Dalton Transactions Blog

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.

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

Sustainable chemistry is a key area of research, with catalysis leading the way by performing many chemical transformations while only requiring stoichometric amounts. Yet, a problematic area of homogeneous catalysis is high amounts of organic and toxic solvents required, where the catalyst must be separated, and in almost all cases destroyed, in order to recover the product.

This research, carried out at the University of Girona, in Spain, looked at the hydration of harmful nitriles using a ruthenium based homogeneous catalyst, to its non-toxic amide. This is the first instance of these types of catalysts doing this hydration in solely water or glycerol. This could have a big impact on producing industrially important chemicals much more cheaply and in a sustainable way, while also allowing the removal of toxic chemicals in environmentally friendly media.

Two catalysts were investigated: [RuCl₂(pypz-H)(DMSO)₂] (2), and [RuCl₂(pz-H)(DMSO)₃] (3). (pypz-H = asymmetric didentate 2-(3-pyrazolyl) pyridine ligand; pz-H = monodentate pyrazole ligand; DMSO = dimethyl sulfoxide) Both were tested in H₂O at 80^oC, at 1 mol % of ruthenium. The substrates included various small organics with a nitrile and another functional group. The conversion of the substrate was above 80% in many cases and selectivity to the corresponding amide, over 98% in almost all cases. In general, catalyst (3) performed better, reasoned as greater flexibility of the catalytic intermediate, having only monodentate ligands. This means more labile sites for the reactants to coordinate. Free DMSO was found after the reaction suggesting these are the labile sites at the metal centre. A further study demonstrated how using glycerol allows recycling of the catalyst with no loss of conversion, where the products go into organic media and the catalyst remains in the glycerol.

This is an excellent study displaying how homogeneous catalysis can move one step further into the field of green chemistry by using non-toxic and plentiful solvents, such as water. Many of these delicate transformations are performed by expensive metals, such as ruthenium, and this work demonstrates how keeping the catalyst in its original media allows for sequential runs, meaning overall lower amounts of the catalyst are required.

Find out more from the paper:

Ru(II) complexes containing dmso and pyrazolyl ligands as catalysts for nitrile hydration in environmentally friendly media
Íngrid Ferrer, Jordi Rich, Xavier Fontrodona, Montserrat Rodríguez and Isabel Romero
Dalton Trans., 2013,42, 13461-13469
DOI: 10.1039/C3DT51580J, Paper

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

When you hear the phrase “at the click of a button” you expect that something can be done both simply and efficiently. Likewise, the original aim of Click Chemistry as stated by Nobel laureate K. Barry Sharpless in 2001 was to develop simple, efficient chemical reactions that would yield a wide range of new molecules to be tested for applications in pharmaceuticals or materials.

The particular type of reaction most often associated with Click Chemistry is the azide/alkyne cycloaddition, wherein a molecule containing a carbon-carbon triple bond is reacted with a molecule containing a terminal (azide) group of three nitrogen atoms such that they join together resulting in a five-membered “triazolate” heterocycle incorporating the two carbon and three nitrogen atoms.

Over the past twelve years chemists have developed a diverse range of molecules that feature these two functional groups and thus can be combined using this reaction. The variation on this chemistry presented here by the group of Adam S. Veige includes gold and platinum metal atoms in the starting molecules. The grand goal, they state, would be to use this reaction to synthesize perfectly regular polymers incorporating metal atoms linked by the triazolate bridges for possible use in materials.

Impressively, they synthesize in high yield a molecule featuring a gold-platinum-gold motif where the gold and platinum atoms are indeed linked by triazolate bridges using this reaction. They also present other less high-yielding, but nonetheless interesting reactions, including one wherein they link the two gold atoms within a very similar molecule using a bis(diphenylphosphino)methane bridge, forcing the two gold atoms to bend symmetrically to the same side of the molecular plane.

To sum up with an alliteration, such manipulations of multi-metallic molecules may move masterfully towards many materials.

Find out more from the paper:

Inorganic click (iClick) synthesis of heterotrinuclear Pt^II/Au^I₂ complexes
Andrew R Powers, Xi Yang, Trevor J del Castillo, Ion Ghiviriga, Khalil A Abboud and Adam Steven Veige
Dalton Trans., 2013, Accepted Manuscript
DOI: 10.1039/C3DT52105B, Communication

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

Chemotherapy remains the most widely used therapeutic approach to treating cancer. Such drugs work by targeting and killing rapidly dividing cells (a major characteristic of most cancer cells) by impairing mitosis (cell division).¹ These drugs are often highly effective at suppressing or even eliminating cancer in the patient, however, they can also lead to many severe side effects such as immunosuppression and infertility. Free radicals and reactive oxygen species (ROS), a by-product of the chemotherapy process, are frequently implicated as a cause of some of the side effects experienced.² Hence, a drug which simultaneously kills cancer cells and scavenges free radicals and ROS could hypothetically reduce the side effects of chemotherapy while remaining effective against the disease.

In this article, the authors combine two biologically active species into discrete potential drug molecules; hydroxyl-substituted Schiff bases, known to have good free radical scavenging and anti-cancer activity,³ and ferrocene, previously shown to increase the anti-cancer activity of other chemotherapeutic drugs.⁴

Using established methods, the authors thoroughly tested their new compounds for anti-free radical and anti-cancer activity. The results showed that one molecule in particular (“Compound 1”) has good free radical scavenging activity against ABTS.- and DPPH. (assessed by changes in UV-Vis absorbance), as well as displaying cytoprotective activity against radical attacks, delaying free radical oxidative damage to membrane cells. “Compound 1” was also shown to possess good anti-cancer activity against HeLa cancer cell lines, even out-performing clinically used anti-cancer drug Resveratrol. These early findings show promise for the development of chemotherapy treatments which combine antioxidant and anti-cancer activities.

To read more, see:

Synthesis and biological evaluation of hydroxyl-substituted Schiff-bases containing ferrocenyl moieties
Wansong Chen, Weizhu Ou, Liqiang Wang, Yuanqiang Hao, Jianshun Cheng, Juan Li and You-Nian Liu,
Dalton Trans., 2013, DOI: 10.1039/C3DT51977E, Paper

¹ V. Malhorta, M. C. Perry, Cancer Biol. Ther., 2003, 2 (Suppl. 1), S2-4.
² E.-S. E. El-Awady, Y. M. Moustfa, D. M. Abo-Elmatty and A. Radwan, Eur. J. Pharmacol., 2011, 650, 335-341.
³ Y.-F. Li and Z.-Q. Liu, Eur. J. Pharm. Sci., 2011, 44, 158-163.
⁴ B. Zhou, J. Li, B.-J. Feng, Y. Ouyang, Y.-N. Liu and F. Zhou, J. Inorg. Biochem., 2012, 116, 19-25.

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.