PubMed · 13901861
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R S GRIFFITH, H R BLACK. 1961. Erythromycin.. https://doi.org/10.1016/s0031-3955(16)31198-1
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Spot size reduction and increased detection sensitivity in matrix-assisted laser desorption/ionisation (MALDI) of small molecules are accomplished by using an inexpensive and removable hydrophobic coating for MALDI targets, based on 3M Scotch Gard surface treatment. Several variations in sample preparation were explored, such as surface coating technique, identity of the matrix, solvent composition, and the type of metal support plate used. These were investigated on both uncoated and coated surfaces and their impact on spot size, crystal coverage, and sensitivity is presented here. Additionally, crystallisation behaviour obtained on coated plates is compared with that on uncoated plates using scanning electron microscope analysis. To demonstrate the potential of the new coating technique, erythromycin A and valinomycin are studied to determine the increase in detection sensitivity of coated plates in comparison to uncoated plates, and to reveal the suitability of the plates for application in combined high-performance liquid chromatography/MALDI (HPLC/MALDI), where widely varying solvent compositions and droplet volumes are observed. It is shown that enhancements in detection sensitivities correlate very well with the achieved spot size reduction. The versatility of the coated plates is also exhibited by the ease of removing the surface layer, after which the plates can be rigorously cleaned without worry about damaging the hydrophobic surface, followed by a quick reapplication of new hydrophobic coating material. This makes the non-polar coating superior to more expensive commercial hydrophobic-coated targets, which are much more delicate to clean. Furthermore, cleaning and reapplication eliminate potential carry-over effects and the easy application procedure also makes the fabrication of inexpensive, disposable MALDI targets readily possible.
Chemical shift modeling, utilizing the DFT B3LYP/D95** method, provides the spectral assignment of the 35 visible 13C resonances from the solid-phase erythromycin A dihydrate. A new resonance at 110.8ppm is observed in the high-resolution 13C CP/MAS spectrum upon the application of heat or sample desiccation. With the use of the dipolar-dephasing spectral editing technique, this resonance is identified as a hemiketal carbon and the alternative hypothesis, a conformational change to the anomeric carbon of the desosamine sugar, is ruled out. Hence, the formation of a cyclic hemiketal in erythromycin A while in the solid phase is proven by solid-state NMR. The principal components of the 13C chemical-shift tensor corresponding to this hemiketal are reported. This is the first measurement of hemiketal 13C principal values. The delta11 and delta22 components are unique compared to anomeric carbon values reported in the literature.
The effects of erythromycin (a 14-membered ring macrolide) and rokitamycin (a 16-membered ring macrolide) on the viability of the Streptococcus pyogenes M phenotype were studied by means of flow cytometry and fluorescence microscopy by using a combination of two fluorochromes (syto 9 and propidium iodide) that stains live bacteria green and dead bacteria red. In order to apply the flow cytometry, a bacterial sonication procedure was expressly set up to separate single cells from the long, intralaced S. pyogenes chains of up to 30 to 40 cells that have previously prevented the application of flow cytometry to this type of bacteria. The association of flow cytometry using an appropriate sonication procedure, together with a combination of fluorescent probes, offered the possibility of very quickly investigating the different microbiological effects of rokitamycin at 2 microg/ml, which was active on the S. pyogenes M phenotype, and of erythromycin at doses of up to 32 microg/ml, which was not.