Complexation Constants Research Articles

Effects on the complexation of heavy metals onto biochar-derived WEOM extracted from low-temperature pyrolysis

Biochar-derived water-extractable organic matter (WEOM) was obtained under low-temperature pyrolysis (300 °C) using corncob as raw material. WEOM may affect the mobility and bioavailability of soil heavy metals (HMs) through complexation when biochar was used for soil HM remediation. Herein, the characteristics of complexation between HMs (Cr(III) and Cu(II)) and biochar-derived WEOM were investigated by using spectroscopic techniques in conjunction with parallel factor (PARAFAC) analysis and two-dimensional correlation spectroscopy (2D–COS). Six components were identified by PARAFAC modeling, in which protein-, fulvic- and humic-like components accounted for 48.86%, 25.63% and 25.51%, respectively. A nonlinear model was employed to determine the conditional stability constant (KM) and total ligand concentration (CL) of WEOM-HM complexes. The log KM values were in the range of 4.02–5.04 for WEOM-Cr(III) and 4.04–6.58 for WEOM-Cu(II). The 2D–COS in conjunction with log-transformed synchronous fluorescence spectroscopy (SFS) suggested that WEOM components were preferentially complexed with HMs in the following order: 433/270, 433/335, 496/270, 496/335, 370/335, 433/402, 496/402, 335/290, 402/290 for Cr(III), and 290/280, 390/280, 433/280, 496/280, 433/335, 496/335, 390/335, 433/420, 496/402, 335/290, 316/290 for Cu(II). The results of 2D–FTIR–COS suggested a preferential bonding of Cr(III) to the C–N group of alkyl, and Cu(II) to the CO group of alcohols, ethers and esters. Meanwhile, the CO group of ethers and the CN group of alkyl indicated preferential susceptibilities for the addition of Cr(III) and Cu(II) at different concentrations. In addition, protein-like components had remarkably higher total ligand concentration (CL) than fulvic- or humic-like components.

Tripodal scaffolds with three appended imidazole thiones for Cu(I) chelation and protection from Cu-mediated oxidative stress

Imidazole thiones appear as interesting building blocks for Cu(I) chelation and protection against Cu-mediated oxidative stress. Therefore, a series of tripodal molecules derived from nitrilotriacetic acid appended with three imidazole thiones belonging either to histamine-like or histidine-like moieties were synthesized. These tripods demonstrate intermediate affinity between that previously measured for tripodal analogues bearing three thiol moieties such as cysteine and those grafted with three thioethers, like methionines, consistently with the thione group in the imidazole thione moiety existing as a tautomer between a thiol and a thione. The two non-alkylated tripods derived from thioimidazole, TH and TH* demonstrated three orders of magnitude larger affinity for Cu(I) (logKpH 7.4 = 14.3) than their analogues derived from N,N′-dialkylated thioimidazole TMe and TEt (logKpH 7.4 = 11–11.6). Their efficiency to inhibit Cu-mediated oxidative stress is demonstrated by several assays involving ascorbate consumption or biomolecule damages and correlates with their ability to chelate Cu(I), related to their conditional complexation constants at pH 7.4. The two non-alkylated tripods derived from thioimidazole, TH and TH* are significantly more powerful in reducing Cu-mediated oxidative stress than their analogues derived from N,N′-dialkylated thioimidazole TMe and TEt.

NMR Indirect Spin–Spin Coupling Constants in a Modern Quasi-Relativistic Density Functional Framework

A quasi-relativistic implementation of NMR indirect spin-spin coupling constants is presented. The exact two-component (X2C) Hamiltonian and its diagonal local approximation to the unitary decoupling transformation (DLU) are utilized together with the (modified) screened nuclear spin-orbit approach. In a restricted kinetic balance, the finite nucleus model is available for both the scalar and vector potentials. The implementation supports density functionals up to the fourth rung of Jacob's ladder, i.e., (range-separated) hybrid and local hybrid functionals based on a seminumerical ansatz. We assess the quality of our quasi-relativistic X2C approach by comparison with "fully" relativistic four-component results for small main-group molecules and alkynyl compounds. The mean absolute error introduced by the DLU scheme is less than 0.05 × 1019 T J-2 of the reduced coupling constant for the small main-group molecules and 0.5 Hz for the alkynyl compounds. Thus, the error is significantly smaller than finite nucleus size effects for heavy elements. The basis set convergence and the impact of different density functional approximations are further studied. We propose a simple scheme to develop segmented-contracted relativistic all-electron basis sets for NMR spin-spin couplings. Our implementation allows us to perform calculations of extended molecules with reasonable computational effort, which is illustrated for the 1J(119Sn, 31P) coupling constant of a low-valent tin phosphinidenide complex. The corresponding results are in good agreement with the experimental findings.

Impact of the encapsulated salt characteristics on its release from multiple W/O/W emulsions

AbstractW/O/W emulsions based on Miglyol oil and stabilized by polyglycerol polyricinoleate and sodium caseinate were prepared with similar characteristics in terms of internal droplet diameter, oil globule diameter, internal aqueous fraction and fat globules fraction. The emulsions differ only by the nature of the encapsulated salt in the inner aqueous droplets. The release of each encapsulated salt from the internal to the external aqueous phase was followed during 30 days at 25°C, showing for all cases that the double structure was preserved with time and the release increased during storage, mainly according to diffusion/permeation mechanism and resulting in a competition between the chelation and the hydration enthalpy of the salt. Double emulsions encapsulating different Magnesium salts have shown that the release depends strongly on the anion via its magnesium chelation and its hydration enthalpy. Indeed, as the complexation constant of Mg2+ with its counterion increases, the leakage decreases. On the other hand, as the hydration enthalpy of Mg2+ counterion decreases, the leakage decreases too. Likewise, double emulsions encapsulating different chloride salts have shown that the release depends also on the cation via its hydration enthalpy and its chelation with caseinate affecting accordingly the stiffening of the globule/water interface, more pronounced for bivalent than for monovalent cations. It was thus directly highlighted that the release from W/O/W emulsions was well controlled by the characteristics of the salt, and anion and cation diffuse accompanied at a rate ensuring the electroneutrality of the diffusive species. These results are very useful not only in term of fundamental understanding but also on application level, especially for food supplementation such as of dairy product.Practical applicationsThe search for an innovative functional effect can lead to food supplementation with bioactive substances which can be either molecules or living bioactive cells. However, the direct addition of these substances to food can induce chemical degradation, aggregation of proteins and generate an unpleasant taste. These drawbacks can be avoided or at least reduced by encapsulation. Despite their thermodynamic instability, W/O/W emulsions are promising systems for encapsulation of hydrophilic species in their internal aqueous phase and hence find applications among others in food for taste masking or supplementation. The release of the encapsulated species to the external aqueous phase should be controlled, depending on the desired application. The release depends also on the characteristics of the encapsulated salt. A better understanding of its impact on the stability of the double emulsion will allow targeting formulation of stable emulsions and hence contributing to their better industrial development.

Novel dioxidomolybdenum complexes containing ONO chelators: Synthesis, physicochemical properties, crystal structures, Hirshfeld surface analysis, DNA binding/cleavage studies, docking, and in vitro cytotoxicity

AbstractA series of dioxidomolybdenum (VI) complexes, [MoO2(ESB)H2O]·DMF (1), [MoO2(ESB)MeOH] (2), and [MoO2(ESB)H2O]·EtOH (3), containing 3‐ethoxysalicylaldehyde benzoylhydrazone have been synthesized and analysed using various spectral and analytical techniques such as elemental analyses, IR spectra, UV–Vis absorption spectra, X‐ray crystallography, and Hirshfeld surface analysis. Based on the elemental and spectral analysis, six‐coordinate geometry was assigned for these complexes wherein the hydrazone ligand binds to the metal centre in its dianionic enolate form through ONO donor set. Distorted octahedral geometry of complexes 1 and 2 was evidenced from their crystal structures, which is typical for many cis‐dioxido complexes of MoVI. The proligand and the new complexes were examined for their DNA binding, DNA cleavage, and cytotoxic properties. The DNA binding efficiency of the compounds in terms of their binding constants (Kb) of the metal complexes was observed to be 1.3727 × 105 M−1, 3.0194 × 104 M−1, and 1.13206 × 104 M−1 for [MoO2(ESB)H2O]·DMF (1), [MoO2(ESB)MeOH] (2), and [MoO2(ESB)H2O]·EtOH (3), respectively, indicating that these complexes strongly bind to DNA. To determine the binding interactions of the complexes with DNA and protein (BSA), molecular docking studies were carried out. Gel electrophoresis study reveals the fact that the complexes cleaved supercoiled pUC‐18 DNA to nicked form (Form II) in the presence and absence of H2O2. The complexes showed significantly high cytotoxicity against MCF‐7 (breast cancer cells).

Dispersion characteristics of complex electromechanical parameters of porous piezoceramics

In this paper, the results of experimental study of dispersion characteristics of complex electromechanical parameters of ferroelectrically “hard” porous piezoceramics based on PZT composition were presented. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. The complex constants of porous piezoceramics with relative porosity 16% and their frequency dependences were measured using the piezoelectric resonance analysis method. As a result of experimental studies, regions of elastic, piezoelectric and electromechanical dispersion, characterized by anomalies in the frequency dependences of the imaginary and real parts of the complex constants of porous piezoelectric ceramics were found. It was revealed also that the microstructural features of porous piezoceramics determine the character of frequency dependences of complex electromechanical parameters of porous piezoelectric ceramics. In conclusion, the microstructural and physical mechanisms of electromechanical losses and dispersion in porous piezoceramics were discussed.

A Virtual Instrument for Measuring the Piezoelectric Coefficients of a Thin Disc in Radial Resonant Mode

In this paper, we describe and present a Virtual Instrument, a tool that allows the determination of the electromechanical, dielectric, and elastic coefficients in polarised ferroelectric ceramic discs (piezoceramics) in the linear range, including all of the losses when the piezoceramics are vibrating in radial mode. There is no evidence in the recent scientific literature of any automatic system conceived and implemented as a Virtual Instrument based on an iterative algorithm issued as an alternative to solve the limitations of the ANSI IEEE 176 standard for the characterisation of piezoelectric coefficients of thin discs in resonant mode. The characterisation of these coefficients is needed for the design of ultrasonic sensors and generators. In 1995, two of the authors of this work, together with other authors, published an iterative procedure that allowed for the automatic determination of the complex constants for lossy piezoelectric materials in radial mode. As described in this work, the procedures involved in using a Virtual Instrument have been improved: the response time for the characterisation of a piezoelectric sample is shorter (approximately 5 s); the accuracy in measurement and, therefore, in the estimates of the coefficients has been increased; the calculation speed has been increased; an intuitive, simple, and friendly user interface has been designed, and tools have been provided for exporting and inspecting the measured and processed data. No Virtual Instrument has been found in the recent scientific literature that has improved on the iterative procedure designed in 1995. This Virtual Instrument is based on the measurement of a unique magnitude, the electrical admittance (Y = G + iB) in the frequency range of interest. After measuring the electrical admittance, estimates of the set of piezoelectric coefficients of the device are obtained. The programming language used in the construction of the Virtual Instrument is LabVIEW 2019®.

A spectrofluorimetric method for the determination of pindolol in natural waters using various organic and cyclodextrin media.

A simple, sensitive, and rapid spectrofluorimetric method was developed for the determination of the β-blocker pindolol. The native fluorescence of pindolol was measured in different organic solvents and in cyclodextrin aqueous media. The highest fluorescence signal was obtained in 2-propanol at λem = 303 nm with λex = 260 nm. Analytical figures of merit for the spectrofluorimetric determination of pindolol were satisfactory, with wide linear dynamic range (LDR) values of two orders of magnitude, and rather low limit of detection (LOD) values between 0.2 and 8.7 ng/mL. Moreover, the addition of cyclodextrins (HP-β-CD and β-CD) in aqueous media enhanced the fluorescence of pindolol. In addition, the inclusion complexes of pindolol with cyclodextrins were investigated and the stability constants of complexes were calculated by means of the method of nonlinear regression (NLR). The method was successfully applied to the analysis of tap water and natural water samples, spiked with pindolol.

Purification of Glutathione Reductase From Some Tissues of Capoeta umbla and the Inhibitory Effects of Some Metal Ions on Enzyme Activity

The aim of this study was to determine the in vitro inhibitory effects of some metal ions (silver ion (Ag+), cadmium ion (Cd2+), cobalt ion (Co2+), copper ion (Cu2+), nickel ion (Ni2+), lead ion (Pb2+) and zinc ion (Zn2+)) on glutathione reductase (GR) enzyme activities that purified from the gill, kidney and liver tissues of Capoeta umbla. For this purpose, the enzyme was purified from the gill, kidney and liver of C. umbla freshwater fish using ammonium sulfate precipitation and affinity column chromatography methods using 2′,5′-ADP Sepharose 4B. Within this study, the GR enzyme was purified for the first time from the tissues of C. umbla. Enzyme purity and molecular weight were determined using the sodium dodecyl sulfate polyacrylamide gel electrophoresis method. In addition, the inhibitory effects of different metal ions (Ag+, Cd2+, Co2+, Cu2+, Ni2+, Pb2+ and Zn2+) on GR enzyme activities of the gill, kidney and liver tissue of C. umbla were investigated under in vitro conditions. The metal ion concentrations inhibiting 50% of enzyme activity (IC50) were obtained by plotting activity percentage versus [I] figures. Finally, the dissociation constants of the enzyme inhibitor complex (Ki), and the inhibition types, were calculated from Lineweaver–Burk plots. In vitro inhibition rank order was determined as Ag+>Co2+>Pb2+>Zn2+>Cu2+ for C. umbla gill GR; Ag+>Pb2+>Co2+> Ni2+>Zn2+ for C. umbla liver GR; Ag+>Cu2+>Co2+>Pb2+>Ni2+ for C. umbla kidney GR. From these results, we showed that Ag+ metal ion is the most potent inhibitor of GR enzyme on gill, liver and kidney tissues. Our results also demonstrate that these metals might be dangerous at low micromolar concentrations for C. umbla GR enzyme.

Thermodynamic Design of Electrolyte for CuO/Cu2O Bilayer by Anodic Electrodeposition

Electrodeposition of multilayered semiconductors requires a bath design to electrodeposit the upper layer(s) without dissolving the base layer(s) below. We present herein a reliable approach to bath design based on thermodynamics from the viewpoint of complexation with ligands. A CuO/Cu2O bilayer film was targeted as an example. We searched a thermodynamic database of complexation constants for ligands that could form a complex with Cu(II) but not with Cu(I), and identified monoethanolamine as one of the best candidates. Using a Cu(II)-monoethanolamine alkaline aqueous bath, we experimentally confirmed that a CuO upper layer could be deposited without dissolving the Cu2O base layer. We believe that this design is applicable to other bilayer films produced by electrochemical techniques.

Використання полімерних композиційних матеріалів для підвищення біодоступності гесперидина

Purpose. Investigation of the influence of the composition of polymeric solubilizers on the phase solubilization in water of the model active pharmaceutical ingredient of flavonoid nature hesperidin.Methods. Hesperidin was chosen as a model substance of characteristic chemical structure. Pharmaceutically acceptable high molecular weight polymers based on polyvinylpyrrolidone (PVP) with a molecular weight of from 2500 to 58000 D were used for research; cetylpyridinium chloride; β-cyclodextrin. Phase solubilization of hesperidin was investigated by the method of Higuchi and Connors. The concentration of hesperidin was determined spectrophotometrically by absorption at 284 nm. The phase solubility diagram was constructed as the dependence of the concentration of hesperidin in solution on the concentration of the polymer. The obtained phase solubility profiles of hesperidin were compared with standard curves. For different compositions at the experiment temperature of 37 ± 0.5 °C, the stability constant and the dissociation constant of intermolecular complexes were calculated.Scientific novelty. The influence of the composition of polymer solubilizers on the phase solubilization in water of the model API of flavonoid nature of hesperidin was established. Practical significance. The optimal composition of the polymer composite material with hesperidin in the form of a solid dispersed system to maximize the solubility of flavonoids in water is substantiated. Results. The influence of the composition of polymer solubilizers on the phase solubilization in water of the model API of flavonoid nature of hesperidin was investigated. Based on the results of graphical analysis of the obtained data, it was concluded that the solubility of hesperidin increases with increasing number of polymers with different molecular weights and surfactants. The increase in solubility depends on the composition. When adding several polymers or a combination of a polymer with a surfactant, the solubility increases significantly more than when adding one compound. It is shown that the maximum value of solubility increase is observed in the system with polymer C and K surfactant - 42.7 times. It was found that the stability constants of polymeric composite materials of hesperidin based on polyvinylpyrrolidones are in the range from 161.87 to 219.88 M-1, which indicates favorable conditions for the formation of complexes.

PRECIPITATION OF METAL HYDROXIDES FROM AQUEOUS SOLUTIONS AS A RESULT OF SPONTANEOUS CONDENSATION OF POLYNUCLEAR HYDROXOCOMPLEXES

Background. Generally, it is assumed that the formation of a solid phase (precipitate) happens when the activities of the involved ions would exceed those defined by the thermodynamic solubility product. However, in case of precipitation of metal hydroxides, this is a simplification, and the real pattern is more complicated, since metal ions form strong mono- and polynuclear hydroxocomplexes in a solution. Formation of such complexes, especially those with zero charge, should result in the deviation from the common solubility product rule. Objective. The aim of this paper is to develop a precipitation model, which takes into account the effect of the formation of the hydroxocomplexes on the solubility of a metal hydroxide. Eventually, this solubility includes the sum of the concentrations of metal ions, and all neutral, positively and negatively charged hydroxocomplexes involved in all equilibria in aqueous solution. Methods. We assume that formation of the solid precipitate is the result of spontaneous condensation of polynuclear neutral hydroxocomplexes when their concentrations in a solution exceed a certain critical value. These critical concentrations can be estimated from the consideration of all equilibria with the assumption that the equilibrium constants for the formation of neutral polynuclear complexes when their nuclearity increases by one are approximately equal and do not significantly depend on the size of the particle. Results. Using this approach, we developed the model, which predicts spontaneous condensation with formation of a precipitate. Also, we calculated the dependencies of pH-logCM for precipitation of various divalent cation hydroxides. It was shown that there exist minimal concentrations, below which no precipitates are formed at any pH value. Conclusions. Such approach also explains the nature of linear correlations between logarithms of solubility products and stability constants of neutral complexes described in literature. These results are important for the development and optimization of industrial wastewater treatment processes.

Critical Reappraisal of Methods for Measuring Urine Saturation with Calcium Salts.

Background: Metabolic and physicochemical evaluation is recommended to manage the condition of patients with nephrolithiasis. The estimation of the saturation state (β values) is often included in the diagnostic work-up, and it is preferably performed through calculations. The free concentrations of constituent ions are estimated by considering the main ionic soluble complexes. It is contended that this approach is liable to an overestimation of β values because some complexes may be overlooked. A recent report found that β values could be significantly lowered upon the addition of new and so far neglected complexes, [Ca(PO4)Cit]4− and [Ca2H2(PO4)2]. The aim of this work was to assess whether these complexes can be relevant to explaining the chemistry of urine. Methods: The Ca–phosphate–citrate aqueous system was investigated by potentiometric titrations. The stability constants of the parent binary complexes [Cacit]− and [CaPO4]−, and the coordination tendency of PO43− toward [Ca(cit)]− to form the ternary complex, were estimated. βCaOx and βCaHPO4 were then calculated on 5 natural urines by chemical models, including or not including the [CaPO4]− and [Ca(PO4)cit]4− species. Results: Species distribution diagrams show that the [Ca(PO4)cit]4− species was only noticeable at pH > 8.5 and below 10% of the total calcium. β values estimated on natural urine were slightly lowered by the formation of [CaPO4]− species, whereas [Ca(PO4)cit]4− results were irrelevant. Conclusions: While [CaPO4]− species have an impact on saturation levels at higher pHs, the existence of ternary complex and of the dimer is rejected.

Inclusion complex of thymol and hydroxypropyl-β-cyclodextrin (HP-β-CD) in polymeric hydrogel for topical application: Physicochemical characterization, molecular docking, and stability evaluation

The current investigation aimed to prepare and characterize the inclusion complex of thymol with hydroxypropyl-β-cyclodextrin (HP-β-CD) to uniformly incorporate in hydrogel system for its topical application. An inclusion complex of thymol with HP-β-CD was formulated through different methods viz. physical mixture, kneading, and co-precipitation. Phase solubility study was carried out to find the stability constant of complex. Further, the inclusion complex of thymol with HP-β-CD was characterized by DSC, FT-IR, and 1H NMR spectroscopy. The molecular docking studies were also performed to understand the molecular interactions of stable supra-molecular host-guest inclusion complex of thymol with HP-β-CD. After that inclusion complex was incorporated in carbopol 940 hydrogel and evaluated for its drug content, pH, homogeneity, rheological behavior, and in-vitro release. The phase solubility graph demonstrated AL type correlation with apparent stability constant (K1:1) of 370 M−1. The inclusion complex formulated by the co-precipitation technique exhibited the highest dissolution rate (98.73%) of thymol as compared to kneading and physical methods. The DSC, FT-IR and 1H NMR spectroscopic analysis confirmed the formation of inclusion complex between thymol and HP-β-CD. The molecular docking study has confirmed that the binding affinity of thymol with the HP-β-CD was −9.6 kcal/mol, indicating desirable stability of the prepared inclusion complex. The diffusion flux of thymol in a form of inclusion complex was found to be approximately 4.4 folds higher as compared to that of thymol in the hydrogel system for topical administration. The in vitro release of thymol from carbopol 940 hydrogel system exhibited a sustained release profile with thixotropic behaviour. The thymol in a form of inclusion complex was found to be stable in the developed hydrogel system according to ICH guidelines. Therefore, incorporation of thymol in form of inclusion complex in hydrogel system is an effective approach to improve its biopharmaceutical performance for topical administration.

Improved water solubility of quercetin by preparing complexation with cyclodextrins in binary solvent

The antioxidant capacity of polyphenols have been widely used in food and pharmaceutical industries. Quercetin (Quer) is a polyphenolic flavonoid that shows several biological effects such as antioxidant, antitumor, antibacterial and antiproliferative effects both in-vitro and in-vivo. However, the solubility of quercetin in water is poor. Thus, it is essential to improve solubility of quercetin in pharmaceuticals by making its complexation with other compounds. In this study, the synthesis of the 2-hydroxypropyl-β-cyclodextrin complex with quercetin (Quer-HPβCD) in the form of nanoparticles in water-ethanol solvents has been carried out. The results showed that the obtained yield of (Quer-HPβCD) complexation in binary solvent was greater than that in pure water. The highest Y value was 80% in a binary solvent with 20% v/v of ethanol. The composition, morphology, structural and thermodynamic properties of the nanoparticles Quer-HPβCD have been determined. This study demonstrated that using mixed water- ethanol solvent and lyophilization technique was able to produce quercetin nanoparticles with significantly smaller particle size. The nanoparticles have a spherical shape with an average size of about 40-60 nm. The results of the phase solubility diagram showed that in water the solubility of quercetin increased and linearly depended on the concentration of host’s molecule while Quer and HP-βCD obtained a 1:1 stoichiometric complex. The stability constant of (Quer-HPβCD) complex was found to be logK = 2.56. The Gibbs energy change of the complexation reaction was found to be -14.60 kJ/mol.

Gallium-aluminum systematics of marine hydrogenetic ferromanganese crusts: Inter-oceanic differences and fractionation during scavenging

Despite its status as a critical metal in the EU and the U.S., the geochemical behavior of gallium (Ga) in the Earth’s surface environment is not yet well constrained, which is in marked contrast to its geochemical partner aluminum (Al). Especially hydrogenetic ferromanganese crusts which may represent a potential future unconventional resource of critical metals, are surprisingly underexplored with regard to their Ga-Al systematics. This study presents the first data on the Ga-Al pair in hydrogenetic Fe-Mn crusts from various locations in the Pacific Ocean and from the Rio Grande Rise in the SW Atlantic. We also provide Ga-Al data for certified reference materials for Fe-Mn nodules NOD-P-1, NOD-A-1, and JMn-1. Our results also show that marine hydrogenetic Fe-Mn crusts cannot be considered an unconventional Ga resource, in marked contrast to several other critical metals.Aluminum and Ga concentrations in these precipitates are not controlled by detrital components. Both elements show a geochemical behavior comparable to that of the hydroxide-dominated elements Zr and Hf during scavenging from ambient seawater by hydrogenetic Fe-Mn crusts. The Ga/Al mass ratios of Atlantic (0.10–0.16 g/kg) and Pacific crusts (0.18–1.2 g/kg) are about one and a half orders of magnitude lower than those of respective ambient seawater and mimic the inter-oceanic fractionation of the Ga-Al pair between these two ocean basins. Without exception, the Atlantic Fe-Mn crusts show lower Ga/Al ratios than the Pacific crusts. The systematically lower Ga/Al ratios of the crusts relative to those of seawater reveal preferential scavenging of Al relative to Ga during the formation of Fe-Mn crusts. This is in line with previous studies that reported a higher particle reactivity of Al compared to Ga in the marine environment. However, this fractionation trend contradicts predictions based on a simplified model commonly used to approximate trace element scavenging by marine metal (hydr)oxides based on hydrolysis constants, which favors Ga enrichment relative to Al as the hydrolysis constant of Ga is higher than that of Al. The observed Ga-Al fractionation may be related to the preferential retention of Al compared to Ga on the surface of the Fe-Mn (oxyhydr)oxides because in contrast to Ga, desorption of Al is characterized by very slow reaction kinetics or is even irreversible. Alternatively, stronger organic complexation of dissolved Ga than Al in seawater (which is supported by the stability constants of various organic Ga and Al complexes) and the resulting preferential retention of Ga over Al in solution by dissolved organic ligands may be another viable mechanism to explain the observed Ga-Al fractionation between hydrogenetic Fe-Mn crusts and seawater. While more experimentally determined thermodynamic data are necessary, the rather consistent difference between hydrogenetic Fe-Mn crusts and ambient seawater supports an important role of organic ligands in the chemical speciation of Ga in seawater.

The study of domain orientation processes in ferroelectric ceramics in weak electric fields

The paper studies domain orientation processes in ferroelectric ceramics induced by a weak dc electric field. The field dependences of the complex elastic, electromechanical, and piezoelectric parameters of the PZT type ferroelectric ceramics were measured using the piezoelectric resonance analysis method for the radial extensional mode of thin piezoceramic disks. The method used ensures high accuracy in determining the complex constants of piezoelectric materials, as well as their changes under external influences. A physical interpretation of the results is proposed.

Nerve Growth Factor Peptides Bind Copper(II) with High Affinity: A Thermodynamic Approach to Unveil Overlooked Neurotrophin Roles.

Nerve growth factor (NGF) is a protein essential to neurons survival, which interacts with its receptor as a non-covalent dimer. Peptides belonging to NGF N-terminal domain are able to mimic the activity of the whole protein. Such activity is affected by the presence of copper ions. The metal is released in the synaptic cleft where proteins, not yet identified, may bind and transfer to human copper transporter 1 (hCtr1), for copper uptake in neurons. The measurements of the stability constants of copper complexes formed by amyloid beta and hCtr1 peptide fragments suggest that beta-amyloid (Aβ) can perform this task. In this work, the stability constant values of copper complex species formed with the dimeric form of N-terminal domain, sequence 1–15 of the protein, were determined by means of potentiometric measurements. At physiological pH, NGF peptides bind one equivalent of copper ion with higher affinity of Aβ and lower than hCtr1 peptide fragments. Therefore, in the synaptic cleft, NGF may act as a potential copper chelating molecule, ionophore or chaperone for hCtr1 for metal uptake. Copper dyshomeostasis and mild acidic environment may modify the balance between metal, NGF, and Aβ, with consequences on the metal cellular uptake and therefore be among causes of the Alzheimer’s disease onset.

Reactive extraction of cis,cis-muconic acid from aqueous solution using phosphorus-bonded extractants, tri-n-octylphosphineoxide and tri-n-butyl phosphate: Equilibrium and thermodynamic study

• The muconic acid extraction by TOPO and TBP have been done firstly in the literature. • Different solvents used to solve TOPO and TBP. • Kinetic studies of the extraction mucconic acid was studied firstly in the literature. cis,cis- Muconic acid falls under the category of carboxylic acids and finds application mostly in biodegradable polymers, agrochemicals, and the food industry. Owing to the high thermal reactivity based upon the two-terminal carboxylic groups present in their structure, the chemical industry has widely used carboxylic acids. The major obstacle encountered during the production of carboxylic acids is their recovery from aqueous solutions and fermentation media. Therefore, the recovery of HccMA by reactive extraction as a particular product capture method, using tri- n -octylphosphine oxide (TOPO) and tri- n -butyl phosphate (TBP) in organic diluents such as 1-butanol, isoamyl alcohol, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), diisobutyl ketone, isobutanol, n -hexane, dimethyl glutarate, ethyl propionate, and diethyl carbonate (DEC) was executed in this study. This method was experimentally conducted to explore the most proper extractant and diluent combination. Extraction experiments were also conducted with pure diluents alone to examine the extractant effect on the extraction system. The important extraction parameters like distribution coefficient ( K D ), extraction efficiency ( E %), loading ratio ( Z ), dimerization constant ( D ), partition coefficient ( P ), and complexation constant ( K E 11 ) were determined. Mass action law model interpreted the obtained results. For HccMA/TOPO extraction system, the maximum extraction efficiency was found 93.19% in the presence of n -hexane as a diluent. For HccMA/TBP extraction system, the maximum extraction efficiency was found 90.37% in the presence of ethyl propionate as a diluent. Thermodynamic studies at variable temperatures were also carried out to estimate ΔH, ΔS, and ΔG of the process. To investigate the feasibility of designing a counter-current liquid–liquid extraction column, the number of theoretical stages (NTS) were assessed by theodified Kremser equation and found between 3 and 5 to et the desired extraction efficiency.

Functional Phenylboronate Polymers for the Recovery of Diols, Sugar Alcohols, and Saccharides from Aqueous Solution.

The ongoing transition from fossil to renewable feedstocks demands new efficient processes for an economically viable production of biomass‐derived commodities and fine chemicals. Novel energy‐ and material‐efficient product purification and separation will play a crucial role due to altered product and feed composition. The present study comprises the synthesis and tests of cross‐linked p‐vinylphenylboronate polymers for the separation of 18 diols, sugar alcohols, and saccharides, which can be obtained during biomass processing. The separation was based on molecular recognition, that is, esterification of the phenylboronate with vicinal diols. A correlation of the molecular complexation constant, the polymer swelling, and the maximum adsorption capacity was found. The adsorption curves over time were recorded. Preliminary results on competitive adsorption of binary mixtures showed a high potential for the separation of substrates with significantly different complexation constants. Desorption tests implied easier desorption of substrates that only adsorb on the outer polymer shell.