Chemistry

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Shiv Nadar University

Dual-room-temperature phosphorescence (DRTP) from organic molecules is of utmost importance in chemical physics. The Dexter-type triplet-to-triplet energy transfer mechanism can therefore be used to achieve DRTP at ambient conditions. Here, we report two donor–acceptor (D–A)-based guests (CQN1, CQN2) in which the donor (D) and acceptor (A) parts are held in angular orientation around the C–N single bond. Spectroscopic analysis along with computational calculations revealed that both guests are incapable of emitting either thermally activated delayed fluorescence (TADF) or RTP at ambient conditions due to large singlet–triplet gaps, which are presented to show host (benzophenone, BP)-sensitized DRTP via multiple intermolecular triplet-to-triplet energy transfer (TTET) channels that originate from the triplet state (T1BP) of BP to the triplet states (T1D, T1A) of the D and A parts (TTET-I:T1BP → T1D; TTET-II:T1BP → T1A). In addition, an intramolecular TTET channel that occurs from the T1D to T1A states of the D and A parts of CQN2 is also activated due to the low triplet (T1D)–triplet (T1A) gap at ambient conditions. The efficiency of TTET processes was found to be 100%. The phosphorescence quantum yields (ϕP) and lifetimes (τP) were shown to be 13–20% and 0.48–0.55 s, respectively. Given the high lifetime of the DRTP feature of both host–guest systems (1000:1 molar ratio), a data security application is achieved. This design principle provides the first solid proof that DRTP via radiative decay of the dark triplet states of the D and A parts of D–A-based non-TADF systems is possible, revealing a method to increase the efficiency and lifetime of DRTP. © 2022 The Authors. Published by American Chemical Society

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(SoNS) School of Natural Sciences

ACS Omega

Molecular-Level Understanding of Dual-RTP via Host-Sensitized Multiple Triplet-to-Triplet Energy Transfers and Data Security Application

Selenium (Se), an essential trace element present in several antioxidant enzymes, is responsible for protecting cells from oxidative damage. In the recent past, a large number of naturally inspired Se-containing biomimetic molecular oxidation catalysts have been developed. In this report, a selenium-doped graphitic material (Se-DG) was synthesized using glucose and benzeneseleninic acid (BSA) via a simple hydrothermal method. Se-DG has shown glutathione peroxidase (GPx)-like activity and carried out epoxidation of various aromatic and aliphatic alkenes using H2O2, a green oxidant. In most cases, ∼90% conversion with ∼75% yield of epoxide was achieved in acetonitrile medium. The adduct of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) with hydroperoxyl radical ( OOH) was observed in HRMS which confirmed that the Se-DG produced OOH from H2O2via hydrogen atom abstraction (HAA). A mechanistic insight of the olefin epoxidation was described in the presence of hydrocarbons and it was observed that the hydroxyl radical ( OH) generated during the epoxidation facilitated C-H activation successfully. The plausible reaction mechanism of epoxidation was established with density functional theory (DFT) using Gaussian code. © 2022 The Royal Society of Chemistry

Catalysis Science and Technology

Peroxide activation by selenium-doped graphite

Sustainable polybenzoxazines sourced from renewable feedstock has emerged as an area of interest due to the inherent presence of a high number of reactive and additional functionalities. Plants are a rich source of flavan-3-ol viz., catechin (CAT) with four phenolic-OH and one aliphatic secondary-OH that can be a viable substitute to petro-phenols. In this current work, a biobased benzoxazine monomer, viz. CAT-fa, is synthesized using CAT and carbohydrate sourced furfurylamine (fa). Interestingly, an unexpected tris-oxazine (instead of tetra-oxazine) benzoxazine monomer is obtained. The unreacted phenolic-OH is involved in intramolecular H-bonding with the neighboring oxazine ring. Upon heat treatment, H-bonded hydroxyl groups become free and initiate ring-opening polymerization reaction at a low temperature of ≈125 °C exhibiting the latent catalyst effect. The ring-opening polymerization of the monomer and the thermal stability of polybenzoxazine are analyzed by differential scanning calorimetry, thermal gravimetric analysis, rheometry, and Fourier transform infrared spectroscopy. The polymerization reaction is proposed to proceed by the ring-opening reaction by cleavage at the oxygen of the pyran ring and O─CH2-N bond in oxazine ring to generate multiple polar functionalities to enable extensive H-bonding interactions. This work supports the potential of catechin as a green synthon to form sustainable polymers to employ H-bonding interactions and latent-catalytic potential. © 2022 Wiley-VCH GmbH.

Macromolecular Chemistry and Physics

Catechin and Furfurylamine Derived Biobased Benzoxazine with Latent-Catalyst Effect

A new series of (co)polycarbonates bearing pendent azido groups was synthesized by polycondensation of varying molar proportions of 4, 4’-(5-azidopentane-2, 2-diyl) diphenol and bisphenol-A with triphosgene. The chemical structures, compositions and random nature of (co)polycarbonates were confirmed by NMR spectroscopy. Inherent viscosities and number-average molecular weights of (co)polycarbonates were in the range 0.63–0.77 dL g−1 and 35,400–43,400 g mol−1, respectively indicating the formation of reasonably high molecular weight polymers. (Co)polycarbonates could be cast into tough, transparent and flexible films from chloroform solutions. (Co)polycarbonates were further characterized using IR spectroscopy, XRD, TGA and DSC. The thermal crosslinking of (co)polycarbonates bearing pendant azido groups was studied by DSC analysis. Independently, (co)polycarbonates bearing pendant azido groups were exposed to UV irradiation at wavelength of 254 nm and decomposition reaction of azido groups was monitored by FT-IR spectroscopy. The complete decomposition of azido groups was observed with exposure time of 30 min. The formed cross-linked (co)polycarbonates exhibited improved % char yield values compared to parent (co)polycarbonates. The measurement of mechanical properties of representative crosslinked (co)polycarbonates indicated increase in tensile strength and Young's modulus and decrease in % elongation compared to corresponding parent linear (co)polycarbonates. © 2022 Wiley-VCH GmbH.

ChemistrySelect

Synthesis, Characterization and UV-Crosslinking of Aromatic (Co)polycarbonates Bearing Pendant Azido Groups

Biologically potent and synthetically significant 1,2-dihydronaphthalene derivatives have gained considerable attention due to their wide applications in industrial as well as in medicinal fields also. A mild and efficient metal-free protocol via the rearrangement of cyclopropylcarbinols has been reported to construct these 1,2-dihydronaphthalene skeletons utilizing cyclopropane ring as the scaffold. We obtained conjugated dienes and, in some cases, homoallylic chlorides as major products in good to excellent yields. They have no literature precedence till date. The fate of this rearrangement depends on the substituent patterns of the cyclopropane bearing aryl moiety. Besides the synthetic studies, to get deep insight into the electronic transitions, time dependent DFT studies have also been performed. © 2022 Wiley-VCH GmbH.

Metal Free Approach towards the Synthesis of Structurally Diverse 1, 2-Dihydronaphthalene Scaffolds and Theoretical Investigation

Mitochondrial functions are heavily influenced by acid-base homeostasis. Hence, elucidation of the mitochondrial pH is essential in living cells, and its alterations during pathologies is an interesting question to be addressed. Small molecular fluorescent probes are progressively applied to quantify the mitochondrial pH by fluorescence imaging. Herein, we designed a unique small molecular fluorescent probe, PM-Mor-OH, based on the lipophilic morpholine ligand-conjugated pyridinium derivative of "IndiFluors". The morpholine-conjugated fluorescent probe usually localized the lysosome. However, herein, we observed unusual phenomena of morpholine-tagged PM-Mor-OH that localized mitochondria explicitly. The morpholine ligand also plays a pivotal role in tuning optical properties via photoinduced electron transfer (PET) during internal pH alteration (ΔpHi). In the mitophagy process, lysosomes engulf damaged mitochondria, leading to ΔpHi, which can be monitored using our probe. It exhibited "ratiometric"emission at single wavelength excitation (ex. 488) and is suitable for monitoring and quantifying the ΔpHi using confocal microscope high-resolution image analysis during mitophagy. The bathochromic emission shifts due to intramolecular charge transfer (ICT) in basic pH were well explained by the time-dependent density functional theory (TD-DFT/PCM). Similarly, the change in the emission ratio (green/red) with pH variations was also validated by the PET process. In addition, PM-Mor-OH can quantify the pH change during oxidative stress induced by rapamycin, mutant A53T α-synuclein-mediated protein misfolding stress in mitochondria, and during starvation. Rapamycin-induced mitophagy was further elucidated by the translocation of mCherry Parkin to damaged mitochondria, which well correlates with our probe. Thus, PM-Mito-OH is a valuable probe for visualizing mitophagy and can act as a suitable tool for the diagnosis of mitochondrial diseases. © 2022 American Chemical Society.

Life Sciences

Analytical Chemistry

PET- and ICT-Based Ratiometric Probe: An Unusual Phenomenon of Morpholine-Conjugated Fluorophore for Mitochondrial pH Mapping during Mitophagy

The human innate immune system eliminates invading pathogens through phagocytosis. The first step of this process is activating the nicotinamide adenine dinucleotide phosphate oxidase (Nox2) that utilizes NADPH to produce superoxide anion radicals and other reactive oxygen species (ROS). These ROS then alter the mitochondrial membrane potential and increase peroxide in the mitochondria. The peroxide reacts with myeloperoxidase (MPO) and chloride ions to produce pro-inflammatory oxidant hypochlorous acid (HOCl), which causes oxidative stress leading to cell death. The adverse effects of HOCl are highly associated with cardiovascular disease, neurodegenerative disorders, acute lung injuries, inflammatory diseases, and cancer. Therefore, mapping HOCl in the Nox2 pathway is crucial for an in-depth understanding of the innate immune system. Herein, we developed a unique pentacyclic pyridinium probe, PM-S, that exhibited efficient photoinduced electron transfer (PeT) with HOCl triggered methyl(phenyl)sulfane. PM-S showed several advantages, including better chemical stability, large Stokes shifts (&gt;6258 cm−1), high sensitivity (∼50 nM) and specificity to mitochondria, compared to its parent pyrylium PY-S derivative. This probe is also efficient in studying the HOCl produced via the Nox2 pathway in HepG2 and HeLa cells. Analysis using a simple microplate reader and FACS analysis with various inhibitors and inducers supported the mechanistic understanding of Nox2, which can offer an advanced platform for monitoring the inflammatory process more efficiently. © 2022 The Royal Society of Chemistry

Journal of Materials Chemistry B

An efficient PeT based fluorescent probe for mapping mitochondrial oxidative stress produced via the Nox2 pathway

Scientists are rigorously looking for an efficient vaccine against the current pandemic due to the SARS-CoV-2 virus. The reverse vaccinology approach may provide us with significant therapeutic leads in this direction and further determination of T-cell/B-cell response to antigen. In the present study, we conducted a population coverage analysis referring to the diverse Indian population. From the Immune epitope database (IEDB), HLA- distribution analysis was performed to find the most promiscuous T-cell epitope out of In silico determined epitope of Spike protein from SARS-CoV-2. Epitopes were selected based on their binding affinity with the maximum number of HLA alleles belonging to the highest population coverage rate values for the chosen geographical area in India. 404 cleavage sites within the 1288 amino acids sequence of spike glycoprotein were determined by NetChop proteasomal cleavage prediction suggesting the presence of adequate sites in the protein sequence for cleaving into appropriate epitopes. For population coverage analysis, 179 selected epitopes present the projected population coverage up to 97.45% with 56.16 average hit and 15.07 pc90. 54 epitopes are found with the highest coverage among the Indian population and highly conserved within the given spike RBD domain sequence. Among all the predicted epitopes, 9-mer TRFASVYAW and RFDNPVLPF along with 12-mer LLAGTITSGWTF and VSQPFLMDLEGK epitopes are observed as the best due to their decent docking score and best binding affinity to corresponding HLA alleles during MD simulations. Outcomes from this study could be critical to design a vaccine against SARS-CoV-2 for a different set of populations within the country. Communicated by Ramaswamy H. Sarma. © 2022 Informa UK Limited, trading as Taylor & Francis Group.

Journal of Biomolecular Structure and Dynamics

Deciphering the immunogenic T-cell epitopes from spike protein of SARS-CoV-2 concerning the diverse population of India

In the era of the diabetes pandemic, injectable hydrogels (HGs) capable of releasing the desired amount of insulin under hyperglycemic conditions will significantly advance smart insulin development. Several smart boronic acid-based polymer HGs release insulin under high-glucose conditions. However, the correlation of insulin release characteristics with rheological properties is not well understood yet. Herein, we report a generalized and facile fabrication strategy of a new class of glucose-responsive hydrogels by crosslinking a biocompatible polymer, poly(vinyl alcohol) with pinacol esters of bisboronic acids via transesterification reactions. We show the versatility of the method by fabricating four hydrogels with diverse rheological properties. The HGs embody more than 70% water amenable for hosting insulin in the matrix. HG with high storage modulus, derived from 1,4-benzenediboronic acid bis(pinacol) ester releases ∼3 fold less insulin compared to softer HGs derived from acetylene-1,2-diyl bis(boronic acid pinacol ester) and bis[(pinacolato)boryl]methane under hyperglycemic conditions. We find that HG derived from the bis[(pinacolato)boryl]methane crosslinker exhibits superior insulin release properties due to the softness of the hydrogel matrix. We further show that the newly formulated gel is injectable without any structural change in the released insulin molecules and does not cause cytotoxicity. We believe that glucose-responsive hydrogels with tunable viscoelastic properties will pave the way for developing a variety of hydrogels with programmable insulin release properties. © 2022 The Royal Society of Chemistry.

Repurposing pinacol esters of boronic acids for tuning viscoelastic properties of glucose-responsive polymer hydrogels: effects on insulin release kinetics

Although pyridinic-nitrogen (pyri-N) doped graphene is highly active for the oxygen reduction reaction (ORR) of fuel cells in alkaline media, the activity critically decreases under acidic conditions. We report on how to prevent the deactivation based on the mechanistic understanding that (Formula presented.) governs the ORR kinetics. First, we considered that the deactivation is due to the hydration of pyri-NH+, leading to a lower shift of the redox potential. Introducing the hydrophobic cavity prevented the hydration of pyri-NH+ but inhibited the proton transport. We then increased proton conductivity in the hydrophobic cavity by introducing SiO2 particles coated with ionic liquid polymer/Nafion® which kept the high onset potentials with an increased current density even in acidic media. © 2022 Wiley-VCH GmbH.