Bidentate Form Research Articles

Molecular insights into histidine adsorption on Na-montmorillonite, anatase, and goethite

The adsorption of amino acids (AAs) on minerals plays a role in the geochemical processes that determine the availability of nutrients in the environment. Histidine can be used as typical basic AA because it is frequently detected in natural waters, soils, and sediments. Herein, the pH effects and time factor were analyzed to reveal the molecular-level mechanisms of histidine adsorption on Na-montmorillonite, anatase, and goethite. Attenuated total reflectance Fourier transform infrared (ATR–FTIR) flow-cell measurements, X-ray diffraction (XRD), and density functional theory (DFT) calculations were used to determine the adsorbed species structures and the time-dependent adsorption/desorption processes. The structures of adsorbed histidine were governed by pH conditions, but were not affected by time variations. The histidine adsorbed on the minerals was in the cationic (pH 4), neutral zwitterionic (pH 7.5), and anionic (pH 10.5) forms, which was consistent with those dissolved in solution at the same pH. Adsorption on the clay mineral montmorillonite was favorable due to the dominant interlayer adsorption mechanism at pH 4 and hydrophobic attraction (external basal surface) at pH 4–10.5. Histidine adsorption on the two metal (hydr)oxides was dominated by inner-sphere surface complexation, which involved one or two O atoms of the COO− group. The adsorbed histidine was in the monodentate form on anatase and in the bidentate form on goethite.

New Fe(III) Trichlorido Complex of a Bidentate N'-(thiophen-2-ylmethylene)isonicotinohydrazide Ligand: Synthesis, X-ray Structure, Spectral Characterization, and Electrochemistry Study

Fe(III) complex of the hydrazone from (E)-N'-(thiophen-2-ylmethylene)isonicotinohydrazide (HL) has been synthesized and characterized by elemental analysis, electrical conductance in non-aqueous solvents, FT-IR and electronic spectroscopies, room temperature magnetic measurement, electrochemistry study as well as by X-ray diffraction structure determination. In the complex, the ligand acts in its neutral bidentate form, coordinating through the carbonyl oxygen and azomethine nitrogen. A high spin octahedral geometry assigned to the Fe(III) complex were further confirmed by room temperature magnetic moment data. Elemental analysis showed that Fe(III) complex is composed of metal and ligands in a molar ratio of 1:1. This complex of Fe(III) is a neutral electrolyte in DMF solution. The electrochemistry study shows that a one electron process determined the electrochemical reaction is governed by an electron transfer with an irreversible process. The structure of the complex has also been determined by X-ray diffraction revealing an octahedral environment around the Fe(III) ion.

Biological Effects in Cancer Cells of Mono- and Bidentate Conjugation of Cisplatin on PAMAM Dendrimers: A Comparative Study.

Cisplatin (cis-diamminedichloroplatinum(II)) is a potent chemotherapeutic agent commonly used to treat cancer. However, its use also leads to serious side effects, such as nephrotoxicity, ototoxicity, and cardiotoxicity, which limit the dose that can be safely administered to patients. To minimize these problems, dendrimers may be used as carriers for cisplatin through the coordination of their terminal functional groups to platinum. Here, cisplatin was conjugated to half-generation anionic PAMAM dendrimers in mono- and bidentate forms, and their biological effects were assessed in vitro. After preparation and characterization of the metallodendrimers, their cytotoxicity was evaluated against several cancer cell lines (A2780, A2780cisR, MCF-7, and CACO-2 cells) and a non-cancer cell line (BJ cells). The results showed that all the metallodendrimers were cytotoxic and that the cytotoxicity level depended on the cell line and the type of coordination mode (mono- or bidentate). Although, in this study, a correlation between dendrimer generation (number of carried metallic fragments) and cytotoxicity could not be completely established, the monodentate coordination form of cisplatin resulted in lower IC50 values, thus revealing a more accessible cisplatin release from the dendritic scaffold. Moreover, most of the metallodendrimers were more potent than the cisplatin, especially for the A2780 and A2780cisR cell lines, which showed higher selectivity than for non-cancer cells (BJ cells). The monodentate G0.5COO(Pt(NH3)2Cl)8 and G2.5COO(Pt(NH3)2Cl)32 metallodendrimers, as well as the bidentate G2.5COO(Pt(NH3)2)16 metallodendrimer, were even more active towards the cisplatin-resistant cell line (A2780cisR cells) than the correspondent cisplatin-sensitive one (A2780 cells). Finally, the effect of the metallodendrimers on the hemolysis of human erythrocytes was neglectable, and metallodendrimers' interaction with calf thymus DNA seemed to be stronger than that of free cisplatin.

Complexation of uranyl with benzoic acid in aqueous solution at variable temperatures: potentiometry, spectrophotometry and DFT calculations.

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.

Pd(II), Ni(II), and Cu(II) complexes of α,α'-ditolylmethanone dipyrroethene.

Dipyrromethenes containing two pyrrole rings connected by one meso-carbon are versatile monoanionic bidentate ligands and form coordination complexes with many metals/nonmetals/metalloids. Dipyrroethenes containing one additional meso-carbon compared to dipyrromethenes have more space between coordinating pyrrole nitrogens and provide a good coordination environment but have not been explored as ligands in coordination chemistry. Dipyrroethenes are dianionic bidentate ligands and by suitable modifications, the coordination environment of dipyrroethenes can be changed further. Herein, we successfully synthesized α,α'-ditolylmethanone dipyrroethene which is a bipyrrolic tetradentate ligand with an ONNO ligand core and used it for the synthesis of novel Pd(II), Ni(II), and Cu(II) metal complexes by treating it with respective metal salts in CH2Cl2/CH3OH at room temperature. The X-ray crystallographic structure of the metal complexes showed that the M(II) ion was coordinated to the ONNO atoms of the ligand in a perfect square planar geometry. The NMR studies of Pd(II) and Ni(II) complexes also supported the highly symmetric nature of the metal complexes. The absorption spectra of the metal complexes showed strong bands in the region of 300-550 nm. The electrochemical studies of metal complexes revealed that only ligand-based oxidation and reduction were observed. The DFT and TD-DFT studies were in agreement with the experimental observations. Our preliminary studies indicated that the Pd(II) complex can be used as a catalyst for the Fujiwara-Moritani olefination reaction.

Design of Hemilabile N,N,N-Ligands in Copper-Catalyzed Enantioconvergent Radical Cross-Coupling of Benzyl/Propargyl Halides with Alkenylboronate Esters

The enantioconvergent radical C(sp3)-C(sp2) cross-coupling of alkyl halides with alkenylboronate esters is an appealing tool in the assembly of synthetically valuable enantioenriched alkenes owing to the ready availability, low toxicity, and air/moisture stability of alkenylboronate esters. Here, we report a copper/chiral N,N,N-ligand catalytic system for the enantioconvergent cross-coupling of benzyl/propargyl halides with alkenylboronate esters (>80 examples) with good functional group tolerance. The key to the success is the rational design of hemilabile N,N,N-ligands by mounting steric hindrance at the ortho position of one coordinating quinoline ring. Thus, the newly designed ligand could not only promote the radical cross-coupling process in the tridentate form but also deliver enantiocontrol over highly reactive alkyl radicals in the bidentate form. Facile follow-up transformations highlight its potential utility in the synthesis of various enantioenriched building blocks as well as in the late-stage functionalization for drug discovery.

Conformation and Metal Cation Binding of Zwitterionic Alanine Tripeptide in Saline Solutions by Infrared Vibrational Spectroscopy and Molecular Dynamics Simulations.

In this work, linear infrared (IR) spectroscopy and molecular dynamics (MD) simulations were used to examine the interaction of different metal cations (Na+, Ca2+, Mg2+, and Zn2+) with backbone (amide C═O) and C-terminal carboxylate (COO-) groups in zwitterionic alanine tripeptide (Ala3) in aqueous solutions with varying saline concentrations. Circular dichroism spectra and MD results suggest that Ala3 is predominantly in polyproline-II (PPII) conformation, whose amide-I and asymmetric carboxylate stretching IR vibration signatures are also supported by quantum-chemistry calculations. The zwitterionic form of Ala3 separates the two amide-I modes in frequency, which are weakly coupled modes, as revealed by two-dimensional IR measurement, and can be used to probe backbone-cation interactions at different scenarios (near charged or neutral chemical groups respectively). Cation concentration-dependent IR frequency red shifts in the amide-I mode are seen for both amide-I modes, whereas blue shifts are also seen in the amide-I mode far from the NH3+ group. The observed spectral changes are discussed from the perspective of the salting-in and salting-out abilities of the cations. In addition, all the metal cations studied here (except Zn2+) can specifically coordinate to the COO- group in bidentate and pseudo-bridging forms simultaneously. For Zn2+, only the pseudo-bridging form exists. Our results shed light on the macroscopic protein salting-in and salting-out phenomena from the perspective of key chemical bonds in peptides.

Semi-quantitative design of synergetic surficial/interfacial sites for the semi-continuous oxidation of glycerol

Qualitatively identifying the dominant catalytic site for each step of a semi-continuous reaction and semi-quantitatively correlating such different sites to the catalytic performance is of great significance toward the integration of multiple well-optimized sites on a heterogeneous catalyst. Herein, a series of structurally defined TiOx-based catalysts were synthesized to provide a feasible approach to investigate the aforementioned issues using the semi-continuous oxidation of glycerol as a model reaction. Detailed investigations have verified the simultaneous presence of two kinds of Pt active sites: 1) Negatively charged Pt bound to the oxygen vacancies of modified TiOx in the form of Ptδ−-Ov-Ti3+ sites and 2) metallic Pt (Pt0 site) located away from the interface. Meanwhile, the proportion of surficial and interfacial sites varies over this series of catalysts. Combined in situ FTIR experiments revealed that the reaction network was well-tuned via a site cooperation mechanism: The surficial Pt0 sites dissociatively adsorb the OH group of glycerol with a monodentate bonding geometry and the Ptδ−-Ov-Ti3+ sites dissociate the C=O bond of the aldehyde group in a bidentate form. Furthermore, CO-FTIR spectroscopy confirmed a correlation between the reaction rate/product selectivity and the fraction of surficial/interfacial sites. A rational proportion of surficial and interfacial sites is key to enabling a high yield of glyceric acid. The most active catalyst with 32% surface sites and 68% interfacial sites exhibited 90.0% glycerol conversion and 68.5% GLYA selectivity. These findings provide a deeper understanding of the structure-activity relationships using qualitative identification and semi-quantitative analysis.

Green synthesis for new Co(II), Ni(II), Cu(II) and Cd(II) hydrazone-based complexes; characterization, biological activity and electrical conductance of nano-sized copper sulphate

A series of new hydrazone complexes were prepared and perfectly elucidated to be 1:1 molar ratio with Cd(II) complex, while 1:2 (M:L) with Co(II), Ni(II) and Cu(II) complexes. The bidentate form of bonding was proposed for all complexes, either in octahedral or square-planer geometry with the Ni(II) complex. The UV-Vis spectral data as well as the magnetism of complexes (except Cd(II) one) suggested the geometry of complexes around the central atoms as well as the ligand field parameters (10Dq, B & β). In addition, the spin Hamiltonian parameters attribute to S = 1/2 and I = 3/2, were calculated for Cu(II) complex according to its ESR spectrum. XRD and SEM analyses were performed for selected complexes and the particle size of Ni(II) complex appeared in nan-scale. The DFT approach was used to optimize the ligand and its complexes under valence double-zeta polarized basis set and the correlation-consistent basis set. The ligand exhibited favorable characteristic for O(11) and O(12) atoms as orientation, nucleophilicity and charges, which help their priority in coordination. Genotoxicity of H2PHNH ligand and its Cd(II), Cu(II), and Ni(II) complexes degraded ctDNA into two distinct bands. Conductometric analysis for copper sulfate was performed in its bulk or nano-sized as well as in absence or presence of H2PHNH ligand. Using Fuoss-Hsia-Fernández-Prini (FHFP) equation, the molar conductance (Λm), the limiting molar conductance (Λo), Onsager slope (S), Walden product (Λo ηo), ion-pair interaction constant (KA), degree of dissociation (α), and activity coefficient (γ±) were calculated. The obtained data were elaborately discriminated according to the state of CuSO4 used (bulk & nano-sized) also in absence or presence of the ligand. Moreover, the thermodynamic parameters as well as the molar ratio of the formed complexes, were estimated in all systems studied. Finally, in bulk or nano-sized CuSO4 in presence of H2PHNH complexes, the formation constants and Gibbs free energies obey this order: Kf(1:2) > Kf (1:1) [M:L].

Use of Half-Generation PAMAM Dendrimers (G0.5-G3.5) with Carboxylate End-Groups to Improve the DACHPtCl2 and 5-FU Efficacy as Anticancer Drugs.

The DACHPtCl2 compound (trans-(R,R)-1,2-diaminocyclohexanedichloroplatinum(II)) is a potent anticancer drug with a broad spectrum of activity and is less toxic than oxaliplatin (trans-l-diaminocyclohexane oxalate platinum II), with which it shares the active metal fragment DACHPt. Nevertheless, due to poor water solubility, its use as a chemotherapeutic drug is limited. Here, DACHPtCl2 was conjugated, in a bidentate form, with half-generation PAMAM dendrimers (G0.5–G3.5) with carboxylate end-groups, and the resulting conjugates were evaluated against various types of cancer cell lines. In this way, we aimed at increasing the solubility and availability at the target site of DACHPt while potentially reducing the adverse side effects. DNA binding assays showed a hyperchromic effect compatible with DNA helix’s disruption upon the interaction of the metallodendrimers and/or the released active metallic fragments with DNA. Furthermore, the prepared DACHPt metallodendrimers presented cytotoxicity in a wide set of cancer cell lines used (the relative potency regarding oxaliplatin was in general high) and were not hemotoxic. Importantly, their selectivity for A2780 and CACO-2 cancer cells with respect to non-cancer cells was particularly high. Subsequently, the anticancer drug 5-FU was loaded in a selected metallodendrimer (the G2.5COO(DACHPt)16) to investigate a possible synergistic effect between the two drugs carried by the same dendrimer scaffold and tested for cytotoxicity in A2780cisR and CACO-2 cancer cell lines. This combination resulted in IC50 values much lower than the IC50 for 5-FU but higher than those found for the metallodendrimers without 5-FU. It seems, thus, that the metallic fragment-induced cytotoxicity dominates over the cytotoxicity of 5-FU in the set of considered cell lines.

Nitrate ions effects on solvent extraction of rare earth elements from aqueous solutions by D2EHPA: Experimental studies and molecular simulations

The number and positioning manner of the ligands present in the first shell of every cation of rare earth elements are key parameters in determining the stoichiometry of the reactions of solvent extraction from nitrate systems, especially when acidic extractants are used. In addition to determining the hydration and coordination of nitrate ligands around lanthanum and yttrium cations in an aqueous electrolyte, this paper investigated stoichiometry by combining the results of studies on molecular dynamics simulation and solvent extraction experiments. The analysis of the results of the Radial Distribution Function clearly showed the presence of one and two nitrate ligands, respectively, in the first hydration shells of lanthanum and yttrium. Considering the effect of nitrate anion, the identified ionic complexes of the rare earth elements in the electrolyte were [LaNO3·(H2O)7]2+ and [Y(NO3)2·(H2O)4]+. The overlap between the results of slope analysis and molecular dynamics elucidated that two and one ligands from the Di-(2-Ethylhexyl) phosphoric acid extractant were required for the complete extraction of lanthanum and yttrium ionic complexes, respectively. The DFT-employing geometry studies on ionic complexes in the aqueous phase revealed that the direction of the nitrate ligand in the first coordination shell of these elements was in a bidentate form. The results of this study, besides assisting with the better interpretation of the difference between the extraction of light and itinerant rare elements by D2EHPA, are greatly effective in designing new extractants in order to extract these elements more selectively.

Molecular Design of Novel Chemicals for Iron Sulfide Scale Removal

Scale deposition is a pertinent challenge in the oil and gas industry. Scales formed from iron sulfide are one of the troublous scales, particularly pyrite. Moreover, the use of biodegradable environmentally friendly chemicals reduces the cost compared to the conventional removal process. In this work, the chelating abilities of four novel chemicals, designed using the in silico technique of density functional theory (DFT), are studied as potential iron sulfide scale removers. Only one of the chemicals containing a hydroxamate functional group had a good chelating ability with Fe2+. The chelating strength and ecotoxicological properties of this chemical were compared to diethylenetriaminepentaacetic acid (DTPA), an already established iron sulfide scale remover. The new promising chemical surpassed DTPA in being a safer chemical and having a greater binding affinity to Fe2+ upon optimization, hence, a better choice. The presence of oxime (-NHOH) and carbonyl (C=O) moieties in the new chemical showed that the bidentate form of chelation is favored. Moreover, the presence of an intramolecular hydrogen bond enhanced its chelating ability.

Raman and ab initio analyses of ion pairs in concentrated K[B(OH)4] droplets.

In this study, microscopic Raman spectroscopy and Ab initio quantum chemical calculation were used to determine the structural details of ion pairs and their transformation in concentrated K[B(OH)4] droplets. The Raman experiment shows that the vsym-B(OH)4- undergoes a downward shift with the decrease of WSR. The contact ion pairs (CIPs) change to solvent shared ion pairs when the molar water-to-solute ratio (WSR) is bigger than 6; CIPs are the dominant species when 1.33<WSR<6, where K+ bonds to [B(OH)4-] in bidentate form (CIP-II); the CIPs quickly dehydrate and associate to triple ion pairs (TIPs) when WSR<5. Raman experiment and ab initio quantum chemical calculation show that TIPs are mainly present in "anionic" type such as {[B(OH)4-]K+[B(OH)4-](H2O)n}, where K+ bonds to two [B(OH)4-] in bidentate or/and tridentate form (TIP-a-II or/and TIP-a-III). When WSR <1.33, most TIPs convert to complex clusters such as chain-like structure. The remaining TIPs associate to six-membered ring structure [B3O3(OH)4-] and the relative content increases from 0 to 20% when the WSR ranges from 1.33 to 0.55.

Specific and non-specific interactions between metal cations and zwitterionic alanine tripeptide in saline solutions reported by the symmetric carboxylate stretching and amide-II vibrations.

The "specific" interaction between metal cations (Na+, Ca2+, Mg2+, and Zn2+) and the charged COO- group, and the "non-specific" interaction between these cations and the peptide backbone of a zwitterionic trialanine (Ala3) in aqueous solutions were examined in detail, using linear infrared (IR) absorptions of the COO- symmetric stretching and the amide-II (mainly the C-N stretching) modes as IR probes. Different IR spectral changes in peak positions and intensities of the two IR probes clearly demonstrate their sensitivities to nearby cation distributions in distance and population. Quantum chemistry calculations and molecular dynamics simulations were used to describe the cation-peptide interaction picture. These combined results suggest that Na+ and Ca2+ tend to bind to the COO- group in the bidentate form, while Mg2+ and Zn2+ tend to bind to the COO- group in the pseudo-bridging form. The results also show that while all three divalent cations indirectly interact with the peptide backbone with large population, Ca2+ and Mg2+ can be sometimes distributed very close to the backbone. Such a non-specific cation interaction can be moderately sensed by the C-N stretching of the amide-II mode when cations approach the polar amide C[double bond, length as m-dash]O group, and is also influenced by the NH3+ charge group located at the N-terminus. The results suggest that the experimentally observed complication of the Hofmeister cation series shall be understood as a combined specific and non-specific cation-peptide interactions.

Synthesis, Characterization and Reactivity of Nitrosyl Ruthenium Complexes with the Non-stereoidal Anti-inflammatory Diflunisal

The Na2[Ru(NO)Cl3 (df)] (I) and cis-[Ru(NO)(df)(cyclen)]Cl2 (II) complexes (df=diflunisal (5-(2,4-difluorophenyl)-2-hydroxybenzoic acid, cyclen=1, 4, 7, 10-tetraazacyclododecane) have been synthesized and characterized by elemental analysis, electronic (UV-Vis) and vibrational (FTIR) spectroscopic techniques. FTIR data suggests different modes of coordination of the ligand diflunisal in these complexes, i.e., coordinated in the bidentate form in the compound I and in the monodentate form in the compound II, and that df is coordinated to ruthenium by carboxylate group in a monodentate mode for both complexes. The FTIR spectra also display v(NO) at 1880 cm-1 and 1892 cm-1 for I and II, respectively, indicating a nitrosonium (NO+) character. Electronic spectra suggest that df is coordinated to the metal center in both complexes in catecholate form. Detailed electrochemical studies showed that complexes I and II display {RuNO}6/7 process at -420 mV and at -400 mV (vs. Ag/AgCl) respectively, and df ligand is oxidized at 1120 mV and at 770 mV, respectively. Controlled potential electrolysis at -750 mV or chemical reduction with Zn(Hg) amalgam results in NO release from both complexes.

Modified Zinc Oxide Nanoparticles for Corrosion Resistance Applications

Atmospheric corrosion is a big threat to the steel structures. This is because it compromises its structural integrity, aesthetic aspects and overall efficiency. An attempt has been made to counteract this through surface engineering of substrates including glass and steel by using modified zinc oxide nanoparticles to increase hydrophobicity. The synthesis of zinc oxide nanoparticles is carried out by using sol-gel method, thereafter these particles were modified by using stearic acid; a fatty acid. The zinc oxide nanoparticles were characterized by using X-ray diffraction analysis (XRD) which confirms the presence of hexagonal wurtzite structure. Moreover, the Scanning Electron microscopy (SEM) reveals the hexagonal wurtzite morphology of as prepared nanoparticles. Fourier transform infrared spectroscopy (FTIR) confirms the grafting of stearic acid on the surface of ZnO in bidentate form. The water Contact Angle obtained by using sessile drop method gives a statistical value of 140o which is of great interest due to higher water repellency and lower surface contact area. Finally, corrosion test was carried out on the coated steel substrate by means of conventional corrosion testing technique and it is observed that the coated sample decays three times slower than that of its bare steel counterpart.

Modified Zinc Oxide Nanoparticles for Corrosion Resistance Applications

Atmospheric corrosion is a big threat to the steel structures. This is because it compromises its structural integrity, aesthetic aspects and overall efficiency. An attempt has been made to counteract this through surface engineering of substrates including glass and steel by using modified zinc oxide nanoparticles to increase hydrophobicity. The synthesis of zinc oxide nanoparticles is carried out by using sol-gel method, thereafter these particles were modified by using stearic acid; a fatty acid. The zinc oxide nanoparticles were characterized by using X-ray diffraction analysis (XRD) which confirms the presence of hexagonal wurtzite structure. Moreover, the Scanning Electron microscopy (SEM) reveals the hexagonal wurtzite morphology of as prepared nanoparticles. Fourier transform infrared spectroscopy (FTIR) confirms the grafting of stearic acid on the surface of ZnO in bidentate form. The water Contact Angle obtained by using sessile drop method gives a statistical value of 140o which is of great interest due to higher water repellency and lower surface contact area. Finally, corrosion test was carried out on the coated steel substrate by means of conventional corrosion testing technique and it is observed that the coated sample decays three times slower than that of its bare steel counterpart.

Design and synthesis of a calcium modified quaternized chitosan hollow sphere for efficient adsorption of SDBS

In this study, a new pleated hollow sphere material (CS@Ca@CTA) was prepared by mixing chitosan (CS) and calcium chloride (CaCl2) in acetic acid solutions followed by crosslinking with glutaraldehyde (GA), and quaternized using (3-chloro-2 hydroxypropyl) trimethylammonium chloride (CTA). The natural biopolymer chitosan (CS) was used to prepare an environmentally friendly adsorbent material which can efficiently adsorb sodium dodecylbenzene sulfonate (SDBS). The adsorption of SDBS on CS@Ca@CTA can be efficiently improved by CTA at different pH values and Ca can promote the precipitation. The adsorption process of SDBS is as follows. First, SDBS can be adsorbed by electrostatic attraction and Cl- of CTA is used to ion exchange DBS- of SDBS. Then DBS- can bind stably with the Ca2+ in a bidentate form. Furthermore, CS contains NH2 and OH groups, which can provide enormous vacant active sites to adsorb SDBS, and a pleated surface have an ability to capture SDBS. The results indicated that the saturated adsorption capacity of CS@Ca@CTA up to 2300 mg g-1 at pH 3.0 within 240 min. Additionally, adsorption kinetics, isotherm and thermodynamic parameters were discussed. The aim of this article is to present CS@Ca@CTA, which has a great effect on adsorbing the SDBS.

Reactive Blue 4 as a Single Colorimetric Chemosensor for Sequential Determination of Multiple Analytes with Different Optical Responses in Aqueous Media: Cu2+-Cysteine Using a Metal Ion Displacement and Cu2+-Arginine Through the Host-Guest Interaction.

In the current study, we reported a novel label-free and facile colorimetric approach for the sequential detection of copper ion (Cu2+), L-arginine (Arg), and L-cysteine (Cys) in the H2O (10.0mmolL-1 HEPES buffer solution, pH7.0) using Reactive Blue 4 (RB4). First, the presence of Cu2+ led to a naked-eye color and spectral changes according to the binding site-signaling subunit approach. Then, the RB4-Cu2+ complex was successfully applied for Cys and Arg through different recognition pathways. The optical signals for Arg were observed due to its association involving the amino group, as well as the participation of the carboxylate group in a bidentate form to the complex, while selective behavior for Cys was explained by a metal displacement mechanism. The limits of detection for Cu2+, Arg, and Cys were calculated to be 1.96, 1.06, and 1.33μmolL-1, respectively. It could also be employed for the determination of three analytes in environmental, biological, and pharmaceutical samples. Importantly, the test strips based on RB4-Cu2+ complex could be used as a solid-state sensor for the detection of Cys and Arg. In addition, NAND and IMPLICATION molecular logic gates were obtained by using chemical inputs and UV-Vis absorbance signal as the output. Graphical Abstract.

Reaction mechanism of NH3-SCR denitrification over rare-earth concentrate

A rare-earth concentrate obtained from Bayan Obo tailings was used as catalyst for low-temperature selective catalytic reduction (SCR) of NOx. X-ray powder diffraction analysis, scanning electron microscopy, and diffuse reflectance infrared Fourier-transform spectroscopy (in situ DRIFTS) methods were applied to characterize the crystal structure, surface topography, and reaction mechanism of the catalyst. Porous structure and a new CeO2 phase appeared after the catalyst was calcined at 500 °C, and Fe, Nd, La, and other metal elements exhibited better dispersion in the catalyst. In situ DRIFTS revealed Lewis and Bronsted acidic sites on the catalyst surface. The presence of oxygen promoted dehydrogenation of NH3. Considerable amounts of bidentate, nitrate, and bridging nitrate form at oxidation-active centers of the catalyst as a result of NO + O2 adsorption for subsequent reaction with amino species in NH3-SCR. Meanwhile, adsorbed amino species could react with gaseous NOx. Temperature-programmed desorption results showed that the calcined rare-earth concentrate exhibited better adsorption capacity, especially for NO, compared with noncalcined material. The selective catalytic reduction reaction over the rare-earth concentrate catalyst predominantly follows the Langmuir–Hinshelwood mechanism.