Anordnung und Orientierung kationischer Tenside auf ebenen Silicatoberflächen

Zusammenfassung Die n-Alkylammoniumderivate der glimmerartigen Schichtsilicate können als Modellsubstanzen für die Anordnung kationischer Tenside an Festkörpergrenzflächen herangezogen werden. Im ersten Teil der Arbeit wird die Darstellung durch Kationenaustausch aus den natürlichen Schichtsilicaten beschrieben. Es wird ausführlich auf die Fehlerquellen hingewiesen, die reproduzierbare Messungen erschweren.

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Summary The n-alkylammonium derivatives of mica-type layer silicates are suitable models for studies about the arrangement of cationic tensides at solid interfaces. Part I of the paper deals with the preparation of these compounds by a simple cation exchange reaction. Sources for errors in obtaining reproducible data are discussed in detail.

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Mit 1 Abbildung in 3 Einzeldarstellungen und 3 Tabellen     

Liquid-Crystalline Solvents as Mechanistic Probes. 10. Dynamics of Intramolecular Quenching of Pyrenyl Fluorescence in the Liquid-Crystalline and Isotropic Phases of a Cholesteric Solvent1

Abstract

The effect of cholesteric order in a 59.5/15.6/24.9 (w/w/w) mixture of cholesteryl oleate/cholesteryl nonanoate/cholesteryl chloride (CM) on the intramolecular fluorescence quenching of l,3-bis(l-pyrenyl) propane (P3P) has been explored. A comparison with fluorescence quenching of N,N-dimethyl-4-[3-(l-pyrenyl)propyl]aniline (P3D) in CM is made. From the Arrhenius activation parameters for quenching in the cholesteric and isotropic phases, it is concluded that the motions which take the ground state conformers of P3P to their quenching transition state are nearly impervious to macroscopic CM mesophase order: in the cholesteric phase, E'_a = 10.5±0.4 kcal mol^?1 and ΔS^? = 1 ± 1 eu; in the isotropic phase, E'_a = 10.0 ± 0.2 kcal mol^?1 and ΔS^? = 0 ± 0.5 eu. An explanation of these results is advanced.     

Live Monitoring of Cargo Release From Peptide‐Based Hybrid Nanocapsules Induced by Enzyme Cleavage

The miniemulsion process is used as a new route for the preparation of enzyme‐responsive nanocapsules with payload‐release properties. Peptide‐based hybrid nanocapsules are prepared via interfacial polyaddition containing a water‐soluble dye that is efficiently encapsulated inside. The influence of the synthetic parameters as the functionality of the peptide and the nature of the dispersed phase on the structure of the nanocapsules were investigated. After redispersion in water, the enzymatic cleavage of the peptide sequence and the release of the fluorescent dye are both monitored in real time. This is evidenced because of the quenching FRET system framing the recognition site in the peptide sequence, and the fluorescence recovery of the self‐quenched encapsulated dye respectively.     

Synthesis and fluorescence sensing properties of novel pyrene-armed calix[4]arene derivatives

Fluorogenic tert-butylcalix[4]arenes bearing two pyrene pendant groups at the lower rim were synthesized. Based on ratiometric changes of monomer and excimer emissions, the pyrene amine derivative of calix[4]arene has been found to act as a selective sensor for Pb²⁺ and Cu²⁺ ions, respectively, due to a conformational change upon chelation of these ions.     

Fluorescence properties of some 2-(4-amino-substituted-3-nitrophenyl)-3-hydroxyquinolin-4(1H)-ones

2-(4-Amino-substituted-3-nitrophenyl)-3-hydroxyquinolin-4(1H)-ones have been studied to evaluate their fluorescence properties and possible use as molecular fluorescent probes. The amino group was substituted with various alkyl moieties possessing a suitable terminal functional group (such as hydroxy or amino group) that could serve to bind a 3-hydroxyquinolin-4(1H)-one (3HQ) fluorescence label to a biomolecule. Besides simple hydrocarbon chains, ligands containing ethylenoxy units as optimal spacers were also tested. The structure-fluorescence properties and theoretical applicability of the studied molecules are discussed.     

Sonochemical preparation of GaSb nanoparticles

A room temperature sonochemical method for the preparation of GaSb nanoparticles using less hazardous Ga and antimony chloride (SbCl(3)) as the precursors has been described. The formation of GaSb has been confirmed by means of XRD, EDAX, and XPS characterization. TEM and SAED results show that the as-prepared solid consists of nanosized GaSb crystals with sizes in the range 20-30 nm. The photoacoustic spectrum result reveals that the GaSb nanoparticles have a direct band gap of about 1.21 eV. On the basis of the control experiments and the extreme conditions produced by ultrasound, an ultrasound-assisted in-situ reduction/combination mechanism has been proposed to explain the reaction.     

Insights into the Gelating Abilities of Ricinelaidic Acid and its Ammonium Salts: How do Stereochemistry,Charge, and Chain Lengths Control Gelation of a Long‐Chain Alkenoic Acid?

The gelating abilities of ricinelaidic acid (d ‐REA), the trans‐isomer of ricinoleic acid (d ‐RA), and a series of its alkylammonium and alkane‐α,ω‐diammonium salts have been examined in a wide range of organic liquids. The gelation efficiency of the trans acid is much better than that of the cis, although neither is as efficient as is the completely saturated molecular gelator analogue, (R)‐12‐hydroxystearic acid (d ‐12HSA). The formation of ammonium salts also improves the gelation ability of d ‐REA in high polarity liquids. The gelating properties are highly dependent upon the chain length of the alkyl group of the alkylammonium salts, but not very dependent on the chain length of the alkane‐α,ω‐diammonium salts. Structural insights from Fourier transform infrared spectroscopy and powder X‐ray diffraction indicate that the absence or presence of unsaturation, the incorporation of (charged) ammonium centers, and the different chain lengths of the alkylammonium salts lead to different packing arrangements and different strengths of H‐bonding interactions within the gel assemblies of the d ‐REA derivatives. Insights into the relationships among the various systematic structural changes to d ‐REA and the properties of their aggregated structures, including the gel states, are provided.     

Synthesis and general properties of silated-hydroxypropyl methylcellulose in prospect of biomedical use

Synthesis of grafting silane on a hydro soluble cellulose ether (HPMC) was described. In alkaline medium, this derivate is under gel form. With a decrease of the pH, a self-hardening occurs due to the silanol condensation. For potential biomedical use, we described the silated-HPMC synthesis, the gel behavior after steam sterilization and the parameters of the silanol condensation i.e. pH, silane percentage and temperature. Minimum kinetic of the condensation was observed for pH between 5.5 and 6.5. So temperature catalyzed the reaction and the self-hardening speed was increased by silane percentage.     

Structures of Organo Alkali Metal Complexes and Related Compounds

The investigation of the reactivity and structure of organometallic compounds of alkali metals has experienced a blustering development in the last decades. This class includes compounds that are especially important for our understanding of chemical bonding and also quite simple, for example methyl alkali metal complexes, whose structures have been unequivocally determined. Organometallic compounds of alkali metals (and also magnesium) generally exist as ion aggregates whose properties can be significantly modified through solvation by, for example, ether or amines. Important advances in the synthesis of new compounds, especially those of the heavier alkali metals, have been based on these results. It was long believed that the alkali metals had little tendency to undergo coordination and that their coordination chemistry would offer few surprises. This picture has now changed completely. Results from crystal structure investigations have revealed a variety of often surprising structure types (rings, heterocubanes, chains, layers, etc.) not only with the organometallic compounds but also with the amides, imides, alkoxides, phenoxides, enolates, and even halides. A comparison reveals interesting similarities between compounds that appear to be so different and leads to a general classification of the structure types possible with C, N, O, and halo ligands.