The Efficiency of RP-TLC for Lipophilicity Assessment. A Comparative Study on a Series of Pyrrolyl-Acetic Acid Derivatives,Inhibitors of Aldose Reductase

JPC – Journal of Planar Chromatography – Modern TLC - The lipophilicity of a series of pyrrolyl-acetic acid derivatives, inhibitors of the aldose reductase enzyme, was assessed by...     

Optical trapping and manipulation of micrometer and submicrometer particles

Subwavelength features in conjunction with light‐guiding structures have gained significant interest in recent decades due to their wide range of applications to particle and atom trapping. Lately, the focus of particle trapping has shifted from the microscale to the nanoscale. This few orders of magnitude change is driven, in part, by the needs of life scientists who wish to better manipulate smaller biological samples. Devices with subwavelength features are excellent platforms for shaping local electric fields for this purpose. A major factor that inhibits the manipulation of submicrometer particles is the diffraction‐limited spot size of free‐space laser beams. As a result, technologies that can circumvent this limit are highly desirable. This review covers some of the more significant advances in the field, from the earliest attempts at trapping using focused Gaussian beams, to more sophisticated hybrid plasmonic/metamaterial structures. In particular, examples of emerging optical trapping configurations are presented.

     

Synthesis of amphoteric polystyrene particles using mixed initiators

The synthesis of amphoteric polystyrene latex particles, using a mixture of cationic (amidinium based) and anionic (carboxylic acid based) initiators in a surfactant-free emulsion polymerization reaction is investigated; this extends work described in an earlier paper by Bolt et al. Electrophoretic mobility measurements show the effect of the initiator concentration ratio on the isoelectric point (IEP) of the particles. A good correlation with theoretical predictions is obtained. Particle size and polydispersity are determined as a function of the lag time between the addition of each initiator. An increase in particle size and polydispersity is observed at short lag times. It is shown that this is due to the ratio of the cationic to anionic surface charge approaching unity during the reaction. At long lag times an increase in polydispersity may occur due to late-stage, secondary nucleation upon addition of the second initiator. Increasing the reaction pH to reduce the degree of ionization of the cationic initiator greatly reduces the polydispersity and has a significant effect on the IEP of the particles. This effect is ascribed to the burial of a fraction of the neutral amidine groups below the particle surface due to their increased solubility in the monomer. Slow addition of the second initiator was found to reduce the polydispersity of the particles, while maintaining an IEP value consistent with that expected for the ratio of initiators added.     

A Method Based on the Radon Transform for Three-Dimensional Elastodynamic Problems of Moving Loads

An integral transform procedure is developed to obtain fundamental elastodynamic three-dimensional (3D) solutions for loads moving steadily over the surface of a half-space. These solutions are exact, and results are presented over the entire speed range (i.e., for subsonic, transonic and supersonic source speeds). Especially, the results obtained here for the tangential loads (one of these loads is along the direction of motion and the other is orthogonal to the direction of motion) are quite new in the literature. The solution technique is based on the use of the Radon transform and elements of distribution theory. It also fully exploits as auxiliary solutions the ones for the corresponding plane-strain and anti-plane shear problems (the latter problems are 2D and uncoupled from each other). In particular, it should be noticed that the plane-strain problem here is completely analogous to the original 3D problem, not only with respect to the field equations but also with respect to the boundary conditions. This makes the present technique more advantageous than other techniques, which require first the determination of a fictitious auxiliary plane-strain problem through the solution of an integral equation. Our approach becomes particularly simple when there is no angular dependence in the boundary conditions (i.e., when axially symmetric problems regarding their boundary conditions are considered). On the contrary, no such constraint needs to be fulfilled as regards the material response (and, therefore, the governing equations of the problem) and/or also possible loss of axisymmetry due to the generation of shock (Mach-type) waves in the medium. Therefore, the solution technique can easily deal with general 3D problems having a largely arbitrary radial dependence in the boundary conditions and involving: (i) material anisotropy in static and dynamic situations, and (ii) asymmetry caused by changes in the nature of governing PDEs due to the existence of different velocity regimes (super-Rayleigh, transonic, supersonic) in dynamic situations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sh surface Waves in a Homogeneous Gradient-Elastic Half-Space with Surface Energy

The existence of SH surface waves in a half-space homogeneous material (i.e. anti-plane shear wave motions which decay exponentially with the distance from the free surface) is shown to be possible within the framework of the generalized linear continuum theory of gradient elasticity with surface energy. As is well-known such waves cannot be predicted by the classical theory of linear elasticity for a homogeneous half-space, although there is experimental evidence supporting their existence. Indeed, this is a drawback of the classical theory which is only circumvented by modelling the half-space as a layered structure (Love waves) or as having non-homogeneous material properties. On the contrary, the present study reveals that SH surface waves may exist in a homogeneous half-space if the problem is analyzed by a continuum theory with appropriate microstructure. This theory, which was recently introduced by Vardoulakis and co-workers, assumes a strain-energy density expression containing, besides the classical terms, volume strain-gradient and surface-energy gradient terms. This revised version was published online in August 2006 with corrections to the Cover Date.     

A validated SIM GC/MS method for the simultaneous determination of dextromethorphan and its metabolites dextrorphan, 3‐methoxymorphinan and 3‐hydroxymorphinan in biological matrices and its application to in vitro CYP2D6 and CYP3A4 inhibition study

Dextromethorphan is used as a probe drug for assessing CYP2D6 and CYP3A4 activity in vivo and in vitro. A SIM GC/MS method without derivatization for the simultaneous determination of dextromethorphan and its metabolites, dextrorphan, 3‐methoxymorphinan and 3‐hydroxymorphinan, in human plasma, urine and in vitro incubation matrix was developed and validated. Calibration curves indicated good linearity with a coefficient of variation (r) better than 0.995. The lower limit of quantitation was found to be 10 ng/mL for all analytes in all matrices. Intra‐day and inter‐day precision for dextromethorphan and its metabolites was better than 9.02 and 9.91%, respectively and accuracy ranged between 91.76 and 106.27%. Recovery for dextromethorphan, its metabolites and internal standard levallorphan was greater than 72.68%. The method has been successfully applied for the in vitro inhibition of metabolism of dextromethorphan by CYP2D6 and CYP3A4 using known inhibitors of CYPs such as quinidine and verapamil. Copyright © 2009 John Wiley & Sons, Ltd.     

Stability of token passing rings

A sufficient stability condition for the standard token passing ring has been known since the seminal paper by Kuehn in 1979. However, this condition was derived without formal proof, and the proof seems to be of considerable interest to the research community. In fact, Watson observed that in the performance evaluation of token passing rings, it is convenient to derive stability conditions ... (without proof). Our intention is to fill this gap, and to provide a formal proof of thesufficient and necessary stability condition for the token passing ring. In this paper, we present the case when the arrival process to each queue is Poisson but service times and switchover times are generally distributed. We consider in depth a gatedl-limited (l ) service discipline for each station. We also indicate that the basic steps of our technique can be used to study the stability of some other multiqueue systems.This research was supported by NSF Grant CCR-8900305, and in part by AFOSR Grant 90-0107, and by Grant R01 LM05118 from the National Library of Medicine.     

Hydrodynamic Limit of Condensing Two-Species Zero Range Processes with Sub-critical Initial Profiles

Two-species condensing zero range processes (ZRPs) are interacting particle systems with two species of particles and zero range interaction exhibiting phase separation outside a domain of sub-critical densities. We prove the hydrodynamic limit of nearest neighbour mean zero two-species condensing ZRP with bounded local jump rate for sub-critical initial profiles, i.e., for initial profiles whose image is contained in the region of sub-critical densities. The proof is based on H.T. Yau’s relative entropy method, which relies on the existence of sufficiently regular solutions to the hydrodynamic equation. In the particular case of the species-blind ZRP, we prove that the solutions of the hydrodynamic equation exist globally in time and thus the hydrodynamic limit is valid for all times.     

Transport of photochemical ozone along the western Adriatic shore near a petrochemical plant

Summary During the warm months, the whole area surrounding Ravenna's petrochemical plant, which is about 5 km inshore of the northern Adriatic coast (Po Valley region), is subject to photochemical reactions producing high values of ozone concentration. The transport offshore of oxidants' precursors by the land breeze, photochemical reactions and subsequent transport inshore of oxidants by the sea breeze, may cause high concentrations of ozone along the coast up until the late evening. Similar phenomena have already been observed in other coastal regions. Classifying the ozone data into days with different circulations, the following can be seen: on days with W or NW circulation, a regular diurnal variation of ozone correlated with solar radiation is found; with winds from E or SE, the ozone variations are irregular and ozone concentrations can maintain high levels ((40÷70) p.p.b.) even during the nightime. This is a report of the results of several field measurements aimed at showing the ozone production and destruction processes, as well as its recirculation mechanisms under breeze conditions. Paper presented at the 1^o Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 19–22, 1984, Rome.