120 research outputs found
Model of Controlled Synthesis of Uniform Colloid Particles: Cadmium Sulfide
The recently developed two-stage growth model of synthesis of monodispersed
polycrystalline colloidal particles is utilized and improved to explain growth
of uniform cadmium sulfide spheres. The model accounts for the coupled
processes of nucleation, which yields nanocrystalline precursors, and
aggregation of these subunits to form the final particles. The key parameters
have been identified that control the size selection and uniformity of the CdS
spheres, as well as the dynamics of the process. This approach can be used to
generally describe the formation of monodispersed colloids by precipitation
from homogeneous solutions.Comment: 20 pages in PD
Charge Inversion of Phospholipids by Dimetal Complexes for Positive Ion-Mode Electrospray Ionization Mass Spectrometry Analysis
Phospholipids
are vital constituents of living cells, as they are
involved in signaling and membrane formation. Mass spectrometry analysis
of many phospholipids is preferentially performed in the negative
ion-mode because of their acidic nature. Here we have studied the
potential of a digallium and dizinc complex to charge-invert a range
of different types of phospholipids and measured their ion yield and
fragmentation behavior in positive ion-mode tandem mass spectrometry.
The dimetal complexes bind specifically the phosphate groups of phospholipids
and add an excess of up to three positive charges per phosphate group.
Three different phosphoinositide phosphates (mono-, di-, and triphosphorylated
inositides), a phosphatidic acid, a phosphatidylcholine, a phosphatidylethanolamine,
and a phosphatidylglycerol were investigated. The intensities obtained
in positive ion-mode of phosphoinositide phosphates and phosphatidic
acid bound to {LGa<sub>2</sub>}<sup>5+</sup> were between 2.5- and
116-fold higher than that of the unmodified lipids in the negative
ion-mode. Native phosphoinositide ions yielded upon CID in the negative
ion-mode predominantly product ions due to losses of H<sub>3</sub>PO<sub>4</sub>, PO<sub>3</sub><sup>–</sup> and H<sub>2</sub>O. In comparison, CID spectra of {LGa<sub>2</sub>}<sup>5+</sup>-bound
phosphoinositides generally resulted in fragment ions corresponding
to loss of the full diglyceride chain as well as the remaining headgroup
bound to {LGa<sub>2</sub>}<sup>5+</sup> as the most abundant peaks.
A number of signature fragment ions of moderate abundance were observed
that allowed for distinction between the three regioisomers of 1,2-diÂ(9Z-octadecenoyl)-<i>sn</i>-glycero-3-[phosphoinositol-x,y-bisphosphate] (PIÂ(3,4)ÂP<sub>2</sub>, PIÂ(3,5)ÂP<sub>2</sub>, PIÂ(4,5)ÂP<sub>2</sub>)
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