The theory of Ostwald ripening

Developments in the theory of Ostwald ripening since the classic work of I. M. Lifshitz and V. V. Slyozov (LS) are reviewed and directions for future work are suggested. Recent theoretical work on the role of a finite volume fraction of coarsening phase on the ripening behavior of two-phase systems is reformulated in terms of a consistent set of notation through which each of the theories can be compared and contrasted. Although more theoretical work is necessary, these theories are in general agreement on the effects of a finite volume fraction of coarsening phase on the coarsening behavior of two-phase systems. New work on transient Ostwald ripening is presented which illustrates the broad range of behavior which is possible in this regime. The conditions responsible for the presence of the asymptotic state first discovered by LS, as well as the manner in which this state is approached, are also discussed. The role of elastic fields during Ostwald ripening in solid-solid mixtures is reviewed, and it is shown that these fields can play a dominant role in determining the coarsening behavior of a solid-solid system.     

Detection of Escherichia coli using immunomagnetic separation and bacteriophage amplification coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The application of whole cell analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has emerged as a valuable tool for rapidly identifying/detecting bacteria. This technique requires minimal sample preparation and is simple to perform, but is generally limited to purified samples of bacteria at concentrations greater than 1.0 x 10(6) cells/mL. In this paper, we describe a bacterial detection method that integrates immunomagnetic separation with bacteriophage amplification prior to MALDI-MS analysis. The developed method consists of three main stages: (1) isolation of a target bacterium by immunomagnetic separation; (2) infection of the immuno-captured bacterium with a lytic bacteriophage; and (3) assay of infected medium for bacteriophage progeny using MALDI-MS to produce a molecular weight signal for the virus capsid protein. With this technique, the presence of Escherichia coli in broth was determined in less then 2 h total analysis time at a concentration of approximately 5.0 x 10(4) cells/mL.     

Detection of bacteria from biological mixtures using immunomagnetic separation combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A rapid method for identifying specific bacteria from complex biological mixtures using immunomagnetic separation coupled to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry has been developed. The technique employs commercially available magnetic beads coated with polycolonal antibodies raised against specific bacteria and whole cell analysis by MALDI-MS. A suspension of a bacterial mixture is mixed with the immunomagnetic beads specific for the target microorganism. After a short incubation period (20 mins) the bacteria captured by the beads are washed, resuspended in deionized H(2)O and directly applied onto a MALDI probe. Liquid suspensions containing bacterial mixtures can be screened within 1 h total analysis time. Positive tests result in the production of a fingerprint mass spectrum primarily consisting of protein biomarkers characteristic of the targeted microorganism. Using this procedure, Salmonella choleraesuis was isolated and detected from standard bacterial mixtures and spiked samples of river water, human urine, and chicken blood.     

Capillary supercritical fluid chromatography of archaebacterial glycerol tetraether lipids

The analysis of bacterial glycerol tetraethers by capillary supercritical fluid chromatography is described. Complete separation of ethers, differing only by the number of cyclopentane rings present in the isopranyl side chains could be achieved. On a 50% methylphenylpolysiloxane coated capillary, the ethers eluted in the order of increasing cyclopentane content. The analysis revealed the presence of two previously unreported structural isomers of glycerol tetraethers. The method can be used qualitatively and quantitatively as a fast and sensitive screening test for such compounds in living organisms and sedimentary organic matter.     

Carbon tether rigidity as a stereochemical tool directing intramolecular radical cyclizations

The phenyl group incorporated into a carbon tether provides for the synthesis of 1,5-cyclodecadiynes with 95-100% d,l-diastereoselectivity due to intrinsic conformational constraints and preorganization of the Co₂(CO)₆-complexed propargyl intermediates.     

Coherent Raman spectra of the nu1 mode of carbon suboxide

High-resolution (0.001 cm(-1)) coherent anti-Stokes Raman spectroscopy (CARS) has been used to study the nu1 symmetric CO stretching mode of the quasi-linear molecule carbon suboxide, C3O2. Q-branch transitions are seen that originate from the ground state and from thermally populated levels of the nu7 CCC bending mode, which is of unusually low frequency. The intensity variation of the Q-branch features on cooling to about 120 K in a jet expansion requires the reversal of the order of assignment given in a previous Raman study at low resolution. The identification of the nu1 sigma(g)+ <-- sigma(g)+ transition from the ground state is confirmed by the absence of J(odd) Q-branch lines in the resolved CARS spectrum. Analysis of this band in terms of a quasi-linear model gives a good fit to the observed transitions and leads to vibrational-rotational parameters (in cm(-1)) of nu1 = 2199.9773(12) and (B' - B') = -2.044(6) x 10(-4). Other transitions originating from higher nu7 levels occur at only slightly lower wavenumber values and permit the calculation of the double minimum potential in the Q7 bending coordinate. The results indicate that the ground-state barrier to linearity (21.5 cm(-1)) increases by only 0.6 cm(-1) when the CO symmetric stretch is excited.     

Capillary supercritical fluid chromatography with simultaneous flame ionization and mass spectrometric detection

A simple interface between a capillary supercritical fluid chromatograph and an Extranuclear Simulscan mass spectrometer is described. The SFC column is directly inserted into the ion source through the existing GC-interface. The system is equipped with a splitting device which allows simultaneous EI/MS and flame ionization detection when CO₂ is used as the supercritical phase. The effect of source temperature and pressure on CO₂ clustering was studied for optimization of source conditions. The performance of the system was evaluated with a series of model compounds and standard mixtures.