Equilibrium binding model of bile salt-mediated chiral micellar electrokinetic capillary chromatography.

Optimum concentration of bile salts in chiral separations depends on both the aggregation properties of the surfactant and the stability of the analyte-micelle complexes. An equilibrium model is proposed in which these two effects are treated separately. First the aggregation constants should be determined under the experimental conditions of the chiral MEKC analysis. With these data, the equilibrium concentrations of bile salt aggregates can be calculated at any total surfactant concentration. Using the Offord equation to approximate the mobilities of the enantiomer-bile salt complexes, a model function has been derived to fit the experimental mobilities. The method yields the binding constants of the enantiomers to each aggregate present. Those species are assumed to be important in the chiral recognition process, which have significantly different stability constants for the enantiomers. The method is demonstrated by the chiral separation of R- and S-1,1'-binaphthyl-2,2'-diyl hydrogen phosphate with sodium taurodeoxycholate. Based on the calculated binding constants, tetrameric aggregates are assumed to be the discriminating species, while no significant difference in enantiomer binding to dimers was found.

Auditory brainstem potentials in uraemia.

Evoked response audiometry was carried out to assess the viability of the auditory pathway in haemodialysed patients. The latency of the waves III and V and I-V interpeak latencies were significantly longer in the renal patients compared to the control group. The I-V interpeak latency was longer in 8 of our 13 patients than the upper limit (4.38 ms) in our laboratory. The possible cause for the central auditory dysfunction may be multifactorial, including the effect of metastatic calcifications, repeated occurrence of disequilibrium syndrome, or some small, molecular, toxic, metabolic substance. The significance of the different factors may vary among different haemodialysis centres.

Metabolites of gentamicin-producing Micromonospora species I. Isolation and identification of metabolites.

From the cultural broth of a Micromonospora species 25 aminocyclitol antibiotics were isolated by repeated ion-exchange chromatographic processes. The main components of the metabolites were identified as gentamicin C1, C2, and C1a. The other previously reported gentamicin type antibiotics and some other degradation products including gentamicin A, B, B1, X2, sisomicin, garamine, gentamines etc., were identified by chemical, PMR, and mass spectroscopic studies. Besides these, seven new gentamicin type antibiotics were isolated and characterized.