Ajeet Kumar Singh

@ictmumbai.edu.in

Ph.D. Scholar, Department of Chemistry
Institute of Chemical Technology Mumbai- IOC Odisha Campus Bhubaneswar

Ajeet Kumar Singh


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https://researchid.co/ajeetkr23

EDUCATION

Ph.D. Chemistry

RESEARCH, TEACHING, or OTHER INTERESTS

Chemistry, Physical and Theoretical Chemistry, Inorganic Chemistry, Electrochemistry
13

Scopus Publications

191

Scholar Citations

7

Scholar h-index

6

Scholar i10-index

Scopus Publications

  • Late-stage N-Me selective alkenylation and alkynylation of drugs and unactivated tertiary amines using photoredox catalysis
    Swagata Paul, Somenath Mahato, Sanat Kumar Mahapatra, Sarani Dey, Debasmita Paul, Suparna Mondal, Arpan Naskar, Srinivasa Srikar, Saitosh Mohanty, Saleha Khatun, Debraj Ghorai, Ajeet Kumar Singh, Sagarika Das, Nihar Ranjan Jana, Boudhayan Bandyopadhyay, Abhijit Das, Lisa Roy, Santanu Panda
    Nature Communications, 2026
    Late-stage functionalization (LSF) of marketed drugs facilitates novel chemical space around drug leads. Considering alkyl tertiary amines are present in a large number of life-saving drugs, the development of a LSF strategy to introduce functionalizable groups provides a toolbox for future drug discovery. The introduction of vinyl and alkyne groups into a marketed drug also offers numerous advantages and potential applications, including augmented structural diversity, bio-orthogonal labeling, click chemistry, pharmacological modulation, and drug conjugation strategies. Herein, we report a synthetic strategy for N-methyl selective alkenylation and alkynylation of aliphatic tertiary amines using organophotoredox catalysis and their application to the late-stage functionalization of marketed drugs. Molecular modeling followed by bioactivity studies of novel imipramine alkenylated and alkynylated analogues shows improved efficiency compared to imipramine in reducing the depressive state, justifying the importance of N-methyl selective alkenylation and alkynylation. A thorough investigation of the reaction mechanism has been conducted to understand the regioselective formation of the N-Me selective product. DFT calculations combined with experimental evidence indicate that the regioselective outcome is controlled by the radical addition step not the radical formation step, which mostly remains unknown. The development of a Late-stage functionalization strategy to introduce functionalizable groups provides a toolbox for future drug discovery. Herein, the authors report a synthetic strategy for the N-methyl selective alkenylation and alkynylation of aliphatic tertiary amines using organophotoredox catalysis, and its application to the late-stage functionalization of marketed drugs.
  • Accessing Triplet State via Enhanced Intersystem Crossing in Covalent Organic Frameworks for Natural Sunlight-Driven Photocatalysis
    Amitha Agnes Fernandes, Ajeet Kumar Singh, Sk. Jubeda Begum, Sunny Sarkar, Varadharajan E., Santu Ruidas, Anita Das, Astam K. Patra, Lisa Roy, Asim Bhaumik, Sasanka Dalapati
    Chemsuschem, 2026
    Small changes in molecular structure can modify the energy landscape by altering the electronic functions of the covalent organic frameworks (COFs) toward photocatalytic reactions. Herein, porphyrin‐based visible‐light photosensitizers embedded in crystalline and porous COFs are showcased, offering substantial utilization of natural sunlight during photocatalysis. A detailed investigation of photophysical, photoelectrochemical, and photocatalysis reaction kinetics, along with controlled experiments, suggests that π‐conjugation in COFs plays an indispensable role in highly selective and efficient photocatalysis by in situ generating singlet oxygen ( 1 O 2 ) from triplet molecular oxygen via an energy or electron‐transfer mechanism. The pharmaceutically important sulfoxide precursors with various functional group tolerances were synthesized via selective oxidation under mild and environmentally friendly synthesis conditions. The metal‐free COF catalyst was recycled at least five times without deteriorating the photocatalytic activity. The density functional theory calculation further reveals that efficient access to the low‐energy triplet state, via enhanced intersystem crossing efficiency, relies on the molecular design of sustainable COF catalysts that influence 1 O 2 generation kinetics, high selectivity, and conversion. Sunlight‐driven photocatalysis under mild conditions without requiring toxic reagents or nonrecyclable additives is an emerging strategy to access value‐added chemicals in a “greener” and sustainable fashion, considering the energy efficiency and environmental safety.
  • Non-equilibrium autopoietic vesicles driven by intrinsic catalysis
    Sangam Jha, Soumili Roy, Antara Reja, Ajeet Kumar Singh, Lisa Roy, Dibyendu Das
    Chem, 2025
  • Minimal catalytic dissipative assemblies via cooperation of an amino acid, a nucleobase precursor and a cofactor
    Syed Pavel Afrose, Soumili Roy, Pratip Bhattacharyya, Ajeet Kumar Singh, Lisa Roy, Dibyendu Das
    Chemical Science, 2025
    Functional cooperation between a heterocycle, amino acid and cofactor with an aromatic substrate formed catalytic non-equilibrium networks. The dissipative assemblies showed oxidative degradation of the substrate, leading to autonomous disassembly.
  • Toward Rational Design of Mononuclear Nickel Complexes as Water Oxidation Catalysts Exploring the Ligand Effects on the Rate-Determining Step
    Ajeet Kumar Singh, Lisa Roy
    Chemphyschem, 2024
    The major impediment in realizing a carbon‐neutral hydrogen fuel economy is the cost and inadequacy of contemporary electrochemical water splitting approaches towards the energy intensive oxygen evolution reaction (OER). The O−O bond formation in the water oxidation half‐cell reaction is both kinetically and thermodynamically challenging and amplifies the overpotential requirement in most of the active water oxidation catalysts. Herein, density functional theory is employed to interrogate 20 Ni(II) complexes, out of which 17 are in silico designed molecular water oxidation catalysts, coordinated to electron‐rich tetra‐anionic redox non‐innocent phenylenebis(oxamidate) and dibenzo‐1,4,7,10‐tetraazacyclododecane‐2,3,8,9‐tetraone parent ligands and their structural analogues, and identify the role of substituent changes or ligand effects in the order of their reactivity. Importantly, our computational mechanistic analyses predict that the activation free energy of the rate‐determining O−O bond formation step obeys an inverse scaling relationship with the global electrophilicity index of the intermediate generated on two‐electron oxidation of the starting complex. Additionally, the driving force is directly correlated with this OER descriptor which enables two‐dimensional volcano representation and thereby extrapolation towards the ideal substitution with the chosen ligand. Our study, therefore, establish fundamental insights to overcome the imperative overpotential issue with simple and precise computational rationalization preceding experimental validation.
  • Evolution in the Design of Water Oxidation Catalysts with Transition-Metals: A Perspective on Biological, Molecular, Supramolecular, and Hybrid Approaches
    Ajeet Kumar Singh, Lisa Roy
    ACS Omega, 2024
    Increased demand for a carbon-neutral sustainable energy scheme augmented by climatic threats motivates the design and exploration of novel approaches that reserve intermittent solar energy in the form of chemical bonds in molecules and materials. In this context, inspired by biological processes, artificial photosynthesis has garnered significant attention as a promising solution to convert solar power into chemical fuels from abundantly found H2O. Among the two redox half-reactions in artificial photosynthesis, the four-electron oxidation of water according to 2H2O → O2 + 4H+ + 4e– comprises the major bottleneck and is a severe impediment toward sustainable energy production. As such, devising new catalytic platforms, with traditional concepts of molecular, materials and biological catalysis and capable of integrating the functional architectures of the natural oxygen-evolving complex in photosystem II would certainly be a value-addition toward this objective. In this review, we discuss the progress in construction of ideal water oxidation catalysts (WOCs), starting with the ingenuity of the biological design with earth-abundant transition metal ions, which then diverges into molecular, supramolecular and hybrid approaches, blurring any existing chemical or conceptual boundaries. We focus on the geometric, electronic, and mechanistic understanding of state-of-the-art homogeneous transition-metal containing molecular WOCs and summarize the limiting factors such as choice of ligands and predominance of environmentally unrewarding and expensive noble-metals, necessity of high-valency on metal, thermodynamic instability of intermediates, and reversibility of reactions that create challenges in construction of robust and efficient water oxidation catalyst. We highlight how judicious heterogenization of atom-efficient molecular WOCs in supramolecular and hybrid approaches put forth promising avenues to alleviate the existing problems in molecular catalysis, albeit retaining their fascinating intrinsic reactivities. Taken together, our overview is expected to provide guiding principles on opportunities, challenges, and crucial factors for designing novel water oxidation catalysts based on a synergy between conventional and contemporary methodologies that will incite the expansion of the domain of artificial photosynthesis.
  • Computational Mechanistic Insights on Homogeneous Water Oxidation Versus Catalyst Deactivation: A Case Study with Mononuclear Nickel and Copper Complexes
    Ajeet Kumar Singh, Lisa Roy
    European Journal of Inorganic Chemistry, 2023
    Water splitting is a potential pathway for hydrogen gas evolution and thereby realization of a carbon‐neutral sustainable energy scheme. However, oxidation of water to dioxygen is the major impediment in conversion of solar energy to fuel. Herein, density functional studies are conducted to explore the reactivity conduits of two molecular electro‐catalysts consisting of nickel and copper tetra‐anionic tetradentate amide ligand complexes of the type [(L1)MII]2−, where L1=o‐phenylenebis(oxamidate), and their substitutionally modified analogues. While nickel complexes demonstrate complex borderline chemistry between homogeneous and heterogeneous pathways, showing competition between water oxidation and molecular species degradation, copper complexes display robust and efficient molecular water oxidation behavior. Our analysis predict that this disparity is primarily due to the reversible O−O bond formation in nickel complexes, which provide the platform necessary for a direct attack of OH−/H+ on the metal and terminally accessible amidate groups of the 2e− oxidized anionic intermediate, [(L1⋅)NiIII(OH)]1−, respectively. This intermediate streamline ligand deactivation with a comparatively higher driving force for nickel complexes in acidic medium. Contrarily, the copper complexes display radical character on the hydroxyl ligand in the corresponding intermediate, [(L1⋅)CuII(OH⋅)]1−, that expedite O−O interaction, leading to predominant homogeneous water oxidation under all conditions.
  • Probing Molecular Chirality on the Self-Assembly and Gelation of Naphthalimide-Conjugated Dipeptides
    Soumen Kuila, Ajeet Kumar Singh, Akash Shrivastava, Sukantha Dey, Tukai Singha, Lisa Roy, Biswarup Satpati, Jayanta Nanda
    Journal of Physical Chemistry B, 2023
    In this work, 1,8-naphthalimide (NMI)-conjugated three hybrid dipeptides constituted of a β-amino acid and an α-amino acid have been designed, synthesized, and purified. Here, in the design, the chirality of the α-amino acid was varied to study the effect of molecular chirality on the supramolecular assembly. Self-assembly and gelation of three NMI conjugates were studied in mixed solvent systems [water and dimethyl sulphoxide (DMSO)]. Interestingly, chiral NMI derivatives [NMI-βAla-lVal-OMe (NLV) and NMI-βAla-dVal-OMe (NDV)] formed self-supported gels, while the achiral NMI derivative [NMI-βAla-Aib-OMe, (NAA)] failed to form any kind of gel at 1 mM concentration and in a mixed solvent (70% water in DMSO medium). Self-assembly processes were thoroughly investigated using UV-vis spectroscopy, nuclear magnetic resonance (NMR), fluorescence, and circular dichroism (CD) spectroscopy. A J-type molecular assembly was observed in the mixed solvent system. The CD study indicated the formation of chiral assembled structures for NLV and NDV, which were mirror images of one another, and the self-assembled state by NAA was CD-silent. The nanoscale morphology of the three derivatives was studied using scanning electron microscopy (SEM). In the case of NLV and NDV, left- and right-handed fibrilar morphologies were observed, respectively. In contrast, a flake-like morphology was noticed for NAA. The DFT study indicated that the chirality of the α-amino acid influenced the orientation of π-π stacking interactions of naphthalimide units in the self-assembled structure that in turn regulated the helicity. This is a unique work where molecular chirality controls the nanoscale assembly as well as the macroscopic self-assembled state.
  • Pathway Complexity in Supramolecular Copolymerization and Blocky Star Copolymers by a Hetero-Seeding Effect
    Payel Khanra, Ajeet Kumar Singh, Lisa Roy, Anindita Das
    Journal of the American Chemical Society, 2023
    This study unravels the intricate kinetic and thermodynamic pathways involved in the supramolecular copolymerization of the two chiral dipolar naphthalene monoimide (NMI) building blocks (O-NMI and S-NMI), differing merely by a single heteroatom (oxygen vs sulfur). O-NMI exhibits distinct supramolecular polymerization features as compared to S-NMI in terms of its pathway complexity, hierarchical organization, and chiroptical properties. Two distinct self-assembly pathways in O-NMI occur due to the interplay between the competing dipolar interactions among the NMI chromophores and amide-amide hydrogen (H)-bonding that engenders distinct nanotapes and helical fibers, from its antiparallel and parallel stacking modes, respectively. In contrast, the propensity of S-NMI to form only a stable spherical assembly is ascribed to its much stronger amide-amide H-bonding, which outperforms other competing interactions. Under the thermodynamic route, an equimolar mixture of the two monomers generates a temporally controlled chiral statistical supramolecular copolymer that autocatalytically evolves from an initially formed metastable spherical heterostructure. In contrast, the sequence-controlled addition of the two monomers leads to the kinetically driven hetero-seeded block copolymerization. The ability to trap O-NMI in a metastable state allows its secondary nucleation from the surface of the thermodynamically stable S-NMI spherical "seed", which leads to the core-multiarmed "star" copolymer with reversibly and temporally controllable length of the growing O-NMI "arms" from the S-NMI "core". Unlike the one-dimensional self-assembly of O-NMI and its random co-assembly with S-NMI, which are both chiral, unprecedentedly, the preferred helical bias of the nucleating O-NMI fibers is completely inhibited by the absence of stereoregularity of the S-NMI "seed" in the "star" topology.
  • A convenient route to a vinylogous dicyano aryl based AIEgen with switchable mechanochromic luminescence properties
    Saurajit Ghosh, Himanshi Bhambri, Ajeet Kumar Singh, Sanjay K. Mandal, Lisa Roy, Partha Sarathi Addy
    Chemical Communications, 2023
    A convenient two step synthetic protocol is reported to obtain a mechanochromic luminescent molecule with switchable optical property.
  • Tuning of the Supramolecular Helicity of Peptide-Based Gel Nanofibers
    Souvik Misra, Pijush Singh, Ajeet Kumar Singh, Lisa Roy, Soumen Kuila, Sukantha Dey, Ajit K. Mahapatra, Jayanta Nanda
    Journal of Physical Chemistry B, 2022
  • Solvophobically-Driven Merocyanine Dye Assembly: Predominant Dipole-Dipole Interactions Over Hydrogen-Bonding
    Aritra Rajak, Ajeet Kumar Singh, Lisa Roy, Anindita Das
    Chemnanomat, 2022
  • Stimuli-responsive luminescent supramolecular assemblies and co-assemblies through orthogonal dipole-dipole interactions and halogen bonding
    Akshoy Jamadar, Ajeet Kumar Singh, Lisa Roy, Anindita Das
    Journal of Materials Chemistry C, 2021

RECENT SCHOLAR PUBLICATIONS

  • Late-stage N-Me selective alkenylation and alkynylation of drugs and unactivated tertiary amines using photoredox catalysis
    S Paul, S Mahato, SK Mahapatra, S Dey, D Paul, S Mondal, A Naskar, ...
    Nature Communications , 2026
    2026
  • Accessing Triplet State via Enhanced Intersystem Crossing in Covalent Organic Frameworks for Natural Sunlight‐Driven Photocatalysis
    AA Fernandes, AK Singh, SJ Begum, S Sarkar, V E, S Ruidas, A Das, ...
    ChemSusChem 19 (3), e202502392 , 2026
    2026
  • Non-equilibrium autopoietic vesicles driven by intrinsic catalysis
    S Jha, S Roy, A Reja, AK Singh, L Roy, D Das
    Chem 11 (12) , 2025
    2025
    Citations: 4
  • Minimal catalytic dissipative assemblies via cooperation of an amino acid, a nucleobase precursor and a cofactor
    SP Afrose, S Roy, P Bhattacharyya, AK Singh, L Roy, D Das
    Chemical Science 16 (18), 7838-7846 , 2025
    2025
    Citations: 2
  • Toward Rational Design of Mononuclear Nickel Complexes as Water Oxidation Catalysts Exploring the Ligand Effects on the Rate‐Determining Step
    A Kumar Singh, L Roy
    ChemPhysChem 25 (20), e202400533 , 2024
    2024
    Citations: 2
  • Evolution in the design of water oxidation catalysts with transition-metals: a perspective on biological, molecular, supramolecular, and hybrid approaches
    AK Singh, L Roy
    ACS omega 9 (9), 9886-9920 , 2024
    2024
    Citations: 45
  • Cover Feature: Computational Mechanistic Insights on Homogeneous Water Oxidation Versus Catalyst Deactivation: A Case Study with Mononuclear Nickel and Copper Complexes (Eur. J …
    AK Singh, L Roy
    European Journal of Inorganic Chemistry 26 (34), e202300626 , 2023
    2023
  • Computational Mechanistic Insights on Homogeneous Water Oxidation Versus Catalyst Deactivation: A Case Study with Mononuclear Nickel and Copper Complexes
    AK Singh, L Roy
    European Journal of Inorganic Chemistry 26 (34), e202300412 , 2023
    2023
    Citations: 3
  • Probing Molecular Chirality on the Self-Assembly and Gelation of Naphthalimide-Conjugated Dipeptides
    S Kuila, AK Singh, A Shrivastava, S Dey, T Singha, L Roy, B Satpati, ...
    The Journal of Physical Chemistry B 127 (21), 4808-4819 , 2023
    2023
    Citations: 11
  • Pathway complexity in supramolecular copolymerization and blocky star copolymers by a hetero-seeding effect
    P Khanra, AK Singh, L Roy, A Das
    Journal of the American Chemical Society 145 (9), 5270-5284 , 2023
    2023
    Citations: 59
  • A convenient route to a vinylogous dicyano aryl based AIEgen with switchable mechanochromic luminescence properties
    S Ghosh, H Bhambri, AK Singh, SK Mandal, L Roy, PS Addy
    Chemical Communications 59 (30), 4463-4466 , 2023
    2023
    Citations: 14
  • Tuning of the Supramolecular Helicity of Peptide-Based Gel Nanofibers
    S Misra, P Singh, AK Singh, L Roy, S Kuila, S Dey, AK Mahapatra, ...
    The Journal of Physical Chemistry B 126 (51), 10882-10892 , 2022
    2022
    Citations: 13
  • Solvophobically‐Driven Merocyanine Dye Assembly: Predominant Dipole‐Dipole Interactions Over Hydrogen‐Bonding
    A Rajak, A Kumar Singh, L Roy, A Das
    ChemNanoMat 8 (6), e202200082 , 2022
    2022
    Citations: 9
  • Stimuli-responsive luminescent supramolecular assemblies and co-assemblies through orthogonal dipole–dipole interactions and halogen bonding
    A Jamadar, AK Singh, L Roy, A Das
    Journal of Materials Chemistry C 9 (35), 11893-11904 , 2021
    2021
    Citations: 29

MOST CITED SCHOLAR PUBLICATIONS

  • Pathway complexity in supramolecular copolymerization and blocky star copolymers by a hetero-seeding effect
    P Khanra, AK Singh, L Roy, A Das
    Journal of the American Chemical Society 145 (9), 5270-5284 , 2023
    2023
    Citations: 59
  • Evolution in the design of water oxidation catalysts with transition-metals: a perspective on biological, molecular, supramolecular, and hybrid approaches
    AK Singh, L Roy
    ACS omega 9 (9), 9886-9920 , 2024
    2024
    Citations: 45
  • Stimuli-responsive luminescent supramolecular assemblies and co-assemblies through orthogonal dipole–dipole interactions and halogen bonding
    A Jamadar, AK Singh, L Roy, A Das
    Journal of Materials Chemistry C 9 (35), 11893-11904 , 2021
    2021
    Citations: 29
  • A convenient route to a vinylogous dicyano aryl based AIEgen with switchable mechanochromic luminescence properties
    S Ghosh, H Bhambri, AK Singh, SK Mandal, L Roy, PS Addy
    Chemical Communications 59 (30), 4463-4466 , 2023
    2023
    Citations: 14
  • Tuning of the Supramolecular Helicity of Peptide-Based Gel Nanofibers
    S Misra, P Singh, AK Singh, L Roy, S Kuila, S Dey, AK Mahapatra, ...
    The Journal of Physical Chemistry B 126 (51), 10882-10892 , 2022
    2022
    Citations: 13
  • Probing Molecular Chirality on the Self-Assembly and Gelation of Naphthalimide-Conjugated Dipeptides
    S Kuila, AK Singh, A Shrivastava, S Dey, T Singha, L Roy, B Satpati, ...
    The Journal of Physical Chemistry B 127 (21), 4808-4819 , 2023
    2023
    Citations: 11
  • Solvophobically‐Driven Merocyanine Dye Assembly: Predominant Dipole‐Dipole Interactions Over Hydrogen‐Bonding
    A Rajak, A Kumar Singh, L Roy, A Das
    ChemNanoMat 8 (6), e202200082 , 2022
    2022
    Citations: 9
  • Non-equilibrium autopoietic vesicles driven by intrinsic catalysis
    S Jha, S Roy, A Reja, AK Singh, L Roy, D Das
    Chem 11 (12) , 2025
    2025
    Citations: 4
  • Computational Mechanistic Insights on Homogeneous Water Oxidation Versus Catalyst Deactivation: A Case Study with Mononuclear Nickel and Copper Complexes
    AK Singh, L Roy
    European Journal of Inorganic Chemistry 26 (34), e202300412 , 2023
    2023
    Citations: 3
  • Minimal catalytic dissipative assemblies via cooperation of an amino acid, a nucleobase precursor and a cofactor
    SP Afrose, S Roy, P Bhattacharyya, AK Singh, L Roy, D Das
    Chemical Science 16 (18), 7838-7846 , 2025
    2025
    Citations: 2
  • Toward Rational Design of Mononuclear Nickel Complexes as Water Oxidation Catalysts Exploring the Ligand Effects on the Rate‐Determining Step
    A Kumar Singh, L Roy
    ChemPhysChem 25 (20), e202400533 , 2024
    2024
    Citations: 2
  • Late-stage N-Me selective alkenylation and alkynylation of drugs and unactivated tertiary amines using photoredox catalysis
    S Paul, S Mahato, SK Mahapatra, S Dey, D Paul, S Mondal, A Naskar, ...
    Nature Communications , 2026
    2026
  • Accessing Triplet State via Enhanced Intersystem Crossing in Covalent Organic Frameworks for Natural Sunlight‐Driven Photocatalysis
    AA Fernandes, AK Singh, SJ Begum, S Sarkar, V E, S Ruidas, A Das, ...
    ChemSusChem 19 (3), e202502392 , 2026
    2026
  • Cover Feature: Computational Mechanistic Insights on Homogeneous Water Oxidation Versus Catalyst Deactivation: A Case Study with Mononuclear Nickel and Copper Complexes (Eur. J …
    AK Singh, L Roy
    European Journal of Inorganic Chemistry 26 (34), e202300626 , 2023
    2023