Effective Positive Charge Research Articles

SCIENTIFIC PREDICTION OF MAGNESIUM OXIDE NANOPARTICLES TOXICITY AND ASSESSMENT OF ITS HAZARD FOR HUMAN HEALTH

Aim: To study biological effects of magnesium oxide nanoparticles on human health. Methods: Toxicity and potential hazards of magnesium oxide nanoparticles exposure was performed using mathematical models containing data on physical, chemical, molecular biological, biochemical, cytological and ecological properties with calculation of coefficients of hazard (D) and incompleteness of data evaluation (U) of magnesium nanoscale. Size and shape of the nanomaterial were defined using dynamic laser light scattering and scanning electron microscopy. Surface area was determined by the Brunauer, Emmet and Taylor method. Results: Magnesium oxide nanoparticles have a size of 5-100 nm and specific surface area of 64,5 m2/g. They are insoluble in water, can have hydrophobic or hydrophilic properties and have an effective positive charge. They can generate reactive oxygen species, damage DNA, interact with protein structures, destroying cell membrane, cause mitochondrial dysfunction, morphological changes and cell death, impact on proteomic and metabolic profiles, increasing the concentration digestive enzymes, carbohydrates, amino- acid and fatty acids. Besides, the material under investigation has such long-term effects of action: allergenicity, mutagenicity and embryotoxicity. D-coefficient was 1, 872. Conclusions: Magnesium oxide nanoparticles have a high degree of potential hazard for human health. The results warrant toxicological studies and assessment of toxicological-hygienic characteristics of magnesium oxide nanoparticles at various routes of intake for development of effective measures to prevent negative effect of magnesium oxide nanoparticles on human health.

Preparation, electronic structure and piezooptical properties of solid solutions Tl3PbBr5–I

Abstact Phase diagram of the Tl3PbBr5–Tl3PbI5 section of the reciprocal system 2TlI + PbBr2⇔2TlBr + PbI2 was investigated by differential thermal and X-ray phase analysis methods on 18 alloys. The section is quasi-binary, of eutectic type, with the invariant point coordinates 76 mol% Tl3PbI5 and 355 °C. The addition of Tl3PbI5 results in stabilization of the high-temperature (HT) modification of Tl3PbBr5 forming a substitution solid solution, which at room temperature occupies the concentration range of ∼9–71 mol% Tl3PbI5. The solid solution range of low-temperature (LT) Tl3PbBr5 is minor (0–∼6 mol% Tl3PbI5), and that of Tl3PbI5 is in the range of ∼71–100 mol% Tl3PbI5. Tl3PbBr2.5I2.5 crystals were grown by Bridgman-Stockbarger method; they belong to wide-gap semiconductors with Eg decreasing from 2.45 eV at 100 K to 2.36 eV at 300 K. Based on X-ray photoelectron (XP) core-level spectra, one can conclude that the Tl3PbBr2.5I2.5 crystal reveals the XP fine-structure peculiarities well ascribed to thallium, lead, bromine and iodine, constituent atoms of the quaternary halide under consideration. Treatment of the Tl3PbBr2.5I2.5 crystal with 3 keV Ar+ ions reveals that the Pb–I bonds are somewhat weaker in this compound, as compared to the Pb–Br, Tl–Br and Tl–I bonds. Comparison with the similar XP measurements of the related ternary bromide and iodide (Tl3PbBr5 and Tl3PbI5) indicates that the positive effective charge of lead atoms gradually decreases when going from Tl3PbBr5 to Tl3PbBr2.5I2.5 and, further, to Tl3PbI5, while the charge state of thallium atoms does not change in the above sequence of compounds. In the sequence Tl3PbBr5 → Tl3PbBr2.5I2.5 → Tl3PbI5 the relative peak intensity of the XP valence-band spectrum monotonously decreases. The laser stimulated piezooptics at 1150 nm excited by 1540 nm Er:glass nanosecond laser and its second harmonic generation are reported.

On the Nature of the Effective Surface Charge Transformation on InAs Crystals during Anodic Oxide Layer Growth

The dynamics of fluorine atoms distribution over the thickness of the grown anodic oxide layers and the effective surface charge on InAs crystals under these layers are investigated. Anodic oxidation is performed in an alkaline electrolyte to which a fluorochemical component in the galvanostatic mode is added at the anode current densities of 0.05 and 0.5 mA cm–2. The layer’s thickness changes by 32–51 nm by setting a final voltage of 15 to 25 V on the electrodes during the growth. The layer’s thickness and refractive index are measured by an ellipsometric technique and the distribution of the thickness of fluorine atoms is measured by photoelectron spectroscopy combined with ion etching. Simultaneously, MIS structures are fabricated from the grown layers and their capacitance–voltage characteristics are calculated to determine the effective surface charge and density of the surface states at different layer thicknesses. The main results of the investigations are that, with regardless of anodic current, density the grown layers are compacted, the fluorine atoms distribution profile shifts toward InAs, and the positive effective surface charge gradually decreases from 3.6 × 1011 to 2.0 × 1011 cm–2 at densities of the surface states of (6–7) × 1011 eV–1 cm–2 in all cases. It is concluded based on comparison of the obtained data with the theoretical concepts on the charge structure of MIS structures that the built-in charge is gradually removed from the interface with InAs during the anodic oxide layer’s growth, which explains the observed decrease in the effective surface charge when the layer’s thickness increases. This result indicates, that the layer’s growth rate is faster than rate of the built-in layer charge shifting toward InAs.

SCIENTIFIC FORECASTING OF TOXICITY AND EVALUATION OF HAZARD POTENTIAL OF ALUMINUM OXIDE NANOPARTICLES FOR HUMAN HEALTH

Aim: scientific forecasting toxicity and evaluation potential hazard of the biological action of aluminum oxide nanoparticles for human health. Methods: forecasting toxicity and assessment of potential hazards was carried out according to the results of forecasting-analytical modeling complexes of indicators characterizing physico-chemical, molecular biological, biochemical, cytological and ecological properties with calculation coefficients of hazard (D) and incompleteness of data evaluation (U) of nanoscale aluminum. Own research on the establishment of size and shape of nanomaterial were performed using dynamic laser light scattering and scanning electron microscopy, specific surface area were determined by the method of Brunauer, Emmet and Taylor. Results: aluminum oxide nanoparticles have a size of 30-40 nm, specific surface area 113 m2/g insoluble in water, superhydrophobic, have an effective positive charge. They are have the ability to generate reactive oxygen, damage DNA, disrupt protein expression, depolarize cell membrane, cause morphological changes and cell death, disturb the mitochondrial metabolism, impact on proteomic and metabolic profiles, inducing pro-inflammatory cytokine interleikin-1, ß, tumor necrosis factor and cluster of differentiation 86, 80 and 40. Besides, the material under investigation has such long-term effects of aaction: carcinogenicity and immunotoxicity. Conclusions: based on the results of forecasting modeling, established: aluminum oxide nanoparticles have a high degree of potential hazard for human health (coefficient D = 2,202 that is included in the range 1,780-2,449 and correspond to a high degree of potential hazard). The results indicate necessity for toxicological studies and preparation toxicological-hygienic characteristics of aluminum oxide nanoparticles at various routes of intake for development of effective preventive measures of negative impact on workers and consumers in contact with nanoproducts.

The MgO(111) versus MgO(100) supported Au ultrasmall particles as a model catalyst for carbon monoxide oxidation

Adsorption and reaction of carbon monoxide and oxygen on gold ultrasmall particles deposited on MgO(111) and MgO(100) films in ultra-high vacuum have been studied by surface sensitive spectroscopic and structural techniques. The 3 nm thick MgO(111) and MgO(100) films were formed on Mo(110) and Mo(100) supports, respectively, as templates to grow the corresponding oxide structures. It is found that, unlike MgO(100), and many other oxide surfaces, reported in the literature, the Au particles of and average size of c.a. 2–3 nm, deposited on MgO(111), acquire an effective positive charge as a result of charge transfer from the metal as an effect stabilizing the uncompensated dipolar moment of the polar substrate. Gold nanoparticles on both MgO(111) and MgO(100) are active model catalysts for carbon monoxide oxidation by oxygen, as revealed by temperature desorption studies. However the effect of MgO(111) support is markedly more pronounced due to stronger interaction of precursor CO and O2 induced by specific state of supported Au ultrasmall particles.

Theoretical study of V20O50 oxovanadate cluster compounds with alkali metal atoms

The energies and structural and spectroscopic characteristics of model М n V20O50 systems corresponding to compounds of the V20O50 oxovanadate cluster with alkali metal atoms (M = Li, K; n = 1–20) have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, in the K n V20O50 compounds, all the metal atoms are coordinated in the outer sphere to the edges of the hollow dodecahedral V20O50 cage to form three-center Ot−K−Ot bridges with terminal oxygen atoms. In the Li n V20O50 compounds, the metal atoms can be coordinated both outside and inside the V20O50 cage. At n = 4, the most favorable isomer is endohedral Li4O4@V20O46 in the quintet state (S = 5), in which the four Li atoms are located in the inner cavity of the inverted O4@V20O46 isomer of the oxovanadate cluster with four O atoms oriented to the cage center and form with them a corrugated eight-membered ring Li4O4. The decrease in energy caused by the formation of the endohedral isomer (4Li + V20O450 → Li4O4@V20O46) is estimated at ~377 kcal/mol. The exohedral isomer 4Li • V20O50 (S = 5), in which the Li atoms are coordinated to the outside of the V20O50 cage, is ~23 kcal/mol less favorable. For the other members of the Li series with n from 4 to 20, the endohedral isomers with the inner Li4O4 ring remain preferable. At n > 4, the extra Li atoms fill the outer sphere of the cage, being coordinated to its edges to form three-center Ot−Li−Ot bridges with terminal oxygen atoms. The specific energy of formation of Li n V20O50 (by the scheme nLi + V20O450 → Li4O4@V20O46Lin-4) per Li atom monotonically decrease from ~98 (n = 2) to ~80 kcal/mol (n = 20). For K n V20O50, these energies are ~20−25 kcal/mol lower than for the lithium analogues and decrease from ~80 (n = 2) to ~64 kcal/mol (n = 12). The atoms of both alkali metals in the M n V20O50 systems have large positive effective charges (0.85e−0.92e for K and 0.65e−0.78e for Li), which also monotonically decrease with increasing n. The addition of each alkali metal atom is accompanied by its ionization (М → М+) along with the reduction of one of the neighboring pentavalent vanadium atoms to the tetravalent state (VV → VIV) and localization of the unpaired electron in its 3d shell. For all Li n V20O50 complexes, the states with maximal multiplicity and parallel spins are the most preferable.

Hysteresis in the transfer characteristics of MoS2 transistors

We investigate the origin of the hysteresis observed in the transfer characteristics of back-gated field-effect transistors with an exfoliated MoS2 channel. We find that the hysteresis is strongly enhanced by increasing either gate voltage, pressure, temperature or light intensity. Our measurements reveal a step-like behavior of the hysteresis around room temperature, which we explain as water-facilitated charge trapping at the MoS2/SiO2 interface. We conclude that intrinsic defects in MoS2, such as S vacancies, which result in effective positive charge trapping, play an important role, besides H2O and O2 adsorbates on the unpassivated device surface. We show that the bistability associated to the hysteresis can be exploited in memory devices.

Modification of hysteresis behaviors of protein monolayer and the corresponding structures with the variation of protein surface charges

Successive compression-decompression cycles of the surface pressure (π) − specific molecular area (A) isotherms of protein (BSA) monolayers show that reversible hysteresis persists if the protein molecules contain effective positive or negative surface charges. However, for neutral condition, i.e., close to the isoelectric point of the protein, irreversibility in the hysteresis behaviour dominates. Out-of-plane structures obtained from the X-ray reflectivity analysis suggest that at lower surface pressure monomolecular layer of BSA is formed on the water surface. With increasing surface pressure, molecules start to lift-up from the water surface in such a way that semi-major axis makes an angle with the water surface. Depending on the surface pressure and surface charge of BSA, monomolecular or bimolecular layer of tilted BSA molecules is formed on the water surface, however, formation of bimolecular layer is observed when the pH is relatively closer to the BSA isoelectric point. After complete decompression, tilted monomolecular or bimolecular structures again transform into monomolecular layer as evidenced from the structural analysis of the films deposited at lower surface pressures in the second compression, however, structural hysteresis varies depending upon the subphase pH or protein surface charge. Structures obtained from the films deposited at first and second compressions at lower pressure implies that although structural dissimilarity is present but structural hysteresis is only present near the isoelectric point of BSA and becomes negligible below and above that pH. Competitive electrostatic and van der Waals interactions are responsible for such hysteresis behaviours and structural modifications.

A deep-level transient spectroscopy study of gamma-ray irradiation on the passivation properties of silicon nitride layer on silicon

Plasma-enhanced chemical vapor deposited silicon nitride (SiNx) films are extensively used as passivation material in the solar cell industry. Such SiNx passivation layers are the most sensitive part to gamma-ray irradiation in solar cells. In this work, deep-level transient spectroscopy has been applied to analyse the influence of gamma-ray irradiation on the passivation properties of SiNx layer on silicon. It is shown that the effective carrier lifetime decreases with the irradiation dose. At the same time, the interface state density is significantly increased after irradiation, and its energy distribution is broadened and shifts deeper with respect to the conduction band edge, which makes the interface states becoming more efficient recombination centers for carriers. Besides, C–V characteristics show a progressive negative shift with increasing dose, indicating the generation of effective positive charges in SiNx films. Such positive charges are beneficial for shielding holes from the n-type silicon substrates, i. e. the field-effect passivation. However, based on the reduced carrier lifetime after irradiation, it can be inferred that the irradiation induced interface defects play a dominant role over the trapped positive charges, and therefore lead to the degradation of passivation properties of SiNx on silicon.

Development of docetaxel and alendronate-loaded chitosan-conjugated polylactide-co-glycolide nanoparticles: <i>In vitro</i> characterization in osteosarcoma cells

Purpose: To develop docetaxel (DTX)- and alendronate (ALN)-loaded, chitosan (CS)-conjugated polylactide- co-glycolide (PLGA) nanoparticles (NPs) to increase therapeutic efficacy in osteosarcoma cells.Methods: Drug-loaded PLGA NPs were prepared by nanoprecipitation and chemically conjugated by the carboxylic group of PLGA to the amine-bearing CS polymer. The nanocarrier was characterized by dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and differential scanning calorimetry as well as by in vitro drug release and cell culture studies.Results: NP size was within the tumour targeting range (~200 nm) with an effective positive charge (20 mV), thus increasing cellular uptake efficiency. Morphological analysis revealed clear spherical particles with uniform dispersion. The NPs exhibited identical sustained release kinetics for both DTX and ALN. CS-conjugated PLGA with dual-drug-loaded (DTX and AL) NPs showed typical time-dependent cellular uptake and also displayed superior cytotoxicity in MG-63 cells compared with blank NPs, which were safe and biocompatible.Conclusion: Combined loading of DTX and ALN in NPs increased the therapeutic efficacy of the formulation for osteosarcoma treatment, thus indicating the potential benefit of a combinatorial drug regimen using nanocarriers for effective treatment of osteosarcoma.Keywords: Chitosan, Docetaxel, Alendronate, Nanocarriers, Sustained-release kinetics, Polylactide-coglycolide, Osteosarcoma, Cellular uptake

Secondary interactions in decachloro-closo-decaborates of alkali metals M2[B10Cl10] (M = K+ and Cs+): 35Cl NQR and X-ray studies

New salts containing bulky decachloro-closo-decaborate dianion of composition M2[B10Cl10] (M=K+ and Cs+) were synthesized and characterized using the IR, 11B NMR and 35Cl NQR spectroscopies, powder and single crystal X-ray diffractions. The potassium salt was obtained as solvate K2[B10Cl10]·3H2O, and cesium salt – as solvates Cs2[B10Cl10]·H2O and Cs2[B10Cl10]·2H2O. Using 35Cl NQR, the interatomic contacts, caused by secondary interactions, were selected of all the totality of interatomic contacts, measured by X-ray diffraction. The B–Cl…H secondary bonds were identified in all the compounds, whereas no contributions to the electric field gradient on the appropriate chlorine atoms were registered from cations M (M=K or Cs). The high coordination numbers of alkali ions screened the effective positive charge on them leading to insignificant perturbation of the chlorine electron density distribution which resulted in negligibly small splitting of the 35Cl NQR spectra due to the alkali cations.

Investigations on the local structures and spin Hamiltonian parameters for the orthorhombic Rh2+ centers R4 and R5 in AgCl microcrystals

The local structures and spin Hamiltonian parameters (SHPs, g factors, hyperfine structure constants and superhyperfine parameters) are theoretically investigated for the two orthorhombic Rh2+centers R4 and R5 in AgCl microcrystals. Center R4 is ascribed to the impurity Rh2+substituted for Ag+ with two H2O molecules substituted for the nearest neighbor ligands Cl− along the [100] and [010] axes, each with one next nearest neighbor Ag+ vacancy (VAg) due to charge compensation. The impurity Rh2+is found to experience a small off-center displacement 0.006Å along the [1¯1¯0] axis because of the electrostatic interactions of the substitutes and the VAg. Center R5 is attributed to the impurity Rh2+substituted for Ag+ associated with one H2O molecule substituted for the nearest neighbor ligand Cl− along the [100] axis and one next nearest VAg along the [010] axis. Due to the effective positive charge of the substitute, Rh2+ is repulsed away from the substitute by about 0.008Å along the [1¯00] axis, while the intervening ligand Cl− in Rh2+and VAg suffers a small inward displacement 0.010Å towards the center of octahedron. The calculated SHPs based on the above local structures show good agreement with the experimental data for both centers.

Influence of CO annealing in metal-oxide-semiconductor capacitors with SiO2 films thermally grown on Si and on SiC

Understanding the influence of SiC reaction with CO, a by-product of SiC thermal oxidation, is a key point to elucidate the origin of electrical defects in SiC metal-oxide-semiconductor (MOS) devices. In this work, the effects on electrical, structural, and chemical properties of SiO2/Si and SiO2/SiC structures submitted to CO annealing were investigated. It was observed that long annealing times resulted in the incorporation of carbon from CO in the Si substrate, followed by deterioration of the SiO2/Si interface, and its crystallization as SiC. Besides, this incorporated carbon remained in the Si surface (previous SiO2/Si region) after removal of the silicon dioxide film by HF etching. In the SiC case, an even more defective surface region was observed due to the CO interaction. All MOS capacitors formed using both semiconductor materials presented higher leakage current and generation of positive effective charge after CO annealings. Such results suggest that the negative fixed charge, typically observed in SiO2/SiC structures, is not originated from the interaction of the CO by-product, formed during SiC oxidation, with the SiO2/SiC interfacial region.

Directed assembly of single colloidal gold nanowires by AFM nanoxerography.

Ultrathin gold nanowires (NWs) dispersed in hexane were prepared by chemical reduction of HAuCl4 in oleylamine, along with nanospheres (NSs), side products of the reaction. X-ray photoelectron spectroscopy and small-angle X-ray scattering evidenced a stabilization of these nano-objects by oleylammonium chloride surfactants. The directed assembly of these nano-objects on surfaces was performed by atomic force microscopy (AFM) nanoxerography in a few seconds. Selective assembly of gold NWs only occurred on positively charged patterns, while NSs assembled more specifically on the negatively charged ones. This sorting suggests that the strong electric field generated by the charge patterns induced a negative effective charge on the gold NWs and a weak positive effective charge on the NSs. Such difference could be explained by the ion organization at the colloid surface, monolayered in the case of NWs, and bilayered in the case of NSs. By adjusting the design of the positive patterns and the experimental conditions of development, single gold nanowires were successfully assembled by AFM nanoxerography on predefined sites of surfaces without damaging them, opening the way for future electrical and mechanical characterizations.

Strong electronic polarization of the C60 fullerene by imidazolium-based ionic liquids: accurate insights from Born-Oppenheimer molecular dynamic simulations.

Fullerenes are known to be polarizable due to their strained carbon-carbon bonds and high surface curvature. The electronic polarization of fullerenes is steadily of practical importance because it leads to non-additive interactions and, therefore, to unexpected phenomena. For the first time, hybrid density functional theory (HDFT) powered Born-Oppenheimer molecular dynamics (BOMD) simulations have been conducted to observe electronic polarization and charge transfer phenomena in the C60 fullerene at finite temperature (350 K). The non-additive phenomena are fostered by the three selected imidazolium-based room-temperature ionic liquids (RTILs). We conclude that although charge transfer appears nearly negligible in these systems, electronic polarization is indeed significant, leading to a systematically positive effective electrostatic charge on the C60 fullerene: +0.14e in [MMIM][Cl], +0.21e in [MMIM][NO3], and +0.17e in [MMIM][PF6]. These results are, to a certain extent, unexpected and provide a motivation for considering novel C60-RTILs systems. HDFT BOMD is a powerful tool for investigating electronic effects in RTIL and fullerene containing nuclear-electronic systems.

In situ study on reverse polarity effect in Cu/Sn–9Zn/Ni interconnect undergoing liquid–solid electromigration

Synchrotron radiation real-time imaging technology was used to in situ study the interfacial reactions in Cu/Sn–9Zn/Ni solder interconnects undergoing liquid–solid electromigration (L–S EM). The reverse polarity effect, evidenced by the continuous growth of intermetallic compound (IMC) layer at the cathode and the thinning of the IMC layer at the anode, was resulted from the abnormal directional migration of Zn atoms toward the cathode in electric field. This abnormal migration behavior was induced by the positive effective charge number (Z∗) of Zn atoms, which was calculated to be +0.63 based on the Cu fluxes and the consumption kinetics of the anode Cu. Irrespective of the flowing direction of electrons, the consumption of Cu film was obvious while that of Ni film was limited. The dissolution of anode Cu followed a linear relationship with time while that of cathode Cu followed a parabolic relationship with time. It is more damaging with electrons flowing from the Ni to the Cu than that from the Cu to the Ni. The simulated Zn concentration distributions gave an explanation on the relationship between abnormal migration behavior of Zn atoms and the dissolution of Cu film under electron wind force. The abnormal directional migration of Zn atoms toward the cathode prevented the dissolution of cathode substrate, which is beneficial to improve the EM reliability of micro-bump solder interconnects.

Reverse polarity effect and cross-solder interaction in Cu/Sn–9Zn/Ni interconnect during liquid–solid electromigration

The diffusion behavior of Zn atoms and Cu–Ni cross-solder interaction in Cu/Sn–9Zn/Ni interconnects during liquid–solid electromigration were investigated under a current density of 5.0 × 103 A/cm2 at 230 °C. Under the combined effect of chemical potential gradient and electron wind, Zn atoms with positive effective charge number would directionally diffuse toward the Cu interface under both flowing directions of electrons. When electrons flowed from Cu substrate to Ni substrate, EM significantly enhanced the diffusion of Cu atoms to the opposite Ni interface, resulting in the formation of interfacial Cu5Zn8; while no Ni atoms diffused to the opposite Cu interface. When electrons flowed from Ni substrate to Cu substrate, only a small amount of Cu atoms diffused to the opposite Ni interface, resulting in the formation of a thin interfacial (NiCu)3(SnZn)4 (containing 3 wt% Cu); EM significantly accelerated the diffusion of Ni atoms to the Cu interface, resulting in the formation of a large amount of (NiCu)3(SnZn)4 at the Cu interface. Even under downwind diffusion, no apparent consumption of Cu substrate was observed due to the formation of a thick and dense Cu5Zn8 layer at the Cu interface. It is more damaging with electrons flowing from Ni to Cu than that from Cu to Ni.

Influence of Cation Substitution and Activator Site Exchange on the Photoluminescence Properties of Eu3+-Doped Quaternary Pyrochlore Oxides

Stannate-based pyrochlore-type red phosphors CaGd(1-x)SnNbO7:xEu(3+), Ca(1-y)Sr(y)Gd(1-x)SnNbO7:xEu(3+), and Ca(0.8-x)Sr0.2GdSnNbO(7+δ): xEu(3+) were prepared via conventional solid-state method. Influence of cation substitution and activator site control on the photoluminescence properties of these phosphors are elucidated using powder X-ray diffraction, Rietveld analysis, Raman spectrum analysis, and photoluminescence excitation and emission spectra. The Eu(3+) luminescence in quaternary pyrochlore lattice exemplifies as a very good structural probe for the detection of short-range disorder in the lattice, which otherwise is not detected by normal powder X-ray diffraction technique. The Eu(3+) emission due to magnetic dipole transition ((5)D0-(7)F1 MD) is modified with the increase in europium concentration in the quaternary pyrochlore red phosphors. (5)D0-(7)F1 MD transition splitting is not observable for low Eu(3+) doping because of the short-range disorder in the pyrochlore lattice. Appearance of narrow peaks in Raman spectra confirms that short-range disorder in the crystal lattice disappears with progressive europium doping. By using Sr as a network modifier ion in place of Ca we were able to increase the f-f transition intensities and europium quenching concentration. The influence of effective positive charge of the central Eu(3+) ions when it replaces a metal ion having lower oxidation state such as Ca(2+) was also investigated. The relative intensities of A1g (∼500 cm(-1)) and F2g (∼330 cm(-1)) Raman vibrational modes get inverted when Eu(3+) ions replaces Ca(2+) ions instead of Gd(3+) as trivalent europium ions can attract the electron cloud of oxygen ions strongly in comparison with divalent calcium ions. The influence of positive charge effect of Eu(3+) in Ca0.7Sr0.2GdSnNbO7+δ:0.1Eu(3+) phosphor is greatly strengthened the charge transfer band and (7)F0-(5)L6 transition intensities than that of the Ca0.8Sr0.2Gd0.9SnNbO7:0.1Eu(3+) phosphor. Our results suggest that the photoluminescence properties can be enhanced by simple compositional adjustments in the quaternary pyrochlore-type red phosphors.

Luminescence and other spectroscopic properties of purple and green Cr-clinochlore

For the first time ever, the luminescence spectra of Cr3+ centers in two chlorite crystals are presented. Chromium ions occupy the strong crystal-field site M4 in the brucite sheet and the intermediate crystal-field site in the inner octahedral sheet for purple and green chlorite, respectively. We discuss the influence of an effective positive charge on the Cr3+ ion and an effective negative charge of ligands on the differences in the values of the Dq and B parameters. It is concluded that the presence of Fe2+ ions and other point defects, as well as concentration quenching, causes the very short luminescence lifetimes of chromium ions.

Effects of a Delocalizable Cation on the Headgroup of Gemini Lipids on the Lipoplex-Type Nanoaggregates Directly Formed from Plasmid DNA

Lipoplex-type nanoaggregates prepared from pEGFP-C3 plasmid DNA (pDNA) and mixed liposomes, with a gemini cationic lipid (CL) [1,2-bis(hexadecyl imidazolium) alkanes], referred as (C16Im)2Cn (where Cn is the alkane spacer length, n = 2, 3, 5, or 12, between the imidazolium heads) and DOPE zwitterionic lipid, have been analyzed by zeta potential, gel electrophoresis, SAXS, cryo-TEM, fluorescence anisotropy, transfection efficiency, fluorescence confocal microscopy, and cell viability/cytotoxicity experiments to establish a structure-biological activity relationship. The study, carried out at several mixed liposome compositions, α, and effective charge ratios, ρeff, of the lipoplex, demonstrates that the transfection of pDNA using CLs initially requires the determination of the effective charge of both. The electrochemical study confirms that CLs with a delocalizable positive charge in their headgroups yield an effective positive charge that is 90% of their expected nominal one, while pDNA is compacted yielding an effective negative charge which is only 10-25% than that of the linear DNA. SAXS diffractograms show that lipoplexes formed by CLs with shorter spacer (n = 2, 3, or 5) present three lamellar structures, two of them in coexistence, while those formed by CL with longest spacer (n = 12) present two additional inverted hexagonal structures. Cryo-TEM micrographs show nanoaggregates with two multilamellar structures, a cluster-type (at low α value) and a fingerprint-type, that coexist with the cluster-type at moderate α composition. The optimized transfection efficiency (TE) of pDNA, in HEK293T, HeLa, and H1299 cells was higher using lipoplexes containing gemini CLs with shorter spacers at low α value. Each lipid formulation did not show any significant levels of toxicity, the reported lipoplexes being adequate DNA vectors for gene therapy and considerably better than both Lipofectamine 2000 and CLs of the 1,2-bis(hexadecyl ammnoniun) alkane series, recently reported.