Weird Words of Science 12: A need for speed

The nectar busily gathered by the bees outside my window has a high sucrose content. The bees add the enzyme invertase to the nectar to catalyze the inversion of the sucrose to glucose and fructose that are the major sugars in honey. Humans can speed up the same reaction by heating the syrup or by adding a touch of acid.

Both enzyme and catalysis are lofty words lifted by scientists in the 19th century to serve more prosaic ends.

Enzyme's first meaning in the bread used for the Eucharist in the Greek Orthodox tradition. It means "leavened". It's not such a stretch to borrow the word to describe stuff that encouraged cellular reactions to proceed, what had been called the ferment.

Catalysis was originally used to describe the collapse of a nation, its origins can be traced to the mid 17th century. It comes from the Greek "to loosen". In the 19th century, Berzelius suborned the term to describe the process by which chemical reactions are facilitated. Catalysts participate in a reaction, but are in the end are restored to their original form, like molecular Phoenixes. Why did Berzelius settle on this term? Did he hope to imply that the constraints which bound the reaction to a slow pace are loosened by a catalyst?

Turning Sugar Inside Out

This week's worksheet in general chemistry asks my students to analyze the chemical kinetics (the speed) of this reaction:

C₁₂H₂₂O₁₁ (sucrose or table sugar) + H₂O (water) -> C₆H₁₂O₆ (glucose) + C₆H₁₂O₆ (fructose).

It's called the inversion of sucrose, and the resulting mix of glucose and fructose is tagged invert sugar. The name suggests that table sugar has been turned inside out or perhaps upside down, but in fact it's simply been split into two simpler sugars. The inversion is not of the sugar itself, but of the way it bends polarized light. If you pass a beam of polarized light through a solution of regular table sugar, the light will "rotate" or bend to the left. The mixture of glucose and fructose "inverts" the rotation, and bends the beam to the right.

Invert sugar is less like to crystalize than regular sugar, making it ideal for sweetening candy or jams. The reaction in the absence of a catalyst is slow at room temperature, but can be completed . The simplest way to catalyze the reaction is with an acid, often citric acid or ascorbic acid (Vitamin C), and many jam recipes call for one or the other.

So why do these compounds "bend" polarized light? Like many biological molecules, they are chiral or handed. The right handed or D form bends the polarized light toward the right, the left handed form (denoted L) left.

---

Another name for the D form of glucose is dextrose, named for the direction in which it bends polarized light.

Dandelion Wine

At a party Saturday night someone mentioned a rumor about extracting illegal drugs from dandelions. This was news to me, I hadn't thought that dandelions had all that much to offer pharmacologically. Google didn't produce any hits, nor did my students know anything (though they did tell me that on MythBusters they'd made nitrous oxide from ingredients you could obtain at home). There is some evidence from rat models that dandelion extracts can interfere with antibiotic absorption (particulary those in the same class as ciprofloxacin), and it has potential for control of blood sugar, but I can't find anything in PubMed more interesting than that.

How did the leopard get it spots?

Biomorphogenesis, the process by which biological forms arise during development, is a fascinating area that crosses many fields, including computer science, mathematics, biology and chemistry. How do the stripes develop on a zebra? Alan Turing, one of the first computer scientists and the man who developed the computational engine that cracked the Enigma code in World War II, took on this problem in the early 1950s. In 1952 he published, "The Chemical Basis of Morphogenesis" [Phil. Trans. R. Soc. London B 1952, 237, 37-72]. He posits in this paper that oscillating chemical reactions, such as the Belousov-Zhabotinsky reaction, could lead to temporal-spatial differences in pigmentation. You can see why this might be the case in this animation of the reaction.

The BZ reaction is complex, the proposed mechanism consists of almost 20 steps - much more complex than those we are discussing in general chemistry this week! You can watch the BZ reaction in this video clip - the color changes look like magic.

pH Potpouri

The term pH has been in use for nearly a century. It is a logarithmic measure of the hydrogen ion concentration ([H⁺]): pH = -log₁₀[H⁺]. (Technically, there aren't bare protons (H⁺) floating around in solutions, but that's another post!) The original symbol was p_H. and introduced by Sörensen in 1909. Theories vary as to the origin of the p - all agree it means power but whether in Latin, French or German, seems in dispute. I would hazard it was either German or Latin as the original paper was published in German (Biochem. Zeitschr.). If I were not on the road, I'd look it up.

The modern form pH was introduced in 1920, "as a matter of typographical convenience".

Recyle, Reuse

A quick flip through my students' problem sets tells me more about them than just their ability to do quantum mechanics. My greener students make good use of the reverse side of the mountain of pages their colleagues print out every day. The paper drafts and announcements on the back side often catch my eye and offer a window into a student world I don't often get to see. Of course, recycling sheets for writing is hardly a new phenomenon. Palimpsests are parchment or vellum pages that have been erased by various methods and reused. The earlier, generally chemical, methods of erasure left faint traces of the original writing on the sheets. As methods improved, and relied more on mechanical means, such as sanding with pumice, the erasure became more complete.

In my quantum chemistry class we talked about fluorescence today. A common example of fluorescence is the odd luminescence of white t-shirts under a black light. The black light is a source of UV light, which excites some of the molecules in the detergent residue (yep - that bright white shirt is not quite as clean as you think!). The molecules then re-emit light at a slightly lower energy, which happens to be in the visible, and that we perceive as an eerie glow. The glow is present even in daylight, but the amount of visible radiation emitted through fluorscence is so much smaller than what is in incident sunlight that it swamps out the effect. But it does make your whites look subtly brighter, which is why detergent companies include "brighteners" in their formulations.

So what do white shirts have to do with palimpsests? X-rays are just another form of light (albeit very high energy light) and can cause fluorescence, too. Iron in the ink is the source of the fluorescence. Researchers at Stanford have recently uncovered not only an Archimedes manuscript hidden underneath a 13th century Byzantine prayer book, but also a text by Hyperides, a contemporary of Aristotle. The discovery of this text extends the known works of Hyperides by 20%!

A Request to Readers

In March I'm giving a talk at the American Chemical Society National Meeting in Chicago. To prepare for the talk, I'd like to know more about my audience beyond what I can get from technorati and StatCounter. If you're a regular reader, can you tell me what is interesting about this blog? Do you learn anything from it?

Thanks!

Half-awake, half-life

I had a moderate allergic reaction to peanuts last night. I took diphenhydramine (Benadryl) and the hives had subsided by this morning. Lecturing on perturbation theory was more challenging. I felt like I was walking in a fog. Which got me to wondering, just what was the half-life of Benadryl? Benadryl has a relatively long half-life, between 8 and 10 hours. A typical 50 mg dose leads to a peak blood level of around 80 nanograms/ml. Most people feel drowsy at blood levels around 30 nanograms/ml. Assuming first order kinetics apply to the breakdown/elimination of Benadryl, a 30 nanogram/ml is not unlikely 10 to 15 hours later. Which would certainly explain my fogged state this morning! But not so foggy as to be unable to work the kinetics....

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.