Kinetic ambiguity, resolution

In order to determine optical purity, it is necessary to know [tto]. In natural product synthesis, the rotation of the target is usually known, but the original authors may not have established that the isolated material was enantiomerically and chemically pure. One course of action is to resolve a sample and measure [ad yourself. This may prove tedious, but it has the advantage of eliminating any ambiguities between sample and standard. Another possibility is to calculate [tto] by isotopic dilution or kinetic resolution. 

Neither the X-ray structural information nor the kinetic information in hand unambiguously resolves this question for any one of the enzymes for which high resolution structural information is available. This is partially a consequence of the ambiguity inherent in any attempt to construct a catalytic mechanism based primarily on a structural and/or chemical knowledge of stable (ground-state) enzyme-inhibitor or enzyme-quasisubstrate complexes. Note that these considerations are equally apropos to other physico-chemical techniques (e.g., UV-visible, IR, NMR, and ESR spectroscopic techniques) when applied to the investigation of those species detectable at equilibrium. Furthermore, the available kinetic information pertaining to the composition of the transition state(s) for the chemical step(s) is insufficient to allow the resolution of this question. 

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