Category: Chemistry

This week in The ChemWeb Alchemist, I report how Illinois chemists have developed a novel catalytic approach that side-steps functional group modifications to streamline organic syntheses. The Alchemist also discovers that a serendipitous finding leads to a bright spot in observing electron transfer in single molecules under the scanning tunneling microscope. While mixed signals appear in C&EN regarding the safety of bisphenol A.

In Africa, extracts of the leaves of the so-called hemorrhage plant could provide medical science with a new approach to faster, cleaner wound healing. Finally this week, upping the glucosinolate content of an entirely different group of plants, brassica crops, might not only help cabbage, broccoli, and cauliflower ward off pests and so save on pesticide use, but could also boost the cancer-fighting powers of these foods for people who eat them.

Speedy synthesis – University of Illinois chemists hope to meet the efficiency challenge in organic chemistry by exploiting a newly developed class of carbon-hydrogen catalyst. Christina White and her colleagues are creating a new chemical toolbox of highly selective and reactive catalysts that are tolerant of other functionality. “By offering fewer steps, fewer functional group manipulations and higher yields, this toolbox will change the way chemists make molecules,” White claims. A palladium/sulfoxide catalyst provides the team with a selective method for directly inserting nitrogen functionality into relatively inert C-H bonds without having to manipulate functional groups. The team has reported streamlined syntheses of various compounds, including a peptidase inhibitor drug candidate, a nucleotide-sugar L-galactose, and the chemotherapeutic reagent acosamine. She and her colleagues are currently applying the technology to synthesizing the antibiotic erythromycin A.

Read this week’s Alchemist for summaries and direct links to all featured chemistry news

In a past life I was deputy editor on the RSC journal Chemical Communications and recall the excitement and tension around the time we published Sir Harry Kroto’s pioneering fullerene paper. At the time, there were all kinds of imaginative plans emerging for what might be done with these odd all-carbon soccerball shaped molecules.

However, it was not the spherical, nor the spheroidal, fullerenes that became the darlings of materials scientists and nanotechnologists the world over. Instead it was their stretched cousins – the carbon nanotubes. Resembling a sub-microscopic roll of chicken wire, these long, hollow molecules have been touted as potential components for the future of microelectronics, as conducting connectors for nano devices, as catalysts and even as smart drug delivery agents.

Chemical scientists have developed various methods for synthesising nanotubes that are just a single atom thick, others that have a double wall, like two layers of rolled up chickenwire, all just a few nanometres in cross-sectional diameter. However, according to researchers writing in the International Journal of Nanotechnology (2007, 4, 618-633) there are no widely accepted techniques for producing useful quantities of short nanotubes of a specific length.

Simon Smart, G.Q. Lu, and D.J. Martin of the Australian Institute for Bioengineering and Nanotechnology, University of Queensland, Australia, and W.C. Ren and H.M. Cheng of Shenyang National Laboratory for Materials Science, of the Chinese Academy of Sciences, have now devised a production method for making shortened double-walled carbon nanotubes using by high-energy ball milling.

On the everyday scale of things, a ball mill is type of cylindrical grinder within which are loose balls (ceramic, steel, or flint pebbles, commonly) and to which is added the material to be milled. The ideal technique for shortening nanotubes has to have three characteristics, say the researchers. First, from a practical point of view, it should be able to produce gram quantities of individual samples. Secondly, it has to be able to shorten the nanotubes without significantly impacting on their purity of destroying the nanotubes entirely. Finally, the method has to be controllable so that it can shorten the nanotubes reproducibly and accurately.

Other researchers have attempted to shorten nanotubes using ultrasonic agitation, chemical cutting techniques, and ball milling. Ultrasound is not particularly controllable in terms of producing large quantities of nanotubes of a similar length while chemical methods are convoluted and can damage the nanotube walls. So, Smart and colleagues have focused on ball milling. This technique requires no chemical additives and can have a high throughput.

The team tested the shortened nanotubes using transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS).

The researchers now plan to use their ball-milled carbon nanotubes in novel polymer nanocomposite materials and to carry out toxicological studies. It should be possible to disperse these shorter nanotubes much more effectively in composite materials, explain the researchers, because they do not form bundles so readily as long nanotubes but would still endow the nanocomposite with novel strength and flexibility properties. “In fact, early results are showing that in polyurethane elastomers, the shorter nanotubes out perform the longer ones,” Smart told Sciencebase. He adds that, “These materials are most suited towards polymer nanocomposite materials. The presence of
carbonyl functional groups on the sidewalls does lend itself towards further chemistry and possible applications in drug delivery or sensing applications. However, at this stage of research, the ball milling process induces too many defects for use in applications that utilize the nanotubes
unique electronic properties.”

It’s a bumper summer special issue over on Reactive Reports, with an interview with Chemistry Central OA advocate Bryan Vickery and a stash of breaking chemistry stories

Reactive Profile–Bryan Vickery, Chemistry Central
Bryan Vickery did his BSc and PhD in electrochemistry at Liverpool University, England, but eschewed damaged jeans and fume cupboards for the world of electronic publishing.

 

 

Attractive Changing Colors  Yadong Yin and colleagues at the University of California, Riverside, have discovered that a simple magnet can be used to change the color of nanoparticles of iron oxide in aqueous suspension.

 

 

 

Fairytale Insulin Substitute  People with type I diabetes could one day be prescribed an extract from pumpkins that will drastically cut their reliance on daily insulin injections.

 

 

Multichannel Microchemical Factory 
In the mid-nineties, microchemistry was set to revolutionize the chemical industry.

 

 

No Munchies with Cannabinoid Antagonist  The pharmaceutical rimonabant latches on to the cannabinoid 1 (CB1) receptors in the brain and blocks their activity.

 

 

Contaminated Seabirds  A new approach to monitoring seabirds for contamination with polychlorinated biphenyls (PCBs) and other persistent organic pollutants (POPs) has been developed by scientists in Japan.

TL:DR – David Bradley Science Writer provides the molecular structure of bleach

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It seems to be something of an obsession with sciencebase.com visitors, but for some nothing would delight them more than to discover the systematic name for bleach, the chemical formula for bleach, the molecular structure of bleach, or to find a molecular model of bleach.

Well, the structure of bleach depends on what you mean by bleach. There are various kinds of chemical agents that will “remove” the colour from pigmented materials. Perhaps most commonly considered bleach is the liquid mixture that contain sodium hypochlorite (NaOCl, Na for sodium, O for oxygen, Cl for chlorine atoms). This is the active ingredient in the common household bleaches that “get right up under the rim” and “kill all known germs”. It is the “hypo” part of the name that gives it its bleaching properties without the O it would simply be sodium chloride or common salt, and if the O were in the wrong place – NaClO – we’d have sodium chlorite (a less powerful oxidising agent used to whiten textiles without harming cellulose fibres).

There are now several non-chlorine bleaches available for domestic use such as those containing hydrogen peroxide (H₂O₂), this material is well known as a bleach and often associated with people who allegedly have more fun). To the right you can see a simple molecular model of hydrogen peroxide.