@article { ISI:000263320900032, title = {Sequence-specific unusual (1 -> 2)-type helical turns in alpha/beta-hybrid peptides}, journal = {Journal of the American Chemical Society}, volume = {130}, number = {52}, year = {2008}, month = {DEC}, pages = {17743-17754}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

This article describes novel conformationally ordered (alpha/beta-hybrid peptides consisting of repeating L-proline-anthranilic acid building blocks. These oligomers adopt a compact, right-handed helical architecture determined by the intrinsic conformational preferences of the individual amino acid residues. The striking feature of these oligomers is their ability to display an unusual periodic pseudo beta-turn network of nine-membered hydrogen-bonded rings formed in the forward direction of the sequence by 1{\textendash}\>2 amino acid interactions both in solid-state and in solution. Conformational investigations of several of these oligomers by single-crystal X-ray diffraction, solution-state NMR, and ab initio MO theory suggest that the characteristic steric and dihedral angle restraints exerted by proline are essential for stabilizing the unusual pseudo beta-turn network found in these oligomers. Replacing proline by the conformationally flexible analogue alanine (Ala) or by the conformationally more constrained alpha-amino isobutyric acid (Aib) had an adverse effect on the stabilization of this structural architecture. These findings increase the potential to design novel secondary structure elements profiting from the steric and dihedral angle constraints of the amino acid constituents and help to augment the conformational space available for synthetic oligomer design with diverse backbone structures.

}, issn = {0002-7863}, doi = {10.1021/ja804297f}, author = {Prabhakaran, Panchami and Kale, Sangram S. and Puranik, Vedavati G. and Rajamohanan, P. R. and Chetina, Olga and Howard, Judith A. K. and Hofmann, Hans-Joerg and Sanjayan, Gangadhar J.} } @article { ISI:000261163000013, title = {Structural elucidation of propargylated products of 3-substituted-1,2,4-triazole-5-thiols by NMR techniques}, journal = {Magnetic Resonance in Chemistry}, volume = {46}, number = {12}, year = {2008}, month = {DEC}, pages = {1168-1174}, publisher = {JOHN WILEY \& SONS LTD}, address = {THE ATRIUM, SOUTHERN GATE, CHICHESTER PO19 8SQ, W SUSSEX, ENGLAND}, abstract = {

Propargylation of 3-substituted-1,2,4-triazole-5-thiols, which predominantly exist as their thione tautomers, was carried out with the view to synthesize different heterocycles and study their biological activity. Three different products namely, a mono S-propargyl and two S,N-dipropargyl regioisomers, arising from N1/N2 substitution, were isolated and characterized. Unambiguous structural elucidation of the regioisomers of S,N-dipropargyl derivatives was achieved by means of (13)C-(1)H HMBC technique. The proportion of the regioisomers was found to vary with the substituent on the 1,2,4-triazole thiols. No product corresponding to N4 substitution was isolated from any of the reactions carried out. Copyright (C) 2008 John Wiley \& Sons, Ltd.

}, keywords = {(1)H NMR, (13)C NMR, (15)N NMR, 1, 2, 4-triazoles, HMBC, NMR, Regioisomers}, issn = {0749-1581}, doi = {10.1002/mrc.2307}, author = {Chaudhary, Preeti M. and Chavan, Sayalee R. and Kavitha, M. and Maybhate, Shailaja P. and Deshpande, Sunita R. and Likhite, Anjali P. and Rajamohanan, P. R.} } @article { ISI:000266269600030, title = {Sterically controlled naphthalene homo-oligoamides with novel structural architectures}, journal = {Organic \& Biomolecular Chemistry}, volume = {7}, number = {11}, year = {2009}, month = {MAR}, pages = {2458-2465}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Herein we report novel naphthalene homo-oligoamides, derived from 4-amino-3-methoxy-naphthalene-2-carboxylic acid and 4-amino-1-methoxy-naphthalene-2-carboxylic acid as monomer building blocks, that display an anti-periplanar arrangement of the naphthyl rings, primarily induced by steric interactions between adjacent groups and functionalities.

}, issn = {1477-0520}, doi = {10.1039/b822076j}, author = {Prabhakaran, Panchami and Puranik, Vedavati G. and Chandran, Jima N. and Rajamohanan, P. R. and Hofmann, Hans-Joerg and Sanjayan, Gangadhar J.} } @article { ISI:000288835000010, title = {Structure-property of thermoplastic polyurethane-clay nanocomposite based on covalent and dual-modified laponite}, journal = {Journal of Computational and Theoretical Nanoscience}, volume = {4}, number = {1}, year = {2011}, month = {JAN}, pages = {65-73}, publisher = {AMER SCIENTIFIC PUBLISHERS}, address = {26650 THE OLD RD, STE 208, VALENCIA, CA 91381-0751 USA}, abstract = {

Modification of surface of clay platelets by ionic and covalent modification techniques renders it to be easily dispersed in polymers like, Thermoplastic Polyurethane (TPU). Only ionic or covalent modification techniques in isolation are not sufficient to achieve uniform nanoscale dispersion of Laponite (synthetic hectorite nanoclay) in TPU. Hence, the dual modification of Laponite (both ionic and covalent) is performed and the effects of the modification on the morphology, thermal and rheological behaviors of the TPU-modified clay nanocomposites have been studied. The degree of exfoliation of clay platelet in TPU matrix is found to be higher for dual functionalized nanoclays compared to their singly modified counterparts. Interestingly, dual modified Laponite clays prepared by using two different techniques (ionic followed by covalent and covalent followed by ionic) exhibit different morphology and properties. The dual modified clays significantly alter the equilibrium morphology of TPU. The storage modulus of the dual modified Laponite-TPU nanocomposite in the glassy region (at -60 degrees C) land in the rubbery region (+98 degrees C) is improved by 172.8\% and 85\%, respectively as compared to the neat TPU. Similarly, the onset of degradation is found to be enhanced by 28.7 degrees C as compared to the neat TPU.

}, keywords = {Dual modification, Laponite Nanocomposite, Morphology, Structure-Property, Thermoplastic polyurethane}, issn = {1936-6612}, doi = {10.1166/asl.2011.1174}, author = {Mishra, Ananta K. and Rajamohanan, P. R. and Nando, Golok B. and Chattopadhyay, Santanu} } @article { ISI:000331861300008, title = {Solid-state NMR investigations of a MgCl2 center dot 4(CH3)(2)CHCH2OH molecular adduct: a peculiar case of reversible equilibrium between two phases}, journal = {Journal of Physical Chemistry A}, volume = {118}, number = {7}, year = {2014}, month = {FEB}, pages = {1213-1219}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

MgCl2 center dot xROH molecular adducts are extensively employed as a support material for Ziegler-Natta polyolefin catalysis. However, their structural properties are not well understood. Recently, we reported on the preparation of an isobutanol adduct, MgCl2 center dot 4(CH3)(2)CHCH2OH (MgiBuOH) (Dalton Trans. 2012, 41, 11311), which is very sensitive to the preparation conditions, such as the temperature and refluxing time. For the present study, the structural properties of MgiBuOH adducts prepared under different conditions have been investigated thoroughly by solid-state NMR and nonambient XRD. Formation of two phases has been confirmed, and in situ variable temperature solid-state NMR measurements confirm the coexistence of two phases as well as the oscillation from one to another phase. It is expected that such molecular adducts could have a significant role in organic transformation reactions due to an oscillating structural component. An understanding of phase oscillation with the Mg2+ ion as the central metal ion might shed some light toward understanding various biological and structural functions.

}, issn = {1089-5639}, doi = {10.1021/jp412331s}, author = {Thushara, K. S. and Ajithkumar, Thalasseril G. and Rajamohanan, P. R. and Gopinath, Chinnakonda S.} } @article { ISI:000329266500032, title = {Structural investigations of porous MgCl2-2-butanol molecular adduct as support for olefin polymerization}, journal = {Applied Catalysis A-General}, volume = {469}, year = {2014}, month = {JAN}, pages = {267-274}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

A new heterogeneous Ziegler-Natta (Z-N) catalyst support material, MgCl2 center dot 4(CH3CH(OH)CH2CH3) (Mg2BuOH) has been synthesized. 2-Butanol, a linear, secondary alcohol was chosen for the generation of an active MgCl2 support which results in a Z-N catalyst with TiCl4. Significant feature of this work is the formation of rod shaped molecular adduct with highly porous character. Adduct material is characterized by XRD, TG-DTA, Raman spectroscopy, solid-state NMR and SEM. Activity of the Z-N catalyst supported on Mg2BuOH for ethylene polymerization is comparable with that of commercially available heterogeneous Z-N catalyst. However, there is scope to improve the activity by optimizing textural properties. (C) 2013 Elsevier B.V. All rights reserved.

}, keywords = {heterogeneous catalysis, MgCl2, Molecular adduct, NMR, Polyolefin, Ziegler-Natta catalyst}, issn = {0926-860X}, doi = {10.1016/j.apcata.2013.10.002}, author = {Thushara, K. S. and Ajithkumar, Thalasseril G. and Rajamohanan, P. R. and Gopinath, Chinnakonda S.} } @article { ISI:000361935600025, title = {Star telechelic poly(L-lactide) ionomers}, journal = {Macromolecules}, volume = {48}, number = {18}, year = {2015}, month = {SEP}, pages = {6580-6588}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Poly(L-lactide) (PLA), a biodegradable and biorenewable polymer, has many excellent properties that are equivalent to those of petroleum-derived plastics such as polystyrene, aromatic polyesters, etc. However, a major disadvantage of PLA which limits its processability is its poor melt elasticity. In this work we explore the possibility of improving the viscoelastic properties of PLA melt by incorporating ionic groups on the polymer. Specifically, we demonstrate the synthesis of star telechelic PLA anionomers by a three-step procedure involving synthesis of Star PIA, converting the hydroxyl end groups into carboxylic acid end groups, and finally converting these into ionic groups. Rheology data showed a dramatic increase in the elasticity of the star telechelic ionomer melts relative to the Star PLA melts. The viscoelasticity of star telechelic ionomers melts could be modulated by varying the number of ionic groups per molecule.

}, issn = {0024-9297}, doi = {10.1021/acs.macromol.5b01854}, author = {Kulkarni, Amruta and Lele, Ashish K. and Sivaram, Swaminathan and Rajamohanan, P. R. and Velankar, Sachin and Chatterji, Apratim} } @article { ISI:000346263800042, title = {Synthesis and characterization of PEPO grafted carboxymethyl guar and carboxymethyl tamarind as new thermo-associating polymers}, journal = {Carbohydrate Polymers}, volume = {117}, year = {2015}, month = {MAR}, pages = {331-338}, publisher = {ELSEVIER SCI LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, abstract = {

New thermo associating polymers were designed and synthesized by grafting amino terminated poly(ethylene oxide-co-propylene oxide) (PEPO) onto carboxymethyl guar (CMG) and carboxymethyl tamarind (CMT). The grafting was performed by coupling reaction between-NH2 groups of PEPO and -COOH groups of CMG and CMT using water-soluble EDC/NHS as coupling agents. The grafting efficiency and the temperature of thermo-association, T-assoc in the copolymer were studied by NMR spectroscopy. The graft copolymers, CMG-g-PEPO and CMT-g-PEPO exhibited interesting thermo-associating behavior which was evidenced by the detailed rheological and fluorescence measurements. The visco-elastic properties (storage modulus, G{\textquoteright}; loss modulus, G{\textquoteright}{\textquoteright}) of the copolymer solutions were investigated using oscillatory shear experiments. The influence of salt and surfactant on the T-assoc was also studied by rheology, where the phenomenon of {\textquoteleft}{\textquoteleft}Salting out{\textquoteright}{\textquoteright} and {\textquoteleft}{\textquoteleft}Salting in{\textquoteright}{\textquoteright} was observed for salt and surfactant, respectively, which can give an easy access to tunable properties of these copolymers. These thermo-associating polymers with biodegradable nature of CMG and CMT can have potential applications as smart injectables in controlled release technology and as thickeners in cosmetics and pharmaceutical formulations. (C) 2014 Elsevier Ltd. All rights reserved.

}, keywords = {Carboxymethyl guar, Carboxymethyl tamarind, Pluronics, Rheology, Solution behavior, Thermo-associating polymers}, issn = {0144-8617}, doi = {10.1016/j.carbpol.2014.09.073}, author = {Gupta, Nivika R. and Torris, Arun A. T. and Wadgaonkar, Prakash P. and Rajamohanan, P. R. and Ducouret, Guylaine and Hourdet, Dominique and Creton, Costantino and Badiger, Manohar V.} }