Chemical Science Blog

Potential energy surfaces of reactions are usually measured in the gas phase. However the vast majority of chemical reactions in the laboratory are conducted in solvent. What effect do these solvent molecules have on the potential energy surfaces that have been measured in the gas phase? Andrew Orr-Ewing and colleagues have been finding out.

They have used ultrafast time-resolved broadband infra-red absorption spectroscopy to study the reaction of chlorine atoms with hydrocarbons in chlorinated solvent.

Two timescales were found, which corresponded to prompt reaction of the chlorine atom with the hydrocarbon, which was most likely located in the immediate solvent shell, and a slower reaction following diffusion into the bulk solvent. The presence of solvent molecules also partially suppresses the presence of vibrationally excited products that occur when the exothermic reaction is sufficient to form vibrationally hot products.

This work extends previous experiments conducted with cyanide radicals in solvent and general conclusions on the effect of solvent molecules on the potential energy surface are now emerging.

To find out more, download the Chemical Science article today (free to access until the 7th of December 2012).

A new and efficient way to make β-lactams, the key components of common antibiotics such as penicillin, has been developed by US scientists.

The team made the β-lactams from simple aldehydes via a multi-component catalytic asymmetric aziridination reaction. The reaction is high-yielding, stereospecific and diastereoselective. It should aid new drug discovery.

Read the Chemical Science article in full:

Multifaceted Interception of 2-Chloro-2-Oxoacetic Anhydrides: A Catalytic Asymmetric Synthesis of b-Lactams
L Huang et al.
Chem. Sci., 2012, DOI: 10.1039/c2sc21240d

Unlike conventional electromagnetic interactions, the chemical bond has not been quantified in strength by any known property of the participating species, until now.

Scientists in China say that bond energy (EAB), a quantitative measure of the bond strength, can be decoupled into two contributions of the participating reactants, which is a new principle.

The team verified their theory with more than 300 bonds, including covalent bonds in molecules and adsorption bonds on metal surfaces; this can be applied in a wide range of chemical reactions. Particularly, the characteristic complex quantity, termed ‘chemical amplitude’ can be used to describe accurately the chemical reactivity of both molecules and metal surfaces, which is an advantage when studying heterogeneous catalysis.

The work should allow scientists to make a direct evaluation of the bond energy and also reveal new aspects of the chemical interaction, they say.

Read this ‘HOT’ Chemical Science Edge Article:

Bond-Energy Decoupling: Principle and Application to Heterogeneous
Catalysis Bing Huang , Lin Zhuang , Li Xiao and Juntao Lu
Chem. Sci., 2012, DOI: 10.1039/C2SC21232C

US scientists have reported a new method to create antibody mimics that could be used to make new and improved therapeutics.

Fusion proteins contain segments derived from two or more different precursors. The proteins allow multiple biological functions to be combined in a single entity. The most successful fusion protein therapeutics contain the crystallisable fragment (Fc) region of antibodies. But they are not easy to make and modify. The team has come up with two strategies to modify antibody Fc fragments using chemical modification, leading to the creation of novel Fc-synthetic molecule hybrids.

The strategy also allows Fc domains to be used as building blocks that can be appended to virtually any class of synthetic molecules. This allows the pharmacokinetic improvements imparted by Fc to be used in many different drug delivery contexts, and could add potential immunological function to many different constructs.

Read the ‘HOT’ Chemical Science article today:
Synthetically Modified Fc Domains as Building Blocks for Immunotherapy Applications
C Netirojjanakul et al, Chem. Sci., 2012, DOI: 10.1039/c2sc21365f

A stimuli-responsive system that brings chemists one step closer to mimicking the complexity of biological networks has been developed by scientists in the UK, Australia and the US.

Biological systems are complicated as they can produce multiple responses to stimuli at the same time. The team says that the key to unravelling the origin of life may come from studying the complex interactions of molecules.

They have discovered a self-assembled cage molecule that consists of a system of interconverting diastereomers in solution. When anionic guest molecules are added, the system adapts, expressing a new combination of diastereomers that synergistically bind the guest molecules. Not only do the cage diastereomers interconvert, the volume of the individual cages adapts physically through the rotation of bonds, providing a tailored binding pocket for the guest lined with hydrogen-bond donors.

This two-fold adaptation is a feature of the responses to external stimuli displayed by biological systems, something that has not previously been observed in synthetic systems. Complex and functional synthetic systems of this type will lead to the design of more effective systems for host-guest recognition and the development of systems approaching the complexity of those that exist in nature.

Read the ‘HOT’ Chemical Science article today:

A Stimuli Responsive System of Self-Assembled Anion-Binding Fe₄L₆⁸⁺ Cages
Jack Kay Clegg, Jonathan Cremers, Andrew J Hogben, Boris Breiner, Maarten M. J. Smulders, John D. Thoburn and Jonathan Nitschke
Chem. Sci., 2012, DOI: 10.1039/C2SC21486E

Viable alternatives to fossil fuels are a vital area of research for chemists as current deposits dwindle. To combat our reliance on these fuels, US scientists have discovered a new route for turning the carbohydrate cellulose – the most abundant organic molecule on Earth – into 5-(hydroxymethyl)furfural (HMF), a promising precursor molecule to alternative fuels.

Whereas conventional methods for converting carbohydrates into HMF have involved the use of harsh reaction conditions and toxic heavy metal catalysts, the route proposed by Ronald Raines and co-workers at the University of Wisconsin-Madison uses a one-pot, low temperature approach that utilises less toxic organocatalysts instead.  

Converting cellulose to HMF is a three-step process. It consists of hydrolysis of cellulose to glucose, isomerisation of glucose to fructose and dehydration of fructose to HMF. The hardest step is the transformation from glucose to fructose and it is difficult to achieve this without using a catalyst. So, the team used a phenylboronic acid organocatalyst combined with magnesium chloride and mineral acids to get HMF in yields of up to 54%, a yield comparable to using toxic heavy metal catalysts. Phenylboronic acids have some catalytic activity, but the magnesium chloride and mineral acids are needed to boost the efficiency of the conversion process.

View the whole Chemistry World article…

Read the Chemical Science paper in full:

Organocatalytic conversion of cellulose into a platform chemical
Benjamin R. Caes , Michael J. Palte and Ronald T. Raines
Chem. Sci., 2013, DOI: 10.1039/C2SC21403B

A new way to make 2-arylphenols, which are found in organocatalysts, sensors, phosphite ligands, and biologically active substances has been devised by scientists in the US.

Simple and cheap aryl chlorides can be used to directly arylate unprotected phenols without transition metals. This is the first general, regioselective intermolecular phenol ortho-arylation process that uses aryl chlorides as one of the coupling components. It is the most direct synthetic pathway to 2-arylphenols – no protecting group manipulations are required.

The team also made arylated binaphthol derivatives. Additionally, they have presented the shortest pathway to date for the synthesis of helicenes – one step from commercially available reagents.

Read this ‘HOT’ Chemical Science article today:

Divergent Reaction Pathways for Phenol Arylation by Arynes: Synthesis of Helicenes and 2-Arylphenols
T Truong and O Daugulis
Chem. Sci., 2012, DOI: 10.1039/c2sc21288a