Strong Acidic Conditions Research Articles

バイオマット表面でのＳｉ‐生体鉱物化作用サイクルモデル

Biomats (microbial mats) have been studied to elucidate and initiation of life and its evolution. Biomats are complicated architecture consisting of microbes and minerals. A microbe needs a suitable adjustment to severe working conditions to survive. In case of this study, in silicified biomats, Si-biomineralization work under strong acidic conditions. Here, a model of interaction cycles between Si and microbes in biomats is proposed, based on observations of modern Si-biomineralization, associated with red algae, Cyanidium caldarium-dominated silicified mats.

Assembly of Hydrothermally Stable Aluminosilicate Foams and Large-Pore Hexagonal Mesostructures from Zeolite Seeds under Strongly Acidic Conditions

Although the assembly of aluminosilicate foams and large-pore hexagonal mesostructures from zeolite BEA, MFI, and FAU seeds requires a reduction in pH from initially very basic values (pH > 12) to ...

Synthesis and characterization of periodic porous benzene-silica hybrid powders with cubic and hexagonal symmetries

AbstractOrganosilica powders with uniformly distributed bridging benzene groups have been synthesized from the condensation of bis- or tris-(triethoxysilyl)benzene in the presence of cetyltrimethylammoniumbromide. The syntheses were performed under strong acidic conditions and the organic groups were always incorporated without cleavage of the Si-C bonds as indicated by solid state MAS NMR studies. Depending on the nature of the precursors, materials with different ordering were obtained: a 2D-hexagonal (p6m) phase was formed from the 1,3-bis(triethoxysilyl)benzene, whereas the 1,4-bis(triethoxysilyl)benzene lead to a cubic Pm3n phase. The surfactant was removed either by solvent extraction or by controlled calcination, which did not affect the mesostructure of the materials.

Profile Distributions of Lead, Zinc, and Copper in Dystric Cambisols Developed from Granite and Gneiss of the Sudetes Mountains, Poland

Total contents of Pb, Zn and Cu were examined in twenty-five soilprofiles of forested Dystric Cambisols developed from granite andgneiss in the area of the Sudetes Mountains (SW Poland). Sequential extraction of heavy metals was also carried out to study relations between metal content and soil compounds. Profile distribution differed among the metals examined: Pb concentrations decreased gradually from surface with depth, whereas those of Zn increased with depth of soil profile, obtaining their maximum in the bedrock horizon. Cu was found to accumulate in topsoil and decrease with depth, but showed secondary increase of the concentration in bedrock. Organic matter was found to be a crucial factor of Pb binding and distribution, while iron oxides played the most important rolein Zn binding. Both organic matter and oxides were important factors of Cu distribution. The results of sequential extractionshow that all studied elements are mobile under strong acidicconditions in investigated Cambisols. Thus, total contents of Zn and Cu in bedrock cannot be used as geochemical background or as reference levels for assessing the contamination of soilsurface with these metals.

Aggregation in SiO 2 sols from sodium silicate solutions

The structure of the aggregation of SiO 2 sols in aqueous solution is investigated by small angle X-ray scattering experiments. In a sodium water glass solution an ion exchange results in an aggregation of the colloids. The aggregation clusters can be characterized by their size, fractal dimension describing the mass distribution and the size of the primary units. When the pH of the gel preparation varies from 2 to 5.8, the gelation time decreases strongly, while the value of the fractal dimension of the aggregation clusters remains constant at about 2.2. However, if the pH exceeds 5.8, the gelation time increases again and the fractal dimension decreases to a value of nearly 1.7. This process is attributable to the increase of the surface charge of the aggregating particles as pH goes up and to the resulting Coulomb repulsion. A corresponding behaviour was found under strong acid conditions. The experimental facts are in contrast to results of computer simulations in the literature.

Isolation and characterization of glyoxal-arginine modifications.

5-(4,5-Dihydroxy-2-imino-1-imidazolidinyl)norvaline (1) was identified as the only product of the early reaction of arginine with glyoxal, which was slowly degraded to N(5)-[[(carboxymethyl)amino](imino)methyl]ornithine (3, N(7)-carboxymethylarginine). No other structures could be detected within a range of pH 4-8 and 20-50 degrees C in reaction conditions. The rates of formation for both products increased with pH and temperature. In equilibrium, the vincinal diol groups of 1 were 86% trans configured. The formation of 1 was reversible, as could be shown by cis-trans isomerization of the separated isomers and by regeneration of arginine in the presence of the alpha-dicarbonyl trapping reagents, o-phenylenediamine and aminoguanidine. Both 1 and 3 were converted to 5-(2-imino-5-oxo-1-imidazolidinyl)norvaline (2) only under strong acidic conditions.

Chemical Structures of (+)-Catechin-Formaldehyde Reaction Products (Stiasny Precipitates) Under Strong Acid Conditions: Part 1. Solid-State 13C-NMR Analysis

Summary To determine more accurately the amount of polyflavanoids in tannin extracts from radiata pine bark, which react with formaldehyde, it is important to elucidate chemical structures of (﹢)-catechin-formaldehyde reaction products (Stiasny precipitates). The Stiasny value of 106.4% for (﹢)-catechin was obtained from the reaction with formaldehyde under strong acid conditions. This value is almost identical to the value calculated from the Stiasny precipitates, which were formed in the ratio of two molecules of (﹢)-catechin to three molecules of formaldehyde. The solid-state 13C NMR spectrum was measured to elucidate the structures of the Stiasny precipitates, and analysed on the basis of the chemical shifts of (﹢)-catechin. The NMR results indicate that C-6 and C-8 in the A-ring are bonded by methylene bridges to form polymers, and also form methylene bridges with C2′, C5′ or C6′ in the B-ring of a catechin unit. Consequently, the reaction products of (﹢)-catechin-formaldehyde under strong acid conditions (Stiasny precipitates) are (﹢)-catechin-polymers, which consist of two moles of (﹢)-catechin and three moles of formaldehyde. The methylene bridges are formed mostly between A-rings, and less frequently, between A- and B-rings and between B-rings of the catechin units.

Kinetics and Mechanism of the Reduction of Chromium(VI) and Chromium(V) byD-Glucitol andD-Mannitol

The oxidation of D-glucitol and D-mannitol by CrVI yields the aldonic acid (and/or the aldonolactone) and CrIII as final products when an excess of alditol over CrVI is used. The redox reaction occurs through a CrVI→CrV→CrIII path, the CrVI→CrV reduction being the slow redox step. The complete rate laws for the redox reactions are expressed by: a) −d[CrVI]/dt {kM2 H [H+]2+kMH [H+]}[mannitol][CrVI], where kM2 H (6.7±0.3)⋅10 M s−1 and kMH (9±2)⋅10 M s−1; b) −d[CrVI]/dt {kG2 H [H+]2+kGH [H+]}[glucitol][CrVI], where kG2 H (8.5±0.2)⋅10 M s−1 and kGH (1.8±0.1)⋅10 M s−1, at 33°. The slow redox steps are preceded by the formation of a CrVI oxy ester with λmax 371 nm, at pH 4.5. In acid medium, intermediate CrV reacts with the substrate faster than CrVI does. The EPR spectra show that five- and six-coordinate oxo-CrV intermediates are formed, with the alditol or the aldonic acid acting as bidentate ligands. Pentacoordinate oxo-CrV species are present at any [H+], whereas hexacoordinate ones are observed only at pH<2 and become the dominant species under stronger acidic conditions where rapid decomposition to the redox products occurs. At higher pH, where hexacoordinate oxo-CrV species are not observed, CrV complexes are stable enough to remain in solution for several days to months.

Synthesis of aldehyde building blocks protected as acid labile N-Boc N,O-acetals: toward combinatorial solid phase synthesis of novel peptide isosteres.

The synthesis of (RS)-3'-tert-butoxycarbonyl-perhydro-1', 3'-oxazine-2'-yl acetic acid and the syntheses of the simple and C-2 substituted 3'-tert-butoxycarbonyl-perhydro-1',3'-oxazine-2'(RS)-yl propionic acids from simple starting materials are presented. The simple compounds were prepared from 1,3-propanediol and 1, 4-butanediol, respectively, via a short series of facile steps, in 70% overall yield in both cases. For the syntheses of the C-2 substituted compounds of the longer homologue, (RS)-3'-tert-butoxycarbonyl-perhydro-1',3'-oxazine-2'-yl propionic acid, a malonic ester route was selected, thus allowing easy incorporation of various side chains. The stability of the novel aldehyde protection group, the N-Boc N,O-acetal moiety, under various acidic conditions was investigated, and it was found to cleanly and rapidly yield the aldehyde under strong acidic conditions or, if desired, slower under less harsh conditions. As a demonstration of the use of the building blocks, one building block was coupled to a solid support and, after unmasking of the aldehyde, submitted to three different types of nucleophilic reactions (Pictet-Spengler condensation, reductive amination, Horner-Wadsworth-Emmons olefination) followed by further chemical modification, and the identity of the structures were verified after cleavage from the resin.

P-15 高温・酸性環境下における微生物と物質の挙動(7. 環境修復を含めた地質汚染調査・対策と微生物による重金属の除去および残土の諸問題,ポスターセッション,一般発表)

P-15 高温・酸性環境下における微生物と物質の挙動(7. 環境修復を含めた地質汚染調査・対策と微生物による重金属の除去および残土の諸問題,ポスターセッション,一般発表)

4-Electron Reduction of Dioxygen On a Glassy Carbon Electrode Modified by Polyaniline-Co2-Porphyrin Complex

The 4-electron reduction of oxygen to water in an acidic atmosphere (pH: 0.5) takes place on a glassy carbon electrode by electro-catalysis under the atmospheric conditions using the dinuclear Co-porphyrin-polyaniline complex. The π-conjugated polymer complex shows an excellent and stable catalytic activity in strong acidic conditions.

In vitro stability of polyether and polycarbonate urethanes.

The in vitro structural stability of poly-ether-urethanes (PEUs) and poly-carbonate-urethanes (PCUs) was examined under strong acidic (HNO3) or alkaline (NaClO) oxidative conditions and in presence of a constant strain state. Polyurethane (PU) samples were represented by sheets solvent-cast from commercial pellets or by tubular specimens cut from commercial catheters. The specimens were strained at 100% uniaxial elongation over appropriate extension devices and completely immersed into the oxidative solutions at 50 degrees C for 7-14 days. The changes induced by the oxidative treatments were then evaluated by molecular weight analysis, tensile mechanical tests, and scanning electron microscopy. In the experiments with solvent-cast samples, the PEU Pellethane was degraded more in the alkaline oxidative conditions and mainly in the absence of an applied uniaxial stress. All the tested PCUs were, on the contrary, more affected by the acidic oxidative agent. All the PCUs proved to have overall better stability than the PEU. The susceptibility to oxidation was also dependent on the shape and bulk/surface organisation acquired by the same polymer during its processing. When the oxidative test was applied to catheters made of a PEU and a PCU, the results confirmed the better stability of poly-carbonate-urethanes.

Alkoxyallylsilanes: Functional Protecting Groups

Allyl- t-butylmethylsilyl groups were shown to function as alcohol protecting groups whose hydrolytic stability was greater than t-butyldimethylsilyl (TBS) and Si(SiMe 3) 3 (sisyl) groups. Pseudo-first-order rate constants for the acidic hydrolysis of primary, benzylic, and secondary allyl- t-butylmethylsilyl ethers in AcOD/THF- d 8/D 2O were determined to be 2.94×10 −3, 8.26×10 −4, and 8.26×10 −4 s −1, respectively. The regioselectivity of acidic hydrolysis of allylbenzyloxy- t-butylmethylsilane 1 was examined under strong acid ( p-TsOH/CD 2Cl 2) and weak acid (AcOD/THF- d 8/D 2O) conditions. In both cases, benzyl alcohol was initially produced exclusively from silicon–oxygen bond cleavage: allylic cleavage was only subsequently observed over time. However, the allyl group of the silyl ether could be hydrosilylated. The resulting alkoxy-functionalized disiloxane had greater hydrolytic stability under acidic conditions than the starting alkoxyallyl- t-butylmethylsilane.

The Low Calorie Sweetener Stevioside: Stability and Interaction with Food Ingredients

The stability of the low calorie sweetener stevioside during different processing and storage conditions, as well as the effects of its interaction with the water-soluble vitamins ascorbic acid, thiamin, riboflavin, pyridoxine and nicotinic acid, the organic acids acetic acid, citric acid, tartaric acid and phosphoric acid, the other common low calorie sweeteners saccharin, cyclamate, aspartame, acesulfame, neohesperidin dihydrochalcone, and caffeine in coffee and tea, were evaluated. Incubation of solid stevioside at elevated temperatures for 1 h showed good stability up to 120°C, whilst forced decomposition was noticed at temperatures exceeding 140°C. In aqueous solution stevioside was remarkably stable in a pH range of 2–10 under thermal treatment up to 80°C; however, under strong acidic conditions (pH 1), a significant decrease in the stevioside concentration was detected. Up to 4 h of incubation with individual water-soluble vitamins in aqueous solution at 80°C showed no significant changes with regard to stevioside and the B-vitamins, whereas a protective effect of stevioside on the degradation of ascorbic acid was observed, resulting in a significant delayed degradation rate. In the presence of other individual low calorie sweeteners, practically no interaction was found at room temperature after 4 months of incubation in aqueous media. Stability studies of stevioside in solutions of organic acids showed a tendency towards enhanced decomposition of the sweetener at lower pH values, depending on the acidic medium. In stevioside-sweetened coffee and tea, very few significant chances in caffeine content or in stevioside content were found.

Invertase Production Is Related to the Nitrogen Source in Hansenula anomala

Differences in invertase accumulation of Hansenula anomala cultivated in ammonium and nitrate are reported. Media supplemented with sucrose and ammonium sulfateas the solecarbon and nitrogen source, respectively, show strong media acidification (pH 3.0 or lower), and vigorous cell growth. Invertase activity was not detected under such conditions. A cell-free imitation experiment suggests that, under such low pH, extensive chemical break-down of sucrose (>22%) occurs. Thus, H. anomala is able togrow under strong acidic conditions that permit sucrose metabolism by the uptake of monosaccharides generated from chemical hydrolysis. In addition, invertase activity is not present in cells grown in nitrate as nitrogen source at pH 5.0, but at pH 7.0 activity is detected. If ammonium is supplied instead of nitrate, cells grown at pH 5.0 show invertase activity and at pH 7.0 high levels of activity are detected. These results indicate a specific physiological response of the sucrose metabolism to the presence of alternate nitrogen source.

Pilot plant scale extraction of alginate from Macrocystis pyrifera. 1. Effect of pre-extraction treatments on yield and quality of alginate

In the extraction of alginate from brown seaweeds, the acid pre-extraction treatment has been considered by many authors as an essential step because it makes the alginate more readily soluble in an alkaline solution. At pilot plant level, extractions were made (i) using formalin treatment prior to the acid pre-extraction treatment (ii) using different acid treatments so the calcium ions exchanged varied from 83% to 4%. The use of formalin treatment gave a product with less color. During the acid pre-extraction treatment, it was possible to reduce the calcium exchanged from 33.4% to almost zero with a maximum reduction in alginate yield of 7%. The degree of acid treatment was positively correlated to calcium exchanged and yield but negatively correlated with alginate viscosity. Using strong acid conditions the viscosity was 168 mPa s, while mild acid conditions produced an alginate with 623 mPa s. The direct extraction from calcium alginate to sodium alginate is possible because strong alkaline conditions were used, pH 10 at 80 °C for two hours and with a low water volume. The best pre-extraction treatment to obtain an alginate with high viscoity is to hydrate the alga with 0.1% formalin overnight, then wash the alga once with hydrochloric acid at pH 4 using a batch system with continuous agitation during 15 min.

High-performance chelation ion chromatography for the determination of traces of bismuth in lead by means of a novel hypercrosslinked polystyrene resin

A method for the determination of trace bismuth in lead using a high-performance chelating ion chromatography (HPCIC) system is described. A novel high-efficiency chelating column was prepared from a neutral hypercrosslinked polystyrene resin, MN200 (Purolite). It was found that the unmodified material had metal complexing properties similar to resins containing immobilized chelating dyestuffs. The resin was very stable in strong acid conditions and was therefore suitable for the investigation of metal ions with high positive charge. Bismuth was eluted with good peak shapes using halogen acids. Hydrobromic acid was chosen as it gave more sensitive detection than hydrochloric acid. Detection was carried out by direct UV–Vis absorption measurement of the bismuth bromide complex so no post-column reaction system was required. No interference was observed from lead halides at 370 nm. A certified lead reference material (CRM 288B) was used to successfully validate the method. The detection limit for bismuth was found to be 10 μg l −1 and analysis times were less than 5 min from the time of injection.

Determination of99Tc in reactor loop decontamination liquid waste using extraction chromatography

A new analytical method has been developed to determine99Tc in samples of aqueous radioactive waste containing high levels of60Co (103–106 Bq/l) in mixed forms (simple cationic60Co2+ and coordinated complex forms). The method consists of selective extraction of the99Tc with a combination of cation exchange and solid-phase extraction resins under strong acid conditions. Quantification of the isolated99Tc is accomplished using liquid scintillation counting. The method provides high recoveries (>98%), is simpler than classical solvent extraction methods, eliminates the use of chlorinated organic solvents and the time of analysis is reduced by a factor of 2 when compared to solvent extraction methods.

Oxo substituents markedly alter the phase II metabolism of alpha-hydroxybutenylbenzenes: models probing the bioactivation mechanisms of tamoxifen.

The P450-catalyzed hydroxylation of tamoxifen to give alpha-hydroxytamoxifen [(E)-4-{4-[2-(dimethylamino)ethoxy]phenyl}-3,4-diphenyl-3-buten-2- ol] and subsequent formation of reactive sulfate esters which alkylate DNA has been proposed to be a potential carcinogenic pathway for tamoxifen. In the present study, the ability of alpha-hydroxytamoxifen analogs to form GSH and sulfate conjugates was investigated in order to understand the structural features influencing reactivity. The para oxo analogs 1 [1-(4-methoxyphenyl)-3-hydroxy-1-butene], 2 [1-(4-hydroxyphenyl)-3-hydroxy-1-butene], and 4 [1-(4-hydroxyphenyl)-1-phenyl-3-hydroxy-1-butene] reacted with GSH instantaneously under strong acidic conditions to yield GSH conjugates in greater than 90% yields. Interestingly, the meta phenolic analogs 3 [1-(3-hydroxyphenyl)-3-hydroxy-1-butene] and 5 [1-(3-hydroxyphenyl)-1-phenyl-3-hydroxy-1-butene] did not react with GSH to any significant extent under similar conditions. Characterization of the GSH conjugates with 1H-NMR, electrospray mass spectrometry, and UV showed that all of the conjugates resulted from attack of GSH at the alpha-position of the substrates with displacement of the hydroxyl group. The formation of a single pair of diastereomeric conjugates strongly supported adduct formation to proceed through a direct S(N)2 displacement mechanism and not through a quinone methide (4-alkyl-2,5-cyclohexadien-1-one) intermediate. At physiological pH and temperature only the para hydroxy analogs 2 and 4 gave GSH conjugates, a reaction which seems to be catalyzed by isoforms of glutathione S-transferase. Similar substituent effects were observed in the sulfotransferase-mediated formation of alpha-hydroxy sulfate esters in that only the para hydroxy analogs formed conjugates at the aliphatic hydroxyl group. Finally, the present investigation showed a remarkable difference in the reactivities of para and meta phenolic analogs of alpha-hydroxybutenylbenzenes toward GSH and sulfate conjugation reactions.

Condensation Reactions of Softwood and Hardwood Lignin Model Compounds Under Organic Acid Cooking Conditions

In order to examine the condensation reactions of softwood and hardwood lignin during organic acid cooking, mixtures of benzyl alcohol type lignin model compounds with guaiacyl and syringyl units as the sources of benzyl cations and creosol and 5-methoxycreosol as the sources of electron-rich aromatic carbons were cooked under acidic pulping conditions. From the yield of the condensation products in the initial reactions, it was shown that the carbonium cations of guaiacyl nuclei were more reactive than those of syringyl nuclei. Syringyl type aromatic ring carbons had higher reactivities than guaiacyl type ones. The cleavage of the benzyl ether bond in syringyl compounds was slower than that of guaiacyl compounds. The diphenylmethane structures formed by the condensation reaction between veratryl alcohol and 5-methoxycreosol were found to be unstable under the strong acidic cooking conditions. It is concluded that the condensation reactions between benzylic cations from the guaiacyl compounds and the electron rich aromatic ring carbons of syringyl ones are very fast, but the condensation products are unstable under the strong acidic pulping conditions. When the guaiacyl nuclei react as an electron-rich aromatic carbon, the reaction is slower but the condensation product is much more stable. These differences in reactivities, and the stabilities of the condensation products, may contribute to the resistance of softwood toward complete delignification on acid pulping.