Binding the hydrophobic fluorescent probe, 2-p-toluidinylnaphthalene-6-sulfonate,by polycations that contain apolar pendant groups: Equilibrium dialysis and fluorescence measurements

The thermodynamic parameters for the interaction of the hydrophobic fluorescent probe, 2-p-toluidinylnaphthalene-6-sulfonate (TNS), and polycations that contain a piperidinium cation and various nonpolar pendant groups were calculated. Binding is exothermic and involves a positive entropy gain. The contribution of the entropy term to the free energy change tends to increase with increasing hydrophobicity of the polymers. The intensity of the fluorescence of TNS is enhanced when the probe binds to the polycations. The nature and phenomena of hydrophobic fluorescent probe binding with the polymers are discussed.     

Temperature dependence on the binding of butyl orange by bovine serum albumin: The effect of urea

The effect of urea on the extent of the binding of butyl orange by bovine serum albumin has been examined by an equilibrium dialysis method. The first binding constants and the thermodynamic parameters for the formation of the first dye anion–protein complex have been calculated. Addition of urea to the binding system causes a marked decrease in the absolute magnitude of the free energy change. The enthalpy change during binding becomes more exothermic, and the entropy change tends to decrease with increasing concentration of urea. These results can be interpreted in terms of the concept that urea reduces the structure of the aqueous environment and hence lowers the tendency of apolar groups of the dye and the albumin to participate in the formation of hydrophobic interactions.     

Effect of sulphonic acid on the aqueous solubility of disperse dyes

Summary The solubilities of the following compounds in water andp-toluenesulphonic acid aqueous solution were determined at 5, 25 and 40 C: azobenzenep-aminoazobenzene,p-hydroxyazobenzene,p-N, N-dimethylaminoazobenzene and 1-phenylazo-4-aminonaphthalene. Prom the results the thermodynamic parameters for the transfer of one mole of the compound from water top-toluenesulphonic acid aqueous solution were calculated. It was found that the process was nearly athermal: furthermore, it was invariably accompanied by a positive unitary entropy change. The solubilizing mechanism of aromatic sulphonic acids was explained in terms of an adduct-formation with the compound to be dissolved by means of hydrophobic and nonpolarvan der Waals interactions.

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Zusammenfassung Die Löslichkeiten folgender Verbindungen in Wasser und wÄ\rigerp-ToluolsulphonsÄure-Lösung wurden bei 5, 25 und 40 C bestimmt: Azobenzol,p-Aminoazobenzol,p-Hydroxyazobenzol,p-N,N-dimethylammoazobenzol undL-Phenylazo-4-aminonaphthalin. Aus den Ergebnissen wurden die thermodynamischen Parameter für den übergang eines Mols der Verbindung von Wasser zup-ToluolsulphonsÄurewÄ\rigen Lösungen berechnet. Es wurde gefunden, da\ die Prozesse nahezu athermisch sind. Au\erdem sind sie sÄmtlich durch eine positive und gleichmÄ\ig gro\e EntropieÄnderung begleitet. Der Lösungsmechanismus aromatischer SulphonsÄuren wird in den Begriffen einer Adduktbildung mit der Komponente erklÄrt, die durch die hydrophoben unpolarenvan-der-Waals-Wechselwirkungen entsteht.

     

Oxidation of Sulfides with Hydrogen Peroxide Catalyzed by Vitamin B2 Derivatives

5-Ethyl-3-methyl-2′,4′:3′,5′-di-O-methylenedioxyriboflavinium perchlorate (1, DMRFlEt⁺ClO₄ ^–), derived readily from commercially available vitamin B₂ (riboflavin), exhibits high catalytic activity for the oxidation of organic sulfides with hydrogen peroxide. The reaction provides an efficient and selective method for the oxidative transformation of organic sulfides to the corresponding sulfoxides under mild conditions.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details.]     

Rendering poly(amidoamine) or poly(propylenimine) dendrimers temperature sensitive

The poly(amidoamine) dendrimers having terminal isobutyramide (IBAM) groups were prepared by the reaction of isobutyric acid and the amine-terminated poly(amidoamine) dendrimers with generations (G) of 2 to 5 by using a condensing agent, 1,3-dicyclohexylcarbodiimide. 1H and 13C NMR revealed that an IBAM group was attached to essentially every chain end of the dendrimers. While the IBAM-terminated G2 dendrimer was soluble in water, the IBAM-terminated G3, G4, and G5 dendrimers exhibited the lower critical solution temperatures (LCSTs) at 75, 61, and 43 degrees C, respectively. Because the density of the terminal IBAM groups in the periphery of the dendrimer progressively increases with increasing dendrimer generation, the interaction of the IBAM groups might take place more efficiently, resulting in a remarkable decrease in the LCST. In addition, attachment of IBAM groups to poly(propylenimine) dendrimers could give the temperature-sensitive property, indicating that this is an efficient method to render dendrimers temperature sensitive.