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221.
Zhou AJ Qin LJ Beedle CC Ding S Nakano M Leng JD Tong ML Hendrickson DN 《Inorganic chemistry》2007,46(20):8111-8113
Room-temperature reactions of N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine with manganese(II) salts yield a novel family of Mn(12) clusters incorporating the same Mn(12)O(4) core and tunable oxidation states of Mn(III)(x)Mn(II)(12-x) (x = 8, 10, and 12). Magnetic susceptibility data indicate that the spin of the ground state increases as the number of Mn(III) ions is increased, leading to increases in the magnitude of the out-of-phase ac susceptibility signal as the number of Mn(III) ions is increased. 相似文献
222.
Beu SC Hendrickson CL Marshall AG 《Journal of the American Society for Mass Spectrometry》2011,22(3):591-601
Radiofrequency (rf) multipole ion guides are widely used to transfer ions through the strong magnetic field gradient between
source and analyzer regions of external source Fourier transform ion cyclotron resonance mass spectrometers. Although ion
transfer as determined solely by the electric field in a multipole ion guide has been thoroughly studied, transfer influenced
by immersion in a strong magnetic field gradient has not been as well characterized. Recent work has indicated that the added
magnetic field can have profound effects on ion transfer, ultimately resulting in loss of ions initially contained within
the multipole. Those losses result from radial ejection of ions due to transient cyclotron resonance that occurs when ions
traverse a region in which the magnetic field results in an effective cyclotron frequency equal to the multipole rf drive
frequency divided by the multipole order (multipole order is equal to one-half the number of poles). In this work, we describe
the analytical basis for ion resonance in a rf multipole ion guide with superposed static magnetic field and compare with
results of numerical trajectory simulations. 相似文献
223.
Leonard Nyadong Ellen D. Inutan Xu Wang Christopher L. Hendrickson Sarah Trimpin Alan G. Marshall 《Journal of the American Society for Mass Spectrometry》2013,24(3):320-328
We present the first coupling of laser spray ionization inlet (LSII) and matrix assisted ionization inlet (MAII) to high-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) for generation of electrospray-like ions to take advantage of increased sensitivity, mass range, and mass resolving power afforded by multiple charging. We apply the technique to top-down protein analysis and characterization of metalloproteins. We also present a novel method for generation of multiply-charged copper–peptide complexes with varying degrees of copper adduction by LSII. We show an application of the generated copper–peptide complexes for protein charge state and molecular weight determination, particularly useful for an instrument such as a linear ion trap mass analyzer. 相似文献
224.
Lawrence J Yang EC Edwards R Olmstead MM Ramsey C Dalal NS Gantzel PK Hill S Hendrickson DN 《Inorganic chemistry》2008,47(6):1965-1974
High-frequency electron paramagnetic resonance (HFEPR) data are presented for four closely related tetranuclear Ni(II) complexes, [Ni(hmp)(MeOH)Cl]4.H2O (1a), [Ni(hmp)(MeOH)Br]4.H2O (1b), [Ni(hmp)(EtOH)Cl]4.H2O (2), and [Ni(hmp)(dmb)Cl]4 (3) (where hmp(-) is the anion of 2-hydroxymethylpyridine and dmb is 3,3'-dimethyl-1-butanol), which exhibit magnetic bistability (hysteresis) and fast magnetization tunneling at low temperatures, properties which suggest they are single-molecule magnets (SMMs). The HFEPR spectra confirm spin S = 4 ground states and dominant uniaxial anisotropy (DSz(2), D < 0) for all four complexes, which are the essential ingredients for a SMM. The individual fine structure peaks (due to zero-field splitting) for complexes 1a, 1b, and 2 are rather broad. They also exhibit further (significant) splitting, which can be explained by the fact that there exists two crystallographically distinct Ni 4 sites in the lattices for these complexes, with associated differences in metal-ligand bond lengths and different zero-field splitting (ZFS) parameters. The broad EPR lines, meanwhile, may be attributed to ligand and solvent disorder, which results in additional distributions of microenvironments. In the case of complex 3, there are no solvate molecules in the structure, and only one distinct Ni 4 molecule in the lattice. Consequently, the HFEPR data for complex 3 are extremely sharp. As the temperature of a crystal of complex 3 is decreased, the HFEPR spectrum splits abruptly at approximately 46 K into two patterns with very slightly different ZFS parameters. Heat capacity data suggest that this is caused by a structural transition at 46.6 K. A single-crystal X-ray structure at 12(2) K indicates large thermal parameters on the terminal methyl groups of the dmb (3,3-dimethyl-1-butanol) ligand. Most likely there exists dynamic disorder of parts of the dmb ligand above 46.6 K; an order-disorder structural phase transition at 46.6 K then removes some of the motion. A further decrease in temperature (<6 K) leads to further fine structure splittings for complex 3. This behavior is thought to be due to the onset of short-range magnetic correlations/coherences between molecules caused by weak intermolecular magnetic exchange interactions. 相似文献
225.
Sorai M Burriel R Westrum EF Hendrickson DN 《The journal of physical chemistry. B》2008,112(14):4344-4350
Magnetic and thermal properties of the iron(III) spin crossover complex [Fe(3MeO-salenEt)(2)]PF(6) are very sensitive to mechanochemical perturbations. Heat capacities for unperturbed and differently perturbed samples were precisely determined by adiabatic calorimetry at temperatures in the 10-300 K range. The unperturbed compound shows a cooperative spin crossover transition at 162.31 K, presenting a hysteresis of 2.8 K. The anomalous enthalpy and entropy contents of the transition were evaluated to be Delta(trs)H = 5.94 kJ mol(-1) and Delta(trs)S = 36.7 J K(-1) mol(-1), respectively. By mechanochemical treatments, (1) the phase transition temperature was lowered by 1.14 K, (2) the enthalpy and entropy gains at the phase transition due to the spin crossover phenomenon were diminished to Delta(trs)H = 4.94 kJ mol(-1) and Delta(trs)S = 31.1 J K(-1) mol(-1), and (3) the lattice heat capacities were larger than those of the unperturbed sample over the whole temperature range. In spite of different mechanical perturbations (grinding with a mortar and pestle and grinding in a ball-mill), two sets of heat capacity measurements provided basically the same results. The mechanochemical perturbation exerts its effect more strongly on the low-spin state than on the high-spin state. It shows a substantial increase of the number of iron(III) ions in the high-spin state below the transition temperature. The heat capacities of the diamagnetic cobalt(III) analogue [Co(3MeO-salenEt)(2)]PF(6) also were measured. The lattice heat capacity of the iron compounds has been estimated from either the measurements on the cobalt complex using a corresponding states law or the effective frequency distribution method. These estimations have been used for the evaluation of the transition anomaly. 相似文献
226.
227.
Vladimirov G Hendrickson CL Blakney GT Marshall AG Heeren RM Nikolaev EN 《Journal of the American Society for Mass Spectrometry》2012,23(2):375-384
Particle-in-Cell (PIC) ion trajectory calculations provide the most realistic simulation of Fourier transform ion cyclotron
resonance (FT-ICR) experiments by efficient and accurate calculation of the forces acting on each ion in an ensemble (cloud),
including Coulomb interactions (space charge), the electric field of the ICR trap electrodes, image charges on the trap electrodes,
the magnetic field, and collisions with neutral gas molecules. It has been shown recently that ion cloud collective behavior
is required to generate an FT-ICR signal and that two main phenomena influence mass resolution and dynamic range. The first
is formation of an ellipsoidal ion cloud (termed “condensation”) at a critical ion number (density), which facilitates signal
generation in an FT-ICR cell of arbitrary geometry because the condensed cloud behaves as a quasi-ion. The second phenomenon
is peak coalescence. Ion resonances that are closely spaced in m/z coalesce into one resonance if the ion number (density) exceeds a threshold that depends on magnetic field strength, ion
cyclotron radius, ion masses and mass difference, and ion initial spatial distribution. These two phenomena decrease dynamic
range by rapid cloud dephasing at small ion density and by cloud coalescence at high ion density. Here, we use PIC simulations
to quantitate the dependence of coalescence on each critical parameter. Transitions between independent and coalesced motion
were observed in a series of the experiments that systematically varied ion number, magnetic field strength, ion radius, ion
m/z, ion m/z difference, and ion initial spatial distribution (the present simulations begin from elliptically-shaped ion clouds with
constant ion density distribution). Our simulations show that mass resolution is constant at a given magnetic field strength
with increasing ion number until a critical value (N) is reached. N dependence on magnetic field strength, cyclotron radius,
ion mass, and difference between ion masses was determined for two ion ensembles of different m/z, equal abundance, and equal cyclotron radius. We find that N and dynamic range depend quadratically on magnetic field strength
in the range 1–21 Tesla. Dependences on cyclotron radius and Δm/z are linear. N depends on m/z as (m/z)–2. Empirical expressions for mass resolution as a function of each of the experimental parameters are presented. Here, we provide
the first exposition of the origin and extent of trade-off between FT-ICR MS dynamic range and mass resolution (defined not
as line width, but as the separation between the most closely resolved masses). 相似文献
228.
Sydora OL Henry TP Wolczanski PT Lobkovsky EB Rumberger E Hendrickson DN 《Inorganic chemistry》2006,45(2):609-626
A convenient synthesis of (t)Bu(3)SiSH and (t)Bu(3)SiSNa(THF)(x)() led to the exploration of "(t)Bu(3)SiSMX" aggregation. The dimer, [((t)Bu(3)SiS)Fe](2)(mu-SSi(t)Bu(3))(2) (1(2)), was formed from [{(Me(3)Si)(2)N}Fe](2)(mu-N(SiMe(3))(2))(2) and the thiol, and its dissolution in THF generated ((t)Bu(3)SiS)(2)Fe(THF)(2) (1-(THF)(2)). Metathetical procedures with the thiolate yielded aggregate precursors [X(2)Fe](mu-SSi(t)Bu(3))(2)[FeX(THF)]Na(THF)(4) (3-X, X = Cl, Br) and cis-[(THF)IFe](2)(mu-SSi(t)Bu(3))(2) (4). Thermal desolvations of 3-Cl, 3-Br and 4 afforded molecular wheels [Fe(mu-X)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-FeX, X = Cl, Br) and the ellipse [Fe(mu-I)(mu-SSi(t)Bu(3))](14)(C(6)H(6))(n) (6-FeI). Related metathesis and desolvation sequences led to wheels [Co(mu-Cl)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-CoCl) and [Ni(mu-Br)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-NiBr). The nickel wheel disproportionated to give, in part, [((t)Bu(3)SiS)Ni](2)(mu-SSi(t)Bu(3))(2) (7), which was also synthesized via salt metathesis. X-ray structural studies of 1(2) revealed a roughly planar Fe(2)S(4) core, while 1-(THF)(2), 3-Br, and 4 possessed simple distorted tetrahedral and edge-shared tetrahedral structures. X-ray structural studies revealed 5-MX (MX = FeCl, FeBr, CoCl, NiBr) to be wheels based on edge-shared tetrahedra, but while the pseudo-D(6)(d) wheels of 5-FeCl, 5-CoCl, and 5-FeBr pack in a body-centered arrangement, those of pseudo-C(6)(v)() 5-NiBr exhibit hexagonal packing and two distinct trans-annular d(Br...Br). Variable-temperature magnetic susceptibility measurements were conducted on 5-FeCl, 5-CoCl, 5-FeBr, and 6-FeI, and the latter three are best construed as weakly antiferromagnetic, while 5-FeCl exhibited modest ferromagnetic coupling. Features suggesting molecular magnetism are most likely affiliated with phase changes at low temperatures. 相似文献