Ultrasonic solvent extraction of gallium with Kelex 100

Using ultrasound for the solvent extraction of gallium with Kelex 100 dramatically increased the rates (up to 15 times) of extraction in both artificial and real solutions. Among the modifiers, 2-undecanone performed the best; among the diluents, Escaid 200 produced the best results. With the application of ultrasound, temperature did not effect gallium extraction. Further, through the intermittent use of ultrasound, energy consumption can be decreased significantly.     

Enhancement of the metal-binding properties of chitosan through synthetic addition of sulfur- and nitrogen-containing compounds

Several new chitosan derivatives were synthesized with the intent of forming polymers that could be used in hazardous waste remediation as toxic metal-binding agents in aqueous environments. The ability of these derivatives to bind Cu²⁺, Pb²⁺, Cd²⁺, and Fe²⁺ was tested and compared to chitosan. Four of the new compounds, the products of the reaction of chitosan with mercaptosuccinic acid, thiirane, pyridoxal hydrochloride, and succinamide, show promising results as binding agents for the above metal ions. The compound with mercaptosuccinic acid bound twice as much Cd²⁺, five times as much Pb²⁺, and virtually no Fe²⁺ when compared to chitosan. The compound with thiirane bound three times as much Pb²⁺, whereas the pyridoxal hydrochloride derivative bound 30% more Cu²⁺ and twice the Pb²⁺. The succinamide derivative gave results comparable to chitosan, but with decreased solubility at low pH. © 1993 John Wiley & Sons, Inc.     

Design,preparation, and characterization of new high-refractive index hybrid organic–inorganic polysiloxanes: Innovative coatings for optoelectronic applications

The current demand for high-refractive index materials is very high due to their importance in optoelectronic applications. Such materials already exist in the market, but they present many disadvantages. They might contain toxic metals; their preparation can be challenging or produce high quantity of waste. Consequently, there is an urgent need to produce new friendly coatings with high-refractive index. Hybrid organic–inorganic polysiloxanes can offer a solution to this problem. They can be easily prepared from nontoxic alkoxy silanes using the sol–gel chemistry process. Herein, a series of new hybrid polysiloxanes are synthesized from the monomer 1–(2–(triethoxysilyl)ethyl)triphenylsilane and other silanes. The preparation of the macromolecules is optimized at both stages of the sol–gel process. The polymers are characterized by gel permeation chromatography and NMR spectroscopy. Spin coating of the materials on silicon wafers, followed by film thickness and refractive index measurements, indicates that the new polysiloxanes can have refractive indexes as high as 1.6 with thicknesses varying from 2200 to 3700 nm. Consequently, it is expected that the new materials described in this report are valuable for optoelectronic applications such as high-dielectric constant (high-k) gate oxides, interlayer high-k dielectrics, or high-refractive index abrasion resistant coatings.     

Characterization of new class III lantibiotics--erythreapeptin, avermipeptin and griseopeptin from Saccharopolyspora erythraea, Streptomyces avermitilis and Streptomyces griseus demonstrates stepwise N-terminal leader processing

Lantibiotics are a large group of ribosomally synthesized peptides post-translationally modified to incorporate the amino acid lanthionine. They are classified, according to their biosynthetic pathway and bioactivity, into three major subtypes. Of Actinomycetes type III lantibiotics, only four peptides (SapB, SapT, LabA1, and LabA2) have been described and structurally characterized, although homologous gene clusters are abundant in other Actinomycetes. All these gene clusters share a similar architecture with a characteristic Ser/Ser/Cys motif in precursor peptides, which has previously been suggested to act as a precursor for lanthionine (SapB) and labionin (LabA2) rings. Mass spectrometry screening led to the discovery and characterization of three new representatives of type III lantibiotics: Avermipeptin (Avi), Erythreapeptin (Ery), and Griseopeptin (Gri) from Streptomyces avermitilis DSM 46492, Saccharopolyspora erythraea NRRL 2338, and Streptomyces griseus DSM 40236, respectively. Apart from the assignment of these peptides to their corresponding gene clusters, additional investigations on Avi, Ery and Gri peptides indicate stepwise leader processing by putative aminopeptidase-like protease(s), thus yielding mixtures of differently N-terminal-processed lantibiotic peptides. Similar peptide processing was observed for a heterologously expressed eryth biosynthetic gene cluster expressed in a Streptomyces host system. Remarkably, all isolates of the new type III lantibiotics contain both the amino acids lanthionine and labionin, thus implying dual-mode cyclase activity of the processing lyase-kinase-cyclase enzymes. These findings have implications for the structures and maturation of other type III lantibiotics from Actinomycetes.     

Hydrogen generation under sunlight by self ordered TiO2 nanotube arrays

Highly ordered TiO₂ nanotube arrays generate a considerable interest for hydrogen generation by an electrochemical photocell, since ordered architecture of nanotube arrays provides a unidirectional electric channel for electron's transport. Here, we report the hydrogen generation by highly ordered TiO₂ nanotube arrays under actual sunlight in KOH electrolyte. The two-electrode electrochemical cell included an adjustable anode compartment capable of tracing the trajectory of the sun and a set of alkaline batteries connected with a rheostat for application of external bias. The results showed that the photocurrent responses of nanotube arrays match well with the intensity of solar irradiance on a clear summer day. Addition of ethylene glycol into KOH electrolyte as a hole scavenger enhanced the rate of hydrogen generation. A maximum photocurrent density of 31 mA/cm² was observed at 13:30 h, by focusing the sunlight with an intensity of 113 mW/cm² on the surface of the TiO₂ nanotube arrays in 1 M KOH electrolyte with 10 vol% ethylene glycol under an applied bias of 0.5 V. The observed hydrogen generation rate was 4.4 mL/h cm² under the focalized solar irradiance with an intensity between 104 mW/cm² and 115 mW/cm² from 10:00 to 14:20 h.     

Role of Transformative Capacity in River Basin Management Transformations

To tackle problems related to water quantity and quality, transformations in water management systems have become of increasing interest. Transformative capacity can be defined as the ability first to adapt to changes, and if needed, to carry out fundamental changes in a specific system. Using a framework of ten components of transformative capacity and an analysis of earlier historical research, policy documents and data gathered in a stakeholder scenario workshop, we examine the relationship between past and future transformations and transformative capacity in river basin management in the River Vantaa basin, located in southern Finland. In the past, River Vantaa was heavily polluted by municipal wastewater. The water quality has gradually improved but is still not considered good. The most successful changes have been concentrated on point source pollution, such as municipal wastewater, and they have mostly been driven by public administration and municipal coordination. In the future, more effort should be put on diffuse pollution, especially agricultural loading, and this requires changes in societal values and new forms of governance. We show how the past transformations have partly been driven by transformative capacity, but some transformations have enabled changes in the components of transformative capacity, indicating the interconnectedness of the different components. Furthermore, the interplay between transformations and transformative capacity occurs across spatial and temporal scales. We discuss how transformations take time, how transformative capacity evolves over longer time-spans, and how capacity and trajectories in local and wider scales are in a continuous interaction.

     

Reaction mechanism of gold dissolution with bromine

The dissolution of gold with elemental bromine was studied by using a rotating disc technique. The main parameters studied were bromine and bromide concentrations, stirring speed, pH, and temperature. The effect of various salts, manganese, and hydrogen peroxide was also examined. The dissolution kinetics of gold with Br₂ and NaBr mixture is complex. The reaction mechanism is a function of solution composition, which determines the kind of adsorbing species. For an excess concentration of bromide ions, the rate expression is Rate = (2k _cl7 k _al6)^1/2 K ₁₅ [Br ₃ ⁻ ] and for an excess concentration of bromine, the rate expression is Rate = (2k _c27 k _a29)^1/2 [Br⁻]^1/2 {K₂₅ [Br₂]³/(1 +K ₂₅ [Br₂]³)}^1/2 Gold in bromine solutions dissolves according to electrochemical/chemical (EC) mechanisms. The electrochemical component of the mechanism is responsible for the formation of AuBr₂. In the chemical component of the mechanism, this monovalent gold bromide disproportionates into gold and stable AuBr ₄ ⁻ , which reports into solution. With respect to pH, there are two characteristic dissolution regions. In the pH range of 1 to 7, gold dissolution rates were insensitive to pH. Above pH 7, gold dissolution rates decreased with increase of pH.     

Synthesis of surface imprinted nanospheres for selective removal of uranium from simulants of Sambhar salt lake and ground water

Imprinted polymer nanospheres for uranium were prepared by complexing uranyl ion on to quinoline-8-ol functionalized 3-aminopropyltrimethoxysilane modified silica nanoparticles followed by surface imprinting with 4-VP (4-vinyl pyridine), HEMA (2-hydroxy ethyl methacrylate) and EGDMA (ethylene glycol dimethacrylate) as the functional monomers and cross linking agent respectively with AIBN (2,2'-azo-bis-isobutyronitrile) as initiator and 2-methoxyethanol as the porogen. Non-imprinted polymer material was also prepared under similar conditions omitting uranyl ion. The above materials were used for solid phase extraction of uranium. Recent realization that its chemical toxicity is dominant than radiation hazards makes decontamination a relevant topic for environmental point of view, particularly in the light of projected global thrust for uranium fuel based atomic power plants. The material offers high retention capacity of 97.1 μmol g(-1) for 10 mg L(-1) of uranium that does not require tedious grinding and sieving steps, is water compatible and works in the pH range of 5-7, making it ideal for possible use in decontamination of polluted natural water samples or front end effluents of nuclear power reactors.     

Protein profiles and total antioxidant capacity of water‐soluble and water‐insoluble fractions of white brined goat cheese at different stages of ripening

This study deals with proteolysis and total antioxidant capacity of proteins of white brined cheese prepared from overheated goat milk and ripened for fifty days. Proteolytic changes were reflected through the relatively low level of soluble nitrogen (50 days ripened cheese had 15.32 g/100 g of water‐soluble nitrogen, 8.1 g/100 g of TCA‐soluble nitrogen and 2.69 g/100 g of PTA‐SN), intensive proteolysis of α_s2‐CN during initial 10 days of ripening (up to 50.70% of initial content) and its much slower degradation through further 40 days, slow but continual decrease of β‐CN content (up to 85.14% of residual content) and high level of proteolytic products tightly bounded into gel network. Total antioxidant capacity of water‐soluble and water‐insoluble fractions increased after cheese ripening. These findings could be useful for better understanding and control over the production of white brined goat cheese as highly valuable functional product.