Using a system that accelerates the serendipitous discovery of new reactions by evaluating hundreds of DNA-encoded substrate combinations in a single experiment, we explored a broad range of reaction conditions for new bond-forming reactions. We discovered reactivity that led to a biomolecule-compatible, Ru(II)-catalyzed, visible light-induced azide reduction reaction. In contrast with current azide reduction methods, this reaction is highly chemoselective and is compatible with alcohols, phenols, acids, alkenes, alkynes, aldehydes, alkyl halides, alkyl mesylates, and disulfides. The remarkable functional group compatibility and mild conditions of this reaction enabled azide reduction to be performed on nucleic acid and oligosaccharide substrates without the detectable occurrence of side reactions. The reaction was also performed in the presence of a protein enzyme without loss of enzymatic activity, in contrast with two commonly used azide reduction methods. The visible light dependence of this reaction provides a means of photouncaging functional groups such as amines and carboxylates on biological macromolecules without using UV irradiation.

In the absence of continuous K-fiber attachment between each kinetochore and the spindle pole, one or more additional mechanisms dependent on dynein-mediated kinetochore transport exist to ensure proper chromosome segregation during mitosis.

The reduced development of COVID-19 for children compared to adults provides some tantalizing clues on the pathogenesis and transmissibility of this pandemic virus. First, ACE2, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor, is reduced in the respiratory tract in children. Second, coronavirus associated with common colds in children may offer some protection, due to cross-reactive humoral immunity and T cell immunity between common coronaviruses and SARS-CoV-2. Third, T helper 2 immune responses are protective in children. Fourth, surprisingly, eosinophilia, associated with T helper 2, may be protective. Fifth, children generally produce lower levels of inflammatory cytokines. Finally, the influence of the downturn in the global economy, the impact of living in quarters among families who are the most at risk, and factors including the openings of some schools, are considered. Those most disadvantaged socioeconomically may suffer disproportionately with COVID-19.

In this paper, we report an experimental study of electrokinetic transport and separation of double-stranded deoxyribonucleic acid (dsDNA) oligonucleotides in custom-fabricated fused-silica nanochannels filled with a gel-free sodium borate aqueous buffer. Mixtures of fluorescently labeled dsDNA molecules in the range of 10-100 base pair (bp), fluorescein, and fluorescein-12-UTP (UTP) were separated in less than 120 s in channels of depth ranging from 40 to 1560 nm. We varied the channel depth and background buffer concentration to achieve a 0.006-0.2 range of Debye length-to-channel-half-depth ratio (lambdaD/h), and a 0.004-1.7 range of the ratio of length of dsDNA molecule to channel half-depth (l/h). We find observed oligonucleotide migration times depend on both l/h and lambdaD/h. Electrophoretic mobility estimates agree well with published (micrometer-scale channel) values for background electrolyte (BGE) concentrations greater than approximately 10 mM. At BGE concentrations of 1 and 5 mM, mobility estimates in our nanochannels are higher than published values. Of the cases studied, the highest separation sensitivities were achieved in 100 nm channels with 1-10 mM ion density buffers. Potential applications of this technology include rapid small-scale sequencing and other fluorescence-based oligonucleotide separation and detection assays.