By application of 20 fs laser pulses, vibrational wave packets of low-energy modes (mainly 357 and 421
cm-1) were generated in the perylene chromophore that gave rise to periodic beats that lasted longer than 1
ps in transient absorption signals. Electron transfer from the excited singlet state of the perylene chromophore,
attached as molecule DTB−Pe via the −CH2−phosphonic acid group to anatase TiO2, was measured in
ultrahigh vacuum with a time constant of 75 fs. The vibrational wave packet that was generated in the donor
state continued its motion for several hundred femtoseconds in the product state of the reaction, i.e., in the
ionized chromophore. This is direct proof for electron transfer occurring from a nonrelaxed vibrational
population that was created by the short laser pulse in the donor molecule. The rise of the product state
showed a staircase-like time dependence. The steps are attributed to electron transfer that occurs preferentially
each time the vibrational wave packet (frequency 480 cm-1) reaches a crossing point for the potential curves
of reactant and product state. Such wave-packet modulation of heterogeneous electron transfer can arise if
the density of electronic acceptor states in the electrode is changing strongly over an energy range on the
order of the reorganization energy below the excited molecular donor orbital.
Background:
Abnormalities in intracellular calcium (Ca) cycling during Ca overload can cause triggered activity because spontaneous calcium release (SCR) activates sufficient Ca-sensitive inward currents to induce delayed afterdepolarizations (DADs). However, little is known about the mechanisms relating SCR and triggered activity on the tissue scale.
Methods and Results:
Laser scanning confocal microscopy was used to measure the spatiotemporal properties of SCR within large myocyte populations in intact rat heart. Computer simulations were used to predict how these properties of SCR determine DAD magnitude. We measured the average and standard deviation of the latency distribution of SCR within a large population of myocytes in intact tissue. We found that as external [Ca] is increased, and with faster pacing rates, the average and SD of the latency distribution decreases substantially. This result demonstrates that the timing of SCR occurs with less variability as the sarcoplasmic reticulum (SR) Ca load is increased, causing more sites to release Ca within each cell. We then applied a mathematical model of subcellular Ca cycling to show that a decrease in SCR variability leads to a higher DAD amplitude and is dictated by the rate of SR Ca refilling following an action potential.
Conclusions:
Our results demonstrate that the variability of the timing of SCR in a population of cells in tissue decreases with SR load and is dictated by the time course of the SR Ca content.
We generalize the concepts of alignment and 3D alignment by moderately intense laser pulses to control both the overall rotations and the torsional motions of polyatomic molecules. Torsional control is applied to manipulate charge transfer events, hence introducing a potential route to light controlled molecular switches. Potential applications in areas such as molecular assembly, molecular spectroscopies, energy transfer, and molecule-based junctions are envisioned.
We extend the concept of alignment by short intense pulses to dissipative environments within a density matrix formalism and illustrate the application of this method as a probe of the dissipative properties of dense media. In particular, we propose a means of disentangling rotational population relaxation from decoherence effects via strong laser alignment. We illustrate also the possibility of suppressing rotational relaxation to prolong the alignment lifetime through choice of the field parameters. Implications to several disciplines and a number of potential applications are proposed.
Decay of excited state absorption, owing to charge injection into the conduction band continuum of semiconductor states, is obtained via a qualitative theoretical model. The density matrix formalism is utilized to obtain an expression for the sequential pump-probe signal in terms of the nonlinear third-order polarization of the molecular system. Electron transfer slower than the pump and probe pulses is assumed and reorganization of the molecule upon charge injection is ignored while obtaining the final expressions. The lifetime of the excited state decouples from nuclear motion as a consequence. Decay of the excited state into a continuum of electronic states is examined for various energy positions of the injecting state and for different bandwidths of the continuum. The decay can be fitted by exponential functions for the majority of the cases considering different dimensionalities of the semiconductor continuum. Model calculations are performed for the snapshot limit of the pump-probe signal. Under the assumed conditions one obtains oscillations due to vibronic coherences that are superimposed on temperature-independent irreversible charge transfer decays, as is reported in recent experiments.
Although the development of abnormal myocardial mechanics represents a key step during the transition from hypertension to overt heart failure (HF), the underlying ultrastructural and cellular basis of abnormal myocardial mechanics remains unclear. We therefore investigated how changes in transverse (T)-tubule organization and the resulting altered intracellular Ca(2+) cycling in large cell populations underlie the development of abnormal myocardial mechanics in a model of chronic hypertension. Hearts from spontaneously hypertensive rats (SHRs; n = 72) were studied at different ages and stages of hypertensive heart disease and early HF and were compared with age-matched control (Wistar-Kyoto) rats (n = 34). Echocardiography, including tissue Doppler and speckle-tracking analysis, was performed just before euthanization, after which T-tubule organization and Ca(2+) transients were studied using confocal microscopy. In SHRs, abnormalities in myocardial mechanics occurred early in response to hypertension, before the development of overt systolic dysfunction and HF. Reduced longitudinal, circumferential, and radial strain as well as reduced tissue Doppler early diastolic tissue velocities occurred in concert with T-tubule disorganization and impaired Ca(2+) cycling, all of which preceded the development of cardiac fibrosis. The time to peak of intracellular Ca(2+) transients was slowed due to T-tubule disruption, providing a link between declining cell ultrastructure and abnormal myocardial mechanics. In conclusion, subclinical abnormalities in myocardial mechanics occur early in response to hypertension and coincide with the development of T-tubule disorganization and impaired intracellular Ca(2+) cycling. These changes occur before the development of significant cardiac fibrosis and precede the development of overt cardiac dysfunction and HF.
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