Basic pHs Research Articles

Cucurbit[n]urils (n = 6–8) used as host molecules on supramolecular complexes formed with two different drugs: Emodin and indomethacin

We present the characterization of supramolecular complexes formed by cucurbit[n]urils, (n = 6,7,8) with the anti-tumoral drug emodin and the non-steroidal anti-inflammatory drug indomethacin at several pHs. Both drugs exhibit poor water solubility and host-guest complexes constitute an option to increase the drugs’ solubility and stability. We use different spectroscopic techniques: UV–vis, 1H NMR and fluorescence. Our study shows that emodin forms complexes at pH = 2 with cucurbit[6]uril with stoichiometry (1:1) (host:guest), as well as complexes with cucurbit[7]uril and cucurbit[8]uril with stoichiometry (2:1) but no complexes are found at basic pHs. In the case of indomethacin, complexes are formed with cucurbit[6]uril and cucurbit[8]uril at pH = 6, with stoichiometries (2:1) and (1:1) respectively. The data presented here can be useful in the development of new drug delivery systems employing these supramolecular assemblies.

Chitosan and Its Derivatives for Application in Mucoadhesive Drug Delivery Systems.

Mucoadhesive drug delivery systems are desirable as they can increase the residence time of drugs at the site of absorption/action, provide sustained drug release and minimize the degradation of drugs in various body sites. Chitosan is a cationic polysaccharide that exhibits mucoadhesive properties and it has been widely used in the design of mucoadhesive dosage forms. However, its limited mucoadhesive strength and limited water-solubility at neutral and basic pHs are considered as two major drawbacks of its use. Chemical modification of chitosan has been exploited to tackle these two issues. In this review, we highlight the up-to-date studies involving the synthetic approaches and description of mucoadhesive properties of chitosan and chitosan derivatives. These derivatives include trimethyl chitosan, carboxymethyl chitosan, thiolated chitosan, chitosan-enzyme inhibitors, chitosan-ethylenediaminetetraacetic acid (chitosan-EDTA), half-acetylated chitosan, acrylated chitosan, glycol chitosan, chitosan-catechol, methyl pyrrolidinone-chitosan, cyclodextrin-chitosan and oleoyl-quaternised chitosan. We have particularly focused on the effect of chemical derivatization on the mucoadhesive properties of chitosan. Additionally, other important properties including water-solubility, stability, controlled release, permeation enhancing effect, and in vivo performance are also described.

Fluorescence regional integration and differential fluorescence spectroscopy for analysis of structural characteristics and proton binding properties of fulvic acid sub-fractions

Structural characteristics and proton binding properties of sub-fractions (FA3–FA13) of fulvic acid (FA), eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluorescence regional integration (FRI) and differential fluorescence spectroscopy (DFS). Humic-like (H-L) and fulvic-like (F-L) materials, which accounted for more than 80% of fluorescence response, were dominant in five sub-fractions of FA. Based on FRI analysis, except the response of F-L materials in FA9 and FA13, maximum changes in percent fluorescence response were less than 10% as pH was increased from 2.5 to 11.5. Contents of carboxylic and phenolic groups were compared for fluorescence peaks of FA sub-fractions based on pH-dependent fluorescence derived from DFS. Static quenching was the dominant mechanism for binding of protons by FA sub-fractions. Dissociation constants (pKa) were calculated by use of results of DFS and the modified Stern-Volmer relationship. The pKa of H-L, F-L, tryptophan-like and tyrosine-like materials of FA sub-fractions exhibited ranges of 3.17–4.06, 3.12–3.97, 4.14–4.45 and 4.25–4.76, respectively, for acidic pHs. At basic pHs, values of pKa for corresponding materials were in ranges of 9.71–10.24, 9.62–10.99, 9.67–10.31 and 9.33–10.28, respectively. At acidic pH, protein-like (P-L) materials had greater affinities for protons than did either H-L or F-L materials. The di-carboxylic and phenolic groups were likely predominant sites of protonation for both H-L and F-L materials at both acidic and basic pHs. Amino acid groups were significant factors during proton binding to protein-like materials of FA sub-fractions at basic pH.

Synthesis of a hybrid organic-inorganic polyethersulfone membrane incorporated with phosphotungstic acid: Controversial performance in removal of dinitroaniline herbicides from water

Abstract Present study focused on removal of one type of highly employed and poisonous herbicides (trifluralin and ethalfluralin as dinitroaniline herbicides) from water using membrane technology. To this aim, composite membranes were prepared using polyethersulfone as base polymer and different concentrations of phosphotungstic acid as superhydrophilic additive. Scanning electron microscopy, atomic force microscopy, water contact angle, bulk porosity and mean pore size measurements as well as pure water tests were employed for characterization of membranes. To mimic real circumstances existing in surface water, experiments were conducted at acid, neutral and basic pHs, and also, effects of ionic environment on removal of herbicides was probed by controlling the sodium and calcium concentration in feed solution. Water permeability was remarkably improved due to induced changes in composite membranes. Surprisingly, fabricated membranes behaved contrarily in removal of dinitroanilines belonged to the same class of herbicides with similar size and molecular weight. According to the results, efficiency of membranes was affected by several factors relating to both membrane and herbicide as well as solution pH. Moreover, evaluation of antifouling characteristics of membranes demonstrated higher resistance of composite membranes against fouling.

Degradation of acrylamide during chlorination as a precursor of haloacetonitriles and haloacetamides

Acrylamide is a monomer of polyacrylamide, which is widely used in the water treatment process as a flocculant. The degradation kinetics and formation of disinfection by-products (DBPs) during acrylamide chlorination were investigated in this study. The reaction between chlorine and acrylamide followed a pseudo-first-order kinetics. A kinetic model regarding acrylamide chlorination was established and the rate constants of each predominant elementary reaction (i.e., the base-catalyzed reaction of acrylamide with ClO− as well as the reactions of acrylamide with HOCl and ClO−) were calculated as 7.89×107M−2h−1, 7.72×101M−1h−1, and 1.65×103M−1h−1, respectively. The presence of Br− in water led to the formation of HOBr and accelerated the rate of acrylamide degradation by chlorine. The reaction rate constant of acrylamide with HOBr was calculated as 1.33×103M−1h−1. The degradation pathways of acrylamide chlorination were proposed according to the intermediates identified using ultra-performance liquid chromatography and electrospray ionization-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). Five chlorinated DBPs including chloroform (CF), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), dichloroacetamide (DCAcAm), and trichloroacetamide (TCAcAm) were identified during acrylamide chlorination. The formation of CF, DCAN, DCAcAm, and TCAcAm kept increasing, while that of TCAN increased and then decreased with increasing reaction time. As the chlorine dosage increased from 0.75 to 4.5mM, DCAN became the dominant DBP. Large amounts of CF, DCAN, and TCAN were formed at basic pHs. The hydrolysis of DCAN and TCAN led to the formation of DCAcAm and TCAcAm, respectively. The results of this study elucidated that acrylamide can be a precursor for the formation of haloacetonitriles (HANs) and haloacetamides (HAcAms) during drinking water treatment.

Copper, nickel and zinc complexes of a new water-soluble thiosemicarbazone ligand: Synthesis, characterization, stability and biological evaluation

New water soluble Schiff base thiosemicarbazone ligand, namely (sodium 4-hydroxy-3-{[(methylaminocarbonothioyl)hydrazono]methyl}-benzene sulfonate) (NaH2L) was obtained by the reaction of methylthiosemicarbazide with sulfonate salicylaldehyde and characterized by elemental analysis, spectroscopic methods (UV–Vis, FTIR, 1HNMR, and 13CNMR) and electrospray ionization mass spectrometry. The X-ray structure of NaH2L (NaH2L·CH3OH·0.5H2O) shows that sodium atoms are interconnected through sulfonate groups of the ligands into one-dimensional coordination polymer network. Reaction of the ligand with metal acetates produced following complexes: [Cu(HL)]2, NiHL and ZnHL. All complexes were characterized by means of elemental analysIs, IR spectroscopy, and ESI-Mass measurements. The dinuclear structure of the copper complex was determined by single-crystal X-ray crystallography and showed the square pyramidal geometry for each metal center. NaH2L, [Cu(HL)]2, and NiHL showed high solubility in water (50, 25 and 25g/L, respectively, at 25°C), while solubility of ZnHL was very low. NiHL was stable at all pH ranges for 4days while stability of NaH2L and [Cu(HL)]2 was decreasing at acidic and basic pHs. Among all this compounds, only NiHL showed some low antimicrobial activity. Antioxidant activity of the compounds for scavenging activity of DPPH• and ferric reducing antioxidant power (FRAP) was evaluated and the ligand indicated the strongest radical scavenging relative to the complexes and l-ascorbic acid as standard. The anti-proliferative effect of the ligand and their corresponding complexes was evaluated on the human leukemia cell lines, KG1-aand K562·The KG1-a cells underwent apoptosis upon a single dose (at IC50 value) of the NiHL as most active complex.

Sulfonate-terminated carbosilane dendron-coated nanotubes: a greener point of view in protein sample preparation.

Reduction or removal of solvents and reagents in protein sample preparation is a requirement. Dendrimers can strongly interact with proteins and have great potential as a greener alternative to conventional methods used in protein sample preparation. This work proposes the use of single-walled carbon nanotubes (SWCNTs) functionalized with carbosilane dendrons with sulfonate groups for protein sample preparation and shows the successful application of the proposed methodology to extract proteins from a complex matrix. SEM images of nanotubes and mixtures of nanotubes and proteins were taken. Moreover, intrinsic fluorescence intensity of proteins was monitored to observe the most significant interactions at increasing dendron generations under neutral and basic pHs. Different conditions for the disruption of interactions between proteins and nanotubes after protein extraction and different concentrations of the disrupting reagent and the nanotube were also tried. Compatibility of extraction and disrupting conditions with the enzymatic digestion of proteins for obtaining bioactive peptides was also studied. Finally, sulfonate-terminated carbosilane dendron-coated SWCNTs enabled the extraction of proteins from a complex sample without using non-environmentally friendly solvents that were required so far. Graphical Abstract Green protein extraction from a complex sample employing carbosilane dendron coated nanotubes.

Catalytic reduction of 4-nitrophenol by palladium-resin composites

Catalytic reduction of 4-nitrophenol (4-NP) by palladium-resin catalysts is promising for 4-NP detoxification, in situ regeneration of the catalysts, and recycling of the products. In this study, we examined the catalytic reduction of 4-NP by Pd0-based catalysts supported on three neutral resins and two anion exchange resins, using hydrogen gas as the electron donor. The reduction kinetics followed the same trend as the adsorption kinetics, i.e., faster adsorption and reduction were observed at acidic pHs for the neutral resins and at basic pHs for the anionic resins (4-NP pKa=7.15). The Langmuir-Hinshelwood model based on surface reaction as the rate determining step fitted the kinetic data well. These findings point to the significant role of adsorption in the overall catalytic reaction. Cl− inhibited the reactivity of the neutral resins less than that of the anion exchangers due to the hydrophobic nature of the former. The longevity of the catalysts was examined in two tests: (1) 1mM 4-NP was repeatedly spiked into the same catalysts for eight times, where the accumulation of 4-NP and the sole reduction product (4-aminophenol) on the resin surfaces resulted in the gradual loss in the catalytic activity, which was largely restored after regeneration, and (2) the catalysts were subjected to fresh influent in each adsorption and catalytic reduction cycle for seven times, where the catalysts sustained their reactivity through the seven cycles, significantly eliminating the need for frequent regeneration.

Properties of In situ polymerized poly(3,4‐ethylenedioxythiophene)/alumina composites for energy storage applications

ABSTRACTComposites formed by poly(3,4‐ethylenedioxythiophene) and alumina (PEDOT/Al2O3) have been prepared by in situ anodic polymerization. For this purpose, the stability of 1:1 and 4:1 monomer:alumina aqueous solutions has been examined as a function of the pH (2.3, 4.0, 7.0, 8.8, or 10.8). Results indicate that the monomer behaves as a dispersant that remains stable at the studied basic pHs despite they are close to the isoelectric point of alumina. Although the thermal stability of the composites is considerably affected by the pH of the reaction medium, its influence on the surface morphology is very small. Independently, of the synthetic conditions, the electrochemical properties were better for PEDOT/Al2O3 than for pure PEDOT, reflecting that alumina particles promote the charge mobility. The highest specific capacitance (SC; 141 F/g), which was 55% higher than that obtained for pure PEDOT, was achieved for the composite prepared at pH = 8.8 using a 4:1 monomer:alumina ratio. These conditions favor the participation of OH– groups as secondary doping agents without degrading the polymer matrix and enhance the specific surface of the films, facilitating the ionic mobility. On the other hand, application of a multi‐step polymerization strategy has shown that interfaces originated by consecutive steps enhance the SC. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1131–1141

Near‐Infrared Electrochemiluminescence from Au Nanoclusters Enhanced by EDTA and Modulated by Ions

AbstractNear‐infrared electrochemiluminescence (ECL) from Au‐thiolate nanoclusters is activated by electrode reactions and enhanced by ethylenediamine tetraacetic acid (EDTA). The enhancement effect is higher at pH 7.4 than at more basic or acidic pHs. Magnesium ions are found to modulate the ECL signals through complexation with EDTA and the interaction with the Au nanoclusters. The chemical system and the signal modulation mechanism are believed to be generalizable and advantageous for future sensing and analysis applications with the following merits: 1) Ambient ECL without oxygen removal, 2) high enhancement at physiological pH values, 3) in the near‐IR spectrum window with low interference, 4) rich and tunable redox activity of the Au nanoclusters, and 5) EDTA representing other ionophores or chelaters as versatile coreactants.

Capacity Fade of NaTi2(PO4)3 in Aqueous Electrolyte Solutions: Relating pH Increases to Long Term Stability

The inherent chemical stability of NaTi2(PO4)3 in aqueous solutions with higher pH values, and resulting implications for using this material as an anode are explored. Scanning electron microscopy, x-ray powder diffraction, and Fourier transform infrared spectroscopy were used to investigate morphological, structural, and chemical changes for samples exposed to varying basic pHs at 25°C and 70°C. Significant structural degradation and precipitation of a secondary phase were observed in all samples prepared at 70°C along with 25°C samples exposed to more extreme pH solutions. Infrared spectroscopy results indicated a loss of phosphate from the precipitated material, while x-ray diffraction shows that the secondary phases were from the layered sodium titanate family. Cyclic voltammetry of the samples indicated some degree of capacity loss for all of the samples, while some showing features related to the observed secondary phase that has some electrochemical functionality. The implications of these results on the stability of NaTi2(PO4)3 in various electrolyte environments is discussed.

Fabrication of dye sensitized solar cells with improved multi-layer photonodes of hydrothermally grown TiO2 nanocrystals in different autoclaving pHs

In this research dye sensitized solar cells (DSCs) with multilayer photopanodes made of small and large TiO2 nanocrystals were fabricated. These nanocrystals were hydrothermally grown in two different basic autoclaving pHs of 10.0 and 12.0. The dominant sizes of TiO2 NCs were measured about 15 and 70 nm for the growth in the mentioned pHs, respectively. The layers composed of 15 nm TiO2 nanocrystals were well-transparent with high amount of dye adsorption. That is while the layers made of 70 nm TiO2 nanoparticles demonstrated a high level of light scattering and lower amount of dye adsorption. Different multilayer photoanodes including one, two and three sub-layers of 15 nm TiO2 nanocrystals and one over-layer of 70 nm TiO2 nanoparticles were fabricated. Then the influence of the semi-scattering over-layer of the photanodes on the performance of corresponding DSCs was investigated. The results demonstrated that a maximum efficiency of 7.7% was achieved for a cell with a multilayer photoanode made of three sub-layers of small TiO2 nanocrystals and one over-layer of 70 nm TiO2 nanoparticles. This efficiency was increased about 16% compared to that of the cell with simple three layer photoanode. The reason was mainly attributed to the increased dye loading amount of the photoanodes with one semi-light scattering over-layer.

Development of palladium-resin composites for catalytic hydrodechlorination of 4-chlorophenol

Polymeric resins have been widely used for the removal of halogenated compounds, however, the sustainability of resin adsorption is compromised by frequent resin regeneration and further treatment/disposal of concentrated brine. Palladium (Pd)-based catalytic hydrogenation is promising to treat various classes of contaminants, including halogenated compounds, and the development of Pd-polymeric resin composites is advantageous because the composites can convert halogenated compounds to less toxic chemicals in situ and mitigate challenges associated with resin regeneration. In this work, three neutral resins (MN200, MN100, and XAD4) and two anion exchange resins (IRA910 and IRA96) were used as Pd supports to evaluate 4-chlorophenol (4-CP) hydrodechlorination reactivity. Similar 4-CP adsorption and reduction kinetics were observed, i.e., adsorption and reduction were both faster at acidic pHs for the neutral resins but faster at basic pHs for the anionic resins. The developed Langmuir–Hinshelwood kinetic model based on surface reaction as the rate determining step also suggested an enhancing effect of adsorption on the catalytic reactivity. When adsorption was constant, the reactivity of the catalysts increased with increasing solution pH. This is because higher pH mitigates the adverse impacts of the dehalogenation products (i.e., H+ and Cl−) on the catalytic reaction. The inhibition effect of Cl− was more pronounced on IRA910 than on MN200. IRA910 with anion exchange functional groups facilitates Cl− adsorption and promotes the production of PdCl3− and PdCl42− species, which are inactive for catalytic reduction. The accumulation of phenol, the dominant product in 4-CP reduction, on resin resulted in catalytic activity loss over eight cycles when 4-CP was repeatedly spiked into the same reactor; the catalytic activity was largely restored after resin regeneration.

Development of a nanoparticle system based on a fructose polymer: Stability and drug release studies

New drug delivery systems (DDSs) with levan or its carboxymethylated form, as carriers, and 5-fluorouracil as a drug, are produced in this work. Levan is obtained after cultivating A. nectaris and polymer nanoparticles are created in water by a self-assembled process. The effect of pH and the ionic strength on polymer nanoparticles aggregation is studied. Basic pHs produces a particle size between 300 and 400nm with a Z-potential around −20mV because a basic medium promotes repulsion forces. DDSs of 300–400nm and a Z-potential about −25mV are prepared by taking advantage of the amphiphilic properties of the levan. The drug is bound to either levan or carboxymethyllevan surfaces by electrostatic interactions, obtaining the best results at basic pHs. 45–70% of the drug is released from the levan in 23h depending on the pH preparation, whereas only a low percentage of the drug is released from the carboxymethyllevan.

Production of recombinant lipase B from Candida antarctica in Pichia pastoris under control of the promoter PGK using crude glycerol from biodiesel production as carbon source

The use of new constitutive promoters and recycled carbon sources in the recombinant production of industrial proteins such as lipases in the cell factory Pichia pastoris is desirable, in order to improve production and minimize the cost of the culture medium. With this aim, the recombinant production of lipase B from Candida antarctica (rLipB) in P. pastoris under the PGK promoter, using crude glycerin from biodiesel, was assessed. Study of the best culture conditions made possible a significant increase in production. The optimal culture conditions used minimal medium containing crude glycerol as the carbon source, starting the batch with 100g/L, and subsequently making four pulses of this crude glycerol, of 25g/L each. The lipase produced was characterized and compared to commercially available lipase from Aspergillus niger, sold by Novozymes. rLip B proved to be stable in basic pHs and temperatures lower than 55°C, the optimum conditions being pH 7.0 and 30°C. The selectivity for medium-sized carbon chains was similar in both, and tributyrine (C4:0) was the best triacylglycerol studied. The results showed that this approach is a viable alternative to produce rLipB with this new promoter, using crude glycerol.

224 - Cytosolic Fe-Superoxide Dismutase Protects Trypanosoma Cruzi from Host-Derived Superoxide and Increases Pathogen Virulence in Vivo

Trypanosoma cruzi, the causative agent of Chagas Disease, contains Fe-dependent superoxide dismutases (Fe-SODs). After invasion, parasites have to deal with large amounts of superoxide radical (O2●–) produced during macrophage phagocytosis (NADPH-oxidase activation) and, in cytokine-activated macrophages (iNOS induction), with nitric oxide (●NO) and peroxynitrite. In this work, we studied the relevance of T. cruzi cytosolic Fe-SOD (Fe-SODB) during infection in vitro and in vivo. Fe-SODB-overexpressing parasites (TcFeSODB) were generated using the plasmid pRIBOTEX and expression evaluated by western-blot, immunocytochemistry and activity measurements. TcFeSODB parasites had less intra-parasite peroxynitrite generation than wt when exposed to O2●–- and ●NO fluxes, as evaluated by the oxidation of fluorescein boronate. They were also more resistant to macrophage killing (24hs after infection to J774A.1 or primary macrophages). These enhanced resistance, provided by high Fe-SOD levels in T. cruzi, was lost in NADPH-oxidase knockout macrophages (from gp91-/- mice). In the phagosome (pH ≈ 5-6), O2●–could be protonated (HO2●, pKa = 4,88) and diffuse towards parasite cytosol. This was confirmed by exposing the parasites to external fluxes of O2●– (generated by the system xanthine-oxidase/xanthine) at acidic and basic pHs (6 and 8 respectively). Intra-parasite 2-hydroxyethidium content (O2●–-specific product of dihydroethidium oxidation) was larger at pH=6 than pH=8. Additional entry mechanisms also participate, as the anion channel inhibitor NPPB, but not DIDS, decreased 2-hydroxyethidium detection. Inhibition of macrophage’s v-ATPase proton pump and prevention of phagosome acidification also decreases 2-hydroxyethidium detection in trypomastigotes 2h after infection. These results clearly show that O2●–can reach the parasite cytosol during phagocytosis. Finally, parasitemia in C57BL/6 infected mice (n=5) was larger (40%) for TcFeSODB than in wt parasites, demonstrating that Fe-SODB acts as a virulence factor in the mouse model of Chagas Disease.

Deciphering the factors defining the pH-dependence of a commercial glycoside hydrolase family 8 enzyme.

A prerequisite to the use of any enzyme in any industrial process is an understanding of its activity and stability under process conditions. Glycoside hydrolase family 8 enzymes include many important biotechnological biocatalysts yet little is known of the performance of these with respect to pH. A better understanding of this parameter and its relationship to structure and function in these enzymes will allow for an improved use of these in industry as well as an enhanced ability in their engineering and optimisation for a particular application. An in-depth analysis of the pH induced changes in activity, irreversible inactivation, conformation, stability and solubility of a commercial glycoside hydrolase family 8 xylanase was carried out with the aim of identifying the factors determining the pH dependence of this enzyme. Our study showed that different phenomena play different roles at the various pHs examined. Both reversible and irreversible processes are involved at acidic pHs, with the irreversible processes dominating and being due to protein aggregation and precipitation. At basic pHs, loss of activity is principally due to reversible processes, possibly deprotonation of an essential catalytic residue, but at higher pHs, near the pI of the protein, precipitation again dominates while structure unfolding was discerned at the higher pHs investigated. Such insights demonstrate the complexity of factors involved in the pH dependence of proteins and advances our knowledge on design principles and concepts for engineering proteins. Our results highlight the major role of protein precipitation in activity and stability losses at both low and high pHs but it is proposed that different strategies be used in tailoring the enzyme to overcome this in each case. Indeed the detailed understanding obtained here will allow for a more focused, informed and hence successful tailoring of glycoside hydrolase family 8 proteins for a specific pH and process application.

Evolved alkaline fungal laccase secreted by Saccharomyces cerevisiae as useful tool for the synthesis of C–N heteropolymeric dye

Enzymatic production of C–N heteropolymeric dyes at alkaline pHs is an attractive process for the textile industry. In this work, we have designed a fungal laccase by directed evolution so that it may be used at alkaline pHs for the synthesis of C–N heteropolymeric dyes (C–N polydye) from catechol and 2,5-diaminobenzenesulfonic acid (2,5-DABSA). Firstly, several medium- and high-redox potential fungal laccases from previous laboratory evolution campaigns were benchmarked for the synthesis of the C–N polydye at pH 8.0, choosing an alkaline laccase mutant from Myceliophthora thermophila as the departure point for further engineering. Mutant libraries were then constructed, expressed in Saccharomyces cerevisiae and screened using a high-throughput colorimetric assay for the detection of the C–N polydye. By combining directed and focused molecular evolution, a novel, strongly expressed alkaline laccase variant was identified. This laccase was secreted at 37mg/L and its catalytic efficiency for the oxidation of catechol and 2,5-DABSA at pH 8.0 was enhanced 3.5-fold relative to that of the wild-type, promoting the synthesis of the C–N polydye at basic pHs. While the improved expression was mostly the result of accumulating mutations that favor the yeast’s codon usage together with the recovery of a secretion mutation, the enhanced C–N polydye synthetic activity of the mutant laccase was dependent on the alkaline mutations it inherited. Readily secreted, this laccase mutant would appear to be a valuable platform for organic synthesis at basic pHs.

Fusion between fluid liposomes and intact bacteria: study of driving parameters and in vitro bactericidal efficacy.

BackgroundPseudomonas aeruginosa represents a good model of antibiotic resistance. These organisms have an outer membrane with a low level of permeability to drugs that is often combined with multidrug efflux pumps, enzymatic inactivation of the drug, or alteration of its molecular target. The acute and growing problem of antibiotic resistance of bacteria to conventional antibiotics made it imperative to develop new liposome formulations for antibiotics, and investigate the fusion between liposome and bacterium.MethodsIn this study, the factors involved in fluid liposome interaction with bacteria have been investigated. We also demonstrated a mechanism of fusion between liposomes (1,2-dipa lmitoyl-sn-glycero-3-phosphocholine [DPPC]/dimyristoylphosphatidylglycerol [DMPG] 9:1, mol/mol) in a fluid state, and intact bacterial cells, by lipid mixing assay.ResultsThe observed fusion process is shown to be mainly dependent on several key factors. Perturbation of liposome fluidity by addition of cholesterol dramatically decreased the degree of fusion with P. aeruginosa from 44% to 5%. It was observed that fusion between fluid liposomes and bacteria and also the bactericidal activities were strongly dependent upon the properties of the bacteria themselves. The level of fusion detected when fluid liposomes were mixed with Escherichia coli (66%) or P. aeruginosa (44%) seems to be correlated to their outer membrane phosphatidylethanolamine (PE) phospholipids composition (91% and 71%, respectively). Divalent cations increased the degree of fusion in the sequence Fe2+ > Mg2+ > Ca2+ > Ba2+ whereas temperatures lower than the phase transition temperature of DPPC/DMPG (9:1) vesicles decreased their fusion capacity. Acidic as well as basic pHs conferred higher degrees of fusion (54% and 45%, respectively) when compared to neutral pH (35%).ConclusionBased on the results of this study, a possible mechanism involving cationic bridging between bacterial negatively charged lipopolysaccharide and fluid liposomes DMPG phospholipids was outlined. Furthermore, the fluid liposomal-encapsulated tobramycin was prepared, and the in vitro bactericidal effects were also investigated.

Cs(I) Cation Enhanced Cu(II) Catalysis of Water Oxidation.

We report here a new catalytic water oxidation system based on Cu(II) ions and a remarkable countercation effect on the catalysis. In a concentrated fluoride solution at neutral to weakly basic pHs, simple Cu(II) salts are highly active and robust in catalyzing water oxidation homogeneously. F(-) in solution acts as a proton acceptor and an oxidatively robust ligand. F(-) coordination prevents precipitation of Cu(II) as CuF2/Cu(OH)2 and lowers potentials for accessing high-oxidation-state Cu by delocalizing the oxidative charge over F(-) ligands. Significantly, the catalytic current is greatly enhanced in a solution of CsF compared to those of KF and NaF. Although countercations are not directly involved in the catalytic redox cycle, UV-vis and (19)F nuclear magnetic resonance measurements reveal that coordination of F(-) to Cu(II) is dependent on countercations by Coulombic interaction. A less intense interaction between F(-) and well-solvated Cs(+) as compared with Na(+) and K(+) leads to a more intense coordination of F(-) to Cu(II), which accounts for the improved catalytic performance.