Chemistry

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Shiv Nadar University

A fully biobased benzoxazine monomer, V-fa (using <a href="https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/vanillin">vanillin</a> and furfurylamine) was grafted onto chitosan (CS) at different weight ratios (CXVY) using "grafting to" benign <a href="https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/schiff-base">Schiff base</a> chemistry. Incorporation of V-fa onto CS increased the tensile strength and improved chemical resistance of the CS-graft-V-fa films. Reversible labile linkages, expansion of CS galleries and leaching out of phenolic species from biobased <a href="https://www.sciencedirect.com/topics/materials-science/polymer-films">polymer films</a> led to an improved <a href="https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/antibacterial-activity">antibacterial activity</a> against Staphylococcus aureus, which is ∼125 times higher than the bare CS film, V-fa and oligomeric V-fa. The leached out species from films were analyzed extensively by NMR, FTIR, GPC, ABTS and HRMS analysis. Oxidative-stress seems to be responsible for <a href="https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/antibacterial-activity">antibacterial activity</a>. Current work illustrates an attractive synthetic approach and the improved antibacterial performance of biobased CS-graft-poly(V-fa) films which may hold as a potential alternative for wound-healing and implant applications in future.

(SoNS) School of Natural Sciences

Carbohydrate Polymers

Antibacterial performance of fully biobased chitosan-grafted-polybenzoxazine films: Elaboration and properties of released material

Organic room-temperature phosphorescence (RTP) materials with persistent RTP (PRTP) have attracted huge interest in inks, bioimaging, and photodynamic therapy. However, the design principle to increase the lifetime of organic molecules is underdeveloped. Herein, we show donor(D4)–acceptor(A) molecules (TOEPh, TOCPh, TOMPh, TOF and TOPh) with similar orientation of donor rings in aggregates that cause a large number of noncovalent interactions. We observed that TOEPh, TOCPh, TOMPh and TOF showed PRTP, whereas TOPh showed only phosphorescence emission (ΦP = ∼11%) with no PRTP property at ambient conditions. The spectroscopic and single-crystal X-ray analyses confirm the molecular assembly via J-aggregation with a face-to-face orientation of the donor rings. The crystal structure analysis (TOEPh, TOCPh, TOMPh, TOF) reveals that moderate π···π interactions (3.706 to 4.065 Å) between the donor rings cause the enhancement of the phosphorescence lifetime (26 to 245 ms), whereas the short phosphorescence lifetime (12 ms) of TOPh was observed because of the absence of π···π interactions. We found that TOEPh shows a long lifetime (245 ms) as compared to other derivatives because of the presence of ethoxy (−OEt) groups that enables spin–orbit coupling caused by strong lone pair (O)···π interactions present in the molecule. Utilizing the PRTP feature of TOEPh and the fluorescence emission of TOPh, we have shown data security applications in poly(methyl methacrylate).

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ACS Omega

Effect of π···π Interactions of Donor Rings on Persistent Room-Temperature Phosphorescence in D4−A Conjugates and Data Security Application

Herein, we have reported a blue LED mediated manganese pentacarbonyl bromide catalysed incorporation of carbene moieties from aryl diazoesters onto 1H-pyrroles via their selective C2−H activation. A manganese metal-carbene has been identified as the active catalyst to facilitate the reaction. Eighteen mono substituted pyrrole derivatives were isolated in good to excellent yields (67→82%) and the disubstituted products were also formed in minor quantities (5 to 8%). HPLC based kinetics study enabled optimization of the reaction. Control experiments, FT-IR, NMR and GC-MS based characterization elucidated the putative reaction mechanism. (Figure presented.). © 2021 Wiley-VCH GmbH

Advanced Synthesis and Catalysis

Blue LED Induced Manganese (I) Catalysed Direct C2−H Activation of Pyrroles with Aryl Diazoesters

The coexistence of ferroelectricity and negative thermal expansion (NTE) in a material is rare and has yet to be observed in a purely organic single-component system. Here, we report the bifunctional characteristics of 2-(4-(trifluoromethyl)phenyl)-1H-phenanthro [9,10-d] imidazole, a single-component system, exhibiting uniaxial ferroelectricity and anisotropic NTE properties in its various crystal forms. This purely organic material exists in trimorphic and hydrated forms. While one of the two polar forms retains its ferroelectric phase up to ∼497 K, the other exhibits a reversible large NTE below room temperature (RT), and a third centric form divests these properties. Further, the noncentric hydrated form also experiences NTE below RT. The mechanisms of ferroelectricity and NTE in this material are elucidated based on the analyses of their single-crystal X-ray structures. The interconversion of the trimorphs is demonstrated via thermal analyses. The experimental value of the in-crystal spontaneous polarization (4.6 μC/cm2) agrees well with that estimated from the periodic theoretical calculations. Given its promising figures of merit for ferroelectricity including a low coercive field (5.8 kV/cm), unusual thermal behavior, switching from NTE to positive thermal expansion, and a minimal volumetric change, this lightweight material is expected to find potential applications in nonexpansive organic electronics. © 2021 American Chemical Society.

ACS Applied Electronic Materials

Ferroelectricity and Uniaxial Negative Thermal Expansion in a Purely Organic Multifunctional Material

A unique and highly water-soluble ICT-based fluorescent probe is developed for efficient detection and discrimination of reactive monocarbonyl formaldehyde (FA) from dicarbonyl methylglyoxal (MGO)/glyoxal (GO) by modulating the ICT process, which was confirmed by photophysical and TD-DFT analysis. The probe is applied in cellular imaging and quantifying FA in preserved food and MGO in manuka honey. © The Royal Society of Chemistry 2021.

Chemical Communications

ICT based water-soluble fluorescent probe for discriminating mono and dicarbonyl species and analysis in foods

Polybenzoxazines obtained especially from green synthons are facing challenges of the requirement of high ring-opening polymerization (ROP) temperature of the monomer, thus affecting their exploration at the industrial front. This demands effective structural changes in the monomer itself, to mediate catalyst-free polymerization at a low energy via one-step synthesis protocol. In this regard, monomers based on disulfide-linked bisbenzoxazine were successfully synthesized using cystamine (biobased) and cardanol (agro-waste)/phenol. Reduction of the disulfide bridge in the monomer using dithiothreitol under mild conditions in situ transformed the oxazine ring in the monomer, via neighboring group participation of the -SH group in a transient intermediate monomer, into a thiazolidine structure, which is otherwise difficult to synthesize. Structural transformation of ring-opening followed by the ring-closing intramolecular reaction led to an interconversion of O-CH2-N containing a six-membered oxazine ring to S-CH2-N containing a five-membered thiazolidine ring and a phenolic-OH. The structure of the monomer with the oxazine ring and its congener with the thiazolidine ring was characterized by spectroscopic methods and X-ray analysis. Kinetics of structural transformation at a molecular level is studied in detail, and it was found that the reaction proceeded via a transient 2-aminoethanethiol-linked benzoxazine intermediate, as supported by nuclear magnetic resonance spectroscopy and density functional theory studies. The thiazolidine-ring-containing monomer promotes ROP at a substantially low temperature than the reported mono-/bisoxazine monomers due to the dual mode of facilitation of the ROP reaction, both by phenolic-OH and by ring strain. Surprisingly, both the monomer structures led to the formation of a similar polymer structure, as supported by thermogravimetric analysis and Fourier transform infrared study. The current work highlights the benefits of inherent functionalities in naturally sourced feedstocks as biosynthons for the new latest generation of benzoxazine monomers. © 2021 American Chemical Society.

Biomacromolecules

Self-Polymerization Promoting Monomers: In Situ Transformation of Disulfide-Linked Benzoxazines into the Thiazolidine Structure

Herein we report a series of telescoping methodologies for one pot synthesis of biologically relevant γ-carboline derivatives 6 and spiro[pyrrolidinone-3,3′]indole 7. Initially the three consecutive steps of cyclopropanation, phthalimide deprotection, and Boc-deprotection have been congregated in a single reaction vessel to afford a ∼1:1 mixture of 6 and 7. Next, careful optimization of the reaction sequence and the conditions generated an orthogonal approach to access compounds 6 and 7 exclusively. Air oxidation of the γ-carbolinones 6 afforded aromatic γ-carbolines 8. © 2021 American Chemical Society.

Journal of Organic Chemistry

Orthogonal Syntheses of γ-Carbolinone and Spiro[pyrrolidinone-3,3′]indole Derivatives in One Pot through Reaction Telescoping

The stereoselectivity and stereospecificity of the triflate-mediated intramolecular Schmidt reaction of substituted 3-(1-azidocyclohexyl)propanol derivatives leading to octahydro-1H-pyrrolo[1,2-a]azepine, the structural skeleton of several important families of alkaloids such as the Stemona alkaloids, has been examined. The reaction involves an initial intramolecular SN2 reaction between the azide moiety and the triflate affording an intermediate spirocyclic aminodiazonoium salt that undergoes the expected 1,2-shift/N2-elimination followed by hydride-mediated iminium salt reduction. Remarkably, chiral alcohols are converted to the azabicyclic derivative with no or limited racemization. The initial asymmetric alcohol center controls the diastereoselectivity of the whole process, leading to the formation of one out of the four possible diastereoisomers of disubstituted octahydro-1H-pyrrolo[1,2-a]azepine. The origin of the stereoselectivity is rationalized based on theoretical calculations. The concise synthesis of (−)-(cis)-3-propylindolizidine and (−)-(cis)-3-butyllehmizidine, two alkaloids found in the venom of workers of the ant Myrmicaria melanogaster, is reported.

Angewandte Chemie - International Edition

Stereoselective and Stereospecific Triflate-Mediated Intramolecular Schmidt Reaction: Ready Access to Alkaloid Skeletons**

Organic room-temperature phosphorescence (RTP) materials with persistent RTP (PRTP) have attracted huge interest in inks, bioimaging, and photodynamic therapy. However, the design principle to increase the lifetime of organic molecules is underdeveloped. Herein, we show donor(D4)-acceptor(A) molecules (TOEPh, TOCPh, TOMPh, TOF and TOPh) with similar orientation of donor rings in aggregates that cause a large number of noncovalent interactions. We observed that TOEPh, TOCPh, TOMPh and TOF showed PRTP, whereas TOPh showed only phosphorescence emission (φP = 11\%) with no PRTP property at ambient conditions. The spectroscopic and single-crystal X-ray analyses confirm the molecular assembly via J-aggregation with a face-to-face orientation of the donor rings. The crystal structure analysis (TOEPh, TOCPh, TOMPh, TOF) reveals that moderate π···πinteractions (3.706 to 4.065 Å) between the donor rings cause the enhancement of the phosphorescence lifetime (26 to 245 ms), whereas the short phosphorescence lifetime (12 ms) of TOPh was observed because of the absence of π···πinteractions. We found that TOEPh shows a long lifetime (245 ms) as compared to other derivatives because of the presence of ethoxy (-OEt) groups that enables spin-orbit coupling caused by strong lone pair (O)···πinteractions present in the molecule. Utilizing the PRTP feature of TOEPh and the fluorescence emission of TOPh, we have shown data security applications in poly(methyl methacrylate). © 2021 The Authors. Published by American Chemical Society.