• Bulletin of the Korean Chemical Society
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• v.26 no.11
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• pp.1706-1710
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• 2005

The excited-state intramolecular proton transfer (ESIPT) fluorescence in the 2-(2'-hydroxyphenyl)benzoxazole (HBO) derivatives with different electron donor and acceptor substituents was studied by spectroscopic and theoretical methods. Changes in the electronic transition, energy levels, and orbital diagrams of HBO analogues were investigated by the semi-empirical molecular orbital calculation and were correlated with the experimental spectral position of ESIPT keto emission. It was found that the presence of substituents, regardless of their nature, resulted in the red-shifted absorption relative to HBO. However, the spectral change of the ESIPT fluorescence was differently affected by the nature of substituent: hypsochromic shift with electron donor and bathochromic shift with electron acceptor.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.958-962
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• 2012

In single-molecule fluorescence experiment, the oxygen scavenging system is indispensable for avoiding photo-bleaching of fluorescent dyes. Here we report that the gloxy-based oxygen scavenging system commonly used in single molecule fluorescence experiments can disturb the solution pH considerably. To track in situ pH change, we utilized the pH-sensitive conformational transition of i-motif and examined the transition with ensemble and single-molecule FRET measurements. Based on our results, we also suggested several practical remedies for the stability of the solution pH.

• BMB Reports
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• v.53 no.5
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• pp.241-247
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• 2020

As an intracellular degradation system, autophagy is an essential and defensive cellular program required for cell survival and cellular metabolic homeostasis in response to various stresses, such as nutrient deprivation and the accumulation of damaged organelles. In general, autophagy flux consists of four steps: (1) initiation (formation of phagophore), (2) maturation and completion of autophagosome, (3) fusion of autophagosomes with lysosomes (formation of autolysosome), and (4) degradation of intravesicular components within autolysosomes. The number of genes and reagents that modulate autophagy is increasing. Investigation of their effect on autophagy flux is critical to understanding the roles of autophagy in many physiological and pathological processes. In this review, we summarize and discuss ways to analyze autophagy flux quantitatively and qualitatively with the use of imaging tools. The suggested imaging method can help estimate whether each modulator is an inhibitor or a promoter of autophagy and elucidate the mode of action of specific genes and reagents on autophagy processes.

• Journal of Plant Biology
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• v.10 no.3_4
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• pp.1-3
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• 1967

Observations were made on Crinum and Catharanthus pollen growth in artificial media by an ultraviolet transmission fluorescence microscope showing synergistic effect on pollen growth with calcium (Ca) and aureomycin. Bright yellow fluorescence of aureomycin enabling to trace out at tissue or cellular level did reveal that the greater accumulation of fluorescence occurred in the pollen tube wall if Ca was supplemented to the media than when aureomycin alone was present. The promotive pollen growth the media of Ca alone was further enhanced by the addtion of aureomycin. It was assumed that the promoted pollen growth with aureomycin in the Ca media was probably brought about by a supporting role of aureomycin in the Ca action.

• Journal of Photoscience
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• v.6 no.2
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• pp.61-65
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• 1999

The fluorescence properties and photoisomerization behavior of 1-(9-anthryl)-2-(n-quinolinyl)ethene (n-AQE, n=2-4) have been investigated in various solvents. t-3-AQE is strongly fluorescent, but does not accomplish photoisomerization, similar to parent hydrocarbon compound, t-1-(9-anthryl)-2-phenylethene (t-9-APE) or t-1-(9-anthryl)-2-(1-naphthyl)ethene (t-1-ANE). Fluorescence and photoisomerization oft-2-AQE and t-4-AQE are strongly affected by solvent polarity. Dependence of fluorescence quantum yield on the solvent polarity is moderate for t-2-AQE and large for t-4-AQE. In nonpolar solvent (in n-hexane), they exhibit relatively strong fluorescence, but do not isomerize to cis isomer on irradiation, even if inefficient isomerization is observed for t-4-AQE. However, as solvent polarity increases, their fluorescences become weak with efficient photoisomerization to corresponding cis isomer. Intramolecular charge-transfer excited state is presumed to contribute to photoisomerization. The S$_1$ decay parameters were found to be solvent-dependent due to the charge-transfer character of lowest S$_1$ state. In polar solvents, the activation barrier to twisting is reduced enhancing the isomerization of r-2-AQE and t-4-AQE in the singlet manifold.

• Bulletin of the Korean Chemical Society
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• v.13 no.3
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• pp.325-331
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• 1992

By using the general theoretical framework proposed recently for treating the fluorescence quenching kinetics, we investigate the effect of light pulse intensity on the decay of fluorescence which follows excitation of fluorophors by the light pulse of very short but finite duration. It is seen that conventional theory breaks down when the exciting light pulse has a pulse width comparable to the fluorescent lifetime and its intensity is very high. We also find that even when the light intensity is not too high, conventional theory may fail in either of the following cases: (i) when the quencher concentration is high, (ii) when there is an attractive potential of mean force between the fluorophor and quencher, or (iii) when the energy transfer from the fluorophor to the quencher may also occur at a distance, e.g., via dipole-dipole interaction. The validity of the predictions of the present theory may thus be tested by fluorescence quenching experiments performed under such situations.

• BMB Reports
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• v.40 no.5
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• pp.644-648
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• 2007

Exposure of algae or plants to irradiance from above the light saturation point of photosynthesis is known as high light stress. This high light stress induces various responses including photoinhibition of the photosynthetic apparatus. The degree of photoinhibition could be clearly determined by measuring the parameters such as absorption and fluorescence of chromoproteins. In cyanobacteria and red algae, most of the photosystem (PS) II associated light harvesting is performed by a membrane attached complex called the phycobilisome (PBS). The effects of high intensity light (1000-4000 ${\mu}mol$ photons $m^{-2}s^{-1}$) on excitation energy transfer from PBSs to PS II in a cyanobacterium Spirulina platensis were studied by measuring room temperature PC fluorescence emission spectra. High light (3000 ${\mu}mol$ photons $m^{-2}s^{-1}$) stress had a significant effect on PC fluorescence emission spectra. On the other hand, light stress induced an increase in the ratio of PC fluorescence intensity of PBS indicating that light stress inhibits excitation energy transfer from PBS to PS II. The high light treatment to 3000 ${\mu}mol$ photons $m^{-2}s^{-1}$ caused disappearance of 31.5 kDa linker polypeptide which is known to link PC discs together. In addition we observed the similar decrease in the other polypeptide contents. Our data concludes that the Spirulina cells upon light treatment causes alterations in the phycobiliproteins (PBPs) and affects the energy transfer process within the PBSs.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1673-1678
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• 2013

Lumazine protein is a member of the riboflavin synthase superfamily and the intense fluorescence is caused by non-covalently bound to 6,7-dimethyl 8-ribityllumazine. To figure out the binding modes and the structure of the N-terminal domain of lumazine protein, the wild type of protein extending to amino acid 118 (N-LumP 118 Wt) and mutants of N-LumP 118 V41W, S48W, T50W, D64W, and A66W from Photobacterium leiognathi were purified. The biochemical properties of the wild type and mutants of N-LumP 118 proteins were analyzed by absorbance and fluorescence spectroscope. The peak of absorbance and fluorescence of lumazine ligand were shifted to longer wavelength on binding to N-LumPs. The observed absorbance value at 410 nm of lumazine bound to N-LumP 118 proteins indicate that one mole of N-LumP 118 proteins bind to one mole of ligand of lumazine. Fluorescence analysis show that the maximum peak of fluorescence of N-LumP S48W was shifted to the longest wavelength by binding with 6,7-dimethyl 8-ribityllumazine and was shown to the greatest quench effect by acrylamide among all tryptophan mutants.

• Journal of Mechanical Science and Technology
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• v.14 no.10
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• pp.1143-1150
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• 2000

The effects of ambient conditions on vaporizing sprays from a high-pressure swirl injector were investigated by an exciplex fluorescence method. Dopants used were 2% fluorobenzene and 9% DEMA (diethyl-methyl-amine) in 89% solution of hexane by volume. In order to examine the behavior of liquid and vapor phases inside of vaporizing sprays, ambient temperatures and pressures similar to engine atmospheres were set. It was found that the ambient pressure had a significant effect on the axial growth of spray, while ambient temperature had a great influence on the radial growth. The spatial distribution of vapor phase at temperatures above 473K became wider than that of liquid phase after half of injection duration. From the analysis of the area ratio for each phase, the middle part (region II) in the divided region was the region which liquid and vapor phases intersect. For liquid phase, fluorescence-intensity ratio was greatly changed at lms after the start of injection. However, the ratio of vapor phase was nearly uniform in each divided region throughout the injection.

• Bulletin of the Korean Chemical Society
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• v.28 no.9
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• pp.1573-1578
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• 2007

Fluorescence quenching of norfloxacin (NOR) by Cu2+, Ni2+, Co2+ and Mn2+ was studied in water. The change in the fluorescence intensity and lifetime was measured as a function of quencher concentration at various temperatures. According to the Stern-Volmer plots, the NOR was quenched both by collisions and complex formation with the same quencher. However, the static quenching had a more important effect on the emission. Large static and dynamic quenching constants support significant ion-dipole and orbital-orbital interactions between NOR and cations. The both quenching constants by Cu2+ were the largest among quenchers. Also, quenching mechanism of Cu2+ was somewhat different. The change in the absorption spectra due to the quencher provided information on static quenching. The fluorescence of NOR was relatively insensitive to both the dynamic and static quenching compared with other quinolone antibiotics. This property can be explained by the twisted intramolecular charge transfer.