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Biologicallypotentdioxomolybdenum(VI)complexeswithnitrogen-sulfurandnitrogen-oxygendonarligands:Synthesis,characterisationandantimicrobialactivityINTRODUCTIONMolybdenumisanimportanttransitionelement,whichhasamajorroleastraceelementsandisanin-dispensableconstituentofenzymesthatareinvolvedinthefunctionofnitrogenfixingnitrogenase[1].
Alargenum-berofstableandaccessibleoxidationstatesandcoor-dinationnumberrendermolybdenumtobeaversatiletransitionelement.
Molybdenumistheonlyelementinthesecondandthirdtransitionserieswhichplaysmajorroleastraceelementinenzymes.
Thepresenceofcis-dioxymolybdenumcation[MoO2]+2intheoxidizedformofcertainmolybdoenzymeshasrecentlygeneratedtre-AshuChaudhary1*,R.
V.
Singh21DepartmentofChemistry,BanasthaliUniversity,Rajasthan,(INDIA)2DepartmentofChemistry,UniversityofRajasthan,Jaipur-302004,(INDIA)E-mail:ashuchaudhary21@gmail.
comReceived:24thJuly,2008;Accepted:29thJuly,2008mendousinterest[2].
Thecis-[MoO2]+2centredominatesthechemistryofdomolybdenum(VI)complexes[3]andparticipatesinmanyoxygenatomtransferreactions[4-6].
Schiffbasesareanimportantclassofligandsinco-ordinationchemistryandhavemanyapplications[7]invariousfields.
ThechemistryofSchiffbasecomplexescontinuestoattractmanyresearchers[8,9]becauseoftheirwideapplicationsinfoodindustry,dyeindustry,ana-lyticalchemistry,catalysis,antimicrobialactivity,agrochemicalactivity[10]andpharmacologicalapplications[11].
TheSchiffbaseshavebeenfoundtobeactiveagainstdifferenttypesofbacteriaandviruses.
IthasnowbeenobservedthatsomeoftheseshowincreasedKEYWORDSDioxomolybdenum(VI)complexes;Spectralstudies;Schiffbase;Antimicrobialstudies.
ABSTRACTMolybdenum(VI)complexesof3,4,5-trimethoxybenzaldehydethiosemicarbazone(TBTSCZH),3,4,5-trimethoxybenzaldehydesemicarbazone(TBSCZH),3,4,5-trimethoxy-benzaldehydebenzothiazoline(TBBZTH)and3,4,5-trimethoxybenzaldehyde-S-benzyldithiocarbazate(TBDTCZH)havebeensynthesizedandcharacterizedbyphysico-chemicalandspectroscopicstudies.
ThecomplexesMoO2(L)2(whereLrepresentedthedeprotonatedformoftheligands),wereformedbythereactionsbetweendioxobis(2,4-pentanedionato-O,O')molybdenum(VI)andtheligandsTBTSCZH,TBSCZH,TBBZTHandTBDTCZHbyusingbothtechniques(thermalandmicro-wave).
Thestructuralfeaturesofthesemolybdenumcomplexeswereex-ploredbyIR,1HNMR,13CNMRandmolecularweightdeterminations.
Anoctahedralarrangementofligandsaroundthecentralmolybdenumatomisproposed.
Allthefourligandsandtheircomplexeshavebeenscreenedfortheirbiologicalactivityonseveralpathogenicfungiandbacteriaandthedatashowgoodactivityofthesecomplexesandligands.
2008TradeScienceInc.
-INDIAFullPaperICAIJ,3(3),2008[188-192]AnIndianJournalTradeScienceInc.
Volume3Issue3September2008InorganicCHEMISTRYAshuChaudharyandR.
V.
Singh189FullPaperICAIJ,3(3)September2008InorganicCHEMISTRYInorganicCHEMISTRYAnIndianJournalactivitywhenadministeredintheformofazomethinemetalcomplexes[12].
Inviewoftheimportanceofthedioxomolybdenum(VI)complexes,wehavesynthesizedandcharacterizedsomenewcomplexesofthesaidpo-tentialbidentateligands.
EXPERIMENTALAllthechemicalsandsolventsusedweredriedandpurifiedbythestandardmethods.
Dioxobis(2,4-pentanedionato)molybdenum(VI)waspreparedac-cordingtotheliteraturemethod[13].
PreparationoftheLigandsThedifferentrouteswereemployedforthesynthe-sisoftheligands.
Theseare-1.
MicrowaveassistedsynthesisFormicrowaveassistedsynthesisoftheligandsTBTSCZH,TBSCZH,TBBZTHandTBDTCZHthethiosemicarbazide,semicarbazidehydrochloride,2-aminothiophenolandS-benzyldihiocarbazatewerere-actedwith3,4,5-trimethoxybenzaldehydeinethanolicmedia,usingaconventionalmicrowaveoven,wheretheconsumptionofethanolassolventisverylittle(2-3ml).
Thereactionswerecompletedinashortperiod(4-8minutes).
ThecompletionofthereactionischeckedbyTLC.
2.
ConventionalheatingsynthesisForthecomparisonpurpose,aboveligandswerealsosynthesizedbythethermalmethod.
Forthistheweighedamountsof3,4,5-trimethoxybenzaldehydeandthiosemicarbazide,semicarbazidehydrochlorideand2-aminothiophenolandS-benzyldihiocarbazateweremixedtogetherin100mlethanolin250mlbeaker.
Thecontentswererefluxedfor4-16hrs.
onanoilbath.
Thesolidproductswereprecipitated.
Theseweredriedinvacuumandrecrystallizedfromthesamesolvent.
AcomparisonbetweenthermalmethodandmicrowavemethodhasbeengiveninTABLE1.
Theligandsusedare:Preparationofthecomplexes1.
MicrowaveAssistedMethod:Inmicrowaveas-sistedsynthesisthereactionsofdioxobis(2,4-pentanedionato-O,O')molybdenum(VI)withtheligands(TBTSCZH,TBSCZH,TBBZTHandTBDTCZH)werecarriedoutin1:2molarratios,using2-3mlofdrymethanolasasolventusingmi-crowaveoven.
Theproductswererecoveredfromthemicrowaveovenanddriedunderreducedpres-sure.
Theresultingproductswererepeatedlywashedwithdrycyclohexaneandthenfinallydriedat40-60o/0.
5mmfor3-4hours.
2.
ConventionalHeatingMethod:Thesemolybdenum(VI)complexeswerealsosynthesizedbythether-malmethod.
Inthethermalmethodinsteadof4-7minutesreactionswerecompletedin14-16hoursandyieldofproductswerealsolesserthanobtainedbythemicrowaveassistedsynthesis(TABLE1).
RESUTLSANDDISCUSSIONThereactionsofthedioxobis(2,4-pentanedionato-O,O')molybdenum(VI)withthesaidmonofunctionalHCOCH3OCH3OCH3NNHCSNH2HCOCH3OCH3OCH3NNCSHNH2(TBTSCZH)HCOCH3OCH3OCH3NNCOHNH2HCOCH3OCH3OCH3NNHCONH2(TBSCZH)HCOCH3OCH3OCH3NHSHCOCH3OCH3OCH3NHSHCOCH3OCH3OCH3NNHCSSCH2C6H5HCOCH3OCH3OCH3NNCSHSCH2C6H5(TBBZTH)(TBDTCZH).
190Biologicallypotentdioxomolybdenum(VI)complexesFullPaperICAIJ,3(3)September2008AshuChaudharyandR.
V.
Singh191FullPaperICAIJ,3(3)September2008InorganicCHEMISTRYInorganicCHEMISTRYAnIndianJournalservedintheregion3430-3350cm-1intheligandsat-tributedtoasymmetricandsymmetricmodesoftheNH2groupremainatnearlythesamepositioninthecom-plexes,indicatingthenon-involvementofthisgroupinchelation.
InadditiontothisthespectrumoftheligandTBDTCZHshowsdoubletat2900and2950cm-1,whichcanbeattributedtosymmetricandasymmetricvibrationsofS-CH2-C6H5grouping16andreducedtoaweakdoubletinthespectraofthecomplexes.
InthespectrumoftheligandTBBZTHtheabsenceof(SH)at2600-2530cm-1and(C=N)at1620-1590cm-1isastrongevidencefortheringstructure.
Oncomplexation,thebandat3240-3150cm-1duetoNHstretchingvibrationsofthebenzothiazoline,disap-pearsandabandat1600cm-1isobserveddueto(C=N)vibrations.
Thechelationofthisbenzothiazolineandthesaidligandsthroughtheazomethinenitrogenandthiolicsulphurfurthergetssupportbytheappear-anceofthenewbandsatca.
650cm-1,435cm-1and360cm-1,inthespectraofthecomplexesdueto(Mo-O),(MoN)and(Mo-S),respectively.
Adoubletinthespectraofthecomplexesatca.
910cm-1,whichmaybeassignedtosym(O=Mo=O)andasy.
(O=Mo=O),respectively,indicatesthecisMoO2struc-ture.
1HNMRspectraThebondingpatterndiscussedabovegetsfurthersupportbytheprotonmagneticresonancespectralstud-iesoftheligandsandtheircomplexes.
The1HNMRspectraoftheligandsTBTSCZH,TBSCZHandTBDTHshowsignalsdueto–NHgroup(10.
65-10.
98ppm)and–SHgroup(7.
88-7.
96ppm).
Incaseofthecorrespondingcomplexthesignalsdueto–NHand–SHprotonsoftheligandunitdisappearindi-catingdeprotonationandsimultaneouscovalentbondformationthroughnitrogenandsulphur.
Allthesaidfreeligandsandtheirmolybdenumcomplexesshowmultip-letsintheregion6.
25-8.
80ppmattributabletoaro-maticprotons,whichappearalmostatthesameposi-tionintherespectiveligands.
TheNH2protonsgivesingletat3.
48-4.
20intheligandsTBTSCZHandTBSCZHaswellastheircorrespondingmolybdenum(VI)complexes.
ItshowsthattheNH2groupisnottakingpartinthecomplexation.
The1HNMRspectrumoftheligandTBBZTHshowsthesignalof–NHprotonat5.
40ppmwhichfoundabsentinthespectraofthemolybdenum(VI)complexesconfirmingthedeprotonationof–NHgroupandcoordinationofmolybdenumwithnitrogenatom.
TheH-C=Nsignalisfoundinupfieldorshieldedre-gioninbenzothiazolineligandanditsmolybdenum(VI)complexesascomparedtothethiosemicarbazone,semicarbazoneanddithiocarbazateandtheirmolybdenum(VI)complexes.
ThespectrumoftheligandTBDTCZHalsoshowsanadditionalpeakat1.
78ppmduetoS-CH2-Phprotonsandthispeakappearsindeshieldregioninitscorrespondingmetalcomplex.
13C-NMRspectraThe13CNMRspectraofoneoftheligandanditscorrespondingmetalcomplexeshavebeenrecordedinCDCl3.
Thechemicalshiftvaluesofthecarbonatomattachedtotheazomethinenitrogen,thiolicsulfuroramidooxygen,showconsiderableshiftwhichfurthersupporttheproposedcoordinationinthecomplexes.
Onthebasisoftheabovestudiesthecoordinationpatternshowninfigure1isconcluded.
AntimicrobialstudiesBioefficiencyoftheparentligandsandtheircom-plexeswastestedinvitroforthegrowthinhibitingpo-tentialagainstvariousfungalandbacterialstrainsusingRadialGrowthMethodandPaperDiscTechnique,re-spectively.
FungalstrainsM.
phaseolina,F.
oxysporumandBacterialstrainsS.
aureusandK.
aerogenous,wereused.
Thebiocidalactivityhavebeencomparedwiththeconventionalfungicide.
Bavistinandtheconven-tionalbactericide,Streptomycin.
AllthescreeningdataaregiveninTABLES3and4.
Itisapparentthatsulfurcontainingcompoundsaremoretoxicthantheoxygencontainingcompounds.
ItXMoXNOONWhere,X=SandOandNXisthedonorsystemoftheligandsFigure1.
192Biologicallypotentdioxomolybdenum(VI)complexesFullPaperICAIJ,3(3)September2008