Divalent gold complex isolated for the first time in a pure form / New fundamental insight also provides possible explanation of the mechanism of action of cytostatic gold(+III) porphyrins
According to text book knowledge, the usual oxidation states of gold in compounds are +I and +III. The divalent form (+II), on the other hand, prefers to form polynuclear compounds or simply undergoes transformation into the mono- and trivalent forms. However, the elements next to gold in the periodic table are quite different in this respect.
The ions of the coinage metals, copper(+II) and silver(+II), are usually present in divalent form and this is also the case for gold's neighbors to its left and right, platinum(+II) and mercury(+II). It has been postulated that when gold undergoes photochemical catalysis reactions, the +II state may form, but definitive evidence has not been provided to date. The corresponding proof has just been advanced by researchers at Johannes Gutenberg University Mainz (JGU) in a recent publication.
A team of chemists led by Professor Katja Heinze at the Institute of Inorganic Chemistry and Analytical Chemistry of JGU has been able to isolate and analyze gold in the very rare oxidation state +II. This provides the missing links in the homologous series of the coinage metal ions copper(+II), silver(+II), gold(+II), and in the 'relativistic' triad of platinum(+II), gold(+II), and mercury(+II).
"Fundamental data unknown to date such as ion size, preferred structural arrangement, and the reactivity of gold(+II) have now been made available," explained Sebastian Preiß, doctoral candidate in Heinze’s team, who was able to isolate the gold(+II) complex in its pure form for the first time. The findings have been published in Nature Chemistry.
The stabilization of the very labile gold(+II) ion was achieved by the researchers with the help of a so-called porphyrin used to encapsulate the gold(+II) ion. In combination with magnesium or iron ions in the center, respectively, the porphyrin macrocycle is present in the green pigment of plants (chlorophyll), and in the red pigment of the blood (heme).
With gold(+II) at its center, porphyrin blocks the normal reaction pathways of gold(+II), i.e., the formation of polynuclear compounds or the conversion to the more stable gold(+I) and gold(+III) complexes. "This enabled for the first time to investigate this unique class of stable mononuclear gold(+II) complexes and to describe them comprehensively," summarized Professor Katja Heinze.
Interestingly, the arrangement of the four atoms next to the gold(+II) ion is not square planar with the atoms placed at equal distances to the gold as in the case of the corresponding structures of gold's neighboring elements copper(+II), silver(+II), platinum(+II), and mercury(+II). Instead, the structure shows a rhombic distortion with two short and two long distances. In technical terms, this previously unobserved phenomenon in the case of gold(+II) ions can be attributed to a second-order Jahn-Teller effect caused by the relativistic properties of gold.
Because this new gold(+II) compound can also be prepared from the gold(+III) complex present in potent anti-cancer agents, the researchers tried to find out whether the gold(+II) porphyrin also plays a role in biological systems. They discovered that the gold(+II) complex can be generated under near physiological conditions from a cytostatic gold(+III) agent.
On exposure to atmospheric oxygen, the gold(+II) porphyrin forms reactive oxygen species (ROS), which are known to induce apoptosis, or programmed cell death. "We thus have a plausible functional chain starting with a cytostatic agent and leading to targeted cell death with the gold(+II) porphyrin acting as an important link in the chain," emphasized Heinze. "A major impetus for us to continue with research in this field is that curiosity-driven fundamental research about unusual species enabled us to reach insights that could well be relevant to medical applications," concluded Heinze.
Gold in its divalent form is stable in the center of porphyrins.
Ill./©: Katja Heinze, JGU
Sebastian Preiß et al.
Structure and reactivity of a mononuclear gold(II) complex
Nature Chemistry, 7 August 2017
Contact and further information:
Professor Dr. Katja Heinze
Institute of Inorganic Chemistry and Analytical Chemistry
Johannes Gutenberg University Mainz
55099 Mainz, GERMANY
phone +49 6131 39-25886
fax +49 6131 39-27277
http://www.uni-mainz.de/presse/aktuell/1802_ENG_HTML.php – "Scientists develop molecular thermometer for contactless measurement using infrared light", 14 June 2017
http://www.uni-mainz.de/presse/aktuell/1212_ENG_HTML.php – "Mainz University to coordinate new DFG priority program in photochemistry", 25 April 2017
http://www.uni-mainz.de/presse/17824_ENG_HTML.php – "Katja Heinze receives research award for intelligent food packaging with freshness indicator", 5 Dec 2014
Petra Giegerich | idw - Informationsdienst Wissenschaft
One step closer to reality
20.04.2018 | Max-Planck-Institut für Entwicklungsbiologie
The dark side of cichlid fish: from cannibal to caregiver
20.04.2018 | Veterinärmedizinische Universität Wien
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Physics and Astronomy
20.04.2018 | Interdisciplinary Research
20.04.2018 | Physics and Astronomy