Gated response

Upon irradiation at 435 nm in toluene, an extremely high stereoselectivity was observed, with a ratio of M- s-18a to P-trans-18b of 99 1. Compared to chiroptical switch 17, with a donor and acceptor moiety in the lower half, compound 18 suffers from poor reversibility, which can be attributed to the favorable donor-acceptor interaction in M-cis-18a. In view of the potential of gated response switching systems (see Section 5.4.1), it is noteworthy that the preference for the cis-form helicity can only be changed to a preference for the trans-form if the favorable donor-acceptor interaction is eliminated. This feature implies that it is possible to lock photochemi-cally written information and that it then, irrespective of the wavelengths used, cannot be unlocked except by affecting the donor-acceptor interaction. 

A highly desirable property in information storage systems based on molecular switches is gated response.1491 Gated photochemical reactivity implies that no change occurs upon irradiation unless another external stimulus, either physical or chemical, is applied to the system. Scheme 18 shows a typical write-lock-unlock-erase cycle involving photoisomerization and protonation. 

A major advantage is the potential to lock (and protect) written information in the photobistable material. A number of chemical gated systems involving mutual regulation of the photochromic event and, for instance, fluorescence, ion binding, or electrochemical properties have been reported.1501 Scheme 19 illustrates a chiral gated response system based on donor-acceptor substituted alkene 17.[511 The photochemical isomerization process of both the M-ds and the P-trans form was effectively blocked by the addition of trifluoroacetic acid. Protonation of the dimethyl-amine donor unit of M-rfs-17a and P-trons-17b resulted in an ineffective acceptor-acceptor (nitro and ammonium) substituted thioxanthene lower half. Since the stereoselective photoisomerization of 17 relies on the presence of both a donor and acceptor unit, photochemical switching could be restored by deprotonation by the addition of triethylamine. 

Patrick G, Straumanis JJ, Struve FA, Fitz-Gerald MJ, Leavitt J, Manno JE (1999) Reduced P50 auditory gating response in psychiatrically normal chronic marihuana users a pilot study. Biol Psychiatry 45 1307-1312... 

The first publications describing [33] the controlled unthreading and rethreading of pseudorotaxanes from our laboratories appeared in the early 1990s. The pseudorotaxane machines produced to date fall into two distinct classes - one that relates to switches (basic on-off actions in response to an applied stimulus), and the other to gates (responses to two stimuli that mimic the operation of a logic function). 

Enhancement was measured as the increase in peak area observed on addition of the agonist carbamylchol Ine (carb), which Is commonly used to generate an ion-gated response from AChR. 

To relate 7c,sat to a gate response time tg, consider one MOSFET driving an identical MOSFET as load capacitance. Then the current from (Eq. 7.12) charges this capacitance to a voltage Vd in a gate response time Tg given by (Shoji, 1988)... 

Thus, on an intrinsic level, the gate response time is a multiple of the transit time of an electron from source to drain, which is L/v t in velocity saturation. At shorter 7, a linear reduction in delay with I is predicted, whereas for longer devices the improvement can be quadratic in L, depending on how Vs is scaled as L is reduced. 

The PFPD has much lower LOD and better sensitivity than FPD technology. The MDL of sulfur and phosphorous is in the 10" to lO- " g/sec area (see Aviv Amirav et al. on www.tau.ac.il/chemistry/amirav/pfpd.shtml). In addition, the PFPD can simultaneously detect several element combinations using only one photomultiplier. Element identification can be achieved through the dual-gate-response ratio method. This detection technique is capable of identifying sulfur, phosphorous, nitrogen, arsenic, and many other elements with no interference from hydrocarbons. Thus, the PFPD would be very suitable for TIC detection. 

Voltage-gated Ca2+ channels are Ca2+-selective pores in the plasma membrane of electrically excitable cells, such as neurons, muscle cells, (neuro) endocrine cells, and sensory cells. They open in response to membrane depolarization (e.g., an action potential) and permit the influx of Ca2+ along its electrochemical gradient into the cytoplasm. 

Gating, a property of many ion channels, is the active transition between open and closed states in response to specific signals, such as membrane voltage or the presence of neurotransmitters. 

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