Excess Positive Charge Research Articles

Redshift of Green Photoluminescence of Ca3Sc2Si3O12 : Ce3 + Phosphor by Charge Compensatory Additives

The luminescence wavelength of , which is a green-emitting phosphor under blue light excitation, was moved toward longer wavelength by addition of Mg. This modification is very valuable for commercial applications because it increases the brightness of the phosphor by increasing the overlap with the visibility curve. Magnesium is likely incorporated into the Sc position of the host crystal because the ionic radius of Mg is close to that of Sc. The substitution probably compensates for the excess positive charge induced by incorporation of Ce into the Ca position. The content of Ce in the host crystal was increased by increasing the amount of Mg in the raw material mixture; the inverse relationship was also observed. The spectral shift was also observed by adding Na or Li, which probably substituted the Ca position and compensated the excess charge induced by Ce in the Ca position. The change in luminescence spectra occurred irrespective of the type of charge compensatory additive used. Therefore, the spectral modification was mainly due to the increase in activator. Modification of the luminescence decay characteristics by the additives was also examined. The decay curve of the phosphor containing Mg showed a nonexponential profile.

Wormlike Aggregates from a Supramolecular Coordination Polymer and a Diblock Copolymer

The formation of wormlike micelles in mixed systems of a supramolecular coordination polymer Zn-L2EO4 and a diblock copolymer P2MVP41-b-PEO205 is investigated by light scattering and Cryo-TEM. By direct mixing at a stoichiometric charge ratio, the above mixtures proved to be capable of formation of spherical micelles with a radius of about 25 nm (Yan et al. Angew. Chem., Int. Ed.; 2007, 46, 1807-1809). Lately, we find wormlike micelles with a hydrodynamic radius >150 nm in a mixture with excess positive charge, that is, a negative charge fraction f- < 0.5. The transformation between wormlike and spherical micelles can be realized by variation of the mixing ratio through different protocols. Upon addition of negatively charged Zn-L2EO4 to a mixture with excess positively charged P2MVP41-b-PEO205, most of the wormlike micelles are transformed into spherical ones; upon addition of positively charged P2MVP41-b-PEO205 to a mixture of pure spherical micelles, wormlike micelles can be produced again. The effect of sample preparation protocol, sample history, and concentration on this transformation process is systematically reported in this article. A possible mechanism for the formation of wormlike micelles is proposed.

Electrolytic charge inversion at the liquid–solid interface in a nanopore in a dopedsemiconductor membrane

The electrostatics of a nanopore in a doped semiconductor membrane immersed in anelectrolyte is studied with a numerical model. Unlike dielectric membranes that alwaysattract excess positive ion charges at the electrolyte/membrane interface whenever anegative surface charge is present, semiconductor membranes exhibit more versatility incontrolling the double layer at the membrane surface. The presence of dopant charge in thesemiconductor membrane, the shape of the nanopore and the negative surfacecharge resulting from the pore fabrication process have competing influenceson the double layer formation. The inversion of the electrolyte surface chargefrom negative to positive is observed for n-Si membranes as a function of themembrane surface charge density, while no such inversion occurs for dielectric and p-Simembranes.

Investigation on imidazoline amide adsorption and electrochemical behaviour of coupled steels

The adsorption behaviour of imidazoline derivative as a cationic inhibitor on the galvanic electrode has been investigated by electrochemical methods, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). The galvanic electrode was prepared by coupling N80 carbon steel and S31803 stainless steel, and all experiments were performed in NaCl solution in the presence or absence of the inhibitor. Electrochemical experiments reveal stainless steel and carbon steel carry positive and negative excess charges in NaCl solution. For the galvanic electrode, positive and negative charges are carried on the carbon steel side and stainless steel side respectively, and the inhibitor is a type of cathodic inhibitor for galvanic corrosion. Fourier transform infrared spectroscopy and AFM were used to analyse the protective layer formed on the electrodes, a weaker adsorbability of the inhibitor on the anode (carbon steel side) of the galvanic electrode was measured. Results show the protective layer formed on the single carbon steel electrode is compact. In the case of coupling carbon steel and stainless steel, the adsorption film on the anode (carbon steel side) of galvanic electrode (GE) is not intact but defective. A major cause of failure of inhibiting galvanic corrosion is proposed based on the results obtained from electrochemical methods, FTIR and AFM.

Thermal Behavior of Polyelectrolyte Multilayer Microcapsules: 2. Insight into Molecular Mechanisms for the PDADMAC/PSS System

Polyelectrolyte multilayer capsules consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) were used as a model system to study the temperature-dependent behavior of polyelectrolyte multilayer films in aqueous media. Shells terminated with PSS shrink upon heating, whereas PDADMAC-terminated ones swell, independent of the nature of the first layer, as measured by means of confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Elemental analysis shows that the initial exponential layer growth of the film leads to a nearly neutral overall charge in the first case or a high positive excess charge in the latter. Depending on this overall charge either surface tension, due to an unfavorable polymer-solvent interaction, or electrostatics dominates, resulting in a shrinkage or expansion of capsules, respectively. Thus, it is possible to swell temperature-shrunk capsules by coating them with an additional PDADMAC layer. Micro-DSC measurements prove that polyelectrolyte multilayers undergo a glass transition in water at which the wall material softens, allowing the rearrangements to occur. It is found that the thermal history has an influence on the temperature behavior of capsules, especially on those ones terminated with PDADMAC. Also, the molecular weight of the polyelectrolytes affects the rearrangement of capsules. The lower the molecular weight and thus the smaller the entanglement of chains, the easier polyelectrolytes can rearrange.

Fougerite: From field experiment to the homologation of the mineral

Fougerite has been approved as a new mineral by the International Mineralogical Association in February 2004. Its characteristic blue-green colour is used as a universal criterion to identify the gley soils. By oxidation, it transforms into lepidocrocite. The discovery of fougerite in 1996 was the result of 10 years of a study of in situ seasonal dynamics of the system soil–solution, which led to the confirmation of the ancient assumption of the existence of a mixed hydroxide of the group of green rusts (GRs) in gleys. Synthetic GRs consist of a brucitic layer of Fe(II)–Fe(III), whose excess positive charge, due to Fe 3+, is compensated in the interlayer by different anions, such as sulphate, chloride, oxalate, carbonate, etc. Physical, chemical, and mineralogical characterizations have been performed as a complement, and have confirmed the first results. In fougerite from Fougères, Mg is present in the layer in addition to Fe; the nature of the interlayer anion, which can vary depending on the environment, remains an open question. To cite this article: F. Trolard, C. R. Geoscience 338 (2006).

The effect of segregated transition metal ions on the grain boundary resistivity of gadolinium doped ceria: Alteration of the space charge potential

The effect of segregated transition metals on the grain boundary resistivity of 1 mol% Gd-doped ceria has been investigated. The main focus of interest is whether the space charge potential that causes the blocking effect of the grain boundaries of the ceria can be extrinsically modified. The introduction of a small amount (< 0.5 mol%) of transition metals (Fe, Co, Mn and Cu) to 1 mol% Gd-doped ceria results in significant reductions in only the grain boundary resistivities of the samples attributed to exclusive segregation of the transition metals into the grain boundary core. In the case of Co- and Fe-doped samples, the grain boundary resistivity is lowered by an order of magnitude. EELS line scans across the grain boundaries of the Fe-doped sample have indicated that the grain boundaries are free of a secondary phase of transition metal oxide and that the Fe in the grain boundary likely exists as point defects. These results strongly suggest that it is indeed possible to reduce the excess positive charge in the grain boundary core, and thus the grain boundary resistivity in a ceria electrolyte, extrinsically as initially postulated. A defect chemistry model which explains partial counterbalance to the positive grain boundary core charge has been suggested. The resistivity minimum shown for the samples with different Fe concentration indicates that there is an optimum concentration of transition metal in the grain boundary core of the ceria necessary for such a countbalance.

Molecular Dynamics Simulations of Electrolyte Solutions at the (100) Goethite Surface

Molecular dynamics simulations of electrolyte solutions in contact with a neutral (100) goethite (alpha-FeOOH) surface were used to probe the structure of the mineral-water interface and gain insight into the adsorption properties of monovalent ions. Three electrolyte solutions were considered: NaCl, CsCl, and CsF. The electrolyte ions were chosen to cover a range of ionic sizes and affinities for the aqueous phase. The molecular dynamics simulations indicate the presence of a structured interfacial region resulting from the strong interaction of water with the mineral surface. The specific arrangement and preferred orientation of water that arise from this interaction create adsorption sites in the interfacial region, i.e., as far as 15 A away from the surface, and hence give rise to a strong correlation between the water and ion distributions. The structure of the hydrated ion, its effect on the water arrangement at the interface, and the strength of the ion-water bond are found to be key factors that determine the location and extent of ion adsorption at the interface. Additionally, in all simulations, we find a build up of positive charges near the surface due to cation adsorption, which is compensated by an accumulation of anions in the next few angströms. This creates an excess of negative charges, which is in turn compensated by an excess of positive charges, and so on. As we modeled a neutral surface, the structure of the electrolyte distribution arises from the complex interplay of the interactions between the surface, water, and the electrolyte ions rather than from the need to neutralize a surface charge. In addition, our simulations indicate that the electrolyte distribution does not resemble that of a classical electrical double layer. Indeed, our calculations predict the presence of several condensed layers and oscillations in the net charge away from the surface.

Amphoteric Hydrogel Capsules: Multiple Encapsulation and Release Routes

We show that chemical cross-linking of hydrogen-bonded poly(methacrylic acid)/poly(vinylpyrrolidone) (PMAA/PVPON) capsules deposited onto silica core with ethylenediamine (EDA) followed by core dissolution and pH-triggered removal of PVPON produces amphoteric hydrogel hollow capsules, whose walls are composed of cross-linked PMAA and contain amino groups provided by the cross-linker. The capsules exhibit highly reversible swelling at acidic and basic pH values due to excess positive and negative charges in the capsule wall and are of minimum size at pH 5.5. Apart from covalent cross-linking, the hydrogel capsule wall is also stitched through ionic pairing in a wide interval of pH. At pH 5−6, where carboxylic acid groups are protonated, the capsule wall expands (and hydrogel capsules increase in size) in salt solutions as a result of dissociation of ionic cross-links. In contrast, at pH > 6 and pH < 5, where hydrogel wall acquires charge, salt results in the hydrogel contraction and in a decrease of capsule size. In addition to pH and ionic strength, capsule swelling can be controlled by the number of cross-links achieved through variation of cross-linking time. We also show that these soft hydrogel capsules easily flatten when in contact with a solid surface and that the degree of flattening is governed by the surface and capsule charge and the degree of cross-linking in the capsule wall. Finally, we demonstrate that this pH- and ionic-strength-dependent swelling of hydrogel capsules affords multiple routes for encapsulation and controlled release of macromolecules.

Trapping of the S2to S3State Intermediate of the Oxygen-Evolving Complex of Photosystem II

Photosystem II preparations poised in the S(2)...Q(A) state produce no detectable intermediate during straightforward illumination at liquid helium temperatures. However, upon flash illumination in the range of 77-190 K, they produce a transient state which at -10 degrees C advances to S(3) or after rapid cooling to 10 K gives rise to a 116 G wide metalloradical EPR signal. The latter decays with half-times on the order of a few minutes, presumably by charge recombination, and can be regenerated repeatedly by illumination at 10 K. The constraints for Tyr Z oxidation are attributed to the presence of excess positive charge in S(2). Elevated temperatures are required presumably to overcome a thermal barrier in the deprotonation of Tyr Z(+) or most likely to allow secondary proton transfer away from the base partner of Tyr Z. Treatment with 5% (v/v) MeOH appears to remove the constraints for Tyr Z oxidation, and a 160 G wide metalloradical EPR signal is produced by illumination at 10 K, which decays with a half-time of ca. 80 s. Formation of the metalloradical signals is accompanied by reversible changes in the Mn multiline signal. The intermediates are assigned to Tyr Z(*) magnetically interacting with the Mn cluster in S(2), S(2)Y(Z)(*). A molecular model which extends an earlier suggestion and provides a plausible explanation of a number of observations, including the binding of small molecules to the Mn cluster, is presented.

Adsorption behavior and synergistic mechanism of a cationic inhibitor and KI on the galvanic electrode

The synergistic effect between KI and imidazoline derivative as a cationic inhibitor for inhibiting galvanic corrosion has been investigated by using electrochemical methods, atomic force microscopy and Fourier transform infrared (FTIR) spectroscopy. A galvanic electrode was prepared by coupling N80 carbon steel and S31803 stainless steel, and all experiments were performed in NaCl solution in the presence or absence of imidazoline derivative (MAD) and KI. Zero charge potential experiments reveal carbon steel and stainless steel carry positive and negative excess charges in NaCl solution, respectively, and stainless steel carries negative excess charge in NaCl solution with KI. Polarization curves and galvanic current measurements suggest that, for the galvanic corrosion, both MAD and KI are mainly cathodic type inhibitors, and a synergistic effect exists between KI and MAD. FTIR and AFM were used to analyze the inhibitor film formed on the surface of the electrodes. Results show that in the presence of KI, compared with that in the absence of KI, the inhibitor film on the anode of galvanic electrodes (GE) is more compact, and the adsorbability of the inhibitor on the surface of carbon steel is strengthened. A suitable mechanism of corrosion inhibition is proposed based on the results obtained from electrochemical measurements, AFM and FTIR. It is found that the anion I − can change the distribution of excess charge on the surface of galvanic electrode, thus helps the inhibitor to adsorb on both the cathodic area and the anodic area.

Two-Dimensional Charge Delocalization in X-Shaped Phenylenevinylene Oligomers

A combined experimental and theoretical study of the optoelectronic properties of charged two-dimensional X-shaped phenylenevinylene oligomers (X-mers) is presented. Cations and anions of X-mers were produced by irradiation of solutions with high-energy electron pulses. The optical absorption spectra were measured using time-resolved visible/near-infrared spectroscopy in the range of 500−1600 nm (0.8−2.5 eV). The optical absorption spectra were also calculated using the singly excited configuration interaction method with an intermediate neglect of differential overlap reference wave function (INDO/s-CIS) together with a density functional theory (DFT) optimized geometry. The INDO/s-CIS calculations reproduce the main absorption features of charged X-mers near 1.6−1.7 eV. The charge distributions calculated with DFT show that the excess positive charge is mostly localized on the phenylene units containing methoxy substituents. In contrast, the excess negative charge is delocalized over the entire oligomer...

Reactivity of some S-bridge containing diphenyl derivatives (sulfides, sulfoxides, sulfones) towards ortho-positronium atoms in dimethylsulfoxide solution

The effect of changes in the chemical structure of organic sulfur compounds on their reactivity towards an ortho-positronium ( o-Ps) atom was investigated by positron annihilation lifetime spectroscopy in dimethylsulfoxide solutions. S-bridge containing molecules with very similar structural frameworks were selected as model systems, such as, diphenyl sulfide, sulfoxide and sulfone, and their derivatives. The effect of the type of the S-bridge on the reactivity increased in the order of S < SO < SO 2 in all groups of the compounds with similar substituents on their phenyl groups. The same trend was observed for the calculated excess positive charge on the sulfur atoms and the LUMO energies of the molecules too. As it was expected, electron-withdrawing substituents on the aromatic rings increased both the reactivity and the negative values of the LUMO energy of the molecules (COOH < NO 2) whereas those with electron-donating character (CH 3O) showed the opposite effect.

Synthesis of layered zinc hydroxide chlorides in the presence of Al(III)

Zinc hydroxide chloride particles were synthesized by hydrolysis of ZnCl 2 solutions dissolving AlCl 3 at different atomic Al/Zn ratios from 0 to 1.0 and characterized by various techniques. Increasing Al/Zn ratio changed the crystal phases of the products as ZnO→ZnO+ZHC (Zn 5(OH) 8Cl 2·H 2O)→ZHC→LDH (layered double hydroxides, Zn–Al–Cl) and the particle morphology as agglomerates (ZnO)→fine particles (ZnO)→plates (ZHC)+rods (ZnO)→plates (ZHC)→plates (LDH). The atomic Cl/Zn ratios of LDH particles formed at Al/Zn⩾0.3 were ca. 0.3 despite the increase of Al/Zn ratio, being due to the intercalation of CO 3 2− into the LDH crystal. The OH − content of LDH estimated by TG was reduced by the deprotonation of OH − to counteract the excess positive charge produced by replacing Zn(II) with Al(III). ZHC exhibited a high adsorption selectivity of H 2O.

The adsorption behavior and corrosion inhibition mechanism of anionic inhibitor on galvanic electrode in 1% NaCl solution

The adsorption behavior of dodecanoic acid and its sodium salt (DDAS) as an anionic inhibitor on the galvanic electrode has been investigated by using electrochemical methods, Fourier transform infrared spectroscopy (FT-IR), and atomic force microscopy (AFM). The galvanic electrode was prepared by coupling N80 carbon steel (CS) and S31803 stainless steel (SS), and all experiments were performed in NaCl solution at pH 4 in the presence or absence of DDAS. Electrochemical experiments reveal SS and CS carry positive and negative excess charges in NaCl solution at pH 4, and DDAS is mainly anodic type inhibitor for the galvanic corrosion. FT-IR and AFM were used to analyze the protective layer formed on the electrodes, a stronger adsorbability of the inhibitor on the anode (CS) of GE was measured. Results indicate the protective layer formed on the single CS electrode is less compact than which on the coupled CS. The adsorption regulation of anionic inhibitor on the galvanic electrode is summarized based on the results obtained from electrochemical methods, FT-IR and AFM.

Calculation of the space charge in electrodeposition from a binary electrolyte

Abstract We present the results of a numerical calculation of the space charge first described in a model proposed by Chazalviel to explain the onset of ramified growth in electrodeposition from a binary electrolyte. Our results confirm that, when the ionic concentration goes to zero at the cathode the system departs from electroneutrality. However, the excess of positive charges at the cathode critically depends on the parameters of the system. In typical conditions, it may rise up to 10 −4 mol/L. The extension of the space charge region is approximately 200 nm.

Carrier Accumulation in Silicon-On-Insulator Structures Containing Ge Nanocrystals in the Burried SiO&lt;sub&gt;2&lt;/sub&gt; Layer

Electro-physical properties of metal-oxide-silicon (MOS) structures and MOS transistors, prepared in the top silicon layer of silicon-on-insulator (SOI) structures containing Ge nanocrystals in the buried SiO2 layers, have been studied. It was obtained that carrier accumulation in MOS structures depend on the direction of built-in electrical field in MOS structures. Accumulation of the excess negative charges in the case of p-channel transistors is associated with electron trapping on Ge nanocrystals synthesized in the buried dielectric. In the case of n-channel transistor, positive charge related to the Si/SiO2 interface or to the charged oxide is accumulated. The Ge atoms diffused to the SiO2/Si interface can stimulate the formation of the excess positive charge.

Chemical Bonding in the Complexes XeF 5 + XF 6 − (X = P, As, Sb, and Bi)

Ab initio quantum-chemical calculations of the complexes XeF 5 + XF 6 − (X = P, As, Sb, and Bi) were performed with the use of relativistic pseudopotentials for heavy atoms and full-electron basis sets. The chemical bonds were characterized by the parameters of critical points (electron density, its Laplacian, total electron energy, and its kinetic and potential components). It was demonstrated that the interaction between the XeF 5 + cation and the XF 6 − anion in XeF 5 + XF 6 − follows a key-lock scheme involving directed interactions of bridging fluorine atoms Fb → Xe and that the structuring function of the lone electron pair of the Xe atom is to compensate the destabilizing electrostatic interaction between the Xe and X atoms bearing excess positive charges.

Modulation of Charge in the Phosphate Binding Site of Escherichia coli ATP Synthase

This paper presents a study of the role of positive charge in the P(i) binding site of Escherichia coli ATP synthase, the enzyme responsible for ATP-driven proton extrusion and ATP synthesis by oxidative phosphorylation. Arginine residues are known to occur with high propensity in P(i) binding sites of proteins generally and in the P(i) binding site of the betaE catalytic site of ATP synthase specifically. Removal of natural betaArg-246 (betaR246A mutant) abrogates P(i) binding; restoration of P(i) binding was achieved by mutagenesis of either residue betaAsn-243 or alphaPhe-291 to Arg. Both residues are located in the P(i) binding site close to betaArg-246 in x-ray structures. Insertion of one extra Arg at beta-243 or alpha-291 in presence of betaArg-246 retained P(i) binding, but insertion of two extra Arg, at both positions simultaneously, abrogated it. Transition state stabilization was measured using phosphate analogs fluoroaluminate and fluoroscandium. Removal of betaArg-246 in betaR246A caused almost complete loss of transition state stabilization, but partial rescue was achieved in betaN243R/betaR246A and alphaF291R/betaR246A. BetaArg-243 or alphaArg-291 in presence of betaArg-246 was less effective; the combination of alphaF291R/betaN243R with natural betaArg-246 was just as detrimental as betaR246A. The data demonstrate that electrostatic interaction is an important component of initial P(i) binding in catalytic site betaE and later at the transition state complex. However, since none of the mutants showed significant function in growth tests, ATP-driven proton pumping, or ATPase activity assays, it is apparent that specific stereochemical interactions of catalytic site Arg residues are paramount.

Antibacterial effect of Cu2+-exchanged montmorillonite on Aeromonas hydrophila and discussion on its mechanism

Montmorillonite (MMT) and its Cu2+-exchanged montmorillonite (Cu-MMT) were used to study the antibacterial activity on Aeromonas hydrophila. The results indicated that MMT had no antibacterial activity. The minimum inhibitory concentration (MIC) and bactericidal concentration (MBC) of Cu-MMT on A. hydrophila are found to be 150 and 600 mg/L, respectively. The continuance of the antibacterial activity of Cu-MMT was much longer than copper sulfate. In order to reveal the mechanism of the antibacterial activity of Cu-MMT, the Cu release from Cu-MMT in tryptic soy broth (TSB) was investigated. In the first 2 h, Cu concentration in the supernatant reaches saturated value, about 1.22-2.27% of the overall Cu in Cu-MMT suspended in the medium. The washed Cu-MMT in TSB for 24 h retained their full antibacterial activity; whereas, the supernatants from the washed pellets showed very little antibacterial activity. These findings suggested that the antibacterial activity of Cu-MMT was mainly localized on the clay surface, and not due to the release of Cu2+ into solution. The excessive positive charge of Cu-MMT would make Cu-MMT attract A. hydrophila with negatively charged cellular wall. In this case, the copper cation would act directly on the bacteria adsorbed on the surface of Cu-MMT, instead of into the medium. The mechanism for the antibacterial activity of Cu-MMT may involve the enhanced affinity of Cu-MMT for A. hydrophila and the antibacterial activity of Cu2+.