Alkali environments in tellurite glasses

Neutron diffraction measurements are reported for five binary alkali tellurite glasses, xM2O · (100 − x)TeO2 (containing 10 and 20 mol% K2O, 10 and 19 mol% Na2O, and 20 mol% 7Li2O), together with 23Na MAS NMR measurements for the sodium containing glasses. Differences between neutron correlation functions are used to extract information about the local environments of lithium and sodium. The Na–O bond length is 2.37(1) Å and the average Na–O coordination number, nNaO, decreases from 5.2(2) for x = 10 mol% Na2O to 4.6(1) for x = 19 mol% Na2O. The average Li–O coordination number, nLiO, is 3.9(1) for the glass with x = 20 mol% Li2O and the Li–O bond length is 2.078(2) Å. As x increases from 10 to 19 mol% Na2O, the 23Na MAS NMR peak moves downfield, confirming an earlier report of a correlation of peak position with sodium coordination number. The close agreement of the maximum in the Te–O bond distribution for sodium and potassium tellurite glasses of the same composition, coupled with the extraction of reasonable alkali coordination numbers using isostoichiometric differences, gives strong evidence that the tellurium environment in alkali tellurites is independent of the size of the modifier cation used

Comprehensive full-length sequence analyses of human parechoviruses: diversity and recombination

Human parechoviruses (HPeVs) are highly prevalent pathogens among very young children. Although originally classified into two serologically distinct types, HPeV1 and -2, recent analyses of variants collected worldwide have revealed the existence of 12 further types classified genetically by sequence comparisons of complete genome sequences or the capsid (VP1) gene. To investigate the nature of HPeV evolution, its population dynamics and recombination breakpoints, this study generated 18 full-length genomic sequences of the most commonly circulating genotypes, HPeV1 and -3, collected over a time span of 14 years from The Netherlands. By inclusion of previously published full-length sequences, 35 sequences were analysed in total. Analysis of contemporary strains of HPeV1 and those most similar to the prototype strain (Harris) showed that HPeV1 variants fall into two genetically distinct clusters that are much more divergent from each other than those observed within other HPeV types. Future classification criteria for HPeVs may require modification to accommodate the occurrence of variants with intermediate degrees of diversity within types. Recombination was frequently observed among HPeV1, -4, -5 and -6, but was much more restricted among HPeV3 strains. Favoured sites for recombination were found to flank the capsid region, and further sites were found within the non-structural region, P2. In contrast to other HPeV types, the majority of the HPeV3 sequences remained monophyletic across the genome, a possible reflection of its lower diversity and potentially more recent emergence than other HPeV types, or biological and/or epidemiological constraints that limit opportunities for co-infections with potential recombination partners