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1、ARTICLEpubs.acs.org/JACSAnharmonicVibrationalModesofNucleicAcidBasesRevealedby2DIRSpectroscopyChunteSamPeng,KevinC.Jones,andAndreiTokmakoff*DepartmentofChemistry,MassachusettsInstituteofTechnology,Cambridge,Massachusetts02139,UnitedStatesbSSupportingInformationABST
2、RACT:Polarization-dependenttwo-dimensionalinfrared(2DIR)spectraofthepurineandpyrimadinebasevibrationsoffivenucleotidemonophosphates(NMPs)wereacquiredinD2OatneutralpHinthe1frequencyrange15001700cm.Thedistinctivecross-peaksbetweentheringdeformationsandcarbonylstret
3、chesofNMPsindicatethatthesevibrationalmodesarehighlycoupled,incontrastwiththetraditionalpeakassignment,whichisbasedonasimplelocalmodepicturesuchasCdO,CdN,andCdCdoublebondstretches.Amodelofmultipleanharmo-nicallycoupledoscillatorswasemployedtocharacterizethetransit
4、ionenergies,vibrationalanharmonicitiesandcouplings,andtransitiondipolestrengthsandorientations.Nosimpleorintuitivestructuralcorrelationsarefoundtoreadilyassignthespectralfeatures,exceptinthecaseofguanineandcytosine,whichcontainasinglelocalCOstretchingmode.Tohelpin
5、terpretthenatureofthesevibrationalmodes,weperformeddensityfunctionaltheory(DFT)calculationsandfoundthatmultipleringvibrationsarecoupledanddelocalizedoverthepurineandpyrimidinerings.Generally,thereisclosecorrespondencebetweentheexperimentalandcomputationalresults,p
6、rovidedthattheDFTcalculationsincludeexplicitwaterssolvatinghydrogen-bondingsites.Theseresultsprovidedirectexperimentalevidenceofthedelocalizednatureofthenucleotidebasevibrationsviaanonperturbativefashionandwillserveasbuildingblocksforconstructingastructure-basedmo
7、delofDNAandRNAvibrationalspectroscopy.I.INTRODUCTIONregionsofinterestthatreflectnucleicacidconformations.(a)Bandsoriginatedfromthein-planebasevibrations,suchasCdONucleicacids,DNAandRNA,canadoptvarioussecondarystretch,CdNstretch,andND2bendingmodes,arelocatedinthestr
8、ucturesthroughhydrogen-bondinteractionsbetweenthe115001800cmregion.(b)Thebase-ribosevibrationsthatarenucleicacidbases.Thesebase-pairedsecondarystructu
