Browsing by Author "Rakesh Kumar Verma"

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Biodegradation of Polyurethane (PU) and Polyvinyl Chloride (PVC)
(Springer Nature, 2024) Manjul Gondwal; Akanksha Gwasikoti; Anjum Qureshi; Prem Prakash Solanki; Rakesh Kumar Verma; Bhanu Pratap Singh Gautam
The accumulation of plastic trash has been recognized as a significant environmental issue that impacts all forms of life, natural ecosystems, and the global economy. In these circumstances, it is crucial to prioritize the search for environ mentally friendly alternatives, such as biodegradation instead of conventional dis posal methods. Currently, there is limited knowledge regarding the mechanisms and effectiveness of plastic biodegradation. The purpose of this study is to provide a concise overview of the biodegradation processes of polyurethane (PU) and polyvi nyl chloride (PVC), highlighting their significance in terms of environmental sus tainability and waste management. Biodegradation, which harnesses the power of microbes and enzymes, holds immense promise in tackling the environmental issues associated with synthetic polymers. Biodegradation refers to the natural process by which microbes and enzymes break down organic matter. To effectively develop strategies for managing plastic waste and promoting sustainability, it is essential to have a thorough understanding of the mechanisms and factors that affect the biodeg radation of polyurethane (PU) and polyvinyl chloride (PVC). © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Chemoselective Intramolecular Rauhut-Currier Reaction on a Labile Framework of Enone and Acrylamide: Tricyclohexylphosphine as a Stable and Economical Catalyst
(John Wiley and Sons Inc, 2024) Rakesh Kumar Verma; Mansingh Bairwa; Kishor Chandra Bharadwaj
Intramolecular Rauhut-Currier (IRC) reaction is an atom-economical way of making carbocyclic and heterocyclic rings. However, its sensitivity towards electronic and steric parameters limits the reaction and stems the need for further development. Acrylamides have been one such left out of their sensitivity. Herein we report an IRC reaction, using acrylamide as a source of initial enolate. The cyclization has been achieved on a labile and challenging framework, prone to decomposition. Different control experiments have addressed the instability of the precursor. Protocol was further extendable to annulation for benzo analogs. We also report tricyclohexylphosphine (PCy3) as a stable, commercial, and easy-to-use nucleophilic catalyst in the field of IRC reactions as compared to earlier well-established trimethyl and tributyl phosphines. Me3P and Bu3P although useful, are sensitive, prone to oxidation, and need careful handling. The protocol leads to the synthesis of piperidone and dihydroquinolone frameworks. A quick study to test the feasibility of catalyzing the Morita-Baylis-Hillman (MBH) reaction by PCy3 was also done successfully, although in moderate yields. © 2024 Wiley-VCH GmbH.
Domino Sequence of Ketimization and Electrophilic Amination for an Inverse Aza Intramolecular Morita-Baylis-Hillman Adduct
(American Chemical Society, 2024) Mansingh Bairwa; Rakesh Kumar Verma; Kishor Chandra Bharadwaj
Morita-Baylis-Hillman (MBH) reaction, typically catalyzed by a Lewis base, is a popular and useful method for C-C bond formation. Unfortunately, it is limited by a slow reaction rate and has sensitivity toward steric and electronic parameters. Despite tremendous efforts, the versatility of the reaction keeps the quest open for new mechanistic and catalytic pathways. Here, we have reported a Bro̷nsted acid-catalyzed, electrophilic amination (Umpolung of imine) as a method for an inverse Aza Intramolecular MBH adduct in the form of 2-acylindole. Umpolung of imine with nitrogen acting as an electrophilic center has been achieved. Interestingly, the reaction was also shown to occur under catalyst-free conditions also. The expected products of ketimine formation, 6π electrocyclization, or quinoline formation were least/not observed. A large number of examples have demonstrated the reaction strength. β-aryl-substituted acrylate and acrylamide (cinnamates and cinnamides), which are extremely sluggish in conventional MBH chemistry, are the highlights of the developed methodology. The annulated product exhibited keto-enol tautomerism, which was proven by 1H NMR integrals. As an application, another tandem reaction in the form of Michael addition on a highly complex amine was carried out to provide spiro-annulated indole. © 2024 American Chemical Society.
Epigenetic regulation of salinity stress responses in cereals
(Springer Science and Business Media B.V., 2022) Md. Mahtab Rashid; Anukool Vaishnav; Rakesh Kumar Verma; Pradeep Sharma; P. Suprasanna; R.K. Gaur
Cereals are important crops and are exposed to various types of environmental stresses that affect the overall growth and yield. Among the various abiotic stresses, salt stress is a major environmental factor that influences the genetic, physiological, and biochemical responses of cereal crops. Epigenetic regulation which includes DNA methylation, histone modification, and chromatin remodelling plays an important role in salt stress tolerance. Recent studies in rice genomics have highlighted that the epigenetic changes are heritable and therefore can be considered as molecular signatures. An epigenetic mechanism under salinity induces phenotypic responses involving modulations in gene expression. Association between histone modification and altered DNA methylation patterns and differential gene expression has been evidenced for salt sensitivity in rice and other cereal crops. In addition, epigenetics also creates stress memory that helps the plant to better combat future stress exposure. In the present review, we have discussed epigenetic influences in stress tolerance, adaptation, and evolution processes. Understanding the epigenetic regulation of salinity could help for designing salt-tolerant varieties leading to improved crop productivity. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.