Zinc binding promotes greater hydrophobicity in Alzheimer's Aβ42 peptide than copper binding: Molecular dynamics and solvation thermodynamics studies

The aggregation of Aβ42 peptides is considered as one of the main causes for the development of Alzheimer's disease. In this context, Zn²⁺ and Cu²⁺ play a significant role in regulating the aggregation mechanism, due to changes in the structural and the solvation free energy of Aβ42. In practice, experimental studies are not able to determine the latter properties, since the Aβ42–Zn²⁺ and Aβ42–Cu²⁺ peptide complexes are intrinsically disordered, exhibiting rapid conformational changes in the aqueous environment. Here, we investigate atomic structural variations and the solvation thermodynamics of Aβ42_, Aβ42–Cu²⁺, and Aβ42–Zn²⁺ systems in explicit solvent (water) by using quantum chemical structures as templates for a metal binding site and combining extensive all-atom molecular dynamics (MD) simulations with a thorough solvation thermodynamic analysis. Our results show that the zinc and copper coordination results in a significant decrease of the solvation free energy in the C-terminal region (Met35-Val40), which in turn leads to a higher structural disorder. In contrast, the β-sheet formation at the same C-terminal region indicates a higher solvation free energy in the case of Aβ42_. The solvation free energy of Aβ42 increases upon Zn²⁺ binding, due to the higher tendency of forming the β-sheet structure at the Leu17-Ala42 residues, in contrast to the case of binding with Cu²⁺. Finally, we find the hydrophobicity of Aβ42–Zn²⁺ in water is greater than in the case of Aβ42–Cu²⁺.     

Enhanced orange–red emission of SrZn2(PO4)2:Sm3+ via codoping Eu2+ as a sensitizer

A series of Eu²⁺‐, Sm³⁺‐ and Eu²⁺/Sm³⁺‐doped SrZn₂(PO₄)₂ samples were synthesized using a solid‐state reaction. SrZn₂(PO₄)₂:Eu²⁺ presented a broad emission band due to 4f⁶5d–4f⁷ transition of the Eu²⁺ ion. The spectra of SrZn₂(PO₄)₂:Sm sintered in air and H₂/N₂ were identical in every aspect, except for a very small difference in intensity. A Eu²⁺–Sm³⁺ energy transfer scheme was proposed to realize the sensitization of Sm³⁺ ion emission by Eu²⁺ ions, and UV‐convertible Sm³⁺‐activated red phosphor was obtained in SrZn₂(PO₄)₂:Eu²⁺, Sm³⁺. Copyright © 2015 John Wiley & Sons, Ltd.     

Photoluminescence enhancement in Na3SO4Cl:X (X = Ce3+, Eu3+ or Dy3+) material

The compound Na₃SO₄Cl X (X = Ce³⁺, Eu³⁺ or Dy³⁺) prepared by the wet chemical method was studied for its photoluminescence (PL) and energy transfer characteristics. The PL from Na₃SO₄Cl:Ce³⁺ shows strong emission at 322 nm at an excitation of 272 nm. Therefore, an efficient Ce³⁺ → Dy³⁺, Eu²⁺ → Dy³⁺ and Eu²⁺ → Eu³⁺ energy transfer had taken place in this host. The Dy³⁺ emission caused by Ce³⁺ → Dy³⁺ energy transfer under ultraviolet (UV) wavelengths peaked at around 477 nm and 572 nm due to ⁴ F_9/2 → ⁶H_15/2 and ⁶H_13/2 transitions with yellow–orange emission in the Na₃SO₄Cl lattice. An intense Dy³⁺ emission was observed at 482 and 576 nm caused by the Eu²⁺ → Dy³⁺ energy transfer process and due to ⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2 transitions respectively. The Eu³⁺ blue to red light emission caused by the Eu²⁺ → Eu³⁺ energy transfer peaked at 593 nm and 617 nm due to ⁵D₀ → ⁵D₃ transitions. The presence of trivalent Eu in Na₃SO₄Cl suggested the presence of Eu³⁺ in the host compound that occupied two different lattice sites and that peaked at 593 and 617 nm due to ⁵D₀ → ⁷ F₁ and ⁵D₀ → ⁷ F₂ transitions respectively. The trivalent europium ion is very useful for studying the nature of metal coordination in various systems due to its non‐degenerate emitting ⁵D₀ state. The present paper discusses the photoluminescence characteristics of Eu²⁺ → Dy³⁺ and Eu²⁺ → Eu³⁺ energy transfer. This compound may be useful as a lamp phosphor. Copyright © 2015 John Wiley & Sons, Ltd.     

Research of the entry of rare earth elements Eu3+ and La3+ into plant cell

Whether rare earth elements can enter into plant cells remains controversial. This article discusses the ultracellular structural localization of lanthanum (La³⁺) and europium (Eu³⁺) in the intact plant cells fed by rare earth elements Eu³⁺ and La³⁺. Eu-TTA fluorescence analysis of the plasmalemma, cytoplast, and mitochondria showed that Eu³⁺ fluorescence intensities in such structures significantly increased. Eu³⁺ can directly enter or be carried by the artificial ion carrier A23187 into plant cells through the calcium ion (Ca²⁺) channel and then partially resume the synthesis of amaranthin in the Amaranthus caudatus growing in the dark. Locations of rare earth elements La³⁺ and Eu³⁺ in all kinds of components of cytoplasmatic organelles were determined with transmission electron microscope, scanning electron microscope, and energy-dispersive X-ray microanalysis. The results of energy-dispersive X-ray microanalysis indicated that Eu³⁺ and La³⁺ can be absorbed into plant cells and bind to the membranes of protoplasm, chloroplast, mitochondrion, cytoplast, and karyon. These results provide experimental evidence that rare earth elements can be absorbed into plant cells, which would be the basis for interpreting physiological and biochemical effects of rare earth elements on plant cells.     

Synthesis and luminescence study of Eu3+‐doped SrYAl3O7 phosphor

Rare‐earth ions play an important role in eco‐friendly solid‐state lighting for the lighting industry. In the present study we were interested in Eu³⁺ ion‐doped inorganic phosphors for near ultraviolet (UV) excited light‐emitting diode (LED) applications. Eu³⁺ ion‐activated SrYAl₃O₇ phosphors were prepared using a solution combustion route at 550°C. Photoluminescence characterization of SrYAl₃O₇:Eu³⁺ phosphors showed a 612 nm emission peak in the red region of the spectrum due to the ⁵D₀→⁷F₂ transition of Eu³⁺ ions under excitation at 395 nm in the near‐UV region and at the 466 nm blue excitation wavelength. These red and blue emissions are supported for white light generation for LED lighting. Structure, bonding between each element of the sample and morphology of the sample were analysed using X‐ray diffraction (XRD) and scanning electron microscopy (SEM), which showed that the samples were crystallized in a well known structure. The phosphor was irradiated with a ⁶⁰Co‐γ (gamma) source at a dose rate of 7.2 kGy/h. Thermoluminescence (TL) studies of these Eu³⁺‐doped SrYAl₃O₇ phosphors were performed using a Nucleonix TL 1009I TL reader. Trapping parameters of this phosphor such as activation energy (E), order of kinetics (b) and frequency factor (s) were calculated using Chen's peak shape method, the initial rise method and Ilich's method.     

White light emission and energy transfer of LaMgAl11O19:Eu3+, Tb3+ phosphors

White-light-tunable LaMgAl₁₁O₁₉:x%Tb³⁺, y%Eu³⁺ series phosphors were prepared using the gel-combustion method. The structure and luminescence properties were studied, and the energy transfer of Eu³⁺ and Tb³⁺ in the LaMgAl₁₁O₁₉ system was also discussed. The results showed that the LaMgAl₁₁O₁₉ matrix exhibited strong emission in the blue-light region under the excitation of ultraviolet light, which resulted in conditions suitable for the preparation of white-light-tunable phosphors. The emission spectra of LaMgAl₁₁O₁₉:2%Tb³⁺, y%Eu³⁺ (y = 2%–9%) series phosphors were obtained through optimization experiments. It could be seen from the CIE diagram that by adjusting the doping quantities of Eu³⁺ and Tb³⁺ in the LaMgAl₁₁O₁₉ host, multicolor luminescence and white light emission in a single host could be achieved. By calculating the energy transfer efficiency and critical distance between Eu³⁺ and Tb³⁺ series phosphors, the mechanism of energy transfer between Tb³⁺ and Eu³⁺ was found to be the interaction between electric quadruples.     

Eu3+–Eu2+‐doped xAl2O3–ySiO2 and xAl2O3–zMgO composites phosphors

In this paper, the Eu³⁺–Eu²⁺ (4%, molar ratio)‐doped xAl₂O₃–ySiO₂ (x = 0–2.5, y = 1–5) and xAl₂O₃–zMgO (x = 0–1.5, z = 0–3) composites phosphors with different Al₂O₃ to SiO₂ (A/S) and Al₂O₃ to MgO (A/M) ratios were prepared using a high‐temperature solid‐state reaction under air atmosphere. The effects of the A/S and A/M on luminescence properties, crystal structure, electron spin resonance, and Commission Internationale de l’Eclairage chromaticity coordinates of the samples were systematically analyzed. These results indicated that the different A/S and A/M ratios in the matrix effectively affected the crystal phase, degrees of self‐reduction of Eu³⁺, and led the relative emission intensity of Eu²⁺/Eu³⁺ to change and adjust.     

ZnWO4:Eu3+ phosphor with intense blue LED excitation: photoluminescence and electron density distribution analysis

A high intensity 464 nm excitable ZnWO₄:Eu³⁺ red‐emitting phosphor for warm white lighting applications was prepared using a solid‐state reaction method by varying the dopant Eu³⁺ concentration. Crystalline purity and phase identification was confirmed and revealed using powder X‐ray diffraction and Rietveld refinement analysis. The surface morphology of Zn_1‐xEu_xWO₄ (x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05) was examined using scanning electron microscopy (SEM) techniques. From SEM analysis, the ZnWO₄:Eu³⁺ phosphor prepared at 1–3% molar Eu³⁺ concentrations exhibited a small pebble‐like morphology with a smooth surface. On increasing the molar concentration of Eu³⁺ to >3%, the pebble stone morphology disappeared and a large, smooth irregular polygon‐shaped granular‐like morphology was obtained. Of the higher mol% Eu³⁺, the 4% Eu³⁺‐doped ZnWO₄ showed the best photoluminescence properties with high intensity and sharp excitation at 395 and 464 nm, followed by red emission centred at 615 nm with excellent CIE coordinates (x = 0.58 and y = 0.41) in the core red region. Elemental composition and chemical state analysis were carried out for the 4% Eu³⁺‐doped ZnWO₄ phosphor using X‐ray photoelectron spectroscopy and energy dispersive X‐ray spectroscopy studies. Based on all the above analyses, the Eu³⁺‐doped ZnWO₄ phosphor was found to be a very efficient red‐emitting phosphor under near‐UV light as well as under visible light excitation and could be used for white LED and field emissive displays applications.     

Luminescence study of Eu3+doped Li6Y(BO3)3 phosphor for solid‐state lighting

In this study, Li₆Y_1–xEu_x(BO₃)₃ phosphor was successfully synthesized using a modified solid‐state diffusion method. The Eu³⁺ ion concentration was varied at 0.05, 0.1, 0.2, 0.5 and 1 mol%. The phosphor was characterized for phase purity, morphology, luminescent properties and molecular transmission at room temperature. The XRD pattern suggests a result closely matching the standard JCPDS file (#80‐0843). The emission and excitation spectra were followed to discover the luminescence traits. The excitation spectra indicate that the current phosphor can be efficiently excited at 395 nm and at 466 nm (blue light) to give emission at 595 and 614 nm due to the ⁵D₀ → ⁷F_j transition of Eu³⁺ ions. Concentration quenching was observed at 0.5 mol% Eu³⁺ in the Li₆Y_1–xEu_x(BO₃)₃ host lattice. Strong red emission with CIE chromaticity coordinates of phosphor is x = 0.63 and y = 0.36 achieved with dominant red emission at 614 nm the ⁵D₀ → ⁷ F₂ electric dipole transition of Eu³⁺ ions. The novel Li₆Y_1–xEu_x(BO₃)₃ phosphor may be a suitable red‐emitting component for solid‐state lighting using double‐excited wavelengths, i.e. near‐UV at 395 nm and blue light at 466 nm. Copyright © 2015 John Wiley & Sons, Ltd.     

Density functional theoretical study on the preferential selectivity of macrocyclic dicyclohexano-18-crown-6 for Sr+2 ion over Th+4 ion during extraction from an aqueous phase to organic phases with different dielectric constants

The preferential selectivity of dicyclohexano-18-crown-6 (DCH18C6) for bivalent Sr⁺² ion over tetravalent Th⁺⁴ ion was investigated using generalized gradient approximated (GGA) BP86 and the hybrid B3LYP density functional, employing split valence plus polarization (SV(P)) and triple-zeta valence plus polarization (TZVP) basis sets in conjunction with the COSMO (conductor-like screening model) solvation approach. The calculated theoretical selectivity of DCH18C6 for Sr⁺² ion over Th⁺⁴ ion was found to be in accord with the selectivity for Sr⁺² ion over Th⁺⁴ ion observed when performing liquid–liquid extraction experiments in different organic solvents. While 1:1(M:L) stoichiometric complexation reactions can be used to predict the preferential selectivity of Sr²⁺ ion over Th⁴⁺ ion, the results obtained are not consistent with the experimental results observed upon increasing the dielectric constant of the solvent. The calculated theoretical gas-phase data for the free energy of complexation, ?G, fail to explain the selectivity for Sr⁺² ion over Th⁺⁴ ion. However, when 1:2 (M:L) stoichiometric complexation reactions (reported in previous X-ray crystallography studies) are considered, correct and consistent results for the selectivity for Sr⁺² ion over a wide range of dielectric constants are predicted. The distribution constant for Sr²⁺ and Th⁴⁺ ions was found to gradually increase with increasing dielectric constant of the organic solvent, and was found to be highest in nitrobenzene. The selectivity data calculated from ??G _ext are in excellent agreement with the results obtained from solvent extraction experiments.

The structure and luminescence properties of Mn2+/Eu2+/Er3+‐doped MgO‐Ga2O3‐SiO2 glasses and glass‐ceramics

The MgO–Ga₂O₃–SiO₂ glasses and glass‐ceramics samples doped with Eu²⁺/Mn²⁺/Er³⁺ and heated in reductive atmosphere were prepared by the sol–gel method. The structure, morphology and the luminescence properties were studied using X‐ray diffraction, high‐resolution transmission electron microscope, fluorescence spectra, and up‐conversion emission. The luminescence characteristics of doped ions could be influenced by temperature and matrix component. The characteristic emission of Mn²⁺, Eu²⁺ and Er³⁺ were seen and the energy transfer efficiency from Eu²⁺ to Mn²⁺ was enhanced as Mn²⁺ concentration was increased. In addition, the two‐photon process was determined for the Er³⁺‐doped samples.     

155Eu3+ as a probe of metal ion and cationic drug binding sites on native and heat-denatured DNA

A flow-dialysis apparatus suitable for the study of high affinity metal ion binding sites in macromolecules has been utilized to study ¹⁵⁵Eu³⁺ exchange processes, as a function of pH, in both ‘native’ and ‘heat-denatured’ DNA. ‘Free exchange’ of ¹⁵⁵Eu³⁺ was found to occur at a significantly faster rate at pH = 7.0 than at pH = 6.0 for both forms of DNA; while non-radioactive Eu³⁺-induced ‘displacement’ of bound ¹⁵⁵Eu³⁺ occurred at a significantly faster rate at pH = 6.0 than at pH = 7.0 for both species of DNA. These results are consistent with a greater ‘entropic’ driving force for metal ion:DNA complexation at the lower pH value. The effect of ethidium bromide on ¹⁵⁵Eu³⁺ exchange was also examined as a function of pH. The intercalating agent was found to accelerate ¹⁵⁵Eu³⁺ displacement at pH = 6.0 and decelerate displacement at pH = 7.0. All three sets of experiments (i.e., free- exchange of bound ¹⁵⁵Eu³⁺, Eu³⁺-induced displacement of bound ¹⁵⁵Eu³⁺ and ethidium ion-induced displacement of bound ¹⁵⁵Eu³⁺) indicate that the ¹⁵⁵Eu³⁺ ion can serve as a useful probe of metal ion and drug binding sites in nucleic acid polymers, and constitutes a particularly sensitive probe at pH = 6.0.     

Effect of Dy3+ or Eu2+ co‐activator on a BaCa(SO4)2:Ce3+ mixed alkaline earth sulfate phosphor

The individual emission and energy transfer between Ce³⁺ and Eu²⁺ or Dy³⁺ in BaCa(SO₄)₂ mixed alkaline earth sulfate phosphor prepared using a co‐precipitation method is described. The phosphor was characterized by X‐ray diffraction (XRD) and photoluminescence (PL) studies and doped by Ce;Eu and Dy rare earths. All phosphors showed excellent blue–orange emission on excitation with UV light. PL measurements reveal that the emission intensity of Eu²⁺ or Dy³⁺ dopants is greater than when they are co‐doped with Ce³⁺. An efficient Ce³⁺ → Eu²⁺ [²T_2g(4f⁶5d) → ⁸S_7/2(4f₇)] and Ce³⁺ → Dy³⁺ (⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2) energy transfer takes place in the BaCa(SO₄)₂ host. A strong blue emission peak was observed at 462 nm for Eu²⁺ ions and an orange emission peak at 574 nm for Dy³⁺ ions. Hence, this phosphor may be used as a lamp phosphor. Copyright © 2015 John Wiley & Sons, Ltd.     

Spectral investigations on Eu3+,Sm3+‐doped and Sm3+/Eu3+ co‐doped potassium‐fluoro‐phosphate glass emitting intense orange‐red for lighting applications

Potassium fluoro‐phosphate (KFP) glass singly doped with different concentrations of europium (Eu³⁺) or samarium (Sm³⁺) or co‐doped (Sm³⁺/Eu³⁺) was prepared, and their luminescence spectra were investigated. The phase composition of the product was verified by X‐ray diffraction analysis. Optical transition properties of Eu³⁺ in the studied potassium phosphate glass were evaluated in the framework of the Judd–Ofelt theory. The radiative transition rates (A_R), fluorescence branching ratios (β), stimulated emission cross‐sections (σ_e) and lifetimes (τ_exp) for certain transitions or levels were evaluated. Red emission of Eu³⁺ was exhibited mainly by the ⁵D₀→⁷F₂ transition located at 612 nm. Concentration quenching and energy transfer were observed from fluorescence spectra and decay curves, respectively. It was found that the lifetimes of the ⁵D₀ level increased with increase in concentration and then decreased. By co‐doping with Sm³⁺, energy transfer from Sm³⁺ to Eu³⁺ occurred and contributed to the enhancement in emission intensity. Intense orange‐red light emission was obtained upon sensitizing with Sm³⁺ in KFP glass. This approach shows significant promise for use in reddish‐orange lighting applications. The optimized properties of the Sm³⁺/Eu³⁺ co‐doped potassium phosphate glass might be promising for optical materials.     

Luminescence in Li3Al2(PO4)3:Eu2+

A series of efficient Li₃Al₂(PO₄)₃:Eu²⁺ novel phosphors were synthesized by the facile combustion method. The effects of dopant on the luminescence behavior of Li₃Al₂(PO₄)₃ phosphor were also investigated. The phosphors were characterized by X‐ray diffraction, field emission scanning electron microscope and photoluminescence techniques. The result shows that all samples can be excited efficiently by near‐ultraviolet excitation under 310 nm. The emission was observed for Li₃Al₂(PO₄)₃:Eu²⁺ phosphor at 425 nm, which corresponded to the d → f transition. The concentration quenching of Eu²⁺ was observed in Li₃Al₂(PO₄)₃:Eu²⁺ when the Eu concentration was at 0.5 mol%. The prepared powders exhibited intense blue emission at the 425 nm owing to the Eu²⁺ ion by Hg‐free excitation at 310 nm (i.e., solid‐state lighting excitation). Consequently, the availability of such a phosphor will significantly help in the development of blue‐emitting solid‐state lighting applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Tunable luminescence and energy transfer in Ca3SiO4Cl2:Ce3+,Li+,Mn2+,Eu2+ phosphors

A series of color‐tunable Ca_{3–2x‐y‐z}SiO₄Cl₂ (CSC):xCe³⁺,xLi⁺,yMn²⁺,zEu²⁺ phosphors with low temperature phase structure was synthesized via the sol–gel method. An energy transfer process from Ce³⁺ to Mn²⁺ in CSC:0.01Ce³⁺,0.01Li⁺,yMn²⁺ (y = 0.03–0.09) and the mechanism was verified to be an electric dipole–dipole interaction. The Ce³⁺ and Mn²⁺ emission intensities were greatly enhanced by co‐doping Eu²⁺ ions into CSC:0.01Ce³⁺,0.01Li⁺,0.07Mn²⁺ phosphors due to competitive energy transfers from Eu²⁺/Ce³⁺ to Mn²⁺, and Ce³⁺ to Eu²⁺. Under 332 nm excitation, CSC:0.01Ce³⁺,0.01Li+,0.07Mn²⁺,zEu²⁺ (z = 0.0005–0.002) exhibited tunable emission colors from green to white with coexisting orange, green and violet‐blue emissions. These phosphors could have potential application in white light‐emitting diodes.     

Synthesis,PL characterizations and concentration quenching effect in Dy3+ and Eu3+ activated LiCaBO3 phosphor

LiCaBO₃:Dy³⁺/Eu³⁺ phosphors were synthesized by a solid‐state reaction. The synthesized materials were characterized using powder X‐ray diffraction pattern (XRD) for confirmation. All the structural parameters were calculated from the XRD data. Scanning electron microscopy (SEM) images showed rod‐like morphology. Photoluminescence (PL) emission spectra showed two emissions (484 and 577 nm) in Dy³⁺‐doped LiCaBO₃:Dy³⁺phosphors with the concentration quenching effect and the critical distance was calculated to be about 22.76 Å. LiCaBO₃:Eu³⁺ phosphor was effectively excited by a near‐UV light of 392 nm. The emission spectra exhibited the transition from ⁵D₀ level to ⁷F_J (J = 0–2) with main emission at 614 nm, which comes from the electrodipole transition because of the asymmetric point group. The quenching concentration of Eu³⁺ is about 0.2 mol%, and the critical distance was calculated to be about 38.93 Å. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhanced red emission from BaMoO4: Eu3+ by Bi3+ co‐doping

A series of Bi³⁺,Eu³⁺‐doped BaMoO₄ phosphors was synthesized using a hydrothermal method. The crystal structure, morphology and optical properties of the phosphors were studied using X‐ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence (PL) measurements. Three different particle morphologies were detected in the SEM observation. The energy dispersive spectroscopy (EDS) results indicated that the solubility of Bi³⁺ in spherical or rugby‐like BaMoO₄ particles was very low and the excess Bi³⁺ element was cumulated in the irregular particles. Characteristic emissions of Eu³⁺ ions (⁵D₀ → ⁷F_J; J = 0, 1, 2, 3, 4) were observed under excitation in ultraviolet (UV) light, with the most intense transition being the ⁵D₀ → ⁷F₂ transition. Energy transfer from MoO₄^2? and Bi³⁺ to Eu³⁺ can be readily achieved. Red emission intensity of Eu³⁺ was enhanced by a factor of two by co‐doping with a small amount of Bi³⁺. Optical properties as a function of Bi³⁺ content were studied and the optimum Bi³⁺ content in BaMoO₄ nanocrystals was determined to be 0.4 mol%.     

Optical properties of Eu2+/Eu3+ mixed valence phosphor Ca2SiO2F2:Eu2+/Eu3+

The Eu²⁺/Eu³⁺ mixed valence phosphor Ca₂SiO₂F₂:Eu²⁺/Eu³⁺ was prepared using a solid‐state reaction synthesis method in a CO atmosphere, and the optical properties were investigated. The spectroscopic properties revealed that Ca²⁺ ions were occupied by both Eu²⁺ and Eu³⁺ ions in Ca₂SiO₂F₂, and both ions were able to generate their characteristic emissions. A broad 5d → 4f Eu²⁺ band at ~470 nm and narrow 4f → 4f Eu³⁺ peaks upon excitation with n‐UV light were observed. The ratio between Eu²⁺ and Eu³⁺ emissions changed regularly, and the relative intensity of the red component from Eu³⁺ became systematically stronger with increasing overall Eu content. As a result, the emission color of these phosphors can be tunable from blue to pink under n‐UV light excitation.     

Interaction of Eu3+ with yeast alcohol dehydrogenase

The activity of yeast alcohol dehydrogenase is markedly enhanced by Eu³⁺ ions. At pH 7.0 two binding constants for Eu³⁺, 1.0 × 10^–2 and 2.0 × 10^–3 M, were obtained using a Scatchard plot. The presence of Zn²⁺ ions restricts the Eu³⁺-induced increase in the activity of yeast alcohol dehydrogenase. Studies on the tryptophan fluorescence of the enzyme in the absence and presence of Eu³⁺ or Zn²⁺ ions showed that Eu³⁺ affects tertiary or quaternary structures, which is consistent with its activation of the enzyme. The presence of Zn²⁺ reverses the conformational changes caused by Eu³⁺. Comparison of the effects of Eu³⁺ with Zn²⁺ for apo-yeast alcohol dehydrogenase indicates that their binding sites on the protein are different.