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 (4spy) 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.

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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.Thermoregulation is an important process in mammals. Changes in environmental temperature are monitored mainly by the sensory neurons of the dorsal root ganglia (8). The hypothalamus integrates the neural information and the peripheral autonomic nervous system regulates the body temperature by tuning the cutaneous blood circulation (7). The local mechanism of peripheral blood circulation failure by low temperatures, known as Raynaud's phenomenon, has been not well elucidated at present (7). The molecular system of sensing temperature in mammals is based on the transient receptor potential (TRP) ion channel family (5, 12). Among them, only TRPA1 and TRPM8 channels are thought to be sensors of cold, both of which are known to exist in the sensory neurons of dorsal root ganglia. A study of calcium ion imaging revealed that relatively large numbers of peripheral sympathetic neurons are responsible for cold, although TRPA1 and TRPM8 channels are absent in those neurons (9).Up to date, there has been no direct evidence that peripheral sympathetic neurons sense the cold stimuli and release their transmitters without input from the afferent sensory system. The aim of this study is to detect the exocytotic transmitter release in PC12 cells, a culture model of sympathetic neurons, after cold stimulation under electron microscopy. It is difficult to detect exocytotic figures in neuro-endocrine cells as their processes are extremely fast. Rapid freeze fixation is a useful and excellent method, but it needs a special apparatus and is unsuitable for a quantitative analysis. Tannic acid-glutaraldehyde-osmium fixation is known to preserve exocytotic figures relatively well, especially those of cored vesicles including bioamines and neuropeptides (1-4). PC12 cells were sub-cultured with 10% FBSDulbecco's modified Eagle's medium at 37°C in a 5% CO 2 incubator. Cells were inoculated in culture dishes at 10 6 cells/cm 2 and then placed in a 25°C incubator for 30 min. For the control (no treatment), the culture dishes were...