Host concentrations

We have shown that host 54 can be employed to extract TCO4 from aqueous solutions at relatively low concentrations. When a NOjMe solution of 54 [CF3S03J4 (3.25 mM) is vortexed with a equal volume saline solution of Na[Tc04] (3.25 mM) spiked with radiotracer " TCO4, 84(1)% of the radioactivity is transferred into the organic phase. Up to 88(2)% of the TCO4 can be extracted if the host concentration is increased to 10 mM. Remarkably, the extraction can also be performed in the... 

While the above technique can be used in many cases, it does require uncomplicated voltammetry and that significant Ey2 shifts are observed at guest concentrations >10 times the host concentration. If these conditions are not met, then an alternative strategy is needed. The most powerful is to use CV simulation software to fit the experimental CVs to the square scheme or a more complicated mechanism if necessary. This method allows determination of the thermodynamic parameters and possibly the kinetic parameters as well. 

Figure 6.36 Chemical shift of various protons for host 6.74 as a function of host concentration. (Copyright Wiley VCH Verlag GmbH Co. KGaA. Reproduced by permission).

One may question, moreover, whether true catalysis is involved, or the rate augmentation rather emerges from a shift in the equilibrium constant (see Section B), visualizing the large host concentrations necessary to observe the rate effect. In the light of the inconclusive measures taken to exclude influences of micellation (from the product distribution data one would assume aggregation of the host to take place in contrast to N(CH3>4 salt) and the little detailed definition of the rate processes compared, the utility of these results to the improvement of molecular catalysts appears limited. 

If the host concentration c is varied at a fixed guest concentration c and the estimated... 

If the shift of one and the same proton at several different host concentrations c is... 

Current density as a function of drive voltage for red phosphorescent OLEDs with neat SBFK and mixed SBFK+NPB hosts. Concentration of Ir(l-piq)3 is 6%. See Figure 14.37 captions for device structures. 

Both new compounds A and B gave satisfactory microanalyses and NMR spectra. Selected amino acids (R)- and (S)-alanine (Ala), (R)- and (S)-phenylglycine (PhGly) and (R)- and (S)- B-phenylalanine ( p-PhAla) as their sodium and potassium salts were dried in vacuo over phosphorus pentoxide prior to use and served as guest species. The host/guest ratio was 2 1 in deuteriochloroform solutions. Dissolution of solid salt was accomplished in an ultrasonic bath within 20 to 100 min. The host concentration was ca. 0.1 M. All the variable-temperature spectra were recorded with JEOL-JNM-4H-100 spectrometer at 100 MHz with TMS as internal standard and lock. The anomeric proton served as an NMR probe. The free energy of activation at the coalescence temperature was calculated from the expression 7 ... 

Enhancement factors of the transport of the guests (solid) through CI Ch /n-hexane (3 1) in a 1 N hydrochloric acid solution at host concentrations of mol/l (in the i... 

As expected from the conformationally mobile sidechains and the predominantly lipophilic and/or hydrophobic binding mechanism there is relatively little selectivity, apart from an increase of AG with increasing lipophilicity of the substrate. Nevertheless, this is probably the first host system for which the inclusion of open chain substrates like diethylether has been proven by NMR shielding variations [22]. NMR measurements at host concentrations between 5 x 10 M and... 

Acetonitrile (Ajax Chemicals HPLC Grade) solutions of constant calixarene anion (host) concentration and varying tetramethylammonium ion, choline or acetyl choline (guest) concentrations were prepared by appropriate dilutions of 10 mol L stock solutions of the tetrapropylammonium salts of the calixarenes, tetramethylammonium trifiate, choline triflate and acetylcholine perchlorate. Spectra were recorded in the range 200-350 nm on a Hewlett-Packard 8452 Diode Array spectrophotometer. Nonlinear least-squares fitting of absorbance vs. composition data to models of the reaction system was conducted using a program written locally by Dr. E. S. Kucharski. 

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