Dalton Transactions Blog

Posted on behalf of Stuart Bartlett, web writer for Dalton Transactions

The capture of inert gases, such as CO₂, is a fundamental process across biology and transition metal chemistry. There are many advantages to CO₂ fixation; one important example is to reduce greenhouse gas emissions from waste streams. The Piers group in Calgary have found that platinum(II) complexes with sterically imposing diimine ligands can undergo CO₂ insertion reversibly into a Pt-OH bond to give new carbonate ligands.

These complexes are easily synthesised from a platinum precursor, trans-[Pt(SMe₂)₂Cl(R)] {R = Me, Ph} , in the presence of a diimine ligand followed by chloride abstraction using Ag₂O/H₂O to give [Pt(NN)(OH)(R)] {NN = Diimine-(3,5-bis-(2,6-diisopropylphenyl)benzene)}. Also, by using a dichloride precursor, the dihydroxo species can also be obtained. This dihydroxo species was found to react immediately with 1 atm CO₂ to yield [(NN)Pt(CO₃-η²)] nearly quantitatively. At a lower temperature of 205 K, NMR studies showed the presence of a [(NN)Pt(CO₃H)₂] complex, which reverted back to [(NN)Pt(CO₃-η²)] when warmed up. This process is thought to occur via de-insertion of CO₂, to give the initial Pt-OH bond, followed by H₂O elimination back to [(NN)Pt(CO₃-η²)].

Analysis of the mixed hydroxo-alkyl species, [Pt(NN)(OH)(R)], showed ~50% insertion of CO₂ into the Pt-OH bond at room temperature, increasing to 100% at 260 K. Using NMR analysis, this was observed to be a fully reversible process upon heating back to room temperature, giving the initial [Pt(NN)(OH)(R)] complex. Alkane elimination (R-H) was not observed in any circumstances, whereas CO₂ elimination as seen as the more favoured route. Also at the lower temperatures, where the CO₂ is retained, the alkane elimination barrier is thought to be too high.

This research displays how important transition metal chemistry can be in reactions of chemically inert species, such as CO₂, at normal temperatures. This reversible capture points to many important areas, such as biological reactions of enzymes, possible pathways to develop new synthons in organic chemistry and industrial applications for reversible CO₂ capture.

Find out more from the article:

Reversible insertion of carbon dioxide into Pt(II)–hydroxo bonds
Tracy L. Lohr, Warren E. Piers and Masood Parvez
Dalton Trans., 2013, 42, 14742-14748
DOI: 10.1039/C3DT51701B

Stuart Bartlett is currently doing a 1 year postdoc position with David Cole-Hamilton at the University of St Andrews, focusing on the conversion of renewable oils towards fine chemical production using metathesis. He obtained his PhD from the University of Southampton investigating the mechanism of ethene oligomerisation catalysis using NMR and X-ray Absortion Spectroscopy.

Posted on behalf of Ian Mallov, web writer for Dalton Transactions

One of chemistry’s small, fascinating deviations from scientific expectation is the tendency of a few types of metal atoms to attract instead of repel each other when they are formally positively charged. This tendency is known for several of the lower late transition metals, including mercury, platinum and palladium. But the attraction is strongest in that most innately alluring of metals, gold, and the concept has its own Latinized term: aurophilicity.

Fernández and co-workers report unique examples of these interactions between positively-charged gold atoms. Gold(I) complexes bound to carbene ligands are a class of compounds of which there are many known and useful variants. Though expensive, they’ve been used with considerable success to catalyze transformations of organic molecules. In their paper, these chemists use Fischer-type carbenes, excellent at accepting electron density from the metal to which they bind, but rarely used in gold chemistry.

X-ray diffraction studies of their synthesized (via transmetallation from tungsten(0) analogues) gold compounds in the solid state, together with theoretical studies by Density Functional Theory computations affirm the attractions between gold atoms of adjacent molecules. They also prepared a ferrocene-bridged dinuclear gold complex, utilizing the ferrocene bridge as a rigid, “semi-support” for the gold atoms (picture two flexible branches at opposite ends of a solid trunk) and the solid-state and calculated structures show the gold atoms, well out on these “branches,” bending toward one another and at a distance even closer than the gold atoms in the “unsupported” complexes.

There is even an explanation offered: using Second-Order Perturbation Theory computations, it appears that electron density is donated from a doubly-occupied d-orbital of one gold atom into an empty p-orbital of the adjacent atom, and the energies associated with this interaction are indeed significant.

Find out more from the paper:

Fischer-type gold(I) carbene complexes stabilized by aurophilic interactions
Daniela I. Bezuidenhout, Belinda van der Westhuizen, Amos J. Rosenthal, Michael Wörle, David C. Liles and Israel Fernández
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C3DT52961D

Ian Mallov is currently a Ph.D. student in Professor Doug Stephan’s group at the University of Toronto. His research is focused on synthesizing new Lewis-acidic compounds active in Frustrated Lewis Pair chemistry. He grew up in Truro, Nova Scotia and graduated from Dalhousie University and the University of Ottawa, and worked in chemical analysis in industry for three years before returning to grad school.

Posted on behalf of Liana Allen, web writer for Dalton Transactions

Protein purification is an essential step in the study and characterisation of naturally occurring molecules and the understanding of their functions in different biological processes. Before an in-depth study can be achieved, the protein of interest needs to be separated not only from the non-protein constituents of the tissue or cell culture, but also from any other proteins present. The latter is usually the most difficult aspect of the separation process.

Protein tagging is a common way of separating target proteins from other biological materials. In an example of this tagging method, target proteins are deliberately expressed with histidine (His) residues, which have a high affinity for binding to metal ions. This technique is popular due to its easy adaptation to any protein tagging system, however it also has limitations including long operation times and the necessity for pretreatment of the organic matter. Recently, this separation procedure has been improved by immobilising the metal ions on solid supports such as silica nano-spheres, though low surface area and low surface metal ion density have thus far limited practical application of this.

In this paper, the authors report an efficient synthesis of nickel functionalised silica nano-spheres and demonstrate their superior performance in the affinity purification of His-tagged proteins. By first chemically affixing nickel ions to the surface of silica nano-spheres, then removing the silica cores, hollow spheres are created, with greater surface area and higher Ni²⁺ surface density than the current nano-particle materials used for protein separation. The authours demonstrate that His-tagged TRX proteins could be separated directly from crude E. coli cell material using their hollow, Ni²⁺ functionalised nano-spheres. Moreover, after washing and sonicating, the nano-spheres could be reused up to five times while maintaining the same high efficiency.

To read more, see:

Preparation of hollow nickel silicate nanospheres for separation of His-tagged proteins
Yonghui Wu, Guanxiao Chang, Yanbao Zhao and Yu Zhang
Dalton Transactions, 2013, Advance Article, DOI:10.1039/c3dt52084f

Dr. C. Liana Allen is currently a post-doctoral research associate in the group of Professor Scott Miller at Yale University, where she works on controlling the enantio- or regioselectivity of reactions using small peptide catalysts. Liana received her Ph.D. in organic chemistry at Bath University with Professor Jonathan Williams, where she worked on developing novel, efficient syntheses of amide bonds.