Chemical Science Blog

Scientists in Germany have prepared gold conjugates with mitochondria-localising peptides. Using these conjugates, the team studied the mechanism of action of gold-based anti-cancer drug candidates.

The team showed that the conjugates were able to break resistance against the commonly used anti-cancer drug cisplatin in p53 mutant cells lines.

Link to journal article
A Spontaneous Gold(I)-Azide Alkyne Cycloaddition Reaction Yields Gold-Peptide Bioconjugates which Overcome Cisplatin Resistance in a p53-Mutant Cancer Cell Line
S D Koster et al
Chem. Sci., 2012, DOI: 10.1039/c2sc01127a

US scientists have used inorganic nodes in metal-organic frameworks (MOFs) as chelating ligand platforms for unusual coordination chemistry; using a MOF’s secondary building units for coordination chemistry is virtually unexplored.

They used the Zn₄O secondary building units of the well known MOF-5 (Zn₄O(1,4-benzenedicarboxylate)₃) as tripodal chelating ligands and kinetically trapped a Ni²⁺ ion in an unusual tetrahedral all-oxygen ligand field. In doing so, they also demonstrated that MOFs can serve as veritable platforms for synthesising inorganic clusters (i.e. a NiZn₃O(carboxylate)₆ unit) that have no analogues in molecular chemistry.

Link to journal article
Lattice-Imposed Geometry in Metal-Organic Frameworks: Lacunary Zn₄O Clusters in MOF-5 Serve as Tripodal Chelating Ligands for Ni²⁺
C K Brozek and M Dinca
Chem. Sci., 2012, DOI: 10.1039/c2sc20306e

Carbon-based drug delivery vehicles such as carbon ‘nano-needles’ have the potential to eliminate the severe side-effects caused by platinum anticancer drugs, but scientists have found it difficult to control the drug’s containment and release. Cisplatin is hydrophilic so trying to contain it within a nanotube’s hydrophobic interior is difficult – the drug readily gets replaced with water. Conversely, strongly hydrophobic-hydrophobic interactions between a drug and the nanotube may prevent the drug’s efficient release.

Scientists from Singapore have trapped a strongly hydrophobic Pt(IV) prodrug in carbon nanotubes and have shown that chemical reduction causes a dramatic reversal in hydrophobicity to release the active Pt(II) complex.

Link to journal article
Platinum(IV) prodrugs entrapped within multiwalled carbon nanotubes: Selective release by chemical reduction and hydrophobicity reversal
J Li et al
Chem. Sci., 2012, DOI: 10.1039/c2sc01086k

Scientists in Germany have made a new mesoporous material (carbon nitride nanorods) that can chaperone metal nanoparticles. The hybrid nanorods are catalytic and were shown to successively trigger water reduction to form hydrogen then activation of the hydrogen to reduce nitrophenol. The nanorods could potentially be used as a matrix for other nanoparticles, leading to a variety of applications.

Link to journal article
Mesoporous g-C3N4 nanorods as multifunctional supports of ultrafine metal nanoparticles: hydrogen generation from water and reduction of nitrophenol with tandem catalysis in one step
X-H Li, X Wang and M Antonietti
Chem. Sci. ,2012, DOI: 10.1039/c2sc20289a

Scientists in Australia, China and Canada have made new photocatalysts that, in the presence of sunlight, can oxidise stable compounds such as toluene using oxygen at room temperature. Oxidation of toluene to commercial chemicals is a major industrial process, but it is conducted under high temperatures and oxygen pressures, or requires recovery of homogeneous cobalt catalysts.

The new photocatalysts work via a mechanism that is different from those of any known photocatalysts: the surface complexes are anchored on the surface of metal hydroxides by chemical bonds and can absorb light generating free radicals on the surface. These then initiate aerobic oxidation of the stable alkyl aromatic molecules. So, they can use sunlight to drive the production of fine organic chemicals in an efficient, green and chemoselective manner.

Link to journal article
Driving Selective Aerobic Oxidation of Alkyl Aromatics by Sunlight on Alcohol Grafted Metal Hydroxides
S Sarina et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20114c

Systems chemistry focuses on achieving controllable outputs from the interactions and reactions of a mixture of chemical components. In this way, researchers hope to mimic biological systems, which utilise highly complex series of interconnected signalling processes and feedback loops to respond to a wide range of external stimuli.

Christoph Schalley’s group in Berlin have reported a fascinating example of supramoleular systems chemistry, using a range of non-covalent interactions and self assembly properties of a simple bis-urea starting molecule. Like many bis-ureas, 1 was found to form an organogel due to hydrogen bonding interactions between the urea groups on adjacent molecules. Disrupting these interactions reverses the gel formation, leaving a sol phase. In this case, the authors found three different chemical input signals to switch the gel to a sol: adding chloride anions to hydrogen bond to the urea groups, adding potassium cations to bind within the crown ether groups, and by adding the ammonium threads 2 (2 equivalents) or 3 (1 equivalent) to form a rotaxane.

Each of these binding processes can also be reversed by chemically removing the guest, regenerating the gel phase. Silver cations were used to precipitate the chloride, a cryptand was added to tightly bind to the potassium, and the rotaxane threads were deprotonated using a base. In this way, a large number of input signals were used to yield a controllable and observable chemical property. These processes were used to construct various logic gates, in which a logic output (the formation or dissolution of a gel phase) resulted from one or more logic inputs (the addition of one or more of the above reagents).

This work uses host guest chemistry to produce real-world, observable results from a large number of chemical input signals. It is an inspiring example of how simple binding processes can be incorporated into complex sequences and systems. You can download the full article here.