01050nas a2200169 4500008004100000245008200041210006900123260000800192300001600200490000700216520046600223100002600689700002000715700001700735700002300752856010500775 2011 eng d00aBorazine as a sensor for fluoride ion: a computational and experimental study0 aBorazine as a sensor for fluoride ion a computational and experi cMAY a3636–36390 v523 a

The computational and experimental studies have revealed that even simple molecule like borazine can act as a sensor for fluoride ions. This study further reported the various binding modes of analytes using quantum chemical calculations and the nature of such interactions have been examined using electron density surface analysis. Total charge transfer analysis (qCT) correlates well with the binding affinities of analytes with the borazine receptor.

1 aKesharwani, Manoj, K.1 aSuresh, Moorthy1 aDas, Amitava1 aGanguly, Bishwajit uhttps://library.ncl.res.in/content/borazine-sensor-fluoride-ion-computational-and-experimental-study01326nas a2200157 4500008004100000245013300041210006900174260000800243300001600251520069100267100002100958700002000979700002400999700001701023856012801040 2011 eng d00aCompetitive binding of Ba2+and Sr2+ to 18-crown-6 in a receptor with a 1-methoxyanthraquinone analogue as the other binding site0 aCompetitive binding of Ba2and Sr2 to 18crown6 in a receptor with cOCT a4680–46903 a

Owing to their immense biological significance, development of sensors for the selective detection of alkaline earth metal ions has attracted vast research interest. In this article we have reported the synthesis, characterisation and ion binding studies of a new RuII-polypyridyl-crown-anthraquinone complex (5). Studies confirm selective binding of BaII, SrII and CaII ions, with Kmath image > Kmath image >> Kmath image, over all other metal ions, to the crown ether moiety and not to the methoxy anthraquinone component, the latter being the second binding site available and known for its affinity towards alkaline earth metal ions from one of our previous reports.

1 aBanerjee, Tanmay1 aSuresh, Moorthy1 aGhosh, Hirendra, N.1 aDas, Amitava uhttps://library.ncl.res.in/content/competitive-binding-ba2and-sr2-18-crown-6-receptor-1-methoxyanthraquinone-analogue-other02700nas a2200217 4500008004100000245005900041210005700100260000800157300001400165490000700179520203200186100002002218700002402238700002602262700001902288700002302307700002802330700002002358700001702378856008702395 2011 eng d00aFolding and unfolding movements in a [2]pseudorotaxane0 aFolding and unfolding movements in a 2pseudorotaxane cDEC a138–1440 v763 a

A new dibenzo[24]crown-8 derivative (1) was synthesized and functionalized with aromatic moieties such as naphthalene and coumarin units. These two fluorophores are known to form an effective FRET (Forster resonance energy transfer) pair, and this formed the basis for the design of this host crown ether derivative. Results of the steady-state and time-resolved fluorescence studies confirmed the resonance energy transfer between the donor naphthalene moiety and acceptor coumarin fragment, while NMR spectra and computational studies support a folded conformation for the uncomplexed crown ether 1. This was found to form an inclusion complex, a [2]pseudorotaxane type with imidazolium ion derivatives as the guest molecules with varying alkyl chain lengths ([C4mim]+ or [C10mim]+). The host crown ether (1) tends to adopt an open conformation on formation of the interwoven inclusion complex (1·[C4mim]+ or 1·[C10mim]+). This change in conformation, from the folded to a open one, was predicted by computational as well as 1H NMR studies and was confirmed by single crystal X-ray structure for one (1·[C4mim]+) of the two inclusion complexes. The increase in the effective distance between the naphthalene and coumarin moieties in the open conformation of these inclusion complexes was also supported by the decrease in the effective FRET process that was operational between naphthalene and coumarin moieties in the free molecule (1). Importantly, this inclusion complex formation was found to be reversible, and in the presence of a stronger base/polar solvent, such as triethyl amine/DMSO, the deprotonation/effective solvation of the cationic imidizolium ions ([C4mim]+ or [C10mim]+) resulted in decomplexation or dethreading with restoration of the original emission spectra for 1, which signifies the subsequent increase in the FRET process. Thus we could demonstrate that a molecular folding-unfolding type of movement in the crown ether derivative could be induced by chemical input as an imidazolium ion.

1 aSuresh, Moorthy1 aMandal, Amal, Kumar1 aKesharwani, Manoj, K.1 aAdarsh, N., N.1 aGanguly, Bishwajit1 aKanaparthi, Ravi, Kumar1 aSamanta, Anunay1 aDas, Amitava uhttps://library.ncl.res.in/content/folding-and-unfolding-movements-2pseudorotaxane01341nas a2200157 4500008004100000245012300041210006900164260000800233300001400241490000600255520073900261100002401000700002001024700001701044856012201061 2011 eng d00aStudies on [3]pseudorotaxane formation from a bis-azacrown derivative as host and imidazolium ion-derivatives as guest0 aStudies on 3pseudorotaxane formation from a bisazacrown derivati cMAR a4811-48170 v93 a

A new host molecule, having two azacrown derivatives bridged by luminescent naphthalene diimide functionality, is found to form a [3]pseudorotaxane derivative with imidazolim ion-based guest molecules in non-polar solvents through hydrogen-bonded adduct formation. Depending upon the length of the covalent linker that links the imidazolium ion and the luminescent naphthalene fragment in the guests, the [3]pseudorotaxane adducts adopt different conformation or orientation with varying π–π/donor–acceptor interaction. The mechanism for the naphthalene-based luminescence quenching by NDI fragment on adduct formation was found to be a combination of static, as well as dynamic with static quenching as the dominant one.

1 aMandal, Amal, Kumar1 aSuresh, Moorthy1 aDas, Amitava uhttps://library.ncl.res.in/content/studies-3pseudorotaxane-formation-bis-azacrown-derivative-host-and-imidazolium-ion01290nas a2200205 4500008004100000245011900041210006900160260000800229300001600237490000700253520056400260100002400824700002000848700001800868700001500886700001800901700002100919700001700940856012700957 2012 eng d00aRecognition of Hg2+ion through restricted imine isomerization: crystallographic evidence and imaging in live cells0 aRecognition of Hg2ion through restricted imine isomerization cry cJUN a2980–29830 v143 a

A newly synthesized imine-based receptor (L) showed remarkable specificity toward the Hg2+ ion in aqueous media over other metal ions. Coordination of L to Hg2+ induces a turn-on fluorescence response. This was explained based on the restricted imine isomerization along with PET on coordination to Hg2+. X-ray structural evidence tends to favor a C–C bond rotation rather than C═N isomerization for adopting a favorable conformation in L for coordination to Hg2+. This reagent could be used for imaging the accumulation of Hg2+ ions in HeLa cells.

1 aMandal, Amal, Kumar1 aSuresh, Moorthy1 aDas, Priyadip1 aSuresh, E.1 aBaidya, Mithu1 aGhosh, Sudip, K.1 aDas, Amitava uhttps://library.ncl.res.in/content/recognition-hg2ion-through-restricted-imine-isomerization-crystallographic-evidence-and01866nas a2200169 4500008004100000245014500041210006900186260000800255300001600263490000700279520120700286100002401493700002001517700001801537700001701555856012401572 2012 eng d00aRestricted conformational flexibility of a triphenylamine derivative on the formation of host-guest complexes with various macrocyclic hosts0 aRestricted conformational flexibility of a triphenylamine deriva cMAR a3906–39170 v183 a

Herein, we report the host–guest-type complex formation between the host molecules cucurbit[7]uril (CB[7]), β-cyclodextrin (β-CD), and dibenzo[24]crown-8 ether (DB24C8) and a newly synthesized triphenylamine (TPA) derivative 1X3 as the guest component. The host–guest complex formation was studied in detail by using 1H NMR, 2D NOESY, UV/Vis fluorescence, and time-resolved emission spectroscopy. The chloride salt of the TPA derivative was used for recognition studies with CB[7] and β-CD in an aqueous medium. The restricted internal rotation of the guest molecule on complex formation with either of these two host molecules was reflected in the enhancement of the emission quantum yield and the average excited-state lifetime for the triphenylamine-based excited states. Studies with DB24C8 as the host molecule were performed in dichloromethane, a medium that maximizes the noncovalent interaction between the host and guest fragments. The Förster resonance energy transfer (FRET) process involving DB24C8 and 1(PF6)3, as the donor and acceptor fragments, respectively, was established by electrochemical, steady-state emission, and time-correlated single-photon counting studies.

1 aMandal, Amal, Kumar1 aSuresh, Moorthy1 aDas, Priyadip1 aDas, Amitava uhttps://library.ncl.res.in/content/restricted-conformational-flexibility-triphenylamine-derivative-formation-host-guest02415nas a2200169 4500008004100000245008000041210006900121260000800190300001400198490000600212520184400218100002002062700002402082700001502106700001702121856010702138 2013 eng d00aFirst demonstration of two-step FRET in a synthetic supramolecular assembly0 aFirst demonstration of twostep FRET in a synthetic supramolecula cMAR a2380-23860 v43 a

We report a trichromophoric pseudorotaxane (3NPC) that demonstrates a two-step FRET-based relay comprising of primary donor–primary acceptor/secondary donor–secondary acceptor pairs. To achieve this, naphthalene (1) and coumarin (3) were used as the primary donor and secondary acceptor, respectively; while pyrene (2 or T) unit, having spectral overlap with both 1 and 3, was used as the primary acceptor as well as the secondary donor. Results of time resolved and steady-state emission studies reveal that sequential resonance energy transfer (FRET 1 → 2 → 3) and direct resonance energy transfer (FRET 1 → 3) processes are operational simultaneously. In the sequential energy transfer process (1 → 2 → 3) of the triad system, pyrene acts as a transmitter and makes the whole supramolecular assembly behave as a linear energy transferring wire. Sensitised emission of the coumarin moiety, i.e. the secondary and eventual final acceptor, offers the possibility of evaluating the performance of this linear trichromophoric system by one and two-step FRET mechanisms. Formation of an interwoven complex between the host (NCC24O8) and the guest (T) components, utilizing various non-bonding interactions (intercomponent [N+–H⋯O], [C–H⋯O] and π–π stacking interactions) has been confirmed by 1H NMR studies in solution and a single crystal X-structural study in the solid state. The formation constant (Kf = 2.31 × 103 M−1) for the [2]pseudorotaxane was evaluated using isothermal titration calorimetric studies. The complex gives rise to the first crystal structure of a self-assembled [2]pseudorotaxane that demonstrates sequential two-step FRET based energy transfer in a self-assembled triad that is held in an assembly through non-covalent interactions, such as hydrogen bonding and π–π stacking.

1 aSuresh, Moorthy1 aMandal, Amal, Kumar1 aSuresh, E.1 aDas, Amitava uhttps://library.ncl.res.in/content/first-demonstration-two-step-fret-synthetic-supramolecular-assembly02265nas a2200229 4500008004100000022001400041245013900055210006900194260007100263300001400334490000700348520137500355100002401730700002001754700002601774700002701800700001901827700002301846700002301869700001701892856012601909 2013 eng d a0022-326300aMolecular interactions, proton exchange, and photoinduced processes prompted by an inclusion process and a [2]pseudorotaxane formation0 aMolecular interactions proton exchange and photoinduced processe a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcAUG a9004-90120 v783 a

Appropriate design of the host and guest components allows formation of a novel [2]pseudorotaxane complex with an interrupted photoinduced electron transfer (PET)-coupled fluorescence resonance energy transfer (FRET) response. This is the first example of an inclusion complex with NO6-based azacrown ether as the host unit (H). Different guest molecules (G1, G2, G3, and G4) with varying stopper size are used for the studies. Unlike G1, G2, and G3, G4 with a relatively bulkier stopper fails to form a [2]pseudorotaxane complex. Isothermal titration microcaloiimetry measurements reveal a systematic increase in the association constant for H.G1, H.G2, and H.G3 with a change in the stopper size. Thermodynamic data suggest that the formation of H.G1/H.G2/H.G3 is exclusively driven by a large positive entropic gain (T Delta S = 19.69/26.80/21.81 kJ.mol(-1)), while the enthalpy change is slightly negative for H.G1/H.G3 (-2.61/-1.97 kJ.mol(-1)) and slightly positive for H.G2 (Delta H = 5.98 kJ.mol(-1)). For these three inclusion complexes, an interrupted PET-coupled FRET response is observed with varying efficiency, which is attributed to the subtle differences in acidity of the NH2+ unit of the guest molecules and thus the proton exchange ability between the host and respective guest. This is substantiated by the results of the computational studies.

1 aMandal, Amal, Kumar1 aSuresh, Moorthy1 aKesharwani, Manoj, K.1 aGangopadhyay, Monalisa1 aAgrawal, Manoj1 aBoricha, Vinod, P.1 aGanguly, Bishwajit1 aDas, Amitava uhttps://library.ncl.res.in/content/molecular-interactions-proton-exchange-and-photoinduced-processes-prompted-inclusion-0