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Langmuir ; 33(40): 10588-10597, 2017 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-28918640


Supramolecular host-guest interactions between randomly methylated ß-cyclodextrin (RM ß-CD) and side-chain phenylalanine (Phe) and Phe-Phe dipeptide-based homopolymers have been employed for the amplification of fluorescence emission of otherwise weakly fluorescent amino acid Phe. The host-guest complex has been characterized by 1H and 13C NMR spectroscopy, two-dimensional rotating-frame overhauser spectroscopy, Fourier-transform infrared spectroscopy, UV-visible spectroscopy, and fluorescence spectroscopy. To gain insights into the origin of fluorescence in homopolymers, density functional theory calculations were performed where phenyl moieties inside the less polar core of ß-CD were observed to form a π-π coupled complex resulting in an enhanced emission. Furthermore, the complex-forming ability of Phe, the guest molecule, has been employed in tuning the cloud point temperature (TCP) of statistical copolymers derived from side-chain Phe/Phe-Phe-based methacrylate monomers and N-isopropylacrylamide. By varying the co-monomer feed ratios in the statistical copolymer and hence the concentration of RM ß-CD throughout the polymer chain, host-guest interaction-assisted broad tunability in TCP of the supramolecular polymeric complex has been achieved.

Fenilalanina/química , Substâncias Macromoleculares , Polímeros , Espectrometria de Fluorescência , Temperatura
Artigo em Inglês | MEDLINE | ID: mdl-23041920


Interaction of a dye which is structurally similar to a ketocyanine dye with metal ions (alkali, alkaline earth and transition metal) has been studied by monitoring the electronic absorption, steady state and time resolved fluorescence parameters of the dye. The dye (S(0) state) forms a 1:1 complex with cations as indicated by the appearance of a new band at a longer wavelength. Equilibrium constant and other thermodynamic parameters for complexation have been determined. The interaction between the dye and the cation is mostly electrostatic in nature. Spectroscopic results have been supplemented by DFT calculation. For very low concentration of cations, where complexation is insignificant, the absorption band of the dye undergoes a slight blue shift. Enhancement of fluorescence intensity has been observed in the same concentration range. Both phenomena have been explained in terms of formation of a weak association complex where one/more cation replace equivalent solvent molecules in the cybotatic region around the dye. The binding constant of the weak association complex involving cation and the dye (S(1) state) has been determined and has been found to depend on the charge-to-size ratio of the cations. Measurement of fluorescence lifetime of the dye indicates that the association complex is slowly decaying relative to solvated dye. At higher concentration of metal ions, however, fluorescence of the dye is quenched by the metal ions. A red shift of fluorescence maximum has also been observed in this concentration range.

Álcalis/química , Corantes/química , Íons/química , Elementos de Transição/química , Elétrons , Teoria Quântica , Espectrometria de Fluorescência , Espectrofotometria
J Phys Chem A ; 114(38): 10388-94, 2010 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-20828117


The interaction of a ketocyanine dye with a cobalt(II) ion has been studied in solution by monitoring the electronic absorption and emission spectral characteristics of the dye. A new absorption band at a longer wavelength appears in solutions containing cobalt(II) ions. An isosbestic point is observed for systems containing a fixed dye concentration and varying Co(2+) ion concentration, pointing to the formation of a complex. The stoichiometry of the complex has been found to be 1:1. Equilibrium constant has been determined from the observed data. The nature of interaction between the dye (S(0) state) and the Co(II) ion is mostly electrostatic. Spectroscopic results have been supported by DFT/TDDFT calculation. The fluorescence band is characterized by a small blue shift. In the concentration range of 10(-3)-10(-4) M of the Co(II) ion, a quenching of the dye fluorescence is noticed. The Stern-Volmer plot points to the operation of both static and dynamic mechanisms of quenching. For a micromolar concentration of the Co(II) ion, however, an enhancement of fluorescence intensity with a slight blue shift has been observed, which has been explained in terms of formation of a different type of complex in the S(1) state at this concentration level. The value of lifetime increases at the micromolar level of concentration of the Co(II) ion, where the intensity increases and then remains practically unchanged as more salt is added to the system. Values of the decay constant for the different photophysical processes have been calculated. Complexation in the S(1) state is characterized by a slower decay of the excited dye by a nonradiative path.

Carbocianinas/química , Cobalto/química , Compostos Organometálicos/química , Íons/química , Simulação de Dinâmica Molecular , Estrutura Molecular , Teoria Quântica , Espectrometria de Fluorescência , Espectrofotometria Infravermelho , Espectrofotometria Ultravioleta