Department of Chemistry

Indian Institute of Technology Palakkad&nbsp;(IIT Palakkad or IIT PKD) is a public autonomous&nbsp;engineering&nbsp;and&nbsp;research&nbsp;institute located in&nbsp;Palakkad,&nbsp;Kerala. It was&nbsp;one of the five new&nbsp;IITs&nbsp;proposed in the&nbsp;2014 Union budget of India. The campus was inaugurated on 3 August 2015. The institute has 94 faculty, 978 students, and 63 non-teaching staffs.

IT Palakkad currently offers four-year Bachelor of Technology (B.Tech) and two years MS programmes in 8 different engineering disciplines including&nbsp;Computer Science, Electrical, Mechanical, Civil among others.

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IIT Palakkad

Coordination-driven self-assembly of oxalato-bridged half-sandwich p-cymene ruthenium complex [Ru2(μ-η4-C2O 4)(MeOH)2(7eta;6-p-cymene)2](O 3SCF3)2 (1a) with several ditopic donors (La-Ld) in methanol affords a series of bi- and tetranuclear metallamacrocycles (2a and 3-5). Similarly, the combination of 2,5-dihydroxy-1,4-benzoquinonato (dhbq)-bridged binuclear complex [Ru 2(μ-η4-C6H2O 4)(MeOH)2(η6-p-cymene)2](O 3SCF3)2 (1b) with a flexible bidentate amide linker (La) in 1:1 molar ratio gave the corresponding tetranuclear complex 2b. All the macrocycles were isolated as their triflate salts in high yields and were fully characterized by various spectroscopic techniques. Finally, the molecular structures of all the assemblies were determined unambiguously by single-crystal X-diffraction analysis. Interestingly, the combination of acceptor 1a or 1b with an unsymmetrical linear ditopic donor La results in a self-sorted linkage isomeric (head-to-tail) macrocycle (2a or 2b) despite the possibility of formation of two different isomeric macrocycles (head-to-head or head-to-tail) due to different connectivity of the donor. Molecular structures of the complexes 2a and 2b showed tetranuclear rectangular geometry with dimensions of 5.51 Å × 13.29 Å for 2a and 7.91 Å × 13.46 Å for 2b. In both cases, two binuclear RuII2 building blocks are connected by a μ-N-(4-pyridyl)isonicotinamide donor in a head-to-tail fashion. Surprisingly, the macrocycle 2a loses one counteranion and cocrystallizes with monodeprotonated 1,3,5-trihydroxybenzene via strong intermolecular π-π stacking and hydrogen bonding. The tweezer complex 3 showed strong fluorescence in solution, and it showed fluorescence sensing toward nitroaromatic compounds. A fluorescence study demonstrated a marked quenching of the initial fluorescence intensity of the macrocycle 3 upon gradual addition of trinitrotoluene and exhibits significant fluorescence quenching response only for nitroaromatic compounds compared to various other aromatic compounds tested. © 2011 American Chemical Society.

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Organometallics

Constructions of 2D-metallamacrocycles using half-sandwich Ru II2 precursors: Synthesis, molecular structures, and self-selection for a single linkage isomer

A dinuclear organometallic acceptor 4,4′-bis[trans-Pt(PEt 3)2(O3SCF3)(ethynyl)]biphenyl (1) containing Pt-ethynyl functionality is synthesized. Multinuclear NMR ( 1H, 31P, and 13C), infrared (IR), and electrospray ionization mass spectrometry (ESI-MS) including single-crystal X-ray diffraction analysis established the formation of 1. Equimolar treatment of acceptor 1 separately with three different "clip" type ditopic donors (La-Lc) yielded [2 + 2] self-assembled three metallamacrocycles 2a-2c, respectively. These macrocycles were characterized by various spectroscopic techniques, and their sizes/shapes were obtained through geometry optimization using molecular mechanics universal force field (MMUFF) simulations. Attachment of unsaturated ethynyl functionality to biphenyl building unit helped to make the macrocycles (2a-2c) π-electron rich and thereby fluorescent in nature. Furthermore, 2c in solution has been examined to be suitable for sensing electron-deficient nitroaromatic like picric acid, which is often considered as a secondary chemical explosive. The fluorescence study of 2c showed a marked quenching of initial emission intensity upon titrating with picric acid (PA), and it exhibited the largest fluorescence quenching response with high selectivity among various other electron deficient aromatic compounds tested. © 2011 American Chemical Society.

Inorganic Chemistry

Self-assembly of metallamacrocycles using a dinuclear organometallic acceptor: Synthesis, characterization, and sensing study

Communication between two molecules, one confined and excited (triplet or singlet) and one free and paramagnetic, has been explored through quenching of fluorescence and/or phosphorescence by nitroxides as paramagnetic radical species. Quenching of excited states by nitroxides has been investigated in solution, and the mechanism is speculated to involve charge transfer and/or exchange processes, both of which require close orbital interaction between excited molecule and quencher. We show in this report that such a quenching, which involves electron-electron spin communication, can occur even when there is a molecular wall between the two. The excited state molecule is confined within an organic capsule made up of two molecules of a deep cavity cavitand, octa acid, that exists in the anionic form in basic aqueous solution. The nitroxide is kept free in aqueous solution. 1H NMR and EPR experiments were carried out to ascertain the location of the two molecules. The distance between the excited molecule and the paramagnetic quencher was manipulated by the use of cationic, anionic, and neutral nitroxide and also by selectively including the cationic nitroxide within the cavity of cucurbituril. Results presented here highlight the role of the lifetime of the encounter complex in electron-electron spin communication when the direct orbital overlap between the two molecules is prevented by the intermediary wall. © 2011 American Chemical Society.

Langmuir

Interaction between encapsulated excited organic molecules and free nitroxides: Communication across a molecular wall

Ultrafast forster resonance energy transfer (FRET) in a RTIL-P123 gel is studied by femtosecond up-conversion technique. The mixed gel consists of a tri-block copolymer, (PEO)20-(PPO)70-(PEO)20 and a room temperature ionic liquid (RTIL) (1-pentyl-3-methyl-imidazolium bromide, [pmim][Br]). The acceptor rhodamine 6G (R6G) being ionic, stays in the peripheral corona region of the micellar aggregates of the gel. We use two donor dyes of different hydrophobicity. The hydrophobic neutral donor coumarin 153 (C153) resides in the core while the hydrophilic ionic donor coumarin 343 (C343) is located in the corona. As a result donor-acceptor distances are different for the two donors. Thus by varying the donor one can study region dependent FRET processes in the RTIL-P123 gel.

Journal of the Indian Chemical Society

Region dependent ultrafast FRET in an ionic liquid-P123 gel: A femtosecond study

A structural chameleon: A porous layered carbon material (PLC) containing nanographene domains was prepared by graphitizing glucose within the nanoscopic voids of an aminoclay template. The size of the pores in the PLC was altered reversibly by a mesoscale order-disorder transformation brought about by an applied mechanical force (see picture). This pore flexibility was exploited for the size-selective separation of dye molecules. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Angewandte Chemie - International Edition

Observation of pore-switching behavior in porous layered carbon through a mesoscale order-disorder transformation

A π-electron rich supramolecular polymer as an efficient fluorescent sensor for electron deficient nitroaromatic explosives has been synthesized, and the role of H-bonding in dramatic amplification of sensitivity/fluorescence quenching efficiency in the solid state has been established. © The Royal Society of Chemistry 2011.

Chemical Communications

Supramolecular polymer for explosives sensing: Role of H-bonding in enhancement of sensitivity in the solid state

The present work illustrated an accurate GC/MS measurement for the low isotopomer enrichment assay of formic acid, acetic acid, propionic aicd, butyric acid, and pentanoic acid. The pentafluorobenzyl bromide derivatives of these very short chain fatty acids have high sensitivity of isotopoic enrichment due to their low natural isotopomer distribution in negative chemical ionization mass spectrometric mode. Pentafluorobenzyl bromide derivatization reaction was optimized in terms of pH, temperature, reaction time, and the amount of pentafluorobenzyl bromide versus sample. The precision, stability, and accuracy of this method for the isotopomer analysis were validated. This method was applied to measure the enrichments of formic acid, acetic acid, and propionic acid in the perfusate from rat liver exposed to Krebs-Ringer bicarbonate buffer only, 0-1 mM [3,4-13C2]-4-hydroxynonanoate, and 0-2 mM [5,6,7-13C3]heptanoate. The enrichments of acetic acid and propionic acid in the perfusate are comparable to the labeling pattern of acetyl-CoA and propionyl-CoA in the rat liver tissues. The enrichment of the acetic acid assay is much more sensitive and precise than the enrichment of acetyl-CoA by LC-MS/MS. The reversibility of propionyl-CoA from succinyl-CoA was confirmed by the low labeling of M1 and M2 of propionic acid from [5,6,7- 13C3]heptanoate perfusates. © 2010 Elsevier Inc. All rights reserved.

Analytical Biochemistry

Isotopomer enrichment assay for very short chain fatty acids and its metabolic applications

A microfluidic strategy for the encapsulation and stimulus-responsive release of molecules with distinct polarities from the interior of microgels is reported. The approach relies on (i) the generation of a primary O/W emulsion by the ultrasonication method, (ii) MF emulsification of the primary emulsion, and (iii) photopolymerization of the monomer present in the aqueous phase of the droplets, thereby transforming them into microgels. Non-polar molecules are dissolved in oil droplets embedded in the microgels. Polar molecules are physically associated with the hydrogel network. Upon heating, the microgels contract and release polar and non-polar cargo molecules. The approach paves the way for stimuli-responsive vehicles for multiple drug delivery. Poly( N -isopropylacrylamide) microgel particles encapsulated with oil droplets are synthesized using microfluidics. The particles are loaded with molecules of different polarities. A temperature-induced release of the cargo is observed. This has potential for multiple drug delivery systems. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Macromolecular Bioscience

Microgels for the encapsulation and stimulus-responsive release of molecules with distinct polarities

Metabolomics is a data-based research strategy, the aims of which are to identify biomarker pictures of metabolic systems and metabolic perturbations and to formulate hypotheses to be tested. It involves the assay by mass spectrometry or NMR of many metabolites present in the biological system investigated. In this minireview, we outline studies in which metabolomics led to useful biomarkers of metabolic processes. We also illustrate how the discovery potential of metabolomics is enhanced by associating it with stable isotopic techniques. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.

Fulltext

Journal of Biological Chemistry

Metabolomics, pathway regulation, and pathway discovery

Single molecule force spectroscopy (SMFS) has recently given access to an unprecedented level of information regarding the stress-response of a host of biopolymers at the single chain level. However, the difficulty of designing handles for the specific attachment of the different ends of polysaccharide chains to substrates, such as piezoelectric scanners, cantilevers or microbeads; particularly in contrast to nucleotides and proteins, has meant that progress in more sophisticated single carbohydrate measurements has been relatively slow. Herein, methods for generating specific covalent attachments of the terminal sugar residue at one end of a pectin chain to polystyrene microspheres are demonstrated. Using FT-IR spectroscopy in combination with density functional theory (DFT) calculations the attachment was unequivocally shown to be mediated by the introduction of a C-N bond between the reducing end of the polysaccharide chain and a pre-aminated bead. © 2011 Elsevier Ltd All rights reserved.

Carbohydrate Polymers

Towards polysaccharide handles for single molecule experiments: Spectroscopic evidence for the selective covalent coupling of terminal sugar residues to desired substrates