Thermodynamic and Fluorescence Studies on the Interaction of Cholesterol with Palmitoyl-Oleoyl Phosphatidylcholine and Sphingomyelin

Studies on the interaction of cholesterol (CHOL) with palmitoyl-oleoyl phosphatidylcholine (POPC) and sphingomyelin (SPM) are considered to be important because of the occurrence of strong interactions between sphingolipids and CHOL, which lead to the formation of microdomains or rafts within biological membranes. In the present investigation, studies on the surface pressure (π)-area ( A ) measurements and fluorescence microscopic studies on monolayers of the above mentioned system have been reported. Ideality/nonideality of mixing, excess area, and free energy changes during the formation of the monolayers at different surface pressures for the mixed lipid systems were evaluated from the π– A data. Interactions were found to be repulsive at lower CHOL content, which became associative at higher CHOL content. Condensing effects of CHOL on the mixed monolayers were found. Fluorescence studies on the systems revealed similar overall results.     

Effect of Dilution Ratio on Amount of Asphaltenes Separated from Stock Tank Oil

We have investigated the effect of n‐alkane dilution on the amount of asphaltene separated from stock ‐tank oil. Asphaltenes were produced from three different oils by mixing each oil with varying amounts of n‐alkanes, including n‐pentane, n‐hexane, and n‐heptane. The n‐alkane:oil ratio ranged from 1∶1 to 1000∶1. With increasing n‐alkane:oil ratio, the amount of separated asphaltene initially increased, passed through a maximum, then decreased gradually with further dilution. The maximum occurred at an n‐alkane:oil ratio of around 30∶1 to 40∶1 for n‐hexane and n‐heptane, and 80∶1 for n‐pentane. A two‐component thermodynamic model based on Flory‐Huggins theory was adapted to match the observed trend of produced asphaltene by assuming a polydisperse model of the asphaltene fraction.     

Mesogenic ketohexose and aldopentose derivatives: anomalous behaviour of the alkyl D-fructopyranosides

The thermotropic and lyotropic behaviour of a number of alkyl ketopyranosides, alkyl ketofuranosides, an alkyl pentopyranoside and an alkyl pentofuranoside were studied. With the exception of the alkyl beta-D-fructopyranosides, all the compounds display the expected smectic A* phases. The three alkyl fructopyranoside homologues studied (octyl, decyl and dodecyl) display a novel, rather viscous mesophase (monotropic), the nature of which is as yet unclear. The unknown phase is not a smectic A phase, because a phase transition from smectic A* to phase X is observed for both the decyl and the dodecyl derivative. The lyotropic behaviour of all the compounds in this study is quite similar to that reported earlier for other monoalkylated monosaccharide derivatives, except that the unknown phase X is again observed for the fructopyranoside derivatives.     

Small‐Molecule Control of Intracellular Protein Levels through Modulation of the Ubiquitin Proteasome System

Traditionally, biological probes and drugs have targeted the activities of proteins (such as enzymes and receptors) that can be readily controlled by small molecules. The remaining majority of the proteome has been deemed “undruggable”. By using small‐molecule modulators of the ubiquitin proteasome, protein levels, rather than protein activity, can be targeted instead, thus increasing the number of druggable targets. Whereas targeting of the proteasome itself can lead to a global increase in protein levels, the targeting of other components of the UPS (e.g., the E3 ubiquitin ligases) can lead to an increase in protein levels in a more targeted fashion. Alternatively, multiple strategies for inducing protein degradation with small‐molecule probes are emerging. With the ability to induce and inhibit the degradation of targeted proteins, small‐molecule modulators of the UPS have the potential to significantly expand the druggable portion of the proteome beyond traditional targets, such as enzymes and receptors.     

Enhancement of the Photoresponse in Organic Field‐Effect Transistors by Incorporating Thin DNA Layers

A mechanistic study of the DNA interfacial layer that enhances the photoresponse in n‐type field‐effect transistors (FET) and lateral photoconductors using a solution‐processed fullerene derivative embedded with disperse‐red dye, namely PCBDR, is reported. Incorporation of the thin DNA layer simultaneously leads to increasing the electron injection from non‐Ohmic contacts into the PCBDR active layer in dark and to increasing the photocurrent under irradiation. Such features lead to the observation of the enhancement of the photoresponsivity in PCBDR FETs up to 10³. Kelvin probe microscopy displays that in the presence of the DNA layer, the surface potential of PCBDR has a greater change in response to irradiation, which is rationalized by a larger number of photoinduced surface carriers. Transient absorption spectroscopy confirms that the increase in photoinduced carriers in PCBDR under irradiation is primarily ascribed to the increase in exciton dissociation rates through the PCBDR/DNA interface and this process can be assisted by the interfacial dipole interaction.     

An ‘impossible’ macrocyclisation using conformation directing protecting groups

A p-benzenetricarboxamide macrocycle linked through secondary cis amides is obtained via cyclisation and subsequent deprotection of a folded linear precursor. Secondary benzamides strongly prefer the trans conformation, therefore this synthesis can be considered ‘impossible’ without recourse to protecting groups.     

Aromatische Substanzen

Ohne Zusammenfassung     

On the interplay between the Hilbert transform and conjugate harmonic functions

As is well‐known, there is a close and well‐defined connection between the notions of Hilbert transform and of conjugate harmonic functions in the context of the complex plane. This holds e.g. in the case of the Hilbert transform on the real line, which is linked to conjugate harmonicity in the upper (or lower) half plane. It also can be rephrased when dealing with the Hilbert transform on the boundary of a simply connected domain related to conjugate harmonics in its interior (or exterior). In this paper, we extend these principles to higher dimensional space, more specifically, in a Clifford analysis setting. We will show that the intimate relation between both concepts remains, however giving rise to a range of possibilities for the definition of either new Hilbert‐like transforms, or specific notions of conjugate harmonicity. Copyright © 2006 John Wiley & Sons, Ltd.