Pore coupling

Vapor-phase alkylation of benzene by ethene and propene over HY, LaY, and REHY has been studied in a tubular flow reactor. Transient data were obtained. The observed rate of reaction passes through a maximum with time, which results from build-up of product concentration in the zeolite pores coupled with catalyst deactivation. The rate decay is related to aromatic olefin ratio temperature, and olefin type. The observed rate fits a model involving desorption of product from the zeolite crystallites into the gas phase as a rate-limiting step. The activation energy for the desorption term is 16.5 heal/mole, approximately equivalent to the heat of adsorption of ethylbenzene. For low molecular weight alkylates intracrystalline diffusion limitations do not exist. 

On-line protein digestion has been achieved by trypsin adsorbed in a porous PVDF (poly [vinylidene fluoride]) membrane (0.45-pm pore) coupled in a PDMS chip. In this way, on-chip protein digestion and subsequent MS analysis have been carried out for horse heart cytochrome c [817]. 

Overall membrane compression Lipid-domain interface fluctuations Free volume fluctuations Local depressions and distortions Transient hydrophobic pores Transient hydrophilic pores Foot-in-the-door hydrophilic pores Composite hydrophilic pores Membrane enzyme changes Membrane macromolecule protrusion changes Rupture and REB not actually described (5) Suggested alternative to transient pores (6) Transport of nonpolar species (7) Possible precursors to hydrophilic pores (8, 9) Possible precursor to hydrophilic pores (10) Key to quantitative descriptions (10-16) Candidate metastable pores" Candidate metastable pores Coupling to membrane macromolecules (17) Candidate signaling change mechanism... 

The model described earlier assumed that wd was very large and h c was very small. Relaxation time measurements for water in rocks found that Ti and T2 were almost independent of temperature in the range 25-175 °C. This suggests that diffusion is not playing a significant role, and so supports the fast-exchange assumption. It thus appears that molecules sample only a limited volume of pore space before they are relaxed in the case of water in rocks. However, the diffusion and pore-coupling rates may be important in other systems. 

In the formula, K, D, e, P and a respectively are permeability coefficient of coal seam, permeability coefficient of raw coal, damage parameter of coal, increase multiples of permeability coefficient after damage, gas pressure coefficient of pore, coupling coefficient between the stress and the pore gas pressure. 

Several important technological applications, such as battery devices and electrocatalysis, need a very large effective surface of contact between the electrode and the electrolyte. This expanded surface can be developed on porous electrode surfaces. The complexity of the random structure of the porous electrode and various experimental situations related to mass-transport impedance in the pores, coupled with interfacial kinetics inside the pores, led investigators initially to investigate simple single-pore models. Of the possible shapes modeled, the cylindrical pore with a length I and a radius r has been... 

An uneventful coupling of two hemispherical cavitand molecules — a tetrameth-anethiol and a tetrakis(chloromethyl)precursor (see p. 169) — yielded D.J. Cram s (1988) carcerand . ft entraps small molecules such as THF or DMF, cesium or chloride ions, or argon atoms as permanently imprisoned guests . Only water molecules are small enough to pass through the two small pores of this molecular (prison) cell. 

Siace the pores ia an aerogel are comparable to, or smaller than, the mean free path of molecules at ambient conditions (about 70 nm), gaseous conduction of heat within them is iaefficient. Coupled with the fact that sohd conduction is suppressed due to the low density, a siUca aerogel has a typical thermal conductivity of 0.015 W/(m-K) without evacuation. This value is at least an order of magnitude lower than that of ordinary glass and considerably lower than that of CFC (chloro uorocarbon)-blown polyurethane foams (54). 

Polypeptide Synthesis and Analysis. Sihca or controUed-pore glass supports treated with (chloromethyl)phenylethyltrimethoxysilane [68128-25-6] or its derivatives are replacing chloromethylated styrene—divinylbenzene (Merrifield resin) as supports in polypeptide synthesis. The sdylated support reacts with the triethyl ammonium salt of a protected amino acid. Once the initial amino acid residue has been coupled to the support, a variety of peptide synthesis methods can be used (34). At the completion of synthesis, the anchored peptide is separated from the support with hydrogen bromide in acetic acid (see Protein engineering Proteins). 

Other immobilization methods are based on chemical and physical binding to soHd supports, eg, polysaccharides, polymers, glass, and other chemically and physically stable materials, which are usually modified with functional groups such as amine, carboxy, epoxy, phenyl, or alkane to enable covalent coupling to amino acid side chains on the enzyme surface. These supports may be macroporous, with pore diameters in the range 30—300 nm, to facihtate accommodation of enzyme within a support particle. Ionic and nonionic adsorption to macroporous supports is a gentle, simple, and often efficient method. Use of powdered enzyme, or enzyme precipitated on inert supports, may be adequate for use in nonaqueous media. Entrapment in polysaccharide/polymer gels is used for both cells and isolated enzymes. 

Zorbax PSM Bimodal and Trimodal columns are packed with mixed pore-size packing to achieve linear size separations over a broad molecular weight range (Table 3.3). Zorbax PSM Bimodal columns are packed with PSM 60 and PSM 1000 particles, and Trimodal columns contain PSM 60, PSM 300, and PSM 3000 particles (Fig. 3.4). Carefully selecting and mixing different pore-size particles in columns provide much better linearity than coupling columns that are each packed with single pore-size particles. 

As with other size-exclusion techniques, the pore size of the selected Zorbax GF column should provide resolution over the molecular size range of the proteins that are to be separated. The Zorbax GF-250 column separates proteins in the range of 4000 to 400,000 Da. The Zorbax GF-450 provides separation over the range of 10,000 to 1,000,000 Da. When these two columns are coupled, they can be used to separate proteins with molecular weights of 4000 to 1,000,000. 

Big-conductance Ca2+ sensitive K+ (BKca) channels are activated by calcium surge and membrane depolarization. BKCa channels are specifically blocked by iberiotoxin and less selectively by charybdotoxin. BKCa channels are composed of pore-forming a and auxiliary (3 subunits. Both BKCa,a andBKca, 3 subunits as well as their efficient coupling in the heteromultimeiic formation of BKca channel complexes are important for the function of BKCa channels. 

In view of the accessibility of zeolite A (only linear molecules adsorb) the coupling will take place at the outer surface of the zeolite crystals. Indeed, Ag-Y and especially a Ag-loaded amorphous silica-alumina, containing a spectrum of wider pores, mrned out to be much better promoter-agents (ref. 28). The silica-alumina is etched with aqueous NaOH and subsequently exchanged with Ag(I). 

The recent identification of STIMl, a sensor of ER Ca + concentrations that couples depletion of ER Ca stores with activation of CRAG channels, and CRACM1 (also known as Orail), the pore-forming subunit of the CRAG channel, has increased our... 

Johansson and coworkers [182-184] have analyzed polyacrylamide gel structure via several different approaches. They developed an analytical model of the gel structure using a single cylindrical unit cell coupled with a distribution of unit cells. They considered the distribution of unit cells to be of several types, including (1) Ogston distribution, (2) Gaussian distribution of chains, and (3) a fractal network of pores [182-184]. They [183] used the equilibrium partition coefficient... 

The effects of various pore-size distributions, including Gaussian, rectangular distributions, and continuous power-law, coupled with an assumption of cylindrical pores and mass transfer resistance on chromatographic behavior, have been developed by Goto and McCoy [139]. This study utilized the method of moments to determine the effects of the various distributions on mean retention and band spreading in size exclusion chromatography. 

One approach to extend such theories to more complex media is network theory. This approach utihzes solutions for transport in single pores, usually in one dimension, and couples these solutions through a network of nodes to mimic the general structure of the porous media [341], The complete set of equations for aU pores and nodes is then solved to determine overall transport behavior. Such models are computationally intense and are somewhat heuristic in nature. 

Figure 12-14. The creatine phosphate shuttle of heart and skeletal muscle. The shuttle allows rapid transport of high-energy phosphate from the mitochondrial matrix into the cytosol. CKg, creatine kinase concerned with large requirements for ATP, eg, muscular contraction CIC, creatine kinase for maintaining equilibrium between creatine and creatine phosphate and ATP/ADP CKg, creatine kinase coupling glycolysis to creatine phosphate synthesis CK, , mitochondrial creatine kinase mediating creatine phosphate production from ATP formed in oxidative phosphorylation P, pore protein in outer mitochondrial membrane.

Figure 8. A schematic for the toxin binding sites on the voltage-gated Na channel. Toxin-free open and closed conformations are drawn at the left and center. Separate sites are depicted within the membrane for activators such as BTX, VTD (A), and brevetoxin (B) these are coupled to each other and to the a-peptide toxin site (a), which is kinetically linked to the -peptide toxin site (P see ref. 20). Near the outer opening of the pore is a site (G) for STX and TTX which is affected by binding at site A and which can modify inactivation gating.

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