From favorable atomic configurations to supershell structures: a new interpretation of conductance histograms.

Simulated minimum cross-section histograms of breaking Al nanocontacts are produced using molecular dynamics. The results allow a new interpretation of the controverted conductance histogram peaks based on preferential geometrical arrangements of nanocontact necks. As temperature increases, lower conductance peaks decrease in favor of broader and higher conductance structures. This reveals the existence of shell and supershell structures favored by the increased mobility of Al atoms.     

UV spectrophotometric flow-injection assay of tetracycline antibiotics retained on Sephadex QAE A-25 in drug formulations

A flow injection analysis system with solid phase spectrophotometric transduction has been developed for the assay of tetracycline (TC), doxycicline (DTC), oxycicline (OTC) and chlortetracycline (CTC). The packing material of the flow-through cell consists of Sephadex QAE A-25 resin on which tetracyclines are temporarily retained. The carrier itself acts as the desorbing solution. The measurements of the intrinsic absorbance of tetracyclines (1000 μl of sample volume) were made at 380 nm (TC, DTC and OTC) and 387 nm (CTC). The detection limits were found to be 0.069 (TC and OTC), 0.081 (DTC) and 0.121 (CTC) μg ml⁻¹ and the linear dynamic range extended between 0.5 and 12 (TC, DTC and OTC) and 1–20 μg ml⁻¹ (CTC). The relative standard deviations (n=10) ranged between 0.7 and 1.2%. A study of the potentially interfering species was carried out. Using the proposed method, tetracyclines were satisfactorily determined without any interference from excipients in pharmaceutical preparations.     

Microseparation techniques for the study of the enantioselectivity of drug–plasma protein binding

Stereoselectivity in protein binding can have a significant effect on the pharmacokinetic and pharmacodynamic properties of chiral drugs. The investigation of enantioselectivity of drugs in their binding with human plasma proteins and the identification of the molecular mechanisms involved in the stereodiscrimination by the proteins represent a great challenge for clinical pharmacology. In this review, the separation techniques used for enantioselective protein binding experiments are described and compared. An overview of studies on enantiomer–protein interactions, enantiomer–enantiomer interactions as well as chiral drug–drug interactions, including allosteric effects, is presented. The contribution of individual plasma proteins to the overall enantioselective binding and the animal species variability in drug–plasma protein binding stereoselectivity are reviewed. Copyright © 2008 John Wiley & Sons, Ltd.     

Comparison of rheological behavior of branched polypropylene prepared by chemical modification and electron beam irradiation under air and N2

Chemical and electron beam irradiation methods were used to introduce a branched structure into polypropylene and propylene–ethylene copolymer. The chemical method was carried out in an internal mixer using initiator and TMPTMA monomer. In irradiation method, the polymer was irradiated by electron beam under air and nitrogen atmosphere. The branched structure in the modified polymer was confirmed by rheological measurements. While degradation was significant in chemical method, branching occurred efficiently by irradiation under air. Small amount of ethylene in the propylene copolymer promoted branching over degradation.     

Open tubular liquid chromatography: Recent advances and future trends

Nano-liquid chromatography (nanoLC) is gaining significant attention as a primary analytical technique across various scientific domains. Unlike conventional high-performance LC, nanoLC utilizes columns with inner diameters (i.ds.) usually ranging from 10 to 150 μm and operates at mobile phase flow rates between 10 and 1000 nl/min, offering improved chromatographic performance and detectability. Currently, most exploration of nanoLC has focused on particle-packed columns. Although open tubular LC (OTLC) can provide superior performance, optimized OTLC columns require very narrow i.ds. (< 10 μm) and demand challenging instrumentation. At the moment, these challenges have limited the success of OTLC. Nevertheless, remarkable progress has been made in developing and utilizing OTLC systems featuring narrow columns (< 2 μm). Additionally, significant efforts have been made to explore larger columns (10–75 μm i.d), demonstrating practical applicability in many situations. Due to their perceived advantages, interest in OTLC has resurged in the last two decades. This review provides an updated outlook on the latest developments in OTLC, focusing on instrumental challenges, achievements, and advancements in column technology. Moreover, it outlines selected applications that illustrate the potential of OTLC for performing targeted and untargeted studies.     

On the singular sector of the Hermitian random matrix model in the large N limit

The one-cut case of the Hermitian random matrix model in the large N limit is considered. Its singular sector in the space of coupling constants is analyzed from the point of view of the hodograph equations of the underlying dispersionless Toda hierarchy. A deep connection with the singular sector of the hodograph equations of the 1-layer Benney (classical long wave equation) hierarchy is stablished. This property is a consequence of the fact that the hodograph equations for both hierarchies describe the critical points of solutions of Euler-Poisson-Darboux equations.