ChemicalYearInReview3Word文档下载推荐.docx
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ChemicalYearInReview3Word文档下载推荐.docx
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1.SurpriseFromSN2Snapshots
Byanalyzingsnapshotsofsingle-moleculecollisions,aninternationalresearchteamuncoveredunanticipateddetailsaboutthemechanismoftheclassicbimolecularnucleophilicsubstitution(SN2)reaction(C&
EN,Jan.14,page9;
Science2008,319,183).InadditiontoprovidingdirectevidenceforthetraditionalSN2mechanisminthegasphase,RolandWesterandcolleaguesattheUniversityofFreiburg,inGermany,togetherwithWilliamL.HaseandcolleaguesatTexasTechUniversitydetectedanadditionalunexpectedpathway.Inthis"
roundaboutmechanism"
thenucleophilebumpsintothesubstrate,spinningthesubstrate360º
beforesubstitutionandleaving-groupdisplacementoccur.Tovisualizethesedetails,theFreiburgteamcrossedbeamsofreactantsinavacuumanddetectedthedirectionalandspeeddistributionsoftheproducts.Thedatasuggestedatleasttworeactionmechanisms,oneofwhichisthetraditionalSN2pathway.Atomic-levelchemicaldynamicssimulationsbytheTexasTechscientistswereinaccordwiththatconclusion,buttheyalsodiscoveredthatsomedatawereduetotheroundaboutmechanism."
Beforeperformingthesimulationswewouldneverhavethoughttheroundaboutmechanismwasinplay,"
Hasesaid.Theseresults"
challengesomeofourcherishedmodelsofelementaryreactionmechanisms,"
saidBenjaminJ.Whitaker,areactiondynamicsexpertattheUniversityofLeeds,inEngland.
2.PeekingAtCatalyticReactions
Withanewnuclearmagneticresonanceimagingtechnique,researcherswereabletogetaneyeoncatalytichydrogenationreactionstakingplaceinsidemicroreactors(C&
EN,Jan.28,page13;
Science2008,319,442).Thescientistsexpectthemethodtobeusefulforstudyingandoptimizingindustrialcatalystsandcatalyticreactors.AlexanderPines,Louis-S.Bouchard,andcoworkersatLawrenceBerkeleyNationalLaboratoryandtheUniversityofCalifornia,Berkeley,developedthemethodbytakingadvantageoftheparaformofhydrogen(p-H2)toamplifytheNMRsignalofpropanemadebythehydrogenationofpropene.Onitsown,p-H2hasnoobservableNMRsignal,butinahydrogenationreactionthepairedhydrogenatomsbecomemagneticallyinequivalent,resultinginanenhancedNMRsignal.Theresearchersusedthemethodtomappropaneformationandtherebypinpointactiveregionsinthemicroreactorcatalystbed.
3.MeasuringAtomicFriction
Forthefirsttime,scientistsdeterminedtheforcesneededtomoveasingleatomacrossasurface.Withthisadvance,it'
snowpossibletoquantifyfrictionattheatomiclevel.Knowinghowtightlyanatomoramolecule"
sticks"
toasurfacewillbeinvaluableinnanoelectronicsdesignandinbioengineering.AndreasJ.HeinrichandMarkusTernesofIBM'
sAlmadenResearchCenter,inSanJose,Calif.;
physicsprofessorFranzJ.GiessibloftheUniversityofRegensburg,inGermany;
andcolleaguesusedamodifiedatomicforcemicroscopeatultrahighvacuumandatemperatureofonly5Ktomeasureboththelateralandverticalforcesexertedonacobaltatomandcarbonmonoxidemoleculeasthemicroscopetipdraggedthemacrossaplatinumorcoppersurface(C&
EN,Feb.25,page6;
Science2008,319,1066).Sincethe1990s,manygroupshavesucceededinmanipulatingsurfaceatoms,butmeasuringtheforcesassociatedwiththatmovementissomething"
wealldreamedabout,"
saidLudwigBartels,achemistryprofessorattheUniversityofCalifornia,Riverside.
4.
MolecularTargetForDEETDiscovered
SinceWorldWarII,peopleacrosstheglobehaveliberallyappliedN,N-diethyl-m-toluamide,betterknownasDEET,towardoffmosquitoesandotherinsectsthatnotonlyareannoyingbutcantransmitdiseases.ButnooneknewexactlyhowthemostcommonlyusedactiveingredientintopicalbugrepellantsworkeduntilLeslieB.VosshallandcolleaguesatRockefellerUniversityreportedthatDEETinhibitscertainmosquitoandfruitflyolfactoryreceptors(C&
EN,March17,page42;
Science2008,319,1838).PreviousworkbyotherresearchershadshownthatDEETaffectsinsects'
abilitytosniffouthumanodors,suchasthosecausedbylacticacid.ButVosshallandcolleagueswerethefirsttopinpointDEET'
smoleculartargets:
olfactoryreceptorsthatformacomplexwithacoreceptorcalledOR83b.Tofindthesereceptors,theresearcherscombinedageneticapproachwithaninvitroreconstitutionofinsectodorantreceptors.KnowinghowDEETaffectsreceptorscouldleadtonewinsectrepellentsthat,forexample,couldmoresafelybeusedonyoungchildren.
5.ImagingTechniqueTracksSugarsInLiveAnimals
Itisnowpossibletoimagecarbohydratesastheyareproducedoncellsurfacesofliveanimals,thankstoaresearchteamattheUniversityofCalifornia,Berkeley(C&
EN,May5,page8;
Science2008,320,664).Cellglycans(oligosaccharides)arekeymarkersandmediatorsofmanyphysiologicalprocesses,butpreviouslytheycouldn'
tbevisualizedinlivingorganisms.CarolynR.Bertozziandcoworkersfedazide-derivatizedsugarstozebrafish,whichincorporatedthemodifiedsugarsintotheirglycans.Theresearchersthenuseddifluorinatedcyclooctynereagentswithattachedfluorescentprobestomarktheglycanssotheycouldbevisualizedbyopticalimagingtechniques.Theapproachmakesitpossibletoobservepatternsofglycanexpressionthatpreviouslywouldhavebeenundetectable.Thescientistsdemonstratedthemethodbyusingittodetectchangesinglycanbiosynthesisinspecificlocationsinlivezebrafish.Theabilityofthemethod"
todeterminehowglycansaredistributedspatiallywithinatissueandintimecanhelptorevealtheirfunctionalrolesandtoidentifycell-surfacemarkersindicativeofthephysiologicalstatusofcells,"
commentedglycan-imagingspecialistMaryL.KraftoftheUniversityofIllinois,Urbana-Champaign.
6.Two-For-OneCatalyst
Byentrappingasolublerhodiumcomplexinsideaporousmatrixofsilveratoms,ateamofIsraelichemistsinitiatedanewapproachtoheterogeneouscatalysis(C&
EN,Sept.1,page9;
J.Am.Chem.Soc.2008,130,11880).Chemistsoftenharnesssolublehomogeneouscatalystsforsurface-basedheterogeneousreactionsbyfixingthecatalystonanorganicpolymeroraninorganicoxidesuchassilica—materialsthatarenonconducting.Thecatalyst-in-metalcompositedevelopedbyItzikYosef,RaedAbu-Reziq,andDavidAvnirofHebrewUniversityofJerusalemmarksthefirsttimeahomogeneouscatalysthasbeen"
heterogenized"
inaconductingmaterial.Trappingtherhodiumcomplexina"
seaofelectrons"
enhancesitscatalyticactivity,presumablybyalteringitselectrondonor-acceptorpropertiesandmodifyingsubstratebinding.Tomakethematerial,theresearchersaddedzincpowdertoasolutioncontainingarhodiumphosphinecyclooctadienecatalystandsilvernitrate.Thezincreducesthesilvercations,andassilvercrystallitesform,theyaggregateandprecipitateoutofthesolution,takingthecatalystwithit.Thiscatalystentrapmentprocess"
isawatersheddevelopmentinscience,"
commentedorganometallicchemistHowardAlperoftheUniversityofOttawa.Sincetheoriginalreport,Avnir'
sgrouphasusedthetechniquetoentrapanacidicpolymerinsilverasanacidcatalyst,entrapactiveenzymesinsilverandingold,anddopesilverwithdifferentreagentstoimproveitscatalyticperformance.
7.
Peptide-ProducingPowerhouses
Whenbacteriawanttobuildintricatepeptides,theyemploymegacatalystscallednonribosomalpeptidesynthetase(NRPS)enzymes.Justoneoftheseenormousassembly-lineenzymescanpossessasmanyas40catalyticsites,locatedinsequentialmodulesthatlengthenthechainonepeptidebondatatime.BecausemanyofthepeptidesproducedthroughNRPSenzymesarepotentantibiotics—thinkpenicillinorvancomycin—researcherswanttofigureouthowtoharnesstheenzymestoproduceexistingantibioticsandengineernewones.Tothatend,biochemistMohamedA.MarahieloftheUniversityofMarburg,inGermany,andcolleaguespublishedthefirstX-raycrystalstructureofanentireNRPSmodule(C&
EN,Oct.6,page48;
Science2008,321,659).Shortlythereafter,ateamofchemistsledbyGerhardWagnerandChristopherT.WalshofHarvardMedicalSchoolpublishedanuclearmagneticresonancestructureofcomponentsofasimilarmodule(Nature2008,454,903).ThetwostructuresrepresentthefirstviewsofhowseparatecatalyticdomainsareorganizedwithinanNRPSenzyme,notedJanetL.Smith,abiochemistattheUniversityofMichigan,AnnArbor.Thefindingswill"
allowustofigureouthowtoengineerNRPSenzymestodoevenmorevariedchemistry,"
shesaid.
8.
Gibberellin'
sRoleInPlantPuberty
Makinglemonsandgrapesplumper,persuadingasparagustosendoutmoreshoots,andwakingupawidevarietyofseedsfromdormancyareallpartoftheplanthormonegibberellin'
sjobdescription.Buthowthisditerpenoidcarboxylicacidgetsdowntobusinesshaslongbeenamystery.Thisyear,Japanesescientistsprovidedsomekeyinformationbyre
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