Elucidation of the structure is a central problem in the study of natural and synthesized products, since enantiomers, due to their different spatial orientation, can exhibit markedly varying biological and pharmacological properties. Circular dichroism is a widely used tool for determination of spatial structure of molecules. This method is based on different absorption of left- and right-handed light by chiral molecules. However, CD spectra can be measured only if the molecule has both electric and magnetic transition moments. Organic molecules often do not have magnetic transition moment, and their CD spectra are silent. In this case, CD spectra can still be measured using chirality transfer or induced chirality (ICD). Intrinsically achiral metalloporphyrins are able to exhibit optical activity by inducing circular dichroism (CD) signal by axial coordination of a chiral guest. Due to a unique set of physicochemical properties metalloporphyrins are often used as a key element in chemical sensors [1]. Besides detection of small molecules in gas phase and in solution [2], the porphyrin-based supramolecular systems have found a wide application as various chirality probes [3,4]. On the example of mono- and bis-metalloporphyrins ICD spectra will be rationalized based on TD-DFT approach. Will be shown how significant is an influence of a guest conformation on a CD profile of mono-porphyrins. Will be discussed synergy between axial ligation and peripheral substitution. Will be considered how distortion of porphyrin unit is reflected on CD spectra of mono- and bis-porphyrin complexes. Will be shown how critical it is for CD spectra simulations to determine the relative position of porphyrin subunits in bis-porphyrin complexes.

References:
[1] Paolesse R, Nardis S, Monti D, Stefanelli M, Di Natale C. Chem. Rev. 2017; 117: 2517–2583.
[2] D’Amico A, Di Natale C, Paolesse R, Macagnano A, Mantini A. Sens. Actuator B-Chem. 2000; 65: 209–215.
[3] Hembury GA, Borovkov VV, Inoue Y. Chem. Rev. 2008; 108: 1–73.
[4] Borovkov V, Symmetry 2014; 6: 256–294.

A well-known fluorophore molecule pyrene was encapsulated into a stable metal organic framework by in situ encapsulation method. The existing metal-organic framework (MOF) called UiO-66 (UiO = University of Oslo) was served as host material for pyrene fluorophore. The fluorescence of pyrene was quenched after encapsulation inside the porous host. Recovery of quenched fluorescence was accomplished by anion induced host dissolution followed by release of fluorophore molecule. Using this anion induced dissolution; a selective sensing of fluoride anion in pure aqueous was achieved. It showed a fast response time, excellent selectivity and sensitivity for sensing of fluoride anion via fluorescence ‘turn-on’ mechanism. The excellent detection performance of this method in aqueous medium makes it a promising method for real-field water monitoring utilizing MOF material.

Electronic tongues (ETs) have attracted considerable interest due to their capability to discriminate and analyse foods and beverages and to their potential to contribute to quality management. ETs are based on sensor arrays with low selectivity and high cross-selectivity combined with statistical tools that analyse the outputs from multiple sensors. Compared to other analytical methodologies, this type of device has interesting practical characteristics such as possible online application, no need for pretreatment of samples, and the capability to assess several chemical compounds in a single analysis. The aim of this work was to construct an all-solid-state potentiometric e-tongue with an array of sensors based on polymeric membranes, to be applied in the dairy industry.

In order to obtain an array of sensors with improved sensitivity, the membranes have been modified with gold nanoparticles. In addition, enzymes as galactose oxidase, urease and lactate dehydrogenase have been covalent bonded to the PVC surface to increase the selectivity of the sensor.

The responses of the sensors towards standard solutions indicate that sensors modified with gold nanoparticles and covalently associated enzymes showed a greater ability to differentiate between increasing concentrations of products of interest found in milk (urea, lactic acid, galactose, etc.) Moreover, the electronic tongue developed was able to perform the discrimination of milk with different nutritional characteristics using statistical analysis (PCA) showing as a result five differentiated groups, which were also ordered according to the fat content of the samples. In addition, the results of the study showed that the electronic tongue developed could be used as a prediction system for different chemical parameters, such as pH, acidity, protein or fat, of future milk samples by applying partial least squares analysis with regression coefficients above 0.90 for two variables in the parameters studied.

The integration of silver nanomaterials as electron mediators in electrochemical biosensors has proven to be an efficient strategy to promote the electron transfer from the active site of the enzyme to the electrode due to their high surface-to-volume ratio and high conductivity [1]. Silver nanomaterials can be found in a variety of shapes and sizes, and the appropriate selection can be crucial to improve the affinity with biomolecules and the electrochemical response. In this work, two voltametric bioelectronic tongues (bioET) formed by biosensors based on the combination of enzymes with silver nanoparticles (AgNPs) (bioET-1) or silver nanowires (AgNWs) (bioET-2) have been developed and used to analyze milks. Each array was formed by six biosensors formed by enzymes (glucose oxidase, galactose oxidase, lactate dehydrogenase, β-galactosidase, urease and a blank), capable to detect compounds usually found in milks. Principal component analysis (PCA) has revealed the ability of both biosensor systems to discriminate between milk samples with different fat contents, but with some differences, attributed to the structure employed in the detection. The method developed is simple, and the short response time permits its use in assaying milk samples online.

Membrane proteins that participate in multiple vital functions of every living organism such as transport, signaling and respiration, provide 80 to 90% of the relevant targets for the pharmaceutical industries. The family of cytochrome bd oxidase enzymes is of large interest for the development of future antibiotics as they were found only in the respiratory chain of the prokaryotes and they are believed to be involved in bacterial adaptability mechanisms. They catalyze the reduction of molecular oxygen in water and oxidation of quinols and contribute to the proton motive force required for ATP synthesis. Due to their hydrophobic nature, membrane proteins are more difficult to handle than soluble proteins. Protein film voltammetry is a very convenient technique, because it allows working at a very low concentration and optimize the electrode surface to the nature of the enzyme. Here, we have developed a biosensor for the study of terminal oxidases based on their immobilization on gold nanoparticles modified with a self-assembled monolayer of thiols. The stability of the protein films can be optimized by varying the nature of thiols and amount of lipids.

This enzyme-based electrochemical sensor was successfully used for the inhibition screening of a target-focused library of 34 compounds which belong to the families of quinones, naphthoquinones, phenols, quinolones, coumarins and flavonoids against cytochrome bd oxidase. Moreover, the developed device was applied for the study of the catalytic reaction of the enzyme with small gaseous signaling molecules.

The present study investigated the effect of malaxation times (Mt: 0, 15, 30, 45 and 60 min), during the industrial extraction of cv. Arbequina oils at 25 ºC on total phenolic content and bitterness index of olive pastes. Additionally, the possibility of applying a lab-made potentiometric electronic tongue (E-tongue), comprising 40 lipid/polymer sensor membranes with cross sensitivity, to discriminate the olive pastes according to the Mt, was evaluated. The results pointed out that the olive pastes’ total phenolic contents significantly decreased (P-value < 0.001, one-way ANOVA) with the increase of the Mt (from 2.21±0.02 to 1.99±0.03 g GAE/kg olive paste), being observed a linear decreasing trend (R-Pearson = -0.910). Similarly, the bitterness index also decreased with the Mt (23.4±0.3 to 21.9±0.4 oleuropein/kg olive paste). These findings may be tentatively attributed to the migration of the phenolic compounds from the olive pastes to the extracted oil and water phases, during the malaxation process. Finally, the E-tongue signals, acquired during the analysis of the olive pastes’ methanolic extracts (methanol:water, 80:20 v/v), together with a linear discriminant analysis (LDA), coupled with a simulated annealing (SA) algorithm, allowed to establish a successful classification model. The E-tongue-LDA-SA model, based on 11 selected non-redundant sensors, allowed to correctly discriminate all the studied olive pastes according to the Mt (sensitivities of 100% for training and leave-one-out cross-validation). The satisfactory performance of E-tongue could be tentatively explained by the known capability of lipid/polymeric sensor membranes to interact with phenolic compounds, through electrostatic interactions and/or hydrogen bonds, which total content depended on the Mt.

The present work elucidates, for the first time, the electrochemical behavior of some of the most relevant endocrine-disrupting phenols using unmodified carbon screen-printed electrodes (SPEs). The electrochemical reversibility and mass-transport mechanism of phenol (PHOH), pentachlorophenol (PCP), 4-tert octylphenol (OP) and bisphenol A (BPA) were studied with cyclic voltammetry (CV) and linear sweep voltammetry (LSV), respectively. Subsequently, the electrochemical oxidation of the aforementioned phenols is revealed for the entire pH range (from 2 to 12) using a Britton Robinson (BR) buffer via square wave voltammetry (SWV). Furthermore, the stability of the redox behavior of the four different phenols is investigated at their optimal pH (pH=12) over time. Calibration curves exhibit a linear range between 5 and 50 µM with excellent peak potential (E_p) and peak current (I_p) reproducibility (RSD_PHOH E_p = 0.69% and RSD_PHOH I_p = 2.36%, RSD_PCP E_p = 0.49% and RSD_PCP I_p = 4.14%, RSD_OP E_p = 1.55% and RSD_OP I_p = 8.38%, and RSD_BPA E_p = 1.15% and RSD_BPA I_p = 0.31% at 10 µM, N=3) and limits of detection (LOD) of LOD_PHOH = 0.93 ± 0.02 µM, LOD_PCP = 0.92 ± 0.09 µM, LOD_OP = 0.33 ± 0.03 µM and LOD_BPA = 0.18 ± 0.01 µM. Afterwards, binary and complex mixtures of phenols were effectively analyzed in the BR buffer (pH 12) using SWV to investigate their electrochemical fingerprint. Finally, the approach was validated with real samples from a local river and compared with lab-bench standard method (high-performance liquid chromatography with a photodiode array detector (HPLC-DAD)).

Perfluoroalkylcarboxylic acids (PFCAs) have been produced in large quantities in industry around the world. Multiple C–F bonds on the alkyl chain allows them to exhibit high stability, high temperature resistance, and water and oil repellency. However, these properties also enhance their environmental persistence to result in bioaccumulation and biomagnification.^[1,2] With this reason, a convenient method to detect PFCAs in high sensitivity may play an important role to prevent the spread of environmental pollution. In this study, we newly designed a pyridine-bridged bispyrrole having N-fluoroalkyl imino groups (BPFI) that specifically serve as color and spectroscopic indicators of PFCAs.

We have synthesized BPFI from a pyridine-bridged bispyrrole having two formyl groups, which was synthesized through multi-step procedures, and 1H,1H-perfluorooctylamine. The product was characterized by means of NMR spectroscopy and mass spectrometry. In the UV-Vis absorption spectroscopy, BPFI showed the lowest energy absorption band at λ_max= 330 nm in CH₃CN. Although it showed no changes in color and spectrum upon mixing with common carboxylic acids such as acetic acid, and trichloroacetic acid, red-shift of the absorption band occurred upon mixing with PFCAs such as perfluoroheptanoic acid and heptadecafluoronanoic acid. BPFI also showed fluorescence with λ_max at 432 nm upon excitation at 320 nm. Its fluorescence intensity was slightly decreased upon mixing with the common carboxylic acids, but was dramatically decreased upon mixing with PFCAs. Further, color of the emission upon excitation at 365 nm with a commercially available handy UV light was specifically changed from blue to green upon mixing with PFCAs. We expect that BPFI will be a convenient reagent to detect PFCAs.

[1] S. Taniyasu, N. Yamashita, E. Yamazaki , G. Petrick, K. Kannan, Chemosphere, 2013, 90, 1686–1692.

[2] T. Stahl1, D. Mattern, H. Brunn, Environ. Sci. Eur. 2011, 23, 38.

Organic semiconductors can be used as highly sensitive fluorescent sensors for the detection of nitroaromatic explosives such as TNT. When trace-level vapours of explosives encounter an organic fluorescent sensor, molecules from the vapour are absorbed into the film and modify the light-emitting properties. Specifically, an electron is transferred from a photogenerated exciton in the sensor to a sorbed nitroaromatic molecule which results in fluorescence quenching and indicates the presence of explosives in the surrounding environment. The response to ppb levels of explosives is very rapid, however for many organic fluorescent sensors, the quenching of fluorescence is irreversible which make them single use sensors, and imposes a limitation in terms of reusability of the sensors. Here, we present a study of thermal desorption of 2,4-DNT from thin film explosives sensors made from the commercial fluorescent polymer, Super Yellow. Thermal cycling of the sensor results in recovery of fluorescence thereby making them reusable, and providing a route to confirm that fluorescence quenching arises from analyte response. To optimise the sensors performance in terms of reusability, Super Yellow sensors, and blend of Super Yellow/Poly carbazole (PVK) sensors were fabricated. The sensors were exposed to 2,4-DNT vapour in a custom-made chamber while monitoring their fluorescence, and then heated to an optimum desorption temperature to desorb the DNT molecules from the sensors. Finally, the improvement of the sensors made from the polymer blend, and the effect of temperature on the sensors is discussed. This method can be applied to other organic fluorescent sensors, removing the limitation of single use sensors.

Pathogen infections are among the main factors that threaten crop production and quality worldwide, being their early detection a step of paramount importance to efficiently manage plant pathologies. The methods currently employed for plant disease detection often require the presence of visible signs of the infection, which affects the efficacy of protection measures, since symptoms only appear later on. Hence, alternative methods based on proximal optical sensing (POS) have recently been investigated, introducing new perspectives in the phytopathology field. They rely on findings that interactions between host plants and pathogens induce changes in the biochemical and internal structure of leaves, causing modifications in their optical properties. Within this scope, a study carried out in a walk-in plant growth chamber, analyzed the potential of POS as an effective approach for early disease detection. A compact, modular sensing system, combining direct UV-Vis spectroscopy with optical fibers, supported by a robust Self-Learning Artificial Intelligence (SLAI), was applied to evaluate the modifications promoted by the bacteria Xanthomonas euvesicatoria (Xeu) in tomato leaves (cv. Cherry). Plant infection was achieved by spraying a bacterial suspension (10⁸ CFU mL⁻¹) until run-off occurred, and a similar approach was followed for the control group where only water was applied. A total of 270 spectral measurements – from 195 to 1100 nm – were performed on leaves, on five different time instances, including pre- and post-inoculation measurements. The acquired data from the assays performed, from both healthy and inoculated leaves, was then analyzed by an innovative SLAI, which allowed their distinction and differentiation. These results suggest that this in vivo, non-destructive POS technique may be promising for assessing changes in the spectral behavior of diseased crop leaves. Consequently, the present work encourages future usage and improvement of these optical devices, as well as its enhancement to perform diagnosis directly in the field.