Roguetheoryofsmellgetsaboost 1. Acontroversialtheoryofhowwesmell, whichclaimsthatourfinesenseofodourdependsonquantummechanics, hasbeengiventhethumbsupbyateamofphysicists. 2. CalculationsbyresearchersatUniversityCollegeLondon (UCL) showthattheideathatwesmellodourmoleculesbysensingtheirmolecularvibrationsmakessenseintermsofthephysicsinvolved. 3. Thatsstillsomewayfromprovingthatthetheory, proposedinthemid-1990sbybiophysicistLucaTurin, iscorrect. Butitshouldmakeotherscientiststaketheideamoreseriously. 4. Thisisabigstepforward, saysTurin, whohasnowsetuphisownperfumecompanyFlexitralinVirginia. Hesaysthatsincehepublishedhistheory, ithasbeenignoredratherthancriticized. 5. Mostscientistshaveassumedthatoursenseofsmelldependsonreceptorsinthenosedetectingtheshapeofincomingmolecules, whichtriggersasignaltothebrain. Thismolecularlockandkeyprocessisthoughttoliebehindawiderangeofthebodysdetectionsystems: itishowsomepartsoftheimmunesystemrecogniseinvaders, forexample, andhowthetonguerecognizessometastes. 6. ButTurinarguedthatsmelldoesntseemtofitthispictureverywell. Moleculesthatlookalmostidenticalcansmellverydifferentsuchasalcohols, whichsmelllikespirits, andthiols, whichsmelllikerotteneggs. Andmoleculeswithverydifferentstructurescansmellsimilar. Moststrikingly, somemoleculescansmelldifferenttoanimals, ifnotnecessarilytohumanssimplybecausetheycontaindifferentisotopes (atomsthatarechemicallyidenticalbuthaveadifferentmass)。 7. Turinsexplanationforthesesmellyfactsinvokestheideathatthesmellsignalinolfactoryreceptorproteinsistriggerednotbyanodourmoleculesshape, butbyitsvibrations, whichcanenourageanelectrontojumpbetweentwopartsofthereceptorinaquantum-mechanicalprocesscalledtunnelling. Thiselectronmovementcouldinitiatethesmellsignalbeingsenttothebrain. 8. Thiswouldexplainwhyisotopescansmelldifferent: theirvibrationfrequenciesarechangediftheatomsareheavier. Turinsmechanism, saysMarshallStonehamoftheUCLteam, ismorelikeswipe-cardidentificationthanakeyfittingalock. 9. Vibration-assistedelectrontunnellingcanundoubtedlyoccuritisusedinanexperimentaltechniqueformeasuringmolecularvibrations. Thequestioniswhetherthisispossibleinthenose, saysStonehamscolleague, AndrewHorsfield. 10. StonehamsaysthatwhenhefirstheardaboutTurinsidea, whileTurinwashimselfbasedatUCL, Ididntbelieveit。 But, headds, becauseitwasaninterestingidea, IthoughtIshouldproveitcouldntwork. Ididsomesimplecalculations, andonlythenbegantofeelLucacouldberight. NowStonehamandhisco-workershavedonethejobmorethoroughly, inapapersoontobepublishedinPhysicalReviewLetters. 11. TheUCLteamcalculatedtheratesofelectronhoppinginanosereceptorthathasanodorantmoleculeboundtoit. Thisratedependsonvariousproperties
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