Short peptide alpha helices induced by multiple metal clips

Alpha helices are key structural components of proteins and important recognition motifs in biology. New techniques for stabilizing short peptide helices could be valuable for studying protein folding, modeling proteins, creating artificial proteins, and may aid the design of inhibitors or mimics of protein function. We previously reported* that 5-15 residue peptides, corresponding to the Zn-binding domain of thermolysin, react with [Pd(en)(ONO,),]in DMF-d’ and 90% H,O 10% DzO to form a 22-membered [Pd(en)(H*ELTH*)]2+ macrocycle that is helical in solution and acts as a template in nucleating helicity in both Cand N- terminal directions within the longer sequences in DMF. ~f~~&g7$$& d&qx~m ~. y AC&q& In water, however, there was less a-helicity observed, testifying to #..q,& &$--Lb &l-- &.$;,J~p?:~~q&~+~~ ’ w w the difficulty of fixing intramolecular amide NH...OC H-bonds in 6,“;;” ( k.$ U”C.a , p d$. competition with the H-bond donor solvent water. To expand the utility of [Pd(en)(H*XXXH*)]*+ as a helix- @r4”8 & oJ#:& &G& @-qd ,‘d@-gyp promoting module in solution, we now report the result that Ac- ‘$4: %$yyy + H*ELTH*H*VTDH*-NH,(l), AC-H*ELTH*AVTDYH*ELTH*- NH, (2) and AC-H*AAAH*H*ELTH*H*VTDH*-NH* (3) react with multiple equivalents of [Pd(en)(ONO,),] to produce exclusively 4-6 respectively in both DMF-d7 and water (90% Hz0 10% D,O). Mass spectrometry, 15N- and 2D ‘H- NMR spectroscopy, and CD spectra were used to characterise the structures 4-6, and their three dimensional structures were calculated from NOE restraints using simulated annealing protocols. Results demonstrate (a) selective coordination of metal ions at (i, i+4) histidine positions in water and DMF, (b) incorporation of 2 and 3 a turn-mimicking modules [Pd(en)(HELTH)]2+ in lo-15 residue peptides, and (c) facile conversion of unstructured peptides into 3- and 4- turn helices of macrocycles, with well defined a-helicity throughout and more structure in DMF than in water.

Formation of mononuclear and chloro-bridged binuclear copper(II) complexes of patellamide D, a naturally occurring cyclic peptide: influence of anion and solvent

Patellamide D (patH(4)) is a cyclic octapeptide isolated from the ascidian Lissoclinum patella. The peptide possesses a 24-azacrown-8 macrocyclic structure containing two oxazoline and two thiazole rings, each separated by an amino acid. The present spectrophotometric, electron paramagnetic resonance (EPR) and mass spectral studies show that patellamide D reacts with CuCl, and triethylamine in acetonitrile to form mononuclear and binuclear copper(II) complexes containing chloride. Molecular modelling and EPR studies suggest that the chloride anion bridges the copper(II) ions in the binuclear complex [Cu-2(patH(2))(mu-Cl)](+). These results contrast with a previous study employing both base and methanol, the latter substituting for chloride in the copper(II) complexes en route to the stable mu-carbonato binuclear copper(II) complex [Cu-2 (patH(2))(mu-CO3)]. Solvent clearly plays an important role in both stabilising these metal ion complexes and influencing their chemical reactivities. (C) 2004 Elsevier Inc. All rights reserved.

Pressure and temperature effects on metal-to-metal charge transfer in cyano-bridged Co-III-Fe-II complexes

The effects of pressure and temperature on the energy (E-op) of the metal-to-metal charge transfer (MMCT, Fe-II --> Co-III) transition of the cyano-bridged complexes trans - [(LCoNCFe)-Co-14(CN)(5)](-) and cis-[(LCoNCFe)-Co-14(CN)(5)](-) (where L-14 = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) were examined. The changes in the redox potentials of the cobalt and iron metal centres with pressure and temperature were also examined and the results interpreted with Marcus Hush theory. The observed redox reaction volumes can mainly be accounted for in terms of localised electrostriction effects. The shifts in E-op due to both pressure and temperature were found to be less than the shifts in the energy difference (E degrees) between the Co-III-Fe-II and Co-II-Fe-III redox isomers. The pressure and temperature dependence of the reorganisational energy, as well as contributions arising from the different spin states of Co-II, are discussed in order to account for this trend. To study the effect of pressure on Co-III electronic absorption bands, a new cyano-bridged complex, trans - [(LCoNCCo)-Co-14(CN)(5)], was prepared and characterised spectroscopically and structurally. X-Ray crystallography revealed this complex to be isostructural with trans -[(LCoNCFe)-Co-14(CN)(5)] center dot 5H(2)O.

Organochlorine and heavy metal concentrations in blubber and liver tissue collected from Queensland (Australia) dugong (Dugong dugon)

Tissue samples of liver and blubber were salvaged from fifty-three dugong (Dugong dugon) carcasses stranded along the Queensland coast between 1996 and 2000. Liver tissue was analysed for a range of heavy metals and blubber samples were analysed for organochlorine compounds. Metal concentrations were similar in male and female animals and were generally highest in mature animals. Liver concentrations of arsenic, chromium, iron, lead, manganese, mercury and nickel in a number of individual animals were elevated in comparison to concentrations previously reported in Australian dugong. Dieldrin, DDT (and its breakdown products) and/or heptachlor epoxide were detected in 59% of dugong blubber samples. In general, concentrations of organochlorines were similar to those reported in dugong 20 years earlier, and were low in comparison to concentrations recorded from marine mammal tissue collected elsewhere in the world. With the exception of lead, the extent of carcass decomposition, the presence of disease or evidence of animal starvation prior to death did not significantly affect dugong tissue concentrations of metals or organochlorines. The results of the study suggest that bioaccumulation of metals and organochlorine compounds (other than dioxins) does not represent a significant risk to Great Barrier Reef dugong populations, particularly in the context of other pressures associated with coastal development and other anthropogenic activities. (c) 2004 Elsevier Ltd. All rights reserved.

The geochemistry of radioactive waste disposal

The present study attempted to identify the significant parameters which affect radionuclide migration from a low level radioactive waste disposal site located in a clay deposit. From initial sorption studies on smectite minerals, increased Kd with decreasing initial cation concentration was observed, and three sorption mechanisms were identified. The observation of anion dependent sorption was related to the existence of a mechanism in which an anion-cation pair are bound to the clay surface through the anion. The influence of competing cations, typical of inorganic groundwater constituents, depended on: (1) Ni/Co:Mn+(Mn+ = competing cation) ratio, (2) nature of M^n+, (3) total solution ionic strength. The presence of organic material in groundwater is well documented, but its effect on cation sorption has not been established. An initial qualitative investigation involving addition of simple organic ligands to Ni(Co)-hectorite samples demonstrated the formation of metal complexes in the clay interlayers, although some modified behaviour was observed. Further quantitative examination involving likely groundwater organic constituents and more comprehensive physical investigation confirmed this behaviour and enabled separation of the organic compounds used into two classes, according to their effect on cation sorption; (i) acids, (ii) amine compounds. X-ray photoelectron spectroscopy, scanning electron microscopy and Mossbauer spectroscopy were used to investigate the nature of transition metal ions sorbed onto montmorillonite and hectorite. Evidence strongly favoured the sorption of the hexaaquo cation, although a series of sorption sites of slightly different chemical characteristics were responsible for broadened peak widths observed in XPS and Mossbauer investigations. The surface sensitivity of XPS enabled recognition of the two surface sorption sites proposed in earlier sorption studies. Although thermal treatment of Fe^3+/Fe^2+-hectorite samples left iron atoms bonded to the silicate sheet structure, Mossbauer evidence indicated the presence of both ferric and ferrous iron in all samples.

Organotellurium compounds for metal organic vapour phase epitaxy

The infra-red detector material cadmium mercury telluride can be grown by the technique of Metal Organic Vapour Phase Epitaxy using simple alkyl telluride compounds as the source of tellurium. New tellurium precursors are required in order to overcome handling and toxicity problems and to reduce the growth temperature in preparing the material. A range of diaryltellurium(IV) dicarboxylates and some 2-(2'-pyridyl)phenyl-tellurium(II) and tellurium(IV) monocarboxylates have been synthesised and characterised by infra-red, 13C N.M.R. and mass spectroscopy. Infra-red spectroscopy has been used to determine the mode of bonding of the carboxylate ligand to tellurium. Synthetic methods have been devised for the preparation of diorganotritellurides (R2Te3) and mixed diorganotetrachalcogenides (RTeSeSeTeR). A mechanism for the formation of the tritellurides based on aerobic conditions is proposed. The reaction of ArTe- with (ClCH2CH2)3N leads to tripod-like multidentate ligands (ArTeCH2CH2)3N which form complexes with the ions Hg(II), Cd(II), Cu(I), Pt(II) and Pd(II). Synthetic routes to aryltelluroalkylamines and arylselenoalkylamines are also reported. The crystal structure of 2-(2'-pyridyl)phenyltellurium(II) bromide has been solved in which there are six molecules present within the unit cell. There are no close intermolecular Te---Te interactions and the molecules are stabilised by short Te---N intramolecular contacts. The crystal structure of 2-(2'-pyridyl)phenylselenium(II)-tribromomercurate(II) is also presented. A study of the Raman vibrational spectra of some tellurated azobenzenes and 2-phenylpyridines shows spectra of remarkably far superior quality to those obtained using infra-red spectroscopy.

Effects of Natural Organic Matter on the Dissolution Kinetics and Bioavailability of Metal Oxide Nanoparticles

The rapid development of nanotechnology and wider applications of engineered nanomaterials (ENMs) in the last few decades have generated concerns regarding their environmental and health risks. After release into the environment, ENMs undergo aggregation, transformation, and, for metal-based nanomaterials, dissolution processes, which together determine their fate, bioavailability and toxicity to living organisms in the ecosystems. The rates of these processes are dependent on nanomaterial characteristics as well as complex environmental factors, including natural organic matter (NOM). As a ubiquitous component of aquatic systems, NOM plays a key role in the aggregation, dissolution and transformation of metal-based nanomaterials and colloids in aquatic environments.

The goal of this dissertation work is to investigate how NOM fractions with different chemical and molecular properties affect the dissolution kinetics of metal oxide ENMs, such as zinc oxide (ZnO) and copper oxide (CuO) nanoparticles (NPs), and consequently their bioavailability to aquatic vertebrate, with Gulf killifish (Fundulus grandis) embryos as model organisms.

ZnO NPs are known to dissolve at relatively fast rates, and the rate of dissolution is influenced by water chemistry, including the presence of Zn-chelating ligands. A challenge, however, remains in quantifying the dissolution of ZnO NPs, particularly for time scales that are short enough to determine rates. This dissertation assessed the application of anodic stripping voltammetry (ASV) with a hanging mercury drop electrode to directly measure the concentration of dissolved Zn in ZnO NP suspensions, without separation of the ZnO NPs from the aqueous phase. Dissolved zinc concentration measured by ASV ([Zn]ASV) was compared with that measured by inductively coupled plasma mass spectrometry (ICP-MS) after ultracentrifugation ([Zn]ICP-MS), for four types of ZnO NPs with different coatings and primary particle diameters. For small ZnO NPs (4-5 nm), [Zn]ASV was 20% higher than [Zn]ICP-MS, suggesting that these small NPs contributed to the voltammetric measurement. For larger ZnO NPs (approximately 20 nm), [Zn]ASV was (79±19)% of [Zn]ICP-MS, despite the high concentrations of ZnO NPs in suspension, suggesting that ASV can be used to accurately measure the dissolution kinetics of ZnO NPs of this primary particle size.

Using the ASV technique to directly measure dissolved zinc concentration, we examined the effects of 16 different NOM isolates on the dissolution kinetics of ZnO NPs in buffered potassium chloride solution. The observed dissolution rate constants (kobs) and dissolved zinc concentrations at equilibrium increased linearly with NOM concentration (from 0 to 40 mg-C L-1) for Suwannee River humic acid (SRHA), Suwannee River fulvic acid and Pony Lake fulvic acid. When dissolution rates were compared for the 16 NOM isolates, kobs was positively correlated with certain properties of NOM, including specific ultraviolet absorbance (SUVA), aromatic and carbonyl carbon contents, and molecular weight. Dissolution rate constants were negatively correlated to hydrogen/carbon ratio and aliphatic carbon content. The observed correlations indicate that aromatic carbon content is a key factor in determining the rate of NOM-promoted dissolution of ZnO NPs. NOM isolates with higher SUVA were also more effective at enhancing the colloidal stability of the NPs; however, the NOM-promoted dissolution was likely due to enhanced interactions between surface metal ions and NOM rather than smaller aggregate size.

Based on the above results, we designed experiments to quantitatively link the dissolution kinetics and bioavailability of CuO NPs to Gulf killifish embryos under the influence of NOM. The CuO NPs dissolved to varying degrees and at different rates in diluted 5‰ artificial seawater buffered to different pH (6.3-7.5), with or without selected NOM isolates at various concentrations (0.1-10 mg-C L-1). NOM isolates with higher SUVA and aromatic carbon content (such as SRHA) were more effective at promoting the dissolution of CuO NPs, as with ZnO NPs, especially at higher NOM concentrations. On the other hand, the presence of NOM decreased the bioavailability of dissolved Cu ions, with the uptake rate constant negatively correlated to dissolved organic carbon concentration ([DOC]) multiplied by SUVA, a combined parameter indicative of aromatic carbon concentration in the media. When the embryos were exposed to CuO NP suspension, changes in their Cu content were due to the uptake of both dissolved Cu ions and nanoparticulate CuO. The uptake rate constant of nanoparticulate CuO was also negatively correlated to [DOC]×SUVA, in a fashion roughly proportional to changes in dissolved Cu uptake rate constant. Thus, the ratio of uptake rate constants from dissolved Cu and nanoparticulate CuO (ranging from 12 to 22, on average 17±4) were insensitive to NOM type or concentration. Instead, the relative contributions of these two Cu forms were largely determined by the percentage of CuO NP that was dissolved.

Overall, this dissertation elucidated the important role that dissolved NOM plays in affecting the environmental fate and bioavailability of soluble metal-based nanomaterials. This dissertation work identified aromatic carbon content and its indicator SUVA as key NOM properties that influence the dissolution, aggregation and biouptake kinetics of metal oxide NPs and highlighted dissolution rate as a useful functional assay for assessing the relative contributions of dissolved and nanoparticulate forms to metal bioavailability. Findings of this dissertation work will be helpful for predicting the environmental risks of engineered nanomaterials.

Formation of sub-7 nm feature size PS-b-P4VP block copolymer structures by solvent vapour process

The nanometer range structure produced by thin films of diblock copolymers makes them a great of interest as templates for the microelectronics industry. We investigated the effect of annealing solvents and/or mixture of the solvents in case of symmetric Poly (styrene-block-4vinylpyridine) (PS-b-P4VP) diblock copolymer to get the desired line patterns. In this paper, we used different molecular weights PS-b-P4VP to demonstrate the scalability of such high χ BCP system which requires precise fine-tuning of interfacial energies achieved by surface treatment and that improves the wetting property, ordering, and minimizes defect densities. Bare Silicon Substrates were also modified with polystyrene brush and ethylene glycol self-assembled monolayer in a simple quick reproducible way. Also, a novel and simple in situ hard mask technique was used to generate sub-7nm Iron oxide nanowires with a high aspect ratio on Silicon substrate, which can be used to develop silicon nanowires post pattern transfer.

Inputs from a mercury-contaminated lagoon: impact on the nearshore waters of the Atlantic Ocean

Ria de Aveiro, a Portuguese coastal lagoon that exchanges water with the Atlantic Ocean, received the effluent from a chlor-alkali industry for over 50 years; consequently several tons of mercury had been buried in the sediments of an inner basin. To assess the importance (and seasonal variation) of the lagoon waters as carriers of mercury to the nearby coastal area, we measured total mercury levels in several compartments: in surface sediments, in surface and deep waters (including dissolved and particulate matter!, and in biota. Dissolved (reactive and total) mercury concentrations both in surface and deep waters were low (<1 to 15 ng L '). Mean mercury values in suspended particulate matter varied hetween 0.2 and 0.6 jxg g ' and in sediments between 1 and 9 ng g '. Aquatic organisms displayed levels below regulatory limits but exhibited some bioaccumulation of mercury, with concentrations ranging from 0.05 to 0.8 ^ig g ' Idry weight (dw)|. No seasonal pattern was found in this study for mercury-related determinations. Levels found in the estuary mouth during ebb tide provide evidence for the transport of mercury to the coastal zone. No significant changes in the partition of mercury between dissolved and particulate phases were found in the coastal waters in comparison with the values found in the estuary mouth. In spite of the high levels of mercury found inside some areas of the lagoon, the wide web of islands and channels allows some spreading of contaminants before they reach the coastal waters. Moreover, the low efficiency of local marine sediments in trapping mercury contributes to a dilution of mercury transported in suspended particulate matter over a broader area, reducing the impact in the nearby manne coastal zone.

Toxic metal recovery from spent hydroprocessing catalyst

Spent hydroprocessing catalysts (HPCs) are solid wastes generated in refinery industries and typically contain various hazardous metals, such as Co, Ni, and Mo. These wastes cannot be discharged into the environment due to strict regulations and require proper treatment to remove the hazardous substances. Various options have been proposed and developed for spent catalysts treatment; however, hydrometallurgical processes are considered efficient, cost-effective and environmentally-friendly methods of metal extraction, and have been widely employed for different metal uptake from aqueous leachates of secondary materials. Although there are a large number of studies on hazardous metal extraction from aqueous solutions of various spent catalysts, little information is available on Co, Ni, and Mo removal from spent NiMo hydroprocessing catalysts. In the current study, a solvent extraction process was applied to the spent HPC to specifically remove Co, Ni, and Mo. The spent HPC is dissolved in an acid solution and then the metals are extracted using three different extractants, two of which were aminebased and one which was a quaternary ammonium salt. The main aim of this study was to develop a hydrometallurgical method to remove, and ultimately be able to recover, Co, Ni, and Mo from the spent HPCs produced at the petrochemical plant in Come By Chance, Newfoundland and Labrador. The specific objectives of the study were: (1) characterization of the spent catalyst and the acidic leachate, (2) identifying the most efficient leaching agent to dissolve the metals from the spent catalyst; (3) development of a solvent extraction procedure using the amine-based extractants Alamine308, Alamine336 and the quaternary ammonium salt, Aliquat336 in toluene to remove Co, Ni, and Mo from the spent catalyst; (4) selection of the best reagent for Co, Ni, and Mo extraction based on the required contact time, required extractant concentration, as well as organic:aqueous ratio; and (5) evaluation of the extraction conditions and optimization of the metal extraction process using the Design Expert® software. For the present study, a Central Composite Design (CCD) method was applied as the main method to design the experiments, evaluate the effect of each parameter, provide a statistical model, and optimize the extraction process. Three parameters were considered as the most significant factors affecting the process efficiency: (i) extractant concentration, (ii) the organic:aqueous ratio, and (iii) contact time. Metal extraction efficiencies were calculated based on ICP analysis of the pre- and post–leachates, and the process optimization was conducted with the aid of the Design Expert® software. The obtained results showed that Alamine308 can be considered to be the most effective and suitable extractant for spent HPC examined in the study. Alamine308 is capable of removing all three metals to the maximum amounts. Aliquat336 was found to be not as effective, especially for Ni extraction; however, it is able to separate all of these metals within the first 10 min, unlike Alamine336, which required more than 35 min to do so. Based on the results of this study, a cost-effective and environmentally-friendly solventextraction process was achieved to remove Co, Ni, and Mo from the spent HPCs in a short amount of time and with the low extractant concentration required. This method can be tested and implemented for other hazardous metals from other secondary materials as well. Further investigation may be required; however, the results of this study can be a guide for future research on similar metal extraction processes.

Fabrication and optimizing of metal nano silicate as toxic metal absorbent from sea water

Pure Water, is a crucial demand of creature life. Following industrial development, extra amount of toxic metals such as chromium enters the environmental cycle through the sewage, which is considered as a serious threat for organisms. One of the modern methods of filtration and removal of contaminants in water, is applying Nano-technology. According to specific property of silicate materials, in this article we try to survey increased power in composites and various absorption in several morphologies and also synthesis of Nano-metal silicates with different morphologies as absorbent of metal toxic ions. At first, we synthesize nano zink silicate with three morphologies considering context and the purpose of this survey. 1) Nano synthesis of zink silicate hollow cavity by hydrothermal method in mixed solvent system of ethanol/glycol polyethylene. 2) Zink nano wires silicate in a water-based system by controlling the amount of sodium silicate. 3) Synthesis of nano zink silicate membrane. After synthesizing, we measured the cadmium ion absorbance by synthesized nano zink silicates. Controlling PH, is the applied absorption method. Next step, we synthesized nano zink-magnesium silicate composite in two various morphologies of nanowires and membrane by different precent of zink and magnesium, in order to optimize synthesized nano metal silicate. We used zink nitrate and magnesium nitrate and also measured cadmium absorption by synthesized nano metal silicates in the same way of PH control absorption. In the 3rd step, in order to determine the impact of the type of metal in nano metal silicate, we synthesized nano magnesium silicate and compared its absorption with nano zink silicate. Furthermore, we calculated the optimal concentration in one of synthesizes. Optimal concentration is the process which has the maximum absorption. While applying two methods of absorption in the test, finally we compared the effect of absorption method on the absorption level. Below you find further steps of synthesis: 1) Using IR, RAMAN, XRD spectroscopy to check the accuracy of synthesis. 2) Checking the dispersion of nano particles in ethanol solution by light microscope. 3) Measuring and observing particles with scanning electron microscope (SEM). 4) Using atomic absorption device for measuring the cadmium concentration in water-based solutions. The nano metal silicates were synthesized successfully. All of synthesized nano absorbents have the cadmium ion absorbency. The cadmium absorption via nano absorbents depend on various factors such as kind of metal in nano silicate and percent of metal in nano metal silicate composite. Meanwhile the absorption and PH control of medium containing the absorbent and solution would affect the cadmium absorption.

Influence of the metal center on the morphology of coordination compounds thin films

Thin film morphology of tris-(8-hydroxyquinolate) aluminium (III) (Alq3) and bis-(8-hydroxyquinolate) oxovanadium (IV) (VOq2) are compared. Alq3 films deposited onto mica at 300K look almost featureless, but dendrimers or randomly distributed needle-shaped crystallites appear as a consequence of crystallization in time. We show that a possible origin of this process is exposure to solvent vapors. On the other hand, VOq2 films retain their textured morphology as thickness increases because of stabilizing intermolecular interactions between vanadyl groups.

Selenite and Selenate Effects on Mercury (Hg2+) Uptake and Distribution in Tilapia, Oreochromis niloticus L., Assessed by Chronic Bioassay

Aquatic organisms are considered excellent biomarkers of mercury (Hg) occurrence in the environment. Selenium (Se) acts in antagonism to this metal, stimulating its elimination, and reducing its toxicity. In this paper, tilapia (Oreochromis niloticus) were chronically acclimated in sub-lethal Hg2+, Hg2+ + Se4+ and Hg2+ + Se6+ concentrations. Distribution and bioaccumulation of both elements were evaluated in fish tissues. The kidney was the main target of the Hg and Se uptake, and the presence of Hg induced the Se hepatic elimination. The Hg bioaccumulation in the gill, spleen and heart were higher in the presence of Se6+ than in the presence of Se4+.

Influence of the metal center on the morphology of coordination compounds thin films

Thin film morphology of tris-(8-hydroxyquinolate) aluminium (III) (Alq3) and bis-(8-hydroxyquinolate) oxovanadium (IV) (VOq2) are compared. Alq3 films deposited onto mica at 300K look almost featureless, but dendrimers or randomly distributed needle-shaped crystallites appear as a consequence of crystallization in time. We show that a possible origin of this process is exposure to solvent vapors. On the other hand, VOq2 films retain their textured morphology as thickness increases because of stabilizing intermolecular interactions between vanadyl groups.