Beyond the Conventional Limitation of Photocycloaddition Reaction in the Roomy Nanospace of a Metal-Organic Framework.

Topochemical reactions provide selective products based on the molecular position; however, they generally require molecules to be placed in strictly limited orientations and distances, making them less versatile. In this study, we found that by confining trans-4-styrylpyridine (4-spy) as a reactive substrate in a flexible metal-organic framework (MOF) nanospace, [2+2] cycloadducts can be selectively obtained, even when the distance between two C═C bonds of 4-spy in the crystal is 5.9 Å, which is much larger than the conventionally observed upper limit (4.2 Å). Such an unusual cyclization reaction is suggested to occur due to the transient proximity of the 4-spy due to the "swing" motion in the nanospace. The MOF nanospace, with its high degree of molecular structural freedom, can be applied to different platforms that do not require the fine constraints of reactive distances for solid-phase reactions.

Colorimetric paper-based sarcosine assay with improved sensitivity.

This manuscript reports on a simple paper-based bienzymatic colorimetric assay for sarcosine as an important urinary biomarker of prostate cancer. All required assay reagents are pre-deposited on hydrophilic filter paper spots surrounded by a hydrophobic barrier. Sarcosine in the sample solution is selectively oxidized in the presence of sarcosine oxidase (SOx), resulting in the formation of hydrogen peroxide, which is subsequently detected through the horseradish peroxidase (HRP)-catalyzed conversion of the colorless indicator 3,3',5,5'-tetramethylbenzidine (TMB) into its blue-colored oxidation product. By the modification of the paper with positively charged poly(allylamine hydrochloride) (PAH), a linear response to sarcosine between 0 and 10 µM and a significant lowering of the limit of detection (LOD) (0.6 µM) compared to the unmodified paper substrate (12.6 µM) has been achieved. The improvement of the LOD was attributed to the fact that the presence of the polymer limits the enzyme-driven colorimetric reaction to the surface of the paper substrate, resulting in stronger color development. In experiments in artificial urine matrix, the bicarbonate anion was identified as an inhibitor of the colorimetric reaction. This inhibition was successfully eliminated through on-device sample pH adjustments with pH-buffer components pre-deposited onto assay devices. The LOD for sarcosine achieved in artificial urine matrix (2.5 µM) is below the 5 µM threshold value for this urinary biomarker required for diagnostic purposes. Finally, good selectivity over all 20 natural amino acids and satisfactory long-term storage stability of reagent-modified paper substrates at - 20 °C for a period of 50 days were confirmed.

Cold stimulation evokes exocytotic vesicle release from PC12 cells.

The mechanism of peripheral blood circulation failure by low temperatures, known as Raynaud's phenomenon, is not well understood at present. We examined the possibility that the efferent fibers of peripheral sympathetic neurons may release transmitters directly by cold sensation. PC12 cells, a culture model of sympathetic neurons, were placed at 25°C for 30 min, fixed with the tannic acid-glutaraldehyde-osmium method and observed by electron microscopy. The number of omega-shaped exocytotic vesicle figures increased significantly compared with that in the control (37°C), although it was lower than that of the positive control (high potassium stimulation at 25°C and 37°C). As it is known that PC12 cells and sympathetic neurons do not express the typical cold sensing channels (TRPA1 and TRPM8), our results suggest that the peripheral sympathetic neurons may have an unknown cold monitoring system which reacts to low temperatures, release transmitters by exocytosis and directly regulate local blood circulation.