Nucleation of ice and its management in ecosystems
Nucleation of ice and its management in ecosystems
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DOI：
10.1098/rsta.2002.1141
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发表时间：
2003-03-15
期刊：
影响因子：
--
通讯作者：
Franks, F
中科院分区：
文献类型：
--
作者：
Franks, F
除了气相和液态外，水还可以以多种不同的固体状态存在。其中一些是研究得很好的晶态冰和笼状水合物，但至少有两种可区分的无定形固体形式也被证明存在。这种可能的凝聚态的多样性意味着多种跃迁，每一种跃迁都可能与成核步骤相关联。对于非晶态是否可以被视为亚稳相，多晶化现象是否可以用相变来处理，仍然存在分歧。在地球水圈中，在给定的温度、压力和过饱和条件下，水蒸气可以形成几种结晶和无定形的水相，经典的成核理论被认为可以很好地解释在高层大气中观察到的凝结形式的水的增长。许多陆地生物能够在暴露在零度以下的温度下激活机制来控制冰的成核和增长，从而使极端冰冻干燥的致命影响降至最低。这些机制涉及的物质包括碳水化合物、氨基酸和所谓的冷休克蛋白，但干扰冰核形成的实际机制虽然有很好的文献记载，但尚不完全清楚。与产生抗冻性和耐冻性的生化过程相关的基因控制尤其如此。冷应激的分子生物学目前是一个深入研究的课题。
In addition to the gas and liquid phases, water can exist in many different solid states. Some of these are the well-studied crystalline ice polymorphs and the clathrate hydrates, but at least two distinguishable amorphous solid forms have also been shown to exist. This diversity of possible condensed states implies a multiplicity of transitions, each of them presumably associated with a nucleation step. Disagreement still exists as to whether the amorphous states can be regarded as metastable phases, and whether the phenomenon of polyamorphism can be treated in terms of phase transitions. In the Earth's hydrosphere, several of the crystalline and amorphous water phases can be formed from vapour, under given conditions of temperature, pressure and supersaturation, and classical nucleation theory is believed to account reasonably well for the observed growth of condensed forms of water in the upper atmosphere.Many terrestrial organisms are able to activate mechanisms to control the nucleation and growth of ice when exposed to sub-zero temperatures, thus enabling them to minimize the lethal effects of extreme freeze desiccation. The substances involved in these mechanisms include carbohydrates, amino acids and so-called cold-shock proteins, but the actual mechanisms of interfering with ice nucleation, although quite well documented, are as yet imperfectly understood. This is particularly true for the genetic control associated with biochemical processes that produce freeze resistance and freeze tolerance. The molecular biology of cold stress is currently a subject of intensive study.