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Hydrophobic Chains (hydrophobic + chain)
Selected AbstractspH-independent hydrolysis of 4-nitrophenyl 2,2-dichloropropionate in aqueous micellar solutions: relative contributions of hydrophobic and electrostatic interactionsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2001Omar A. EI Seoud Abstract The pH-independent hydrolysis of 4-nitrophenyl 2,2-dichloropropionate (NPDCP) in the presence of aqueous micelles of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, alkyltrimethylammonium chlorides, alkyldimethylbenzylammonium chlorides (alkyl,=,cetyl and dodecyl) and polyoxyethylene(9) nonylphenyl ether was studied spectrophotometrically. The observed rate constants, kobs, decrease in the following order: bulk water >cationic micelles >anionic micelles >non-ionic micelles. This order is different from that observed for pH-independent hydrolysis of 4-nitrophenyl chloroformate (NPCF), whose reaction is faster in cationic micelles than in bulk water. A proton NMR study on solubilization of a model ester, 4-nitrophenyl 2-chloropropionate, showed that the methylene groups in the middle of the surfactant hydrophobic chain are most affected by the solubilizate. Lower polarity and high ionic strength of interfacial water decrease the rates of hydrolysis of both NPCF and NPDCP, but the fraction of the former ester that diffuses to the interface is probably higher than that of the latter. Therefore, whereas the (negatively charged) transition state of NPCF is stabilized by cationic interfaces and destabilized by anionic interfaces, that of NPDCP is negligibly affected by ionic interfaces, which explains the observed rate retardation by all ionic micelles. Calculated activation parameters corroborate our explanation. Copyright © 2001 John Wiley & Sons, Ltd. [source] Do dendritic amphiphiles self-assemble in water?JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2001A Fourier transform pulse-gradient spin-echo NMR study Abstract Amphiphilic poly(amidoamine) (PAMAM) dendrimers were synthesized having an average of 7,46 hydrophobic chains of varying lengths (C10,C14) attached to the periphery of 64 amine groups. The synthesis was performed in three steps: (1) protection of a desired number of amines with BOC groups; (2) reaction of the remaining amine groups with long-chain acid chlorides; and (3) deprotection from the BOC groups to produce the amphiphilic dendrimers as HCl salts. The behavior of the dendrimers in aqueous media was examined by pulse-gradient spin-echo (FT-PGSE) NMR and dynamic light scattering. Self-diffusion data on dendrimers with 22 or fewer chains, along with dynamic light scattering on concentrations of ,16 wt%, gave no indication of dendrimer,dendrimer self-assembly via hydrocarbon chains exposed on the dendrimer surface. It is concluded that dendrimers with 7,22 chains, each having 10,14 carbons, behave as unimolecular entities with chains coiled largely within the dendrimer periphery. Only when the number of chains becomes very large (ca ,34) are chains forced externally where they can promote hydrophobically induced self-assembly. Monomeric dendrimers possessing the full range of functional polarity have great potential in enzyme modeling. Copyright © 2001 John Wiley & Sons, Ltd. [source] Randomization of Amyloid-,-Peptide(1-42) Conformation by Sulfonated and Sulfated Nanoparticles Reduces Aggregation and CytotoxicityMACROMOLECULAR BIOSCIENCE, Issue 10 2010Ana M. Saraiva Abstract The amyloid-, peptide (A,) plays a central role in the mechanism of Alzheimer's disease, being the main constituent of the plaque deposits found in AD brains. A, amyloid formation and deposition are due to a conformational switching to a ,-enriched secondary structure. Our strategy to inhibit A, aggregation involves the re-conversion of A, conformation by adsorption to nanoparticles. NPs were synthesized by sulfonation and sulfation of polystyrene, leading to microgels and latexes. Both polymeric nanostructures affect the conformation of A, inducing an unordered state. Oligomerization was delayed and cytotoxicity reduced. The proper balance between hydrophilic moieties and hydrophobic chains seems to be an essential feature of effective NPs. [source] General Synthesis and Aggregation Behaviour of New Single-Chain Bolaphospholipids: Variations in Chain and Headgroup StructuresCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2008Simon Drescher Abstract The chemical structures of polymethylene-1,,-bis(phosphocholines) that self-assemble into nanofibres was modified on the one hand in the hydrophobic chain region, by introduction of sulfur and oxygen atoms, and on the other hand by variation of the polar headgroup structure with functionalised tertiary amines. The temperature-dependent self-assembly of these novel bolaphospholipids into nanofibres and spherical micelles was investigated by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The thermal stabilities of the nanofibres strongly depend on the chemical compositions of the headgroups and of the hydrophobic chains. The insertion of new functionalities in the headgroup region by click chemistry makes these substances interesting for potential applications in bioscience and materials science. [source] | ||||||||||