Recent X-ray crystallographic and NMR evidence indicates that relatively weak intramolecular edge-to-face interactions between aromatic rings can affect or determine the conformation of organic molecules in the solid state and in solution. Experimental estimates indicate that these interactions are energetically attractive by ca. 1.5 kcal mol(-1) but disfavored in solution by entropic factors due to the restricted internal mobility. Hence, these interactions are more manifest at low temperature in solution or in crystal structures where conformational entropy effects are negligible.

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BackgroundEstablishing reliable methods for assessing the microbiome within the built environment is critical for understanding the impact of biological exposures on human health. High-throughput DNA sequencing of dust samples provides valuable insights into the microbiome present in human-occupied spaces. However, the effect that different sampling methods have on the microbial community recovered from dust samples is not well understood across sample types. Heating, ventilation, and air conditioning (HVAC) filters hold promise as long-term, spatially integrated, high volume samplers to characterize the airborne microbiome in homes and other climate-controlled spaces. In this study, the effect that dust recovery method (i.e., cut and elution, swabbing, or vacuuming) has on the microbial community structure, membership, and repeatability inferred by Illumina sequencing was evaluated.ResultsThe results indicate that vacuum samples captured higher quantities of total, bacterial, and fungal DNA than swab or cut samples. Repeated swab and vacuum samples collected from the same filter were less variable than cut samples with respect to both quantitative DNA recovery and bacterial community structure. Vacuum samples captured substantially greater bacterial diversity than the other methods, whereas fungal diversity was similar across all three methods. Vacuum and swab samples of HVAC filter dust were repeatable and generally superior to cut samples. Nevertheless, the contribution of environmental and human sources to the bacterial and fungal communities recovered via each sampling method was generally consistent across the methods investigated.ConclusionsDust recovery methodologies have been shown to affect the recovery, repeatability, structure, and membership of microbial communities recovered from dust samples in the built environment. The results of this study are directly applicable to indoor microbiota studies utilizing the filter forensics approach. More broadly, this study provides a better understanding of the microbial community variability attributable to sampling methodology and helps inform interpretation of data collected from other types of dust samples collected from indoor environments.Electronic supplementary materialThe online version of this article (10.1186/s40168-018-0407-6) contains supplementary material, which is available to authorized users.

A range of ortho-disubstituted C-aryl aldimines has been synthesized. N.m.r. spectroscopic analysis revealed a significant proportion of the Z-isomer a t equilibrium in solution. The E-Z-isomer distribution is critically examined in terms of electronic, steric, and solvent effects. The effect of trace amounts of carboxylic acid on imine stereomutation is discussed.THE barrier to E-Z-isomerization about a carbonnitrogen double bond is very sensitive to the nature of the s u b s t i t u e n t ~. ~-~The barrier to interconversion in simple N-alkylimines is sufficiently large (> 80 k J mol-l)for the latter process to be slow on the n.m.r. time-scale at ambient temperature. N.m.r. techniques have previously been applied in the detection and estimation of E-Z-ketimine isomer ratios at equilibrium.2,6 HOWever, other studies 7-9 using similar methods led to the conclusion that aldimines exist completely (>99%) in the E-configuration.