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Is it possible to create a 100% identical copy of a chemical? For example, a 100% identical copy of vitamin A would have the same shape, the same formula, and the same structure.

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    $\begingroup$ With such a general question, I will give you the general question: "Yes." $\endgroup$ – Gimelist Oct 15 '14 at 12:02
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    $\begingroup$ define 'identical'. $\endgroup$ – permeakra Oct 15 '14 at 12:47
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    $\begingroup$ It is 100% possible to A) take something like naturally occurring vitamin A and purify it and B) synthesize vitamin A in a lab and purify it, and then C) mix up the two samples in such a way that nobody could figure out which was which. $\endgroup$ – Jason Patterson Oct 15 '14 at 13:11
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    $\begingroup$ Although with many biological molecules we have much more difficulty synthesizing just the one handedness that nature manages. But those with the correct chirality are just the same as any others. $\endgroup$ – Jon Custer Oct 15 '14 at 14:18
  • $\begingroup$ By identical i mean exactly the same, with exactly the same functions and side effects. $\endgroup$ – Konrad Oct 15 '14 at 15:43
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I agree with most of what the commenters and @jerepierre have written, with one or two exceptions.

Is it possible to create a 100% identical copy of a chemical?

If your question were asked in an introductory chemistry class, I believe most instructors would answer with a simple "yes", for the reasons outlined above. On the other hand, if your question were asked in an advanced chemistry class, or perhaps in a court of law, then I believe the answer would likely be "no". A frustrating dichotomy, but such is life.

Let me explain the "no" answer. To begin with, realize that simple molecules carry deuterium and $\ce{^13C}$ at levels found in natural abundance. Next, note that the way an organism would synthesize a vitamin, hormone, protein, etc., is likely different than the way a chemist might synthesize it in the laboratory. The differences would lie in the raw materials used in the process as well as the actual synthetic pathway.

Each step in a synthesis that requires breaking (or making) a carbon-hydrogen bond or a carbon-carbon bond will result in isotopic fractionation. Simply put, $\ce{C-H}$ bonds and $\ce{^12C-^12C}$ bonds are easier to break than the corresponding $\ce{C-D}$ bonds and $\ce{^13C-^12C}$ bonds. Therefore, if we repeatedly break some number of (they can be different or the same) C-H bonds and/or C-C bonds, then our final product will be enriched in molecules with lower deuterium and $\ce{^13C}$ content, the degree of enrichment being dependent upon the difference in the number of carbon-hydrogen and carbon-carbon bond breaking and bond making steps between the synthetic process as carried out within the organism and as carried out on the lab bench. There may be further fractionation if the starting material used by the body has required C-H and/or C-C bond making and breaking and has, therefore, also suffered isotopic fractionation. Such fractionation can easily be monitored through comparison of the mass spectra of natural and synthetic compounds.

In addition to this isotopic differentiation between synthetic and natural products, there will also exist a difference in reaction by-products and contaminants created in these two different synthetic processes.

Both methods (isotopic fractionation and by-product/impurity differences) could be used to determine if, for example, the testosterone in an athlete's body was produced naturally within the body or synthetically outside the body. Also, we are probably all aware of various reports were a synthetic version of a drug (often illicit, but not always) naturally produced by a plant or metabolite has produced death upon administration due to toxic by-products produced in the lab synthetic route - clearly a different side-effect profile.

So in answer to your question, no, it is not possible to synthesize a natural product in the lab that will be 100% identical to the same material produced in a living organism.

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    $\begingroup$ Excellent points as usual. $\endgroup$ – jerepierre Oct 17 '14 at 23:00
  • $\begingroup$ A very informative answer as usual. However, I feel like the correct or perhaps most inclusive answer should be that it depends on the molecule and method used to synthesize it. It seems possible to create many biomolecules by purifying the enzymes involved in the natural biosynthetic pathway. Surely then there would be no difference between the products created in vitro and in vivo. $\endgroup$ – canadianer Oct 18 '14 at 0:20
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    $\begingroup$ This argument can be applied equally to the natural world also, and isotopic analysis is a well-established and widely used technique to establish the origin and authenticity of many foods and plant-based produce, such as grapes, wines, oranges, olive oils etc. SNIF-NMR has been around for over 20 years, and many other NMR/GCMS methods are being developed.....con't. $\endgroup$ – long Oct 18 '14 at 0:49
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    $\begingroup$ ...By your argument (which makes a very good point), two identical species of grape on opposite sides of a country (or even the next valley) do not produce the same tartaric acid -See this paper as an example. One could argue that with so much variation in the natural world no two living organisms can produce identical compounds either. $\endgroup$ – long Oct 18 '14 at 0:50
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    $\begingroup$ @canadianer Good point! If the bench synthesis, using the actual biosynthetic enzyme, also used the identical biosynthetic starting material used in the natural process, then I agree with your statement. If the bench synthesis used a different starting material then the natural process uses, then isotope ratios in the two products will be different from each other. Whether they will be different enough to observe the difference I don't know, but they will be different. $\endgroup$ – ron Oct 18 '14 at 3:06
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If you are asking if a compound, such as vitamin A, can be resynthesized to give the same chemical structure, the answer is yes. That is routine and carried out naturally inside organisms and by chemists in the lab.

The effect that you suggest in the comment is more likely related to a different phenomenon. Most likely the sample is different if there is a different effect. It would be similar to eating a carrot versus taking a vitamin A pill. One could ingesting the same amount of vitamin A from either source, but the body might process them differently based on the other "stuff" in the sample. In the carrot, there's the rest of the plant. In the pill, there are excipients that are used to bind the material of the pill, make it shelf stable, and convenient to take.

When drugs are synthesized, they have to be made (and analyzed) following rigorous regulations to ensure that every sample of drug that goes out meets the specifications of the previous batch. Even though the active ingredient may be structurally identical to the previous batch, impurities must be within established specifications. The sample must have the same crystalline form so that it dissolves identically to prior batches. That's just one example of the lengths that chemists to through to replicate the composition of a sample, which in many respects is more difficult than replicating a chemical structure.

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