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Acid Leads (acid + lead)
Selected AbstractsMolecular cloning and expression regulation of PRG-3, a new member of the plasticity-related gene familyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2004Nicolai E. Savaskan Abstract Phospholipid-mediated signalling on neurons provokes diverse responses such as neurogenesis, pattern formation and neurite remodelling. We have recently uncovered a novel set of molecules in the mammalian brain, named plasticity-related genes (PRGs), which mediate lipid phosphate phosphatase activity and provide evidence for their involvement in mechanisms of neuronal plasticity. Here, we report on a new member of the vertebrate-specific PRG family, which we have named plasticity-related gene-3 (PRG-3). PRG-3 is heavily expressed in the brain and shows a specific expression pattern during brain development where PRG-3 expression is found predominantly in neuronal cell layers and is already expressed at embryonic day 16. In the mature brain, strongest PRG-3 expression occurs in the hippocampus and cerebellum. Overexcitation of neurons induced by kainic acid leads to a transient down-regulation of PRG-3. Furthermore, PRG-3 is expressed on neurite extensions and promotes neurite growth and a spreading-like cell body in neuronal cells and COS-7 cells. In contrast to previously described members of the PRG family, PRG-3 does not perform its function through enzymatic phospholipid degradation. In summary, our findings feature a new member of the PRG family which shows dynamic expression regulation during brain development and neuronal excitation. [source] Aqueous Processing and Stabilization of Manganese Zinc Ferrite Powders via a Passivation,Dispersion ApproachJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2002Michael M. Mandanas A dispersion scheme for aqueous processing of manganese zinc ferrite suspensions is presented. The addition of oxalic acid leads to the formation of a uniform negative charge on the surface such that a cationic polyelectrolyte, polyethyleneimine (PEI), adsorbs and provides electrosteric dispersion. At 0.5 w/w (weight percent with respect to the dry powder) oxalic acid addition, there is a relatively uniform negative surface charge (approximately ,30 mV) within the suspension pH range investigated (3,10), eliminating the isoelectric point (pH ,7.6) present for the as-received metal oxide powder. At the addition of 0.5 w/w PEI on an oxalate-treated surface, the surface charge is constant and positive (,20 mV) through a wide pH range, ,5,10. The resulting rheological data for passivation,dispersion of relatively high-solids manganese zinc ferrite suspensions (,80 wt%) demonstrate improved colloid stability with improved rheological properties. The resulting apparent viscosity and Bingham yield point is 0.01 Pa·s (12.0 cP) and 0.24 Pa (2.4 dynes/cm2), respectively. A sulfonated napthalene-based dispersant, typically used in industry, gives an apparent viscosity and Bingham yield point of 0.03 Pa·s (32 cP) and 3.1 Pa (31 dynes/cm2), respectively. [source] Citric acid traps to replace sulphuric acid in the ammonia diffusion of dilute water samples for 15N analysisRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 4 2006Patrick Schleppi The analysis of 15N in aqueous samples requires the concentration of dissolved nitrogen (N) into a small volume that can be analysed by mass spectrometry. This is conveniently achieved by the NH3 diffusion technique, where NH is captured on small acidified filters enclosed in PTFE. NO can be analysed the same way by reducing it to NH with Devarda's alloy. H2SO4 is commonly used for the acidification of the filters. During combustion, however, this acid leads to the production of SO2 and elemental sulphur, which both have detrimental effects on the mass spectrometer. We propose here to replace H2SO4 with citric acid because it is combusted completely to CO2 and H2O in the elemental analyser before entering the mass spectrometer. Citric acid was found to give comparable results in terms of N recovery and 15N values, both for NH and for NO samples. Blank samples revealed that N contamination was slightly lower using citric instead of sulphuric acid as acidifier of the glass filters. NH samples first concentrated over cation-exchange columns were strongly acidic and several methods were tested to raise the pH for the subsequent diffusion. These samples gave incomplete N recoveries, but this problem was independent of the acid used on the filters and of the final pH of the sample. Complete recovery was achieved only by increasing the volume of the eluate from the columns. Citric acid can thus generally be recommended instead of H2SO4 for ammonia diffusion. Copyright © 2006 John Wiley & Sons, Ltd. [source] Shape-Persistent Macrocycles Functionalised with Coumarin Dyes: Acid-Controlled Energy- and Electron-Transfer ProcessesCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2008Carlo Giansante Dr. Abstract We have investigated the spectroscopic properties (absorption spectra, emission spectra, emission lifetimes) of three triads in CH2Cl2: C2-M-C2, C343-M-C343, and C2-M-C343, in which M is a shape-persistent macrocyclic hexagonal backbone composed of two 2,2,-bipyridine (bpy) units embedded in opposing sides, and C2 and C343 are coumarin,2 and coumarin,343, respectively. All the components are strongly fluorescent species (,=0.90, 0.79, and 0.93 for M, C2, and C343, respectively, as established by investigating suitable model compounds). In each triad excitation of M leads to almost quantitative energy transfer to the lowest coumarin-localised excited state. Upon addition of acid, the two bpy units of the M component undergo independent protonation leading to monoprotonated (e.g., C2-M,H+ -C2) and diprotonated (e.g., C2-M,2,H+ -C2) species. Further addition of acid leads to protonation of the coumarin component so that each triad is involved in four protonation equilibria. Protonation causes strong (and reversible, upon addition of base) changes in the absorption and fluorescence properties of the triads because of inversion of the excited-state order and/or the occurrence of electron-transfer quenching processes. Il presente lavoro riporta lo studio effettuato in CH2Cl2 delle proprietà spettroscopiche (spettri di assorbimento ed emissione, tempi di vita degli stati eccitati) di tre triadi: C2-M-C2, C343-M-C343 e C2-M-C343. M rappresenta un macrociclo rigido a struttura esagonale in cui sono incorporate in posizioni diametralmente opposte due unità 2,2,-dipiridina (bpy), mentre C2 e C343 indicano, rispettivamente, la cumarina,2 e la cumarina,343. Tutte le unità componenti le triadi sono fortemente luminescenti (,=0.90, 0.79 e 0.93 per M, C2 e C343, rispettivamente, come stabilito studiando opportuni composti modello). In ciascuna triade l'eccitazione selettiva di M porta ad un trasferimento di energia al più basso stato eccitato localizzato sulle cumarine con un'efficienza praticamente unitaria. Aggiunte crescenti di acido inducono, dapprima, l'indipendente protonazione delle due unità bpy del componente M con formazione delle specie monoprotonate (per esempio, C2-M,H+ -C2) e diprotonate (per esempio, C2-M,2,H+ -C2) e, successivamente la protonazione delle cumarine. Ciascuna triade è quindi coinvolta in quattro equilibri di protonazione che, invertendo l'ordine energetico degli stati eccitati e/o favorendo l'insorgere di processi di trasferimento elettronico che spengono le emissioni, sono accompagnati da modifiche consistenti (e reversibili per aggiunta di base) delle proprietà spettroscopiche (assorbimento ed emissione) delle triadi esaminate. [source] Photoinduced Energy- and Electron-Transfer Processes in Dinuclear RuII,OsII, RuII,OsIII, and RuIII,OsII Trisbipyridine Complexes Containing a Shape-Persistent Macrocyclic SpacerCHEMPHYSCHEM, Issue 1 2006Margherita Venturi Prof. Abstract The PF6,salt of the dinuclear [(bpy)2Ru(1)Os(bpy)2]4+complex, where 1 is a phenylacetylene macrocycle which incorporates two 2,2,-bipyridine (bpy) chelating units in opposite sites of its shape-persistent structure, was prepared. In acetonitrile solution, the Ru- and Os-based units display their characteristic absorption spectra and electrochemical properties as in the parent homodinuclear compounds. The luminescence spectrum, however, shows that the emission band of the RuIIunit is almost completely quenched with concomitant sensitization of the emission of the OsIIunit. Electronic energy transfer from the RuIIto the OsIIunit takes place by two distinct processes (ken=2.0×108and 2.2×107s,1at 298 K). Oxidation of the OsIIunit of [(bpy)2Ru(1)Os (bpy)2]4+by CeIVor nitric acid leads quantitatively to the [(bpy)2RuII(1)OsIII(bpy)2]5+complex which exhibits a bpy-to-OsIIIcharge-transfer band at 720 nm (,max=250,M,1cm,1). Light excitation of the RuIIunit of [(bpy)2RuII(1)OsIII(bpy)2]5+is followed by electron transfer from the RuIIto the OsIIIunit (kel,f=1.6×108and 2.7×107s,1), resulting in the transient formation of the [(bpy)2RuIII(1)OsII(bpy)2]5+complex. The latter species relaxes to the [(bpy)2RuII(1)OsIII(bpy)2]5+one by back electron transfer (kel,b=9.1×107and 1.2×107s,1). The biexponential decays of the [(bpy)2*RuII(1)OsII(bpy)2]4+, [(bpy)2*RuII(1)OsIII(bpy)2]5+, and [(bpy)2RuIII(1)OsII(bpy)2]5+species are related to the presence of two conformers, as expected because of the steric hindrance between hydrogen atoms of the pyridine and phenyl rings. Comparison of the results obtained with those previously reported for other Ru,Os polypyridine complexes shows that the macrocyclic ligand 1 is a relatively poor conducting bridge. [source] | ||||||||||