Anion Sensing by Fluorescent Expanded Calixpyrroles.

Expanded calixpyrrole-type macrocycles, calix[2]benzo[4]pyrroles, bearing fluorescent moieties attached via conjugated vinyl spacers, have been synthesized from the corresponding formyl derivatives through Knoevenagel condensation. The anion-binding properties of the resulting fluorescent macrocycles have been studied by means of NMR, UV/Vis, and fluorescence spectroscopies. Our main focus has been on dicarboxylates matching the size of the binding cavity of the calix[2]benzo[4]pyrrole skeleton. The observed anion-binding properties were compared with those of the regular calix[4]pyrroles bearing identical fluorophores. Surprisingly, the parent calix[4]pyrroles appear to be equally efficient, if not more so, for sensing anions such as dicarboxylates. Affinity constants determined for various anions and dianions show the sensors S1-S5 to be highly cross-reactive. The cross-reactivity of the sensors was utilized in a microchip-based array, which showed perfect (100 %) classification of 18 analytes utilizing only five sensors. Finally, the same array was used to quantitatively analyze dicarboxylates such as oxalate and malonate. The data from the array were subjected to linear regression, allowing the determination of various concentrations of dianions with low error (<2 %).

Enhancing the Visible-Light Absorption and Excited-State Properties of Cu(I) MLCT Excited States.

A computationally inspired Cu(I) metal-to-ligand charge transfer (MLCT) chromophore, [Cu(sbmpep)2]+ (sbmpep = 2,9-di(sec-butyl)-3,8-dimethyl-4,7-di(phenylethynyl)-1,10-phenanthroline), was synthesized in seven total steps, prepared from either dichloro- or dibromophenanthroline precursors. Complete synthesis, structural characterization, and electrochemistry, in addition to static and dynamic photophysical properties of [Cu(sbmpep)2]+, are reported on all relevant time scales. UV-Vis absorption spectroscopy revealed significant increases in oscillator strength along with a concomitant bathochromic shift in the MLCT absorption bands with respect to structurally related model complexes (ε = 16 500 M-1 cm-1 at 491 nm). Strong red photoluminescence (Φ = 2.7%, λmax = 687 nm) was observed from [Cu(sbmpep)2]+, which featured an average excited-state lifetime of 1.4 µs in deaerated dichloromethane. Cyclic and differential pulse voltammetry revealed ∼300 mV positive shifts in the measured one-electron reversible reduction and oxidation waves in relation to a Cu(I) model complex possessing identical structural elements without the π-conjugated 4,7-substituents. The excited-state redox potential of [Cu(sbmpep)2]+ was estimated to be -1.36 V, a notably powerful reductant for driving photoredox chemistry. The combination of conventional and ultrafast transient  absorption and luminescence spectroscopy successfully map the excited-state dynamics of [Cu(sbmpep)2]+ from initial photoexcitation to the formation of the lowest-energy MLCT excited state and ultimately its relaxation to the ground state. This newly conceived molecule appears poised for photosensitization reactions involving energy and electron-transfer processes relevant to photochemical upconversion, photoredox catalysis, and solar fuels photochemistry.

Photoinduced structural distortions and singlet-triplet intersystem crossing in Cu(i) MLCT excited states monitored by optically gated fluorescence spectroscopy.

Copper(i) phenanthroline complexes represent viable earth-abundant alternatives to the ubiquitous Ru(ii) tris-bipyridine photosensitizers owing to their similar metal-to-ligand charge transfer (MLCT) properties. A well-established complication of Cu(i) phenanthroline complexes is that they can undergo significant photo-induced structural rearrangements, leading to excited states that are highly susceptible to exciplex formation and short-lived. In this work, a comprehensive analysis of the photo-induced structural distortions and singlet-triplet intersystem crossing dynamics of a series of four sterically encumbered Cu(i) phenanthroline chromophores has been conducted, namely, [Cu(dsbp)2]+ (dsbp = 2,9-di-sec-butyl-1,10-phenanthroline), [Cu(dsbtmp)2]+ (dsbtmp = 2,9-di-sec-butyl-3,4,7,8-tetramethyl-1,10-phenanthroline), [Cu(dipp)2]+ (dipp = 2,9-di-isopropyl-1,10-phenanthroline), and [Cu(diptmp)2]+ (diptmp = 2,9-di-isopropyl-3,4,7,8-tetramethyl-1,10-phenanthroline). Upconverted fluorescence decay kinetics were measured at wavelengths along the blue side of the photoluminescence spectrum. The experimental results displayed strong wavelength dependence of the singlet emission, with rapid sub-picosecond decay dominating at higher energies. At lower emission energies, increasing contribution of a longer decay component was revealed. This wavelength dependence is a signature of the excited state structural rearrangement of the phenanthroline ligands which concomitantly lower the excited state energy. The obtained time constants were in excellent agreement with those measured in the complementary ultrafast transient absorption experiments. The sub-picosecond component (prompt fluorescence) is associated with the photo-induced structural rearrangement that lowers the energy of the singlet excited state. The longer decay component represents the lifetime of the S1 excited state, and thus the time-scale of singlet-triplet intersystem crossing. Lastly, the observed dual emission was further characterized by constructing picosecond time-resolved emission spectra from the measured kinetic data. These qualitative luminescence spectra capture the resulting emission from both the S1 initial state and the S1 flattened state, providing further insight into the energy-lowering excited state distortion across the series.

Antibody- and Label-Free Phosphoprotein Sensor Device Based on an Organic Transistor.

An antibody- and label-free detection of a phosphoprotein (α-casein) has been achieved using an organic field-effect transistor (OFET)-based sensor. The fabricated OFET device possesses an extended-gate electrode functionalized with an artificial phosphoprotein receptor (Zn(II)-dipicolylamine complex, Zn(II)-DPA). It is shown that the OFET responds to the molecular recognition processes involving the Zn(II)-DPA at the extended-gate electrode. The binding of α-casein to the receptor in a HEPES solution results in an analyte-specific changes of the drain current of the OFET. The successful demonstration of the antibody- and label-free detection using the OFET could pave the way to the development of low-cost, disposable, and portable electronic sensor devices.

Anion binding modes in meso-substituted hexapyrrolic calix[4]pyrrole isomers.

We report on the synthesis of a new receptor for anions, meso-substituted hexapyrrolic calix[4]pyrrole 1. The calix[4]pyrrole's core features two additional pyrrole side-arms suspended above or below the calix[4]pyrrole core. This hexapyrrolic calix[4]pyrrole 1 is formed as cis- and trans-configurational isomers, the structures of which have been determined by single crystal X-ray diffraction. The anion binding experiments revealed interesting difference in the binding mode: The cis-1 isomer binds anions in a mixed binding mode featuring a combination of hydrogen bonding and anion-π interactions resulting in an unexpected strong binding. On the other hand, the trans-1 isomer displays only hydrogen bonding and lower affinity for anions. This is unexpected as one would assume both isomers to display the same binding modes. Overall, the titrations of 1 using UV spectrophotometry and NMR titrations by anions reveal that cis-isomer 1 displays higher affinity (10(5)-10(6) M(-1)) and cross-reactivity for anions, while the trans-isomer 1 shows a more selective response to anions. Such differences in binding mode in configurational isomers are so far unexplored and a feature deserving further study.

Intramolecular indicator displacement assay for anions: supramolecular sensor for glyphosate.

One of the well-known strategies for anion sensing is an indicator (dye) displacement assay. However, the disadvantage of the dye displacement assays is the low sensitivity due to the excess of the dye used. To overcome this setback, we have developed an "Intramolecular Indicator Displacement Assay (IIDA)". The IIDAs comprise a receptor and a spacer with an attached anionic chromophore in a single-molecule assembly. In the resting state, the environment-sensitive anionic chromophore is bound by the receptor, while the anionic substrate competes for binding into the receptor. The photophysical properties of the dye exhibit change in fluorescence when displaced by anions, which results in cross-reactive response. To illustrate the concept, we have prepared IID sensors 1 and 2. Here, the characterization of sensors and microtiter arrays comprising the IIDA are reported. The microtiter array including IID sensors 1 and 2 is capable of recognizing biological phosphates in water. The utility of the IIDA approach is demonstrated on sensing of a phosphonate herbicide glyphosate and other biologically important anions such as pyrophosphate in the presence of interferent sodium chloride.

Corrosion by Polythionic Acid in the Oil and Gas Sector: A Brief Overview.

Polythionic acid (PTA) corrosion is a significant challenge in the refinery industry, leading to equipment degradation, safety risks, and costly maintenance. This paper comprehensively investigates the origin, progression, mechanism, and impact of PTA corrosion on various components within refinery operations. Special attention is afforded to the susceptibility of austenitic stainless steels and nickel-based alloys to PTA corrosion and the key factors influencing its occurrence. Practical strategies and methods for mitigating and preventing PTA corrosion are also explored. This paper underscores the importance of understanding PTA corrosion and implementing proactive measures to safeguard the integrity and efficiency of refinery infrastructure.

Effect of Aluminosilicates' Particle Size Distribution on the Microstructural and Mechanical Properties of Metakaolinite-Based Geopolymers.

The present study focused on investigating the differences in properties between calcined and milled aluminosilicates with different particle size distributions. Two types of clay, i.e., kaolin and kaolinitic claystone, were subjected to calcination at 750 °C, and subsequent milling to obtain different fractions with distinct particle size distributions. These fractions were then combined with a potassium alkaline activator and quartz sand in a 50:50 weight ratio to form a geopolymer composite. The geopolymer binders were then characterized using a mercury intrusion porosimeter (MIP), scanning electron microscopy (SEM), and a rotary rheometer. Mechanical tests were conducted on the geopolymer composites prepared from aluminosilicates with varying particle size distributions. The findings indicated that aluminosilicates with a finer particle size distribution exhibited higher levels of dissolved aluminum (10,000 mg/kg) compared to samples with coarser particle size distributions (1000 mg/kg). Additionally, as the particle size distribution decreased, the dynamic viscosity of the geopolymer binders increased, while the average pore size decreased. Finally, the mechanical properties of the geopolymer composites derived from both tested aluminosilicates demonstrated a decline in performance as the mean particle size increased beyond 10 µm.

Iptycene-based fluorescent sensors for nitroaromatics and TNT.

Small-molecule fluorescent sensors (1-5) for the recognition of nitroaromatic compounds, such as 2,4-dinitrotoluene and the explosive TNT, were obtained by using a three-step dehydrohalogenation cycloaddition protocol. The interaction of the receptors and nitroaromatics was studied both in solution and in the solid state by using fluorescence spectroscopy and X-ray crystallography, respectively. It is shown that the iptycene receptors 1-5 provide a cavity suitable for binding nitroaromatic compounds in an edge-to-face mode, rather than simple ring-stacking interactions. The results obtained inspired us to develop an inexpensive, reliable and robust sensor for vapour detection of explosives. Polymer nanofibres are particularly suitable for the production of such TNT sensors as they accelerate the mass exchange between the polymer and the vapours of TNT. Quenching of the sensors took place within 1 min compared to 10 min for a glass-slide assay. Hence, the sensor performance can be improved by optimising the matrix material and morphology without resynthesising the sensor moieties.

Effect of Different Types of Aluminosilicates on the Thermo-Mechanical Properties of Metakaolinite-Based Geopolymer Composites.

In this study, the effect of different types of aluminosilicates on the thermo-mechanical properties of metakaolinite-based geopolymer binders and composites was examined. The metakaolinite-based geopolymer binders and composites were produced from three different types of aluminosilicates (one metakaolin and two calcined claystones) and a potassium alkaline activator. Chamotte was added as a filler, amounting to 65% by volume, to create geopolymer composites. Geopolymer binders were characterized by X-ray diffraction, rotary rheometer and scanning electron microscopy. The mechanical properties, thermal dilatation and thermal conductivity were investigated on geopolymer composites with three different aluminosilicates before and after exposure to high temperatures (up to 1200 °C). The results showed that the geopolymer binders prepared from calcined claystones had a lower dynamic viscosity (787 and 588 mPa·s) compared to the geopolymer binders prepared from metakaolin (1090 mPa·s). Geopolymer composites based on metakaolin had lower shrinkage (0.6%) and higher refractoriness (1520 °C) than geopolymers from calcined claystones (0.9% and 1.5%, 1500 °C and 1470 °C). Geopolymers based on calcined kaolinitic claystones are a promising material with higher compressive (95.2 and 71.5 MPa) and flexural strength (12.4 and 10.7 MPa) compared to geopolymers based on metakaolin (compressive strength 57.7 MPa).

Effect of K/Al Molar Ratio on the Thermo-Mechanical Properties of Metakaolinite-Based Geopolymer Composites.

A metakaolinite-based geopolymer binder was prepared by using calcined claystone as the main raw material and potassium as the alkaline activator. Chamotte was added (65 vol%) to form geopolymer composites. Potassium hydroxide (KOH) was used to adjust the molar ratio of K/Al and the effect of K/Al on thermo-mechanical properties of geopolymer composites was investigated. This study aimed to analyze the effect of K/Al ratio and exposure to high temperatures (up to 1200 °C) on the compressive and flexural strengths, phase composition, pore size distribution, and thermal dilatation. With an increasing K/Al ratio, the crystallization temperature of the new phases (leucite and kalsilite) decreased. Increasing content of K/Al led to a decline in the onset temperature of the major shrinkage. The average pore size slightly increased with increasing K/Al ratio at laboratory temperature. Mechanical properties of geopolymer composites showed degradation with the increase of the K/Al ratio. The exception was the local maximum at a K/Al ratio equal to one. The results showed that the compressive strength decreases with increasing temperature. For thermal applications above 600 °C, it is better to use samples with lower K/Al ratios (0.55 or 0.70).

Effect of Filler Type on the Thermo-Mechanical Properties of Metakaolinite-Based Geopolymer Composites.

Metakaolinite-based geopolymer binder was prepared at room temperature by mixing calcined claystone and potassium alkaline activator. Various granular inorganic fillers were added, amounting to 65 vol % to form geopolymer composites. The effect of four types of fillers (sand quartz, chamotte, cordierite, and corundum) on the thermo-mechanical properties of metakaolinite-based geopolymer composites were investigated. The samples were also examined by an X-ray diffraction method to determine their phase composition. The pore size distributions were determined by a mercury intrusion porosimeter. The XRD revealed the crystallization of new phase (leucite) after thermal exposure at 1000 °C and higher. Geopolymer binders had low mechanical properties (flexural strength 2.5 MPa and compressive strength 45 MPa) and poor thermo-mechanical properties (especially high shrinkage-total shrinkage 9%) compared to geopolymer composites (flexural strength up to 13.8 MPa, compressive strength up to 95 MPa and total shrinkage up to 1%). The addition of fillers reduced the shrinkage of geopolymers and improved their mechanical properties. The results have shown that the compressive strength tested in situ and after exposure to high temperature are in conflict. Geopolymer composites with the addition of chamotte had the best mechanical properties before and after thermal exposure (compressive strength up to 95 MPa). The average pore size diameters increased with the increasing temperature (from 10 nm to approx. 700 nm). The fillers addition decreased the pore volume (from 250 mm3/g to approx. 100 mm3/g).

Rigid duplex alpha-cyclodextrin reversibly connected with disulfide bonds. Synthesis and inclusion complexes.

The rigid duplex cyclodextrin 6 composed of two alpha-cyclodextrin macrocycles connected with two disulfide bonds in "transannular" (C6(I), C6(IV)) positions was prepared from partially debenzylated alpha-cyclodextrin 1 in four steps in 73% overall yield. In the last key step involving oxidative coupling of the thiol 5, predominance of the target duplex 6 can be attained under conditions of thermodynamic control. The structure of duplex cyclodextrin was established by MS as well as 2-D NMR methods and confirmed by a single-crystal X-ray analysis. The ability of the duplex cyclodextrin 6 to bind alpha,omega-alkanediols (C9-C14) and 1-alkanols (C9 and C10) was studied by isothermal titration calorimetry in aqueous solutions. The stability constants of the complexes gradually increase with the alkyl chain length and reach an unprecedently high value of K = 8.6 x 10(9) M(-1) for 1,14-tetradecanediol. It was found that the doubly bridged dimer 6 exhibits higher binding affinity toward the series of alpha,omega-alkanediols than the singly bridged analogue 10 by about 2 orders of magnitude in K (M(-1)) or 3.1-3.3 kcal/mol in deltaG(o), the enhancement being due to enthalpic factors. Theoretical calculations using DFT-D methods suggest that the enthalpic contribution stems from dispersion interactions.

A mercury(II) ion sensor device based on an organic field effect transistor with an extended-gate modified by dipicolylamine.

Herein, we report an organic field effect transistor (OFET) with an extended-gate modified by an artificial receptor for the detection of mercury(II) ions (Hg(2+)) in water. The sensor device is easy to fabricate, reusable, disposable, and portable. Thus OFET sensors could be applied for low-cost on-site detection of Hg(2+).