CrystEngComm Blog

Highly selective and sensitive surface enhanced Raman spectroscopy (SERS) probes for the pesticide thiram have recently been reported by Zou and Wang et al.

SERS can provide low-cost, non-destructive, fast detection of potential environmental pollutants such as thiram.   This sulfur-containing pesticide and fungicide is commonly used to protect orchard fruits and soya but is toxic to humans both in acute doses and by long-term exposure to smaller quantities.

An effective SERS substrate has a rough metal surface – typically made of noble metals such as Ag – which adsorbs the molecules of interest.  The surface is coated on a glass or a core metal oxide particle, such as Fe₃O₄.   After oleate-modified Ag microspheres were found to possess selective thiram detection by surface-ligand exchange, attempts were made to generate Ag composite microspheres with oleate modifications, using a gel system.  However, the dumb-bell shaped particles produced showed a poor SERS performance, due to the lack of so-called hot-spots – areas where surface enhancement is intense.

In the new paper, the successful preparation of oleate-modified silver composite microspheres with dense hot-spots is demonstrated.  The Fe₃O₄ microspheres, capped with polyacrylate groups are prepared by a solvothermal method.  The carboxylate groups interact with Ag ions which are subsequently reduced using sodium borohydrate.  The surface Ag particles seed further coating by Ag in the presence of oleate in a gel system (see diagram below), completely covering the Fe₃O₄ microsphere in oleate-modified Ag nanoparticles.

The spherical particles produced show SERS detection of thiram at trace amounts, with the thiram spectrum detected at a concentration as low as 1 x 10⁻⁸ M.  Under the same conditions, two other common pesticides, methyl parathion and trichorfon, show no SERS signals. The results suggest that the system could potentially be used for the selective detection of traces of thiram in solution.

For more details, see the full paper at:

Gel-assisted synthesis of oleate-modified Fe₃O₄@Ag composite microspheres as magnetic SERS probe for thiram detection
Haihong Zheng, Bingfang Zou, Lin Chen, Yongqiang Wang, Xiaoli Zhang and Shaomin Zhou
CrystEngComm, 2015, Advance Article
DOI: 10.1039/C5CE01017A

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

A facile new preparation of shape-controlled tungsten trioxide (WO₃) sensors is reported in a recent paper by Zhang et al.  These sensors show good selectivity towards the hazardous gas hydrogen sulfide (H₂S) at a relatively low operating temperature.

Detection of hazardous gases is necessary to monitor environmental pollution and ensure levels do not exceed legally permitted limits.  In the case of H₂S, the general industry ceiling limit is 20 ppm.  At concentrations of above 50 ppm, eye damage is likely and at higher concentrations (above 320 ppm) pulmonary oedema and breathing problems resulting in death can occur.  There is, therefore, a demand for cheap, reliable and selective sensors for identifying low concentrations of H₂S.

Metal-oxide semiconductors such as WO₃ are attractive potential sensors which are relatively cheap and easy to fabricate.  As the sensing ability of the particles depends on their morphology, the preparation of shape-controlled particles is a requirement.  Zhang et al achieve this by reacting sodium tungstate and potassium sulfate in an acidic environment.  Adding oxalic acid and heating at 100^oC then calcining the resulting product produces WO₃ microflowers, of diameter 16 μm. Study of the reaction shows it can be divided into four processes.  Crucially, during the final stage, needle-like nanosheets grow radially from central particles to produce a flower-like morphology (see the scheme below).

These particles have excellent potential for application as H₂S sensors – at 160^oC they show high sensitivity and sensor response along with good repeatability and selectivity towards H₂S.  The high performance of WO₃ microflowers is related to their structure.  They are assembled from nanosheets composed of several nanowhiskers in parallel, giving highly exposed surfaces and so more pathways for gas absorption and electron exchange.  The nanosheets are homogeneous and single-crystalline so electron transport can occur between particles without overcoming boundary barriers which would decrease the sensitivity.

For more details, read the full paper at:

Low-temperature solvothermal synthesis of hierarchical flower-like WO₃nanostructures and their sensing properties for H₂S
Bingxin Xiao, Qi Zhao, Chuanhai Xiao, Tianye Yang, Pan Wang, Fei Wang, Xiaodong Chen and Mingzhe Zhang
CrystEngComm, 2015
DOI: 10.1039/C5CE00870K

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

A new paper by Wang et al. reports the facile synthesis of dispersed polyacrylic acid (PAA)/calcium carbonate nanoparticles which show ultrahigh loading capacity for the liver cancer drug doxorubin (DOX), in addition to its pH sensitive release.

While calcium carbonate particles are attractive potential drug delivery vehicles due to their biocompatibility and pH sensitivity, previously synthesised particles have been micrometer sized and show only limited drug uptake, both of which present barriers to their use.   These issues have now been overcome.  Using PAA-sodium salt as a template, PAA/calcium carbonate particles were produced with an average size of 120 nm by ion exchange followed by heating in carbon dioxide (see diagram below).

The presence of carboxylate groups in PAA is the root of the new nanoparticles’ high uptake of positively charged molecules such as DOX– up to 98 % loading efficiency was observed.  Release of DOX was shown to be faster in mildly acidic conditions like that in extracellular cancer cells, allowing targeting of these cells.

The anti-cancer activity of DOX-loaded PAA/calcium carbonate particles in vitro was compared to DOX-free particles and free DOX using the standard MTT assay.   Cytotoxicity of free DOX was similar to that of the DOX-loaded particles, while the DOX-free particles showed no cytotoxicity.   The performance of free-DOX was also compared to DOX-loaded nanoparticles in vivo.   Compared to the control, the group treated with DOX-loaded nanoparticles showed a 76 % reduction in liver tumour size, while the group treated with free DOX showed a 41 % reduction.   In addition, there were no toxic effects observed for DOX-loaded particles.

These results demonstrate the potential application of PAA/calcium carbonate nanoparticles as delivery vehicles for doxorubin.  Further studies are being carried out to investigate the inclusion of magnetic and/or fluorescent compounds to produce multifunctional materials for simultaneous cancer diagnostic and therapeutic application.

For more information, see the full paper at:

Designed preparation of polyacrylic acid/calcium carbonate nanoparticles with high doxorubicin payload for liver cancer chemotherapy
Hanzhu Shi, Lu Li, Lingyu Zhang, Tingting Wang, Chungang Wang, Dongxia Zhu and Zhongmin Su
CrystEngComm, 2015, Advance Article
DOI: 10.1039/C5CE00708A

__________________________________________________________________________________________________

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

A new paper by Yu-Bin Dong et al reports a metal-organic framework (MOF) which not only reversibly adsorbs two different classes of volatile organic compounds (VOCs), but within each class also shows selectivity allowing separation of chemically similar examples.

VOCs are widely used in the chemical industry but their release into the environment is undesirable, as they can cause damage both to the environment and to human health.  Porous materials such as MOFs are attractive as potential adsorbents of VOCs and could also allow separation of examples with similar boiling points, which proves difficult by other methods such as distillation.

The new MOF consists of ditriazole-N-butylcarbazole ligands bridging Cu ions, forming a framework with square-like pores.  The ligand butyl groups point into the pores, making them hydrophobic.   The adsorption of VOCs classified as chlorocarbons (e.g. CH₂Cl₂) and aromatic solvents such as benzene and toluene were shown to be fully reversible under ambient conditions.

Tests on the selectivity towards chlorocarbons showed that CHCl₃ was adsorbed in preference to CH₂Cl₂ from a mixture.  This suggests that, unusually, selectivity may be based on the polarity of the molecules rather than the size – CHCl₃ is larger but less polar than CH₂Cl₂.

In the case of the aromatic molecules, it proved possible to separate benzene and toluene from mixtures of toluene/ethylbenzene/xylene and ethylbenzene/xylene, respectively.   In both these systems, the larger molecules are adsorbed in preference to the smaller (benzene or toluene, respectively) – see diagram below.

Rather than being determined by the size or polarity of the solvent molecules, this can be explained if the hydrophobic properties are considered.  More hydrophobic molecules, such as ethylbenzene, are preferentially adsorbed into the hydrophobic pores present in the MOF, where they form favourable hydrophobic interactions.

The MOF reported here adds to the range available that show specific properties with regards to adsorption and separation of VOCs, unusually demonstrating specificity related to both the polarities and hydrophobicity of the VOCs.

For more information read the full paper at:

CrystEngComm, 2015, Advance Article
DOI: 10.1039/C5CE00547G

__________________________________________________________________________________________________

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

In a recent paper, Langford et al report the formation of three new molecular porous materials with tunable channels.  Tunability of the size and shape of the channels is important in the design of materials for gas sensing, guest exchange, catalysis and drug delivery.  Other important factors such as thermal and solvent stabilities are also good.

The new compounds are readily prepared from tin(IV) porphyrin phenolates. Their structures feature a one-dimensional hourglass-shaped channel lined with methyl groups.  The nature of the channel is readily varied by changing the methyl substitution of the phenolate component.  In this way, the pore radius can be varied from 3.1 Å to 4.5 Å (see diagram below, showing the three compounds down the crystallographic c axis with channels shown as orange spheres and phenolic methyl groups lining the channel shown in purple).

The compounds are robust compared to other molecular porous materials, thought to be due to a combination of stabilisation by hydrogen bonding and stacking of the aromatic groups.  In combination with the tunability, this suggests potential use for guest exchange or in small molecule capture applications and further investigation of this is ongoing.

For more information see the full paper at:

Supramolecular materials with robust and tunable channels constructed from tin(IV)porphyrin phenolates
Shuang Wang, Craig Forsyth and Steven J. Langford
CrystEngComm, 2015,17, 3060-3063

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

Nitrobenzene is an important industrial material used in the production of aniline, dyes, pharmaceuticals and explosives.  However, it is highly toxic, considered likely to be a human carcinogen and does not readily degrade so accurate sensing of nitrobenzene in the environment, even at very low concentrations, is required.

A new paper presents a Cd-based metal-organic framework (MOF) as a highly selective and efficient sensor of nitrobenzene.  The MOF is based on a new flexible ligand with aromatic character, chosen to complement nitrobenzene’s electron withdrawing character.  The ligand, 1,1-(1,4-phenylenebis(methylene))bis(1H-pyrazole-3,5-dicarboxylicacid) and a source of Cd react under hydrothermal conditions to form the new Cd-MOF.

This shows a fluorescence emission when excited at 297 nm which is quenched by the presence of nitrobenzene (see diagram below).

The suggested mechanism of quenching involves photoinduced electron transfer. Quenching is inversely related to the concentration of nitrobenzene and significant quenching occurs at concentrations as low as 50 ppm nitrobenzene. Thus, Cd-MOF is suggested as a sensitive, rapid probe for low concentrations of nitrobenzene.

For the full paper see:

A new Cd(II)-based metal–organic framework for highly sensitive fluorescence sensing of nitrobenzene

Yu-Pei Xia, Yun-Wu Li, Da-Cheng Li, Qing-Xia Yao, Yu-Chang Du and Jian-Min Dou

CrystEngComm, 2015, Advance Article
DOI: 10.1039/C5CE00162E

__________________________________________________________________________________________________

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

Some crystals can deform on exposure to UV or visible light as a photoreaction proceeds during which the reactant and product are both present. This causes internal strain, which can result in crystals bending, jumping or twisting. For a well-defined response to occur, control of crystal size and shape are vital. Micron-sized crystals (microcrystals) are more likely to exhibit the desired behaviour, as larger crystals may shatter owing to the internal stresses produced.

A new paper outlines a method for producing uniform microcrystals. This is demonstrated by the synthesis of (E)-3-(anthracen-9-yl)acrylic acid (9-AYAA) from its t-butyl ester analogue by tumble mixing with phosphoric acid and a surfactant (sodium dodecyl sulfate, SDS). The size and shape can be controlled by the reaction temperature, concentration of phosphoric acid and SDS, the ester concentration and the mixing method. The optimised reaction conditions produce uniform 9-AYAA microwires, which undergo coiling (during the photoreaction) and uncoiling (as the reaction reaches completion) on exposure to 475 nm light, as shown in the figure below.

The new method involves an in-situ chemical reaction (acid hydrolysis) followed by re-precipitation and can also be successfully used to produce 9-AA (9-anthraldehyde) microplates under similar conditions. The authors attribute the success of their syntheses to the slow growth of the products and conclude the strategy could be used to produce microcrystals of uniform size and shape in other systems.

For more details, see the full paper at:

Chemical reaction method for growing photomechanical organic microcrystals
Rabih O. Al-Kaysi, Lingyan Zhu, Maram Al-Haidar, Muhannah K. Al-Muhannah, Kheireddine El-Boubbou, Tarafah M. Hamdan and Christopher J. Bardeen
CrystEngComm, 2015, DOI: 10.1039/C4CE02387K

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

Carbon dioxide (CO₂) can be reduced to give methane using light, in the presence of a catalyst. This process is attractive as it provides a potential feedstock for other processes as well as removing the greenhouse gas CO₂ from the atmosphere. The catalyst is key to the photoreduction, and ZnGaNO is a promising candidate as it is stable, environmentally friendly and absorbs light in the visible region, which is suitable for the reduction of CO₂.

A new paper reports the synthesis of ZnGaNO nanorods by molten salt ion exchange, which represents a milder method than that used conventionally. This involves use of ZnCl₂ as both a source of Zn and a molten salt. It is nitrided at 750 °C for five hours, along with KGaO₂, as represented below.

The as-prepared nanorods show enhanced performance as catalysts for CO₂ reduction. The rate of methane evolution is four times higher than that using ZnGaNO from solid state synthesis. As the photoreaction takes place on the surface of the catalyst, the larger surface area of the nanorods is thought to be significant. In addition, the nanorods possess a higher concentration of Zn ions owing to a lower synthesis temperature, which facilitates better energy absorption. There are also less surface defects in the nanorods, so recombination of carriers is disfavoured.

For more details, see the full paper at:

Molten salt ion exchange route to ZnGaNO single crystal nanorods for improved CO₂ photoreduction to CH₄
P. Zhou, S. C. Yan and Z. G. Zou
CrystEngComm, 2015, DOI: 10.1039/C4CE02198C

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

Control of the crystal form of pharmaceutically important molecules such as paracetamol is crucial to the successful development of drug molecules.  Conventional crystallisation from organic solvents can lead to unwanted forms with poor physicochemical properties.  Crystallisation from ionic liquids (ILs) offers a potential alternative.  ILs are composed entirely of ions and have low melting points as their cationic components are large and unsymmetrical, resulting in low lattice energies.

A new paper shows how the crystallisation of paracetamol, commonly used to reduce pain and fever, from ILs can be controlled.   Use of two ILs, 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF₆]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) was studied, under cooling crystallisation conditions.

The thermodynamically stable monoclinic I form of paracetamol was obtained from both ILs but the crystal size and shape varied with the IL used, the solution concentration and the mechanism of crystal growth.  One of the samples produced is shown below.

Crystal habits not commonly produced by conventional crystallisation could be produced – elongated prisms from [bmim][PF₆] and trigonal bipyramids from [hmim][PF₆]. These results suggest that ILs have potential value for the crystal engineering of pharmaceutically important molecules.

For full details, see the paper at:

Crystallisation control of paracetamol from ionic liquids

K. B. Smith, R. H. Bridson and G. A. Leeke

CrystEngComm, 2014, Advance Article
DOI: 10.1039/C4CE01796J

___________________________________________________________________________________________________

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

As the number of cars continues to increase, the problem of hazardous exhaust fumes such as nitrogen dioxide (NO₂) becomes more pressing.  New gas sensors are required to determine the quantities of these gases quickly and accurately.  These are often made of metal oxide semiconductors, including tungsten trioxide (WO₃), which are easily fabricated, low cost materials.  Nano-sized structures typically possess better gas adsorption properties than the bulk material due to favourable surface effects but particles of different shapes (morphologies) could also have different gas-sensing properties.

A new paper presents a method of producing three different morphologies of WO₃ nanostructures and studies their gas-sensing abilities.  In the simple hydrothermal synthesis, control of morphology is achieved using different amounts of citric acid, thereby changing the number of available carboxyl-groups.  This produces nanoparticles (0D), nanoplates (2D) and hierarchical microspheres (3D).  Among these 3 morphologies, the hierarchical structures are found to show the best gas-sensing properties towards NO₂ (see diagram below), with a high sensitivity, a fast response time and operating at a relatively low temperature (200^oC).

Authors conclude that this is due to an increased number of defects present in the structure which increases the number of gas adsorption sites on the surface, while their internal structure accelerates transport of the gas molecules to the sensing sites.

For more information, see the full article at:

Carboxyl-directed hydrothermal synthesis of WO₃ nanostructures and their morphology-dependent gas-sensing properties

Shouli Bai, Kewei Zhang, Xin Shu, Song Chen, Ruixian Luo, Dianqing Li and Aifan Chen

CrystEngComm, 2014, Advance Article
DOI: 10.1039/C4CE01167H

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.