@article {46702, title = {Photocatalytic hydrogen generation and CO2 conversion using g-C3N4 decorated dendritic fibrous nanosilica: role of interfaces between silica and g-C3N4}, journal = {ACS Applied Energy Materials}, volume = {3}, year = {2020}, month = {SEP }, pages = {8150-8158}, type = {Article}, abstract = {

We have synthesized g-C3N4 decorated over dendritic fibrous nanosilica (DFNS). The generation of C-N-Si interfaces by coating each fiber of DFNS with g-C3N4 not only provided high surface area but also affected the optical and electronic properties of the composite. The catalyst synthesis reproducibility issue of g-C3N4 was resolved using a vacuum-sealed quartz tube. The extended light absorption in the visible region, enhanced lifetime of photogenerated charge carriers due to the formation of interfaces between silica and g-C3N4 (confirmed by solid-state NMR), and increased surface area result in the improved photocatalytic activity of DFNS/g-C(3)N(4)for hydrogen generation and CO2 conversion.

}, keywords = {CO2 conversion, DFNS, g-C3N4, Hydrogen generation, nanocatalysts, photocatalysts, Solid-state NMR}, issn = {2574-0962}, doi = {10.1021/acsaem.0c01265}, author = {Rawool, Sushma A. and Samanta, Anupam and Ajithkumar, T. G. and Kar, Yusuf and Polshettiwar, Vivek} } @article {49106, title = {In situ monitoring of competitive coformer exchange reaction by 1H MAS solid-state NMR}, journal = {Molecualr Pharmaceutics}, volume = {21}, year = {2024}, month = {FEB }, pages = {1479-1489}, type = {Article}, abstract = {

In a competitive coformer exchange reaction, a recent topic of interest in pharmaceutical research, the coformer in a pharmaceutical cocrystal is exchanged with another coformer that is expected to form a cocrystal that is more stable. There will be a competition between coformers to form the most stable product through the formation of hydrogen bonds. This will cause destabilization of the pharmaceutical products during processing or storage. Therefore, it is important to develop a mechanistic understanding of this transformation by monitoring each and every step of the reaction, employing a technique such as H-1 nuclear magnetic resonance (NMR). In this study, an in situ monitoring of a coformer exchange reaction is carried out by H-1 magic angle spinning (MAS) solid-state NMR (SSNMR) at a spinning frequency of 60 kHz. The changes in caffeine maleic acid cocrystals on addition of glutaric acid and caffeine glutaric cocrystals on addition of maleic acid were monitored. In all of the reactions, it has been observed that caffeine glutaric acid Form I is formed. When glutaric acid was added to 2:1 caffeine maleic acid, the formation of metastable 1:1 caffeine glutaric acid Form I was observed at the start of the experiment, indicating that the centrifugal pressure is enough for the formation. The difference in the end product of the reactions with a similar reaction pathway of 1:1 and 2:1 reactant stoichiometry indicates that a complete replacement of maleic acid has occurred only in the 1:1 stoichiometry of the reactants. The polymorphic transition of caffeine glutaric acid Form II to Form I at higher temperatures was a crucial reason that triggered the exchange of glutaric acid with maleic acid in the reaction of caffeine glutaric acid and maleic acid. Our results are novel since the new reaction pathways in competitive coformer exchange reactions enabled understanding the remarkable role of stoichiometry, polymorphism, temperature, and centrifugal pressure.

}, keywords = {caffeine cocrystal, coformer exchange reaction, in situ monitoring, polymorphism, Solid-state NMR}, issn = {1543-8384}, doi = {10.1021/acs.molpharmaceut.3c01118}, author = {Hareendran, Chaithanya and Alsirawan, Bashir and Paradkar, Anant and Ajithkumar, T. G.} } @article {49515, title = {Probing the effect of fluorine on hydrogen bonding interactions in a pharmaceutical hydrate using Advanced Solid-State NMR}, journal = {Molecular Pharmaceutics}, volume = {22}, year = {2025}, month = {MAR }, pages = {1869-1880}, type = {Article}, abstract = {

Structural studies of pharmaceutical hydrates are essential to understanding stability-related issues, especially during the heating process of formulation. A thorough understanding of the hydration and dehydration behavior of active pharmaceutical ingredient (API) hydrate is also important since phase transitions can occur during the formulation process. This is because dehydration could result in a considerable rearrangement in the structure if water-API hydrogen bonding is present. We perform advanced solid-state NMR experiments on regorafenib monohydrate to investigate the role of fluorine in hydrogen bonding interaction, and the results are compared to its anhydrous form and its structural analogue, namely, sorafenib. Our results show that significant structural changes could not be observed on dehydration. Based on our study, it can be concluded that the introduction of fluorine restricts the intramolecular hydrogen bonding and the asymmetry in the structure of regorafenib monohydrate is absent, in comparison to sorafenib.

}, keywords = {DQSQ, Hydrogenbonding, pharmaceutical hydrate, regorafenib, Solid-state NMR}, issn = {1543-8384}, doi = {10.1021/acs.molpharmaceut.4c01055}, author = {Hareendran, Chaithanya and Ajithkumar, T. G.} } @article {50044, title = {Effect of sulfonation density on acid strength in ion exchange resins: Insights from solid-state NMR and density functional theory}, journal = {Molecular Catalysis}, volume = {593}, year = {2026}, month = {MAR }, pages = {115794}, type = {Article}, abstract = {

Ion-exchange (IE) resins are widely used as solid acid catalysts; however, their surface acidity remains poorly characterized because their limited thermal stability precludes conventional NH3-based acidity measurements. Moreover, acid-site accessibility in IE resins is strongly governed by solvent- or reactant-induced swelling. Here, we investigate the surface acidity of commercial Amberlyst and Indion IE resins using \& sup3;\& sup1;P MAS NMR (Magic Angle Spinning Nuclear Magnetic Resonance), employing TMPO as a molecular probe dispersed on the resin with moderately swelling dichloromethane, thereby capturing the swollen-state acidity relevant for predicting catalytic activity. The deconvolution of the P-31 MAS NMR spectra reveals three distinct acid-strength zones arising from inhomogeneous sulfonation of the polymer matrix. The overall acidity, quantified by the area-weighted average P-31 chemical shift (delta), increases monotonically with sulfonation density. Notably, only resins containing acid sites stronger than similar to 80 ppm exhibited measurable catalytic activity in alpha-pinene isomerization, establishing a direct correlation between acidity and activity. Density functional theory (DFT) calculations on representative resin models, supported by electron-density analyses, attribute the enhancement of acid strength at higher sulfonation densities to cooperative hydrogen-bonding networks among neighboring sulfonic acid groups. Together, these findings establish P-31 MAS NMR-derived surface acidity as a catalytically relevant descriptor for the rational selection of IE resins in liquid phase acid-catalyzed chemistries.

}, keywords = {Acid strength, Density functional theory, heterogeneous catalysis, Ion-exchange resins, Solid acids, Solid-state NMR}, issn = {2468-8231}, doi = {10.1016/j.mcat.2026.115794}, author = {Tumulu, Goutam Narayan and Datar, Sarvesh and Shelke, Ankita and Swain, Gitanjali and Ajithkumar, T. G. and Thirumalaiswamy, Raja and Mohan, Ojus and Mahajani, Sanjay M.} } @article {50075, title = {Fly-ash-based geopolymers: leachability and solid-state NMR investigations}, journal = {Bulletin of Materials Science}, volume = {49}, year = {2026}, month = {MAR}, pages = {54}, type = {Article}, abstract = {

This study aims to explore how leaching impacts the microstructure of a selected fly ash-derived geopolymer and evaluate its potential for near-surface disposal of radioactive waste. The uniqueness of this geopolymer formulation is its ability to form an aluminosilicate network that remains resistant to structural changes upon contact with water. The leach index of base elements such as Ca, Al, Na and Si was between 11 and 13, suggesting that the formulation is superior to Portland cement or conventional hydraulic cement. Solid-state NMR reveals that the water-interacted specimen has no contamination of the zeolite phase and all the Na is incorporated into the aluminosilicate geopolymer gel network, which also confirms that the glassy network of the geopolymer is responsible for imparting low leachability of base elements from its structure, and there is no labile sodium available for exchange as in zeolites.

}, keywords = {aluminosilicate network, Fly ash, Geopolymers, leaching, Solid-state NMR}, issn = {0250-4707}, doi = {10.1007/s12034-025-03487-2}, author = {Nadol, Athulya and Ajithkumar, T. G. and Singla, Rashmi and Alex, T. C. and Kumar, Sanjay and Bhatt, Himal and Deo, M. N. and Sen, Debasis and Ambashta, R. D. and Bajpai, R. K. and Shivakumar, Y. C. and Manohar, S.} }