Cationic Forms Research Articles

Interaction of Three-Pole ions of carnosine and anserine with an anionic micelle of SDS: Molecular dynamics simulations

Molecular dynamics simulations of the interaction of an anionic micelle of 64 SDS molecules with carnosine and anserine (a substituted analogue) in their three-pole cationic form were performed. The formation of hydrogen bonds between the peptides and the micelle has been established. The H-bond lengths range from 0.184 to 0.198 nm. The H-binding sites in the peptides are the protonated amino group and the NH group in the protonated imidazole fragment, and in the case of carnosine, the uncharged NH group in the OCNH peptide fragment. The binding sites in the micelle are the anionic oxygen atoms located closer to the micelle surface. The ethereal oxygen atoms that bind the sulfo group to the surfactant hydrophobic tail do not show noticeable activity in the formation of hydrogen bonds. The average numbers and the lifetimes of the peptide - SDS and peptide - water H-bonds were determined. The differences in the orientations of equally charged three-pole ions of carnosine and anserine relative to the anionic micelle were discussed. For carnosine associated with the micelle, the ψ-dihedral angle in the alanine residue appears in two discrete zones due to the COO– group rotation. The two zones correspond to two peptide conformers differing in the about-turn of the CH2NH3+ fragment on the micelle surface. The steric correspondence of the peptides and micelle controls the process of H-bonding between them and leads to significant differences in the orientation of equally charged ions of the peptides on an anionic micelle.

Fragmentation of the PAH cations of Isoviolanthrene and Dicoronylene: A case made for interstellar cyclo[n]carbons as products of universal fragmentation processes

The photo-induced fragmentation pathways of the cationic forms of isoviolanthrene (C34H18) and dicoronylene (C48H20) are systematically studied with mass spectrometry employing an ion trap coupled with a laser system. The mass spectra of these structurally different species display similar fragmentation products, akin to previous work on three dibenzopyrene isomers, but also display some differences. The products formed in the largest yields are pure carbon clusters, which are likely in the form of ionized cyclo[n]carbons (n = 11–15). These findings are relevant to get a full picture of the molecular makeup of interstellar space, particularly in heavily irradiated regions where polycyclic aromatic hydrocarbon (PAH) molecules are omnipresent and subject to harsh irradiation and are broken down into smaller components. These interstellar species are expected to include the PAH derivatives observed here, but which are not identified in space yet.

IR-spectroscopic study of complex formation of nitrogen oxides (NO, N2O) with strong Lewis acid sites and the reactivity of adsorbed species in CO and CH4 oxidation

The formation of complexes and transformations of nitrogen oxides (NO, N2O) on strong Lewis acid sites of HZSM-5, H[Ga]ZSM-5, ZnO/HZSM-5 zeolites and dealuminated mordenites was investigated by diffuse-reflectance IR spectroscopy. Adsorbed N2O that is formed by disproportionation of NO is capable of oxidizing CO and CH4 molecules to CO2. The behaviour of strong Lewis acid sites in zeolites and cationic forms of zeolites in the NO disproportionation and CO or CH4 oxidation was comparatively studied.

Thermodynamic and Kinetic Features of Bi3+ Complexes with the Azamacrocycles H4BATA and H4DOTA

AbstractIn current research, we determined the stability constants and kinetic properties of Bi3+ complexes with the benzoazacrown ligand H4BATA along with the H4DOTA ligand. Correct determination of the stability constants is possible when equilibrium with the free forms of the cation is observed. Unlike potentiometric titration, it is possible to apply the free‐ion selective radiotracer extraction (FISRE) method with highly stable complexes at low pH values, where the true equilibrium with the free cation forms in the solution is achieved. FISRE clarified the stability constants of Bi3+ complexes with H4BATA towards higher values. According to the UV spectroscopy data, the H4BATA ligand binds Bi3+ at room temperature within a few minutes at pH 1. We also defined the acid‐assisted mechanism of complex dissociation, where monoprotonated and deprotonated forms of the complex were found to be inert. In summary, the H4BATA ligand is highly suitable for use as a component of bismuth‐based radiopharmaceuticals.

A theoretical study of the effect of exchange cations in surface of ZSM-5 lamellar zeolites

The electronic properties of various cationic forms of MFI type lamellar zeolites were studied using DFT calculations and compared with their bulk counterparts. In this study, Na+ and H+ cations were considered for the effect of charge deficit compensation on the surface of lamellar zeolites. The results show that lamellar zeolites in different cationic forms exhibit two distinct band gap widths, whose values are lower than those of their bulk counterparts and arise from the surface atoms. Furthermore, the results suggest that the Na+ cation behaves as a structure-directing agent on the surface, while H+ passivates the surface of the lamellar zeolites.

Study of thermal decomposition of hay-based activated biocarbons modified with nanolayers of ionic polyacrylamide

The thermal behaviour of hay-based activated carbons modified with adsorption nanolayers of ionic polymers were investigated. The anionic and cationic forms of polyacrylamides (PAM) with different contents of ionizable groups were applied. Using spectrophotometry, potentiometric titration, microelectrophoresis, DCS (Differential Centrifugal Sedimentation) and thermal analysis methods, the adsorption and electrokinetic, properties, as well as thermal stability of studied activated biocarbons—PAM systems were established. It was shown that PAM adsorbed amounts on the activated biocarbon surfaces were considerably higher for cationic polyacrylamides than for anionic ones. The conducted TG-DSC-FTIR/MS analysis in helium showed a significant influence of the synthesis conditions on the content of oxygen surface groups of activated biocarbons obtained in conventional or microwave muffle furnace. The measurements carried out in the oxidizing atmosphere for the polymer-modified samples showed similarity to the original materials and were characterized by three main stages of decomposition: dehydration, decomposition of surface functional groups and, at high temperatures—combustion process. The main decomposition products were CO2 and H2O.

Redox flow desalination for tetramethylammonium hydroxide removal and recovery from semiconductor wastewater

As part of humankind’s path towards more sustainable water technologies, redox flow desalination (RFD) has emerged as a promising technology due to its high energy efficiency and easy operation. So far, RFD research has focused on removing and recovering inorganic salts such as lithium-ions, heavy metal ions, or phosphate and nitrate ions. Thus, the potential of RFD in water desalination and resource recovery processes has not been fully demonstrated. Therefore, this study aimed to assess RFD for the valorization of tetramethylammonium hydroxide (TMAH) as value-added organic compounds from wastewater beyond inorganic elements, which is widely being used as an etching solvent, photoresist developer, and surfactant in semiconductor and display industries. By applying a low cell voltage (<1.2 V), a reversible redox reaction allowed a continuous removal of TMAH from the wastewater stream and a simultaneous recovery for reuse as a form of tetramethylammonium cation. The TMAH removal rate was approximately 4.3 mM/g/h with a 40% recovery ratio. With various operational conditions (i.e., TMAH concentration, cell voltage, and flow rate), our system exhibited a high potential for the valorization of TMAH with 60% reduction in capital cost compared to conventional desalination processes.

Imidazole-amino acids. Conformational switch under tautomer and pH change

Replacement of the main chain peptide bond by imidazole ring seems to be a promising tool for the peptide-based drug design, due to the specific prototropic tautomeric as well as amphoteric properties. In this study, we present that both tautomer and pH change can cause a conformational switch of the studied residues of alanine (1–4) and dehydroalanine (5–8) with the C-terminal peptide group replaced by imidazole. The DFT methods are applied and an environment of increasing polarity is simulated. The conformational maps (Ramachandram diagrams) are presented and the stability of possible conformations is discussed. The neutral forms, tautomers τ (1) and π (2), adapt the conformations αRτ (φ, ψ = − 75°, − 114°) and C7eq (φ, ψ = − 75°, 66°), respectively. Their torsion angles ψ differ by about 180°, which results in a considerable impact on the peptide chain conformation. The cation form (3) adapts both these conformations, whereas the anion analogue (4) prefers the conformations C5 (φ, ψ = − 165°, − 178°) and β2 (φ, ψ ~ − 165°, − 3°). Dehydroamino acid analogues, the tautomers τ (5) and π (6) as well as the anion form (8), have a strong tendency toward the conformations β2 (φ, ψ = − 179°, 0°) and C5 (φ, ψ = − 180°, 180°). The preferences of the protonated imidazolium form (7) depend on the environment. The imidazole ring, acting as a donor or acceptor of the hydrogen bonds created within the studied residues, has a profound effect on the type of conformation.

Periodic DFT computation of rotational barriers for linear molecules in zeolites: Validation via zero-point energies and isotopic heat difference values of adsorbed H2/D2

A climbing image nudged elastic band (cNEB) algorithm was applied on the basis of density functional theory (DFT) calculations of the rotational barriers of eight linear molecules (H2, N2, O2, CO, CO2, NO, N2O, C2H2) adsorbed in NaY and NaCaY periodic zeolite models at the MeII cation sites (the Na or Ca metal cation in the SII site) located near the 6R windows. A specific approach is applied for molecules with positive quadrupole (H2, C2H2) and small negative quadrupole (3O2) moments while applying cNEB. The obtained T-geometry relative to the cation is the most frequent case for H2 adsorption in cationic form sieves and metalorganic frameworks (MOFs). The computed barriers for the T- and other linear (L) orientations are in good correlation with the quadrupole moments taken from literature irrespective of the dipole values (CO, NO, N2O). In the case of NaY, the Al distribution per 6R sites is also discussed which allowed finding particular favorite adsorption sites. The calculated zero-point energies relative to the obtained rotational barriers regarding the H2 - D2 pair result in a qualitative agreement with the experimental isotopic difference in the H2/D2 adsorption heats in NaY which ultimately lead to the H2/D2 separation coefficient.

Crystal Engineering of Ionic Cocrystals Sustained by Azolium···Azole Heterosynthons.

Crystal engineering of multi-component molecular crystals, cocrystals, is a subject of growing interest, thanks in part to the potential utility of pharmaceutical cocrystals as drug substances with improved properties. Whereas molecular cocrystals (MCCs) are quite well studied from a design perspective, ionic cocrystals (ICCs) remain relatively underexplored despite there being several recently FDA-approved drug products based upon ICCs. Successful cocrystal design strategies typically depend on strong and directional noncovalent interactions between coformers, as exemplified by hydrogen bonds. Understanding of the hierarchy of such interactions is key to successful outcomes in cocrystal design. We herein address the crystal engineering of ICCs comprising azole functional groups, particularly imidazoles and triazoles, which are commonly encountered in biologically active molecules. Specifically, azoles were studied for their propensity to serve as coformers with strong organic (trifluoroacetic acid and p-toluenesulfonic acid) and inorganic (hydrochloric acid, hydrobromic acid and nitric acid) acids to gain insight into the hierarchy of NH+···N (azolium-azole) supramolecular heterosynthons. Accordingly, we combined data mining of the Cambridge Structural Database (CSD) with the structural characterization of 16 new ICCs (11 imidazoles, 4 triazoles, one imidazole-triazole). Analysis of the new ICCs and 66 relevant hits archived in the CSD revealed that supramolecular synthons between identical azole rings (A+B-A) are much more commonly encountered, 71, than supramolecular synthons between different azole rings (A+B-C), 11. The average NH+···N distance found in the new ICCs reported herein is 2.697(3) Å and binding energy calculations suggested that hydrogen bond strengths range from 31-46 kJ mol-1. The azolium-triazole ICC (A+B-C) was obtained via mechanochemistry and differed from the other ICCs studied as there was no NH+···N hydrogen bonding. That the CNC angles in imidazoles and 1,2,4-triazoles are sensitive to protonation, the cationic forms having larger (approximately 4.4 degrees) values than comparable neutral rings, was used as a parameter to distinguish between protonated and neutral azole rings. Our results indicate that ICCs based upon azolium-azole supramolecular heterosynthons are viable targets, which has implications for the development of new azole drug substances with improved properties.

Brain Effects of SC-Nanophytosomes on a Rotenone-Induced Rat Model of Parkinson's Disease-A Proof of Concept for a Mitochondria-Targeted Therapy.

Mitochondria are an attractive target to fight neurodegenerative diseases due to their important functions for cells and the particularly close relationship between the functional connectivity among brain regions and mitochondrial performance. This work presents a mitochondria-targeted therapy designed to modulate the functionality of the mitochondrial respiratory chain and lipidome, parameters that are affected in neurodegeneration, including in Parkinson’s disease (PD). This therapy is supported by SC-Nanophytosomes constructed with membrane polar lipids, from Codium tomentosum, and elderberry anthocyanin-enriched extract, from Sambucus nigra L. SC-Nanophytosomes are nanosized vesicles with a high negative surface charge that preserve their properties, including anthocyanins in the flavylium cation form, under conditions that mimic the gastrointestinal tract pH changes. SC-Nanophytosomes, 3 µM in phospholipid, and 2.5 mg/L of EAE-extract, delivered by drinking water to a rotenone-induced PD rat model, showed significant positive outcomes on disabling motor symptoms associated with the disease. Ex vivo assays were performed with two brain portions, one comprising the basal ganglia and cerebellum (BG-Cereb) and the other with the cerebral cortex (C-Cortex) regions. Results showed that rotenone-induced neurodegeneration increases the α-synuclein levels in the BG-Cereb portion and compromises mitochondrial respiratory chain functionality in both brain portions, well-evidenced by a 50% decrease in the respiratory control rate and up to 40% in complex I activity. Rotenone-induced PD phenotype is also associated with changes in superoxide dismutase and catalase activities that are dependent on the brain portion. Treatment with SC-Nanophytosomes reverted the α-synuclein levels and antioxidant enzymes activity to the values detected in control animals. Moreover, it mitigated mitochondrial dysfunction, with positive outcomes on the respiratory control rate, the activity of individual respiratory complexes, and the fatty acid profile of the membrane phospholipids. Therefore, SC-Nanophytosomes are a promising tool to support mitochondria-targeted therapy for neurodegenerative diseases.

GO/ionic surfactant inspired photophysical modulation of rhodamine B in Reline with or without additives

Photophysical behaviour of rhodamine B (RB) in deep eutectic solvents (DES, formed by quaternary ammonium salt and hydrogen bond donor (HBD) in a specific eutectic ratio) with or without graphene oxide (GO) or ionic surfactants, is less known. The nature of Reline (choline chloride (ChCl): urea (HBD), 1:2), a well-known DES, has been designed by adding glycerol or water as the second HBD for sustained movement of RB. Effects of GO, surfactant, or GO + surfactant, in controlling RB movement, at various sites (GO surface, surfactant micelle, DES surface, or background solvent), have been fluorometrically reported. The basic nature of Reline (pH = 10.38) causes modification of GO surface (deprotonated site) and nature of RB (cationic → zwitter ionic). Above Reline-inspired changes have been found to modify interactions of RB with GO and/or sodium dodecyl sulphate (SDS, an anionic surfactant) or cetyl trimethyl ammonium bromide (CTAB, a cationic surfactant). SDS (10 mMdm−3, < critical micelle concentration (CMC) in Reline) shows ∼ 2.6, 1.6, and 1.4 fold fluorescence intensity enhancement of RB (in water, pure Reline, and methanol, respectively). However, GO and/or CTAB shows quenching behaviour. Further, the fluorescence of RB shows weak dependence on changing the second HBD (water or glycerol). DES-controlled cationic vs zwitterionic form of RB is responsible for the interaction and sustained movement towards GO surface, micellar surface, or negatively charged ion-pair formation (with SDS monomers). Findings of the work have implications in searching potential fluorescent levels/sensors for photophysics, photobiology, or wider vehicle means for sustained drug delivery.

Driving Force behind the Amorphization in the Crystalline Cathode Structures during Alkali Metal Ion Intercalation for Electrochemical Energy Storage

Development of cathode structures suitable for Na-ion and K-ion batteries is still one of the major challenges on the way to the design of next-generation alkali metal-ion batteries. Although Li, Na and K belong to the same alkali metal group with a single charge in their cation form, intercalation of Na+ and K+ ions in electrodes is difficult since ionic radii of Na+ (0.98 Å) and K+ (1.38 Å) are larger than that of Li+ (0.69Å). Intercalation of alkali metal ions results in volumetric expansions in the electrode structure. Even modest expansions in brittle cathodes can cause particle fracturing in a larger crystalline-size scale. Intercalation of larger ions can cause structural collapse and amorphization induced by continuous accumulation of strains and distortions. However, the lack of understanding behind the amorphization mechanisms in the crystalline electrodes upon ion intercalation materials hinders the development of electrode structures suitable for these large ions.In the first part of the talk, we will first report the utilization of in situ digital image correlation and in-operando X-ray diffraction (XRD) techniques to probe dynamic changes in the amorphous phase of iron phosphate during potassium intercalation1. A new experimental approach allows to monitor dynamic physical and structural changes in the amorphous phase of the electrodes. This method offers new insights to study mechanics of ion intercalation in the amorphous nanostructures.In the second part of the talk, we will discuss the electrochemical and mechanical response of the iron phosphate cathodes upon Li, Na and K ion intercalation. Strain evolution during Li and Na intercalation results in more linear dependence on the state of charge / discharge. However, strains generated in the electrode shows nonlinear behavior during insertion / extraction of K ions. Strain rate calculations showed that K ion intercalation results in a progressive increase in the strain rate, whereas Li and Na intercalation induce nearly constant strain rates2. Our results shows that strain rates are critical factor for the amorphization of the crystalline structure, rather than the absolute value of electrochemical strains. These observations provide a fundamental insight into the impact of alkali ions on the redox chemistry and associated chemomechanical deformations.Acknowledgement: This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (Award number DE-SC0021251).

ADSORPTION STUDY OF ACETONE ON THE SORBENTS BASED ON MONTMORILLONITE

Corresponding cation forms of the montmorillonite samples taken from the Ag-Dere bentonite deposit were obtained by processing them with Co2+ and Ni2+ salts. The nature and amount of acid sites formed on the surfaces of the obtained samples were studied by adsorption of acetone using the derivatographic method. The critical diameter of the acetone molecule is d = 5.6A0 and pkα = -7.2. Analysis of derivatograms shows that the mass loss changes depending on the ionic radius, nature and temperature of the cation exchanges as follows: Co2+ mont&gt; Ni2+ mont&gt; natural mont. Based on the conducted study it was estableshed that there are weak, medium and strong electron-acceptor centers on the surface of the sorbent which differ energetically. The endothermic effect observed on the DTA curve at a temperature range of 219.3–566.30C characterizes the physical adsorption of an acetone molecule on the surface of a montmorillonite sample. The effects observed at 706.9 and 775.70C characterize the strong acid sites. The amount of electron-acceptor centers formed on the surface of monmorillonite changes depending on the charge of cation exchangers. The number of electron-acceptor centers formed on the surface of Co2+ bentonite is higher than in other samples. The amount (a.mmol.g) and desorption energy (E, kDc, mol-1) of acetone molecule desorbed from the active sites in different temperature ranges were calculated. It was determined that the most capable of adsorbing acetone molecules is Co2+-montimorillonite, which can be used as a sorbent to prevent envoiremental pollution with acetone. Corresponding cation forms of the montmorillonite samples taken from the Ag-Dere bentonite deposit were prepared by processing with Co2+ and Ni2+ salts. The nature and amount of acid sites formed on the surfaces of the obtained samples were studied by adsorption of acetone using the derivatographic method. Based on the conducted study it was estableshed that there are weak, medium, strong electron-acceptor centers on the surface of the sorbent which differ energetically. The amount (a.mmol.\g) and desorption energy (E, kDc, mol-1) of acetone molecule desorbed from the active sites in different temperature ranges were calculated. As a result of the research, it was found that the most capable of adsorbing acetone molecules is Co2+-form of montimorillonite, which can be used as a sorbent to prevent envoiremental pollution with acetone

Spectral Properties Echoing the Tautomerism of Milrinone and Its Application to Fe3+ Ion Sensing and Protein Staining.

Knowledge on the spectral properties of the tautomers of milrinone (MLR) in solvents and solid-state, as well as under light conditions is of critical importance from both theoretical and practical points of view. Herein, we investigated the spectral properties of MLR in different conditions using UV-Vis and fluorescence spectroscopies. The experimental results demonstrated that MLR can undergo the tautomerization reaction induced by solvent polarity, light and pH, eliciting four tautomeric structures (enol, keto, anion, and cation forms). The interesting multi-functional groups in MLR enable it to coordinate with metal ions or to recognize gust molecules by H-bonding. In the use of MLR as an excited-state intermolecular proton transfer (inter-ESPT) fluorescent probe, a highly sensitive and selective analysis of Fe3+ was developed, which offered a sensitive detection of Fe3+ with the detection limit of 3.5 nM. More importantly, MLR exhibited the ability of anchoring proteins and led to the recognition-driven turn-on inter-ESPT process, highlighting the potential for the probe to image proteins in electrophoresis gels. The spectral experimental results revealed the possible degradation mechanism, so that we can better understand the side effects of oral preparations. The use of the available drug as an inter-ESPT fluorescent probe is simple and accurate, providing a good method for Fe3+ ion sensing and protein staining.

Proton Storage in Metallic H1.75MoO3 Nanobelts through the Grotthuss Mechanism.

The proton, as the cationic form of the lightest element-H, is regarded as most ideal charge carrier in "rocking chair" batteries. However, current research on proton batteries is still at its infancy, and they usually deliver low capacity and suffer from severe acidic corrosion. Herein, electrochemically activated metallic H1.75MoO3 nanobelts are developed as a stable electrode for proton storage. The electrochemically pre-intercalated protons not only bond directly with the terminal O3 site via strong O-H bonds but also interact with the oxygens within the adjacent layers through hydrogen bonding, forming a hydrogen-bonding network in H1.75MoO3 nanobelts and enabling a diffusion-free Grotthuss mechanism as a result of its ultralow activation energy of ∼0.02 eV. To the best of our knowledge, this is the first reported inorganic electrode exhibiting Grotthuss mechanism-based proton storage. Additionally, the proton intercalation into MoO3 with formation of H1.75MoO3 induces strong Jahn-Teller electron-phonon coupling, rendering a metallic state. As a consequence, the H1.75MoO3 shows an outstanding fast charging performance and maintains a capacity of 111 mAh/g at 2500 C, largely outperforming the state-of-art battery electrodes. More importantly, a symmetric proton ion full cell based on H1.75MoO3 was assembled and delivered an energy density of 14.7 Wh/kg at an ultrahigh power density of 12.7 kW/kg, which outperforms those of fast charging supercapacitors and lead-acid batteries.

Sorption-Assisted Ultrafiltration Hybrid Method for Treatment of the Radioactive Aqueous Solutions

The paper presents results of studies on the possibility of using the ultrafiltration method supported by sorption on low-cost, easily accessible aluminosilicates to purify water contaminated with radionuclides. An aqueous solution contaminated with radionuclides in the form of cations at different oxidation states—Cs(I)-137, Co(II)-60 and Am(III)-241—as well as pertechnetate anions—TcO4−-99m—was treated by the proposed hybrid method. In the presented work, the influence of the important process parameters (i.e., pH, sorbent dosage, temperature and feed flow rate) on the removal efficiency of radionuclides was studied. The obtained results showed that hazardous impurities, both in the form of cations and anions, may be effectively removed from water by the application of sorption-assisted UF (SAUF) using the clay-salt slimes as a sorbent. As a final stage of the work, we treated the simulated liquid radioactive waste using the SAUF method, also showing satisfactory results in its purification efficiency.

A multifunctional fluorescent probe for dual-color visualization of intracellular mitochondria and lipid droplets and monitoring of SO2 in vivo

Mitochondria and lipid droplets (LDs) are organelles involved in intracellular lipid and energy metabolism, and their complicated interplays are critical for maintaining cellular homeostasis. However, the fluorescent probes capable of simultaneously and discriminatively visualizing mitochondria and LDs are severely insufficient, which greatly limits the investigation of the interaction between two organelles in cells. In addition, abnormal SO2 levels can have harmful effects on living organisms. Monitoring the changes of SO2 levels in vivo is of great significance for biological and medical research. In this work, a SO2-dependent strategy was proposed for the first time to construct the new functional fluorescence conversion probe MLD-SO2 for two-color visualization of mitochondria and LDs. Under normal physiological conditions, the cationic form enabled the probe to selectively target the mitochondria and emit red fluorescence. In addition, based on SO2-driven nucleophilic addition reaction, the probe MLD-SO2 was converted to the neutral lipophilic structure in the presence of SO2, which targeted to LDs and displayed a strong blue emission. Importantly, mitochondria and LDs could be visualized simultaneously in the red and blue emission channels under the appropriate amount of SO2 exposure. Furthermore, the probe MLD-SO2 has been successfully employed to monitor the SO2 changes in zebrafish and mung bean sprouts. The remarkable imaging performances render the novel probe MLD-SO2 as a powerful tool for deciphering the interactions between mitochondrial and LDs and monitoring SO2 in different organisms.

Insight into response of ion-exchanger-based electrodes sensitive to highly lipophilic physiologically active amines

The concentration profiles change of the cationic form of verapamil in the sample solution and its molecular form in the membrane in the process of sequential twofold dilution at pH = 6. Dashed lines designate the concentration of verapamil without taking into account the processes of extraction and re-extraction of its molecular form. • An insight on the nature of a verapamil-sensing electrode response is outlined. • Protolytic equilibrium is not the only factor that impairs the electrode response. • Partition of the molecular form of verapamil into the membrane should be avoided. • The partition constant can be estimated from the potentiometric data. • Dynamic diffusion model allows quantitative predicting the electrode response. The influence of electrode conditioning algorithms, as well as the composition of the internal reference solution and measurement conditions on the analytical characteristics of an electrode reversible to cations of highly hydrophobic physiologically active amines, was studied in detail for the first time using the example of a verapamil-sensitive electrode with a polyvinyl chloride membrane containing tetrakis-(4-chlorophenyl) borate as a cation exchanger and plasticized with ortho -nitrophenyloctyl ether. It has been shown that to ensure the Nernstian slope of the electrode response, a low detection limit, and prevent the potential drift, the most important condition is to exclude the extraction of the amine molecular form from both the internal and the test solution into the membrane phase during measurements. The experimental data obtained are well described in terms of the dynamic diffusion model of the boundary potential and make it possible to formulate general principles for working with electrodes sensitive to ions of highly lipophilic physiologically active amines.

Synthesis and characterization of kaolinite-based granular adsorbents for the removal of Cu(II), Cd(II), Co(II), Zn(II), and Cr(VI) from contaminated water

The object of this study is granular adsorbents based on kaolinite and zero-valent iron. The ceramic mass for their preparation contained polyvinyl alcohol as a powder-forming additive. It was established that its addition in quantities of 1.8–3.3 % practically does not change the porosity of the granules but increases their strength. X-ray phase and chemical analyzes confirmed the presence of a layer of zero-valent iron on the surface of the granules. The structural and sorption characteristics of sorption materials have been studied and the calculations of the main parameters of their porous structure were carried out. It is shown that when modifying granules with zero-valent iron, there is a decrease in the specific surface area and micropores volume for samples without a powder-forming additive by almost 2 times compared to the original granules. Moreover, these values almost do not change for samples obtained with the addition of polyvinyl alcohol. It was found that the application of the reaction layer to the granules leads to a significant increase in their sorption capacity with respect to heavy metal ions Cu(II), Cd(II), Co(II), Zn(II), and Cr(VI). It has been shown that the resulting adsorbents can be used for wastewater treatment containing a mixture of these toxicants. It was found that the values of maximum sorption on modified samples are 10–20 times higher than those for the original granules. A feature of the obtained adsorbents is the ability to simultaneously remove metal ions, both in the form of cations and anions. A significant increase in the sorption values of Cr(VI) anionic forms, which are difficult to remove from water by natural ion exchangers, has been established. It has been shown that granules based on kaolinite and zero-valent iron are effective adsorbents for water purification from heavy metal ions. The resulting materials can be used for wastewater treatment of electroplating industries and hydrometallurgical industry