Anion transfer to the membrane phase affects the extraction efficiency of salt transport by cation
carriers 1 and 3. Addition of anion receptors 5 or 6 to cation carriers 1, 3, or 4 in the membrane phase enhances
the transport of salts under conditions in which the cation carriers alone do not transport salt. The extraction
of salt by the carrier mixtures is larger than by cation or anion carrier only, but the rate of diffusion is lower.
Ditopic receptors 8 and 9 transport CsCl or KCl much faster than monotopic anion receptor 7 or cation receptors
1 and 2. The faster transport is due to a higher extraction constant K
ex despite a lower diffusion constant of the
ditopic salt complex.
Mixtures of derivatives of coumarin‐2 and coumarin‐343 can self‐assemble on silicon wafers to form monolayers in which light harvesting and energy transfer take place (see picture). Photophysical properties, such as donor quenching and fluorescence amplification, were tuned by varying the molar ratio of the donor and acceptor chromophores on the surface or by increasing the number of coumarin‐2 chromophores on the donor adsorbate through the use of a dendritic linker.
A series of crown boronic acids, 1−4, were
synthesized and studied as carriers for catecholamine
transport
through bulk liquid membranes (BLMs) and supported liquid membranes
(SLMs). Carrier 1 greatly facilitated the
transport of primary catecholamines through BLMs; whereas, the more
lipophilic analogues 3 and 4 were less
effective.
A combination of kinetic, mass spectral, and NMR evidence suggests
that the transported species in BLMs is the
cyclic, zwitterionic, 1:1 complex 7. The SLM transport
studies used a liquid membrane of 2-nitrophenyl octyl
ether
supported by a thin, flat sheet of porous polypropylene. In the
absence of carrier there was neglible dopamine
transport (<5 × 10-9
mol/m2·s) at pH 7.2. When the membrane contained
carrier 3 (33 mM or about 2% wt),
facilitated catecholamine transport was observed in the order of
dopamine (5 × 10-7 mol/m2·s)
> epinephrine (1.5
× 10-7 mol/m2·s) >
norepinephrine (0.8 × 10-7
mol/m2·s). SLMs containing carrier 3 were
stable, implying that
carrier 3 is a very good candidate for transport mechanism
studies. Crown boronic acid 4 was an even better
transport
carrier of primary catecholamines with a transport order of
norepinephrine (4.7 × 10-6
mol/m2·s) > dopamine (3.5
× 10-6 mol/m2·s) ≫
epinephrine (3 × 10-8
mol/m2·s). It is 10 times more effective than an
equimolar mixture of
boronic acid 5 and crown 6, which is one of best
examples of ditopic cooperativity yet observed in SLM
transport.
SLMs containing 4, however, did not exibit long-term
stability. Overall, it is possible that a device based on
SLMs
containing crown boronic acid carriers can be developed to selectively
extract catecholamines from clinical samples.
Reaction of aminomethylcavitands with iso(thio)cyanates gives (thio)urea-functionalized resorcinarene cavitands, which represent a novel class of neutral anion receptors. The complexation of halide anions has been studied both with infrared and 1 H NMR spectroscopy. The receptors have a small preference for chloride over the other halides; p-fluorophenylthiourea cavitand 8a gives the highest association constant (K ass ) 4.7 × 10 5 M -1 with chloride in CDCl 3 ). A cooperative effect of the ligating (thio)urea moieties is indicated by the lower affinity of the corresponding tris(thio)urea-functionalized cavitands. For the first time facilitated membrane transport of halide anions through supported liquid membranes is achieved.
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