Fragmentation of the tryptophan cluster [Trp9-2H]2- induced by different activation methods

Electrospray ionization (ESI) of tryptophan gives rise to multiply charged, non‐covalent tryptophan cluster anions, [Trp_n–xH]^x?, in a linear ion trap mass spectrometer, as confirmed by high‐resolution experiments performed on a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. The smallest multiply charged clusters that can be formed in the linear ion trap as a function of charge state are: x = 2, n = 7; x = 3, n = 16; x = 4, n = 31. The fragmentation of the dianionic cluster [Trp₉–2H]^2? was examined via low‐energy collision‐induced dissociation (CID), ultraviolet photodissociation (UVPD) at 266 nm and electron‐induced dissociation (EID) at electron energies ranging from >0 to 30 eV. CID proceeds mostly via charge separation and evaporation of neutral tryptophan. The smallest doubly charged cluster that can be formed via evaporation of neutral tryptophans is [Trp₇–2H]^2?, consistent with the observation of this cluster in the ESI mass spectrum. UVPD gives singly charged tryptophan clusters ranging from n = 2 to n = 9. The latter ion arises from ejection of an electron to give the radical anion cluster, [Trp₉–2H]^?.. The types of gas‐phase EID reactions observed are dependent on the energy of the electrons. Loss of neutral tryptophan is an important channel at lower energies, with the smallest doubly charged ion, [Trp₇–2H]^2?, being observed at 19.8 eV. Coulomb explosion starts to occur at 19.8 eV to form the singly charged cluster ions [Trp_x–H]^? (x = 1–8) via highly asymmetric fission. At 21.8 eV a small amount of [Trp₂–H–NH₃]^? is observed. Thus CID, UVPD and EID are complementary techniques for the study of the fragmentation reactions of cluster ions. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient Eley-Rideal reactions of H atoms with single Cl adsorbates on Au(111)

Density functional theory is used to construct an interaction model for H atoms with Cl over Au(111). Single-adsorbate Eley-Rideal reactions are investigated with quantum and quasiclassical methods. The reaction cross sections, amounting to 2-3 A(2), are much larger than for HD recombinations on metals. This can be traced to the adsorbed Cl being relatively far above the surface, the H-Cl interaction prevailing over the H-substrate attraction for a sizable range of impact parameters.     

An efficient optical pressure measurement in compressible flows: Laser-induced iodine fluorescence

The understanding of complex phenomena, the experimental validation of calculation codes, and the construction of data bases in fluid mechanics require the development of non-intrusive experimental techniques. The laser-induced fluorescence of a gaseous molecule seeded into a gas flow can be related to the flowfield thermodynamic parameters, such as pressure and temperature. An experimental method is described, that allows the removal of the temperature dependence of the fluorescence signal. A narrow-bandwidth single-line laser is tuned to the center of an absorption line, whose temperature dependence of the Boltzmann fraction can be neglected. The experimental set-up requires a single-line dye laser and a high resolution spectral analysis device.The accuracy of the method, checked in a static vessel, appears to be better than 5%. The method has been successfully tested with a supersonic jet issuing from an underexpanded nozzle.The experimental results have been compared to those of an Euler calculation. A mean difference of 14% has been observed, but a major part of this can be attributed to the difference between inviscid and real gas calculation.List of Symbols A ₂₁ spontaneous emission Einstein coefficient - B _v rotational energy of the J level for the v vibrational level - B _e first order approximation of B _v - c velocity of light - C _opt optical constant - E(v) vibrational energy of the v level - f ₁ Boltzmann fraction - FCF _i Franck-Condon factor of the ith line - f _v vibrational fraction - tf _r rotational fraction - g efficient spectral power density - h Planck constant - I ₂ X iodine molecule in the X state - I ₂ B iodine molecule in the B state - [I ₂ X] molecular concentration of I ₂ X - [I ₂ B] molecular concentration of I ₂ B - I _i relative intensity of the ith absorption line - J rotational level of the fundamental state - J rotational level of the excited state - k Boltzmann constant - k _c collisional broadening coefficient - m iodine molecular mass - n ₀ initial concentration of iodine in the absorbing state - P pressure - P _laser laser power - P _l(v) laser power spectral density - P _sl2 iodine vapor pressure - Q quenching rate - Q _v vibrational partition function - T temperature - v vibrational level of the fundamental state - v vibrational level of the excited state - V _c collection volume - X _{l 2} iodine molar fraction - wave length - v _D Doppler linewidth, at half maximum - v _c collisional linewidth at half maximum - Vl laser frequency - (v) Dirac function - v _i spectral location of a line, referenced to the laser frequency     

Methodological issues in the application of monofractal analyses in psychological and behavioral research

A number of recent research works tried to apply fractal methods to psychological or behavioral variables. Quite often, nevertheless, the use of fractal analyses remains rudimentary, and the goal of researchers seems limited to evidencing the presence of long- range correlation in data sets. This article presents some recent developments in monofractals theory, and some related methodological refinements. We also discuss a number of specific issues related to the application of fractal methods in psychological and behavioral research. Finally, we consider the potential use of such approach for a renewal of classical issues in psychology and behavioral science.     

Ab initio vibrational predissociation dynamics of He-I2(B) complex

Three-dimensional quantum mechanical calculations on the vibrational predissociation dynamics of HeI2 B state complex are performed using a potential energy surface accurately fitted to unrestricted open-shell coupled cluster ab initio data, further enabling extrapolation for large I2 bond lengths. A Lanczos iterative method with an optimized complex absorbing potential is used to determine energies and lifetimes of the vibrationally predissociating He,I2(B,v') complex for v'相似文献   

Two-dimensional electron systems in inversion layers of p-type Hg0.8Zn0.2Te metal-insulator-semiconductor structures

Strong oscillations on capacitance and conductance have been observed in p-type Hg0.8Zn0.2Te metal-insulator-semiconductor structures, made by using a recent process for the interface passivation. This behaviour is attributed to a two-dimensional electron gas in the n-inversion layer and the variation of the conductance maximums with temperature indicates that the dominant perpendicular transport mechanism for electrons is an incoherent two-step tunnelling through deep levels in the gap. Three models have been used to describe the quantum confinement: the simple variational method, the triangular potential approximation and the propagation matrix method. The later approach takes into account the non parabolicity of the conduction band structure and uses a finite height barrier at the insulator-semiconductor interface. A very good agreement between experimental and calculated values for the two lowest subband energy is obtained. Received 9 February 1999     

Bis­[1‐(p‐chloro­phenyl)‐5‐iso­propyl­biguanide‐κ2N2,N4]­nickel(II) dichloride di­methyl­form­amide solvate

The asymmetric unit of the title compound, [Ni(C₁₁H₁₆ClN₅)₂]Cl₂·C₃H₇NO, contains one monomeric nickel(II) com­plex cation, two Cl⁻ anions and one di­methyl­form­amide sol­vent mol­ecule. The Ni atom is coordinated to each of two 1‐­(p‐chloro­phenyl)‐5‐iso­propyl­biguanide (proguanil) ligands via two N atoms. The complex exhibits a square‐planar coordination, with the Ni atom lying 0.021 (2) Å out of the basal plane. The crystal packing is characterized by several hydrogen bonds.     

Magnetic properties and magnetic structures of the CeScSi-type RMgPb (R=Ce–Nd,Sm, Gd–Tm) compounds

Investigations made by powder X-ray diffraction, magnetic measurements and neutron powder diffraction on the CeScSi-type ternary magnesium plumbides RMgPb (R=Ce–Nd, Sm, Gd–Tm) are reported. Macroscopic magnetic measurements performed in the 2–300 K temperature range show that these compounds follow a Curie–Weiss law in the paramagnetic state (except SmMgPb) and behave antiferromagnetically at low temperature (T_Ν≤61 K). Field dependence of the magnetization performed at 5 K evidence metamagnetic-like behaviors (H_crit<7 T). Neutron powder diffraction evidenced complex antiferromagnetic structures in fair agreement with the magnetic data. PrMgPb and NdMgPb compounds present a commensurate antiferromagnetic structure, while (Tb–Er)MgPb are characterized by incommensurate sine-wave modulated magnetic structure down to lower temperature or square-wave magnetic structure due to appearance of higher odd integer harmonics. CeMgPb and TmMgPb evidence more complex sine-wave modulated magnetic structures, never encountered with the CeScSi-type structure, characterized by two propagation vectors. These results are discussed and compared with those of the isotypic RMgSn compounds.     

The magnetic structure of EuPdSn

The TiNiSi-type structure, antiferromagnetic ordering and divalent state of europium in EuPdSn have been confirmed by neutron powder diffraction. The Néel temperature is 16.2(3) K. The magnetic diffraction peaks can be indexed with a propagation vector k = [0, 0.217, q(z)] (q(z) ≤ 0.02) at 13.2 K, and k = [0, 0.276, 0] at 3.6 K, indicating an incommensurate antiferromagnetic structure at both temperatures. At 13.2 K, the best refinement is obtained with a sinusoidally modulated magnetic structure and europium magnetic moments oriented in the (a,b) plane with an azimuthal angle ? of 66(4)°relative to the a-axis. By 3.6 K, the magnetic structure of EuPdSn has transformed to an (a,b) planar helimagnetic structure (a 'flat spiral').