Channel types

Packing of the cyclodexthn molecules (a, P, P) within the crystal lattice of iaclusion compounds (58,59) occurs in one of two modes, described as cage and channel stmctures (Fig. 7). In channel-type inclusions, cyclodextrin molecules are stacked on top of one another like coins in a roU producing endless channels in which guest molecules are embedded (Fig. 7a). In crystal stmctures of the cage type, the cavity of one cyclodextrin molecule is blocked off on both sides by neighboring cyclodextrin molecules packed crosswise in herringbone fashion (Fig. 7b), or in a motif reminiscent of bricks in a wall (Fig. 7c). 

Fig. 7. Schemes of crystalline cyclodextrin inclusion compounds (a) channel type (b) cage herringbone type (c) cage brick type (58).

A number of processes have been used to produce carbon black including the oil-furnace, impingement (channel), lampblack, and the thermal decomposition of natural gas and acetjiene (3). These processes produce different grades of carbon and are referred to by the process by which they are made, eg, oil-furnace black, lampblack, thermal black, acetylene black, and channel-type impingement black. A small amount of by-product carbon from the manufacture of synthesis gas from Hquid hydrocarbons has found appHcations in electrically conductive compositions. The different grades from the various processes have certain unique characteristics, but it is now possible to produce reasonable approximations of most of these grades by the od-fumace process. Since over 95% of the total output of carbon black is produced by the od-fumace process, this article emphasizes this process. 

The flow in the diffuser is usually assumed to be of a steady nature to obtain the overall geometric configuration of the diffuser. In a channel-type diffuser the viscous shearing forces create a boundary layer with reduced kinetic energy. If the kinetic energy is reduced below a certain limit, the flow in this layer becomes stagnant and then reverses. This flow reversal causes... 

The object interacts with a flowing medium. Sails interact with the wind, rafts float downstream, a spacecraft is propelled by the stream of photons (light) from the sun. This is more of a channeling type of propulsion m that the propelled object deflects the flowing stream m such a way that it is forced to move in desired direction. 

Figure 12-6E. Channel-type valves. (Used by permission Ingersoll-Rand Company.)...

In order to accomplish these diverse physiological tasks described above, nature has created at least five different types of Ca2+ channels. These are termed L-, N-, P/Q-, R-, and T-type. Although they are all structurally similar (Fig. 1) they differ with respect to their biophysical properties. Some of them need only weak depolarizations to open and inactivate fast (e.g., T-type Ca2+ channels), whereas others require strong depolarizations and inactivate more slowly (e.g. P- or L-type Ca2+ channels). Channel types also differ with respect to their sensitivity to drugs. This selectivity is exploited for pharmacotherapy. 

Gene Trivial name Kv-channel type Disease... 

The cyclodextrins also form channel-type complexes, in which the host... 

Several hundred species of Conus snails produce a wide array of small (12-30 AA) and mostly tightly disulfide bonded peptide ligands with high affinity for a diverse set of receptor and ion channel types. 

C36H60O30,C3H7O3S-,Na+,9 H20 Cyclomaltohexaose-sodium 1-pro-panesulfonate, nonahydrate (ACDPRS)129 P212121 Z= 2 Dx = 1.42 R = 0.08 for 2,219 intensities. This structure is a channel type, with the molecules of cyclomaltohexaose stacked head-to-tail. It is almost isomorphous with the sodium benzenesulfonate complex.275... 

C36H60O30,C6H5O3S -Na+-10 H20 Cyclomaltohexaose - sodium ben-zenesulfonate, decahydrate (CDXBZS)275 P212121 Z = 2 D = 1.47 R = 0.07 for 2,894 intensities. This is a channel-type structure, with a conformation very similar to that of the potassium acetate280 and Methyl Orange complexes.281 All of the pyranose residues have the 4Cl conformation, and the primary alcohol groups are in the gauche-trans orientation. 

Crystallization of 5 in the open air from an initially aprotic solvent (N,N-dimethyl-acetamide) led to a non-layered structure which is characterized by a three-dimensional lattice of loosely-packed host species interspaced by channel-type zones accommodating the solvent guest components (Fig. 9). 

Fig. 14. Stereoview of the 1 1 9 benzene clathrate, showing a channel-type arrangement of the benzene guest species 38)...

Aromatic derivatives of cyclotriphosphazenes, rigid six-membered ring systems built on a framework of alternating P and N atoms, provide one of the more beautiful early examples of hosts that form channel-type clathrates and can be useful for molecular separations 32,42>, Although these clathrate systems were discovered by accident, the conclusions that emerged from their investigation have been extremely helpful for the molecular design of other potential host molecules. 

Fig. 18. Stereoview of the channel-type clathrate structures formed by host 12 with benzene (shown schematically) or o-xylene...

The detailed structures of several clathrates have been characterized, and a certain degree of selectivity on complexation with different isomers has been detected 21). Most of these complexes are of the channel type, but some of them have structures which simultaneously qualify for channel and cage type descriptors representative examples are illustrated in Figs. 19-21. The crystal data of the complexes are summarized in Table 1. 

Lla. Landau. U., LBL-2702 Ph.D. thesis. University of California, Berkeley, January 1976. Lib. Landau, U., and Tobias, C. W., Mass Transport and Current Distribution in Channel Type Electrolyzers in the Laminar and Turbulent Flow Regimes, Ext. Abstr., No. 266, Electrochemical Society Meeting, Washington D.C., May 1976, 663. 

Ion channels are macromolecular complexes that form aqueous pores in the lipid membrane. We have learned much about ion channel function from voltage clamp and patch clamp studies on channels still imbedded in native cell membranes [1-6, 8]. A diversity of channel types was discovered in the different cells in the body, where the repertoire of functioning channels is adapted to the special roles each cell plays [5]. The principal voltage-gated ones are the Na+, K+ and Ca2+ channels, and most of these are opened by membrane depolarizations. Figure 6-5A summarizes the major functional properties of a voltage-gated... 

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