Low molecular weight organogelators derived from threefold symmetric tricarbamates

A group of new low molecular weight organogelators based on threefold symmetric tricarbamate were synthesized and characterized. The tricarbamates with long alkyl chains were able to gelate a wide range of polar and nonpolar organic solvents such as acetonitrile and cyclohexane, generally at concentrations lower than 20 g/L. The best organogel formation was obtained using a threefold symmetric tricarbamate in n-dodecane, in which a sufficiently transparent gel was formed at the critical gelation concentration 1 g/L. Intermolecular hydrogen bonding by the tricarbamate in a nonpolar solvent benzene-d₆ was indicated by ¹H NMR spectra. Its maximum UV absorption was 11 nm higher in chloroform than in n-dodecane, and this red shift indicated increased conjugation between the benzene core and the carbamate substituents, which confirmed a change in its conformation from nonpolar to polar solvent. The self-assembling behavior of the tricarbamate in dilute solutions was investigated by TEM. Fiber-like networks were observed in a large range of solution concentrations.     

Selective adsorption of D- and L-phenylalanine on molecularly-imprinted polymerized organogels formed using polymerizable gelator N-octadecyl maleamic acid

The polymerizable gelator N-octadecyl maleamic acid (ODMA) can self-assemble in selected polymerizable organic solvents, such as 2-hydroxyethyl methacrylate (HEMA) and methylacrylic acid (MAA) to form thermally stable polymerizable organogels. A mixture consisting of HEMA and MAA as the monomer and functional monomer, PEG dimethacrylates (PEG200DMA) as the crosslinker, BOC-L-phenylalanine (BPA) or L-phenylalanine ethyl ester (PEE) as the chiral templates, was gelatinized by ODMA firstly and subsequently polymerized by in situ UV irradiation or thermal initiation. The molecularly imprinted polymerized organogels were obtained after the removal of the templates through ethanol extraction. Selective adsorption of D- and L-phenylalanine was performed on the polymerized organogels. The results indicate rather high adsorption efficiency obtained for L-phenylalanine compared with that for D-phenylalanine, which was found to be dependent on the concentrations of ODMA, content of template, and the method of polymerization. Herein, the concentration of ODMA in the organogels played an important role for the adsorption efficiency of D- and L-phenylalanine.     

双组分有机低分子凝胶的研究进展

双组分有机低分子凝胶的研究已成为纳米化学新兴研究领域的热点之一, 形成双组分有机低分子凝胶的有机分子具有多种结构, 例如: 巴比妥酸衍生物、氨基酸衍生物、糖类衍生物、金属有机化合物、胆固醇类衍生物和树枝状分子等. 较系统地综述了目前已知的双组分凝胶及其所涉及的有机低分子凝胶因子的主要结构类型, 并展望了双组分有机低分子凝胶的应用前景.     

Hybrid Hydrogels Assembled from Phenylalanine Derivatives and Agarose with Enhanced Mechanical Strength

A roadblock for supramolecular hydrogels is their poor mechanical properties. Herein, to enhance the mechanical strength of supramolecular hydrogels, agarose(AG) was incorporated into the low molecular weight hydrogelator(G1). The results of scanning electron microscopy(SEM), circular dichroism(CD) and Fourier transform infrared spectroscopy(FTIR) prove that G1 gelators can self-assemble into cross-linked network together with AG. The mechanical properties of the gels are characterized by a rotary rheometer and the mechanical properties of the hybrid hydrogels(Hgel) can be significantly improved and may be further tuned by changing the ratio of the two components. For example, the elastic modulus of Hgel Ⅱ[m(G1):m(AG)=7:3] is about 2 times higher than that of G1 hydrogel. The results demonstrate that the mechanical property of hybrid supramolecular hydrogels can be adjusted through the formation of a cross-linked network.     

由凝胶因子形成的十四酸异丙酯超分子凝胶制备与表征

采用双十八烷基-L-苯丙氨酸(Bis18-L-Phe)为凝胶因子,制备了具有热可逆性的十四酸异丙酯(IPM)超分子凝胶。IPM凝胶相转变温度(Tgel)随Bis18-L-Phe浓度增大而增加。偏光显微镜(POM)显示在整个IPM凝胶中形成了相互缠绕的针状聚集体。FT-IR光谱分析表明Bis18-L-Phe分子间酰胺的氢键作用是IPM凝胶形成的一个重要驱动力。IPM凝胶动力学研究表明凝胶时间随Bis18-L-Phe浓度的增大而缩短,随着温度升高而延长,因此IPM凝胶时间可以通过温度和Bis18-L-Phe浓度调控。     

分子凝胶中可聚合凝胶因子的聚集态及分形结构研究

利用X射线衍射(XRD)及原子力显微镜(AFM)研究了可聚合凝胶因子4，4′—二 (α-甲基丙烯酰氧基—1，3—亚乙氧基碳基丙酰氨基)二苯甲烷(BMDM)在二苯醚凝 胶中的聚集态及分形结构。研究结果表明，凝胶纤维束是由大量细长的薄带状的单 元纤维有序堆积成的，单元纤维的宽度约为3nm，厚度为0．1—0．2nm；凝胶因子 聚集体则是一种规则的片层结构，具有自相似性和分形特征。利用分形理论中的 Sandbox法计算结果也表明分子凝胶具有分形特征，计算得分形维数D＝1．853。     

Nanowires Formed by the Co‐Assembly of a Negatively Charged Low‐Molecular Weight Gelator and a Zwitterionic Polythiophene

Conjugated organic nanowires have been prepared by co‐assembling a carboxylate containing low‐molecular weight gelator (LMWG) and an amino acid substituted polythiophene derivative (PTT). Upon introducing the zwitterionic polyelectrolyte PTT to a basic molecular solution of the organogelator, the negative charges on the LMWG are compensated by the positive charges of the PTT. As a result, nanowires form through co‐assembly. These nanowires are visualized by both transmission electron microscopy (TEM) and atomic force microscopy (AFM). Depending on the concentration and ratio of the components these nanowires can be micrometers long. These measurements further suggest that the aggregates adopt a helical conformation. The morphology of these nanowires are studied with fluorescent confocal laser scanning microscopy (CLSM). The interactions between LMWG and PTT are characterized by steady‐state and time‐resolved fluorescence spectroscopy studies. The steady‐state spectra indicate that the backbone of the PTT adopts a more planar and more aggregated conformation when interacting with LMWG. The time‐ resolved fluorescence decay studies confirm this interpretation.     

Recent advancement and development of chitin and chitosan-based nanocomposite for drug delivery: Critical approach to clinical research

This review depicts the exposure of chitin and chitosan base multifunctional nanomaterial composites for promising applications in field of biomedical science structure, synthesis as well as potential application from a colossal angle. We elaborated critically each of the chitin and chitosan base nanomaterial with its potential application toward biomedical science. For different biomedical applications it use in form of hydrogels, microsphere, nanoparticles, aerogels, microsphere and in form of scaffold. Due to this it had been blended with different polymer such as starch, cellulose, alginate, lipid, hyaluronic acid, polyvinyl alcohol and caboxymethyl cellulose. In this review article, a comprehensive overview of combination of chitin and chitosan base nanomaterial with natural as well as synthetic polymers and their biomedical applications in biomedical field involving drug delivery system all the technical scientific issues have been addressed; highlighting the recent advancements.     

自组装分子凝胶的原位光聚合及其聚合物研究

合成了一种以二胺为基础的可聚合凝胶因子4,4’-二（α-甲基丙烯酰氧基- 1,3-亚乙氧基羰基丙酰氨基）二苯甲烷（BMDM）,利用在特定结构区域的非共价 键相互作用自组装形成有序的三维纤维网络,使有机溶剂凝胶化。并利用紫外光引 发聚合,“锁定”凝胶网络,形成稳定的有序高级结构。光聚合后,分子凝胶的稳 定时间超过1年;而光聚合前,分子凝胶的稳定时间一般只有几天到几十天。由电 镜和偏光显微镜研究的凝胶形态学表明,凝胶中存在由相互缠结的三维纤维网络构 成的球晶。DSC研究表明,未聚合的分子凝胶中球晶结构的解缔（peak 1）须克服 一个势垒,势能为ΔH = 0.8 kJ·mol~(-1),这主要是一种范德华弱相互作用。而 发生的凝胶-溶胶相转变（peak 2）,则说明了自组装纤维中BMDM分子间存在氢键 等次价键相互作用。这种次价键能即为凝胶-溶胶相转变热焓ΔH = 22.3 kJ· mol~(-1)。聚合凝胶只有体积相变而无凝胶-溶胶相转变,且聚合凝胶的体积相变 温度要比光聚合前的凝胶-溶胶相转变温度高出约为110 ～ 120 ℃。研究干聚合凝 胶在丙酮中的溶胀特性发现,其溶胀过程遵循二级溶胀动力学,影响该凝胶溶胀行 为的因素主要是交联程度。     

Direct Electrochemistry of Horseradish Peroxidase Immobilized in a Low Molecular Weight Gel

The ternary system of dodecylpyridinium bromide (DDPB)/acetone/H₂O with appropriate composition can form a gel spontaneously and the gel is stable in hydrophobic ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([Bmim]PF₆). Based on the gelation phenomenon we observed, the low molecular weight gelator (LMWG) was first tried to immobilize horseradish peroxidase (HRP) on glassy carbon electrode (GCE). The scanning electron microscope (SEM) images, the UV‐Vis spectra and the bioactivity measurement indicate that the gel is suitable for the immobilization of HRP. The direct electrochemistry of the HRP‐gel modified GCE (HRP‐gel/GCE) in [Bmim]PF₆ shows a pair of well‐defined and quasi‐reversible redox peaks with the heterogeneous electron transfer rate constant (k_s) being 14.4 s^?1, indicating that the direct electron transfer between HRP and GCE is fast. The HRP‐gel/GCE is stable and reproducible. Also the electrode exhibits good electrocatalytic effect on the reduction of trichloroacetic acid (TCA), showing good promise in bioelectrocatalysis.