Post Tagged with: "Angewandte"

Explosive Solutions

mercury azides

Instead of starting at the beginning of a paper I want to kick off this commentary with a statement from near the end:

Caution! Covalent azides are potentially hazardous and can decompose explosively under various conditions! Especially Hg2(N3)2, α– and β-Hg(N3)2, and [Hg2N]N3 in this work are extremely friction/shock-sensitive and can explode violently upon the slightest provocation. Appropriate safety precautions (safety shields, face shields, leather gloves, protective clothing) should be taken when dealing with large quantities. Hg compounds are highly toxic! Experimental details can be found in the Supporting Information.”

This wonderful statement appears in a recent publication by Professors Schultz and Villinger at the University of Rostock in Germany. They discuss the preparation of mercury azides and the azide of something called Millon’s Base. This compound was new to me and it turns out to be nitridodimercury hydroxide, [Hg2N]OH.2H2O, which Millon1 discovered by the reaction of mercurous oxide and ammonia in the mid 1800s. In a classic example of understatement the authors’ state that as is the case with most transition metal nitrogen compounds the extremely low energy barriers to explosive decomposition result in difficulties in the isolation and manipulation of said species! Curtius, of rearrangement fame, was apparently the first person to isolate mercury azide Hg2(N3)2 from the reaction of hydrogen azide and mercury2. I guess this was after the discovery of his famous rearrangement.

Structural data for this compound is available from x-ray and revealed two modifications, called α and β. Due to its lability the β modification has not been fully characterised. Schultz etal have now rectified this situation and also report the preparation of the azide salt, [Hg2N]N3 of Millon’s base. They prepared α & β-Hg(N3)2, the latter compound by slow diffusion of aqueous sodium azide into a solution of mercury (II) nitrate separated by a layer of aqueous sodium nitrate. In this synthesis one wonders how any yield was obtained because when the needles of β-Hg(N3)2 begin to form in the lower mercury(II) nitrate layer spontaneous explosions occur during crystal growth. If you want large crystals of either modification, usually obtained by slow crystallisation, I would not recommend it as apparently large crystals seem to explode when you look at them the wrong way, even in solution they detonate. Explosive solutions would be a great name for a company! Anyway, in spite of these difficulties an X-ray structure along with a melting point was obtained.

Turning now to the synthesis of the azide of Millon’s base the authors note that the normal method always produced a mixture of the two modifications. Pure α-[Hg2N]N3 was obtained by treatment of α-[Hg2N]Br with concentrated aqueous sodium azide for 300 days, so you need patience when dealing with these compounds, not only because they are explosive but they suffer from long reaction times. However starting with β-[Hg2N]NO3 the reaction was faster, only taking 4 days for the exchange with azide but produced a mixture of modifications. However, they did manage to obtain both modifications.

Elemental analysis could not be carried out due to their explosive nature and both modifications are sensitive towards heat, shock and especially friction. The bigger the crystal the more sensitive it is. However, slow heating in a DSC instrument showed that they are stable up to 283°C for the β form and 313°C for the α. Rapid heating in a closed vessel caused violent heavy detonation accompanied by a bright blue flash.

The paper has some fascinating x-ray pictures of all the molecules discussed and allowed determination of the N-Hg bond lengths. Together with the chemistry and the dangers involved in this chemistry, a great piece of work has evolved into a wonderful very readable paper. Congratulations to all who participated.

 

References:

1      E. Millon, J. Prakt. Chem. 1839, 16, 58.

2      T. Curtius, Chem. Ber. 1890, 23, 3023

A Chemist Doing Biology

My postdoctoral research has just begun (started 1.5 months ago) and it will heavily rely on using mice. Thus far I have imaged, dissected, injected, xenografted, castrated, you name it and I’ve already done it or will be doing it to mice. As chemists we are sheltered from the bloody side of science. Sure some chemists on the biological side may have done cell culture or a gel here and there, but most chemists don’t handle things that bite you while your injecting the nanoparticles you made to monitor the progress of the cancer you gave them weeks earlier. Because of this I will be making a series of posts tagged a Chemist Doing Biology chronicling my adventures into Biology.

Brief background: I am a Chemist not a Biologist, my PhD was equal measures of nuclear/radio-chemistry, materials chemistry, organic synthesis, and electronic circuit design (sigh). My new research group is all chemists even though we are in the Pharmacology department. My first task in the group, take the graduate student’s Gd-encapsulated nanoparticles and inject them into mice. Then extract the lymph nodes and get ICP-AES data. A daunting task for a chemist to accomplish, especially with no biologists in the group or anyone having in vivo experience.

Fortunately, I found a happy biology graduate student willing to take her research time to teach me how to do the injection/dissection of the poor mice. When the day arrives, the chemistry graduate student and I whisk the biologist down to the animal cages. We gown up, bring our nanoparticles and chemical reagents in a box, we show the biologist the mice and proceed to the procedure room. We give the mice anesthesia, hand the biologist our nanoparticles and hope for the best. It is at this moment where the disconnect between hardcore Biologists and hardcore Chemists becomes evident.

Biologist, “Can you hand me the syringe?”

Chemists, “They don’t keep the syringes in the procedural room?”

Biologist, “No. Where are your surgical tools, I thought you wanted to extract the lymph nodes?”

Chemists, “I thought you would bring the surgical equipment since you were going to show us how to dissect?”

Biologist, “That’s not how it works. All my mice are immune compromised, so I don’t want to risk using my equipment with wild type mice.”

Mitch to the chemistry grad student in my best postdoc voice, “Well, you better go find some equipment if you want to get your experiment done today.”

Grad student flies out in search of a miracle. I do my best to laugh off the situation with the biologist. The biologist is taking it well, but I was definitely embarrassed. After 10 minutes the chemistry graduate student returns with syringes, needles, scissors, and cutting blades.

Biologist picks up scissors, “These are not surgical scissors, these are to cut paper I can’t use these.” Looks at our cutting blades, “Is that a box cutter? That definitely won’t work on something as small as a mouse. You’re going to have to order real surgical equipment.”

Although that day went horribly wrong at least we learned what would be needed for the next attempt. Last month we used our new surgical tools and performed the dissection of the mice as we originally planned with the biologist. The data from that experiment is amazing and compliments the graduate student’s in vitro work beautifully. The paper is already done and waiting for the PI to submit to Angew.

Next Time: My first tail vein injection and the story of the fainting biologist.

Mitch

By July 6, 2010 10 comments in vivo chemistry

Most Popular Chemistry Papers 2010 (1/3)

There are finally enough people visiting ChemFeeds (~150/day) that metrics like most accessed chemistry paper might actually be statistically significant information. So below I present the top two most clicked on abstracts from ChemFeeds for the first third of 2010.

First Place: Emil Knoevenagel and the Roots of Aminocatalysis
by Benjamin List in Angewandte Chemie International Edition
(DOI: 10.1002/anie.200906900)

2nd Place: Total Synthesis of the N,C-Coupled Naphthylisoquinoline Alkaloids Ancistrocladinium A and B and Related Analogues
by Gerhard Bringmann, Tanja Gulder†, Barbara Hertlein, Yasmin Hemberger and Frank Meyer in Journal of American Chemical Society
(DOI: 10.1021/ja9097687)

Some Notes on the metrics. This information probably says more about the people visiting ChemFeeds than the quality of the papers. It would appear ChemFeeds visitors skewer heavily towards the organic synthetics. Perhaps with the recent addition of being able to click on category feeds like all materials and all physical feeds it’ll balance out.

Mitch

By May 1, 2010 2 comments chem 2.0

NanoPropulsion


Stephen J. Ebbens

Jonathan Howse

The current state of the art in nanopropulsion devices was recently reviewed by Ebbens and Howse in an article last Friday.[SoftMatter] A short summary of the nano- systems is presented below with video action shots when I could find them.

The Whitesides

Catalyst: Pt
Fuel: H2O2
Propulsion: Bubble propulsion
Terrain: Aqueous meniscus
Max Speed: 2 cm/s
Mitch’s Name: The Karl Benz (since it was the first)
Article: Autonomous Movement and Self-Assembly

The Sen-Mallouk-Crespi

Catalyst: Pt
Fuel: H2O2
Propulsion: Self electrophoresis/Interfacial tension
Terrain: Settled near boundary in aqueous solution
Max Speed: 6.6 um/s
Mitch’s Names: The Ford Mustang of nanopropulsion. (It is a hot rod, get it?)
Article: Catalytic Nanomotors: Autonomous Movement of Striped Nanorods

The Jones-Golestanian

Catalyst: Pt
Fuel: H2O2
Propulsion: Pure self diffusiophoresis
Terrain: Free aqueous solution
Max Speed: 3um/s
Mitch’s Name: The Volkswagen Beetle
Article: Self-Motile Colloidal Particles: From Directed Propulsion to Random Walk

The Mano-Heller

Catalyst: Glucose oxidase and Biliruben oxidase
Fuel: Glucose
Propulsion: Self electrophoresis
Terrain: Aqueous meniscus
Max Speed: 1 cm/s
Mitch’s Name: The Komatsu Truck (because it is huge)
Article: Bioelectrochemical Propulsion

The Feringa

Catalyst: Synthetic catalse
Fuel: H2O2
Propulsion: Bubble/interfacial
Terrain: Acetonitrile solution
Max Speed: 35 um/s
Mitch’s Name: The F150 (has some exhaust issues)
Article: Catalytic molecular motors: fuelling autonomous movement by a surface bound synthetic manganese catalase

The Sen-Mallouk

Catalyst: Pt (CNT) (+cathodic reactions at Au)
Fuel: H2O2/N2H4
Propulsion: Self electrophoresis
Terrain: Settled near boundary in aqueous solution
Max Speed: 200 um/s
Mitch’s Names: The Ford Mustang GT (has more kick than the regular version)
Article: Bipolar Electrochemical Mechanism for the Propulsion of Catalytic Nanomotors in Hydrogen Peroxide Solutions

The Feringa v2

Catalyst: Glucose oxidase and catalse
Fuel: Glucose
Propulsion: Local oxygen bubble formation
Terrain: Free aqueous buffer solution
Max Speed: 0.2–0.8 um/s
Mitch’s Name: The Chevrolet Nova (more hot rod action)
Article: Autonomous propulsion of carbon nanotubes powered by a multienzyme ensemble

The Gibbs-Zhao

Catalyst: Pt
Fuel: H2O2
Propulsion: Bubble release mechanism
Terrain: Aqueous solution
Max Speed: 6 um/s
Mitch’s Name: The Rover
Article: Autonomously motile catalytic nanomotors by bubble propulsion

The Bibette

Engine: External magnetic field
Propulsion: Flagella
Terrain: Aqueous solution
Max Speed: unknown
Mitch’s name: The BMW Mini E (because there is no such thing as a magnetic car)
Article: Microscopic artificial swimmers

The Sagués

Engine: External magnetic field
Propulsion: Doublet rotation coupling with boundary interactions
Terrain: Settled near boundary in aqueous solution
Max Speed: 3.2 um/s
Mitch’s Name: The Smart ED
Article: Magnetically Actuated Colloidal Microswimmers

The Fischer

Engine: External magnetic field
Propulsion: Propeller drive
Terrain: Aqueous solution
Max Speed: 40 um/s
Mitch’s Name:
Article: Controlled Propulsion of Artificial Magnetic Nanostructured Propellers

The Najafi-Golestanian

Engine: Conformation changes in linking units
Propulsion: Time irreversible translations
Terrain: Free solution
Max Speed: ?
Mitch’s Name: The Eternal Concept Car
Article: Propulsion at low Reynolds number



Some devices that were not included by the authors of the review article, but should definitely be included in any list like this are below:

The Gracias

Engine: External magnetic field
Propulsion: Brute Force
Terrain: Aqueous solution
Max Speed: ?
Mitch’s Name: The Truck Cranes
Article: Tetherless thermobiochemically actuated microgrippers

Tetherless Microgrippers Grabs Tissue SampleWatch today’s top amazing videos here

The Nelson

null
Engine: External electromagnetic fields
Propulsion: Flagella
Terrain: ?
Max Speed: 18 um/s
Mitch’s Name: The Tesla Roadster (simply awesome)
Article: Characterizing the Swimming Properties of Artificial Bacterial Flagella

Artificial SpermWatch more funny videos here




Link to Review Article: In pursuit of propulsion at the nanoscale

Mitch

By January 16, 2010 6 comments materials chemistry