Investigation on the interactions of silymarin to bovine serum albumin and lysozyme by fluorescence and absorbance

The interactions of silymarin with bovine serum albumin (BSA) and lysozyme (LYS) were investigated in physiological buffer (pH = 7.4) by fluorescence spectroscopy and UV–vis absorption spectroscopy. The mechanism study indicated that silymarin could strongly quench the intrinsic fluorescence of BSA and LYS through static quenching procedures. At 291 K, the values of the binding constant K_A were 4.20×10⁴ and 4.71×10⁴ L mol^?1 for silymarin–BSA and silymarin–LYS, respectively. Using thermodynamic equations, the conclusion that hydrophobic and electrostatic forces played an important role in stabilizing complex of silymarin–BSA or silymarin–LYS was obtained. The effects of Cu²⁺, Mg²⁺, Ca²⁺, Fe²⁺, and Fe³⁺ on the binding were also studied at 291 K. According to Förster’s nonradiative energy transfer theory, the distances r₀ between donor and acceptor were calculated to be 3.36 and 2.71 nm for silymarin–BSA and silymarin–LYS, respectively. Synchronous fluorescence spectra showed that the conformation of BSA and LYS were changed by silymarin.     

Spectroscopic studies on the interaction of bovine serum albumin with ginkgolic acid: Binding characteristics and structural analysis

The interaction between ginkgolic acid (GA, C15:0) and bovine serum albumin (BSA) is investigated by several spectroscopic methodologies. At first, the binding characteristics of GA and BSA are determined by fluorescence emission spectra. It is showed that GA quenches the fluorescence of BSA and the static quenching constant K_LB is 11.7891×10⁴ L mol^?1 s^?1 at 297 K. GA and BSA form a 1:1 complex with a binding constant of 9.12×10⁵ L mol^?1. GA binds to the Sudlow's drug binding site II in BSA, and the binding distance between them is calculated as 1.63 nm based on the Förster theory. The thermodynamic parameters indicate that the interaction between BSA and GA is driven mainly by hydrophobic forces. On the other hand, structural analysis indicates that GA binding results in an increased hydrophobicity around the tryptophan residues of BSA as revealed by the synchronous fluorescence spectra, and a decrease in α-helix as revealed by the far-UV CD spectra. In addition, ANS, UV–vis and RLS experiments confirmed that GA binding causes a certain structural changes in BSA. These findings provide the binding information between BSA and GA, and may be helpful for pharmacokinetics and the design of dosage forms of GA.     

Interactions between 4-(2-dimethylaminoethyloxy)-N-octadecyl-1,8-naphthalimide and serum albumins: Investigation by spectroscopic approach

A novel 4-(2-dimethylaminoethyloxy)-N-octadecyl-1,8-naphthalimide (DON) has been synthesized as a spectrofluorimetric probe for the determination of proteins. Photophysics of DON in different solvents has been delineated in this paper. Progressive redshift with polarity of solvents in emission and absorption spectra hints at intramolecular charge transfer. The interactions of DON with serum albumins (i.e., human serum albumin (HSA) and bovine serum albumin (BSA)) were studied by fluorescence and absorption spectroscopy. Fluorescence data revealed that the quenching of HSA/BSA by DON were static quenching and the DON–HSA/BSA complexes were formed. The binding constant (K_b) for HSA and was found to be 8.44×10^?4 and 60.26×10^?4 M^?1 and the number of binding sites (n) were 1.00 and 1.40, respectively. The thermodynamic parameters, ΔH and ΔS, for the DON–HSA system was calculated to be ?14.83 kJ mol^?1 and 23.61 J mol^?1 K^?1, indicating the hydrogen bonds and hydrophobic interactions were the dominant intermolecular force. ΔH and ΔS for the binding of DON with BSA was ?60.08 kJ mol^?1 and ?90.7441 mol^?1 K^?1, suggesting the hydrogen bonds and van der Waals force played the main role in the interaction. The results of displacement experiments showed that DON bound HSA/BSA occurred at the Trp-214 proximity, located in subdomain IIA of the serum albumin structure (the warfarin binding pocket). The effect of DON on the conformation of HSA was also analyzed by synchronous and three-dimensional fluorescence spectra. The fluorescence of DON could be quenched by HSA, based on which, a fluorometric method for the determination of microamount protein using DON in the medium of HCl?Tris buffer solution (pH=7.4) was developed. The linear range of the calibration curves was 0.1–10.0 μM for HSA, 0.1–11.2 μM for BSA and 0.2–9.7 μM for egg albumin (EA). The detection limit (3σ) for HSA was 1.12×10^?10 M, for BSA it was 0.92×10^?10 M and for EA it was 4.33×10^?10 M. The effect of metal cations on the fluorescence spectra of DON in ethanol was also investigated. The method has been applied to detect the total proteins in human serum samples and the results were in good agreement with those reported by the hospital.     

Study on the conjugation mechanism of colistin sulfate with bovine serum albumin and effect of the metal ions on the reaction

Colistin sulfate (CS) can quench the fluorescence of bovine serum albumin (BSA) in an aqueous solution at pH 7.40. The static fluorescence-quenching process between BSA and CS was confirmed and the binding constant, the number of binding sites and thermodynamic data for the interaction between BSA and CS were also obtained. Results showed that the order of magnitude of binding constant (K_a) was 10⁴, and the number of binding site (n) in the binary system was approximately equal to 1; electrostatic force played an important role on the conjugation reaction between BSA and CS. On the basis of the Förster theory of the resonance energy transfer, the binding distance (r) between CS and BSA was less than 7 nm. Comparing the quenching of protein fluorescence excited at 280 nm and 295 nm and from the site marker replacement experiments, it was shown that the primary CS binding site was located in the sub-domain IIA (site I) of BSA. Synchronous fluorescence spectra clearly revealed that the binding of CS with BSA can induce conformation changes in BSA. In addition, the effects of common metal ions on the binding constants of CS–BSA complex were also discussed. It was shown that, except Cu²⁺, the high metal ion concentrations improved the CS efficacy.     

Interactions between β-carboline alkaloids and bovine serum albumin: Investigation by spectroscopic approach

β-Carboline alkaloids are present in medicinal plants such as Peganum harmala L. that have been used as folk medicine in anticancer therapy. BSA¹ is the major soluble protein constituent of the circulatory system, and has many physiological functions including the transport of a variety of compounds. This study is the first attempt to investigate the binding of β-carboline alkaloids to BSA by using a constant protein concentration and varying drug concentrations at pH 7.2. FTIR² and UV–Vis³ spectroscopic methods were used to analyze the binding modes of β-carboline alkaloids, the binding constants and the effects of drug complexation on BSA stability and conformation. Spectroscopic evidence showed that β-carboline alkaloids bind BSA via hydrophobic interaction and van der Waals contacts along with H-bonding with the –NH groups, with overall binding constants of K_{harmine–BSA}=2.04×10⁴ M^?1, K_{tryptoline–BSA}=1.2×10⁴ M^?1, K_{harmaline–BSA}=5.04×10³ M^?1, K_{harmane–BSA}=1.41×10³ M^?1 and K_{harmalol–BSA}=1.01×10³ M^?1, assuming that there is one drug molecule per protein. The BSA secondary structure was altered with a major decrease of α-helix from 64% (free protein) to 59% (BSA–harmane), 56% (BSA–harmaline and BSA–harmine), 55% (BSA–tryptoline), 54% (BSA–harmalol) and β-sheet from 15% (free protein) to 6–8% upon β-carboline alkaloids complexation, inducing a partial protein destabilization.     

Interactions between imazethapyr and bovine serum albumin: Spectrofluorimetric study

The interaction between imazethapyr (IMA) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy. The Stern–Volmer quenching constant (K_SV) at three temperatures was evaluated in order to determine the quenching mechanism. The dependence of fluorescence quenching on viscosity was also evaluated for this purpose. The results showed that IMA quenches the fluorescence intensity of BSA through a static quenching process. The values of the binding constant for the formed BSA–IMA complex and the number of binding sites were found to be 1.51×10⁵ M^?1 and 0.77, respectively, at room temperature. Based on the calculated thermodynamic parameters, the forces that dominate the binding process are hydrogen bonds and van der Waals forces, and the binding process is spontaneous and exothermic. The quenching of protein fluorescence by iodide ion was used to probe the accessibility of tryptophan residues in BSA and the change in accessibility induced by the presence of IMA. According to the obtained results, the BSA–IMA complex is formed in the site where the Trp-134 is located, causing it to become less exposed to the solvent.     

Study of the interaction between tosufloxacin tosylate and bovine serum albumin by multi-spectroscopic methods

The interaction of tosufloxacin tosylate (TSFX) and bovine serum albumin (BSA) was studied by fluorescence spectroscopy, UV–vis spectroscopy and FT-IR spectroscopy. The results indicated that the intrinsic fluorescence of BSA was quenched by TSFX through a static quenching mechanism, and the effective binding constants (K_a) were obtained by means of the modified Stern–Volmer equation. Thermodynamic parameters showed that electrostatic interaction was mostly responsible for the binding of TSFX to BSA. The binding distance (r) between TSFX and Trp-212 was determined to be 3.90 nm according to Föster non-radiative energy transfer theory. BSA had a single class of binding site at Sudlow' site I in subdomain IIA for TSFX. The effects of TSFX on the conformation of BSA were analyzed by synchronous fluorescence spectra and three-dimensional fluorescence spectra, and the results exhibited that the hydrophobicity of tryptophan microenvironment was decreased. In FT-IR spectra, Fourier self-deconvolution, secondary derivative and the curve-fitting process were carried out to obtain the components of BSA secondary structure at 298 K and 310 K. The full basic data indicated that the presence of TSFX resulted in α-helix and β-sheet changing into β-turn and random, which displayed that TSFX induced the unfolding of the polypeptides of BSA.     

Spectral characteristics and fluorescence quenching of N,N′-bis(4-pyridyl)-3,4:9,10-perylenebis(dicarboximide) (BPPD)

The photophysical properties such as electronic absorption, molar absorptivity, emission spectra, fluorescence quantum yield and fluorescence lifetime of N,N′-bis(4-pyridyl)-3,4:9,10-perylene bis(dicarboximide) (BPPD) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity, while the fluorescence quantum yield (?_f) is solvent dependent. The ground state geometry has been computed by using density functional theory (DFT), the transition from HOMO to LUMO from perylene core with maximum absorption at 512 nm and HOMO–LUMO energy difference equal 2.53 eV. BPPD dye undergoes molecular aggregation to dimmer or higher aggregates in dimethyl sulfoxide (DMSO). Crystalline solids of BPPD gives excimer-like emission at 676 nm. The fluorescence quenching of BPPD is also studied using hydrated ferric oxide nanoparticle (FeOOH), and the Stern–Volmer rate constants (K_sv) were calculated as 8×10⁶ and 9.2×10⁶ M^?1 in ethanol and ethylene glycol, respectively.     

Synthesis and investigations on the stability of La0.8Sr0.2CuO2.4+δ at high temperatures

For application in solid oxide fuel cells La_0.8Sr_0.2CuO_2.4+δ was synthesized and the phase evolution was characterized after quenching from different temperatures and after slow cooling. A single phase perovskite was found after quenching from 950 °C. The electrical conductivity of the La_0.8Sr_0.2CuO_2.4+δ perovskite exhibited metallic behavior reaching values of about 270 S/cm at 800 °C in air. The thermal expansion between 30 and 800 °C gave a thermal expansion coefficient of 11.1 × 10^− 6 K^− 1.At higher temperatures, the perovskite was transformed to the K₂NiF₄-type structure via an intermediate stage that can be best described as a LaSrCuO₄ phase with preferential growing of {020} lattice planes. After sintering at 1100 °C and slow cooling in the furnace a phase mixture of (La,Sr)CuO_4+δ and (La,Sr)CuO_2.4+δ perovskite was obtained. This phase mixture showed higher electrical conductivity (400 S/cm at 800 °C) and smaller thermal expansion coefficient (9.6 × 10^− 6 K^− 1) than the single phase La_0.8Sr_0.2CuO_2.4+δ perovskite.     

Analysis of Tb3+- and melittin-binding with the C-terminal domain of centrin in Euplotes octocarinatus

Centrin is a low molecular mass (20 KDa) protein that belongs to the EF-hand superfamily. In this work, the interaction between the Tb³⁺-saturated C-terminal domain of Euplotes octocarinatus centrin (Tb₂-C-EoCen) and 2-p-toluidinylnaphthalene-6-sulfonate (TNS) was investigated using difference UV–vis spectra and the fluorescence spectra methods. In 100 mM N-2-hydroxy-ethylpiperazine-N-2-ethanesulfonic acid (Hepes) at pH 7.4, with the addition of Tb₂-C-EoCen, four new peaks were observed at 265 nm, 278 nm, 317 nm and 360 nm by absorptivity compared with blank solution of TNS. At the same time, the reaction could be measured by fluorescence spectra. The fluorescence emission of TNS was shifted from 480 nm to 445 nm in the presence of Tb₂-C-EoCen. Meanwhile, its fluorescence intensity was increased markedly. The 1:1 stoichiometric ratio of C-EoCen to TNS was confirmed by fluorescence titration curves. The conditional binding constants of TNS with C-EoCen and Tb₂-C-EoCen were calculated to be log K_{(C-EoCen-TNS)}=5.32±0.04  M^?1 and log K_{(Tb2-C-EoCen-TNS)}=5.58±0.12 M^?1, respectively. In addition, the protein of Tb₂-C-EoCen binding with melittin was also studied. Based on the fluorescence titration curves, the 1:1 stoichiometric ratio of Tb₂-C-EoCen to melittin was confirmed. And the conditional binding constant of C-EoCen with melittin was calculated to be log Ka′=6.79±0.17 M^?1.     

Mangiferin binding to serum albumin is non-saturable and induces conformational changes at high concentrations

The binding interaction between mangiferin (MGF), which a natural xanthone isolated from mangoes, and bovine serum albumin (BSA) was studied with absorbance and fluorescence spectroscopy, cyclic voltammetry and molecular modeling. The data were analyzed to assess the binding mechanism, effect of pH and ionic strength, conformational changes in the protein and electrical charge transfer involved. The MGF–BSA complex exhibited positive cooperativity with a 1:1 stoichiometry (K_d=0.38 mmol L^?1) for the first binding site and a non-saturable binding at high ligand concentrations. Furthermore, the data also suggest an increase in drug bioavailability in the acidic region and relatively low ionic strength values, which are close to physiological levels. The data suggest a specific electrostatic interaction together with hydrophobic effects and H-bonding displayed in MGF binding to the BSA IIA subdomain. Synchronous fluorescence spectra indicate that there are conformational changes in the polypeptide backbone upon ligand binding. Cyclic voltammetry indicates that there is an irreversible charge transfer between MGF and BSA that is modulated by diffusion on the electrode surface, where two electrons are transferred. These results can help the knowledge of the pharmacokinetic activities of natural or chemical xanthone-based drugs.     

Spectroscopic study on the interaction of eugenol with salmon sperm DNA in vitro

Fluorescence spectra, absorption spectra, melting temperature, ionic strength effect, and viscosity experiments were described that characterize the interaction of eugenol with salmon sperm DNA in vitro. Eugenol was found to bind but weakly to DNA, with binding constants of 4.23×10³, 3.62×10³ and 2.47×10³ L mol^?1 at 18, 28 and 38 °C respectively. The Stern–Volmer plots at different temperatures suggested that the quenching type of fluorescence of eugenol by DNA was a static quenching. Both the relative viscosity and the melting temperature of DNA were increased by the addition of eugenol. The changes of ionic strength had no affect on the binding. In addition, the binding constant of eugenol with single stranded DNA (ssDNA) was larger than that of eugenol with double stranded DNA (dsDNA). These results revealed that the binding mode of eugenol to DNA was intercalative binding. The thermodynamic parameters ΔH, ΔG and ΔS were also obtained according to the Van't Hoff equations, which suggested that hydrogen bond or van der Waals force might play an important role in a binding of eugenol to DNA. Based on the theory of the Förster energy transference, the binding distance between DNA and eugenol was determined as 4.40 nm, indicating that the static fluorescence quenching of eugenol by DNA was also a non-radiation energy transfer process.     

Mixed conductivity,stability and thermomechanical properties of Ni-doped La(Ga,Mg)O3−δ

Perovskite-type LaGa_0.65Mg_0.15Ni_0.20O_3−δ exhibiting oxygen transport comparable to that in K₂NiF₄-type nickelates was characterized as a model material for ceramic membrane reactors, employing mechanical tests, dilatometry, oxygen permeability and faradaic efficiency measurements, thermogravimetry (TG), and determination of the total conductivity and Seebeck coefficient in the oxygen partial pressure range from 10^− 15 Pa to 40 kPa. Within the phase stability domain which is similar to La₂NiO_4+δ, the defect chemistry of LaGa_0.65Mg_0.15Ni_0.20O_3−δ can be adequately described by the ideal solution model with oxygen vacancies and electron holes to be the only mobile defects, assuming that Ni²⁺ may provide two energetically equivalent sites for hole location. This assumption is in agreement with the density of states, estimated from thermopower, and the coulometric titration and TG data suggesting Ni⁴⁺ formation in air at T < 1150 K. The hole conductivity prevailing under oxidizing conditions occurs via small-polaron mechanism as indicated by relatively low, temperature-activated mobility. The ionic transport increases with vacancy concentration on reducing p(O₂) and becomes dominant at oxygen pressures below 10^− 7–10^− 5 Pa. The average thermal expansion coefficients in air are 11.9 × 10^− 6 and 18.4 × 10^− 6 K^− 1 at 370–850 and 850–1270 K, respectively. The chemical strain of LaGa_0.65Mg_0.15Ni_0.20O_3−δ ceramics at 1073–1123 K, induced by the oxygen partial pressure variations, is substantially lower compared to perovskite ferrites. The flexural strength determined by 3-point and 4-point bending tests is 167–189 MPa at room temperature and 85–97 MPa at 773–1173 K. The mechanical properties are almost independent of temperature and oxygen pressure at p(O₂) = 1–2.1 × 10⁴ Pa and 773–1173 K.     

Hydrothermal synthesis of functionalized CdS nanoparticles and their application as fluorescence probes in the determination of uracil and thymine

A novel, sensitive, and convenient method for the determination of uracil and thymine by functionalized CdS nanoparticles (NPs) was proposed. CdS NPs were prepared by hydrothermal process and modified with thioglycollic acid (TGA) in aqueous solution. The fluorescence intensity of functionalized CdS NPs was quenched in the presence of uracil or thymine. Under optimal conditions, the relative fluorescence intensity (F₀/F) was proportional to the concentration in the range of 9.0×10^?6–1.0×10^?4 mol/L for uracil (r=0.9985) and 8.8×10^?7–1.5×10^?4 mol/L for thymine (r=0.9960). The corresponding detection limits were 9.6×10^?7 mol/L and 3.2×10^?7 mol/L, respectively. In addition, the possible quenching mechanism was also discussed.     

Ionic conductivity of brownmillerite-type calcium ferrite under oxidizing conditions

The thermogravimetric and Mössbauer spectroscopy studies showed that, at atmospheric oxygen pressure, the oxygen content in Ca₂Fe₂O₅ brownmillerite is very close to stoichiometric at 300–1270 K. The orthorhombic lattice of calcium ferrite undergoes a transition from primitive (space group Pnma) to body-centered (I2mb) at 950–1000 K, which is accompanied with decreasing thermal expansion coefficient (TEC) and increasing activation energy for the total conductivity, predominantly p-type electronic. The steady-state oxygen permeation through dense Ca₂Fe₂O₅ ceramics is limited by the bulk ionic conduction. The ion transference numbers in air vary in the range 0.002–0.007 at 1123–1273 K, increasing with temperature. Analysis of stereological factors, which may affect oxygen diffusivity, suggests a dominant role of the ion jumps along octahedral and, possibly, tetrahedral layers of the brownmillerite structure. The ionic conductivity of calcium ferrite is higher than that of Ca₂FeAlO_5+δ, but lower compared to the oxygen-deficient perovskite phases based on SrFeO_3−δ where the diffusion pathways form a three-dimensional network. The average TECs of Ca₂Fe₂O₅ ceramics, calculated from dilatometric data in air, are 13.1 × 10^− 6 K^− 1 at 370–950 K and 11.3 × 10^− 6 K^− 1 at 970–1270 K.     

Interaction of the flavonoid hesperidin with bovine serum albumin: A fluorescence quenching study

The interaction between the flavonoid hesperidin and bovine serum albumin (BSA) was investigated by fluorescence and UV/Vis absorption spectroscopy. The results revealed that hesperidin caused the fluorescence quenching of BSA through a static quenching procedure. The hydrophobic and electrostatic interactions play a major role in stabilizing the complex. The binding site number n, and apparent binding constant K_A, corresponding thermodynamic parameters ΔG^o, ΔH^o, ΔS^o at different temperatures were calculated. The distance r between donor (BSA) and acceptor (hesperidin) was obtained according to fluorescence resonance energy transfer. The effect of Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, and Mn²⁺ on the binding constants between hesperidin and BSA were studied. The effect of hesperidin on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy and UV/Vis absorption spectroscopy.     

Spectroscopic study of interaction of styrylcyanine dye Sbt and its derivatives with bovine serum albumin

The spectral-fluorescent characteristics of styrylcyanine dye Sbt ((E)-2-(4-(dimethylamino) styryl)-3-methylbenzo[d]thiazol-3-ium iodide) and homodimers, dyes conjugated with two chromophores in aqueous solutions without and in the presence of bovine serum albumin (BSA), are studied. It is established that in the presence of BSA for dyes Dbt-5 and Dbt-10, an increase of the absorptivity, a slight broadening and the emergence of new band on the short wavelength range with λ_max=410 nm is observed; also hypsochromic shift of the absorption and fluorescence at 30 nm and 7 nm, respectively for the dye D-183 is observed. The intensity of the fluorescence emission fundamental band in all the studied dyes in the presence of BSA increases by 3.5 to 55 times. The binding constant (K) and number of binding sites (N) of studied dyes with BSA are determined. The dependence of the binding constants with BSA from the dipole moment of dye molecules is identified, which shows that in addition to the electrostatic attraction forces between molecules of styrylcyanine dyes with BSA, hydrophobic interactions are essential. It is shown that the aggregation of dye affects the processes of interaction of the dyes with the BSA.     

Photoluminescence properties of a new Eu2+-activated CaLaGa3S7 yellowish-green phosphor for white LED applications

A thiogallate chalcogenide phosphor CaLaGa₃S₇:Eu²⁺ was synthesized by a solid-state reaction at 950 °C in a H₂S atmosphere. The photoluminescence excitation,emission spectra, concentration quenching, fluorescence lifetime, and thermal quenching process of the phosphor were investigated in detail. It was found that the synthesized phosphor emitted intense and broadband yellowish-green light with a peak at 554 nm. Thus, the proposed phosphor is suitable for the development of blue or near UV LED. The critical dopant concentration of Eu²⁺ (R_c=15 Å) per unit formula was found to be 0.15 mol. At room temperature, the fluorescence lifetime of Eu²⁺ in CaLaGa₃S₇ was found to be 0.216 μs. The activation energy for thermal quenching was 0.29 eV. The chromaticity coordinates of our phosphor is very close in color to Y₃Al₅O₁₂:Ce³⁺. Therefore, CaLaGa₃S₇:Eu²⁺ can be a good alternative as a yellowish-green phosphor and can be used for white light generation in phosphor-converted LEDs.     

Study on the luminescence behavior of lanthanide ions using luminol as probe

Using luminol as the probe, the luminescence behavior of trivalent lanthanide ions (Ln³⁺=La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺ and Lu³⁺) in aqueous solution was first investigated by fluorescence, and the sensitivity enhanced by 3–5 orders of magnitude compared with the Ln³⁺ intrinsic fluorescence. It was found that Ln³⁺ with luminol could form a 1:1 association complex which remarkably enhanced the fluorescence signal of luminol. The increment of fluorescence intensity was proportional to the concentration of Ln³⁺ in the range of 1.0–70.0 nmol L^?1, and the linear correlation equation, ΔI_F=AC_Ln+B, was given. The relationships of A (defined as sensitivity factor) with some physical parameters (atomic number Z, ionic radius γ_±, standard redox potential E^o and hydration enthalpy ΔH_hyd) were discussed. The good symmetry of A vs. Z plot for light lanthanides (LLG) and the heavy lanthanides (HLG) and linear relations of A with Z, γ_±, E^o and ΔH_hyd should originate in the special features of Ln³⁺ electronic configurations [Xe]4fⁿ (n=0–14). Using the proposed model of Ln³⁺–luminol interaction, lg[ΔI_F/(I_Fo–ΔI_F)]=rlg[Ln]+lg k, the association constant k was obtained over the range of 1.95×10⁶–2.63×10⁷ L mol^?1.     

White-light generation through Ce3+/Mn2+-codoped and Eu2+-doped Ba1.2Ca0.8SiO4 T-phase phosphors

Hexagonal Ba_1.20Ca_0.8?2x?ySiO₄:xCe³⁺,xLi⁺,yMn²⁺ phosphors exhibit two emission bands peaking near 400 and 600 nm from the allowed f–d transition of Ce³⁺ ions and the forbidden ⁴T₁–⁶A₁ transition of Mn²⁺ ions, respectively. The strong interaction between Ce³⁺/Mn²⁺ ions is investigated in terms of energy transfer, crystal field effect, and microstructure by varying their concentrations. They show a higher quenching temperature of 250 °C than that of a commercially used (Ba,Sr)₂SiO₄:Eu²⁺ phosphor (150 °C). Finally, mixtures of these phosphors with green-emissive Ba_1.20Ca_0.70SiO₄:0.10Eu²⁺ are tested and yielded correlated color temperatures from 3500 to 7000 K, and color rendering indices up to 95%.