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Supramolecular analytical chemistry has emerged as a new discipline at the interface of supramolecular and analytical chemistry. It focuses on analytical applications of molecular recognition and self-assembly. One of the important outcomes of the supramolecular analytical chemistry is the understanding of molecular aspects of sensor design, synthesis and binding studies of sensors while using rigorous methods of analytical chemistry as a touchstone to verify the viability of the supramolecular aspects of the sensor design. This critical review provides a simplified version of the chemometric procedures involved in realizing a successful analytical experiment that utilizes cross-reactive optical sensor arrays, and summarizes the current research in this field. This review also shows several examples of use of described chemometric methods for evaluation of chemosensors and sensor arrays. Thus, this review is aimed mostly at the readers who want to test their newly-developed chemosensors in cross-reactive arrays (169 references).

The focus of this study was to demonstrate that, in the luminescent sensors, the signal transduction may possibly be the most important part in the sensing process. Rational design of fluorescent sensor arrays for cations utilizing extended conjugated chromophores attached to 8-hydroxyquinoline is reported. All of the optical sensors utilized in the arrays comprise the same 8-hydroxyquinoline (8-HQ) receptor and various conjugated chromophores to yield a different response to various metal cations. This is because the conjugated chromophores attached to the receptor are partially quenched in their resting state, and upon the cation coordination by the 8-HQ, the resulting metalloquinolinolate complex displays a change in fluorescence. A delicate balance of conjugation, fluorescence enhancement, energy transfer, and a heavy metal quenching effect results in a fingerprint-like pattern of responses for each sensor-cation complex. Principal component analysis (PCA) and linear discriminant analysis (LDA) are used to demonstrate the contribution of individual sensors within the array, information that may be used to design sensor arrays with the smallest number of sensor elements. This approach allows discriminating between 10 cations by as few as two or even one sensor element. Examples of arrays comprising various numbers of sensor elements and their utility in qualitative identification of Ca(2+), Mg(2+), Cd(2+), Hg(2+), Co(2+), Zn(2+), Cu(2+), Ni(2+), Al(3+), and Ga(3+) ions are presented. A two-member array was found to identify 11 analytes with 100% accuracy. Also the best two of the sensors were tested alone and both were found to be able to discriminate among the samples with 99% and 96% accuracy, respectively. To illustrate the utility of this approach to a real-world application, identification of enhanced soft drinks based on their Ca(2+), Mg(2+), and Zn(2+) cation content was performed. The same approach to reducing array elements was used to construct three- and two-member arrays capable of identifying these complex analytes with 100% accuracy.

The use of the 3,4-difluoro-1H-pyrrole as a building block for the preparation of octamethyloctafluorocalix[4]pyrrole and 2,3-di(3‘,4‘-difluoropyrrol-2‘yl)quinoxaline is described. These latter two entities act as neutral anion receptors and were found to bind anions such as fluoride, chloride, or dihydrogen phosphate with an enhanced affinity compared to their non-fluorinated congeners as judged from 1H NMR, 19F NMR, and fluorescence emission spectroscopic analyses. The increase in affinity was especially high in case of chloride and dihydrogen phosphate anion, with the 2,3-di(3‘,4‘-difluoropyrrol-2‘-yl)quinoxaline system, in particular, displaying an affinity for H2PO4 - that was improved by 3 orders of magnitude as compared to its non-fluorinated congener. This improvement in the affinity for the dihydrogen phosphate is accompanied by change of color from pale yellow to orange, thus allowing the use of such compounds as naked-eye sensors for phosphate anion. In the case of the octafluorocalix[4]pyrrole system X-ray diffraction analyses revealed the presence of four different macrocyclic conformations in the solid state, as well as close intermolecular contacts mediated by apparent CF- -HN hydrogen bonds.

A new Ru(II) complex is described which serves as a luminescence lifetime-based sensor for fluoride and cyanide anions (KF = 640 000 mol-1, KCN = 430 000 mol-1). This chromophore displays observable changes in its UV-vis and steady-state luminescence spectra upon cyanide binding. Prior to cyanide addition, this complex exhibits a single-exponential lifetime (tau = 377 +/- 20 ns). With increasing cyanide concentrations, the intensity decays are composed of two exponentials: long tau (320-370 ns) and short tau (13-17 ns). The average lifetimes shorten as a function of cyanide concentration since the fractional intensity shifts from an initial dominant long lifetime component to the short lifetime component. This work represents the first example of a direct method for the luminescence lifetime-based sensing of anions.