CrystEngComm Blog

Organic crystals with never-before-seen curved fractal structures have been discovered by researchers in China. They used the unusual shapes to design a dress, whose striking patterns won a national fashion competition.

Guoqing Zhang, Xuepeng Zhang and their team at the University of Science and Technology of China first intended to construct a series of organic ligands for water-based acrylic paints. By performing a routine Claisen condensation reaction between a ketone and an ester, they obtained a number of pyridine-substituted β-diketone compounds as fluffy crystals, with varying positions of nitrogen-substitution in the pyridine ring.

Interested? The full story can be read in Chemistry World.

The original article can be read below and is free to access until 9^th June 2017:

Curved fractal structures of pyridine-substituted β-diketone crystals
Zongzheng Qian, Dongxue Li, Tongqing Xie, Xuepeng Zhang,* Yang He, Yuejie Ai and Guoqing Zhang*
CrystEngComm, 2017, 19, 2283-2287
DOI:10.1039/C7CE00462A

The growth and design of organic crystals is often focused on linear regularity and the optical or electronic properties of the resulting crystals.  Crystallisation is influenced by many factors including the presence of interactions between atoms or groups of atoms.  However, when these are absent or insignificant, another kind of morphology can develop – the curved fractal.   A new paper by Zhang et al. looks at the formation of a curved fractal structure and shows an application of these beyond the scientific realm.

Fractals are defined by the existence of the similar patterns occurring independent of the level of detail observed e.g. as seen in Koch snowflakes.  A series of pyridyl diketones, with varying position of ring nitrogen and substitution, and a β-diketone were prepared and their properties compared.

The luminescent 1-(4-methoxyphenyl)-3-(pyridin-2-yl)propane-1,3-dione (PBDK1) showed, uniquely among the structures studied, a curved fractal structure visible using an electron microscope (seen below in fluorescence mode).  The highest curvature was observed for crystals obtained by evaporation from a solution in acetone at 5.0 mg mL⁻¹ or above, on glass.  Under these conditions, the relatively weak (compared with the 3- and 4-pyridyl analogues) potential intermolecular interactions in PBDK1 can be disrupted by surface tension effects.   This allows molecular slippage and dislocation to occur during crystal growth. The observed curved fractal pattern was transferred onto fabric and the design incorporated in a dress which won first place at the 2016 National Women’s Fashion Design Competition of China.

This work suggests some of the factors involved in the formation of curved fractal structures and also shows that interest in these extends beyond the scientific and into the realm of fashion design.

For more information, read the paper at:

Curved fractal structures of pyridine-substituted β-diketone crystals

Zongzheng Qian, Dongxue Li, Tongqing Xie, Xuepeng Zhang, Yang He, Yuejie Ai and Guoqing Zhang

DOI: 10.1039/C7CE00462A

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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 published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.

A new method of producing vanillin (3-methoxy-4-hydroxybenzaldehyde) from ferulic acid using a catalytic MOP has been reported.

Vanillin, one of the main chemical components of vanilla, is an important flavouring agent in the food, cosmetic and other industries.  However, although it can be extracted from vanilla pods, less than 1% of the required quantity is obtained in this way.  The remainder is obtained by chemical synthesis using strong oxidising agents and toxic solvents.  Biotechnological production is also possible but there are problems with time-scale, purification and the nature of the bacteria used.   There is, therefore, a demand for cleaner, greener methods of production of vanillin.

This paper reports the production of vanillin in 60% yield from ferulic acid and hydrogen peroxide, when a MOP (metal-organic polyhedron) is used as a catalyst.  Like MOFs (metal-organic frameworks), MOPs are constructed from metal ions and organic ligands but rather than forming frameworks, MOPs are discrete polyhedra. MOFs have been widely studied as potential catalysts but MOPs are practically untried.  Reasons for this include their relative lack of stability and tendency to aggregate.   This paper uses the MOP formed from copper(II) and a ligand from 9H-carbazole-3,6-dicarboxylic acid.  There are also coordinated dimethylformamide and water molecules in the structure.

The catalyst is activated by removing the coordinated solvent molecules by heating.  Ferulic acid and hydrogen peroxide are then reacted in the presence of the MOP.  Best results are obtained when the reaction mixture is sonicated (to reduce possible aggregation of MOP molecules).  A mechanism is proposed starting with coordination of peroxide to the active Cu(II) coordination site (schematically shown above).

The recovered catalyst exhibits a loss of crystallinity and after 5 cycles activity shows a decline.  However, the paper demonstrates the potential for the catalytic use of MOPs for the simple production of vanillin and other compounds.

For more details, read the full paper here:

Synthesis of vanillin via a catalytically active Cu(II)-metal organic polyhedron

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 published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.

 

Following the success of Peer Review Week in September 2016 (dedicated to reviewer recognition) during which we published a list of our top reviewers, we are delighted to announce that we will continue to recognise the contribution that our reviewers make to the journal by announcing our Outstanding Reviewers each year.

We would like to highlight the Outstanding Reviewers for CrystEngComm in 2016, as selected by the editorial team, for their significant contribution to the journal. The reviewers have been chosen based on the number, timeliness and quality of the reports completed over the last 12 months.

We would like to say a big thank you to those individuals listed here as well as to all of the reviewers that have supported the journal. Each Outstanding Reviewer will receive a certificate to give recognition for their significant contribution.

Professor Dino Aquilano, University of Torino
Dr Timur Atabaev, Seoul National University
Dr Ian Dance, Unversity of New South Wales
Dr Laszlo Fabian, University of East Anglia
Professor Huiging Fan, Northwestern Polytechnical University
Dr Goutam Kole, SRM University
Dr Mahesh Kumar, Indian Institute of Technology Jodhpur
Dr Zheng Ren, University of Connecticut
Dr Dongpeng Yan, Beijing Normal University
Dr Jiatao Zhang, Beijing Institute of Technology

We would also like to thank the CrystEngComm board and the Inorganic community for their continued support of the journal, as authors, reviewers and readers.

If you would like to become a reviewer for our journal, just email us with details of your research interests and an up-to-date CV or résumé.  You can find more details in our author and reviewer resource centre

Drugs are often prepared in crystalline form.  However, the relative thermodynamic stability of crystalline compounds can limit water solubility and bioavailability in the body.  An alternative is to make the drugs in an amorphous form that is less stable and more soluble.  Unfortunately, this form tends to revert to the crystalline form during manufacture, processing or storage, which can limit its usefulness.   A new paper by Aiguo Zeng et al., aims to increase understanding of the crystallisation of amorphous drugs, using loratadine (shown below) as a model compound.

Loratadine is a widely-available, non-sedating anti-histamine, used to treat hay-fever and other allergies.  It has been on the market since 1993 and is included in the World Health Organisation’s Model List of Essential Medicines.

Four amorphous samples were prepared by quench-cooling – where molten compounds are rapidly cooled so they have insufficient time to arrange into a crystal lattice.  Study of the samples obtained by cooling at 298 K, 277 K, 253 K and 233 K showed no significant differences in the crystallisation mechanism with quenching temperature.

However, the tendency to crystallise increased with decreasing quench-cooling temperature.  Authors attribute this to the differences in molecular mobility and relaxation of the samples, especially the so-called Johari-Goldstein process of loratadine, involving motion of all atoms in the molecule. This finding will allow the preparation of  loratadine with a lower tendency to crystallise but which retains the beneficial properties of the amorphous form.   It will also inform studies of the amorphous form of other drug molecules.

For more details, read the full paper at:

Ruimiao Chang, Qiang Fu, Yong Li, Mingchan Wang, Wei Du, Chun Chang and Aiguo Zeng  

CrystEngComm, 2017, Advance Article
DOI: 10.1039/C6CE01645F, Paper
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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 published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.

Many potential applications of metal-organic frameworks (MOFs) rely on the size and nature of the available free volume or pores within the framework structure.  These include use for gas storage or capture and catalysis.   Tuning of the pores is typically achieved by variation of the metal ions or organic ligands.  Lengthening the organic chains can lead to increased pore size but is often limited by a decrease in stability of the framework. A new paper by Yan-Zhen Zheng and colleagues at Xi’an Jiaotong University and the University of Arizona reports a new method of structurally modifying MOFs by insertion of alkali metal ions.

In a series of experiments, a heterometallic MOF with O-containing ligands was modified by the insertion of alkali metal ions into the coordination environment formed by two bridged lanthanide centres.  Initially, 2D or 3D Cu-Pr MOFs were formed with bridging isonicotinate ligands, by reacting isonicotinic acid, CuI and Pr(NO₃)₃ in a range of organic solvents.  The reaction producing one of these MOFs, {[Pr₃(Cu₄I₄)3(ina)₉(DMF)₄](DMF)}n (where ina is isonicotinato and DMF is N,N-dimethylformamide), was then repeated with the addition of NaCl, KCl, RbCl  or CsCl.

In the NaCl and KCl reactions, new MOFs were produced incorporating Na⁺ or K⁺ ions, with void volumes of 53% and 61%, respectively (compared with 10% for the alkali metal ion free MOF).

Reaction involving the next largest ion, Rb⁺, produced an unstable MOF which could not be studied further.  However, reaction with the larger Cs⁺ ion produced a new MOF which didn’t contain this ion, but with a void volume of 59%.

The authors suggest that their method of inducing structural variation using appropriately-sized alkali metal ions should be extendable to other ligand systems for the production of a variety of MOFs with novel structures and functions.

For more information, read the full paper at:
An alkali-ion insertion approach to structurally transform metal–organic frameworks
Yue-Qiao Hu, Mu-Qing Li, Teng Li, Yan-Yan Wang, Zhiping Zheng and Yan-Zhen Zheng
CrystEngComm, 2016, Advance Article
DOI: 10.1039/C6CE00540C
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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 published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.