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Herein, we present a dark-green crystalline tetranuclear Cu(II) Schiff base complex {C1 = [Cu4L4](ClO4)4(DMF)4(H2O)} using a N,N,O donor ligand (HL), namely 2-(((2-hydroxypropyl)imino)methyl)-6-methoxyphenol. Spectro-photometrical investigation on the β-lactamase-like activity of this coordinately saturated system revealed its catalytic inefficiency towards hydrolysis of nitrocefin as a model substrate. This complex has attracted significant interest as a promising photo-catalyst owing to its narrow band gap (2.40 eV) as predicted from DFT calculations and its higher responsivity towards UV light. Therefore, C1 is effectively involved in the photocatalytic reduction of perchlorate to Cl− in the presence of a hole scavenger (H2O–MeOH) under prolonged UV irradiation and itself becomes photo-cleaved to yield a new dark-brown colored chlorobridged dinuclear crystalline complex C2 {[CuL(H2O)2Cl3]H2O}. Furthermore, C2 was deployed as a functional β-lactamase model and was found to show a remarkable catalytic proficiency towards the hydrolysis of nitrocefin in 70 : 30 (V/V) MeOH–H2O medium. This pro-catalyst C2 has been speculated to generate an aqua bridged active catalyst that plays a crucial factor in hydrolysis. This phenomenon was again experimentally established by potentiometric pH titration where C2 displays only one pKa value (7.11) in the basic pH range, indicating the deprotonation of the bridged water molecule. Based on several other kinetic studies, it may be postulated that the hydrolysis of nitrocefin is initiated by the nucleophilic attack of a bridging hydroxide, followed by very fast protonation of the intermediate to furnish the hydrolyzed product. It is noteworthy that the rate of nitrocefin hydrolysis is greatly inhibited in the presence of external chloride concentration. To the best of our knowledge, this is the first report on the photochemical behavior of such a tetranuclear copper(II) Schiff base complex. Our current interest is focused on inventing a potent β-lactamase inhibitory therapeutic as well as elucidating its mechanism through comprehensive chemical analysis. [ABSTRACT FROM AUTHOR]

In this work, the study of the new ligand 3,3′-bis[N,N-bis(pyridine-2-ylmethyl)aminomethyl]-2,2′-dihydroxybiphenyl (L) is reported, where a central 2,2′-biphenol (BPH) fluorophore was functionalized at 3,3′-positions with two dipicolylamine (DPA) side arms as receptor units. Following the synthesis and full chemical–physical characterization, the acid–base and Zn2+-coordination abilities of L were investigated through a combination of potentiometric, UV-Vis, fluorescence, NMR, XRD and DFT measurements. The optical properties of the ligand turned out to be strongly dependent on the pH, being straightforwardly associated with the protonation state of the BPH moiety, whereas its peculiar design allowed to form stable mono and dinuclear Zn2+ complexes. In the latter species, the presence of two Zn2+ ions coordinatively unsaturated and placed at close distance to each other, prompted us to test their usefulness as metallo-receptors for two environmental pollutants of great relevance, ibuprofen and ketoprofen. Potentiometric and fluorescence investigations evidenced that these important non-steroidal anti-inflammatory drugs (NSAIDs) are effectively coordinated by the metallo-receptors and, of relevance, both the stability and the fluorescence properties of the resulting ternary adducts are markedly affected by the different chemical architectures of the two substrates. This study aims at highlighting the promising perspectives arising from the use of polyamino phenolic ligands as chemosensors for H+/Zn2+ and other additional anionic targets in their metal-complexed forms. [ABSTRACT FROM AUTHOR]

Polymeric membrane ion-selective electrodes (ISEs) have been widely used in environmental monitoring. However, in complicated marine environments, marine biofouling usually becomes a sticky problem for these electrodes. Herein, for the first time, a novel maintenance-free antifouling potentiometric marine sensor based on a self-polishing coating (SPC) is proposed. The SPC is synthesized by using the seeded emulsion polymerization method based on the triisopropylsilyl methacrylate monomer as the regulator of the self-renewal rate. This coating can be simply modified onto the electrode surface by drop-casting. The silyl acrylate side groups of the obtained SPC on the sensor surface can be hydrolyzed in the marine alkaline medium. The shear movement of seawater driven by sea waves, wind, gravity, or vibration removes the leftover (fouled) brittle polymer backbone and thus the fouling marine microorganisms. As a proof-of-concept experiment, a polymeric membrane Ca2+-ISE is chosen as a model. Compared to the unmodified electrode, the SPC-coated Ca2+-ISE exhibits remarkable improved antifouling properties in terms of superior anti-adhesive abilities towards marine microorganisms, such as bacterial cells and algae and excellent long-term stability even in the presence of high levels of marine microorganisms. Since no additional manual maintenance is required for maintaining the antifouling abilities of the sensor, the proposed self-polishing sensor may lay an important foundation for construction of unattended long-term potentiometric monitoring systems in real marine environments. [ABSTRACT FROM AUTHOR]

Polymeric membrane ion-selective electrodes (ISEs) have been widely used in environmental monitoring. However, in complicated marine environments, marine biofouling usually becomes a sticky problem for these electrodes. Herein, for the first time, a novel maintenance-free antifouling potentiometric marine sensor based on a self-polishing coating (SPC) is proposed. The SPC is synthesized by using the seeded emulsion polymerization method based on the triisopropylsilyl methacrylate monomer as the regulator of the self-renewal rate. This coating can be simply modified onto the electrode surface by drop-casting. The silyl acrylate side groups of the obtained SPC on the sensor surface can be hydrolyzed in the marine alkaline medium. The shear movement of seawater driven by sea waves, wind, gravity, or vibration removes the leftover (fouled) brittle polymer backbone and thus the fouling marine microorganisms. As a proof-of-concept experiment, a polymeric membrane Ca2+-ISE is chosen as a model. Compared to the unmodified electrode, the SPC-coated Ca2+-ISE exhibits remarkable improved antifouling properties in terms of superior anti-adhesive abilities towards marine microorganisms, such as bacterial cells and algae and excellent long-term stability even in the presence of high levels of marine microorganisms. Since no additional manual maintenance is required for maintaining the antifouling abilities of the sensor, the proposed self-polishing sensor may lay an important foundation for construction of unattended long-term potentiometric monitoring systems in real marine environments. [ABSTRACT FROM AUTHOR]

Mobile phase pH is a critically important parameter in reversed-phase liquid chromatographic (RPLC) separations involving analytes that display acidic or basic properties in the pH range used for the mobile phase. The main problem in measuring mobile phase pH lies in the fact that RPLC mobile phases are typically aqueous–organic mixtures. In addition to experimental difficulties, the pH values refer to different aqueous–organic compositions that cannot be correctly compared. Given this situation, the unified pH (wabs pH, also termed as) based on the absolute chemical potential of the solvated proton has been proposed as a rigorous way of characterising mobile phase acidity that is fully inter-comparable between mobile phases of any composition. Here we report the wabs pH values of 78 reversed-phase liquid chromatography-mass spectrometry mobile phases that were carefully measured by potential differences in a symmetric cell with two glass electrode half-cells and almost ideal ionic liquid triethylamylammonium bis((trifluoromethyl)sulfonyl)imide [N2225][NTf2] salt bridge with multiple overlapping measurements. The system of altogether 300 Δ wabs pH values was anchored to the pH value of standard pH 7.00 aqueous buffer solution. The consistency standard deviation of the whole set of measurements was 0.09 pH units. In addition to the differential potentiometric reference method, simpler measurement methods that use double junction reference or double junction combined electrodes were tested and were found suitable for routine laboratories if high accuracy is not required. [ABSTRACT FROM AUTHOR]

In this article, we present the synthesis and characterization of new acyclic pyridine-containing polyaminocarboxylate ligands H4aPyta and H6aPyha, which differ in structural rigidity and the number of chelating groups. Their abilities to form complexes with Cu2+, Ga3+, Y3+, and Bi3+ cations, as well as the stability of the complexes, were evaluated by potentiometric titration method, radiolabeling with the corresponding radionuclides, in vitro studies, mass spectrometry, and HPLC. The structures of the resulting complexes were determined using NMR spectroscopy and DFT calculations. The results obtained made it possible to evaluate the influence of the structural features of the complexes on their stability. The developed chelators H4aPyta and H6aPyha were proved to be promising for further research in the field of radiopharmaceuticals. [ABSTRACT FROM AUTHOR]

Co(II) and Ni(II) complexes of two tri-pyridine-based ligands with two hydroxy and two amide exchangeable protons (TDTA) and with six amide exchangeable protons (TMTP) were investigated for application as paraCEST-based magnetic resonance imaging (MRI) contrast agents. The two hydroxy groups present in the TDTA ligand were found to be passive while the amide group was active towards the CEST process. In the case of the Co(II) and Ni(II) complexes of the TMTP ligand, all three coordinated amide groups participated in the exchange process, and excellent CEST signals were observed. The X-ray structure of the four complexes revealed the seven-coordinate geometry of Co(II) complexes and the six-coordinate geometry of Ni(II) complexes. The presence of amide protons and hydroxy protons in the complexes was detected by the NMR method. The stability of the complexes in solution at high temperatures, in different pH ranges and acidic conditions, in the presence of competing cations, and biologically relevant anions was investigated. Potentiometric titrations were carried out to determine the ligand's protonation constants and the complexes' thermodynamic stability constant at 25.0 °C and I = 0.15 mol L-1 NaClO4. ParaCEST studies of [Co(TMTP)]2+ and [Ni(TMTP)]2+ at variable pH and variable pulse power are highlighted. [ABSTRACT FROM AUTHOR]

Investigation of the fundamental coordination chemistry between U(VI) and simple organic ligands is important to understand the chemical behavior of U(VI) in the natural environment and separation processes. In this work, the complexation of U(VI) with a common carboxylic acid, benzoic acid, has been systematically investigated through potentiometry, spectrometry and DFT calculations. Three successive complexes (UO2L+, UO2L2 and UO2L3−, L = benzoate ion) between U(VI) and benzoic acid are successfully identified in aqueous solution and their corresponding thermodynamic parameters (stability constant, enthalpy and entropy) are determined. Notably, this is the first time that the previously missing 1 : 2 and 1 : 3 (U to L) complexes in aqueous solution and their complexation thermodynamics have been reported, which would aid in more accurate prediction of the chemical behavior of U(VI) in the presence of benzoic acid. Moreover, the structures of the complexes are elucidated using DFT calculations, which show that benzoic acid coordinates to U(VI) in a bidentate form in all the complexes. [ABSTRACT FROM AUTHOR]

Designing an excellent OER catalyst in an alkaline environment is severe yet essential for industrial H2 application under the electrochemical technique. This study has achieved multiple modifications on CoN nanowires, the classic OER catalyst, via a facile room-temperature NaBH4 spontaneous hydrolysis. This facile process simultaneously generates oxygen vacancies and robust BN species. It wraps hydrophilic BOx motifs on the OER response CoN nanowires, producing OER active Co–N–B species, increasing active numbers and guaranteeing structural stability. It suggests that a low NaBH4 concentration (0.1 mol L−1) treatment endows CoNNWAs/CC with excellent OER performance and robust structure, which can drive a current density of 50 mA cm−2 with only 325 mV overpotentials with more than 24 hours' durability. Even, the catalyst can drive 1000 mA cm−2 around 480 mV overpotential. This study allows a novel strategy for designing high-performance OER catalysts. [ABSTRACT FROM AUTHOR]

A novel and straightforward approach to accurately predict, through direct potentiometric measurements, the complexing properties and adsorption capacity of novel carbon-based hybrid scavengers toward particular metal ions is described. This innovative approach establishes a linear free-energy relationship (LFER) between the complexing properties of the free-complexing function in solution and the complexing retention capacity of the functionalized carbon-based hybrid material (complexing function supported). In particular, we report the first detailed study concerning the metal ion complexing properties, as well as the complexing mechanisms involved in covalently-bonded carbon-supported hyperbranched polyethyleneimines, towards a series of metal ions of environmental and technical interest, such as Mn2+, Cd2+, Hg2+, Pd2+ and Cr3+. The study based on adsorption isotherm measurements and potentiometric studies of non-bonded hyperbranched polyethyleneimines (HBPEIs) (free in solution) and carbon-supported HBPEI (hybrid material, C-PEI) revealed that bonded HBPEI molecules fully define and control the metal ion complexing abilities of C-PEI, while the carbon structure acts only as a solid support. These results corroborate the prevalence of a reliable linear free-energy relationship (LFER) between the retention capacities of the hybrid material (C-PEI) and the complexing properties of free HBPEI in solution, which supposes a novel approach to easily predict the metal ion complexing properties of carbon-based hybrid materials, through a simple potentiometric titration analysis of the free complexing ligand in solution. This approach has the potential to predict retention capacities of solid materials (actual or proposed) exhibiting surfaces functionalized with HPBEI. [ABSTRACT FROM AUTHOR]

Receptor L, composed of a tripropylenetetramine chain linking the 2 and 7 positions of an acridine unit via methylene bridges, behaves as a pentaprotic base in aqueous solution. The first four protonation steps occur on the tetra-amine chain, while the acridine nitrogen protonates only below pH 4. The penta-protonated receptor assumes a folded conformation, resulting in a cleft delimited by the aliphatic tetramine and acridine moieties, in which anions of appropriate size can be hosted. Potentiometric titrations reveal that F− forms the most stable complexes, although the stability constants of the Cl− and Br− adducts are unusually only slightly lower than those observed for F− complexes. A remarkable drop in stability is observed in the case of I− adducts. Oxo-anions, including H2PO4−, NO3− and SO42−, are not bound or weakly bound by the protonated receptor, despite the known ability of charged oxygens to form stable O−⋯HN+ salt bridges. This unexpected stability pattern is explained in the light of the X-ray crystal structures of H5LCl5·4H2O, H5LBr5·4H2O, H5L(NO3)5·3H2O and H5L(H2PO4)5·(H3PO4)2·4H2O complexes, coupled with MD simulations performed in the presence of explicit water molecules, which reveal that Cl− and, overall, Br− possess the optimal size to fit the receptor cleft, simultaneously forming strong salt bridging interactions with the ammonium groups and anion⋯π contacts with protonated acridine. I− and oxo-anions are too large to conveniently fit the cavity and are only partially enclosed in the receptor pocket, remaining exposed to solvent, with a lower entropic stabilization of their complexes. Although F− could be enclosed in the cavity, its smaller size favours the F−⋯HN+ salt bridging interaction from outside the receptor pocket. The fluorescence emission of the acridinium unit is quenched by anion binding. The quenching ability parallels the stability of the complexes and is related to the relevance of the anion⋯π contacts in the overall host–guest interaction. [ABSTRACT FROM AUTHOR]

Based on the pKa determination of cyclovirobuxine D (CVB-D) using the method of potentiometry, we predicted the ionization state of CVB-D at physiological pH. Thus, by taking advantage of the ionization state and consequent non-covalent interactions between protonated CVB-D and deprotonated polymerized bromothymol blue (poly-BTB) under physiological conditions, we developed a simple and reusable electrochemical sensor that contains a poly-BTB/SWNT-modified electrode for electro-inactive CVB-D detection in biological fluids using poly-BTB as both the recognition unit and the electrochemical probe. Upon being immersed in the solution of CVB-D, the poly BTB-based electrode shows a current decrease due to the interaction-driven binding of CVB-D on the electrode surface. The current decrease in the electrochemical sensor toward CVB-D concentration shows a linear relationship in the dynamic ranges of 0.01–1 μM and 1–50 μM with a detection limit of 1.65 nM based on 3σ. The sensor can be easily regenerated through the removal of the binding of CVB-D from the electrode surface by highly negatively charged heparin, and it presents high repeatability with an RSD of less than 4.0% for seven measurements. In animal experiments, the electrochemical sensor was selective and sensitive for CVB-D determination in plasma and liver homogenates. The electrochemical sensor is readily accessible, robust, and cost-effective and holds good promise for more applications in biological and clinical fields associated with CVB-D using less technically demanding and simple operating procedures. [ABSTRACT FROM AUTHOR]

The acidic structure in an iron-based ionic liquid (Fe-IL) is significantly affected by the valent variation and solvent effect during the catalytic reaction. However, the magnetic property of Fe-IL limits the utilization of commonly used characterization methods that require a magnetic field for the structural analysis of Fe-IL. Herein, a quantitative pyridine-IR spectrum method was developed by analyzing the slope of straight lines (Slope(X)) in IA(X) ~ n(Py) relationship graph (IA(X): integrated area of nPyH+ or nPy-L (cm-1); n(Py): the mole of added pyridine (mol)) to determine the structural forms of Brønsted and Lewis acid in Fe-IL, as well as the Lewis activity according to the Beer's law. Different Fe-IL systems, such as Fe-ILaq (from FeCl3.6H2O), Fe-ILnon-aq (from non-aqueous FeCl3) and Fe-ILnon-aq + HCl, were designed and synthesized with similar cationic and anionic structures, in which the Lewis acidity and Lewis activity are significantly influenced by Brønsted acidity. The results showed that the Brønsted acidity in Fe-ILnonaq is lower than that in Fe-ILaq, and Fe-ILnon-aq can be transferred into Fe-ILaq after protonation. The Slope(L) of FeCl4 - has the value of 0.21-0.28 in Fe-ILnon-aq and Fe-ILaq before protonation, and protonation could significantly decrease the value of Slope(L) and Lewis activity, which is mainly caused by the steric hindrance of FeCl4 - with the increased amount of the Brønsted acidic structure of Fe-Cl-HCl. In addition, the solvent effect of polyethylene glycol dimethyl ether (NHD), which is a commonly used organic solvent for the absorption of an acidic gas, on the acidic structure and Lewis activity of Fe-IL was also investigated. We found that relatively free HCl that is combined with the Fe-Cl bond in the Fe-ILaq/NHD complex can be predicted by analyzing the slope of IA(X) B n(Py), and the Lewis activity of FeCl4 - decreases with increasing volume ratio of NHD. It is confirmed by density functional theory (DFT) calculation that the decreased Lewis activity of Fe-IL caused by the protonation and solvent effect is mainly attributed to the decreased electron-withdrawing ability of FeCl4 - and the bond length of the Fe-Cl bond. Furthermore, DFT calculation and CV characterization further demonstrate the reliability of the developed quantitative pyridine-IR method by analyzing the slope of IA(X) B n(Py). [ABSTRACT FROM AUTHOR]

The shells of P. placenta are composed of foliated calcite laths packed as layered structures and have high mechanical properties and optical transparency. However, the biomineralization mechanism and the influence of the organic matrix on the formation of the foliated calcite laths in the shells of P. placenta are not known. The acid-soluble matrix (ASM) was extracted from the shells of P. placenta and characterized in detail. Sixteen proteins including calcium-binding and chitin-binding proteins were associated to shell formation via proteome analysis of ASM. The ASM was found to be enriched with Gly, Asp and Ser. By tracking the Ca2+ concentration in the solution in the presence of ASM by a potentiometric method, we find that the ASM has a strong effect to stabilize the amorphous calcium carbonate (ACC) precursor in solution with a nucleation time of about 7733 s and a retardation factor of about 2.3, while the concentration of the ASM was 0.3 μg mL−1. In particular, the ASM can inhibit the (secondary) nucleation of calcium carbonate for 10 and 24 hours on the shell surfaces of P. placenta and the glass substrate in the aqueous solution, respectively. An explosive secondary nucleation and quick crystal growth from 50 nm to 10 μm can be finished on the shell surfaces in one hour, in between 10 h and 11 h of reaction time, via a gas diffusion process. This indicates that the ASM has a very strong effect to stabilize ACC and inhibit nucleation. The formation of ACC in the solution and its transformation to calcite crystals on the substrates were tracked by dynamic light scattering, selected-area electron diffraction, infrared spectroscopy, scanning electron microscopy, and confocal laser scanning microscopy. It was found that the ASM was doped in the preliminary nanocrystals with a size of about 50–100 nm, which were formed on the shell surfaces via secondary nucleation, and was occluded into the calcite crystals without preferred adsorption on particular crystal planes. The calcite crystals formed on the shell surfaces became more and more rounded and lost {104} planes with increasing concentration of the ASM in the solution, indicating that the ASM can stabilize other planes instead of the thermodynamic {104} planes. The in vitro crystallization study in this work shows that ASM extracted from the shells of P. placenta has a strong effect on the biomineralization process of foliated calcite laths of P. placenta. [ABSTRACT FROM AUTHOR]

Paper-based microfluidic solution sampling is a viable option for potentiometric sensors to be used for the determination of analytes in samples with high solid-to-liquid ratios. Unfortunately, heavy metal sensitive electrodes cannot be easily integrated with paper-based solution sampling as heavy metals have strong physicochemical adsorption affinity towards paper substrates. In this work, paper substrates were modified with an ion-selective membrane (ISM) cocktail (used for the preparation of Pb2+-ion-selective electrodes (ISEs)) and coupled with model heavy metal Pb2+-ISEs. It was found that the super-Nernstian response of Pb2+-ISEs was eliminated when 10 to 50 mg ml−1 of the ISM cocktail was used for the modification of paper substrates. The modification of the paper substrates by Pb2+-ISM allowed the elimination of adsorption sites. In addition, it resulted in an improvement of sensor performance in terms of their detection limits to be similar to those for conditioned electrodes in standard beaker-based measurements. It is believed that the elimination of super-Nernstian response of the electrodes and improving the potentiometric responses and detection limits of ISEs were attributed to the compatibility improvement of the paper substrates and Pb2+-ISEs to the same type of ISM. [ABSTRACT FROM AUTHOR]

With the extensive usage of gadolinium-based contrast agents (GBCAs) in magnetic resonance imaging (MRI), gadolinium deposition has been observed in the brain, kidneys, liver, etc., and this is also closely related to the development of nephrogenic systemic fibrosis (NSF) in patients with renal dysfunction. Chelation, thereby promoting the elimination of deposited Gd(III), seems to be promising for alleviating these problems. Despite many ligands suitable for chelation therapy having been studied, the decorporation of transition metals (e.g. iron, copper, lead, etc.) and actinides (e.g. uranium, plutonium, etc.) has long been a primary concern, whereas the study of Gd(III) has been extremely limited. Due to their excellent metal binding abilities in vivo and therapeutic effects toward neurodegenerative diseases, bidentate hydroxypyridinone ligands are expected to be able to remove Gd(III) from the brain, kidneys, bones, and liver. Herein, the Gd(III) decorporation efficacy of a bidentate hydroxypyridinone ligand (Me-3,2-HOPO) has been evaluated. The complexation behavior between Me-3,2-HOPO and Gd(III) in solution and solid states was characterized with the assistance of potentiometric titration and X-ray diffraction techniques, respectively. Solution-based thermodynamic studies illustrate that the dominant species of complex between Gd(III) and Me-3,2-HOPO (HL) is GdL2+ (log β120 = 11.8 (3)) at pH 7.4. The structure of the Gd–Me-3,2-HOPO crystal obtained from a room temperature reaction reveals the formation of a Gd(III) dimer that is chelated by four ligands as a result of metal ion hydration and ligand complexation. Cellular Gd(III) removal assays illustrate that Me-3,2-HOPO could effectively reduce final amounts of gadolinium by 77.6% and 66.1% from rat renal proximal tubular epithelial (NRK-52E) cells and alpha mouse liver 12 (AML-12) cells, respectively. Our current results suggest the potential of bidentate HOPO ligands as an effective approach to treat patients suffering from Gd(III) toxicity. [ABSTRACT FROM AUTHOR]

Research shows that redox complementarity and synergism among the ingredients of heterogeneous catalysts can enhance the performance of the catalyst. In this research, a porous CuMoO4@Co3O4 nanosheet electrocatalyst is prepared, which is uniformly decorated on nickel foam (NF) by hydrothermal reactions and the impregnation method. The CuMoO4@Co3O4 is an efficient bifunctional catalyst with prominent electrocatalytic activity and durability. It requires overpotentials of only 54 and 251 mV to obtain current densities of 10 and 50 mA cm−2 for the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER) in 1.0 mol L−1 KOH, corresponding to Tafel slope values of 98.8 and 87.4 mV dec−1, respectively. Furthermore, the CuMoO4@Co3O4 shows excellent stability of 120 h chronopotentiometry at a current density of 100 mA cm−2 for the HER/OER. Notably, an alkaline electrolyzer (with CuMoO4@Co3O4 as the HER and OER electrodes) can deliver a current density of 10 mA cm−2 at a low voltage of 1.51 V. The catalytic activity of CuMoO4@Co3O4 can be attributed to the structure of the porous nanosheets and the synergistic effect between CuMoO4 and Co3O4. [ABSTRACT FROM AUTHOR]

The effect of leakage of the plasticizer from the ion-selective membrane into the ion-to-electron transducer of all-solid-state potentiometric sensors is considered for the first time. The plasticizer can be transferred to the transducer phase, either during ion-selective membrane application or later; in both cases, its presence can affect the performance of the sensors. Clearly, this effect is most pronounced if the transducer is dispersible in the plasticizer. Towards this end, it is shown that application as the transducer of plasticizer dispersable poly(3-hexylthiophene) compared to typically used (non-dispersible) poly(3-octylthiophene) results in sensors offering higher reproducibility of recorded potentials equal to ±1.4 mV and ±2.5 mV, respectively (within-day test, n = 6). Although poly(3-hexylthiophene) was also found in the membrane in the solvent dispersed, neutral emission active form, the analytical parameters of poly(3-hexylthiophene) based sensors including selectivity were improved or comparable to those of classical poly(3-octylthiophene) transducer sensors. [ABSTRACT FROM AUTHOR]

Potentiometric ion-selective sensors are attractive analytical tools as they have simple apparatus and facile use; however their analytical parameters cannot be easily tuned. To tailor the performance of these sensors, application of instrumental control – electrochemical trigger – is usually required. The proposed approach offers a self-powered instrument-free alternative. It benefits from a spontaneous redox process for the ion-selective electrode bypassed by a zinc wire and a resistor connected in series. Spontaneous oxidation of zinc induces charge flow and the accompanying reduction of the solid contact material of the sensor, magnitude of the current and finally the potential of the electrode can be controlled by adjusting the bypass resistance. The ultimate result of the proposed approach is qualitatively equivalent to recording sensor response under polarized electrode potentiometry conditions, however, it does not require application of a galvanostat. The change in the magnitude of the resistance connected can be used to tailor analytical parameters such as detection limit, linear response range, and selectivity of the sensor. As a model example, potassium-selective all-solid-state sensors with a polypyrrole solid contact were used. [ABSTRACT FROM AUTHOR]

Succinimidedioxime (H3sA) and glutarimidedioxime (H3gA) are two homologous compounds that represent one of the functional groups of amidoxime adsorbents for extracting uranium from seawater. These small imidedioximes can be conveniently prepared by the reactions of the relevant di-nitriles with hydroxylamine at elevated temperatures. The complexation of uranyl(VI) with H3sA is thermodynamicallyand structurally studied with potentiometric titration, IR spectroscopy, and computation in comparison with H3gA. With similar protonation properties, the interactions between uranyl(VI) and the two ligands are quite different in terms of coordination modes and strength. For complex species of the samestoichiometries formed at low pH, the stability constants of H3sA with uranyl complexes are significantlysmaller than those of H3 gA. Simulation in seawater environment shows that H3sA can compete with carbonate, but it is a weaker ligand than H3 gA for binding uranyl(VI). In near-neutral solutions bothligands form insoluble uranyl complexes but with different stoichiometries and coordination modes, which are identified through composition analyses and DFT calculations. Different from H3gA, in favor of the 1: 2 uranyl(VI) complex species, H3sA tends to form a cross-linked 2: 2 binuclear complex with uranyl. These results help understanding the interaction mechanism between the functional groups of amidoxime polymer materials and uranyl ions in seawater. [ABSTRACT FROM AUTHOR]

HPMPA is an acyclic nucleoside phosphonate analogue of AMP which displays antiviral properties. Therefore, its acid–base behavior as well as that of related compounds like PMEA, 9-[2-(phosphonomethoxy)ethyl]adenine, are for many reasons (e.g., binding to enzymes, coordination of metal ions) of general interest. HPMPA can accept two protons at the phosphonate and two more at the adenine residue, but not all acidity constants are accessible by potentiometric pH titrations. Therefore, we measured the chemical shifts of the nine non-exchangeable HPMPA protons by 1H NMR in D2O in dependence on pD in the range from 1 to 12. The corresponding results allowed identifying the protonation sites and, transferred to aqueous solution, they gave also the acidity constants. The most basic site is the phosphonate group followed by N1 of adenine. The pKa values increase from ca. −0.27 [–N7(H)+] via 1.27 [–PO(OH)2] and 4.23 [–N1(H)+] to 6.86 [–PO(OH)−]. In the fully protonated species charge repulsion exists between N1(H)+ and N7(H)+; therefore, the affinity of N7 for H+ is not correctly reflected by the measured acidity constant (ca. −0.27). Needed is the intrinsic micro acidity constant which reflects the H+ affinity of N7 under conditions where N1 is unprotonated; we abbreviate this species as +H·N7(HPMPA)N1. The corresponding microconstant is estimated to be pk N7–N1H·N7–N1 3.5; the minor species +H·N7(HPMPA)N1 occurs with an estimated formation degree between about 5 to 20%. The basicity of the adenine nitrogens decreases in the order N1 > N7 > N3. [ABSTRACT FROM AUTHOR]

We report the synthesis of the macrocyclic ligands 3,9-PC2AMH (2,2′-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,9-diyl)diacetamide) and 3,9-PC2AMtBu (2,2′-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,9-diyl)bis(N-tert-butyl)acetamide) which contain a pyclen platform functionalized with acetamide or tert-butylacetamide pendant arms at positions 3 and 9 of the macrocyclic unit. The corresponding Co(II) and Ni(II) complexes were prepared, isolated and characterised as potential paramagnetic chemical exchange saturation transfer (paraCEST) agents. The X-ray structures of the Ni(II) complexes reveal six-coordination of the ligands to the metal ion. The Co(II) complex with 3,9-PC2AMtBu shows a similar six-coordinate structure in the solid state, while the Co(II) complex with 3,9-PC2AMH contains a seven-coordinate metal ion, seventh coordination being completed by the presence of an inner-sphere water molecule. The structure of the Co(II) complexes was investigated using 1H NMR spectroscopy and computational methods. The complexes present a seven-coordinate structure in solution, as demonstrated by the analysis of the paramagnetic shifts using density functional theory. Ligand protonation constants and stability constants of the complexes with 3,9-PC2AMH were determined using potentiometric titrations (I = 0,15 M NaCl). The Co(II) complex was found to be more stable than the Ni(II) analogue (log KCoL = 14.46(5) and log KNiL = 13.15(3)). However, the Ni(II) and Co(II) complexes display similar rate constants characterizing the proton-assisted dissociation mechanism. The presence of highly shifted 1H NMR signals due to the amide protons in slow exchange with bulk water results in sizeable CEST signals, which are observed at +67 and +15 ppm for the Co(II) complex with 3,9-PC2AMH and +42 and +7 ppm for the Ni(II) analogue at 25 °C. [ABSTRACT FROM AUTHOR]

Neodymium (Nd), a technologically important metal ion, has emerged as a major contaminant in aquatic systems in recent years owing to its surge in electrical and electronic applications as a permanent magnet. The chelating molecules present in hydro- and biospheres could substantially enhance its absorption and lead to transportation and migration of Nd from the source. The mechanistic understanding of the Nd interaction with naturally relevant biomoieties present in flora and fauna is of primitive importance to estimate the toxicological effects of the metal ion. The present studies aimed at understanding the aquatic interaction of Nd with two biomoieties namely pyrazine-2-carboxylic acid (P2C) and pyrazine-2,3-dicarboxylic acid (P23C) by multiple experimental determinations and theoretical estimations. Potentiometry and spectrophotometry were employed to determine the aquatic speciation and thermodynamic stability of the complexes. Both techniques supported the formation of MLi (i = 1–4) complexes by Nd(III) with P2C and MLi (i = 1–3) complexes with P23C. The Nd–P23C complexes are more stable than the Nd–P2C complexes for ML formation, while the opposite trend is observed for the ML2 and ML3 complexes. Titration calorimetry was used to determine the enthalpies of complexation which was found to be exothermic and majorly favored by entropy contributions. The formation of the Nd(III)–P2C complexes is more exothermic than that of the respective Nd(III)–P23C complexes. Density functional theory was employed for the geometry optimization of the predicted complexes and for the estimation of the bond distances and partial charges on the coordinating atoms in the optimized geometries. Experimental insights provide crucial inputs at the macro (thermodynamic) level and theoretical calculations help in understanding the complexation process at the molecular level. [ABSTRACT FROM AUTHOR]

Rigid derivatives of the acyclic ligand PDTA4− (H4PDTA = propylenediamine-N,N,N′,N′-tetraacetic acid) were prepared by functionalization of a 1,3-diaminocyclobutyl spacer. The new ligands contain either four acetate groups attached to the central scaffold (H4L1) or incorporate pyridyl (H2L2) or propylamide (H2L3) units replacing two of the carboxylate groups. The ligand protonation constants and the stability constants of their Mn2+ complexes were determined using potentiometric and spectrophotometric titrations. The stability of the [Mn(L1)]2− complex was found to be significantly higher than that of the flexible [Mn(PDTA)]2− derivative (log KMnL = 10.78 and 10.01, respectively). A detailed study of the 1H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles and 17O NMR measurements evidence that the [Mn(L1)]2− and [Mn(L2)] complexes display a hydration equilibrium in solution involving a seven-coordinate species with an inner-sphere water molecule and a six-coordinate species that lacks a coordinated water molecule. As a result the 1H relaxivities of these complexes are somewhat lower than that of [Mn(EDTA)]2− and related systems. The introduction of propylamide groups in [Mn(L3)] shifts the hydration equilibrium to the seven-coordinate species, which results in a 1H relaxivity (r1p = 3.7 mM−1 s−1 at 22 MHz and 25 °C) exceeding that of [Mn(EDTA)]2− (r1p = 3.3 mM−1 s−1 at 22 MHz and 25 °C). The parameters that control the relaxivities in this family of complexes were determined by simultaneous fitting of the experimental 1H NMRD and 17O NMR data (transverse relaxation rates and chemical shifts), with the aid of computational studies performed at the DFT and CASSCF/NEVPT2 levels. These studies provide detailed insight of the parameters that control the efficiency of these relaxation agents at the molecular level. [ABSTRACT FROM AUTHOR]

Amide-based chelators DTPAm, EGTAm and ampam were synthesized to investigate which chelator most ideally coordinates [nat/203Pb]Pb2+ ions for potential radiopharmaceutical applications. ¹H NMR spectroscopy was used to study each metal--ligand complex in the solution state. The ¹H NMR spectrum of [Pb(DTPAm)]2+ revealed minimal isomerization and fluxional behaviour compared to [Pb(EGTAm)]2+ and [Pb(ampam)]2+, both of which showed fewer spectral changes indicative of less static behaviour. The solidstate coordination properties of each complex were also examined from single crystal structures that were studied by X-ray diffraction (XRD). In the solid-state, octadentate DTPAm coordinated Pb2+ to form an eight-coordinate hemidirected complex; octadentate EGTAm coordinated Pb2+ forming a ten-coordinate holodirected complex with a bidentate NO3- ion also coordinated to the metal centre; decadentate ampam completely encapsulated the Pb2+ ion to form a ten-coordinate holodirected complex with a C2 axis of symmetry. Potentiometric titrations were carried out to assess the thermodynamic stability of each metal--ligand complex. The pM values obtained for [Pb(DTPAm)]2+, [Pb(EGTAm)]2+ and [Pb(ampam)]2+ were 9.7, 7.2 and 10.2, respectively. The affinity of each chelator for Pb2+ ions was tested by [203Pb]Pb2+ radio-labeling studies to evaluate their prospects as chelators for [203/212Pb]Pb2+-based radiopharmaceuticals. DTPAm radiolabeled [203Pb]Pb2+ ions achieving molar activities as high as 3.5 MBq µmol-1 within 15 minutes, at 25 °C, whereas EGTAm and ampam produced lower molar activities of 0.25 MBq µmol-1 within 30 minutes, at 37 ºC. EGTAm and ampam were therefore deemed unsuitable for [203/212Pb]Pb2+-based radiopharmaceutical applications, while DTPAm warrants further studies. [ABSTRACT FROM AUTHOR]

A green route to oxidize terpenic alcohols (nerol and geraniol) with H2O2 over a solid catalyst was developed. The Dy-doped ZnWO4 catalyst was synthesized by coprecipitation and microwave-assisted hydrothermal heating, containing different dysprosium loads. All the catalysts were characterized through infrared spectroscopy, powder X-ray diffraction, surface area and porosimetry, transmission electronic microscopy image, and n-butylamine potentiometric titration analyses. The influence of main reaction parameters such as temperature, the stoichiometry of reactants, loads, and catalyst nature was assessed. ZnWO4 2.0 mol% Dy was the most active catalyst achieving the highest conversion (98%) and epoxide selectivity (78%) in nerol oxidation. The reaction scope was extended to other terpenic alcohols (i.e., geraniol, borneol, and α-terpineol). The highest activity of ZnWO4 2.0 mol% Dy was assigned to the lower crystallite size, higher surface area and pore volume, higher acidity strength and the greatest dysprosium load. [ABSTRACT FROM AUTHOR]

Preparation of a stable U(V) complex in an aqueous medium is a challenging task owing to its disproportionation nature (conversion into more stable U(VI) and U(IV) species) and sensitivity to atmospheric oxygen. The stable uranyl (UO22+)/dipicolinic acid (DPA) complex ([U(VI)O2(DPA)(OH)(H2O)]−) was formed at pH 10.5–12.0, which was confirmed by potentiometric and spectrophotometric titrations, and NMR, ESI-MS and EXAFS spectroscopy. The complex [U(VI)O2(DPA)(OH)(H2O)]− can be electrochemically reduced on the Pt electrode at −0.9 eV (vs. Ag/AgCl) to [U(V)O2(DPA)(OH)(H2O)]2− in aqueous medium under an anaerobic environment. According to cyclic voltammetric analysis, a pair of oxidation and reduction waves at E′0 = −0.592 V corresponds to the [U(VI)O2(DPA)(OH)(H2O)]−/[U(V)O2(DPA)(OH)(H2O)]2− redox couple and the formation of [U(V)O2(DPA)(OH)(H2O)]2− was confirmed by the electron stoichiometry (n = 0.97 ± 0.05) of the reduction reaction of [U(VI)O2(DPA)(OH)(H2O)]−. The pentavalent uranyl complex [U(V)O2(DPA)(OH)(H2O)]2− was further characterized via UV-vis-NIR absorption spectrophotometry and X-ray absorption (XANES and EXAFS) spectroscopy. The [U(V)O2(DPA)(OH)(H2O)]2− complex is stable at pH 10.5–12.0 in anaerobic water for a few days. DFT calculation shows the strong complexing ability of DPA stabilizing the unstable oxidation state U(V) in aqueous medium. [ABSTRACT FROM AUTHOR]

The stability constants of Mn2+ complexes with ligands containing a trans-1,2-cyclobutanediamine spacer functionalized with picolinate and/or carboxylate functions were determined using potentiometric titrations (25 °C, 0.1 M KCl). The stability constant of the complex with a hexadentate ligand containing four acetate groups (L14−, log KMnL = 10.26) is improved upon replacing one (L24−, log KMnL = 14.71) or two (L34−, log KMnL = 15.81) carboxylate groups with picolinates. The [Mn(L1)]2− complex contains a water molecule coordinated to the metal ion in aqueous solutions, as evidenced by 1H NMRD studies and 17O chemical shifts and transverse relaxation rates. The 1H relaxivities determined at 60 MHz (3.3 and 2.4 mM−1 s−1 at 25 and 37 °C, respectively) are comparable to those of monohydrated complexes such as [Mn(edta)]2−. The exchange rate of the inner-sphere water molecule (k 298ex = 248 × 106 s−1) is slightly lower than that of the edta4− analogue. DFT calculations (M11/def2-TZVP) suggest that the water exchange reaction follows a dissociatively activated mechanism, providing activation parameters in reasonably good agreement with the experimental data. DFT calculations also show that the 17O hyperfine coupling constant A/ is affected slightly by changes in the Mn–Owater distance and the orientation of the water molecule with respect to the Mn–O vector. [ABSTRACT FROM AUTHOR]

Worldwide, prostate cancer is considered to be one of the three most commonly occurring cancers amongst the male population. Clinically, early detection of diverse forms of cancer before they spread and become incurable plays an important role in treatment strategy. Therefore, the development of fast, accurate, sensitive, and low-cost analytical methodologies and techniques for the detection of cancer biomarkers is an attractive research area for scientists globally. Herein, a Schiff base ligand (A1) was prepared via the refluxing of 3-aminobenzoic acid with 1,2-phenylenediamine. After that, a nano Cu complex (N1) was synthesized by reacting A1 with copper chloride. The produced A1 and N1 were characterized using several techniques to determine their physicochemical properties. A density functional theory study was carried out to rationalize the experimental work and support the obtained results. Moreover, the nano Cu complex (N1) was used for the fabrication of a potentiometric membrane biosensor for the early detection of the prostate-specific antigen (PSA). The results reveal that the electrode displays a stable Nernstian response of 29.26 ± 0.87 mV per decade for PSA in a linear dynamic range of 5.0 pg mL−1–10.0 ng mL−1, in a pH range of 6.5–9.2, with a short response time of 25 ± 5 s. The lifetime was between 5–7 weeks under different storage conditions. The detection (LOD) and quantification (LOQ) limits were 0.098 and 0.297 pg mL−1, respectively. The presence of different interfering species on the potentiometric biosensor response against PSA was investigated. The sensing mechanism of N1 toward PSA and the applicability of the developed electrode for the screening and quantification of PSA in real serum samples were also studied. [ABSTRACT FROM AUTHOR]

A signal amplification strategy based on the horseradish peroxidase catalyzed polymerization of dopamine on a polymeric ion-selective membrane surface is proposed for the sensitive chronopotentiometric detection of an aptamer–target binding event. [ABSTRACT FROM AUTHOR]

The benzaldehyde acetalization reaction catalyzed by UiO-66, and its fluorinated analog UiO-66F, was carried out in a batch-type reactor at room temperature and atmospheric pressure, and the full kinetic study was performed using the Langmuir–Hinshelwood and Eley–Rideal models. It was established that the Eley–Rideal model is the one that best fits the experimental data. The catalytic results indicated that both MOFs enable carrying out the acetalization reaction. However, UiO-66F has the highest activity, which could be attributed to its high acidity. Both structures were characterized by N2 physisorption, thermogravimetry, powder X-ray diffraction, potentiometric titrations, and infrared spectroscopy. The highest acidity displayed by UiO-66F was explained by DFT studies and experimental studies. [ABSTRACT FROM AUTHOR]

The proton spin–spin relaxation times (T2) of ion-selective electrode membranes with differences in the polymerization degree of the incorporated poly(vinyl chloride) (PVC) polymers were investigated. T2 measurements were performed using Hahn-Echo, Solid-Echo and Carr–Purcell-Meiboom-Gill (CPMG) pulse sequences. Analyses of the T2 measurements by Hahn-Echo pulse sequences could realize the estimation of the homogeneity and compatibility for a series of ion-selective electrode membranes and reveal a relationship with the electromotive force (EMF) response in the low-concentration region of the Na+ ions. On the other hand, the normalized derivative spectra from T2 measurements by Solid-Echo and CPMG pulse sequences could approximately visualize the degree of plasticization for such potentiometric polymeric membranes. Moreover, differences in the polymerization degrees of the incorporated PVCs were scarcely found to affect the selectivity coefficients of the Na+-ISEs based on bis(12-crown-4). [ABSTRACT FROM AUTHOR]

Macrocyclic ligands obtained by N-functionalization of 1,4,7,10-tetraazacyclododecane (cyclen) have been widely studied due to their remarkable complexing properties toward a variety of transition metals and lanthanides. Despite a plethora of cyclen-based molecules described in the literature, ones bearing sulphur-containing functional groups have been almost ignored. Herein, a novel series of derivatives with hanging sulphide side-arms have been investigated: 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S), 1,4,7,tris[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7,tris[2-(methylsulfanyl)ethyl]-10-methylacetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), and 1,7,bis[2-(methylsulfanyl)ethyl]-4,10-diacetic-1,4,7,10-tetraazacyclododecane (DO2A2S). 1,4,7,10-Tetra-n-buthyl-1,4,7,10-tetraazacyclododecane (DOT-n-Bu) was included as well in this study for comparison purposes. These compounds have been synthesized and then experimentally and theoretically characterized. Their protonation constants (pKa) have been determined at 25 °C in 0.15 M aqueous NaNO3 and in 0.15 M aqueous tetramethylammonium chloride by potentiometric titrations and partly by UV-vis spectrophotometric measurements. Density functional theory (DFT) calculations have been performed for cyclen, DO4S, and DO3S to investigate the conformations, the thermodynamics of protonation equilibria and to rationalize the relevant electronic transitions. Stability constants of the Na+ complexes (log βNa) were computed for DO4S, DO3S, DO3SAm, and DO2A2S. For all compounds, the monodimensional 1H-NMR and bidimensional (COSY, NOESY, and HMQC) spectra have been obtained in D2O as a function of pD. Results indicate that sulphur-containing pendant arms induce partly unpredictable pKa, NMR, UV-Vis, and log βNa properties on the molecules, and that these properties significantly differ from those of the corresponding compounds without sulphur (e.g. cyclen and DOT-n-Bu). Furthermore, potentiometric and 1H NMR titrations were performed in order to evaluate the complexation ability of DO4S, DO3S and DO2A2S toward Cd2+ as a case-example of soft metal ions. The obtained complexes show remarkable stability and are stronger than those formed with cyclen and its most common derivative DOTA especially at acidic pH, thus demonstrating that these compounds can be promising chelators of soft metal ions. [ABSTRACT FROM AUTHOR]

A symmetrical squaraine-based ligand, sbdpa, bearing two dipicolylamine (dpa) units, was synthesized for the first time, using an environment friendly procedure, such as one-pot and solvent-free reaction. The sbdpa ligand was found to have a small blue-green emission, in aqueous solution, due to a photoinduced electron transfer (PET) mechanism. Metal complexes of sbdpa with a large panel of cations, Na+, K+, Ag+, Mg2+, Ca2+, Ba2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, and Pb2+, were prepared in aqueous buffered solution and screened, in search of a selective response for one of them. A turn-on fluorescence response was then found only for Hg2+, as a consequence of a chelation-enhanced fluorescence (CHEF) effect that disrupts the PET mechanism in sbdpa. Subsequently, the complexation behaviour of Hg2+ with sbdpa was investigated in aqueous solution by potentiometric titrations and other spectroscopic techniques. The acid–base reactions of the ligand were also studied by potentiometry, as well as by 1H-NMR and UV-vis titrations. For comparison purposes, the complexation of two other divalent cations, Cu2+ and Zn2+, was also assessed by potentiometry. Additionally, results are compared with dpa all along the study. Both mono- and dinuclear complexes of sbdpa were found for the three metal cations studied the mercury(II) complex having the largest thermodynamic stability. These findings support a stronger uptake of Hg2+ cation by sbdpa, possibly involving at least one oxygen atom from the squaraine moiety on its coordination sphere. [ABSTRACT FROM AUTHOR]

In this work, we have assessed the activity of various Keggin heteropolyacid (HPA) salts in a new one-pot synthesis route of valuable products, which were obtained from the oxidation of terpenic alcohols (i.e., aldehyde, epoxide, and diepoxide), using a green oxidant (i.e., hydrogen peroxide) at mild conditions (i.e., room temperature). Lacunar Keggin HPA sodium salts were the goal catalysts investigated in this reaction. Starting from the HPAs (H3PW12O40, H3PMo12O40, and H4SiW12O40), we synthesized lacunar sodium salts (Na7PW11O39, Na7PW11O39 and Na8SiW11O39) and a saturated salt (Na3PW12O40). All of them were investigated in oxidation reactions in a homogeneous phase with nerol as a model molecule. Na7PW11O39 was the most active and selective towards the oxidation products. All the catalysts were characterized by FT-IR, TG/DSC, BET, XRD, and SEM-EDS analyses and potentiometric titration. The main reaction parameters were assessed. Geraniol, α-terpineol, β-citronellol and borneol were also successfully oxidized. Special attention was dedicated to correlating the composition and properties of the catalysts with their activity. [ABSTRACT FROM AUTHOR]

Porous Co3O4 nanoplates constructed by loosely interconnected nanoparticles were synthesized via an L -lysine assisted hydrothermal treatment and subsequent thermal annealing. The hydrothermal conditions of reaction time, reaction temperature and reactant concentrations were investigated in detail. The results suggested that the high affinity of L -lysine could effectively control the redissolution–recrystallization and even restrict the dehydration–condensation reaction of the Co(OH)2 precursor, and thus played the key role for the preparation of the resulting porous Co3O4 nanoplates. Cyclic voltammetry and amperometric methods were used to evaluate the electrochemical performance of the resulting porous Co3O4 nanoplates toward glucose sensing in an alkaline medium. The sensors constructed by the porous Co3O4 nanoplates exhibited a fast response time (within 5 s), a detection limit of 2.7 μM, a sensitivity of 212.92 μA cm−2 mM−1, a linear range from 0.05 mM to 3.2 mM and good stability at a low applied potential (0.38 V vs. Ag/AgCl), suggesting its high performance towards non-enzymatic glucose sensing. [ABSTRACT FROM AUTHOR]

Commercial micro/mesoporous activated carbons were utilized as metal-free catalysts for the desulfurization of a model fuel, i.e. 4,6-dimethyldibenzothiophene (4,6-DMDBT) in hexadecane under ambient conditions. Both adsorption and catalytic oxidation were investigated as means of 4,6-DMDBT removal. The effect of chemical modification/oxidation of the carbon surface via treatment with two different acids (HNO3 or H2SO4) aiming to introduce additional functional groups was also investigated. The catalysts were characterized by FT-IR spectroscopy, N2 porosimetry, potentiometric titration, Boehm titration, and SEM-EDX, while adsorption and catalytic oxidation activity towards sufloxides and sulfones were assessed by GC-MS and UV-Vis analysis. The surface chemistry of the carbons, expressed by the density of the acidic functional groups, was found to be the most critical parameter with regard to adsorption or to catalytic oxidative performance. The surface modification of carbons by oxidation had a positive impact on the catalytic oxidation activity, leading to a 100% conversion of 4,6-DMDBT towards the corresponding sulfoxide and sulfone, compared to 67% with the parent non-oxidized carbon. Reusability tests showed that the oxidation activity of the carbons can be maintained for at least 5 cycles. [ABSTRACT FROM AUTHOR]

An electrochemical platform was proposed for highly sensitive and selective analysis of sialic acid based on molecularly imprinted polymers (MIPs), which were electropolymerized with the monomer molecules of 3-aminophenylboronic acid (ABA) on a carbon cloth (CC) electrode in the presence of template molecules. The fabricated sensor, named the PABA/CC-based MIP electrode, could be used for the detection of sialic acid because the reversible and covalent boronic acid–diol binding was sensitive to the electrochemical potential of the prepared sensor. The utilization of a CC film as the substrate could improve the sensitivity due to its good electrical conductivity and large surface area. Under the optimized conditions, a good relationship between the change in potential and the concentration of sialic acid was obtained in the range from 40 μM to 440 μM with a detection limit of 0.5 μM. The resulting MIP sensor also displayed good selectivity, reproducibility and stability. Moreover, this sensor was successfully applied for the evaluation of the sialic acid level in infant formulas. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis and characterization of the metal free low valent fluoroborylene [(Me-cAAC)2BF] (1) stabilized by cyclic (alkyl)(amino) carbene (cAAC). The fluoroborylene 1 is obtained by the reductive defluorination of Me-cAAC:BF3 with 2.0 equivalents of KC8 in the presence of 1.0 equivalent of Me-cAAC. Due to its highly electron rich nature, 1 underwent one-electron oxidation with 1.0 equivalent of lithium tetrakis(pentafluorophenyl)borate [LiB(C6F5)4] to form the radical cation [(Me-cAAC)2BF]Ṗ+[B(C6F5)4]− (2). DFT studies suggested that the lone pair of electrons is localized on the boron atom in 1, which explains its unprecedented reactivity. Both compounds 1 and 2 were characterized by X-ray crystallography. The radical cation 2 was studied by EPR spectroscopy. [ABSTRACT FROM AUTHOR]

Six different sensors were fabricated and compared for the potentiometric determination of a widely used serotonin receptor agonist zolmitriptan (ZT), which is mainly used for the treatment of acute migraine attacks. Owing to its five-membered lactone ring, ZT was found susceptible to alkaline hydrolysis. The composition of PVC-membrane was systematically optimized via comparing the responses of different membranes. Membranes 1 to 4 contained dioctyl sebacate (DOS) in addition to different ion exchangers, namely, sodium tetraphenylborate (sensor 1), sodium phosphotungstate (sensor 2), sodium phosphomolybdate (sensor 3), and ammonium reineckate (sensor 4). The third sensor demonstrated the best sensitivity with near-Nernstian slope and was selected for the next step. To assess the plasticizer effect, the relatively non-polar plasticizer DOS used in sensor 3 was compared to high dielectric constant plasticizer nitrophenyl octyl ether (NPOE) in sensor 5; it was observed that the latter possessed better sensitivity (LOQ = 6.66 × 10−6 mol L−1), slope (52.821 mV decade−1), and response time. The effect of ionophore on sensor performance was evaluated, where hydroxypropyl β-cyclodextrin was further incorporated as an ionophore (sensor 6), resulting in remarkably higher sensitivity (LOQ = 3.33 × 10−6 mol L−1), better near-Nernstian slope (59.915 mV decade−1), and faster response time. The pH and temperature effects as well as the selectivities of the ionophore-free membrane (sensor 5) and the ionophore-containing membrane (sensor 6) were compared to evaluate the effect of the ionophore on the sensor performance. The developed sensors (5 and 6) were found to be selective for ZT in the presence of different interfering ions as well as a ZT alkaline degradation product. The sensor performances were assessed as per IUPAC recommendations and used for the determination of ZT in the presence of its degradation product in the raw material, orodispersable tablets, and in spiked plasma samples. The stability of sensor response over a wide pH range (pH 2 to 8) enabled selective inline ZT release profile monitoring at different physiological pH values in the presence of its hydrolytic degradation product. [ABSTRACT FROM AUTHOR]

Potentiometric sensing of ions with ion-selective electrodes (ISEs) is a powerful technique for selective and sensitive measurement of ions in complex matrices. The application of ISEs is generally limited to laboratory settings, because most commercially available ISEs and reference electrodes are large, delicate, and expensive, and are not suitable for point-of-use or point-of-care measurements. This work utilizes cotton thread as a substrate for fabrication of robust and miniaturized ISEs that are suitable for point-of-care or point-of-use applications. Thread-based ISEs selective for Cl−, K+, Na+, and Ca2+ were developed. The cation-selective ISEs were fabricated by coating the thread with a surfactant-free conductive ink (made of carbon black) and then coating the tip of the conductive thread with the ion-selective membrane. The Cl− ISE was fabricated by coating the thread with an Ag/AgCl ink. These sensors exhibited slopes (of electrical potential vs. log concentration of target ion), close to the theoretically-expected values, over four orders of magnitude in concentrations of ions. Because thread is mechanically strong, the thread-based electrodes can be used in multiple-use applications as well as single-use applications. Multiple thread-based sensors can be easily bundled together to fabricate a customized sensor for multiplexed ion-sensing. These electrodes require volumes of sample as low as 200 μL. The application of thread-based ISEs is demonstrated in the analysis of ions in soil, food, and dietary supplements (Cl− in soil/water slurry, K+ and Na+ in coconut water, and Ca2+ in a calcium supplement), and in detection of physiological electrolytes (K+ and Na+ in blood serum and urine, with sufficient accuracy for clinical diagnostics). [ABSTRACT FROM AUTHOR]

Many siderophores incorporate as bidentate chelating subunits linear and more seldomly cyclic hydroxamate groups. In this work, a comparative study of the uranyl binding properties in aqueous solution of two monohydroxamic acids, the prototypical linear N-methylacetohydroxamic acid (NMAH) and the cyclic analog 1-hydroxypiperidine-2-one (PIPOH), has been carried out. The complex [UO2(PIPO)2(H2O)] crystallized from slightly acidic water solutions (pH ＜ 5), and its molecular structure was determined by X-ray diffraction. The uranyl speciation in the presence of both ligands has been thoroughly investigated in a 0.1 M KNO3 medium at 298.2 K by the combined use of four complementary techniques, i.e., potentiometry, spectrophotometry, Raman spectroscopy, and affinity capillary electrophoresis. Preorganization of the hydroxamate ligand for chelation by incorporation into a cyclic structure, as in PIPO−, results in an increase of nearly one order of magnitude in the formation constants of the uranyl complexes of 1 : 1 and 1 : 2 metal/ligand stoichiometries. [ABSTRACT FROM AUTHOR]

The coordination properties and photochemical response of two fluorescent ligands 2,5-bis{2-[bis(2-pyridylmethyl)aminomethyl]phenyl}[1,3,4]oxadiazole (L1) and 2,5-bis{2-[(1,4,7-triazacyclononane-1-yl)methyl]phenyl}[1,3,4]oxadiazole (L2) towards ZnII and CdII are reported. The ligands contain the 2,5-diphenyl[1,3,4]oxadiazole (PPD) fluorescent probe linked to two coordinating units, namely dipicolylamine (DPA) for L1 and 1,4,7-triazacyclononane (TACN) for L2, through a methylene spacer. Both ligands form mononuclear and dinuclear complexes with these metal ions in aqueous or hydro-alcoholic media. With regard to L1, only the mononuclear CdII complex is highly fluorescent at 368 nm, while the mononuclear ZnII and dinuclear CdII and ZnII complexes are not emissive. Ligand L2 forms an excimer emitting at 474 nm only in the presence of one equivalent of CdII, and potentiometric, spectrophotometric, spectrofluorimetric, and NMR studies and DFT calculations were performed to explain this peculiarity. The discrimination between CdII and ZnII is mainly due to the different coordination environments of the metal ions in the mononuclear complexes; namely CdII is coordinated by both the side arms of each ligand, while ZnII is bound only to one coordinating unit. [ABSTRACT FROM AUTHOR]

The recognition of quinolinic carboxylic acids as natural chelants and the recent observation of a high production of 8-hydroxyquinoline-2-carboxylic acid (8-HQA) in the gut of several Noctuid larvae (e.g. Spodoptera littoralis) has inspired the study of the chelation properties of 8-HQA towards Fe2+ and Fe3+. Here, we report a detailed characterization of the thermodynamic solution behaviour of Fe2+/8-HQA and Fe3+/8-HQA systems as a function of the pH value. The acid–base properties of 8-HQA and its binding ability towards Fe2+ and Fe3+ have been investigated over a wide range of pH values (2.0 ≤ pH ≤ 11.0) by ISE-H+ (glass electrode) potentiometric titrations in KCl(aq) at I = 0.2 mol dm−3 and at T = 298.15 K. For both oxidation states, various FeLqHr species are formed, with q = 1, 2 (and 3), and −2 ≤r≤ 1. The presence of the main FeLqHr species was confirmed by HESI-HRMS. ESR measurements have also been performed to get some extra information on the Fe3+ coordination, indicating a distorted octahedral symmetry around the metal center. Quantum mechanical calculations have been carried out in order to characterize the structural features of selected metal complexes. The complexing ability of 8-HQA is generally much higher for Fe3+ than Fe2+. Nevertheless, the sequestering ability of 8-HQA towards these two oxidation states of this metal ion, obtained by the calculation of several pL0.5 values, resulted in it being highly dependent on the pH value: (i) at relatively low pH values, it is higher for Fe3+ (pL0.5 = 6.3 at pH = 3.0) than for Fe2+ (pL0.5 = 3.1 at pH = 3.0); (ii) it is almost the same at pH = 8.1 (Fe3+: pL0.5 = 8.3; Fe2+: pL0.5 = 8.1); (iii) it is higher for Fe2+ at high pH values (pL0.5 = 8.9 for Fe2+ and pL0.5 = 6.2 for Fe3+ at pH = 10.0). The determination of the stability constants of the Fe2+/8-HQA and Fe3+/8-HQA complexes was also complemented by data obtained by the ligand-competition approach, using EDTA as a competing ligand over a wide range of cation and ligand concentrations and ratios. This also allowed a more thorough investigation of both the Fe2+/EDTA and Fe3+/EDTA systems, providing an accurate stability constant dataset for the Fep(EDTA)qHr species under the above-mentioned experimental conditions, which are commonly used in biological studies. [ABSTRACT FROM AUTHOR]

Nickel(ii) and zinc(ii) complexes of the 19–22 peptide fragments of rat amylin were studied by potentiometric, UV-vis, CD and NMR spectroscopic methods. The results revealed that in contrast with the corresponding copper(ii) complexes, the –SSNN– sequence (or 19–22 residues of rat amylin) cannot be the primary anchoring site for nickel(ii) and zinc(ii) ions. For nickel(ii) containing systems, an increased stability of the corresponding complexes was, however, measured and explained by an equilibrium between the common (NH2,3N−(peptide)) and (NH2,2N−(peptide),N−(asparagine)) coordination modes in a basic solution. From the comparison of the results obtained for the copper(ii), nickel(ii) and zinc(ii) ions, it can be unambiguously stated that the rat amylin have an outstanding affinity for copper(ii) binding. [ABSTRACT FROM AUTHOR]

Methods based on potentiometric measurement have been developed for immunoassays, but most exhibit low sensitivities and are unsuitable for early diagnosis of disease. Herein we design a new potentiometric immunosensing platform for the sensitive detection of carcinoma antigen 15-3 (CA 15-3) by coupling with enzymatic biocatalytic precipitation and a nanogold labeling technique. The sandwich-type immunoreaction is carried out on a monoclonal anti-CA 15-3 capture antibody-modified working electrode, using horseradish peroxidase (HRP) and polyclonal anti-CA 15-3 detection antibody-labeled gold nanoparticles. Upon the introduction of target CA 15-3, the carried HRP molecules with an immunocomplex catalyze the oxidation of 4-chloro-1-naphthol (4-CN) into the insoluble benzo-4-chlorohexadienone. The formed product coated on the surface of the modified electrode results in a change of the electrical potential. Under optimal conditions, the shift in the electrical potential relative to the background signal increases with the increasing target CA 15-3 concentration, and exhibits a good linear relationship within the dynamic range of 0.01–30 U mL−1 at a detection limit of 7.8 mU mL−1. Good precision and reproducibility, and high specificity were acquired for the analysis of 15 human serum specimens, giving well matched results with those obtained from a human CA 15-3 ELISA kit. [ABSTRACT FROM AUTHOR]

Herein a new potentiometric immunoassay for the point-of-care detection of enterovirus 71 (EV71) was developed by using a silver (Ag+) ion-selective electrode (ISE). Initially, the carboxylated dendrimer-doped AgCl nanospheres were synthesized by the reverse micelle method. Then the synthesized nanospheres were used to label a polyclonal mouse anti-EV71 antibody via a typical carbodiimide coupling method. The immunoreaction was executed on a monoclonal anti-EV71 antibody-coated microplate by using biofunctional AgCl nanospheres as the detection antibody. With a sandwich-type immunoassay format, the carried AgCl nanospheres could be dissolved in the presence of NH3·H2O, and the released silver ions were determined with an external silver ion-selective electrode. Under optimal conditions, the shift in the potential increased with the increase in the EV71 concentration, in a wide linear range of 0.3–300 ng mL−1, with a detection limit of 0.058 ng mL−1. Intra- and inter-assay relative standard deviations with identical batches were less than 4.15% and 6.15%, respectively. By validating the spiked serum samples, our system shows consistency with the enzyme-linked immunosorbent assay (ELISA) kit. [ABSTRACT FROM AUTHOR]

Newly developed modified and in situ modified carbon paste sensors were developed for the determination of chlorpromazine hydrochloride (CPZHC) in pharmaceutical formulations and biological fluids (urine and serum). The developed electrodes were characterized and optimized with respect to the main experimental parameters affecting the electrode performance including the composition, pH, temperature, response time, lifespan and interferences. The electrodes chemically modified with CPZ-TPB (electrode I) and CPZ-RN (electrode II) ion pairs exhibit a linear response over a concentration range of 1.0 × 10−6–1.0 × 10−2 mol L−1 with Nernstian slope values of 59.00 ± 1.75 and 55.50 ± 1.70 mV decade−1 at 25 °C over the pH range of 2–6 and 4–8, respectively. Meanwhile, in situ electrodes modified with NaTPB (electrode III), PTA (electrode IV) and RN (electrode V) ion pairing agents exhibited a linear response within the concentration ranges from 1.0 × 10−6 to 1.0 × 10−2, 1.0 × 10−6 to 1.0 × 10−2 and 1.0 × 10−7 to 1.0 × 10−2 mol L−1 with Nernstian slope values of 57.80 ± 0.37, 59.70 ± 0.88 and 59.57 ± 0.95 mV decade−1 at room temperature (25 °C) over the pH range of 2–6, 4–8 and 2–6, respectively. The dynamic response time of the modified electrodes was 7 s for a duration time of 53 and 35 days for electrodes (I) and (II), respectively. Meanwhile, the in situ modified electrodes had a fast dynamic response time of 11, 8 and 13 s for the duration time of 24, 42 and 58 days, respectively, for electrodes III, IV and V. The sensors were found to have good selectivity for CPZHC in the presence of some metal ions, sugars and glycine. Successfully, the developed sensors were used for the determination of CPZHC in neurazine tablets, urine and serum using calibration, potentiometric titration and standard addition methods. The obtained results were compared successfully with respect to those obtained using the official method. The proposed sensors showed significantly high selectivity, response time, accuracy, precision, limit of detection (LOD) and limit of quantification (LOQ) compared with other proposed methods, which confirmed the potential applicability of the developed method for the determination of CPZHC in real pharmaceutical tablets, serum and urine. [ABSTRACT FROM AUTHOR]