Dynamics of ammonium and ammonia in solutions is closely related to the metabolism of ammoniac compounds, therefore plays an important role in various biological processes. NMR measurements indicated that the reorientation dynamics of NH4+ is faster in its aqueous solution than in methanol, which deviates from the Stokes-Einstein-Debye rule since water has higher viscosity than methanol. To address this intriguing issue, we herein study the reorientation dynamics of ammonium ion in both solutions using numerical simulation and an extended cyclic Markov chain model. An evident decoupling between translation and rotation of methanol is observed in simulation, which results in the deviation of reorientation from the Stokes-Einstein-Debye rule. Slower hydrogen bond (HB) switchings of ammonium with methanol comparing to that with water, due to the steric effect of the methyl group, remarkably retards the jump rotation of ammonium. The observations herein provide useful insights into the dynamic behavior of ammonium in the heterogeneous environments including the protein surface or protein channels. 相似文献
A dual-polarity linear ion trap (LIT) mass spectrometer was developed in this study, and the method for simultaneously controlling and detecting cations and anions was proposed and realized in the LIT. With the application of an additional dipolar DC field on the ejection electrodes of an LIT, dual-polarity mass spectra could be obtained, which include both the mass-to-charge (m/z) ratio and charge polarity information of an ion. Compared with conventional method, the ion ejection and detection efficiency could also be improved by about one-fold. Furthermore, ion–ion reactions within the LIT could be dynamically controlled and monitored by manipulating the distributions of ions with opposite charge polarities. This method was then used to control and study the reaction kinetics of ion–ion reactions, including electron transfer dissociation (ETD) and charge inversion reactions. A dual-polarity collision-induced dissociation (CID) experiment was proposed and performed to enhance the sequence coverage of a peptide ion. Ion trajectory simulations were also carried out for concept validation and system optimization.
Zusammenfassung Es wird über eine Methode zur Bestimmung von Halogenidionen in Halogenidgemischen berichtet. Die Endpunktindikation erfolgt nach dem Prinzip der Polarisationsspannungstitration und liefert scharf ausgeprägte Titrationsendpunkte in der Reihenfolge der Schwerlöslichkeit der Ag-Halogenide. Insbesondere wird auch der für Serienanalysen erforderlichen Einfachheit und geringen Störanfälligkeit Rechnung getragen. Das Verfahren eignet sich für die Analyse anorganischer Halogenidgemische, für die Bestimmung von CN–- und SCN– -Ionen und für die Analyse organischer Halogenverbindungen im Makro- und Halbmikromaßstab nach deren Aufschluß. Die Meßanordnung kann außerdem für die Bestimmung von Kalium und für die Endpunktindikation einiger chelatometrischer Titrationen eingesetzt werden.
Summary A method is described for the determination of halogenide in mixtures of halogenides. End points are sharply indicated by the polarisation titration technique in the order of solubility of the silver halogenides. The method is suitable for the analysis of mixtures of inorganic halogenides, for the determination of CN– and SCN–ions, and for the analysis of organic halogen compounds in macro and semimicro scale after decomposition. For routine analyses it offers the advantage of being simple and only slightly liable to interferences. Moreover, the assembly can be used for the determination of potassium and for the end point indication in some chelatometric titrations.
Effective temperatures of ions during traveling wave ion mobility spectrometry (TWIMS) analysis were measured using singly
protonated leucine enkephalin dimer as a chemical thermometer by monitoring dissociation of the dimer into monomer, as well
as the subsequent dissociation of monomer into a-, b-, and y-ions, as a function of instrumental parameters. At fixed helium cell and TWIMS cell gas flow rates, the extent of dissociation
does not vary significantly with either the wave velocity or wave height, except at low (<500 m/s) wave velocities that are
not commonly used. Increasing the flow rate of nitrogen gas into the TWIMS cell and decreasing the flow rate of helium gas
into the helium cell resulted in greater dissociation. However, the mobility distributions of the fragment ions formed by
dissociation of the dimer upon injection into the TWIMS cell are nearly indistinguishable from those of fragment ions formed
in the collision cell prior to TWIMS analysis for all TWIMS experiments. These results indicate that heating and dissociation
occur when ions are injected into the TWIMS cell, and that the effective temperature subsequently decreases to a point at
which no further dissociation is observed during the TWIMS analysis. An upper limit to the effective ion temperature of 449 K
during TWIMS analysis is obtained at a helium flow rate of 180 mL/min, TWIMS flow rate of 80 mL/min, and traveling wave height
of 40 V, which is well below previously reported values. Effects of ion heating in TWIMS on gas-phase protein conformation
are presented. 相似文献
An efficient and simple amine‐catatalyzed azide conjugate addition to α,β‐unsaturated aldehydes has been developed. In the presence of a catalytic amount of tertiary amine with a 1:1 mixture of NaN3 and 37% HCl in CH2Cl2, α,β‐unsaturated aldehydes provided β‐azido aldehydes, which could be transformed into 1,3‐amino alcohols. 相似文献
The influence of doping with niobium on the structure and oxygen nonstoichiometry of strontium ferrite SrFe1 − xNbxO3 − δ (x = 0.05, 0.1, 0.2, 0.3, and 0.4) was studied. The content of oxygen in the doped derivatives was determined by coulometric
titration as a function of temperature (650–950°C) and oxygen partial pressure in the gas phase (10−4−1 atm). The partial molar enthalpies Δ(x, δ) and entropies Δ(x, δ) of oxygen in SrFe1 − xNbxO3 − δ were calculated. An analysis of Δ(x, δ) dependences showed that the model of a random distribution of ions and vacancies over accessible sites in the oxygen
sublattice allowed the experimental data to be described satisfactorily. An increase in the partial enthalpy Δ(x, δ) as nonstoichiometry δ decreased was indicative of weak repulsive interactions between oxygen ions in the structure of
SrFe1 − xNbxO3 − δ.
Original Russian Text ? P.V. Anikina, A.A. Markov, M.V. Patrakeev, I.A. Leonidov, V.L. Kozhevnikov, 2009, published in Zhurnal
Fizicheskoi Khimii, 2009, Vol. 83, No. 5, pp. 811–817. 相似文献
We report a γ-ray irradiation reduction method to prepare MnO/reduced graphene oxide (rGO) nanocomposite for the anode of lithium ion batteries. γ-Ray irradiation provides a clean way to generate homogeneously dispersed MnO nanoparticles with finely tuned size on rGO surface without the use of surfactant. The MnO/rGO composite enables a fully charge/discharge in 2 min to gain a reversible specific capacity of 546 (mA·h)/g which is 45% higher than the theoretical value of commercial graphite anode. 相似文献
First Circular / Pre-registration (e-mail edition) July 14-18, 2003 Kanazawa Institute of Technology, Nonoichi, Ishikawa Pref., JAPAN Organized by Japan Association of Ion Exchange (JAIE) INVITATION On behalf of the Japan Association of Ion Exchange (J… 相似文献
New perovskite oxide phases BaCe1 − xInxO3 − x/2 (x = 0.1–0.8) (space group Pbnm) have been synthesized. The unit cell volume of the resulting solid solutions monotonically decreases with an increase in
the degree of substitution of indium for cerium due to the contraction of octahedra in perovskite blocks. The thermodynamic
stability of the compound BaCe0.75In0.25O2.875 was studied by the solution calorimetry method, and barium cerates were shown to be thermodynamically stable with respect
to binary oxides at room temperature. The structure of occupied and vacant states in BaCe1 − xInxO3 − x/2 was determined on the basis of X-ray emission, absorption, and photoelectron spectra, and the energy gap was estimated at
∼2 eV. 相似文献
Type studies on competitive polyatomic anion versus acetonitrile coordination in the self-assembly of a series of [Ag2(X)m(bip)(NCCH3)n](X)2−m (X− = NO3−, CF3SO3−, ClO4−, BF4−, and PF6−; m = 0, 2; n = 0, 2, 4; bip = 1,4-bis(2-isonicotinoyloxyethyl)piperazine) were carried out. Each bip spacer acts as an N4 tetradentate ligand and is linked to four silver(I) centers through two pyridine and two piperazine moieties, producing a
double strand consisting of two 20-membered ring units. The coordinating environment around the silver(I) center is subtly
determined by the competition of the polyatomic anions with acetonitrile, that is, by the Ag···NCCH3 versus Ag···X interactions. The coordinating ability of acetonitrile is inversely proportional to the order of the coordination
ability of the Hoffmeister series of polyatomic anions, NO3− ≫ CF3SO3− > ClO4− > BF4− ≫ PF6−. 相似文献
Apparent molar volumes (V2,φ) and heat capacities (Cp2,φ) of glycine in known concentrations (1.0, 2.0, 4.0, 6.0, and 8.0 mol⋅kg−1) of aqueous formamide (FM), acetamide (AM), and N,N-dimethylacetamide (DMA) solutions at T=298.15 K have been calculated from relative density and specific heat capacity measurements. These measurements were completed
using a vibrating-tube flow densimeter and a Picker flow microcalorimeter, respectively. The concentration dependences of
the apparent molar data have been used to calculate standard partial molar properties. The latter values have been combined
with previously published standard partial molar volumes and heat capacities for glycine in water to calculate volumes and
heat capacities associated with the transfer of glycine from water to the investigated aqueous amide solutions, D[`(V)]2,tro\Delta\overline{V}_{\mathrm{2,tr}}^{\mathrm{o}} and D[`(C)]p2,tro\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}} respectively. Calculated values for D[`(V)]2,tro\Delta\overline{V}_{\mathrm{2,tr}}^{\mathrm{o}} and D[`(C)]p2,tro\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}} are positive for all investigated concentrations of aqueous FM and AM solutions. However, values for D[`(C)]p2,tro\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}} associated with aqueous DMA solutions are found to be negative. The reported transfer properties increase with increasing
co-solute (amide) concentration. This observation is discussed in terms of solute + co-solute interactions. The transfer properties
have also been used to estimate interaction coefficients. 相似文献
It is well documented since the early days of the development of atmospheric pressure ionization methods, which operate in the gas phase, that cluster ions are ubiquitous. This holds true for atmospheric pressure chemical ionization, as well as for more recent techniques, such as atmospheric pressure photoionization, direct analysis in real time, and many more. In fact, it is well established that cluster ions are the primary carriers of the net charge generated. Nevertheless, cluster ion chemistry has only been sporadically included in the numerous proposed ionization mechanisms leading to charged target analytes, which are often protonated molecules. This paper series, consisting of two parts, attempts to highlight the role of cluster ion chemistry with regard to the generation of analyte ions. In addition, the impact of the changing reaction matrix and the non-thermal collisions of ions en route from the atmospheric pressure ion source to the high vacuum analyzer region are discussed. This work addresses such issues as extent of protonation versus deuteration, the extent of analyte fragmentation, as well as highly variable ionization efficiencies, among others. In Part 1, the nature of the reagent ion generation is examined, as well as the extent of thermodynamic versus kinetic control of the resulting ion population entering the analyzer region.
