Molecule pumps

Suppose there are twice as many molecules pumped into the same volume as shown in Figure 17.3. Then the air density—the number of molecules per given volume—is double. If the molecules move at the same average kinetic energy, or, equivalently, if they have the same temperature, then, to a close approximation, the number of collisions will be doubled. This means the pressure is doubled. 

ECOC (Electro-Chemical Ozone Cell) is the Electrochemical ozonometer based on the electrochemical concentration cell (ECC) ozonesonde. The air sample is pumped through the ECC where ozone molecules are completely absorbed by the potassium iodide solution which causes an electric current to flow through the external circuit connected to the cell electrodes. Each ozone molecule produces a two electron flow in the outer circuit. Thus measurement of the electric current allows to determine a number of ozone molecules pumped into the ECC in one second. This number can be converted to ozone pressure using a pump productivity and air temperature at the pump output. 

The lipid bilayer of biological membranes, as discussed in Chapter 12. is intrinsically impermeable to ions and polar molecules. Permeability is conferred by two classes of membrane xoXems, pumps and channels. Pumps use a source of free energy such as ATP or light to drive the thermodynamically uphill transport of ions or molecules. Pump action is an example of active transport. Channels, in contrast, enable ions to flow rapidly through membranes in a downhill direction. Channel action illustrates passive transport, or facilitated diffusion. 

Nevertheless, the selectivity of action of many of these toxins means they have been harnessed in medical therapeutics (more so in experimental pharmacology and physiology). Toxins that have been, or still are, used in medicine include atropine and hyoscine, botulinum toxin, colchicine, digitalis alkaloids, eserine, morphine, ouabain, picrotoxin, strychnine, veratridine, vinca alkaloids and many more. These work by an action at a defined molecular site, whether ion channel, neurotransmitter receptor, enzyme, carrier molecule (pump) or intracellular organelle. Several of these particular examples have their most obvious effects on neurotransmission, and are dealt with under neurotoxins. 

About 50 ABC Small-Molecule Pumps Are Known in Mammals... 

G protein-coupled receptors (e.g., (5-adrenergic receptor) Glucose transporters (e.g., GLUT1) Voltage-gated Ca2+ channels ABC small molecule pumps CFTR (Cl ) channel Sec61 Connexin... 

The ABC superfamily comprises ATP-hydrolyzing small-molecule pumps. Many ABC proteins mediate the export of various lipids from cells (see Table 18-2). 

Figure 13 Comparison of the experimental and a quantum mechanically computed (by exact wave packet propagation using an ab initio computed potential energy) spectrum of a nonrotating Na, molecule pumped to its B electronic state. (Courtesy of Experiment by S. Rutz, E. Schreiber, and L. Woste Computations by B. Reischl, all of the Free University of Berlin) (a) The short time dynamics Shown is the population of the excited state vs. time as determined by a pump-probe experiment and by the computation (points connected by a straight-line segments). The periodicity (about 320 fs) is due to the symmetric stretch motion, (b) A frequency spectrum. The long time dynamics (as reflected in the well-resolved spectrum) show the contribution of a different set of vibrational modes. The dominant peaks can be identified as the radial pseudorotation motion of Na,(B) while the splittings are due to the angular pseudorotational motion. (Adapted from B. Reischl, Chem. Phys. Lett., 239 173 (1995) and V. Bonacic-Koutecky, J. Gaus, J. Manz, B. Reischl, and R. de Vivie-Riedle, to be published.)...

Using the same procedure as employed for CHjF/Oj above, and assuming n =n (number of molecules pumped by the laser to 2) with all other = 0, the values of /2 are 0.20 for path 1 and — 0.06 for path 2. Experimental measurements are presently underway to determine which of these paths is the correct one. In this case the experimental studies can be performed on a single species because population loss from V2 requires 500 collisions, while overall V-T/R relaxation of via... 

A [/im] molecule pump pump power [W] (sub)mm power [mW] reference(s) footnotes... 

A [fjtm] Molecule Pump Reference Freq. [MHz] Footnotes... 

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