Zhong Jinlian, Fu Hongyu, Jia Xinjian, Lou Haoxiang, Wan Tiantian, Luo Haiqing, Liu Huijin, Zhong Dichang, Luo Xuzhong
Key Laboratory of Organo-pharmaceutical Chemistry of Jiangxi Province, Gannan Normal University Ganzhou 341000 P. R. China
RSC Adv. 2019 Apr 16;9(21):11824-11832. doi: 10.1039/c8ra09058k. eCollection 2019 Apr 12.
In this study, we report a pH-/thermo-responsive hydrogel formed by ,'-dibenzoyl-l-cystine (DBC). It is difficult to dissolve DBC in water even on heating, and it exhibits no gelation ability. Interestingly, DBC is readily soluble in NaOH solution at room temperature and the self-assembled hydrogels are obtained by adjusting the basic DBC aqueous solution with HCl to achieve a given pH value (<3.5). When NaOH is added to the hydrogel (pH > 9.4), it becomes a sol again. This small-molecule hydrogel is characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, rheological measurement and differential scanning calorimetry. The results indicate that the DBC hydrogel exhibits excellent mechanical properties, thermo-reversibility, and pH-responsive properties. Fortunately, the single crystal of DBC is obtained by volatilizing its acid aqueous solution. It crystallizes in the monoclinic space group 2 ( = 2) with lattice parameters = 10.8180 (11) Å, = 9.0405 (9) Å, = 10.9871 (11) Å and = 90.798 (3)°. By comparing the X-ray diffraction result of the DBC single crystal with that of its xerogel, the self-assembled structure of DBC in hydrogel has been ascertained. The gelators are self-assembled strong intermolecular hydrogen bonds linking neighboring amide and carboxyl groups, π-π stacking interactions for aromatic rings, and hydrogen bonds between water molecules. In addition, the release behavior of salicylic acid (SA) molecules from the DBC gel is also investigated taking into account the DBC concentration, phosphate buffer solution (PBS) pH and SA concentration. When the concentrations of DBC and SA are 3.0 g L and 200 mg L, respectively, the release ratio in PBS (pH = 4.0) reaches 58.02%. The diffusion-controlled mechanism is in accordance with Fickian diffusion control within the given time range.
在本研究中，我们报道了一种由L，L'-二苯甲酰-L-胱氨酸（DBC）形成的pH/温度响应水凝胶。即使加热，DBC也难以溶于水，并且它没有凝胶化能力。有趣的是，DBC在室温下易溶于NaOH溶液，通过用HCl调节碱性DBC水溶液以达到给定的pH值（<3.5）可获得自组装水凝胶。当向水凝胶中加入NaOH（pH>9.4）时，它又变成溶胶。通过扫描电子显微镜、傅里叶变换红外光谱、流变学测量和差示扫描量热法对这种小分子水凝胶进行了表征。结果表明，DBC水凝胶具有优异的力学性能、热可逆性和pH响应性能。幸运的是，通过挥发其酸性水溶液获得了DBC单晶。它以单斜空间群P21/c结晶，晶格参数a = 10.8180（11）Å，b = 9.0405（9）Å，c = 10.9871（11）Å，β = 90.798（3）°。通过比较DBC单晶与其干凝胶的X射线衍射结果，确定了DBC在水凝胶中的自组装结构。凝胶因子通过相邻酰胺基和羧基之间的强分子间氢键、芳环的π-π堆积相互作用以及水分子之间的氢键自组装而成。此外，还考虑了DBC浓度、磷酸盐缓冲溶液（PBS）pH和水杨酸（SA）浓度，研究了SA分子从DBC凝胶中的释放行为。当DBC和SA的浓度分别为3.0 g/L和200 mg/L时，在PBS（pH = 4.0）中的释放率达到58.02%。在给定的时间范围内，扩散控制机制符合菲克扩散控制。
