| What an excellent article. For me, it's also a timely discussion in that a short while ago (from my records on August 19 2019) I was looking at the Wikipedia article on aspartame when I realized that there was a significant error on the page. The skeletal formula was correct but the ball-and-stick model was incorrect in that it had an extra hydrogen tacked onto the aspartic acid group—the NH2 was misrepresented as NH3. Being somewhat surprised at the error—as one would have thought that both representations would have been generated in the same software, Avogadro etc., thus the error should have occurred in both or not at all—so I dug a little deeper. I recalled that I had previously visited Wiki's Aspartame page some years back so I went looking to see if I had kept a copy of the page and sure enough I had saved it (it's not unusual for me to save Wiki pages). Anyway, upon reexamination of the earlier page, I found that the ball-and-stick formula was also incorrect therein. Clearly, I'd not noticed the error back then. The date of that earlier viewing was April 5, 2012, so the Wikipedia page has had that blatant error present for over 9 years—it could be much longer as I never checked when the page was originally posted! Given both its notoriety and controversy, how could such a large mistake exist in this Aspartame page for so long without anyone noticing it? I then tried to correct the error. I attempted to edit the page only to be informed that my domain was unacceptable and so I could not do so. I then resorted to contacting Wiki by other means and informing them of the error and they corrected fault within hours. If anyone has a reasonable explanation for why this error could exist so long on Wiki without being corrected then I'd love to know. Moreover, why would only the balls-and-stick be in error when it is normal for both representations to be generated on a common piece of software? Second Matter: "Searle patented this product, naming it Nutrisweet and Equal. Officially, aspartame has a half-life of about 300 days in solution at about pH 4, about the pH of soft drinks, but half life means that half if it as gone by that time. And if the cans are exposed to a hot storeroom or stored in a warm summer garage, they may deteriorate faster." I'd rarely have the opportunity to drink 'old' artificially sweetened drinks of this sort. First I don't drink many of them, and second, I only buy them in the supermarket where there's a very fast turnover of stock. That said, I find Diet Coca Cola unbearably sweet and almost undrinkable when its chilled and completely undrinkable when warm, the others, Zero etc., I find so sweet that they're undrinkable under any conditions. Could it be that drink manufactures are actually increasing sweetness past the so-called 'bliss point' to allow for the deterioration/aging of aspartame? Perhaps they're aiming for some 'ideal' or average date past manufacture where the maximum number of punters would likely be consuming the stuff. Does anyone know or have factual information about such matters? |
I am sure you meant well, but as far as I can see, the original ball-and-stick model was indeed correct--and the current edited version is wrong. Amino acids, as well as most things made from amino acids, exist as zwitter ions in solid form as well as in aqueous solution. The carboxyl groups are comparatively strong acids, the amino groups are comparatively strong bases, so there is a proton transferred to NH2, making it NH3+. That proton is missing from the carboxyl group resulting in a carboxylate group (COO-). The positive and negative charges cancel each other and the result is a zwitter ion with two charged atoms/groups, but no charge overall. The newer version still has a carboxylate group (COO-), but no NH3+ group, making it negatively charged. That probably exists, at high pH values.