Moderate Alkaline Research Articles

Effect of pH and Phosphate on Calcium Carbonate Polymorphs Precipitated at near-Freezing Temperature

The effects of pH and phosphate on the precipitation of calcium carbonate polymorphs from aqueous solution were investigated. Experiments were carried out at near-freezing temperature and two different pH conditions (pH 13.4 and 9.0). At each pH condition, solutions having different concentrations of CaCl2 and NaHCO3 were mixed to achieve Ca/CO3 ratios of 1:1 and 10:1 at different pumping rates with and without phosphate. Results showed that, at pH 13.4, only ikaite was formed, independent of pumping rate, Ca/CO3 ratio, and phosphate. At pH 9.0, the precipitate was predominantly vaterite in the absence of phosphate and ikaite in the presence of phosphate regardless of the ratio of Ca/CO3. These results indicate that at low temperatures and moderate alkaline conditions (pH 9.0), phosphate can act as a switch between ikaite and vaterite polymorphs. Contrastingly, at higher alkaline conditions (pH 13.4) phosphate is not prerequisite and the high pH in itself is enough to trigger ikaite formation over vaterite.

Blood oxygen affinity increases during digestion in the South American rattlesnake, Crotalus durissus terrificus

Digesting snakes experience massive increases in metabolism that can last for many days and are accompanied by adjustments in the oxygen transport cascade. Accordingly, we examined the oxygen-binding properties of the blood in the South American rattlesnake (Crotalus durissus terrificus) during fasting and 24 and 48h after the snakes have ingested a rodent meal corresponding to 15% (±2%) of its own body mass. In general, oxygen–hemoglobin (Hb–O2) affinity was significantly increased 24h post-feeding, and then returned toward fasting values within 48h post-feeding. Content of organic phosphates ([NTP] and [NTP]/[Hb]), hemoglobin cooperativity (Hill's n), and Bohr Effect (ΔlogP50/ΔpH) were not affected by feeding. The postprandial increase in Hb–O2 affinity in the South American rattlesnake can be almost entirely ascribed by the moderate alkaline tide that follows meal ingestion. In general, digesting snakes were able to regulate blood metabolites at quite constant levels (e.g., plasma osmolality, lactate, glucose, and total protein levels). The level of circulating lipids, however, was considerably increased, which may be related to their mobilization, since lipids are known to be incorporated by the enterocytes after snakes have fed. In conclusion, our results indicate that the exceptional metabolic increment exhibited by C. d. terrificus during meal digestion is entirely supported by the aerobic pathways and that among the attending cardiorespiratory adjustments, pulmonary Hb–O2 loading is likely improved due to the increment in blood O2 affinity.

Copper modified-TiO2 catalysts for hydrogen generation through photoreforming of organics. A short review

An intense scientific activity was recorded during the last several years in the field of preparation, characterization and use of copper-based TiO2 photocatalysts for hydrogen generation through photocatalytic reforming of organics. Different copper species were used dissolved in aqueous solution or incorporated on the TiO2 surface as single co-catalyst or in the presence of a second catalyst (e.g., graphene, carbon fibers) to (1) effectively separate the electron–hole pairs, thus reducing the occurrence of the recombination reaction, and (2) extend the light absorption to the visible range of the solar spectrum. Many organic species (e.g., methanol, glycerol, formic acid) were proposed as sacrificial agents for hydrogen generation, although the prevailing idea is that of using organic compounds currently found in industrial wastewaters. The pH value was recognized as a fundamental variable in photocatalytic H2 generation via copper modified-TiO2 catalysts. A positive effect to promote hydrogen generation was associated to an increase in pH until moderate alkaline values. On the other hand, a release in the solution of cupric ions and a consequent decrease in photocatalytic activity were observed when decreasing pH. A relevant lack of information was recorded about the efficiencies of hydrogen generation which were reported only in few papers. Therefore, this critical literature review has been performed with the aim of providing a complete background to select the most efficient approaches and eventually promote new competitive systems for hydrogen generation via photoreforming for industrial applications.

Alkaline Durable 2-Methyl-1-Vinylimidazolium-Based Anion Exchange Membranes Prepared by Radiation-Induced Grafting for Hydrazine Hydrate Fuel Cells

Introduction An anion exchange membrane (AEM) is one of the key materials for alkaline-type fuel cells (AEMFC), which have potential advantages against proton exchange membrane fuel cells (PEMFC). In the AEMFC, electrochemical reactions are more facile than in acidic medium, and non-precious metals such as nickel, cobalt and iron can replace platinum as the catalyst.1,2 Because of high temperature and highly basic fuel cell operating condition, it is desirable to develop alkaline durable AEMs. In recent years, we have developed imidazolium-type AEMs by radiation-induced grafting for AEMFCs, especially in direct hydrazine fuel cells and found that poly(1-vinylimidazolium (VIm))-grafted and copoly(VIm/styrene)-grafted AEMs (AEM1 and AEM2) shows moderate alkaline stability; the AEMs degraded via the initial β-elimination and following ring opening reactions of the imidazolium unit.3,4 Therefore, we synthesized the AEM based on a poly(2-methyl-1-vinylimidazolium (MVIm)) grafts by radiation-induced grafting to improve long-term stability by suppressing β-elimination and ring opening reactions. Experimental The ETFE films were irradiated with a 60Co γ-ray source (JAEA Takasaki, Gunma, Japan) at room temperature in argon atmosphere with an absorption dose of 50 kGy. The pre-irradiated ETFE films were immediately immersed into the argon-purged monomer solution consisting of 50 wt% MVIm or a mixture of MVIm/stylene (8 : 2 weight ratio) in 1,4-dioxane. The imidazole groups in the grafted-ETFE were N-alkylated using methyl iodide. The resultant AEMs (an iodide form) were immersed in 1 M NaHCO3 solution at 60°C for 24 h to convert into a HCO3 - form, followed by the ion-exchange reaction with OH- in 1 M KOH solution at room temperature for 16 h to givethe anion forms of the AEMs (AEM3 and AEM4), as shown in Scheme 1. The ionic conductivity was measured by two-point probe AC impedance spectroscopy at 100% relative humidity in N2-purged deionized water. The ion exchange capacity (IEC) was measured using standard back titration methods. Results and discussion The poly(MVIm)- and copoly(MVIm/styrene)-grafted ETFE films (precursors of AEM3 and AEM4) were prepared with grafting degrees of 36 and 55%, respectively. The copolymer-type AEM4 was synthesized for reduction of steric and electrostatic repulsions between adjacent imidazolium cations. The N-alkylation for AEM3 proceeds quantitatively. Thus, molar ratio of MVIm and stylene in AEM4 determined from the weight gain after N-alkylation given that the N-alkylation of the imidazole groups proceeded in a quantitative maner was estimated as 1.0 : 1.4. AEM3 and AEM4 with IECs of 0.99 and 0.93 mmol g-1 showed ionic conductivities of 55 and 53 mS cm-1 at 60°C, respectively.The alkaline stability of AEMs was evaluated by monitoring the change in conductivity of AEMs in 1 M KOH at 80°C. Figure 1 shows the normalized conductivities of the AEMs on the basis of the initial conductance as a function of immersion time. The homopolymer-type AEM1 and AEM3 showed similar profiles for conductivity decreases, indicating the donimant β-elimination at an initial stage for homopolymer-type imidazolium grafts in the AEMs due to the steric and electrostatic repulsions. Copolymer-type AEM3, which had no 2-methyl group on the imidazolium group, showed a slower degradation rate after the fast decrease at the initial stage. Furthermore, copolymer-type AEM4, which had 2-methyl group on the imidazolium group, showed slower decreases at the initial stage and kept excellent long-term stability with keeping maintenance factor of 22% (12 mS cm-1) after 600 h immersion. The above results strongly indicate that the introducition of methyl group at 2-position of imidazolium unit drastically enhances the long-term durability in alkaline solutions at elevated temperatures due to the resistance of nucleophilic ring opening reactions of the imidazolium cations. Accordingly, the 2-methylimidazolium units in copolymer grafts in AEMs are promising an anion exchange group for highly alkaline durable direct hydrazine fuel cells. Acknowledgement This work was supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) from the Japan Science and Technology Agency (JST).

Role of additives; sodium dodecyl sulphate and manganese chloride on morphology of Zn1−xMnxO nanoparticles and their photoluminescence properties

In the present study Zn1−xMnxO (x = 0, 0.05 and 0.1) nanoparticles (NPs) have been synthesised in aqueous solution phase at mild reaction temperature 100 °C in moderate alkaline medium (pH = 9.5), and the role of external additives; like sodium dodecyl sulphate and manganese chloride on the morphology and size of the products has been explored on the basis of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectral analyses data. ZnO hexagonal nano-plates, core–shell like spherical/ellipsoidal Zn0.95Mn0.05O structures and thin sheets, thorn/needle mixed shaped Zn0.9Mn0.1O structures have been observed in TEM and SEM images. Zn(OH)2 formed in moderate alkaline medium, converted to Zn(II) hydroxo complex ions on dissolution, which further recrystallizes to produce wurtzite ZnO at 100 °C. From XRD and EDX analysis, successful doping of Mn2+ ions at the Zn2+ sites in ZnO host has been proved. In the photoluminescence spectra, the observed blue shifts in NBE peaks and decrease of emissions intensity on Mn doping have thoroughly been discussed in the present investigation.

The pH in the Microenvironment of Human Mesenchymal Stem Cells Is a Critical Factor for Optimal Osteogenesis in Tissue-Engineered Constructs

The present study aimed at elucidating the effect of local pH in the extracellular microenvironment of tissue-engineered (TE) constructs on bone cell functions pertinent to new tissue formation. To this aim, we evaluated the osteogenicity process associated with bone constructs prepared from human Bone marrow-derived mesenchymal stem cells (hBMSC) combined with 45S5 bioactive glass (BG), a material that induces alkalinization of the external medium. The pH measured in cell-containing BG constructs was around 8.0, that is, 0.5 U more alkaline than that in two other cell-containing materials (hydroxyapatite/tricalcium phosphate [HA/TCP] and coral) constructs tested. When implanted ectopically in mice, there was no de novo bone tissue in the BG cell-containing constructs, in contrast to results obtained with either HA/TCP or coral ceramics, which consistently promoted the formation of ectopic bone. In addition, the implanted 50:50 composites of both HA/TCP:BG and coral:BG constructs, which displayed a pH of around 7.8, promoted 20-30-fold less amount of bone tissue. Interestingly, hBMSC viability in BG constructs was not affected compared with the other two types of material constructs tested both in vitro and in vivo. Osteogenic differentiation (specifically, the alkaline phosphatase [ALP] activity and gene expression of RUNX2, ALP, and BSP) was not affected when hBMSC were maintained in moderate alkaline pH (≤7.90) external milieu in vitro, but was dramatically inhibited at higher pH values. The formation of mineralized nodules in the extracellular matrix of hBMSC was fully inhibited at alkaline (>7.54) pH values. Most importantly, there is a pH range (specifically, 7.9-8.27) at which hBMSC proliferation was not affected, but the osteogenic differentiation of these cells was inhibited. Altogether, these findings provided evidence that excessive alkalinization in the microenvironment of TE constructs (resulting, for example, from material degradation) affects adversely the osteogenic differentiation of osteoprogenitor cells.

Inoculation and alkali coeffect in volatile fatty acids production and microbial community shift in the anaerobic fermentation of waste activated sludge

Batch fermentations of waste activated sludge (WAS) at alkaline pH with different inocula were performed. Paper mill anaerobic granular sludge (PAS) and dyeing mill anaerobic sludge (DAS) were used as inocula. At pH 10 the inoculation did not increase the volatile fatty acids (VFAs) production compared to the non-inoculated samples fermented in the same conditions, and the maximal VFAs yield of non-inoculated WAS was higher than inoculated WAS. However, at pH 9 the inoculation with PAS increased the sludge hydrolysis and VFAs production was 1.7-fold higher than that in non-inoculated WAS (yield 52.40mg/g of volatile solid). Denaturing gradient gel electrophoresis analysis revealed that 3 bacterial species, identified as Proteocatella, Tepidibacter, and Clostridium, disappeared when inoculated with PAS at pH 9 or at pH⩾10. The results showed that the inoculation with PAS can be helpful to achieve a relatively high VFAs production from WAS in a moderate alkaline environment.

English

The economic and ecological function of pectinase enzymes in industries is gaining much attention with the need of highly productive strains of microorganisms to reduce production cost. The present investigation is a comparative evaluation of Bacillus sp. pectinases. The three isolates isolated from agro-waste, Bacillus stearothermophilus, Bacillus cereus and Bacillus subtilis , showed very high pectinase activities with pectin as the substrate. The three isolates also showed varying degree of preference for banana peels and wheat bran but their activity towards orange peel was very low compared to other substrate. The effect of temperature on the pectinase of the three isolates showed that B. stearothermophilus had optimum temperature at 60°C while B. cereus and B. subtilis both showed optimum activity at 50°C. On the effect of pH, B. stearothermophilus , B. cereus and B. subtilis showed optimum pectinase activities at pH 7.5, 8.0 and 9.0, respectively. Metal ions enhanced the activity of pectinase produced by the three isolates. The study exhibited that B. stearothermophilus gave the most pectinase activity, optimum temperature and a moderate alkaline pH, possibly making it a better source for industrial purpose. Key words : Pectinase, enzymes, pectin, bacteria, Bacillus species.

Study on the Conversion of Ammonia by Electrochemical Oxidation

The removal of high concentration ammonia in wastewater was investigated by an indirect electrochemical oxidation method using titanium electrodes coated with ruthenium and iridium (RuO2-IrO2-TiO2/Ti). The effect of different initial pH on ammonia removal by electrochemical oxidation was studied. The concentrations variation of ammonia, total nitrogen, nitrate nitrite, and free cholorines, chloramines was analyzed under the conditions with and without pH controlling. The results indicate that ammonia removal efficiency was higher under the moderate alkaline condition than that under neutral one. During the electrolysis process, nitrate and nitrite concentrations were very low, even below their detecting limits. The concentrations of free chlorines and chloramines were significantly affected by pH, as trichloramine and free chlorines were mainly produced in the reaction without pH controlling, while monochloramine was mainly produced in a stable alkalescene.

Activity enhancement of ZSM-35 in dimethyl ether carbonylation reaction through alkaline modifications

A series of ZSM-35 zeolites with different alkaline treatment degrees were prepared. The precise effects of alkaline treatment on composition, morphology, porosity, transportation and acidity of the samples were characterized by means of multiple techniques including N2 sorption, transmission electron microscopy (TEM), intelligent gravimetric analyzer (IGA) and Fourier transform infrared spectroscopy (FTIR). ZSM-35 after moderate alkaline treatment exhibited enhanced carbonylation activity compared with the parent sample. As revealed by the N2 adsorption and TEM results, alkaline treatment could induce the deaggregation of ZSM-35 clusters and remove the amorphous debris on the surface of ZSM-35 platelets. Furthermore, an improved diffusion behavior of the dimethyl ether reactant molecule was observed on the alkali-treated sample from IGA experiments which directly led to the better catalytic performance for the carbonylation of the dimethyl ether with carbon monoxide. Mesoporosity created by severe alkaline leaching does not enhance the catalytic properties of ZSM-35 in dimethyl ether carbonylation reaction. Especially, a decrease in reaction stability was observed due to the limitation effect of carbonaceous deposit formation.

Stable photoluminescent ZnO@Cd(OH)2 core–shell nanoparticles synthesized via ultrasonication-assisted sol–gel method

Core–shell structured ZnO@Cd(OH)2 nanoparticles with stable and improved luminescence have been prepared successfully via a facile ultrasonication-assisted sol–gel method. Their composition and structure have been confirmed by high resolution transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and infrared spectra. The size of the nanoparticles decreases gradually along with the increase in the shell thickness, indicating that Cd(OH)2 shells can hider ZnO cores growth and aggregation effectively. The as-prepared core–shell nanoparticles can be stored at room temperature for several weeks without luminescence efficiency reduction, and they are quite stable at elevated temperatures or in moderate alkaline solutions due to the protection of the Cd(OH)2 shell.

Operating condition optimization of corncob hydrothermal conversion for bio-oil production

The effect of reaction temperature, retention time, biomass content, and catalyst loading on bio-oil yield, carbon content, and carbon recovery of corncob hydrothermal conversion was investigated and optimized via response surface methodology (RSM). The four variables ranged from 280 to 340°C for temperature, 12–48min for retention time, 9–21% for biomass solid content, and 0.76–2.25% for catalyst loading. It was found from RSM modeling that higher bio-oil yield and higher carbon recovery could be achieved at relatively low temperatures and short retention times with high biomass solid contents and moderate alkaline catalyst loadings in the test ranges. A maximum bio-oil yield of 41.3% and maximum carbon recovery of 47.1% were obtained at 280°C, 12min, and 21% biomass solid content with 1.03–1.56% catalyst loading. Bio-oil carbon content was found affected only by the reaction temperature and biomass solid content in the RSM model. Higher temperature and lower biomass solid content were favored. The highest bio-oil carbon content of 74.8% was achieved at 340°C with 9% biomass solid content. The predicted bio-oil yield, carbon content and carbon recovery were in close agreement with validation experiment results, indicating that the RSM models were accurate in designing and optimizing the hydrothermal conversion of corncobs.

Characterization of wetland soils developed on limestones parent material In Cross River State, south eastern Nigeria

Wetland soils developed on limestone parent materials were characterized and classified. In the study, eight (8) profile pits were sunk in 3 sites within Cross River State in 2006, described and sampled according to FAO (1988) guidelines. The samples were analysed in the laboratory using routine methods. Results obtained for morphological studies and physicochemical analysis showed that the soils were generally deep to shallow, moderately well drained to poorly-drained with weak red to light grey, Dark reddish brown to reddish brown, yellowish brown in colour. Thesoils are weak, medium, and crumb, moderate and sub-angular blocky structure. The texture ranged from sandy loam, silt, loam, loamy sand, sandy clay and clay loam. Bulk density values ranged between 1.20 g/cm3 and 1.85 g/cm3 with a mean of 1.37 g/cm3. Particle density values ranged from 2.18 g/cm3 to 3.70 g/cm3 with a mean of 2.74 g/cm3. The soils showed total porosity of 50% on the average which indicated good soils for maximum plant growth. The soils are slightly alkaline to moderate alkaline in reaction. Organic matter, total nitrogen, Available phosphorus contents,calcium, magnesium, potassium, and sodium contents were rated as low to moderate. An effective cation exchange capacity value of 10.36 cmol/kg was rated moderate with base saturation values above 82 per cent for these soils. The soils were classified as Inceptisols and Alfisols.

A two-step pH-dependent liquid–liquid extraction combined with HPLC-fluorescence method for the determination of 10-hydroxycamptothecin in mouse liver tissue

Context: Liquid–liquid extraction (LLE) shows high efficiency in the plasma sample preparation. However, this extraction method is not optimal for the biological samples containing complex organic interferences, such as liver and brain tissues. Some plant secondary metabolites can be converted between water-insoluble and water-soluble forms by pH adjustment.Objective: A two-step pH-dependent LLE method was introduced in this study to eliminate both water-soluble and lipidic interferences using the properties of pH-dependent interconvertible forms of analytes during sample preparation. A sensitive and reliable method using a reverse-phase HPLC coupled with a fluorescence detector was developed and validated.Materials and methods: 10-Hydroxycamptothecin (HCPT) with internal standard camptothecin and liver tissues were used as model compounds and biological samples. The lactone form of HCPT was converted to the water-soluble carboxylate form under moderate alkaline conditions, and the water-insoluble interferences were extracted with a nonpolar solvent. Afterward, the water-insoluble lactone form of HCPT was regenerated by acidification and then extracted using an organic solvent in a second LLE step.Results: The calibration curve was linear (r2 > 0.999) for HCPT concentrations ranging from 2.5 to 160 ng/mL. The mean recoveries of HCPT were 114.94 ± 3.98, 104.30 ± 2.44 and 95.90 ± 1.40% (n = 6) at concentrations of 2.5, 10 and 80 ng/mL, respectively. The stability determination data showed that no significant degradation occurred under the experimental conditions. This method was successfully applied to liver tissue distribution study of HCPT in mice.Discussion and conclusion: This two-step LLE can be applied to distribution studies of compounds with pH-dependent interconvertible forms in other biological matrices.

Mechanisms of hydrolysis of phenyl- and benzyl 4-nitrophenyl-sulfamate esters

The kinetics of hydrolysis at medium acid strength (pH interval 2-5) of a series of phenylsulfamate esters 1 have been studied and they have been found to react by an associative S(N)2(S) mechanism with water acting as a nucleophile attacking at sulfur, cleaving the S-O bond with simultaneous formation of a new S-O bond to the oxygen of a water molecule leading to sulfamic acid and phenol as products. In neutral to moderate alkaline solution (pH ≥ ~ 6-9) a dissociative (E1cB) route is followed that involves i) ionization of the amino group followed by ii) unimolecular expulsion of the leaving group from the ionized ester to give N-sulfonylamine [HN=SO(2)] as an intermediate. In more alkaline solution further ionization of the conjugate base of the ester occurs to give a dianionic species which expels the aryloxide leaving group to yield the novel N-sulfonylamine anion [(-)N=SO(2)]; in a final step, rapid attack of hydroxide ion or a water molecule on it leads again to sulfamic acid. A series of substituted benzyl 4-nitrophenylsulfamate esters 4 were hydrolysed in the pH range 6.4-14, giving rise to a Hammett relationship whose reaction constant is shown to be consistent with the E1cB mechanism.

The role of hydroxyl and oxyl anion radicals in selectivity of oxygen delignification

Abstract The concentration of the hydroxyl radical generated during oxygen delignification was measured with a radical trapping agent. The N,N′-(5-nitro-1,3-phenylene)-bisglutaramide (NPG) was found to be effective but the experiments revealed that at pH higher than 11.5 the anionic form of hydroxyl radical – the oxyl anion radical – causes up to four times more chain cleavage than the hydroxyl radical. It was also found that the effect of both radicals in the pulp moderated at higher partial oxygen pressure and in the presence of hemicelluloses. The implications are that selectivity can be improved by maintaining a moderate alkaline pH profile, increasing the oxygen partial pressure, and retaining hemicelluloses in the brownstock.

Highly acidic mesoporous aluminosilicates prepared from preformed HY zeolite in Na2SiO3 alkaline buffer system

Mesoporous aluminosilicates (YM) were hydrothermally synthesized by assembling zeolite subunits, which were generated by the hydrolysis of HY zeolite in Na2SiO3 aqueous solution, in the presence of cetyltrimethylammonium bromide (CTAB). The Na2SiO3 aqueous solution plays two roles in the synthesis. It provides a moderate alkaline medium with buffering effect for the desilication of HY zeolite and it acts as a supplementary silica source. The desilication of HY zeolite was optimized in terms of reaction temperature and time. Characterizations by XRD, nitrogen isotherms and TEM indicated that YM possessed a well-ordered mesostructure. FT-IR, UV-Raman, 27Al MAS NMR, NH3-TPD, and pyridine-adsorbed IR showed that the characteristics of Y zeolite, such as double six-membered ring subunits, tetrahedral coordination aluminum and high ratio of Bronsted/Lewis acidity sites, were preserved in YM. SEM observation revealed YM possesed a different morphology from either mesoporous MCM-41 or Y zeolite. No separate zeolite crystals were found in the TEM observation. The hydrothermal stability of YM towards refluxed water (120 h) and steam (873 K, 6 h), and the activity in acid-catalyzed cumene cracking (623 K) were compared with MCM-41 prepared with conventional method or parent HY. Because of the uniform structure and surface properties, YM was more hydrothermally stable than MCM-41; it also exhibited more efficient catalytic activitation than MCM-41 and HY in cumene cracking.

Micro Segmented-Flow Technique for Continuous Synthesis of Different Kinds of ZnO Nanoparticles in Aqueous and in DMSO Solution

The segmented flow technique is used for continuous synthesis of ZnO nanoparticles under micro reaction conditions. The experimental setup consisted of syringe pumps and T-type injectors, PTFE tubings as well as PTFE knot mixers in a thermostated bath. ZnO nanoparticles were obtained by generation under strong alkaline conditions and elevated temperature in aqueous solution and by precipitation under moderate alkaline conditions in DMSO solution. In aqueous solution, small compact nanoparticles (diameters below 100 nm) were obtained at high temperature (90°C) and high reactant concentrations. Larger crystals, nanoneedles and nanoflowers (submicron and lower micro range) were obtained at reduced concentrations and reduced temperature (70°C). Compact nanocrystals with diameters of a few hundred nanometers are formed by the reaction of zinc acetate with tetramethylammoniumhydroxide in the presence of polyethylene glycole (at 80°C). In nearly all cases, a strong effect of flow rate on nanoparticle quality was observed. Enhanced flow rates (up to 5000 μL/min) lead to an improvement of shape homogeneity and size distribution.

Comparison of properties and mode of action of six secreted xylanases from Chrysosporium lucknowense

Eight homogeneous xylanases were purified from crude multienzyme preparations produced by various mutant strains of the fungus Chrysosporium lucknowense. Peptide mass fingerprinting showed that the isolated enzymes are the products of six different genes of C. lucknowense, three of them encoding xylanases belonging to family 10 of glycoside hydrolases (GH) and three other genes encoding enzymes of the GH11 family. Intact Xyn10A and Xyn10B possessed a family 1 CBM at the N- and C-terminus, respectively; each of the enzymes was also isolated in the form without CBM. The GH11 family xylanases displayed very high specific activities against various xylans, the Xyn11A being the most active (329–494 U mg −1). In hydrolysis of glucuronoxylan and arabinoxylan, xylanases belonging to the same family were characterized by very similar kinetic behavior and composition of the final products. The GH10 family xylanases showed greater catalytic versatility and formed shorter oligosaccharides than those of family 11. Xyn10A, Xyn10B and Xyn11A were characterized by broad pH optima and displayed high activity in neutral and moderate alkaline medium. The GH10 family xylanases demonstrated high thermostability retaining more than 70% of activity after 1-h incubation at 60 °C. These properties make the C. lucknowense xylanases promising candidates for different biotechnological applications.

Histopathologic Limbus Evolution After Alkaline Burns

To study the histopathologic evolution of the corneal limbus after alkaline burns according to the clinical severity and therapy used. A prospective study of 15 eyes from 12 patients (9 men and 3 women) with moderate and severe alkaline burns was performed. All patients were divided into 2 groups in accordance with the clinical ocular severity and the therapy that was used: medical therapy, amniotic membrane transplantation (AMT), autologous limbal transplantation (ALT), and ALT combined with AMT (ALT + AMT). Biopsies were obtained from affected limbal areas immediately after the ocular burn and 9 months later. Limbal regeneration was limited to small areas in patients with moderate burns treated with medical therapy; in contrast, the limbal structure showed significant stromal and epithelial regeneration in patients with moderate burns treated with AMT. There was an important stromal regeneration with an incomplete reepithelialization in patients with severe burns treated with AMT. Patients treated with ALT showed a good reepithelialization with a defective stromal regeneration. Epithelial and stromal regeneration was notable in patients with severe burns treated with ALT + AMT. In patients with moderate alkaline burns, AMT improved both limbal stromal and epithelial regeneration more effectively than medical therapy. In patients with severe burns, the best reepithelialization and stromal regeneration were obtained with ALT + AMT.