用聚联乙炔囊泡为载体,将bola型两亲分子1,12-二乳清酸十二胺盐(DDO)对三聚氰胺的分子识别作用用肉眼可见的颜色变化显示出来.通过比较不同碳链长度的聚联乙炔囊泡对分子识别过程的反映,发现二十三烷基-2.4-二炔酸(TCDA)囊泡的显色灵敏度较高.研究表明,TCDA肉眼可见的颜色变化来自于DDO与三聚氰胺多重氢键的形成以及溶液环境中水结构的变化.为了更好地理解显色机理,用差示扫描量热(DSC)仪详细研究了分子识别过程中聚联乙炔囊泡的相变行为及热力学参数.结果表明:TCDA囊泡和带有识别分子的DDO/TCDA囊泡在三聚氰胺存在下,相变温度Tm均向高温方向移动,并且,随三聚氰胺浓度的增加,Tm值逐渐增大直至囊泡瓦解；但是Tm值的变化没有与囊泡变色必然关联,仅仅DDO/TCDA囊泡具有变色现象,而且,只有当三聚氰胺的浓度超过分子识别氢键形成所需理论量时,肉眼才能可见明显的由蓝到红的颜色变化.为了理解溶液中过量的三聚氰胺对囊泡变色的作用,选用蔗糖和尿素作为典型的水结构促进剂和水结构破坏剂(chaotrope),详细研究了它们对聚联乙炔囊泡反映分子识别过程中相变温度的影响及显色规律.结果表明,过量的三聚氰胺在溶液中起到类似尿素水结构破坏剂的作用.这种作用和分子识别过程中多重氢键的形成对聚联乙炔囊泡的变色缺一不可.本研究首次揭示了由水结构破坏剂参与的聚联乙炔囊泡变色机理,有助于理解共轭聚合物热相变过程中的Hofmeister效应.%The interaction between melamine and 1,12-diaminododecanediorotate (DDO), a bolaamphiphile bearing molecular recognition sites for amine functional groups,was transformed into visible color changes using polymerlzed 2,4-tricosadiynoic acid (TCDA) vesicles.TCDA was found to be more sensitive than other polydiacetylene vesicles with various alkane chain-lengths in reporting the molecular recognition event.Colorimetric changes occurred as a result of modifications in the conjugated backbone of TCDA triggered by changes in the chemical environment associated with the recognition process.To better understand this mechanism,the influence of melamine on the thermotropic behavior of polydiacetylene vesicles and the thermodynamics were investigated via differential scanning calorimetry (DSC).It was found that the phase transitions of both TCDA and DDO/TCDA vesicles were shifted to higher temperatures when melamine was present,and that the magnitude of this shift increased as the melamine levels were raised.Color changes associated with the molecular recognition process were only observed with the unaided eye when melamine was introduced at levels well in excess of those theoretically required.Using sucrose and urea as model kosmotropic and chaotropic compounds,respectively,the effect of such solutes on the phase transition of polydiacetylene vesicles and equilibrium energetics of the molecular recognition were examined.Results indicate that the excess melamine likely behaves as a chaotrope in the colloid.In combination with the multipoint hydrogen bond formation between melamine and DDO,these effects are responsible for the blue-red color transition of the DDO/TCDA vesicles.Identification of this chaotrope-assisted color visualization mechanism for PDA vesicles provides new insights into the Hofmeister series effect on the conformation change of conjugated polymers.
展开▼
