Does the Red Shift in UV-Vis Spectra Really Provide a Sensing Option for Detection of -Nitrosamines Using Metalloporphyrins?

-nitrosamines are widespread cancerogenic compounds in human environment, including water, tobacco products, food, and medicinal products. Their presence in pharmaceuticals has recently led to several recalls of important medicines from the market, and strict controls and tight limits of -nitrosamines are now required. Analytical determination of -nitrosamines is expensive, laborious, and time-inefficient making development of simpler and faster techniques for their detection crucial. Several reports published in the previous decade have demonstrated that cobalt porphyrin-based chemosensors selectively bind -nitrosamines, which produces a red shift of characteristic Soret band in UV-Vis spectra. In this study, a thorough re-evaluation of metalloporphyrin/-nitrosamine adducts was performed using various characterization methods. Herein, we demonstrate that while -nitrosamines can interact directly with cobalt-based porphyrin complexes, the red shift in UV-Vis spectra is not selectively assured and might also result from the interaction between impurities in -nitrosamines and porphyrin skeleton or interaction of other functional groups within the -nitrosamine structure and the metal ion within the porphyrin. We show that pyridine nitrogen is the interacting atom in tobacco-specific -nitrosamines (TSNAs), as pyridine itself is an active ligand and not the -nitrosamine moiety. When using Co(II) porphyrins as chemosensors, acidic and basic impurities in dialkyl -nitrosamines (e.g., formic acid, dimethylamine) are also UV-Vis spectra red shift-producing species. Treatment of these -nitrosamines with KCO prevents the observed UV-Vis phenomena. These results imply that cobalt-based metalloporphyrins cannot be considered as selective chemosensors for UV-Vis detection of -nitrosamine moiety-containing species. Therefore, special caution in interpretation of UV-Vis red shift for chemical sensors is suggested.