Gas-phase conformation-specific photofragmentation of proline-containing peptide ions

Singly-protonated proline-containing peptides with N-terminal arginine are photodissociated with vacuum ultraviolet (VUV) light in an ESI linear ion trap/orthogonal-TOF (LIT/o-TOF). When proline is the n^th residue from the N-terminus, unusual b _n + 2 and a _n + 2 ions are observed. Their formation is explained by homolytic cleavage of the C_α− C bond in conjunction with a rearrangement of electrons and an amide hydrogen. The latter is facilitated by a proline-stabilized gas-phase peptide conformation.     

Factors that impact the vacuum ultraviolet photofragmentation of peptide ions

Several groups have investigated the photodissociation of peptide ions with ultraviolet light. Significant differences have been reported with 157 and 193 nm excitation. Recent studies have shown that the mass analyzer can also influence the observed photofragment distribution. Comparison of experiments using different peptides, wavelengths, and mass analyzers is undesirably complicated. In the present work, several peptides are analyzed with both 157 and 193 nm photodissociation in tandem-TOF and linear ion trap mass spectrometers. The results indicate that the fragment ion distribution can be influenced by both the photodissociation wavelength and the mass analyzer. The two wavelengths generate similar spectra in an ion trap but quite different results in a tandem-TOF instrument.     

State-resolved UV photofragmentation spectrum of the metal dication complex [Zn(pyridine)(4)](2+)

A combined theoretical and experimental study of electronic transitions in the complex [Zn(pyridine)(4)](2+) provides the first example of a state-resolved electronic spectrum to be recorded for a dication complex in the gas phase.     

Two-photon dissociation spectroscopy of state-selected HCl+ and DCl+ ions.

HCl+ and DCl+ ions were formed via the R(1) pump line of the f3delta2(v'=0)<--sigma+(v'=0) REMPI process. For these ions, the two-photon dissociation spectroscopy, resonance-enhanced via the A2sigma+(v')<--pi3/2(v'=0) transition, was investigated for various intermediate states of HCl+ (v'=4,5,6) and DCl+ (v'=6,7,8,9). From the analysis of the data, spectroscopic parameters of the X and the A states were derived (including the lambda-doubling in the X state and the spin-rotation coupling in the A state). Some of the parameters deviate considerably from literature data. The spectra provide clear evidence that the REMPI process employed for forming the ions has a very high rotational selectivity.     

Coherent control of indirect photofragmentation in the weak-field limit: control of transient fragment distributions

We demonstrate theoretically that laser-induced coherent quantum interference control of asymptotic states of dissociating molecules is possible--even in the (one-photon) weak-field limit starting from a single vibrational eigenstate--when resonances are in play. This is illustrated for the NaI molecule, where it is shown that the probability of observing atomic fragments as well as the distribution of their relative momenta can be changed by a phase modulated pulse with a fixed bandwidth. This type of control is restricted to finite times during the indirect fragmentation.     

Waveform control of orientation-dependent ionization of DCl in few-cycle laser fields

Strong few-cycle light fields with stable electric field waveforms allow controlling electrons on time scales down to the attosecond domain. We have studied the dissociative ionization of randomly oriented DCl in 5 fs light fields at 720 nm in the tunneling regime. Momentum distributions of D(+) and Cl(+) fragments were recorded via velocity-map imaging. A waveform-dependent anti-correlated directional emission of D(+) and Cl(+) fragments is observed. Comparison of our results with calculations indicates that tailoring of the light field via the carrier envelope phase permits the control over the orientation of DCl(+) and in turn the directional emission of charged fragments upon the breakup of the molecular ion.     

Exchange and reduction of Cu(2+) ions in clinoptilolite

The ion-exchange and reduction processes for Cu(2+) ions in clinoptilolite from the Caimanes deposit (Moa, Cuba) were studied at different temperatures. The ion-exchange studies were done to determine the kinetic parameters of Cu(2+) removal from solution by this clinoptilolite modified previously to NH(+)(4) form, and thermodynamic parameters of Cu(2+) elution from zeolite using NH(4)Cl solution. The results show that temperature increase favors the exchange and that it is a reversible process. The external diffusion rate appreciably increases with temperature, while, the internal diffusion coefficient rises relatively little. This means that besides ion exchange other processes (such as precipitation of the low-solubility phase and/or salt adsorption) occur, which cause copper removal from solution and affect the intracrystalline diffusion of the ions. For steric reasons the exchange of [Cu(H(2)O)(6)](2+) ions from a solution must occur with a number of water molecules n smaller than 6 (6 > n > or = 0). Cu(2+) reduction by hydrogen and the formation of Cu-particles in the clinoptilolite were verified. The Cu(2+) reduction mechanism is complex, indirect, and sensitive to reduction temperature; consequently, Cu(+)(n) states intermediate between Cu(2+) and Cu(0) should be present in the reduced samples.     

Upconversion emission enhancement of Gd3+ ions induced by surface plasmon field in Au@NaYF4 nanostructures codoped with Gd(3+)-Yb(3+)-Tm(3+) ions

Au nanoparticles (NPs) attached β-NaYF(4) nanocrystals codoped with Gd(3+)-Yb(3+)-Tm(3+) were synthesized by a facial solution method. The UV-vis-near-infrared absorption spectrum shows typical surface plasmon resonance band of Au NPs in addition to the characteristic absorption peaks of Yb(3+) ion. X-ray diffraction and selected area electron diffraction results indicate the existence of Au NPs. The transmission electron microscopic image reveals the formation of Au@NaYF(4) nanostructures. Enhanced ultraviolet (UV) upconversion luminescence (UCL) was observed in the nanostructures under the excitation of 980-nm infrared laser. The largest enhancement factor was obtained as 76 for the (6)I(J)→(8)S(7/2) emission of Gd(3+) ions, which was much larger than those emission enhancement factors of Tm(3+). It is for the first time to our knowledge that the emission enhancement of Gd(3+) ions was obtained. Local field enhancement induced by Au NPs was found to be responsible for the UCL enhancement, which is the further experimental evidence of local field enhancement theory. Magnetic measurements of the Au@NaYF(4) nanostructure indicated it would have potential application in magnetic resonance imaging.     

Fission product yields in the fast-neutron fission of238U

The fission yields of 38 fission products in the fast-neutron induced fission of²³⁸U have been determined using a rapid, multiscaling gamma-ray spectroscopic method. To obtain absolute yields for fission products having half-lives ranging from 32 s to 40 d, a total of 56 multi-scaling gamma-ray spectra were collected using various irradiation and cooling periods. Gamma-rays and photopeak areas of interest were assigned to the fission products by their energies and half-lives. Fission product activities were evaluated from spectral data using growth and decay calculations and fission yields were determined by normalizing the¹⁴⁰Ba yield to the average value from reported data. The depleted uranium target, covered with a boron-cadmium thermal neutron shield, was used to keep interference from the fission of²³⁵U minimal. Results for the cumulative fission yields, including 17 mostly short-lived fission products measured for the first time, are compared with previous measurements and with the recommended yields in recent evaluations. The agreement, and some discrepancies, in the comparisons are discussed. No explicit even-odd pairing effects are observed in the fission yield data for fast-neutron induced fission of²³⁸U.     

Investigations of the EPR zero-field splitting and the defect structure for Mn(2+) and Fe(3+) ions in anatase crystals

The EPR zero-field splittings D of Mn(2+) and Fe(3+) ions in anatase crystals at room and low temperatures are calculated from the high-order perturbation formula of zero-field splitting D for 3d(5) ions in tetragonal symmetry based on the dominant spin-orbit coupling mechanism. The calculated results are consistent with the observed values. From the calculations, Mn(2+) and Fe(3+) ions are suggested to substitute for Ti(4+) ions in anatase (in the previous paper, Mn(2+) ion was suggested at an interstitial site rather than substitutional site) and the defect structures (characterized mainly by the local oxygen parameter u) for both tetragonal Mn(2+) and Fe(3+) impurity centers are estimated. The different zero-field splitting at room and low temperatures are due mainly to the change of local oxygen parameter u with the temperature. These results are discussed.     

Surfactant-mediated control of CBPQT(4+)-dialkoxynaphthalene complexation

The addition of the surfactant SDS to an aqueous solution containing 1·2 results in the disassembly of the latter via the simultaneous incorporation of 1 into a micelle and the precipitation of 2 by an anion exchange reaction.     

On the infrared spectrum of L-lysinium(2+) sulfate

It is argued that the infrared spectrum of L-lysine sulfate (L-Lys2+·SO4(2-)) published by Krishnakumar et al. [V. Krishnakumar, S. Manohar, R. Nagalakshmi, Spectrochim. Acta A75 (2010) 1394-1397] cannot belong to this crystal species. To confirm this, crystals (L-Lys2+·SO4(2-)) were synthesized and identified by XRD, and ATR FTIR and Raman spectra of L-Lys2+·SO4(2-) were registered and are discussed.     

On the photochemistry of IONO2: absorption cross section (240-370 nm) and photolysis product yields at 248 nm

The absolute absorption cross section of IONO(2) was measured by the pulsed photolysis at 193 nm of a NO(2)/CF(3)I mixture, followed by time-resolved Fourier transform spectroscopy in the near-UV. The resulting cross section at a temperature of 296 K over the wavelength range from 240 to 370 nm is given by log(10)(sigma(IONO(2))/cm(2) molecule(-1)) = 170.4 - 3.773 lambda + 2.965 x 10(-2)lambda(2)- 1.139 x 10(-4)lambda(3) + 2.144 x 10(-7)lambda(4)- 1.587 x 10(-10)lambda(5), where lambda is in nm; the cross section, with 2sigma uncertainty, ranges from (6.5 +/- 1.9) x 10(-18) cm(2) at 240 nm to (5 +/- 3) x 10(-19) cm(2) at 350 nm, and is significantly lower than a previous measurement [J. C. M?ssinger, D. M. Rowley and R. A. Cox, Atmos. Chem. Phys., 2002, 2, 227]. The photolysis quantum yields for IO and NO(3) production at 248 nm were measured using laser induced fluorescence of IO at 445 nm, and cavity ring-down spectroscopy of NO(3) at 662 nm, yielding phi(IO) 相似文献   

A bifunctional rhodamine derivative as chemosensor for recognizing Cu~(2+) and Hg~(2+) ions via different spectra

A new simple bifunctional chemosensor 1 based on rhodamine was synthesized by hydrazide and formylformic acid,which could detect Cu~(2+) and Hg~(2+) via dif ferent detecting methods in CH3 CN-HEPES buffer solution(20 mmol/L,pH 7.4)(1:9,v/v) respectively.When sensor 1 bound with Cu~(2+),it showed a colorimetric change,while a selective enhancement in fluorescence occurred upon 1 binding with Hg~(2+),resulting from the spirolatam-ring opening process.The binding modes of 1 with Cu~(2+) and Hg~(2+) were investigated based on UV,fluorescence change,ESI-Mass and Job's Plot data.Moreover,sensor 1 could selectively detect target ion in a mixed solution of Cu~(2+) and Hg~(2+),and the two metal ions do not inte rfere with each other in the process of detecting Cu~(2+) or Hg~(2+) with 1.     

A DNAzyme cascade for the amplified detection of Pb(2+) ions or L-histidine

DNAzyme cascades activated by Pb(2+)- or L-histidine-dependent DNAzymes yield the horseradish peroxidase-mimicking catalytic nucleic acids that enable the colorimetric or chemiluminescence detection of Pb(2+) or L-histidine.     

Electron-ion coincidence study of photofragmentation of the CdCl(2) molecule

In this work, the photofragmentation subsequent to valence and Cd4d photoionization of cadmium dichloride (CdCl₂) were studied using He I and synchrotron excitation. The measurements were performed with a photoelectron‐photoion coincidence (PEPICO) setup, and the connection between the singly ionized electronic states and cationic fragments was investigated. The valence‐ionized states were found to lead to , Cd⁺ and CdCl⁺. The Cd4d^{? 1} states were found to lead only to Cl⁺ ions. The observed charge transfer effect between Cd and Cl was concluded to take place due to internal conversion or fluorescence decay to dissociating valence states either directly or through consecutive fragmentation. The fragmentation energetics were investigated with molecular ab initio calculations, and the calculated energies were found to agree with the detected fragment appearances. Copyright © 2011 John Wiley & Sons, Ltd.     

Infrared spectra of DCl in liquid alkanes

Preliminary results are reported on the effect of solute-solvent interactions on the form of the DCl fundamental infrared absorption band. It is found that the band shape varies as a function of alkane chain length and isomerism. The results are interpreted in terms of the correlation function for DCl reorientation.     

ZnSe:Mn/ZnSe纳米晶体中的Mn~(2+)离子扩散

以ZnSe:Mn/ZnSe纳米晶体为基础,分析了Mn~(2+)离子在纳米晶体中的扩散行为.通过电子顺磁共振(EPR)谱参数确定Mn~(2+)离子处在纳米晶体内部.考虑到合成过程,确定Mn~(2+)离子处于纳米晶体的核壳界面.通过荧光光谱来揭示不同退火温度和退火时间下的纳米晶体的光学性质.不同退火条件情况下纳米晶体中各元素的含量由电感耦合等离子体(ICP)发射光谱得到.随着退火温度的增加和退火时间的延长,相同物质的量的纳米晶体中Mn元素含量逐渐变小直到为零,Zn和Se的含量几乎不变.相同退火温度不同退火时间下的电子透射显微镜照片说明退火对纳米晶体的形貌和粒径几乎没有影响.