The Sticking Point - or Weird Words of Science 11: Eutectic

It would be an understatement to say that my youngest son is not looking forward to his annual flu shot. Last week, the Philadelphia Inquirer had a piece on helping kids cope with the pain of immunizations. Son was not particularly impressed with the advice, but he noticed that they refered to a cream which could be applied to diminish the pain of injections. "What is it, Mom?" "EMLA, I think." "EMLA?" "A eutectic mixture of local anesthetics..." Somewhere around mixture, I think I lost him!

What is a eutectic mixture? Eutectic comes from the Greek eutektos for "easily melted"(any resemblence to tectonic is, I believe, purely accidental - tectonic also comes from the Greek, but for building, not melting!). An eutectic mixture is one in which the melting point of the mix is lower than the melting point of either of the components. The binary phase diagram has a "eutectic point". EMLA is a mixture of equal weights of lidocaine and prilocaine, made into an emulsion.

It's apparently quite effective, but requires a lead time of several hours (and the foresight to ask the pediatrician for a prescription!).

"What was to be demonstrated" needed to be demonstrated!

A student in my office hours today asked me what the term QED meant at the bottom of a page, and got a (very short) lesson in Latin. Quod erat demonstrandum, "what was to be demonstrated", is a translation of the Greek hoper edei deixai used by Euclid to close a proof. Modern mathematical publications often substitute other symbols, including a  or simply note: proven.

Orion brandy anyone?

I'll admit to being a Trekkie at some time in my life, but Dr. McCoy's stash of Saurian brandy aside, there is alcohol in interstellar space. More than 120 molecules and ions -- including ethanol -- have been identified by radioastronomers in interstellar space. The transitions between different molecular rotational states give rise to very specific lines, which can be used as molecular fingerprints.

The lines which helped identify ethanol are rotations around the carbon-carbon single bonds, rather like little propellers turning. The lines arise from vicinity of the Orion Nebula (a mere 1500 light years away), which can be seen just under Orion's belt.

Isotope Counts

In my quantum chemistry class we are exploring molecular vibrations. The characteristic frequency of vibration depends on the masses of the atoms in the vibrating bond. Not every student in my class is a chemist, a fact that was driven home when I assigned a problem asking students to compute the fundamental vibrational frequency of an molecule with a deuterium atom.

Most elements have several naturally occuring isotopes - forms of the element which have the same number of protons,but varying numbers of neutrons. For example, the most abundant form of the element carbon has a mass number (the sum of the number of protons and neutrons) of 12. One percent of carbon atoms, however, have an extra neutron and a mass number of 13. Carbon-14 has two extra neutrons, and is radioactive. Chemists often use isotopic substitution as a way to "tag" molecules (particularly if the isotope is radioactive).

Deuterium is an isotope of hydrogen - much of its chemical behavior is exactly the same as that of hydrogen,it just weighs more, twice as much to be precise. Unlike other elements, where the isotopes are designated by their usual name plus their mass number, isotopes of hydrogen get their own names. Deuterium has a mass number of 2, tritium a mass number of (surprise) 3. Tritium is radioactive and has a half-life of around 12 years.

In 1955, in his novel "The Mouse that Roared", Irish writer Leonard Wibberly coined "quadium" for hydrogen-4, which at the time had not been made. Since then, hydrogen-4 has been created. It is a fleeting species, its half-life is just over 10^-22 seconds!

Strands of Life

The Nobel prize in medicine and physiology today went to two American scientists, Andrew Fire and Craig Mello, for their work on gene silencing and double-stranded RNA. When we think double-stranded, we often think of another pair of Nobel laureates (Watston and Crick) and a related molecule, DNA. RNA indeed is typically single-stranded, and uses a modified set of bases relative to DNA, subsitituting uracil for thymine. (Wikipedia has a nice diagram.)

The double-stranded version, dubbed RNAi, interferes with the decoding of genes in cells, hence the "gene-silencing" tag.

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A colleagues hazards that Nobel winners are getting younger every year. Is it because the time between discovery and award is shrinking or is it that younger scientists are making more critical discoveries?