Stability of Amphiphilic Dendrimers at the Water/Air Interface (original) (raw)
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Amphiphilic Dendrimers as Building Blocks in Supramolecular Assemblies
Journal of the American Chemical Society, 1998
The self-assembly of amphiphilic dendrimers based on poly(propylene imine) dendrimers of five different generations with up to 64 end groups modified with long hydrophobic chains has been studied. At the air-water interface stable monolayers form in which the dendritic surfactants presumably adopt a cylindrical shape; all the chains are aligned perpendicular to the water surface, and the dendritic poly(propylene imine) core faces the aqueous phase. Electron microscopy and dynamic light-scattering measurements performed on aqueous solutions of the amphiphiles at pH) 1 showed the formation of small spherical aggregates with diameters varying between 20 and 200 nm. X-ray diffraction of cast films of these aggregates revealed bilayer thicknesses of 48-54 Å. A phase transition was detected by measuring fluorescence anisotropy. The theoretical volumes of the dendritic amphiphiles were in good agreement with those calculated from the monolayer experiments and X-ray diffraction data. Hence, the amphiphilic dendrimers within the aggregates in solution have the same highly asymmetric conformation as that proposed at the air-water interface. Calculations showed that the shape of the dendritic poly(propylene imine) core in the aggregates is distorted and that the axial ratio (r b :r a) ranges from 1:2.5 for the first generation to approximately 1:8 for the three highest generation of dendrimer. This behavior illustrates the high flexibility of the poly(propylene imine) dendrimers.
Studies of a novel polymerizable amphiphilic dendrimer
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2000
In the present study, we have synthesized a polymerizable amphiphilic dendrimer by attaching 10,12-pentacosadiynoic acid (PDA) to a third generation poly(amidoamine) (PAMAM) dendrimer core (PDA-PAMAM). This dendrimer was characterized by 1 H NMR and MALDI-TOF mass spectroscopy. The amphiphilic property of this dendrimer has been studied. Surface pressure and surface dipole moment-area isotherm measurements have shown that PDA-PAMAM forms a stable monolayer at the air-water interface with a limiting molecular area of 460 A , 2 per molecule. The compressed monolayer can be readily polymerized upon UV irradiation, as like other PDA derivatives. The topography of the monolayer was observed by Brewster angle microscopy (BAM) as well as by the environmental scanning electron microscopy (ESEM). We found a good correlation between the size and shape of monolayer domains observed with the BAM and ESEM techniques. To our knowledge, this is the first time wet mode ESEM has been used to characterize L-B film. The wet mode ensures that L-B films remain intact without being damaged by the high vacuum system of traditional SEM. As a preliminary study, we have found that this new dendrimer forms colloidal particles in chloroform solution and can be readily polymerized by UV irradiation.
Colloid and Polymer Science, 2013
Amphiphilic carbosilane dendrimers with novel architectural layout have been synthesized. These dendrimers contain peripheral groups consisting of covalently bound promesogenic fragments and hydrophilic (oligoethyleneglycolic) linkages which are connected to a carbosilane core in two distinct ways: as spacer or as tail arrangement. Such molecules have a block structure where the hydrophilic and hydrophobic blocks are distributed within the dendrimer forming layers of different polarity. The hydrophilic layer is either enclosed between two hydrophobic parts of the molecule or is situated on the periphery. The synthetic strategy for achieving these structures is described. The interfacial properties of the dendrimers were studied and the influence of the dendritic structure's organization on the Langmuir film formation process is assessed.
Synthesis and Surface Chemistry Study of a New Amphiphilic PAMAM Dendrimer
Langmuir, 2000
A new disk-shaped amphiphilic dendrimer has been synthesized by attaching sixty-four 12-hydroxydodecanoic acid chains to a fourth generation poly(amido amine) (PAMAM) dendrimer core. Surface pressure and surface potential-area isotherm measurements have shown that the dendrimer forms a stable monolayer at the air/water interface with limiting molecular area of 160 Å 2 /molecule. This small area relative to the huge size of the dendrimer suggests that the dendrimer molecules form an edge-on disk-shaped structure at the air/water interface. The topography of the dendrimer monolayer was observed by Brewster angle microscopy (BAM) at air/water interface as well as by environmental scanning electron microscopy (ESEM) as a Langmuir-Blodgett film. The striplike monolayer domains observed from BAM images correspond to the monolayer topography as observed from ESEM images.
Organization of Hybrid Dendrimer−Inorganic Nanoparticles on Amphiphilic Surfaces
Macromolecules, 2002
Multiple length scale structuring of organic-inorganic composites is a powerful technique for the creation of materials and devices. Because of quantum size effects, nanoscale inorganic structures can show special electronic, optical, optoelectronic, and magnetic behavior. 1,2 To take advantage of these unique properties, one has to be able to design such nanostructures in a controlled manner and to organize the nanoparticles on larger length scales. The design of materials structured on multiple length scales from the molecular to the macroscopic level has recently come into focus as modular chemistry. As with the development of any new materials, a parallel requirement is the need for appropriate measurement methods to characterize the properties of these materials.
Macromolecules, 2018
A family of amphiphilic diblock Janus dendrimers were synthesized by chemoselective "click" coupling of poly(benzyl ether) dendrons, PBE, and poly-(ether−ester), PEE, dendrons based on three different ethylene glycol spacers. The well-defined defect-free structure of these dendrimers was proven by MALDI-TOF. In aqueous solutions these dendrimers were able to self-assemble into vesicles with diameter ranging from 140 nm to 3.6 μm or solid micelles (10 to 14 nm diameter). The form of these assemblies was affected by the spacer length between branching points and by the generations of both dendrons. The ethylene glycol moieties in the PEE dendrons induced notable thermosensitivity with sharp transitions observed for all members of the series. The presence of two triazole groups at each branching point was further exploited to fabricate palladium bearing nanomaterials with potential application in catalysis.
Langmuir, 1997
The structure of a series of poly(amidoamine) dendrimers Gn(C12) generated from a diaminododecane core have been investigated using the photophysical properties of an external dye, nile red. The modified dendrimers Gn(C12) show the ability to host the hydrophobic dye, nile red, in aqueous solution. The ability of Gn(C12) to host nile red has been compared to corresponding amino-core Gn(NH3) and diaminoethanecore Gn(C2) dendrimers of the same generation size. The emission of nile red in aqueous media is significantly enhanced in the presence of Gn(C12) and not at all for Gn(NH3) and Gn(C2). These results imply a strong tendency for the nile red probe to associate with the long methylene chain of the modified dendrimers in aqueous solutions. Moreover, the interactions of these dendrimers with anionic surfactants generate supramolecular assemblies which greatly enhance their ability to accomodate the nile red. Fluorescence polarization and emission as a function of pH were also studied in an effort to elucidate the interaction of the nile red probe with the dendrimer-surfactant assemblies.
A constitutional isomeric library synthesized by a modular approach has been used to discover six amphiphilic Janus dendrimer primary structures, which self-assemble into uniform onion-like vesicles with predictable dimensions and number of internal bilayers. These vesicles, denoted onion-like dendrimersomes, are assembled by simple injection of a solution of Janus dendrimer in a water-miscible solvent into water or buffer. These dendrimersomes provide mimics of double-bilayer and multibilayer biological membranes with dimensions and number of bilayers predicted by the Janus compound concentration in water. The simple injection method of preparation is accessible without any special equipment, generating uniform vesicles, and thus provides a promising tool for fundamental studies as well as technological applications in nanomedicine and other fields. synthetic membranes | biomembrane mimics | multibilayer vesicles M ost living organisms contain single-bilayer membranes composed of lipids, glycolipids, cholesterol, transmembrane proteins, and glycoproteins (1). Gram-negative bacteria (2, 3) and the cell nucleus (4), however, exhibit a strikingly special envelope that consists of a concentric double-bilayer membrane. More complex membranes are also encountered in cells and their various organelles, such as multivesicular structures of eukaryotic cells (5) and endosomes (6), and multibilayer structures of endoplasmic reticulum (7, 8), myelin (9, 10), and multilamellar bodies . This diversity of biological membranes inspired corresponding biological mimics. Liposomes ( ) self-assembled from phospholipids are the first mimics of singlebilayer biological membranes (13-16), but they are polydisperse, unstable, and permeable . Stealth liposomes coassembled from phospholipids, cholesterol, and phospholipids conjugated with poly(ethylene glycol) exhibit improved stability, permeability, and mechanical properties (17-20). Polymersomes (21-24) assembled from amphiphilic block copolymers exhibit better mechanical properties and permeability, but are not always biocompatible and are polydisperse. Dendrimersomes (25-28) self-assembled from amphiphilic Janus dendrimers and minidendrimers (26-28) have also been elaborated to mimic single-bilayer biological membranes. Amphiphilic Janus dendrimers take advantage of multivalency both in their hydrophobic and hydrophilic parts (23, 29-32). Dendrimersomes are assembled by simple injection (33) of a solution of an amphiphilic Janus dendrimer (26) in a water-soluble solvent into water or buffer and produce uniform (34), impermeable, and stable vesicles with excellent mechanical properties. In addition, their size and properties can be predicted by their primary structure (27). Amphiphilic Janus glycodendrimers self-assemble into glycodendrimersomes that mimic the glycan ligands of biological membranes (35). They have been demonstrated to be bioactive toward biomedically relevant bacterial, plant, and human lectins, and could have numerous applications in nanomedicine .
Journal of Polymer …, 2005
Amphiphilic poly(amidoamine) (PAMAM) dendrimers consisting of a hydrophilic dendrimer core and hydrophobic aromatic dansyl or 1-(naphthalenyl)-2phenyldiazene (NPD) shells have been synthesized. These amphiphilic dendrimers from the zero generation to the third generation self-assemble into vesicular aggregates in water. The self-assembly behavior of these dendrimers strongly depends on their generations. The generation dependence has been further investigated by an exploration of their electrochemical properties. For the PAMAM-NPD aggregates, the photoisomerization process leads to a change in the aggregate size. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5512-5519, 2005
Cationic amphiphilic dendrimers with tunable hydrophobicity show in vitro activity
Environmental Chemistry Letters, 2018
The widespread use of antibiotics has led to an increase in the number of strains resistant to major antibacterial pharmaceuticals. Many synthesized quaternary ammonium compounds possess antibacterial, antifungal and antiviral properties. Incorporation of quaternary ammonium moieties into dendrimers represents a promising strategy for the preparation of novel antimicrobial biomaterials. Here, poly(quaternary ammonium) chloride dendrimers were synthesized by functionalizing poly(propylene imine) (PPI) dendrimer with various lengths of alkyl chains. In vitro antimicrobial assays indicate that the amphiphilic dendrimers are potent antimicrobial agents with activity against multidrug-resistant pathogens such as the methicillin-resistant Staphylococcus aureus.