obtained in Part I (Nicol et al., 2024) that enhanced rates for leaching of chalcopyrite from flotation concentrates from two different sources can be obtained in acidic chloride solutions in the presence of chlorate ions. The measurements of the solution potentials during leaching with chlorate are similar to those obtained previously and confirm that chlorine generated by the chlorate-chloride reaction is the active oxidant.Uranium is dissolved even in the absence of chlorate by iron(III) as the oxidant. The latter is re-generated by reaction of iron(II) with chlorate. The dissolution of gold requires higher potentials, and it is only leached when the potential approaches 1.0 V in concentrated chloride solutions. At low chloride concentrations (1 M), gold is not dissolved because of apparent passivation.An electrochemical study of the behaviour of gold in chloride solutions in the presence of sulfide ions has shown that the passivation is probably the result of the formation of a layer of Au2S on the gold surface at low potentials before the addition of chlorate to the leach solutions i.e., before the generation of sufficient chlorine concentrations. At potentials above about 0.95 V Au2S is unstable being oxidised to AuCl2− and elemental sulfur thereby eliminating passivation.

Electrochemical Behavior of Plasma-Nitrided Austenitic Stainless Steel in Chloride Solutions.

The application possibilities of austenitic stainless steels in high friction, abrasion, and sliding wear conditions are limited by their inadequate hardness and tribological characteristics. In order to improve these properties, the thermochemical treatment of their surface by plasma nitriding is suitable. This article is focused on the corrosion resistance of conventionally plasma-nitrided AISI 304 stainless steel (530 °C, 24 h) in 0.05 M and 0.5 M sodium chloride solutions at room temperature (20 ± 3 °C), tested by potentiodynamic polarization and electrochemical impedance spectroscopy. Optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy are used for nitrided layer characterization. The experiment results confirmed the plasma-nitrided layer formation of increased micro-hardness related to the presence of Cr2N chromium nitrides and higher surface roughness compared to the as-received state. Both of the performed independent electrochemical corrosion tests point to a significant reduction in corrosion resistance after the performed plasma nitriding, even in a solution with a very low chloride concentration (0.05 mol/L).

Persulfate activation by biochar and iron: Effect of chloride on formation of reactive species and transformation of N,N-diethyl-m-toluamide (DEET)

Fenton-like processes using persulfate for oxidative water treatment and contaminant removal can be enhanced by the addition of redox-active biochar, which accelerates the reduction of Fe(III) to Fe(II) and increases the yield of reactive species that react with organic contaminants. However, available data on the formation of non-radical or radical species in the biochar/Fe(III)/persulfate system are inconsistent, which limits the evaluation of treatment efficiency and applicability in different water matrices. Based on competition kinetics calculations, we employed different scavengers and probe compounds to systematically evaluate the effect of chloride in presence of organic matter on the formation of major reactive species in the biochar/Fe(III)/persulfate system for the transformation of the model compound N,N‑diethyl-m-toluamide (DEET) at pH 2.5. We show that the transformation of methyl phenyl sulfoxide (PMSO) to methyl phenyl sulfone (PMSO2) cannot serve as a reliable indicator for Fe(IV), as previously suggested, because sulfate radicals also induce PMSO2 formation. Although the formation of Fe(IV) cannot be completely excluded, sulfate radicals were identified as the major reactive species in the biochar/Fe(III)/persulfate system in pure water. In the presence of dissolved organic matter, low chloride concentrations (0.1 mM) shifted the major reactive species likely to hydroxyl radicals. Higher chloride concentrations (1 mM), as present in a mining-impacted acidic surface water, resulted in the formation of another reactive species, possibly Cl2•−, and efficient DEET degradation. To tailor the application of this oxidation process, the water matrix must be considered as a decisive factor for reactive species formation and contaminant removal.

Enhanced electrochemical disinfection for decentralized sewage treatment through nickel foam cathode modified with CoFe2O4-spinel ferrite and multi-way carbon nanotubes

Electrochemical disinfection is characterized by its simple operation and maintenance, along with effective sterilization capabilities, making it ideal for decentralized wastewater treatment in rural areas. As a bimetallic oxide, spinel ferrite exhibits excellent catalytic activity for the oxygen reduction reaction (ORR). Herein, a novel cathode was fabricated from nickel foam modified with spinel ferrite and multi-way carbon nanotubes (CoFe2O4-MWCNTs@NF). The modification successfully strengthens the electrochemical cathode reaction to generate strong oxidants such as hydrogen peroxide and Hydroxyl radical, enabling the disinfection of water bodies with low chloride concentrations. Compared to other influencing factors (including current density, aeration rate, and electrode spacing), the impact of conductivity on hydrogen peroxide generation is relatively minor. Modified electrodes still exhibited effective disinfection capabilities in water with low conductivity. At a current density of 2 mA/cm², the CoFe2O4-MWCNTs@NF electrode achieved 4.00 log removal of E.coli in real treated sewage within 15 minutes, with an energy consumption of 1.038 kWh/m³. Electrochemical disinfection also had a certain degradation ability for sulfonamides and quinolones antibiotics in water. The disinfection and antibiotic removal effects of the modified electrode demonstrated its potential for practical applications.

Transport Characteristics and Corrosion Behavior of Ultra-High Performance Fiber-Reinforced Concrete with the Key Mix Parameters

The presence of low-quality coarse aggregates and exposure to aggressive conditions are the two major problems with the durability of concrete. Therefore, an alternative concrete with enhanced properties to prevent fluid and ionic mobility compared to conventional concrete is needed. This study investigated the effects of main mix parameters on the transport characteristics and corrosion behavior of ultra-high performance fiber-reinforced concrete (UHPFRC). A set of 27 UHPFRC mixtures with different combinations of w/b ratio, cement, and silica fume contents, based on a 33-factorial experiment design, were prepared and tested for water permeability, chloride penetrability, electrical resistivity, chloride profile, and corrosion current density. The results showed that UHPFRC mixtures exhibited excellent durability properties characterized by negligible water penetration (< 15 mm), negligible and very low chloride permeability when the w/b ratio was 0.15 (< 100 Coulombs) and up to 0.2 (< 300 Coulombs), respectively, and very low chloride concentrations at the rebar level (0.03–0.18 wt.%). All resistivity values were within the range of 26.7–78.8 kΩ cm (> 20 kΩ cm) and pH values were 12.41–13.01, indicating the implausible likelihood of corrosion in the UHPFRC mixtures. This was confirmed through the corrosion current density measurements of reinforced UHPFRC specimens after 450 days of chloride exposure, which were below the critical limit for the corrosion initiation of reinforcing steel. Finally, the experimental data were statistically analyzed and fitted for all the listed tests, and models were developed for them using the regression analysis such that regression coefficients were within 0.90–0.99.

Noise-induced hearing loss alters potassium-chloride cotransporter KCC2 and GABA inhibition in the auditory centers

Homeostatic plasticity, the ability of neurons to maintain their averaged activity constant around a set point value, is thought to account for the central hyperactivity after hearing loss. Here, we investigated the putative role of GABAergic neurotransmission in this mechanism after a noise-induced hearing loss larger than 50 dB in high frequencies in guinea pigs. The effect of GABAergic inhibition is linked to the normal functioning of K + –Cl– co-transporter isoform 2 (KCC2) which maintains a low intracellular concentration of chloride. The expression of membrane KCC2 were investigated before and after noise trauma in the ventral and dorsal cochlear nucleus (VCN and DCN, respectively) and in the inferior colliculus (IC). Moreover, the effect of gabazine (GBZ), a GABA antagonist, was also studied on the neural activity in IC. We show that KCC2 is downregulated in VCN, DCN and IC 3 days after noise trauma, and in DCN and IC 30 days after the trauma. As expected, GBZ application in the IC of control animals resulted in an increase of spontaneous and stimulus-evoked activity. In the noise exposed animals, on the other hand, GBZ application decreased the stimulus-evoked activity in IC neurons. The functional implications of these central changes are discussed.

Real-time imaging reveal anisotropic dissolution behaviors of silver nanorods

The morphology and size control of anisotropic nanocrystals are critical for tuning shape-dependent physicochemical properties. Although the anisotropic dissolution process is considered to be an effective means to precisely control the size and morphology of nanocrystals, the anisotropic dissolution mechanism remains poorly understood. Here, using in situ liquid cell transmission electron microscopy, we investigate the anisotropic etching dissolution behaviors of polyvinylpyrrolidone (PVP)-stabilized Ag nanorods in NaCl solution. Results show that etching dissolution occurs only in the longitudinal direction of the nanorod at low chloride concentration (0.2 mM), whereas at high chloride concentration (1 M), the lateral and longitudinal directions of the nanorods are dissolved. First-principles calculations demonstrate that PVP is selectively adsorbed on the {100} crystal plane of silver nanorods, making the tips of nanorods the only reaction sites in the anisotropic etching process. When the chemical potential difference of the Cl− concentration is higher than the diffusion barrier (0.196 eV) of Cl− in the PVP molecule, Cl− penetrates the PVP molecular layer of {100} facets on the side of the Ag nanorods. These findings provide an in-depth insight into the anisotropic etching mechanisms and lay foundations for the controlled preparation and rational design of nanostructures.

From grass to gas and beyond: Anaerobic digestion as a key enabling technology for a residual grass biorefinery

Roadside grass clippings hold potential as a sustainable source of bioenergy as they do not compete with crops for land use, and are only partially utilized for low-value applications. In this study, we proposed using roadside grass as a sole feedstock for anaerobic digestion (AD) in three different settings, and assessed the potential of producing biomaterials and fertilizers from grass-based digestate. Wet continuous digestion at pilot scale and dry batch digestion at pilot and large scales resulted in biogas yields up to 700 Nm3.t−1 DOM with a methane content of 49–55 %. Despite promising results, wet AD had operational problems such as clogging and poor mixing; once upscaled, the dry digestion initially also presented an operational problem with acidification, which was overcome by the second trial. Digested grass fibers from the pilot dry AD were processed into biomaterials and performed similarly or better than the undigested fibers, while around 20 % performance reduction was observed when compared to reference wood fibers. A mass balance indicated reduced fiber recovery when higher biogas production was obtained. The liquid fraction from the pilot dry AD was characterized for its nutrient content and used as a biofertilizer in another study. In contrast, the leachate collected from the large-scale dry AD had a low nitrogen content and high chloride content that could hinder its further use. Finally, a regional market analysis was conducted showing that the biocomposites produced with the available grass fibers could substitute at least half of the current European market based on our results.

A novel pathogenic SLC12A5 missense variant in epilepsy of infancy with migrating focal seizures causes impaired KCC2 chloride extrusion.

The potassium-chloride co-transporter 2, KCC2, is a neuron-specific ion transporter that plays a multifunctional role in neuronal development. In mature neurons, KCC2 maintains a low enough intracellular chloride concentration essential for inhibitory neurotransmission. During recent years, pathogenic variants in the KCC2 encoding gene SLC12A5 affecting the functionality or expression of the transporter protein have been described in several patients with epilepsy of infancy with migrating focal seizures (EIMFS), a devastating early-onset developmental and epileptic encephalopathy. In this study, we identified a novel recessively inherited SLC12A5 c.692G>A, p. (R231H) variant in a patient diagnosed with severe and drug-resistant EIMFS and profound intellectual disability. The functionality of the variant was assessed in vitro by means of gramicidin-perforated patch-clamp experiments and ammonium flux assay, both of which indicated a significant reduction in chloride extrusion. Based on surface immunolabeling, the variant showed a reduction in membrane expression. These findings implicate pathogenicity of the SLC12A5 variant that leads to impaired inhibitory neurotransmission, increasing probability for hyperexcitability and epileptogenesis.

Fluoride and Chloride Ions Concentration and their Health Implications in Groundwater within Bwari Area Council, Abuja, Nigeria

According to the World Health Organization, fluoride in drinking water, either below or above the established permissible range, can adversely affect oral health, including tooth decay and dental fluorosis. The objective of this study was to evaluate fluoride and chloride ion concentration and their health implications in groundwater within Bwari Area Council, Abuja, Nigeria using ion-selective electrode potentiometric titration for fluoride ion and Argentometric titration for chloride ion determinations. The results showed a high fluoride concentration in well water samples ranging from 0.126 mg/L to 0.216 mg/L, compared to borehole water samples ranging from 0.013 mg/mL to 0.052 mg/L. Among the chloride concentrations, the highest levels were observed in the well water sample A (96.09 mg/L), followed by borehole samples, A (63.08 mg/L) and B (49.35 mg/L). The lowest chloride concentration was recorded in the borehole sample H (11.82 mg/L). Notably, both well and borehole water sources in the studied communities had fluoride concentrations below the established minimum WHO standard (0.5 mg/L). The chloride concentrations in the groundwater samples from the study area fell within WHO standards (&lt; 250 mg/L). The results from this study suggest that the continuous consumption of water from these community sources, without additional sources of fluoride, may increase the risk of tooth decay. Therefore, addressing this issue and ensuring appropriate water treatment measures is vital for maintaining optimal oral health in the region.

Promotion of chloride removal from MSWI fly ash by an accelerated wet-carbonation process to enhance ash recycling in cement manufacture

Chlorides, sulfates, and heavy metals are the three main factors preventing the recycling of municipal solid waste incineration (MSWI) fly ash as an alternative material for cement clinker production, of which chloride plays the main role due to its extremelly hign content in fly ash. This study evaluated three wet-based pretreatment methods (water-washing, CO2-aided washing, and flue gas-aided washing) to remove chlorides using MSWI fly ashes from 13 incineration plants in China. Water washing was suitable for removing Cl- from MSWI fly ash containing a limited amount of less-soluble Cl-containing salts (Ca(OH)Cl, Ca2Al(OH)6(H2O)2Cl, and Ca6(CO3)2(OH)7Cl). However, for fly ash with a significant proportion of these less-soluble Cl-containing salts, injection of CO2/flue gas during washing promoted their decomposition and increased the chloride removal rates by 2–12%. Compared with chloride, the removal rate of sulfate was lower under all treatment scenarios and ranged from 7% to 47%. Therefore, caution should be taken when exploring techniques for the deep removal of chloride from MSWI fly ash, as sulfates may be the limiting factor in fly ash samples with low chloride contents when utilizing the fly ash for cement clinker production. Heavy metals in fly ash were not a limiting factor for any ash samples (either raw ash or treated ash) when utilizing the fly ash for clinker production. However, the dissolution of heavy metals in the washing solution deserves more attention, as a large amount of wastewater will be generated during wet-based pretreatment methods. This study confirmed that CO2/flue gas injection during washing promoted the removal of the less-soluble harmful components of fly ash, expanding the applications of ash materials.

Differential Effects of Benzalkonium Chloride on Human Trabecular Meshwork Cells Not Treated or Treated with Transforming Growth Factor-β2 or Dexamethasone.

Purpose: The objective of the present study was to evaluate the effects of low concentrations of benzalkonium chloride (BAC) (10-7%, 10-6%, or 10-5%) on healthy and glaucomatous human trabecular meshwork (HTM) cells. For this purpose, we used in vitro models replicating a healthy HTM and HTM with primary open-angle glaucoma (POAG) or steroid-induced glaucoma (SG) using two-dimensional (2D) cultures of HTM cells not treated or treated with a 5 ng/mL solution of transforming growth factor-β2 or 250 nM dexamethasone (DEX). Methods: Analyses were carried out for (1) the intercellular affinity function of 2D HTM monolayers, as determined by transepithelial electrical resistance (TEER) measurements; (2) cell viability; (3) cellular metabolism by using a Seahorse bioanalyzer; and (4) expression of extracellular matrix (ECM) molecules, an ECM modulator, and cell junction-related molecules. Results: In the absence and presence of BAC (10-7% or 10-5%), intercellular affinity function determined by TEER and cellular metabolic activities were significantly and dose dependently affected in both healthy and glaucomatous HTM cells despite the fact that there was no significant decrease in cell viabilities. However, the effects based on TEER values were significantly greater in the healthy HTM. The mRNA expression of several molecules that were tested was not substantially modulated by these concentrations of BAC. Conclusions: The findings reported herein suggest that low concentrations of BAC may have unfavorable adverse effects on cellular metabolic capacity by inducing increases in the intercellular affinity properties of the HTM, but those effects of BAC were different in healthy and glaucomatous HTM cells.

Longitudinal serum chloride as a marker for poor prognosis in severely ill COVID-19 patients: A joint model approach

Coronavirus Disease 2019 (COVID-19) has been responsible for an international health crisis that demanded incredible efforts from the scientific community to understand the disease, its risk factors, and consequences. In this work, we seek to investigate the role of serum chloride and main Strong Ion Difference (mSID) on the survival of severely ill COVID-19 patients treated in the Intensive Care Unit (ICU). Electrolyte measurements were taken daily from each patient from their admission to death or discharge. ICU survival time was measured in days from admission, and discharged patients were considered censored. The longitudinal trajectories of chloride and mSID were associated with patients’ survival times using joint models for longitudinal and time-to-event data. A total of 58 COVID-19 patients were enrolled, and 21 died during hospitalization. Older patients had lower concentrations of chloride overall, and both chloride and mSID increased over time for patients on average. Age was a significant risk factor for ICU mortality, along with the slope of estimated longitudinal trajectory of chloride. Patients with decreasing chloride levels during ICU stay had increased hazard of death. This results of this study suggest that acquired hypochloremia may be an important marker of disease progression and risk of death in patients with severe COVID-19. As such, chloride should be further validated as longitudinal marker for monitoring prognosis during the course of ICU stay. Neither the current values or the slope of the trajectory of mSID were associated with mortality in this sample. The association between the longitudinal trajectory’s slope and ICU mortality is important to understand the dynamics of the disease on a patient level, and could only be quantified by using the joint model framework.

Antibody desolvation with sodium chloride and acetonitrile generates bioactive protein nanoparticles.

About 30% of the FDA approved drugs in 2021 were protein-based therapeutics. However, therapeutic proteins can be unstable and rapidly eliminated from the blood, compared to conventional drugs. Furthermore, on-target but off-tumor protein binding can lead to off-tumor toxicity, lowering the maximum tolerated dose. Thus, for effective treatment therapeutic proteins often require continuous or frequent administration. To improve protein stability, delivery and release, proteins can be encapsulated inside drug delivery systems. These drug delivery systems protect the protein from degradation during (targeted) transport, prevent premature release and allow for long-term, sustained release. However, thus far achieving high protein loading in drug delivery systems remains challenging. Here, the use of protein desolvation with acetonitrile as an intermediate step to concentrate monoclonal antibodies for use in drug delivery systems is reported. Specifically, trastuzumab, daratumumab and atezolizumab were desolvated with high yield (∼90%) into protein nanoparticles below 100 nm with a low polydispersity index (<0.2). Their size could be controlled by the addition of low concentrations of sodium chloride between 0.5 and 2 mM. Protein particles could be redissolved in aqueous solutions and redissolved antibodies retained their binding activity as evaluated in cell binding assays and exemplified for trastuzumab in an ELISA.

Effects of pockmark activity on iron cycling and mineral composition in continental shelf sediments (southern Baltic Sea)

AbstractPockmarks are formed as a result of gas (methane) or/and groundwater outflow from the sea bottom. Methane, the second most important (after CO2) greenhouse gas, has a significant impact on biogeochemical processes in the bottom sediments by affecting the cycling of some elements, e.g. C, Fe, and S. Active pockmarks may also lead to changes in water column conditions by causing nutrients release from sediments. In the present study, we have focused on the impact of biogeochemical processes in pockmarks (methanogenesis, anaerobic methane oxidation, and groundwater seepage) on the transformation of iron (Fe) and the mineral composition of the sediment. In pore water, concentrations of hydrogen sulfide, phosphate, ammonia, sulfate, chloride, dissolved inorganic carbon, iron, and methane were analyzed. In the sediment, Fe speciation was performed using sequential extraction. The mineral composition was determined using powder X-Ray diffraction and scanning electron microscopy. The results from two pockmarks (with active gas seepage and groundwater infiltration) and two reference stations in the southern Baltic Sea show that geochemical conditions in pockmark sediments are significantly different from those in the typical muddy sea bottom. Pore water in pockmarks is characterized by lower sulfate and higher dissolved carbon concentrations as compared to areas of the seafloor where such structures are absent. This is due to the outflow of groundwater, which was confirmed by lower chloride concentration. In addition, sulfate is used to oxidize methane diffusing from deeper layers. Sediments in pockmarks are enriched in Fe(II) carbonates and depleted in Fe(III) (oxy)hydroxides, resulting from the anaerobic oxidation of methane with Fe(III) (Fe-AOM). Ferrous iron produced in large quantities during Fe-AOM is precipitated with carbonates.

Exploring Novel Sensor Design Ideas through Concentration-Induced Conformational Changes in PEG Single Chains

Polyethylene glycol (PEG) is an artificial polymer with good biocompatibility and a low cost, which has a wide range of applications. In this study, the dynamic response of PEG single chains to different ion concentrations was investigated from a microscopic point of view based on single-molecule force spectroscopy, revealing unique interactions that go beyond the traditional sensor-design paradigm. Under low concentrations of potassium chloride, PEG single chains exhibit a gradual reduction in rigidity, while, conversely, high concentrations induce a progressive increase in rigidity. This dichotomy serves as the cornerstone for a profound understanding of PEG conformational dynamics under diverse ion environments. Capitalizing on the remarkable sensitivity of PEG single chains to ion concentration shifts, we introduce innovative sensor-design ideas. Rooted in the adaptive nature of PEG single chains, these sensor designs extend beyond the traditional applications, promising advancements in environmental monitoring, healthcare, and materials science.

Insight into ion exchange behavior of LDHs: Asynchronous chloride adsorption and intercalated ions release processes

Cl− adsorption and intercalated ions release processes during LDHs are highly intricate phenomena. In this study, ion exchange performance of LDHs with specific cation interlayers and intercalated anions (CaAl–NO3-LDHs, CaAl–NO2-LDHs, CaFeAl–NO3-LDHs and CaFeAl–NO2-LDHs) were extensively investigated. The results indicate that in the presence of low chloride concentration, the intercalated anions are prematurely released due to partial dissolution of LDHs in neutral deionized water and ion exchange with OH− in alkaline simulated concrete pore solution. Therefore, Cl− adsorption of LDHs and release process of intercalated anions in LDHs are not completely synchronized. Compared to partial LDHs dissolution, the accelerating effect of OH− exchange on intercalated anion release in simulated concrete pore solution is more pronounced. Further, higher stability of LDHs in testing solutions is mainly corresponding to higher binding energy between intercalation ions and cation interlayers, thus saturated Cl− adsorption content of NO3-LDHs with high binding energy is higher than NO2-LDHs with low binding energy, and saturated Cl− adsorption content of CaAl-LDHs with high binding energy is higher than CaFeAl-LDHs with low binding energy in testing solutions.

Interplay of chloride levels and palladium(ii)-catalyzed O-deallenylation bioorthogonal uncaging reactions.

The palladium-mediated uncaging reaction of allene substrates remains a promising yet often overlooked strategy in the realm of bioorthogonal chemistry. This method exhibits high kinetic rates, rivaling those of the widely employed allylic and propargylic protecting groups. In this study, we investigate into the mechanistic aspects of the C-O bond-cleavage deallenylation reaction, examining how chloride levels influence the kinetics when triggered by Pd(ii) complexes. Focusing on the deallenylation of 1,2-allenyl protected 4-methylumbelliferone promoted by Allyl2Pd2Cl2, our findings reveal that reaction rates are higher in environments with lower chloride concentrations, mirroring intracellular conditions, compared to elevated chloride concentrations typical of extracellular conditions. Through kinetic and spectroscopic experiments, combined with DFT calculations, we uncover a detailed mechanism that identifies AllylPd(H2O)2 as the predominant active species. These insights provide the basis for the design of π-allylpalladium catalysts suited for selective uncaging within specific cellular environments, potentially enhancing targeted therapeutic applications.