[en] Cellulose nanocrystals (CNCs) have high aspect ratios, polydisperse size distributions, and a strong propensity for aggregation, all of which make them a challenging material for detailed size and morphology characterization. A CNC reference material produced by sulfuric acid hydrolysis of softwood pulp was characterized using a combination of dynamic light scattering (DLS), atomic force microscopy (AFM), transmission electron microscopy, and X-ray diffraction. As a starting point, a dispersion protocol using ultrasonication was developed to provide CNC suspensions with reproducible size distributions as assessed by DLS. Tests of various methods for AFM sample preparation demonstrated that spin coating on a positively charged substrate maximizes the number of individual particles for size analysis, while minimizing the presence of agglomerates. The effects of sample-to-sample variability, analyst bias, and sonication on size distributions were assessed by AFM. The latter experiment indicated that dispersion of agglomerates by sonication did not significantly change the size distribution of individual CNCs in suspension. Comparison with TEM data demonstrated that the two microscopy methods provide similar results for CNC length (mean ~ 80 nm); however, the particle width as measured by TEM is approximately twice that of the CNC height (mean 3.5 nm) measured by AFM. The individual crystallite size measured by X-ray diffraction is intermediate between the two values, although closer to the AFM height, possibly indicating that laterally agglomerated CNCs contribute to the TEM width. Overall, this study provides detailed information that can be used to assess the factors that must be considered in measuring CNC size distributions, information that will be useful for benchmarking the performance of different industrially sourced materials.

[en] The glycosphingolipid globoside (globotetraosylceramide, Gb4Cer) has been proposed to be the cellular receptor of human parvovirus B19. Quantitative measurements of the binding of parvovirus B19 to Gb4Cer were performed to explore the molecular basis of the virus tropism. Solid-phase assays with fluorescence-labeled liposomes or ¹²⁵iodine-labeled empty capsids were used to characterize the specificity of binding. In addition, surface plasmon resonance on lipid layers, as well as isothermal titration microcalorimetry, was utilized for real-time analysis of the virus-receptor interaction. These studies did not confirm binding of Gb4Cer to recombinant B19 VP2 capsids, suggesting that Gb4Cer does not function on its own as the cellular receptor of human parvovirus B19, but might be involved in a more complex recognition event. The biochemical results were further confirmed by cryo-electron microscopy image reconstructions at 10 A resolution, in which the structures of empty capsids were compared with empty capsids incubated with Gb4Cer