Accurate whole-spectrum measurements of intracellular pH and [Na+]

Fluorescent measurements of intracellular H⁺ and Na⁺ are improved by using whole spectra of the fluorescent indicators BCECF and SBFI, respectively. The extra data in whole spectra enable both an accurate calibration and a ready detection of artifacts which are not possible to identify using a more conventional data analysis that relies upon only two wavelength windows in the fluorescence spectra. The whole-spectrum technique is applicable to cell suspensions in a conventional fluorimeter (as is reported here with SBFI), as well as to attached cells using a fluorimeter combined with an inverted epifluorescence microscope. The spectral method was highly reproducible in that pairs of successive pH measurements differed, on average, by only 0.01±0.02 U. Random uncertainty from sample to sample was estimated numerically from the standard deviation of measurements on ionophore-treated cells. When full-spectrum analysis was employed, this scatter showed a two-fold improvement over results obtained using the two-wavelength ratio method. Because SBFI has a relatively narrow dynamic range, whole-spectrum analysis has been applied to improve the accuracy of sodium determinations. The calibrated system measured [Na⁺]_i with excellent linearity over the range 2–150 mM and with an accuracy of approximately 5 mM.     

X-ray and molecular mechanics studies on the crystal and molecular structure of the leucoacetate of ventilatone A

Molecular details of the leucoacetate of ventilatone A have been obtained by X-ray crystallographic and molecular mechanics calculations. In the crystalline state (space group P1,Z=2) the two independent molecules of the asymmetric unit appear to be disordered as some unusual geometrical features are evident. As these two molecules are related by a pseudo center of symmetry details of space group assignment are presented. Evidence of bond order in the molecules is supported by previously published spectroscopic data.     

Mechanism of cyclic dye regeneration during eosin‐sensitized photoinitiation in the presence of polymerization inhibitors

A visible light photoinitiator, eosin, in combination with a tertiary amine coinitiator is found to initiate polymerization despite the presence of at least 1000‐fold excess dissolved oxygen, which functions as an inhibitor of radical polymerizations. Additionally, 0.4 μM eosin is able to overcome 100‐fold excess (40 μM) 2,2,6,6‐Tetramethyl‐1‐piperidinyloxy (TEMPO) inhibitor, initiating polymerization after only a 2 min inhibition period. In contrast, 40 μM Irgacure‐2959, a standard cleavage‐type initiator, is unable to overcome even an equivalent amount of inhibitor (40 μM TEMPO). Through additional comparisons of these two initiation systems, a reaction mechanism is developed which is consistent with the kinetic data and provides an explanation for eosin's relative insensitivity to oxygen, TEMPO, and other inhibitors. A cyclic mechanism is proposed in which semireduced eosin radicals react by disproportionation with radical inhibitors and radical intermediates in the inhibition process to regenerate eosin and effectively consume inhibitor. In behavior similar to that of eosin, rose bengal, fluorescein, and riboflavin are also found to initiate polymerization despite the presence of excess TEMPO, indicating that cyclic regeneration likely enhances the photoinitiation kinetics of many dye photosensitizers. Selection of such dye initiation systems constitutes a valuable strategy for alleviating inhibitory effects in radical polymerizations. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6083–6094, 2009     

Palladium-catalysed cross-coupling of 2-trimethylsilylpyridine with aryl halides

Palladium-catalysed cross-coupling of 2-trimethylsilylpyridine with aryl halides in the presence of stoichiometric silver(I) oxide, and catalytic TBAF allows the rapid preparation of the corresponding pyridin-2-ylaryl compounds in moderate to good yields under mild thermal conditions.     

Multigraph realizations of degree sequences: Maximization is easy, minimization is hard

The following minimization problem is shown to be NP-hard: Given a graphic degree sequence, find a realization of this degree sequence as loopless multigraph that minimizes the number of edges in the underlying support graph. The corresponding maximization problem is known to be solvable in polynomial time.     

On the stabilization of leading-edge vortices with spanwise flow

The influence of spanwise flow on the development and stabilization of leading-edge vortices (LEVs) on a foil (without rotational acceleration) has been investigated. The plunging swept wing/fin geometry used in this study, characteristic of fish-like tails, has been found to be insufficient in the stabilization of LEVs. Direct force measurements and visualizations, including Particle Image Velocimetry and lead precipitation, show that despite the presence of a strong spanwise flow at higher sweepback angles, the vortex breaks off and convects downstream at the same relative time as found for low sweepback angles, which experience little spanwise contribution. Although the LEV stabilization is insensitive to bulk spanwise flow, the LEV and tip vortex have been observed to maintain a stronger connection with one another at higher sweepback angles. This result implies that despite similar forces developing for low and high sweepback angles alike, the resulting vortex-wake topologies can vary significantly from one another.     

Time and scale Hurst exponent analysis for financial markets

We use a new method of studying the Hurst exponent with time and scale dependency. This new approach allows us to recover the major events affecting worldwide markets (such as the September 11th terrorist attack) and analyze the way those effects propagate through the different scales. The time-scale dependence of the referred measures demonstrates the relevance of entropy measures in distinguishing the several characteristics of market indices: “effects” include early awareness, patterns of evolution as well as comparative behaviour distinctions in emergent/established markets.