Cation transporters

Bradshaw and his coworkers have listed several motivations for their explorations in this area. One objective of [the] research program is to prepare and study a series of multi-dentate compounds which resemble naturally occurring macrocyclic compounds . Further, Bradshaw and his coworkers have said that it is our hope that we can prepare macrocycles to mimic the selectivities of the naturally occurring cyclic antibiotics and thereby make available models for the investigation of biological cation transportation and selectivity processes . These workers have presented a number of comparisons with valinomy-cin . The other expressly stated goal of their research is to prepare molecules which will allow us to systematically examine the parameters which affect complex stability and to understand that stability in terms of AH and TAS values for complex formation . 

A second source of inspiration for studying the open-chained equivalents of crown ethers was the observation that a number of naturally occurring antibiotics enhance cation transport and bear a structural similarity to open-chained crown ethers. A number of groups have examined neutral synthetic ionophores and a variety of novel cation carriers is now available. This is discussed in Sect. 7.4, below. 

An important feature of such films is their low ionic conductivity that restricts cation transport through the film substance. Electronic semiconduction, however, permits other electrode processes (oxidation of H2O to O2) to take place at the surface without further significant film growth. At elevated anodic potentials adsorption and entry of anions, particularly chloride ions, may lead to instability and breakdown of these protective films (Sections 1.5 and 1.6). 

Mass transport measurements have shown that cation transport predominates in FeO (Fe ) and Fej04 (Fe, Fe ), whereas anion transport predominates in FejOj (0 ). This leads to the well-accepted growth scheme for multi-layered scale growth on iron shown in Fig. 7.3, with the governing equations for individual layer growth being ... 

Complex ions used for electroplating are anions. The cathode tends to repel them, and their transport is entirely by diffusion. Conversely, the field near the cathode assists cation transport. Complex cyanides deserve some elaboration in view of their commercial importance. It is improbable that those used are covalent co-ordination compounds, and the covalent bond breaks too slowly to accommodate the speed of electrode reactions. The electronic structure of the cyanide ion is ... 

Table 4. Amounts of cation transported by the synthetic ionophores through chloroform liquid membrane after 2 days...

Fig. 4. Relationship between the amounts of cation transported after 1 d and the concentration of NaOH added into the source phase.3 (Cited from Ref. 23))...

On the other hand, Bartsch et al. have studied cation transports using crown ether carboxylic acids, which are ascertained to be effective and selective extractants for alkali metal and alkaline earth metal cations 33-42>. In a proton-driven passive transport system (HC1) using a chloroform liquid membrane, ionophore 31 selectively transports Li+, whereas 32-36 and 37 are effective for selective transport of Na+ and K+, respectively, corresponding to the compatible sizes of the ring cavity and the cation. By increasing the lipophilicity from 33 to 36, the transport rate is gradually... 

The Energetics Problem of Cation Transport Across Lipid Bilayer Membranes A qualitative perspective of the barrier presented by a lipid bilayer membrane can be obtained from the Bom expression2) for solvation energy, SE,... 

A second approach to promoting high cationic transport is to choose a molecular solvent which has the ability to interact with anions than cations. A number of electron deficient borates such as... 

Methly-4-phenyl-l, 2,3,6-tetrahydropytidine Organic Cation Transporters... 

Substrate specificity is determined by high affinity for the cognate neurotransmitter substrate. However, low affinity uptake does also have a part in the clearance of transmitters from the interstitial space (e.g., in uptake mediated by the extraneuronal monoamine transporter, EMT) and in the intestinal absoiption of glycine and glutamate. It is obvious that there is an evolutionary relation of neurotransmitter transporters and amino acid and cation transporters in epithelia. 

Nerve growth factor snake venoms zinc, 6, 613 Neurospora crassa calcium transport, 6, 571 cation transport, 6, 559 Neurosporin, 6, 676 Neurotransmitters secretion calcium, 6, 595 Neutral complexes electrical properties, 6, 143 Neutron absorbers... 

The ionic conductivity of the MEEP/metal salt systems was improved by adding a-Al203 particles into the complexes. Chen-Yang [603] obtained a conductivity 0=9.7x10" S cm" for the composite polymer complex MEEP/Li-CIO4/2.5 wt% AI2O3. The cation transport number was in this case 0.77. 

The organic cation transporters (OCTs) facilitate the uptake of many cationic drugs across different barrier membranes from kidney, liver, and intestine... 

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