Abstract
A potential hypoxia-sensitive system host-guest complex of three calixarenes (including two with four anionic carboxyl and sulphonate azo fragments on the upper rim and a newly synthesized bis-azo adduct of calixarene in the cone configuration with azo fragments on the lower rim with the most widespread cationic and zwitterionic rhodamine dyes (123, 6G and B)) was studied using UV-VIS spectrometry and fluorescence as well as 1D and 2D NMR techniques. It was found that all three calixarenes form a complex with rhodamine dyes with a 1:1 composition. The association constants of calixarene-dye complexes with sulfonate calixarenes, especially in the case of tetra-anionic calixarene, turned out to be higher compared with carboxyl calixarene due to the more intense electrostatic interactions. For the first time using an HRESI MS technique, it was shown that the treatment of rhodamine 6G and 123 with sodium dithionite (SDT) produces a non-fluorescent leuco form of the dye, and only rhodamine B can be used with SDT without the occurrence of a side reduction. Moreover, it was identified that in addition to the reduction in the azo groups, SDT causes partial cleavage of the aryl ether bonds. The found features of SDT should be taken into account when SDT is used as an azoreductase mimic.
Highlights
The main cellular energy processes that occur in the mitochondria depend on the normal concentration of oxygen in the tissues [1,2]
The sulfonate aromatic derivatives are capable of more intense electrostatic interactions compared with the carboxylate ones
In addition to the known anionic tetra-azo calixarenes with azo fragments on the upper rim, a bis-azo adduct of calixarene in the cone configuration with azo fragments on the lower rim was synthesized for the first time
Summary
The main cellular energy processes that occur in the mitochondria depend on the normal concentration of oxygen in the tissues [1,2]. The phenomenon of hypoxia accompanies the development of many pathological conditions in the human body but is an important and characteristic manifestation of most large tumors, which is explained by an imbalance in oxygen consumption in normal and tumor cells due to changes in the tumor vasculature [3,4]. Hypoxia is an important indicator of aggressive tumors. A rapid visualization of hypoxia is one of the most important steps in the early diagnosis of various natural tumors. Systems that respond to hypoxia can be used for imaging and for selective drug delivery and the effective treatment of tumors [5,6]. Methods for hypoxia visualization are based on the “covalent”
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