Local entropic effects of polymers grafted to soft interfaces

In this paper, we study the equilibrium properties of polymer chains end-tethered to a fluid membrane. The loss of conformational entropy of the polymer results in an inhomogeneous pressure field that we calculate for Gaussian chains. We estimate the effects of excluded volume through a relation between pressure and concentration. Under the polymer pressure, a soft surface will deform. We calculate the deformation profile for a fluid membrane and show that close to the grafting point, this profile assumes a cone-like shape, independently of the boundary conditions. Interactions between different polymers are also mediated by the membrane deformation. This pair-additive potential is attractive for chains grafted on the same side of the membrane and repulsive otherwise. Received 20 April 2000     

Control of block copolymer morphology: An example of selective morphology induced by self‐assembly formation condition

An example case of selective morphology by simply varying pH and heating profile based on a diblock copolymer, i.e., poly(N‐isopropylacrylamide) (PNIPAAM) and poly[2‐(dimethylamino)ethyl acrylate] (PDMAEA) is reported. A variation of pH induces an aggregation of the block copolymers in either micelles or vesicles. In a subsequent step, temperature variation triggers the formation of vesicular structures. This demonstrates not only the temperature but also the heating rate that tunes the nanostructures from micelles to vesicles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

ATRP synthesis and association properties of thermoresponsive anionic block copolymers

Thermosensitive anionic block copolymers of sodium 2‐acrylamido‐2‐methylpropanesulfonate (AMPS) and N‐isopropylacrylamide (NIPAAM) with different block lengths were prepared by atom transfer radical polymerization (ATRP). Controlled polymerization was achieved by using ethyl 2‐chloropropionate (ECP) as initiator and CuCl/CuCl₂/tris(2‐dimethylaminoethyl)amine (Me₆TREN) catalytic system in DMF:water 50:50 (v/v) mixtures at 20 °C. Blocks lengths ranging from 36 to 98 repeating units were obtained. The association properties in aqueous solutions at different NaCl ionic strengths were studied as a function of temperature and polymer concentration by dynamic light scattering, fluorescence spectroscopy, and energy‐filtered transmission electron microscopy. The block copolymers with a higher pNIPAAM/pAMPS ratio formed spherical core‐shell type micelles independently of the ionic strength. The block copolymers with lower pNIPAAM/pAMPS ratio formed core‐shell type micelles at high ionic strength. Larger particles were observed at low ionic strength, which could be due to the formation of vesicles or compound micelles/micellar clusters. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4830–4842, 2008     

Effects of Acid and Base on the Inductive Efficiency of Oligonucleotide on the Vesicle Formation from Single-Chained Cationic Surfactant

Recently, we reported for the first time that oligonucleotide could induce single‐chained cationic surfactant molecules to aggregate into vesicles and the facilitative efficiency of oligonucleotide on vesicle formation was dependent on its size and sequence. In the present paper, we will continue to study the effects of acid and base on the facilitative efficiency of oligonucleotide on vesicle formation. It is found that proton ions show little effect on the facilitative efficiency while hydroxide ions make it decreased. Moreover, the percentage of oligonucleotide involved in vesicle formation in basic solution is much lower than that in acidic solution (which is almost equal to that in water). Since the structures and properties of DNA/amphiphile complex are very important for its application as nonviral gene carrier, this study may provide some helpful information for gene therapy.     

检测维生素C的囊泡荧光传感器的制备

利用合成的含有识别基团苯硼酸和荧光读出基团萘的新型双亲化合物(DNMPBA)在THF/水选择性溶剂中自组织成囊泡,囊泡的相变温度为56.8℃;当向囊泡体系加维生素C时,DNMPBA囊泡中的萘生色基在345nm的荧光峰强度急剧减弱.荧光强度减弱归于所形成的硼酸酯增强了DNMPBA双亲化合物中一个氧原子孤对电子对萘生色基的淬灭作用.DNMPBA囊泡与维生素C的相互作用而导致体系荧光强度变化,使该体系有可能应用于检测生物物质如维生素C的化学传感器.     

新型含苯硼酸和喹啉的囊泡荧光多糖传感器的制备

利用合成的含有识别基团苯硼酸和荧光读出基团喹啉的新型双亲化合物对硼酸苯甲基-8-十六烷氧基溴化喹啉(BHQB)在水中自组织成囊泡,囊泡的相变温度为52.4℃;当向囊泡体系加糖时,BHQB囊泡中的喹啉生色基在508nm的荧光峰强度急剧减弱,425nm处荧光逐渐增强.荧光强度变化可能归于所形成的硼酸酯改变了双亲化合物中硼原子的杂化轨道形式,进一步引起了整个分子内部的电子云排布所致.BHQB囊泡与糖的相互作用而导致体系荧光强度变化,并且这种变化的幅度与加入糖的种类和量均有关.因此体系有可能应用于检测生物物质如糖的化学传感器.     

Self‐Assembly of Discrete Homochiral,Helical, Hydrogen‐Bonded Nanocages: From Vesicles to Microspheres and Tubules Capable of Gelating Solvents

The chiral tris‐monodentate imidazolinyl ligands 1 a – c exhibit a strong tendency to form the discrete, helical [2+3] nanocages 3 ([ 1 ₂ ?2 ₃]) with tartaric acids 2 . Circular dichroism (CD) spectra and theoretical calculations reveal that supramolecular handedness of capsulelike architectures is determined only by the chirality of the imidazolinyl ligands rather than tartaric acids. The chirality of imidazolinyl ligands is transferred to the helicity of the complexes through the directed hydrogen bonds between the N3 atom of imidazoline rings and the carboxyl of tartaric acids. These hydrogen‐bonded nanocages can spontaneously self‐assemble into spherical vesicles, during which the hydrogen bonding that arises from the hydroxyl groups of tartaric acids plays a crucial issue. The vesicles formed by [{(S,S,S)‐ 1 a }₂( 2 ^L)₃] ( 3 a ) may further evolve into microspheres that gelate organic solvents after being aged at ?20 °C for 24 h, and can also be unprecedentedly transformed to tubular assemblies capable of rigidifying the solvents when subjected to ultrasound irradiation.     

CO2-switchable vesicles-network structure transition and drug release property

A series of amphiphilic triblock polymers based on poly(ethylene glycol) (PEG) and two symmetrical poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) blocks was synthesized via the Atom Transfer Radical Polymerization (ATRP) method. Conductivity, pH, and viscosity tests demonstrated the CO₂-switchability jointly; Cryogenic transmission electron microscopy (Cryo-TEM), Dynamic light scattering (DLS) revealed the self-assembly morphology transformation from unilamellar vesicle to network structure when bubbling CO₂. These changes were all attributed to the protonation of tertiary amine groups in PDMAEMA blocks and the mechanism was proved by ^?H NMR. The vesicles have a relatively low release rate of drug; once stimulated by CO₂, the release rate will be accelerated. The polymeric vesicle has the possibility to find potential applications in drug delivery and release domains.