Genipin, a naturally occurring iridoid, represents an interesting class of reactive dyes. This colorless molecule produces brilliant blue dyes in the presence of primary aliphatic amines. The mechanism behind this unique reaction has been suggested to proceed via an oxidative polymerization reaction, albeit few studies have investigated this process. By utilizing aromatic amines, we demonstrate that the dye absorption properties can be redshifted to form green dyes as opposed to the blue that is most associated with aliphatic amines. Characterization of the green material with gel-permeation chromatography, mass spectrometry, and electrochemical experiments suggest an alternate structure of the dye molecules and led us to revisit the mechanism behind this reaction. Generation of dyes from the reaction of genipin and methylamine or various aniline derivatives revealed the complete absence of polymeric material and instead revealed a material that contains an open-shell configuration as determined by EPR spectroscopy. Herein we report the first findings that dyes formed from the reaction of genipin with amines form persistent radicals that are likely responsible for their vibrant colors, as opposed to the previously suggested polymer formation.

中文翻译：

---

胺对Genipin染料形成的取代作用–对染料来源的认识

Genipin是一种天然存在的虹彩化合物，代表了一类有趣的活性染料。在伯脂族胺的存在下，该无色分子产生亮蓝色染料。尽管很少有研究研究该过程，但已提出该独特反应背后的机理是通过氧化聚合反应进行的。通过利用芳香胺，我们证明了染料的吸收特性可以发生红移，从而形成绿色染料，而与脂肪族胺最相关的蓝色则相反。用凝胶渗透色谱，质谱和电化学实验对绿色材料进行表征，表明染料分子具有另一种结构，这使我们重新审视了该反应背后的机理。由Genipin与甲胺或各种苯胺衍生物反应生成的染料表明，完全不存在聚合材料，取而代之的是，该材料包含通过EPR光谱确定的开壳构型。在本文中，我们报告了第一个发现，即从Genipin与胺反应形成的染料形成持久性自由基，这可能是导致其鲜艳的颜色的原因，与先前建议的聚合物形成相反。