7,7′-(3,3′-Dibenzyl-3H,3′H-4,4′-bi-1,2,3-triazole-5,5′-di­yl)bis­(4-methyl-2H-chromen-2-one)

The title compound, a bis-5,5′-triazole, C38H28N6O4, was observed as a side-product from the Sharpless–Meldal click reaction of the corresponding coumarin alkyne and benzyl­azide. Although the compound was present as a minor component, it crystallized in preference to the major product. The two triazole rings are almost orthogonal to each other [dihedral angle = 83.8 (1)°]. However the 4 and 4′ coumarin systems are close to coplanar with their respective triazole rings [23.6 (1) and 15.1 (1)°]. Each of the benzene rings packs approximately face-to-face with the opposing coumarin ring systems, with inter­planar angles of 7.7 (1) and 25.3 (1)° and distances of 3.567 (2) and 3.929 (2) Å between the respective centroids of the opposing rings

Detection of Cellular Sialic Acid Content Using Nitrobenzoxadiazole Carbonyl-Reactive Chromophores

The selective ligation of hydrazine and amino-oxy compounds with carbonyls has gained popularity as a detection strategy with the recognition of aniline catalysis as a way to accelerate the labeling reaction in water. Aldehydes are a convenient functional group choice since there are few native aldehydes found at the cell surface. Aldehydes can be selectively introduced into sialic acid containing glycoproteins by treatment with dilute sodium periodate. Thus, the combination of periodate oxidation with aniline-catalyzed ligation (PAL) has become a viable method for detection of glycoconjugates on live cells. Herein we examine two fluorescent nitrobenzoxadiazole dyes for labeling of glycoproteins and cell surface glycoconjugates. We introduce a novel 4-aminooxy-7-nitro-benz-[2,1,3-<i>d</i>]-oxadiazole (NBDAO) (<b>5</b>) fluorophore, and offer a comparison to commercial dyes including the known 4-hydrazino-7-nitro-benz-[2,1,3-<i>d</i>]-oxadiazole (NBDH) (<b>2</b>) and Bodipy FL hydrazide. We confirm specificity for sialic acid moieties and that both dyes are suitable for in vitro and in vivo labeling studies using PAL and fluorescence spectroscopy. The dyes examined here are attractive labeling agents for microscopy, as they can be excited by a 488 nm laser line and can be made in a few synthetic steps. These carbonyl-reactive chromophores provide a one step alternative to avidin–biotin labeling strategies and simplify the detection of sialic acid in cells and glycoproteins

The NANOGrav 15 yr Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational-wave Background

The NANOGrav 15 yr data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such low-frequency gravitational waves, here we analyze the signal as coming from a population of supermassive black hole (SMBH) binaries distributed throughout the Universe. We show that astrophysically motivated models of SMBH binary populations are able to reproduce both the amplitude and shape of the observed low-frequency gravitational-wave spectrum. While multiple model variations are able to reproduce the GWB spectrum at our current measurement precision, our results highlight the importance of accurately modeling binary evolution for producing realistic GWB spectra. Additionally, while reasonable parameters are able to reproduce the 15 yr observations, the implied GWB amplitude necessitates either a large number of parameters to be at the edges of expected values or a small number of parameters to be notably different from standard expectations. While we are not yet able to definitively establish the origin of the inferred GWB signal, the consistency of the signal with astrophysical expectations offers a tantalizing prospect for confirming that SMBH binaries are able to form, reach subparsec separations, and eventually coalesce. As the significance grows over time, higher-order features of the GWB spectrum will definitively determine the nature of the GWB and allow for novel constraints on SMBH populations