Kobayashi Atsuko, Golash Harry N, Kirschvink Joseph L
Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan.
Division of Mechanical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
Cryobiology. 2016 Jun;72(3):216-24. doi: 10.1016/j.cryobiol.2016.04.003. Epub 2016 Apr 14.
An outstanding biophysical puzzle is focused on the apparent ability of weak, extremely low-frequency oscillating magnetic fields to enhance cryopreservation of many biological tissues. A recent theory holds that these weak magnetic fields could be inhibiting ice-crystal nucleation on the nanocrystals of biological magnetite (Fe3O4, an inverse cubic spinel) that are present in many plant and animal tissues by causing them to oscillate. In this theory, magnetically-induced mechanical oscillations disrupt the ability of water molecules to nucleate on the surface of the magnetite nanocrystals. However, the ability of the magnetite crystal lattice to serve as a template for heterogeneous ice crystal nucleation is as yet unknown, particularly for particles in the 10-100 nm size range. Here we report that the addition of trace-amounts of finely-dispersed magnetite into ultrapure water samples reduces strongly the incidence of supercooling, as measured in experiments conducted using a controlled freezing apparatus with multiple thermocouples. SQUID magnetometry was used to quantify nanogram levels of magnetite in the water samples. We also report a relationship between the volume change of ice, and the degree of supercooling, that may indicate lower degassing during the crystallization of supercooled water. In addition to supporting the role of ice-crystal nucleation by biogenic magnetite in many tissues, magnetite nanocrystals could provide inexpensive, non-toxic, and non-pathogenic ice nucleating agents needed in a variety of industrial processes, as well as influencing the dynamics of ice crystal nucleation in many natural environments.
一个突出的生物物理谜题聚焦于微弱的极低频振荡磁场增强多种生物组织冷冻保存的明显能力。最近的一种理论认为，这些微弱磁场可能通过使存在于许多动植物组织中的生物磁铁矿（Fe3O4，一种反立方尖晶石）纳米晶体振荡，从而抑制冰晶成核。在该理论中，磁致机械振荡破坏了水分子在磁铁矿纳米晶体表面成核的能力。然而，磁铁矿晶格作为异质冰晶成核模板的能力尚不清楚，尤其是对于尺寸在10 - 100纳米范围内的颗粒。在此我们报告，在超纯水样品中添加痕量的细分散磁铁矿，在使用带有多个热电偶的可控冷冻设备进行的实验中测量发现，过冷现象的发生率大幅降低。利用超导量子干涉仪磁力测定法对水样中的纳克级磁铁矿进行了量化。我们还报告了冰的体积变化与过冷度之间的关系，这可能表明过冷水结晶过程中脱气程度较低。除了支持生物源磁铁矿在许多组织中冰晶成核的作用外，磁铁矿纳米晶体还可为各种工业过程提供所需的廉价、无毒且无致病性的冰核剂，并影响许多自然环境中冰晶成核的动力学。
