Assembly and mechanical properties of phosphorus dendrimer/polyelectrolyte multilayer microcapsules

We report the preparation, characterization, and mechanical properties of polyelectrolyte/phosphorus dendrimer multilayer microcapsules. The shells of these microcapsules are composed either by alternating poly(styrenesulfonate) (PSS) and positively charged dendrimer G4(NH+Et2Cl-)96 or by alternating poly(allylamine hydrochloride) (PAH) and negatively charged dendrimer G4(CH-COO-Na+)96. The same multilayers were constructed on planar support to examine their layer-by-layer growth and to measure the multilayer thickness. Surface plasmon resonance spectroscopy (SPR) showed regular linear growth of the assembly upon each bilayer deposited. We probe the mechanical properties of these polyelectrolyte/dendrimer microcapsules by measuring force-deformation curves with the atomic force microscope (AFM). The experiment suggests that they are much softer than PSS/PAH microcapsules studied before. This softening is attributed to an enhanced permeability of the polyelectrolyte/dendrimer multilayer shells as compared with multilayers formed by linear polyelectrolytes. In contrast, Young's modulus of both dendrimer-based multilayers was found to be on the same order as that of PSS/PAH multilayers.     

Phosphorus Dendrimers: Nano-objects for Nanosciences

Summary: The influence of the size (the generation) of phosphorus dendrimers on their properties is discussed in three main fields of applications: catalysis, new materials, and biology. Typical examples are given to illustrate these three fields: Knoevenagel condensation for catalysis, elaboration of highly sensitive DNA chips for materials, transfection experiments, and anti-prion activity for biology.     

Dendrimers and DNA: combinations of two special topologies for nanomaterials and biology

Interactions between two precisely defined three-dimensional architectures (DNA and dendrimers) are described. Highly synergetic effects occur, as illustrated in two cases: dendrimers can be used as three-dimensional linkers for oligonucleotides, affording highly sensitive microarrays (biochips), and positively charged dendrimers strongly interact with DNA, allowing penetration inside cells (genetic transfection).     

Phosphorus-containing dendrimers bearing galactosylceramide analogs: self-assembly properties

We report the synthesis and the supramolecular auto-assembly of catanionic phosphorus-containing dendrimers mimicking multisite analogs of galactosylceramide.     

Comparative IR spectroscopic study of phosphorus-containing dendrimers built of thiophosphoryl, cyclophosphazene and phthalocyanine cores

The FTIR spectra of four generations of phosphorus-containing dendrimers built of thiophosphoryl, cyclophosphazene and phthalocyanine cores with terminal benzaldehyde and P–Cl groups have been recorded and analyzed. FT-Raman spectra of four generations of phosphorus dendrimers built of cyclotriphosphazene core with terminal benzaldehyde groups have been detected. Their spectral pattern is determined by the ratio T_n/R_n (T_n—number of terminal groups, R_n—number of repeating units). This ratio trends to r − 1 (r—branching functionality of repeating unit), and becomes constant, when the generation number is higher than 3. Experimental IR spectra of dendrimers built of thiophosphoryl, cyclophosphazene and phthalocyanine cores are very closely similar. The dependence of band full width at half height in IR spectra on the number of dendrons is established. The possibility appears to separate the bands assigned to the core, repeating units and terminal groups of dendrimers by difference spectroscopy method.     

Surface, core, and structure modifications of phosphorus-containing dendrimers. Influence on the thermal stability

Three new series of phosphorus-containing dendrimers are described. Their solubility depends on the type of end groups they bear. Perfluoroalkyl chains give dendrimers soluble in chlorofluorocarbons, whereas guanidinium and pyridinium derivatives give water-soluble compounds. The thermal stability of these compounds, as well as of 19 other dendrimers of various generations, having various cores, or various end groups, or branching points is studied. The main feature of this study is that the internal structure of these dendrimers is thermally stable at least up to 376°C. The number of the generation has practically no influence, whereas the principal criterion influencing the thermal stability is the type of end groups. The water-soluble cationic dendrimers are the least stable, but even those are stable up to 225°C. For most of these dendrimers, an important percentage of mass (around 50%) is retained even at a temperature as high as 1000°C. In the best case, up to 70% of the initial mass is retained at 1000°C.     

Naked Au55 clusters: dramatic effect of a thiol-terminated dendrimer

Reaction of the thiol-terminated fourth-generation dendrimer 2-G4 (96 SH groups) with the gold cluster compound Au55(PPh3)12Cl6 in a 3:1 molar ratio in dichloromethane results in the formation of bare Au55 clusters. The cuboctahedrally shaped Au55 particles coalesce to well-formed microcrystals (Au55) infinity. The role of the dendrimer is not only to remove the phosphine and chlorine ligands but also to act as an ideal matrix for perfect crystal growth. Transmission electron microscopy (TEM), small- and wide-angle X-ray diffraction (SAXRD and WAXRD) measurements indicate a structure where rows of edge-linked Au55 building blocks form a distorted cubic lattice. The X-ray data fit best if a 5% reduction of the Au-Au bond length in the Au55 clusters is assumed, in agreement with previous extended X-ray absorption fine structure (EXAFS) measurements. Energy-dispersive X-ray spectroscopy (EDX) analyses and IR investigations show the absence of PPh3 and Cl in the microcrystals.     

Polyazaphosphorus macrocycles: Synthesis,reactivity, complexation

A general synthesis of various polyazaphosphorus macrocycles involving [1 + 1], [2 + 2], or [3 + 3] cyclocondensations is reviewed, as well as the attempted synthesis of cryptands. Selective reduction (imino functions) methylation (PS groups), silylation (PO groups) are reported. Preparations of some macrocycle complexes are described.