Mechanism of Isotopic Fractionation of Transition Metals through Organic-Inorganic Interactions

较重元素(如铁、铜、锌或锗)的自然同位素变化的研究在生物学、行星科学、地球科学和环境科学等许多研究领域都有重大影响。最近的一系列过渡金属同位素研究表明，铁和锌的同位素组成在很大程度上是通过生物诱导过程而分馏的。这表明重元素的同位素比值可以作为地质样品的一种新的生物标志物(同位素生物标志物)。然而，重元素大量同位素分馏的机制仍不清楚。为了了解重元素大同位素分馏的机理，并讨论大同位素分馏与生物过程之间的遗传联系，必须从一系列生化样品中获得更准确和可靠的同位素数据。由于重元素的…，检测重元素同位素组成的自然变化是非常困难的同位素分馏幅度较小的主要原因是相对质量差较小。为了克服这一问题，利用多收集-电感耦合等离子体质谱(MC-ICPMS)对重元素，特别是过渡金属进行了灵敏和精确的同位素比值测量。将样品标准包络技术与新开发的法拉第前置放大器慢响应校正技术相结合，可以显著提高同位素比值测量的精度和重复性。得到的铁、锌同位素比值数据的精密度和可靠性与热电离质谱(TIMS)获得的同位素数据相当。应该指出的是，ICPMS测量所需的锌和铁的总量几乎比TIMS技术低一个数量级。这表明ICPMS技术现已成为大多数过渡金属的灵敏和快速同位素比值测量的标准技术。一系列12个月的红细胞样品中的铁和锌没有明显的季节变化。这可以用人体内这些元素的微小交换效率(每天1毫克)来解释。红细胞样品中的Fe同位素主要是分馏的(~1.5‰/amu)，而锌同位素的变化很小(~0.3‰/amu)。此外，红细胞样品中富集了较轻的铁同位素，而富集了较重的锌同位素。这表明这些元素的摄入量或代谢效率存在明显差异。在红细胞样品中观察到的铁和锌同位素的另一个有趣的特征是，男性人体的铁同位素比率明显轻于女性人体的铁同位素组成。这表明铁对雄性机体的摄取效率低于对雌性机体的摄入量。本文提供的数据清楚地表明，利用ICPMS技术获得的铁和锌同位素比值可以为阐明生化反应中过渡金属的同位素分馏提供强有力的线索。较少

The study of natural isotopic variations for heavier elements (e. g. , Fe, Cu, Zn or Ge) had a significant influence in many research fields such as biology, planetary, Earth, and environmental sciences. Recent series of isotopic study for transition metals revealed that the isotopic compositions of Fe and Zn were largely fractionated through biologically induced processes. This indicates that isotopic ratios of heavy elements can be used as a new biomarker for geological samples (Isotopic Biomarker). However, the mechanisms of large isotopic fractionation of heavy elements were still unclear. In order to understand the mechanism of large isotopic fractionation of heavy elements, and also to discuss the genetic link between the large isotopic fractionation and biological processes, further precise and reliable isotopic data must be obtained from series of biochemical samples.Detection of natural variation in isotopic composition of the heavy elements was very difficult because of their … More small magnitude of isotopic fractionation mainly due to small relative mass differences. To overcome this, sensitive and precise isotopic ratio measurements for heavy elements, especially for transition metals, have been made by means of a multiplecollector-ICP-Mass Spectrometry (MC-ICPMS). The precision and repeatability of the isotopic ratio measurements can be remarkably improved by a combination of sample-standard bracketing technique and newly developed correction for slow response of the Faraday preamplifiers. The precision and reliability of the resulted Fe and Zn isotopic ratio data were comparable to the isotopic data obtained by a thermal ionisation-mass spectrometry (TIMS). It should be noted that total amount of Zn and Fe required for the ICPMS measurements were almost order of magnitude lower than those for TIMS technique. This indicates that the ICPMS technique becomes now standard technique for sensitive and rapid isotopic ratio measurements for most transition metals.The isotopic ratios of Fe and Zn in human blood cell (BRC) samples were measured. No significant seasonal change could be found both for Fe and Zn obtained from series of 12-month RBC samples. This can be explained by a small exchange efficiency (1 mg per day) of these elements in human body. The Fe isotopes in the RBC samples were largely fractionated (~1.5‰/amu), whereas Zn isotopes in the RBC samples showed very small variations (~0.3‰/amu). Moreover, lighter-Fe isotopes were enriched in the RBC samples, whilst heavier-Zn isotopes were enriched in the RBC samples. This indicates the clear difference in intake or metabolic efficiencies of these elements. Another interesting feature observed on Fe and Zn isotopes in the RBC samples were that isotopic ratios of Fe for male human bodies were significantly lighter than Fe isotopic composition of female bodies. This indicates that intake efficiency of Fe for male bodies were less effective than that for female bodies. The data presented here demonstrate clearly that the Fe and Zn isotopic ratios obtained by the ICPMS technique can give strong clues to elucidate the isotopic fractionation of transition metals occurring in biochemical reactions. Less