Amphoteric Properties Research Articles

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

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

Regulating microstructure of organic ammonium cations enables interface defect management and stability improvement in 2D/3D perovskite solar cells

Two-dimensional (2D) perovskites with tunable spacer cations show considerable photoelectric properties and thus make great application prospect for 2D/3D heterojunction perovskite solar cells (PSCs). Herein, three quaternary ammonium cations (tetraethylammonium, tetrapropylammonium and tetrabutylammonium) with specific microstructure are employed to modify perovskite/hole transport layer interface. The influence of cation configuration on the crystallization, defect density and carrier transport of the 2D/3D films has been systematically studied. Owing to strong ionic interactions with peovskite crystal terminal, stable 2D perovskite barriers will be formed to block the migration channel of water molecules in air and organic ions in perovskite, leading to the improved stability of PSCs. More importantly, both the positive and negative defects could be effectively passivated attributing to the surfactant and amphoteric properties of quaternary ammonium cations. As a result, the optimal perovskite device modified by tetrabutylammonium shows the best power conversion efficiency (PCE) of 21.92 % with high Voc of 1.17 V and superior humidity and thermal resistance. Our work provides a simple and effective strategy to stabilize the interface in PSCs and verifies the role of cation microstructure in modulating the properties of 2D perovskite.

Investigation of the protective capabilities of glass from laser sounding depending on its elemental composition

One of the most vulnerable issues in the technical protection of information is to obtain data via leakage through the opto-electronic channel.
 In this paper, studies of the protective capabilities of glass from laser sounding depending on its elemental composition were carried out using such indicators as the coefficients of reflection and absorption of the laser beam by the window glass.
 As a result of the work, an experimental installation based on a continuous solid-state laser was assembled.
 The study of the elemental composition of window glass, which is produced by modern industry, X-ray fluorescence method and the study of the coefficients of reflection and absorption of glass samples in the experimental setup showed that the studied window glass chemically belongs to quartz (silicate).
 All chemical elements involved in its formation can be divided into 3 groups: glass-forming, transitional, modifiers, which affects the optical properties of the studied glasses, as the elements used have different not only qualitative but also quantitative parameters.
 Absorption increases if the number of chemical elements that exhibit amphoteric and non-metallic properties and have (-charge) decreases, and increases if the number of chemical elements in the glass that exhibit the most alkaline, alkaline earth properties and in which the radius of cations (+ions) increases.
 Systematization of the elemental and quantitative composition of the studied window glass in accordance with the periods and groups of the periodic table of chemical elements, enabled the relationship between the electronic structure of chemical elements and the protective properties of glass

METHOD OF EVALUATION OF TRANSFER NUMBERS IN ION-EXCHANGE MATERIALS

A new method of differential itn-metry has been developed for accurate determination of ion transfer numbers in materials with ion-exchange properties. Such materials include ion exchange membranes, liquid phase ion exchangers and ionic liquids, industrial ion exchange resins. The method is intended as an alternative simplified assessment of the functional properties of ion-exchange resins used in industrial technologies of water purification, water treatment, and extraction at enterprises of various industries. Such accurate information is obtained in special laboratories at enterprises by long-term and expensive physical and chemical methods. Transfer numbers give an indirect assessment of the quality of ion exchangers, but the method of differential itn-metry gives a result in a short 30-minute experiment on the electrolysis of a NaOH or NaCl solution in a three-chamber electrolyzer reactor. The electrolyzer-reactor contains an electrolyte volume of up to 40 cm3. The middle chamber of the electrolyzer-reactor has a variable width from 0.05 to 0.2 cm and an area of 10 cm2 perpendicular to the direction of the electric current.
 The primary result of each experiment was the functions of the electrolyte concentration dynamics C(τ) in the extreme cathode and anode chambers of the electrolyzer- reactor, where the dynamics of the readings of the flow resistometric sensor developed by us were recorded during the electrolysis process. The effective transfer number itn* was determined by mathematical data processing using a system of approximation functions.
 The method of differential itn-metry will be effective for other resins with amphoteric properties. The use of such a method could be used in works for the study of a wide range of problems in environmental monitoring and management of environmental projects.

Dynamic Changes of Ni-Al LDH Nanosheets under Potential Cycling Investigated by In Situ Electrochemical Atomic Force Microscopy

Nickel-aluminum layered double hydroxides (Ni-Al LDHs) are widely used in energy storage and conversion devices, and the impact of the Ni/Al molar ratio on the structural evolution and kinetic process is of great significance for improving reaction kinetics and efficiency. In this paper, the morphological evolutions and nanomechanical property changes of Ni-Al-n LDH (n is the Ni/Al molar ratio) nanosheets during potential cycling were explored by in situ electrochemical atomic force microscopy. The conversion of Ni2+ into Ni3+ and the amphoteric properties of Al3+ during potential cycling resulted in the dissolution of Ni-Al-n LDH nanosheets. The dissolution rate of Ni-Al-2 LDH nanosheets was slower than those of Ni-Al-2.5 LDH and Ni-Al-3 LDH nanosheets. Meanwhile, the Young’s modulus value of the dissolved area was much larger than that of the undissolved area, and the dissolved area exhibited a harder property. It was attributed to the different microcrystalline structures of Ni-Al LDH nanosheets affected by the Ni/Al molar ratio and the rearrangement of Ni2+ and Al3+ during the reaction. The slow dissolution of Ni-Al-2 LDH nanosheets was beneficial to improving the electrochemical performance, while the fast dissolution of Ni-Al-2.5 LDH and Ni-Al-3 LDH nanosheets was not conducive to the electrochemical performance. Understanding the effect of the Ni/Al molar ratio on the morphological evolutions and nanomechanical property changes of Ni-Al LDH nanosheets during potential cycling has important guiding significance for the subtle compositional modification and structural design of Ni-Al LDHs as an electrode material.

Generating High‐valent Iron‐oxo ≡FeIV=O Complexes in Neutral Microenvironments through Peroxymonosulfate Activation by Zn−Fe Layered Double Hydroxides

AbstractThe universal limit on the pH conditions is disturbing peroxymonosulfate (PMS)‐triggered high‐valent iron‐oxo systems in environmental applications. Here, we propose for the first time the construction of a neutral microenvironment on the surface of Zn−Fe layered double hydroxide (ZnFe‐LDH) by using the amphoteric properties of zinc hydroxide, which continuously generates ≡FeIV=O over a wide pH range of 3.0–11.0 in activating PMS. The ≡Zn(OH)2 moiety offers a neutral microenvironment at the phase interface, which mitigates the self‐decomposition of ≡FeIV=O by protons and the hydrolysis reaction of iron by hydroxyl groups, which is supported by the Mossbauer spectra, density functional theory calculations and designed experiments. Consequently, ZnFe‐LDH/PMS can satisfy the stability in long‐term experiments, selectivity under conditions with high salinity or natural organic matter and efficient treatment of actual wastewater.

Generating High‐valent Iron‐oxo ≡FeIV=O Complexes in Neutral Microenvironments through Peroxymonosulfate Activation by Zn−Fe Layered Double Hydroxides

The universal limit on the pH conditions is disturbing peroxymonosulfate (PMS)-triggered high-valent iron-oxo systems in environmental applications. Here, we propose for the first time the construction of a neutral microenvironment on the surface of Zn-Fe layered double hydroxide (ZnFe-LDH) by using the amphoteric properties of zinc hydroxide, which continuously generates ≡FeIV =O over a wide pH range of 3.0-11.0 in activating PMS. The ≡Zn(OH)2 moiety offers a neutral microenvironment at the phase interface, which mitigates the self-decomposition of ≡FeIV =O by protons and the hydrolysis reaction of iron by hydroxyl groups, which is supported by the Mossbauer spectra, density functional theory calculations and designed experiments. Consequently, ZnFe-LDH/PMS can satisfy the stability in long-term experiments, selectivity under conditions with high salinity or natural organic matter and efficient treatment of actual wastewater.

Single-molecule polyamidoxime adsorbent for highly efficient uranium recovery and removal

Inspired by single-atom catalysts (SACs), a “single-molecule” polyamidoxime (SM-PAO) adsorbent is designed to implement ultra-fast and “nothing left” enrichment of uranium in a water environment. The amphoteric property of SM-PAO is systematically characterized and discussed for the first time. The amidoxime functional groups are nearly 100% accessible due to the dissolution of SM-PAO in solution with pH below or above the isoelectric point of SM-PAO sol (∼ pH 5). The collection of uranium-loaded adsorbent is realized by virtue of the dissolution-precipitation transformation of the SM-PAO. A record high adsorption capacity, 2221.9 mg-U/g-Ads, is achieved within several minutes’ interaction and the bonding mechanism of adsorption is explained by the X-ray photoelectron spectroscopy. An automatic cleaning of uranium-polluted wastewater to potable water is demonstrated to show the great potential of SM-PAO adsorbent for practical application.

Synthesis of a Waterborne Melamine Resin and its Retanning Behaviors Investigation

Recently, the application of waterborne melamine resin (WMR) is greatly increasing in the leather industry because of its convenient operation, but it often suffers from poor storage stability. Here, two waterborne melamine resin retanning agents (WMRs) with high storage stability were prepared using melamine, glutaraldehyde and collagen hydrolysates (CHs) as raw materials at different mole ratios. FTIR, 13C-NMR and XPS were used to characterize the chemical structure of synthesized resins, and their retanning behaviors for wet blue and wet white leather were fully investigated. The particle sizes of WMR1 and WMR2 were 28.73 nm and 8.78 nm, and their zeta potentials were 4.0 and 4.5, respectively. The introduction of CHs provided not only good water solubility but also amphoteric properties to synthesized resins, thereby resulting in high absorption of retanning and fatliquoring agents. Moreover, the retanning application investigation of WMRs manifested good storage stability and excellent overall performance, which are comparable with commercial retanning agents. This work showed that glutaraldehyde and CH could be used as starting materials in the synthesis of environmentally friendly WMR.

Bovidae-based gelatin: Extractions method, physicochemical and functional properties, applications, and future trends.

Gelatin is one of the most important multifunctional biopolymers and is widely used as an essential ingredient in food, pharmaceutical, and cosmetics. Porcine gelatin is regarded as the leading source of gelatin globally then followed by bovine gelatin. Porcine sources are favored over other sources since they are less expensive. However, porcine gelatin is religiously prohibited to be consumed by Muslims and the Jewish community. It is predicted that the global demand for gelatin will increase significantly in the future. Therefore, a sustainable source of gelatin with efficient production and free of disease transmission must be developed. The highest quality of Bovidae-based gelatin (BG) was acquired through alkaline pretreatment, which displayed excellent physicochemical and rheological properties. The utilization of mammalian- and plant-based enzyme significantly increased the gelatin yield. The emulsifying and foaming properties of BG also showed good stability when incorporated into food and pharmaceutical products. Manipulation of extraction conditions has enabled the development of custom-made gelatin with desired properties. This review highlighted the various modifications of extraction and processing methods to improve the physicochemical and functional properties of Bovidae-based gelatin. An in-depth analysis of the crucial stage of collagen breakdown is also discussed, which involved acid, alkaline, and enzyme pretreatment, respectively. In addition, the unique characteristics and primary qualities of BG including protein content, amphoteric property, gel strength, emulsifying and viscosity properties, and foaming ability were presented. Finally, the applications and prospects of BG as the preferred gelatin source globally were outlined.

Green Synthesis of De Novo Bioinspired Porous Iron-Tannate Microstructures with Amphoteric Surface Properties

Bioinspired porous microstructures of iron-tannate (Fe(III)-TA) coordination polymer framework were synthesized by catenating natural tannic acid with iron(II), using a scalable aqueous synthesis method in ambient conditions. The chemical composition, morphology, physiochemical properties, and colloidal stability of microstructures were elucidated. The surface area (SBET) and the desorption pore volume were measured to be 70.47 m2/g and 0. 44 cm3/g, respectively, and the porous structure was confirmed with an average pore dimension of ~27 nm. Microstructures were thermally stable up to 180 °C, with an initial weight loss of 13.7% at 180 °C. They exhibited high chemical stability with pH-responsive amphoteric properties in aqueous media at pH levels ranging from 2 to 12. Supporting their amphoteric sorption, microstructures exhibited rapid removal of Pb+2 from water, with 99% removal efficiency, yielding a maximum sorption capacity of 166.66 mg/g. Amphoteric microstructures of bioinspired metal–phenolate coordination polymers remain largely unexplored. Additionally, natural polyphenols have seldomly been used as polytopic linkers to construct both porous and pH-responsive amphoteric coordination polymer frameworks with a robust structure in both acidic and basic media. Thus, this de novo porous microstructure of Fe(III)-TA and its physiochemical surface properties have opened new avenues to design thermally and chemically stable, eco-friendly, low-cost amphoteric sorbents with multifunctionality for adsorption, ion exchange, separation, storage, and sensing of both anions and cations present in heterogeneous media.

Combined experimental and computational study of Al2O3 catalyzed transamidation of secondary amides with amines.

Amides are the most extensively used substances in both synthetic organic and bioorganic chemistry. Unfortunately, the traditional synthesis of amides suffers from some important drawbacks, including low atom efficiency, high catalyst loading, separation of products from the reaction mixture and production of byproducts. Al2O3 is an amphoteric catalyst that activates the carbonyl carbon of the secondary amide group and helps the C–N cleavage of the reactant amide group by attacking the N–H hydrogen. By using the concepts of amphoteric properties of Al2O3, amides were synthesized from secondary amides and amines in the presence of triethylamine solvent. Several aliphatic and aromatic amines were used for the transamidation of N-methylbenzamide in the presence of the Al2O3 catalyst. Moreover, using the Gaussian09 software at the DFT level, HUMO, LUMO and the intrinsic reaction coordinates (IRCs) have also been calculated to find out the transition state of the reaction and energy. In this study, five successful compounds were synthesized by the transamidation of secondary amides with amines using a reusable Al2O3 catalyst. The catalyst was reused several times with no significant loss in its catalytic activity. The products were purified by recrystallization and column chromatography techniques. This catalytic method is effective for the simultaneous activation of the carbonyl group and N–H bond by using the Al2O3 catalyst.

Amphoteric Property of Hydrogen in Oxide Materials Probed by Muon

Amphoteric Property of Hydrogen in Oxide Materials Probed by Muon

Effect of Fe/SiO2 Ratio and Fe2O3 on the Viscosity and Slag Structure of Copper-Smelting Slags

Secondary copper smelting is an effective means of treating waste resources. During the smelting process, the viscous behavior of the smelting slags is essential for smooth operation. Therefore, the effects of Fe/SiO2 ratio and Fe2O3 contents on the viscous behavior of the FeO−Fe2O3−SiO2−8 wt%CaO−3 wt%MgO−3 wt%Al2O3 slag system were investigated. The slag viscosity and activation energy for viscous flow decrease with increasing Fe/SiO2 from 0.8 to 1.2, and increase as the Fe2O3 content increases from 4 wt% to 16 wt% at Fe/SiO2 ratio of 1.2. However, under the conditions of Fe/SiO2 of 0.8 and 1.0, the viscosity and activation energy for viscous flow show a minimum value at Fe2O3 content of 12 wt%. Fe2O3 exhibits amphoteric properties. In addition, the increase in Fe2O3 content raises the breaking temperature of the slag, while the Fe/SiO2 ratio has the opposite effect. Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy show that increases in Fe/SiO2 ratio lead to simplification of the silicate network structure, while increases in Fe2O3 content improves the formability of the network. This study provides theoretical support for the related research and application of secondary copper smelting.

Preparation of highly efficient Ni-doped layered perovskite grafted graphene oxide NixSr1-xTiO3-RGO heterojunction photocatalyst with enhanced visible-light photocatalytic activity for MB degradation

Two-dimensional layered semiconductor photocatalysts have attracted much attention due to their excellent performance. Layered photocatalyst, however, generally has low visible-light utilization and is easy to self-polymerize. In this study, layered photocatalyst NixSr1-xTiO3 was prepared by doping Nickelin perovskite, and then loaded on RGO with a larger specific surface area. Heterojunction photocatalyst with high performance was successfully prepared. The results show that doping Ni will introduce an occupied energy level between the band gaps, effectively reducing the forbidden bandwidth, and the wavelength of 600 nm still has a high optical response. Much elevated photocatalytic degradation was investigated after further loading NixSr1-xTiO3 onto RGO. As a carrier, RGO can improve the self-polymerization of the catalyst and form heterojunction with NixSr1-xTiO3. The transfer of photogenerated carriers is promoted relying on the potential difference between the two sides of the heterojunction interface and the electron transport channel of RGO. We also noticed that the unique amphoteric molecular properties of RGO can improve the dispersion of NixSr1-xTiO3-RGO in dye wastewater. To sum up, the synergistic effect of reducing band gaps, inhibiting heterojunction structure and improving dispersion are the reasons for more efficient activity.

Anthracene-Based Zwitterion with a Small HOMO–LUMO Energy Gap

AbstractWe have designed and synthesized an anthracene-based zwitterion, 2-methyl-2-azoniaanthracene-7-olate. The zwitterion shows amphoteric redox properties and low-energy-light absorption originating from the small HOMO–LUMO energy gap of ca. 1.7 eV. DFT calculations show that the combination of replacing the C–H with N+–Me and introducing O− is necessary to alter the electronic structure and properties of anthracene significantly.

Role of pH on photocatalytic degradation of phenol derivatives using metal supported on mesoporous materials

Photocatalysis is a promising advanced oxidation process (AOPs). It is often used in the degradation of phenolic derivatives due to their simplicity and easy handling, by converting organic molecules with total mineralisation into nontoxic H2O and CO2. In this study, a combination of microwave-assisted (MW) and facile electrochemical method was applied in the synthesis of catalysts (Fe-MTN and Cu-MZN). The characterisation of catalysts was tested using XRD, UV–Vis DRS and FTIR. It was found that there was no new bonding formed when Fe was introduced onto MTN, while the introduction of Cu onto MZN formed a new Zn-O-Cu. The introduction of Fe and Cu onto MTN and MZN also decreased the bandgap energy from 3.15 to 2.35 eV and 2.92 to 2.63 eV, respectively. The pH of the solution is one of the essential parameters that need to be measured in the photocatalytic process due to the amphoteric properties of semiconductor, which influenced the surface-charged properties of the catalysts. Fe-MTN and Cu-MZN were used in photocatalytic degradation of 2-chlorophenol (2-CP) and 2,4-diclorophenol (2,4-DCP), respectively. After the effect of pH over 2-CP and 2,4-DCP was tested in the range of 3 to 11, the greatest degradation of 2-CP using Fe-MTN was at pH 5 with 99% while 100% degradation of 2,4-DCP at pH 3 for Cu-MZN. These results are probably due to the amphoteric characteristic of catalyst, where it can be tested using point zero charged (pHZPC). The pHZPC value of Fe-MTN and Cu-MZN was 6.1 and 5.5, respectively illustrated that the photoactivity of both catalysts better in acidic condition compared to an alkaline condition.

Layer-by-layer electrostatic self-assembled coatings based on flaxseed gum and chitosan for Mongolian cheese preservation

Mongolian cheese, a daily essential dairy product of Mongolians, is nutritious but susceptible to microbial contamination. Edible coatings consisted of casein, chitosan and flaxseed gum were developed to extend the shelf life of Mongolian cheese by self-assembly on its surface. Due to the amphoteric properties of casein, positive and negative charges were obtained as a template by adjusting the isoelectric points. With chitosan as the positive charge provider and flaxseed gum as the negative charge provider, edible coatings were formed on the surface of Mongolian cheese by layer-by-layer electrostatic self-assembly technology. Chitosan inhibited the proliferation of internal microorganisms (molds and yeasts) when it was the innermost layer, and resisted the invasion of foreign microorganisms (Escherichia coli and Staphylococcus aureus) while it was the outermost layer. And, this effect became stronger with the increase of layer numbers. The layer-by-layer electrostatic self-assembly technology of polysaccharide not only improved the quality of Mongolian cheese but extended its shelf life.

Computational study of first-row transition metals in monodoped 4H-SiC

Electronic structure calculations of 4H-SiC doped with various transition metals reveal dilute magnetic semiconductor behavior in a material suitable for high-power and high-frequency semiconductor devices. Our results are consistent with prior work on V, Cr, and Mn doping and explore additional metals: Fe, Co, and Ni. Charge-state calculations show that the latter maintain amphoteric semi-insulating properties while offering a non-zero stable spin polarization and also greater asymmetry in the spin density of states than previously studied dopants. This indicates possible enhanced half-metal properties. Our results are consistent with crystal field theory, which helps interpret the observed spin states and assess the degree of charge localization and, subsequently, the range and strength of interactions relevant to ionization/capture and charge transport. These findings provide new avenues to tune the behavior of 4H-SiC for electronic device applications.

Multi-Smart and Scalable Bioligands-Free Nanomedical Platform for Intratumorally Targeted Tambjamine Delivery, a Difficult to Administrate Highly Cytotoxic Drug.

Cancer is one of the leading causes of mortality worldwide due, in part, to limited success of some current therapeutic approaches. The clinical potential of many promising drugs is restricted by their systemic toxicity and lack of selectivity towards cancer cells, leading to insufficient drug concentration at the tumor site. To overcome these hurdles, we developed a novel drug delivery system based on polyurea/polyurethane nanocapsules (NCs) showing pH-synchronized amphoteric properties that facilitate their accumulation and selectivity into acidic tissues, such as tumor microenvironment. We have demonstrated that the anticancer drug used in this study, a hydrophobic anionophore named T21, increases its cytotoxic activity in acidic conditions when nanoencapsulated, which correlates with a more efficient cellular internalization. A biodistribution assay performed in mice has shown that the NCs are able to reach the tumor and the observed systemic toxicity of the free drug is significantly reduced in vivo when nanoencapsulated. Additionally, T21 antitumor activity is preserved, accompanied by tumor mass reduction compared to control mice. Altogether, this work shows these NCs as a potential drug delivery system able to reach the tumor microenvironment, reducing the undesired systemic toxic effects. Moreover, these nanosystems are prepared under scalable methodologies and straightforward process, and provide tumor selectivity through a smart mechanism independent of targeting ligands.