Mechanical Characterization of Micrometric Chitosan-Coated Vesicle by Atomic Force Microscopy

This article reports the main results obtained for the stabilization of DOPC liposomes by coating with chitosan. We investigated the compression between two planes of isolated GUV, combining force spectroscopy measurements with scanning probe microscopy (SPM) and epifluorescence microscopy observations. We obtained reproducible and reversible force-deformation curves for individual vesicles in the range of small deformation (relative deformation up to 0.3). Force-deformation curves were analyzed using a simple elastic model, which well describes the observed radius-dependency of the force response and allows determining the stretching modulus for bare vesicle and effective bending and stretching moduli for chitosan-coated membranes. Results first show that chitosan coating increases the effective stretching modulus of the lipid membranes, second, confirm that chitosan is adsorbed flat on the membrane, and finally lead us to assume that the chitosan coating structure can be regarded as a physical network of connected chitosan patches.     

Supramolecular assembly of a succinyl-calix[4]arene derivative in multilamellar vesicles

Abstract

Amphiphilic calixarenes are interesting building blocks with high propensity to assemble in well-defined supramolecular architectures. In this work, we report that a succinyl-calix[4]arene derivative (2), exposing four terminal carboxylic acid groups at the calixarene upper rim and four dodecyl chains at the lower rim, forms discrete and stable nanoaggregates in aqueous medium. Field-emission scanning electron microscopy and transmission electron microscopy images showed that the aggregates of 2 possess a spherical shape and a vesicular structure with a multilamellar wall. The vesicular nature was confirmed by encapsulation of a hydrophilic dye rhodamine B. A preliminary study also evidenced that compound 2 increases water solubility of a hydrophobic drug such as curcumin.     

Order-Disorder Transition of Carboxyl Terminated Chains in Polydiacetylenes Vesicles Probed by Second Harmonic Generation and Two-Photon Fluorescence

To understand and control the interfacial properties of polydiacetylenes (PDAs) vesicles with π-conjugated backbone is very important for their colorimetric sensing of chemical and biological targets. In this work, we adopted 10, 12-pentacosadiynoic acid (PCDA) as the model molecule to prepare PDAs vesicles in aqueous solution with different forms (from monomer to blue-to-purple-to-red phase) by controlling the UV irradiation dose. The variations of the interfacial conformation of PDAs vesicles during chromatic transitions were inspected by the adsorption behaviors of probe molecules (4-(4-diethylaminostyry)-1-methylpyridinium iodide, D289) on vesicle surface with surface-specific second harmonic generation (SHG) and zeta potential measurements. Resonant SHG signal from D289 adsorbed on vesicle surface attenuated sharply, and the adsorption free energy as well as the corresponding two-photon fluorescence signal decreased slightly in chromatic transitions. While, the change in the surface density of the adsorbed D289 molecules for PDAs vesicles with different forms was relatively small as estimated from zeta potential measurements. The attenuation of the SHG intensity was thus attributed to the overall order-disorder transition and the changed orientation of D289 molecules caused by the gradual distortion of carboxyl head group driven by backbone perturbation.     

Aggregation behaviors of amine-oxide gemini surfactants

The micellar aggregation of a series of gemini surfactants [N, N’-dimethyl-N, N’-bis(2-alkylamideethyl)-ethylenediamine oxide (alkyl?=?C₁₁H₂₃, C₁₃H₂₇, C₁₅H₃₁)] in aqueous media has been investigated. The results show that there is an excellent agreement among the critical micelle concentration (CMC) values obtained by surface tension and steady-state fluorescence methods. Because of the occurrence of self-coiling or the formation of pre-micellization, the CMC values, the I₁/I₃ values, and the micelle aggregation numbers (N_agg) at CMC (N_m) increase with the hydrophobic alkyl chain length increasing. Besides, vesicles are observed above the CMC for all these surfactants.     

Synthesis and self-assembly of reactive H-shaped block copolymers

The H-shaped block copolymers (PTMSPMA)₂-PEG(PMPSTMSPMA)₂ with two compositions, (EG)₉₁-b-(TMSPMA)₉₂ and (EG)₄₅₅-b-(TMSPMA)₁₇₆ have been successfully synthesized by atom transfer radical polymerization (ATRP) of tri(methoxylsilyl)propyl methacrylate (TMSPMA) at room temperature in methanol. The initiation system applied was composed of 2,2-bis(methylene α-bromoisobutyrate)propionyl terminated poly(ethylene glycol) (Br₂PEGBr₂) with M _n = 4000 or 2000, CuBr and 2,2′-bipyridine. The macroinitiator, Br₂PEGBr₂, was prepared by the reaction of two hydroxyl groups terminated PEG with 2,2-bis(methylene α-bromoisobutyrate)propionyl chloride. The NMR spectroscopy and GPC measurements were used to characterize the structure and molecular weight and molecular weight distribution of the resultant copolymers. The H-shaped block copolymers Sam 1 and Sam 2 were self-assembled in DMF/water mixtures and then the trimethoxysilyl groups in PTMSPMA were cross-linked by condensation reaction in the presence of triethylamine. Stable large-compound vesicles with 10 nm diameter of cavities were formed for Sam 1 which contains a short PEG chain. However, the self-assembling of the Sam 2 in the selective solvents resulted in big vesicles aggregates. These two different morphologies of aggregates are attributed to their relative chain length of water soluble PEG. The vesicles formed from Sam1 with short PEG chains have big surface energy which will lead them to self-assemble further, forming large-compound vesicles. __________ Translated from Acta Polymerica Sinica, 2007, 10: 974–978 [译自: 高分子学报]     

探索脑化学纳米电化学监测单细胞、单囊泡、突触间隙释放化学信号分子及形貌分析

针对已有的微米及纳米电化学监测单囊泡、单突触及突触间隙释放, 扫描电化学显微镜用于单细胞释放前后形貌变化的定量分析, 微流控与阵列电极集成芯片, 用于细胞灌注培养及监测释放化学信号分子的研究工作进行了评述. 同时, 对近几年此领域的前沿研究进行了简要评论, 并对其未来发展提出了一些新的观点.     

Production and purification of bacterial membrane vesicles for biotechnology applications: Challenges and opportunities

Bacterial membrane vesicles (BMVs) are bi-layered nanostructures derived from Gram-negative and Gram-positive bacteria. Among other pathophysiological roles, BMVs are critical messengers in intercellular communication. As a result, BMVs are emerging as a promising technology for the development of numerous therapeutic applications. Despite the remarkable progress in unveiling BMV biology and functions in recent years, their successful isolation and purification have been limited. Several challenges related to vesicle purity, yield, and scalability severely hamper the further development of BMVs for biotechnology and clinical applications. This review focuses on the current technologies and methodologies used in BMV production and purification, such as ultracentrifugation, density-gradient centrifugation, size-exclusion chromatography, ultrafiltration, and precipitation. We also discuss the current challenges related to BMV isolation, large-scale production, storage, and stability that limit their application. More importantly, the present work explains the most recent strategies proposed for overcoming those challenges. Finally, we summarize the ongoing applications of BMVs in the biotechnological field.     

Spontaneous vesicles of sodium dihexadecylphosphate in HEPES buffer

The formation of spontaneous vesicles of dihexadecylphosphate (DHP) in a HEPES buffered solution at pH 7.4, the size, morphology and melting temperature, obtained by cryogenic transmission electron microscopy (cryo-TEM) and differential scanning calorimetry (DSC), are reported. The vesicles were formed by simply mixing a 5.0 mM lipid-solvent mixture at a temperature (75 degrees C) safely above the higher melting temperature T(m)=70.4 degrees C of DHP. The vesicle diameter ranges from 100 to 332 nm and their geometry is spherical, faceted or oblong. T(m) increases from 66.8 to 70.4 as DHP concentration is raised from 0.6 to 5.0 mM.     

Transformation of Structure and Properties of Vesicles Induced by Transition Metal Ions

This paper proved that octodecyl propylenediamine could form vesicles in pure water and aqueous solution of CuCl2 or Cu（NO3）2. The structure and morphology of vesicles were different when the copper （Ⅱ） salt was added to the solution. The results showed that both the counterions and the ligands had strong influence on the configuration of coordinated structures and packing model in bilayer membrane of vesicles.     

合成双分子膜多元体系的激发态能量转移

发现在４－（４－癸氧基联苯－４－氧基三甲基）溴化铵双分子膜体系内，从联苯给体通过结合在膜表面上的达旦黄传递到罗丹明Ｂ受体的三元激发态的能量转移效率较高．探讨了囊泡在此能量转移过程中的特殊功能作用和能量转移的机制．同时还观察到了在此体系内通过静电相互作用，组织在囊泡表面上的达旦黄、荧光黄、罗丹明Ｂ和四苯基卟啉间的多元能量转移，这种能量转移可改善光的输出，扩展光波的覆盖范围．