Liu Chuangjun, Best Quinn A, Suarez Brian, Pertile Jack, McCarroll Matthew E, Scott Colleen N
Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, IL, 62901, USA.
J Fluoresc. 2015 Mar;25(2):231-7. doi: 10.1007/s10895-015-1519-z. Epub 2015 Feb 17.
A series of fluorescent pH probes based on the spiro-cyclic rhodamine core, aminomethylrhodamines (AMR), was synthesized and the effect of cycloalkane ring size on the acid/base properties of the AMR system was explored. The study involved a series of rhodamine 6G (cAMR6G) and rhodamine B (cAMR) pH probes with cycloalkane ring sizes from C-3 to C-6 on the spiro-cyclic amino group. It is known that the pKa value of cycloalkylamines can be tuned by different ring sizes in accordance with the Baeyer ring strain theory. Smaller ring amines have lower pKa value, i.e., they are less basic, such that the relative order in cycloalkylamine basicity is: cyclohexyl > cyclopentyl > cyclobutyl > cyclopropyl. Herein, it was found that the pKa values of the cAMR and cAMR6G systems can also be predicted by Baeyer ring strain theory. The pKa values for the cAMR6G series were shown to be higher than the cAMR series by a value of approximately 1.
合成了一系列基于螺环罗丹明核心的荧光pH探针——氨甲基罗丹明（AMR），并探讨了环烷烃环大小对AMR体系酸碱性质的影响。该研究涉及一系列在螺环氨基上具有从C-3到C-6环烷烃环大小的罗丹明6G（cAMR6G）和罗丹明B（cAMR）pH探针。众所周知，根据拜尔环张力理论，环烷基胺的pKa值可通过不同的环大小进行调节。较小环的胺具有较低的pKa值，即它们的碱性较弱，因此环烷基胺碱性的相对顺序为：环己基＞环戊基＞环丁基＞环丙基。在此发现，cAMR和cAMR6G体系的pKa值也可以用拜尔环张力理论来预测。结果表明，cAMR6G系列的pKa值比cAMR系列高约1个单位。
