Synthesis and thermal behavior of Janus dendrimers,part 1

Eight Janus-type dendrimers up to the second generation were synthesized, and their thermal properties were evaluated. Compounds consist of the dendritic bisMPA based polyester moieties, and either 3,4-dihexyloxybenzoic acid or 3,4-dihexadecyloxybenzoic acid moieties, attached to opposite sides of the pentaerythritol core. The structures of the molecules were verified with ¹H NMR, ¹³C NMR, ESI TOF mass spectrometry and elemental analysis. The thermal stability was evaluated by thermogravimetric analysis, displaying onset decomposition temperatures (T_d) ranging from 241 to 308 °C. Phase transitions were studied by differential scanning calorimetry. Based on the performed studies it was confirmed that OH terminated dendrimers 2, 4, 6 and 8 exhibited liquid crystalline phases. Also, the X-ray powder diffraction measurements were accomplished for the dendrimers having terminal hydroxyl groups.     

Cationic and fluorescent "Janus" dendrimers

Two synthetic routes to "Janus"-type dendrimers possessing ammonium groups on one side and fluorescent dansyl derivatives on the other side are described. These surface-block dendrimers are obtained by the coupling of two different dendrons, built from the hexafunctional cyclotriphosphazene core. Their characterization and their photophysical behavior are reported. The largest compound possesses 10 ammonium groups and 5 dansyl groups; it is potentially useful as a fluorescent label in materials science and biology.     

Self-organizable vesicular columns assembled from polymers dendronized with semifluorinated Janus dendrimers act as reverse thermal actuators

The synthesis and structural analysis of polymers dendronized with self-assembling Janus dendrimers containing one fluorinated and one hydrogenated dendrons are reported. Janus dendrimers were attached to the polymer backbone both from the hydrogenated and from the fluorinated parts of the Janus dendrimer. Structural analysis of these dendronized polymers and of their precursors by a combination of differential scanning calorimetry, X-ray diffraction experiments on powder and oriented fibers, and electron density maps have demonstrated that in both cases the dendronized polymer consists of a vesicular columnar structure containing fluorinated alkyl groups on its periphery. This vesicular columnar structure is generated by a mechanism that involves the intramolecular assembly of the Janus dendrimers into tapered dendrons followed by the intramolecular self-assembly of the resulting dendronized polymer in a vesicular column. By contrast with conventional polymers dendronized with self-assembling tapered dendrons this new class of dendronized polymers acts as thermal actuators that decrease the length of the supramolecular column when the temperature is increased and therefore, are called reverse thermal actuators. A mechanism for this reversed process was proposed.     

Functional Janus dendrimers containing carbazole with liquid crystalline,optical and electrochemical properties

ABSTRACT

Novel liquid crystalline Janus dendrimers that combine a mesogenic block and an electroactive block have been synthesised. The mesogenic block is based on two third-generation Percec-type dendrons bearing six or eight terminal dodecyloxy alkyl chains, whereas the electroactive blocks are formed by one or two carbazole units. The liquid crystal behaviour was investigated by polarised-light optical microscopy, differential scanning microscopy and X-ray diffraction. The Janus dendrimers with one electroactive unit exhibited cubic or columnar liquid crystal phases, whereas the Janus dendrimers with two electroactive units did not show liquid crystalline behaviour. The UV-vis absorption and emission properties of the Janus dendrimers were investigated. The spectra suggested the existence of π-π stacking and the formation of aggregates in the solid state. Electrodeposition of the carbazole-containing dendrimers afforded semi-globular particles in which the number of electropolymerizable units and the flexible or rigid character of the linker have a decisive influence in the particle size.     

Synthesis, optical, electrochemical, and thermal studies on triazole-based dendrimers with diphenylamine as surface group

Fréchet-type dendrimers with hole-transporting diphenylamine as surface group and electron-transporting triazole moiety as building block have been synthesized by convergent synthetic strategy through ‘click chemistry’ methodology. First generation dendrimer exhibits longer relaxation time, higher quantum yield in the fluorescence spectrum, and better thermal stability than the zero and second generation dendrimers. CV studies showed irreversible reduction potential and the formation of radical cation due to diphenylamine moiety.     

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.     

Synthesis and cubic nonlinear optical behavior of phenyl and ferrocenyl-ended resorcinarene-based dendrimers

Dendrimers were synthesized with phenyl and ferrocenyl-ended groups joined by vinyl moieties. All the dendrons used for dendrimers synthesis had showed trans configuration. This configuration as well as the ‘cone’ conformation of the resorcinarenes was preserved in the dendrimers, as it was shown by ¹H NMR spectroscopy. The chemical structure and purity of the synthesized dendrimers were confirmed by ¹H and ¹³C NMR, FAB+, MALDI-TOF, electrospray mass spectra, and elemental analysis. Cubic nonlinear optical behavior of this first generation of resorcinarene dendrimers was studied. The χ⁽³⁾ values estimated from the THG Maker-fringe technique for the phenyl and ferrocenyl-ended resorcinarene dendrimers dispersed in thin solid films are of the order of 10⁻¹³ and 10⁻¹² esu, respectively.     

Synthesis,thermal and optical properties of new nanosized polyamides containing N-phenyl- and O-naphthyl-s-triazine rings; part 2

We report the chemistry and properties of two new series of well-defined nano sized spheres aramides-containing N- and O-naphthyl-s-triazines. The polymers were carefully characterized by different techniques including infrared, ultraviolet, fluorescent emission, elemental, thermal analyses and scanning electron microscopy (SEM). The polymers were readily soluble in polar aprotic solvents while insoluble neither in water nor halogenated solvents. Thermal analyses data up to 900°C showed high thermal behavior and the polymers were classified either as “slow burning polymers” or “self-extinguishing polymers” based on their calculated the limiting oxygen index. Interestingly, the naphthyl / phenyl interchange has dramatic improvement on the thermal properties. Obviously, the pyridine / phenylene interchange has no influence on the thermal properties of the addressed polymers. Thermal stability of the aniline-containing polymers proved to be comparable to their naphthylamine analogues. Polymers containing p-phenylene moieties exhibited better thermal results compared to their analogues containing m-phenylene moieties. Benzidine containing polymers and sulfone containing polymers exhibited better thermal stabilities than their analogues containing either ether or methylene flexible linkages. The kinetic data obtained from the nonisothermal decomposition of the prepared polyamides series were also studied. The polymers exhibited emissions ranging from blue to orange wavelength depending on the nature of the signaling unit. The naphthyl / phenyl interchange led to either appreciable red-shifted absorptions in some cases or blue-shifted absorptions in other cases and this behavior may be attributed to the contorted, twisted structural nature of the naphthalene ring. Such attracting properties make these polymers good candidates for applications such as processable high-temperature materials and also as heat-resistant polymeric materials.     

Design and synthesis of novel amphiphilic Janus dendrimers for bone-targeted drug delivery

In this paper, we synthesized a range of amphiphilic Janus dendrimers, which consisted of acidic amino acid and naproxen molecules as the peripheral groups, as novel potential bone-targeting dendritic drug delivery. These dendrimers take advantage of a dendritic display to carry multiple drug molecules and targeting moieties simultaneously. All of the dendrimers exhibited more than 80% binding rates to hydroxyapatite (HAP), especially the [G₂]-dendrimers (2a and 2b) showed dramatic binding rates (>95%). Moreover, the solubility of naproxen was remarkably enhanced by the dendritic drug delivery system, especially the naproxen concentration of 2b achieved 5.37 mg/ml, which is more than 28-fold over that of native drug. Furthermore, cell viability studies showed that all the dendrimers exhibited no significant cytotoxicity against HEK293 cells. These results provided an effective entry to the development of new bone-targeting drugs.     

Synthesis, curing behavior and thermal properties of fluorene containing benzoxazines

A series of difunctional fluorene-based benzoxazine monomers were synthesized from the reaction of 9,9-bis-(4-hydroxyphenyl)-fluorene with formaldehyde and primary amines including aniline, o-toluidine, n-butylamine, and n-octylamine. Their chemical structures were confirmed by FT-IR, ¹H and ¹³C NMR analyses. The curing behaviors of the precursors were monitored by differential scanning calorimetry (DSC) and FT-IR. The thermal properties of cured polymers were evaluated with DSC and thermogravimetric analysis (TGA). The fluorene-based polybenzoxazines show the typical curing characteristic of oxazine ring-opening for difunctional benzoxazines centred at 231-250 °C, and remarkably higher glass transition temperature and better thermal stability ascribed to the high rigidity, high aromatic content, and intermolecular and intramolecular hydrogen bonding. The thermal decomposition temperature and char yield of aromatic amine-fluorene-based polybenzoxazines are much higher than those of aliphatic amine-based polybenzoxazines.     

Synthesis,structure, and function of internally functionalized dendrimers

The past three decades have witnessed an exponential increase in the structural diversity and applications of dendrimers, spanning across drug delivery and diagnostics, protein, and enzyme mimicry, solubility enhancement, coatings, light harvesting, and catalysis. The dendrimer community has recently focused on internally functionalized dendrimers (IFDs) owing to their advanced design and functionality. The synthesis of IFDs relies on advanced orthogonal chemistries and/or (de)protection schemes, as well as careful purification to minimize polydispersity of composition and molecular weight. The studies published on IFDs, however, lay scattered across the chemical literature, and a comprehensive presentation of structural rationale, synthetic procedures, and technologically relevant applications is missing. To address this need, this review presents a comprehensive collection and discussion of all available studies on IFDs, detailing their methods of synthesis and their structure–function correlations. The wide variety of internal functionalities, including hydroxyl, amine, carboxylic acid, allyl, alkyne, and imidazole groups, enables myriad applications in biochemistry, chemical and biomedical engineering, and material science. Particular focus is given to IFDs that are amenable to modular synthetic strategies, which promote higher synthetic yield and scalability, and therefore possess stronger translational and commercial potential. As such, this review guides research groups pursuing the difficult task of IFD rational design and synthesis providing them a concise roadmap to their mission.     

Janus粒子制备研究*

具有不对称双面结构的Janus粒子以其独特性能,在乳液稳定、光学、生物传感、药物输送、电子学等领域具有潜在的应用前景。本文就近年来Janus粒子制备技术的研究进展进行了总结,详细地介绍了Janus粒子主要制备方法,包括微流体合成、拓扑选择表面改性、模板导向自组装、可控相分离及可控表面成核,并指出了各种Janus粒子制备技术存在的问题及其发展方向,认为基于可控相分离及表面成核的合成方法成本较低,产率较大,有可能得到更为广泛的应用。     

Synthesis and thermal behavior of gem-dinitro valerylated polystyrene

Commercial polystyrene has been chemically modified with 4,4-dinitro valeryl chloride by use of Friedel–Crafts acylation reaction in the presence of anhydrous aluminum chloride in a mixture of 1,2-dichloroethane and nitrobenzene. The modified polystyrene containing –COCH₂CH₂C(NO₂)₂CH₃ fragments in side phenyl rings, named gem-dinitro valerylated polystyrene (GDN-PS), was characterized by an Ubbelohde’s viscometer, FTIR, and ¹H NMR spectroscopy. Simultaneous thermogravimetry–differential thermal analysis and differential scanning calorimetry (DSC) have been used to study thermal behavior of the polymer. The results of TG analysis revealed that the main thermal degradation for the GDN-PS occurs during two temperature ranges of 200–300 and 300–430 °C. The DTA curve of GDN-PS is showing a visible exothermic peak at 253.8 °C corresponding to the decomposition of gem-dinitro valeryl groups. The decomposition kinetic of the gem-dinitro groups for GDN-PS with degree of substitution (DS) 11 % was studied by non-isothermal DSC under various heating rates. Kinetic parameters such as activation energy and frequency factor for thermal decomposition of GDN-PS with DS 11 % were evaluated via the ASTM E698 and two isoconversional methods.     

Synthesis,physico-chemical characterization and thermal behavior of new complexes with N4O2 donor set

Three new coordinative compounds of the type [Co(en)₂CO₃]·0.75H₂O (1) and [M(en)₂(H₂O)₂]CO₃ ((2) M:Ni, (3) M:Cu; en: ethylenediamine) were synthesized and characterized. The IR and UV–Vis spectral data indicate that ethylenediamine acts as chelate, while carbonate ions act as bidentate chelate ligand for (1)/counter ion for (2) and (3) generating complexes with octahedral stereochemistry. The thermal behavior provided confirmation of the complexes composition, as well as the number and the nature of water molecules and the intervals of thermal stability. The biological assays revealed a good activity against Enterococcus faecium for copper complex.     

Synthesis and physical behavior of amphiphilic dendrimers with layered organization of hydrophilic and hydrophobic blocks

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 properties of aramid dendrimers

The synthesis, characterisation and properties of simple low molecular weight aromatic amide dendrimers is described. The insights into the problems inherent in the synthesis of such systems provided by molecular modelling studies are discussed along with possible strategies for circumventing them. Preliminary results concerning blends of aramid dendrimers with poly(hexamethyleneadipamide) are presented.     

Synthesis and oxygenation of selenophosphate dendrimers

The backbone of a selenophosphate-based dendrimer of generation 3 having three and four carbon chains is flexible enough to allow its chemical modification by means of partial or complete oxygenation with bulky peroxide.     

Synthesis, aggregation, and chiroptical properties of chiral, amphiphilic dendrimers

The syntheses of amphiphilic dendrimers based on 3,5-dihydroxybenzyl alcohol containing tri- or tetrafunctional chiral central cores and allyl ester termini are described. Water solubility is imparted to the dendrimers via a palladium-catalyzed deprotection of the peripheral allyl esters. This method affords complete deprotection of the carboxylate surface because, in contrast to the basic hydrolysis of methyl ester termini, the solubility of partially hydrolyzed intermediates is maintained throughout the course of the deprotection, thereby avoiding precipitation during the reaction. Chiroptical analysis indicates that the structure of the dendrimers collapses in water, resulting in an increased steric effect upon the central core that is manifested by lower optical rotatory power. However, contributions to the chiroptical properties from the dendron branch segments were not evident in water or organic media, suggesting that chiral substructures were not developing in the branch segments of the dendrimers. Multiangle light scattering studies revealed that the dendrimers experienced significant aggregation in aqueous media that decreased at higher generations. This behavior could be rationalized by a change in conformational preference from a disklike conformation at low generations to a more globular conformation at higher generations.