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Stability of Medium-Bridged Twisted Amides in Aqueous Solutions

Szostak, Michal; Yao, Lei; Aubé, Jeffrey
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 06/03/2009 EN
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“Twisted” amides containing non-standard dihedral angles are typically hypersensitive to hydrolysis, a feature that has stringently limited their utility in water. We have synthesized a series of bridged lactams that contain a twisted amide linkage but which exhibit enhanced stability in aqueous environments. Many of these compounds were extracted unchanged from aqueous mixtures ranging from the strongly basic to the strongly acidic. NMR experiments showed that tricyclic lactams undergo reversible hydrolysis at extreme pH ranges, but that a number of compounds in this structure class are indefinitely stable under physiologically relevant pH conditions; one bicyclic example was additionally water-soluble. We examined the effect of structure on the reversibility of amide bond hydrolysis, which we attributed to the transannular nature of the amino acid analogs. These data suggest that medium-bridged lactams of these types should provide useful platforms for studying the behavior of twisted amides in aqueous systems.

Electrochemical Behavior of Quinoxalin-2-one Derivatives at Mercury Electrodes and Its Analytical Use

Zimpl, Milan; Skopalova, Jana; Jirovsky, David; Bartak, Petr; Navratil, Tomas; Sedonikova, Jana; Kotoucek, Milan
Fonte: The Scientific World Journal Publicador: The Scientific World Journal
Tipo: Artigo de Revista Científica
Publicado em 30/04/2012 EN
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Derivatives of quinoxalin-2-one are interesting compounds with potential pharmacological activity. From this point of view, understanding of their electrochemical behavior is of great importance. In the present paper, a mechanism of electrochemical reduction of quinoxalin-2-one derivatives at mercury dropping electrode was proposed. Pyrazine ring was found to be the main electroactive center undergoing a pH-dependent two-electron reduction process. The molecule protonization of nitrogen in the position 4 precedes the electron acceptance forming a semiquinone radical intermediate which is relatively stable in acidic solutions. Its further reduction is manifested by separated current signal. A positive mesomeric effect of the nonprotonized amino group in the position 7 of the derivative III accelerates the semiquinone reduction yielding a single current wave. The suggested reaction mechanism was verified by means of direct current polarography, differential pulse, cyclic and elimination voltammetry, and coulometry with subsequent GC/MS analysis. The understanding of the mechanism was applied in developing of analytical method for the determination of the studied compounds.

Molecular mechanisms of cobalt-catalyzed hydrogen evolution

Marinescu, Smaranda C.; Winkler, Jay R.; Gray, Harry B.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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Several cobalt complexes catalyze the evolution of hydrogen from acidic solutions, both homogeneously and at electrodes. The detailed molecular mechanisms of these transformations remain unresolved, largely owing to the fact that key reactive intermediates have eluded detection. One method of stabilizing reactive intermediates involves minimizing the overall reaction free-energy change. Here, we report a new cobalt(I) complex that reacts with tosylic acid to evolve hydrogen with a driving force of just 30 meV/Co. Protonation of CoI produces a transient CoIII-H complex that was characterized by nuclear magnetic resonance spectroscopy. The CoIII-H intermediate decays by second-order kinetics with an inverse dependence on acid concentration. Analysis of the kinetics suggests that CoIII-H produces hydrogen by two competing pathways: a slower homolytic route involving two CoIII-H species and a dominant heterolytic channel in which a highly reactive CoII-H transient is generated by CoI reduction of CoIII-H.

Metal–organic frameworks constructed from monomeric, dimeric and trimeric phenanthroline citrate zinc building units

Zhang, Rong-Hua; Xia, Wen-Sheng; Wang, Hong-Xin; Zhou, Zhao-Hui
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Adduct of mononuclear and dinuclear citrate zinc complex [Zn(Hcit)(phen)(H2O)][Zn2(Hcit)(phen)2(H2O)3]·13.5H2O (1) and its aggregate [Zn3(Hcit)2(phen)4]n·14nH2O (2) (H4cit = citric acid, phen = 1,10-phenanthroline) were synthesized in weak acidic solutions. The former was obtained from the reaction of zinc nitrate, citric acid and phenanthroline in a molar ratio of 3 : 2 : 3, while a slightly excess of phenanthroline results in the formation of the polymeric product 2 in a molar ratio of 3 : 2 : 4. Transformation of 1 to 2 was finished by the reaction of 1 with an equimolar of phenanthroline in 72% yield. Reverse conversion of 2 to 1 is obtained in 77% yield, showing an equilibrium between 1 and 2. Neutral compound 1 consists of one monomeric anionic unit [Zn(Hcit)(phen)(H2O)]− and one dimeric cationic unit [Zn2(Hcit)(phen)2(H2O)3]+ that connect each other by strong hydrogen bonds [O6⋯O4w 2.636(2); O7⋯O3w 2.630(3) Å]. In 2, the citrate ligand links each trinuclear unit [Zn3(Hcit)2(phen)4] to generate an infinite 1D chain that extents into a 3D supramolecular structure by intra- and inter-molecular hydrogen bonds. Moreover, 1 and 2 exhibit strong fluorescence at room temperature.

Oxidation of tricyclic antidepressant drugs with chloramine-T in acidic solutions: kinetic, mechanistic and thermodynamic studies

Sukhdev, Anu; Puttaswamy, Puttaswamy
Fonte: Springer International Publishing AG Publicador: Springer International Publishing AG
Tipo: Artigo de Revista Científica
Publicado em 30/01/2013 EN
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The kinetics of the oxidation of two tricyclic antidepressants (TCA) namely, imipramine (IMP) and clomipramine (CLM) with sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in HClO4 medium was studied at 300 K. The two reactions followed identical kinetics with a first-order dependence of rate on [CAT]o and fractional order dependence on [TCA]o. The reaction is catalyzed by H+ ions with a fractional order dependence. The reaction was studied at different temperatures and activation parameters were evaluated. The reaction constants involved in the mechanism were computed. The solvent isotope effect was studied using D2O. Addition of p-toluenesulfonamide retards the reaction rate. The rate increased with decreasing dielectric constant of the medium. Variation of ionic strength of the medium and addition of halide ions (Cl- or Br-) showed no effect on the rate. The stoichiometry of the reaction was found to be 1:1 and the oxidation products were identified as imipramine-5-N-oxide and clomipramine-5-N-oxide. The rate of oxidation of IMP is faster than CLM. The observed results have been explained in terms of a mechanism and a relevant rate law has been deduced.

An 17O NMR Study of Hydrolyzed Nb(V) in Weakly Acidic and Basic Aqueous Solution

Klemperer, Walter G.; Marek, Keith A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Time-dependent 17O NMR spectra of basified decaniobate (Nb10O286−) solutions displayed intense resonances assigned to the well-known protonated hexaniobate anion (Nb6O198−) and two other species identified as heptaniobate (Nb7O229−) and protonated tetracosaniobate (Nb24O7224−) anions. The decaniobate ion showed no sign of protonation from pH 6 – 10, in contrast with the hexaniobate ion which was protonated at doubly-bridging oxygen sites at pH 10–13. Most (> 90%) of the heptaniobate formed 1 h after basification was transformed into other species after 3 weeks. Tetracosaniobate was formed reversibly from decaniobate, but only when KOH, NaOH and [(CH3)4N]OH were employed; none was observed after basification with [(n-C4H9)4N]OH. Moreover, far more tetracosaniobate was formed from KOH than from [(CH3)4N]OH. This effect was attributed to a tetracosaniobate cation binding site that binds K+ more readily than (CH3)4N+ but is too small to accommodate (n-C4H9)4N+.

Molecular Self-Assembly at Metal-Electrolyte Interfaces

Phan, Thanh Hai; Wandelt, Klaus
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 25/02/2013 EN
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The self-assembly of molecular layers has become an important strategy in modern design of functional materials. However, in particular, large organic molecules may no longer be sufficiently volatile to be deposited by vapor deposition. In this case, deposition from solution may be a promising route; in ionic form, these molecules may even be soluble in water. In this contribution, we present and discuss results on the electrochemical deposition of viologen- and porphyrin molecules as well as their co-adsorption on chloride modified Cu(100) and Cu(111) single crystal electrode surfaces from aqueous acidic solutions. Using in situ techniques like cyclic voltametry and high resolution scanning tunneling microscopy, as well as ex-situ photoelectron spectroscopy data the highly ordered self-assembled organic layers are characterized with respect to their electrochemical behavior, lateral order and inner conformation as well as phase transitions thereof as a function of their redox-state and the symmetry of the substrate. As a result, detailed structure models are derived and are discussed in terms of the prevailing interactions.

Why Is Saline So Acidic (and Does It Really Matter?)

Reddi, Benjamin AJ
Fonte: Ivyspring International Publisher Publicador: Ivyspring International Publisher
Tipo: Artigo de Revista Científica
Publicado em 17/04/2013 EN
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Commercial 0.9% saline solution for infusion has a pH around 5.5. There are many reasons for this acidity, some of them still obscure. It is also true that infusion of normal saline can lead to metabolic acidaemia, yet the link between the acidity of saline solution and the acidaemia it can engender is not straightforward. This commentary draws together the known and putative sources of acidity in saline solutions: it turns out that the acidity of saline solution is essentially unrelated to the acidaemia complicating saline infusion.

Microbial Oxidation of Fe2+ and Pyrite Exposed to Flux of Micromolar H2O2 in Acidic Media

Ma, Yingqun; Lin, Chuxia
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 13/06/2013 EN
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At an initial pH of 2, while abiotic oxidation of aqueous Fe2+ was enhanced by a flux of H2O2 at micromolar concentrations, bio-oxidation of aqueous Fe2+ could be impeded due to oxidative stress/damage in Acidithiobacillus ferrooxidans caused by Fenton reaction-derived hydroxyl radical, particularly when the molar ratio of Fe2+ to H2O2 was low. When pyrite cubes were intermittently exposed to fluxes of micromolar H2O2, the reduced Fe2+-Fe3+ conversion rate in the solution (due to reduced microbial activity) weakened the Fe3+-catalyzed oxidation of cubic pyrite and added to relative importance of H2O2-driven oxidation in the corrosion of mineral surfaces for the treatments with high H2O2 doses. This had effects on reducing the build-up of a passivating coating layer on the mineral surfaces. Cell attachment to the mineral surfaces was only observed at the later stage of the experiment after the solutions became less favorable for the growth of planktonic bacteria.

Selective Conversion of CO2 to CO with High Efficiency using an Inexpensive Bismuth Based Electrocatalyst

DiMeglio, John L.; Rosenthal, Joel
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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The wide-scale implementation of solar and other renewable sources of electricity requires improved means for energy storage. An intriguing strategy in this regard is the reduction of CO2 to CO, which generates an energy rich commodity chemical that can be coupled to liquid fuel production. In this work, we report an inexpensive Bismuth Carbon Monoxide Evolving Catalyst (Bi-CMEC) that can be formed upon cathodic polarization of an inert glassy carbon electrode in acidic solutions containing Bi3+ ions. This catalyst can be used in conjunction with ionic liquids to effect the electrocatalytic conversion of CO2 to CO with appreciable current density at overpotentials below 0.2 V. Bi-CMEC is selective for production of CO, operating with a Faradaic efficiency of approximately 95%. When taken together these correspond to a high energy efficiency for CO production, on par with that which has historically only been observed using expensive silver and gold cathodes.

Potential Pitfalls and Solutions for Use of Fluorescent Fusion Proteins to Study the Lysosome

Huang, Ling; Pike, Douglas; Sleat, David E.; Nanda, Vikas; Lobel, Peter
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 21/02/2014 EN
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Use of fusion protein tags to investigate lysosomal proteins can be complicated by the acidic, protease-rich environment of the lysosome. Potential artifacts include degradation or release of the tag and acid quenching of fluorescence. Tagging can also affect protein folding, glycosylation and/or trafficking. To specifically investigate the use of fluorescent tags to reveal lysosomal localization, we tested mCherry derivatives as C-terminal tags for Niemann-Pick disease type C protein 2 (NPC2), a luminal lysosomal protein. Full-length mCherry was released from the NPC2 chimera while deletion of the 11 N-terminal residues of mCherry generated a cleavage-resistant (cr) fluorescent variant. Insertion of proline linkers between NPC2 and crmCherry had little effect while Gly-Ser linkers promoted cleavage. The NPC2-crmCherry fusion was targeted to the lysosome and restored function in NPC2-deficient cells. Fusion of crmCherry to known and candidate lysosomal proteins revealed that the linkers had different effects on lysosomal localization. Direct fusion of crmCherry impaired mannose 6-phosphorylation and lysosomal targeting of the lysosomal protease tripeptidyl peptidase I (TPP1), while insertion of linkers corrected the defects. Molecular modeling suggested structural bases for the effects of different linkers on NPC2 and TPP1 fusion proteins. While mCherry fusion proteins can be useful tools for studying the lysosome and related organelles...

Human Serum Albumin Conjugates of 7-Ethyl-10-hydroxycamptothecin (SN38) for Cancer Treatment

Sepehri, Nima; Rouhani, Hasti; Ghanbarpour, Ahmad Reza; Gharghabi, Mehdi; Tavassolian, Faranak; Amini, Mohsen; Ostad, Seyed Nasser; Ghahremani, Mohammad Hossein; Dinarvand, Rassoul
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
EN
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SN38 (7-ethyl-10-hydroxy-comptothecin) is a potent metabolite of irinotecan, which has been approved for treatment of metastatic colorectal cancer. Considering the notable potency of SN38, it has been introduced as an anticancer candidate. In this study, human serum albumin (HSA) conjugates of SN38 were formulated to overcome the solubility problem beside improving the active form stability and tumor tissue targeting. In this target, two different molar ratios of conjugates (SN38 : HSA 15 : 1 and 60 : 1) were prepared by derivatization of 20-hydroxyl group of SN38 with glycine, followed by addition of succinyl group to glycine through which HSA was covalently attached. The conjugates with particle size of about 100 nm revealed enhanced water solubility and were relatively stable in neutral and acidic solutions. For SN38-HSA-15 and SN38-HSA-60 IC50 values were compared with irinotecan in HT-29 human colon cancer cells. Furthermore, biodistribution studies of SN38-HSA conjugate resulted in proper blood concentration level within 4 h. Moreover, blood cytotoxicity assay revealed no toxicity effect on liver and spleen. Collectively, our present investigation offers a water-soluble form of SN38 attached to HSA and suggests using favorable properties as a promising anticancer agent for further preclinical and clinical investigations.

Platinum-modified covalent triazine frameworks hybridized with carbon nanoparticles as methanol-tolerant oxygen reduction electrocatalysts

Kamiya, Kazuhide; Kamai, Ryo; Hashimoto, Kazuhito; Nakanishi, Shuji
Fonte: Nature Pub. Group Publicador: Nature Pub. Group
Tipo: Artigo de Revista Científica
Publicado em 22/09/2014 EN
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Covalent triazine frameworks, which are crosslinked porous polymers with two-dimensional molecular structures, are promising materials for heterogeneous catalysts. However, the application of the frameworks as electrocatalysts has not been achieved to date because of their poor electrical conductivity. Here we report that platinum-modified covalent triazine frameworks hybridized with conductive carbon nanoparticles are successfully synthesized by introducing carbon nanoparticles during the polymerization process of covalent triazine frameworks. The resulting materials exhibit clear electrocatalytic activity for oxygen reduction reactions in acidic solutions. More interestingly, the platinum-modified covalent triazine frameworks show almost no activity for methanol oxidation, in contrast to commercial carbon-supported platinum. Thus, platinum-modified covalent triazine frameworks hybridized with carbon nanoparticles exhibit selective activity for oxygen reduction reactions even in the presence of high concentrations of methanol, which indicates potential utility as a cathode catalyst in direct methanol fuel cells.

INSIGHTS INTO PREVENTIVE MEASURES FOR DENTAL EROSION

Magalhães, Ana Carolina; Wiegand, Annette; Rios, Daniela; Honório, Heitor Marques; Buzalaf, Marília Afonso Rabelo
Fonte: Faculdade de Odontologia de Bauru da Universidade de São Paulo Publicador: Faculdade de Odontologia de Bauru da Universidade de São Paulo
Tipo: Artigo de Revista Científica
Publicado em /04/2009 EN
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Dental erosion is defined as the loss of tooth substance by acid exposure not involving bacteria. The etiology of erosion is related to different behavioral, biological and chemical factors. Based on an overview of the current literature, this paper presents a summary of the preventive strategies relevant for patients suffering from dental erosion. Behavioral factors, such as special drinking habits, unhealthy lifestyle factors or occupational acid exposure, might modify the extent of dental erosion. Thus, preventive strategies have to include measures to reduce the frequency and duration of acid exposure as well as adequate oral hygiene measures, as it is known that eroded surfaces are more susceptible to abrasion. Biological factors, such as saliva or acquired pellicle, act protectively against erosive demineralization. Therefore, the production of saliva should be enhanced, especially in patients with hyposalivation or xerostomia. With regard to chemical factors, the modification of acidic solutions with ions, especially calcium, was shown to reduce the demineralization, but the efficacy depends on the other chemical factors, such as the type of acid. To enhance the remineralization of eroded surfaces and to prevent further progression of dental wear...

Solution conformation, backbone dynamics and lipid interactions of the intrinsically unstructured malaria surface protein MSP2

Zhang, Xuecheng; Perugini, Matthew A.; Yao, Shenggen; Adda, Christopher G.; Murphy, Vincent J.; Low, Andrew; Anders, Robin F.; Norton, Raymond S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Merozoite surface protein 2 (MSP2), one of the most abundant proteins on the surface of the merozoite stage of Plasmodium falciparum, is a potential component of a malaria vaccine, having shown some efficacy in a clinical trial in Papua New Guinea. MSP2 is a GPI-anchored protein consisting of conserved N- and C-terminal domains and a variable central region. Previous studies have shown that it is an intrinsically unstructured protein with a high propensity for fibril formation, in which the conserved N-terminal domain plays a key role. Secondary structure predictions suggest that MSP2 contains long stretches of random coil with very little α-helix or β-strand. Circular dichroism spectroscopy confirms this prediction under physiological conditions (pH 7.4) and in more acidic solutions (pH 6.2 and 3.4). Pulsed field gradient NMR diffusion measurements showed that MSP2 under physiological conditions has a large effective hydrodynamic radius consistent with an intrinsic pre-molten globule state, as defined by Uversky. This was supported by sedimentation velocity studies in the analytical ultracentrifuge. NMR resonance assignments have been obtained for FC27 MSP2, allowing the residual secondary structure and backbone dynamics to be defined. There is some motional restriction in the conserved C-terminal region in the vicinity of an intramolecular disulfide bond. Two other regions show motional restrictions...

The Connection between Microphysical Morphology and Atmospheric Particle Phase Transitions

Smith, Mackenzie Lynn
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
EN_US
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The phase of atmospheric particles can influence heterogeneous chemistry, cloud formation, and radiative forcing. Sulfate particles ranging from sulfuric acid to ammonium sulfate are the largest contributor arising from anthropogenic activities to the global fine aerosol burden. Multi-component inorganic particles of neutralized or partially neutralized crystalline components and acidic solutions can form via uptake of gaseous ammonia. Under some atmospheric conditions, secondary organic material can combine with sulfate species to form internally mixed organic-sulfate particles. The way in which interactions between the constituents in ambient multi-component particles affect the phase of the overall particle are not well understood, especially for complex mixtures containing secondary organic material. This thesis presents measurements of relative humidity-dependent phase transitions of atmospherically relevant multicomponent particles, measured using tandem differential mobility analyzer (TDMA) setups. Particle morphologies implied by these measurements and their impact on other atmospheric processes are discussed. The connection between particle morphology and hygroscopic phase transitions is first discussed in the context of internally mixed ammonium bisulfate and letovicite particles. Unexpected differences in the deliquescence behavior of individual particles of identical diameter and overall composition were observed. From the deliquescence data...

Estudo eletroqu?mico de ligas met?licas alum?nio-sil?cio em meio ?cido

SANTOS, Luana Santana dos
Fonte: Universidade Federal do Pará Publicador: Universidade Federal do Pará
Tipo: Dissertação de Mestrado
POR
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As ligas a base de alum?nio-sil?cio apresentam baixo peso espec?fico, boa resist?ncia mec?nica e resist?ncia ? corros?o, t?m sido amplamente utilizadas como substitutas de algumas ligas ferrosas na fabrica??o de pe?as em diversos segmentos industriais. Nesta pesquisa estudou-se o comportamento eletroqu?mico do alum?nio e suas ligas alum?nio-sil?cio 0,3 e 0,7% em massa, em el?tr?litos de ?cido sulf?rico e ?cido clor?drico, ambos a 0,1 mol/L. Os resultados das t?cnicas eletroqu?micas mostraram que o Si provocou um deslocamento para valores mais positivos do potencial de corros?o, observou-se uma regi?o de passividade nas curvas an?dicas dos eletrodos em ?cido sulf?rico, este fen?meno de passiva??o n?o ocorreu em ?cido clor?drico. Os diagramas de Nyquist apresentaram dois arcos,um capacitivo na regi?o de altas frequ?ncias, relacionado ? forma??o da camada ?xida e, um indutivo em baixas frequ?ncias, atribu?do a adsor??o de ?nions na superf?cie met?lica, as semelhan?as nos diagramas mostram que os fen?menos eletroqu?micos s?o id?nticos e independentes da adi??o de Si. Os diagramas de imped?ncia, tamb?m, mostraram menor resist?ncia de polariza??o das ligas Al-Si. Considerando, apenas, os estudos eletroqu?micos pode-se afirmar que os eletrodos n?o apresentaram diferen?as relevantes entre si e a suscetibilidade a corros?o nestas solu??es ?cidas n?o implica em uma caracter?stica desfavor?vel a sua aplica??o.; ABSTRACT: The alloys based on aluminum-silicon have low specific weight...

The structure of an interdomain complex that regulates talin activity

Goult, B.; Bate, N.; Anthis, N.; Wegener, K.; Gingras, A.; Patel, B.; Barsukov, I.; Campbell, I.; Roberts, G.; Critchley, D.
Fonte: Amer Soc Biochemistry Molecular Biology Inc Publicador: Amer Soc Biochemistry Molecular Biology Inc
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
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Talin is a large flexible rod-shaped protein that activates the integrin family of cell adhesion molecules and couples them to cytoskeletal actin. It exists in both globular and extended conformations, and an intramolecular interaction between the N-terminal F3 FERM subdomain and the C-terminal part of the talin rod contributes to an autoinhibited form of the molecule. Here, we report the solution structure of the primary F3 binding domain within the C-terminal region of the talin rod and use intermolecular nuclear Overhauser effects to determine the structure of the complex. The rod domain (residues 1655–1822) is an amphipathic five-helix bundle; Tyr-377 of F3 docks into a hydrophobic pocket at one end of the bundle, whereas a basic loop in F3 (residues 316–326) interacts with a cluster of acidic residues in the middle of helix 4. Mutation of Glu-1770 abolishes binding. The rod domain competes with β3-integrin tails for binding to F3, and the structure of the complex suggests that the rod is also likely to sterically inhibit binding of the FERM domain to the membrane.; Benjamin T. Goult, Neil Bate, Nicholas J. Anthis, Kate L. Wegener, Alexandre R. Gingras, Bipin Patel, Igor L. Barsukov, Iain D. Campbell, Gordon C. K. Roberts and David R. Critchley

Why is saline so acidic (and does it really matter?)

Reddi, B.
Fonte: Ivyspring International Publisher Publicador: Ivyspring International Publisher
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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Commercial 0.9% saline solution for infusion has a pH around 5.5. There are many reasons for this acidity, some of them still obscure. It is also true that infusion of normal saline can lead to met-abolic acidaemia, yet the link between the acidity of saline solution and the acidaemia it can en-gender is not straightforward. This commentary draws together the known and putative sources of acidity in saline solutions: it turns out that the acidity of saline solution is essentially unrelated to the acidaemia complicating saline infusion.; Benjamin AJ Reddi

Removal of natural organic matter using self-assembled monolayer technology

Chow, C.W.K.; Majewski, P.; Bauer, S.; Fabris, R.; Drikas, M.
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
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25.75%
The use of nanotechnologies in water treatment for the removal of natural organic matter (NOM) is a relatively new concept. Using simple self-assembled monolayer (SAM) techniques, a silica substrate was modified as an adsorbent and tested for its potential for reduction of water quality parameters such as UV absorbance, colour and dissolved organic carbon (DOC). Silica particles that were coated with an amino-siloxane SAM (NH2-SAM) were evaluated in both a high surface area powder form and also a more realistic granular sand form. Initial results using direct stirred contact with powdered NH2-SAM showed promising results with 60% reduction of UV254 after 1 h and up to 70% removal of DOC with higher doses and contact times. NH2-SAM powder removed NOM in a broader and less selective molecular weight (MW) range than coagulation treatment and this removal was enhanced by pH control at 6, especially for medium MW components. When NH2-SAM sand was applied, the significantly reduced effective surface area resulted in lower DOC removal but colour removal was still considerable for realistic treatment plant contact times. Attempted regeneration with acidic solutions showed greater effectiveness at lower applied pH, however recovery of adsorption capacity reduced with successive adsorption/regeneration cycles highlighting the need for further refinement of operating conditions for more effective application of this relatively simple water treatment technology.; Christopher W.K. Chow...