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Benzthiazole-basedmultifunctionalchemosensor:fluorescentrecognitionofFe3þandchromogenicrecognitionofHSO4VimalK.Bhardwaja,PreetiSalujaa,GeetaHundalb,M.S.Hundalb,NarinderSingha,*,DooOkJangc,*aDepartmentofChemistry,IndianInstituteofTechnologyRopar,Rupnagar140001,Punjab,IndiabDepartmentofChemistry,GuruNanakDevUniversity,Amritsar143005,Punjab,IndiacDepartmentofChemistry,YonseiUniversity,Wonju220-710,RepublicofKoreaarticleinfoArticlehistory:Received28September2012Receivedinrevisedform26November2012Accepted27November2012Availableonline3December2012Keywords:ChemosensorFe(III)HSO4FluorescentChromogenicabstractAbenzthiazole-basedmultifunctionalchemosensorwasdesignedwithsiderophoreslikebindingsitesforrecognitionofFe3þandbothhydrogenbonddonorandacceptorbindingsitesforoxyanionHSO4.ThesensorrecognizesFe3þselectivelythroughenhancementoffluorescenceemissionintensityat440nmandrecognizesHSO4throughabathochromicshiftinUVevisspectrafrom315nmto365nmwithclearisosbesticpointsat345nmand395nm.TherecognitionofbothFe3þandHSO4isfreefromtheinterferencefromtheothercationsandanions,respectively.
2012ElsevierLtd.Allrightsreserved.1.IntroductionRecently,therehasbeensignificantinterestinthedesignanddevelopmentofartificialopticalchemosensorsthatrecognizebi-ologicallyandenvironmentallyimportantanalytes.1Considerableeffortshavebeenmadetodevelopmultifunctionalsensorsthatsimultaneouslyrecognizemultipleanalytes.2Duetotheirhighsensitivityandpromptanalytedetection,UVevisabsorptionspectroscopyandfluorescentspectroscopy-basedanalyticaltech-niquesareimmenselypreferred.Alargenumberofchemosensorshavebeenproposedtoselectivelydetectcationsandanionsbyasimpleturn-onorturn-offresponse.3Mostofthesechemosensorsareselectiveforonlyoneparticularanalyte.4Invariouscomplexmolecularevents,thesimultaneousrecognitionofdifferentana-lytesisrequiredtoscreenformanytargetmoleculesatthesametime.Ironplaysanimportantroleinseveralbiologicalactivities.5Irondeficiencyistoxicandcanleadtoanumberofsevereneurologicaldisorders,developmentaldefects,andmalfunctions.6Alackofadequateironlevelsinthebloodleadstoanemia.7Tosupplementironlevelsinthebody,pharmacologicalformsthatusetheoralroutearerecommended,suchasironsulfateandferroglycinesulfate.However,ironsupplementationleadstoaccumulationofexternallyadministeredironinthebody,whichhasdeleteriouseffects.Forinstance,ahighlevelofironinserumincreasestheriskofseveraltypesoftumors.8IronexcessalsoleadstoAlzheimer’sdisease,whichisresponsibleforsomeneuraldisorders.9Withexcessironcontent,counteranioncontent(sulfate/hydrogensul-fate)alsoincreases,whichcanalsohaveharmfuleffectsonthebody.Highdosesofsulfatemaycauselaxativeeffectsthatleadtodiarrhea.10Ironandsulfate/hydrogensulfatecontentshouldbesi-multaneouslymonitored.Althoughtherearenumberofsensorsthatseparatelydetectiron11andsulfate/hydrogensulfateions,12tobestofourknowledge,thereisnosensorforsimultaneousesti-mationofFe3þandHSO4.Therefore,developingmultipleanalytesensorscanbequitechallenging.ThecurrentworkfocusesonrecognizingFe3þandHSO4simultaneously.Acoordinationspherethatconsistsofanarrayofhydrogenbonddonorsandacceptorsisrequired.Forthispurpose,wedesignedandsynthesizedsensors1and2asshowninScheme1.Thedesignofthesensorsisbaseduponthereportsavailableinliteratureonironchelatingagents,suchassiderophoresandothersyntheticdesigns.13Thecoordinationsphereoftheseagentsmakesuseofthebindingunitscontainingphenolsubstituentalongwithsp2-nitrogendonor.Thus,theinsertionsofthesebindingsitesinourdesignsmightbebeneficialforironrecognition.Ontheotherhand,thesebindingsitesshowbothahydrogenbonddonorandacceptor,makinganinterestingcombinationforthecoordinationofoxy-anions,suchasHSO4.*Correspondingauthors.E-mailaddresses:[e-mail](N.Singh),[e-mail](D.O.Jang).ContentslistsavailableatSciVerseScienceDirectTetrahedronjournalhomepage:
2012ElsevierLtd.Allrightsreserved.(2013)1606e16102.ResultsanddiscussionBenzthiazole-basedsensors1and2weresynthesizedbycon-densationof2-(2-aminophenyl)-benzthiazolewith2-hydroxy-naphthaldehydeorsalicylaldehyde,respectively.Thecompoundswerecharacterizedbyspectroscopicmethods.Thepresenceofiminelinkageswasconfirmedbyobservingsignalsat9.58and8.98ppmin1HNMRspectraandbandsat1610and1635cm1inIRspectra.Thestructureofsensor1wasalsoconfirmedwithasinglecrystalX-raycrystallographyimage,asshowninFig.1.Thecrystalstructureofsensor1showsthatallbondparametersarenormal.Thebenzthiazoleringandnaphthylringwererotatedby15.10(5)and47.29(4)withrespecttothecentralphenylrings.TheeOHgroupformedintramolecularH-bondswithimineNandS,withO1eH1A/N2(2.567(2)A,1.84A,147),andwithO1eH1A/S1(3.441(2)A,2.94A,121).Downfieldchemicalshiftofhydroxylprotoninsensor1and2isverifyingintramolecularhydrogenbondinginboth.Thechemicalshiftvalueforhydroxylprotoninthecaseofsensor1is14.67ppmandinthecaseofsensor2is11.59ppm,indicatingextensivehydrogenbondinginsensor1.UVevisabsorptionandfluorescencespectroscopywereusedtoexamineth