@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:000269185000035, title = {Sensitivity enhancement of Si-29 double-quantum dipolar recoupling spectroscopy by Carr-Purcell-Meiboom-Gill acquisition method}, journal = {Chemical Physics Letters}, volume = {478}, number = {4-6}, year = {2009}, month = {AUG}, pages = {287-291}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

An enhancement in the detection sensitivity of dipolar recoupled Si-29 double-quantum magic-angle spinning experiment is shown with a Carr-Purcell-Meiboom-Gill (CPMG) train of pi pulses during the acquisition period. Symmetry-adapted pulse schemes, such as POST-C7 and SR26(4)(11), are used for the double-quantum excitation. Application of POST-C7-CPMG method for framework characterisation is demonstrated in the disordered and catalytically important ZSM-5 molecular sieve. Based on the observed double-quantum dipole-dipole correlations and the known T-site Si connectivities, the assignment of all the signals is made for the orthorhombic phase of the as-synthesised (CN form) material. (C) 2009 Elsevier B. V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2009.07.066}, author = {Goswami, M. and Madhu, Perunthiruthy K. and Dittmer, J. and Nielsen, N. C. and Ganapathy, Subramanian} } @article { ISI:000274459600009, title = {Evidence for the co-existence of distorted tetrahedral and trigonal bipyramidal aluminium sites in SrAl12O19 from Al-27 NMR studies}, journal = {Solid State Communications}, volume = {150}, number = {5-6}, year = {2010}, month = {JAN}, pages = {262-266}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

Strontium aluminate, SrAl12O19, is a ceramic material having the hexagonal magnetoplumbite-type structure, with multiple Al coordination environments. An earlier low-field Al-27 solid-state NMR study reported five different Al sites in this system: one AlO4, one AlO5, and three AlO6 sites; whereas a later high-field study showed that the AlO5 site is a distorted AlO4 site with a very large quadrupolar coupling constant (similar to 20 MHz). Our magic angle spinning (MAS) and 3-quantum magic angle spinning (3QMAS) NMR studies at 7.05 T unambiguously show evidence for an AlO5 site. However, evidence for the presence of a distorted AlO4 site is obtained from studies at high fields (16.4 and 17.6 T), in addition to the AlO5 site. Thus the present solid-state NMR studies give evidence for the simultaneous presence of both the five-coordinated and distorted four-coordinated sites in this system. (C) 2009 Elsevier Ltd. All rights reserved.

}, keywords = {Local structure, MQMAS, Nuclear magnetic resonance, Strontium aluminate}, issn = {0038-1098}, doi = {10.1016/j.ssc.2009.11.008}, author = {Harindranath, K. and Viswanath, K. Anusree and Chandran, C. Vinod and Braeuniger, Thomas and Madhu, Perunthiruthy K. and Ajithkumar, Thalasseril G. and Joy, Pattayil Alias} } @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 { ISI:000354255400032, title = {SBA-15-oxynitrides as a solid-base catalyst: effect of nitridation temperature on catalytic activity}, journal = {Angewandte Chemie-International Edition}, volume = {54}, number = {20}, year = {2015}, month = {MAY}, pages = {5985-5989}, publisher = {WILEY-V C H VERLAG GMBH}, address = {BOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANY}, abstract = {

Solid bases, such as SBA-15-oxynitrides, have attracted considerable interest for potential applications as catalysts in important industrial processes. Reported herein is that by simply tuning the temperature of nitridation (ammonolysis), the catalytic activity of these solid bases can be enhanced. Solid-state NMR spectroscopy and XPS studies provided the reasoning behind this change in activity.

}, keywords = {heterogeneous catalysis, Nanostructures, NMR spectroscopy, photoelectron spectroscopy, solid-state structures}, issn = {1433-7851}, doi = {10.1002/anie.201501015}, author = {Singh, Baljeet and Mote, Kaustubh R. and Gopinath, Chinnakonda S. and Madhu, Perunthiruthy K. and Polshettiwar, Vivek} } @article {47502, title = {Photoactive anthraquinone-based host-guest assembly for long-lived charge separation}, journal = {Journal of Physical Chemistry C }, volume = {125}, year = {2021}, month = {MAY}, pages = {10891-10900}, type = {Article}, abstract = {Porous 2D covalent organic frameworks (COF) that are assembled axially through weak p-stacking interactions can provide reticular charge transport channels while playing host to kinetically stabilized reactive molecular redox states. Here we demonstrate a host-guest supramolecular charge transfer (CT) assembly using photoactive anthraquinone-based COF as an acceptor while incarcerating the electron donor N,N-dimethylaniline (DMA) inside it. Employing femtosecond broadband transient absorption spectroscopy in combination with electron paramagnetic resonance (EPR) studies, we show that the CT occurs rapidly within <110 fs after photoexcitation, subsequently leading to long-lived charge separation with 13\% quantum efficiency at room temperature. The photoinduced EPR signature of the long-lived confined DMA cation radical confirms the disparate regions of charge localization while H-1-C-13 correlation experiments using solid-state NMR spectroscopy enumerate the packing of the amines inside the host-guest COF assembly. Our work demonstrates the potency of charge transport pathways in supramolecular assemblies for efficient charge separation which if optimally tuned should pave the way for COF-based photocatalytic reaction centers.}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.1c02497}, author = {Jha, Ajay and Mote, Kaustubh R. and Chandra, Suman and Madhu, Perunthiruthy K. and Dasgupta, Jyotishman} }