Lanthanide paramagnetic probes for NMR spectroscopic studies of molecular核磁共振
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LanthanideparamagneticprobesforNMRspectroscopicstudiesofmolecularconformationaldynamicsinsolution:Applicationstomacrocyclicmolecules
S.P.Babailov*A.V.Nikolaev’sInstituteofInorganicChemistry,SiberianBranch,RussianAcademyofSciences,Novosibirsk,RussianFederationReceived12February2007Availableonline21April2007
Keywords:DynamicNMRspectroscopy;NuclearOverhausereffect;NMRlineshape;Spinsaturationtransfer;Selectivemagnetizationtransfer;Spin–latticerelaxation;Lanthanide-inducedshifts;Lanthanides;DOTA-likeligands;Macrocyclicpolyethers;Porphyrins
Contents1.Introduction................................................................................12.Paramagneticshiftandrelaxationreagents...........................................................22.1.3d-and4f-Shiftreagents:applicationsinnonaqueousmedia..........................................22.2.Applicationsof3d-and4f-relaxationreagentsinnonaqueousmedia....................................32.3.Lanthanidecoordinationcompoundsbiomedicineapplicationsinaqueousmedia...........................33.Paramagneticlanthanide-inducedshiftsandenhancementofspin–latticerelaxationrates..........................44.ExperimentalproceduresforLISandrelaxationratesanalysis.............................................55.DynamicNMR(DNMR)spectroscopystudiesoflanthanidecomplexes......................................75.1.DNMRbandshapeanalysisinlanthanideparamagneticcomplexes.....................................75.2.DynamicNMRapplicationsforlanthanideparamagneticcomplexeswithcrownethers......................105.3.DNMRApplicationstolanthanideparamagneticcomplexeswithDOTAandrelatedligands.................135.4.DNMRapplicationstolanthanideparamagneticcomplexeswithporphyrins.............................146.NMRinvestigationsofsymmetricmacrocyclicpolyethersandporphyrinsincomplexeswithmetalcations............166.1.Complexesofdiamagneticmetalcations.......................................................166.2.Complexesofparamagneticlanthanidecations..................................................166.3.Spatialstructureandparamagneticpropertypeculiaritiesinnonaqueoussolutions.........................177.Conclusion................................................................................17Acknowledgments...........................................................................18References.................................................................................18
1.Introduction
In1969itwasreported[1]thatthe1HNMRchemicalshiftsoforganiccompoundscontainingdonor-activehet-eroatomswithloneelectronpairs(O,N,S,etc.)changedramaticallywhenso-calledlanthanide(Ln)shiftreagents
0079-6565/$-seefrontmatterÓ2007ElsevierB.V.Allrightsreserved.
doi:10.1016/j.pnmrs.2007.04.002*Tel.:+73833391835;fax:+73833309489.E-mailaddress:babajlov@che.nsk.suwww.elsevier.com/locate/pnmrsProgressinNuclearMagneticResonanceSpectroscopy52(2008)
1–21(LSR)areaddedtosolutionsofthesecompoundsinrela-tivelyinertnonaqueoussolvents.Sincethattime,manyori-ginalpapersandreviewshavebeenpublishedonvariousaspectsofusingthepropertiesofLSR,oninteractionsofLSRwithvarioustypesoforganiccompounds[1–23],onnuclearspininteractionswiththeparamagneticmetalcen-ter[27–51],andonthelanthanide-inducedshifts(LIS)andrelaxationrateenhancementbothinaqueous[13,14,24,25,35,36,46]andnonaqueoussolvents[2,5,9,31].Overthepast10yearstherehasbeenaresurgenceofinterestinthecoordinationchemistryoflanthanidecom-plexesinsolution.Arenewedinterestinthisworkmayberelatedtoanenhancedappreciationoftherichfunction-alityoflanthanidecomplexes.Thehigh-spinparamagne-tismandlongelectronicrelaxationtimeofGd3+havemadeitpre-eminentamongcontrastagentsformagneticresonanceimaging(MRI)[13,14,46–49].Relatedcom-plexesofmanyotherlanthanidecationswithmuchshorterelectronicrelaxationtimesareeffectiveNMRLSR[13,14,46–49].Lanthanidecomplexesinsolutionexhibitawell-definedluminescence[15–19]whichischaracterizedbynarrowemissionbands,largeStokes’shifts,andlongexcited-statelifetimes.Europiumandterbiumcomplexespossessexcited-statelifetimesinsolutionofupto5msandemitintheredandgreen;theyhavebeenusedasprobesinfluoroimmunoassaysandshowconsiderablepromiseinluminescenceimagingandassensorsforcertainbioactiveions[13,14].Thenear-IRemissionfromtheexcitedstateofNd3+,Yb3+,andEr3+islesslong-lived,butcomplexesoftheseionsoffermuchpromiseasprobesinvivosincetissueisrelativelytransparenttoincidentlightwithawavelengthofaround1000nm.Duringthelastdec-ades,therehasbeengrowthofinterestinstudiesoflantha-nidecationswithmacrocyclicligands(inparticularwithmacrocyclicpolyethers(MCPE)andporphyrins).MCPEandporphyrinsarepromisingextractantsandNMRana-lyticalreagentsandareregardedbymanyresearchersasmodelcompoundsfornaturalionophores[52–82,21,84–98].Moreoverlanthanideb-diketonatecomplexeswithMCPEareusedasphotoresists[95],andtherearepros-pectsforusingphotosensitivephthalocyanine[99]andsty-ryldyesderivativesofMCPEinmolecularelectronics[96,97,100].Inthepastfewyearsseveralexcellentreviewshaveappearedwhichgiveamoreprecisedefinitiontoaspectsofcontrastagentstructureandsolutiondynamics[90,101–103],biomedical[92]andNMRapplications[21,102,103],complexdesignfeatures[84],thermodynamicaspectsofcomplexformation[85,102],thedevelopmentofluminescentlanthanidecomplexesoperatinginaqueousmedia[13,19,86–90],andthediagnosticandtherapeuticusesoflanthanide-texaphyrinand-porphyrincomplexes[13,91–94].Inarecentreview[13]dedicatedtotheanalysisofNMRinvestigationresultsinthefieldofintramolecularchemicalexchangeprocessesforlanthanidecomplexesinaqueoussolution,thenumerousexamplesofconforma-tionaldynamicsstudiesindiamagneticlanthanumcom-plexeswereconsideredindetail.Thekineticsdatawereobtainedinitiallybyusingacomplete13CNMRlineshapeanalysismethod.TherewereonlyafewexamplesofdynamicsstudiesinparamagneticEuandYbcomplexes,theinitialkineticsdatabeingobtainedbyusingtheselec-tivemagnetizationtransfer(MT)methodandexchangespectroscopy(EXSY)[74,75,121,122].However,themeth-odologyofdifferentdynamicNMRmethods(notonlyMTandEXSYbutotherssuchaslineshapeanalysis,takingintoaccountthetemperaturevariationofLIS,andspinsaturationtransfer)ofstudyofparamagneticlanthanidecomplexeswithMCPEandporphyrinsinnonaqueoussolutionshasnotbeensystematicallyreviewedyet.HerethisproblemisconsideredfromthepointofparamagneticprobeapplicationforstudyofconformationaldynamicsofMCPEandporphyrinsinnonaqueoussolutions.Forcom-parisonanumberofexamplesofNMRinvestigationsofintramoleculardynamicsforlanthanidecomplexesinaque-oussolutionswithothermacrocyclicligands(thearche-typalligandinthisseriesofcomplexesisDOTA)areconsidered.Inthepresentwork,themethodologyofpara-magneticCe,Pr,Nd,Eu,Dy,andYbprobeapplicationsforthestudyoftheenthalplyandentropychangesinchem-icalexchangeprocessesarediscussed,aswellastheadvan-tagesofthismethodincomparisonwithDNMRstudiesofdiamagneticsubstances.Inparticular,therelativerangesofthechemicalexchangerateconstantstobemeasuredareconsidered.Inaddition,thisarticleconsidersrecentstudiesofintra-molecularexchangeprocesses,anddiscussesadvancesindynamicmagneticresonancespectroscopyandinmethodsfortheanalysisofparamagneticpropertiesoflanthanidecomplexes.
