Millisecond range

During the course of these studies the necessity arose to study ever-faster reactions in order to ascertain their elementary nature. It became clear that the mixing of reactants was a major limitation in the study of fast elementary reactions. Fast mixing had reached its high point with the development of the accelerated and stopped-flow teclmiques [4, 5], reaching effective time resolutions in the millisecond range. Faster reactions were then frequently called inuneasurably fast reactions [ ]. 

The previous application — in accord with most MD studies — illustrates the urgent need to further push the limits of MD simulations set by todays computer technology in order to bridge time scale gaps between theory and either experiments or biochemical processes. The latter often involve conformational motions of proteins, which typically occur at the microsecond to millisecond range. Prominent examples for functionally relevant conformatiotial motions... 

The current amplitude cannot be increased at free will, because the clamp voltage will usually not exceed + 100 mV. A simple calculation reveals that, given the limitations above, channels need to have a conductance of 10 pS, and time constants in the millisecond range to be detected. Any channel smaller or faster than this will escape detection in this analysis. 

In the absence of reversible reaction, for example when water acts as the lone nucleophile, QMP11 is consumed with a half-life of approximately 0.5 h as measured by its diminished ability to cross-link DNA (Scheme 9.18).69 Elimination of acetate to form the first of two possible QM intermediates (QM12) is likely rate-determining in this process since subsequent addition by water is estimated to occur with a half-life in the millisecond range.56 The resulting hydroxy substituent at the benzylic position does not eliminate and regenerate QM12 under ambient conditions. Thus, water... 

At present time, these studies cannot be carried out, due to the short lifetimes involved, but with more intense sources of light it may be possible to reduce the measurement time enabling the measurement of 9 in the millisecond range with FTIR ellipsometry. 

Most optical centers show luminescence decay times in the nanoseconds-milliseconds range. However, many other physical processes involved in optical spectroscopy are produced in the picoseconds-femtoseconds range, and mnch more complicated instrumentation becomes necessary. For instance, interband Inminescence in solids, which is of particular interest in semiconductors, can involve decay times in the range of picoseconds. Pulses generated from solid state lasers have already reached this femtosecond domain. 

Recently, studies were reported measuring the kinetics of stimulation of both cAMP and 3 using a mixing device and rapid quenching, in the millisecond range, in rat olfactory cilia (67). The response to a mixture of < orants peaks within 25 to 50 milliseconds, the time frame expected for receptors, with both cAMP and IP3. Similar measurements of the change in concentration of cAMP or IP3 were also done in the taste cell. Here mice, which were bred as bitter tasters and nontasters , were used as subjects. The bitter stimuli, sucrose octaacetate, strychnine and denatonium benzoate, were shown to increase IP3 levels in a membrane preparation from "taster" mice in the presence of GTP-protein and Ca but not in membranes from "nontaster" mice (68). 

The availability of automatic ellipsometers56 greatly helps all this. It is possible to program the ellipsometer to print a readout of, for example, refractive index and thickness as a function of potential. The technique could be applied more widely, a developmental possibility being that it could enable the operator to follow changes in spectra (and thus interpret what molecular changes cause them) in the millisecond range. One of the frontiers of development of techniques in electrochemistry could be the use of ellipsometric spectroscopy. 

Reticulum ATPase [105,106], Owing to the long-lived nature of the triplet state, Eosin derivatives are suitable to study protein dynamics in the microsecond-millisecond range. Rotational correlation times are obtained by monitoring the time-dependent anisotropy of the probe s phosphorescence [107-112] and/or the recovery of the ground state absorption [113— 118] or fluorescence [119-122], The decay of the anisotropy allows determination of the mobility of the protein chain that cover the binding site and the rotational diffusion of the protein, the latter being a function of the size and shape of the protein, the viscosity of the medium, and the temperature. 

The rate of sampling with piezoelectric sensors is limited by their physical characteristics and present technology to the millisecond range for applications in the liquid phase. The technique is versatile in that it can be used in a variety of locations. The solid state electronics necessary to operate the piezoelectric sensor are easily miniaturized, and data can be recorded continuously or periodically. A small computer with a reasonable memory could easily record data over long times. There may be some problems in deep-sea locations, simply because of the complications in packaging the sensor for high-pressure environments, although this problem may be surmountable. 

Presynaptic G-protein coupled receptors for a large number of neurotransmitters, both autoreceptors and receptors for extrinsic signals, suppress Ca2+-channel gating in response to an action potential. This mechanism of action appears to be the dominant mechanism involved in short-term plasticity mediated by presynaptic receptors. A typical example is depolarization-induced suppression of inhibition (DSI), which is the short-term suppression of presynaptic GABA-release induced by the depolarization of the postsynaptic cell (Diana and Marty, 2004). DSI is caused when the postsynaptic depolarization causes the release of endocannabinoids from the postsynaptic cell, and the endocannabinoids then bind to presynaptic CB1 receptors whose activation suppresses presynaptic Ca2+-channels. Like many other forms of presynaptic suppression mediated by activation of presynaptic receptors, this effect is short-lasting (in the millisecond range). The precise mechanisms by which Ca2+-channels are suppressed appear to vary between receptors, but the outcome is always a very effective short-term decrease in synaptic signaling. 

Besides the emission spectrum, the lifetime of the excited state is an important feature. Many organic fluorescent molecules display very short lifetimes, in the pico- to nanosecond range, while the species of interest in this chapter (except Am(III) and Eu(II)) have rather long lifetimes, in the micro- to millisecond range. This lifetime value results from the combination of the two types of processes evoked above (radiative and non-radiative), together... 

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