Hydrophilic channels

Storing the treated PDMS under water maintained the channel hydrophilicity for > 1 week [1025]. This loss of hydrophilic PDMS surface was possibly caused by the migration of uncross-linked PDMS oligomers to the surface [251]. 

The traditional flow-EEE method, also called symmetrical flow FTP, utilizes a channel with permeable depletion and accumulation walls. The cross-flow liquid enters the channel through a microfiltration frit that acts as the depletion wall and exits through an ultrafiltration membrane that acts as the accumulation wall. Membranes with nominal MW cutoffs in the range of 5000-30,000 Da are used to ensure that the protein sample remains in the FTP channel. Hydrophilic ultra-filtration membranes made from regenerated cellulose, cellulose acetate, and modified polyethersulfone have been used. 

Since the outside of the barrel faces hydrophobic lipids of the membrane and the inside forms the solvent-exposed channel, one would expect the P strands to contain alternating hydrophobic and hydrophilic side chains. This requirement is not strict, however, because internal residues can be hydrophobic if they are in contact with hydrophobic residues from loop regions. The prediction of transmembrane p strands from amino acid sequences is therefore more difficult and less reliable than the prediction of transmembrane a helices. 

The outer membrane of gram-negative bacteria is a permeability barrier that allows the passive diffusion of small hydrophilic antibiotics only through aqueous channels, the porins. Drugs larger than 800 Da are... 

The most likely way for pardaxin molecules to insert across the membrane in an antiparallel manner is for them to form antiparallel aggregates on the membrane surface that then insert across the membrane. We developed a "raft"model (data not shown) that is similar to the channel model except that adjacent dimers are related to each other by a linear translation instead of a 60 rotation about a channel axis. All of the large hydrophobic side chains of the C-helices are on one side of the "raft" and all hydrophilic side chains are on the other side. We postulate that these "rafts" displace the lipid molecules on one side of the bilayer. When two or more "rafts" meet they can insert across the membrane to form a channel in a way that never exposes the hydrophilic side chains to the lipid alkyl chains. The conformational change from the "raft" to the channel structure primarily involves a pivoting motion about the "ridge" of side chains formed by Thr-17, Ala-21, Ala-25, and Ser-29. These small side chains present few steric barriers for the postulated conformational change. 

In this pardaxin oligomer channel, the a helices cross at an angle of 25 and the model predicts a hydrophilic interior allowing for passage of ions. 

The ai polypeptide contains the receptors for the Ca " channel effectors as it can be photolabelled by DHPs and PAAs [30,39-41,56,57,63] and various other Ca channel effectors. The other subunits do not appear to be required for proper binding of Ca channel effectors [64], although there is some evidence from biochemical studies that the other subunits may modulate binding [65]. The oti and y subunits are very hydrophobic, while the a.2jd and jS subunits are very hydrophilic [57]. The a [30], 2, 6 and y [57] peptides are glycosylated, but oc is much less so than 2 [30]. The of both a peptides varies slightly on different types of SDS gels... 

P 21] Solutions of 10 M 4-(l-pyrenyl)butyric acid in ethanol and 10 M sulfuric acid in ethanol were contacted in a micro-mixing tee/micro channel flow configuration at room temperature and at 50 °C [91]. Pressure-driven feed was used. The glass surface of the micro channels was either tuned hydrophobic (by exposure to octadecyltrichlorosilane) or hydrophilic (by wetting with a sulfuric acid/hydrogen peroxide mixture). 

Ghosh [548] used cellulose nitrate microporous filters (500 pm thick) as scaffold material to deposit octanol into the pores and then under controlled pressure conditions, displace some of the oil in the pores with water, creating a membrane with parallel oil and water pathways. This was thought to serve as a possible model for some of the properties of the outermost layer of skin, the stratum comeum. The relative proportions of the two types of channel could be controlled, and the properties of 5-10% water pore content were studied. Ibuprofen (lipophilic) and antipyr-ine (hydrophilic) were model drugs used. When the filter was filled entirely with water, the measured permeability of antipyrine was 69 (in 10 6 cm/s) when 90% of the pores were filled with octanol, the permeability decreased to 33 95% octanol content further decreased permeability to 23, and fully octanol-filled filters indicated 0.9 as the permeability. 

By swelling with aqueous electrolyte, cations (and, to lesser extent, also anions) penetrate together with water into the hydrophilic regions and form spherical electrolyte clusters with micellar morphology. The inner surface of clusters and channels is composed of a double layer of the immobilized —SO3 groups and the equivalent number of counterions, M+. Anions in the interior of the clusters are shielded from the —SOJ groups by hydrated cations and water molecules. On the other hand, anions are thus... 

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