Miscibility behavior and nanostructure of monolayers of the main phospholipids of Escherichia coli inner membrane

We report a thermodynamic study of the effect of calcium on the mixing properties at the air-water interface of two phospholipids that mimic the inner membrane of Escherichia coli: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol. In this study, pure POPE and POPG monolayers and three mixed monolayers, χ(POPE) = 0.25, 0.5, and 0.75, were analyzed. We show that for χ(POPE) = 0.75, the values of the Gibbs energy of mixing were negative, which implies attractive interactions. We used atomic force microscopy to study the structural properties of Langmuir-Blodgett monolayers that were transferred onto mica substrate at lateral surface pressures of 25 and 30 mN m(-1). The topographic images of pure POPE and POPG monolayers exhibited two domains of differing size and morphology, showing a step height difference within the range expected for liquid-condensed and liquid-expanded phases. The images captured for χ(POPE) = 0.25 were featureless, and for χ(POPE) = 0.5 small microdomains were observed. The composition that mimics quantitatively the proportions found in the inner membrane of E. coli , χ(POPE) = 0.75, showed large liquid condensed domains in the liquid expanded phase. The extension of each domain was quantitatively analyzed. Because calcium is used in the formation of supported bilayers of negatively charged phospholipids, the possible influence of the nanostructure of the apical on the distal monolayer is discussed.     

Electrokinetic supercharging in CE for the separation and preconcentration of barbiturate drugs in urine samples

Three barbiturate drugs, barbital, phenobarbital, and secobarbital were separated and analyzed by electrokinetic supercharging. The influence of different parameters on electrokinetic supercharging performance was evaluated using both univariated and multivariated optimization processes. The parameters studied were sample pH, concentration, and length of the leading and terminating electrolytes, electrokinetic injection of the sample and composition and hydrodynamic injection of the solvent plug. The leading electrolyte (50 mM NaCl) was hydrodynamically injected (50 mbar × 120 s) prior to the sample that was adjusted to pH 9.6 and electrokinetically injected at ?8.5 kV for 300 s. The terminating electrolyte (100 mM of 2‐(cyclohexylamino) ethanesulphonic acid) was then hydrodynamically injected (50 mbar × 140 s). The results showed that this strategy enhanced detection sensitivity around 1050‐fold compared with normal hydrodynamic injection, providing detection limits ranging between 1.5 and 2.1 ng/mL for standard samples with good repeatability in terms of peak area (values of relative standard deviation, %RSD < 3). The applicability of the optimized method was demonstrated by the analysis of human urine samples spiked with the studied compounds at different concentration levels and further liquid–liquid extraction step. The estimated detection limits obtained in the urine samples extract ranged between 8 and 15 ng/mL.     

In-line solid-phase extraction–capillary electrophoresis coupled with mass spectrometry for determination of drugs of abuse in human urine

In-line solid-phase extraction–capillary electrophoresis coupled with mass spectrometric detection (SPE–CE–MS) has been used for determination of 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), codeine (COD), hydrocodeine (HCOD), and 6-acetylmorphine (6AM) in urine. The preconcentration system consists of a small capillary filled with Oasis HLB sorbent and inserted into the inlet section of the electrophoresis capillary. The SPE–CE–MS experimental conditions were optimized as follows: the sample (adjusted to pH 6.0) was loaded at 930 mbar for 60 min, elution was performed with methanol at 50 mbar for 35 s, 60 mmol L⁻¹ ammonium acetate at pH 3.8 was used as running buffer, the separation voltage was 30 kV, and the sheath liquid at a flow rate of 5.0 μL min⁻¹ was isopropanol–water 50:50 (v/v) containing 0.5% acetic acid. Analysis of urine samples spiked with the four drugs and diluted 1:1 (v/v) was studied in the linear range 0.08–10 ng mL⁻¹. Detection limits (LODs) (S/N = 3) were between 0.013 and 0.210 ng mL⁻¹. Repeatability (expressed as relative standard deviation) was below 7.2%. The method developed enables simple and effective determination of these drugs of abuse in urine samples at the levels encountered in toxicology and doping.     

The conformational free-energy landscape of β-D-mannopyranose: evidence for a (1)S(5) → B(2,5) → (O)S(2) catalytic itinerary in β-mannosidases

The mechanism of glycosidic bond cleavage by glycosidases involves substrate ring distortions in the Michaelis complex that favor catalysis. Retaining β-mannosidases bind the substrate in a (1)S(5) conformation, and recent experiments have proposed an unusual substrate conformational pathway ((1)S(5) → B(2,5) → (O)S(2)) for the hydrolysis reaction. By means of Car-Parrinello metadynamics simulations, we have obtained the conformational free-energy surface (FES) of a β-d-mannopyranose molecule associated with the ideal Stoddart conformational diagram. We have found that (1)S(5) is among the most stable conformers and simultaneously is the most preactivated conformation in terms of elongation/shortening of the C1-O1/C1-O5 bonds, C1-O1 orientation, and charge development at the anomeric carbon. Analysis of the computed FES gives support to the proposed (1)S(5) → B(2,5) → (O)S(2) catalytic itinerary, showing that the degree of preactivation of the substrate in glycoside hydrolases (GHs) is related to the properties of an isolated sugar ring. We introduce a simple preactivation index integrating several structural, electronic, and energetic properties that can be used to predict the conformation of the substrate in the Michaelis complex of any GH.     

Littlewood-Paley Formulas and Carleson Measures for Weighted Fock Spaces Induced by A ∞ $A_{\infty }$ -Type Weights

Potential Analysis - We obtain Littlewood-Paley formulas for Fock spaces ${\mathcal {F}}_{\beta ,\omega }^{q}$ induced by weights $\omega \in {A}_{\infty }^{restricted} = \cup _{1 \le p &lt;...     

On Integral Equations Related to Weighted Toeplitz Operators

For weighted Toeplitz operators T^N_j{{\mathcal T}^N_\varphi} defined on spaces of holomorphic functions in the unit ball, we derive regularity properties of the solutions f to the equation T^N_j(f)=h{{\mathcal T}^N_\varphi(f)=h} in terms of the regularity of the symbol φ and the data h. As an application, we deduce that if f\not o 0{f\not\equiv0} is a function in the Hardy space H ¹ such that its argument [`(f)]/f{\bar f/f} is in a Lipschitz space on the unit sphere \mathbb S{{\mathbb S}}, then f is also in the same Lipschitz space, extending a result of Dyakonov to several complex variables.     

Effects of permeability and viscosity in linear polymeric gels

We propose and analyze a mathematical model of the mechanics of gels, consisting of the laws of balance of mass and linear momentum of the polymer and liquid components of the gel. We consider a gel to be an immiscible and incompressible mixture of a nonlinearly elastic polymer and a fluid. The problems that we study are motivated by predictions of the life cycle of body‐implantable medical devices. Scaling arguments suggest neglecting inertia terms, and therefore, we consider the quasi‐static approximation to the dynamics. We focus on the linearized system about stress‐free states, uniform expansions, and compressions and derive sufficient conditions for the solvability of the time‐dependent problems. These turn out to be conditions that guarantee local stability of the equilibrium solutions. We also consider non‐stress free equilibria and states with residual stress and derive an energy law for the corresponding time‐dependent system. The conditions that guarantee stability of solutions provide a selection criteria of the material parameters of devices. The boundary conditions that we consider are of two types, displacement‐traction and permeability of the gel surface to the fluid. We address the cases of viscous and inviscid solvent, assume Newtonian dissipation for the polymer component, and establish existence of weak solutions for the different boundary permeability conditions and viscosity assumptions. We present two‐dimensional, finite element numerical simulations to study stress concentration on edges, this being the precursor to debonding of the gel from its substrate. Copyright © 2015 John Wiley & Sons, Ltd.     

Separation and on-column preconcentration of some nonsteroidal anti-inflammatory drugs by microemulsion electrokinetic capillary chromatography using high-speed separations

Various strategies have been investigated for separating a group of nonsteroidal anti-inflammatory drugs (NSAIDs) by microemulsion electrokinetic capillary chromatography (MEEKC) using high-speed separations. The parameters that of affect the separation, such as the nature of the oil droplet and the buffer, and the surfactant concentration have been studied. In addition, several organic solvents were used to decrease the retention of the analytes in the oil droplet phase and to improve the resolution of the NSAIDs. The optimum microemulsion background electrolyte (BGE) solution made of 0.8% w/w ethyl acetate, 6.6% w/w butan-1-ol, 6.0% w/w acetonitrile, 1.0% w/w sodium dodecyl sulfate (SDS), and 85.6% w/w of 10 mM sodium tetraborate at pH 9.2 resolved the drugs within 8 min. The short-end injection procedure is an alternative for reducing the analysis time. When this procedure was used, the microemulsion BGE solution consisted of 0.8% w/w ethyl acetate, 6.6% w/w butan-1-ol, 17.0% w/w methanol, 1.0% w/w SDS, and 74.6% w/w of 10 mM sodium tetraborate, pH 9.2, and the NSAIDs were separated within 3 min. The reversed electrode polarity stacking mode (REPSM) technique was applied to the on-line concentration of the NSAIDs. In this technique, the sample matrix was pumped out of the capillary using a polarity-switching step. When this technique was applied, the sensitivity was enhanced up to 40-fold and the limits of detection (LODs) were in the low microg.L(-1) levels.