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.

Posted on behalf of Lewis Downie, web writer for Dalton Transactions

Some synthetic techniques can cause differing morphologies and sometimes be more efficient with both time and energy. One technique which is becoming more prevalent is microwave synthesis. Microwave assisted synthesis is solution based and therefore considered “soft” but has been found to allow the synthesis of a number of materials and in particular ones based around metal organic frameworks.

Use of microwave energy leads to the fast and uniform heating of a solution when compared to, say, solvothermal reaction techniques. It also leads to a greater number of potential nucleation points. These differences can lead to a more homogenous and rapidly synthesised product. For the synthesis of Fe(OH)(1,4-NDC)•2H₂O (1,4-NDC = 1,4-naphthalenedicarboxylate), “PCP-Fe”, it is found that all these advantages occur.

PCP-Fe is normally synthesised hydrothermally, involving a 3 day heating period. This leads to the formation of cubic crystals (~ 10 μm³) with a broad size distribution. Microwave irradiation can reduce synthesis time to as short as one minute, however 30 minutes is found to produce crystalline, homogenous particles of PCP-Fe. The microwave synthesised particles are smaller and of differing morphology (prisms of ~ 15 μm in length and 3 μm in width) which is expected from a technique which provides many and rapid nucleation opportunities.

A number of other studies were performed in order to optimise the synthesis with mixed results. Modifying the reaction time leads to a number of varying, yet similar morphologies – thirty minutes is found to lead to the most uniform structures. Decreased reaction time leads to an increase in defects and a corresponding lowering of crystallinity. Variance in reagent concentration also has a direct effect on crystallinity – an inverse relationship is described.

The microwaved sample also appears to show improved gas adsorption properties. This is suggested to be directly related to the smaller particle size when compared to the hydrothermal sample. This shows the importance of morphology when assessing material properties and also the understanding of a number of synthetic techniques in order to access different morphologies.

Find out more from the paper:
Rapid synthesis of iron 1,4-naphthalenedicarboxylate by microwave irradiation with enhanced gas sorption
Yongbing Lou, Jinxi Chen, Jing Jiang and Qilong Bao
Dalton Trans., 2013, Accepted Manuscript
DOI: 10.1039/C3DT52546E, Paper

Lewis Downie has wide ranging interests in the chemical sciences but has a background in functional materials. His main research focus is the investigation of these materials using crystallographic techniques. He is currently a postdoctoral research assistant at the University of St Andrews, U.K.

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

Picric acid is an organic compound which has an explosive power more powerful than TNT. It is widely used in munitions and explosives, but also appears in the pharmaceuticals and dye industries as a chemical reagent. Picric acid can cause several negative health effects, such as skin irritation and respiratory system damage.¹ Therefore, it is an important challenge to develop sensors that can detect picric acid safely and reliably, for both the recognition of explosives and the detection of its presence as an environmental pollutant.²

The most promising method of detecting picric acid is called ‘fluorescence quenching’, as this is a highly sensitive and inexpensive technique. In this paper, the authors report the synthesis of a new material which can detect picric acid in this manner. Taking advantage of the reliable, rigid way the metal platinum forms complexes with other molecules (‘ligands’), the authors make a novel material which naturally contains pores the correct size to accommodate picric acid molecules. Interaction of the ‘ligands’ and the picric acid once it has entered one of these pores induces a ‘fluoresence quenching’ response, allowing picric acid to be detected at very low concentrations, both in a liquid and as a gas.

To read more, see:

Pt^II₆ nanoscopic cages with an organometallic backbone as sensors for picric acid
Dipak Samanta and Partha Sarathi Mukherjee
Dalton Trans., 2013, Advance Article
DOI: 10.1039/C3DT52268G, Paper

¹ B. Roy, A. K. Bar, B. Gole, P. S. Mukherjee, J. Org. Chem., 2013, 78, 1306.
² M. E. Germain, M. J. Knapp, Chem. Soc. Rev., 2009, 38, 2543.

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.

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

If you’ve ever donated blood you may recognize leishmaniasis as a disease on the questionnaire that may prevent you from doing so. Caused by parasites transmitted to humans by the bite of sandflies, British troops serving in the Middle East in World War I referred to it as “Jericho’s Buttons,” as many contracted the disease, with its characteristic button-shaped red skin lesions, near the ancient city of Jericho. Today new cases of leishmaniasis are estimated at 1.5-2 million worldwide per year, most in Latin America, the Indian sub-continent and the Middle-East. Leishmaniasis caused over 50,000 deaths worldwide in 2010.

The best-known cures for the disease are two drugs based, strangely, on antimony, like its periodic table neighbour arsenic known for forming compounds of extreme toxicity. These drugs – sodium stibogluconate (SSG) and meglumine antimoniate (MGA) – have been used for over seventy years. They must be administered by injection and closely monitored, and pockets of population have developed resistance to them. Though in the long-term a vaccine is hoped for, in the near term new or more easily-administered drugs are needed.

Andrews et. al. explore the curative potential – as well as the human toxicity – of twenty-six new compounds of antimony. These compounds were obviously designed to have some similar features to the existing SSG and MGA, but also to be simple. They feature two carboxylate groups, and three phenyl, benzyl, or ortho-, meta-, or para-tolyl groups bound to antimony. Many syntheses required only simple salt metathesis reactions between antimony(V)triorgano dibromides and sodium or potassium carboxylates at room temperature.

The researchers tested each in varying concentrations for toxicity on human primary fibroblast cells, and for anti-leishmanial activity on L. major promastigote parasites. As they state, the molecular mechanism by which SSG and MGA works in the body has not been confirmed, but is suspected to proceed via reduction of the antimony(V) species to an antimony(III) species by thiols. Their findings, though preliminary, show the trend that the meta- and para-tolylantimony molecules were the most effective against L. major promastigotes, while the ortho-tolyl derivatives were less effective, and those featuring phenyl or benzyl groups were more toxic to cells.

Their work certainly seems a useful step in establishing trends for designing new antimony drugs to combat leishmaniasis. One wonders, however, about issues of excretion of these drugs or their products from the human body – particularly in areas of the world whose water treatment lags behind First World standards.

Find out more from the paper:

Anti-leishmanial activity of heteroleptic organometallic Sb(V) compounds
uhammad Irshad Ali, Muhammad Khawar Rauf, Amin Badshah, Ish Kumar, Craig M. Forsyth, Peter C. Junk, Lukasz Kedzierski and Philip C. Andrews
Dalton Trans., 2013, Advance Article
DOI: 10.1039/C3DT51382C, Paper

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 Lewis Downie, web writer for Dalton Transactions

Hg²⁺ is a potentially toxic ion which one would want to assess in drinking water and other potential sources of human consumption. It can have adverse effects on human health and negative consequences in the environment. Unfortunately, its detection is particularly difficult due to the electronic configuration of Hg²⁺ – this diamagnetic state leads to challenges when measuring by spectroscopic or magnetic means. In general chemosensors for such applications have to be complex. Recently, a simpler pyrene-pyrimidine based chemosensor has been reported for Hg²⁺.¹

Inspired by this, the current work has linked a heterocyclic coumarin moiety to pyrimidine. In this molecule the electronic, and therefore chromophoric properties, are affected by binding to Hg²⁺. This change in colour – from green to red when bound – is induced by intramolecular charge transfer due to a strong “push-pull” interaction between the NEt₂ group bound to the coumarin and the pyrimidine.

This colour change response appears to be selective for Hg²⁺ as no response is seen for Cu²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Pb²⁺, Zn²⁺, Cr³⁺, Mn²⁺ or Cd²⁺. The same selectivity is observed when more than one metal ion is present. It is suggested that the particular sensitivity for Hg²⁺ is mainly due to a size effect – the Hg²⁺ alone is capable of keeping the two aryl systems present in the same plane, which then allows the conjugation of the whole system beginning at the lone pair of the nitrogen on the NEt₂ group found on the chromophore.

This system has a colour change which is visible to the naked eye and it is even possible to discern the concentration of the Hg²⁺ by eye. This property became apparent when paper was coated with the chemoselective material and a solution of a known concentration of Hg²⁺ led to different shades of orange; this shows promise as a simple and portable Hg²⁺ detector. It has also been found that the addition of KI to the reaction leads to the removal of Hg²⁺ from the chemoreceptor and a return to the green colour. Further addition of Hg²⁺, however, leads to the red colour being re-established. This continued addition of KI followed by Hg²⁺ can go on for a number of cycles with little change to the efficacy.

Find out more from the paper:

‘Pet’ vs. ‘Push-Pull’ induced ICT: A remarkable Coumarinyl-appended Pyrimidine based Naked Eye Colorimetric and Fluorimetric Sensor for detection of Hg²⁺ ion in aqueous media with test strips
Shyamaprosad Goswami, Avijit Kumar Das and Sibaprasad Maity
Dalton Trans., 2013, Accepted Manuscript
DOI: 10.1039/C3DT52252K, Communication

^1. J. Weng, Q. Mei, Q. Ling, Q. Fan, W. Huang, Tetrahedron, 2012, 68, 14, 3129-3134

Lewis Downie has wide ranging interests in the chemical sciences but has a background in functional materials. His main research focus is the investigation of these materials using crystallographic techniques. He is currently a postdoctoral research assistant at the University of St Andrews, U.K.

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

Titanium dioxide (TiO₂) is a material with many interesting and attractive characteristics; for example, it is low-cost, non-toxic and relatively chemically inert.¹ Due to these features, TiO₂ is frequently used in fields such as solar energy, sensors and environmental protection.² The latter area exploits titanium dioxide’s ability to act as a photocatalyst – meaning it uses UV light (from solar radiation) to catalyse a chemical reaction – to decontaminate water containing organic pollutants.

Despite these favourable properties, use of titanium dioxide has disadvantages. The efficiency of TiO₂ as a photocatalyst is fairly low – it can only use about 4% of the solar energy it receives. Moreover, recovery of TiO₂ nanoparticles from water after decontamination is challenging. A commonly used strategy to overcome these issues is to incorporate the TiO₂ into another functional material as a core-shell composite.³ One such functional material is carbon nanotubes (CNTs), which, in addition to aiding in removal of TiO₂ from water, have been shown to enhance the efficiency of TiO₂ as a photocatalyst.

In this paper the authors present an improved, facile preparation of the carbon nanotube–TiO₂ composite. Previous syntheses had major drawbacks as they required harsh reaction conditions (high temperatures and pressures) and side reactions occurred during the synthesis. The method reported here proceeds at ambient temperature and pressure and uses simple chemical reactions to first modify the nanotubes, then uniformly coat them in a 10-20 nm thick layer of titanium dioxide particles. Improved photocatalytic activity of the CNT-TiO₂ composite was demonstrated by the authors by examining the photodegredation of an organic dye, methyl orange. Additionally, the material was recoverable and could be reused up to five times with only slight loss of activity.

To read more, see;

Facile synthesis of carbon nanotube-inorganic hybrid materials with improved photoactivity
Yong Yu, Jun Chen, Zi-Ming Zhou and Yuan-Di Zhao
Dalton Trans., 2013, DOI: 10.1039/C3DT51673C

¹ J. Sambur, T. Novet, B. A. Parkinson, Science, 2010, p63.
² D. Kuang et al., ACS Nano, 2008, p1113.
³ T.-D. Nguyen-Phan et al., Chem. Eng. J., 2011, p226.

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.

Posted on behalf of Lewis Downie, web writer for Dalton Transactions

Metal organic frameworks (MOFs) can show a range of structures and properties and have proved an interesting avenue for contemporary research into areas such as gas storage and heterogeneous catalysis. These applications have tended to use transition metals and as such the metal coordination is typically four or six-fold. The use of lanthanide ions increases the variety of coordination numbers and also gives access to more properties which make use of the electronic structure of the lanthanides: namely magnetic and luminescent behaviours. If the MOF consists not only of lanthanides but also conjugated ligands then it is possible to increase electronic communication between metal centres and also electromagnetically sensitise them. With this in mind, Zhao et al. have hydrothermally synthesised a range of MOFs based on the trivalent lanthanide metal centres Pr, Eu, Gd, Tb, Dy, Ho and Er and the organic linker 4-(carboxymethoxy)isophthalic acid.

The extraordinary flexibility of the metal coordination site is quite exceptional, and due to changing cation size there is the appearance of two different structure types. For the largest cation, Pr³⁺, a 2D framework is formed with Pr³⁺ showing a coordination sphere of ten. This is composed of a number of varying ligands; three bidentate and two monodentate carboxyl groups from 4-(carboxymethoxy)isophthalic acid and two coordinating water molecules. This compound is very stable for a MOF with thermogravimetric analysis (TGA) indicating decomposition at 400° C. As the lanthanide increases in size the coordination drops to eight; this is found for all the other lanthanide materials synthesised and they are all isostructural. The phase found for the smaller lanthanides is significantly different however – in this case the structure is found to be a 3D framework. There are also three crystallographically distinct Ln³⁺ cations showing a range of binding types as before. TGA measurements again suggest that the material is particularly temperature stable.

As previously mentioned MOFs which contain lanthanides can show some interesting behaviours and the examples reported in this paper are no exception. Examples of luminescence are found in the frameworks containing Eu³⁺ (red), Tb³⁺(green) and Dy³⁺ (yellow). The magnetic properties of the materials were also investigated. Measurements indicate that they may have weak antiferromagnetic interactions, however, as the effects are quite small this is difficult to resolve over the behaviour of the free Ln³⁺ ions.

Find out more:

Several (4,4)- and (5,6,8)-connected lanthanide–organic frameworks: structures, luminescence and magnetic properties
Xiao-Qing Zhao, Xu-Hui Liu and Bin Zhao
Dalton Trans., 2013, Advance Article
DOI: 10.1039/C3DT51769A, Paper

Lewis Downie has wide ranging interests in the chemical sciences but has a background in functional materials. His main research focus is the investigation of these materials using crystallographic techniques. He is currently a postdoctoral research assistant at the University of St Andrews, U.K.