Investigating the Role of Conformational Effects on Laccase Stability and Hyperactivation under Stress Conditions

Fungal laccase from Steccherinum ochraceum 1833 displays remarkable stability under different harsh conditions: organic/buffer mixtures, thermal treatment, and microwave radiation. The behavior is particularly significant in the light of the sharp inactivation observed for two different fungal laccases. Laccase from S. ochraceum 1833 also displays hyperactivation under mild thermal treatment (60 °C). Molecular dynamics simulations at 80 °C explained how this laccase retains the geometry of the electron transfer pathway, thereby assuring electron transfer through the copper ions and thus maintaining its catalytic activity at high temperature. Spectroscopic studies revealed that the thermal activation corresponds to specific conformational changes in the protein. The results indicate that this laccase is potentially applicable under denaturing conditions that might be beneficial for the biotransformation of recalcitrant substrates.     

Direct Chemical Activation of a Rationally Engineered Signaling Enzyme

Few chemical strategies for activating enzymes have been developed. Here we show that a biarsenical compound (FlAsH) can directly activate a rationally engineered protein tyrosine phosphatase (Shp2 PTP) by disrupting autoinhibitory interactions between Shp2's N‐terminal SH2 domain and its PTP domain. We found that introducing a tricysteine motif at a loop of Shp2's N‐SH2 domain confers affinity for FlAsH; binding of FlAsH to the cysteine‐enriched loop relieves Shp2's inhibitory interdomain interaction and substantially increases the enzyme's PTP activity. Activation of engineered Shp2 is substrate independent and is observed in the contexts of both purified enzyme and complex proteomes. A chemical means for activating Shp2 could be useful for investigating its roles in signaling and oncogenesis, and the loop‐targeting strategy described herein could provide a blueprint for the development of target‐specific activators of other autoinhibited enzymes.     

Disinfection by-products from halogenation of aqueous solutions of terpenoids

We report the formation of trihalomethanes and other disinfection by-products from four polyfunctional terpenoids during simulated chlorination of natural waters. Complex suites of products were identified by closed loop stripping analysis (CLSA)/gas chromatography-mass spectrometry (GC-MS) from halogenation of β-carotene and retinol. β-Ionone appeared to be a key intermediate in the halogenation of β-carotene and retinol, reacting further under the reaction conditions to produce trans-β-ionone-5,6-epoxide and β-cyclocitral. Halogenation of the four terpenoids also produced trihalomethanes (THMs), most likely through haloform reaction on methyl ketone groups within many of the intermediates. Since halogenation of retinol produced a significant quantity of THMs at a slow reaction rate, retinol-based structures may possibly contribute to the slow reacting phase of THM formation in natural waters. Two polyhydroxyphenol model compounds were halogenated for comparison. The only products identified by CLSA/GC-MS from halogenation of 4′,5,7-trihydroxyflavanone and ellagic acid were THMs. 4′,5,7-Trihydroxyflavanone rapidly produced THMs, with an extremely high molar yield (94%) at pH 7. Terpenoids of the β-ionone and retinol type should be considered to be significant THM precursors, while 4′,5,7-trihydroxyflavanone has been shown to be an extremely significant THM precursor, potentially present within natural organic matter in water treatment processes and distribution systems.     

Insights from Theory on the Relationship Between Surface Reactivity and Gold Atom Release

Density functional theory, informed by experimental studies, is used to investigate the interplay of surface morphology, the adsorption site of reactants, the nature of the interaction between adsorbates and the surface, the potential energy landscape for adsorbates on the surface, adsorbate coverage, temperature, and the dynamic evolution of these factors during adsorption and reaction. We summarize our current understanding of Au atom release on the (111) surface and the corresponding effects on adsorption and reactivity. Gold was selected for these investigations because of the recent intense interest in the activity of gold nanoparticles for several important catalytic reactions. Fundamental experimental studies on Au single-crystal surfaces have established that atomic O is extremely active for oxidation of CO and olefins, that the local bonding of O is an important factor in determining the reactivity and selectivity for oxidation, and that Au atom release is induced by electronegative adsorbates, such as O, Cl, and S. These experimental results guided our theoretical studies. Density functional theory is an extremely useful tool since it evaluates the energetics associated with the incorporation of gold into the adsorbate layer, while providing fundamental physical insight into the underlying cause of gold incorporation. We use our results from static DFT calculations along with ab initio molecular dynamics simulations to understand the effect of surface morphology on the activity of gold for CO oxidation. Our investigation of Au atom release and incorporation induced by electronegative atoms clearly illustrates the importance of using experiments in combination with theory to establish the importance of and the underlying reasons for metal atom release and the affect on bonding and reactivity.     

Dechlorination of polychlorinated biphenyls in industrial transformer oil by radiolytic and photolytic methods

Used electrical transformer oils containing low or high concentrations of polychlorinated biphenyls (PCBs) were treated using electron, gamma, and ultraviolet radiation, and the conditions for complete dechlorination were developed. Dechlorination was determined by analysis of the inorganic chloride formed and the concentrations of remaining PCBs. Transformer oil containing approximately 95 microg g(-1) PCB (approximately 3.5 mmol L(-1) Cl) is completely dechlorinated by irradiation with 600 kGy after the addition of 10% triethylamine (TEA). Transformer oil containing >800,000 microg g(-1) PCB (17.7 mol L(-1) Cl) requires an additional solvent to prevent solidification. When this oil is diluted with 2-propanol (2-PrOH) and TEA (v/v/v, 1/79/20), complete dechlorination is achieved with a dose of 2500 kGy. Ultraviolet photolysis of the same oil/2-PrOH/TEA solutions led to 90% dechlorination after exposure for 120 h in our experimental setup. Such yields were obtained by radiolysis with a dose of 2000 kGy (300 h in our Gammacell). Replacing TEA with KOH in 2-PrOH solutions greatly increases the yield of dechlorination in both the radiolytic and the photolytic experiments, demonstrating that a chain reaction plays a role in both of these treatment methods and suggesting that both methods deserve further consideration for large-scale application.     

LAS glass–ceramic scaffolds by three-dimensional printing

Highly porous (>60% open porosity) glass–ceramic scaffolds with remarkable mechanical properties (compression strength of ～15 MPa) were produced by indirect 3D printing. Precursor glass powders were printed into 3D ordered structures and then heat treated to sinter and develop crystalline phases. The final glass–ceramic contained a β-spodumene solid solution together with a secondary phase of lithium disilicate.The precision of the printed geometry and the density of the struts in the scaffold depended on several processing parameters (e.g. powder size and flowability, layer thickness) and were improved by increasing the binder saturation and drying time. Two types of powders with different particle size distribution (PSD) and flowability were used. Powders with a larger PSD, could be processed within a wider range of printing parameters due to their good flowability; however, the printing precision and the struts density were lower compared to the scaffolds printed using the powder in a smaller average PSD.     

Family conflict and child adjustment: Evidence for a cognitive-contextual model of intergenerational transmission.

Three cohorts of 10- to 14-year-old adolescents were sampled to obtain perceptions of their parents' conflict-resolution styles, their own conflict-resolution styles, and their behavioral adjustment, to test J. H. Grych and F. D. Fincham's (1990) cognitive-contextual model of the relationship of marital conflict to child adjustment. As found previously, boys and girls were not exposed to different levels or types of interparental conflict, although boys tended to blame themselves more. Adolescents' reports of their own conflict-resolution styles with siblings were clearly related to level and types of their more general adjustment levels. A series of regressions supported Grych and Fincham's model for internalizing problems (and avoidant resolution style) in adolescents; only minimal support was found with externalizing problems (and attacking resolution style). Gender-specific patterns of intergenerational transmission of resolution styles were found and are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)