@article { ISI:000247076200015, title = {Cross- and axial-peak intensities in 2D-SLF experiments based on cross-polarization - the role of the initial density matrix}, journal = {Journal of Magnetic Resonance}, volume = {185}, number = {2}, year = {2007}, month = {APR}, pages = {308-317}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, address = {525 B ST, STE 1900, SAN DIEGO, CA 92101-4495 USA}, abstract = {

Simulations and experiments on simple oriented systems have been used to estimate the relative ratio of cross-peak to axial-peak intensities in 2D-SLF experiments based on dipolar oscillations during cross-polarization (CP). The density matrix prior to dipolar evolution is considered and for an isolated spin pair, it is shown that direct calculations of the ratios match well with simulations and experimental results. Along with the standard CP pulse sequence, two other pulse sequences namely CP with polarization inversion (PI-CP) and another novel variation of the standard CP experiment (EXE-CP) reported recently have been considered. Inclusion of homonuclear dipolar coupling has been observed to increase the axial-peak intensities. In combination with Lee-Goldburg (LG) decoupling, experiments on an oriented liquid crystalline sample have been carried out and the performance of the pulse schemes have been compared. The applicability of the new pulse sequence for different samples and different nuclei is discussed. Such studies are expected to lead to a better understanding of the experiments and to the design of useful pulse sequences. (C) 2007 Elsevier Inc. All rights reserved.

}, keywords = {cross polarization, oriented molecules, PISEMA, SLF}, issn = {1090-7807}, doi = {10.1016/j.jmr.2007.01.007}, author = {Das, Bibhuti B. and Ajithkumar, Thalasseril G. and Sinha, Neeraj and Opella, Stanley J. and Ramanathan, K. V.} } @article {BHONDE, title = {Clickable SBA-15 mesoporous materials: synthesis, characterization and their reaction with alkynes}, journal = {Journal of Materials Chemistry}, volume = {19}, number = {10}, year = {2009}, month = {JAN}, pages = {1409-1416}, publisher = {ROYAL SOC CHEMISTRY}, type = {Article}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

SBA-15 mesoporous silica has been functionalized with azidopropyl groups through both one-pot co-condensation and post-synthetic grafting. For both these methodologies, azidopropyltriethoxysilane was used to introduce the azidopropyl groups. The azidopropyl modified SBA-15 material synthesized by one-pot co-condensation had hexagonal crystallographic order, pore diameters up of 50 angstrom, and the content of azidopropyl groups was found to be 1.3 mmol g(-1). The presence of the azidopropyl group was confirmed by multinuclear ((13)C, (29)Si) solid state NMR and IR spectroscopy. Both these materials underwent very efficient Cu(I)-catalyzed azide alkyne {\textquoteleft}{\textquoteleft}click{\textquoteright}{\textquoteright} reaction (CuAAC) with a variety of alkynes. Nearly 85\% of the azide present in the SBA-15 material was converted to the corresponding triazole when propargyl alcohol was used as the substrate. This methodology was also used to incorporate mannose into SBA-15. Incubation of this mannose labeled SBA-15 with fluorescein labeled Concanavalin-A led to the formation of a fluorescent silica-protein hybrid material. The ease of synthesis for the azide labeled SBA-15 material together with its ability to undergo very efficient chemoselective CuAAC in water would make it a very attractive platform for the development of covalently anchored catalysts, enzymes and sensors.

}, issn = {0959-9428}, doi = {10.1039/b815350g}, author = {Malvi, Bharmana and Sarkar, Bibhas R. and Pati, Debasis and Mathew, Renny and Ajithkumar, Thalasseril G. and Sen Gupta, Sayam} } @article { ISI:000288045600024, title = {Composition-structure-property (Zn2+ and Ca2+ ion release) evaluation of Si-Na-Ca-Zn-Ce glasses: potential components for nerve guidance conduits}, journal = {Materials Science \& Engineering C-Materials for Biological Applications}, volume = {31}, number = {3}, year = {2011}, month = {APR}, pages = {669-676}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Bioactive glasses have demonstrated tailored therapeutic ion release, primarily with respect to the augmentation of hard tissues. However, controlled degradation and release of therapeutic ions from biomaterials may also play an important role in soft tissue regeneration such as repair of peripheral nerve discontinuities. In this study, three silica based glasses (0.5SiO(2)-0.2CaO-0.13ZnO-XNa2O-(0.17-X) CeO2) where, (0.04 \< X \< 0.14) were synthesised and characterised. The local environment of the Si-29 isotope was probed for each glass using Si-29 MAS-NMR, whilst the thermal characteristics of each glass were examined using DTA. Following these analyses, ion release profiles for Ca2+ and Zn2+ were evaluated; an equivalent specific surface area of 1 m(2) of each glass powder was incubated (37 degrees C) in 10 ml of citric acid buffer and TRIS-HCl buffer solution (pH 3.0 and pH 7.4 respectively) for incubation periods of up to 30 days. The Zn2+ concentration of each filtrate was analysed using flame Atomic Absorption Spectroscopy (Varian AA240FS Fast Sequential AAS) and the Ca2+ concentration of each filtrate was determined using Inductively Coupled Plasma-Mass Spectrometer (Varian 820 ICP-MS). Results obtained from the Si-29 MAS-NMR spectra indicated Q(2) structures pervading the network. An analytical model was proposed to analyse the ion release profiles for each glass, and indicated heterogeneous dissolution of glass networks. The ion release data demonstrates that ion release in the range (19.26-3130 ppm) for Ca2+ and in the range (5.97-4904 ppm) for Zn2+ occurred. Release of such elements, at appropriate levels, from peripheral nerve guidance conduits may be advantageous with respect to the repair of peripheral nerve discontinuities. (C) 2011 Elsevier B.V. All rights reserved.

}, keywords = {Bioglass, Dissolution, Modelling}, issn = {0928-4931}, doi = {10.1016/j.msec.2010.12.016}, author = {Zhang, X. F. and Kehoe, S. and Adhi, S. K. and Ajithkumar, Thalasseril G. and Moane, S. and O{\textquoteright}Shea, H. and Boyd, D.} } @article {42898, title = {Correlations between structure, microstructure, density and dielectric properties of the lead-free ferroelectrics Bi0.5(Na,K)0.5TiO3}, journal = {Journal of Advanced Dieletrics}, volume = {5}, year = {2015}, month = {NOV}, pages = {1550028 Page 1-6}, doi = {10.1142/S2010135X15500289}, author = {Anjali, K. and Ajithkumar, Thalasseril G. and Joy, Pattayil Alias} } @article {46413, title = {Covalent self-assembly in two dimensions: connecting covalent organic framework nanospheres into crystalline and porous thin films}, journal = {Journal of the American Chemical Society}, volume = {141}, year = {2019}, month = {DEC }, pages = {20379}, type = {Article}, chapter = {20371}, abstract = {

Insolubility of covalent organic frameworks (COFs) in organic solvents is one of the major obstacles for the potential application of these extended networks such as drug delivery, sensing, optoelectronics, and semiconductor device fabrication. The present work proposes a unique way to make uniform, solution-processable, crystalline, and porous COF nanospheres directly from the homogeneous solution of amine and aldehyde via spatial and temporal control of the nucleation and growth. This strategy of direct nucleation simultaneously showcases the caliber to tune the size of the COF nanospheres from 25 to 570 nm. We have also demonstrated the concept of mesoscale covalent self-assembly of those solution-processable COF nanospheres in the liquid-liquid interface (DCM-water bilayer) for the very first time, transmuting them into self-standing COF thin films with long-range ordered arrangements in two dimensions. The crystalline and porous (with TpAzo showing highest S-BET of 1932 m(2) g(-1)) free-standing COF thin films could be fabricated in a wide range of thicknesses from as low as 21 nm to as high as 630 nm. Both beta-ketoenamine (TpAzo, TpDPP) and imine (TpOMeAzo, TpOMeDPP) linked COF thin films have been synthesized via mesoscale covalent self-assembly of the solution-processable COF nanospheres illustrating the generality of this eloquent methodology. Further, the solution processability has been tested and utilized to cast COF thin films uniformly in the inner and outer surface of an alumina hollow fiber membrane. The COF thin film-alumina hollow fiber membrane composites have showcased promising selective molecular separation of He and O-2, He and CO2, and He and N-2.

}, issn = {0002-7863}, doi = {10.1021/jacs.9b10788}, author = {Sasmal, Himadri Sekhar and Halder, Arjun and Kunjattu, Shebeeb and Dey, Kaushik and Nadol, Athulya and Ajithkumar, Thalasseril G. and Bedadur, Prachiti Ravindra and Banerjee, Rahul} } @article {46867, title = {Connecting microscopic structures, mesoscale assemblies, and macroscopic architectures in 3D-printed hierarchical porous covalent organic framework foams}, journal = {Journal of the American Chemical Society}, volume = {142}, year = {2020}, month = {MAY }, pages = {8252-8261}, type = {Article}, abstract = {

The induction of macro and mesopores into two-dimensional porous covalent organic frameworks (COFs) could enhance the exposure of the intrinsic micropores toward the pollutant environment, thereby, improving the performance. However, the challenge is to build a continuous hierarchically porous macro-architecture of crystalline organic materials in the bulk scale. In this regard, we have strategized a novel synthetic method to create hierarchically porous COF foams consisting of ordered micropores (2-2.2 nm) and disordered meso and macropores (50 nm to 200 mu m) as well as ordered macropores (1.5 mm to 2 cm). Herein, graphene oxide was used for creating disordered macro and mesopores in COF-GO foams. Considering the rheological features of the precursor hydrogel, we could integrate crystalline and porous COF-GO foams into self-supported three-dimensional (3D)-printed objects with the desired shapes and sizes. Therefore, we have engineered the 3D macro-architecture of COF-GO foams into complex geometries keeping their structural order and continuous porosity intact over a range of more than a million (10(-9) m to 10(-3) m). The interconnected 3D openings in these COF-GO foams further enhance the rapid and efficient uptake of organic and inorganic pollutants from water (\>95\% removal within 30 s). The abundant distribution of interconnected macroporous volume (55\%) throughout the COF-GO foam matrix enhances the flow of water (1.13 x 10(-3) m.s(-1)) which results in efficient mass transport and adsorption.

}, issn = {0002-7863}, doi = {10.1021/jacs.0c00555}, author = {Mohammed, Abdul Khayum and Usgaonkar, Saurabh and Kanheerampockil, Fayis and Karak, Suvendu and Halder, Arjun and Tharkar, Minakshi and Addicoat, Matthew and Ajithkumar, Thalasseril G. and Banerjee, Rahul} } @article {48745, title = {Covalent organic framework cladding on peptide-amphiphile-based biomimetic catalysts}, journal = {Journal of the American Chemical Society}, volume = {145}, year = {2023}, month = {JUN }, pages = {12793-12801}, type = {Article}, abstract = {

Peptide-based biomimetic catalysts are promising materialsforefficient catalytic activity in various biochemical transformations.However, their lack of operational stability and fragile nature innon-aqueous media limit their practical applications. In this study,we have developed a cladding technique to stabilize biomimetic catalystswithin porous covalent organic framework (COF) scaffolds. This methodologyallows for the homogeneous distribution of peptide nanotubes insidethe COF (TpAzo and TpDPP) backbone, creating strong noncovalent interactionsthat prevent leaching. We synthesized two different peptide-amphiphiles,C10FFVK and C10FFVR, with lysine (K) and arginine(R) at the C-termini, respectively, which formed nanotubular morphologies.The C10FFVK peptide-amphiphile nanotubes exhibit enzyme-likebehavior and efficiently catalyze C-C bond cleavage in a buffermedium (pH 7.5). We produced nanotubular structures of TpAzo-C10FFVK and TpDPP-C10FFVK through COF claddingby using interfacial crystallization (IC). The peptide nanotubes encasedin the COF catalyze C-C bond cleavage in a buffer medium aswell as in different organic solvents (such as acetonitrile, acetone,and dichloromethane). The TpAzo-C10FFVK catalyst,being heterogeneous, is easily recoverable, enabling the reactionto be performed for multiple cycles. Additionally, the synthesis ofTpAzo-C10FFVK thin films facilitates catalysis inflow. As control, we synthesized another peptide-amphiphile, C10FFVR, which also forms tubular assemblies. By depositingTpAzo COF crystallites on C10FFVR nanotubes through IC,we produced TpAzo-C10FFVR nanotubular structuresthat expectedly did not show catalysis, suggesting the critical roleof the lysines in the TpAzo-C10FFVK.

}, issn = {0002-7863}, doi = {10.1021/jacs.3c03562}, author = {Kumar Mahato, Ashok and Pal, Sumit and Dey, Kaushik and Reja, Antara and Paul, Satyadip and Shelke, Ankita and Ajithkumar, Thalasseril G. and Das, Dibyendu and Banerjee, Rahul} } @article {48833, title = {Covalent organic framework thin-film photodetectors from solution-processable porous nanospheres}, journal = {Journal of the American Chemical Society}, volume = {145}, year = {2023}, month = {JAN}, pages = {1649-1659}, type = {Article}, abstract = {

The synthesis of homogeneous covalent organic framework (COF) thin films on a desired substrate with decent crystallinity, porosity, and uniform thickness has great potential for optoelectronic applications. We have used a solution-processable sphere transmutation process to synthesize 300 +/- 20 nm uniform COF thin films on a 2 x 2 cm2 TiO2-coated fluorine-doped tin oxide (FTO) surface. This process controls the nucleation of COF crystallites and molecular morphology that helps the nanospheres to arrange periodically to form homogeneous COF thin films. We have synthesized four COF thin films (TpDPP, TpEtBt, TpTab, and TpTta) with different functional backbones. In a close agreement between the experiment and density functional theory, the TpEtBr COF film showed the lowest optical band gap (2.26 eV) and highest excited-state lifetime (8.52 ns) among all four COF films. Hence, the TpEtBr COF film can participate in efficient charge generation and separation. We constructed optoelectronic devices having a glass/FTO/TiO2/COF-film/Au architecture, which serves as a model system to study the optoelectronic charge transport properties of COF thin films under dark and illuminated conditions. Visible light with a calibrated intensity of 100 mW cm-2 was used for the excitation of COF thin films. All of the COF thin films exhibit significant photocurrent after illumination with visible light in comparison to the dark. Hence, all of the COF films behave as good photoactive substrates with minimal pinhole defects. The fabricated out-of-plane photodetector device based on the TpEtBr COF thin film exhibits high photocurrent density (2.65 +/- 0.24 mA cm-2 at 0.5 V) and hole mobility (8.15 +/- 0.64 x10-3 cm2 V-1 S-1) compared to other as synthesized films, indicating the best photoactive characteristics.

}, issn = {0002-7863}, doi = {10.1021/jacs.2c09838}, author = {Bag, Saikat and Sasmal, Himadri Sekhar and Chaudhary, Sonu Pratap and Dey, Kaushik and Blaette, Dominic and Guntermann, Roman and Zhang, Yingying and Poloz, Miroslav and Kuc, Agnieszka and Shelke, Ankita and Vijayaraghavan, Ratheesh K. and Ajithkumar, Thalasseril G. and Bhattacharyya, Sayan and Heine, Thomas and Bein, Thomas and Banerjee, Rahul} }