Strong Acidic Conditions Research Articles

Exhaustive Syntheses of Naphthofluoresceins and Their Functions

Naphthofluorescein and/or seminaphthofluorescein derivatives possessing the additional benzene units to one or both sides of fluorescein were exhaustively constructed through Friedel-Crafts type reactions between corresponding aroylbenzoic acids and dihydroxynaphthalenes. Compound 4 works as a one-dye pH indicator, which shows red in strong acid condition and blue in basic solution. Compound 23 (diacetate of compound 4) shows good transitivity to the HEK 293 cells and acts as a fluorescent pigment for the living cell imaging. Compounds 5, 6, and 9 show fluorescent emission in the NIR region (>700 nm) and imply the potentialities of NIR fluorescent probes.

Transformations of Griseofulvin in Strong Acidic Conditions – Crystal Structures of 2′-Demethylgriseofulvin and Dimerized Griseofulvin

The structure of griseofulvic acid, C16H15ClO6, at 100 K has orthorhombic (P2(1)2(1)2) symmetry. It is of interest with respect to biological activity. The structure displays intermolecular O-H...O, C-H...O hydrogen bonding as well as week C-H...pi and pi...pi interactions. In strong acidic conditions the griseofulvin undergoes dimerization. The structure of dimerized griseofulvin, C34H32C12O12 x C2H6O x H2O, at 100 K has monoclinic (P2(1)) symmetry. The molecule crystallized as a solvate with one ethanol and one water molecule. The dimeric molecules form intermolecular O-H...O hydrogen bonds to solvents molecules only but they interact via week C-H...O, C-H...pi, C-Cl...pi and pi...pi interactions with other dimerized molecules.

Effect of temperature, pH, and NaCl on the inactivation kinetics of murine norovirus.

We investigated the resistance of murine norovirus (MNV) and coliphage MS2, a culturable human norovirus surrogate, to temperature, salt, and pH. Virus inactivation was measured by plaque, real-time TaqMan reverse transcription (RT) PCR, and long-template RT-PCR assays. Both MNV and MS2 were rapidly inactivated at temperatures above 60°C. Similarly, MNV tolerated low salt concentrations (0.3% NaCl) to a greater degree than high salt concentrations (3.3 to 6.3% NaCl). MNV was relatively resistant to strong acidic conditions (pH 2) and was more tolerant of slightly acidic (pH 4) or neutral (pH 7) conditions. In contrast, MS2 was resistant to high salinity. Overall, temperature had a greater effect on infectivity than salt or low pH. Additionally, temperature and low pH had a synergistic effect on MNV infectivity. Both real-time and long-template RT-PCR assays significantly underestimated the inactivation by temperature, salt, and pH. The inactivation kinetics of both MNV and MS2 under various environmental conditions gave a good fit by the Weibull model (R² > 0.9). This study suggests both the capacity of infectious human norovirus to persist in the face of various environmental conditions and its sensitivity to high temperatures, which may provide a mechanism of protection against this virus.

Hydrothermal incorporation of Ce(La) ions into the framework of ZSM-5 by a multiple pH-adjusting co-hydrolysis

Ce and La incorporated ZSM-5 zeolitic materials with different metal loadings were synthesized via the multiple pH-adjusting procedures involving a co-hydrolysis of TEOS (tetraethyl-orthosilicate) with rare earth salts under a strong acidic condition, a further gelation under a weak acidic condition, and a final basic hydrothermal crystallization. Thus obtained Ce(La)-ZSM-5, as well as Ce or La ion-exchanged ZSM-5 samples, were characterized by XRD, SEM, TG, UV–vis, 29Si MAS NMR, FT-IR, N2-physisorption, and elemental analysis. The characterizations provide systematic and complementary evidences to demonstrate the incorporation of Ce(La) ions into the tetrahedral sites of ZSM-5 framework. The upper limits of the rare earth loadings in the synthesis gel and the final product are ca. 50 and 70 of the molar ratio of Si/Ce(La), respectively. It is observed that the synthesized Ce(La)-ZSM-5 zeolites possess an unusual morphology of microspheres that are assembled by numerous cubic prism-shaped nanocrystallines.

Ultra Acidic Strong Cation Exchange Enabling the Efficient Enrichment of Basic Phosphopeptides

We present a straightforward method to enrich phosphopeptides with multiple basic residues, an under-represented class in common enrichment strategies. Our method is based on a two-dimensional strong cation exchange (SCX) strategy, operating at two different acidic pHs, enabling both separation and enrichment of different classes of phosphopeptides. The principle of enrichment is based on the change of net charge of phosphorylated peptides under strong acidic conditions in the second SCX, whereas the net charge of regular peptides remains unchanged, thus enabling separation based on net charge. Application of our tandem SCX approach to a modest amount of human cells allowed the identification of over 10,000 unique "basic" phosphopeptides of which many represent putative targets of basophilic kinases.

Sorption removal of cephalexin by HNO3 and H2O2 oxidized activated carbons

Cephalexin’s traces within pharmaceutical effluents have toxic impact toward ecological and human health. Low-cost activated carbon derived from Trapa natans husk was oxidized with hydrogen peroxide and nitric acid, and tested for their ability to remove cephalexin from aqueous solutions. Oxidization with H2O2 showed negative effect on the cephalexin sorption, whereas HNO3 oxidization improved the adsorption. The cephalexin adsorption isotherms on the native and HNO3 oxidized carbons correlated well with the Freundlich equation while their kinetics followed the pseudo-second order model. The removal of cephalexin by the native and HNO3 oxidized carbons was found to be most favored at low ionic strength and strong acidic conditions. Based on the thermal and FTIR analyses, the interaction mechanisms of the interaction between cephalexin and the carbons were proposed. Electrostatic attraction, hydrophobic interaction and chemical bonding with surface functional groups were demonstrated as primary mechanisms for cephalexin removal. The nitrogen functionalities on the carbon surface were considered to be an important factor affecting the adsorption process.

Phosphorus Release from the Sediments in Rongcheng Swan Lake under Different pH Conditions

Rongcheng Swan Lake is a coastal lagoon in eastern Shandong Peninsula, China, whose water quality and ecological environment has deteriorated in recent years. The effect of pH on phosphorus (P) release from the sediments and the contribution of P fractions to release in Swan Lake were investigated. The results showed that the sediments released significant amount of P under the strong acidic (pH 3) and alkaline conditions (pH 9), especially at pH 3; whereas under the strong alkaline (pH 10) and neutral conditions, a low quantity of P was released in this lagoon. The sediments in northwestern lake (site 1) showed significantly higher P release than that in the west (site 2). Under the strong acidic condition, the maximum release rates at sites 1 and 2 were 204.49 and 159.12 μg/m2/day, respectively; while at pH 9, the maximum were 190.52 and 10.12 μg/m2/day, respectively. P fractions in the sediments indicated that P release was mainly from BD-P, HCl-P and NaOH-P fractions in Swan Lake. Under the strong acidic condition, the contribution of HCl-P to release was high; whereas under alkaline condition the release of NaOH-P was great. Due to the high proportions of mobile P (NaOH-P+BD-P) to total P in surface sediments, P release potential in northwestern sediments is large under the slightly alkaline environment of Swan Lake.

PH-driven hydrothermal synthesis and formation mechanism of all BiPO4 polymorphs

Understanding of formation mechanism of inorganic solids by solution chemistry is always disturbed by the interference effect of the impurities from starting materials. Herein, we exploited a new two-step route to the selective synthesis of BiPO4 of different polymorphs with an aim to eliminate the impurity interference effect. The first step is the room-temperature solution synthesis of a hexagonal phase (HP), and the second step involves sufficient washing of HP and a subsequent hydrothermal treatment of HP under given conditions. The formation mechanism of BiPO4 nanocrystals of different polymorphs was studied by monitoring the reaction parameters like pH, reaction temperature, time, and impurity ions as well as by sample characterizations using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. It is found that the pH of the solution is the determinant parameter for the selective synthesis of BiPO4 polymorphs. Namely, at 240 °C and under strong acidic conditions (pH < 1), HP underwent a phase transformation to a low-temperature monoclinic phase (LTMP), while under neutral or weakly acidic conditions (3 < pH < 7), HP transferred to a high-temperature monoclinic phase (HTMP). Further increasing the solution pH value up to 14 led to the formation of P-doped Bi2O3, a phase which is never accessible by conventional solution chemistry but firing in air at T > 750 °C. Based on these observations, two kinds of phase transition mechanisms were discussed.

Azo-hydrazone tautomerism observed from UV-vis spectra by pH control and metal-ion complexation for two heterocyclic disperse yellow dyes

The azo-hydrazone tautomerism of two pyridine-2,6-dione based Disperse Yellow dyes has been achieved by pH control and metal-ion complexation, respectively, which is evidenced by UV-visible spectra using pH-titration, (1)H NMR and X-ray single-crystal diffraction techniques for two dyes and one neutral dinuclear dye-metal complex. pH-titration experiments under strong and weak acidic conditions (HCl and HOAc) as well as strong and weak alkaline conditions (NaOH and ammonia) demonstrate that there is an equilibrium between the azo (HL(1-A) and HL(2-A)) and hydrazone (HL(1-H) and HL(2-H)) tautomers for two dyes in solution but the hydrazone form is dominant under conventional conditions. The hydrazone proton is also observed in the (1)H NMR spectra of HL(1-H) and HL(2-H) which can be verified by the hydrogen-deuterium exchange and the presence of cooperative six-membered intramolecular hydrogen rings involving the hydrazone proton in their X-ray single-crystal structures. Moreover, the azo-hydrazone tautomerism is evidenced by the formation of a novel neutral dinuclear dye-metal complex Cu(2)(L(2-A))(4), where all the ligands are in the azo form and two types of coordination modes are present for four L(2-A) ligands. Namely, the side two ligands serve as the bidentate capping ligands, while the middle ones act as the quadridentate bridging ligands linking adjacent Cu(II) centers in a reverse fashion.

A Lead Film Electrode for Adsorptive Stripping Voltammetric Analysis of Ultratrace Tungsten(VI) in Acidic Medium

AbstractFor the first time an in situ plated lead film electrode was applied to adsorptive stripping voltammetry at relatively strong acidic conditions of, e.g., pH 2. As an example of the application of such electrode a procedure for ultratrace W(VI) determination by adsorptive stripping voltammetry was elaborated. The procedure is based on the preconcentration of the W(VI)‐Alizarin Red S complex at an in situ plated lead film electrode held at −0.575 V (vs. Ag/AgCl), followed by a negatively sweeping square wave voltammetric scan. The proposed voltammetric procedure was applied to W(VI) determination in natural water samples.

Photocatalytic Degradation of Methyl Orange Using a TiO2/Ti Mesh Electrode with 3D Nanotube Arrays

To further improve the photocatalytic techniques for water purification and wastewater treatment, we successfully prepared a new type of TiO(2)/Ti mesh photoelectrode, by anodization in ethylene glycol solution. The three-dimensional arrays of nanotubes formed on Ti mesh show a significant improvement in photocatalytic activity, compared to the nanotube arrays formed on foil. This can be demonstrated by about 22 and 38% enhancement in the degradation efficiency per mass and per area, respectively, when TiO(2)/Ti mesh electrode was used to photocatalyze methyl orange (MO). Furthermore, the effects of different parameters on MO photodegradation were investigated, such as different photoelectrode calcination temperature, the initial pH value of MO solution, and the present of hydrogen peroxide. The superior photocatalytic activity could be achieved by the TiO(2)/Ti mesh photoelectrode calcinated at 550 °C, due to the appearance of mixed crystal phases of anatase and rutile. In strong acidic or caustic conditions, such as pH 1 or 13, a high degradation efficiency can be both obtained. The presence of H(2)O(2) in photocatalytic reactions can promote photocatalytic degradation efficiencies. Moreover, the experimental results demonstrated the excellent stability and reliability of the TiO(2)/Ti mesh electrode.

Utilization of agricultural waste chestnut shell for the removal of Reactive Brilliant Red K-2G from aqueous solution

Chestnut shell, an agricultural residue, was used as a low-cost adsorbent to remove Reactive Brilliant Red K-2G (RBR) from aqueous solution. Batch adsorption experiments were conducted to study the effects of initial solution pH value, adsorbent dosage, initial dye concentration and temperature on the adsorption. It was proved that strong acidic condition was favorable for the adsorption process and the optimal pH value was 1.0. Freundlich isotherm was appropriate for describing the experimental data. The kinetics study revealed that the adsorption of RBR onto chestnut shell followed the pseudo-second order model well. The external mass transfer mainly governed the adsorption rate. Thermodynamic studies demonstrated the spontaneous and exothermic natures of the adsorption process. The FTIR analysis indicated that functional groups such as amine, hydroxyl and phenolic compounds on the chestnut shell may be the active binding sites for the adsorption of RBR.

Protonated N,N′-Dioxide-4,4′-bipyridine, an Interesting Synthon for the Building of Polar H-Bonded Networks?

A slow liquid–gas diffusion method in strong acid conditions has allowed stabilizing for the first time in the solid state the diprotonated form of the 4,4′-bipyridine-N,N′-dioxide (bp4do), H2bp4do2+ as two polymophs of the chloride salt (H2bp4do)Cl2, while in the presence of a metallic salt M(III)Br3 (M = Bi, Sb), the monoprotonated form Hbp4do+ is mainly stabilized as (Hbp4do)2[Sb2Br8] and (H2bp4do)(Hbp4do)4[Bi4Br18]·2H2O. The dehydration of this last phase leads to (H2bp4do)(Hbp4do)4[Bi4Br18]. In the structures of (H2bp4do)Cl2 salts, the hydroxyl H atoms point toward the chloride anions leading to close (O)H···Cl contacts in the range 1.831–1.839 A. A one-dimensional network of H-bonded Hbp4do+ cations is found in the structure of (Hbp4do)2[Sb2Br8], whereas H-bonded supramolecular cations of five entities are found in the structures of bromobismuthate salts. In all the halometallate structures, X-ray analyses (293 K and 120 K data) did not allow us to locate the acid H atoms of protonated bp4do molecul...

Chitosan microgel: Effect of cross-linking density on pH-dependent release

Chitosan microgels were prepared by a spray-drying method using glutaraldehyde (GA) as a cross-linker. Two kinds of microgels, so-called soft microgel and hard microgel, were prepared using a chitosan to GA ratio of 1: 0.08, and 1: 0.67, respectively. The surfaces of hard microgels were more even that those of soft microgels. The swelling ratio, a measure of degree of swelling, of the soft microgel was pH-sensitive, and it decreased from 1,765% to 1,230%, when the pH increased from 4.0 to 9.0. The deprotonation of amino groups of chitosan could account for the decrease in swelling ratio. The swelling ratio of hard microgels was almost invariable in response to pH change (4.0 to 9.0), and it was much less than that of soft microgels, possibly due to the high cross-linking density. The degree of release from the soft microgels decreased from 65% to 12% when the pH of medium increased from 4.0 to 6.0. FITC-dextran would readily diffuse out of the microgel, possibly due to the larger meshes of the microgels in a strong acidic condition (e.g., pH 4.0). However, the degree of release increased from 12% to 82% when the pH of medium increased from 6.0 to 9.0. In this pH range, the fluorescence dye is believed to be released mainly by a squeezing-out.

SYNTHESIS AND CHARACTERIZATION OF CHITOSAN NANOPARTICLES WITH ENHANCED ANTIMICROBIAL ACTIVITY

The present paper demonstrates how the antimicrobial properties of chitosan can be enhanced by converting it into nanoparticles of desired size and surface charge using TPP (tripolyphosphate) initiated gelation process. It has been investigated and found that ionic gelation of cationic chitosan macromolecules offers a flexible and easily controllable process for systematically and predictably manipulating the particle size and surface charge of chitosan nano-particles which is an important property for antimicrobial effect. Variations in chitosan to TPP weight ratio, pH of chitosan solution and chitosan solution concentration during nanoparticle formation were examined systematically for their effects on nanoparticle size, intensity of surface charge, so as to enable faster synthesis of chitosan nanoparticles with desired properties to have optimum antimicrobial property. The data on particle size and zeta potential was obtained by dynamic light scattering (DLS) and electrophoretic mobility measurement of the chitosan nanoparticles respectively. UV-VIS absorption of bacterial suspension was measured at 610 nm to evaluate the bacterial reduction. Solution pH of chitosan was demonstrated to be the most critical factor in controlling particle size and surface charge. At very strong acidic condition of chitosan solution, cross-linking was less resulting in lower conversion of chitosan to chitosan nanoparticles which was reaffirmed by colloidal titration of the surface groups of the chitosan nanoparticles with negatively charged polyelectrolytes poly(vinyl sulfate kalium salt). It was found that variation in size and surface charge of chitosan nanoparticles could be achieved by changing all the above mentioned process parameters and resulted in significant variation in their antimicrobial activity.

Synthesis of zinc tin oxide (ZTO) nanocrystallites at room temperature through association with peptide-containing bolaamphiphile molecules

Single crystalline zinc tin oxide (ZTO) nanocrystallites were prepared at room temperature through association with a peptide-containing bolaamphiphile molecule. The bolaamphiphile molecules self-assembled to form spherical structures with creation of ZTO nanocrystallites inside. ZTO nanocrystallite synthesis was achieved only when the bolaamphiphile molecule was present, while a mixture of amorphous Sn and Zn precipitates was formed in the absence of the bolaamphiphile molecule. The bolaamphiphile molecule is thought to stabilize the Zn2+ and Sn4+ precursor ions by ligation and to induce subsequent condensation forming crystalline ZTO. The ZTO formation was achieved only at a strong acidic condition that promotes dissociation and ionization of Zn and Sn precursors and represses formation of ZnO and H2SnO3. The prepared ZTO nanocrystallites had almost the same band gap energy as ZTO nanoparticles prepared by the conventional hydrothermal process. The outcomes of this study indicate that the controlled mineralization of metal precursor ions in a peptide-containing bolaamphiphile molecule suspension can be an alternative method to synthesize metal oxides at room temperature, while maintaining their crystalline structure and optoelectrical properties.

Solvent-free synthesis of reactive inorganic precursors for preparation of organic/inorganic hybrid materials

Prehydrolyzed-condensed precursors containing amino or glycido groups were prepared via sol gel process using various alkoxysilanes in the bulk, without addition of solvent in any step of their preparation. The influence of the experimental set-up, the functionality and ratio of alkoxysilanes, and type of catalyst, on the structure buildup was studied. In the case of amino precursors, the sol–gel process was carried out at weak basic conditions while in the case of glycido precursors the sol–gel process was catalyzed by acid or neutral pH. The sol–gel process was monitored by 29Si NMR in solution and the structure of the prehydrolysed-condensed precursors was characterized by small-angle X-Ray scattering. The systems with high content of tetraethoxysilane led to the fast gel formation. In weak acid medium tetraethoxysilane formed larger, more condensed species as well as small structures (based on Q 1, Q 2 and Q 3 species) with silanol groups. Strong acidic conditions led to the fast formation of insoluble silica particles in liquid (sol) phase containing monomeric alkoxysilanes. The most suitable precursor formulations based on the alkoxysilanes with amino groups, as well as the most efficient set-up, were selected and used to prepare hybrid organic/inorganic networks based on an epoxy matrix. These networks were characterized using dynamic mechanical analysis.

A systems biology approach sheds new light on Escherichia coli acid resistance.

In order to develop an infection, diarrhogenic Escherichia coli has to pass through the stomach, where the pH can be as low as 1. Mechanisms that enable E. coli to survive in low pH are thus potentially relevant for pathogenicity. Four acid response systems involved in reducing the concentration of intracellular protons have been identified so far. However, it is still unclear to what extent the regulation of other important cellular functions may be required for survival in acid conditions. Here, we have combined molecular and phenotypic analysis of wild-type and mutant strains with computational network inference to identify molecular pathways underlying E. coli response to mild and strong acid conditions. The interpretative model we have developed led to the hypothesis that a complex transcriptional programme, dependent on the two-component system regulator OmpR and involving a switch between aerobic and anaerobic metabolism, may be key for survival. Experimental validation has shown that the OmpR is responsible for controlling a sizeable component of the transcriptional programme to acid exposure. Moreover, we found that a ΔompR strain was unable to mount any transcriptional response to acid exposure and had one of the strongest acid sensitive phenotype observed.

Selective Sulfoxidation of Thioethers and Thioaryl Boranes with Nitrate, Promoted by a Molybdenum–Copper Catalytic System

The catalytic reduction of nitrate by molybdo-enzymes plays a central role in the global biological cycle of nitrogen. However, the use of nitrates as oxidants in synthetic organic chemistry is very limited and typically requires very strong acidic and other extreme reaction conditions. We have developed a highly chemoselective and efficient catalytic process for the sulfoxidation of thioethers and arylthioethers containing boronic acid or boronic ester functional groups, using nitrate salts as oxidants. This homogeneous catalytic reaction was carried out in acetonitrile, where the MoO(2)Cl(2)(OPPh(3))(2) complex 1 or a mixture of complex 1 with Cu(NO(3))(2) were used as catalysts. We examined the reaction mechanism using (1)H, (15)N, and (31)P NMR techniques and (18)O-labeled sodium nitrate (NaN(18)O(3)) and show that the thioethers are oxidized by nitrate, generating nitrite. Our work adds to the existing chemical transformations available for organoboron compounds, providing straightforward accessibility to a variety of new substrates that could be suitable for Suzuki cross-coupling chemistry.

Microgels formed by electrostatic and hydrophobic interaction of naphthaleneacetic acid with β-cyclodextrin-grafted polyethyleneimine

Microgels were prepared by physically cross-linking β-cyclodextrin-grafted polyethyleneimine (βCD-PEI) using a hydrophobic acidic compound, naphthaleneacetic acid (NAA). Under a strong acidic condition (e.g., pH 3.0), fibrous microgels were observed on a scanning electron microscope (SEM) possibly due to the intermolecular electrostatic interaction of NAA with PEI. In the range of pH 4.0 to pH 8.0, globular microgels were found possibly because an intramolecular electrostatic interaction prevails over an intermolecular interaction. At pH 9.0 and pH 10.0, neither fibrous nor globular microgels were observed due to lack of the electrostatic interaction and the hydrophobic interaction of NAA with βCD-PEI. The release of fluorescein isothiocyanate-dextran (FITC-dextran; M.W., 10,000) from the microgels increased with increasing pH. At pHs higher than pH 3.0, not only the diffusion of the solute, but also the dissolution of the microgels could contribute to the release.