Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.     

Investigation and interpretation of band broadening in size exclusion chromatography

Study of Band Broadening occurring in Size Exclusion Chromatography (SEC) is reported using very narrow PS standards obtained and characterised by Temperature Gradient Interaction Chromatography (TGIC). Chromatograms are fitted by Exponentially Modified Gaussian functions (EMG) and mapping of band broadening is obtained for different column sets. Interpretation of the skewing of the chromatograms is proposed with a new model using Brownian motion properties inside the pores. That explains why band broadening and tailing become so important near total exclusion volume.     

Novel sheathless CE-MS interface as an original and powerful infusion platform for nanoESI study: from intact proteins to high molecular mass noncovalent complexes

Development of nano-electrospray (nanoESI) sources allowed to increase significantly the sensitivity which is often lacking when studying biological noncovalent assemblies. However, the flow rate used to infuse the sample into the mass spectrometer cannot be precisely controlled with nanoESI and the robustness of the system could represent an issue. In this study, we have used a sheathless capillary electrophoresis–mass spectrometry (CESI) prototype as a nanoESI infusion device. The hydrodynamic mobilization of the capillary content was characterized and the ability of the system to generate a stable electrospray under controlled flow rate conditions ranging from 4 up to 900 nL/min was demonstrated. The effect of the infusing flow rate on the detection of an intact model protein analyzed under native conditions was investigated. Results demonstrated a significant increase in sensitivity of 46-fold and a signal-to-noise ratio improvement of nearly 5-fold when using an infusing flow rate from 456.9 down to 13.7 nL/min. The CESI prototype was further used to detect successfully the β ring homodimer in its native conformation. Obtained results were compared with those achieved with conventional ESI. Intensity signals were increased by a factor of 5, while sample consumption decreased 80 times. β ring complexed with the P14 peptide was also studied. Finally, the CESI interface was used to observe the quaternary structure of native hemocyanins from Carcinus maenas crabs; this high molecular complex coexisting under various degrees of complexation and resulting in masses ranging from 445 kDa to 1.34 MDa.     

Coupling porous sheathless interface MS with transient‐ITP in neutral capillaries for improved sensitivity in glycopeptide analysis

IgG antibodies are modulated in their function by the specific structure of the N‐glycans attached to their Fc (fragment crystallizable) portions. However, the glycosylation analysis of antigen‐specific IgGs is a challenging task as antibody levels to a given antigen only represent a fraction of the total IgG levels. Here, we investigated the use of a transient‐ITP (t‐ITP)—MS method for highly sensitive IgG1 glycosylation profiling as a complementary method to a high‐throughput nano‐RPLC‐MS method. It was found that t‐ITP‐CZE using neutrally coated separation capillaries with a large volume injection (37% of capillary volume) and interfaced to MS with a sheathless porous sprayer yielded a 40‐fold increase in sensitivity for IgG1 Fc glycopeptide analysis when compared to the conventional strategy. Furthermore, the glycoform profiles found with the t‐ITP‐CZE strategy were comparable to those from nano‐RPLC‐MS. In conclusion, the use of the highly sensitive t‐ITP‐CZE‐MS method will provide information on IgG Fc glycosylation for those samples with IgG1 concentrations below the LODs of the conventional method.     

The numerical integration of relative equilibrium solutions. The nonlinear Schrodinger equation

We analyse different error propagation mechanisms for conservativeand nonconservative time-integrators of nonlinear Schrödingerequations. We use a geometric approach based on interpretingwaves as relative equilibria.     

Infrasound and sound: differentiation of their psychophysiological effects through use of genetically deaf animals

The effects of steady-state acoustic stimulation on resistance of fatigue, as shown by reduction of swimming time, was studied on three sublines of mice, one of which is genetically deaf. High frequency (500-10000 Hz) reduce swimming time from 25% to 50% in mice with normal hearing at a 60-80-dB threshold, but have no effect on deaf mice. Low frequencies and infrasounds (6-50 Hz) reduce swimming time in all mice similarly, even deaf animals, but the threshold is higher (160-115 dB). The use of genetically deaf animals therefore permits elimination of the auditory component; differentiation of the effects of air-borne from those of mechanical vibrations are thus possible.     

Application de la G.P.C. a l'etude de la distribution moleculaire de polyesters non-lineaires

Molecular distribution of stoichiometric copolycondensate trimethylolpropane/azelaïc acid with conversion is investigated. Weight fractions of the first oligomers determined by G.P.C. agree with theoretical forecasts.     

Comparison of different capillary isoelectric focusing methods--use of "narrow pH cuts" of carrier ampholytes as original tools to improve resolution

Two capillary isoelectric focusing (CIEF) systems have first been optimized: one uses a bare silica capillary and 30% (v/v) of glycerol in the separation medium while the other uses a coated capillary and an aqueous background electrolyte. To perform permanent capillary coating, two neutral polymers have been compared: hydroxypropylcellulose (HPC) and polyvinylalcohol (PVA). HPC coating gave best results for electroosmotic flow (EOF) limitation on a wide pH range: as compared to a bare silica capillary, it allowed to decrease EOF by 96% at pH 7.2 after acidic and basic treatments, whereas PVA coating lead only to a 76% decrease. The glycerol CIEF system was more satisfying for the separation of model proteins classically used as pI markers. Finally, the use of "narrow pH cuts" of carrier ampholytes added to commercial ampholyte mixtures allowed increasing resolution up to a factor 2.4 at a chosen pH for the separation of pI markers and milk proteins.     

Loading capacity of carrier ampholytes--based buffers in capillary electrophoresis

Narrow pH cuts of carrier ampholytes (CAs), originally designed for IEF, have been used as BGEs in CE. Their physicochemical properties, rather high buffering capacity and low conductivity, allow very efficient protein separations under high electric field strength. Due to their isoelectric properties, CA BGEs are expected to present a low ionic concentration and consequently a low loading capacity. In this study, we developed a simple method that allows the estimation of the loading capacity of a UV-absorbing BGE by CE. We first characterized in terms of loading capacity, classical ammediol-chromate UV-absorbing BGEs and a 10 mM histidine solution, a classical isoelectric buffer. Then, the loading capacity of four different CA-based BGEs has been assessed. Experimental results have shown that the CA-based buffers were presenting a rather high loading capacity, comparable to classical buffer ones and far higher than the one of the 10 mM histidine solution.     

Integral resource capacity planning for inpatient care services based on bed census predictions by hour

The design and operations of inpatient care facilities are typically largely historically shaped. A better match with the changing environment is often possible, and even inevitable due to the pressure on hospital budgets. Effectively organizing inpatient care requires simultaneous consideration of several interrelated planning issues. Also, coordination with upstream departments like the operating theatre and the emergency department is much-needed. We present a generic analytical approach to predict bed census on nursing wards by hour, as a function of the Master Surgical Schedule and arrival patterns of emergency patients. Along these predictions, insight is gained on the impact of strategic (ie, case mix, care unit size, care unit partitioning), tactical (ie, allocation of operating room time, misplacement rules), and operational decisions (ie, time of admission/discharge). The method is used in the Academic Medical Center Amsterdam as a decision-support tool in a complete redesign of the inpatient care operations.