Dalton Transactions Blog

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.