@article { ISI:000226728000011, title = {Increasing the sensitivity of 2D high-resolution NMR methods applied to quadrupolar nuclei}, journal = {Journal of Magnetic Resonance}, volume = {172}, number = {2}, year = {2005}, month = {FEB}, pages = {268-278}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, address = {525 B ST, STE 1900, SAN DIEGO, CA 92101-4495 USA}, abstract = {

Gan and Kwak recently proposed a soft-pulse added mixing (SPAM) idea in the classical two-pulse multiple-quantum magic-angle spinning scheme. In the SPAM method, a soft pi/2 pulse is added after the second hard-pulse (conversion pulse) and all coherence orders in between them are constructively used to obtain the signal. We, here, further extend this idea to distributed samples where the signal mainly results from echo pathways and that from anti-echo pathways dies Out after a few t(1) increments. We show that, with a combination of SPAM and collection of fewer anti-echoes, an enhancement of the signal to noise ratio by a factor of ca. 3 may be obtained over the z-filtered version. This may prove to be useful even for samples with long T{\textquoteright}(2) relaxation times. (C) 2004 Elsevier Inc. All rights reserved.

}, keywords = {high-resolution, quadrupolar nuclei, sensitivity, Solid-state NMR}, issn = {1090-7807}, doi = {10.1016/j.jmr.2004.11.001}, author = {Amoureux, J. P. and Delevoye, L. and Steuernagel, S. and Gan, Zhengting and Ganapathy, Subramanian and Montagne, L.} } @article { ISI:000240781100009, title = {Effect of spacer groups on the performance of MCM-41-supported platinum cluster-derived hydrogenation catalysts}, journal = {Journal of Catalysis}, volume = {242}, number = {2}, year = {2006}, month = {SEP}, pages = {332-339}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, address = {525 B ST, STE 1900, SAN DIEGO, CA 92101-4495 USA}, abstract = {

MCM-41 was functionalized with (EtO)(3)SiCH2Cl, (MeO)(3)SiCH2CH2CH2Cl, and (CH3)Cl2SiCH2Cl. The functionalized materials were characterized by solid-state NMR (CPMAS, Si-29 and C-13) and XPS. The NMR data indicate that three new silicon environments were created by(EtO)(3)SiCH2Cl and (MeO)(3)SiCH2CH2CH2Cl, whereas with (CH3)Cl2SiCH2Cl, two new silicon environments were obtained. XPS results from Si 2p core level and the valence band from the material functionalized by (MeO)(3)Si(CH2)(3)Cl was found to be the same as that of the corresponding fresh catalyst (1a), in contrast to that of the materials functionalized by the other two silane reagents. After further functionalization with triethylamine, these materials were used as inorganic anion exchangers to support the cluster anion [Pt-12(CO)(24)](2-). Solid-state NMR (29Si, C-13, N-15) was used to establish the presence of the quaternary ammonium group in the cluster-supported species. Analogous materials were also created using fumed silica as the support, and all of the cluster-supported materials were tested as catalysts for the hydrogenation of methyl pyruvate, acetophenone, nitrobenzene, benzonitrile, ethylacetoacetate, 4-nitrotoluene, cyclohexanone, allyl alcohol, and styrene. The best activity was obtained for the catalyst that had MCM-41 as the support and chloropropyl as the spacer group. TEM showed that the supports and the spacer groups had observable effects on the platinum crystallite size of the catalysts. (c) 2006 Elsevier Inc. All rights reserved.

}, keywords = {functionalized inorganic oxides, hydrogenation catalysts, MCM-41, platinum carbonyl cluster, Solid-state NMR, spacer groups, XPS}, issn = {0021-9517}, doi = {10.1016/j.jcat.2006.06.016}, author = {Maity, Niladri and Basu, Susmit and Mapa, Maitri and Rajamohanan, Pattuparambil R. and Ganapathy, Subramanian and Gopinath, Chinnakonda S. and Bhaduri, Sumit and Lahiri, Goutam Kumar} } @article { ISI:000259337100008, title = {Heteronuclear dipolar decoupling effects on multiple-quantum and satellite-transition magic-angle spinning NMR spectra}, journal = {Magnetic Resonance in Chemistry}, volume = {46}, number = {10}, year = {2008}, month = {OCT}, pages = {948-954}, publisher = {JOHN WILEY \& SONS LTD}, type = {Article}, address = {THE ATRIUM, SOUTHERN GATE, CHICHESTER PO19 8SQ, W SUSSEX, ENGLAND}, abstract = {

We here report on the influence of heteronuclear dipolar decoupling on the Al-27 3QMAS, 5QMAS, and the double-quantum filter-satellite-transition magic-angle spinning (DQF-STMAS) spectra of a strongly dipolar-coupled system, gibbsite. The requirements for heteronuclear dipolar decoupling increase with the order of coherence evolving in the indirect dimension of a two-dimensional (2D) experiment. The isotropic line width of the high-resolution 2D spectra, in samples like gibbsite, is composed of four parts: the distribution of isotropic shifts (delta(ISO), delta(QIS)), the homogeneous broadening related to the proton-proton flip-flop terms, the Al-27-Al-27 homonulcear dipolar couplings, and the H-1-Al-27 heteronuclear dipolar couplings. It is shown that, even in the case of gibbsite, where a strong proton-proton bath exists, the main resolution limiting factor in these experiments resides in the H-1-Al-27 dipolar interaction. Copyright (C) 2008 John Wiley \& Sons, Ltd.

}, keywords = {heteronuclear broadening, heteronuclear decoupling, homogeneous broadening, MQMAS, quadrupolar nuclei, Solid-state NMR, STMAS, TPPM}, issn = {0749-1581}, doi = {10.1002/mrc.2286}, author = {Ganapathy, Subramanian and Delevoye, L. and Arnoureux, J. P. and Madhu, Perunthiruthy K.} } @article { ISI:000324309600011, title = {Basic structural motif and major biophysical properties of Amyloid-beta are encoded in the fragment 18-35}, journal = {Chemical Physics}, volume = {422}, number = {SI}, year = {2013}, month = {AUG}, pages = {80-87}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Aggregation and misfolding of the amyloid beta (A beta) peptide is thought to initiate Alzheimer{\textquoteright}s disease (AD). Here we study the role played by its central segment (A beta(18-35)) in determining these properties. A beta(18-35) has a solubility of 18 mu M. The soluble fraction consists mainly of small oligomers, which have mixed beta-sheet and random coil structures. The monomer is mostly a random coil with some residual compactness. Aggregated A beta(18-35) forms fibrils of width 3.0 +/- 0.7 nm, which is consistent with a hairpin shape. Each of these properties has a close similarity to A beta(40). Remarkably, solid state NMR indicates that the fibrils also retain the secondary structure and tertiary contacts of A beta(40). This is the shortest fragment of A beta reported so far which preserves its fibrillar architecture, including the hairpin turn, as well as its solution phase conformational properties. Residues 18-35 should therefore be a key target of AD therapeutics. (C) 2013 Published by Elsevier B. V.

}, keywords = {Alzheimer{\textquoteright}s disease, Fluorescence correlation spectroscopy, Protein aggregation, Solid-state NMR}, issn = {0301-0104}, doi = {10.1016/j.chemphys.2013.01.010}, author = {Chandrakesan, Muralidharan and Sarkar, Bidyut and Mithu, Venus Singh and Rajiv M. Abhyankar and Bhowmik, Debanjan and Nag, Suman and Sahoo, Bankanidhi and Shah, Riddhi and Gurav, Sushma and Banerjee, Raja and Dandekar, Sucheta and Jose, Jaya C. and Sengupta, Neelanjana and Madhu, Perunthiruthy K. and Maiti, Sudipta} } @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.} }