Hydrogen silsesquioxanes (HSQ or H-resin), represented by (HSiO3/2)2n or TH(2n), are an important class of polymers that have gained popularity as spin-on dielectrics by the electronic industry. Previously in the literature, small oligomeric species such as (HSiO3/2)2n, where n = 4-16, have been identified by GC-MS. However, nondestructive mass spectral results for larger H-resin molecules have not been reported, likely due to the nonpolar nature of these molecules. We have utilized a number of "soft" ionization techniques such as field desorption (FD), desorption chemical ionization (DCI), and matrix-assisted laser desorption/ionization (MALDI), and demonstrated that they are amenable to hydrogen silsesquioxanes. The [TH(2n) - H]+* ions were observed by FD-MS while [TH(2n) + NH4]+ and [TH(2n) + Na]+ ions were found utilizing DCI and MALDI, respectively. Based upon the MS results, the polymer compositions as well as molecular weight information can be easily obtained. The detailed structures of H-resin components, however, remain a difficult issue, which cannot be answered by MS data alone. With these preliminary MS results, we have clearly demonstrated that mass spectrometry with the above-mentioned ionization techniques is an invaluable tool that can be utilized when attempting to solve the challenge set forth by the complexity of hydrogen silsesquioxane materials. 相似文献
During the metabolic work-up of a patient presenting with neonatal convulsions, we consistently observed the presence of unusual peaks in the gas chromatographic-mass spectrometric analysis of urinary organic acids. The gas chromatographic-mass spectrometric characteristics of the unusual peaks suggested that they corresponded to derivatives of N-acetylated amino acids. The tentative identification was confirmed by the identity of retention times and mass spectra of the trimethylsilyl derivatives of the authentic compounds. We describe our observations that led to the identification of the various N-acetylated amino acids in this first patient with a confirmed deficiency of aminoacylase I, an enzyme involved in the cytosolic degradation of N-terminally modified proteins. The potential and limitations of urinary organic acid analysis for the detection of N-acetylated amino acids was further studied using pure compounds. In addition, we provide mass spectral data for 37 trimethylsilyl derivatives from 17 N-acetylated amino acids, most of which have not been reported previously. Our data provide valuable information that will help the clinical laboratorians who are responsible for organic acid analysis to recognize this new condition and could aid its detection in other patients. 相似文献
A novel set-up for Fourier transform ion cyclotron resonance mass spectrometry (FTICR) is reported for simultaneous infrared multiphoton dissociation (IRMPD) and electron-capture dissociation (ECD). An unmodified electron gun ensures complete, on-axis overlap between the electron and the photon beams. The instrumentation, design and implementation of this novel approach are described. In this configuration the IR beam is directed into the ICR cell using a pneumatically actuated mirror inserted into the ion-optical path. Concept validation was made using different combinations of IRMPD and ECD irradiation events on two standard peptides. The ability to perform efficient IRMPD, ECD and especially simultaneous IRMPD and ECD using lower irradiation times is demonstrated. The increase in primary sequence coverage, with the combined IRMPD and ECD set-up, also increases the confidence in peptide and protein assignments. 相似文献
For an odd prime p, define
, where z is an integer (mod p) and the summands are Legendre symbols. The function Hp(z) was explicitly evaluated for z=1 by Evans (1981) and for z=−1 by Greene and Stanton (1986). Koike (1992) determined Hp(1/4) (mod p), and Ono (1998) evaluated Hp(z) for z=1/4,−1/8, and 1/64. This paper evaluates Hp(z) for infinitely many new classes of arguments z.
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Label-free imaging mass spectrometry provides a new look into different research areas. Will chemical mass microscopy on a biological system move from hype to hope?
Let s(x) denote the maximum number of non-overlapping unit squares which can be packed into a large square of side length x. Let W(x)=x2−s(x) denote the “wasted” area, i.e., the area not covered by the unit squares. In this note we prove that
Polymerizable surfactants (surfmers) 12-acryloyloxy-dodecanoic acid and 11-acrylamidoundecanoic acid and their respective sodium salts were prepared and then polymerized to form their corresponding oligomers using reversible addition-fragmentation chain transfer (RAFT). Different concentrations of both the surfmers, their sodium salts, and their RAFT oligomers were used as polysoaps in the emulsion polymerization of styrene. Stabilities of the pre-emulsions before polymerization were determined and compared. After polymerization, particle sizes and polydispersities of the resulting polystyrene latices were determined. Sodium dodecyl sulfate (SDS) was used as a reference surfactant to compare the particle sizes and stabilities of the pre-emulsions prepared using surfmers and polymeric surfactants (polysoaps) as particle stabilizers. Emulsion polymerization of styrene using these surfmers and polysoaps all led to latices which were stable for a period of more than six months, as indicated by constant particle sizes, whereas latices prepared using the conventional surfactant, SDS, were not as stable. 相似文献
Advanced manufacturing has received considerable attention as a tool for the fabrication of cell scaffolds however, finding ideal biocompatible and biodegradable materials that fit the correct parameters for 3D printing and guide cells to align remain a challenge. Herein, a photocrosslinkable smectic-A (Sm-A) liquid crystal elastomer (LCE) designed for 3D printing is presented, that promotes cell proliferation but most importantly induces cell anisotropy. The LCE-based bio-ink allows the 3D duplication of a highly complex brain structure generated from an animal model. Vascular tissue models are generated from fluorescently stained mouse tissue spatially imaged using confocal microscopy and subsequently processed to create a digital 3D model suitable for printing. The 3D structure is reproduced using a Digital Light Processing (DLP) stereolithography (SLA) desktop 3D printer. Synchrotron Small-Angle X-ray Diffraction (SAXD) data reveal a strong alignment of the LCE layering within the struts of the printed 3D scaffold. The resultant anisotropy of the LCE struts is then shown to direct cell growth. This study offers a simple approach to produce model tissues built within hours that promote cellular alignment. 相似文献