Sarkar Sougata, Dutta Soumen, Chakrabarti Susmita, Bairi Partha, Pal Tarasankar
Department of Chemistry, Indian Institute of Technology , Kharagpur 721302, India.
ACS Appl Mater Interfaces. 2014 May 14;6(9):6308-16. doi: 10.1021/am501491u. Epub 2014 Apr 30.
Thiourea (TU), a commercially available laboratory chemical, has been discovered to introduce metallogelation when reacted with copper(II) chloride in aqueous medium. The chemistry involves the reduction of Cu(II) to Cu(I) with concomitant oxidation of thiourea to dithiobisformamidinium dichloride. The gel formation is triggered through metal-ligand complexation, i.e., Cu(I)-TU coordination and extensive hydrogen bonding interactions involving thiourea, the disulfide product, water, and chloride ions. Entangled network morphology of the gel selectively develops in water, maybe for its superior hydrogen-bonding ability, as accounted from Kamlet-Taft solvent parameters. Complete and systematic chemical analyses demonstrate the importance of both Cu(I) and chloride ions as the key ingredients in the metal-organic coordination gel framework. The gel is highly fluorescent. Again, exclusive presence of Cu(I) metal centers in the gel structure makes the gel redox-responsive and therefore it shows reversible gel-sol phase transition. However, the reversibility does not cause any morphological change in the gel phase. The gel practically exhibits its multiresponsive nature and therefore the influences of different probable interfering parameters (pH, selective metal ions and anions, selective complexing agents, etc.) have been studied mechanistically and the results might be promising for different applications. Finally, the gel material shows a highly selective visual response to a commonly used nitroexplosive, picric acid among a set of 19 congeners and the preferred selectivity has been mechanistically interpreted with density functional theory-based calculations.
硫脲（TU）是一种市售的实验室化学品，已发现其在水介质中与氯化铜（II）反应时会引发金属凝胶化。其化学反应过程包括将Cu（II）还原为Cu（I），同时硫脲被氧化为二氯二硫代双甲脒。凝胶的形成是通过金属-配体络合引发的，即Cu（I）-TU配位以及涉及硫脲、二硫化物产物、水和氯离子的广泛氢键相互作用。凝胶的缠结网络形态在水中选择性地形成，这可能是由于其优异的氢键能力，从Kamlet-Taft溶剂参数可以看出。完整而系统的化学分析表明，Cu（I）和氯离子都是金属有机配位凝胶框架中的关键成分。该凝胶具有高荧光性。此外，凝胶结构中仅存在Cu（I）金属中心，这使得凝胶具有氧化还原响应性，因此它表现出可逆的凝胶-溶胶相变。然而，这种可逆性不会导致凝胶相发生任何形态变化。该凝胶实际上表现出其多响应性质，因此已经从机理上研究了不同可能的干扰参数（pH值、选择性金属离子和阴离子、选择性络合剂等）的影响，其结果可能对不同应用具有前景。最后，该凝胶材料对一组19种同系物中的一种常用硝基炸药苦味酸表现出高度选择性的视觉响应，并且基于密度泛函理论的计算从机理上解释了这种优先选择性。
