This review summarizes the state-of-the-art knowledge of heme ligation in the gas phase. The unique aspect of the gas phase approach is to allow a step-by-step ligation of heme and thus enables the analysis of the properties of -four, -five and -six coordinate hemes in vacuo, under conditions directly comparable with quantum calculations. This approach also allows the characterization of situations uncommon in Nature, completing the coordination spectrum of hemes: four coordinate heme and protonated heme, an intermediate between ferrous and ferric heme. Therefore, a complete set of systems is described for the ferrous and ferric cases and there is no discontinuity between the two oxidation states of iron, so that the same mechanisms are at work, donation and back donation of different strengths depending upon the ligand. The similarity of ligation properties in ferrous and ferric hemes is consistent with calculations of the electron density at the Fe atom level, rather independent of the formal oxidation state in contrast with the porphyrin cycle. Hemes spin states have been reviewed, for they identify the electronic distribution of the metal. In ligated ferrous and ferric hemes, we find that binding energy measurements combined with spectroscopy describe their properties most effectively.

本综述总结了气相血红素连接的最新知识。气相方法的独特之处在于允许逐步连接血红素，从而能够在真空中分析 -4、-5 和 -6 坐标血红素的特性，在与量子计算直接可比的条件下。这种方法还允许表征自然界中不常见的情况，完成血红素的协调谱：四协调血红素和质子化血红素，亚铁和三价血红素之间的中间体。因此，针对亚铁和三价铁的情况描述了一套完整的系统，并且铁的两种氧化态之间没有不连续性，因此相同的机制在起作用，不同强度的捐赠和回捐赠取决于配体。亚铁和三价铁血红素中连接特性的相似性与 Fe 原子水平的电子密度计算一致，与卟啉循环相比，与形式氧化态无关。已经审查了 Hemes 自旋状态，因为他们确定了金属的电子分布。在结扎的亚铁和三价铁血红素中，我们发现结合能测量结合光谱学最有效地描述了它们的特性。