Redox-robust pentamethylamidoferrocenyl metallodendrimers that cleanly and selectively recognize the H2PO4- anion

The first pentamethylferrocenyl (Fc*) dendrimers are synthesized from DSM polyamine dendrimers (generations 1 to 5) and cleanly and selectively recognize the H2PO4- anion.     

Carbosilane liquid crystalline dendrimers with terminal chiral mesogenic groups: structure and properties

This paper presents a systematic study of two series of carbosilane liquid crystalline (LC) dendrimers from first to fifth generations bearing 8, 16, 32, 64 and 128 terminal chiral mesogenic groups, respectively. All the LC dendrimers synthesized are characterized by the same glass transition temperature around -5°C. It has been shown that the LC dendrimers of the lower generations (G-1-G-3) form a ferroelectric SmC* phase over a very broad temperature range up to about 180°C, while the LC dendrimers of the higher generations (G-4 and G-5) display a rectangular columnar mesophase (Col_r). Schemes of packing in the SmC* and Col_r mesophases formed by the LC dendrimers are suggested and discussed. Electrical measurements on the ferroelectric LC dendrimers have shown that an increase in generation number leads to a decrease in the value of the spontaneous polarization and an increase in switching time.     

From star-shaped to dendritic poly(ethylene oxide)s: Toward increasingly branched architectures by anionic polymerization

Polymers with dendritic structure are a category of macromolecular architectures that has received considerable attention in the last decade. These polymers, also referred to as dendrimers, exhibit a degree of branching equal to unity. Interest in dendrimers whose branching points are linked to each other by generations of macromolecular size is in contrast quite new. This paper describes a new synthetic strategy which allows access to poly(ethylene oxide) (PEO) with dendritic structure. PEO dendrimers with different degree of compactness have been synthesized upon modifying the size of successive generations.     

Carbosilane liquid crystalline dendrimers with terminal chiral mesogenic groups: structure and properties

This paper presents a systematic study of two series of carbosilane liquid crystalline (LC) dendrimers from first to fifth generations bearing 8, 16, 32, 64 and 128 terminal chiral mesogenic groups, respectively. All the LC dendrimers synthesized are characterized by the same glass transition temperature around -5°C. It has been shown that the LC dendrimers of the lower generations (G-1-G-3) form a ferroelectric SmC* phase over a very broad temperature range up to about 180°C, while the LC dendrimers of the higher generations (G-4 and G-5) display a rectangular columnar mesophase (Col_r). Schemes of packing in the SmC* and Col_r mesophases formed by the LC dendrimers are suggested and discussed. Electrical measurements on the ferroelectric LC dendrimers have shown that an increase in generation number leads to a decrease in the value of the spontaneous polarization and an increase in switching time.     

Synthesis of poly(propyl ether imine) dendrimers and evaluation of their cytotoxic properties

In this paper, we report the synthesis of several poly(propyl ether imine) dendrons and dendrimers. These dendrons and dendrimers were constructed by involving an ether as the linker component and an imine as the branching component. The divergent syntheses of dendrons and dendrimers were established with the aid of two alternate Michael addition reactions and two alternate reduction reactions in a four-step iterative synthetic sequence. Dendrons up to three generations were synthesized and some of the dendrons were attached to a benzenoid core so as to obtain dendrimers up to two generations containing 12 carboxylic acids at the periphery. Divergent synthesis involving ether as the core was found to be more facile, and dendrimers up to three generations having 16 carboxylic acids at the periphery were achieved in good to excellent yields in each individual step. The adopted synthetic sequence allows us to install either alcohol, an amine, or a carboxylic acid at their peripheries. The carboxylic acid-terminated dendrons and dendrimers were evaluated as to their cytotoxic properties, and while most dendrons and dendrimers did not exhibit any measurable cytotoxicity, even up to 100 microg/mL, the second-generation dendrimer with the benzenoid core exhibited a mild toxicity at concentrations above 30 microg/mL.     

Synthesis and comparative studies of carbosilane liquid crystalline dendrimers with chiral terminal mesogenic groups

A new series of carbosilane liquid crystalline (LC) dendrimers from the first to the third generations with 8, 16 and 32 chiral terminal mesogenic groups, respectively, has been synthesized. The molecular structures and purity of all new compounds were confirmed by ¹H NMR spectroscopy and GPC analysis. Data of polarization microscopy and SAX analysis demonstrated that all LC dendrimers synthesized form a chiral smectic SmC* phase at temperatures below 50 °C. It has been found that bistable electrooptical switching is observed for all dendrimers. The influence of chiral mesogenic fragment length on phase behavior and ferroelectric properties of carbosilane LC dendrimers is discussed.     

Synthesis,structure, and phase behavior of carbosilane LC dendrimers with terminal butoxyphenylbenzoate mesogenic groups

Two series of carbosilane LC dendrimers with terminal protonated and deuterated butoxyphenylbenzoate mesogenic groups linked to carbosilane dendritic matrices of the first to fifth generations via an undecylene spacer have been synthesized. The chemical structure of new dendrimers has been studied by ¹H NMR spectroscopy and gel-permeation chromatography. The dendrimers of first-fourth generations are characterized by formation of the smectic C mesophase in a wide temperature range, whereas much more complex columnar supramolecular structures are formed in dendrimers of the fifth generation. Structural studied of mesophases by X-ray diffraction and small-angle neutron scattering show that segregation takes place in mixtures of deuterated and protonated LC dendrimers; as a result, huge aggregates composed of hundreds of chemically unbound molecules develop and the sizes of these aggregates reversibly change with temperature.     

Design, synthesis, and photochemical behavior of poly(benzyl ester) dendrimers with azobenzene groups throughout their architecture

A new class of dendrons and dendrimers containing azobenzene units (bearing up to 29 azobenzene groups for four generations) were designed and synthesized with the convergent method, which uses azobenzene derivatives as monomers and benzyl ester groups as linkages leading to photoresponsive dendrons and dendrimers with azobenzene units throughout their architecture. Photochemical isomerization experiments revealed that all of the dendrons and dendrimers undergo trans-cis isomerization by irradiation and cis-trans isomerization by either irradiation or heating.     

Synthesis of cationic water-soluble light-harvesting dendrimers

Four generations of phenylenefluorene (1F)- and phenylenebis(fluorene) (2F)-terminated polyamidoamine (PAMAM) dendrimers were synthesized by coupling activated esters with commercially available PAMAM precursors. Treatment of Boc-terminated pendant groups on the optically active units with 3 M HCl in dioxane yields cationic water-soluble dendrimers. Fluorescence resonance energy transfer (FRET) experiments with the cationic dendrimers as the donor and double stranded DNA containing a fluorescein label as the acceptor reveal cooperative optical behavior.     

Single-component films of different generations of dendrimers bearing a diphenylanthracene core

Different generations of carboxyl-terminated poly(aryl ether) dendrimers bearing a diphenylanthracene core were designed and synthesized. It is interesting to see that not only two-generation dendrimers but also one-generation dendrimers can be fabricated into thin films by self-deposition. Fluorescence spectra indicate that increasing the generation number of a dendrimer can effectively control the quenching of the fluorescence. Moreover, the fluorescence property of the diphenylanthracene core of the dendrimers in a solid film is quite similar to that of one in a solution, which is important for designing light-emitting materials.     

Synthesis and studies of Rh(I) catalysts within and across poly(alkyl aryl ether) dendrimers

In order to study the efficiencies of catalytic moieties within and across dendrimer generations, partially and fully functionalized dendrimers were synthesized. Poly(alkyl aryl ether) dendrimers from zero to three generations, presenting 3 to 24 peripheral functionalities, were utilized to prepare as many as 12 catalysts. The dendrimer peripheries were partially and fully functionalized with triphenylphosphine in the first instance. A rhodium(I) metal complexation was performed subsequently to afford multivalent dendritic catalysts, both within and across generations. Upon synthesis, the dendritic catalysts were tested in the hydrogenation of styrene, in a substrate-to-catalyst ratio of 1:0.001. Turn-over-numbers were evaluated for each catalyst, from which significant increases in the catalytic activities were identified for multivalent catalysts than monovalent catalysts, both within and across generations.     

Segment block dendrimers via Diels-Alder cycloaddition

Segment block dendrimers consisting of polyester and polyaryl ether dendrons were synthesized using reagent free Diels-Alder cycloaddition reactions. Three generations of furan functionalized polyaryl ether dendrons were reacted with maleimide functionalized polyester dendrons of the same generation to obtain segment block dendrimers in good yields. The thermoreversible nature of these macromolecules was investigated by subjecting them to elevated temperatures in the presence of anthracene as a scavenger diene.     

Synthesis and biological evaluation of mannose-6-phosphate-coated multivalent dendritic cluster glycosides

The synthesis of multivalent dendritic cluster glycosides of mannopyranosyl-6-phosphate is presented. Poly(amido amine)-based dendrimers of 0.5-3.5 generations, containing carboxylic acid peripheral functionalities, were utilized so as to install 4, 8, 16 and 32 mannopyranosyl-6-phosphate residues at the peripheries of the dendrimers. Amide bond formation between an amine-tethered mannopyranosyl-6-phosphate monomer unit and carboxylic acid-functionalized dendrimers was conducted to synthesize the dendritic cluster glycosides. The constitutions of the Man-6-P-containing dendrimers were assessed by 1H, 13C and 31P NMR spectroscopies and the sugar content analysis by a resorcinol assay. Preliminary biological studies with few newly synthesized Man-6-P-containing dendrimers showed that these compounds could bind the purified goat liver mannose 6-phosphate receptor (MPR 300) protein.     

Preparation of gold-, gold/silver-dendrimer nanocomposites in the presence of benzoin in ethanol by UV irradiation

Gold- and gold/silver-dendrimer nanocomposites have been synthesized by UV irradiation of their salts dissolved in ethanol containing dendrimers. As dendrimers, poly(amidomaine) PAMAM dendrimers and poly(propyleneimine) PPI dendrimers of various generations were used. The photoreduction of their salts is greatly accelerated by using benzoin as a photoinitiator. The sizes of gold in the nanocomposites are affected by the concentration of benzoin as well as the concentration of dendrimers, but are hardly changed with the kind of dendrimers. For gold/silver-dendrimer nanocomposites, the absorption spectra of gold/silver nanoparticles in the nanocomposites are very similar to the theoretical spectra of gold/silver alloy nanoparticles, suggesting the formation of gold/silver alloy nanoparticles. From the comparison of TEM and DLS measurements, it is found that the metal-dendrimer nanocomposites consist of metal nanoparticles covering by dendrimer molecules.     

Synthesis of poly(alkyl aryl ether) dendrimers

Poly(alkyl aryl ether) dendrimers of up to four generations composed of a phloroglucinol core, branching components, and pentamethylene spacers are synthesized by a divergent growth methodology. A repetitive synthetic sequence of phenolic O-alkylation and O-benzyl deprotection reactions are adopted for the synthesis of these dendrimers. The peripheries of the dendrimers contain 6, 12, 24, and 48 phenolic hydroxyl groups, either in the protected or unprotected form, for the first, second, third, and fourth generations, respectively. Because of the presence of hydrophilic exterior and relatively hydrophobic interior regions, alkaline aqueous solutions of these dendrimers are able to solubilize an otherwise insoluble pyrene molecule and these supramolecular complexes precipitate upon neutralization of the aqueous solutions.     

Synthesis of non-cytotoxic poly(ester-amine) dendrimers as potential solubility enhancers for drugs: methotrexate as a case study

This study describes the synthesis of two new families of dendrimers based on the esterification of N-alkylated 3-amine-1-propanol with two different cores, adipic acid (1st and 2nd generations) and ethylenediamine (generation 1.5), both with carboxylic acid end groups, offering a wide variety of further modifications at the periphery. According to the cytotoxic evaluation of the dendrimers and their possible degradation products within cell lines, these materials could be considered as innocuous. In preliminary studies, the synthesized dendrimers proved to be potential enhancers of solubility of highly hydrophobic drugs, like methotrexate, widely used in chemotherapy.     

Analysis of poly(amidoamine)-succinamic acid dendrimers by slab-gel electrophoresis and capillary zone electrophoresis

Ethylenediamine (EDA)-core poly(amidoamine) (PAMAM) succinamic acid dendrimers (Ex.SAH, where x refers to the generation) were synthesized and analyzed by polyacrylamide gel electrophoresis (PAGE), size-exclusion chromatography (SEC), potentiometric acid-base titration, and capillary zone electrophoresis (CZE). Various generations (E1.SAH-E7.SAH) PAMAMs and a succinamic acid terminated core-shell tecto(dendrimer) (E5(E3.SAH)(n)) were first analyzed by PAGE. PAGE results show that the relative mobilities of generation 2 to generation 7 dendrimers decreased with the increasing number of generations. The molecular mass of a generation 5 core generation 3 shell tecto(dendrimer) (denoted as E5(E3.SAH)(n)) was determined to be between the Mw of E6.SAH and E7.SAH. CZE analysis allowed the evaluation of electrophoretic properties of given-generation dendrimers. The electrophoretic mobilities of individual generations PAMAM polyanions are similar, indicating that the separation mainly depends on their approximately identical charge/mass ratio. The E5(E3.SAH)(n) tectodendrimer had a lower electrophoretic mobility, which was consistent with its lower charge/mass ratio. The combination of PAGE and CZE analysis provides an alternative and effective way to characterize this group of PAMAM-succinamic acid dendrimers.     

Self‐assembly of a new class of amphiphilic poly(amidoamine) dendrimers and their electrochemical properties

Amphiphilic poly(amidoamine) (PAMAM) dendrimers consisting of a hydrophilic dendrimer core and hydrophobic aromatic dansyl or 1‐(naphthalenyl)‐2‐phenyldiazene (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. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5512–5519, 2005     

Donor-acceptor interactions in red-emitting thienylbenzene-branched dendrimers with benzothiadiazole core

Synthesis and characterization of dendrimers containing thienylbenzene repeating units, red-emitting benzothiadiazole core, and triarylamine peripheries that bear naphthyl units are reported. The relevant dendrimers of different generations are classified as G(nb) (n=1-3), while the tert-butyl dendrimers G(na) with the acceptor alone were also synthesized to serve as control chromophores that avoid donor-acceptor interactions. The resulting dendrimers are capable of harvesting photon energy through efficient energy transfer among donor-acceptor moieties, so that highly luminescent red fluorophores result. Transient fluorescence studies suggest that the energy transfer and its efficiency are approximately unity in all G(a) dendrimers, whereas the rate of energy transfer for the G(b) dendrimers is suppressed, that is, charge transfer from the core to the periphery is a significant quenching pathway. These dendrimers are amorphous in nature with high glass transition temperatures (176-201 degrees C). Electroluminescent devices were fabricated by using the dendrimers as hole-transporting emitters, and the devices exhibit promising red emission parameters.     

Palladium(0) nanoparticles stabilized by phosphorus dendrimers containing coordinating 15-membered triolefinic macrocycles in periphery

A new family of phosphorus dendrimers containing on their surfaces 3, 6, 12, and 96 15-membered azamacrocycles has been synthesized. The coordinating ability of these macrocycles to palladium(0) atoms allowed the preparation of new dendrimers of several generations containing the corresponding metal complexes and several new nanoparticulated materials, where nanoparticles are stabilized mainly by the complexed dendrimers of the zero, first, and fourth generations. No reduction process of palladium(II) salts was needed to prepare nanoparticles of 2.5-7.9 nm diameter. All the new compounds and materials have been characterized by NMR, IR, elemental analysis and/or matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) spectrometry, high-resolution transmission electron microscopy, and electron diffraction. Also UV-vis spectra were obtained. The Mizoroki-Heck reaction has been catalyzed in a homogeneous and heterogeneous manner by using four different materials; in all cases, the catalyst could be recovered and reused several times.