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A new gadolinium(III)-based coordination polymer (CP), [Gd(3,5-pydc)1.5(CO2)0.5(H2O)4]·3H2O (1, where 3,5-pydc = 3,5-pyridinedicarboxylate), has been successfully synthesized using a slow diffusion method at room temperature. Single-crystal X-ray diffraction study of 1 confirmed its one-dimensional ladder-like structure. The Gd3+ ions are in a distorted tricapped trigonal prismatic geometry. Two types of 3,5-pydc ligands are present in the structures: in one case, the pyridine nitrogen remains vacant, whereas in the other case, the pyridine nitrogen is coordinated with CO2 to form zwitterionic carbamate. The phase purity of 1 has been confirmed by powder X-ray diffraction, thermogravimetric analysis and IR spectroscopic studies. The aqueous dispersion of compound 1 exhibits weak luminescence emission at 385 nm upon excitation at 270 nm. To explore the ligand-sensitized metal-centred luminescence, we have prepared a composite by mixing the CP with Tb3+ ions (Tb@1). The formation of the composite has been confirmed by IR spectroscopic studies in the solid state. The composite showed excellent ligand-sensitized metal-centred luminescence. We have utilized this luminescence property for the sensing of anions in aqueous media. The composite shows luminescence quenching behaviour in the presence of Cr2O72−, CrO42−, and NO2−, with high sensitivity, and their limits of detection are 147 ppb, 142 ppb and 20 ppb, respectively. Selectivity experiments show that the detection of these three anions is highly selective in the presence of other common anions. Detailed experimental studies suggest that the preferable interaction of the three anions with the Tb3+ ions inside the composite and the reduction of the excitation energy are probably responsible for the quenching behaviour. [ABSTRACT FROM AUTHOR]

Excited-state proton transfer (ESPT) from pyranine (8-hydroxypyrene-1,3,6-trisulfonate, HPTS) to acetate was studied in [gamma]-cyclodextrin ([gamma]-CD) and 2-hydroxypropyl-[gamma]-cyclodextrin (HP-[gamma]-CD). It was found that, in both the cyclodextrins, ESPT from HPTS to acetate was much slower than in bulk water and ESPT of HPTS in substituted [gamma]-cyclodextrin was slower than that in the unsubstituted one.

Two compact denatured states of glutaminyl-tRNA synthetase (GInRS) under equilibrium conditions in the presence of a naturally occurring osmolyte, L-glutamate are characterized. Dynamic light scattering studies reveal that both the compact denatured states are aggregated under the measurement conditions.

Fluorescence anisotropy decay and solvation dynamics of coumarin 153 (C153) are studied in dimethyl beta-cyclodextrin (DIMEB) and trimethyl beta-cyclodextrin (TRIMEB) nanocavity in water. Solvation dynamics of C153 in DIMEB exhibits a very fast (2.4 ps) component (41%) and two slower components of 50 ps (29%) and 1450 ps (30%).

Solvation dynamics of coumarin 480 (C480) is studied in a nanoporous sol-gel matrix. Its effect in the presence of cetyltrimethylammonium bromide is studied.

A new cadmium based MOF [Cd(C5N1S1H4)(C6O5H3)] (C5N1S1H4 = 4MPy, C6O5H3 = HFDA), Cd_1, was synthesized by a solvothermal reaction using 2,5-furandicarboxylic acid (H2FDA) and 4-mercaptopyridine (4MPyH) formed in situ by the S–S bond rupture of the aldrithiol-4 ligand. Single crystal X-ray data of Cd_1 confirmed a two-dimensional structure arranged in an ABAB... fashion in three dimensions where the nitrogen atom of the pyridine ring of 4MPy remains free. The aqueous dispersion of Cd_1 showed room temperature phosphorescence at 520 nm upon excitation at 330 nm. Luminescence lifetime studies revealed that the emission at 520 nm originates from a triplet state which became populated through intersystem crossing (ISC) from the singlet excited state. A trace amount of Hg2+ ions interacted very strongly with Cd_1 and significantly altered its UV-vis absorption and luminescence spectra. After interacting with the Hg2+ ions, the emission of Cd_1 at 520 nm gradually disappeared with a concomitant increase of the low intensity fluorescence at 383 nm. The ISC is hampered by the coordination of Hg2+ ions with two S atoms of the 4MPy moiety of two adjacent 1D chains (inter-layer) and a huge reduction of the structure's flexibility. On the other hand, the interactions between metal ions and Cd_1via the free N atom of the pyridine moiety resulted in the increase of the fluorescence intensity at 383 nm, however the phosphorescence intensity did not change significantly. These studies indicate that the interactions between Hg2+ ions and S atoms are highly selective due to the soft–soft interaction whereas the interactions between the N atoms and all the metal ions are not selective. A ratiometric luminescence approach has been employed to establish Cd_1 as a detector of Hg2+ in aqueous medium selectively over other common metal ions. The estimated quenching constant and detection limit of Cd_1 for Hg2+ were found to be 1.15 × 106 M−1 and 37.5 nM (equivalent to 7.40 ppb) in water. [ABSTRACT FROM AUTHOR]

A new zinc-based two-dimensional coordination polymer, [Zn(5-AIP)(Ald-4)]·H2O (5-AIP = 5-amino isophthalate, Ald-4 = aldrithiol-4), 1, has been synthesized at room temperature by the layer diffusion technique. Single-crystal X-ray diffraction analysis of 1 showed a two-dimensional bilayer structure. An aqueous suspension of 1 upon excitation at 300 nm displayed an intense blue emission at 403 nm. The luminescence spectra were interestingly responsive and selective to Al3+, Cr3+ and Fe3+ ions even in the presence of other interfering ions. The calculated detection limits for Al3+, Cr3+ and Fe3+ were 0.35 μM (≡8.43 ppb), 0.46 μM (≡22.6 ppb) and 0.30 μM (≡15.85 ppb), respectively. Notably, with the cumulative addition of Al3+ ions, the luminescence intensity at 403 nm decreased steadily with a gradual red shift up to 427 nm. Afterward, this red shifted peak showed a turn-on effect upon further addition of Al3+ ions. On the other hand, for Cr3+ and Fe3+ ions, there was only drastic luminescence quenching and a large red shift up to 434 nm. This indicated the formation of a complex between 1 and these metal ions, which was also supported by the UV-Visible absorption spectra of 1 that showed the appearance of a new band at 280 nm in the presence of these three metal ions. The FTIR spectra revealed that these ions interacted with the carboxylate oxygen atom of 5-AIP and the nitrogen atom of the Ald-4 ligand in the structure. The luminescence lifetime decay analysis manifested that a charge-transfer type complex was formed between 1 and Cr3+ and Fe3+ ions that resulted in huge luminescence quenching due to the efficient charge transfer involving the vacant d-orbitals, whereas for Al3+ ions having no vacant d-orbital, turn-on of luminescence occurred because of the increased rigidity of 1 upon complexation. [ABSTRACT FROM AUTHOR]

A terbium doped yttrium based metal–organic framework [Y1.8Tb0.2(CAM)3(H2O)4]·2H2O, 1, {where H2CAM = chelidamic acid}, was successfully synthesized using a hydrothermal technique to be used as a phosphor material along with a large Stokes shift and low self-quenching of luminescence. To confirm the structure and phase purity of compound 1, single-crystals of the isomorphous pure yttrium-based compound [Y2(CAM)3(H2O)4]·2H2O, 1a, were synthesized under similar experimental conditions. The single-crystal X-ray data of compound 1a confirmed a two-dimensional metal–organic framework formed by the connectivity of the Y3+ ion with the carboxylates of chelidamate ligands, while the hydroxyl groups of the chelidamate ligands remain free. The phase purity of compounds 1 and 1a was confirmed by powder X-ray diffraction. Compound 1 was systematically characterized by TGA, IR, SEM, EDX-elemental mapping and BET analysis. The aqueous solution of compound 1 shows a weak visible green emission upon excitation at 280 nm. The emission of compound 1 was utilized to detect the pH response, keeping in mind the favourable presence of free hydroxyl groups. It was observed that the emission intensity increased 4.2 times when the pH was increased from pH 7 to pH 9 along with a sudden jump at pH > 7.5. The luminescence lifetime decay studies also showed a gradual increase in the lifetime of Tb3+ centered emission from 0.75 ms (pH 7) to 0.99 ms (pH 9). The luminescence response of compound 1 in the biologically important pH range of 7–9 based on the free hydroxyl groups may be very much useful for real-life applications. [ABSTRACT FROM AUTHOR]

To study the photophysics and understand the mechanism of metal ion sensing, a luminescent cobalt-based metal–organic compound, [Co(bpds)(bdc)(H2O)2]·bpds (1), was synthesized at room temperature from 4,4′-bipyridyl disulphide (bpds) and 1,4-benzene dicarboxylic acid (bdc) by layer diffusion. Structure determination based on single-crystal X-ray analysis revealed a parallel interpenetrated structure of two-dimensional layers along with a layer of uncoordinated bpds ligand. An aqueous suspension of 1 showed intense blue emission at 421 nm. In the presence of few micromolar of Al3+ ions, a dramatic change in the luminescence spectrum around an isoemissive point was observed with the appearance of a new peak at 380 nm. A similar phenomenon was observed in the presence of Fe3+ ions. For other metal ions, no significant changes in the luminescence spectrum of 1 were observed. Detailed lifetime decay analysis and Fourier-transform infrared spectroscopy revealed that Al3+ ions form charge-transfer complexes (or adducts) with uncoordinated bpds ligands through pyridine nitrogen atoms, resulting in a new emission peak at 380 nm. Time-resolved study revealed that the quenching of luminescence was dynamic in nature and associated with an increase in the non-radiative rate constant. Moreover, the luminescence property of 1 was ultrasensitive to the presence of Al3+ and Fe3+ ions in water, even in a mixture of many other ions, with detection limits of 0.35 and 0.25 μM, respectively. [ABSTRACT FROM AUTHOR]

We unambiguously demonstrate the 'up' versus 'down' alignment of a pair of prototypical solute molecules adsorbed at the air/water interface for the first time using heterodyne-detected electronic sum frequency generation spectroscopy. This molecular alignment is also reproduced by classical molecular dynamics (MD) simulation theoretically. Furthermore, the MD simulation indicates distinctly different interface-specific hydration structures around the two solute molecules, which dictate the molecular alignment at the interface. It is concluded that the hydrophilicity difference between the terminal functional groups of the solute governs the molecular orientation and surrounding hydration structures at the interface. [ABSTRACT FROM AUTHOR]

The primary steps of photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to five coumarin dyes are studied in an anionic micelle [sodium dodecyl sulfate (SDS)] and a neutral micelle [triton X-100 (TX-100)] using femtosecond upconversion. The rate of PET in micelle is found to be highly nonexponential. In both the micelles, PET displays components much faster (∼10 ps) than the slow components (180–2900 ps) of solvation dynamics. The ultrafast components of electron transfer exhibit a bell-shaped dependence on the free energy change. This is similar to Marcus inversion. The rates of PET in TX-100 and SDS micelle are, in general, faster than those in cetyltrimethylammonium bromide (CTAB) micelle. In the SDS and TX-100 micelle, the Marcus inversion occurs at -ΔG0 ∼0.7 eV which is lower than that (∼1.2 eV) in CTAB micelle. Possible causes of variation of PET in different micelles are discussed. [ABSTRACT FROM AUTHOR]

Fluorescence resonance energy transfer (FRET) from coumarin 480 (C480) to fluorescein 548 (F548) in a sodium dioctyl sulfosuccinate (AOT) reverse micelle is studied by picosecond and femtosecond emission spectroscopy. In bulk water, at the low concentration of the donor (C480) and the acceptor (F548), no FRET is observed. However, when the donor (C480) and the acceptor (F548) are confined in a AOT reverse micelle very fast FRET is observed. The time constants of FRET were obtained from the rise time of the emission of the acceptor (F548). In a AOT microemulsion, FRET is found to occur in multiple time scales—3, 200, and 2700 ps. The 3 ps component is assigned to FRET in the water pool of the reverse micelle with a donor-acceptor distance, 16 Å. The 200 ps component corresponds to a donor-acceptor distance of 30 Å and is ascribed to the negatively charged acceptor inside the water pool and the neutral donor inside the alkyl chains of AOT. The very long 2700 ps component may arise due to FRET from a donor outside the micelle to an acceptor inside the water pool and also from diffusion of the donor from bulk heptane to the reverse micelle. With increase in the excitation wavelength from 375 to 405 nm the relative contribution of the FRET due to C480 in the AOT reverse micelle (the 3 and 200 ps components) increases. [ABSTRACT FROM AUTHOR]

Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline to coumarin dyes in cetyltrimethylammonium bromide (CTAB) micelle is studied using femtosecond upconversion spectroscopy. The rate of PET in a CTAB micelle is found to be highly nonexponential with components much faster (∼10 ps) than the slow components of solvation dynamics. The ultrafast components of electron transfer exhibits a bell-shaped dependence on the free energy change which is similar to the Marcus inversion. [ABSTRACT FROM AUTHOR]

Ultrafast fluorescence resonance energy transfer (FRET) from coumarin 153 (C153) to rhodamine 6G (R6G) is studied in a neutral PEO20–PPO70–PEO20 triblock copolymer (P123) micelle and an anionic micelle (sodium dodecyl sulfate, SDS) using a femtosecond up-conversion setup. Time constants of FRET were determined from the rise time of the acceptor emission. It is shown that a micelle increases efficiency of FRET by holding the donor and the acceptor at a close distance (intramicellar FRET) and also by tuning the donor and acceptor energies. It is demonstrated that in the P123 micelle, intramicellar FRET (i.e., donor and acceptor in same micelle) occurs in 1.2 and 24 ps. In SDS micelle, there are two ultrafast components (0.7 and 13 ps) corresponding to intramicellar FRET. The role of diffusion is found to be minor in the ultrafast components of FRET. We also detected a much longer component (1000 ps) for intramicellar FRET in the larger P123 micelle. [ABSTRACT FROM AUTHOR]

Excitation wavelength (λex) dependence of solvation dynamics of coumarin 480 (C480) in the micellar core of a water soluble triblock copolymer, PEO20-PPO70-PEO20 (Pluronic P123), is studied by femtosecond and picosecond time resolved emission spectroscopies. In the P123 micelle, the width of the emission spectrum of C480 is found to be much larger than that in bulk water. This suggests that the P123 micelle is more heterogeneous than bulk water. The steady state emission maximum of C480 in P123 micelle shows a significant red edge excitation shift by 25 nm from 453 nm at λex=345 nm to 478 nm at λex=435 nm. The solvation dynamics in the interior of the triblock copolymer micelle is found to depend strongly on the excitation wavelength. The excitation wavelength dependence is ascribed to a wide distribution of locations of C480 molecules in the P123 micelle with two extreme environments—a bulklike peripheral region with very fast solvent response and a very slow core region. With increase in λex, contribution of the bulklike region having an ultrafast component (<=2 ps) increases from 7% at λex=375 nm to 78% at λex=425 nm while the contribution of the ultraslow component (4500 ps) decreases from 79% to 17%. [ABSTRACT FROM AUTHOR]

Temperature dependence of solvation dynamics and fluorescence anisotropy decay of 8-anilino-1-naphthalenesulfonate (ANS) bound to a protein, bovine serum albumin (BSA), are studied. Solvation dynamics of ANS bound to BSA displays a component (300 ps) which is independent of temperature in the range of 278–318 K and a long component which decreases from 5800 ps at 278 K to 3600 ps at 318 K. The temperature independent part is ascribed to a dynamic exchange of bound to free water with a low barrier. The temperature variation of the long component of solvation dynamics corresponds to an activation energy of 2.1 kcal mol-1. The activation energy is ascribed to local segmental motion of the protein along with the associated water molecules and polar residues. The time scale of solvation dynamics is found to be very different from the time scale of anisotropy decay. The anisotropy decays are analyzed in terms of the wobbling motion of the probe (ANS) and the overall tumbling of the protein. [ABSTRACT FROM AUTHOR]

Femtosecond emission spectroscopy is used for studying excited-state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulfonate, HPTA) in a polymer-surfactant aggregate. The polymer-surfactant aggregate is a supramolecular assembly that has a triblock copolymer [(PEO).sub.20]-[(PPO).sub.70]-[(PEO).sub.20] (P123) and a cationic surfactant, cetyltrimethylammonium chloride (CTAC).