Coalescence Behavior of Pure and Natural Fat Droplets Characterized via Micromanipulation

For two approaching oil droplets, a region of arrested coalescence lies between full coalescence and total stability. Here the fusion of two droplets begins, but they are stopped from fully relaxing into one spherical droplet. The internal rigidity of the solid fat network within each droplet can provide the resistance necessary to arrest the shape change driven by Laplace pressure. These intermediate doublet structures lead to the partially‐coalesced fat networks important for the desired physical properties of ice cream and whipped topping. The use of micromanipulation techniques allows coalescence events between two oil droplets to be microscopically observed. In this study, oil droplets composed of different fats were manipulated at varying elastic moduli, interfacial tension, and radii. It was seen that increasing the elastic moduli of the droplets or increasing droplet radii resulted in coalescence being arrested earlier. Under these experimental conditions, different interfacial tensions did not change the coalescence behavior between two oil droplets.     

Composition of explosives by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Commercial explosives are complex mixtures that contain not only the active explosive agent(s) but also a host of other organic and inorganic compounds. The ultrahigh mass resolving power (m/delta m50% >200,000) and mass accuracy (<1 ppm) of electrospray ionization Fourier transform ion cyclotron resonance (ESI FTICR) mass spectrometry allow for definitive identification of various species in TNT, RDX, and HMX. We are thereby able to correct prior misassignments of the elemental compositions of the most abundant negative ions from electrospray of RDX and HMX. Although the (known) active agents of many explosives may be identified by low-resolution MS or MS/MS, it is the other characteristic components (indigenous or artificial additives) whose presence and elemental composition can potentially identify the source of the product. ESI FTICR mass spectrometry of smokeless powder, TNT, and Powermite resolves and identifies numerous nonactive ingredients, many of which are recovered in a postblast residue. In contrast, the residue recovered from an explosion of military C4 yielded several species derived from RDX but virtually none from other ingredients.     

Identification of intact proteins in mixtures by alternated capillary liquid chromatography electrospray ionization and LC ESI infrared multiphoton dissociation Fourier transform ion cyclotron resonance mass spectrometry.

Here we propose a novel method for rapidly identifying proteins in complex mixtures. A list of candidate proteins (including provision for posttranslational modifications) is obtained by database searching, within a specified mass range about the accurately measured mass (e.g., +/- 0.1 Da at 10 kDa) of the intact protein, by capillary liquid chromatography electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (LC ESI FT-ICR MS). On alternate scans, LC ESI infrared multiphoton dissociation (IRMPD) FT-ICR MS yields mostly b and y fragment ions for each protein, from which the correct candidate is identified as the one with the highest "hit" score (i.e., most b and y fragments matching the candidate database protein amino acid sequence masses) and sequence "tag" score (based on a series of fragment sequences differing in mass by 1 or 2 amino acids). The method succeeds in uniquely identifying each of a mixture of five proteins treated as unknowns (melittin, ubiquitin, GroES, myoglobin, carbonic anhydrase II), from more than 1000 possible database candidates within a +/- 500 Da mass window. We are also able to identify posttranslational modifications of two of the proteins (mellitin and GroES). The method is simple, rapid, and definitive and is extendable to a mixture of affinity-selected proteins, to identify proteins with a common biological function.     

Quantitative in Situ Measurement of Ion Transport in Polypyrrole/Poly(styrenesulfonate) Films Using Rotating Ring-Disk Voltammetry

An approach based on rotating ring-disk electrode (RRDE) voltammetry is described for the quantitative, in situ measurement of ion transport between solution and conducting polymer films. The specific composite film studied in this report is polypyrrole/poly(styrenesulfonate) (pPy(+)/pSS(-)). Cation flux in and out of the polymer was obtained from the mass-transport-limited reduction current for the dopant cation(s) measured at the ring during redox cycling of the polymer. Crucial to this method is the use of a supporting electrolyte that is sterically inhibited from passing into the film and the use of dopant ions that adhere to specific electrochemical constraints. With this method it was possible to quantitatively account for all changes in charge compensation in the film by the specific cation(s) involved. Three different cations were explored alone and in paired combinations. Solutions containing mixtures of dopant cations were studied to determine whether the pPy(+)/pSS(-) films exhibit preferential doping. Kinetic factors, likely due to steric differences in the dopant cations, were found to lead to significant preferential doping of the polymer.     

Effects of plasma total ammonia content and pH on urea excretion in Nile tilapia

Nile tilapia (Oreochromis niloticus) were infused with ammonium salts, acid, and base to investigate the effects of changes in arterial plasma total ammonia content (Tamm) and pH (pHa) on plasma urea-nitrogen (urea-N) levels and urea-N excretory fluxes (Jurea-N). The tilapia did not possess a functional hepatic ornithine urea-cycle (no significant carbamyl phosphate synthetase III activity). Infused substances were dissolved in a saline vehicle and injected twice (5 mL kg-1), the first infusion to "prime" the animal and promote a more marked response to the second infusion, given 2.5 h later. The results reported are those of the second infusion. Infusion of 200 mM NH4Cl increased Tamm, reduced pHa, and increased plasma urea-N and Jurea-N. Two hundred mM NH4HCO3 increased Tamm and arterial plasma total CO2 content (TaCO2), reduced pHa, and increased Jurea-N. Fifty mM HCl reduced pHa but had no effects on urea dynamics. Fifty mM NaOH increased pHa, plasma urea-N levels, and Jurea-N. Two hundred mM NaHCO3 increased pHa, TaCO2, plasma urea-N levels, and Jurea-N. Infusion of the saline vehicle was without effect. The results indicate that ammonia loading and plasma alkalosis both stimulate urea excretion in uricolytic fish. The responses to hyperammonemia or alkalosis were not modified when combined with elevated plasma bicarbonate levels.     

Transferable, plasmid-mediated vanB-type glycopeptide resistance in Enterococcus faecium

An approximately 60-kb transferable, vanB-carrying plasmid has been identified in a clinical Enterococcus faecium strain. A similar plasmid has been observed in an unrelated E. faecium strain, suggesting that plasmid transfer of vanB operons occurs in nature and plays a role in the dissemination of VanB-type resistance among strains of E. faecium.     

XR-C1, a new CHO cell mutant which is defective in DNA-PKcs, is impaired in both V(D)J coding and signal joint formation

DNA-dependent protein kinase (DNA-PK) plays an important role in DNA double-strand break (DSB) repair and V(D)J recombination. We have isolated a new X-ray-sensitive CHO cell line, XR-C1, which is impaired in DSB repair and which was assigned to complementation group 7, the group that is defective in the XRCC7 / SCID ( Prkdc ) gene encoding the catalytic subunit of DNA-PK (DNA-PKcs). Consistent with this complementation analysis, XR-C1 cells lackeddetectable DNA-PKcs protein, did not display DNA-PK catalytic activity and were complemented by the introduction of a single human chromosome 8 (providing the Prkdc gene). The impact of the XR-C1 mutation on V(D)J recombination was quite different from that found in most rodent cells defective in DNA-PKcs, which are preferentially blocked in coding joint formation, whereas XR-C1 cells were defective in forming both coding and signal joints. These results suggest that DNA-PKcs is required for both coding and signal joint formation during V(D)J recombination and that the XR-C1 mutant cell line may prove to be a useful tool in understanding this pathway.     

Repetitive axonal stimulation of the same single motor unit: a longitudinal tracking study

We elicited three single motor unit action potentials (S-MUAPs) via multiple point stimulation and subjected them to repetitive stimulation (RS) in 3 healthy subjects. We tracked each S-MUAP and its RS trains over two separate sessions as well as the compound motor action potential (CMAP) RS trains obtained from the same muscle following whole nerve stimulation. Repetitive axonal stimulation yields consistent results when carefully performed with minimal variation in each S-MUAP RS train from session to session, providing previously unobtainable data regarding neuromuscular junction function in the same single motor unit over time. In this small, normative sample, no significant correlation between S-MUAP and CMAP RS responses was observed.     

Dual microcolumn immunoaffinity liquid chromatography: an analytical application to human plasma proteins

Dual-column microcolumn immunoaffinity chromatography was accomplished by coupling immunoaffinity (IAC) and reversed-phase high-performance liquid chromatography (RP-HPLC) analysis columns. The IAC support was prepared by hydrophobically adsorbing the appropriate antibody onto an octyl silica-based stationary phase contained in a 250-microns-l.d. fused-silica microcolumn. Once the antigen was captured, the antigen-subtracted human plasma could be sent to the RP-HPLC microcolumn for plasma profiling. The antigen was quantitated by desorbing it from the IAC column and transferring it to the RP-HPLC system. Human plasma profiles were generated after removal of albumin, and transferrin and alpha 1-antitrypsin were quantitated with nanogram sensitivity. All analyses were accomplished with less than 1 microL of human plasma.