• Bulletin of the Korean Chemical Society
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• 제23권5호
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• pp.727-735
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• 2002

Proton coupled carbon-13 relaxation experiment was performed to investigate the effect of vicinal protons on spin-lattice relaxation of methylene carbon-13 in n-undecane. A BIRD type pulse sequence was employed as a way to check the validity of describing the 13CH2 moiety as an isolated AX2 spin system. The results show that the presence of vicinal protons exerts substantial influence on the relaxation of methylene carbon-13, indicating that it is not a very good approximation to treat a methylene moiety as an isolated AX2 spin system.

• Bulletin of the Korean Chemical Society
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• 제21권11호
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• pp.1077-1084
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• 2000

The dipolar effect of neighboring protons that are not directly bonded to the carbon of interest on coupled carbon-13 relaxation in a simple organic molecule has been studied by comparing the relaxation behaviors of labeled carbon-13 in $Br13CH_2COOH$ with those in $BrCH_213COOH.$ Various pulse sequences, such as coupled inversion recovery pulse sequence, J-negative and J-positive pulse sequence, and nonselective and selective proton ${\pi}pulse$ sequence, were employed to perform the required coupled spin relaxation experiments. To gain information on various spectral densities, including that of dipolar-CSA cross correlation, the experiments were performed on two different spectrometers, operating, respectively, at 50.31 and 125.51MHz for 13C. The magnitude of CH dipolar spectral densities for $BrCH_213COOH$ was found to be about 8% of those for $Br13CH_2COOH$, which means the effect due to the protons not directly bonded to the carbon of interest is small but not completely negligible.

• Bulletin of the Korean Chemical Society
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• 제24권11호
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• pp.1675-1679
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• 2003

The photodynamics of excited-state intramolecular proton transfer reaction of 1-hydroxyanthraquinone (1-HAQ) and 1-deuterioanthraquinone was investigated in toluene with time-resolved emission and femtosecond transient transmittance techniques at room temperature. The temporal profiles of transient transmittance of 1-HAQ could be well described with multi-decaying time constants. The ultrafast time constant within ca. 260 fs reflects the dynamics of proton transfer. The decay component of 2 ps is assigned to an additional proton translocation process induced by the intramolecular vibrational relaxation, whereas the decay component of 18 ps is assigned to the vibrational cooling process, while the long component (200 ps) can be explained in terms of the relaxation from excited-state keto-tautomer to its ground state. Time-resolved anisotropy decay dynamics and isotope effects on the photodynamics reveals that the ESIPT from enol-tautomer to keto-one of 1-HAQ is barrierless reaction and coupled to a vibrational relaxation process.

• Bulletin of the Korean Chemical Society
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• 제22권11호
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• pp.1197-1201
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• 2001

In the spectrum of uniformly 15N labeled cytochrome c3, the relative linewidths of the doublet peaks of the 15N-coupled imido proton of the coordinated imidazole group were reversed on oxidation. This inversion was explained by the interference relaxation process between the electron-proton dipolar and 15N-1H dipolear interactions. The inversion can be used to assign the imido protons of the coordinated imidazole groups in heme proteins.

• Bulletin of the Korean Chemical Society
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• 제19권9호
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• pp.980-985
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• 1998

The excited-state intramolecular proton transfer (ESIPT) emission has been observed for 0.01 mM p-aminosalicylic acid (AS) in nonpolar aprotic solvents as demonstrated by the large Stokes' shifted fluorescence emission around 440 nm in addition to the normal emission at 330 nm. However in aprotic polar solvent such as acetonitrile, the large Stokes' shifted emission band becomes broadened, indicating existence of another emission band originated from intramolecular charge transfer (ICT). It is noteworthy that in protic solvents such as methanol and ethanol the normal and ICT emissions are quenched as the AS concentration decreases, followed by the appearance of new emission at 380 nm. These results are interpreted in terms of ESIPT coupled charge transfer in AS. Being consistent with these steady-state spectroscopic results, the picosecond time-resolved fluorescence study unravelled the decay dynamics of the ESIPT and ICT state ca. 300 ps and ca. 150 ps, respectively with ca. 40 ps for the relaxation time to form the ICT state.