JACS133 1pp 1166.docx

JACS133 1pp 1166.docx

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JACS1331pp1166

Solution-Processed,High-PerformanceNanoribbonTransistorsBasedonDithioperylene

Solution-processed,high-performance1Dsingle-crystallinenanoribbontransistorsfabricatedfromdithioperylenearedescribed.TheintegrationoftwosulfuratomsintotheperyleneskeletoninducesacompressedhighlyorderedpackingmodedirectedbyS···Sinteractions.Themobilitiesofupto2.13cm2V−1s−1foradithioperyleneindividualnanoribbonmakeitparticularlyattractiveforelectronicapplications.

X-rayandNMRCrystallographyinanEnzymeActiveSite:

TheIndolineQuinonoidIntermediateinTryptophanSynthase

Chemical-leveldetailssuchasprotonationandhybridizationstatearecriticalforunderstandingenzymemechanismandfunction.Evenathighresolution,thesedetailsaredifficulttodeterminebyX-raycrystallographyalone.ThechemicalshiftinNMRspectroscopy,however,isanextremelysensitiveprobeofthechemicalenvironment,makingsolid-stateNMRspectroscopyandX-raycrystallographyapowerfulcombinationfordefiningchemicallydetailedthree-dimensionalstructures.Hereweadoptedthiscombinedapproachtodeterminethechemicallyrichcrystalstructureoftheindolinequinonoidintermediateinthepyridoxal-5′-phosphate-dependentenzymetryptophansynthaseunderconditionsofactivecatalysis.Modelsoftheactivesiteweredevelopedusingasynergisticapproachinwhichthestructureofthisreactivesubstrateanaloguewasoptimizedusingabinitiocomputationalchemistryinthepresenceofside-chainresiduesfixedattheircrystallographicallydeterminedcoordinates.Variousmodelsofchargeandprotonationstateforthesubstrateandnearbycatalyticresiduescouldbeuniquelydistinguishedbytheircalculatedeffectsonthechemicalshiftsmeasuredatspecifically13C-and15N-labeledpositionsonthesubstrate.Ourmodelsuggeststheimportanceofanequilibriumbetweentautomericformsofthesubstrate,withtheprotonationstateofthemajorisomerdirectingthenextcatalyticstep.

Water-SolublePeptide-CoatedNanoparticles:

ControloftheHelixStructureandEnhancedDifferentialBindingtoImmuneCells

ThestabilizingactionofCα-tetrasubstitutedα-aminoacidsinsertedintoasequenceofshortpeptidesallowedforthefirsttimethepreparationofwater-solublenanoparticlesofdifferentmaterialscoatedwithahelix-structuredundecapeptide.Thispeptidecoatingstronglyfavorsnanoparticleuptakebyhumanimmunesystemcells.

APhotocleavableRapamycinConjugateforSpatiotemporalControlofSmallGTPaseActivity

Wedevelopedanovelmethodtospatiotemporallycontroltheactivityofsignalingmolecules.AnewlysynthesizedphotocagedrapamycinderivativeinducedrapiddimerizationofFKBP（FK-506bindingprotein）andFRB（FKBP-rapamycinbindingprotein）uponUVirradiation.WiththissystemandthespatiallyconfinedUVirradiation,weachievedsubcellularlylocalizedactivationofRac,amemberofsmallGTPases.Ourtechniqueoffersapowerfulapproachtostudiesofdynamicintracellularsignalingevents.

Cysteine-ActivatedHydrogenSulfide（H2S）Donors

H2S,thenewlydiscoveredgasotransmitter,playsimportantrolesinbiologicalsystems.However,theresearchonH2ShasbeenhinderedbythelackofcontrollableH2SdonorsthatcouldmimictheslowandcontinuousH2Sgenerationprocessinvivo.Hereinwereportaseriesofcysteine-activatedH2Sdonors.StructuralmodificationsofthesemoleculescanregulatetheratesofH2Sgeneration.ThesecompoundscanbeusefultoolsinH2Sresearch.

EnantioselectiveSynthesisofBiphenolsfrom1,4-DiketonesbyTracelessCentral-to-AxialChiralityExchange

Amethodfortheenantioselectivesynthesisofbiphenolsfromreadilyprepared1,4-diketonesisreported.KeytothesuccessofthismethodisthehighlyselectivetransferofcentraltoaxialchiralityduringadoublearomatizationeventtriggeredbyBF3·OEt2.OnthebasisofX-raycrystallographicdata,astereochemicalmodelforthischiralityexchangeprocessisputforth.

FormationofSnO2HollowNanospheresinsideMesoporousSilicaNanoreactors

WereportaninterestingapproachforefficientsynthesisofSnO2hollowspheresinsidemesoporoussilica“nanoreactors”.Theas-preparedproductsareshowntohaveauniformsizedistributionandgoodstructuralstability.Whenevaluatedfortheirlithiumstorageproperties,theseSnO2hollowspheresmanifestimprovedcapacityretention.

BrightandCompactAlloyedQuantumDotswithBroadlyTunableNear-InfraredAbsorptionandFluorescenceSpectrathroughMercuryCationExchange

Wereportanewstrategybasedonmercurycationexchangeinnonpolarsolventstopreparebrightandcompactalloyedquantumdots（QDs）（HgxCd1−xE,whereE=Te,Se,orS）withequalizedparticlesizeandbroadlytunableabsorptionandfluorescenceemissioninthenear-infrared.ThemainrationaleisthatcubicCdEandHgEhavenearlyidenticallatticeconstantsbutverydifferentbandgapenergiesandelectron/holemasses.Thus,replacementofCd2+byHg2+inCdTenanocrystalsdoesnotchangetheparticlesize,butitgreatlyaltersthebandgapenergy.Aftercappingwithamultilayershellandsolubilizationwithamultidentateligand,thisclassofcation-exchangedQDsarecompact（6.5nmnanocrystalsizeand10nmhydrodynamicdiameter）andverybright（60−80%quantumyield）,withnarrowandsymmetricfluorescencespectratunableacrossthewavelengthrangefrom700to1150nm.

LowReflectivityandHighFlexibilityofTin-DopedIndiumOxideNanofiberTransparentElectrodes

Tin-dopedindiumoxide（ITO）hasfoundwidespreaduseinsolarcells,displays,andtouchscreensasatransparentelectrode;however,twomajorproblemswithITOremain:

highreflectivity（upto10%）andinsufficientflexibility.Together,theseproblemsseverelylimittheapplicationsofITOfilmsforfutureoptoelectronicdevices.Inthiscommunication,wereportthefabricationofITOnanofibernetworktransparentelectrodes.Thenanofibernetworksshowopticalreflectivityaslowas5%andhighflexibility;thenanofibernetworkscanbebenttoaradiusof2mmwithnegligiblechangesinthesheetresistance.

APorphyrinFusedtoFourAnthracenes

Wehavesynthesizedafusedtetraanthracenylporphyrinbyoxidationofameso-anthracenylnickel（II）porphyrinwithFeCl3.Thiscompoundexhibitsanintensered-shiftedabsorptionspectrum（λmax=1417nm;ε=1.2×105M−1cm−1）andasmallelectrochemicalHOMO−LUMOgap（0.61eV）.Thecrystalstructureshowsthatitformsπ-stackeddimerswithashortNi···Nidistance（3.32Å）.

Rhodium-CatalyzedAnti-MarkovnikovIntermolecularHydroalkoxylationofTerminalAcetylenes

Wereportherethefirsttransition-metal-catalyzedanti-Markovnikovintermolecularhydroalkoxylationofterminalacetylenestogiveenolethersinhighyieldswithoutusingbases.Arylacetylenesaswellasalkenyl-andalkylacetyleneswerecoupledwithaliphaticalcohols,andtheproductswereobtainedwithhighZselectivityinmostcases.Effectivecatalystswere8-quinolinolatorhodiumcomplexes,whicharestructurallysimplebuthavebeenrelativelyunexploredascatalysts.

Surface-MediatedProductionofHydroxylRadicalsasaMechanismofIronOxideNanoparticleBiotoxicity

Emergingapplicationsofnanosizedironoxidesinnanotechnologyintroducevastquantitiesofnanomaterialsintothehumanenvironment,thusraisingsomeconcerns.Herewereportthatthesurfaceofγ-Fe2O3nanoparticles20−40nmindiametermediatesproductionofhighlyreactivehydroxylradicals（OH•）underconditionsofthebiologicallyrelevantsuperoxide-drivenFentonreaction.Byconductingcomparativespin-trappingEPRexperiments,weshowthatthefreeradicalproductionisattributedprimarilytothecatalyticreactionsatthenanoparticles’surfaceratherthanbeingcausedbythedissolvedmetalionsreleasedbythenanoparticlesaspreviouslythought.Moreover,thecatalyticcentersonthenanoparticlesurfacewerefoundtobeatleast50-foldmoreeffectiveinOH•radicalproductionthanthedissolvedFe3+ions.Conventionalsurfacemodificationmethodssuchaspassivatingthenanoparticles’surfacewithupto935moleculesofoleateorupto18moleculesofbovineserumalbuminperironoxidecorewerefoundtoberatherineffectiveinsuppressingproductionofthehydroxylradicals.Theexperimentalprotocolsdevelopedinthisstudycouldbeusedasoneoftheapproachesfordevelopinganalyticalassaysforassessingthefreeradicalgeneratingactivityofavarietyofnanomaterialsthatispotentiallyrelatedtotheirbiotoxicity.

PostsyntheticGuanineArylationofDNAbySuzuki−MiyauraCross-Coupling

DirectradicaladditionreactionsattheC8-siteof2′-deoxyguanosine（dG）canaffordC8-Ar-dGadductsthatareproducedbycarcinogenicarylhydrazines,polycyclicaromatichydrocarbons,andcertainphenolictoxins.Suchmodifiednucleobasesarealsohighlyfluorescentforsensingapplicationsandpossessusefulelectrontransferproperties.Thesite-specificsynthesisofoligonucleotidescontainingtheC8-Ar-Gadductcanbeproblematic.Theselesionsaresensitivetoacidsandoxidantsthatarecommonlyusedinsolid-phaseDNAsynthesisandaretoobulkytobeacceptedassubstratesforenzymaticsynthesisbyDNApolymerases.UsingtheSuzuki−Miyauracross-couplingreaction,wehavesynthesizedanumberofC8-Ar-G-modifiedoligonucleotides（dimers,trimers,decamers,anda15-mer）usingarangeofarylboronicacids.Goodtoexcellentyieldswereobtained,andthereactionisinsensitivetothenatureofthebasesflankingtheconvertible8-Br-Gnucleobase,asbothpyrimidinesandpurinesaretolerated.TheimpactoftheC8-Ar-Glesionwasalsocharacterizedbyelectrosprayionizationtandemmassspectrometry,UVmeltingtemp