Biomedical subjects

Chuanfan Ding

Publications and source records attributed to Chuanfan Ding.

5 recordsLinked to original sources

PubMed2006

Linear quadrupoles with added hexapole fields.

Linear quadrupoles with added hexapole fields are described. The shifts in ion oscillation frequency caused by the addition of a hexapole field are calculated within the effective potential model. Methods to construct linear quadrupoles with added hexapole fields with exact electrode geometries and with round rods are discussed. A quadrupole with added hexapole field can be constructed with round rods by rotating two rods (say the y rods) towards an x rod. Computer simulations are used to investigate the possibility of mass analysis with quadrupoles with added hexapole fields. We find that a quadrupole with an added hexapole field in the range 2-12% can provide mass analysis provided the dc is applied with the correct polarity and value. When a rod set is constructed with round rods, other multipoles in the potential degrade the peak shape, resolution and transmission. The largest of these after the quadrupole and hexapole are a dipole and octopole term. With round rod sets, the peak shape can be improved by using different diameters for the x and y rod pairs to minimize the octopole term in the potential and by injecting ions at the field center where the dipole term is zero. Calculations of the boundaries of the stability diagram for this case show the boundaries move out, relative to those of a pure quadrupole field, but remain sharp.

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PubMed2005

Coordination of ScO+ and YO+ by multiple Ar, Kr, and Xe atoms in noble gas matrixes: a matrix isolation infrared spectroscopic and theoretical study.

The combination of matrix isolation infrared spectroscopic and quantum chemical calculation results provide strong evidence that scandium and yttrium monoxide cations, ScO+ and YO+, coordinate multiple noble gas atoms in forming noble gas complexes. The results showed that ScO+ coordinates five Ar, Kr, or Xe atoms, and YO+ coordinates six Ar or Kr and five Xe atoms in solid noble gas matrixes. Hence, the ScO+ and YO+ cations trapped in solid noble gas matrixes should be regarded as the [ScO(Ng)5]+ (Ng = Ar, Kr, or Xe), [YO(Ng)6]+ (Ng = Ar or Kr) or [YO(Xe)5]+ complexes. Experiments with dilute krypton or xenon in argon or krypton in xenon produced new IR bands, which are due to the stepwise formation of the [ScO(Ar)(5-n)(Kr)n]+, [ScO(Kr)(5-n)(Xe)n]+ (n = 1-5), [YO(Ar)(6-n)(Kr)n]+ (n = 1-6), and [YO(Ar)(6-n)(Xe)n]+ (n = 1-4) complexes.

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PubMed2005

Infrared spectra and structures of the OSc(N2), OScNN, and OScNN+ complexes in solid argon.

Scandium monoxide-dinitrogen complexes-OSc(N2), OScNN, and OScNN+-have been prepared by the reactions of laser-evaporated scandium monoxide with N2 or scandium atoms with N2O in solid argon. The ground-state scandium monoxide molecule reacted with N2 to form the side-bonded OSc(N2) complex spontaneously on annealing. This complex rearranged to the end-on bonded OScNN complex upon UV irradiation. Both the OSc(N2) and OScNN complexes in solid argon can be assigned to have 2A' ' electronic ground state with Cs symmetry arising from the 2Delta first excited-state ScO. The neutral complexes can also be photoionized to the OScNN+ cation complex upon UV irradiation.

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PubMed2003

Quadrupole mass filters with octopole fields.

The performance of quadrupole mass filters with added octopole fields in the range 2.0-4.0% has been investigated. The added fields are much greater than those normally added to conventional rod sets by mechanical tolerances or construction errors. Quadrupole rod sets with added octopole fields were constructed with round rods by making one pair of rods greater in diameter than the other pair. For positive ions, resolution at half height of only about 200 is possible if the negative direct current (dc) output of the quadrupole power supply is connected to the smaller rods. If the positive dc output of the quadrupole power supply is connected to the smaller rods, the resolution improves dramatically; a resolution at half height of 5800 has been observed with a rod set with 2.6% added octopole field. For negative ions the best resolution is obtained with the polarity of the dc reversed, i.e. with the negative dc applied to the smaller rods. These findings are unexpected in view of the literature that argues that to obtain high mass resolution with quadrupole mass filters, higher order multipoles must be kept as small as possible. Numerical simulations of peak shapes agree qualitatively with experiments. Simulation of the boundaries of the first stability region for positive ions shows that when the positive dc is applied to the smaller rods, the addition of a 2.0% octopole field causes the boundaries to shift slightly but the boundaries are well defined, and the tip of the stability region remains sharp. When the positive dc is applied to the larger rods, the boundaries of the stability region move out and become diffuse. For instruments that require a rod set that can be used both as a linear trap and a mass filter, these rod sets may offer improved trap performance while still being capable of providing conventional mass analysis.

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PubMed2002

Hydrogen/deuterium exchange of myoglobin ions in a linear quadrupole ion trap.

The hydrogen/deuterium (H/D) exchange of gas-phase ions of holo- and apo-myoglobin has been studied by confining the ions in a linear quadrupole ion trap with D(2)O or CD(3)OD at a pressure of several mTorr. Apo-myoglobin ions were formed by collision-induced dissociation of holo-myoglobin ions between the orifice and skimmer of the ion sampling system. The exchange takes place on a time scale of seconds. Earlier cross section measurements have shown that holo-myoglobin ions can have more compact structures than apo-myoglobin. Despite this, both holo-myoglobin and apo-myoglobin in charge states +8 to +14 are found to exchange nearly the same number of hydrogens (ca. 103) in 4 s. It is possible the ions fold or unfold to new conformations on the much longer time scale of the exchange experiment compared with the cross section measurements.

Apoproteins↗