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A number of carboxylic acids are used as cosmetics. Familiar to many readers will be glycolic acid. It’s used in over-the-counter “cosmeceuticals” to improve skin tone. Also used in professional “chemical peels” is trichloroacetic acid. These acids are all closely related to the familiar acetic acid, but they have “electronegative” substituents.

In the aqueous systems we’re talking about, the strength of an acid is related to its tendency to liberate protons. An acid’s tendency to dissociate into protons is related to the thermodynamic stability of its “conjugate base” - the acid, minus a proton. These electronegative substituents withdraw some electron density from the negative charge on the conjugate base, giving a more potent acid. Read the rest of this entry »

Here’s one many will have heard of - creatine. Most people know it as a bodybuilding supplement; it is used to add lean mass (from working out harder, and it’s contended, some intracellular water retention), as well as allow harder anaerobic workouts before failure. It’s the latter we’re interested in.

Creatine actually occurs endogenously, and it is synthesized by the liver. An enzyme called creatine kinase exists in the body to move a phosphate from ATP to creatine, making N-phosphocreatine and ADP. This reaction is not very thermodynamically favorable - you will only make 1 molecule of phosphocreatine for every 1000 molecules of ATP or so. This is good, because your body needs the ATP for other things (you’ve probably heard of ATP as the “universal energy currency” of the body) as well. Phosphorylation of creatine only happens when your body has a large excess of ATP.

The reverse reaction takes place too, and, as you might guess, phosphocreatine still would prefer to transfer its phosphate to ADP, regenerating ATP. It’s favored in the low-ATP regime - such as during the last repetition of a weightlifting set. This latter reaction is shown below:

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Early readers will remember that one of my favorite things about artificial sweeteners is that they seem to often be discovered by accident. Apparently acesulfame is no exception:

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This one is a much larger molecule than we usually do, but it’s easy to forget that enzymes (and all proteins) are really just very large molecules. Taq polymerase is a DNA polymerase (DNA-copying enzyme) from the microorganism thermus aquaticus, a bacterium that lives in very hot water. Read the rest of this entry »