Guanine-rich oligonucleotides can form a unique G-quadruplex (GQ) structure with stacking units of four guanine bases organized in a plane through Hoogsteen bonding. GQ structures have been detected in vivo and shown to exert their roles in maintaining genome integrity and regulating gene expression. Understanding GQ conformation is important for understanding its inherent biological role and for devising strategies to control and manipulate functions based on targeting GQ. Although a number of biophysical methods have been used to investigate structure and dynamics of GQs, our understanding is far from complete. As such, this work explores the use of the site-directed spin labeling technique, complemented by molecular dynamics simulations, for investigating GQ conformations. A nucleotide-independent nitroxide label (R5), which has been previously applied for probing conformations of noncoding RNA and DNA duplexes, is attached to multiple sites in a 22-nucleotide DNA strand derived from the human telomeric sequence (hTel-22) that is known to form GQ. The R5 labels are shown to minimally impact GQ folding, and inter-R5 distances measured using double electron–electron resonance spectroscopy are shown to adequately distinguish the different topological conformations of hTel-22 and report variations in their occupancies in response to changes of the environment variables such as salt, crowding agent, and small molecule ligand. The work demonstrates that the R5 label is able to probe GQ conformation and establishes the base for using R5 to study more complex sequences, such as those that may potentially form multimeric GQs in long telomeric repeats.

Propanedioyl dihydrazide (PDH), traditionally believed to be non-fluorescent, was first discovered to emit substantial fluorescence in both the solid state and solvents.

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Supported H3PW12O40 (HPW) and supported Cesium-Substituted dodecatungsto-phosphate are eco-friendly solid acid catalysts. A series of different loading H3PW12O40/SiO2 and HPW/diatomite were prepared by a typical incipient wetness impregnation of methanol, meanwhile SiO2 and diatomite supported Cs-salt catalysts were prepared via two-step impregnating method. The catalysts were investigated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The results indicate that the Keggin structure of HPW is intact in the SiO2-supported HPW and SiO2-supported CsHPW. HPW and CsHPW are highly dispersed in the SiO2 at the low loading, while the loading is more than 40% the catalyst grains increase and gather on the surface of the carrier. What's more, diatomite is not a suitable support. HPW and CsHPW have better distribution in the SiO2 than in the diatomite. The activity of catalyst was tested in probe experiment of the alkylation of thiopene (TH) with 1-hexene.