Aqueous Solution Phase Research Articles

Novel ZnFe2O4/WO3, a highly efficient visible-light photocatalytic system operated by a Z-scheme mechanism

Dark red ZnFe2O4 (ZFO) nanoparticles (NPs) of ˜9 nm size and pale yellow WO3 nanowire bundles (NWBs) with high porosity were prepared by hydrothermal reactions, respectively, and coupled to form novel ZFO/WO3 heterojunctions. Tiny ZFO NPs and highly porous WO3 NWBs successfully formed intimate heterojunctions, facilitating charge transport at their interfaces. Under visible-light, ZFO/WO3 composites demonstrated outstanding catalytic activities for decomposing isopropyl alcohol (IPA) in the gas phase and salicylic acid (SA) in aqueous solution. In particular, the amount of CO2 evolved in 2 h during decomposition of IPA was 24.7 ppmv, which was 3.0 times that produced using typical nitrogen-doped TiO2 (N-TiO2). Moreover, its degradation rate constant of SA in the presence of ZFO/WO3 was ˜7 times that of N-TiO2. It was determined that •OH and •O2- radicals were the major active species responsible for oxidation reactions, suggesting that the photocatalytic reactions of ZFO/WO3 occurred via Z-scheme mechanism.

Early stage in situ detection of polynuclear aluminum phases in aqueous solution

Polynuclear cationic aluminum hydroxide phases are known intermediates in the formation of aluminum oxides or (oxide)hydroxides upon hydrolysis of aluminum salt solutions. In the presence of sulfate anions, these aluminum polyoxocations (Al13) can form crystalline Al13 sulfates with varying chemical composition. The formation of these Al13 sulfates in aqueous solution has been poorly understood. Here, we investigate the early stage crystallization of Al13 clusters in a sulfate-containing solution, in situ and in real time. Dynamics associated with Al13 sulfate formation have been obtained for the first time, using synchrotron X-ray diffraction (XRD) of solutions suspended by acoustic levitation. Time-resolved in situ data show that the cubic phase, Na[(AlO4)Al12(OH)24(H2O)12](SO4)4·10H2O, forms after only minutes. The formation mechanism of Al13 sulfates was found to depend on the sulfate:aluminum (SO4:Al) ratio. Ex situ XRD of the product Al13 sulfates in solution shows that for SO4:Al ratio ≤1.5 two other crystalline phases form, and convert to the cubic phase upon washing and drying. In situ XRD for the same ratio shows transient formation of an intermediate during the crystallization process.

Multifunctional Pd/Fe-biochar composites for the complete removal of trichlorobenzene and its degradation products

To elucidate the effect of structure and property of biochar on the structure-activity relationship among the composites of biochar supported Pd/Fe and 1,2,4-trichlorobenzene (1,2,4-TCB) and its dechlorination products, biochar supported Pd/Fe nanoparticles with different mass ratios were investigated for the enhanced removal of 1,2,4-TCB (52 μmol/L) and its dechlorination products. 1,2,4-TCB was removed through the electrochemical dechlorination by Pd/Fe and adsorption by biochar simultaneously. As the mass ratio of CS700 to Pd/Fe was 0.1:1, biochar within the Pd/Fe-CS7000.1 system played a significant role in the adsorption of 1,2,4-TCB. However, there is little adsorption to biochar for dechlorination products due to strong competition by 1,2,4-TCB. As the mass ratio of CS700 to Pd/Fe was increased to 5:1, 1,2,4-TCB was completely removed from the solution by the composites within 0.5 h. The dechlorination products (1,2-DCB, MCB, benzene and trace 1,3-DCB) were completely sequestered on solid phase but absent in aqueous solution. However, the excessive biochar increased the inaccessibility of 1,2,4-TCB or decreased the reactive sites of Pd/Fe leading to the less dechlorination of 1,2,4-TCB. The alkaline biochar did not influence the chemical reactivity of Pd/Fe in the composites and buffered the acid and alkaline solutions with pH being maintained at neutral conditions under initial pH ranging from 3.07 to 10.03. The highly hydrophobicity of biochar could maintain the affinity of the composite for the chlorinated compounds even if the concentration of 1,2,4-TCB was up to 80.9% of its aqueous solubility. This study provides efficient synergistic removal support for the treatment of TCB affected groundwater.

Structural and optical features of lanthanide species-derived functional hydrogels

ABSTRACTAs soft materials represent new features that offer long-range orders, they have received considerable interests in optoelectronic fields. In this contribution, the assembly and characterization of soft materials incorporated by lanthanide complex have been reported. The polymeric hosts are derived from polyvinyl alcohol and polyacrylamide-co-polyacrylic acid. As for the metal complexes, the organic chromophore can sensitize europium or terbium ions simultaneously and green/red emissions are achieved. In the aqueous solution phase, the europium complex generates luminescence quenching effect upon the addition of Cu2+ ions and the detection limit has been determined to be 3.6 μM. In addition, the “on–off” changes can be also observed based on the complex-loaded hydrogels and the mechanical properties are discussed. This responsive soft material will demonstrate great potentials in optical devices, biological analysis, and medical diagnosis fields.

Model and Algorithm for Calculating the Formation of Phases in Aqueous Solutions of Metal Salts

An equilibrium model and an algorithm for processing experimental potentiometric titration data are developed that improve the reliability of results on phase formation in aqueous solutions of metal salts. In creating the model, it is proposed that the formation of polynuclear, heteroligand compounds and fluctuations of the system parameters be considered, and that the laws of molecular solubility, solubility over an intermediate, and identifying the main sediment be used. To derive the material balance equations of the studied systems, software is developed that allows calculations of the number of particles in the system, the values of equilibrium constants, and the composition of compounds, in addition to automatic selection of the functions that describe random processes when estimating the uncertainty of equilibrium constant values.

Ultrasonic-assisted fabrication and release kinetics of two model redox-responsive magnetic microcapsules for hydrophobic drug delivery

The smart biocompatible carriers have an advantage in the high-efficiency delivery and stimuli-responsive release of drugs. This study describes two model magnetic microcapsules (MMC) fabricated by sonicating the hydrophobic drug-loaded oil phase in an albumin aqueous solution, where magnetic nanoparticles are either encapsulated into the core or embedded onto the albumin shell. The as-prepared MMC with magnetic shell (MS) or with magnetic core (MC) shows an appropriate dispersibility with a well-defined spherical morphology in water, an excellent magnetism-mediated shifting ability for targeted drug delivery, and a good biocompatibility for high-level cell viability. Moreover, both the two microcapsules also show a high efficiency to trap the hydrophobic drugs, where the embedding ratios are 87.41% for MMC-MS and 95.31% for MMC-MC, respectively. Meanwhile in current study, the release kinetics and mechanism reveal that the sulfhydryl-crosslinked shell structure endows the MMC with a redox-responsive behavior to release the contents for controlled drug release, and the release rate or the release amount can be adjusted by changing the dosage of reducing agent. Therefore, the MMC have great potential as a smart carrier of hydrophobic drugs for enhancing the therapeutic efficiency.

Liquid Crystal ordering of DNA Dickerson Dodecamer duplexes with different 5’- Phosphate terminations

The onset of liquid crystal (LC) phases in concentrated aqueous solutions of DNA oligomers crucially depends on the end-to-end interaction between the DNA duplexes, which can be provided by the aromatic stacking of the terminal base-pairs or by the pairing of complementary dangling-ends. Here we investigated the LC behavior of three blunt-end 12-base-long DNA duplexes synthesized with hydroxyl, phosphate and triphosphate 5’-termini. We experimentally characterized the concentration-temperature phase diagrams and we quantitatively estimated the end-to-end stacking free energy, by comparing the empirical data with the predictions of coarse-grained linear aggregation models.The preservation of LC ordering, even in presence of the bulky and highly charged triphosphate group, indicates that attractive stacking interactions are still present and capable of induce linear aggregation of the DNA duplexes. This finding strengthens the potential role of chromonic like self-assembly for the prebiotic formation of linear polymeric nucleic acids.

Impact of Elastin-like Protein Temperature Transition on PEG-ELP Hybrid Hydrogel Properties.

Biomaterial hydrogels are made by cross-linking either natural materials, which exhibit inherent bioactivity but suffer from batch-to-batch variations, or synthetic materials, which have a well-defined chemical structure but usually require chemical modification to exhibit bioactivity. Recombinant engineered proteins bridge the divide between natural and synthetic materials because proteins incorporate bioactive domains within the biopolymer backbone and have a well-defined amino acid structure and sequence. Recombinant engineered elastin-like proteins (ELPs) are modeled from the native tropoelastin sequence. ELPs are composed of repeating VPGxG penta-peptide sequences, where x is any guest residue except proline. ELPs undergo a lower critical solution temperature (LCST) transition above which they aggregate into a coacervate phase in aqueous solution. Here we show that the LCST transition impacts hydrogel microarchitecture which may serve as a useful design feature in engineering ELP-based hydrogels. We investigate how the ELP LCST transition contributes to the properties of hybrid poly(ethylene glycol) (PEG) and ELP (PEG-ELP) hydrogels. PEG-ELP hydrogels gelled below the LCST have a homogeneous distribution of ELP, while gelling above the LCST results in the formation of spherical ELP-rich regions within the bulk hydrogel. The ELP-rich microarchitecture is maintained when an amine-reactive cross-linker is incorporated during the gelation process. The formation of ELP-rich regions reduces PEG-ELP hydrogel bulk stiffness and increases optical density. Our characterizations of hydrogels created by using the LCST transition provide design criteria for incorporating microscale features. This may be a useful technique in understanding the role of localized bioactivity at the microscale level within hydrogel systems.

Effect of Amino Acid and Oligopeptide Additives on Formation of Lyotropic Hexagonal Phase in Aqueous Solutions of Sodium Dodecyl Sulphate

Effect of Amino Acid and Oligopeptide Additives on Formation of Lyotropic Hexagonal Phase in Aqueous Solutions of Sodium Dodecyl Sulphate

Structural properties and vibrational analysis of Potassium 5-Br-2-isonicotinoyltrifluoroborate salt. Effect of Br on the isonicotinoyl ring

In this work, the potassium 5-Br-2-isonicotinoyltrifluoroborate salt (B-ITFB) have been experimentally characterized by using FT-IR, FT-Raman and Ultravioleta-visible spectra while Ab-initio calculations in gas and in aqueous solution phases were employed to predict their structural and vibrational properties. Here, the results were compared with those reported for the potassium 2-isonicotinoyltrifluorborate salt (ITFB) in order to know the impact of Br on the 2-isonicotinoyl ring and its effects on the properties of B-ITFB. Potential energy surface using B3LYP/6-311++G** calculations has revealed two conformers for B-ITFB with C1 symmetries where only one of them presents the minimum energy. The incorporation of Br in the 5 position of isonicotinoyl ring generates: (i) a change in the symmetry from CS in ITFB to C1 in B-ITFB, (ii) a decreasing in the solvation energy due to higher size of Br, (iii) notable reduction in the Mulliken charges on all the C atoms of ring and, especially, on the C11 atom of trifluoroborate group in both media, (v) smaller bond order values, (vi) an important inductive acceptor effect, (vii) a decreasing in the electron density distribution, specifically in solution and (viii) a smaller reactivity and low electrophilicity and nucleophilicity indexes, as compared with ITFB. On the other hand, for B-ITFB the force fields in both media, the complete assignments of 45 normal vibration modes and the force constants are reported for first time.

Simultaneous determination of the potent anti-tuberculosis regimen—Pyrazinamide, ethambutol, protionamide, clofazimine in beagle dog plasma using LC–MS/MS method coupled with 96-well format plate

Tuberculosis is one of the top concerns in the world and acutely threatens human health. A new potent candidate regimen containing pyrazinamide (PZA), ethambutol (EMB), protionamide (PTO) and clofazimine (CFZ) was proposed by Parabolic Response Surface/Feedback System Control (FSC/PRS) system and showed excellent outcomes in vitro and vivo studies. Here, a convenient liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) method was developed for the simultaneously determination of four compounds in beagle dog plasma. The plasma samples, 50 μL for each, were pretreated by methanol on 96-well format plates and a further dilution step was designed to reduce predictable matrix effect and lessen the burden of subsequent analysis. The chromatographic separation was achieved on an Agilent SB-Aq column (4.6 mm × 150 mm, 5 μm) at 30 °C by a gradient elution within 6 min. The mobile phase was a mixture of 0.2% formic acid-5 mM ammonium acetate aqueous solution (phase A) and 0.2% formic acid methanol (phase B) with a total flow rate of 1 mL/min. The 30% of post-column eluant was injected into mass spectrometer, equipped with electrospray ionization (ESI) source under positive mode and multiple-reaction monitoring (MRM). This quantification method was proved to be satisfied in selectivity, accuracy, precision, linearity (r2 > 0.998), recovery, matrix effect and stability. Under the specialized conditions, the calibration curves ranged from 20 to 5000 ng/mL for PZA, 1 to 500 ng/mL for EMB, 1 to 500 ng/mL for PTO, and 1 to 200 ng/mL for CFZ. The quantitative accuracy was further assessed under different degrees of hemolyses in detail. This method was proved to be robust and efficient, and successfully applied to the pharmacokinetic study of the new regimen in Beagle dogs.

Simultaneous Quantification of Methotrexate and Its Metabolite 7-Hydroxy-Methotrexate in Human Plasma for Therapeutic Drug Monitoring.

Objective To establish and validate a simple, sensitive, and rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the determination of methotrexate (MTX) and its major metabolite 7-hydroxy-methotrexate (7-OH-MTX) in human plasma. Method The chromatographic separation was achieved on a Zorbax C18 column (3.5 μm, 2.1 × 100 mm) using a gradient elution with methanol (phase B) and 0.2% formic acid aqueous solution (phase A). The flow rate was 0.3 mL/min with analytical time of 3.5 min. Mass spectrometry detection was performed in a triple-quadruple tandem mass spectrometer under positive ion mode with the following mass transitions: m/z 455.1/308.1 for MTX, 471.0/324.1 for 7-OH-MTX, and 458.2/311.1 for internal standard. The pretreatment procedure was optimized with dilution after one-step protein precipitation. Results The calibration range of methotrexate and 7-OH-MTX was 5.0-10000.0 ng/mL. The intraday and interday precision and accuracy were less than 15% and within ±15% for both analytes. The recovery for MTX and 7-OH-MTX was more than 90% and the matrix effect ranged from 97.90% to 117.60%. Conclusion The method was successfully developed and applied to the routine therapeutic drug monitoring of MTX and 7-OH-MTX in human plasma.

Improving the description of solvent pairwise interactions using local solute/solvent three-body functions. The case of halides and carboxylates in aqueous environment.

We propose a general strategy to remediate force-field artifacts in describing pairwise interactions among similar molecules M in the vicinity of another chemical species, C, like water molecules interacting at short distance from a monoatomic ion. This strategy is based on introducing a three-body potential energy term that alters the pairwise interactions among M-type molecules when they lie at short range from the species C. In other words the species C is the center of a space domain where the pairwise interactions among the molecules M is altered. Here, we apply it to improve the description of the water interactions provided by the polarizable water model TCPE/2013 in the vicinity of halides, from F- to At- , and of the prototypical carboxylate anion CH3 COO- . We show the accuracy and the transferability of such an approach to investigate not only the hydration process of single anions but also of a salt solution in aqueous phase. This strategy can be used to remediate the drawbacks of any kind of force fields. © 2019 Wiley Periodicals, Inc.

Exponential Scaling of Water Exchange Rates with Ion Interaction Strength from the Perspective of Dynamic Facilitation Theory.

Water exchange reactions around ionic solutes are ubiquitous in aqueous solution-phase chemistry. However, the extreme sensitivity of exchange rates to perturbations in the chemistry of an ionic solute is not well understood. We examine water exchange around model ions within the language of dynamic facilitation theory, typically used to describe glassy and other systems with collective, facilitated dynamics. Through the development of a coarse-grained, kinetically constrained lattice model of water exchange, we show that the time scale for water exchange scales exponentially with the strength of the solute-solvent interactions.

Mechanism and theory of d-glucopyranose homogeneous acid catalysis in the aqueous solution phase.

A detailed systematic theoretical study of the mechanism of the homogeneous Brønsted-acid catalysis of d-glucose in aqueous solution phase ("acid hydrolysis") is reported. G4MP2 with the SMD solvation model at B3LYP/6-31G(2df,p) are employed to compute the free energies of the molecular and ionic species pertaining to the isomerization, protonation, hydrogen cation transfer and decomposition processes of d-glucopyranose in aqueous solution phase. This information is used to hypothesise a reaction mechanism that is of improved accuracy and completeness from the existing art. It is found that rotation of the d-glucose alkyl carbon-carbon bond is a facile process and is very important to the subsequent catalytic mechanism. This rotation produces two rotameric isomers which are of notably different thermodynamic stability and reactivity, even with regard to the products of this acid catalysis. As a low energy process (ΔG‡ = ∼3.8-6.7 kcal mol-1), the alkyl carbon-carbon bond may rotate toward the hydroxyl group at the adjacent "4" position reducing the energy required to protonate that position by 3.0-7.2 kcal mol-1 (or 15-30%). The combination of two rotomeric isomers with the six structural isomers owing to the oxygen atoms, means that protonated d-glucose cations embark on a complex competition of interconversion and decomposition that is both thermodynamically and kinetically influenced. The calculations support the hypothesis that the acid-catalysed hydrolysis of d-glucose may yield a number of platform chemicals that have not previously been suggested. These include the prospect of three isomers of 5-hydroxymethylfurfural (HMF); 5-(hydroxymethyl)furan-2-carbaldehyde, 5-(hydroxymethyl)furan-3-carbaldehyde and 5-(hydroxymethyl)furan-4-carbaldehyde. Vibrational spectra of these HMF isomers are also computed and compared to experimentally determined infrared spectra of "humins". On this basis, it is cautiously speculated that the alternative HMF isomers, may be monomeric constituent of the polymeric "humins".

Determination of Impurities and Degradation Products/Causes for <i>m</i>-Iodobenzylguanidine Using HPLC-Tandem Mass Spectrometry

m-Iodobenzylguanidinium hemisulfate (MIBGHS) is a precursor in the preparation of radioiodine-labeled m-iodobenzylguanidine (MIBG), which is used as a radio-imaging and therapy agent for neuroendocrine tumors and myocardial sympathetic nerve function. To ensure the quality and efficacy of the medicine and prevent side effects, the precursor purity, source of impurity, and derivatives have to be determined. In this study, the purity of synthesized MIBGHS and the amount of contaminants therein were determined by high-performance liquid chromatography and ultraviolet detection, gradient eluted by ammonium formate aqueous solution and acetonitrile mobile phase on both C8 and phenyl type column. The impurities were identified on the basis of molecular and fragmented ion mass spectra using of electrospray ionization triple quadrupole tandem mass spectrometry. The results revealed the presence of process-related impurities including m-bromobenzylguanidine (MBrBG) and overreacted byproducts. Stress test results indicated that MIBGHS is stable under acidic and dry thermal conditions for at least 72 h but MIBG aqueous solution was deteriorated slowly when exposed to UV light, thermal, oxidative and alkaline environments. Thus, m-iodobenzylamine, the starting material intended for the synthesis of MIBGHS should be analyzed to ensure that it is free from m-bromobenzylamine impurity. Stored under normal condition (-18°C), MIBGHS is stable for at least 12 months. The chemically labile guanidine and amine groups in MIBGHS are the major causes of its instability, while iodide loss from the phenyl group is a minor cause.

Structural, FT-IR, FT-Raman and ECD studies on the free base, cationic and hydrobromide species of scopolamine alkaloid

The complete vibrational assignments for the alkaloid scopolamine as free base, quaternary scopolammonium cationic and hydrobromide species were reported for first time by using the internal coordinates, the scaled quantum mechanical force field (SQMFF) procedure and the experimental FT-IR, FT-Raman spectra of hydrobromide tri-hydrate. Hybrid B3LYP/6-31G* calculations were employed to study two pairs of R and S enantiomers of free base, cationic and hydrobromide forms in gas and aqueous solution phases. The properties in solution were studied with the self-consistent reaction field (SCRF) method and the integral equation formalism variant polarised continuum model (IEFPCM) model while the solvation energies were computed by using the solvation model. The structural, electronic, topological and vibrational properties were studied only for the most stable structure of each form by using natural bond orbital (NBO) and atoms in molecules (AIM) analyses. Also, the Mulliken and Merz-Kollman (MK) charges were evaluated in both media together with the molecular electrostatic potential (MEP) in order to predict the potential nucleophilic and electrophilic reaction sites for each species. The frontier orbitals and some descriptors were investigated for those three species in order to compare with those reported for heroin, morphine, cocaine and tropane alkaloids. Here, the force fields and the complete assignments of the 123, 126 and 129 vibration normal modes expected for the free, cationic and hydrobromine anhydrate form of scopolamine alkaloid are reported. The predicted infrared, Raman and Electronic Circular Dichroism (ECD) support the presence of cationic S2 form of scopolamine in the solid state, in concordance with the corresponding experimental structure determined by X-ray diffraction. In addition, the force constants are reported for the three species of scopolamine.

Estimating n-octanol-water partition coefficients for neutral highly hydrophobic chemicals using measured n-butanol-water partition coefficients

Direct measurement of the n-octanol partition coefficients (KOW) for highly hydrophobic organic chemicals is extremely difficult because of the extremely low concentrations present in the water phase. n-Butanol/water partition coefficients (KBW) are generally much lower than KOW due to the increased solubility of solute in the alcohol saturated aqueous phase, and therefore become easier to measure. We measured the KBW for 25 neutral organic chemicals having measured log KOWs ranging from 2 to 9 and 4 additional highly hydrophobic chemicals, with unmeasured KOWs, having estimated log KOWs ranging from 6 to 18. The measured log KBW and log KOW values were linearly related, r2 = 0.978, and using the regression developed from the data, KOWs were predicted for the 4 highly hydrophobic chemicals with unmeasured KOWs. The resulting predictions were orders of magnitude lower than those predicted by a variety of computational models and suggests the estimates of KOW in the literature for highly hydrophobic chemicals (i.e., log KOW greater than 10) are likely incorrect by several orders of magnitude.

Facile synthesis of the magnetic metal–organic framework Fe3O4/Cu3(BTC)2 for efficient dye removal

Dyeing wastewaters present high hazards for the environment and human health. Advanced dye removal may be achieved by magnetic metal–organic frameworks (MMOFs) due to their high adsorption and catalyst efficiencies. However, the existing synthesis strategies of frameworks are often cumbersome and time-consuming in the presence of toxic solvents. Hence, a simple and environmentally-friendly synthetic method is desired. Here, a kind of MMOF, Fe3O4/Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate), was synthesized via a novel aqueous solution-phase synthesis. The product Fe3O4/Cu3(BTC)2 has a high specific surface area of 755.15 m2 g−1, and excellent magnetic performance of 31.2 emu g−1. The Fe3O4/Cu3(BTC)2 can effectively remove methylene blue from wastewater in the presence of H2O2. After having been finished the dye removal, it was easily separated and recycled several times by use of the magnetic technology.

Development of a 3D-printed modified Scheludko-cell: Potential application for adsorption and thin liquid film study

A systematic study on the formation of thin liquid films (TLFs) of n-dodecane, as an intervening liquid phase in aqueous surfactant solution, was performed using a modified 3D-printed Scheludko-cell (MSC). The formation and stability of TLFs are electrically detected using the current density-voltage (J-Ψ) characteristics of the system, and it is confirmed by in-situ visualization of TLFs. The conductivity of the TLFs is measured using the J-Ψ curve and resistors in a series model of the system. The induced conductivity of the film is measured for different concentrations of potassium chloride (KCl) and sodium dodecyl sulfate (SDS) aqueous solutions. We monitored an increase in TLF conductivity due to the accumulation of inorganic hydrophilic ions like (K+ or Cl−) and adsorption of amphiphilic anion of dodecyl sulfate to the interface. The higher rate of increase in the TLF conductivity in the case of SDS is attributed to the ability of amphiphilic ions to pass through a so-called unscreened potential in the vicinity of oil-aqueous solution interface leading to an unscreenable potential at the boundary of the TLF. The predicted adsorption time-scale of surfactants using the MSC cell in ionic liquid (IL) phase, at O/W interface, is found to be in good agreement with the dynamic interfacial tension test results.