Recent developments in electrophoretic separations on microfluidic devices

Research combining the areas of separation science and microfluidics has gained popularity, driven by the increasing need to create portable, fast, and low analyte-consumption devices. Much of this research has focused on the developments in electrophoretic separations, which use the electrokinetic properties of analytes to overcome many of the problems encountered during system scale-down. In addition, new physical phenomenon can be exploited on the microscale not available in standard techniques. In this study, the innovative developments, including electrophoretic concentration, sample preparation/conditioning, and separation on-chip are reviewed, along with some introductory discussions, from January 2008 to July 2010.     

An amplitude analysis of ππ scattering from new data on the reaction π−p→π+π−n

We have carried out a partial-wave analysis of ππ scattering in the mass range 1.0 to 2.08 GeV/c². We find solutions similar to those obtained in previous analyses below 1.8 GeV/c² but, in addition, we obtain a new solution which does not suffer from violations of unitarity and is compatible with data from other channels. This solution, when continued to 2.08 GeV/c², shows a g meson with mass and width of 1.734± 0.010 GeV/c²and 0.322±0.035 GeV/c² respectively, and an h meson with mass 1.935±0.013 GeV/c²and width 0.263±0.057 GeV/c². The L = 2 partial wave contains the f meson and an additional resonance with parameters m = 1.502±0.025 Gev/c², Γ = 0.165±0.042 GeV/c²and x = 0.19±0.03. If we associate this state with the f′(1514), our ππ branching fraction is considerably higher than previous determinations. An SU(3) fit to the 2⁺ nonet yields a mixing angle of 38.4± 1.3°.     

Critical resonance in the non-intersecting lattice path model

We study the phase transition in the honeycomb dimer model (equivalently, monotone non-intersecting lattice path model). At the critical point the system has a strong long-range dependence; in particular, periodic boundary conditions give rise to a resonance phenomenon, where the partition function and other properties of the system depend sensitively on the shape of the domain.The research leading to this article was conducted in part while the first author was visiting Microsoft.Mathematics Subject Classification (2000): 82B20Revised version: 7 July 2003     

Production of muon pairs in the continuum region by 39.5 GeV/cπ±, K±, p and p beams incident on a copper target

General features of the inclusive hadroproduction of muon pairs of mass greater than 1.5 GeV/c² are shown. For incident π^?, the data extend up to M=5.7 GeV/c² (i.e.M²/s≈0.4). The scaling cross section M³dσ/dM for π^?N reactions is much flatter than that for pN reactions and exceeds the latter by two to three orders of magnitude at large M²/s.     

Non-Destructive Analysis of European Cobalt Blue Glass Trade Beads

Chemical analyses were made of royal blue glass trade beads from two early 17th century, archaeological sites in southern Ontario, Canada and from a glass beadmaking house in Amsterdam, The Netherlands. The results confirm that these beads were all mixed alkali — lime — silica glasses, coloured with Co and with opaque varients opacified with Sn. The groupings by chemistry tend to segregate by bead shapes, so that oval beads group together and circular shaped beads group together. Although the 2 Canadian sites are about 190 km apart, they produced 2 different sets of oval beads of similar chemistry, possibly helping confirm the contemporaneity of the people at both sites. An As/Co atomic ratio of about two may fit with the possible source of Co as a cobalt-arsenide ore (of common name smaltite) from the Hartz Mountains of eastern Germany, a source not far from either Amsterdam or Venice, both well known glass beadmaking centres of the period.     

Changes in adsorbed fibrinogen upon conversion to fibrin

The conversion of adsorbed fibrinogen to fibrin in the presence of the enzyme thrombin was studied using surface plasmon resonance (SPR), a quartz crystal microbalance (QCM), sum frequency generation (SFG), atomic force microscopy (AFM), and an elutability assay. Exposure of adsorbed fibrinogen to thrombin resulted in a mass loss at the surface consistent with fibrinopeptide release and conversion to fibrin. Changes in hydration upon conversion of adsorbed fibrinogen to fibrin were determined from comparisons of acoustic (QCM) and optical (SPR) mass adsorption data. Conversion to fibrin also resulted in the adsorbed layer becoming more strongly bound to the surface and more compact. The elutability of adsorbed fibrinogen by Triton X-100, studied with SPR, decreased from 90 +/- 5 to 6 +/- 2% after conversion to fibrin. The height of the adsorbed monolayer, as determined by AFM, decreased from 5.5 +/- 2.2 to 1.7 +/- 0.8 nm. We conclude that thrombin-catalyzed fibrinopeptide release triggers significant changes in fibrinogen conformation beyond peptide cleavage.     

Chemical control of spin propagation between heterometallic rings

We present a synthetic, structural, theoretical, and spectroscopic study of a family of heterometallic ring dimers which have the formula [{Cr(7)NiF(3)(Etglu)(O(2)CtBu)(15)}(2)(NLN)], in which Etglu is the pentadeprotonated form of the sugar N-ethyl-D-glucamine, and NLN is an aromatic bridging diimine ligand. By varying NLN we are able to adjust the strength of the interaction between rings with the aim of understanding how to tune our system to achieve weak magnetic communication between the spins, a prerequisite for quantum entanglement. Micro-SQUID and EPR data reveal that the magnetic coupling between rings is partly related to the through-bond distance between the spin centers, but also depends on spin-polarization mechanisms and torsion angles between aromatic rings. Density functional theory (DFT) calculations allow us to make predictions of how such chemically variable parameters could be used to tune very precisely the interaction in such systems. For possible applications in quantum information processing and molecular spintronics, such precise control is essential.     

The role of the C8 proton of ATP in the regulation of phosphoryl transfer within kinases and synthetases

Background

The kinome comprises functionally diverse enzymes, with the current classification indicating very little about the extent of conserved regulatory mechanisms associated with phosphoryl transfer. The apparent K _m of the kinases ranges from less than 0.4 μM to in excess of 1000 μM for ATP. It is not known how this diverse range of enzymes mechanistically achieves the regulation of catalysis via an affinity range for ATP varying by three-orders of magnitude.

Results

We have demonstrated a previously undiscovered mechanism in kinase and synthetase enzymes where the overall rate of reaction is regulated via the C8-H of ATP. Using ATP deuterated at the C8 position (C8D-ATP) as a molecular probe it was shown that the C8-H plays a direct role in the regulation of the overall rate of reaction in a range of kinase and synthetase enzymes. Using comparative studies on the effect of the concentration of ATP and C8D-ATP on the activity of the enzymes we demonstrated that not only did C8D-ATP give a kinetic isotope effect (KIE) but the KIE's obtained are clearly not secondary KIE effects as the magnitude of the KIE in all cases was at least 2 fold and in most cases in excess of 7 fold.

Conclusions

Kinase and synthetase enzymes utilise C8D-ATP in preference to non-deuterated ATP. The KIE obtained at low ATP concentrations is clearly a primary KIE demonstrating strong evidence that the bond to the isotopically substituted hydrogen is being broken. The effect of the ATP concentration profile on the KIE was used to develop a model whereby the C8H of ATP plays a role in the overall regulation of phosphoryl transfer. This role of the C8H of ATP in the regulation of substrate binding appears to have been conserved in all kinase and synthetase enzymes as one of the mechanisms associated with binding of ATP. The induction of the C8H to be labile by active site residues coordinated to the ATP purine ring may play a significant role in explaining the broad range of K _m associated with kinase enzymes.