Browsing by Author "Sumit Kumar Panja"

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Anion directed structural diversity in zinc complexes with conformationally flexible quinazoline ligand: Structural, spectral and theoretical studies
(Royal Society of Chemistry, 2016) Nidhi Dwivedi; Sumit Kumar Panja; Monika; Satyen Saha; Sailaja S. Sunkari
In this paper, we report the synthesis, structure and photophysical studies of four new complexes of conformationally flexible 6-chloro-4-phenyl-2-(pyridin-2-yl)quinazoline ligand (L) with Zn(ii). The coordinating ability of the ligand and geometrical preferences of the resultant complexes are tuned by varying the anion of the metal salt as confirmed by structural and DFT studies. The choice of the metal salt (especially anion) directs the stabilisation of different conformations of the ligand arising out of twisting of the pyridyl ring with respect to the quinazoline ring, resulting in complexes with different nuclearity (monomer/dimer) as well as different coordination geometries (tetrahedral/trigonal bipyramidal/octahedral). Photophysical properties are also found to be tuned due to conformational changes on complexation. DFT studies on the ligand establish the conformationally stable forms as observed in the reported structures. © The Royal Society of Chemistry 2016.
Anti-cancer therapeutic potential of quinazoline based small molecules via global upregulation of miRNAs
(2014) Smita Nahar; Debojit Bose; Sumit Kumar Panja; Satyen Saha; Souvik Maiti
Three quinazoline based small molecules showed global upregulation of miRNA expression with a selective enrichment of tumor suppressor miRNAs. The target genes of the upregulated miRNAs were predicted to be enriched for apoptotic pathways. Apoptotic induction following treatment with quinazoline compounds was confirmed by in cellulo studies. Thus, these small molecules having the core structural moiety (2,4-diphenyl-quinazoline) can be used as scaffolds to design activators of miRNA expression paving the way for novel anti-cancer drugs. © 2014 The Partner Organisations.
Catalyst-Free One-Pot Access to Pyrazoles and Disulfide-Tethered Pyrazoles via Deamidative Heteroannulation of β-Ketodithioesters with Semicarbazide Hydrochloride in Water
(Wiley-VCH Verlag, 2018) Suvajit Koley; Sumit Kumar Panja; Sonam Soni; Maya Shankar Singh
An operationally simple, mild, and catalyst-free one-pot protocol to access privileged pyrazoles and disulfide-tethered pyrazoles has been devised by [3+2] heteroannulation of β-ketodithioesters with semicarbazide hydrochloride in water under open air. The pH of the medium played a key role toward the selectivity switch, as refluxing in water led to the formation of pyrazoles, whereas addition of sodium acetate in water enabled the formation of disulfide-tethered pyrazoles. Notably, this protocol involves a tandem sequence of amination/cyclization/dehydration/hydrodesufurization/hydrolysis/deamidative reactions. A mechanistic rationale for this regio-/chemoselective domino reaction is outlined, which is well supported and validated by density functional theory calculations. (Figure presented.). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Evidence of C–F-P and aromatic π–F-P weak interactions in imidazolium ionic liquids and its consequences
(Elsevier B.V., 2018) Sumit Kumar Panja; Nitin Srivastava; Jyoti Srivastava; Namburi Eswara Prasad; Hemanth Noothalapati; Shinsuke Shigeto; Satyen Saha
A simple change from alkyl group to alkene in side chain of imidazolium cation with same anion resulted in a drastic impact on physical properties (e.g., melting point) from bmimPF6 IL to cmimPF6 IL. The underlying reasons have been elucidated by structural and interaction studies with the help of DSC, SCXRD, vibrational and multi-nuclear NMR spectroscopic techniques. Experiments reveal existence of new weak interactions involving the carbon and π cloud of the imidazolium aromatic ring with fluoride of PF6 anion (i.e., C2–F-P and π–F-P) in cmimPF6 but are absent in structurally similar prototype IL, bmimPF6. Though weak, these interactions helped to form ladder type supramolecular arrangement, resulting in quite high melting point for cmimPF6 IL compared to bmimPF6 IL. These findings emphasize that an IL system can behave uniquely because of the existence of uncommon weak interactions. © 2017 Elsevier B.V.
First report of the application of simple molecular complexes as organo-catalysts for Knoevenagel condensation
(Royal Society of Chemistry, 2015) Sumit Kumar Panja; Nidhi Dwivedi; Satyen Saha
A series of molecular complexes have been designed, synthesized and used as organo-catalysts for the first time for very efficient Knoevenagel condensation. Molecular complexes are thermally stable, easily recyclable, and have a low cost of preparation. The role of acidic protons in molecular complexes in Knoevenagel condensations has been identified as the key factor and helps us to provide useful information about the reaction pathway. The acidic proton of a catalyst enhances the electrophilicity of an aldehyde and accelerates the dehydration process of the reaction at room temperature (RT). An eco-friendly, green synthetic protocol for the Knoevenagel condensation is used to synthesize a series of important cyano group containing synthetic precursors for synthesis of biologically active molecules at RT using a minimum amount of catalyst (∼5 mol%) without the need for chromatographic separation techniques. Detailed mechanistic studies and substituent effects of aromatic aldehydes on the reaction have been investigated. In addition, biologically active 2-amino-4H-chromene derivatives have also been synthesized by the Knoevenagel condensation of salicylic aldehydes with active methylene compounds, followed by intramolecular cyclization (via Michael addition) delivering higher yields within shorter reaction times at RT without any need for chromatographic separation. © The Royal Society of Chemistry 2015.
Highly stable naphthalene core based novel cleft-shaped strain molecule: Influence of intermolecular H-bonding architectures
(Royal Society of Chemistry, 2016) Sumit Kumar Panja; Nidhi Dwivedi; Satyen Saha
The significance of intermolecular classical and non-classical H-bonding interactions in the stabilization of a naphthalene core based conformationally rigid cleft-shaped 1,5-dioxocin (BNAP) is presented here. The importance of H-bonding interactions to account for the unusual stability of a catalytically important novel molecule is reported for the first time. In addition to strong CH⋯π interactions, the formation of the unique intermolecular seven-membered H-bonded ring in the crystalline state through classical and non-classical H-bonding interaction was found to provide the unusual stability. This supramolecular structure was also found to impart stability in the presence of a strong acid as evident from the detailed UV-Visible spectroscopic studies. In addition to DFT calculations, the Hirshfeld surfaces, mapped with dnorm, and 2D fingerprint plots, support the existence of these classical and non-classical H-bonding and CH⋯π interactions. Furthermore, BNAP shows its remarkable catalytic activity for the Knoevenagel condensation reaction. © 2016 The Royal Society of Chemistry.
I2-Catalyzed three-component protocol for the synthesis of quinazolines
(Elsevier Ltd, 2012) Sumit Kumar Panja; Nidhi Dwivedi; Satyen Saha
An efficient and one-pot three-component strategy for synthesizing highly functionalized quinazoline derivatives is presented. A mixture of 2-aminobenzophenone, aromatic aldehyde and ammonium acetate in the presence of I2-catalyst provides desired products in excellent yields even at moderate temperature (40 °C) without the involvement of any chromatographic purification. Oxidizing and Lewis acidic properties of molecular I2 have been utilized here. Detailed mechanism has been established based on an isolated intermediate and its single crystal X-ray crystallographic structure. © 2012 Elsevier Ltd. All rights reserved.
Manipulating the proton transfer process in molecular complexes: Synthesis and spectroscopic studies
(Royal Society of Chemistry, 2016) Sumit Kumar Panja; Nidhi Dwivedi; Satyen Saha
The proton transfer process in carefully designed molecular complexes has been investigated directly in the solid and solution phase. SCXRD studies have been employed to investigate the N-H-O bonding interaction sites of the molecular complexes, with additional experimental support from FTIR and Raman spectroscopic studies, to gain information on the relative position of hydrogen in between the N and O centers. Further, the proton transfer process in solution is studied using UV-Visible spectroscopy through monitoring the intramolecular charge transfer (ICT) process in these molecular complexes, which is primarily governed by the number of electron withdrawing groups (nitro groups) on proton donor moieties (NP, DNP and TNP). It is found that the magnitude of the ICT process depends on the extent of proton transfer, which on the other hand depends on the relative stabilities of the constituent species (phenolate species). A correlation is observed between an increase in the number of nitro groups and an increase in the melting point of the molecular complexes, indicating the enhancement of ionic character due to the proton transfer process. The aliphatic H-bonding is identified and monitored using 1H-NMR spectroscopy, which reveals that the identity of molecular complexes in solution interestingly depends on the extent of proton transfer, in addition to the nature of the solvents. The aliphatic C-H-O H-bonding interaction between the oxygen atom of the nitro group and the alkyl hydrogen in piperidinium was also found to play a significant role in strengthening the primary interaction involving a hydrogen transfer process. The conductivity of the molecular complexes increases with an increase in the number of nitro groups, indicating the enhancement in ionic character of the molecular complexes. © 2016 the Owner Societies.
Microheterogeneity in imidazolium and piperidinium cation-based ionic liquids: 1D and 2D NMR studies
(John Wiley and Sons Ltd, 2018) Sumit Kumar Panja; Satyen Saha
Existence of microheterogeneity of imidazolium and piperidinium cation-based ionic liquids (ILs) containing PF6 and NTf2 anions has been investigated by 1D and 2D NMR spectroscopy. 2D NMR (especially NOESY and HOESY) has been employed for studying the interactions present between cation and anion as well as the intermolecular interaction among cations. HOESY spectrum shows that fluorine of anion PF-6 and NTf-2 significantly interacts with proton of the cations. Combined results of HOESY and NOESY for imidazolium IL indicate that the PF-6 and imidazolium cation are distributed in organized manner, resulting a heterogeneous environment in liquid state. We have also observed existence of heterogeneous environment for piperidinium cation-based ILs which is different from imidazolium ILs. It appears that existence of microheterogeneity in IL is ubiquitous and therefore open up the ILs field to revisit. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.
Probing phenol dimer in molecular complex: Role of nitro group and stabilizing agent
(Elsevier B.V., 2019) Sumit Kumar Panja; Supriy Verma; Satyen Saha
The phenol dimer is a prototype molecular cluster system and is considered as a low-barrier H-bond (LBHB) interaction. The phenol dimer influences and catalyses various transformation in biological system but not identified in solid state yet. In present study, p-nitrophenol dimer (NPD) has been identified in the solid state. N-methylpiperidine (MP) is used to stabilise the NPD dimer and formed a stable MPH(PDA) molecular complex. Instead of p-nitrophenol dimer (NPD), the effect of the nitro group, the role of N-methylpiperidine (MP) and H-bonding interaction in MPH(PDA) have been investigated directly by experimental and theoretical studied. It is observed that extent of π electron delocalisation on p-nitrophenol play an important role on stability of p-nitrophenol dimer (NPD). © 2019 Elsevier B.V.
Recyclable, magnetic ionic liquid bmim[FeCl4]-catalyzed, multicomponent, solvent-free, green synthesis of quinazolines
(Royal Society of Chemistry, 2013) Sumit Kumar Panja; Satyen Saha
An atom-efficient, eco-friendly, solvent-free, high yielding, multicomponent green strategy to synthesize highly functionalized quinazoline derivatives by the one-pot reaction of 2-aminobenzophenone, aromatic aldehyde and ammonium acetate is presented. Magnetic IL, butylmethylimidazolium tetrachloroferrate (bmim[FeCl4]) has been used successfully as a catalyst in a multicomponent synthetic strategy for the first time. The catalytic cycle and a tentative reaction mechanism were discussed and experimentally verified. Structural and optical properties of the synthesized quinazolines are also described. © The Royal Society of Chemistry 2013.
Significance of weak interactions in imidazolium picrate ionic liquids: Spectroscopic and theoretical studies for molecular level understanding
(Royal Society of Chemistry, 2015) Sumit Kumar Panja; Nidhi Dwivedi; Hemanth Noothalapati; Shinsuke Shigeto; A.K. Sikder; Abhijit Saha; Sailaja S. Sunkari; Satyen Saha
The effects of interionic hydrogen bonding and π-π stacking interactions on the physical properties of a new series of picrate anion based ionic liquids (ILs) have been investigated experimentally and theoretically. The existence of aromatic (C2-H⋯O) and aliphatic (C7-H⋯O-N22 and C6-H⋯O-N20) hydrogen bonding and π-π stacking interactions in these ILs has been observed using various spectroscopic techniques. The aromatic and aliphatic C-H⋯O hydrogen bonding interactions are found to have a crucial role in binding the imidazolium cation and picrate anion together. However, the π-π stacking interactions between two successive layers are found to play a decisive role in tight packing in ILs leading to differences in physical properties. The drastic difference in the melting points of the methyl and propyl derivatives (mmimPic and pmimPic respectively) have been found to be primarily due to the difference in the strength and varieties of π-π stacking interactions. While in mmimPic, several different types of π-π stacking interactions between the aromatic rings (such as picrate-picrate, picrate-imidazole and imidazolium-imidazolium cation rings) are observed, only one type of π-π stacking interaction (picrate-picrate rings) is found to exist in the pmimPic IL. NMR spectroscopic studies reveal that the interaction of these ILs with solvent molecules is different and depends on the dielectric constant of the solvent. While an ion solvation model explains the solvation in high dielectric solvents, an ion-pair solvation model is found to be more appropriate for low dielectric constant solvents. The enhanced stability of these investigated picrate ILs compared with that of inorganic picrate salts under high doses of γ radiation clearly indicates the importance of weak interionic interactions in ILs, and also opens up the possibility of the application of picrate ILs as prospective diluents in nuclear separation for advanced fuel cycling process. © the Owner Societies 2015.
Temperature sensor probe based on intramolecular charge transfer (ICT) & reversible solute-solvent interaction in solution
(Elsevier B.V., 2019) Sumit Kumar Panja; Satyen Saha
In this present work, we have developed a temperature sensitive ICT probe (KNP) to investigate alternation of ICT process with the temperature in polar protic solvents. The H-bonding interaction is found to play a key role on solute-solvent interaction to become a temperature sensitive ICT probe in solution. From temperature dependent UV–Vis spectra, it is cleared that the solute-solvent interaction is reversible in nature with temperature and affected by concentration in polar protic solvents. The reversible solute-solvent interaction is observed by monitoring the intensity variation of intramolecular charge transfer (ICT) band with temperature in solution. © 2018
Tuning the intramolecular charge transfer (ICT) process in push-pull systems: Effect of nitro groups
(Royal Society of Chemistry, 2016) Sumit Kumar Panja; Nidhi Dwivedi; Satyen Saha
The intramolecular charge transfer (ICT) process in donor-acceptor systems has tremendous importance in various physical and biological systems. Three nitrophenolate salts were synthesized and studied here. The ICT and π → π∗ transition processes were identified in these derivatives using UV-Vis spectroscopy and theoretical calculations. It was observed that by simple substitution with nitro groups, one can generate and control the ICT process by regulating the charge distribution over the molecule. While for a monosubstitute nitro derivative, only one ICT band was observed, additional ICT processes can be generated at will by introducing a second nitro group. The intensity of this second ICT channel can be regulated with introduction of a third nitro group. Further, the association constants and solvation processes for these potassium nitrophenolate derivatives were found to be drastically dependent on the number of ICT channels present in the molecule. Theoretical studies (MEP analysis) support the experimental observations presented here. The results show that by simply introducing additional acceptor groups to the system, one can tune the ICT band efficiently in a conjugate system. © 2016 The Royal Society of Chemistry.