MANIFESTATION OF INTRAMOLECULAR VIBRATIONS IN THE FLUORESCENCE SPECTRA OF MOLECULES IN POLAR MEDIA

2021 ◽  
Vol 0 (1) ◽  
pp. 27-32
Author(s):  
I.P. YERMOLENKO ◽  
◽  
V.A. MIKHAILOVA ◽  
A.I. IVANOV ◽  
◽  
...  
Keyword(s):  
Fluorescence Spectra ◽  
Stokes Shift ◽  
Low Frequency ◽  
Fluorescence Signal ◽  
Intramolecular Vibration ◽  
Time Resolved ◽  
Relaxation Polarization ◽  
Polar Media ◽  
Intramolecular Vibrations ◽  
Boson Model

The effect of a low frequency intramolecular vibration on the nonstationary fluorescence spectrum of a molecule and the dynamics of the Stokes shift is analyzed in the framework of the nonstationary perturbation theory based on the operator of the interaction energy of the electric field of the exciting pump pulse with a dissolved molecule. Using a well-tested spin-boson model, which takes into account not only the reorganization of the relaxation polarization modes of the medium, but also intramolecular vibrations, an analytical expression for the time-resolved fluorescence signal is written, and the conditions under which the oscillations of the maximum of nonstationary fluorescence spectra can manifest themselves are analyzed. It is shown that the reorganization of the medium does not suppress the oscillations of the spectrum maximum.

Reactive oxygen species formation in the transition to hypoxia in skeletal muscle

2005 ◽  
Vol 289 (1) ◽  
pp. C207-C216 ◽  
Author(s):  
Li Zuo ◽  
Thomas L. Clanton
Keyword(s):  
Reactive Oxygen Species ◽  
Skeletal Muscle ◽  
Acute Hypoxia ◽  
Low Frequency ◽  
Metabolic Stress ◽  
Reactive Oxygen ◽  
Fluorescence Signal ◽  
Oxygen Species ◽  
Peroxidase Mimic ◽  
Intracellular Ros

Many tissues produce reactive oxygen species (ROS) during reoxygenation after hypoxia or ischemia; however, whether ROS are formed during hypoxia is controversial. We tested the hypothesis that ROS are generated in skeletal muscle during exposure to acute hypoxia before reoxygenation. Isolated rat diaphragm strips were loaded with dihydrofluorescein-DA (Hfluor-DA), a probe that is oxidized to fluorescein (Fluor) by intracellular ROS. Changes in fluorescence due to Fluor, NADH, and FAD were measured using a tissue fluorometer. The system had a detection limit of 1 μM H2O2 applied to the muscle superfusate. When the superfusion buffer was changed rapidly from 95% O2 to 0%, 5%, 21%, or 40% O2, transient elevations in Fluor were observed that were proportional to the rise in NADH fluorescence and inversely proportional to the level of O2 exposure. This signal could be inhibited completely with 40 μM ebselen, a glutathione peroxidase mimic. After brief hypoxia exposure (10 min) or exposure to brief periods of H2O2, the fluorescence signal returned to baseline. Furthermore, tissues loaded with the oxidized form of the probe (Fluor-DA) showed a similar pattern of response that could be inhibited with ebselen. These results suggest that Fluor exists in a partially reversible redox state within the tissue. When Hfluor-loaded tissues were contracted with low-frequency twitches, Fluor emission and NADH emission were significantly elevated in a way that resembled the hypoxia-induced signal. We conclude that in the transition to low intracellular Po2, a burst of intracellular ROS is formed that may have functional implications regarding skeletal muscle O2-sensing systems and responses to acute metabolic stress.

scholarly journals Theta activity paradoxically boosts gamma and ripple frequency sensitivity in prefrontal interneurons

2021 ◽  
Vol 118 (51) ◽  
pp. e2114549118
Author(s):  
Ricardo Martins Merino ◽  
Carolina Leon-Pinzon ◽  
Walter Stühmer ◽  
Martin Möck ◽  
Jochen F. Staiger ◽  
...  
Keyword(s):  
Low Frequency ◽  
Gamma Oscillations ◽  
Brain State ◽  
Gabaergic Interneurons ◽  
Time Resolved ◽  
Cortical Rhythms ◽  
Brain States ◽  
Fast Spiking ◽  
Fast Oscillations ◽  
Cross Frequency Coupling

Fast oscillations in cortical circuits critically depend on GABAergic interneurons. Which interneuron types and populations can drive different cortical rhythms, however, remains unresolved and may depend on brain state. Here, we measured the sensitivity of different GABAergic interneurons in prefrontal cortex under conditions mimicking distinct brain states. While fast-spiking neurons always exhibited a wide bandwidth of around 400 Hz, the response properties of spike-frequency adapting interneurons switched with the background input’s statistics. Slowly fluctuating background activity, as typical for sleep or quiet wakefulness, dramatically boosted the neurons’ sensitivity to gamma and ripple frequencies. We developed a time-resolved dynamic gain analysis and revealed rapid sensitivity modulations that enable neurons to periodically boost gamma oscillations and ripples during specific phases of ongoing low-frequency oscillations. This mechanism predicts these prefrontal interneurons to be exquisitely sensitive to high-frequency ripples, especially during brain states characterized by slow rhythms, and to contribute substantially to theta-gamma cross-frequency coupling.

scholarly journals Dynamics of Anomalous Temperature-Induced Emission Shift in MOCVD-grown (Al, In)GaN Thin Films

2000 ◽  
Vol 5 (S1) ◽  
pp. 796-802 ◽  
Author(s):  
Yong-Hoon Cho ◽  
G. H. Gainer ◽  
J. B. Lam ◽  
J. J. Song ◽  
W Yang ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Stokes Shift ◽  
Energy Shift ◽  
Peak Position ◽  
Time Resolved ◽  
Temperature Range ◽  
Al Content ◽  
Peak Energy ◽  
Emission Behavior ◽  
Pl Intensity

We present a comprehensive study of the optical characteristics of (Al, In)GaN epilayers measured by photoluminescence (PL), integrated PL intensity, and time-resolved PL spectroscopy. For not only InGaN, but also AlGaN epilayers with large Al content, we observed an anomalous PL temperature dependence: (i) an “S-shaped” PL peak energy shift (decrease-increase-decrease) and (ii) an “inverted S-shaped” full width at half maximum (FWHM) change (increase-decrease-increase) with increasing temperature. Based on time-resolved PL, the S shape (inverted S shape) of the PL peak position (FWHM) as a function of temperature, and the much smaller PL intensity decrease in the temperature range showing the anomalous emission behavior, we conclude that strong localization of carriers occurs in InGaN and even in AlGaN with rather high Al content. We observed that the following increase with increasing Al content in AlGaN epilayers: (i) a Stokes shift between the PL peak energy and the absorption edge, (ii) a redshift of the emission with decay time, (iii) the deviations of the PL peak energy, FWHM, and PL intensity from their typical temperature dependence, and (iv) the corresponding temperature range of the anomalous emission behavior. This indicates that the band-gap fluctuation responsible for these characteristics is due to energy tail states caused by non-random inhomogeneous alloy potential variations enhanced with increasing Al content.

scholarly journals Spectral Properties of Hybrid of Rhodamine (6G) Dyes Doped Epoxy Resin Dissolved in Chloroform

2019 ◽  
Vol 16 (3(Suppl.)) ◽  
pp. 0764 ◽  
Author(s):  
Al-Hamdani Et al.
Keyword(s):  
Epoxy Resin ◽  
Quantum Efficiency ◽  
Fluorescence Spectra ◽  
Room Temperature ◽  
Rhodamine 6G ◽  
Energy Gap ◽  
Radiative Lifetime ◽  
Stokes Shift ◽  
Fluorescence Emission ◽  
Absorption And Fluorescence Spectra

            The research is dealing with the absorption and fluorescence spectra for the hybrid of  an Epoxy Resin doped with organic dye Rhodamine (R6G) of different concentrations (5*10-6, 5*10-5, 1*10-5, 1*10-4, 5*10-4) Mol/ℓ at room temperature. The Quantum efficiency Qfm, the rate of fluorescence emission Kfm (s-1), the non-radiative lifetime τfm (s), fluorescence lifetime τf and the Stokes shift were calculated. Also the energy gap (Eg) for each dye concentration was evaluated. The results showed that the maximum quantum efficiency 62 % and maximum stokes shift 96 nm was obtained in dye concentration 5*10-6 and 1*10-4. The energy gap ranges between 1.066 eV to 1.128 eV depending proportionally on the dye concentrations.

An Introduction to Time-Resolved Pump/Probe Spectroscopy

1985 ◽  
Vol 39 (3) ◽  
pp. 444-451 ◽  
Author(s):  
F. E. Lytle ◽  
R. M. Parrish ◽  
W. T. Barnes
Keyword(s):  
Absorption Spectra ◽  
Ground State ◽  
Fluorescence Spectra ◽  
Excited State Absorption ◽  
Time Dependent ◽  
Triplet Excited State ◽  
Ground State Absorption ◽  
Time Resolved ◽  
Pump Probe ◽  
Probe Spectroscopy

The construction and operating principles of a two-color pump/probe spectrometer are described. This instrument is capable of obtaining ground-state absorption spectra, both singlet-singlet and triplet-triplet excited-state absorption spectra, photoproduct spectra, and stimulated fluorescence spectra. In addition, time-dependent measurements can be made with an impulse response of 250 ps and a free temporal range of 13 ns.

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