Biomedical subjects

David H Powell

Publications and source records attributed to David H Powell.

11 recordsLinked to original sources

PubMed2006

2-Hydroxymethylboronate as a reagent to detect carbohydrates: application to the analysis of the formose reaction.

2-Hydroxymethylphenylboronate is described as a reagent that converts neutral 1,2-diols, as found in simple carbohydrates, into 1:1 anionic complexes that are easily detected by Fourier transform ion cyclotron resonance mass spectrometry. The value of this reagent was demonstrated through its application to analyze complex mixtures of carbohydrates formed in the formose process, often cited as a way that biologically significant carbohydrates might have been generated from formaldehyde under prebiotic conditions. Coupled with isotope studies, the reagent shows that the simplest autocatalytic cycle for the consumption of formaldehyde in this process cannot account for the bulk consumption of formaldehyde.

Boron Compounds↗

PubMed2006

Functionality dependent olefin activity in acyclic diene metathesis polymerization: mass spectrometry characterization of amino acid functionalized olefins.

Mass spectrometry has become an essential tool in delineating the structural properties of a new series of amino acid functionalized acyclic diene metathesis (ADMET) polymers known as bioolefins. These measurements, coupled with the measurement of the polymers chemical and physical properties, assist in the determination of their utility as biomaterials. In the present study, a set of five polymers with different bulk size and electronic properties were chosen for structural analyses by MALDI-TOF, MALDI-FTICR, and DIOS-TOF. The obtained data show that due to the competing metathesis and isomerization during ADMET, depending on their structural properties, the olefins display different selectivity toward main metathesis or isomerized products.

Acids, Acyclic↗

PubMed2005

Desorption/ionization on porous silicon mass spectrometry studies on pentose-borate complexes.

Desorption/ionization on porous silicon mass spectrometry (DIOS-MS) was used to investigate the binding affinities between aldopentose isomers and boron. Boron has been recognized for its importance in pentose synthesis and stabilization in prebiotic conditions. Boron may also account for the fact that ribose, among other aldopentoses, is the favored building block in RNA synthesis. This research started with the detection of aldopentoses in the positive mode through cationization and the aldopentose-borate complexes in the negative mode. Then two competition schemes, one using a pentose structure analogue and the other using 13C-labeled ribose, were designed to compare the relative binding affinities of four aldopentoses (xylose, lyxose, arabinose, and ribose) to boron. Both approaches determined the binding preference to be ribose > lyxose > arabinose > xylose. This work illustrates the potential of DIOS-MS in the analyses of nonvolatile, small molecules in delicate chemical equilibria. Without externally introduced matrices, background signals are not a limiting factor. Furthermore, the possible dramatic change of pH associated with the matrix introduction, which may disturb the equilibria of interest, is avoided.

Boron↗

PubMed2005

Tungsten allylimido complexes Cl4(RCN)W(NC3H5) as single-source CVD precursors for WNxCy thin films. Correlation of precursor fragmentation to film properties.

A mixture of the tungsten allylimido complexes Cl(4)(RCN)W(NC(3)H(5)) (3a, R = CH(3) and 3b, R = Ph) was tested as a single-source precursor for growth of tungsten nitride (WN(x)) or carbonitride (WN(x)C(y)) thin films. Films deposited from 3a,b below 550 degrees C contained amorphous beta-WN(x)C(y), while those deposited at higher temperatures were polycrystalline. Film growth rates from 3a,b ranged from 5 to 10 A/min over a temperature range of 450-650 degrees C, and the apparent activation energy for film growth was 0.15 eV. A plot of the E(a) values for deposition from Cl(4)(RCN)W(NR') [R' = Ph, (i)Pr, allyl] against the N-C imido bond strengths for the analogous amines R'NH(2) is linear, implicating cleavage of the N-C bond as the rate-determining step in film growth. The correlation of mass spectral fragmentation patterns for Cl(4)(RCN)W(NR') with film properties such as nitrogen content supports the significance of facile N-C bond cleavage in film growth.

Journal Article↗

PubMed2004

Discovery and neurochemical screening of peptides in brain extracellular fluid by chemical analysis of in vivo microdialysis samples.

Endogenous peptides from brain extracellular fluid of live rats were analyzed using capillary liquid chromatography (LC)-tandem mass spectrometry (MS2). A 4-mm-long microdialysis probe perfused at 0.6 microL/min implanted into the striatum of anesthetized male rats was used to collect 3.6 microL dialysate fractions that were injected on-line into the capillary LC-MS2 system for analysis. A total of 3349 MS2 spectra were collected from 13 different animals under basal conditions and during localized depolarization evoked by infusion of a high-K+ solution through the microdialysis probe. Subtractive analysis revealed a total of 859 MS2 spectra that were observed only during depolarization. From these spectra, 29 peptide sequences (25 were peptides not previously observed) from 6 different protein precursors were identified using database searching software. Proteins identified include precursors to neuropeptides, synaptic proteins, blood proteins, and transporters. The identified peptides represent candidates for neurotransmitters, neuromodulators, and markers of synaptic activity or brain tissue damage. A screen for neuroactivity of novel proenkephalin fragments that were found was performed by infusing the peptides into the brain while monitoring amino acid neurotransmitters by microdialysis sampling combined with capillary electrophoresis. Three of the six tested peptides evoked significant increases in various neuroactive amino acids. These results demonstrate that this combination of methods can identify novel neurotransmitter candidates and screen for potential neuroactivity.

Amino Acid Sequence↗

PubMed2004

Electrospray sample deposition for matrix-assisted laser desorption/ionization (MALDI) and atmospheric pressure MALDI mass spectrometry with attomole detection limits.

Electrospray sample deposition was explored for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). In this method, nanoliter volumes of matrix/analyte mixture were electrosprayed from a high voltage biased (1-2 kV) fused-silica capillary onto a grounded MALDI plate mounted 100-500 microm from the capillary outlet. Electrospray deposition with these conditions produced sample spots 200-300 microm in diameter thus matching the laser spot size. Varying spray voltage and distance resulted in different crystal sizes and volatilization rates for alpha-cyano-4-hydroxycinnamic acid matrix. Best results were obtained when the sample was deposited as wet droplets as opposed to deposition as dried solid. Under 'wet-spray' conditions, 2-4 microm diameter crystals were formed and detection limits for several neuropeptides were 0.7-25 amol. Samples could be pre-concentrated on the plate by spraying continuously and allowing sample to evaporate in a small spot. Sample volumes as large as 580 nL were deposited yielding a detection limit of 35 pM for neurotensin 1-11. Electrospray sample deposition yielded similar results when using atmospheric pressure-MALDI coupled with a quadrupole ion trap mass spectrometer, except that the sensitivity was approximately seven-fold worse.

Atmospheric Pressure↗

PubMed2004

MALDI-TOFMS compared with other polyphasic taxonomy approaches for the identification and classification of Bacillus pumilus spores.

To verify the efficacy of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) protein profiling for identifying and differentiating bacterial species, several strains of Bacillus pumilus were examined in a thorough taxonomic study incorporating a polyphasic approach. Sixteen isolates of putative B. pumilus isolated from spacecraft assembly facilities, the Mars Odyssey spacecraft, and the International Space Station, were characterized for their biochemical and molecular profiles using the Biolog system, DNA techniques, and MALDI-TOFMS protein profiling. MALDI-TOFMS protein profiling was more accurate than Biolog metabolic profiling, more discriminating than 16S rDNA sequence analysis, and complemented the results of gyrB sequence analysis and DNA-DNA hybridization for the identification of the B. pumilus spores. This is the first report whereby MALDI-TOFMS generated protein profiles from a set of microbes is compared directly with DNA-DNA hybridization yielding a positive correlation. Unique, cluster-specific biomarker peaks have been identified in the spores of the B. pumilus examined in this study. MALDI-TOFMS protein profiling is a rapid and simple analysis and has been demonstrated as a useful taxonomic tool for differentiating spores of the genus Bacillus. For practical purposes, it would be ideal (and necessary) to have a publicly available, standardized MALDI profile database, to facilitate the use of the technique as a diagnostic method to differentiate bacterial species.

Bacillus↗

PubMed2004

Species differentiation of a diverse suite of Bacillus spores by mass spectrometry-based protein profiling.

In this study, we demonstrate the versatility of matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOFMS) protein profiling for the species differentiation of a diverse suite of Bacillus spores. MALDI-TOFMS protein profiles of 11 different strains of Bacillus spores, encompassing nine different species, were evaluated. Bacillus species selected for MALDI-TOFMS analysis represented the spore-forming bacterial diversity of typical class 100K clean room spacecraft assembly facilities. A one-step sample treatment and MALDI-TOFMS preparation were used to minimize the sample preparation time. A library of MALDI-TOFMS spectra was created from these nine Bacillus species, the most diverse protein profiling study of the genus reported to date. Linear correlation analysis was used to successfully differentiate the MALDI-TOFMS protein profiles from all strains evaluated in this study. The MALDI-TOFMS protein profiles were compared with 16S rDNA sequences for their bacterial systematics and molecular phylogenetic affiliations. The MALDI-TOFMS profiles were found to be complementary to the 16S rDNA analysis. Proteomic studies of Bacillus subtilis 168 were pursued to identify proteins represented by the biomarker peaks in the MALDI-TOFMS spectrum. Four small, acid-soluble proteins (A, B, C, and D), one DNA binding protein, hypothetical protein ymf J, and four proteins associated with the spore coat and spore coat formation (coat JB, coat F, coat T, and spoIVA) were identified. The ability to visualize higher-molecular-mass coat proteins (10 to 25 kDa) as well as smaller proteins (<10 kDa) with MALDI-TOFMS profiling is critical for the complete and effective species differentiation of the Bacillus genus.

Bacillus↗

PubMed2003

Internal energy deposition in chemical ionization/tandem mass spectrometry.

The efficiency of the collision-induced dissociation (CID) process as a function of the internal energy deposited into the ion during the ionization event was evaluated. (M + H)+ ions of pyrrole, pyrrolidine, pyridine and piperidine (five and six-membered ring heterocyclics) were generated by chemical ionization (CI). The internal energy of the ions was varied by using different reagent gases. Both high-energy (keV) and low-energy (eV) CID were performed on these ions. The experiments showed that the (M + H)+ ions of the five-membered ring compounds, pyrrole and pyrrolidine, have higher fragmentation efficiencies than the six-membered ring compounds, pyridine and piperidine. Fragmentation efficiencies in high-energy CID clearly correlate with the internal energy deposited by the ionization technique. Experiments showed that the low-energy CID process is more sensitive than high-energy CID to changes in internal energy.

Journal Article↗

PubMed2002

Photophysics of monodisperse platinum-acetylide oligomers: delocalization in the singlet and triplet excited states.

A series of monodisperse Pt-acetylide polymers that contain the [-CC-(p-C6H4)-CC-(t-Pt(PBu3)2)-]n repeat unit has been prepared for n = 1, 2, 3, 4, 5, and 7. The photophysical properties of the series provide information concerning the relationship between the oligomer length and delocalization in the singlet and triplet excited states of the pi-conjugated electron system. The results imply that the singlet excited state is delocalized over approximately 6 repeat units; however, the triplet state is considerably more localized. The triplet energy is almost invariant with oligomer length, but the phosphorescence spectra and triplet nonradiative decay rates indicate that the electron-vibrational coupling in the triplet state decreases with increasing oligomer length.

Journal Article↗

PubMed2002

In vivo neurochemical monitoring by microdialysis and capillary separations.

Microdialysis is valuable for studying the neurochemical changes underlying behavior. Recent advances include the application of the high-sensitivity methods of capillary electrophoresis and capillary liquid chromatography with mass spectrometry to dialysate analysis. These methods have improved temporal resolution, spatial resolution, multi-analyte capability and potential for compound discovery.

Animals↗