Solid-state photochromism of benzopyrans and naphthopyrans (chromenes) was investigated in the temperature range between 300 and 80 K. Variable-temperature diffuse reflectance spectroscopy of microcrystalline powders showed that the extent of photocoloration was greatly enhanced at low temperatures. All the chromenes examined exhibited solid-state photochromism at low temperatures, even when they showed little or no photocoloration at room temperature. The solid-state photochromic properties of the chromenes were quite similar to those reported for analogous photochromic compounds of spiropyrans and spirooxazines, which indicates that these classes of compounds are generally photochromic even in the solid state. Photobleaching reactions of the colored merocyanine forms proceeded at low temperatures through the formation of a colorless intermediate, instead of directly resuming the original closed form. In addition to two stable planar merocyanine forms, which are usually observed in the photochromic reactions in solution, photoreactions at low temperatures allowed us to observe unstable colored species, which were tentatively assigned as nonplanar cisoid forms, and were stabilized in the solid state at low temperatures.
The magnesium ion-requiring step in fertilization of sea urchins was investigated. When eggs were inseminated in Mg-free sea water, several spermatozoa were found to bind to each egg surface with their reacted acrosomes without elevation of fertilization membrane. The number of binding jelly-treated spermatozoa to an egg did not differ regardless of the presence or virtual absence of magnesium ions. Although fertilization did not occur in Ca, Mg-deficient sea water (CM-deficient SW) even when jelly-treated spermatozoa were employed, some eggs could be fertilized by the addition of magnesium to the CM-deficient SW 60 sec after insemination, when jellytreated spermatozoa had completely lost their fertilizing capacity in the CM-deficient SW. The acrosomal process of jelly-treated spermatozoa appeared to penetrate the vitelline layer in the CM-deficient SW. DTT-or pancreatin-treated eggs could not be fertilized in the virtual absence of magnesium. Re-fertilization using the fertilized eggs deprived of fertilization membrane did not occur under conditions of magnesium deficiency. These results suggest that external magnesium ions are indispensable at least for the fertilization process following penetration of the vitelline layer by the spermatozoa, such as fusion of the plasma membrane between an egg and a reacted spermatozoon, or the subsequent step(s) such as sperm penetration into egg interior and egg activation which precedes the cortical reaction.Divalent cations in sea water, i.e., calcium and magnesium, have been shown to be requisite for fertilization of sea urchins. With respect to external calcium ions, DAN (2) showed that they are required to induce the acrosome reaction of sea urchin spermatozoa. Furthermore, recently a small amount of external calcium ions has been shown to be required in the fertilization process following the binding of the spermatozoa with reacted acrosomes to eggs in the sea urchin, Hemicentrotus pulcherrimus (9).With respect to magnesium ions in sea water, CLARK (1) reported that polyspermy could be induced at high percentage rate in sea urchin eggs when high concentration of magnesium was added to sea water. Recently, it was found that fertilization in sea urchins does not take place in the virtual absence of external magnesium ions, even when spermatozoa pre-treated with dissolved egg-jelly are employed, showing that external magnesium ions are requisite at least for the fertilization process following the induction of the acrosome reaction in spermatozoa (7, 8). When spermatozoa were treated with egg-water containing dissolved jelly to undergo the acrosome reaction, their fertilizing capacity was lost within 5 min in natural sea water (1 1).
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