Chemistry

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Resistance to antimicrobial agents in Gram-positive bacteria has become a major concern in the last decade. Recently, nanoparticles (NP) have emerged as a potential solution to antibiotic resistance. We synthesized three reduced graphene oxide (rGO) nanoparticles, namely rGO, rGO-S, and rGO-S/Se, and characterized them using X-ray diffraction (PXRD), Raman analysis, and thermo-gravimetric analysis. Transmission electron microscopy confirmed spherical shape nanometer size S and S/Se NPs on the rGO surface. Antibacterial properties of all three nanomaterials were probed against Gram-positive pathogens Staphylococcus aureus and Enterococcus faecalis, using turbidometeric and CFU assays. Among the synthesized nanomaterials, rGO-S/Se exhibited relatively strong an-tibacterial activity against both Gram-positive microorganism tested in a concentration dependent manner (growth inhibition &gt;90% at 200 µg/mL). Atomic force microscopy of rGO-S/Se treated cells displayed morphological aberrations. Our studies also revealed that rGO composite NPs are able to deposit on the bacterial cell surface, resulting in membrane perturbation and oxidative stress. Taken together, our results suggest a possible three-pronged approach of bacterial cytotoxicity by these graphene-based materials. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

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(SoNS) School of Natural Sciences

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Nanomaterials

Synthesis and Characterization of Sulfur and Sulfur-Selenium Nanoparticles Loaded on Reduced Graphene Oxide and Their Antibacterial Activity against Gram-Positive Pathogens

Polymorphism in drugs and bioactive molecules is not uncommon, and it has remained as one of the critical issues in drug development processes. While improving physicochemical properties of bioactive molecules has been a prime focus of the pharmaceutical chemists, not much efforts have been put toward the improvement of their potency via polymorphic modifications. Here, we consider five cases of 5-arylidene-2-aminothiazolidinones derivatives, the known anticancer agents, and discover eights polymorphs in three out of the five cases. We perform systematic crystallization experiments and detailed crystal structure analysis of the eight polymorphs and two compounds, estimate both their energetic and thermal stabilities, and compare their solid state properties. We also compare in-solution properties, e.g., equilibrium solubility, intrinsic dissolution rate, and phase stability, of three polymorphs of one of the cases. Further, we study the extent of inhibition imposed by those eight polymorphs and seven bulk and crystal forms of the compounds on the proliferation of MCF7 breast cancer cells and also the extent of their binding to the isozyme γ-enolase. Furthermore, we perform MD simulations on the eight polymorphs and one compound to estimate and compare their binding affinity with γ-enolase. Our experimental and MD simulation analyses in general emphasize the importance of polymorphism in improving the biological potency of individual molecules. © 2022 American Chemical Society. All rights reserved.

Molecular Pharmaceutics

Tuning Potency of Bioactive Molecules via Polymorphic Modifications: A Case Study

Solid-state rechargeable zinc-Air batteries (ZABs) are gaining interest as a class of portable clean energy technology due to their advantages such as high theoretical energy density, intrinsic safety, and low cost. It is expected that an appropriately triple-phase boundary (TPB) engineered, bifunctional oxygen reaction (OER and ORR) electrocatalyst at the air-electrode of ZABs can redefine the performance characteristics of these systems. To explore this possibility, an electrode material consisting of manganese-cobalt-based bimetallic spinel oxide (MnCo2O4)-supported nitrogen-doped entangled graphene (MnCo2O4/NEGF) with multiple active sites responsible for facilitating both OER and ORR has been prepared. The porous 3D graphitic support significantly affects the bifunctional oxygen reaction kinetics and helps the system display a remarkable catalytic performance. The air electrode consisting of the MnCo2O4/NEGF catalyst coated over the gas diffusion layer (GDL) ensures the effective TPB, and this feature works in favor of the rechargeable ZAB system under the charging and discharging modes. As an important structural and functional attribute of the electrocatalyst, the porosity and nitrogen doping in the 3D conducting support play a decisive aspect in controlling the surface wettability (hydrophilicity/hydrophobicity) of the air electrode. The fabricated solid-state rechargeable ZAB device with the developed electrode displayed a maximum peak power density of 202 mW cm-2, which is significantly improved as compared to the one based on the Pt/C + RuO2standard catalyst pair (124 mW cm-2). The solid-state device which displayed an initial charge-discharge voltage gap of only 0.7 V at 10 mA cm-2showed only a small increment of 86 mV after 50 h. © 2022 American Chemical Society. All rights reserved.

ACS Applied Energy Materials

Air-Cathode Interface-Engineered Electrocatalyst for Solid-State Rechargeable Zinc-Air Batteries

A large number of people are suffering globally from diabetes due to metabolic disorders characterized by abnormally high blood sugar (glucose), which inflicts severe health issues as well as huge economic burdens. In this study, we have reported an efficient and eco-friendly biosynthesis of hydrophilic zinc oxide nanoparticles (ZnO NPs, labeled as PC1 and C1) for antidiabetic treatment using an aqueous extract of Plumeria obtusa and Tabernaemontana divaricata flowers, respectively. Phase purity, structure, morphology, and dispersibility of the as-synthesized PC1/C1 have been characterized by various analytical techniques such as UV–visible spectroscopy (UV–vis), Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and dynamic light scattering (DLS). The UV–vis spectrum of the PC1/C1 showed maximum absorbance at ~ 370 nm and the PXRD pattern confirmed their hexagonal wurtzite crystalline structure. Besides, SEM displayed sheet and honeycomb-like shape of the PC1 and C1 while FTIR and TGA revealed the attached surface coatings of the PC1/C1. DLS results showed narrow size distribution of the PC1 and C1 in the range of 150–156 and 315–400 nm, respectively. Moreover, the zeta potential values of the as-prepared PC1 and C1 are determined as -47 and -57 mV indicating their good colloidal stability in an aqueous suspension. In vitro study has been performed to show the α-amylase inhibition activity. Furthermore, the PC1/C1 are investigated for their antidiabetic efficacy in streptozotocin (STZ)-induced diabetes in the C57BL/6 male mice. Both the PC1/C1 displayed a significant antidiabetic potential; however, the blood glucose level has been significantly reduced (p &lt; 0.05) in the STZ-induced diabetic mice treated with PC1 as compared to the C1. Overall, PC1 and C1 are found to be very promising antidiabetic candidates for the in vivo antidiabetic treatment. Graphical abstract: [Figure not available: see fulltext.]. © 2022, Institute of Chemistry, Slovak Academy of Sciences.

Chemical Papers

Biosynthesis of hydrophilic zinc oxide nanoparticles using Plumeria obtusa and Tabernaemontana divaricata flower extract for antidiabetic treatment

The latest fourth-generation oxazine-ring substituted thiophene-based benzoxazine monomers and polymers with variation in the degree of phenyl substitution (with and without) in the oxazine-ring were synthesized and characterized. Thiophene-based di-substituted benzoxazine undergoes ring-opening polymerization at a low temperature with a minimal mass loss during polymerization as supported by molecular geometry-guided intramolecular interactions. This class of monomers provides ample opportunities to design at the molecular level high-performance polybenzoxazines with promising smart applications. © 2022 The Royal Society of Chemistry.

Chemical Communications

Synthesis and thermal behaviour of thiophene-based oxazine-ring substituted benzoxazine monomers &amp; polymers

Nanoscale assembly of ultrasmall metal nanoclusters (MNCs) by means of molecular forces has proven to be a powerful strategy to engineer their molecule-like properties in multiscale dimensions. By leveraging depletion attraction as the guiding force, herein, we demonstrate the formation of kinetically trapped NCs assemblies with enhanced photoluminescence (PL) and excited state lifetimes and extend the principle to cluster impregnated cationic nanogels, nonluminescent Au(I)-thiolate complexes, and weakly luminescent CuNCs. We further demonstrate a thermal energy driven kinetic barrier breaking process to isolate these assemblies. These isolated assemblies are thermodynamically stable, built from a strong network among several discrete, ultrasmall AuNCs and exhibit several unusual properties such as high stability in various pH, strong PL, microsecond lifetimes, large Stocks shifts, and higher accumulation in the lysosome of cancer cells. We anticipate our strategy may find wider use in creating a large variety of MNC-based assemblies with many unforeseen arrangements, properties, and applications. © 2022 American Chemical Society.

Journal of Physical Chemistry Letters

Depletion Driven Assembly of Ultrasmall Metal Nanoclusters: From Kinetically Arrested Assemblies to Thermodynamically Stable, Spherical Superclusters

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

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.