New Selective Fluorescent “Turn-On” Sensor for Detection of Hg2+ Based on a 1,8-Naphthalimide Schiff Base Derivative

Journal of Applied Spectroscopy - A new fluorescent “turn-on” sensor for Hg2+, N-allyl-4-(ethylenediamine-5-methylsalicylidene)-1,8-naphthalimide (HL) has been designed by combining a...     

Perylene Diimide Appended with 8-Hydroxyquinoline for Ratiometric Detection of Cu2+ Ions and Metal Displacement Driven “Turn on” Cyanide Sensing

Perylene diimide (PDI) 3 and 4 appended with 8-hydroxyquinoline derivatives have been synthesized and their photophysical and spectroscopic properties have been experimentally determined. Moreover, PDIs 3 and 4 show ratiometric behavior to detect Cu²⁺ colorimetrically with visible color change from coral red to light pink, whereas 3 and 4 show “turn-off” behavior in fluorescence with lowest limit of detection 5?×?10^?7 M. The PDI 3 could be further utilized for ratiometric CN^? detection colorimetrically and as “turn-on” sensor for CN^? detection fluorometrically with lowest limit of detection 8?×?10^?6 M. The comparison of spectroscopic properties of PDI 1-4 highlights the importance of linking 8-hydroxyquinoline units on the PDI core at bay position for achieving Cu²⁺ recognition event into ratiometric signal.

A photoemission study (XPS and UPS) of the superconductor ErBa2Cu4O8 and comparison with YBa2Cu3O7-δ(δ≈0,1)

Core level and valence band photoemission spectra of the 124 superconductor ErBa₂Cu₄O₈ are investigated using MgK , HeI, and HeII radiation and compared with photoemission spectra of orthorhombic YBa₂Cu₃O₇ and tetragonal YBa₂Cu₃O_6.2 samples. It is found that the Cu 2p _3/2 core level and the UPS valence band spectra of ErBa₂Cu₄O₈ and YBa₂Cu₃O₇ are very similar but differ significantly from those of YBa₂Cu₃O_6.2. From the resemblance between the ErBa₂Cu₄O₈ and YBa₂Cu₃O₇ spectra it follows that the electronic structures of these two compounds are closely related in spite of an additional CuO chain in the 124 phase. The differences between the YBa₂Cu₃O_6.2 spectra and the other spectra are explained by the the presence of monovalent copper at the crystallographic Cu(1) sites. The Cu 2p _3/2 lineshapes of the here studied superconductors and some Cu^II compounds are discussed.     

Lattice dynamics of the superconducting Bi2Sr2Ca(Cu,Sn)2O8−y

Phonon anomaly was observed below 140 K for the absorption area (lnA) and the isomer shift () plotted against the temperature (T) in the¹¹⁹Sn Mössbauer study of the Bi₂Sr₂Ca(Cu_0.995Sn_0.005)₂O_8–y superconductor (glass-ceramic,T _c(on)=86 K), which was prepared by heat treatment of the glassy sample. The anomaly suggests that the softening (quenching) of the lattice vibration causes the superconducting transition, as was observed in several YBa₂(Cu, Sn)₃O_7–y superconductors. Fitting of the theoretical curve for the normal phonon of the combined Debye and Einstein model to the lnA versusT and versusT plots yielded _D and _E of 240 and 140 K, respectively. These results suggest that the probe (Sn⁴⁺) was located at the interstitial site close to the Cu site, and the softening of the Cu site vibration could be detected before the superconducting transition took place. Disordered structure seems to be favorable for the detection of phonon anomaly in the Bi system.     

A comparison of the197Au Mössbauer spectra of MAu (M=K,Rb, Cs) with (2, 2, 2-crypt M) Au

Gold-197 Mössbauer spectroscopy has been used to investigate the MAu system (M=K, Kb, Cs). Of the 11 alloys RbAu and CsAu give Mössbauer spectra consistent with cubic gold environments, while (2,2,2-crypt M) Au, (M=K, Pb, Cs) all have cubic gold environments. Comparison of the isomer shifts for the crypted and uncrypted salts leads to the conclusion that in RbAu and CsAu considerable electron density is removed from the gold 5d orbitals.     

A Fe<Superscript>3+</Superscript>/Hg<Superscript>2+</Superscript>-Selective Anthracene-Based Fluorescent PET Sensor with Tridentate Ionophore of Amide/β-Amino Alcohol

A new anthracene-based fluorescent PET sensor 1 with a tridentate ionophore of amide/β-amino alcohol displays very good selectivity and sensitivity for Fe³⁺ (K _a = 1.6 × 10³ M⁻¹) and Hg²⁺ (K _a = 2.1 × 10³ M⁻¹) in CH₃CN–H₂O (3:7, v/v) with detection limit of 1 μM. More fluorescence enhancement was observed when 1 selectively detected Fe³⁺ or Hg²⁺ in CH₃CN and its detection limit was up to 0.03 μM.     

Formation of the (Bi, Pb)2Sr2Ca2Cu3O10+δphase: reaction mechanism and kinetics

In order to elucidate the formation mechanism of the Bi, Pb(2223) phase, extensive investigations have been performed by means of combined differential thermal analysis and thermo-gravimetric measurements, X-ray diffraction as well as scanning electron microscopy and energy dispersive X-ray microanalysis.Starting from co-precipitated oxalate powders, the transformations leading to the formation of the Bi, Pb(2223) phase were studied. Based on these investigations the Bi,  Pb(2223) phase formation process, involving the Bi, Pb(2212), Ca₂PbO₄and alkaline-earth cuprate phases as precursors has been separated into elemental steps. A new model for the formation mechanism of the Bi, Pb(2223) phase will be presented.The Bi, Pb(2223) phase formation kinetics has been studied using the Avrami relation for isothermal phase transformations. The analysis of the Bi, Pb(2223) phase evolution revealed a marked change of the Avrami exponent during the course of the Bi, Pb(2223) phase formation after about 12 hours sintering at 857 ° C.The activation energy for the formation of the Bi, Pb(2223) phase has been determined under various experimental conditions. The nominal composition of the precursor powders, the temperature at which they were calcined as well as the size of their constituents were found to have a significant influence on the value of the activation energy.     

Evolution of incommensurate superstructure and electronic structure with Pb substitution in(Bi_(2-x)Pb_x)Sr_2CaCu_2O_(8+δ) superconductors

High-quality Bi_(2-x)Pb_xSr_2 CaCu_2O_(8+δ)(Bi2212) single crystals have been successfully grown by the traveling solvent floating zone technique with a wide range of Pb substitution(x = 0–0.8).The samples are characterized by transmission electron microscope(TEM) and measured by high resolution laser-based angle-resolved photoemission spectroscopy(ARPES) with different photon energies.A systematic evolution of the electronic structure and superstructure with Pb substitution has been revealed for the first time.The superstructure shows a significant change with Pb substitution and the incommensurate modulation vector(Q) decreases with increasing Pb substitution.In the meantime, the superstructure intensity from ARPES measurements also decreases dramatically with increasing Pb concentration.The superstructure in Bi2212 can be effectively suppressed by Pb substitution and it nearly disappears with a Pb substitution of x = 0.8.We also find that the superstructure bands in ARPES measurements depend sensitively on the photon energy of lasers used;they can become even stronger than the main band when using a laser photon energy of 10.897 eV.These results provide important information on the origin of the incommensurate superstructure and its control and suppression in bismuth-based high temperature superconductors.     

A new global potential energy surface of the ground state of SiH2+ (X2A1) system and dynamics calculations of the Si+ + H2 (v0 = 2, j0 = 0) → SiH+ + H reaction

A global potential energy surface (PES) of the ground state of SiH$_{2}^{+}$ system is built by using neural network method based on 18223 ab initio points. The topographic properties of PES are presented and compared with previous theoretical and experimental studies. The results indicate that the spectroscopic parameters obtained from the new PES are in good agreement with the experimental data. In order to further verify the validity of the new PES, a test dynamics calculation of the Si$^{+} +$ H$_{2}$ ($v_0 = 2, j_{0} = 0$) $\to $ H $+$ SiH$^{+}$ reaction has been carried out by using the time-dependent wave packet method. The integral cross sections and rate constants are computed for the title reaction. The reasonable dynamical behavior indicates that the newly constructed PES is suitable for relevant dynamics investigations.     

Cohesive energy, phonon spectra, and thermodynamic properties of elements with the structures A1, A2, A3, A4—Al, Cu, V, Ti, Mg, Si, and Sn

The dependences of the cohesive (atomization) energy on the interatomic distance for elements Al, Cu, Ti(A₂), V, Mg, Ti(A₃), Si, and Sn are calculated using methods based on the Thomas-Fermi-Dirac-Gambosh statistical atomic theory. The obtained dependences are approximated by the Mie-Grüneisen potential. The phonon spectra calculated on the basis of the Born-Kärmän model and the Born-Kärmän-Blackman-de Lunay approach are used to determine the temperature dependences of the specific heat, free energy, and internal energy of the elements under investigation. The calculated cohesive energy, equilibrium interatomic distances, and temperature dependences of the specific heat agree with the experimental data.     

Absorption spectra and isotope shifts of the(2, 0),(3, 1), and(8, 5) bands of the A~2Π_u-X~2Σ_g~+ system of ~(15)N_2~+ in near infrared

The high-resolution absorption spectra of the(2, 0),(3, 1), and(8, 5) bands of the A~2Π_u–X~2Σ_g~+system of~(15) N_2~+ have been recorded by using velocity modulation spectroscopy technique in the near infrared region. The rotational constants of the X~2Σ_g~+and A~2Π_u states of~(15) N_2~+ were derived from the spectroscopic data. The isotope shifts of these bands of the A~2Π_u–X~2Σ_g~+system of~(14) N_2~+ and~(15) N_2~+ were also analyzed and discussed.     

Formation of 8He in the 9Be(π–, p)X and 10B(π–, pp)X Stopped Pion Absorption Reactions

JETP Letters - The structure of levels of the 8He heavy helium isotope has been studied in the 9Be $$({{\pi }^{ - }},p)X$$ and 10B $$({{\pi }^{ - }},pp)X$$ stopped pion absorption reactions....     

Structural and H2 sorption properties of MgH2�C10?wt%ZrCrM (M?=?Cu, Ni) nano-composites

Magnesium and its hydride MgH₂ are widely regarded as promising candidates for hydrogen storage materials due to its benefits of high gravimetric and volumetric capacity, excellent reversibility, abundance in the earth and a low cost. Much attention has been paid to improve its absorption/desorption kinetics, trying to make it useful for practical applications. To make composite of MgH₂ with other hydrogen storage compounds is an effective method to improve the hydrogen storage properties. In this study nano-composite of MgH₂ with ZrCrCu alloy was prepared using high energy ball-milling for 5 h under Ar atmosphere. Microstructure and morphology of the composites were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM). XRD patterns show that no alloy formation between MgH₂ and elements of the alloys takes place during milling. Different morphology of the powders as-milled and after cycling was observed by SEM. Pressure?Ccomposition isotherms of these composites have been obtained in the pressure range 0.1?C10 bar at 275 and 300 °C. The absorption/desorption kinetics data have been analyzed using pressure 0.1?C5.0 bar at 275 and 300 °C to understand the mechanism of the hydriding/dehydriding reaction processes. A comparison of these results has been attempted with our previous published results of MgH₂?C10 wt%ZrCrNi in order to find the better composite for storage applications. It is observed by DSC curves that the onset temperature of hydrogen desorption is decreased for MgH₂?C10%ZrCrNi in comparison to MgH₂ which further decreased for MgH₂?C10%ZrCrCu. However, little loss in hydrogen absorption/desorption capacity is also observed for ZrCrCu composite in comparison to that of ZrCrNi composite.     

Theoretical study of the superhyperfine parameters for Cu2 + in K2PdX4 (X = Cl, Br)

The superhyperfine parameters T _j (j?=?x, y, z) for Cu^2?+? in the square-planar K₂PdX₄ (X = Cl, Br) are theoretically studied from the perturbation formulas of these parameters for an octahedral 3d⁹ cluster, by considering both the contributions from the crystal-field and charge-transfer mechanisms. The related molecular orbital coefficients are determined from the cluster approach in a uniform way. Based on one adjustable proportional factor ρ for the orbital admixture coefficients, the calculated results of present work show reasonable agreement with the observed values.     

Electrical properties of A′Ca2Nb3O10 (A′=K, Rb, Cs) layered perovskite ceramics

The electrical conductivity properties of Dion-Jacobson type layered perovskites A′Ca₂Nb₃O₁₀ (A′=K, Rb, Cs) was investigated under different gas atmospheres. An increase in the electrical conductivity by about 2–5 orders in magnitude in both ammonia and hydrogen atmospheres is observed compared to air. Among the members of the series, the compound with the smallest size of the alkali ion, i.e. KCa₂Nb₃O₁₀, exhibits the highest conductivity. In air and hydrogen, a single activation energy value in the range 0.25 – 0.80 eV is observed, while in ammonia a sharp increase in the electrical conductivity is found at about 500 °C. The activation energy at low-temperatures (300–500 °C) is attributed to ionic motion and at higher temperatures (500–700 °C) to both defect formation and ionic motion. The unusual electrical conductivity behavior in ammonia is explained on the basis of the model developed for alkali halides. EMF measurements reveal that the layered perovskites are ionic (proton) conductors. The electrical conductivity changes as a function of the ammonia gas concentration; accordingly, layered perovskites appear to be useful solid electrolytes in galvanic cells for practical applications, e.g. for gas sensors. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Synthesis and Analytical Application of a Novel Fluorescent Hg2+ Probe 3′, 6′-Bis(Diethylamino)-2-((2,4-Dimethoxybenzylidene)Amino)Spiro[Isoindoline-1,9′-Xanthene]-3-Thione

A novel probe, 3′,6′ - bis(diethylamino) -2- ((2,4-dimethoxybenzylidene)amino) spiro [isoindoline-1,9′-xanthene]-3-thione (RBS), was designed and synthesized. Its structure was characterized with elemental analysis, IR spectra and ¹H NMR. The probe displayed highly selective and sensitive recognition of Hg²⁺. Reacting with mercury ions in aqueous solution, its fluorescence intensity was enhanced significantly, while its color was changed from colorless to pink. So, a new fluorescence method of detection of Hg²⁺ was proposed. Its dynamic response concentration range and detection limit for Hg²⁺ were 5.00?×?10^?9 M to 1.00?×?10^?6 M detected and 1.83?×?10^?9 M, respectively. Satisfying results were obtained when the probe was applied to detect spiked Hg²⁺ in samples.     

DFT studies on the interaction of PtxRuyMz (M = Fe,Ni, Cu,Mo, Sn,x + y + z = 4, x ≥ 1, y ≥ 1) alloy clusters with O2

The reaction mechanism of O₂ dissociation on Pt_xRu_yM_z (M = Fe, Ni, Cu, Mo, Sn, x + y + z = 4, x ≥ 1, y ≥ 1) alloy catalysts have been investigated with density functional theory calculations in this work. For bare alloy clusters, bimetallic clusters are more stable than the ternary alloy clusters. The geometries of the Pt_xRu_yM_z–O₂ system, O–O bond stretching frequency and electronic-structure details have been investigated. The energies of O₂ adsorption on PtRu clusters are slightly higher than those on Pt_xRu_yM_z clusters, and the more charge transfer to O₂ from the metal cluster, the higher O₂ the adsorption energy obtains. The reaction barriers show that the catalytic performance of trimetallic clusters are better than those of bimetallic clusters, and Pt₂RuM clusters exhibit superior catalytic activity for O₂ dissociation. The different performance of these alloy clusters for O₂ dissociation is scrutinised with aid of molecular orbital and natural bond orbital population analysis.