Star-shaped Oligo Research Articles

Fullerene-Filled Stilbene Stars: The Balance between Isolated C60 Helices and 3D Networks in Liquid-Crystal Self-Assemblies.

A series of shape-persistent star-shaped oligo(phenylene vinylene) liquid crystals and derivatives with fullerene tethered through spacers of different lengths to one arm were successfully synthesized. Solution studies by NMR, UV/Vis and fluorescence spectroscopy revealed the preferential location of the C60 acceptor in the vicinity of the peripheral donor unit, which affects the quenching of the emission of the conjugated stilbenoid scaffold in the donor-acceptor dyad. The fluorescence was completely absent in the liquid crystal phase due to the extraordinary hierarchical self-assembly. In this family of mesogens, the intrinsic free space has to be filled either by an extremely tight packing of the stars or by the fullerenes as guests. The spacer lengths control the nanosegregation of the C60 units in the cavities of the stars in either independent triple helices or unprecedented 3D networks, in which fullerenes are positioned at the interface of neighboring columns. Eventually, the clearing temperature of such large complex donor-acceptor systems can be tuned by an entropy effect defined by the length of the spacer. The accessibility of the isotropic phase without decomposition is an important prerequisite for future alignment studies associated with potential material applications in organic electronics.

Influence of surfactants on depsipeptide submicron particle formation

Surfactants are required for the formation and stabilization of hydrophobic polymeric particles in aqueous environment. In order to form submicron particles of varying sizes from oligo[3-(S)-sec-butylmorpholine-2,5-dione]diols ((OBMD)-diol), different surfactants were investigated. As new surfactants, four-armed star-shaped oligo(ethylene glycol)s of molecular weights of 5–20kDa functionalized with desamino-tyrosine (sOEG-DAT) resulted in smaller particles with lower PDI than with desaminotyrosyl tyrosine (sOEG-DATT) in an emulsion/solvent evaporation method. In a second set of experiments, sOEG-DAT of Mn=10kDa was compared with the commonly employed emulsifiers polyvinylalcohol (PVA), polyoxyethylene (20) sorbitan monolaurate (Tween 20), and D-α-tocopherol polyethylene glycol succinate (VIT E-TPGS) for OBMD particle preparation. sOEG-DAT allowed to systematically change sizes in a range of 300 up to 900nm with narrow polydispersity, while in the other cases, a lower size range (250–400nm, PVA; ∼300nm, Tween 20) or no effective particle formation was observed. The ability of tailoring particle size in a broad range makes sOEG-DAT of particular interest for the formation of oligodepsipeptide particles, which can further be investigated as drug carriers for controlled delivery.

Synthesis and characterization of star-shaped oligo(ethylene glycol) with tyrosine derived moieties under variation of their molecular weight.

Desamino tyrosine (DAT) and desamino tyrosyl tyrosine (DATT) can be used to functionalize the end groups of water soluble polymers. The phenolic groups may enable physical interactions by π- π interaction and hydrogen bonds, which might lead to the formation of a hydrogel by physical crosslinking. However, using star-shaped oligo(ethylene glycols) (sOEG) with a molecular weight of 5 kDa for functionalization with DAT or DATT resulted in the formation of surfactants and not in hydrogels.As the molecular weight of the sOEG polymer chain can have an influence on forming physical cross links, DAT(T)-fuctionalization of sOEGs with higher molecular weight was investigated, the polymers were structurally characterized and for their mechanical properties were evaluated by rheological measurements.Aqueous solutions of DAT(T)-sOEGs with 10 and 20 kDa showed lower storage and loss moduli compared to unfunctionalized sOEGs indicating also the formation of surfactants. Cell-based assays showed that all sOEG solutions did not impair cell viability and were free of endotoxins, which could otherwise induce uncontrolled immune responses.Conclusively, our data suggested that the sOEG solutions have surface active properties without inducing unwanted cellular responses, which is required e.g. in pharmaceutical applications to solubilize hydophobic substances.

Immuno-compatibility of desaminotyrosine and desaminotyrosyl tyrosine functionalized star-shaped oligo(ethylene glycol)s with different molecular weights

ABSTRACTPolymer-based therapeutic strategies require biomaterials with properties and functions tailored to the demands of specific applications leading to an increasing number of newly designed polymers. For the evaluation of those new materials, comprehensive biocompatibility studies including cyto-, tissue-, and immunocompatibility are essential. Recently, it could be demonstrated that star-shaped amino oligo(ethylene glycol)s (sOEG) with a number average molecular weight of 5 kDa and functionalized with the phenol-derived moieties desaminotyrosine (DAT) or desaminotyrosyl tyrosine (DATT) behave in aqueous solution like surfactants without inducing a substantial cytotoxicity, which may qualify them as solubilizer for hydrophobic drugs in aqueous solution. However, for biomedical applications the polymer solutions need to be free of immunogenic contaminations, which could result from inadequate laboratory environment or contaminated starting material. Furthermore, the materials should not induce uncontrolled or undesired immunological effects arising from material intrinsic properties. Therefore, a comprehensive immunological evaluation as perquisite for application of each biomaterial batch is required. This study investigated the immunological properties of sOEG-DAT(T) solutions, which were prepared using sOEG with number average molecular weights of 5 kDa, 10 kDa, and 20 kDa allowing analyzing the influence of the sOEG chain lengths on innate immune mechanisms. A macrophage-based assay was used to first demonstrate that all DAT(T)-sOEG solutions are free of endotoxins and other microbial contaminations such as fungal products. In the next step, the capacity of the different DAT(T)-functionalized sOEG solutions to induce cytokine secretion and generation of reactive oxygen species (ROS) was investigated using whole human blood. It was observed that low levels of the pro-inflammatory cytokines interleukin(IL)-1β and IL-6 were detected for all sOEG solutions but only when used at concentrations above 250 µg·mL-1. Furthermore, only the 20 kDa sOEG-DAT induced low amounts of ROS-producing monocytes. Conclusively, the data indicate that the materials were not contaminated with microbial products and do not induce substantial immunological adverse effectsin vitro,which is a prerequisite for future biological applications.

Enhanced Ionic Conductivity of Semi-IPN Solid Polymer Electrolytes Based on Star-Shaped Oligo(ethyleneoxy)cyclotriphosphazenes

A family of oligo(ethyleneoxy)cyclotriphosphazenes was synthesized as low molecular (or oligomeric) ionic conductors (plasticizer) and incorporated with lithium salt into semi-interpenetrating network (semi-IPN) solid polymer electrolytes (SPEs) for the improvement of ionic conductivity. A novel semi-IPN SPE was prepared by in situ radical polymerization of precursor solution containing a new cross-linker PA6 and plasticizers PMEn (n = 2, 4, 6, 8) based on cyclotriphosphazenes, which exhibited high ionic conductivity of ca. 10–4 S/cm at room temperature with significantly enhanced dimensional stability. The effect of the number of ethyleneoxy (EO) units in plasticizers, lithium salt concentration, and the content of the plasticizers on ionic conductivity of SPEs was investigated. The thermodynamic behaviors of the cyclotriphosphazene plasticizers were also analyzed to figure out the contribution of plasticizers to the improvements of electrochemical properties in the semi-IPN SPEs. Cyclic voltammetry and ...

Synthesis and Characterization of Hydroxy-telechelic Four-arm Star-shaped Oligo(tetrahydrofuran), Their Crosslinking, and Thermomechanical Investigation of the Poymer Network

ABSTRACTHere the synthesis of hydroxy-telechelic four-arm star-shaped oligotetrahydrofuran (4PTHF) with controllable molecular weight was explored, which was perfomed as living cationic ring-opening polymerization of THF using pentaerythritol and trifluoromethanesulfonicanhydride as initiation system. The molecular weights of the 4PTHF were a function of the reaction time. A polymer network was prepared from the hydroxy-telechelic 4PTHF precursor by crosslinking with diisocyanate and the shape-memory properties were determined. High values for Rf and Rr > 98% were obtained even at high programmed elongations, which suggest the 4PTHF-network as a promising shape-memory material. These materials might have a great potential, as the upscaling of synthesis could be successfully demonstrated.

Thermosensitivity of Bile Acid-Based Oligo(ethylene glycol) Stars in Aqueous Solutions

Amphiphilic star-shaped oligo(ethylene glycol)s with a hydrophobic bile acid core and varying number of hydrophilic arms have been made. Their thermal behavior in aqueous solutions depends on the number rather than the length of the arms. The two-armed lithocholate derivative showed the strongest tendency for association and exhibited the lowest cloud point (79 °C) of the oligomers made, as well as another phase separation at a lower temperature (31 °C). The "double thermosensitivity" arising both from the salt-dependent LCST of the oligo(ethylene glycol) segments and the temperature-responsive self-assembly of amphiphilic bile acid derivative provides an interesting path in the design of bile acid-based smart materials.

Release of Aspirin from Biodegradable Polyesterurethane Networks

In this paper, the release of model drug aspirin (ASP) from biodegradable polyesterurethane networks was studied. Poly(D,L-lactide-co-glycolide)urethane (PULG) networks were prepared from hydroxyl telechelic star-shaped oligo(D,L-lactide-co-glycolide) coupled with 1,6-diisocyanate-2,2,4-trimethylhexane and 1,6-diisocyanate-2,4,4-trimethylhexane or isophorone diisocyanate. PULG networks turned from transparent to opaque after ASP loading. PULG networks with lower crosslinking density always resulted in higher drug loaded content. The results of differential scanning calorimetry (DSC) and scanning electron microscope (SEM) measurements demonstrated that ASP was uniformly distributed in the networks. The drug release courses of ASP from PULG networks in phosphate buffered saline pH = 7.0 at 37 °C could be divided into three stages. Firstly, ASP release was at approximately uniform rate from PULG networks; Secondly, the release rate obviously increased for the degradation of the PULG networks; Thirdly, the release rate decreased gradually because most of the ASP had diffused out of the PULG networks. The crosslinking density of polyesterurethane networks also affected drug release rate. The in vitro release test revealed that ASP accelerated the degradation process of PULG, which exhibited a typical erosion-controlled release mechanism.

Star-shaped oligo(fluorene ethynylene)-functionalized truxene derivatives: synthesis, characterization, and their size effects

A series of monodisperse, well-defined, star-shaped truxene derivatives bearing oligo(fluorene ethynylene) (OFE) branches were constructed through a convergent synthetic strategy. The radius of the largest molecule TOFE4 was up to about 4.5 nm. Linear OFE branches with different length were first constructed in high yields alternately using the Sonogashira cross-coupling and propargyl alcohol deprotection reaction. The detailed investigation of their photophysical properties in solution and in film indicated that these star-shaped molecules exhibited obvious size effects on their distinct photoluminescence and electroluminescence behaviors. Furthermore, good performances were achieved from the fabrication of double-layer organic light-emitting diodes using these star-shaped molecules as active materials.

Synthesis and Characterization of Novel Monodisperse Starburst Oligo(fluoreneethynylene) Based on Truxene Moiety

Abstract A series of novel monodisperse star-shaped oligo(fluoreneethynylene)s, which contain hexahexyltruxene as the central core linked with oligo(fluoreneethynylene) as the arms, are presented.

Star-shaped oligo( p-phenylene)-functionalized truxenes as blue-light-emitting materials: synthesis and the structure–property relationship

In this contribution, we described a strategy to prepare a series of well-defined, blue-light-emitting materials with truxene unit as the core and oligo( p-phenylene) (from one to four phenyl units) as the branches. The Suzuki coupling reactions between truxene bromide derivatives and phenylboronic acid or 1,1′-biphenyl-4-boronic acid catalyzed by Pd(0) afforded the desired compounds Tr-1-Ph, Tr-2-Ph, Tr-3-Ph and Tr- 4-Ph. With stepwise increases of the benzene rings, the desired molecules exhibited exceptional photophysical properties as well as increasing thermal stability. T gs increased from 39 °C for Tr-1-Ph to 192 °C for Tr-4-Ph. The absorption and the emission maximum peaks of these four compounds were red-shifted from the ultraviolet to the blue region with the increase of effective conjugation length. All results demonstrated that the physical properties were facilely tuned by connecting different types and different conjugated lengths to C-2, C-7, and C-12 positions of the truxene core.

Polymer gel electrolytes synthesized by photopolymerization in the presence of star-shaped oligo(ethylene glycol) ethers (OEGE)

The photoinitiated cross-linking polymerization of tri(ethylene glycol) dimethacrylate and its copolymerization with cyanomethyl methacrylate in the presence of LiCF 3SO 3 and of various oligo(ethylene glycol) methyl ethers as plasticizer was studied for potential use of the resulting polymer gel electrolytes in lithium batteries. Comparing linear and star-shaped (three and four arm molecules) oligo(ethylene glycol) methyl ethers, the influence of the architecture of the plasticizers on the polymerization course was investigated by means of differential scanning calorimetry. Linear and star-shaped plasticizers with molar masses < 1000 g/mol differ from each other concerning the dependence of their viscosity on their molar mass but not concerning the influence of the viscosity on the polymerization rate. Compared with linear plasticizers, the star-shaped ones have as an essential advantage a distinctly lower tendency to crystallize which is even completely suppressed in some cases. The gels were characterized with regard to the network density of their polymer matrix, to their thermal transitions, thermo-mechanical properties and ionic conductivity. The conductivity of solutions and gels with star-shaped plasticizers was slightly lower than that with linear ones at temperatures above room temperature.

Star-shaped oligo(ethylene glycol) ethers (OEGE) as a new type of plasticizer for polymer gel electrolytes

Star-shaped oligo(ethylene glycol) methyl ethers (three and four arm molecules of various molecular weights) were synthesized and characterized with regard to viscosity, thermal transitions, ability to solvate the electrolyte LiCF 3SO 3 and the ionic conductivity of their LiCF 3SO 3 solutions in comparison to linear oligo(ethylene glycol) methyl ethers. Polymer gel electrolytes were prepared by photopolymerization of tri(ethylene glycol) dimethacrylate (EG 3DMA) or its copolymerization with the polar comonomer cyanomethyl methacrylate (CyMA) in the presence of the oligo(ethylene glycol) ethers mentioned above and of the electrolyte LiCF 3SO 3. The gels were characterized concerning their thermal transitions, thermo-mechanical properties, their ability to solvate the electrolyte and their ionic conductivity. In comparison to the linear plasticizers the star-shaped ones show a distinctly lower tendency to crystallize, which is even completely suppressed in several cases. Intensified ion association was found in LiCF 3SO 3 solutions of the star-shaped plasticizers, if the number of the ethylene glycol units per arm was lower than 4. Therefore, the conductivity of the solutions and the gels was lower than that with linear plasticizers at room temperature. The modification of the polymer matrix by copolymerization with 20 mol% CyMA resulted in a maximum of the ionic conductivity σ≈1×10 −5 S/cm of gels with star-shaped plasticizers at 25 °C.

Star-shaped oligo(ethylene glycol) ethers (OEGE) as a new type of plasticizer for polymer gel electrolytes

Star-shaped oligo(ethylene glycol) methyl ethers (three and four arm molecules of various molecular weights) were synthesized and characterized with regard to viscosity, thermal transitions, ability to solvate the electrolyte LiCF3SO3 and the ionic conductivity of their LiCF3SO3 solutions in comparison to linear oligo(ethylene glycol) methyl ethers. Polymer gel electrolytes were prepared by photopolymerization of tri(ethylene glycol) dimethacrylate (EG3DMA) or its copolymerization with the polar comonomer cyanomethyl methacrylate (CyMA) in the presence of the oligo(ethylene glycol) ethers mentioned above and of the electrolyte LiCF3SO3. The gels were characterized concerning their thermal transitions, thermo-mechanical properties, their ability to solvate the electrolyte and their ionic conductivity. In comparison to the linear plasticizers the star-shaped ones show a distinctly lower tendency to crystallize, which is even completely suppressed in several cases. Intensified ion association was found in LiCF3SO3 solutions of the star-shaped plasticizers, if the number of the ethylene glycol units per arm was lower than 4. Therefore, the conductivity of the solutions and the gels was lower than that with linear plasticizers at room temperature. The modification of the polymer matrix by copolymerization with 20 mol% CyMA resulted in a maximum of the ionic conductivity σ≈1×10−5 S/cm of gels with star-shaped plasticizers at 25 °C.