Molecular recognition of biological systems using calixarene monolayers

Concept A new monolayer of 5-pyrenoylamido-calix[5]arene, bearing a 12 aminododecyl moiety (PyC5-NH2) at a lower rim, was covalently bounded to a quartz silylated substrate [1]. The surface chemical characterization of this hybrid material was carried out by X-ray photoelectron spectroscopy. Is it well known the ability of calixarenes to recognize and host molecules of biological interest. In this context, cation- interactions play a vital function in the recognition of positively charged guests by electron-rich hosts. Here, the sensing properties of the PyC5-NH2 system were probed by luminescence measurements. This system demonstrates to have significant recognition properties for linear alkylammonium ions at ppm levels. The adopted synthetic procedure provided evidence useful in transferring molecular properties to a solid state device. Motivations and Objectives The ease of functionalization, both at lower and upper rim, and the ability to provide rigid and -rich cavities for the selective inclusions of suitable cations have made calixarenes attractive building blocks for the construction of functional nanostructures useful in the sensing field [2]. In this context we developed a pyrene-substituted calix[5]arene covalently bounded to a quartz substrate and studied its capability to detect amines. This model study may provide the basis for applications in the biochemical and environmental fields. Results and Discussion Solution sensing experiments using PyC5-NH2 in presence of alkylammonium ions as n-Bu-HCl, C12NH2-HCl, DBA-HCl, GABA-HCl, cadaverine-2HCl or -Ahx-HCl analytes showed a pronounced luminescence increase upon adding of n-Bu-HCL (red line), C12NH2-HCl (green line) or cadaverine-HCl (blue line) (Fig. 1). Sensing experiments toward the model C12NH2-HCl analyte were performed using the PyC5-NH2 self-assembled monolayer. The observed luminescence spectra are qualitatively similar to those reported in Figure 1. In fact, it is possible to note the increase of luminescence intensity of the PyC5-NH2 self-assembled monolayer after immersion into C12NH2-HCl solutions in the 10-200 ppm range (Fig. 2).