Time-resolved fluorescence and proton NMR studies of tyrosine and tyrosine analogs: correlation of NMR-determined rotamer populations and fluorescence kinetics

Biochemistry ◽  
1986 ◽  
Vol 25 (3) ◽  
pp. 599-607 ◽  
Author(s):  
William R. Laws ◽  
J. B. Alexander Ross ◽  
Herman R. Wyssbrod ◽  
Joseph M. Beechem ◽  
Ludwig Brand ◽  
...  
Keyword(s):  
Proton Nmr ◽  
Time Resolved Fluorescence ◽  
Nmr Studies ◽  
Time Resolved ◽  
Fluorescence Kinetics

Excited state acid catalysis of the 2 + 2 photocycloaddition of methyl 2-naphthoate and acetylacetone; the interaction of a nonfluorescent exciplex with H2SO4

1994 ◽  
Vol 72 (9) ◽  
pp. 2011-2020 ◽  
Author(s):  
Yuan L. Chow ◽  
Carl I. Johansson
Keyword(s):  
Excited State ◽  
Quantum Yield ◽  
Fluorescence Quenching ◽  
Analytical Method ◽  
Acid Catalysis ◽  
Time Resolved Fluorescence ◽  
Time Resolved ◽  
Fluorescence Kinetics ◽  
Quenching Analysis ◽  
Potential Acid

In this paper, the striking acid catalysis of the photocycloaddition of methyl 2-naphthoate (2MN) to acetylacetone (AA) to give 1 and 2 was traced to the enhanced conversion of the nonemissive *(2MN–AA) exciplex to 1 and 2 by H2SO4. The partial reversibility of the exciplex in CH3CN and CH3OH was established by extended fluorescence-quenching analysis using oxygen to perturb the system, whereas time-resolved fluorescence kinetics failed to reveal the presence of this exciplex. A similar analytical method demonstrated the interaction of the nonfluorescent *(2MN–AA) exciplex and H2SO4 with the rate constants of kap = (2 ± 1) × 109 M−1 s−1 in CH3CN and (4 ± 1) × 109 M−1 s−1 in CH3OH. The quantum yield of photocycloadducts was significantly enhanced at high 2MN conversions owing to the retardation of the competing excimer *(2MN)2 formation. In the range of low conversion (< 15%) and [H2SO4] ≤ 1 mM, the quantum yield was shown to be proportional to H2SO4 concentration; the slope from such plots was analyzed to give kap values similar to those obtained from the extended fluorescence-quenching analysis. This agreement, along with the elimination of other potential acid catalytic routes, unambiguously proves that the acid catalysis originates from the interaction of the *(2MN–AA) exciplex with H2SO4.

scholarly journals Picosecond Absorption Spectroscopy of Polymethine Cis-Trans Isomerization

1988 ◽  
Vol 8 (1) ◽  
pp. 39-47 ◽  
Author(s):  
K.-H. Feller ◽  
R. Gadonas ◽  
V. Krasauskas
Keyword(s):  
Quantum Yield ◽  
Absorption Spectra ◽  
Time Resolved Fluorescence ◽  
Absorption Region ◽  
Time Resolved ◽  
Fluorescence Kinetics ◽  
Double Exponential ◽  
A Minor ◽  
Cis Isomer ◽  
Polymethine Dye

Results are presented of time resolved fluorescence and absorption investigations of DDEOCI (3,3'-diethyl-6,6'-diphenyl-9-ethyl-oxacarbocyanine iodide) in solvents which differ in polarity and viscosity. The measured picosecond absorption and fluorescence kinetics probed at various wavelengths of the polymethine dye studied can be fitted to a double exponential decay with a minor fast component of lifetime τ1 and a major slower component of lifetime τ2. Furthermore, probing in the S1←S0 absorption region and in the fluorescence region results in a residual with a lifetime of some ns and belonging to the detected red-shifted photoisomer with a low quantum yield (φ < 10%). The lifetime and the preexponential factors of the two components are in methanolic solution uneffected by changes of the anion.The detected two picosecond lifetime components are supposed to belong to two isomeric species (all-trans and mono-cis isomer) with strongly overlapping absorption spectra.

Spectroscopic and theoretical insights on determination of binding strength and molecular structure for the supramolecular complexes of a designed bisporphyrin with C60 and C70

2012 ◽  
Vol 16 (01) ◽  
pp. 14-24 ◽  
Author(s):  
Partha Mukherjee ◽  
Subarata Chattopadhyay ◽  
Sumanta Bhattacharya
Keyword(s):  
Molecular Electrostatic Potential ◽  
Binding Constants ◽  
Spectroscopic Techniques ◽  
Time Resolved Fluorescence ◽  
Nmr Studies ◽  
Time Resolved ◽  
Average Value ◽  
Molecular Tweezer ◽  
Molecular Electrostatic Potential Maps

The present article examines the binding affinity of the newly designed Zn2-bisporphyrin molecule, syn-1, towards C60 and C70 in toluene medium. The investigation is carried out by UV-vis spectrophotometric, steady state and time-resolved fluorescence spectroscopic techniques. The bisporphyrin, syn-1, serves as an effective and selective molecular tweezer for C70 as average value of binding constants (K) for the non-covalent complexes of syn-1 with C60 and C70 are estimated to be 1.65 × 104 and 1.05 × 105 dm3 · mol-1, respectively. Binding of C70 in the cleft of syn-1 is clearly demonstrated by the quantum chemical calculations at ab initio level of theory. Molecular electrostatic potential maps demonstrate significant redistribution of charges in these supramolecules. Proton NMR studies suggest that the C70 moiety remains at the shallow part of the cleft of syn-1.

Sign in / Sign up

Export Citation Format

Share Document