Browsing by Author "Ray, Saumi"

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Characterization of a Zeolite-Y-Encapsulated Zn(II)Salmphen Complex with Targeted Anticancer Property
(ACS, 2023-11) Chowdhury, Shibasish; Ray, Saumi
Resistance and severe side effects of classical chemotherapeutic drugs are major challenges to cancer therapy. New therapeutic agents and combination therapy are considered potential solutions that enhance the efficacy of the drug as well as reduce drug resistance. The success of a platinum-based anticancer drug, cisplatin, has paved the way to explore metal-centered anticancer therapeutic agents. Herein, the zeolite-Y-encapsulated Zn(II)Salmphen complex is synthesized using a flexible ligand approach. The Zn(II)Salmphen complex and its encapsulation within the supercage of zeolite-Y were characterized by elemental analysis, Fourier transform infrared (FTIR) spectroscopy, UV–vis, fluorescence, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), NMR, and high-resolution mass spectrometry (HRMS) techniques. Elemental analysis, PXRD, and SEM, all together confirm the integrity of the zeolite framework after the encapsulation of Zn(II)Salmphen complex in it, and elemental analysis provides the Si/Al ratio and Zn content present. FTIR and XPS studies indicate the successful encapsulation of the complex. NMR and HRMS studies confirm that the Zn(II)Salmphen complex is dimer; however, within the supercage of zeolite-Y, it is expected to exist as a monomer. The extent of structural modification of the encapsulated Zn(II)Salmphen complex is intimated by electronic spectroscopic studies. The free-state Zn(II)Salmphen is a fluorescent complex, and even the encapsulated Zn(II)Salmphen complex, when taken in dimethyl sulfoxide (DMSO), shows fluorescence. In comparison to cisplatin, encapsulated Zn(II)Salmphen complex displays comparable cytotoxicity (IC50 = 2.0 ± 0.5 μg/mL at 48 h) toward breast cancer cell line, whereas free Zn(II)Salmphen has better cytotoxicity (IC50 = 1.5 ± 0.5 μg/mL at 48 h). Importantly, elemental analysis has revealed that the IC50 value, if calculated only in terms of Zn(II)Salmphen within Zn(II)Salmphen-Y, is as low as 54.59 ng/mL, indicating a very high efficacy of the drug. Interestingly, a 48 h treatment with the encapsulated Zn(II)Salmphen complex shows no toxicity toward immortal noncancerous keratinocyte cells (HaCaT), whereas cisplatin has an IC50 value of 1.75 ± 0.5 μg/mL. Internalization studies indicate that zeolite-Y targets cancer cells better than it does noncancerous ones. Hence, cellular uptake of the zeolite-encapsulated Zn(II)Salmphen complex in cancer cells is more than that in HaCaT cells, resulting in the generation of more reactive oxygen species and cell death. Significant upregulation of DNA damage response protein indicates that DNA-damage-induced cellular apoptosis could be the mechanism of drug action. Overall, the zeolite-encapsulated Zn(II)Salmphen complex could be a better alternative to the traditional drug cisplatin with minimal effect on noncancerous HaCaT cells and can also be utilized as a fluorescent probe in exploring the mechanistic pathway of its activity against cancer cells.
CO2 to Cyclic Carbonate: A Mechanistic Insight of a Benign Route Using Zinc(II) Salophen Complexes
(Wiley, 2023-12) Ray, Saumi
Zinc(II) Schiff base complexes with different substituents at 5, 5’ positions have been synthesized to study the effect of the electronic environment of the metal towards the cycloaddition reaction between CO2 and epoxide. The complexes have been characterized by FT-IR, XPS, NMR, electronic spectroscopy, LC–MS, and TGA. We have used density functional theory to study the electronic structure of the Zn(II) complexes and modelled the electronic spectra and the mechanism of catalysis. Results obtained from DFT and LC–MS indicate the dimeric structures for all the complexes except ZnL4. The monomeric ZnL4 has the strongest electron withdrawing group, i. e., −NO2 at 5, 5’ positions along with two labile water molecules attached to the Zn center. The dimeric complexes exhibit good to moderate yield for cycloaddition reaction to styrene carbonate under solvent-free conditions and a relatively low reaction temperature of 80 °C, with CO2 pressure of ~1 atm. The best yield has been achieved by ZnL4. Different rate-determining steps are captured by the DFT studies for dimeric and monomeric complexes. Without taking any preventing measure of dimerization by attaching the bulky tBu groups, relatively lesser catalytic amounts of all the complexes have shown yields of cyclic carbonate between 53–74 %, depending on the nature of the substituent present.
Efficient oxidative coupling of amines to imines under natural sunlight using a benzothiadiazole-based molecular photocatalyst
(RSC, 2025-01) Ray, Saumi
Developing a ‘greener’ avenue for organic synthesis is a key challenge, which must focus on energy efficiency as well as sustainability. Harnessing solar energy to chemical energy is an efficient way to utilize renewable energy resources. Herein, we report a D–A-type (donor–acceptor-type) small organic molecular photocatalyst (SOMP) “Ph-BT-Ph” with benzothiadiazole as the primary photoactive unit for oxidative coupling of amines to synthesize imines. Photocatalyst Ph-BT-Ph is synthesized using a Suzuki–Miyaura coupling reaction and thoroughly characterized by 1H-NMR, HRMS, and cyclic voltammetry studies. Photoluminescence and lifetime studies of Ph-BT-Ph show a high excited state reduction potential (−1.37 V vs. Ag/AgCl) and longer lifetime (12.64 ns) which make it suitable for photocatalytic organic transformations. The photocatalytic activity of the catalyst has been evaluated on the direct oxidative coupling reaction of amines to synthesize imines in the presence of natural sunlight and O2 as a green oxidant. Catalyst Ph-BT-Ph exhibits excellent photocatalytic performance under optimal reaction conditions by converting >99% amine to imine with >98% selectivity within 2 hours. This high photocatalytic efficiency has been achieved by purging oxygen only for 2 minutes and without any mechanical energy input (no stirring). Quite a moderate amount of catalyst (0.13 mol%) has been employed which results in a high catalytic turnover frequency of 381 h−1. EPR spectroscopy and theoretical studies are performed to understand the reaction mechanism and to determine the active sites of the catalyst. The Ph-BT-Ph catalyst surpasses the photocatalytic efficiencies of many reported metal-free catalysts for oxidative coupling of amines. Such SOMPs, with easily tunable absorption range and well-defined energy-band positions, offer a new class of metal-free and photoactive catalysts for organic synthesis with outstanding performance under greener reaction conditions.
Encapsulated Schiff base nickel complex in zeolite Y: Correlation between catalytic activities and extent of distortion supported by experimental and DFT studies
(Elsiever, 2017-06-01) Ray, Saumi
It is observed that planar Ni(II)–Schiff base complexes of general formulae NiL with L as N, Ń-bis(4-hydroxy salicylidene)ethylenediamine (4-OH-salen) when encapsulated in the supercage of zeolite Y, the complex adopts non-planar geometry. The detailed characterization studies of the 4-OH-Ni-salen complex when compared with Ni-salen complex encapsulated in zeolite Y (Ni-salen-Y) Choudhary et al. (2016) have suggested that the complex undergoes more distortion in order to accommodate itself inside the supercage of zeolite-Y. Optical spectroscopic studies show relatively more blue shifted and intensified d-d transition for 4-OH-Ni-salen complex after encapsulation. We also report the catalytic activities and enhanced magnetization of encapsulated complex though it is diamagnetic in the ‘free’ state. DFT studies of these complexes have been carried out in different spin states and electronic spectra are simulated to have better insight about the geometries adopted by the guest complexes inside the host framework.
Encapsulation of a Ni salen complex in zeolite Y: an experimental and DFT study
(RSC, 2015) Ray, Saumi
It is observed that for a square planar Ni(II)-Schiff base complex of the general formula {Ni(II)L}, where L is {L: N,N′-bis(5-hydroxy-salicylidene)ethylenediamine}, when encapsulated in a supercage of zeolite Y the bulky guest complex adopts a non-planar geometry without disturbing the integrity of the zeolite framework. Detailed comparative characterization is carried out to understand the structural change of the guest complex as a result of steric and electronic interactions with the host framework. UV-Vis spectroscopic studies of the encapsulated and ‘neat’ complex show a significant blue shift in the d–d transition after encapsulation and the diamagnetic ‘neat’ complex exhibits paramagnetism after encapsulation. DFT studies of the Ni(II)-Schiff base complex have been carried out for different spin states in neat and encapsulated form and the UV-Vis spectra are simulated using TD-DFT to understand the observed spectra in detail.
Encapsulation of Cobalt Phthalocyanine in Zeolite-Y: Evidence for Nonplanar Geometry
(ACS, 2003-02) Ray, Saumi
Cobalt (II) phthalocyanine (CoPc) molecules have been encapsulated within the supercage of zeolite-Y. The square-planar complex, being larger than the almost spherical cage, is forced to adopt a distorted geometry on encapsulation. A comparative spectroscopic and magnetic investigation of CoPc encapsulated in zeolite-Y and in the unencapsulated state is reported. These results supported by molecular modeling have been used to understand the nature and extent of the loss of planarity of CoPc on encapsulation. The encapsulated molecule is shown to be the trans-diprotonated species in which the center of inversion is lost due to distortions required to accommodate the square complex within the zeolite. Encapsulation also leads to an enhancement of the magnetic moment of the CoPc. This is shown to be a consequence of the nonplanar geometry of the encapsulated molecule resulting in an excited high-spin state being thermally accessible.
Enhanced catalytic activity and magnetization of encapsulated nickel Schiff-base complexes in zeolite-Y: a correlation with the adopted non-planar geometry
(RSC, 2016) Ray, Saumi
Square planar Ni(II)-Schiff base complexes when encapsulated in a supercage of zeolite Y have shown altered optical, magnetic properties and catalytic activities in comparison to their corresponding free states. Different characterization techniques like XRD analysis, SEM-EDX, AAS, FTIR, UV-Visible spectroscopy and magnetic studies as well as detailed theoretical studies altogether show the differences in the properties of complexes in free and encapsulated states. All these studies have suggested that the largest complex deviates by the maximum amount from its free-state properties and a fascinating correlation between the extent of deviation from molecular dimension and modified catalytic activity of encapsulated complexes is observed.
Evaluating LLMs for zeolite synthesis event extraction (ZSEE) : a systematic analysis of prompting strategies
(2025-12) Ray, Saumi
Extracting structured information from zeolite synthesis experimental procedures is critical for materials discovery, yet existing methods have not systematically evaluated Large Language Models (LLMs) for this domain-specific task. This work addresses a fundamental question: what is the efficacy of different prompting strategies when applying LLMs to scientific information extraction? We focus on four key subtasks: event type classification (identifying synthesis steps), trigger text identification (locating event mentions), argument role extraction (recognizing parameter types), and argument text extraction (extracting parameter values). We evaluate four prompting strategies - zero-shot, few-shot, event-specific, and reflection-based - across six state-of-the-art LLMs (Gemma-3-12b-it, GPT-5-mini, O4-mini, Claude-Haiku-3.5, DeepSeek reasoning and non-reasoning) using the ZSEE dataset of 1,530 annotated sentences. Results demonstrate strong performance on event type classification (80-90\% F1) but modest performance on fine-grained extraction tasks, particularly argument role and argument text extraction (50-65\% F1). GPT-5-mini exhibits extreme prompt sensitivity with 11-79\% F1 variation. Notably, advanced prompting strategies provide minimal improvements over zero-shot approaches, revealing fundamental architectural limitations. Error analysis identifies systematic hallucination, over-generalization, and inability to capture synthesis-specific nuances. Our findings demonstrate that while LLMs achieve high-level understanding, precise extraction of experimental parameters requires domain-adapted models, providing quantitative benchmarks for scientific information extraction.
Fine Mesh Computational Fluid Dynamics Study on Gas-Fluidization of Geldart A Particles: Homogeneous to Bubbling Bed
(ACS, 2016-02-29) Ray, Saumi
Gas-fluidization of Geldart A particles was simulated for a domain of lab-scale dimensions. Hydrodynamics of homogeneous regime and transition to bubbling were studied. In this context a detailed fine mesh simulation study is presented for the first time, using the state-of-the-art two-fluid model (TFM). The effect of particle density was investigated. The fine mesh simulations were analyzed for insights into bed transition from homogeneous to bubbling regime and the effect of interparticle forces (IPFs). Simulations reveal that transition to bubbling occurs over a velocity range rather than at a discrete velocity. We propose an index to quantify the effect of IPFs on bed expansion. During homogeneous expansion this IPF index was found to drop exponentially with velocity. It became negligible as bubbling ensued which is in line with the literature. The simulated average bed voidage was found comparable to the corresponding Eulerian−Lagrangian and experimental data.
The functionality of the hybrid systems driven by molecular dimension of the guest copper Schiff-base complexes entrapped in Zeolite-Y
(Wiley, 2019-01) Ray, Saumi
On encapsulation inside the supercage of zeolite-Y planar Cu (II)–Schiff base complexes show the modified structural, optical and functional properties. The electronic effect of the different substituent groups present in the catalyst plays the decisive role towards their reactivity in the homogeneous phase but after the encapsulation in zeolite Y, reactivity is mainly governed by the molecular dimensions of the guest complexes rather than the electronic factor of the substituent groups attached on them. These systems are well characterized with the help of different characterization tools like XRD analysis, SEM - EDX, AAS, FTIR, XPS, DSC, TGA, BET and UV–Visible spectroscopy and the comparative optical and catalytic studies have provided a rational explanation of enhanced reactivity of zeolite encapsulated metal complexes for various oxidation reactions compared to their corresponding solution states.
Importance of the Nature of Acidic Sites of Different Aluminosilicates on Fixation of Carbon Dioxide with Styrene Oxide
(Wiley, 2023-03) Ray, Saumi
The nature of acidic sites in commercially available aluminosilicates, zeolite Na−Y, zeolite NH4+-ZSM-5, and as-synthesized Al-MCM-41 have been investigated by employing them as catalysts for capturing CO2 by styrene oxide. The catalysts, in tandem with tetrabutylammonium bromide (TBAB), produce styrene carbonate, and the yield of the product is observed to be governed by the acidity of the catalysts and hence, the Si/Al ratio. All these aluminosilicate frameworks have been characterized by IR, BET, TGA, and XRD. XPS, NH3-TPD, and 29Si solid-state NMR studies have been carried out to analyze the Si/Al ratio and the acidity of these catalysts. According to TPD studies, the number of weak acidic sites of these materials follow an order as NH4+-ZSM-5 < Al-MCM-41 < zeolite Na−Y, which is just in accordance with their Si/Al ratios and the yield of the cyclic carbonates obtained, i. e., 55.3 %, 68 %, and 75.4 % respectively. The TPD data and the yield of the product carried out with calcined zeolite Na−Y indicate that not only the weak acidic sites but also the role of strong acidic sites might appear crucial in the cycloaddition reaction.
An insight into the catalytic activity of palladium Schiff-base complexes towards the Heck coupling reaction: routes via encapsulation in zeolite-Y
(RSC, 2019) Ray, Saumi
A small set of palladium Schiff-base complexes were synthesized and entrapped in the supercage of zeolite-Y. All these novel complexes in both states were systematically characterized with the help of different characterization tools like XRD, SEM-EDS, thermal analysis, XPS, IR, electronic spectroscopic and theoretical studies. These systems were thoroughly studied for their catalytic activities towards the Heck coupling reaction between bromobenzene and styrene. The aim was to meticulously compare the performance of the homogeneous catalysts, i.e., neat palladium Schiff-base complexes with that of their heterogeneous encapsulated analogs. The experimental as well as theoretical electronic structure studies suggested significant structural modification of the guest Pd(II)–Schiff-base complexes after encapsulation in zeolite Y. These complexes manifested modified catalytic activities towards the Heck coupling reaction. The theoretical studies reinforced the correlation between the modified catalytic properties and structural alteration of these complexes on encapsulation. These heterogeneous catalysts essentially demonstrated the benefits of easy separation and reusability as compared to the homogeneous analogues.
Mesh size effect on CFD simulation of gas-fluidized Geldart A particles
(Elsiever, 2014) Sande, Priya C; Ray, Saumi
We investigate the effect of mesh size on CFD simulations of a lab-scale sized fluidized bed of Geldart A particles using two-fluid model (TFM), specifically for homogeneous expansion and transition to bubbling. For the first time we have shown a set of lab-scale domain size fine mesh simulations. In this context transient bed voidage profiles have been analyzed in detail. TFM follows the Eulerian–Eulerian approach which has the advantage of being less computationally expensive than Eulerian–Lagrangian approach for an engineering scale. Mesh size has a drastic effect on minimum bubbling velocity. With mesh refining, the observed minimum bubbling velocity approaches its experimental value. On reducing mesh size even up to 1 mm × 1 mm, there was no improvement in capturing homogeneous expansion. Fine mesh simulation revealed void structures and could predict the bubbling transition, though the homogeneous expansion captured was not as much as experimentally observed. Review of several simulations across all the mesh sizes studied, revealed the presence of persisting dilute regions getting triggered around experimental minimum bubbling velocity. Theses persisting dilute regions seem to signal the presence of the bubbling regime. The effect of commonly used drag laws was also studied and it was found that the Gidaspow and Syamlal O'Brien drag laws manifested the dilute region markers at 8 mm/s while for the Wen Yu drag law this value was 10 mm/s. The effect of frictional stress and wall boundary condition for both phases was qualitatively assessed. Omitting frictional stress or changing no-slip to free-slip boundary condition for gas phase had the effect of delaying minimum bubbling velocity.
Palladium–Schiff Base Complexes Encapsulated in Zeolite-Y Host: Functionality Controlled by the Structure of a Guest Complex
(ACS, 2019) Ray, Saumi
A series of palladium complexes of tetradendate Schiff base ligands L1 (N,N′-bis(salicylidene)phenylene-1,3-diamine) and its derivatives L2 and L3 have been synthesized by using the “flexible ligand method” within the supercage of zeolite-Y. These complexes in both their free and encapsulated states have been thoroughly characterized with the help of different characterization tools such as XRD, SEM-EDS, BET, thermal analysis, XPS, IR, and UV–vis spectroscopic studies. All these encapsulated complexes are identified with a dramatic red shift of the d–d transition in their electronic spectra when compared with their free states. Theoretical as well as experimental studies together suggest a substantial modification of the structural parameters of square planar Pd(II)–Schiff base complexes upon encapsulation within the supercage of zeolite-Y. Encapsulated complexes are also subject to show modified catalytic activities toward the Heck reaction. These heterogeneous catalysts can easily be separated from the reaction mixture and reused.
Tuning of Catalytic Property Controlled by the Molecular Dimension of Palladium–Schiff Base Complexes Encapsulated in Zeolite Y
(ACS, 2017) Ray, Saumi
Planar palladium–Schiff base complexes are synthesized, maintaining the order of their molecular dimensions as PdL1 < PdL2 < PdL3 < PdL4 < PdL5 in free state, as well as encapsulated in zeolite Y, where L1: N,N′-bis(salicylidene)ethylenediamine and L2, L3, L4, and L5 are derivatives of L1. All encapsulated complexes have shown better catalytic activity for the sulfoxidation of methyl phenyl sulfide in comparison to their homogeneous counter parts. These hybrid systems are characterized with the help of different characterization techniques such as X-ray diffraction analysis, scanning electron microscopy–energy-dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, Fourier transform infrared, and UV–visible spectroscopy; all of these studies have suggested that the largest complex deviates by the maximum from its free-state properties, and a radical change in the reactivity of the complex is observed.
Unveiling the dichotomy between cobalt(ii)-exchanged x and y faujasite zeolites via oxidative carboxylation of alkene to cyclic carbonate
(ACS, 2025-04) Ray, Saumi
Cobalt(II)-exchanged X and Y zeolites with varying metal loadings were employed to convert CO2 to cyclic carbonates starting from alkenes. The transformation was carried out using O2 as an oxidant in a mixture of O2 and CO2 under atmospheric pressure, and a maximum yield of 35.7% cyclic carbonate was achieved. Studies revealed a stark difference among both the zeolites, primarily arising from a difference in their ion exchange behaviors. Their catalytic and recyclability properties differed as a result of this variation
Zeolite encapsulated Ni(ii) Schiff-base complexes: improved catalysis and site isolation
(RSC, 2020) Ray, Saumi
Two series of zeolite encapsulated Ni(II) Schiff-base complexes, i.e., the Ni(II) sal-1,2-phen and Ni(II) sal-1,3-phen series, have been synthesized in neat and encapsulated states and characterized by using different characterization techniques such as XRD, SEM-EDS, BET, thermal analysis, XPS, IR spectroscopy, UV-vis spectroscopy and magnetic studies. UV-vis spectroscopy, XPS and magnetic studies all together reveal the structural modification of the guest complex and, thereby, the adaptation of electron density around the metal center upon encapsulation. However, encapsulation causes structural alterations for these two series differently and, hence, introduces a certain level of proficiency to these Ni(II) complexes as catalysts for phenol oxidation reaction. However, analysis of catalytic data emphasizes site isolation as a major governing factor for the improved reactivity over the modified electron density around the metal center for phenol oxidation reaction where the heterogeneous mode of catalysis is concerned.
Zeolite-Y encapsulated cobalt(II) Schiff-base complexes employed for photocatalytic dye-degradation and upcycling CO2
(RSC, 2020-12) Ray, Saumi
Planar cobalt(II) Schiff-base complexes show modified structural and functional properties after encapsulation inside zeolite-Y. In the free-state, the reactivity of the cobalt(II) Schiff-base complexes is primarily controlled by the electronic effects of the different substituent groups present in the complexes. However, the encapsulation of these complexes within the supercages of zeolite-Y causes the alteration of the electron density around the metal center and subsequently modifies the reactivity. We have intended to study two environment-friendly reactions, i.e., degradation of rhodamine B dye and transformation of CO2 with catalysts containing relatively lower metal content like cobalt(II) salophen complexes encapsulated in zeolite-Y. To comprehend these systems well, XRD analysis, SEM-EDX, FTIR, XPS, TGA, BET, and UV–visible spectroscopy and DFT studies have been performed. XRD and BET studies along with XPS, experimental and theoretical electronic spectroscopic studies clearly revealed successful encapsulation of the guest complex with some alteration of the electronic environment around the metal center. Catalytic studies identified that encapsulated complexes exhibit the better results for dye degradation. Zeolite-Y encapsulated 5-methoxy cobalt(II) sal-1,2-phen (CoL5-Y) could degrade 89.6% of the dye while neat CoL5 could only degrade 30.2%. Comparative studies of structural and catalytic modifications allowed a rational explanation of enhanced reactivity of zeolite encapsulated metal complexes for the degradation of rhodamine B dye compared to their corresponding free-states. The catalysts showing the maximal and minimal activities for dye degradation in the series, i.e., CoL1, CoL1-Y, CoL5, and CoL5-Y, have been tested for coupling of CO2 and styrene oxide. The TON for CO2 uptake using the heterogeneous catalyst CoL5-Y was found to be 2949, while using the homogeneous counterpart, it was only 339