A π‐Conjugated Porphyrin Complex as Cathode Material Allows Fast and Stable Energy Storage in Calcium Batteries

Rechargeable calcium batteries (RCB) are prospective candidates for sustainable energy storage, as they hold the promise of the high energy density of lithium-ion batteries (LIBs) while simultaneously combining it with highly abundant raw materials. However, for long time, calcium batteries have faced severe issues with regard to cycling stability, until recently developments demonstrated improved battery cycle life when employing CaSn alloy anodes with fluorinated alkoxyborate electrolytes. These findings opened up the possibility to study cathode materials for RCBs not only in a more comparable manner, but also in a practical full cell design. As representative of emerging organic electrode materials (OEMs), we investigated tetrakis(4-pyridyl) porphyrin as both free ligand (H$_2$TPyP) and in the form of its copper MOF complex (CuTPyP−MOF) as active cathode species in RCBs. The cells demonstrated high capacities and excellent cycling stability at the same time. Even at elevated current densities of e. g., 2000 mA/g the full cells delivered stable capacities of ~90 mAh/g proving its excellent rate capability. This study explores the electrochemical performance of porphyrin active materials in calcium batteries and represents a significant step forward in the progress toward organic electrodes for multivalent energy storage systems

Does the Mechanism of the Garratt–Braverman Cyclization Differ with Substrates? A Computational Study on Bispropargyl Sulfones, Sulfides, Ethers, Amines, and Methanes

We studied the variation in mechanism among different bispropargyl substratessulfone, sulfide, ether, amine, and methanetoward Garratt–Braverman (GB) cyclization using density functional theory calculations. Isomerization and cycloaddition are the key steps in the GB cyclization. To compare the reactivity among the various substrates, we computed the free energy of activation (Δ<i>G</i>^⧧) for the cycloaddition and the cyclization steps, whereas we used the theoretically computed p<i>K</i>_a values for the isomerization steps. Our results suggest that the sulfones undergo a relatively fast isomerization followed by slower cyclization, while the ethers undergo a slow isomerization followed by easy cyclization. The methanes and amines are similar to the ethers, and the sulfides showed intermediate behavior. We extended our study to unsymmetrical substrates and compare the results with experiments that suggest the isomerization to be the rate-limiting step for bispropargyl ethers, while cyclization through a diradical intermediate is crucial to the rate for the bispropargyl sulfones. On the basis of these findings, we made predictions on the selectivity of unsymmetrical bispropargyl sulfones, amines, methanes, and sulfides. This is the first detailed mechanistic study on the GB cyclization of bispropargyl substrates other than sulfones

A simple cleft shaped hydrazine-functionalized colorimetric new Schiff base chemoreceptor for selective detection of F− in organic solvent through PET signaling: Development of a chemoreceptor based sensor kit for detection of fluoride

Novel colorimetric hydrazine-functionalized Schiff base chemoreceptor [N1N3bis(perfluorobenzylidene)isophthalahydrazide] NBPBIH has been prepared for selective detection of F−. In this receptor more NH and CN units are incorporated for better colorimetric responses as compared to systems having lesser number of such units. NBPBIH turns from colorless to dark yellow on exposure to F−. The detection event is well supported by UV–vis, fluorescence, 1H and 19F-NMR like spectrophotometric and cyclic voltammetric studies in DMSO because of enhanced fluorescence responses, higher Stokes shift value and for its less toxic nature compared to other solvents. Quenching of fluorescence is explained with photoinduced electron transfer mechanism (PET). The binding constant of NBPBIH with F− is around 0.84 × 105 M−1 and limit of detection of F− is found 1.42 × 10−5 M. Our concern is also to address fluorosis: an issue related to global health problem, affecting millions of common people. It is noteworthy that the existing diagnostic and treatment options are of huge expenses. As an artefact, chemoreceptor assisted simple prototype for detecting excessive fluoride in sample solution has been designed and developed which has potential and good prospect to be applied as a low cost affordable diagnostic kit for fluorosis in largely affected countries like China, India and several others

Colorimetric and fluorimetric response of Schiff base molecules towards fluoride anions, solution test kit fabrication, logical interpretation and DFT-D3 study

Two newly synthesized Schiff base molecules are herein reported as anion sensors. –NO2 substituted receptor (P1) is comparatively more acidic and can sense F−, OAc− and H2PO4−, whereas –CN substituted receptor (P2) is less acidic and is selective for F− only. Reversible UV-Vis response for both receptors with F− can mimic multiple logic gate functions, and several complex electronic circuits based on XNOR, XOR, OR, AND, NOT and NOR logic operations with ‘Write–Read–Erase–Read’ options have been executed. Interesting ‘turn on and off’ fluorescence responses were noticed for the receptors with F−. Intracellular F− detection as a diagnosis of non-skeletal fluorosis was successful using a fluorescence microscope with Candida albicans (prokaryotic cell, a diploid fungus) and pollen grains of Tecoma stans (eukaryotic cell) incubated in 10−6 M fluoride-contaminated hand-pump water collected from Bankura, West Bengal, India. Furthermore, a solution test kit was fabricated for easy and selective detection of F− in an aqueous solvent

Separation/purification of ethylene from an acetylene/ethylene mixture in a pillared-layer porous metal–organic framework

Here we report the synthesis, structure and porous properties of a 3D pillared-layer porous framework of Mn(II)–Mn(III), {[Mn3(bipy)3(H2O)4][Mn(CN)6]2·2(bipy)·4H2O}n (1). The guest-removed framework (1a) shows significant uptake of C2H2, whereas it excludes the other two C2 hydrocarbons (C2H4 and C2H6). Furthermore, excellent separation proficiency for C2H2 from a mixture of C2H2 and C2H4 (1 : 99, v/v) is realized in a breakthrough column experiment under ambient conditions

Explosive and pollutant TNP detection by structurally flexible SOFs: DFT-D3, TD-DFT study and in vitro recognition

Explosive and Pollutant Nitro Aromatics (epNACs) like 2,4,6-trinitrophenol (TNP) has been detected from various surface water specimens by luminescent Schiff base Organic Frameworks (SOFs) by fluorometric method. Fluorescence intensity of the receptor SOFs have been quenched in presence of TNP due to RET and ICT, which has been confirmed through solid and solution level spectroscopic studies like FT-IR, 1H-NMR, fluorescence titration. Modern DFT (DFT-D3) calculations of the possible host guest conformers have been performed for exploration of plausible route of interaction between receptor and epNACs. The outcome of theoretical calculations is in line with experimental findings where TNP and receptor conformation mimic parallel displaced type π- π interaction. TD-DFT has been executed with both receptor and receptor ···TNP adduct, the fluorescence quenching is in line with experimental outcome. Limit of TNP detection has been found as low as 5 μM with 2.97×104 M-1 as binding constant. In real time stepping, TNP as mutagenic agent for aquatic life has been detected inside prokaryotic cells like candidia albicans in ppm level

A rationally designed thymidine-based self-assembled monolayer on a gold electrode for electroanalytical applications

A self-assembled monolayer (SAM) of 1-(3,5-epidithio-2,3,5-trideoxy-&#946;-D-threo-pentofuranosyl)thymine (EFT) on a gold electrode was prepared and characterized by Raman spectral and electrochemical measurements. Voltammetric and electrochemical impedance measurements show that the SAM of EFT on a Au electrode impedes the electron-transfer reaction. The SAM of EFT was successfully used for the voltammetric sensing of urate in neutral solution. The coexisting ascorbate anion does not interfere and therefore the EFT-based electrode was able to quantify urate at the micromolar level in the presence of a large excess amount of ascorbate. To demonstrate the practical applications, the amount of urate in two different human serum samples was quantified by using the EFT-based electrode; the results are in good agreement with those determined by the clinical method. DFT calculations show that both ascorbate and urate have noncovalent interactions including hydrogen-bonding interactions with EFT

Shifting the Reactivity of Bis-propargyl Ethers from Garratt–Braverman Cyclization Mode to 1,5‑H Shift Pathway To Yield 3,4-Disubstituted Furans: A Combined Experimental and Computational Study

Aryl or vinyl substituted bis-propargyl ethers upon base treatment generally form phthalans via the Garratt–Braverman (GB) cyclization pathway. In a major departure from this usual route, several aryl/vinyl bis-propargyl ethers with one of the acetylenic arms ending up with 2-tetrahydropyranyloxy methyl or ethoxy methyl have been shown to follow the alternative intramolecular 1,5-H shift pathway upon base treatment. The reaction has led to the formation of synthetically as well as biologically important 3,4-disubstituted furan derivatives in good yields. The initially formed <i>E</i> isomer in solution (CDCl₃) slowly isomerizes to the <i>Z</i> isomer, indicating greater stability of the latter. The factors affecting the interplay between the 1,5-H shift and GB rearrangement have also been evaluated, and the results are supported by DFT-based computational study

Asymmetric Garratt–Braverman Cyclization: A Route to Axially Chiral Aryl Naphthalene–Amino Acid Hybrids

We report the first example of a highly diastereoselective Garratt–Braverman cyclization leading to the synthesis of chiral aryl naphthalene–amino acid hybrids in excellent yields. The stereogenecity in the amino acid has induced high diastereoselectivity for the reaction. Computations based on density functional theory indicated a lower activation free energy barrier for the <b>M</b> isomer as compared to that for the <b>P</b> diastereomer (ΔΔ<i>G</i> = 3.48 kcal/mol). Comparison of the recorded CD spectrum of the product with the calculated one also supported the preferential formation of the <b>M</b> diastereomer