2015 Chemical & Engineering News article on the "shape" versus "vibration" debate notes that in the "acrimonious, nearly two-decade-long controversy...on the one side are a majority of sensory scientists who argue that our odorant receptors detect specific scent molecules on the basis of their shapes and chemical properties. On the other side are a handful of scientists who posit that an odorant receptor detects an odor molecule's vibrational frequencies". The article indicates that a new study, led by Block et al., takes aim at the vibrational theory of olfaction, finding no evidence that olfactory receptors distinguish vibrational states of molecules. Specifically, Block et al. report that the human musk-recognizing receptor, OR5AN1, identified using a heterologous olfactory receptor expression system and robustly responding to cyclopentadecanone and muscone, fails to distinguish isotopomers of these compounds in vitro. Furthermore, the mouse (methylthio)methanethiol-recognizing receptor, MOR244-3, as well as other selected human and mouse olfactory receptors, responded similarly to normal, deuterated, and carbon-13 isotopomers of their respective ligands, paralleling results found with the musk receptor OR5AN1. Based on these findings, the authors conclude that the proposed vibration theory does not apply to the human musk receptor OR5AN1, mouse thiol receptor MOR244-3, or other olfactory receptors examined. Additionally, theoretical analysis by the authors shows that the proposed electron transfer mechanism of the vibrational frequencies of odorants could be easily suppressed by quantum effects of nonodorant molecular vibrational modes. The authors conclude: "These and other concerns about electron transfer at olfactory receptors, together with our extensive experimental data, argue against the plausibility of the vibration theory." In commenting on this work, Vosshall writes "In PNAS, Block et al.... shift the "shape vs. vibration" debate from olfactory psychophysics to the biophysics of the ORs themselves. The authors mount a sophisticated multidisciplinary attack on the central tenets of the vibration theory using synthetic organic chemistry, heterologous expression of olfactory receptors, and theoretical considerations to find no evidence to support the vibration theory of smell." While Turin comments that Block used "cells in a dish rather than within whole organisms" and that "expressing an olfactory receptor in human embryonic kidney cells doesn't adequately reconstitute the complex nature of olfaction..." Vosshall responds "Embryonic kidney cells are not identical to the cells in the nose ... but if you are looking at receptors, it's the best system in the world." Challenges Despite numerous studies, docking theory has yet to discover structure-odor relations