Mild Alkaline Conditions Research Articles

Silica gel-enhanced oxidation of caffeine by ferrate(VI)

The present paper demonstrates the employment of simple solid silica gel (SiO2) to remarkably enhance the oxidative transformation of caffeine (CAF) by ferrate(VI) (FeO42−, Fe(VI)) in water under environmentally relevant pH conditions (pH∼8.0). Complete oxidative transformation of CAF was achieved at Fe(VI) to CAF molar ratio of 6.0 in the presence of 4g SiO2/L under mild alkaline conditions (pH∼8.0). Comparatively, only 53.0% CAF removal was achieved at the same Fe(VI) to CAF molar ratio of 6.0 in the absence of SiO2 gel at similar pH conditions (pH∼8.0). Variation of particle size and pore volume of SiO2 gel showed no impact on the oxidation of CAF by Fe(VI). In the presence of SiO2 gel, Na+, Mg2+, Ca2+, Cl−, HCO3−, and SO42− ions had no significant effect on the removal of CAF by Fe(VI). Natural organic matter (NOM) in water decreased the removal of CAF by Fe(VI) in the presence of SiO2 gel. The influence of NOM on the removal efficiency of CAF by Fe(VI) could be decreased by increasing the amount of SiO2 gel in water. Identification of three products of CAF by Fe(VI)-SiO2 system suggests a reaction pathway initiated by the attack on the C4C5 double bond of CAF, which is supported by the frontier molecular orbitals calculations of CAF.

Chemoattractant activity of tris-(hydroxymethyl)aminomethane for Brugia pahangi infective third-stage larvae.

Urocanic acid (UCA) is known as a major chemoattractant for Strongyloides stercoralis infective third-stage larvae (L3). Since Brugia pahangi is a skin-penetrating parasitic nematode similar to S. stercoralis, UCA was expected to be a chemoattractant for B. pahangi L3. Thus, the chemoattractant activity of UCA for B. pahangi L3 was assessed. The chemotactic responses of B. pahangi L3 to UCA or acetic acid (CH3COOH) dissolved in amine solutions were assessed using an agar-plate assay. A test solution of 200 mm UCA dissolved in aqueous 270 mm tris(hydroxymethyl)aminomethane (Tris) significantly attracted B. pahangi L3 compared with deionized water (DW), while neither a solution of 200 mm UCA dissolved in aqueous 230 mm ammonia (NH3) nor 290 mm triethylamine (TEA) significantly attracted L3. Similarly, a test solution of 200 mm CH3COOH dissolved with 200 mm Tris significantly attracted L3, but neither a test solution of 200 mm CH3COOH plus 200 mm NH3 nor 200 mm TEA attracted L3. Furthermore, L3 were significantly attracted to 200 mm Tris alone, compared with DW, but avoided 200 mm NH3 and 200 mm TEA. Moreover, the chemoattractant activity of Tris for L3 was observed even at a low concentration of 25 mm, and it was observed in a mild alkaline condition but not in an acidic condition. The present study reveals that Tris is a potential chemoattractant for B. pahangi L3 while UCA is not. This finding will contribute to an understanding of the mechanisms of skin-penetrating infection of filarial L3.

Microfluidization initiated cross-linking of gliadin particles for structured algal oil emulsions

Abstract: The interfacial covalent cross-linking of emulsions can greatly enhance their tolerance to environmental stresses, and also contribute to formation of a new class of food products (e.g., oil gel, oil powder, and capsules). Algal oil is rich in ω-3 polyunsaturated fatty acids, while heat treatment makes it particularly susceptible to oxidation. In this study, microfluidization initiated interfacial covalent cross-linking of gliadin particles to stabilize emulsion as a novel technology to facilely construct structured algal oil product without any thermal or chemical treatment. The coarse emulsions with high algal oil volume fraction ( φ oil= 50%) stabilized by acidic gliadin particles were firstly homogenized using IKA homogenizer, and then emulsions were immediately subjected to mild alkaline pH-shifting processes. Finally, microfluidization initiated cross-linking of gliadin via intermolecular disulfide bonds to prepare stable structured emulsions. The droplet size distribution, FTIR, and SDS-PAGE of emulsions clearly verified that cross-linking was initiated by hydrophobic interaction under mild alkaline conditions, and interfacial disulfide cross-linking of gliadins was triggered by microfluidization. The viscoelastic and mechanical properties of emulsions showed homogenization pressure-dependent behavior. In addition, with increasing homogenization pressure, the increased oxidative stability with reduced lipid hydroperoxides and volatile hexanal of emulsions was also observed. Facile construction of cross-linking by microfluidization may provide a novel technology platform for gliadin based delivery system or edible oil structuring with functional characteristics.

New fructan — the O-specific polysaccharide from Escherichia coli O92

The structure of the O-specific polysaccharide (O-antigen) from Escherichia coli O92 was established. The acid-labile polysaccharide was produced by O-deacylation of the lipopolysaccharide under mild alkaline conditions. The methylation analysis combined with 1D and 2D 1H and 13C NMR spectroscopy demonstrated that the O-specific polysaccharide chain of the lipopolysaccharide is a linear fructan composed of mono-О-acetylated disaccharide repeating units having the structure →1)-β-d-Fruf3Ac-(2→3)-β-d-Fruf-(2→. To the best of our knowledge, this fructan has been hitherto unknown in bacteria.

Electrocoagulation for ammonium removal in Nam Son landfill leachate

In this paper, an electrocoagulation reactor was set up to investigate the ammonium removal in Nam Son landfill leachate. The research focused on studying several factors that affect to the ammonium removal namely current intensity, operating time, initial pH and electrode materials. Mono-polar electrocoagulation reactor was conducted in a batch system with iron electrodes and 1.8 L leachate. The research indicated that current intensity and operating time are directly proportional with NH4+ treatment performance. When applied current increased from 1 to 4A, the NH4+ removal percentage went up from 14.03 to 24.99% after a 1 hour treatment. The effect of initial pH in range of 5 to 10 has showed that the best NH4+ treatment efficiency in neutral and mild alkaline conditions. It is noticeable that iron electrodes had higher NH4+ removal than aluminum one during nearly the first 40 min, however this trend has been reversed later with the advantage belonging to aluminum anode. The optimum operating conditions found are aluminum electrodes, applied current of 3A, electrolysis time of 60 min, raw pH of 8, resulting in NH4+ treatment performance of approximately 24%. As a result, the electrocoagulation method is not really effective in NH4+ removal and might be applied as a pre-treatment.

Metal-Free and Efficient Epoxidation of α,β-Unsaturated Ketones with 1,1,2,2-Tetrahydroperoxy-1,2-Diphenylethane as a Powerful Solid Oxidant

1,1,2,2-Tetrahydroperoxy-1,2-diphenylethane was used for the efficient and metal-free epoxidation of various α,β-unsaturated ketones, carried out under mild alkaline conditions at room temperature.

Production of prebiotic-xylooligosaccharides from alkali pretreated mahogany and mango wood sawdust by using purified xylanase of Clostridium strain BOH3

Xylooligosaccharides (XOS) are emerging prebiotics which can be produced from lignocellulosic biomass including agro-residues and hardwood. In this study, we report the production of XOS from thermal-alkali pretreated hardwood such as mahogany and mango by using a purified xylanase from Clostridium strain BOH3. In the first approach, pure xylan is extracted from mahogany and mango hardwood and then the pure xylan is hydrolyzed by using the xylanase. In this case, 572 and 504mg XOS/g pure xylan were obtained from mahogany and mango woods, respectively. In the second approach, the same xylanase is employed to hydrolyze sawdust of hardwood after different types of pretreatments. After a thermal (121°C for 15min) pretreatment under a mild alkaline (0.05N NaOH) condition, the pretreated mahogany and mango sawdust can be utilized directly to produce 89.5 and 67.6mg XOS/g pretreated sawdust, respectively. XOS produced from the pretreated sawdust show strong prebiotic effects on Bifidobacteria and Lactobacilli. This report shows the possibility of producing XOS from pretreated woody wastes without using pure xylan as a substrate.

Oxidative transformation of a tunichrome model compound provides new insight into the crosslinking and defense reaction of tunichromes

Tunichromes, small oligopeptides with dehydrodopa units isolated from the blood cells of ascidians, have been implicated in the defense reactions, metal binding, wound repair, or tunic formation. Their instability and high reactivity has severely hampered the assessment of their biological role. Experiments conducted with the model compound, 1,2-dehydro-N-acetyldopamine, indicated that the instability of tunichromes is due to this basic structure. Exposure of this catecholamine derivative to even mild alkaline condition such as pH 7.5 causes rapid nonenzymatic oxidation. High performance liquid chromatography and mass spectrometry studies confirmed the production of dimeric and other oligomeric products in the reaction mixture. The nonenzymatic reaction seemed to proceed through the intermediary formation of semiquinone free radical and superoxide anion. Ultraviolet and visible spectral studies associated with the oxidation of tunichromes isolated from Ascidia nigra by tyrosinase indicated the probable formation of oligomeric tunichrome products. Attempts to monitor the polymerization reaction by mass spectrometry ended in vain. Tunichrome also exhibited instability in mild alkaline conditions generating superoxide anions. Based on these studies, a possible role for oxidative transformation of tunichrome in defense reaction, tunic formation and wound healing is proposed.

Release kinetics of esterified p-coumaric acid and ferulic acid from rice straw in mild alkaline solution

The release kinetics of esterified p-coumaric acid (PCA) and ferulic acid (FA) from rice straw under a mild alkaline condition were investigated to collect fundamental data for the design of a recovery process. The results showed that the straw size, NaOH concentration, and temperature were the key parameters governing release kinetics. The analysis demonstrated that FA is released considerably faster than PCA. The close relationship between lignin and the PCA dissolution indicates a reciprocal and/or simultaneous release. Moreover, PCA is broadly distributed in the lignin network but tends to be located more densely in the lignin fraction which is not easily solubilized by alkaline treatment. In contrast, the release of FA is strongly affected by removal of lignin fraction which is easily solubilized. These results suggest that the release kinetics are controlled by the accessibility of NaOH to their ester sites in the lignin/hemicellulose network, and by their localization.

Discerning the Potential of Chitosan Extracted from Bio Resources as a Competent Brain Drug Carrier to Cross the Blood Brain Barrier

Biopolymer such as chitosan is more favoured as a drug carrier in particular to the brain due to its potential to cross the blood brain barrier. This study is a comparative assessment of the extraction of chitosan from natural sources such as mushroom, crab and shrimp using alkali method pursued by physicochemical assays that surmise the excellence of the biopolymer in permeating a central nervous system drug. Commercially, chitosan extracted from crustaceans have been widely used but this study revealed that mushrooms are also a good source for chitosan. An in silico assay enumerates the structural affiliation of the polymer and its binding efficiency. Molecular docking study facilitates to attest the brain targeting efficiency of chitosan on disparity with sodium alginate against the efflux permeability glycoprotein furnishing a minimum binding affinity energy values of -37.2 kcal/mol. The pharmacologically significant descriptors propose a low solubility that avoids the untargeted discharge of drug. Chitosan extracted from a rich protein source such as mushroom in a mild alkaline condition with a high degree of deacetylation has freer amine groups can act as a drug by itself and can readily bind with a drug as a carrier. The synchronised work of biopolymer extraction with that of in silico analysis can further take chitosan as a lead compound for brain drug development and targeting studies.

Addition of corn stover arabinoxylan into hardwood during pulping for improved physical properties

Agricultural residues, such as corn stover, are being considered for biofuels and bioproducts. They represent inexpensive, pentosan-rich feedstock that are available in abundance. These materials are typically pretreated to make them more amenable to biological processes such as fermentation. One such treatment involves extraction using alkali to remove the hemicellulose, leaving the cellulose more accessible for chemical or enzymatic hydrolysis. Extracted xylan hemicellulose may be considered for use in pulp and paper, or for providing a potential value stream from cellulosic ethanol biorefineries. To be useful, the extracted xylan should be concentrated and adsorbed into the pulp using existing equipment or a minimal number of new unit operations. In this work, we explored the concept of size-exclusion membrane-filtration to concentrate xylan that was extracted from corn stover in mild alkaline conditions. We examined hollow-fiber and tangential-flow filtration types and achieved a nearly two-fold increase in the xylan concentration using the former with a 50 kDa molecular weight cut-off (MWCO) membrane. Cassette-type tangential-flow filtration resulted in slightly greater xylan concentration with the use of a 10 kDa MWCO membrane. Hemicellulose extracts were then used as an additive during kraft pulping of hybrid poplar to show that the xylan could be adsorbed onto pulp fibers and retained even after washing. Pulp tensile strength improved after xylan addition following refining. An average of 33% of the xylan added in this method was retained, with xylan loading between 5 wt% and 20 wt%, compared with the control pulp sample that did not have added xylan. These results suggest potential for further exploration of biorefinery extracts use as additive feedstock for pulping. The study, being an evaluation of the proof-of-concept, aims to push research and optimization in this area that will lend well to scale-up and commercialization.

Probing Enhanced Double-Strand Break Formation at Abasic Sites within Clustered Lesions in Nucleosome Core Particles.

DNA is rapidly cleaved under mild alkaline conditions at apyrimidinic/apurinic sites, but the half-life is several weeks in phosphate buffer (pH 7.5). However, abasic sites are ∼100-fold more reactive within nucleosome core particles (NCPs). Histone proteins catalyze the strand scission, and at superhelical location 1.5, the histone H4 tail is largely responsible for the accelerated cleavage. The rate constant for strand scission at an abasic site is enhanced further in a nucleosome core particle when it is part of a bistranded lesion containing a proximal strand break. Cleavage of this form results in a highly deleterious double-strand break. This acceleration is dependent upon the position of the abasic lesion in the NCP and its structure. The enhancement in cleavage rate at an apurinic/apyrimidinic site rapidly drops off as the distance between the strand break and abasic site increases and is negligible once the two forms of damage are separated by 7 bp. However, the enhancement of the rate of double-strand break formation increases when the size of the gap is increased from one to two nucleotides. In contrast, the cleavage rate enhancement at 2-deoxyribonolactone within bistranded lesions is more modest, and it is similar in free DNA and nucleosome core particles. We postulate that the enhanced rate of double-strand break formation at bistranded lesions containing apurinic/apyrimidinic sites within nucleosome core particles is a general phenomenon and is due to increased DNA flexibility.

A hydantoin isoform of cyclic N6-threonylcarbamoyladenosine (ct6A) is present in tRNAs.

N6-Threonylcarbamoyladenosine (t6A) and its derivatives are universally conserved modified nucleosides found at position 37, 3΄ adjacent to the anticodon in tRNAs responsible for ANN codons. These modifications have pleiotropic functions of tRNAs in decoding and protein synthesis. In certain species of bacteria, fungi, plants and protists, t6A is further modified to the cyclic t6A (ct6A) via dehydration catalyzed by TcdA. This additional modification is involved in efficient decoding of tRNALys. Previous work indicated that the chemical structure of ct6A is a cyclic active ester with an oxazolone ring. In this study, we solved the crystal structure of chemically synthesized ct6A nucleoside. Unexpectedly, we found that the ct6A adopted a hydantoin isoform rather than an oxazolone isoform, and further showed that the hydantoin isoform of ct6A was actually present in Escherichia coli tRNAs. In addition, we observed that hydantoin ct6A is susceptible to epimerization under mild alkaline conditions, warning us to avoid conventional deacylation of tRNAs. A hallmark structural feature of this isoform is the twisted arrangement of the hydantoin and adenine rings. Functional roles of ct6A37 in tRNAs should be reconsidered.

Structural characteristics of milled wood lignin (MWL) isolated from green liquor (GL) pretreated poplar (Populus deltoides)

Abstract Pretreatment is one of the key steps for the utilization of lignocellulosic biomasses via biorefinery. Green liquor (GL) pretreatment has been considered as an effective approach to improve the subsequent enzymatic saccharification. For the better understanding of the structural changes of lignin in GL pretreatment, milled wood lignin (MWL) samples isolated from untreated and GL-pretreated poplar by the Björkman method were characterized by means of gel permeation chromatography (GPC), alkaline nitrobenzene oxidation (NBO), Fourier transform-infrared (FT-IR) spectroscopy, and quantitative 13C and 2D heteronuclear single quantum coherence nuclear magnetic resonance (HSQC NMR). The results indicate that the average molecular weight of MWLs decreased after GL pretreatment. Surprisingly, more guaiacyl-propane units are extracted under mild alkaline conditions than syringyl-propane units, which results in a higher condensation degree and higher S/G ratios of MWLs isolated from GL-pretreated poplars. The amount of β–O–4 structures decreased, while the β–β and β-5 structures increased after GL pretreatment. The structure of esterified p-hydroxybenzoic acid was detected in poplar MWL sample and it degraded obviously after GL pretreatment.

Facile epoxidation of α, β-unsaturated ketones with urea-2,2-dihydroperoxypropane as a new oxidant

Various aromatic α, β-unsaturated ketones were successfully transformed into their corresponding epoxides using urea-2,2-dihydroperoxypropane as the oxygen source for the first time. The reactions were carried out under mild alkaline conditions at room temperature in high yields and short reaction times.

Synthesis of 4-hydroxy-2-methylproline derivatives via pyrrolidine ring assembly: chromatographic resolution and diastereoselective synthesis approaches

4-Hydroxy-2-methylproline diastereomers are successfully prepared without the use of an external chiral auxiliary. Dihydroxylation of the key intermediate 2 resulted in lactone 4 as a mixture of diastereomers in good yield. Mesylation, hydrogenation and concomitant intramolecular cyclization of 4 led to the formation of both (2R,4R)- and (2R,4S)-4-hydroxy-2-methylprolines as a mixture of diastereomers. Appropriate protection followed by chromatographic separation resulted in isolation of both cis- and trans-diastereomers in enantiomerically pure form and in equal quantity. In subsequent experiments, the synthesis of the more challenging diastereomers (2R,4R)- and (2S,4S)-4-hydroxy-2-methylproline was achieved by diastereoselective iodolactonization of (R)- or (S)-allylalanine obtained after hydrolysis of intermediate 2, followed by pyrrolidine ring closer under mild alkaline conditions. After selective protection and deprotection, Fmoc-(2R,4R)-α-Me-Hyp(tBu)-OH 14, a building block suitable for solid phase peptide synthesis was obtained.

Dispersant‐free dyeing of poly(lactic acid) fabric with temporarily solubilised disperse dyes from azopyridone derivatives

Poly(lactic acid) fibre is derived from annually renewable crops and known to be 100% compostable. In order to extend its environmental friendliness into the dyeing process, dispersant-free dyeing of poly(lactic acid) fabric with three temporarily solubilised azo disperse dyes based on hydroxypyridone moiety containing a β-sulphatoethylsulphonyl group was investigated. The dyes were successfully applied to poly(lactic acid) fabric without the use of dispersants. The colour yields of the dyes on poly(lactic acid) fabric were observed to be dependent on dyebath pH and dyeing temperature. The optimum results were obtained at pH 4–5 and 110 °C. One of the dyes showed a colour yield as good as that of a commercial disperse dye and good build-up on poly(lactic acid) fabric. All of the dyes could be alkali cleared owing to ionisation of the dye under mild alkaline conditions. Wash fastness was good to very good, and light fastness was good. The chemical oxygen demand levels of the poly(lactic acid) dyeing effluent from the dyes were considerably lower than those from a commercial disperse dye.

Structure and gene cluster of the O-antigen of Escherichia coli O156 containing a pyruvic acid acetal

The lipopolysaccharide of Escherichia coli O156 was degraded under mild acidic and alkaline conditions and the resulting polysaccharides were studied by sugar analysis and 1H and 13C NMR spectroscopy. The following structure of the pentasaccharide repeating unit of the O-polysaccharide was established: [Display omitted] where Rpyr indicates R-configurated pyruvic acid acetal. Minor O-acetyl groups also were present and tentatively localized on the Gal residues. The gene cluster for biosynthesis of the O-antigen of E. coli O156 was analyzed and shown to be consistent with the O-polysaccharide structure.

Removal of methylene blue with hemicellulose/clay hybrid hydrogels

In this study, we chose corn stover hemicellulose for the preparation of hydrogels with admirable adsorption properties under mild alkaline conditions. Clay nanosheets were introduced to this system and hemicellulose/clay hybrid hydrogels were prepared. Morphological, mechanical properties and the methylene blue adsorption behaviors of the prepared hydrogels were studied. Results suggested that the addition of clay not only improved the mechanical strength of hemicellulose-based hydrogels, but also increased the adsorption capacity on methylene blue. Moreover, the adsorptions were confirmed to follow pseudo-second order equation for both gels with and without clay. The maximum adsorption capacities on methylene blue for hemicellulose-based hydrogels with or without clay reached 148.8 and 95.6 mg/g, respectively. These results implied that hemicellulose-based hydrogels could be used as promising adsorbents for the removal of methylene blue from waste water.

Transformation of raw feather waste into digestible peptides and amino acids

ABSTRACTBACKGROUNDMillions of tons of feather waste from the poultry industry are disposed of annually despite containing a high level of keratin. The aim of this study was to compare the hydrolysis of non‐treated feather waste using three different approaches (whole cell microbial digestion, enzymatic and chemical cleavage) and to test the use of hydrolysates as peptone substitutes in a culture medium.RESULTSAmong bacterial isolates, Pseudomonas sp. P5 exhibited the highest keratinolytic activity and efficiency to hydrolyse raw feather material. The hydrolysates contained up to 301 mg L−1 of free amino acids and 6.2 g L−1 of peptides. Hydrolysates obtained by digestion using semi‐purified keratinase from Pseudomonas sp. P5 were richer in amino acids (1191 mg L−1, 56% essential ones) but peptides were present in lower amounts (up to 3.3 g L−1). The third approach was feather treatment under mild alkaline conditions. This provided the highest amount of peptides (17.2 g L−1) but a significantly lower level of amino acids, especially the essential ones.CONCLUSIONSAll approaches tested could convert raw feather waste into products of commercial value with proven use in a cultivation medium. The level of peptides, their molecular size and amino acid composition was dependent on the method used. © 2016 Society of Chemical Industry