Dey Sandeep Kumar, Kumari Sonam, Mandrekar Sonal, Mhaldar Shashank N, Harmalkar Sarvesh S, Janiak Christoph
School of Chemical Sciences, Goa University Taleigao Plateau Goa 403206 India
Institute of Inorganic and Structural Chemistry, Heinrich-Heine University 40204 Düsseldorf Germany
RSC Adv. 2021 Nov 17;11(58):36850-36858. doi: 10.1039/d1ra07677a. eCollection 2021 Nov 10.
Several salicylidene-based colorimetric and fluorimetric anion sensors are known in the literature. However, our H-NMR experimental results (in DMSO-d) showed hydrolysis of imine (-N[double bond, length as m-dash]CH-) bonds in salicylidene-based receptors (SL, CL1 and CL2) in the presence of quaternary ammonium salts (-BuN) of halides (Cl and Br) and oxo-anions (HPO , HSO and CHCOO). The mono-salicylidene compound CL1 showed the most extensive -N[double bond, length as m-dash]CH- bond hydrolysis in the presence of anions. In contrast, the di-salicylidene compound CL2 and the tris-salicylidene compound SL showed comparatively slow hydrolysis of -N[double bond, length as m-dash]CH- bonds in the presence of anions. Anion-induced imine bond cleavage in salicylidene compounds could easily be detected in H-NMR due to the appearance of the salicylaldehyde -CHO peak at 10.3 ppm which eventually became more intense over time, and the -N[double bond, length as m-dash]CH- peak at 8.9-9.0 ppm became considerably weaker. Furthermore, the formation of the salicylidene O-H⋯X (X = Cl/Br) hydrogen-bonded complex, peak broadening due to proton-exchange processes and keto-enol tautomerism have also been clearly observed in the H-NMR experiments. Control H-NMR experiments revealed that the presence of moisture in the organic solvents could result in gradual hydrolysis of the salicylidene compounds, and the rate of hydrolysis has further been enhanced significantly in the presence of an anion. Based on H-NMR results, we have proposed a general mechanism for the anion-induced hydrolysis of imine bonds in salicylidene-based receptors.
文献中已知几种基于水杨醛的比色和荧光阴离子传感器。然而，我们的核磁共振氢谱（在氘代二甲亚砜中）实验结果表明，在卤化物（氯和溴）和含氧阴离子（磷酸氢根、硫酸氢根和醋酸根）的季铵盐（四丁基铵）存在下，基于水杨醛的受体（SL、CL1和CL2）中的亚胺（-N=CH-）键会发生水解。单水杨醛化合物CL1在阴离子存在下显示出最广泛的-N=CH-键水解。相比之下，双水杨醛化合物CL2和三水杨醛化合物SL在阴离子存在下显示出相对较慢的-N=CH-键水解。由于在10.3 ppm处出现水杨醛-CHO峰，并且随着时间的推移该峰最终变得更强，而在8.9 - 9.0 ppm处的-N=CH-峰变得相当弱，因此在核磁共振氢谱中可以很容易地检测到阴离子诱导的水杨醛化合物中亚胺键的断裂。此外，在核磁共振氢谱实验中也清楚地观察到了水杨醛O-H⋯X（X = Cl/Br）氢键复合物的形成、由于质子交换过程导致的峰展宽以及酮-烯醇互变异构。对照核磁共振氢谱实验表明，有机溶剂中的水分会导致水杨醛化合物逐渐水解，并且在阴离子存在下，水解速率会进一步显著提高。基于核磁共振氢谱结果，我们提出了一种基于水杨醛的受体中亚胺键阴离子诱导水解的一般机制。
