Two dimensional mapping of cancer cell extracts by liquid chromatography-capillary electrophoresis with ultraviolet absorbance detection

A two-dimensional liquid chromatography/capillary electrophoresis technique was developed for rapid and comprehensive mapping of cell extracts. The cell extracts were first separated by reversed-phase HPLC based on hydrophobicity. Fractions of the effluent from the HPLC system were collected into 96-well microtiter plates and dried under vacuum. The fractions were reconstituted with deionized water, separated by capillary array electrophoresis based on charge-to-size ratio, and detected by UV absorption at 214 nm. Prior to analysis by multiplexed capillary electrophoresis, the reconstituted fractions were concentrated on-column using large volume sample stacking with polarity switching. In this way, high-resolution analysis of even the minor components in the complicated mixture was possible.     

High accuracy analysis by isotope dilution mass spectrometry using an iterative exact matching technique

The selection of an appropriate isotope dilution mass spectrometry technique for the practical application of this potentially primary method of analysis is highly important. The NARL approach for the application of the exact matching double isotope dilution mass spectrometry technique developed by Henrion is presented. NARL's approach utilises exact matching to minimise the effect of measurement biases within the method but also includes the thorough examination of all other biasing factors. The approach has been successfully tested in international CCQM intercomparisons with other national metrology institutes.     

The structure of metallomicelles

The morphology of micelles formed by two novel metallosurfactants has been studied by small-angle neutron scattering (SANS) and small-angle-X-ray scattering (SAXS). The two surfactants both contain a dodecyl chain as the hydrophobic moiety, but differ in the structure of the head group. The surfactants are Cu(II) complexes of monopendant alcohol derivatives of a) the face-capping macrocycle 1,4,7-triazacyclanonane (tacn), and b) an analogue based upon the tetraazamacrocycle 1,4,7,10-tetraazacyclododecane. Here, neutron scattering has been used to study the overall size and shape of the surfactant micelles, in conjunction with X-ray scattering to locate the metal ions. For the 1,4,7,10-tetraazacyclododecane-based surfactant, oblate micelles are observed, which are smaller to the prolate micelles formed by the 1,4,7-triazacyclononane analogue. The X-ray scattering analysis shows that the metal ions are distributed throughout the polar head-group region, rather than at a well-defined radius; this is in good agreement with the SANS-derived dimensions of the micelle. Indeed, the same model for micelle morphology can be used to fit both the SANS and SAXS data.     

Measurement of adenosine, inosine and hypoxanthine in human term placenta by reversed-phase high-performance liquid chromatography

An analytical method was developed for measuring adenosine, inosine and hypoxanthine in freshly delivered human term placentas. Representative freeze-clamped samples were taken from the sub-maternal surface of each placenta. Acid-soluble extracts of the samples were analyzed by reversed-phase high-performance liquid chromatography on columns packed with 10-micron porous octadecylsilica, using gradient elution with a linear increase in methanol concentration in ammonium phosphate buffer. Resolution of hypoxanthine from xanthine and adenosine from adenine, and quantitation of hypoxanthine and adenosine were achieved using 0.05 M ammonium dihydrogen phosphate, pH 6.5, as the low-strength eluent. Resolution of inosine from a prominent peak of beta-NAD was optimized using 0.02 M ammonium dihydrogen phosphate, pH 5.6, as low-strength eluent. Recovery of standards was greater than 90%. Mean contents (+/- S.D.) of the analytes in placentas from seven normal deliveries were, adenosine 30.6 +/- 11.5 nmol/g, inosine 68.0 +/- 25.8 nmol/g and hypoxanthine 217 +/- 127.5 nmol/g.     

Metal triangles as building blocks in metal cluster chemistry

Many trinuclear metal clusters have structures based on isolated metal triangles with either single bonds (e.g.,M ₃(CO)₁₂ whereM = Fe, Ru, Os) or double bonds (e.g., Re₃ Cl ₁₂ ^3– ) along each edge of the triangle. Individual metal triangles can be joined in the following ways to form more complicated triangulated networks: (1) Bridging an edge of a triangle with a new vertex to give rafts in which adjacent triangles share edges; (2) Bridging a vertex of a triangle with a new edge to give bowties in which adjacent triangles share vertices; (3) Capping a triangular face with a new vertex to give a chain of tetrahedra in which adjacent tetrahedra share faces. Such triangulated metal networks are particularly common in osmium carbonyl chemistry and in mixed osmium/platinum carbonyl derivatives. Platinum triangles of the type Pt₃L₆ are analogous to cyclopropenyl rings and can form sandwiches with one or two mercury atoms in the center such as the mercuric derivative Hg[Pt.₃(µ₂-2,6-Me₂C₆H₃NC)₃] (2,6-Me₂C₆H₃NC)₃]₂ and the mercurous derivative Hg₂[Pt₃(µ₂-CO)₃L₃]₂. Platinum triangles can also be stacked in the absence of filling to give [Pt₃(µ₂-CO)₃(CO)₃] _n ^2– (n=2, 3, 4, 5, 6, 10). Metal triangles also form the faces of metal deltahera of which the octahedron, bicapped square antiprism, and icosahedron are found in globally delocalized transition metal clusters.This article is dedicated to Prof. L. F. Dahl in recognition of his many seminal contributions to metal cluster chemistry.     

Addition of p-azido-L-phenylalanine to the genetic code of Escherichia coli

We report the selection of a new orthogonal aminoacyl tRNA synthetase/tRNA pair for the in vivo incorporation of a photocrosslinker, p-azido-l-phenylalanine, into proteins in response to the amber codon, TAG. The amino acid is incorporated in good yield with high fidelity and can be used to crosslink interacting proteins.     

Rheology of binary colloidal structures assembled via specific biological cross-linking

The selectivity and range of energies offered by specific biological interactions serve as valuable tools for engineering the assembly of colloidal particles into novel materials. In this investigation, high affinity biological interactions between biotin-coated "A" particles (RA = 0.475 microm) and streptavidin-coated "B" particles (RB = 2.75 microm) drive the self-assembly of a series of binary colloidal structures, from colloidal micelles (a large B particle coated by smaller A particles) to elongated chain microstructures (alternating A and B particles), as the relative number of small (A) to large (B) particles (2 < or = NA/NB < or = 200) is decreased at a low total volume fraction (10(-4) < or = phiT < or = 10(-3)). At a significantly higher total volume fraction (phiT > or = 10(-1)) and a low number ratio (NA/NB = 2), the rheological behavior of volume-filling particle networks connected by streptavidin-biotin bonds is characterized. The apparent viscosity (eta) as a function of the shear rate gamma, measured for networks at phiT = 0.1 and 0.2, exhibits shear-rate-dependent flow behavior, and both the apparent viscosity and the extent of shear thinning increase upon an increase of a factor of 2 in the total volume fraction. Micrographs taken before and after shearing show a structural breakdown of the flocculated binary particle network into smaller flocs, and ultimately a fluidlike suspension, with increasing shear rate. Rheological measurements provide further proof that suspension microstructure is governed by specific biomolecular interactions, as control experiments in which the streptavidin molecules on particles were blocked displayed Newtonian flow behavior. This investigation represents the first attempt at measuring the rheology of colloidal suspensions where assembly is driven by biomolecular cross-linking.     

Effect of ethanol on the interaction between poly(vinylpyrrolidone) and sodium dodecyl sulfate

The effect of ethanol on the interaction between the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic polymer poly(vinylpyrrolidone) (PVP) has been investigated using a range of techniques including surface tension, fluorescence, electron paramagnetic resonance (EPR), small-angle neutron scattering (SANS), and viscosity. Surface tension and fluorescence studies show that the critical micelle concentration (cmc) of the surfactant decreases to a minimum value around 15 wt % ethanol; that is, it follows the cosurfactant effect. However, in the presence of PVP, the onset of the interaction, denoted cmc(1), between the surfactant and the polymer is considerably less dependent on ethanol concentration. The saturation point, cmc(2), however, reflects the behavior of the cmc in that it decreases upon addition of ethanol. This results in a decrease in the amount of surfactant bound to the polymer [C(bound) = cmc(2) - cmc] at saturation. The viscosity of simple PVP solutions depends on ethanol concentration, but since SANS studies show that ethanol has no effect on the polymer conformation, the changes observed in the viscosity reflect the viscosity of the background solvent. There are significant increases in bulk viscosity when the surfactant is added, and these have been correlated with the polymer conformation extracted from an analysis of the SANS data and with the amount of polymer adsorbed at the micelle surface. Competition between ethanol and PVP to occupy the surfactant headgroup region exists; at low ethanol concentration, the PVP displaces the ethanol and the PVP/SDS complex resembles that formed in the absence of the ethanol. At higher ethanol contents, the polymer does not bind to the ethanol-rich micelle surface.     

Ru2(ap)4(sigma-oligo(phenyleneethynyl)) molecular wires: synthesis and electronic characterization

Reported in this contribution are the synthesis, characterization, and charge transport properties of wire-like Ru2(ap)4(OPEn), where ap is 2-anilinopyridinate and OPE is -(CCC6H4)nSCH2CH2SiMe3 with n = 1 (1) and 2 (2). Scanning tunneling microscopy (STM) measurements of compound 2 inserted into a SAM of C11 thiol reveal that molecule 2 exhibits (i) the stochastic switching characteristic of wire molecules embedded in insulating SAMs and (ii) higher conductivity than the C11 thiol SAM. More importantly, analysis of the molecular electronic decay constant (beta) exhibits a decrease of at least 15% as compared to purely organic molecular analogues. Hence, the transport characteristics of molecules can be significantly improved for nanoscale electronics through the incorporation of a Ru2 fragment into conjugated backbone.     

Radium-224 in natural waters measured by γ-ray spectrometry

A method based on Ge(Li) γ-ray spectrométry is applied to the determination of ²²⁴Ra (t_{$\text{1}\text{2}$}= 3.64 days) in natural waters. The ²²⁴Ra is first removed from several hundred liters of water by preconcentration onto manganese dioxide-impregnated acrylic fibers. The fibers are leached, radium is coprecipitated with barium sulfate, and the γ-ray activity is counted so that activity ratios among ²²⁴Ra, ²²⁵Ra and ²²⁶Ra can be calculated. Concentrations are determined by using the ²²⁶Ra concentration determined on a small separate sample. Results from samples collected from ground water, estuarine, and continental shelf environments are presented.