Water-soluble Eu(III) and Tb(III) complexes with N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetic acid (Hbpcd) have been synthesized and characterized in their racemic and enantiopure forms. The ligand has been designed to bind Ln(III) ions, providing a dissymmetric environment able to solicit strong chiroptical features while at the same time leaving a few coordination sites available for engaging further ancillary ligands. Potentiometric studies show that Ln(III) complexes have a relatively good stability and that at pH 7 the [Ln(bpcd)] species is largely dominant. DFT calculations carried out on the (S,S)-[Y(bpcd)(HO)] complexes (the closed-shell equivalents of [Eu(bpcd)(HO)] and [Tb(bpcd)(HO)]) indicate that the two trans-O,O and trans-N,N configurations are equally stable in solution and present two coordinated water molecules. This is in agreement with the hydration number ∼2.6 determined by luminescence lifetime measurements on Tb(III) and Eu(III) complexes. A detailed optical and chiroptical spectroscopic characterization has been carried out and reveals that the complexes display an efficient luminescence in the visible spectral range accompanied by a strong CPL activity. A value for g (around 0.1 on the top of the 546 nm band) for the Tb-based complex has been found. This is one of the highest g values measured up to now for chiral Tb complexes. These results suggest that in principle Tb(bpcd)Cl is suitable to be employed as a CPL bioprobe for relevant analytes in aqueous media.

Lactate anion signaling by a chiral Tb(iii) complex based on total and circularly polarized luminescence.

The unprecedented affinity of Eu(bpcd)+ and Eu(bQcd)+ towards HCO3− renders these complexes as high-performing systems for the optical assessment of metabolic acidosis.

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1IntroductionThea nalysis of amino acids (AAs) is usually performed using techniques such as gas [1,2] and liquid [3,4] chromatography or capillary electrophoresis [5][6][7].T hough, the great demand of AA determinations in many important fields,s uch as clinicala nalysiso rf ood and pharmaceuticali ndustry [ 8,9],l eads to then eed of simpler and faster procedures,s uch as sensor-based methods.T hese electroanalyticala pproaches are reported as good methods for the analysis of specific AAs thankst ot he electroactivityp resented by aromaticand thiolg roups [8].Materials traditionally usedi nt he constructiono fs ensors for this kind of applications are carbon,p latinum and gold. But these materials are usually modified in order to increase the sensitivity and introducen ew features due to electrocatalytic activity, which leads to an increase in the range of detectable AAs [10].Theu se of metal oxide-modified sensors (MOS) has increasedd uring the last years duet oi ts great potential in the analysis of manye lectroactive substances [11,12] or even the detection of the presence of some bacteria in complex systems [13].M oreover, the recent availability of these materials in the form of nanopowder has facilitated enormously the possibility of using them as electrode modifiers.P otential of usingM OS materials has widened its scope especially by the use of semiconducting MOS arrays as gas sensors forming electronic noses (ENs). ENs have gained recognition in many fields like food, aromao rm edical diagnosis [ 14].T he large amount of data provided by ENs increases the sensitivity and selectivity of the method just by multivariate data processing, which avoids tedious derivatizationo ro ptimisation of the sensors for eacha nalyte [15,16].H owever,t he use of MOS is only ap ossible option to develop electronic noses and/or electronic tongues (ETs) [17].ETs have been used for more than ad ecade,a nd its use has grown considerably as they present al arge scope of applications,i ncluding environmental analysis, food industry and agriculture [18][19][20].D ue to the good performance of voltammetric techniques to analyze certain AAs, voltammetric ETs have already been presenteda s ag ood approach for their analysis,i nt his case for the ones with oxidizable properties,s uch as cysteine( CYS), tyrosine (TYR) and tryptophan (TRP) [21][22][23].An important weakness of voltammetric ETs residesi n the complexity of the response obtained, as there is an eed to process each voltammogram from eachs ensor. However, huge amounts of data derived from voltammetric analysis have usually been modelleds uccessfully by usingp rior compression which interprets and extracts meaningful data, offsets any matrix effecta nd may allow the resolution of interfering agents and drifts.T he most widely used multivariate data analysis techniques for voltammetric ETs are principal componenta nalysis,p artial least squares regression (PLS) and artificial neural networks (ANNs) [24][25][26].PLS represents the data in new coordinate axes, but in this ca...