Amphiphilic diblock dendrimers with a fullerene core

Amphiphilic dendrimers with a C(60) core have been obtained by cyclization of dendritic 1,3-phenylenebis(methylene)-tethered bis-malonate derivatives at the carbon sphere. The relative position of the two cyclopropane rings in the resulting bis-methanofullerene derivatives has been determined based on the molecular symmetry (C(s)()) deduced from the (1)H and (13)C NMR spectra. The hydrophobic-hydrophilic balance of these dendrimers has been systematically modified by changing the size of the polar headgroup in order to investigate the role of the amphiphilicity both at the air-water interface and during deposition onto solid substrates. Langmuir studies have revealed a conformational change in the dendritic structure with the size of the polar headgroup. Because of a better anchoring onto the water surface, the compounds with the largest polar headgroup adopt a more compact structure and the dendritic branches are forced to wrap the fullerene core. This model is nicely confirmed by the amount of fullerene-fullerene interactions within the Langmuir-Blodgett films as deduced from their absorption spectra.     

Amphiphilic diblock dendrimers: synthesis and incorporation in Langmuir and Langmuir-Blodgett films

A new dendron with peripheral long alkyl chains and containing five C(60) units in the branching shell has been prepared and attached to a Fréchet-type dendron functionalized with ethylene glycol chains. The peripheral substitution of the resulting globular dendrimer with hydrophobic chains on one hemisphere and hydrophilic groups on the other provides the perfect hydrophobic/hydrophilic balance allowing the formation of stable Langmuir films. Furthermore, a perfect reversibility has been observed in successive compression/decompression cycles. The diblock structure of the dendrimer has been also crucial for the efficient transfer of the Langmuir films in order to obtain well-ordered multilayered Langmuir-Blodgett films. This approach appears particularly interesting since functional groups not well adapted for the preparation of Langmuir and Langmuir-Blodgett films such as fullerenes can be attached into the branching shell of the dendritic structure and, thus, efficiently incorporated in thin ordered films.     

Synthesis,mesomorphic behaviour and optoelectronic properties of phosphorus-based thermotropic liquid crystalline dendrimers

A new series of thermotropic phosphorus-based liquid crystalline (LC) dendrimers based on a thiophosphoryl-phenoxymethyl(methylhydrazono) core (thiophosphoryl-PMMH) up to the fifth generation has been synthesised by solution condensation of aldehyde groups, surface-functionalised thiophosphoryl-PMMH dendritic substrates of generation numbers G_0.5 to G_5.5, with the appropriate molar equivalents of the pro-mesogenic n-hexadecylaniline mono-functional building block. Their chemical composition has been confirmed by ¹H/¹³C/³¹P nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis. Optical properties have been studied by ultraviolet-visible absorption, photoluminescence spectroscopy and polarised optical microscopy, and thermal characteristics by differential scanning calorimetry. Electrical studies have been made using the current-voltage characteristics of organic light-emitting diodes consisting of multi-layered indium tin oxide/dendrimer/aluminium tris(8-hydroxyquinoline)Al architecture. It has been demonstrated that the molecular engineering approach adopted can successfully lead to phosphorus-containing dendritic organic semiconductors (OSCs) which show tunable mesomorphic behaviour (extension of the observed smectic mesophase) and (opto) electronic properties, owing to their peripheral decoration with a tunable number of azomethine-based optically active chromophoric units. This rare combination of ‘tunable by design’ properties makes this series of thermostable thiophosphoryl-PMMH-based LC dendrimers a particularly appealing class of OSCs for use in optically and/or electronically active layers of (opto)electronic devices such as light-emitting diodes, field-effect transistors, solar cells and lasers.     

Electrochemically formed fullerene-based polymeric films

The recent results of investigations involving the electrochemical formation of polymers containing fullerenes and studies of their properties and applications are critically reviewed. From a structural point of view, these polymers can be divided into four main categories including (1) polymers with fullerenes physically incorporated into the foreign polymeric network without forming covalent bonds, (2) fullerene homopolymers formed via [2+2] cycloaddition, (3) “pearl necklace” polymers with fullerenes mutually linked covalently to form polymer chains, and (4) “charm bracelet” polymers containing pendant fullerene substituents. The methods of electrochemical polymerization of these systems are described and assessed. The structural features and properties of the electrochemically prepared polymers and their chemically synthesized analogs are compared. Polymer films containing fullerenes are electroactive in the negative potential range due to electroreduction of the fullerene moieties. Related films made with fullerenes derivatized with electron-donating moieties as building blocks are electroactive in both the negative and positive potential range. These can be regarded as “double cables” as they exhibit both p- and n-doping properties. Fullerene-based polymers may find numerous applications. For instance, they can be used as charge-storage and energy-converting materials for batteries and photoactive units of photovoltaic cell devices, respectively. They can be also used as substrates for electrochemical sensors and biosensors. Films of the C₆₀/Pt and C₆₀/Pd polymers containing metallic nano-particles of platinum and palladium, respectively, effectively catalyze the hydrogenation of olefins and acetylenes. Laser ablation of electrochemically formed C₆₀/M and C₇₀/M polymer films (M=Pt or Ir) results in fragmentation of the fullerenes leading to the formation of hetero-fullerenes, such as [C₅₉M]⁺ and [C₆₉M]⁺.Dedicated to Professor Dr. Alan M. Bond on the occasion of his 60th birthday.     

Cation recognition on a fullerene-based macrocycle

Heterocyclic orifices in cage-opened fullerene derivatives are regarded as potential ligands toward metals or ions, being reminiscent of truncated fullerenes as a hypothetical class of macrocycles with spherical π-conjugation. Among a number of cage-opened examples reported thus far, the coordination ability and dynamic behavior in solution still remained unclear due to difficulties in structural determination with multiple coordination sites on the macrocycles. Herein, we present the detailed solution dynamics of a cage-opened C₆₀ derivative bearing a diketo bis(hemiketal) moiety in the presence of alkali metal ions. The NMR spectroscopy disclosed the coordination behavior which is identified as a two-step process with a 1 : 2 stoichiometry. Upon coordination to the Li⁺ ion, the macrocycle largely varies its properties, i.e., increased absorption coefficients in the visible region due to weakly-allowed charge transfer transitions as well as the inner potential field from neutral to positive by the charge delocalization along with the spherical π-surface. The Li⁺-complexes formed in situ underwent unprecedented selective dehydroxyhydrogenation under high-pressure conditions. These findings would facilitate further studies on fullerene-based macrocycles as metal sensors, bulky ligands in organic reactions, and ion carriers in batteries and biosystems.

A fullerene-based Lewis-basic macrocyclic ligand underwent complexation with alkali-metal ions in 1 : 1 and 1 : 2 fashions, resulting in considerable perturbation to absorption properties as well as the potential surface inside the cage.     

富勒烯功能高分子材料的制备与性能研究

对富勒烯功能高分子材料的制备、表征及其性能研究已成为光前国际上的前沿领域之一。从合成角度考虑,以不同的方法对Ｃ６０进行高分子修饰可得到结构、性质各异的富勒烯高分子衍生物,对于研究如何更好地控制Ｃ６０高分子衍生物的结构,探讨了有Ｃ６０参与的聚合反应的机理以及Ｃ６０在高分子衍生物中的作用无疑是很有帮助的。从应用角度考虑,Ｃ６０引入高分子中必将导致新型聚合物的产生。这些新型聚合物表现出许多独特而极具应用     

A new specific fullerene-based fluorescent probe for trypsin

A novel fluorescent probe (C(60)-FL) was designed and synthesized for the direct determination of trypsin, based on photo-induced electron transfer (PET). The probe consists of two functional moieties: fluorescein which performs as a fluorophore and an electron donor, and fullerene (C(60)) which acts as an electron acceptor and trypsin substrate analogue. In the presence of trypsin, the probe exhibited fluorescence increase due to the inhibition of electron transfer by the combination of C(60)-FL with trypsin. The response of the probe to trypsin was direct and rapid. Experimental results showed that the increase in fluorescence intensity is proportional to the concentration of trypsin within the range of 4.40×10(-7) to 7.04×10(-5) g mL(-1) under the optimized experimental conditions. The detection limit of the proposed method was 40 ng mL(-1). The method had high selectivity for trypsin over other enzymes and proteins, such as lipase, α-amylase, bovine serum albumin, zinc metallothionein, glutathione reductase, thioredoxin and α-chymotrypsin etc. The remarkable properties of C(60)-FL help to extend the development of fluorescent probes for investigating enzymes in a biological context.     

Analysis of fullerene-based nanomaterial in serum matrix by CE

With the increasing interest in using nanoparticles as vehicles for drug delivery and image contrast agents, there is a need to develop assays for their detection and quantitation in complex matrices to facilitate monitoring their biodistribution. In this study, we developed a CE approach for the analysis of two nanoparticles: carboxyfullerene (C3) and dendrofullerene (DF1) in both standard solutions and a serum matrix. These highly soluble, charged C(60) derivatives were characterized by CZE using either a bare or dynamically coated fused-silica capillaries. The resolution of both nanoparticles was slightly lower with the coated capillary; however, their migration times were faster. While separation of the DF1 nanoparticles using MEKC resulted in a greater number of observable peaks, the peak profile of C3 was basically unchanged regardless of whether SDS micelles were added to the running buffers or not. The MEKC and/or CZE assays were then used to quantitate the C3 and DF1 nanoparticles in spiked human serum samples. The quantitation of the nanoparticles was linear from 0-500 microg/mL with detection limits ranging from 0.5 to 6 microg/mL.     

Novel mesomorphic Schiff bases

2-(4-Alkoxybenzylideneamino)-4-[(4-nitrophenyl)amino]thiazoles have been synthesized. They show nematic type enantiotropic mesomorphism in the range 41–184°C. Bashkir State University, Ufa 450074. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1559–1560. November, 1997.     

Fluorinated dendrimers

After pioneering works concerning the synthesis of dendrimers and dendrons possessing fluorine atoms in some part of their structure, recent advances are dedicated to the search for uses and applications of these highly branched compounds. Three major fields are concerned: catalysis, materials science and biology to a lesser extend.     

Anhydride-functionalized fullerene: a versatile precursor for fullerene-based materials

Soluble phthalic anhydride-functionalized fullerene was generated via simple pyrolysis of the corresponding di-t-butyl phthalate precursor at 200 °C for 120 min. This non-chemical method for generating electrophilic fullerene may be advantageous for the preparation of various fullerene-containing materials. The utility of the resulting fullerene anhydride was demonstrated by solution coupling reaction with PEG-amine, surface reaction with amine-functionalized glass, and hydrolysis reaction to form amphiphilic fullerene.     

Stilbenoid dendrimers

The first five generations of the stilbenoid dendrimers 1(n) (n = 1-5) have been prepared by a combined coupled synthesis (between the generations of the dendrons 8-12) and convergent synthesis. Wittig-Horner reactions together with a protecting group technique yield monodisperse compounds of high constitutional and configurational purity. The solubility of the stiff molecules, which have primarily a disklike shape in the first and second generations and a cylindrical shape in the third, fourth, and fifth generations, is governed by the alkoxy chains that are attached to the peripheral benzene rings. The number of stilbene building blocks increases according to the formula 3(2(n)-1) from 3 in the first generation (n = 1) to 93 in the fifth generation (n = 5). Consequently, the molecular mass reaches 24,000 in 1(5)b which contains 144 hexyloxy chains. An exact measurement of the mass is provided by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. In solution, the stilbenoid dendrimers 1(n) exhibit a strong tendency to aggregate, which increases from generation to generation. In the pure state, columnar mesophases Col(hd) (1(1)b, 1(1)c, 1(2)b, and 1(2)c) and Col(ob) (1(2)b, 1(2)c) are formed; intramolecular steric hindrance prevents such ordered arrangements in higher generations 1(n) (n = 3, 4, 5).     

Depsipeptide dendrimers

The convergent synthesis of a new class of chiral dendrimers is described. Owing to their structural resemblance to depsipeptides they are called depsipeptide dendrimers. The ex-chiral pool synthesis starts from (R,R)-, (S,S)-, and meso-tartaric acid as branching units and dipeptides or tripeptides consisting of glycine, (L)-alanine, and (L)-leucine as chiral-spacer building blocks. The key intermediates for the convergent assembly of such depsipeptide dendrimers are the peptide-tartaric acid conjugates 13a,b, 19a,b, 25, and 27, which contain either an unprotected C terminus of the peptide chain (13 a,b, 25) or two unprotected hydroxy groups within the tartaric acid termini. Dendra up to the third-generation, by using different combinations of stereoisomeric building blocks, were synthesized and completely characterized. Since this construction principle of chiral depsipeptide dendrimers allows for a wide variation of the length, the primary structure of the peptide spacer, and the configuration of both the amino acid and the tartaric acid moieties, access to new combinatorial libraries is conceptually provided.     

Organocatalytic dendrimers

Dendrimers are a class of synthetic macromolecules that bridge the gap between polymers and small molecules. The dendritic structure provides both the possibility for compartmentalization of reagents as well as offering a multivalent surface, and they are in that respect similar to globular proteins. This perspective article reviews the growing field of organocatalysis with dendrimers and highlights the possibilities that are unattainable for small molecule catalysts.     

Amphiphilic Dipyrrinones

Summary. Replacing the typical lactam β-alkyl substituents of xanthobilirubinic acid and kryptopyrromethenone, two bilirubin analogs long used as model compounds in studies of its photochemistry and metabolism, leads to increased amphiphilicity. Synthesized by base-catalyzed condensation of 3,4-dimethoxypyrrolin-2-one with the appropriate pyrrole α-aldehyde, the 2,3-dimethoxyl analogs of xanthobilirubinic acid and kryptopyrromethenone are yellow-colored dipyrrinones that form intermolecular hydrogen-bonded dimers in the solid, as determined by X-ray crystallography, and in CHCl₃, as revealed by ¹H NMR and vapor pressure osmometry. These two new dipyrrinones are approximately ten times more soluble in water than their parent dipyrrinones.