The Experts below are selected from a list of 87729 Experts worldwide ranked by ideXlab platform

Jianjun Tian - One of the best experts on this subject based on the ideXlab platform.

Guozhong Cao - One of the best experts on this subject based on the ideXlab platform.

Laura J Juszczak - One of the best experts on this subject based on the ideXlab platform.

  • the broken ring reduced aromaticity in lys trp cations and high ph tautomer correlates with lower Quantum Yield and shorter lifetimes
    Journal of Physical Chemistry B, 2014
    Co-Authors: Azaria S Eisenberg, Laura J Juszczak
    Abstract:

    Several nonradiative processes compete with tryptophan fluorescence emission. The difficulty in spectral interpretation lies in associating specific molecular environmental features with these processes and thereby utilizing the fluorescence spectral data to identify the local environment of tryptophan. Here, spectroscopic and molecular modeling study of Lys-Trp dipeptide charged species shows that backbone-ring interactions are undistinguished. Instead, Quantum mechanical ground state isosurfaces reveal variations in indole π electron distribution and density that parallel charge (as a function of pK1, pK2, and pKR) on the backbone and residues. A pattern of aromaticity-associated Quantum Yield and fluorescence lifetime changes emerges. Where Quantum Yield is high, isosurfaces have a charge distribution similar to the highest occupied molecular orbital (HOMO) of indole, which is the dominant fluorescent ground state of the 1La transition dipole moment. Where Quantum Yield is low, isosurface charge distri...

  • the broken ring reduced aromaticity in lys trp cations and high ph tautomer correlates with lower Quantum Yield and shorter lifetimes
    The Journal of Physical Chemistry, 2014
    Co-Authors: Azaria S Eisenberg, Laura J Juszczak
    Abstract:

    Several nonradiative processes compete with tryptophan fluorescence emission. The difficulty in spectral interpretation lies in associating specific molecular environmental features with these processes and thereby utilizing the fluorescence spectral data to identify the local environment of tryptophan. Here, spectroscopic and molecular modeling study of Lys-Trp dipeptide charged species shows that backbone-ring interactions are undistinguished. Instead, Quantum mechanical ground state isosurfaces reveal variations in indole π electron distribution and density that parallel charge (as a function of pK₁, pK₂, and pKR) on the backbone and residues. A pattern of aromaticity-associated Quantum Yield and fluorescence lifetime changes emerges. Where Quantum Yield is high, isosurfaces have a charge distribution similar to the highest occupied molecular orbital (HOMO) of indole, which is the dominant fluorescent ground state of the ¹Lₐ transition dipole moment. Where Quantum Yield is low, isosurface charge distribution over the ring is uneven, diminished, and even found off ring. At pH 13, the indole amine is deprotonated, and Lys-Trp Quantum Yield is extremely low due to tautomer structure that concentrates charge on the indole amine; the isosurface charge distribution bears scant resemblance to the indole HOMO. Such greatly diminished fluorescence has been observed for proteins where the indole nitrogen is hydrogen bonded, lending credence to the association of aromaticity changes with diminished Quantum Yield in proteins as well. Thus tryptophan ground state isosurfaces are an indicator of indole aromaticity, signaling the partition of excitation energy between radiative and nonradiative processes.

Ute Resch Genger - One of the best experts on this subject based on the ideXlab platform.

  • determination of the absolute fluorescence Quantum Yield of rhodamine 6g with optical and photoacoustic methods providing the basis for fluorescence Quantum Yield standards
    Talanta, 2012
    Co-Authors: Christian Wurth, Martin G Gonzalez, Reinhard Niessner, U Panne, Christoph Haisch, Ute Resch Genger
    Abstract:

    Abstract To establish the methodical basis for the development and certification of fluorescence Quantum Yield standards, we determined the fluorescence Quantum Yield Φf of rhodamine 6G (R6G) with two absolute methods with complementary measurement principles, here optical spectroscopy using an integrating sphere setup and pulsed laser photoacoustic spectroscopy (PAS). For the assessment of aggregation- and reabsorption-induced distortions of measured fluorescence Quantum Yields and procedures for the reliable consideration of such effects, this systematic comparison was performed in ethanol and in water employing different concentrations of R6G. In addition, the relative and absolute fluorescence Quantum Yields of these solutions were obtained with a calibrated spectrofluorometer and a commercialized integrating sphere setup. Based upon this systematic comparison, experimental advantages and systematic sources of variation were identified for both methods.

Shixun Wang - One of the best experts on this subject based on the ideXlab platform.