Current trends in green sample preparation before liquid chromatographic bioanalysis

1. Download : Download high-res image (222KB)
2. Download : Download full-size image

     

Rational Design and Synthesis of AT1R Antagonists

Hypertension is one of the most common diseases nowadays and is still the major cause of premature death despite of the continuous discovery of novel therapeutics. The discovery of the Renin Angiotensin System (RAS) unveiled a path to develop efficient drugs to fruitfully combat hypertension. Several compounds that prevent the Angiotensin II hormone from binding and activating the AT1R, named sartans, have been developed. Herein, we report a comprehensive review of the synthetic paths followed for the development of different sartans since the discovery of the first sartan, Losartan.     

Connecting Linear Polymers Molecular Structure to Viscoelastic Properties and Melt Flow Index

A modeling pathway and software tool for linking entangled linear polymer molecular properties to linear viscoelasticity and melt index (MI) values is presented. A reptation model links molecular properties to the flow curve, and then, an ANSYS Polyflow model calculates MI values based on the flow curve predicted. The method is thoroughly tested and validated for uni‐ and bimodal, low‐ and high‐density polyethylene grades. An overall accuracy level in the range of 90% on average is exhibited, considering both model prediction steps: (i) molecular weight distribution to flow curve and (ii) flow curve to MI.

     

Novel disposable microfabricated antimony-film electrodes for adsorptive stripping analysis of trace Ni(II)

This work describes a novel type of antimony electrode for adsorptive stripping voltammetry (AdSV). The electrode was microfabricated by coating a silicon chip with a thin antimony-film by means of sputtering and the active area of the electrode was defined by photolithography. The resulting antimony-film electrodes (SbFEs) were characterized by optical and electrochemical techniques. The sensors were tested for the detection of low concentrations of Ni(II) by AdSV in the presence of dimethylglyoxime. Well-formed stripping peaks and a linear dependence of the stripping peak current on the Ni(II) concentration were observed on the microfabricated SbFEs while comparative measurements attempted with electroplated SbFEs were unsuccessful. Utilizing thin-film technology for the formation of the antimony-film extends the scope of these devices as mercury-free sensors in AdSV.     

Nonlinear evolution of thin liquid films dewetting near soft elastomeric layers

The nonlinear evolution of thin liquid films dewetting near soft elastomeric layers is examined in this work. Evolution equations are derived by applying the lubrication approximation and assuming that van der Waals forces in the liquid cause the dewetting and that the solid can be described as a linear viscoelastic material. Two cases are examined: (i) a liquid layer resting on an elastomer bounded from below by a rigid substrate, and (ii) an elastomer overlying a thin liquid film bounded from below by a rigid substrate. Linear stability analysis is carried out to obtain asymptotic relations which are then compared against solutions of the full characteristic equations. In the liquid-on-solid case, numerical solutions of the evolution equations show that van der Waals forces cause thinning of the liquid film and thickening of the elastomeric solid beneath film depressions. Inclusion of a short-range repulsive force suggests that regular patterns may form in which ridges of fluid rest on depressions in the solid. In the solid-on-liquid case, the van der Waals forces cause the solid layer to break up before the liquid film can dewet. The results presented here support the idea that the dewetting of thin liquid films might be exploited to create topographically patterned surfaces on soft polymeric solids.     

Schmidt number effects in dissipative particle dynamics simulation of polymers

Simulation studies for dilute polymeric systems are presented using the dissipative particle dynamics method. By employing two different thermostats, the velocity-Verlet and Lowe's scheme, we show that the Schmidt number (S(c)) of the solvent strongly affects nonequilibrium polymeric quantities. The fractional extension of wormlike chains subjected to steady shear is obtained as a function of S(c). Poiseuille flow in microchannels for fixed polymer concentration and varying number of repeated units within a chain is simulated. The nonuniform concentration profiles and their dependence on S(c) are computed. We show the effect of the bounce-forward wall boundary condition on the depletion layer thickness. A power law fit of the velocity profile in stratified Poiseuille flow in a microchannel yields wall viscosities different from bulk values derived from uniform, steady plane Couette flow. The form of the velocity profiles indicates that the slip flow model is not useful for the conditions of these calculations.     

Molecular dynamics simulations of pure methane and carbon dioxide hydrates: lattice constants and derivative properties

ABSTRACT

We report extensive molecular dynamics simulation results of pure methane and carbon dioxide hydrates at pressure and temperature conditions that are of interest to various practical applications. We focus on the calculation of the lattice constants of the two pure hydrates and their dependence on pressure and temperature. The calculated lattice constants are correlated using second order polynomials which are functions of either temperature or pressure. Finally, the obtained correlations are used in order to calculate two derivative properties, namely the isothermal compressibility and the isobaric thermal expansion coefficient. The current simulation results are also compared against reported experimental measurements and other simulation studies and good agreement is found for the case of isothermal compressibility. On the other hand, for the case of isobaric thermal expansion coefficient good agreement is found only with other simulation studies, while the simulation studies are in disagreement with experiments, particularly at low temperatures.     

Dissecting Hofmeister Effects: Direct Anion–Amide Interactions Are Weaker than Cation–Amide Binding

Whereas there is increasing evidence for ion‐induced protein destabilization through direct ion–protein interactions, the strength of the binding of anions to proteins relative to cation–protein binding has remained elusive. In this work, the rotational mobility of a model amide in aqueous solution was used as a reporter for the interactions of different anions with the amide group. Protein‐stabilizing salts such as KCl and KNO₃ do not affect the rotational mobility of the amide. Conversely, protein denaturants such as KSCN and KI markedly reduce the orientational freedom of the amide group. Thus these results provide evidence for a direct denaturation mechanism through ion–protein interactions. Comparing the present findings with results for cations shows that in contrast to common belief, anion–amide binding is weaker than cation–amide binding.     

Über den Verteilungssatz der Auxochrome bei Azokörpern,I. Di- und Tetramethoxy-xobenzole

The validity of the rule of repartition of the auxochromes is examined for some symmetric tetramethoxy-azobenzenes, dimethoxy-azobenzenes, and dimethoxy-4′-nitro-azobenzenes whose methoxy groups are in 2,4-, 3,4- and 2,5-position. The rule is confirmed with 2,4-and 2,5-derivatives. The long wave lengths absorption maxima of 3,4,3′,4′-tetramethoxy-azobenzene and of 3,4-dimethoxy-4′-nitro-azobenzene are situated at shorter wave lengths than expected.