Search for: All records

Abstract Serological assays used to estimate the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) often rely on manufacturers’ cutoffs established on the basis of severe cases. We conducted a household-based serosurvey of 4,677 individuals in Chennai, India, from January to May 2021. Samples were tested for SARS-CoV-2 immunoglobulin G (IgG) antibodies to the spike (S) and nucleocapsid (N) proteins. We calculated seroprevalence, defining seropositivity using manufacturer cutoffs and using a mixture model based on measured IgG level. Using manufacturer cutoffs, there was a 5-fold difference in seroprevalence estimated by each assay. This difference was largely reconciled using the mixture model, with estimated anti-S and anti-N IgG seroprevalence of 64.9% (95% credible interval (CrI): 63.8, 66.0) and 51.5% (95% CrI: 50.2, 52.9), respectively. Age and socioeconomic factors showed inconsistent relationships with anti-S and anti-N IgG seropositivity using manufacturer cutoffs. In the mixture model, age was not associated with seropositivity, and improved household ventilation was associated with lower seropositivity odds. With global vaccine scale-up, the utility of the more stable anti-S IgG assay may be limited due to the inclusion of the S protein in several vaccines. Estimates of SARS-CoV-2 seroprevalence using alternative targets must consider heterogeneity in seroresponse to ensure that seroprevalence is not underestimated and correlates are not misinterpreted. 

Ionic liquids (ILs) exhibit unique properties that have led to their development and widespread use for a variety of applications. Development efforts have generally focused on achieving desired macroscopic properties via tuning of the IL through variation of the cations and anions. Both the macroscopic and microscopic properties of an IL influence its tunability and thus feasibility of use for selected applications. Works geared toward a microscopic understanding of the nature and strength of the intrinsic cation-anion interactions of ILs have been limited to date. Specifically, the intrinsic strength of the cation-anion interactions in ILs is largely unknown. In previous work, we employed threshold collision-induced dissociation (TCID) approaches supported and enhanced by electronic structure calculations to determine the bond dissociation energies (BDEs) and characterize the nature of the cation-anion interactions in a series of four 2:1 clusters of 1-alkyl-3-methylimidazolium cations with the hexafluorophosphate anion, [2C n mim:PF 6 ] + . To examine the effects of the 1-alkyl chain on the structure and energetics of binding, the cation was varied over the series: 1-ethyl-3-methylimidazolium, [C 2 mim] + , 1-butyl-3-methylimidazolium, [C 4 mim] + , 1-hexyl-3-methylimidazolium, [C 6 mim] + , and 1-octyl-3-methylimidazolium, [C 8 mim] + . The variation in the strength of binding among these [2C n mim:PF 6 ] + clusters was found to be similar in magnitude to the average experimental uncertainty in the measurements. To definitively establish an absolute order of binding among these [2C n mim:PF 6 ] + clusters, we extend this work again using TCID and electronic structure theory approaches to include competitive binding studies of three mixed 2:1 clusters of 1-alkyl-3-methylimidazolium cations and the hexafluorophosphate anion, [C n-2 mim:PF 6 :C n mim] + for n = 4, 6, and 8. The absolute BDEs of these mixed [C n-2 mim:PF 6 :C n mim] + clusters as well as the absolute difference in the strength of the intrinsic binding interactions as a function of the cation are determined with significantly improved precision. By combining the thermochemical results of the previous independent and present competitive measurements, the BDEs of the [2C n mim:PF 6 ] + clusters are both more accurately and more precisely determined. Comparisons are made to results for the analogous [2C n mim:BF 4 ] + and [C n-2 mim:PF 6 :C n mim] + clusters previously examined to elucidate the effects of the [PF 6 ] - and [BF 4 ] - anions on the binding.