共查询到20条相似文献,搜索用时 140 毫秒
1.
Ana R. Hortal Paola Hurtado Bruno Martínez-Haya 《Applied Physics A: Materials Science & Processing》2008,93(4):935-939
Cation attachment to a model peptide has been investigated in matrix-assisted laser desorption experiments. Angiotensin I
(Asp–Arg–Val–Tyr–Ile–His–Pro–Phe–His–Leu) is chosen as a system for study, and Cu2+ and K+ salts are used as cationizing agents. Three fundamentally different types of samples are investigated: (1) a crystalline
sample of Ang I, metal salt and MALDI matrix, prepared with the conventional dried droplet method; (2) a solvent-free fine
powder mixture of the same three compounds, and (3) a solution of the angiotensin and the metal salt in an ionic liquid matrix
(a molten organic salt that acts as a MALDI active solvent). Effective protonation and cationization of the peptide are achieved
with the three methods. The transition metal systematically provides more efficient cationization than the alkali metal. At
sufficiently high concentration of the salt, the attachment of up to four copper cations to the angiotensin is observed in
the MALDI spectrum. In contrast, only one K+ cation is efficiently bound to the peptide. For a given salt concentration, the highest degree of cationization is obtained
in the laser desorption from the ionic liquid matrix. This is attributed to the efficient transfer of free metal cations to
the desorption plume, where the complexation takes place. 相似文献
2.
The binding interactions of bis‐3‐benzo‐15‐crown‐5 ethers and bis‐3‐benzo‐18‐crown‐6 ethers (neutral hosts) with a series of alkali metal cations Na+, K+, Rb+ and Cs+ (charged guests) were investigated using quantum chemical density functional theory. Different optimized structures, binding energies and various thermodynamic parameters of free crown ethers and their metal cation complexes were obtained based on the Becke, three‐parameter, Lee–Yang–Parr functional using mixed basis set (C, H, O, Na+ and K+ using 6‐31 g, and the heavier cation Rb+ and Cs+ using effective core potentials). Natural bond orbital analysis is conducted on the optimized geometric structures. The main types of driving force host–guest interactions are investigated. The electron donating O offers a lone pair of electrons to the contacting LP* (1‐center valence antibond lone pair) orbitals of metal cations. The bis‐3‐benzocrown ethers are assumed to have sandwich‐like conformations, considering the binding energies to gauge the exact interactions with alkali cations. It is found that there are two different types of complexes: one is a tight ion pair and the other is a separated ion pair. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
3.
I. S. Edelman E. A. Petrakovskaja D. A. Petrov S. M. Zharkov R. I. Khaibullin V. I. Nuzhdin A. L. Stepanov 《Applied magnetic resonance》2011,40(3):363-375
Fused silica plates have been implanted with 40 keV Co+ or Ni+ ions to high doses in the range of (0.25–1.0) × 1017 ions/cm2, and magnetic properties of the implanted samples have been studied with ferromagnetic resonance (FMR) technique supplemented
by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. The high-dose implantation
with 3d-ions results in the formation of cobalt and nickel metal nanoparticles in the irradiated subsurface layer of the SiO2 matrix. Co and Ni nanocrystals with hexagonal close packing and face-centered cubic structures have a spherical shape and
the sizes of 4–5 nm (for cobalt) and 6–14 nm (for nickel) in diameter. Room-temperature FMR signals from ensembles of Co and
Ni nanoparticles implanted in the SiO2 matrix exhibit an out-of-plane uniaxial magnetic anisotropy that is typical for thin magnetic films. The dose and temperature
dependences of FMR spectra have been analyzed using the Kittel formalism, and the effective magnetization and g-factor values have been obtained for Co- and Ni-implanted samples. Nonsymmetric FMR line shapes have been fitted by a sum
of two symmetrical curves. The dependences of the magnetic parameters of each curve on the implantation dose and temperature
are presented. 相似文献
4.
Zero, longitudinal and transverse field μSR measurements have been made on LiH, LiD and NaH. The primary motivation for the
study was to elucidate the behaviour of the muons in the diamagnetic state and analysis of the time‐dependent zero field relaxation
data suggests that negatively charged muonium, Mu-, is formed and takes up a H- vacancy site in these materials. Evidence is presented for a small (approximately 2%) reduction in the Mu-–Li distance relative to the unperturbed nearest neighbour anion‐cation distances in the pure crystal lattices.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
The magnetic susceptibility of Al2REM (REM = Gd, Dy, and Ho) intermetallic compounds is experimentally investigated by the Faraday method in a wide temperature
interval (290–2000 K) in different magnetic fields (0.3–1.3 T). In the crystalline state, the temperature dependences of the
susceptibility follow the generalized Curie–Weiss law. In the liquid phase, the magnetic susceptibility of these intermetallic
compounds above the melting point increases for all examined samples. The parameters of the electronic structure of the compounds
are calculated based on the experimental data. It is established that the effective magnetic moment per rareearth metal atom
is smaller than that characteristic of the free REM+ ion. 相似文献
6.
Irina Kudryavtseva Aleksandr Lushchik Aarne Maaroos Zhannur Azmaganbetova Turlybek Nurakhmetov Zhussupbek Salikhoja 《Central European Journal of Physics》2012,10(4):995-1001
A comparative study of the excitation of luminescence by VUV radiation as well as of thermally and photostimulated luminescence
has been carried out for CaSO4:Tb3+ and CaSO4:Gd3+ phosphors, where Na+ or F− ions are used for charge compensation. The distinction in hole processes for the phosphors with Na+ or F− compensators is determined by the differing thermal stability of the holes localized at/near Tb3+Na+ and Gd3+Na+ (up to 100–160 K) or at/near Tb3+F−
V
Ca and Gd3+F−
V
Ca centers involving also a cation vacancy (up to 400–550 K). Tunnel luminescence in the pairs of localized electrons and holes
nearby Tb3+ or Gd3+ has been detected. The mechanisms of electron-hole, hole-electron and tunnel recombination luminescence as well as a subsequent
released energy transfer to RE3+ ions are considered. 相似文献
7.
《Solid State Ionics》1987,25(1):41-44
Complexes of alkali metal salts with various polymers have for some time been recognized as fast ionic conductors. Polymer electrolyte fast ion conductors are currently under consideration for use in high energy density electrochemical cells. In order to aid in our understanding of the mechanism of ionic conductivity we have examined systematically complexes of poly(ethylene oxide) (PEO) with the alkali metal salt series of Li+, Na+, K+, Rb+ and Cs+ with both tetraflouroborate (BF4-) and trifluoromethanesulfonate (CF3SO4-) anions. The ratio of monomer to salt was 10:1 in all cases. Complex impedance measurements were made on all samples in the temperature range 40°–125°C. With CF3SO4- as the anion a definite trend was apparent with the smallest cation Li+ being the worst conductor and Cs+, the largest cation, being the best. When BF4- salts are used, the Na+ complex is found to be the best conductor and Rb+ the worst. This study, in connection with our earlier studies, has shown that synergy between cation and anion in the polymer matrix is an important consideration in determining the ionic conductivity. 相似文献
8.
Configuration interaction calculations have been carried out on electronic states of the CsLi molecule and the CsLi+ cation. Adiabatic potential energy, spectroscopic constants, dipole moments, and vibrational levels are presented for the
lowest states of 1,3Σ+, 1,3Π, and 1,3Δ symmetries of the alkali dimer CsLi molecule dissociating into Cs (6s, 6p, 5d, 7s, and 7p) + Li (2s, 2p, 3s, 3p, and 3d)
as well as for the lowest 2Σ+, 2Π, and 2Δ electronic states of the CsLi+ cation dissociating into Li (2s, 2p, 3s, 3p, and 3d) + Cs+ and Li+ + Cs (6s, 6p, 5d, 7s, and 7p). The results of the present many-electron configuration interaction calculations on the cation
support the previous core-polarization effective potential calculations. The present calculations on the CsLi molecule are
complementary to previous theoretical work on this system, including recently observed electronic states that had not been
calculated previously. We have used an ab initio approach involving a nonempirical pseudopotential for the Li (1s2) and Cs cores and a core-valence correlation correction. A very good agreement of data from spectroscopic constants for some
of the lowest states of the CsLi and CsLi+ molecules with those available in recent theoretical works has been obtained. The existence of numerous avoided crossings
between electronic states of 2Σ+ and 2Π symmetries is related to a charge transfer process between the two ionic CsLi+ and LiCs+ systems. 相似文献
9.
Intira Yimlamai Sumonman Niamlang Pojjawan Chanthaanont Ruksapong Kunanuraksapong Sairung Changkhamchom Anuvat Sirivat 《Ionics》2011,17(7):607-615
This work is an attempt to search for highly selective sensing materials for ethanol vapor. The electrical conductivity response
of ZSM-5, Y, and mordenite zeolites towards ethanol vapor have been investigated for the effects of the framework, the charge
balancing cation type, and the Si/Al ratio. All zeolites were characterized using XRD, FT-IR, SEM, TGA, BET, and NH3-TPD techniques. For the effect of the zeolite framework type, H+Y has a higher electrical conductivity sensitivity value than that of H+MOR because of a greater pore volume and available surface area. For the effect of the charge balancing cation, all NH4
+ZSM-5 zeolites (Si/Al = 23, 50, 80, 280) show negative responses, whereas the H+Y zeolites (Si/Al = 30, 60, 80) and the H+MOR zeolites (Si/Al = 30, 200) show positive responses. These differing behaviors can be traced to the electrostatic field
at the cation sites in zeolite micropores, and their hydrophilic–hydrophobic character, which affect the adsorption properties
of the zeolites. For the effect of Si/Al ratio, the electrical conductivity sensitivity towards the ethanol decreases with
increasing Si/Al ratio or decreasing Al content, and there is a lesser degree of interaction between ethanol molecules and
the active sites of the zeolites due to its higher hydrophobicity and the lower amount of cations. However, the H+Y (Si/Al = 5.1) and the H+MOR (Si/Al = 19) zeolites have lower conductivity sensitivity than those of H+Y (Si/Al = 30) and H+MOR (Si/Al = 30), respectively. The interactions between the C2H5OH molecules and the zeolites with respect to the electrical conductivity sensitivity were investigated and verified through
infrared spectroscopy. 相似文献
10.
The ionic conduction properties of undoped and doped Tl4HgI6 were investigated using electrical conductivity, dielectrics, differential scanning calorimetry, and X-ray diffraction techniques.
The heavy Tl+-ions diffusion was activated at high temperature, whereas low conductivity at the lower temperature suggested electronic
contribution in undoped Tl4HgI6. The partial replacement of heavy Tl+ ion by suitable cations (Ag+ and Cu+) enhanced the conductivity by several orders of magnitude, whereas diminution in conductivity results with increasing dopants’
concentration in Tl4HgI6. These results can be interpreted in terms of a lattice contraction and vacancy–vacancy interaction (leading to the cluster
formation), respectively. The dielectric values of undoped Tl4HgI6 system gradually increasing with temperature, followed by a sharp change, were observed around 385 K and can be explained
on the basis of increasing number of space charge polarization and ions jump orientation effects. The activation energy of
undoped and doped Tl4HgI6 systems were calculated, and it was found that ionic conductivity activation energy for 5 mol% of cation dopants is much
lower than that of undoped one, and also 10 mol% doped Tl4HgI6 systems. 相似文献
11.
A novel fluorescent Ag+ sensor was developed based on the label-free silver (I) specific oligonucleotide (SSO) and Thioflavine T (ThT) monomer-excimer
switch. C-rich SSO which contain C-C mismatched base pairs can selectively bind to Ag+ ions and the formed duplexes which constructed by C-Ag+-C structure are thermally stabilized without largely altering the double helical structure. ThT give very weak fluorescent
in bulk solution and/or in the presence of SSO. However ThT shows high fluorescence in the presence of SSO and Ag+ at the same time mainly because ThT excimer, which has the high quantum yield, formed and stabilized in the minor or major
groove. Based on the discovery, we developed the novel Ag+ sensor. Under the optimum condition, the selectivity of this system for Ag+ over other metal ions in aqueous solution is remarkably high, and Ag+ can be quantified over the dynamic range of 30–450 nM, with a limit of detection of ~16 nM and a linear correlation coefficient
of 0.995. 相似文献
12.
Moamen S. Refat Mohamed M. Ibrahim Mohamed A. A. Moussa 《Journal of Applied Spectroscopy》2012,78(6):772-781
Charge-transfer complexes (CTC) resulting from interactions of 1,3-di[(E)-1-(2-hydroxyphenyl) methylideneamino]-2-propanol Schiff base with some acceptors such as iodine (I2), bromine (Br2), and picric acid (PiA) have been isolated in the solid state in a chloroform solvent at room temperature.
Based on elemental analysis, UV-Vis, infrared, and 1H NMR spectra, and thermogravimetric analysis (TG/DTG) of the solid CTC, [(Schiff)(I2)] (1), [(Schiff)(Br2)] complexes with a ratio of 1:1 and [(Schiff)(PiA)3] complexes with 1:3 have been prepared. In the picric acid complex, infrared and 1H NMR spectroscopic data indicate that the charge-transfer interaction is associated with a hydrogen bonding, whereas the
iodine and bromine complexes were interpreted in terms of the formation of dative ion pairs [Schiff+, I2∙−] and [Schiff+, Br2∙−], respectively. Kinetic parameters were obtained for each stage of thermal degradation of the CT complexes using Coats–Redfern
and Horowitz–Metzger methods. DC electrical properties as a function of temperature of these charge transfer complexes have
been studied. 相似文献
13.
The electronic band structure and position of the charge neutrality level (CNL) in BN, AlN, GaN, and InN compounds with cubic
and hexagonal lattices are calculated within the density functional theory (DFT-GGA). It is shown that the charge neutrality
level is shifted from the middle of the BN and AlN forbidden band to the upper half of the GaN forbidden band and to the allowed
energy region in the InN conduction band as the cation atomic weight increases. This determines semiinsulating properties
of BN and AlN, n-type conductivity of GaN, and n
+-type conductivity of InN upon saturation of these materials by intrinsic lattice defects due to hard radiation.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 24–31, December, 2008. 相似文献
14.
M. P. Samtsov E. S. Voropai K. N. Kaplevskii D. G. Mel’nikov 《Journal of Applied Spectroscopy》2008,75(5):692-699
We present the results of a study of the spectral luminescence properties of three groups of indotricarbocyanine dyes, each
of which is formed from compounds with the same cation and different anions. In high-polarity solvents, in the absorption
and emission spectra of the dyes we see one type of center; in low-polarity solvents, due to the presence of different ionic
forms of the dyes (free ions, contact ion pairs), we observe either one type or two types of centers. By analysis of the luminescence
of molecular oxygen in the 1.27 μm spectral region, we determined the efficiency of photosensitization of 1O2 formation by dyes in deuterated solvents. We have shown that in low-polarity solvents, the yield for singlet oxygen generation
is higher for indotricarbocyanine dyes which are found in the contact ion pair state and which also contain a heavy atom (I)
in the anion. We have observed that an increase in the fraction of contact ion pairs in solution as the dye concentration
increases or when an additional salt is introduced leads to an increase in the quantum yield for generation of singlet oxygen.
In polar deuterated acetonitrile, the counterion has no effect on the efficiency of photosensitization of oxygen by the dyes.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 684–693, September–October, 2008. 相似文献
15.
A. N. Belemuk Yu. M. Belousov V. P. Smilga 《Journal of Experimental and Theoretical Physics》1997,84(2):402-405
The question of the charge state of the proton (the positive muon) in metals is of fundamental importance for the theory of
metal hydrides. The theory developed here permits determination of the charge state of μ
+ in normal metals. The experimental possibilities of the observation of Mu atoms in metals at various strengths of the external
magnetic field and various temperatures are analyzed.
Zh. éksp. Teor. Fiz. 111, 730–736 (February 1997) 相似文献
16.
LiCoO2 particles were synthesized by a sol-gel process. X-ray diffraction analysis reveals that the prepared sample is a single
phase with layered structure. A hybrid electrochemical capacitor was fabricated with LiCoO2 as a positive electrode and activated carbon (AC) as a negative electrode in various aqueous electrolytes. Pseudo-capacitive
properties of the LiCoO2/AC electrochemical capacitor were determined by cyclic voltammetry, charge–discharge test, and electrochemical impedance
measurement. The charge storage mechanism of the LiCoO2-positive electrode in aqueous electrolyte was discussed, too. The results showed that the potential range, scan rate, species
of aqueous electrolyte, and current density had great effect on capacitive properties of the hybrid capacitor. In the potential
range of 0–1.4 V, it delivered a discharge specific capacitance of 45.9 Fg–1 (based on the active mass of the two electrodes) at a current density of 100 mAg–1 in 1 molL–1 Li2SO4 aqueous electrolyte. The specific capacitance remained 41.7 Fg–1 after 600 cycles. 相似文献
17.
B. A. Kalin N. V. Volkov S. E. Sabo S. V. Zaitsev 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(5):845-851
The results of studying the redistribution of Be, Al, Ti, Fe, Cu, Zr, Mo, and W atoms incorporated in polycrystalline metal
samples under irradiation with He+, (He+ + Ar+), and Ar+ ion beams with a broad energy spectrum and an average energy of 10 keV at irradiation doses of 1 × 1021 ion/cm2 are studied. It is discovered that irradiation at doses exceeding 1 × 1019 ion/cm2 results in local small-crystal formations being produced in a near-surface substrate layer. Their typical dimensions are
less than 1–5 μm, and their the density is up to 1–100. They contain incorporated atoms and impurity atoms with a concentration
of 0.1–10 at %. Subsequent irradiation at a dose of 1 × 1020 ions/cm2 or more leads to disappearance of these formations, mainly because of sputtering processes. 相似文献
18.
Philippe Gravejat Mathieu Lewin éric Séré 《Communications in Mathematical Physics》2009,286(1):179-215
We study the reduced Bogoliubov-Dirac-Fock (BDF) energy which allows to describe relativistic electrons interacting with the
Dirac sea, in an external electrostatic potential. The model can be seen as a mean-field approximation of Quantum Electrodynamics
(QED) where photons and the so-called exchange term are neglected. A state of the system is described by its one-body density
matrix, an infinite rank self-adjoint operator which is a compact perturbation of the negative spectral projector of the free
Dirac operator (the Dirac sea). We study the minimization of the reduced BDF energy under a charge constraint. We prove the
existence of minimizers for a large range of values of the charge, and any positive value of the coupling constant α. Our
result covers neutral and positively charged molecules, provided that the positive charge is not large enough to create electron-positron
pairs. We also prove that the density of any minimizer is an L
1 function and compute the effective charge of the system, recovering the usual renormalization of charge: the physical coupling
constant is related to α by the formula αphys ≃ α(1 + 2α/(3π) log Λ)−1, where Λ is the ultraviolet cut-off. We eventually prove an estimate on the highest number of electrons which can be bound
by a nucleus of charge Z. In the nonrelativistic limit, we obtain that this number is ≤ 2Z, recovering a result of Lieb. This work is based on a series of papers by Hainzl, Lewin, Séré and Solovej on the mean-field
approximation of no-photon QED. 相似文献
19.
Ranber Singh 《Journal of magnetism and magnetic materials》2010,322(3):290-3191
The local magnetic structures around substitutional 3d transition metal impurities at cation sites in zinc blende structures of III-V (GaN, GaAs) and II-VI (ZnTe) semiconductors are investigated by using a spin-polarized density functional theory. We find that Cr-, Co-, Cu-doped GaN, Cr-, Mn-doped GaAs and Cr-, Fe-, Ni-doped ZnTe are half metallic with 100% spin polarization. The magnetic moments due to these 3d transition metal (TM) ions are delocalized quite significantly on the surrounding ions of host semiconductors. These doped TM ions have long range interactions mediated through the induced magnetic moments in anions and cations of host semiconductors. For low impurity concentrations Mn in GaAs also has zero magnetic moment state due to Jahn-Teller structural distortions. Based upon half metallic character and delocalization of magnetic moments in the anions and cations of host semiconductors these above mentioned 3d TM-doped GaN, GaAs and ZnTe seem to be good candidates for spintronic applications. 相似文献
20.
Shiguo Zhang Xiujuan Qi Xiangyuan Ma Liujin Lu Qinghua Zhang Youquan Deng 《Journal of Physical Organic Chemistry》2012,25(3):248-257
Gas‐phase structure, hydrogen bonding, and cation–anion interactions of a series of 1‐(2‐hydroxyethyl)‐3‐methylimidazolium ([HOEMIm]+)‐based ionic liquids (hereafter called hydroxyl ILs) with different anions (X = [NTf2]–, [PF6]–, [ClO4]–, [BF4]–, [DCA]–, [NO3]–, [AC]– and [Cl]–), as well as 1‐ethyl‐3‐methylimizolium ([EMIm]+)‐based ionic liquids (hereafter called nonhydroxyl ILs), were investigated by density functional theory calculations and experiments. Electrostatic potential surfaces and optimized structures of isolated ions, and ion pairs of all ILs have been obtained through calculations at the Becke, three‐parameter, Lee–Yang–Parr/6‐31 + G(d,p) level and their hydrogen bonding behavior was further studied by the polarity and Kamlet–Taft Parameters, and 1H‐NMR analysis. In [EMIm]+‐based nonhydroxyl ILs, hydrogen bonding preferred to be formed between anions and C2–H on the imidazolium ring, while in [HOEMIm]+‐based hydroxyl ILs, it was replaced by a much stronger one that preferably formed between anions and OH. The O–H···X hydrogen bonding is much more anion‐dependent than the C2–H···X, and it is weakened when the anion is changed from [AC]– to [NTf2]–. The different interaction between [HOEMIm]+ and variable anion involving O–H···X hydrogen bonding resulted in significant effect on their bulk phase properties such as 1H‐NMR shift, polarity and hydrogen‐bond donor ability (acidity, α). Copyright © 2011 John Wiley & Sons, Ltd. 相似文献